diff --git a/preprint/preprint__0129baf8281eddc2ad657d6e8fa589609bc12adf1490795c312275d391cb9313/preprint__0129baf8281eddc2ad657d6e8fa589609bc12adf1490795c312275d391cb9313.mmd b/preprint/preprint__0129baf8281eddc2ad657d6e8fa589609bc12adf1490795c312275d391cb9313/preprint__0129baf8281eddc2ad657d6e8fa589609bc12adf1490795c312275d391cb9313.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..b3fc209c79223cae0de0365304af9f20a23cb397
--- /dev/null
+++ b/preprint/preprint__0129baf8281eddc2ad657d6e8fa589609bc12adf1490795c312275d391cb9313/preprint__0129baf8281eddc2ad657d6e8fa589609bc12adf1490795c312275d391cb9313.mmd
@@ -0,0 +1,299 @@
+
+# Micropillar-induced changes in cell nucleus morphology enhance bone regeneration by modulating the secretome
+
+Guillermo Ameer g- ameer@northwestern.edu
+
+Northwestern University https://orcid.org/0000- 0001- 6023- 048X Xinlong Wang Northwestern University https://orcid.org/0000- 0001- 8978- 2851 Yiming Li Northwestern University https://orcid.org/0000- 0003- 2111- 3939 Zitong Lin Northwestern University Indira Pla Northwestern University Raju Gajjela Northwestern University Basil Mattamana Northwestern University Maya Joshi Northwestern University https://orcid.org/0000- 0002- 6028- 475X Yugang Liu Northwestern University https://orcid.org/0000- 0001- 5304- 3459 Huifeng Wang Northwestern University Amy Zun Northwestern University Hao Wang The University of Chicago Ching Wai Northwestern University Vasundhara Agrawal Northwestern University https://orcid.org/0000- 0003- 0913- 9298 Cody Dunton
+
+<--- Page Split --->
+
+Northwestern University
+
+Chongwen Duan Northwestern University
+
+Bin Jiang Northwestern University
+
+Vadim Backman Northwestern University https://orcid.org/0000- 0003- 1981- 1818
+
+Tong Chuan He The University of Chicago Medical Center
+
+Russell Reid Section of Plastic Surgery, The University of Chicago Medical Centre
+
+Yuan Luo Northwestern University https://orcid.org/0000- 0003- 0195- 7456
+
+## Article
+
+Keywords:
+
+Posted Date: January 7th, 2025
+
+DOI: https://doi.org/10.21203/rs.3.rs- 5530535/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on July 11th, 2025. See the published version at https://doi.org/10.1038/s41467- 025- 60760-y.
+
+<--- Page Split --->
+
+## Microtopography-induced changes in cell nucleus morphology enhance bone regeneration by modulating the cellular secretome
+
+Xinlong Wang \(^{1,2}\) , Yiming Li \(^{3}\) , Zitong Lin \(^{3}\) , Indira Pla \(^{4}\) , Raju Gajjela \(^{4}\) , Basil Baby Mattamana \(^{4}\) , Maya Joshi \(^{1}\) , Yugang Liu \(^{1,2}\) , Huifeng Wang \(^{1,2}\) , Amy B. Zun \(^{1}\) , Hao Wang \(^{5}\) , Ching- Man Wai \(^{6}\) , Vasundhara Agrawal \(^{2,7}\) , Cody L. Dunton \(^{2,7}\) , Chongwen Duan \(^{1,2}\) , Bin Jiang \(^{1,2,8}\) , Vadim Backman \(^{1,2,7,9}\) , Tong- Chuan He \(^{1,5}\) , Russell R. Reid \(^{1,10}\) , Yuan Luo \(^{3,11,12}\) , Guillermo A. Ameer \(^{1,2,7,8,11,13,14*}\)
+
+\(^{1}\) Center for Advanced Regenerative Engineering, Northwestern University, Evanston, IL 60208, USA \(^{2}\) Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA \(^{3}\) Department of Preventive Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA \(^{4}\) Proteomics Center of Excellence, Northwestern University, Evanston, IL 60208, USA \(^{5}\) Molecular Oncology Laboratory, Department of Orthopedic Surgery and Rehabilitation Medicine, The University of Chicago Medical Center, Chicago, IL 60637, USA \(^{6}\) Center for Genetic Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA \(^{7}\) Center for Physical Genomics and Engineering, Northwestern University, Evanston, IL 60208, USA \(^{8}\) Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA \(^{9}\) Chemistry of Life Process Institute, Northwestern University, Evanston, IL 60208, USA \(^{10}\) Laboratory of Craniofacial Biology and Development, Section of Plastic and Reconstructive Surgery, Department of Surgery, The University of Chicago Medical Center, Chicago, IL 60637, USA \(^{11}\) Northwestern University Clinical and Translational Sciences Institute, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA \(^{12}\) Center for Collaborative AI in Healthcare, Institute for AI in Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA \(^{13}\) International Institute for Nanotechnology, Northwestern University, Evanston, IL 60208, USA \(^{14}\) Simpson Querrey Institute for Bionanotechnology, Northwestern University, Chicago, IL 60611, USA
+
+<--- Page Split --->
+
+## Abstract
+
+Nuclear morphology, which modulates chromatin architecture, plays a critical role in regulating gene expression and cell functions. While most research has focused on the direct effects of nuclear morphology on cell fate, its impact on the cell secrete and surrounding cells remains largely unexplored, yet is especially crucial for cell- based therapies. In this study, we fabricated implants with a micropillar topography using methacrylated poly(octamethylene citrate)/hydroxyapatite (mPOC/HA) composites to investigate how micropillar- induced nuclear deformation influences cell paracrine signaling for osteogenesis and cranial bone regeneration. In vitro, cells with deformed nuclei showed enhanced secretion of proteins that support extracellular matrix (ECM) organization, which promoted osteogenic differentiation in neighboring human mesenchymal stromal cells (hMSCs). In a mouse model with critical- size cranial defects, nuclear- deformed hMSCs on micropillar mPOC/HA implants elevated Col1a2 expression, contributing to bone matrix formation, and drove cell differentiation toward osteogenic progenitor cells. These findings indicate that micropillars not only enhance the osteogenic differentiation of human mesenchymal stromal cells (hMSCs) but also modulate the secrete, thereby influencing the fate of surrounding cells through paracrine effects.
+
+## Introduction
+
+The nucleus is a dynamic organelle that changes its morphology in response to the cell's status. Its morphology has critical influence on nuclear mechanics, chromatin organization, gene expression, cell functionality and disease development.2- 5 Abnormal nuclear morphologies, such as invagination and blebbing, have functional implications in several human disorders, including cancer, accelerated aging, thyroid disorders, and different types of neuro- muscular diseases.6,7 In addition, severe nuclear deformation is also observed during tissue development, cell migration, proliferation, and differentiation.2 Several structural components within the nucleus—including the nuclear envelope, lamins, nuclear actin, and chromatin—work together to determine its shape and structure.8 Although the underlying mechanisms are not yet fully understood, nuclear deformation has been found to affect cell behaviors through mechanotransduction processes.9 In addition, nuclear morphological changes have been reported to affect nuclear membrane tension and unfolding, which regulate the structure of the nuclear pore complex.10 This, in turn, influences the nuclear shuttling of transcription factors (e.g., YAP) and ions (e.g., Ca2+), ultimately impacting cell functions.11,12 In our previous study, we demonstrated that altering nuclear morphology using micropillar topography affects nuclear lamin A/C assembly, which, in turn, influences chromatin tethering, packing, and condensation.13 These changes affect transcriptional accessibility and responsiveness, thereby regulating gene expression and stem cell differentiation.
+
+To manipulate nuclear morphology, various biophysical tools have been developed, including atomic force microscopy (AFM) nanoindentation, optical, magnetic, and acoustic tweezers, microfluidic devices, micropipette aspiration, plate compression, substrate deformation, and surface topography modulation.14- 21 Among these methods, regulating the surface topography of materials is more accessible and has broader implications for regenerative engineering. One commonly used approach is the fabrication of pillar structures, which are employed to deform cell nuclei and study nuclear properties such as mechanics and deformability.22 These micropillar designs have been utilized to manipulate various cell functions, including migration, adhesion,
+
+<--- Page Split --->
+
+proliferation, and differentiation. \(^{23 - 26}\) A wide range of materials can be used to create these structures, such as poly- L- lactic acid (PLLA), poly(lactide- co- glycolide) (PLGA), OrmoComp (an organic- inorganic hybrid polymer), and methacrylated poly(octamethylene citrate) (mPOC). \(^{13,26 - 28}\) Among these options, mPOC is particularly suitable for bone regeneration due to its major component, citrate, which acts as a metabolic factor to enhance the osteogenesis of mesenchymal stromal cells (MSCs). \(^{29}\)
+
+Although the influence of nuclear morphogenesis on the functions of individual cells is being intensively investigated, its role in regulating cellular secretion remains unclear. Bioactive molecules secreted by cells are crucial for intercellular communication, affecting various biological processes such as inflammation, cell survival, differentiation, and tissue regeneration. \(^{30,31}\) The success of many cell and exosome- based therapies relies on the cellular secretome. In this study, we fabricated micropillars to manipulate nuclear morphology and investigated their effects on the secretome of human mesenchymal stromal cells (hMSCs). We incorporated hydroxyapatite (HA), the primary inorganic component of native bone tissue, with micropatterned methacrylated poly(octamethylene citrate) (mPOC) to create the micropillars, promoting bone formation. Our results showed that mPOC/HA micropillars facilitated osteogenic differentiation of hMSCs compared to flat mPOC/HA samples in vitro. Secretome analysis revealed that hMSCs with deformed nuclei exhibited higher expression levels of bioactive factors associated with extracellular matrix (ECM) components and organization, as well as ossification. In vivo, both mPOC/HA flat and micropillar scaffolds seeded with hMSCs resulted in new bone formation; however, the micropillar group demonstrated significantly greater new bone volume and regenerated tissue thickness. Spatial transcriptomic analysis further confirmed elevated expression of genes related to the regulation of ECM structures, consistent with the secretome analysis results. These findings suggest that the influence of nuclear deformation on the osteogenesis of hMSCs operates through similar mechanisms in both in vitro and in vivo environments. Therefore, microtopography engineering of scaffold to control nuclear morphology is a promising approach to enhance bone regeneration.
+
+## Results
+
+## Influence of micropillar structures on physical and chemical properties of mPOC/HA implants
+
+mPOC prepolymer was synthesized according to our previous report, \(^{32}\) and its successful synthesis was confirmed via the nuclear magnetic resonance (1H NMR) spectrum (Fig. S1a- c). The size of HA nanoparticles is around \(100 \mathrm{nm}\) , as characterized by dynamic light scattering (DLS) (Fig. S1d). To mimic the nature of bone composition, \(^{33} 60\%\) (w/w) HA was mixed with mPOC, and the slurry was used to fabricate flat and micropillar implants using a combination of UV lithography and the contact printing method (Fig. 1a). The square micropillars, with dimensions of 5 by 5 in side length and spacing, were fabricated (Fig. 1b). The height of the micropillars is around \(8 \mu \mathrm{m}\) , which can cause significant nuclear deformation (Fig. 1c,d). \(^{27}\) Fourier transform infrared (FTIR) spectrum shows a similar typical peak of functional groups in mPOC and mPOC/HA implants (Fig. S1e). The surface roughness of the implants was scanned using an atomic force microscope (AFM) (Fig. 1e). The analysis result indicates that the topography didn’t affect the surface roughness of the implants (Fig. 1f). Additionally, we tested the hydrophilicity of flat and micropillar implants via
+
+<--- Page Split --->
+
+water contact angle measurement (Fig. S2). Although, at the initial state, the flat surface was more hydrophilic, there was no significant difference in the water contact angle after a 5- minute stabilization process.
+
+The mechanical properties of the implants were tested using the nano- indentation method. The force- indentation curve of the flat sample has a sharper slope, indicating it is stiffer than the micropillar sample (Fig. S3a). The Young's Modulus of the flat sample \((0.95 \pm 0.12 \mathrm{GPa})\) is significantly higher than that of the micropillars \((0.48 \pm 0.02 \mathrm{GPa})\) and the lateral modulus of the micropillars \((46.88 \pm 1.49 \mathrm{MPa})\) (Fig. S3b,c). However, based on a previous report, the high modulus of the substrates is beyond the threshold that cells can distinguish and does not have an influence on nuclear morphology manipulation. \(^{34,35}\) Accelerated degradation and calcium release tests of the implants were performed in DPBS at \(75^{\circ} \mathrm{C}\) with agitation. \(^{36}\) There is a burst weight loss and calcium release of both flat and micropillar samples at day 1, followed by a gradual change until day 10, and another increase in the degradation and calcium release rate from day 10 to 14 (Fig. 1g,h). The micropillar structure enhanced the degradation and calcium release, but not significantly. According to the images of the samples captured at different time points, the initial burst degradation and calcium release can be attributed to the fast surface erosion of both scaffolds, as many small pores can be observed on their surfaces. From day 10 to 14, scaffolds started break into pieces that may lead to another burst degradation and calcium release (Fig. 1i).
+
+<--- Page Split --->
+
+
+
Figure 1. Fabrication of surface engineered mPOC/HA implants. a. Illustration shows the combination of UV lithography and contact printing to fabricate free-standing mPOC/HA micropillars. b. SEM image shows the micropillar structures made of mPOC/HA. c. Optical microscope image and d. cross-section analysis of mPOC/HA micropillars. e. Surface scanning of flat and micropillar implants by AFM. f. Surface roughness of flat and micropillar implants. N.S., no significant difference, \(\mathrm{n} = 3\) biological replicates. g. Degradation test and h. calcium release of flat and micropillar mPOC/HA implants. N.S., no significant difference, \(\mathrm{n} = 4\) biological replicates, insert plot shows the initial release of calcium within \(24\mathrm{h}\) . i. Representative images of flat and micropillar implants at different time points after accelerated degradation.
+
+<--- Page Split --->
+
+## Nuclear deformation facilitates osteogenic differentiation of hMSCs
+
+Nuclear deformation facilitates osteogenic differentiation of hMSCshMSCs were cultured on the flat and micropillar mPOC/HA surfaces in osteogenic medium and stained for F- actin and nuclei after 3 days (Fig. 2a). Noticeable deformation in both the nucleus and cytoskeleton was observed, consistent with mPOC micropillars. The Nuclear shape index (NSI) was calculated to assess the degree of nuclear deformation. A significantly lower NSI value, indicating more severe deformation, was found in the micropillar group (Fig. 2b). Confocal images were then employed to evaluate the 3D geometry of cell nuclei (Fig. 2c). 3D reconstruction analysis revealed that several geometric parameters, including nuclear volume, surface area, and project area, were significantly decreased on micropillars, while nuclear height was significantly increased (Fig. 2d and Fig. S4).
+
+We then investigated the impact of micropillars on cell adhesion, a crucial aspect for manipulating cell function. Initial cell attachment tests revealed that the micropillar structure did not influence cell attachment on the implants (Fig. 2e). SEM imaging of cell adhesion demonstrated that cells formed lamellipodia on flat surfaces but exhibited more filopodia on micropillars (Fig. 2f). Filopodia were observed on the top, side, and bottom of micropillars, indicating that cells were sensing the 2.5D environment using these antennae- like structures. The majority of cells were found to be viable on both flat and micropillar substrates, as evidenced by live/dead staining (Fig. 2g and Fig. S5). While the micropillars reduced cell metabolic activity (Fig. 2h), there was no significant impact on cell proliferation after 3 days of culture (Fig. 2i).
+
+To assess the impact of mPOC/HA micropillars on the osteogenesis of hMSCs, we stained ALP (alkaline phosphate) on a substrate with a combination of half flat and half micropillar structures (Fig. 2j). Quantification results demonstrated a significant increase in ALP activity on the micropillars (Fig. 2k). Furthermore, additional osteogenic differentiation markers of hMSCs, including RUNX2 and osteocalcin (OCN), were quantified through western blot analysis (Fig. 2l). The quantification of these proteins revealed a significant increase in both RUNX2 and OCN in cells on micropillars, confirming that the structures can effectively promote the osteogenic differentiation of hMSCs (Fig. 2m,n).
+
+<--- Page Split --->
+
+
+Figure 2. Nuclear deformation promotes osteogenic differentiation of hMSCs. a. Staining of nucleus (green) and F-actin (red) of hMSCs on flat and micropillar mPOC/HA surfaces. Insert: high magnification of cell nucleus. Dashed lines indicate micropillars. b. Analysis of nuclear shape index of hMSCs. \(\mathrm{n} = 117\) (flat) and 132 (pillar) collected from 3 biological replicates, \(\mathrm{***p< 0.0001}\) . c. Orthogonal view of cell nucleus on flat and micropillar surfaces. d. Nuclear volume analysis based on 3D construction of the confocal images of cell nuclei. \(\mathrm{n} = 35\) cells collected from 3 biological replicates, \(\mathrm{***p< 0.0001}\) . e. Initial cell attachment on flat and micropillar surfaces. \(\mathrm{n} = 5\) biological replicates, N.S., no significant difference. f. SEM images show the cell attachment on flat and micropillar mPOC/HA surfaces. g. Live/dead staining of hMSCs on flat and micropillar surfaces at 72 h in osteogenic medium. h. Cell metabolic activity of cells on flat and micropillar surfaces tested by a MTT assay. \(\mathrm{n} = 5\) biological replicates, \(\mathrm{***p< 0.0001}\) . i. Cell proliferation tested via DNA content after 72 h induction. \(\mathrm{n} = 5\) biological replicates, N.S., no significant difference. j. ALP staining of hMSCs on flat and micropillar surfaces after 7 d induction. k. ALP activity test of cells after 7 d osteogenic induction. \(\mathrm{n} = 3\) biological replicates. l. Blot images of osteogenic marker OCN and RUNX2 in cells cultured on flat and micropillar implants. GAPDH is shown as a control. Quantification m. OCN and n. RUNX2 according to western blot tests. \(\mathrm{n} = 3\) biological replicates, \(\mathrm{***p< 0.0001}\) .
+
+<--- Page Split --->
+
+## Micropillars modulate the secretome of hMSCs that regulate extracellular matrix formation.
+
+Micropillars modulate the secretome of hMSCs that regulate extracellular matrix formation.Previously, we demonstrated the ability of micropillar implants to enhance in vivo bone formation.13 However, the newly formed bone was not in close contact with the implant. Consequently, we hypothesized that nuclear deformation on micropillars might impact cellular secretion, thereby influencing osteogenesis through paracrine effects. To test this hypothesis, secretome analysis was conducted using medium collected from flat and micropillar samples. Differences in protein secretion levels between the two groups were depicted through principal component analysis (PCA) and a volcano plot, revealing a significant influence of nuclear deformation on the secretome (Fig. 3a,b). Gene ontology (GO) analysis was performed to annotate the significantly altered proteins in relevant processes.38 Top changes in cellular component, molecular functions, biological processes, and biological pathways indicated that micropillars predominantly affected extracellular matrix (ECM)- related processes (Fig. 3c and Fig. S6- 8). Moreover, ossification and collagen fibril organization were identified as biological processes significantly overrepresented by differentially expressed proteins (Fig. 3d). The heatmap plot of proteins associated with collagen- containing extracellular matrix and ossification showed predominant upregulation on micropillars (Fig. 3e). The linkages of proteins and GO terms in biological process highlighted that ECM organization forms the largest cluster and is closely associated with the ossification process (Fig. 3f).
+
+Reactome pathway analysis was further conducted to assess potential downstream effects of secretome changes on micropillars.39 Results indicated that pathways related to ECM organization, ECM proteoglycans, and collagen fibril crosslinking were among the top 15 pathways significantly overrepresented by differential expressed pathways (DEP), predominantly showing upregulation (Fig. 3g and Fig. S9). We also noticed an upregulation in the degradation of the ECM on micropillars, indicating enhanced ECM remodeling which a crucial factor for tissue regeneration.40 These findings suggest that micropillars can influence the ECM formation of hMSCs through paracrine effects. Additionally, we performed proteomic analysis using cells cultured on flat and micropillar mPOC/HA scaffolds (Fig. S10). PCA and volcano plots indicated significant influences of nuclear deformation on protein expression. Pathway analysis revealed significant changes in many cell proliferation- related processes, consistent with previous transcriptomic tests on micropillars.13
+
+<--- Page Split --->
+
+
+Figure 3. Secretome of hMSCs on flat and micropillar mPOC/HA surfaces. a. PCA plot of differentially expressed proteins secreted by hMSCs on flat and micropillars. Cyan: flat; Red: micropillar. b. Volcano plot of proteins secreted by hMSCs seeded on micropillars compared to the flat surface. Blue dots and orange dots indicate significantly downregulated and upregulated proteins secreted by cells on micropillars compared to those on flat surface. Grey dots indicate
+
+<--- Page Split --->
+
+non- significantly changed proteins. A threshold of expression greater than 2 times fold- change with \(p< 0.05\) was considered to be significant. Proteins that are related with collagen- ECM pathways are labelled. c. Top 4 significantly enriched GO and Pathways based on their adjusted p- values. d. The most significant enriched GO terms of the biological domain with respect to biological process. e. Heatmap of proteins that are related with collagen- containing extracellular matrix and ossification. F indicates flat samples and P indicates pillar samples, \(n = 3\) biological replicates for each group. f. The linkages of proteins and GO terms in biological process related with collagen fibers, ECM, and ossification as a network. g. Heatmap of top 15 enriched terms plotted based on Reactome pathway analysis.
+
+## Nuclear deformed cells facilitate osteogenic differentiation of undeformed cells by affecting ECM.
+
+Since the micropillar surfaces can modulate the secrete of hMSCs, we investigated whether the deformed cells could influence the osteogenic differentiation of undeformed cells using a transwell assay (Fig. 4a). The flat and micropillar mPOC/HA surfaces were fabricated at the bottom of cell culture plates to manipulate the nuclear morphology of hMSCs, while undeformed hMSCs were seeded on a transwell membrane with 400 nm nanopores, allowing the exchange of growth factors. After cell attachment, all samples were cultured in osteogenic induction medium. ALP staining of the cells on the transwell membrane showed a higher number of ALP- positive cells when co- cultured with nuclear- deformed cells, indicating enhanced osteogenic differentiation (Fig. 4b,c). Additionally, Alizarin Red S (ARS) staining confirmed increased calcium deposition—a key step in osteogenesis—when the cells were cultured above the micropillar- treated cells (Fig. 4d,e). Based on the secreteome analysis, hMSCs on micropillars appear to promote osteogenesis in the transwell culture by secreting proteins that enhance ECM structure and organization. Collagen staining revealed higher coverage, stronger staining intensity, and more interconnected collagen network structures in the transwell co- cultured with micropillar- treated cells (Fig. 4f,g). In addition, energy dispersive X- ray spectroscopy (EDS) images showed more Ca and P deposition in the transwell co- cultured with micropillar- treated cells (Fig. 4h). Together with the secreteome analysis, these findings suggest that the proteins secreted by cells with deformed nuclei improve ECM organization in undeformed cells, thereby promoting osteogenesis.
+
+<--- Page Split --->
+
+
+Figure 4. The paracrine effect of cells with/without nuclear deformation tested through transwell assay. a. Schematic illustration of the experiment setup. b. ALP staining and c. quantification of ALP positive cells on transwell membrane incubated with undeformed and deformed MSCs \((n = 3)\) . d. ARS staining and e. quantification of cells on transwell membrane incubated with undeformed and deformed MSCs \((n = 6)\) . f. Immunofluorescence staining images of collagen in ECM of cells on transwell membrane incubated with undeformed and deformed MSCs. g. The coverage of collagen analyzed according to the staining images \((n = 4)\) . h. EDS images showing Ca, P, and SEM images of cells on transwell membrane incubated with undeformed and deformed MSCs.
+
+## mPOC/HA micropillar implant promotes bone formation in vivo
+
+To test the in vivo regeneration efficacy of mPOC/HA scaffolds, we created a critical size cranial defect model in nude mice. Two 4 mm diameter critical defects were made on the left and right sides of the skull tissue for the implantation of flat and micropillar scaffolds, respectively (Fig. 5a). The scaffolds were seeded with hMSCs for 24 hours to allow for cell attachment and nuclear deformation (Fig. 5b). After 12 weeks, micro CT was performed to evaluate the bone formation in the living animals. Based on the images, newly formed bone can be observed in the defect area with both flat and micropillar mPOC/HA implants (Fig. 5c and Fig. S11). Comparing this to our previous study using mPOC alone, \(^{13}\) the integration of HA clearly enhanced bone regeneration
+
+<--- Page Split --->
+
+efficacy in vivo. Furthermore, larger bone segments were observed with the micropillar implant treatment. Quantification results confirmed a significantly increased bone volume with micropillar implant treatment (Fig. 5d).
+
+Histology analysis was further performed to evaluate the influences of flat and micropillar mPOC/HA implants on bone regeneration. Trichrome staining images revealed that defects treated with micropillar implants exhibited more osteoid tissue (Fig. 5e and Fig. S12). Moreover, both flat and micropillar mPOC/HA implants showed evidence of newly formed bone tissue, indicating enhanced bone regeneration compared to the mPOC alone scaffold. As no bone segment was observed with flat mPOC implant treatment. \(^{13}\) The thickness of the regenerated tissue was quantified, and the results demonstrated a significant enhancement with micropillar implant treatment (Fig. 5f). Positive staining of osteogenesis markers, including osteopontin (OPN) and osteocalcin (OCN), was observed throughout the regenerated tissues with both flat and micropillar implants, indicating osteoid tissue formation (Fig. 5g,h). The tissue appeared more compact in the micropillar group compared to the flat group. Furthermore, regenerated bone segments were more frequently observed with micropillar implant treatment.
+
+<--- Page Split --->
+
+
+Figure 5. mPOC/HA micropillar implant promotes bone regeneration in vivo. a. Image shows implantation of hMSC seeded flat and micropillar mPOC/HA scaffolds. b. Staining images of nuclei (green) and F-actin (red) of cells on the implants. c. Representative \(\mu \mathrm{CT}\) images of a typical animal implanted with hMSC-seeded flat (left) and micropillar (right) scaffolds at 12-weeks post-surgery. d. Regenerated bone volume in the defect region ( \(\mathrm{n} = 5\) animals). e. Trichrome staining of the defect tissue treated with flat and micropillar implants. f. Average thickness of regenerated tissues with implantation of flat and micropillar scaffolds ( \(\mathrm{n} = 5\) animals). IHC staining of osteogenic marker, g. OPN and h. OCN, in regenerated tissues with flat and micropillar implants.
+
+<--- Page Split --->
+
+## Micropillar implants facilitated bone regeneration in vivo via regulation of ECM organization and stem cell differentiation.
+
+Histological analyses showed more new bone formation with micropillar implants, although the new bone tissue did not directly interact with the micropillar surfaces. To further investigate the transcription profile of the regenerated tissue, we performed spatial transcriptomics (ST) analyses with both flat and pillar samples (Fig. S13). ST represents a powerful tool to investigate the cellular environment and tissue organization by providing a detailed map of gene expression within the native tissue context. Differential gene expression (DGE) analysis revealed changes in expression levels between the two groups. Although only a few genes showed significant differences, all of them were related to ECM structure or organization (Fig. S13). Notably, the expression of Colla2, critical for type I collagen formation (comprising \(90\%\) of the bone matrix), was enhanced in the micropillar group (Fig. 6a). This expression showed a gradient, increasing toward the dura layer, possibly due to the osteogenic contribution of dura cells. We then plotted a heatmap showing the top 10 up- regulated and down- regulated differentially expressed genes (pillar vs. flat) in comparison with those in native skull bone (Fig. 6b). The heatmap indicated that the tissue regenerated with micropillar implants had expression patterns more similar to native skull bone than the flat group. Gene Ontology (GO) analysis of DGEs was further performed to annotate their relevant biological processes (Fig. 6c). Protein localization to extracellular matrix and crosslinking of collagen fibrils were among the top 5 up- regulated processes in the micropillar group. These results are consistent with the secreteome test, all indicating that micropillar structures can influence ECM organization via paracrine effects.
+
+To further investigate the relationship between cell type composition and the regenerated tissues, we performed cellular deconvolution on the ST data using single- cell RNA sequencing (scRNA- seq) references from previously published studies. Several major cell lineages involved in bone regeneration were considered when deconvoluting the data (Fig. 6d). The most abundant cell type in regenerated tissues was late mesenchymal progenitor cells (LMPs), followed by MSCs and fibroblasts (Fig. 6e). There were also small proportions of MSC- descendant osteolineage cells (OLCs), osteocytes, osteoblasts, and chondrocytes. LMPs are identified as the late stage of MSCs through osteogenic differentiation. Among all cell types, the proportion of LMPs, which have high expression of marker genes associated with osteoblasts, was significantly increased in regenerated tissues with micropillar implants, indicating that these deformed cells facilitate the differentiation of MSCs toward the osteolineage (Fig. 6f). Additionally, GO analysis of DGEs (LMP versus other cell types) was performed to investigate the roles of LMPs in regenerated tissue. The results suggest that LMPs do not directly contribute to osteogenesis, a role performed by osteoblasts and osteocytes. Instead, LMPs can affect ECM formation, as the process of extracellular matrix organization is one of the top involved pathways (Fig. 6g). Thus, the results indicate that micropillar implants can facilitate skull tissue regeneration by promoting the differentiation of MSCs and ECM organization via paracrine effects.
+
+<--- Page Split --->
+
+
+Figure 6. Spatial transcriptomic analysis of tissues regenerated with flat and micropillar implants. a. Spatial plot of Colla2 expression profile in tissues regenerated with flat mPOC/HA implant and micropillar mPOC/HA implant. Arrow indicates enhanced expression around dura layer. b. The heatmap showing the top ten up- and down-regulated DEGs (pillar vs flat) in tissues regenerated with flat mPOC/HA implant, micropillar mPOC/HA implant, and native skull tissue. c. Gene Ontology analysis results based on the top 100 up-regulated genes (pillar vs flat). d. Deconvoluted cell types in each spatial capture location in flat and micropillar groups. Each pie chart shows the deconvoluted cell type proportions of the capture location. e. Bar plots of the cell type proportions in tissues regenerated with flat mPOC/HA implant and micropillar mPOC/HA implant. LMPs, MSCs, and fibroblasts are the predominant cell types. f. Violin plot of the proportion of LMPs in flat and micropillar groups. g. Top enriched processes associated with LMP compared with other cell lineages. LMP: late mesenchymal progenitor cells; MSC: mesenchymal stromal cells; OLC: MSC-descendant osteolineage cells
+
+<--- Page Split --->
+
+## Discussion
+
+Micropiliars, as a typical topographical feature, have been extensively studied for their ability to regulate cell functions. Recent researches have shown that rigid micropiliars can deform nuclear morphology, which in turn promotes the osteogenic differentiation of mesenchymal stem cells (MSCs), generating significant interest for bone regeneration applications.26,27 Our previous work demonstrated that mPOC micropiliars enhanced bone regeneration in a mouse cranial defect model.13 The mPOC, a citrate- based biomaterial (CBB), is an excellent candidate for bone regeneration because citrate, an important organic component of bone, plays key roles in skeletal development and bone healing by influencing bone matrix formation and the metabolism of bone- related cells.47 In this study, hydroxyapatite (HA) was incorporated into mPOC to further enhance its regenerative potential, leveraging HA's well- known osteoconductive properties.48 Both in vitro and in vivo experiments confirmed that the addition of HA significantly improved bone regeneration compared to mPOC alone.13 Moreover, several products made from CBB/HA composites have recently received FDA clearance, highlighting the promising clinical potential of mPOC/HA micropiliars for bone regeneration applications.49
+
+Despite recent intensive investigations into nuclear morphogenesis, little is known about its influence on cellular secretion, which can regulate neighboring cells and is critical for regenerative engineering. Previous studies have shown that nuclear mechanotransduction, activated by substrate stiffening or cellular compression, can impact cell secretions.50,51 Here, we found that cells with deformed nuclei exhibited higher expression levels of ECM components and binding proteins that support collagen- enriched ECM organization. Additionally, soluble proteins secreted by these deformed cells were able to diffuse and modulate ECM secretion and organization in neighboring cells, as demonstrated by a transwell assay. The ECM is a complex, dynamic environment with tightly regulated mechanical and biochemical properties that affect essential cell functions, including adhesion, proliferation, and differentiation.52 ECM fiber alignment increases local matrix stiffness, which promotes higher force generation and increases cell stiffness, creating a positive feedback loop between cells and the matrix.53 Furthermore, the organized ECM enhances calcium recruitment and accelerates mineralization, contributing to effective bone regeneration.
+
+Implantation of the flat and micropillar mPOC/HA scaffolds seeded with MSCs resulted in larger new bone volume formation in vivo compared to previous studies using mPOC alone, a finding likely due to the osteoconductive properties of HA. ST analysis revealed a significant upregulation of genes encoding cartilage oligomeric matrix protein (COMP) and fibromodulin (FMOD) in the micropillar group, consistent with the secreteome analysis. COMP binds to matrix proteins like collagen, enhancing ECM organization and assembly.54 As an ECM protein, COMP also promotes osteogenesis by binding to bone morphogenetic protein 2 (BMP- 2), increasing its local concentration and boosting its biological activity.55 FMOD, with a strong affinity for the HA matrix, helps attenuate osteoclast precursor maturation, thereby influencing osteoblast- osteoclast crosstalk.56 These results suggest that nuclear deformation induced by micropiliars may promote osteogenesis in neighboring cells via matricrine effects.
+
+<--- Page Split --->
+
+Despite the enhanced bone regeneration observed, mPOC/HA implants did not achieve complete healing of the cranial defect, likely due to the limited interaction surface of the film scaffold. The influence of the implants, whether through direct chromatin reprogramming guidance or secretome activity, was restricted to cells at the tissue- scaffold interface. Future efforts should focus on the design and fabrication of 3D micropillar implants using additive manufacturing and composite materials to create a more comprehensive 3D cellular microenvironment that promotes bone regeneration. Additionally, the application of micropillars as a platform for delivering bioactive factors could be explored as a strategy to achieve complete cranial bone healing.
+
+In summary, we investigated the effects of nuclear deformation on the cellular secretome using micropillar implants fabricated from an mPOC/HA composite. The mPOC/HA micropillars demonstrated similar properties to a flat substrate in terms of roughness and degradation but had a substantial impact on cellular and nuclear morphology, cell adhesion, cytoskeletal development, and osteogenic differentiation in hMSCs. Nuclear- deformed cells showed increased secretion of proteins and RNA transcriptions that regulate ECM components and organization, promoting osteogenesis in neighboring cells both in vitro and in vivo. These findings suggest that incorporating microtopography into implants holds significant promise for bone regeneration. This study offers valuable insights for the future design and fabrication of bioactive implants in regenerative engineering.
+
+## Materials and Methods
+
+Synthesis and characterization of mPOC pre- polymer.
+
+The mPOC pre- polymer were synthesized according to a previous report. Briefly, the POC pre- polymer was firstly synthesized by reaction of equal molar of citric acid (Sigma- Aldrich, 251275) and 1,8- octandiol (Sigma- Aldrich, O3303) at \(140^{\circ}\mathrm{C}\) oil bath for 60 min. The product was then purified by precipitation in DI water. After lyophilization, 66g POC pre- polymer was dissolved in 540 ml tetrahydrofuran (THF) and reacted with 0.036 mol imidazole (Sigma- Aldrich, I2399) and 0.4 mol glycidyl methacrylate (Sigma- Aldrich, 151238) at \(60^{\circ}\mathrm{C}\) for 6 h. The final product was then purified by precipitation in DI water and lyophilized for storage at - 20 \(^{\circ}\mathrm{C}\) . Successful synthesis of mPOC pre- polymer was characterized using proton nuclear magnetic resonance (1H- NMR, Bruker A600).
+
+## Fabrication and characterization of mPOC/HA micropillar scaffolds
+
+SU- 8 micropillar structures (5x5x8 um) were fabricated according to our previous study. PDMS molds were then fabricated to replicate the invert structures. HA nanoparticles (Sigma- Aldrich, 677418) were mixed with mPOC pre- polymer at weight ratio of 6:4. The \(60\%\) HA was selected to mimic composition of native bone. Photo- initiator (5 mg/ml camphorquinone and ethyl 4- dimethylaminobenzoate) was added to the mPOC/HA slurry. The mixture was then added onto PDMS mold and pressed onto cover glass to prepare free- standing scaffold under exposure with laser (1W, 470 nm). Post- curing of the scaffold was performed in \(80^{\circ}\mathrm{C}\) oven over night. The size of HA nanoparticles was characterized using Dynamic Light Scattering (DLS). The topography of
+
+<--- Page Split --->
+
+micropillars was observed using scanning electron microscope (SEM, FEI Quanta 650 ESEM) and characterized using 3D optical microscope (Bruker). Surface roughness of flat and micropillar scaffolds was characterized using atomic force microscope (AFM, Bruker ICON system). The water contact angle was tested using VCA Optima XE system. The compressive modulus of the scaffolds was characterized using a Tribioindenter (Bruker). Based on a previous report, \(^{58}\) the lateral modulus of micropillars was calculated according to the following equations:
+
+\[k_{L} = \frac{3EI}{L^{3}} (1)\]
+
+The ' \(\mathrm{kL}\) ' is the lateral stiffness, 'E' is the measured modulus, 'I' is the moment area of inertia, and 'L' is the micropillar height. For square micropillars, 'I' can be described as:
+
+\[I = \frac{a^{4}}{12} (2)\]
+
+Where 'a' is the side length of the micropillars. Thus, the lateral modulus of the micropillars ' \(\mathrm{E_{L}}\) ' equals to:
+
+\[E_{L} = \frac{K_{L}L}{A} (3)\]
+
+Where 'A' is the cross- section area of micropillars.
+
+## Degradation and calcium release
+
+To test the degradation of the mPOC/HA scaffold, the dry weight of mPOC/HA scaffolds at day 0 was recorded as the initial weight. Then the scaffolds were merged in \(1\mathrm{ml}\) DPBS solution in \(75^{\circ}\mathrm{C}\) oven. At each designed time point (1, 2, 3, 5, 7, 10 and 14 d), the scaffolds were rinsed with DI water followed by drying at \(60^{\circ}\mathrm{C}\) . The weight was recorded to calculate the weight loss percentage. The calcium release test was also performed with \(75^{\circ}\mathrm{C}\) DPBS (no calcium, no magnesium). At the designed time points, the elution solution was collected and replaced with fresh DPBS (1 ml). The released calcium was detected with inductively coupled plasma mass spectrometry (ICP- MS, ThermoFisher Element 2). Accumulated calcium release was calculated.
+
+## Cell culture
+
+Human mesenchymal stromal cells (hMSCs, PCS- 500- 012) were purchased from the American Type Culture Collection (ATCC) and cultured with the growth medium acquired from ATCC. hMSCs with the passage 4- 6 were seeded onto the flat and micropillar mPOC/HA substrates. To test cell attachment, hMSCs were seeded at 5000 cells/cm \(^2\) and cultured for 3 h followed by PBS rinsing to remove unattached cells. The attached cells were then trypsinized and collected for cell counting. For other experiments, the cells were cultured in growth medium for 24 h to allow cell attachment and spreading followed by incubation with osteogenic induction medium. After 3 d culture, live/dead staining (Thermofisher, L3224), MTT assay (Thermofisher, V13154), and Picogreen assay (Thermofisher, P7589) were performed according to the manufactures' protocol.
+
+Nuclear morphology analysis
+
+<--- Page Split --->
+
+After one day of culture, the cells were fixed with \(4\%\) paraformaldehyde, and cell nuclei were stained using SYTOX™ Green (ThermoFisher, S7020) according to the manufacture's instruction. The nuclear shape index (NSI) was analyzed to evaluate 2D nuclear deformation. \(^{27}\) The stained cells were then imaged using a confocal microscope (Leica SP8) to acquire their 3D morphology. Cell nuclei were reconstructed using the Fiji ImageJ software (https://imagej.net/Fiji). Cell nuclear volume, surface area, project area, height, and the ratio of surface area to volume were measured using 3D objects counter plugin. More than 30 nuclei from 3 biological replicates were imaged and analyzed to calculate the statistics.
+
+## Scanning electron microscope
+
+To visualize cell adhesion on mPOC/HA scaffolds, cells were fixed with \(3\%\) glutaraldehyde (Electron Microscopy Sciences) and rinsed with DI water. Subsequently, the cells underwent dehydration using a series of ethanol concentrations ( \(30\%\) , \(50\%\) , \(70\%\) , \(90\%\) , and \(100\%\) ) for 5 min each, followed by drying using a critical point dryer (Tousimis Samdri) as per the manual. The dehydrated cells were coated with a \(5\mathrm{nm}\) osmium layer and imaged using a scanning electron microscope (SEM, FEI Quanta 650). Captured images were further enhanced for visualization of cellular architecture using Photoshop. Additionally, cells on transwell were imaged using SEM and EDS analysis was performed to evaluate the calcium and phosphate deposition.
+
+## Osteogenic differentiation
+
+hMSCs were seeded onto both flat and micropillar mPOC/HA substrates. One- day post- seeding, osteogenic induction medium (Lonza) was applied to prompt the osteogenic differentiation of hMSCs. After 7 days of induction, cells were washed with PBS buffer and fixed with \(4\%\) paraformaldehyde for 10 minutes. Subsequently, the samples were immersed in a solution of 56 mM 2- amino- 2- methyl- 1,3- propanediol (AMP, pH- 9.9), containing \(0.1\%\) naphthol AS- MX phosphate and \(0.1\%\) fast blue RR salt to stain alkaline phosphatase (ALP). Bright- field images were acquired using a Nikon Eclipse TE2000- U inverted microscope. ALP activity was assessed using the ALP assay kit (K422- 500, Biovision) following the provided manual. Briefly, cells cultured in induction medium for 7 days were homogenized using ALP assay buffer. Subsequently, the non- fluorescent substrate 4- Methylumelliferyl phosphate disodium salt (MUP) was mixed with the homogenized samples to generate a fluorescent signal through its cleavage by ALP. Fluorescence intensity was measured using a Cytation 5 imaging reader (BioTek) at \((\mathrm{Ex / Em} = 360 / 440\mathrm{nm})\) . Enzymatic activity was calculated based on the standard curve and normalized to total DNA content, determined by the Quant- iT PicoGreen dsDNA assay (Invitrogen). The expression levels of OCN and RUNX2 were quantified through Western blot analysis. In brief, cell lysis was performed using radioimmunoprecipitation assay (RIPA) buffer. The relative protein quantities were measured using a Cytation 5 imaging reader. Equal amounts of proteins extracted from flat and micropillar samples were loaded onto a NuPAGE 4- 12% Bis- Tris Gel (Invitrogen) and subsequently transferred to nitrocellulose membranes (Bio- rad). Afterward, membranes were blocked with \(5\%\) milk and incubated with primary antibodies (including GAPDH from Abcam, OCN from Cell Signaling, RUNX2 from Santa Cruz) overnight at \(4^{\circ}\mathrm{C}\) with gentle shaking. Following this, secondary antibodies, diluted at a ratio of 1:5000, were applied and incubated with the membranes at room temperature for 1 hour. Protein bands were
+
+<--- Page Split --->
+
+visualized using the Azure 600 gel imaging system. The acquired images underwent analysis through the 'Gel Analyzer' tool in ImageJ. The intensity of all target protein bands was initially compared to the corresponding GAPDH, and then normalized against a flat surface, which was set as 1. Statistical calculations were based on three biological replicates.
+
+Secretome sample preparation: Analysis of secreted proteins is complicated by high concentrations of serum proteins. Our approach reduced initial sample volume to a \(20~\mu \mathrm{l}\) concentrate using a molecular weight cut off filter (50 kDa, Amicon Ultra- 15 centrifugal, Ultracel, Merck). The concentrate above 50KDa was depleted of the most abundant proteins using a High Select HAS / Immunoglobulin Depletion Midi spin column (A36367, Thermo Fisher Scientific), resulting in a filtrate solution (below 50KDa) and a depleted solution per sample. An acetone / TCA (Trichloroacetic acid) protein precipitation was performed on each solution to create protein pellets and an in- solution trypsin digestion was performed on each pellet. \(100~\mu \mathrm{l}\) of re- suspension buffer (8 M urea in \(400~\mathrm{mM}\) ammonium bicarbonate) was added to the pellet and incubated with mixing for 15 minutes. Disulfide bonds were reduced by addition of \(100~\mathrm{mM}\) dithiothreitol and incubated for 45 minutes at \(55~^\circ \mathrm{C}\) . Sulfhydryl groups were alkylated by addition of \(300~\mathrm{mM}\) iodoacetamide and incubated for 45 minutes at \(25~^\circ \mathrm{C}\) shielded from light. Samples were diluted 4- fold with ammonium bicarbonate to reduce the urea concentration below 2 M. Protein digestion was performed by addition of trypsin (MS- grade, Promega) at a 1:50 ratio (enzyme:substrate) and incubated overnight at \(37~^\circ \mathrm{C}\) . Digestion was halted with the addition of \(10\%\) formic acid (FA) to a final concentration of \(0.5\%\) . Peptides were desalted with C18 spin columns (The Nest Group), dried by vacuum centrifugation, and stored at \(- 20~^\circ \mathrm{C}\) . Peptides were resuspended in \(5\%\) ACN (Acetonitrile) / \(0.1\%\) FA for LC- MS analysis. Peptide concentration was quantified using micro BCA (Bicinchoninic acid) protein assay kit (Thermo Scientific, Ref: 23235).
+
+Proteome sample preparation: Cells were lysed using cell lysis buffer ( \(0.5\%\) SDS, \(50\mathrm{mM}\) Ambi (Ammonium Bicarbonate), \(50\mathrm{mM}\) NaCl (Sodium Chloride), Halt Protease inhibitor). An acetone / TCA protein precipitation was performed on each lysed samples solution to create protein pellets and an in- solution trypsin digestion was performed on each pellet. \(100~\mu \mathrm{l}\) of re- suspension buffer (8 M urea in \(400~\mathrm{mM}\) ammonium bicarbonate) was added to the pellet and incubated with mixing for 15 minutes. Disulfide bonds were reduced by addition of \(100~\mathrm{mM}\) dithiothreitol and incubated for 45 minutes at \(55~^\circ \mathrm{C}\) . Sulfhydryl groups were alkylated by addition of \(300~\mathrm{mM}\) iodoacetamide and incubated for 45 minutes at \(25~^\circ \mathrm{C}\) shielded from light. Samples were diluted 4- fold with ammonium bicarbonate to reduce the urea concentration below 2 M. Protein digestion was performed by addition of trypsin (MS- grade, Promega) at a 1:50 ratio (enzyme:substrate) and incubated overnight at \(37~^\circ \mathrm{C}\) . Digestion was halted with the addition of \(10\%\) formic acid to a final concentration of \(0.5\%\) . Peptides were desalted with C18 spin columns (The Nest Group), dried by vacuum centrifugation, and resuspended in \(5\%\) ACN/ \(0.1\%\) FA for LC- MS analysis. Peptide concentration was quantified using micro BCA Protein Assay Kit (Thermo Scientific, Ref: 23235).
+
+Liquid Chromatography High Resolution Tandem Mass Spectrometry (LC- HRMS/MS) Analysis: Peptides were analyzed using a Vanquish Neo nano- LC coupled to a Exploris 480 hybrid quadrupole- orbitrap mass spectrometer (Thermo Fisher Scientific, USA). The samples were loaded onto the trap column of \(75\mu \mathrm{m}\) internal diameter (ID) x 2cm length (Acclaim PepMapTM
+
+<--- Page Split --->
+
+100, P/N 164535) and analytical separation was performed using a UHPLC C18 column (15cm length \(\times 75\mu \mathrm{m}\) internal diameter, \(1.7\mu \mathrm{m}\) particle size, Ion Opticks, AUR3- 15075C18). For each run, \(1\mu \mathrm{g}\) of peptide sample was injected. Electrospray ionization was performed using a Nanospray Flex Ion Source (Thermo Fisher, ES071) at a positive static spray voltage of \(2.3\mathrm{kV}\) . Peptides were eluted from the analytical column at a flow rate of \(200\mathrm{nL / min}\) using an increasing organic gradient to separate peptides based on their hydrophobicity. Buffer A was \(0.1\%\) formic acid in Optima LC- MS grade water, and buffer B was \(80\%\) acetonitrile, \(19.9\%\) Optima LC- MS grade water, and \(0.1\%\) formic acid: The method duration was 120 minutes. The mass spectrometer was controlled using Xcalibur and operated in a positive polarity. The full scan (MS1) settings used were: mass range 350- 2000 m/z, RF lens \(60\%\) , orbitrap resolution 120,000, normalized AGC target \(300\%\) , maximum injection time of 25 milliseconds, and a \(5\mathrm{E}^{3}\) intensity threshold. Datadependent acquisition (DDA) by TopN was performed through higher- energy collisional dissociation (HCD) of isolated precursor ions with charges of \(2+\) to \(5+\) inclusive. The MS2 settings were: dynamic exclusion mode duration 30 seconds, mass tolerance 5 ppm (both low and high), 2 second cycle time, isolation window \(1.5\mathrm{m / z}\) , \(30\%\) normalized collision energy, orbitrap resolution 15,000, normalized AGC target \(100\%\) , and maximum injection time of 50 milliseconds.
+
+Data analysis: Mass spectrometry files (.raw) were converted to Mascot generic format (.mgf) using the Scripps RawConverter program and then analyzed using the Mascot search engine (Matrix Science, version 2.5.1). MS/MS spectra were searched against the SwissProt database of the organism of interest. Search parameters included a fixed modification of cysteine carbamidomethylation, and variable modifications of methionine oxidation, deaminated asparagine and aspartic acid, and acetylated protein N- termini. Two missed tryptic cleavages were permitted. A \(1\%\) false discovery rate (FDR) cutoff was applied at the peptide level. Only proteins with at least two peptides were considered for further study.
+
+Label- Free Quantification: The samples were acquired on mass spec and the data were searched against a specific database using the MaxQuant application. \(^{59}\) Label- Free Quantification (LFQ) was obtained by LFQ MS1 intensity. The results were filtered with a minimum of 2 unique peptides. Technical replicates were averaged and intensities were Log2 transformed to achieve a normal distribution of the data. Missing values were filtered to keep only proteins quantified in at least 2 samples per group. For statistics, Student t- Test was applied using \(\mathrm{p}< 0.05\) and \(\mathrm{FC} > 2\) to determine which proteins were significantly up- and down- regulated and visualize it by volcano plot. Downstream analyses and visualizations were done using RStudio software (R version 4.3.2, RStudio version 2024.09.0). Principal component analysis (PCA) was done using 'prcomp' R function to visualize a ability of the differential protein expression to distinguish between biological conditions. Heatmap plot was built using 'ComplexHeatmap' R package. GO and Pathways enrichment analysis was done using 'clusterProfiler' R package \(^{60}\) and annotations with adjusted p- values (FDR, Benjamini- Hochberg) \(< 0.05\) were considered significant. Additional packages used include 'org.Hs.eg.db' for human gene annotations and 'enrichplot' for visualization. This analysis considered the entire set of human protein- coding genes as the reference background.
+
+<--- Page Split --->
+
+Transwell assay: The flat and micropillar mPOC/HA surfaces were fabricated in a 24 well plate. The hMSCs were seeded onto the surfaces with 40,000 cells per well. Then a transwell was put in each well and additional hMSCs were seeded inside the transwell (Costar, \(0.4 \mu \mathrm{m}\) polyester membrane) at density of 5,000 cells/ \(\mathrm{cm}^2\) . After cell attachment, osteogenic medium was used to induce osteogenic differentiation of the cells. At 7 days post- induction, the cells on transwell were fixed followed by ALP staining and quantification to investigate the paracrine effect of deformed and undeformed cells on osteogenesis. At 3 weeks post- induction, additional transwells were collected for Alizarin Red S (ARS) staining and quantification to show the calcium deposition influenced by the paracrine effect. At 4 weeks post- induction, the collagen, which is one of the major components in ECM and significantly affected according to the secretome analysis, were stained using anti- collagen antibody (Abcam, ab36064) to investigate the influence of nuclear deformation on ECM organization.
+
+In vivo implantation: The animal study was approved by the University of Chicago Animal Care and Use Committee following NIH guidance (ACUP#71745). Eight- week- old female athymic nude mice obtained from Harlan Laboratories were used for the study. The animals were housed in a separately air- conditioned cabinet at temperature of \(24 - 26^{\circ}\mathrm{C}\) with 12:12 light:dark cycle. The surgeries were performed according to the previous report61. Briefly, animals were treated with \(2\%\) isoflurane delivered by \(100\% \mathrm{O}_2\) and maintained with \(1 - 1.5\%\) isoflurane for anaesthesia. Two critical- sized defects (4 mm diameter) were created on the left and right side of skull of each animal followed by implantation of hMSCs seeded flat and micropillar scaffolds, respectively. After implantation of scaffolds, a larger mPOC film \((1 \times 1.5 \mathrm{cm}^2)\) was attached to the skull with thrombin/fibrinogen to prevent displacement of implants. Skin tissue was closed with 5- 0 nylon interrupted sutures and removed after 2 weeks. The animals were monitored after anaesthesia hourly until recovery. Buprenorphine \(50 \mu \mathrm{g} \mathrm{kg}^{- 1}\) and meloxicam \(1 \mathrm{mg} \mathrm{kg}^{- 1}\) were used for pain relief.
+
+Micro- CT: Micro- CT images of cranial were performed on the XCUBE (Molecules NV) by the Integrated Small Animal Imaging Research Resource (iSAIRR) at The University of Chicago. Spiral high- resolution computed tomography acquisitions were performed with an X- ray source of \(50 \mathrm{kVp}\) and \(440 \mu \mathrm{A}\) . Volumetric computed tomography images were reconstructed by applying the iterative image space reconstruction algorithm (ISRA) in a \(400 \times 400 \times 370\) format with voxel dimensions of \(100 \times 100 \times 100 \mu \mathrm{m}^3\) . An Amira software (Thermo Scientific) was used for 3D reconstruction of the skull tissue and to analyse the bone formation in the defect area. Scale bars were used to standardize the images. Defect recovery is defined as \((\mathrm{Vi} - \mathrm{Vd}) / \mathrm{Vi} \times 100\%\) , where Vi and Vd represent defect volume at initial and designed timepoints, respectively.
+
+Histology analysis: Skull samples were fixed and decalcified in Cal- EX II (Fisher Scientific) for 24 hours, rinsed with PBS, and embedded in paraffin. Tissue sections containing defect sites were cut to \(5 \mu \mathrm{m}\) thickness and stained with H&E and trichrome to assess tissue regeneration. Regenerated tissue thickness was measured using ImageJ, and osteogenesis was evaluated via IHC staining for key osteogenic markers, including OCN and OPN. Mouse skin tissue served as a negative control for all IHC staining.
+
+<--- Page Split --->
+
+Spatial transcriptomics: To confirm the RNA quality of each FFPE tissue block, 1- 2 curls (10um thickness each) were used for RNA extraction using Qiagen RNeasy FFPE kit (Qiagen 73504) according to manufactures' protocol. Extracted RNA was examined by Agilent Bioanalyzer RNA pico chip to confirm the \(\mathrm{DV}200 > 30\%\) . Simultaneously, the tissue morphology was examined on HE stained slide to identify region of interest.
+
+For each FFPE sample, 1 section (5um thickness) was placed on visium slides. Each slide was incubated at \(42^{\circ}\mathrm{C}\) for 3 hours followed by overnight room temperature incubation. Then, the slide was stored at desiccated slide holder until proceeding to deparaffinization.
+
+The deparaffinization, HE staining and imaging and decrosslinking of tissue slides were performed according to 10x Genomics protocol (CG000409 and CG000407) specific for Visium spatial gene expression for FFPE kit. Then, the slides were proceeded to human probe (v2) hybridization and ligation using 10x Genomics Visium spatial gene expression, \(6.5\mathrm{mm}\) kit (10x Genomics, PN- 1000188). The probes were released from tissue slide and captured on visium slide followed by probe extension. Sequencing libraries were prepared according to manufacturer's protocol. Multiplexed libraries were pooled and sequenced on Novaseq X Plus 10Bflowcell 100 cycles kit with following parameter: 28nt for Read 1 and 90nt for Read 2.
+
+We visually identified the implant region in each sample. To exclude low quality capture locations, we removed the capture locations with fewer than 500 unique molecular identifiers, fewer than 500 genes, or \(\geq 25\%\) mitochondrial reads. \(^{61}\) We also filtered out the genes that are expressed in fewer than five capture locations. \(^{61}\) After quality control, flat group had 101 capture locations and 12,701 genes, whereas micropillar group had 73 capture locations and 13,371 genes.
+
+Differential gene expression analysis: To identify the genes differentially expressed in flat and micropillar groups, we performed Wilcoxon rank- sum tests on the merged dataset (174 capture locations) using the FindAllMarkers function in Seurat V3. \(^{62}\) Our testing was limited to the genes present in both implants, detected in a minimum \(1\%\) of cells in either implant, as well as showing at least 0.1 log- fold difference between the two implants.
+
+Cell type deconvolution: To perform cell typing on our data, we first identified three publicly available bone single- cell RNA sequencing (scRNA- seq) references with annotated cell types. \(^{43 - 45}\) The scRNA- seq references were processed, quality controlled, and merged using Seurat V3. Since our samples are nude mice, we excluded all the immune cells from the merged reference. The final merged scRNA- seq dataset contained a total of 12,717 cells and represented all major cell types present in bone tissues.
+
+In 10x Visium data, each capture location contains a mixture of cells. \(^{63}\) Therefore, we performed cell type deconvolution to predict the cell type proportions in each capture location using BayesPrism, a Bayesian deconvolution method shown to work on spatial transcriptomics data. \(^{64,65}\) We excluded chromosomes X and Y, ribosomal, and mitochondrial genes from the analysis to reduce batch effects. We also removed the outlier genes with expression greater than \(1\%\) of the total reads in over \(10\%\) of capture locations. To improve cell typing accuracy, we only used the cell type signature genes for deconvolution analysis. The cell type markers were identified based
+
+<--- Page Split --->
+
+on the differential expression analysis results on the merged scRNA- seq reference. The predicted cell type proportions with above 0.5 coefficient of variation were clipped to zero to reduce noise.
+
+Cell- type- based analyses: We performed Wilcoxon rank- sum tests using the deconvoluted cell type proportions to test if certain cell types are more prevalent in one implant than the other. We further examined the association between cell type proportions and gene expression levels in the two implants through Kendall's correlation analyses. All the p- values were adjusted for multiple testing through the false discovery rate approach. The proportions of three cell types (chondrocyte, OLC, and osteocyte) had over 50 significantly positively correlated genes. For each of these cell types, we performed pathway enrichment analysis of the significantly positively correlated genes using Metascape. \(^{66}\)
+
+Statistical analysis: The results are shown as mean \(\pm\) standard deviation using violin super plots or bar graphs. Statistical analysis was performed using Kyplot software (version 2.0 beta 15). Statistical significance was determined by Student's t- test (flat versus micropillar, two- sided). All experiments presented in the manuscript were repeated at least as two independent experiments with replicates to confirm the results are reproducible.
+
+## Acknowledgement
+
+This work was supported by the National Science Foundation (NSF) Emerging Frontiers in Research and Innovation (EFRI) (no. 1830968 to G.A.A.), and National Institutes of Health (NIH) grants U54CA268084 and R01CA228272, NSF grant EFMA- 1830961 (to V.B.). This work was performed as a collaboration between the Center for Advanced Regenerative Engineering (CARE) and the Center for Physical Genomics and Engineering (CPGE) at Northwestern University. This work made use of the EPIC facility, the NUFAB facility, and the BioCryo facility of Northwestern University's NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS- 2025633), the International Institute for Nanotechnology (IIN) and Northwestern's MRSEC programme (NSF DMR- 1720139). Proteomics services were performed by the Northwestern Proteomics Core Facility, generously supported by NCI CCSG P30 CA060553 awarded to the Robert H Lurie Comprehensive Cancer Center, instrumentation award (S10OD025194) from NIH Office of the Director, and the National Resource for Translational and Developmental Proteomics supported by P41 GM108569. We also thank the help from Dr. Hsiu- Ming Tsai at the Department of Radiology, The University of Chicago for microCT imaging. This work also made use of the Northwestern University NUSeq Core and the Biological Imaging Facility (BIF).
+
+## References
+
+1 Rippe, K. Dynamic organization of the cell nucleus. Curr. Opin. in Genet. Dev. 17, 373- 380 (2007).
+2 Kalukula, Y., Stephens, A. D., Lammerding, J. & Gabriele, S. Mechanics and functional consequences of nuclear deformations. Nat. Rev. Mol. Cell Biol. 23, 583- 602 (2022).
+
+<--- Page Split --->
+
+3 Ramdas, N. M. & Shivashankar, G. V. Cytoskeletal Control of Nuclear Morphology and Chromatin Organization. J. Mol. Biol. 427, 695- 706 (2015).4 Heckenbach, I. et al. Nuclear morphology is a deep learning biomarker of cellular senescence. Nat. Aging 2, 742- 755 (2022).5 Seelbinder, B. et al. Nuclear deformation guides chromatin reorganization in cardiac development and disease. Nat. Biomed. Eng. 5, 1500- 1516 (2021).6 Uhler, C. & Shivashankar, G. V. Nuclear Mechanopathology and Cancer Diagnosis. Trends in cancer 4, 320- 331 (2018).7 Lele, T. P., Levy, D. L. & Mishra, K. Editorial: Nuclear morphology in development and disease. Front. Cell Dev. Biol. 11 (2023).8 Dahl, K. N., Ribeiro, A. J. & Lammerding, J. Nuclear shape, mechanics, and mechanotransduction. Circ. Res. 102, 1307- 1318 (2008).9 Wang, X. et al. Mechanical stability of the cell nucleus - roles played by the cytoskeleton in nuclear deformation and strain recovery. J. Cell Sci. 131 (2018).10 Elosegui- Artola, A. et al. Force Triggers YAP Nuclear Entry by Regulating Transport across Nuclear Pores. Cell 171, 1397- 1410. e1314 (2017).11 Lomakin, A. J. et al. The nucleus acts as a ruler tailoring cell responses to spatial constraints. Science 370, eaba2894 (2020).12 Venturini, V. et al. The nucleus measures shape changes for cellular proprioception to control dynamic cell behavior. Science 370, eaba2644 (2020).13 Wang, X. et al. Chromatin reprogramming and bone regeneration in vitro and in vivo via the microtopography- induced constriction of cell nuclei. Nat. Biomed. Eng. 7, 1514- 1529 (2023).14 Liu, H. et al. In Situ Mechanical Characterization of the Cell Nucleus by Atomic Force Microscopy. ACS Nano 8, 3821- 3828 (2014).15 Kechagia, Z. et al. The laminin- keratin link shields the nucleus from mechanical deformation and signalling. Nat. Mater. 22, 1409- 1420 (2023).16 Wang, X. et al. Intracellular manipulation and measurement with multipole magnetic tweezers. Sci. Robot. 4, eaav6180 (2019).17 Hwang, J. Y. et al. Cell Deformation by Single- beam Acoustic Trapping: A Promising Tool for Measurements of Cell Mechanics. Sci. Rep. 6, 27238 (2016).18 Stöberl, S. et al. Nuclear deformation and dynamics of migrating cells in 3D confinement reveal adaptation of pulling and pushing forces. Sci. Adv. 10, eadm9195 (2024).19 Song, Y. et al. Transient nuclear deformation primes epigenetic state and promotes cell reprogramming. Nat. Mater. 21, 1191- 1199 (2022).20 Shah, P. et al. Nuclear Deformation Causes DNA Damage by Increasing Replication Stress. Curr. Biol. 31, 753- 765. e756 (2021).21 Hanson, L. et al. Vertical nanopillars for in situ probing of nuclear mechanics in adherent cells. Nat. Nanotechnol. 10, 554- 562 (2015).22 Davidson, P. M., Özçelik, H., Hasirci, V., Reiter, G. & Anselme, K. Microstructured Surfaces Cause Severe but Non- Detrimental Deformation of the Cell Nucleus. Adv. Mater. 21, 3586- 3590 (2009).23 Tusamda Wakhloo, N. et al. Actomyosin, vimentin and LINC complex pull on osteosarcoma nuclei to deform on micropillar topography. Biomaterials 234, 119746 (2020).
+
+<--- Page Split --->
+
+24 Cao, X. et al. A Chemomechanical Model for Nuclear Morphology and Stresses during Cell Transendothelial Migration. Biophys. J. 111, 1541- 1552 (2016).25 Liu, R., Yao, X., Liu, X. & Ding, J. Proliferation of Cells with Severe Nuclear Deformation on a Micropillar Array. Langmuir : the ACS journal of surfaces and colloids 35, 284- 299 (2019).26 Carthew, J. et al. Precision Surface Microtopography Regulates Cell Fate via Changes to Actomyosin Contractility and Nuclear Architecture. Adv. Sci. 8, 2003186 (2021).27 Liu, X. et al. Subcellular cell geometry on micropillars regulates stem cell differentiation. Biomaterials 111, 27- 39 (2016).28 Long, Y., Sun, Y., Jin, L., Qin, Y. & Zeng, Y. Micropillars in Biomechanics: Role in Guiding Mesenchymal Stem Cells Differentiation and Bone Regeneration. Adv. Mater. Interfaces 11, 2300703 (2024).29 Xu, H. et al. Citric Acid: A Nexus Between Cellular Mechanisms and Biomaterial Innovations. Adv. Mater. 36, 2402871 (2024).30 Epstein, S. E., Luger, D. & Lipinski, M. J. Paracrine- Mediated Systemic Anti- Inflammatory Activity of Intravenously Administered Mesenchymal Stem Cells. Circ. Res. 121, 1044- 1046 (2017).31 Burdon, T. J., Paul, A., Noiseux, N., Prakash, S. & Shum- Tim, D. Bone Marrow Stem Cell Derived Paracrine Factors for Regenerative Medicine: Current Perspectives and Therapeutic Potential. Bone Marrow Res. 2011, 207326 (2011).32 Wang, Y., Kibbe, M. R. & Ameer, G. A. Photo- crosslinked biodegradable elastomers for controlled nitric oxide delivery. Biomater. Sci. 1, 625- 632 (2013).33 Fernando, S., McEnery, M. & Guelcher, S. A. in Advances in Polyurethane Biomaterials (eds Stuart L. Cooper & Jianjun Guan) 481- 501 (Woodhead Publishing, 2016).34 Ghibaudo, M. et al. Traction forces and rigidity sensing regulate cell functions. Soft Matter 4, 1836- 1843 (2008).35 Badique, F. et al. Directing nuclear deformation on micropillared surfaces by substrate geometry and cytoskeleton organization. Biomaterials 34, 2991- 3001 (2013).36 Ryu, H. et al. Materials and Design Approaches for a Fully Bioresorbable, Electrically Conductive and Mechanically Compliant Cardiac Patch Technology. Adv. Sci. 10, 2303429 (2023).37 Khalili, A. A. & Ahmad, M. R. A Review of Cell Adhesion Studies for Biomedical and Biological Applications. Int. J. Mol. Sci 16, 18149- 18184 (2015).38 Tomczak, A. et al. Interpretation of biological experiments changes with evolution of the Gene Ontology and its annotations. Sci. Rep. 8, 5115 (2018).39 Fabregat, A. et al. Reactome pathway analysis: a high- performance in- memory approach. BMC Bioinformatics 18, 142 (2017).40 Lu, P., Takai, K., Weaver, V. M. & Werb, Z. Extracellular matrix degradation and remodeling in development and disease. Cold Spring Harb Perspect Biol. 3 (2011).41 Zeng, Z., Li, Y., Li, Y. & Luo, Y. Statistical and machine learning methods for spatially resolved transcriptomics data analysis. Genome Biol. 23, 83 (2022).42 Yu, M. et al. Cranial Suture Regeneration Mitigates Skull and Neurocognitive Defects in Craniosynostosis. Cell 184, 243- 256. e218 (2021).43 Dillard, L. J. et al. Single- Cell Transcriptomics of Bone Marrow Stromal Cells in Diversity Outbred Mice: A Model for Population- Level scRNA- Seq Studies. J. Bone Miner. Res. 38, 1350- 1363 (2023).
+
+<--- Page Split --->
+
+44 Han, X. et al. Mapping the Mouse Cell Atlas by Microwell-Seq. Cell 172, 1091- 1107. e1017 (2018).45 Baryawno, N. et al. A Cellular Taxonomy of the Bone Marrow Stroma in Homeostasis and Leukemia. Cell 177, 1915- 1932. e1916 (2019).46 Zhong, L. et al. Single cell transcriptomics identifies a unique adipose lineage cell population that regulates bone marrow environment. eLife 9, e54695 (2020).47 Ma, C. et al. Citrate- based materials fuel human stem cells by metabonegenic regulation. Proc. Natl. Acad. Sci. USA 115, E11741- E11750 (2018).48 Woodard, J. R. et al. The mechanical properties and osteoconductivity of hydroxyapatite bone scaffolds with multi- scale porosity. Biomaterials 28, 45- 54 (2007).49 Wang, H., Huddleston, S., Yang, J. & Ameer, G. A. Enabling Proregenerative Medical Devices via Citrate- Based Biomaterials: Transitioning from Inert to Regenerative Biomaterials. Adv. Mater. 36, 2306326 (2024).50 Vilar, A. et al. Substrate mechanical properties bias MSC paracrine activity and therapeutic potential. Acta Biomater. 168, 144- 158 (2023).51 Li, Y. et al. 3D micropattern force triggers YAP nuclear entry by transport across nuclear pores and modulates stem cells paracrine. Natl. Sci. Rev. 10 (2023).52 Karamanos, N. K. et al. A guide to the composition and functions of the extracellular matrix. The FEBS J. 288, 6850- 6912 (2021).53 Saraswathibhatla, A., Indana, D. & Chaudhuri, O. Cell- extracellular matrix mechanotransduction in 3D. Nat. Rev. Mol. Cell Biol. 24, 495- 516 (2023).54 Cui, J. & Zhang, J. Cartilage Oligomeric Matrix Protein, Diseases, and Therapeutic Opportunities. Int. J. Mol. Sci. 23, 9253 (2022).55 Ishida, K. et al. Cartilage oligomeric matrix protein enhances osteogenesis by directly binding and activating bone morphogenetic protein- 2. Bone 55, 23- 35 (2013).56 Zheng, Z., Granado, H. S. & Li, C. Fibromodulin, a Multifunctional Matricellular Modulator. J. Dent. Res. 102, 125- 134 (2023).57 Feng, X. Chemical and Biochemical Basis of Cell- Bone Matrix Interaction in Health and Disease. Curr. Chem. Biol. 3, 189- 196 (2009).58 Alapan, Y., Younesi, M., Akkus, O. & Gurkan, U. A. Anisotropically Stiff 3D Micropillar Niche Induces Extraordinary Cell Alignment and Elongation. Adv. Healthc. Mater. 5, 1884- 1892 (2016).59 Cox, J. & Mann, M. MaxQuant enables high peptide identification rates, individualized p.p.b.- range mass accuracies and proteome- wide protein quantification. Nat. Biotech. 26, 1367- 1372 (2008).60 Yu, G., Wang, L. G., Han, Y. & He, Q. Y. clusterProfiler: an R package for comparing biological themes among gene clusters. Omics : a journal of integrative biology 16, 284- 287 (2012).61 Qian, J. et al. A pan- cancer blueprint of the heterogeneous tumor microenvironment revealed by single- cell profiling. Cell Res. 30, 745- 762 (2020).62 Stuart, T. et al. Comprehensive Integration of Single- Cell Data. Cell 177, 1888- 1902. e1821 (2019).63 Li, B. et al. Benchmarking spatial and single- cell transcriptomics integration methods for transcript distribution prediction and cell type deconvolution. Nat. Methods 19, 662- 670 (2022).
+
+<--- Page Split --->
+
+64 Chu, T., Wang, Z., Pe'er, D. & Danko, C. G. Cell type and gene expression deconvolution with BayesPrism enables Bayesian integrative analysis across bulk and single- cell RNA sequencing in oncology. Nat. Cancer 3, 505- 517 (2022).65 Niec, R. E. et al. Lymphatics act as a signaling hub to regulate intestinal stem cell activity. Cell Stem Cell 29, 1067- 1082. e1018 (2022).66 Zhou, Y. et al. Metascape provides a biologist- oriented resource for the analysis of systems- level datasets. Nat. Commun. 10, 1523 (2019).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+SupplementaryTable1.xlsxSupplementaryTable2.xlsxSupplementaryTable3.xlsxSupplementaryTable4.xlsxSupplementMicrotopographyinducedchangesincellnucleusmorphologyenhanceboneregenerationbymodulatingthecellularsecretome.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/images_list.json b/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..1abf893469039fa922d741d76f7423090da0c091
--- /dev/null
+++ b/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/images_list.json
@@ -0,0 +1,62 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 60,
+ 100,
+ 700,
+ 720
+ ]
+ ],
+ "page_idx": 29
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 45,
+ 37,
+ 803,
+ 780
+ ]
+ ],
+ "page_idx": 31
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 60,
+ 80,
+ 808,
+ 737
+ ]
+ ],
+ "page_idx": 33
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 45,
+ 30,
+ 700,
+ 789
+ ]
+ ],
+ "page_idx": 35
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9.mmd b/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..9f82e4b5b3edb2224fd22f524917b46549da98d1
--- /dev/null
+++ b/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9.mmd
@@ -0,0 +1,487 @@
+
+# A Transcription Factor Functional Atlas of Germline Development
+
+Roger Pocock roger.pocock@monash.edu
+
+Monash University https://orcid.org/0000- 0002- 5515- 3608
+
+Wei Cao Monash University
+
+Qi Fan Monash University
+
+Gemmarie Amparado Monash University
+
+Dean Begic Monash University
+
+Rasoul Godini Monash University
+
+Sandeep Gopal sandeep.gopal@med.lu.se https://orcid.org/0000- 0002- 6706- 6747
+
+## Resource
+
+Keywords: Germ line, gametes, transcription factors, RNA interference, Caenorhabditis elegans
+
+Posted Date: January 26th, 2024
+
+DOI: https://doi.org/10.21203/rs.3.rs- 3880498/v1
+
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on August 11th, 2024. See the published version at https://doi.org/10.1038/s41467- 024- 51212- 0.
+
+<--- Page Split --->
+
+# A Transcription Factor Functional Atlas of Germline Development
+
+Wei Cao1#, Qi Fan1#, Gemmarie Amparado1, Dean Begic1, Rasoul Godini1, Sandeep Gopal1,2\* and Roger Pocock1\*.
+
+1Development and Stem Cells Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne, Victoria 3800, Australia.2Lund Stem Cell Center, Department of Experimental Medical Science; Lund University; Lund, Sweden.
+
+#Contributed equally to this work.
+
+*Correspondence should be addressed to R.P., W.C. and S.G.
+
+email: roger.pocock@monash.edu, wei.cao@monash.edu and sandeep.gopal@med.lu.se
+
+Keywords: Germ line, gametes, transcription factors, RNA interference, Caenorhabditis elegans
+
+<--- Page Split --->
+
+## ABSTRACT
+
+ABSTRACTFertility requires the faithful proliferation of germ cells and their differentiation into gametes. Controlling these cellular states demands precise timing and expression of gene networks. Transcription factors (TFs) play critical roles in gene expression networks that influence germ cell development. There has, however, been no functional analysis of the entire TF repertoire in controlling in vivo germ cell development. Here, we analyzed germ cell states and germline architecture to systematically investigate the function of 364 germline- expressed TFs in the Caenorhabditis elegans germ line. Using germline- specific knockdown, automated germ cell counting, and high- content analysis of germ cell nuclei and plasma membrane organization, we identify 156 TFs with discrete autonomous germline functions. By identifying TFs that control the germ cell cycle, proliferation, differentiation, germline structure and fertility, we have created an atlas for mechanistic dissection of germ cell behavior and gamete production.
+
+<--- Page Split --->
+
+## INTRODUCTION
+
+INTRODUCTIONThe production of oocytes and sperm (gametes) from germ cells is required for animal reproductive success. To ensure overall fitness, the balance between germ cell proliferation (self-renewal) and differentiation into gametes must be tightly controlled. Model organism research has previously identified regulatory mechanisms that control gene expression and RNA stability to maintain this balance in germ cell behavior. In the Caenorhabditis elegans model, for example, the PUF- domain RNA binding proteins FBF- 1/2 promote germline stem cell fate, with the mammalian ortholog required for the establishment of female germ cells (Crittenden et al., 2002; Mak et al., 2016). Furthermore, the importance of Notch signaling in establishing and maintaining germline stem cell pools was first discovered in C. elegans (Austin and Kimble, 1987). Thus, the C. elegans germ line is a valuable model for discovering conserved mechanisms governing germ cell behavior and fertility. Here, we map the transcription factor (TF) requirements for germ cell and gamete development in C. elegans.
+
+The C. elegans germ line originates from a single embryonic blastomere (P4) that divides into two primordial germ cells (Z2 and Z3) (Fukuyama et al., 2006). These embryonic germ cells are arrested at the G2 stage of the cell cycle and are transcriptionally quiescent to preserve germ cell fate and protect against inappropriate expression of somatic genes (Furuhashi et al., 2010; Seydoux et al., 1996). Transcriptional quiescence in these primordial germ cells (PGCs) is maintained by inhibiting RNA Polymerase II (RNA Pol II) and by nucleosome modifications associated with chromatin repression (Batchelder et al., 1999; Furuhashi et al., 2010). After embryos hatch and larvae start to feed, germline transcription is activated, and Z2 and Z3 exit G2 to commence mitosis during larval stage 1 (L1) (Fukuyama et al., 2006). Germ cells continue to proliferate throughout larval development and into adulthood, with meiosis commencing from larval stage 3 (L3) (Hansen et al., 2004). This initial differentiation program generates sperm, that are deposited in the spermatheca, before the germ line switches to producing oocytes in adults (Ellis and Schedl, 2007). The adult germ line is organized in a distal to proximal manner. The distal progenitor zone (PZ) contains stem cells, mitotically dividing germ cells and meiotic S- phase germ cells, which then enter early meiotic prophase (leptotene and zygotene) in the transition zone (TZ). As germ cells move from the TZ they enter meiotic pachytene prior to gametogenesis. As transcription is activated early during larval development, TFs likely play important roles in germ cell transitions and cell behavior during larval and adult development. Indeed, previous studies have identified key TFs that regulate germ cell and gamete development (Chi and Reinke, 2006; Curran et al., 2009; Edwards et al., 2021; Rodriguez- Crespo et al., 2022). However, no
+
+<--- Page Split --->
+
+systematic in vivo assessment of TF function in the C. elegans germ line, or in any organism, has been conducted. As a result, we sought to identify the TFs required for C. elegans germline development.
+
+Of the 875 TFs encoded by the C. elegans genome, we identified 364 TFs that are expressed in the germ line (Cao et al., 2017; Jimeno- Martin et al., 2022; Tzur et al., 2018). As most of these TFs are also expressed in the soma, we dissected their germline functions by exploiting a germline- specific RNA- mediated interference (RNAi) approach (Cao et al., 2017; Serizay et al., 2020; Zou et al., 2019). Following germline- specific RNAi silencing from the L1 larval stage, we performed semi- automated cell counting and high- content analysis of germ line architecture to interrogate a broad spectrum of readouts in adult germ lines. This analysis encompassed the 'distal germ line' where mitotic germ cells, Notch signaling, and early meiotic transition were analyzed; and the 'proximal germ line' where meiotic progression, oocyte/sperm production and germline structure were analyzed. We identified 156 TFs that regulate germ cell development, including 8 TFs that are essential for fertility. Our research provides a TF functional atlas of germ cell development, which is a valuable resource and experimental platform for understanding how specific germ cell fate decisions and gamete production are controlled.
+
+<--- Page Split --->
+
+## RESULTS
+
+## Transcription Factor Germline Profiling and Genetic Screen Validation
+
+To identify germline- expressed TFs (GTFs), we extruded wild- type adult hermaphrodite germ lines and performed RNA- sequencing from extracted RNA (Figure 1A and Table S1). Combining our germline transcriptome dataset with previously published germline transcriptome studies identified 364 GTFs (Tables S1- 2) (Cao et al., 2017; Tzur et al., 2018). These GTFs were detected in all three of our RNA sequencing samples, both germ lines analyzed in Tzur et al., or GTFs with \(>10\) counts per million in Cao et al. (Table S2) (Cao et al., 2017; Tzur et al., 2018). Of the 364 GTFs, 150 have been ascribed a broad C. elegans reproduction function (sterility/fertility/brood size) (Table S2), however, the precise germline function of these TFs is not well understood.
+
+By analyzing published TF expression profiles, we found that most GTFs are also expressed in the soma (Table S2) (Cao et al., 2017; Serizay et al., 2020). Therefore, to circumvent potential somatic effects of TF silencing, we utilized a germline- specific RNA- mediated interference (RNAi) approach to identify germline- specific TF functions (Zou et al., 2019). Animals lacking the RDE- 1 Argonaute are systemically RNAi- deficient (Tabara et al., 1999). In our genetic screen, we utilized a rde- 1(mkc36) indel mutant in which RDE- 1 is re- supplied under the germline- specific sun- 1 promoter and 3' untranslated region (UTR) - thus enabling germline- specific RNAi (Zou et al., 2019). To test the efficacy of this strain for germline- specific RNAi by feeding, we silenced the RNA Polymerase II encoding gene ama- 1 from the first larval stage (L1) for 66 hrs (Timmons and Fire, 1998). sun- 1p::rde- 1; rde- 1(mkc36) animals fed with ama- 1 RNAi bacteria grew to adulthood however their germ lines did not develop, while ama- 1 RNAi wild- type animals arrested as young larvae (Figure S1A). Thus, germline- specific inhibition of transcription prevents germline development without overtly affecting somatic development. As additional proof- of- concept for the germline- specific RNAi approach, we silenced two genes that autonomously control germline development - gld- 1 (encodes an RNA binding protein) and mog- 7 (encodes a splicing factor). Consistent with previous studies, gld- 1 RNAi causes proximal germline tumors (86% of germlines are tumorous; n=51) and mog- 7 RNAi causes spermatogenic germ lines (32% of germlines are spermatogenic; n=66) in sun- 1p::rde- 1; rde- 1(mkc36) animals (Figure S1A- B) (Cao et al., 2021; Kerins et al., 2010; Nayak et al., 2005). Prior to embarking on a large- scale germline- specific screen, we needed to confirm that somatic RNAi was inhibited in sun- 1p::rde- 1; rde- 1(mkc36) animals. We examined somatic phenotypes caused by RNAi silencing of hypodermal (bli- 3), intestinal (elt- 2), and muscle (unc- 112) genes. We found that knockdown of these genes from the
+
+<--- Page Split --->
+
+L1 stage caused robust somatic phenotypes in wild-type but not in sun- 1p::rde- 1; rde- 1(mkc36) animals, as shown previously (Figure S1C) (Kumsta and Hansen, 2012; Zou et al., 2019).
+
+To enable functional mapping of the 364 GTFs, we obtained RNAi feeding clones: 315 from previously generated RNAi libraries and 49 that we cloned (Table S3) (Jimeno- Martin et al., 2022; Kamath et al., 2003; Rual et al., 2004). All RNAi clones were confirmed by sequencing prior to analysis. We profiled GTF function in the germ line by feeding L1 hermaphrodites with Escherichia coli HT115 bacteria expressing individual TF RNAi clones and imaged and analyzed one- day adult germ lines (Figure 1A). We screened GTF function in hermaphrodite germline development using two parallel approaches for distal and proximal germline analysis (Figure 1A). Distal germline analysis was performed with confocal imaging and semi- automated cell counting of extruded germ lines of the 3xflag::syg- 1; sun- 1p::rde- 1; rde- 1(mkc36) strain that we confirmed exhibits wild- type germ cell number and brood size (Figure 1A and S2). Following GTF RNAi silencing from the L1 stage, we quantified germ cell number in the PZ and TZ by DAPI staining (PZ and TZ size), plus visualized M- phase chromosomes (anti- phospho- histone H3 (pH3) staining) and Notch signaling (SYGL- 1 immunofluorescence) in adults (Figure 1A) (Gopal et al., 2017). For proximal germline analysis, we examined gonad architecture, meiotic cell behavior and gamete development using a transgenic strain co- expressing fluorescent markers targeting chromosomes (mCherry- histone H2B) and plasma membrane (GFP- PI4, 5P2) (Figure 1A and S3). This approach for analyzing the proximal germ line was previously used for a group of 554 essential genes (Green et al., 2011), however, their work analyzed less than 3% of GTFs and used the RNAi soaking method (not germline- specific) from the L4 stage. Thus, our work is distinct to this previous study with regards to genes investigated, phenotypes analyzed and methods/timing of gene silencing.
+
+## Profiling Transcription Factor Function in the Germ Line
+
+To determine the in vivo functional contributions of TFs in the germ line, we performed two independent reverse genetic screens (as described above) to study the distal and proximal germ line. The results of the two screens identified 156 TFs that are important for germline development (Tables S4- 6). Among these GTFs, 82 have previously reported germline phenotypes in C. elegans (Table S7). In both screens, silencing of 8 GTFs resulted in immature germ lines that did not generate embryos in one- day adults (Tables S6), detailed analysis of which will be discussed later. Silencing of an additional 10 GTFs resulted in 20- 100% immature germ lines in the proximal screen only, among which 6 also caused distal phenotypes (Table S5). We hypothesize that the
+
+<--- Page Split --->
+
+sterility phenotype of these 10 genes is likely a synthetic effect of the RNAi silencing and transgenic reporters (mCherry- histone H2B and plasma membrane GFP- PI4, 5P2) used in the proximal screen.
+
+Beyond of the sterility phenotype, we used strict phenotypic criteria to furnish a robust inventory of key GTFs: distal germline analysis ( \(\geq 20\%\) significant change in germ cell number of PZ, TZ, and SYGL- 1+ region compared to control) and proximal germline analysis ( \(\geq 4\) of 8 germlines exhibiting a phenotype). Using these criteria, we found that RNAi silencing of 128 TFs caused germline phenotypes (88 in the distal screen and 52 in the proximal screen), 12 of which caused phenotypes in both screens (Figure 1B- D and Tables S4- 6). We classified TFs that control germline development based on broad DNA- binding domain families and found no obvious overrepresentation of TF family that is functionally required for germline development (Figure 1E). We wondered whether the TFs we identified in our primary screen were previously associated with germ cell/gamete development and reproduction. We thus compared our list of TFs hits to genes associated with the 'reproduction' gene ontology (GO) terms (GO:0019952, GO:0050876) in mice, rats and humans (https://www.flyrnai.org/cgi- bin/DRSC_orthologs.pl). We found that 88 GTFs we identified to regulate C. elegans germline development in our primary screens have mammalian orthologs, of which 43 are associated with germ cell/gamete development and reproduction GO terms (Figure 1 and Table S8).
+
+## Transcriptional Control of Distal Germ Cell Behavior
+
+At the distal progenitor zone, maintenance of the germline stem cell (GSC) pool is influenced by interaction between Notch ligands (LAG- 2/APX- 1), expressed on the somatic distal tip cell, and the GLP- 1 Notch receptor expressed on the surface of germ cells (Austin and Kimble, 1987, 1989; Gao and Kimble, 1995; Henderson et al., 1994; Tax et al., 1994). This Notch ligand- receptor interaction promotes GSC self- renewal by regulating the two redundantly acting post- transcriptional regulators SYGL- 1 and LST- 1 (Chen et al., 2020; Ferdous et al., 2023; Haupt et al., 2019; Shin et al., 2017).
+
+Our primary screen identified 23 GTFs that when silenced have a \(\geq 20\%\) change in progenitor zone (PZ) size (Figure 1 and Table S4). To identify high- confidence regulators of germline development, we performed a secondary screen of these hits in triplicate (Figure 2A and Figure S4). We found that silencing of 11 GTFs robustly repeated our initial findings with significant changes in PZ size (Figure 2A and Figure S4). These factors include two nuclear hormone
+
+<--- Page Split --->
+
+receptors (NHR- 84 and NHR- 146), HSF- 1/HSF1, DAF- 19/RFX, LET- 607/CREB, F54F2.9/DNAJC1, ZK546.5, XND- 1, ZTF- 23, C02F5.12 and C30G4.4. Of these 11 TFs, only HSF- 1 and XND- 1 have known roles in C. elegans germ cell proliferation (Edwards et al., 2021; Mainpal et al., 2015).
+
+The PZ houses self- renewing stem cells, germ cells undergoing final round of the mitotic cell cycle, and germ cells in meiotic S- phase (Fox and Schedl, 2015). To better understand the cellular and molecular effects underpinning the changes in PZ size, we analyzed the roles of these 11 TFs in Notch signaling and the mitotic cell cycle (Figure 2A- H and Figures S4- 5). First, we used a glp- 1(ar202gf) temperature- sensitive gain- of- function mutant that at the permissive temperature of \(15^{\circ}C\) generates \(\sim 25\%\) more PZ germ cells than wild- type animals (Figure 2B- C). We found that RNAi silencing of hsf- 1 and xnd- 1 decreased the number of PZ germ cells in glp- 1(ar202gf) animals at the permissive temperature (Figure 2B- C). This suggests that these TFs are required for excessive germ cell proliferation in glp- 1(ar202gf) animals. In contrast, RNAi silencing of C02F5.12, C30G4.4, daf- 19, F54F2.9 and ZK546.5 increases PZ size in wild- type animals but not in glp- 1(ar202) gain- of- function animals, suggesting that these genes function in the glp- 1 pathway (Figure 2A- B). Further, glp- 1 is epistatic to let- 607, nhr- 84, ztf- 23 and nhr- 146 as glp- 1(ar202) gain- of- function animals have an increase in PZ size irrespective of silencing these GTFs (Figure 2A- B).
+
+Maintenance of the GSC pool in the PZ is regulated by two direct GLP- 1 target genes SYGL- 1 and LST- 1 (Chen et al., 2020; Shin et al., 2017). SYGL- 1 and LST- 1 proteins are present in partially overlapping gradients through the GSC pool (Shin et al., 2017). Previous studies showed that overexpression of SYGL- 1 or LST- 1 can expand the GSC pool (Shin et al., 2017) and sygl- 1 RNAi knockdown can reduce the PZ length (Kershner et al., 2014). Therefore, we quantified endogenous 3xFLAG::SYGL- 1 and 3xFLAG::LST- 1 after silencing of the 11 GTFs that control PZ size to determine their potential roles in regulating Notch signaling (Figure 2D- E and Figure S4B- D). We found that RNAi silencing of C02F5.12 and ZK546.5 increased the number of SYGL- 1+ germ cells, consistent with their knockdown leading to an increase in PZ size (Figure 2A, D- E). This implies that C02F5.12 and ZK546.5 inhibit Notch signaling. Given that RNAi silencing of C02F5.12 and ZK546.5 did not affect the glp- 1(gf) increase of PZ size, they may function upstream of GLP- 1. We also found that RNAi silencing of hsf- 1 and xnd- 1 decreased the number of SYGL- 1+ germ cells, consistent with their knockdown to leading to a decrease in PZ size (Figure 2A, D- E). This suggests that HSF- 1 and XND- 1 promote Notch- signaling. Given that HSF- 1 and
+
+<--- Page Split --->
+
+XND- 1 are required for glp- 1(gf) induced increase in PZ size, they likely function downstream of GLP- 1. Interestingly, both HSF- 1 and XND- 1 have ChIP peaks in the promoter regions of sygl- 1 (ENCSR512EIF, ENCSR327NRA), suggesting a direct regulatory relationship with this Notch target gene (Consortium, 2012; Luo et al., 2020). In contrast to the SYGL- 1+ analysis, we did not detect changes in LST- 1+ in the PZ after silencing these 11 GTFs (Figure S4C- D). These data suggest that the change in PZ size following silencing of C02F5.12, ZK546.5, hsf- 1 and xnd- 1 may be due to altered Notch- dependent SYGL- 1 regulation.
+
+PZ size is also impacted by the mitotic cell cycle that is genetically separable to Notch signaling (Fox and Schedl, 2015). Within the PZ, a cohort of germ cells act as stem cells that self- renew by mitosis or differentiate into gametes (Crittenden et al., 2006; Crittenden et al., 1994). To examine whether any of the 11 GTFs impact progression through the cell cycle, we quantified cell proliferation using 5- ethynyl- 2'- deoxyuridine (EdU) staining (Figure 2F- G) (Fox and Schedl, 2015; Seidel and Kimble, 2015). We silenced each GTF from the L1 stage, fed the resultant adults with EdU- labelled bacteria for 4 hrs or 10 hrs, and then counted EdU+ germ cells (Figure 2F- G). Using these data, we calculated the rate of proliferation as the number of germ cells incorporating EdU per hour (Figure 2F- G). As previously reported, control animals had a proliferation rate of \(\sim 23\) cells/hour (Figure 2F) (Fox and Schedl, 2015). We found that RNAi silencing of C02F5.12, daf- 19 and ZK546.5 increased the germ cell proliferation rate, which may contribute to increases in PZ size observed by increasing number of mitotic cells (Figure 2F- G). Taken together, these results reveal key TFs that control PZ size, likely through fine- tuning Notch signaling, cell cycle dynamics and possibly other mechanisms.
+
+Antibody staining to detect phosphorylation of histone H3 (pH3) at serine 10 is used to mark mitotic M- phase germ cells (Crittenden et al., 2017; Hsu et al., 2000). No pH3+ cells are observed after proliferative zone cells have entered meiosis (Fox and Schedl, 2015). Therefore, changes in the number of pH3+ germ cells could indicate changes in the total number of mitotic germ cells, or changes in M- phase length with respect to the entire cell cycle. We found that of the 11 GTFs analyzed, only hsf- 1 silencing increased the number of pH3+ germ cells (Figure S5A- B). This suggests that hsf- 1 silencing increases mitotic germ cell number or M- phase length, or potentially accelerates other cell cycle phases. However, further investigation of hsf- 1 functions in mitosis and early meiosis is required to explain the contradictory results of decreased PZ size, decreased SYGL- 1+ cells, and unchanged proliferation rate following hsf- 1 silencing. A previous study found that germline- specific HSF- 1 protein depletion from hatching causes a severe reduction in germ
+
+<--- Page Split --->
+
+cells and depletion from the mid- L3 stage causes a decrease in EdU labeled germ cells (Edwards et al., 2021). These contradictory findings suggest the effect of HSF- 1 knockdown on the germ line is dosage or developmental stage dependent. Another method frequently used to assess germline proliferation is the mitotic index (MI), which is the percentage of PZ cells that are M- phase (Crittenden et al., 2023). In addition to hsf- 1, we found silencing of F54F2.9 and nhr- 146 caused changes in MI without changing the absolute number of pH3+ cells (Figure S5A- C). Although silencing of F54F2.9 and nhr- 146 caused changes in PZ size, there were no changes in the number of SYGL- 1+ cells or proliferation rate (Figure 2D and F). Thus, it is possible that these genes are not involved in mitosis, and the change of MI is a result of changes of overall PZ size which also include meiotic M- phase cells.
+
+Proximal to the PZ, the germline TZ houses a cohort of crescent- shaped nuclei that is characteristic of early meiotic prophase (leptotene and zygotene) germ cells (Hubbard, 2007). We found that some GTFs are also required for normal TZ size (ZK546.5, HSF- 1/HSF1, XND- 1, ZTF- 23 and NHR- 146), suggesting that meiotic prophase progression and/or chromosome pairing may be perturbed following silencing of these GTFs (Figure S5D- E). Interestingly, the changes in TZ size paralleled changes in PZ size – ZK546.5 silencing increased PZ and TZ size; hsf- 1, xnd- 1, ztf- 23 and nhr- 146 silencing decreased PZ and TZ size (Figure 2H). This suggests that when these genes are silenced, germ cell output from the PZ impacts TZ size. Finally, we found that 5 out of the 11 GTFs that are important for distal germ cell behavior also impact the proximal germline. ZK546.5 silencing caused incomplete spermatogenesis (7/8 germ lines), ztf- 23 and C02F5.12 silencing caused changes in the number of single array or budded oocytes, and C30G4.4 and nhr- 146 silencing caused germ cell multinucleation (Table S5). Thus, these GTFs likely play roles in both mitotic and meiotic germ cell behavior. Taken together, our distal germline screen discovered multiple GTFs that control germ cell behavior.
+
+## Transcriptional Control of Meiotic Cell Behavior and Gamete Development
+
+As germ cells progress proximally, they mature into sperm during late larval development before committing to the oogenic program. To examine the function of GTFs in these processes we utilized a transgenic strain in which fluorescent markers targeting chromosomes (mCherry- histone H2B) and plasma membrane (GFP- PI4, 5P2) enable gonad architecture to be visualized (Figure 1A and S3) (Essex et al., 2009; Green et al., 2011). We identified GTF functions in the proximal germ line including germline structure (small germ line, narrow rachis), meiosis (multinucleation, meiotic progression and apoptosis), sperm production and behavior
+
+<--- Page Split --->
+
+(spermatogenesis, sperm localization), and oocyte production (germ cell expansion, number of oocytes, oocyte budding and vesiculation) (Figure S3 and Table S5). The most prominent phenotype we observed was multinucleation of germ cells and thus we focused our subsequent analysis on this phenotype.
+
+The C. elegans hermaphrodite gonad is a syncytium with germ cell nuclei partially enclosed by a plasma membrane. Multinucleated germ cells (MNCs) can occur in both wild- type and some mutant animals at varying frequency (Raiders et al., 2018). Persistent MNCs would generate multinuclear oocytes and infertile embryos and are therefore cleared by apoptosis prior to generating gametes. Earlier studies showed that failed germ cell division in the PZ and an unstable rachis can cause multinucleation, while in other cases, including in wild- type animals, MNCs form at specific germline structures called folds (Lan et al., 2019; Raiders et al., 2018). In our primary screen, we identified 26 GTFs that have \(>25\%\) increase in germ lines with MNCs compared to control animals (Table S5- 6). To confirm this result, we selected 10 GTFs with the strongest penetrant phenotypes (DMD- 7/DMRTC1, BAZ- 2/BAZ2A, JUN- 1/JUN, MTER- 4, LIN- 26, MADF- 5, NHR- 40/HNF4, NHR- 114/NR1H3, NHR- 161/PPAR- alpha, and UNC- 62/MEIS) and repeated RNAi silencing in triplicate (Figure 3). We confirmed that silencing of all 10 GTFs increased MNCs in both one- day and two- day adults (Figure 3A- B and Figure S6A- B). Of these TFs, only NHR- 114 had previously been associated with germ cell multinucleation in C. elegans (Gracida and Eckmann, 2013). We used confocal microscopy to analyze the PZ of one- day adults following GTF silencing and detected no MNCs, suggesting that MNC formation is not due to aberrant mitotic division, as shown previously (data not shown) (Lan et al., 2019).
+
+As part of normal germline development, multinucleate cells are removed by physiological apoptosis to prevent them from potentially generating multipoid oocytes (Gumienny et al., 1999; Raiders et al., 2018). The CED- 3 executioner caspase is essential for physiological germline apoptosis (Gumienny et al., 1999), and thus germ lines lacking ced- 3 contain many MNCs (Raiders et al., 2018). To determine whether regulation of germ cell multinucleation by GTFs is dependent on CED- 3, we silenced the 10 GTFs that inhibit MNC formation in ced- 3 mutant animals. As the ced- 3 gene is linked to the pie- 1p::mCherry::his- 58 transgene that is used to count multinucleation events, we used CRISPR/Cas9 genome editing to generate a 3951bp ced- 3(rp190) deletion allele (Figure S7). These animals exhibit overt persistent apoptotic corpses confirming defective apoptosis (Figure S7B- C). Further, we did not detect apoptosis in the germ lines of ced- 3(rp190) animals, and loss of CED- 3 caused an increase in multinucleated germ cells
+
+<--- Page Split --->
+
+(Figure 3B- D), confirming that apoptosis is involved in the clearance of multinucleated germ cells (Raiders et al., 2018).
+
+We next counted germline MNCs in ced- 3(rp190) two- day adults after GTF RNAi silencing from the L1 stage (Figure 3E). We found that RNAi silencing of jun- 1, mter- 4, lin- 26, nhr- 40, nhr- 114, nhr- 161, and unc- 62 caused no change in MNC number in the ced- 3(rp190) background, suggesting that silencing these GTFs lead to increase in multinucleated cells by interfering with apoptosis. In contrast, silencing of dmd- 7, baz- 2 and madv- 5 increased MNCs independent of loss of ced- 3, suggesting that these GTFs promote mono- nucleation through mechanisms that are independent of apoptosis. However, caspase- 3 can play roles outside apoptosis (Dehkordi et al., 2022; Eskandari and Eaves, 2022), therefore it is possible that CED- 3 is involved in multinucleation formation through other mechanisms. In addition, we observed that MNCs are primarily located in the distal half of the pachytene region in wild- type and ced- 3(rp190) animals (Figure 3B), suggesting that mechanisms independent of physiological apoptosis can remove/resolve multinucleation.
+
+A previous study revealed that meiotic germline structure impacts the location and occurrence of multinucleation (Raiders et al., 2018). During proliferation, folds in the germline syncytium are formed and multinucleate cells occur during fold eversion (Raiders et al., 2018). As the size and complexity of germline folds is correlated with multinucleation, we assessed whether the 10 GTFs with high numbers of MNCs regulate germline folding. We used phalloidin to stain the germline actin cytoskeleton after RNAi silencing of these GTFs and measured germline folding by counting the rows and numbers of cells protruding inwards from the single layer of cells that form the tubelike structure in the pachytene region (Figure 3F- G and Figure S6C). We found that RNAi silencing of dmd- 7, baz- 2, mter- 4, lin- 26, nhr- 114 and nhr- 161 caused excess germline folding that may result in the increased multinucleation observed (Figure 3F- G and Figure S6C). Taken together, these data reveal 10 GTFs that act in the germline to maintain uninuclear germ cells. Cell behavior is likely controlled by these TFs through gene networks connected to the apoptotic pathway and germline morphogenesis.
+
+## Essential TFs for Germline Development
+
+Our initial distal germline screen identified 8 TFs (CDC- 5L, ZNF- 622, VEP- 1, F23B12.7, F33H1.4, F58G1.2, REPO- 1, and TBP- 1) that when silenced from the L1 stage result in small germ lines that do not generate embryos in one- day adults (Table S4). These TFs are mostly
+
+<--- Page Split --->
+
+uncharacterized but have predicted general functions in controlling gene expression (Table S4). Analysis of broods after silencing these TFs from the L1 stage showed almost complete sterility (Figure 4A). An exception was repo- 1 RNAi, which generated \(\sim 230(\pm 30.47)\) progeny, however most resultant embryos did not hatch (Figure 4A). To investigate when these TFs are required during development, we performed temporal germline analysis by silencing each TF from the L1 stage and examining germline size and morphology at each larval stage through to adult (Figure 4B and S8).
+
+We found that germline size and morphology were mostly intact during early larval development (L1 through L3) following TF silencing (Figure S8). However, from the L4 stage, TF silencing began to reveal germline defects - silencing of all 8 essential GTFs caused a significant decrease in germline length (Figure 4C). Of note, cdc- 5L and znf- 622 silencing resulted in small germ lines ( \(\sim 50\%\) the length of controls) that contained large nuclei suggesting arrest in the G2 stage of the cell cycle (Figure 4C- D and S8). We continued to monitor germline development for all 8 TF RNAi experiments during the first three days of adulthood to determine the effect on sperm, oocyte, and embryo development (Figure 4E). We found that silencing of some genes prevented or delayed sperm generation (cdc- 5L, znf- 622, vep- 1 and F23B12.7), with all genes defective or delayed in oocyte production and embryogenesis (Figure 4E). In addition, silencing of cdc- 5L, znf- 622, vep- 1 and tbp- 1 caused sterility in three- day adults (Figure 4E). We wondered whether these 8 TFs are continuously required for germline development or perform functions during larval development to enable fertility in adults. We explored this by performing germline- specific RNAi silencing from the mid- L4 stage at which gonad development and spermatogenesis are largely complete (Figure 4F). We found that silencing of repo- 1, F33H1.4, F23B12.7, F58G1.2, tbp- 1 and vep- 1 had similar broods to control animals, albeit with different degrees of embryonic lethality (Figure 4F). In contrast, cdc- 5L and znf- 622 silencing caused approximately \(>50\%\) reduction in brood size (with cdc- 5L RNAi causing \(100\%\) embryonic lethality), suggesting post- developmental roles in germline maintenance (Figure 4F).
+
+To examine the function of the essential GTFs in the oogenic germline, we quantified distal germ cell number in one- day adults following RNAi from the L4 stage (Figure 4G- J). We identified subtle changes in PZ/TZ size, pH3+ cells, and SYGL- 1+ staining (Figure 4G- J). However, these changes are negligible compared to the detrimental effect of silencing these GTFs from the L1 stage (Figure 4A), suggesting that the germ cell cycle and transition to meiosis are largely intact. Further, the minor changes in distal germ line cell numbers suggest that the brood size decrease
+
+<--- Page Split --->
+
+we observed following cdc- 5L and znf- 622 silencing are likely caused by defects in gametogenesis. Taken together, we have identified multiple TFs that control the timing and function of gamete generation and subsequent fertility in C. elegans.
+
+<--- Page Split --->
+
+## DISCUSSION
+
+In this study, we profiled the function of every germline- expressed TF in C. elegans to gain a comprehensive understanding of transcriptional regulation of germline development. To identify autonomous regulatory functions, we first determined that 364 TFs are germline expressed and then depleted their expression specifically in the germ line. We used two independent screening approaches to investigate TF functions from the proliferative germ cell stage to gamete production. Using high- content imaging, semi- automated germ cell counting and cell behavior analysis of \(>6000\) germ lines and \(>3\) million germ cells, we identified 156 TFs that influence germline development, \(>75\%\) of which are undescribed. Furthermore, we identified 8 factors that are essential for fertility. As a result, this study provides a rich resource for mechanistic dissection of TF function in germ cells and potentially new opportunities for manipulating cell fates.
+
+Previous C. elegans forward and reverse genetic screening approaches identified genes that cause sterility or reduced brood sizes (Argon and Ward, 1980; Hirsh and Vanderslice, 1976; Maeda et al., 2001). Further, a large- scale screen of essential genes used the RNAi soaking method to examine proximal germline development (Green et al., 2011); however, \(< 3\%\) of these genes overlapped with our screen. Whether phenotypes observed in these previous studies result from autonomous germline functions or somatic deficits is, however, unclear. Thus, our use of a germline- specific RNAi approach to survey autonomous TF functions, allows for a more refined and robust evaluation of critical germline regulators.
+
+Our primary screen identified 8 factors that are essential for fertility: CDC- 5L, ZNF- 622, VEP- 1, F23B12.7, F33H1.4, F58G1.2, REPO- 1, and TBP- 1. Loss of these factors had previously produced sterile/fertility phenotypes in genetic mutants and/or large- scale RNAi screens (Fraser et al., 2000; Kamath et al., 2003; Kerins et al., 2010; Simmer et al., 2003; Sonnichsen et al., 2005; Sun et al., 2011). Our analysis shows that these factors act autonomously and predominantly during larval development to enable germline function as we observed robust sterility when these factors were silenced from hatching, but not when silenced late in development. Major exceptions were silencing of cdc- 5L, repo- 1 and znf- 622 which caused reduced brood sizes and high proportions of dead eggs even when they were silenced late in development. Previous studies have identified conserved germline functions in mammals for some of these factors. Porcine CDC- 5L is required for fertility and oocyte maturation (Liu et al., 2018), which is consistent with the oogenesis defect induced by C. elegans cdc- 5L silencing. In addition, murine BDP1 is required for spermatogonial stem cell gene expression (Sisakhtnezhad and Heshmati, 2018), which may
+
+<--- Page Split --->
+
+be the cause of sterility and delayed sperm development when the BDP1 C. elegans ortholog VEP- 1 is silenced. Further, the zinc- finger protein CTCF is critical for oocyte development in mice through regulation of chromatin architecture (Wan et al., 2008), which may also impact the oocyte developmental defects we observed in the C. elegans ortholog F58G1.2.
+
+We also identified 128 TFs that control germ cell behavior in the distal germ line, including multiple TFs previously reported. For example, our screen confirmed previous studies identifying a zinc- finger TF LSL- 1 that limits TZ size, and the heat shock factor HSF- 1 and chromatin factor XND- 1 that promote germ cell proliferation in the PZ (Edwards et al., 2021; Mainpal et al., 2015; Rodriguez- Crespo et al., 2022). Our secondary screen focused on the TFs important for controlling PZ size to define whether these factors potentially control Notch signaling and/or mitotic cell cycle - two critical determinants of PZ germ cell behavior. Our analysis identified 5 TFs that limit and 6 TFs that promote PZ size. Key findings from this work suggest that HSF- 1 and XND- 1 are required for excess germ cell proliferation caused by GLP- 1/Notch overexpression. Further, loss of the zinc- finger TFs C02F5.12 and ZK546.5 enhance expression of the GLP- 1 target gene SYGL- 1 and germ cell proliferation rate, suggesting that these genes act in the Notch signaling pathway. Interestingly, C02F5.12 is a paralog of ZIM- 1, ZIM- 2, ZIM- 3, and HIM- 8 that are required for chromosome pairing (Phillips and Dernburg, 2006). However, as with C02F5.12, we found that loss of ZIM- 2 additionally limits PZ size suggesting a pre- meiotic function for these proteins. Further, ZK546.5 also limits size of the TZ - a phenotype it shares with its paralog LSL- 1. Finally, we found that the RFX- type TF DAF- 19 limits the germ cell proliferation in C. elegans. Interaction analysis predicts that DAF- 19 physically interacts with the serine-threonine kinase ATL- 1 and checkpoint kinase CHKR- 1, two kinases that are required for fertility, suggesting a potential mechanism for DAF- 19 function in the germline (Garcia- Muse and Boulton, 2005). A mouse ortholog of DAF- 19, RFX2, is expressed in the testis and required for spermatogenesis (Wu et al., 2016). Thus, future analysis of DAF- 19 functions in sperm development in C. elegans hermaphrodites and males is warranted.
+
+Meiotic development in the C. elegans germline is predominantly regulated by post- transcriptional networks governed by the redundant GLD- 1, GLD- 2, and SCFPROM- 1 proteins (Francis et al., 1995; Jantsch et al., 2007; Kadyk and Kimble, 1998; Nayak et al., 2002). However, the pachytene region is transcriptionally active prior to the transcriptional silencing that occurs in oocytes (Gibert et al., 1984; Starck, 1977). Our analysis of TF function in the proximal germline identified functions in spermatogenesis, oogenesis, gonad structure and meiotic progression. However, the most
+
+<--- Page Split --->
+
+common phenotype we observed was increased multinucleation of meiotic cells where silencing of 26 GTFs caused a robust phenotype. We focused on the 10 GTFs with the most penetrant multinucleation phenotype for secondary analysis. Previous studies revealed that folding of the germline structure and apoptosis impacts multinucleation (Raiders et al., 2018). In consensus with this, we found that silencing of 6/10 of these GTFs (DMD- 7, BAZ- 2, MTER- 4, LIN- 26, NHR- 114 and NHR- 161) caused excess folding in the germline syncytium that may contribute to the multinucleation phenotype. Furthermore, we found that increase in multinucleation caused by silencing of 7/10 of these GTFs is dependent on the presence of the apoptotic executioner caspase, CED- 3. Caspase- 3 is a well- known essential apoptosis inducer, but it can also regulate non- apoptotic processes including axonal differentiation, growth, routing, regeneration and degeneration (Dehkordi et al., 2022). Considering that the molecular mechanism of multinucleation formation and removal is unknown, it is challenging to speculate if CED- 3 only controls this event by inducing apoptosis, or it has additional functions.
+
+Overall, our detailed map of TF function throughout the C. elegans germ line is a valuable resource for mechanistic studies of germ cell and gamete development. Our discovery of multiple TFs with specific functions in the developing germ line suggests that many distinct pathways act to fine- tune gene networks and cell behavior. We anticipate that specific TFs will act downstream of key signaling pathways (e.g., TGF, mTOR, AMPK and insulin signaling) to integrate environmental and genetic cues for optimizing germ cell proliferation, meiotic transition, and progeny production. Together, these transcriptional outputs, when combined, likely provide robustness to the process of delivering the next generation.
+
+## Limitations of the study
+
+We wish to highlight two limitations of our study. First, categorization of TFs was based on the presence of DNA binding domains (Jimeno- Martin et al., 2022). However, these factors may also control other aspects of gene expression such as RNA splicing (CDC- 5L) and translation (ZNF- 622), thus care must be taken when planning mechanistic dissection of their function. Second, we found that the transgenic strain we used to analyze the proximal germ line (OD95) identified more TFs that cause a sterility phenotype than the strain used for distal analysis. This OD95 strain expresses two independently integrated transgenes to mark germ cell nuclei and membranes that may cause sensitivity to certain genetic perturbations.
+
+<--- Page Split --->
+
+## Acknowledgements
+
+AcknowledgementsWe thank members of the Pocock and Gopal laboratories for advice and comments on the manuscript. RNA sequencing and Bioinformatics performed at Monash Micromon Genomics and Monash Bioinformatics Platform. Imaging performed at Monash Microimaging. We thank Nuria Flames for their kind gift of TF RNAi clones. Some strains were provided by the Caenorhabditis Genetics Center (University of Minnesota), which is funded by the NIH Office of Research Infrastructure Programs (P40 OD010440).
+
+## Funding
+
+FundingThis work was supported by the following grants: Australian Research Council DE190100174 (SG) and DP200103293 (RP); National Health and Medical Research Council GNT1161439 (S.G.), GNT1105374 (RP), GNT1137645 (RP) and GNT2018825 (RP, WC and QF).
+
+## Author Contributions
+
+Conceptualization: RP, SG Methodology: RP, SG, WC, QF, RG Investigation: RP, SG, WC, QF, RG, GA, DB Visualization: RP, SG, WC, QF, RG, GA, DB Funding acquisition: SG, RP Project administration: RP, SG, WC Supervision: RP, SG, WC Writing - original draft: RP Writing - review & editing: RP, SG, WC, QF, RG, GA, DB
+
+## Competing interests
+
+Authors declare that they have no competing interests.
+
+## Data and materials availability
+
+All data is available in the main text, supplementary materials, and source data. No accession codes, unique identifiers, or weblinks are in our study and there are no restrictions on data availability. Materials are available upon request from Roger Pocock.
+
+<--- Page Split --->
+
+## FIGURE LEGENDS
+
+## Figure 1. Phenotypic Profiling of Germline Transcription Factor Function
+
+(A) Schematic of the C. elegans hermaphrodite germline (left), identification of germline-expressed TFs by RNA sequencing (center), and representative images and phenotypic readouts for high-content distal and proximal germline analysis (right). The distal germ line is labelled with DAPI (nuclei), SYGL-1 (Notch target gene) and pH3 (M-phase chromosomes). PZ = progenitor zone, TZ = transition zone. The proximal germ line is marked with transgenic fluorophores: red = nuclei; green = plasma membrane. Scale bars = 20 μm.
+
+(B- D) Heatmaps showing phenotypic overview for TF silencing causing distal (B \(\geq 20\%\) change compared to control), proximal (C \(\geq 50\%\) of animals with the phenotype) or distal and proximal germline phenotypes (D). (B) TF family categories (colored boxes); progenitor zone (PZ), transition zone (TZ) and SYGL- \(1^{+}\) region phenotypes shown as percentage change compared to control (blue \(=\) decrease; red \(=\) increase); germline expression of each TF (grey bars \(=\) log2 CPM); mammalian ortholog associated with the reproduction GO term (blue boxes \(=\) No, black boxes \(=\) Yes).
+
+(C) Labelling as in B, except purple \(=\) proximal phenotype; blue \(=\) no phenotype detected. Phenotypes shown in this figure: small germ line, rachis defect (narrow or wide rachis), meiotic defect (multinucleated cells, abnormal meiotic progression), apoptosis, oocyte defect (delayed expansion at the turn, difference in single-array oocyte number, difference in budded oocyte number, vesiculation), sperm defect (mislocated sperm, incomplete spermatogenesis). (D) Labelling as in B and C. Note: the heatmaps do not include essential GTFs identified in the screens – this analysis is detailed in Figure 4 and Table S4.
+
+(E) TF family distribution of the 875 C. elegans TFs, 96 TFs that regulate the distal germ line or are essential for germline development, and 52 TFs that regulate the proximal germline. TF families shown in this figure: bZIP = basic leucine zipper domain, HD = homeodomain, HMG = High mobility group box domain, MYB= myeloblastosis viral oncogene homolog, NHR = nuclear hormone receptors, T-box, WH = winged helix, ZF = zinc finger.
+
+## Figure 2. TF Control of Distal Germ Cell Behavior
+
+(A) Quantification of nuclei number in the PZ of 3xflag::syg1-1; sun-1p::rde-1; rde-1(mkc36) one-day adults. n = 23-24. Green dashed line = average of the control.
+
+<--- Page Split --->
+
+(B and C) Quantification of nuclei number (B) and confocal micrographs (C) of one-day adult germline PZ of sun- 1p::rde- 1; rde- 1(mkc36) treated with control RNAi and glp- 1(ar202); sun- 1p::rde- 1; rde- 1(mkc36) treated with control or experimental RNAi. \(\mathsf{n} = 29 - 34\) . (D and E) Quantification of SYGL- 1+ nuclei number (D) and confocal micrographs of germline PZ (E) of 3xflag::syg- 1; sun- 1p::rde- 1; rde- 1(mkc36) one- day adults. \(\mathsf{n} = 23 - 24\) . Green dashed line \(=\) average of the control (D); yellow dashed line \(=\) PZ/TZ boundary (E - left) and white line \(=\) SYGL- 1 boundary (E - right). (F) Proliferation rates of the C. elegans germ line after GTF RNAi. RNAi was performed from the L1 stage for 66 hrs before commencing EdU labelling, and germ lines collected and imaged after 4 and 10 hrs. The 3xflag::syg- 1; sun- 1p::rde- 1; rde- 1(mkc36) strain was used in this experiment. Results of three independent experiments were shown. \(\mathsf{n} = 9 - 13\) for each experiment. (G) Confocal micrographs showing DAPI and EdU+ nuclei after 4 and 10 hrs of EdU labelling. (H) Heatmap showing the effect of silencing 11 GTF on proliferation rate, mitotic index, and nuclei numbers of PZ, TZ, SYGL- 1+ and pH3+.
+
+RNAi was performed from the L1 stage. Data was generated from three independent experiments, and results were normalized to respective controls in (A) (B) and (D). \(P\) values assessed comparing to control RNAi by multiple unpaired t- test with no correction for multiple comparison (A, B, D and F). Error bars indicate SEM. Scale bars \(= 20 \mu \mathrm{m}\) .
+
+## Figure 3. TF Control of Meiotic Germ Cell Behavior
+
+(A) Quantification of multinucleated germ cells of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data was generated from three independent experiments. \(\mathsf{n} = 30 - 31\) . \(P\) values assessed by one-way ANOVA with no correction for multiple comparison.
+
+(B) Fluorescence micrographs of wild-type or ced-3(rp190) two-day adult germ lines in the pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) strain. Control RNAi and RNAi of dmd-7 and baz-2 were applied from the L1 stage in wild-type animals. Dash lines = border between the TZ (above) and pachytene region (below) of the germ line. Asterisks = multinucleated cells; triangles = apoptotic cells. Scale bar = 20 μm.
+
+(C and D) Quantification of apoptotic germ cells (C) and multinucleated germ cells (D) in two- day adults of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36)
+
+<--- Page Split --->
+
+strain (wild- type and ced- 3(rp190) animals). Data generated from three independent experiments. \(\mathsf{n} = 30 - 33\) . \(P\) values assessed by unpaired t- test.
+
+(E) Quantification of multinucleated germ cells in ced-3(rp190), pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data generated from three independent experiments. \(\mathsf{n} = 30\) . \(P\) values assessed by one- way ANOVA with no correction for multiple comparison.
+
+(F and G) Confocal micrographs of DAPI (white) and phalloidin (pink) staining (F) and quantification of germline folding events in the pachytene region (G) of sun- 1p::rde- 1; rde- 1(mkc36) one- day adults. Images for control RNAi (L4440) and lin- 26 RNAi are shown in F (note - only one plane is shown). Data was generated from four independent experiments. \(\mathsf{n} = 24 - 36\) . Yellow dashed line = border between the TZ (right) and pachytene region (left) of the germ line. \(P\) values assessed by one- way ANOVA with no correction for multiple comparison.
+
+RNAi was performed from the L1 stage. Error bars indicate SEM. Scale bars = 20 μm.
+
+## Figure 4. Essential TFs act Late in Germline Development to Control Fertility
+
+(A) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L1 stage. Data generated from three independent experiments. \(\mathsf{n} = 15 - 18\) .
+
+(B) Timeline of temporal germline analysis showing the time and respective life stages when germline imaging and analysis were performed following egg-laying on control and RNAi plates (RNAi from the L1 stage).
+
+(C) Quantification of germline length of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) animals at the L4 stage following RNAi from the L1 stage. Data was generated from three independent experiments, and results normalized to respective controls. \(\mathsf{n} = 26 - 30\) . \(P\) values assessed by one- way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+(D) DIC (left) and fluorescent micrographs (right) of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) germ lines at the L4 stage following control, cdc-5L and znf-622 RNAi. Blue arrow = vulva. Scale bar = 20 μm.
+
+(E) Heatmap showing the percentage of germ lines producing sperm, oocytes and embryos in day 1, day 2 and day 3 of adulthood following germline-specific RNAi from the L1 stage. For day 2 and day 3 adult analysis, worms were selected from day 1 sterile animals, except for the control group, and incubated for another 48 hrs or 72hrs prior to analysis. Data was generated from three independent experiments. \(\mathsf{n} = 30\) .
+
+<--- Page Split --->
+
+(F) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L4 stage. Data generated from three independent experiments. \(\mathsf{n} = 17 - 18\) . \(P\) values assessed by one-way ANOVA with no correction for multiple comparison. (G-J) Quantification of nuclei number of PZ (G), TZ (H), pH3+ (I) and SYGL-1+ (J) of 3xflag::syg1- 1; sun-1p::rde- 1; rde- 1(mkc36) one-day adult germ lines following RNAi treatment from the L4 stage. \(\mathsf{n} = 22 - 24\) . \(P\) values assessed by one-way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+<--- Page Split --->
+
+## REFERENCES
+
+Argon, Y., and Ward, S. (1980). Caenorhabditis elegans fertilization- defective mutants with abnormal sperm. Genetics 96, 413- 433. Austin, J., and Kimble, J. (1987). Glp- 1 Is Required in the Germ Line for Regulation of the Decision between Mitosis and Meiosis in C- Elegans. Cell 51, 589- 599. Austin, J., and Kimble, J. (1989). Transcript analysis of glp- 1 and lin- 12, homologous genes required for cell interactions during development of C. elegans. Cell 58, 565- 571. Batchelder, C., Dunn, M.A., Choy, B., Suh, Y., Cassie, C., Shim, E.Y., Shin, T.H., Mello, C., Seydoux, G., and Blackwell, T.K. (1999). Transcriptional repression by the Caenorhabditis elegans germ- line protein PIE- 1. Genes Dev 13, 202- 212. Cao, J., Packer, J.S., Ramani, V., Cusanovich, D.A., Huynh, C., Daza, R., Qiu, X., Lee, C., Furlan, S.N., Steemers, F.J., et al. (2017). Comprehensive single- cell transcriptional profiling of a multicellular organism. Science 357, 661- 667. Cao, W., Tran, C., Archer, S.K., Gopal, S., and Pocock, R. (2021). Functional recovery of the germ line following splicing collapse. Cell Death Differ. Chen, J., Mohammad, A., Pazdernik, N., Huang, H., Bowman, B., Tycksen, E., and Schedl, T. (2020). GLP- 1 Notch- LAG- 1 CSL control of the germline stem cell fate is mediated by transcriptional targets Ist- 1 and sygl- 1. PLoS Genet 16, e1008650. Chi, W., and Reinke, V. (2006). Promotion of oogenesis and embryogenesis in the C. elegans gonad by EFL- 1/DPL- 1 (E2F) does not require LIN- 35 (pRB). Development 133, 3147- 3157. Consortium, E.P. (2012). An integrated encyclopedia of DNA elements in the human genome. Nature 489, 57- 74. Crittenden, S.L., Bernstein, D.S., Bachorik, J.L., Thompson, B.E., Gallegos, M., Petcherski, A.G., Moulder, G., Barstead, R., Wickens, M., and Kimble, J. (2002). A conserved RNA- binding protein controls germline stem cells in Caenorhabditis elegans. Nature 417, 660- 663. Crittenden, S.L., Leonhard, K.A., Byrd, D.T., and Kimble, J. (2006). Cellular analyses of the mitotic region in the Caenorhabditis elegans adult germ line. Molecular Biology of the Cell 17, 3051- 3061. Crittenden, S.L., Seidel, H.S., and Kimble, J. (2017). Analysis of the C. elegans Germline Stem Cell Pool. Germline Stem Cells, 2nd Edition 1463, 1- 33. Crittenden, S.L., Seidel, H.S., and Kimble, J. (2023). Analysis of the C. elegans Germline Stem Cell Pool. Methods Mol Biol 2677, 1- 36. Crittenden, S.L., Troemel, E.R., Evans, T.C., and Kimble, J. (1994). GLP- 1 is localized to the mitotic region of the C. elegans germ line. Development 120, 2901- 2911.
+
+<--- Page Split --->
+
+Curran, S.P., Wu, X., Riedel, C.G., and Ruvkun, G. (2009). A soma- to- germline transformation in long- lived Caenorhabditis elegans mutants. Nature 459, 1079- 1084. Dehkordi, M.H., Munn, R.G.K., and Fearnhead, H.O. (2022). Non- Canonical Roles of Apoptotic Casases in the Nervous System. Front Cell Dev Biol 10, 840023. Edwards, S.L., Erdenebat, P., Morphis, A.C., Kumar, L., Wang, L., Chamera, T., Georgescu, C., Wren, J.D., and Li, J. (2021). Insulin/IGF- 1 signaling and heat stress differentially regulate HSF1 activities in germline development. Cell Rep 36, 109623. Ellis, R., and Schedl, T. (2007). Sex determination in the germ line. WormBook, 1- 13. Eskandari, E., and Eaves, C.J. (2022). Paradoxical roles of caspase- 3 in regulating cell survival, proliferation, and tumorigenesis. J Cell Biol 221. Essex, A., Dammermann, A., Lewellyn, L., Oegema, K., and Desai, A. (2009). Systematic analysis in Caenorhabditis elegans reveals that the spindle checkpoint is composed of two largely independent branches. Mol Biol Cell 20, 1252- 1267. Ferdous, A.S., Lynch, T.R., Costa Dos Santos, S.J., Kapadia, D.H., Crittenden, S.L., and Kimble, J. (2023). LST- 1 is a bifunctional regulator that feeds back on Notch- dependent transcription to regulate C. elegans germline stem cells. Proc Natl Acad Sci U S A 120, e2309964120. Fox, P.M., and Schedl, T. (2015). Analysis of Germline Stem Cell Differentiation Following Loss of GLP- 1 Notch Activity in Caenorhabditis elegans. Genetics 201, 167- 184. Francis, R., Maine, E., and Schedl, T. (1995). Analysis of the multiple roles of gld- 1 in germline development: interactions with the sex determination cascade and the glp- 1 signaling pathway. Genetics 139, 607- 630. Fraser, A.G., Kamath, R.S., Zipperlen, P., Martinez- Campos, M., Sohrmann, M., and Ahringer, J. (2000). Functional genomic analysis of C. elegans chromosome I by systematic RNA interference. Nature 408, 325- 330. Fukuyama, M., Rougvie, A.E., and Rothman, J.H. (2006). C. elegans DAF- 18/PTEN mediates nutrient- dependent arrest of cell cycle and growth in the germline. Curr Biol 16, 773- 779. Furuhashi, H., Takasaki, T., Rechtsteiner, A., Li, T., Kimura, H., Checchi, P.M., Strome, S., and Kelly, W.G. (2010). Trans- generational epigenetic regulation of C. elegans primordial germ cells. Epigenetics Chromatin 3, 15. Gao, D.L., and Kimble, J. (1995). Apx- 1 Can Substitute for Its Homolog Lag- 2 to Direct Cell- Interactions Throughout Caenorhabditis- Elegans Development. P Natl Acad Sci USA 92, 9839- 9842.
+
+<--- Page Split --->
+
+Garcia- Muse, T., and Boulton, S.J. (2005). Distinct modes of ATR activation after replication stress and DNA double- strand breaks in Caenorhabditis elegans. EMBO J 24, 4345- 4355.
+
+Gibert, M.A., Starck, J., and Beguet, B. (1984). Role of the gonad cytoplasmic core during oogenesis of the nematode Caenorhabditis elegans. Biol Cell 50, 77- 85.
+
+Gopal, S., Boag, P., and Pocock, R. (2017). Automated three- dimensional reconstruction of the Caenorhabditis elegans germline. Dev Biol.
+
+Gracida, X., and Eckmann, C.R. (2013). Fertility and germline stem cell maintenance under different diets requires nhr- 114/HNF4 in C. elegans. Curr Biol 23, 607- 613.
+
+Green, R.A., Kao, H.L., Audhya, A., Arur, S., Mayers, J.R., Fridolfsson, H.N., Schulman, M., Schloissnig, S., Niessen, S., Laband, K., et al. (2011). A high- resolution C. elegans essential gene network based on phenotypic profiling of a complex tissue. Cell 145, 470- 482.
+
+Gumienny, T.L., Lambie, E., Hartwieg, E., Horvitz, H.R., and Hengartner, M.O. (1999). Genetic control of programmed cell death in the Caenorhabditis elegans hermaphrodite germline. Development 126, 1011- 1022.
+
+Hansen, D., Hubbard, E.J., and Schedl, T. (2004). Multi- pathway control of the proliferation versus meiotic development decision in the Caenorhabditis elegans germline. Dev Biol 268, 342- 357.
+
+Haupt, K.A., Enright, A.L., Ferdous, A.S., Kershner, A.M., Shin, H., Wickens, M., and Kimble, J. (2019). The molecular basis of LST- 1 self- renewal activity and its control of stem cell pool size. Development 146.
+
+Henderson, S.T., Gao, D., Lambie, E.J., and Kimble, J. (1994). lag- 2 may encode a signaling ligand for the GLP- 1 and LIN- 12 receptors of C. elegans. Development 120, 2913- 2924.
+
+Hirsh, D., and Vanderslice, R. (1976). Temperature- sensitive developmental mutants of Caenorhabditis elegans. Dev Biol 49, 220- 235.
+
+Hsu, J.Y., Sun, Z.W., Li, X., Reuben, M., Tatchell, K., Bishop, D.K., Grushcow, J.M., Brame, C.J., Caldwell, J.A., Hunt, D.F., et al. (2000). Mitotic phosphorylation of histone H3 is governed by Ipl1/aurora kinase and Glc7/PP1 phosphatase in budding yeast and nematodes. Cell 102, 279- 291.
+
+Hubbard, E.J. (2007). Caenorhabditis elegans germ line: a model for stem cell biology. Dev Dyn 236, 3343- 3357.
+
+Jantsch, V., Tang, L., Pasierbek, P., Penkner, A., Nayak, S., Baudrimont, A., Schedl, T., Gartner, A., and Loidl, J. (2007). Caenorhabditis elegans prom- 1 is required for meiotic prophase progression and homologous chromosome pairing. Mol Biol Cell 18, 4911- 4920.
+
+<--- Page Split --->
+
+Jimeno- Martin, A., Sousa, E., Brocal- Ruiz, R., Daroqui, N., Maicas, M., and Flames, N. (2022). Joint actions of diverse transcription factor families establish neuron- type identities and promote enhancer selectivity. Genome Res 32, 459- 473.
+
+Kadyk, L.C., and Kimble, J. (1998). Genetic regulation of entry into meiosis in Caenorhabditis elegans. Development 125, 1803- 1813.
+
+Kamath, R.S., Fraser, A.G., Dong, Y., Poulin, G., Durbin, R., Gotta, M., Kanapin, A., Le Bot, N., Moreno, S., Sohrmann, M., et al. (2003). Systematic functional analysis of the Caenorhabditis elegans genome using RNAi. Nature 421, 231- 237.
+
+Kerins, J.A., Hanazawa, M., Dorsett, M., and Schedl, T. (2010). PRP- 17 and the pre- mRNA splicing pathway are preferentially required for the proliferation versus meiotic development decision and germline sex determination in Caenorhabditis elegans. Dev Dyn 239, 1555- 1572.
+
+Kershner, A.M., Shin, H., Hansen, T.J., and Kimble, J. (2014). Discovery of two GLP- 1/Notch target genes that account for the role of GLP- 1/Notch signaling in stem cell maintenance. Proc Natl Acad Sci U S A 111, 3739- 3744.
+
+Kumsta, C., and Hansen, M. (2012). C. elegans rrf- 1 mutations maintain RNAi efficiency in the soma in addition to the germline. PLoS One 7, e35428.
+
+Lan, H., Wang, X., Jiang, L., Wu, J., Wan, X., Zeng, L., Zhang, D., Lin, Y., Hou, C., Wu, S., et al. (2019). An extracellular matrix protein promotes anillin- dependent processes in the Caenorhabditis elegans germline. Life Sci Alliance 2.
+
+Liu, X.M., Wang, Y.K., Liu, Y.H., Yu, X.X., Wang, P.C., Li, X., Du, Z.Q., and Yang, C.X. (2018). Single- cell transcriptome sequencing reveals that cell division cycle 5- like protein is essential for porcine oocyte maturation. J Biol Chem 293, 1767- 1780.
+
+Luo, Y., Hitz, B.C., Gabdank, I., Hilton, J.A., Kagda, M.S., Lam, B., Myers, Z., Sud, P., Jou, J., Lin, K., et al. (2020). New developments on the Encyclopedia of DNA Elements (ENCODE) data portal. Nucleic Acids Res 48, D882- D889.
+
+Maeda, I., Kohara, Y., Yamamoto, M., and Sugimoto, A. (2001). Large- scale analysis of gene function in Caenorhabditis elegans by high- throughput RNAi. Curr Biol 11, 171- 176.
+
+Mainpal, R., Nance, J., and Yanowitz, J.L. (2015). A germ cell determinant reveals parallel pathways for germ line development in Caenorhabditis elegans. Development 142, 3571- 3582.
+
+Mak, W., Fang, C., Holden, T., Dratver, M.B., and Lin, H. (2016). An Important Role of Pumilio 1 in Regulating the Development of the Mammalian Female Germline. Biol Reprod 94, 134.
+
+Nayak, S., Goree, J., and Schedl, T. (2005). fog- 2 and the evolution of self- fertile hermaphroditism in Caenorhabditis. PLoS Biol 3, e6.
+
+<--- Page Split --->
+
+Nayak, S., Santiago, F.E., Jin, H., Lin, D., Schedl, T., and Kipreos, E.T. (2002). The Caenorhabditis elegans Skp1- related gene family: diverse functions in cell proliferation, morphogenesis, and meiosis. Curr Biol 12, 277- 287.
+
+Phillips, C.M., and Dernburg, A.F. (2006). A family of zinc- finger proteins is required for chromosome- specific pairing and synapsis during meiosis in C. elegans. Dev Cell 11, 817- 829.
+
+Raiders, S.A., Eastwood, M.D., Bacher, M., and Priess, J.R. (2018). Binucleate germ cells in Caenorhabditis elegans are removed by physiological apoptosis. PLoS Genet 14, e1007417.
+
+Rodriguez- Crespo, D., Nanchen, M., Rajopadhye, S., and Wicky, C. (2022). The zinc- finger transcription factor LSL- 1 is a major regulator of the germline transcriptional program in Caenorhabditis elegans. Genetics 221.
+
+Rual, J.F., Ceron, J., Koreth, J., Hao, T., Nicot, A.S., Hirozane- Kishikawa, T., Vandenhaute, J., Orkin, S.H., Hill, D.E., van den Heuvel, S., et al. (2004). Toward improving Caenorhabditis elegans phenome mapping with an ORFeome- based RNAi library. Genome Res 14, 2162- 2168.
+
+Seidel, H.S., and Kimble, J. (2015). Cell- cycle quiescence maintains Caenorhabditis elegans germline stem cells independent of GLP- 1/Notch. Elife 4.
+
+Serizay, J., Dong, Y., Janes, J., Chesney, M., Cerrato, C., and Ahringer, J. (2020). Distinctive regulatory architectures of germline- active and somatic genes in C. elegans. Genome Res 30, 1752- 1765.
+
+Seydoux, G., Mello, C.C., Pettitt, J., Wood, W.B., Priess, J.R., and Fire, A. (1996). Repression of gene expression in the embryonic germ lineage of C. elegans. Nature 382, 713- 716.
+
+Shin, H., Haupt, K.A., Kershner, A.M., Kroll- Conner, P., Wickens, M., and Kimble, J. (2017). SYGL- 1 and LST- 1 link niche signaling to PUF RNA repression for stem cell maintenance in Caenorhabditis elegans. Plos Genetics 13.
+
+Simmer, F., Moorman, C., Van Der Linden, A.M., Kuijk, E., Van Den Berghe, P.V., Kamath, R., Fraser, A.G., Ahringer, J., and Plasterk, R.H. (2003). Genome- Wide RNAi of C. elegans Using the Hypersensitive rrf- 3 Strain Reveals Novel Gene Functions. PLoS Biol 1, E12.
+
+Sisakhtnezhad, S., and Heshmati, P. (2018). Comparative analysis of single- cell RNA sequencing data from mouse spermatogonial and mesenchymal stem cells to identify differentially expressed genes and transcriptional regulators of germline cells. J Cell Physiol 233, 5231- 5242.
+
+Sonnichsen, B., Koski, L.B., Walsh, A., Marschall, P., Neumann, B., Brehm, M., Alleaume, A.M., Artelt, J., Bettencourt, P., Cassin, E., et al. (2005). Full- genome RNAi profiling of early embryogenesis in Caenorhabditis elegans. Nature 434, 462- 469.
+
+Starck, J. (1977). Radioautographic study of RNA synthesis in Caenorhabditis
+
+<--- Page Split --->
+
+elegans (Bergerac variety) oogenesis. Biol Cell 30, 181- 182.
+
+Sun, Y., Yang, P., Zhang, Y., Bao, X., Li, J., Hou, W., Yao, X., Han, J., and Zhang, H. (2011). A genome- wide RNAi screen identifies genes regulating the formation of P bodies in C. elegans and their functions in NMD and RNAi. Protein Cell 2, 918- 939.
+
+Tabara, H., Sarkissian, M., Kelly, W.G., Fleenor, J., Grishok, A., Timmons, L., Fire, A., and Mello, C.C. (1999). The rde- 1 gene, RNA interference, and transposon silencing in C. elegans. Cell 99, 123- 132.
+
+Tax, F.E., Yeargers, J.J., and Thomas, J.H. (1994). Sequence of C. elegans lag- 2 reveals a cell- signalling domain shared with Delta and Serrate of Drosophila. Nature 368, 150- 154.
+
+Timmons, L., and Fire, A. (1998). Specific interference by ingested dsRNA [letter]. Nature 395, 854.
+
+Tzur, Y.B., Winter, E., Gao, J., Hashimshony, T., Yanai, I., and Colaiacovo, M.P. (2018). Spatiotemporal Gene Expression Analysis of the Caenorhabditis elegans Germline Uncovers a Syncytial Expression Switch. Genetics 210, 587- 605.
+
+Wan, L.B., Pan, H., Hannenhalli, S., Cheng, Y., Ma, J., Fedorow, A., Lobanenkov, V., Latham, K.E., Schultz, R.M., and Bartolomei, M.S. (2008). Maternal depletion of CTCF reveals multiple functions during oocyte and preimplantation embryo development. Development 135, 2729- 2738.
+
+Wu, Y., Hu, X., Li, Z., Wang, M., Li, S., Wang, X., Lin, X., Liao, S., Zhang, Z., Feng, X., et al. (2016). Transcription Factor RFX2 Is a Key Regulator of Mouse Spermiogenesis. Sci Rep 6, 20435.
+
+Zou, L., Wu, D., Zang, X., Wang, Z., Wu, Z., and Chen, D. (2019). Construction of a germline- specific RNAi tool in C. elegans. Sci Rep 9, 2354.
+
+<--- Page Split --->
+
+## Figures
+
+
+
+Figure 1
+
+Phenotypic Profiling of Germline Transcription Factor Function
+
+<--- Page Split --->
+
+(A) Schematic of the C. elegans hermaphrodite germline (left), identification of germline-expressed TFs by RNA sequencing (center), and representative images and phenotypic readouts for high-content distal and proximal germline analysis (right). The distal germ line is labelled with DAPI (nuclei), SYGL-1 (Notch target gene) and pH3 (M-phase chromosomes). PZ = progenitor zone, TZ = transition zone. The proximal germ line is marked with transgenic fluorophores: red = nuclei; green = plasma membrane. Scale bars = 20 μm.
+
+(B- D) Heatmaps showing phenotypic overview for TF silencing causing distal (B \(\geq 20\%\) change compared to control), proximal (C \(\geq 50\%\) of animals with the phenotype) or distal and proximal germline phenotypes (D). (B) TF family categories (colored boxes); progenitor zone (PZ), transition zone (TZ) and SYGL-1+ region phenotypes shown as percentage change compared to control (blue = decrease; red = increase); germline expression of each TF (grey bars = log2 CPM); mammalian ortholog associated with the reproduction GO term (blue boxes = No, black boxes = Yes).
+
+(C) Labelling as in B, except purple = proximal phenotype; blue = no phenotype detected. Phenotypes shown in this figure: small germ line, rachis defect (narrow or wide rachis), meiotic defect (multinucleated cells, abnormal meiotic progression), apoptosis, oocyte defect (delayed expansion at the turn, difference in single-array oocyte number, difference in budded oocyte number, vesiculation), sperm defect (mislocated sperm, incomplete spermatogenesis). (D) Labelling as in B and C. Note: the heatmaps do not include essential GTFs identified in the screens – this analysis is detailed in Figure 4 and Table S4.
+
+(E) TF family distribution of the 875 C. elegans TFs, 96 TFs that regulate the distal germ line or are essential for germline development, and 52 TFs that regulate the proximal germline.
+
+TF families shown in this figure: bZIP = basic leucine zipper domain, HD = homeodomain, HMG = High mobility group box domain, MYB= myeloblastosis viral oncogene homolog, NHR = nuclear hormone receptors, T-box, WH = winged helix, ZF = zinc finger.
+
+<--- Page Split --->
+
+
+Figure 2
+
+TF Control of Distal Germ Cell Behavior
+
+(A) Quantification of nuclei number in the PZ of 3xflag::syg1-1; sun-1p::rde-1; rde-1(mkc36) one-day adults. \(\mathrm{n} = 23 - 24\) . Green dashed line = average of the control.
+
+<--- Page Split --->
+
+(B and C) Quantification of nuclei number (B) and confocal micrographs (C) of one-day adult germline PZ of sun-1p::rde-1; rde-1(mkc36) treated with control RNAi and glp-1(ar202); sun-1p::rde-1; rde-1(mkc36) treated with control or experimental RNAi. \(n = 29 - 34\) .
+
+(D and E) Quantification of SYGL- 1+ nuclei number (D) and confocal micrographs of germline PZ
+
+(E) of 3xflag::syg1- 1; sun-1p::rde- 1; rde- 1(mkc36) one-day adults. \(n = 23 - 24\) . Green dashed line = average of the control (D); yellow dashed line = PZ/TZ boundary (E - left) and white line = SYGL- 1 boundary (E - right).
+
+(F) Proliferation rates of the C. elegans germ line after GTF RNAi. RNAi was performed from the L1 stage for 66 hrs before commencing EdU labelling, and germ lines collected and imaged after 4 and 10 hrs. The 3xflag::syg1- 1; sun-1p::rde- 1; rde- 1(mkc36) strain was used in this experiment. Results of three independent experiments were shown. \(n = 9 - 13\) for each experiment.
+
+(G) Confocal micrographs showing DAPI and EdU+ nuclei after 4 and 10 hrs of EdU labelling.
+
+(H) Heatmap showing the effect of silencing 11 GTF on proliferation rate, mitotic index, and nuclei numbers of PZ, TZ, SYGL-1+ and pH3+.
+
+RNAi was performed from the L1 stage. Data was generated from three independent experiments, and results were normalized to respective controls in (A) (B) and (D). P values assessed comparing to control RNAi by multiple unpaired t-test with no correction for multiple comparison (A, B, D and F). Error bars indicate SEM. Scale bars = 20 μm.
+
+<--- Page Split --->
+
+
+Figure 3
+
+TF Control of Meiotic Germ Cell Behavior
+
+(A) Quantification of multinucleated germ cells of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data was generated from
+
+<--- Page Split --->
+
+three independent experiments. \(n = 30 - 31\) . P values assessed by one- way ANOVA with no correction for multiple comparison.
+
+(B) Fluorescence micrographs of wild-type or ced-3(rp190) two-day adult germ lines in the pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) strain. Control RNAi and RNAi of dmd-7 and baz-2 were applied from the L1 stage in wild-type animals. Dash lines = border between the TZ (above) and pachytene region (below) of the germ line. Asterisks = multinucleated cells; triangles = apoptotic cells. Scale bar = 20 μm.
+
+(C and D) Quantification of apoptotic germ cells (C) and multinucleated germ cells (D) in two- day adults of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) strain (wild-type and ced-3(rp190) animals). Data generated from three independent experiments. \(n = 30 - 33\) . P values assessed by unpaired t-test.
+
+(E) Quantification of multinucleated germ cells in ced-3(rp190), pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data generated from three independent experiments. \(n = 30\) . P values assessed by one-way ANOVA with no correction for multiple comparison.
+
+(F and G) Confocal micrographs of DAPI (white) and phalloidin (pink) staining (F) and quantification of germline folding events in the pachytene region (G) of sun-1p::rde-1; rde-1(mkc36) one-day adults. Images for control RNAi (L4440) and lin-26 RNAi are shown in F (note - only one plane is shown). Data was generated from four independent experiments. \(n = 24 - 36\) . Yellow dashed line = border between the TZ (right) and pachytene region (left) of the germ line. P values assessed by one-way ANOVA with no correction for multiple comparison.
+
+RNAi was performed from the L1 stage. Error bars indicate SEM. Scale bars = 20 μm.
+
+<--- Page Split --->
+
+
+Figure 4
+
+Essential TFs act Late in Germline Development to Control Fertility
+
+(A) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L1 stage. Data generated from three independent experiments. \(n = 15 - 18\) .
+
+<--- Page Split --->
+
+(B) Timeline of temporal germline analysis showing the time and respective life stages when germline imaging and analysis were performed following egg-laying on control and RNAi plates (RNAi from the L1 stage).
+
+(C) Quantification of germline length of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) animals at the L4 stage following RNAi from the L1 stage. Data was generated from three independent experiments, and results normalized to respective controls. \(\mathrm{n} = 26 - 30\) . P values assessed by one-way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+(D) DIC (left) and fluorescent micrographs (right) of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) germ lines at the L4 stage following control, cdc-5L and znf-622 RNAi. Blue arrow = vulva. Scale bar = 20 μm.
+
+(E) Heatmap showing the percentage of germ lines producing sperm, oocytes and embryos in day 1, day 2 and day 3 of adulthood following germline-specific RNAi from the L1 stage. For day 2 and day 3 adult analysis, worms were selected from day 1 sterile animals, except for the control group, and incubated for another 48 hrs or 72hrs prior to analysis. Data was generated from three independent experiments. \(\mathrm{n} = 30\) .
+
+(F) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L4 stage. Data generated from three independent experiments. \(\mathrm{n} = 17 - 18\) . P values assessed by one-way ANOVA with no correction for multiple comparison.
+
+(G-J) Quantification of nuclei number of PZ (G), TZ (H), pH3+ (I) and SYGL- 1+ (J) of 3xflag::syg1- 1; sun- 1p::rde- 1; rde- 1(mkc36) one-day adult germ lines following RNAi treatment from the L4 stage. \(\mathrm{n} = 22 - 24\) .
+
+P values assessed by one-way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- FigureS1.pdf- FigureS2.pdf- FigureS3.pdf- FigureS4.pdf- FigureS5.pdf- FigureS6.pdf- FigureS7.pdf- FigureS8.pdf
+
+<--- Page Split --->
+
+- TableS1.Germlinetranscriptomeanalysis.xlsx- TableS2WormGTFexpressionandreproductivefunctions.xlsx- TableS3RNAiplasmidusedinthisstudy.xlsx- TableS4Distalgermlineanalysis.xlsx- TableS5ProximalgermlineanalysisV6.xlsx- TableS6156GTFswithgermlinefunctions.xlsx- TableS7PreviouslyreportedphenotypesinC.elegans.xlsx- TableS8GTFfunctionsinotherorganismsGOanalysis.xlsx- TableS9Strainsusedinthisstudy.xlsx- TableS10Oligosusedinthisstudy.xlsx- TableS11Sourcedata.xlsx
+
+<--- Page Split --->
diff --git a/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9_det.mmd b/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..8e493145371f8cf863d2aaa78b6e3066e7da107e
--- /dev/null
+++ b/preprint/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9/preprint__012c200754316231695b8af56a30435ab233e96b827c0370265adf0c1c9cfda9_det.mmd
@@ -0,0 +1,650 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 935, 175]]<|/det|>
+# A Transcription Factor Functional Atlas of Germline Development
+
+<|ref|>text<|/ref|><|det|>[[44, 196, 310, 241]]<|/det|>
+Roger Pocock roger.pocock@monash.edu
+
+<|ref|>text<|/ref|><|det|>[[44, 268, 580, 288]]<|/det|>
+Monash University https://orcid.org/0000- 0002- 5515- 3608
+
+<|ref|>text<|/ref|><|det|>[[44, 293, 220, 333]]<|/det|>
+Wei Cao Monash University
+
+<|ref|>text<|/ref|><|det|>[[44, 339, 228, 378]]<|/det|>
+Qi Fan Monash University
+
+<|ref|>text<|/ref|><|det|>[[44, 384, 232, 424]]<|/det|>
+Gemmarie Amparado Monash University
+
+<|ref|>text<|/ref|><|det|>[[44, 430, 220, 470]]<|/det|>
+Dean Begic Monash University
+
+<|ref|>text<|/ref|><|det|>[[44, 476, 220, 516]]<|/det|>
+Rasoul Godini Monash University
+
+<|ref|>text<|/ref|><|det|>[[44, 522, 180, 562]]<|/det|>
+Sandeep Gopal sandeep.gopal@med.lu.se https://orcid.org/0000- 0002- 6706- 6747
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 608, 128, 625]]<|/det|>
+## Resource
+
+<|ref|>text<|/ref|><|det|>[[44, 645, 866, 666]]<|/det|>
+Keywords: Germ line, gametes, transcription factors, RNA interference, Caenorhabditis elegans
+
+<|ref|>text<|/ref|><|det|>[[44, 683, 330, 703]]<|/det|>
+Posted Date: January 26th, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 721, 475, 741]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 3880498/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 758, 914, 801]]<|/det|>
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 819, 534, 839]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 874, 936, 918]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on August 11th, 2024. See the published version at https://doi.org/10.1038/s41467- 024- 51212- 0.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[183, 83, 819, 102]]<|/det|>
+# A Transcription Factor Functional Atlas of Germline Development
+
+<|ref|>text<|/ref|><|det|>[[70, 278, 932, 331]]<|/det|>
+Wei Cao1#, Qi Fan1#, Gemmarie Amparado1, Dean Begic1, Rasoul Godini1, Sandeep Gopal1,2\* and Roger Pocock1\*.
+
+<|ref|>text<|/ref|><|det|>[[70, 377, 935, 496]]<|/det|>
+1Development and Stem Cells Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne, Victoria 3800, Australia.2Lund Stem Cell Center, Department of Experimental Medical Science; Lund University; Lund, Sweden.
+
+<|ref|>text<|/ref|><|det|>[[70, 575, 368, 593]]<|/det|>
+#Contributed equally to this work.
+
+<|ref|>text<|/ref|><|det|>[[70, 608, 630, 626]]<|/det|>
+*Correspondence should be addressed to R.P., W.C. and S.G.
+
+<|ref|>text<|/ref|><|det|>[[70, 642, 880, 660]]<|/det|>
+email: roger.pocock@monash.edu, wei.cao@monash.edu and sandeep.gopal@med.lu.se
+
+<|ref|>text<|/ref|><|det|>[[70, 836, 928, 856]]<|/det|>
+Keywords: Germ line, gametes, transcription factors, RNA interference, Caenorhabditis elegans
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[71, 84, 185, 101]]<|/det|>
+## ABSTRACT
+
+<|ref|>text<|/ref|><|det|>[[69, 107, 888, 398]]<|/det|>
+ABSTRACTFertility requires the faithful proliferation of germ cells and their differentiation into gametes. Controlling these cellular states demands precise timing and expression of gene networks. Transcription factors (TFs) play critical roles in gene expression networks that influence germ cell development. There has, however, been no functional analysis of the entire TF repertoire in controlling in vivo germ cell development. Here, we analyzed germ cell states and germline architecture to systematically investigate the function of 364 germline- expressed TFs in the Caenorhabditis elegans germ line. Using germline- specific knockdown, automated germ cell counting, and high- content analysis of germ cell nuclei and plasma membrane organization, we identify 156 TFs with discrete autonomous germline functions. By identifying TFs that control the germ cell cycle, proliferation, differentiation, germline structure and fertility, we have created an atlas for mechanistic dissection of germ cell behavior and gamete production.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[71, 84, 228, 101]]<|/det|>
+## INTRODUCTION
+
+<|ref|>text<|/ref|><|det|>[[70, 108, 935, 398]]<|/det|>
+INTRODUCTIONThe production of oocytes and sperm (gametes) from germ cells is required for animal reproductive success. To ensure overall fitness, the balance between germ cell proliferation (self-renewal) and differentiation into gametes must be tightly controlled. Model organism research has previously identified regulatory mechanisms that control gene expression and RNA stability to maintain this balance in germ cell behavior. In the Caenorhabditis elegans model, for example, the PUF- domain RNA binding proteins FBF- 1/2 promote germline stem cell fate, with the mammalian ortholog required for the establishment of female germ cells (Crittenden et al., 2002; Mak et al., 2016). Furthermore, the importance of Notch signaling in establishing and maintaining germline stem cell pools was first discovered in C. elegans (Austin and Kimble, 1987). Thus, the C. elegans germ line is a valuable model for discovering conserved mechanisms governing germ cell behavior and fertility. Here, we map the transcription factor (TF) requirements for germ cell and gamete development in C. elegans.
+
+<|ref|>text<|/ref|><|det|>[[68, 424, 936, 916]]<|/det|>
+The C. elegans germ line originates from a single embryonic blastomere (P4) that divides into two primordial germ cells (Z2 and Z3) (Fukuyama et al., 2006). These embryonic germ cells are arrested at the G2 stage of the cell cycle and are transcriptionally quiescent to preserve germ cell fate and protect against inappropriate expression of somatic genes (Furuhashi et al., 2010; Seydoux et al., 1996). Transcriptional quiescence in these primordial germ cells (PGCs) is maintained by inhibiting RNA Polymerase II (RNA Pol II) and by nucleosome modifications associated with chromatin repression (Batchelder et al., 1999; Furuhashi et al., 2010). After embryos hatch and larvae start to feed, germline transcription is activated, and Z2 and Z3 exit G2 to commence mitosis during larval stage 1 (L1) (Fukuyama et al., 2006). Germ cells continue to proliferate throughout larval development and into adulthood, with meiosis commencing from larval stage 3 (L3) (Hansen et al., 2004). This initial differentiation program generates sperm, that are deposited in the spermatheca, before the germ line switches to producing oocytes in adults (Ellis and Schedl, 2007). The adult germ line is organized in a distal to proximal manner. The distal progenitor zone (PZ) contains stem cells, mitotically dividing germ cells and meiotic S- phase germ cells, which then enter early meiotic prophase (leptotene and zygotene) in the transition zone (TZ). As germ cells move from the TZ they enter meiotic pachytene prior to gametogenesis. As transcription is activated early during larval development, TFs likely play important roles in germ cell transitions and cell behavior during larval and adult development. Indeed, previous studies have identified key TFs that regulate germ cell and gamete development (Chi and Reinke, 2006; Curran et al., 2009; Edwards et al., 2021; Rodriguez- Crespo et al., 2022). However, no
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 82, 934, 152]]<|/det|>
+systematic in vivo assessment of TF function in the C. elegans germ line, or in any organism, has been conducted. As a result, we sought to identify the TFs required for C. elegans germline development.
+
+<|ref|>text<|/ref|><|det|>[[68, 181, 936, 497]]<|/det|>
+Of the 875 TFs encoded by the C. elegans genome, we identified 364 TFs that are expressed in the germ line (Cao et al., 2017; Jimeno- Martin et al., 2022; Tzur et al., 2018). As most of these TFs are also expressed in the soma, we dissected their germline functions by exploiting a germline- specific RNA- mediated interference (RNAi) approach (Cao et al., 2017; Serizay et al., 2020; Zou et al., 2019). Following germline- specific RNAi silencing from the L1 larval stage, we performed semi- automated cell counting and high- content analysis of germ line architecture to interrogate a broad spectrum of readouts in adult germ lines. This analysis encompassed the 'distal germ line' where mitotic germ cells, Notch signaling, and early meiotic transition were analyzed; and the 'proximal germ line' where meiotic progression, oocyte/sperm production and germline structure were analyzed. We identified 156 TFs that regulate germ cell development, including 8 TFs that are essential for fertility. Our research provides a TF functional atlas of germ cell development, which is a valuable resource and experimental platform for understanding how specific germ cell fate decisions and gamete production are controlled.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[72, 84, 168, 101]]<|/det|>
+## RESULTS
+
+<|ref|>sub_title<|/ref|><|det|>[[72, 108, 747, 127]]<|/det|>
+## Transcription Factor Germline Profiling and Genetic Screen Validation
+
+<|ref|>text<|/ref|><|det|>[[70, 133, 936, 325]]<|/det|>
+To identify germline- expressed TFs (GTFs), we extruded wild- type adult hermaphrodite germ lines and performed RNA- sequencing from extracted RNA (Figure 1A and Table S1). Combining our germline transcriptome dataset with previously published germline transcriptome studies identified 364 GTFs (Tables S1- 2) (Cao et al., 2017; Tzur et al., 2018). These GTFs were detected in all three of our RNA sequencing samples, both germ lines analyzed in Tzur et al., or GTFs with \(>10\) counts per million in Cao et al. (Table S2) (Cao et al., 2017; Tzur et al., 2018). Of the 364 GTFs, 150 have been ascribed a broad C. elegans reproduction function (sterility/fertility/brood size) (Table S2), however, the precise germline function of these TFs is not well understood.
+
+<|ref|>text<|/ref|><|det|>[[68, 350, 936, 892]]<|/det|>
+By analyzing published TF expression profiles, we found that most GTFs are also expressed in the soma (Table S2) (Cao et al., 2017; Serizay et al., 2020). Therefore, to circumvent potential somatic effects of TF silencing, we utilized a germline- specific RNA- mediated interference (RNAi) approach to identify germline- specific TF functions (Zou et al., 2019). Animals lacking the RDE- 1 Argonaute are systemically RNAi- deficient (Tabara et al., 1999). In our genetic screen, we utilized a rde- 1(mkc36) indel mutant in which RDE- 1 is re- supplied under the germline- specific sun- 1 promoter and 3' untranslated region (UTR) - thus enabling germline- specific RNAi (Zou et al., 2019). To test the efficacy of this strain for germline- specific RNAi by feeding, we silenced the RNA Polymerase II encoding gene ama- 1 from the first larval stage (L1) for 66 hrs (Timmons and Fire, 1998). sun- 1p::rde- 1; rde- 1(mkc36) animals fed with ama- 1 RNAi bacteria grew to adulthood however their germ lines did not develop, while ama- 1 RNAi wild- type animals arrested as young larvae (Figure S1A). Thus, germline- specific inhibition of transcription prevents germline development without overtly affecting somatic development. As additional proof- of- concept for the germline- specific RNAi approach, we silenced two genes that autonomously control germline development - gld- 1 (encodes an RNA binding protein) and mog- 7 (encodes a splicing factor). Consistent with previous studies, gld- 1 RNAi causes proximal germline tumors (86% of germlines are tumorous; n=51) and mog- 7 RNAi causes spermatogenic germ lines (32% of germlines are spermatogenic; n=66) in sun- 1p::rde- 1; rde- 1(mkc36) animals (Figure S1A- B) (Cao et al., 2021; Kerins et al., 2010; Nayak et al., 2005). Prior to embarking on a large- scale germline- specific screen, we needed to confirm that somatic RNAi was inhibited in sun- 1p::rde- 1; rde- 1(mkc36) animals. We examined somatic phenotypes caused by RNAi silencing of hypodermal (bli- 3), intestinal (elt- 2), and muscle (unc- 112) genes. We found that knockdown of these genes from the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 83, 933, 128]]<|/det|>
+L1 stage caused robust somatic phenotypes in wild-type but not in sun- 1p::rde- 1; rde- 1(mkc36) animals, as shown previously (Figure S1C) (Kumsta and Hansen, 2012; Zou et al., 2019).
+
+<|ref|>text<|/ref|><|det|>[[68, 153, 936, 670]]<|/det|>
+To enable functional mapping of the 364 GTFs, we obtained RNAi feeding clones: 315 from previously generated RNAi libraries and 49 that we cloned (Table S3) (Jimeno- Martin et al., 2022; Kamath et al., 2003; Rual et al., 2004). All RNAi clones were confirmed by sequencing prior to analysis. We profiled GTF function in the germ line by feeding L1 hermaphrodites with Escherichia coli HT115 bacteria expressing individual TF RNAi clones and imaged and analyzed one- day adult germ lines (Figure 1A). We screened GTF function in hermaphrodite germline development using two parallel approaches for distal and proximal germline analysis (Figure 1A). Distal germline analysis was performed with confocal imaging and semi- automated cell counting of extruded germ lines of the 3xflag::syg- 1; sun- 1p::rde- 1; rde- 1(mkc36) strain that we confirmed exhibits wild- type germ cell number and brood size (Figure 1A and S2). Following GTF RNAi silencing from the L1 stage, we quantified germ cell number in the PZ and TZ by DAPI staining (PZ and TZ size), plus visualized M- phase chromosomes (anti- phospho- histone H3 (pH3) staining) and Notch signaling (SYGL- 1 immunofluorescence) in adults (Figure 1A) (Gopal et al., 2017). For proximal germline analysis, we examined gonad architecture, meiotic cell behavior and gamete development using a transgenic strain co- expressing fluorescent markers targeting chromosomes (mCherry- histone H2B) and plasma membrane (GFP- PI4, 5P2) (Figure 1A and S3). This approach for analyzing the proximal germ line was previously used for a group of 554 essential genes (Green et al., 2011), however, their work analyzed less than 3% of GTFs and used the RNAi soaking method (not germline- specific) from the L4 stage. Thus, our work is distinct to this previous study with regards to genes investigated, phenotypes analyzed and methods/timing of gene silencing.
+
+<|ref|>sub_title<|/ref|><|det|>[[70, 698, 614, 717]]<|/det|>
+## Profiling Transcription Factor Function in the Germ Line
+
+<|ref|>text<|/ref|><|det|>[[70, 722, 936, 914]]<|/det|>
+To determine the in vivo functional contributions of TFs in the germ line, we performed two independent reverse genetic screens (as described above) to study the distal and proximal germ line. The results of the two screens identified 156 TFs that are important for germline development (Tables S4- 6). Among these GTFs, 82 have previously reported germline phenotypes in C. elegans (Table S7). In both screens, silencing of 8 GTFs resulted in immature germ lines that did not generate embryos in one- day adults (Tables S6), detailed analysis of which will be discussed later. Silencing of an additional 10 GTFs resulted in 20- 100% immature germ lines in the proximal screen only, among which 6 also caused distal phenotypes (Table S5). We hypothesize that the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 82, 934, 152]]<|/det|>
+sterility phenotype of these 10 genes is likely a synthetic effect of the RNAi silencing and transgenic reporters (mCherry- histone H2B and plasma membrane GFP- PI4, 5P2) used in the proximal screen.
+
+<|ref|>text<|/ref|><|det|>[[68, 181, 935, 546]]<|/det|>
+Beyond of the sterility phenotype, we used strict phenotypic criteria to furnish a robust inventory of key GTFs: distal germline analysis ( \(\geq 20\%\) significant change in germ cell number of PZ, TZ, and SYGL- 1+ region compared to control) and proximal germline analysis ( \(\geq 4\) of 8 germlines exhibiting a phenotype). Using these criteria, we found that RNAi silencing of 128 TFs caused germline phenotypes (88 in the distal screen and 52 in the proximal screen), 12 of which caused phenotypes in both screens (Figure 1B- D and Tables S4- 6). We classified TFs that control germline development based on broad DNA- binding domain families and found no obvious overrepresentation of TF family that is functionally required for germline development (Figure 1E). We wondered whether the TFs we identified in our primary screen were previously associated with germ cell/gamete development and reproduction. We thus compared our list of TFs hits to genes associated with the 'reproduction' gene ontology (GO) terms (GO:0019952, GO:0050876) in mice, rats and humans (https://www.flyrnai.org/cgi- bin/DRSC_orthologs.pl). We found that 88 GTFs we identified to regulate C. elegans germline development in our primary screens have mammalian orthologs, of which 43 are associated with germ cell/gamete development and reproduction GO terms (Figure 1 and Table S8).
+
+<|ref|>sub_title<|/ref|><|det|>[[70, 574, 576, 594]]<|/det|>
+## Transcriptional Control of Distal Germ Cell Behavior
+
+<|ref|>text<|/ref|><|det|>[[70, 599, 936, 766]]<|/det|>
+At the distal progenitor zone, maintenance of the germline stem cell (GSC) pool is influenced by interaction between Notch ligands (LAG- 2/APX- 1), expressed on the somatic distal tip cell, and the GLP- 1 Notch receptor expressed on the surface of germ cells (Austin and Kimble, 1987, 1989; Gao and Kimble, 1995; Henderson et al., 1994; Tax et al., 1994). This Notch ligand- receptor interaction promotes GSC self- renewal by regulating the two redundantly acting post- transcriptional regulators SYGL- 1 and LST- 1 (Chen et al., 2020; Ferdous et al., 2023; Haupt et al., 2019; Shin et al., 2017).
+
+<|ref|>text<|/ref|><|det|>[[70, 795, 935, 914]]<|/det|>
+Our primary screen identified 23 GTFs that when silenced have a \(\geq 20\%\) change in progenitor zone (PZ) size (Figure 1 and Table S4). To identify high- confidence regulators of germline development, we performed a secondary screen of these hits in triplicate (Figure 2A and Figure S4). We found that silencing of 11 GTFs robustly repeated our initial findings with significant changes in PZ size (Figure 2A and Figure S4). These factors include two nuclear hormone
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 82, 934, 177]]<|/det|>
+receptors (NHR- 84 and NHR- 146), HSF- 1/HSF1, DAF- 19/RFX, LET- 607/CREB, F54F2.9/DNAJC1, ZK546.5, XND- 1, ZTF- 23, C02F5.12 and C30G4.4. Of these 11 TFs, only HSF- 1 and XND- 1 have known roles in C. elegans germ cell proliferation (Edwards et al., 2021; Mainpal et al., 2015).
+
+<|ref|>text<|/ref|><|det|>[[69, 205, 936, 546]]<|/det|>
+The PZ houses self- renewing stem cells, germ cells undergoing final round of the mitotic cell cycle, and germ cells in meiotic S- phase (Fox and Schedl, 2015). To better understand the cellular and molecular effects underpinning the changes in PZ size, we analyzed the roles of these 11 TFs in Notch signaling and the mitotic cell cycle (Figure 2A- H and Figures S4- 5). First, we used a glp- 1(ar202gf) temperature- sensitive gain- of- function mutant that at the permissive temperature of \(15^{\circ}C\) generates \(\sim 25\%\) more PZ germ cells than wild- type animals (Figure 2B- C). We found that RNAi silencing of hsf- 1 and xnd- 1 decreased the number of PZ germ cells in glp- 1(ar202gf) animals at the permissive temperature (Figure 2B- C). This suggests that these TFs are required for excessive germ cell proliferation in glp- 1(ar202gf) animals. In contrast, RNAi silencing of C02F5.12, C30G4.4, daf- 19, F54F2.9 and ZK546.5 increases PZ size in wild- type animals but not in glp- 1(ar202) gain- of- function animals, suggesting that these genes function in the glp- 1 pathway (Figure 2A- B). Further, glp- 1 is epistatic to let- 607, nhr- 84, ztf- 23 and nhr- 146 as glp- 1(ar202) gain- of- function animals have an increase in PZ size irrespective of silencing these GTFs (Figure 2A- B).
+
+<|ref|>text<|/ref|><|det|>[[69, 574, 936, 914]]<|/det|>
+Maintenance of the GSC pool in the PZ is regulated by two direct GLP- 1 target genes SYGL- 1 and LST- 1 (Chen et al., 2020; Shin et al., 2017). SYGL- 1 and LST- 1 proteins are present in partially overlapping gradients through the GSC pool (Shin et al., 2017). Previous studies showed that overexpression of SYGL- 1 or LST- 1 can expand the GSC pool (Shin et al., 2017) and sygl- 1 RNAi knockdown can reduce the PZ length (Kershner et al., 2014). Therefore, we quantified endogenous 3xFLAG::SYGL- 1 and 3xFLAG::LST- 1 after silencing of the 11 GTFs that control PZ size to determine their potential roles in regulating Notch signaling (Figure 2D- E and Figure S4B- D). We found that RNAi silencing of C02F5.12 and ZK546.5 increased the number of SYGL- 1+ germ cells, consistent with their knockdown leading to an increase in PZ size (Figure 2A, D- E). This implies that C02F5.12 and ZK546.5 inhibit Notch signaling. Given that RNAi silencing of C02F5.12 and ZK546.5 did not affect the glp- 1(gf) increase of PZ size, they may function upstream of GLP- 1. We also found that RNAi silencing of hsf- 1 and xnd- 1 decreased the number of SYGL- 1+ germ cells, consistent with their knockdown to leading to a decrease in PZ size (Figure 2A, D- E). This suggests that HSF- 1 and XND- 1 promote Notch- signaling. Given that HSF- 1 and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 82, 935, 250]]<|/det|>
+XND- 1 are required for glp- 1(gf) induced increase in PZ size, they likely function downstream of GLP- 1. Interestingly, both HSF- 1 and XND- 1 have ChIP peaks in the promoter regions of sygl- 1 (ENCSR512EIF, ENCSR327NRA), suggesting a direct regulatory relationship with this Notch target gene (Consortium, 2012; Luo et al., 2020). In contrast to the SYGL- 1+ analysis, we did not detect changes in LST- 1+ in the PZ after silencing these 11 GTFs (Figure S4C- D). These data suggest that the change in PZ size following silencing of C02F5.12, ZK546.5, hsf- 1 and xnd- 1 may be due to altered Notch- dependent SYGL- 1 regulation.
+
+<|ref|>text<|/ref|><|det|>[[69, 279, 936, 619]]<|/det|>
+PZ size is also impacted by the mitotic cell cycle that is genetically separable to Notch signaling (Fox and Schedl, 2015). Within the PZ, a cohort of germ cells act as stem cells that self- renew by mitosis or differentiate into gametes (Crittenden et al., 2006; Crittenden et al., 1994). To examine whether any of the 11 GTFs impact progression through the cell cycle, we quantified cell proliferation using 5- ethynyl- 2'- deoxyuridine (EdU) staining (Figure 2F- G) (Fox and Schedl, 2015; Seidel and Kimble, 2015). We silenced each GTF from the L1 stage, fed the resultant adults with EdU- labelled bacteria for 4 hrs or 10 hrs, and then counted EdU+ germ cells (Figure 2F- G). Using these data, we calculated the rate of proliferation as the number of germ cells incorporating EdU per hour (Figure 2F- G). As previously reported, control animals had a proliferation rate of \(\sim 23\) cells/hour (Figure 2F) (Fox and Schedl, 2015). We found that RNAi silencing of C02F5.12, daf- 19 and ZK546.5 increased the germ cell proliferation rate, which may contribute to increases in PZ size observed by increasing number of mitotic cells (Figure 2F- G). Taken together, these results reveal key TFs that control PZ size, likely through fine- tuning Notch signaling, cell cycle dynamics and possibly other mechanisms.
+
+<|ref|>text<|/ref|><|det|>[[69, 647, 936, 914]]<|/det|>
+Antibody staining to detect phosphorylation of histone H3 (pH3) at serine 10 is used to mark mitotic M- phase germ cells (Crittenden et al., 2017; Hsu et al., 2000). No pH3+ cells are observed after proliferative zone cells have entered meiosis (Fox and Schedl, 2015). Therefore, changes in the number of pH3+ germ cells could indicate changes in the total number of mitotic germ cells, or changes in M- phase length with respect to the entire cell cycle. We found that of the 11 GTFs analyzed, only hsf- 1 silencing increased the number of pH3+ germ cells (Figure S5A- B). This suggests that hsf- 1 silencing increases mitotic germ cell number or M- phase length, or potentially accelerates other cell cycle phases. However, further investigation of hsf- 1 functions in mitosis and early meiosis is required to explain the contradictory results of decreased PZ size, decreased SYGL- 1+ cells, and unchanged proliferation rate following hsf- 1 silencing. A previous study found that germline- specific HSF- 1 protein depletion from hatching causes a severe reduction in germ
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[69, 82, 936, 325]]<|/det|>
+cells and depletion from the mid- L3 stage causes a decrease in EdU labeled germ cells (Edwards et al., 2021). These contradictory findings suggest the effect of HSF- 1 knockdown on the germ line is dosage or developmental stage dependent. Another method frequently used to assess germline proliferation is the mitotic index (MI), which is the percentage of PZ cells that are M- phase (Crittenden et al., 2023). In addition to hsf- 1, we found silencing of F54F2.9 and nhr- 146 caused changes in MI without changing the absolute number of pH3+ cells (Figure S5A- C). Although silencing of F54F2.9 and nhr- 146 caused changes in PZ size, there were no changes in the number of SYGL- 1+ cells or proliferation rate (Figure 2D and F). Thus, it is possible that these genes are not involved in mitosis, and the change of MI is a result of changes of overall PZ size which also include meiotic M- phase cells.
+
+<|ref|>text<|/ref|><|det|>[[69, 352, 936, 693]]<|/det|>
+Proximal to the PZ, the germline TZ houses a cohort of crescent- shaped nuclei that is characteristic of early meiotic prophase (leptotene and zygotene) germ cells (Hubbard, 2007). We found that some GTFs are also required for normal TZ size (ZK546.5, HSF- 1/HSF1, XND- 1, ZTF- 23 and NHR- 146), suggesting that meiotic prophase progression and/or chromosome pairing may be perturbed following silencing of these GTFs (Figure S5D- E). Interestingly, the changes in TZ size paralleled changes in PZ size – ZK546.5 silencing increased PZ and TZ size; hsf- 1, xnd- 1, ztf- 23 and nhr- 146 silencing decreased PZ and TZ size (Figure 2H). This suggests that when these genes are silenced, germ cell output from the PZ impacts TZ size. Finally, we found that 5 out of the 11 GTFs that are important for distal germ cell behavior also impact the proximal germline. ZK546.5 silencing caused incomplete spermatogenesis (7/8 germ lines), ztf- 23 and C02F5.12 silencing caused changes in the number of single array or budded oocytes, and C30G4.4 and nhr- 146 silencing caused germ cell multinucleation (Table S5). Thus, these GTFs likely play roles in both mitotic and meiotic germ cell behavior. Taken together, our distal germline screen discovered multiple GTFs that control germ cell behavior.
+
+<|ref|>sub_title<|/ref|><|det|>[[70, 722, 785, 741]]<|/det|>
+## Transcriptional Control of Meiotic Cell Behavior and Gamete Development
+
+<|ref|>text<|/ref|><|det|>[[70, 747, 936, 914]]<|/det|>
+As germ cells progress proximally, they mature into sperm during late larval development before committing to the oogenic program. To examine the function of GTFs in these processes we utilized a transgenic strain in which fluorescent markers targeting chromosomes (mCherry- histone H2B) and plasma membrane (GFP- PI4, 5P2) enable gonad architecture to be visualized (Figure 1A and S3) (Essex et al., 2009; Green et al., 2011). We identified GTF functions in the proximal germ line including germline structure (small germ line, narrow rachis), meiosis (multinucleation, meiotic progression and apoptosis), sperm production and behavior
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 83, 935, 177]]<|/det|>
+(spermatogenesis, sperm localization), and oocyte production (germ cell expansion, number of oocytes, oocyte budding and vesiculation) (Figure S3 and Table S5). The most prominent phenotype we observed was multinucleation of germ cells and thus we focused our subsequent analysis on this phenotype.
+
+<|ref|>text<|/ref|><|det|>[[68, 205, 936, 620]]<|/det|>
+The C. elegans hermaphrodite gonad is a syncytium with germ cell nuclei partially enclosed by a plasma membrane. Multinucleated germ cells (MNCs) can occur in both wild- type and some mutant animals at varying frequency (Raiders et al., 2018). Persistent MNCs would generate multinuclear oocytes and infertile embryos and are therefore cleared by apoptosis prior to generating gametes. Earlier studies showed that failed germ cell division in the PZ and an unstable rachis can cause multinucleation, while in other cases, including in wild- type animals, MNCs form at specific germline structures called folds (Lan et al., 2019; Raiders et al., 2018). In our primary screen, we identified 26 GTFs that have \(>25\%\) increase in germ lines with MNCs compared to control animals (Table S5- 6). To confirm this result, we selected 10 GTFs with the strongest penetrant phenotypes (DMD- 7/DMRTC1, BAZ- 2/BAZ2A, JUN- 1/JUN, MTER- 4, LIN- 26, MADF- 5, NHR- 40/HNF4, NHR- 114/NR1H3, NHR- 161/PPAR- alpha, and UNC- 62/MEIS) and repeated RNAi silencing in triplicate (Figure 3). We confirmed that silencing of all 10 GTFs increased MNCs in both one- day and two- day adults (Figure 3A- B and Figure S6A- B). Of these TFs, only NHR- 114 had previously been associated with germ cell multinucleation in C. elegans (Gracida and Eckmann, 2013). We used confocal microscopy to analyze the PZ of one- day adults following GTF silencing and detected no MNCs, suggesting that MNC formation is not due to aberrant mitotic division, as shown previously (data not shown) (Lan et al., 2019).
+
+<|ref|>text<|/ref|><|det|>[[70, 648, 936, 914]]<|/det|>
+As part of normal germline development, multinucleate cells are removed by physiological apoptosis to prevent them from potentially generating multipoid oocytes (Gumienny et al., 1999; Raiders et al., 2018). The CED- 3 executioner caspase is essential for physiological germline apoptosis (Gumienny et al., 1999), and thus germ lines lacking ced- 3 contain many MNCs (Raiders et al., 2018). To determine whether regulation of germ cell multinucleation by GTFs is dependent on CED- 3, we silenced the 10 GTFs that inhibit MNC formation in ced- 3 mutant animals. As the ced- 3 gene is linked to the pie- 1p::mCherry::his- 58 transgene that is used to count multinucleation events, we used CRISPR/Cas9 genome editing to generate a 3951bp ced- 3(rp190) deletion allele (Figure S7). These animals exhibit overt persistent apoptotic corpses confirming defective apoptosis (Figure S7B- C). Further, we did not detect apoptosis in the germ lines of ced- 3(rp190) animals, and loss of CED- 3 caused an increase in multinucleated germ cells
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[71, 83, 932, 127]]<|/det|>
+(Figure 3B- D), confirming that apoptosis is involved in the clearance of multinucleated germ cells (Raiders et al., 2018).
+
+<|ref|>text<|/ref|><|det|>[[68, 155, 935, 447]]<|/det|>
+We next counted germline MNCs in ced- 3(rp190) two- day adults after GTF RNAi silencing from the L1 stage (Figure 3E). We found that RNAi silencing of jun- 1, mter- 4, lin- 26, nhr- 40, nhr- 114, nhr- 161, and unc- 62 caused no change in MNC number in the ced- 3(rp190) background, suggesting that silencing these GTFs lead to increase in multinucleated cells by interfering with apoptosis. In contrast, silencing of dmd- 7, baz- 2 and madv- 5 increased MNCs independent of loss of ced- 3, suggesting that these GTFs promote mono- nucleation through mechanisms that are independent of apoptosis. However, caspase- 3 can play roles outside apoptosis (Dehkordi et al., 2022; Eskandari and Eaves, 2022), therefore it is possible that CED- 3 is involved in multinucleation formation through other mechanisms. In addition, we observed that MNCs are primarily located in the distal half of the pachytene region in wild- type and ced- 3(rp190) animals (Figure 3B), suggesting that mechanisms independent of physiological apoptosis can remove/resolve multinucleation.
+
+<|ref|>text<|/ref|><|det|>[[68, 475, 936, 791]]<|/det|>
+A previous study revealed that meiotic germline structure impacts the location and occurrence of multinucleation (Raiders et al., 2018). During proliferation, folds in the germline syncytium are formed and multinucleate cells occur during fold eversion (Raiders et al., 2018). As the size and complexity of germline folds is correlated with multinucleation, we assessed whether the 10 GTFs with high numbers of MNCs regulate germline folding. We used phalloidin to stain the germline actin cytoskeleton after RNAi silencing of these GTFs and measured germline folding by counting the rows and numbers of cells protruding inwards from the single layer of cells that form the tubelike structure in the pachytene region (Figure 3F- G and Figure S6C). We found that RNAi silencing of dmd- 7, baz- 2, mter- 4, lin- 26, nhr- 114 and nhr- 161 caused excess germline folding that may result in the increased multinucleation observed (Figure 3F- G and Figure S6C). Taken together, these data reveal 10 GTFs that act in the germline to maintain uninuclear germ cells. Cell behavior is likely controlled by these TFs through gene networks connected to the apoptotic pathway and germline morphogenesis.
+
+<|ref|>sub_title<|/ref|><|det|>[[71, 820, 463, 839]]<|/det|>
+## Essential TFs for Germline Development
+
+<|ref|>text<|/ref|><|det|>[[70, 845, 934, 913]]<|/det|>
+Our initial distal germline screen identified 8 TFs (CDC- 5L, ZNF- 622, VEP- 1, F23B12.7, F33H1.4, F58G1.2, REPO- 1, and TBP- 1) that when silenced from the L1 stage result in small germ lines that do not generate embryos in one- day adults (Table S4). These TFs are mostly
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[69, 82, 935, 250]]<|/det|>
+uncharacterized but have predicted general functions in controlling gene expression (Table S4). Analysis of broods after silencing these TFs from the L1 stage showed almost complete sterility (Figure 4A). An exception was repo- 1 RNAi, which generated \(\sim 230(\pm 30.47)\) progeny, however most resultant embryos did not hatch (Figure 4A). To investigate when these TFs are required during development, we performed temporal germline analysis by silencing each TF from the L1 stage and examining germline size and morphology at each larval stage through to adult (Figure 4B and S8).
+
+<|ref|>text<|/ref|><|det|>[[68, 278, 936, 742]]<|/det|>
+We found that germline size and morphology were mostly intact during early larval development (L1 through L3) following TF silencing (Figure S8). However, from the L4 stage, TF silencing began to reveal germline defects - silencing of all 8 essential GTFs caused a significant decrease in germline length (Figure 4C). Of note, cdc- 5L and znf- 622 silencing resulted in small germ lines ( \(\sim 50\%\) the length of controls) that contained large nuclei suggesting arrest in the G2 stage of the cell cycle (Figure 4C- D and S8). We continued to monitor germline development for all 8 TF RNAi experiments during the first three days of adulthood to determine the effect on sperm, oocyte, and embryo development (Figure 4E). We found that silencing of some genes prevented or delayed sperm generation (cdc- 5L, znf- 622, vep- 1 and F23B12.7), with all genes defective or delayed in oocyte production and embryogenesis (Figure 4E). In addition, silencing of cdc- 5L, znf- 622, vep- 1 and tbp- 1 caused sterility in three- day adults (Figure 4E). We wondered whether these 8 TFs are continuously required for germline development or perform functions during larval development to enable fertility in adults. We explored this by performing germline- specific RNAi silencing from the mid- L4 stage at which gonad development and spermatogenesis are largely complete (Figure 4F). We found that silencing of repo- 1, F33H1.4, F23B12.7, F58G1.2, tbp- 1 and vep- 1 had similar broods to control animals, albeit with different degrees of embryonic lethality (Figure 4F). In contrast, cdc- 5L and znf- 622 silencing caused approximately \(>50\%\) reduction in brood size (with cdc- 5L RNAi causing \(100\%\) embryonic lethality), suggesting post- developmental roles in germline maintenance (Figure 4F).
+
+<|ref|>text<|/ref|><|det|>[[70, 770, 935, 914]]<|/det|>
+To examine the function of the essential GTFs in the oogenic germline, we quantified distal germ cell number in one- day adults following RNAi from the L4 stage (Figure 4G- J). We identified subtle changes in PZ/TZ size, pH3+ cells, and SYGL- 1+ staining (Figure 4G- J). However, these changes are negligible compared to the detrimental effect of silencing these GTFs from the L1 stage (Figure 4A), suggesting that the germ cell cycle and transition to meiosis are largely intact. Further, the minor changes in distal germ line cell numbers suggest that the brood size decrease
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 82, 933, 152]]<|/det|>
+we observed following cdc- 5L and znf- 622 silencing are likely caused by defects in gametogenesis. Taken together, we have identified multiple TFs that control the timing and function of gamete generation and subsequent fertility in C. elegans.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[72, 84, 200, 101]]<|/det|>
+## DISCUSSION
+
+<|ref|>text<|/ref|><|det|>[[70, 107, 936, 350]]<|/det|>
+In this study, we profiled the function of every germline- expressed TF in C. elegans to gain a comprehensive understanding of transcriptional regulation of germline development. To identify autonomous regulatory functions, we first determined that 364 TFs are germline expressed and then depleted their expression specifically in the germ line. We used two independent screening approaches to investigate TF functions from the proliferative germ cell stage to gamete production. Using high- content imaging, semi- automated germ cell counting and cell behavior analysis of \(>6000\) germ lines and \(>3\) million germ cells, we identified 156 TFs that influence germline development, \(>75\%\) of which are undescribed. Furthermore, we identified 8 factors that are essential for fertility. As a result, this study provides a rich resource for mechanistic dissection of TF function in germ cells and potentially new opportunities for manipulating cell fates.
+
+<|ref|>text<|/ref|><|det|>[[70, 378, 936, 570]]<|/det|>
+Previous C. elegans forward and reverse genetic screening approaches identified genes that cause sterility or reduced brood sizes (Argon and Ward, 1980; Hirsh and Vanderslice, 1976; Maeda et al., 2001). Further, a large- scale screen of essential genes used the RNAi soaking method to examine proximal germline development (Green et al., 2011); however, \(< 3\%\) of these genes overlapped with our screen. Whether phenotypes observed in these previous studies result from autonomous germline functions or somatic deficits is, however, unclear. Thus, our use of a germline- specific RNAi approach to survey autonomous TF functions, allows for a more refined and robust evaluation of critical germline regulators.
+
+<|ref|>text<|/ref|><|det|>[[70, 598, 936, 914]]<|/det|>
+Our primary screen identified 8 factors that are essential for fertility: CDC- 5L, ZNF- 622, VEP- 1, F23B12.7, F33H1.4, F58G1.2, REPO- 1, and TBP- 1. Loss of these factors had previously produced sterile/fertility phenotypes in genetic mutants and/or large- scale RNAi screens (Fraser et al., 2000; Kamath et al., 2003; Kerins et al., 2010; Simmer et al., 2003; Sonnichsen et al., 2005; Sun et al., 2011). Our analysis shows that these factors act autonomously and predominantly during larval development to enable germline function as we observed robust sterility when these factors were silenced from hatching, but not when silenced late in development. Major exceptions were silencing of cdc- 5L, repo- 1 and znf- 622 which caused reduced brood sizes and high proportions of dead eggs even when they were silenced late in development. Previous studies have identified conserved germline functions in mammals for some of these factors. Porcine CDC- 5L is required for fertility and oocyte maturation (Liu et al., 2018), which is consistent with the oogenesis defect induced by C. elegans cdc- 5L silencing. In addition, murine BDP1 is required for spermatogonial stem cell gene expression (Sisakhtnezhad and Heshmati, 2018), which may
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 82, 934, 177]]<|/det|>
+be the cause of sterility and delayed sperm development when the BDP1 C. elegans ortholog VEP- 1 is silenced. Further, the zinc- finger protein CTCF is critical for oocyte development in mice through regulation of chromatin architecture (Wan et al., 2008), which may also impact the oocyte developmental defects we observed in the C. elegans ortholog F58G1.2.
+
+<|ref|>text<|/ref|><|det|>[[68, 201, 936, 744]]<|/det|>
+We also identified 128 TFs that control germ cell behavior in the distal germ line, including multiple TFs previously reported. For example, our screen confirmed previous studies identifying a zinc- finger TF LSL- 1 that limits TZ size, and the heat shock factor HSF- 1 and chromatin factor XND- 1 that promote germ cell proliferation in the PZ (Edwards et al., 2021; Mainpal et al., 2015; Rodriguez- Crespo et al., 2022). Our secondary screen focused on the TFs important for controlling PZ size to define whether these factors potentially control Notch signaling and/or mitotic cell cycle - two critical determinants of PZ germ cell behavior. Our analysis identified 5 TFs that limit and 6 TFs that promote PZ size. Key findings from this work suggest that HSF- 1 and XND- 1 are required for excess germ cell proliferation caused by GLP- 1/Notch overexpression. Further, loss of the zinc- finger TFs C02F5.12 and ZK546.5 enhance expression of the GLP- 1 target gene SYGL- 1 and germ cell proliferation rate, suggesting that these genes act in the Notch signaling pathway. Interestingly, C02F5.12 is a paralog of ZIM- 1, ZIM- 2, ZIM- 3, and HIM- 8 that are required for chromosome pairing (Phillips and Dernburg, 2006). However, as with C02F5.12, we found that loss of ZIM- 2 additionally limits PZ size suggesting a pre- meiotic function for these proteins. Further, ZK546.5 also limits size of the TZ - a phenotype it shares with its paralog LSL- 1. Finally, we found that the RFX- type TF DAF- 19 limits the germ cell proliferation in C. elegans. Interaction analysis predicts that DAF- 19 physically interacts with the serine-threonine kinase ATL- 1 and checkpoint kinase CHKR- 1, two kinases that are required for fertility, suggesting a potential mechanism for DAF- 19 function in the germline (Garcia- Muse and Boulton, 2005). A mouse ortholog of DAF- 19, RFX2, is expressed in the testis and required for spermatogenesis (Wu et al., 2016). Thus, future analysis of DAF- 19 functions in sperm development in C. elegans hermaphrodites and males is warranted.
+
+<|ref|>text<|/ref|><|det|>[[70, 771, 936, 914]]<|/det|>
+Meiotic development in the C. elegans germline is predominantly regulated by post- transcriptional networks governed by the redundant GLD- 1, GLD- 2, and SCFPROM- 1 proteins (Francis et al., 1995; Jantsch et al., 2007; Kadyk and Kimble, 1998; Nayak et al., 2002). However, the pachytene region is transcriptionally active prior to the transcriptional silencing that occurs in oocytes (Gibert et al., 1984; Starck, 1977). Our analysis of TF function in the proximal germline identified functions in spermatogenesis, oogenesis, gonad structure and meiotic progression. However, the most
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[69, 82, 936, 399]]<|/det|>
+common phenotype we observed was increased multinucleation of meiotic cells where silencing of 26 GTFs caused a robust phenotype. We focused on the 10 GTFs with the most penetrant multinucleation phenotype for secondary analysis. Previous studies revealed that folding of the germline structure and apoptosis impacts multinucleation (Raiders et al., 2018). In consensus with this, we found that silencing of 6/10 of these GTFs (DMD- 7, BAZ- 2, MTER- 4, LIN- 26, NHR- 114 and NHR- 161) caused excess folding in the germline syncytium that may contribute to the multinucleation phenotype. Furthermore, we found that increase in multinucleation caused by silencing of 7/10 of these GTFs is dependent on the presence of the apoptotic executioner caspase, CED- 3. Caspase- 3 is a well- known essential apoptosis inducer, but it can also regulate non- apoptotic processes including axonal differentiation, growth, routing, regeneration and degeneration (Dehkordi et al., 2022). Considering that the molecular mechanism of multinucleation formation and removal is unknown, it is challenging to speculate if CED- 3 only controls this event by inducing apoptosis, or it has additional functions.
+
+<|ref|>text<|/ref|><|det|>[[69, 426, 936, 619]]<|/det|>
+Overall, our detailed map of TF function throughout the C. elegans germ line is a valuable resource for mechanistic studies of germ cell and gamete development. Our discovery of multiple TFs with specific functions in the developing germ line suggests that many distinct pathways act to fine- tune gene networks and cell behavior. We anticipate that specific TFs will act downstream of key signaling pathways (e.g., TGF, mTOR, AMPK and insulin signaling) to integrate environmental and genetic cues for optimizing germ cell proliferation, meiotic transition, and progeny production. Together, these transcriptional outputs, when combined, likely provide robustness to the process of delivering the next generation.
+
+<|ref|>sub_title<|/ref|><|det|>[[72, 650, 301, 667]]<|/det|>
+## Limitations of the study
+
+<|ref|>text<|/ref|><|det|>[[69, 673, 936, 865]]<|/det|>
+We wish to highlight two limitations of our study. First, categorization of TFs was based on the presence of DNA binding domains (Jimeno- Martin et al., 2022). However, these factors may also control other aspects of gene expression such as RNA splicing (CDC- 5L) and translation (ZNF- 622), thus care must be taken when planning mechanistic dissection of their function. Second, we found that the transgenic strain we used to analyze the proximal germ line (OD95) identified more TFs that cause a sterility phenotype than the strain used for distal analysis. This OD95 strain expresses two independently integrated transgenes to mark germ cell nuclei and membranes that may cause sensitivity to certain genetic perturbations.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[72, 84, 263, 102]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[70, 107, 935, 250]]<|/det|>
+AcknowledgementsWe thank members of the Pocock and Gopal laboratories for advice and comments on the manuscript. RNA sequencing and Bioinformatics performed at Monash Micromon Genomics and Monash Bioinformatics Platform. Imaging performed at Monash Microimaging. We thank Nuria Flames for their kind gift of TF RNAi clones. Some strains were provided by the Caenorhabditis Genetics Center (University of Minnesota), which is funded by the NIH Office of Research Infrastructure Programs (P40 OD010440).
+
+<|ref|>sub_title<|/ref|><|det|>[[71, 281, 155, 299]]<|/det|>
+## Funding
+
+<|ref|>text<|/ref|><|det|>[[71, 305, 934, 373]]<|/det|>
+FundingThis work was supported by the following grants: Australian Research Council DE190100174 (SG) and DP200103293 (RP); National Health and Medical Research Council GNT1161439 (S.G.), GNT1105374 (RP), GNT1137645 (RP) and GNT2018825 (RP, WC and QF).
+
+<|ref|>sub_title<|/ref|><|det|>[[71, 403, 277, 421]]<|/det|>
+## Author Contributions
+
+<|ref|>text<|/ref|><|det|>[[70, 427, 732, 618]]<|/det|>
+Conceptualization: RP, SG Methodology: RP, SG, WC, QF, RG Investigation: RP, SG, WC, QF, RG, GA, DB Visualization: RP, SG, WC, QF, RG, GA, DB Funding acquisition: SG, RP Project administration: RP, SG, WC Supervision: RP, SG, WC Writing - original draft: RP Writing - review & editing: RP, SG, WC, QF, RG, GA, DB
+
+<|ref|>sub_title<|/ref|><|det|>[[71, 649, 268, 666]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[70, 673, 561, 692]]<|/det|>
+Authors declare that they have no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[71, 722, 362, 740]]<|/det|>
+## Data and materials availability
+
+<|ref|>text<|/ref|><|det|>[[70, 747, 934, 815]]<|/det|>
+All data is available in the main text, supplementary materials, and source data. No accession codes, unique identifiers, or weblinks are in our study and there are no restrictions on data availability. Materials are available upon request from Roger Pocock.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[72, 84, 253, 101]]<|/det|>
+## FIGURE LEGENDS
+
+<|ref|>sub_title<|/ref|><|det|>[[70, 108, 770, 127]]<|/det|>
+## Figure 1. Phenotypic Profiling of Germline Transcription Factor Function
+
+<|ref|>text<|/ref|><|det|>[[69, 133, 935, 275]]<|/det|>
+(A) Schematic of the C. elegans hermaphrodite germline (left), identification of germline-expressed TFs by RNA sequencing (center), and representative images and phenotypic readouts for high-content distal and proximal germline analysis (right). The distal germ line is labelled with DAPI (nuclei), SYGL-1 (Notch target gene) and pH3 (M-phase chromosomes). PZ = progenitor zone, TZ = transition zone. The proximal germ line is marked with transgenic fluorophores: red = nuclei; green = plasma membrane. Scale bars = 20 μm.
+
+<|ref|>text<|/ref|><|det|>[[69, 283, 935, 451]]<|/det|>
+(B- D) Heatmaps showing phenotypic overview for TF silencing causing distal (B \(\geq 20\%\) change compared to control), proximal (C \(\geq 50\%\) of animals with the phenotype) or distal and proximal germline phenotypes (D). (B) TF family categories (colored boxes); progenitor zone (PZ), transition zone (TZ) and SYGL- \(1^{+}\) region phenotypes shown as percentage change compared to control (blue \(=\) decrease; red \(=\) increase); germline expression of each TF (grey bars \(=\) log2 CPM); mammalian ortholog associated with the reproduction GO term (blue boxes \(=\) No, black boxes \(=\) Yes).
+
+<|ref|>text<|/ref|><|det|>[[69, 457, 935, 622]]<|/det|>
+(C) Labelling as in B, except purple \(=\) proximal phenotype; blue \(=\) no phenotype detected. Phenotypes shown in this figure: small germ line, rachis defect (narrow or wide rachis), meiotic defect (multinucleated cells, abnormal meiotic progression), apoptosis, oocyte defect (delayed expansion at the turn, difference in single-array oocyte number, difference in budded oocyte number, vesiculation), sperm defect (mislocated sperm, incomplete spermatogenesis). (D) Labelling as in B and C. Note: the heatmaps do not include essential GTFs identified in the screens – this analysis is detailed in Figure 4 and Table S4.
+
+<|ref|>text<|/ref|><|det|>[[69, 629, 935, 747]]<|/det|>
+(E) TF family distribution of the 875 C. elegans TFs, 96 TFs that regulate the distal germ line or are essential for germline development, and 52 TFs that regulate the proximal germline. TF families shown in this figure: bZIP = basic leucine zipper domain, HD = homeodomain, HMG = High mobility group box domain, MYB= myeloblastosis viral oncogene homolog, NHR = nuclear hormone receptors, T-box, WH = winged helix, ZF = zinc finger.
+
+<|ref|>sub_title<|/ref|><|det|>[[70, 777, 545, 795]]<|/det|>
+## Figure 2. TF Control of Distal Germ Cell Behavior
+
+<|ref|>text<|/ref|><|det|>[[70, 801, 933, 844]]<|/det|>
+(A) Quantification of nuclei number in the PZ of 3xflag::syg1-1; sun-1p::rde-1; rde-1(mkc36) one-day adults. n = 23-24. Green dashed line = average of the control.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[68, 82, 936, 430]]<|/det|>
+(B and C) Quantification of nuclei number (B) and confocal micrographs (C) of one-day adult germline PZ of sun- 1p::rde- 1; rde- 1(mkc36) treated with control RNAi and glp- 1(ar202); sun- 1p::rde- 1; rde- 1(mkc36) treated with control or experimental RNAi. \(\mathsf{n} = 29 - 34\) . (D and E) Quantification of SYGL- 1+ nuclei number (D) and confocal micrographs of germline PZ (E) of 3xflag::syg- 1; sun- 1p::rde- 1; rde- 1(mkc36) one- day adults. \(\mathsf{n} = 23 - 24\) . Green dashed line \(=\) average of the control (D); yellow dashed line \(=\) PZ/TZ boundary (E - left) and white line \(=\) SYGL- 1 boundary (E - right). (F) Proliferation rates of the C. elegans germ line after GTF RNAi. RNAi was performed from the L1 stage for 66 hrs before commencing EdU labelling, and germ lines collected and imaged after 4 and 10 hrs. The 3xflag::syg- 1; sun- 1p::rde- 1; rde- 1(mkc36) strain was used in this experiment. Results of three independent experiments were shown. \(\mathsf{n} = 9 - 13\) for each experiment. (G) Confocal micrographs showing DAPI and EdU+ nuclei after 4 and 10 hrs of EdU labelling. (H) Heatmap showing the effect of silencing 11 GTF on proliferation rate, mitotic index, and nuclei numbers of PZ, TZ, SYGL- 1+ and pH3+.
+
+<|ref|>text<|/ref|><|det|>[[70, 451, 935, 546]]<|/det|>
+RNAi was performed from the L1 stage. Data was generated from three independent experiments, and results were normalized to respective controls in (A) (B) and (D). \(P\) values assessed comparing to control RNAi by multiple unpaired t- test with no correction for multiple comparison (A, B, D and F). Error bars indicate SEM. Scale bars \(= 20 \mu \mathrm{m}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[70, 576, 559, 595]]<|/det|>
+## Figure 3. TF Control of Meiotic Germ Cell Behavior
+
+<|ref|>text<|/ref|><|det|>[[70, 601, 936, 696]]<|/det|>
+(A) Quantification of multinucleated germ cells of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data was generated from three independent experiments. \(\mathsf{n} = 30 - 31\) . \(P\) values assessed by one-way ANOVA with no correction for multiple comparison.
+
+<|ref|>text<|/ref|><|det|>[[70, 700, 936, 820]]<|/det|>
+(B) Fluorescence micrographs of wild-type or ced-3(rp190) two-day adult germ lines in the pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) strain. Control RNAi and RNAi of dmd-7 and baz-2 were applied from the L1 stage in wild-type animals. Dash lines = border between the TZ (above) and pachytene region (below) of the germ line. Asterisks = multinucleated cells; triangles = apoptotic cells. Scale bar = 20 μm.
+
+<|ref|>text<|/ref|><|det|>[[70, 825, 935, 869]]<|/det|>
+(C and D) Quantification of apoptotic germ cells (C) and multinucleated germ cells (D) in two- day adults of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 82, 933, 125]]<|/det|>
+strain (wild- type and ced- 3(rp190) animals). Data generated from three independent experiments. \(\mathsf{n} = 30 - 33\) . \(P\) values assessed by unpaired t- test.
+
+<|ref|>text<|/ref|><|det|>[[70, 132, 934, 225]]<|/det|>
+(E) Quantification of multinucleated germ cells in ced-3(rp190), pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data generated from three independent experiments. \(\mathsf{n} = 30\) . \(P\) values assessed by one- way ANOVA with no correction for multiple comparison.
+
+<|ref|>text<|/ref|><|det|>[[70, 230, 934, 374]]<|/det|>
+(F and G) Confocal micrographs of DAPI (white) and phalloidin (pink) staining (F) and quantification of germline folding events in the pachytene region (G) of sun- 1p::rde- 1; rde- 1(mkc36) one- day adults. Images for control RNAi (L4440) and lin- 26 RNAi are shown in F (note - only one plane is shown). Data was generated from four independent experiments. \(\mathsf{n} = 24 - 36\) . Yellow dashed line = border between the TZ (right) and pachytene region (left) of the germ line. \(P\) values assessed by one- way ANOVA with no correction for multiple comparison.
+
+<|ref|>text<|/ref|><|det|>[[70, 379, 839, 399]]<|/det|>
+RNAi was performed from the L1 stage. Error bars indicate SEM. Scale bars = 20 μm.
+
+<|ref|>sub_title<|/ref|><|det|>[[70, 429, 805, 449]]<|/det|>
+## Figure 4. Essential TFs act Late in Germline Development to Control Fertility
+
+<|ref|>text<|/ref|><|det|>[[70, 454, 935, 499]]<|/det|>
+(A) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L1 stage. Data generated from three independent experiments. \(\mathsf{n} = 15 - 18\) .
+
+<|ref|>text<|/ref|><|det|>[[70, 504, 934, 573]]<|/det|>
+(B) Timeline of temporal germline analysis showing the time and respective life stages when germline imaging and analysis were performed following egg-laying on control and RNAi plates (RNAi from the L1 stage).
+
+<|ref|>text<|/ref|><|det|>[[70, 577, 934, 694]]<|/det|>
+(C) Quantification of germline length of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) animals at the L4 stage following RNAi from the L1 stage. Data was generated from three independent experiments, and results normalized to respective controls. \(\mathsf{n} = 26 - 30\) . \(P\) values assessed by one- way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+<|ref|>text<|/ref|><|det|>[[70, 700, 934, 769]]<|/det|>
+(D) DIC (left) and fluorescent micrographs (right) of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) germ lines at the L4 stage following control, cdc-5L and znf-622 RNAi. Blue arrow = vulva. Scale bar = 20 μm.
+
+<|ref|>text<|/ref|><|det|>[[70, 775, 934, 893]]<|/det|>
+(E) Heatmap showing the percentage of germ lines producing sperm, oocytes and embryos in day 1, day 2 and day 3 of adulthood following germline-specific RNAi from the L1 stage. For day 2 and day 3 adult analysis, worms were selected from day 1 sterile animals, except for the control group, and incubated for another 48 hrs or 72hrs prior to analysis. Data was generated from three independent experiments. \(\mathsf{n} = 30\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[66, 81, 936, 280]]<|/det|>
+(F) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L4 stage. Data generated from three independent experiments. \(\mathsf{n} = 17 - 18\) . \(P\) values assessed by one-way ANOVA with no correction for multiple comparison. (G-J) Quantification of nuclei number of PZ (G), TZ (H), pH3+ (I) and SYGL-1+ (J) of 3xflag::syg1- 1; sun-1p::rde- 1; rde- 1(mkc36) one-day adult germ lines following RNAi treatment from the L4 stage. \(\mathsf{n} = 22 - 24\) . \(P\) values assessed by one-way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[119, 84, 260, 101]]<|/det|>
+## REFERENCES
+
+<|ref|>text<|/ref|><|det|>[[115, 108, 864, 901]]<|/det|>
+Argon, Y., and Ward, S. (1980). Caenorhabditis elegans fertilization- defective mutants with abnormal sperm. Genetics 96, 413- 433. Austin, J., and Kimble, J. (1987). Glp- 1 Is Required in the Germ Line for Regulation of the Decision between Mitosis and Meiosis in C- Elegans. Cell 51, 589- 599. Austin, J., and Kimble, J. (1989). Transcript analysis of glp- 1 and lin- 12, homologous genes required for cell interactions during development of C. elegans. Cell 58, 565- 571. Batchelder, C., Dunn, M.A., Choy, B., Suh, Y., Cassie, C., Shim, E.Y., Shin, T.H., Mello, C., Seydoux, G., and Blackwell, T.K. (1999). Transcriptional repression by the Caenorhabditis elegans germ- line protein PIE- 1. Genes Dev 13, 202- 212. Cao, J., Packer, J.S., Ramani, V., Cusanovich, D.A., Huynh, C., Daza, R., Qiu, X., Lee, C., Furlan, S.N., Steemers, F.J., et al. (2017). Comprehensive single- cell transcriptional profiling of a multicellular organism. Science 357, 661- 667. Cao, W., Tran, C., Archer, S.K., Gopal, S., and Pocock, R. (2021). Functional recovery of the germ line following splicing collapse. Cell Death Differ. Chen, J., Mohammad, A., Pazdernik, N., Huang, H., Bowman, B., Tycksen, E., and Schedl, T. (2020). GLP- 1 Notch- LAG- 1 CSL control of the germline stem cell fate is mediated by transcriptional targets Ist- 1 and sygl- 1. PLoS Genet 16, e1008650. Chi, W., and Reinke, V. (2006). Promotion of oogenesis and embryogenesis in the C. elegans gonad by EFL- 1/DPL- 1 (E2F) does not require LIN- 35 (pRB). Development 133, 3147- 3157. Consortium, E.P. (2012). An integrated encyclopedia of DNA elements in the human genome. Nature 489, 57- 74. Crittenden, S.L., Bernstein, D.S., Bachorik, J.L., Thompson, B.E., Gallegos, M., Petcherski, A.G., Moulder, G., Barstead, R., Wickens, M., and Kimble, J. (2002). A conserved RNA- binding protein controls germline stem cells in Caenorhabditis elegans. Nature 417, 660- 663. Crittenden, S.L., Leonhard, K.A., Byrd, D.T., and Kimble, J. (2006). Cellular analyses of the mitotic region in the Caenorhabditis elegans adult germ line. Molecular Biology of the Cell 17, 3051- 3061. Crittenden, S.L., Seidel, H.S., and Kimble, J. (2017). Analysis of the C. elegans Germline Stem Cell Pool. Germline Stem Cells, 2nd Edition 1463, 1- 33. Crittenden, S.L., Seidel, H.S., and Kimble, J. (2023). Analysis of the C. elegans Germline Stem Cell Pool. Methods Mol Biol 2677, 1- 36. Crittenden, S.L., Troemel, E.R., Evans, T.C., and Kimble, J. (1994). GLP- 1 is localized to the mitotic region of the C. elegans germ line. Development 120, 2901- 2911.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 884, 895]]<|/det|>
+Curran, S.P., Wu, X., Riedel, C.G., and Ruvkun, G. (2009). A soma- to- germline transformation in long- lived Caenorhabditis elegans mutants. Nature 459, 1079- 1084. Dehkordi, M.H., Munn, R.G.K., and Fearnhead, H.O. (2022). Non- Canonical Roles of Apoptotic Casases in the Nervous System. Front Cell Dev Biol 10, 840023. Edwards, S.L., Erdenebat, P., Morphis, A.C., Kumar, L., Wang, L., Chamera, T., Georgescu, C., Wren, J.D., and Li, J. (2021). Insulin/IGF- 1 signaling and heat stress differentially regulate HSF1 activities in germline development. Cell Rep 36, 109623. Ellis, R., and Schedl, T. (2007). Sex determination in the germ line. WormBook, 1- 13. Eskandari, E., and Eaves, C.J. (2022). Paradoxical roles of caspase- 3 in regulating cell survival, proliferation, and tumorigenesis. J Cell Biol 221. Essex, A., Dammermann, A., Lewellyn, L., Oegema, K., and Desai, A. (2009). Systematic analysis in Caenorhabditis elegans reveals that the spindle checkpoint is composed of two largely independent branches. Mol Biol Cell 20, 1252- 1267. Ferdous, A.S., Lynch, T.R., Costa Dos Santos, S.J., Kapadia, D.H., Crittenden, S.L., and Kimble, J. (2023). LST- 1 is a bifunctional regulator that feeds back on Notch- dependent transcription to regulate C. elegans germline stem cells. Proc Natl Acad Sci U S A 120, e2309964120. Fox, P.M., and Schedl, T. (2015). Analysis of Germline Stem Cell Differentiation Following Loss of GLP- 1 Notch Activity in Caenorhabditis elegans. Genetics 201, 167- 184. Francis, R., Maine, E., and Schedl, T. (1995). Analysis of the multiple roles of gld- 1 in germline development: interactions with the sex determination cascade and the glp- 1 signaling pathway. Genetics 139, 607- 630. Fraser, A.G., Kamath, R.S., Zipperlen, P., Martinez- Campos, M., Sohrmann, M., and Ahringer, J. (2000). Functional genomic analysis of C. elegans chromosome I by systematic RNA interference. Nature 408, 325- 330. Fukuyama, M., Rougvie, A.E., and Rothman, J.H. (2006). C. elegans DAF- 18/PTEN mediates nutrient- dependent arrest of cell cycle and growth in the germline. Curr Biol 16, 773- 779. Furuhashi, H., Takasaki, T., Rechtsteiner, A., Li, T., Kimura, H., Checchi, P.M., Strome, S., and Kelly, W.G. (2010). Trans- generational epigenetic regulation of C. elegans primordial germ cells. Epigenetics Chromatin 3, 15. Gao, D.L., and Kimble, J. (1995). Apx- 1 Can Substitute for Its Homolog Lag- 2 to Direct Cell- Interactions Throughout Caenorhabditis- Elegans Development. P Natl Acad Sci USA 92, 9839- 9842.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 866, 134]]<|/det|>
+Garcia- Muse, T., and Boulton, S.J. (2005). Distinct modes of ATR activation after replication stress and DNA double- strand breaks in Caenorhabditis elegans. EMBO J 24, 4345- 4355.
+
+<|ref|>text<|/ref|><|det|>[[118, 147, 861, 181]]<|/det|>
+Gibert, M.A., Starck, J., and Beguet, B. (1984). Role of the gonad cytoplasmic core during oogenesis of the nematode Caenorhabditis elegans. Biol Cell 50, 77- 85.
+
+<|ref|>text<|/ref|><|det|>[[118, 194, 783, 228]]<|/det|>
+Gopal, S., Boag, P., and Pocock, R. (2017). Automated three- dimensional reconstruction of the Caenorhabditis elegans germline. Dev Biol.
+
+<|ref|>text<|/ref|><|det|>[[118, 241, 876, 275]]<|/det|>
+Gracida, X., and Eckmann, C.R. (2013). Fertility and germline stem cell maintenance under different diets requires nhr- 114/HNF4 in C. elegans. Curr Biol 23, 607- 613.
+
+<|ref|>text<|/ref|><|det|>[[118, 288, 833, 355]]<|/det|>
+Green, R.A., Kao, H.L., Audhya, A., Arur, S., Mayers, J.R., Fridolfsson, H.N., Schulman, M., Schloissnig, S., Niessen, S., Laband, K., et al. (2011). A high- resolution C. elegans essential gene network based on phenotypic profiling of a complex tissue. Cell 145, 470- 482.
+
+<|ref|>text<|/ref|><|det|>[[118, 369, 835, 418]]<|/det|>
+Gumienny, T.L., Lambie, E., Hartwieg, E., Horvitz, H.R., and Hengartner, M.O. (1999). Genetic control of programmed cell death in the Caenorhabditis elegans hermaphrodite germline. Development 126, 1011- 1022.
+
+<|ref|>text<|/ref|><|det|>[[118, 431, 836, 481]]<|/det|>
+Hansen, D., Hubbard, E.J., and Schedl, T. (2004). Multi- pathway control of the proliferation versus meiotic development decision in the Caenorhabditis elegans germline. Dev Biol 268, 342- 357.
+
+<|ref|>text<|/ref|><|det|>[[118, 495, 875, 544]]<|/det|>
+Haupt, K.A., Enright, A.L., Ferdous, A.S., Kershner, A.M., Shin, H., Wickens, M., and Kimble, J. (2019). The molecular basis of LST- 1 self- renewal activity and its control of stem cell pool size. Development 146.
+
+<|ref|>text<|/ref|><|det|>[[118, 558, 866, 607]]<|/det|>
+Henderson, S.T., Gao, D., Lambie, E.J., and Kimble, J. (1994). lag- 2 may encode a signaling ligand for the GLP- 1 and LIN- 12 receptors of C. elegans. Development 120, 2913- 2924.
+
+<|ref|>text<|/ref|><|det|>[[118, 621, 875, 655]]<|/det|>
+Hirsh, D., and Vanderslice, R. (1976). Temperature- sensitive developmental mutants of Caenorhabditis elegans. Dev Biol 49, 220- 235.
+
+<|ref|>text<|/ref|><|det|>[[118, 668, 870, 735]]<|/det|>
+Hsu, J.Y., Sun, Z.W., Li, X., Reuben, M., Tatchell, K., Bishop, D.K., Grushcow, J.M., Brame, C.J., Caldwell, J.A., Hunt, D.F., et al. (2000). Mitotic phosphorylation of histone H3 is governed by Ipl1/aurora kinase and Glc7/PP1 phosphatase in budding yeast and nematodes. Cell 102, 279- 291.
+
+<|ref|>text<|/ref|><|det|>[[118, 748, 819, 782]]<|/det|>
+Hubbard, E.J. (2007). Caenorhabditis elegans germ line: a model for stem cell biology. Dev Dyn 236, 3343- 3357.
+
+<|ref|>text<|/ref|><|det|>[[118, 796, 875, 860]]<|/det|>
+Jantsch, V., Tang, L., Pasierbek, P., Penkner, A., Nayak, S., Baudrimont, A., Schedl, T., Gartner, A., and Loidl, J. (2007). Caenorhabditis elegans prom- 1 is required for meiotic prophase progression and homologous chromosome pairing. Mol Biol Cell 18, 4911- 4920.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 83, 870, 135]]<|/det|>
+Jimeno- Martin, A., Sousa, E., Brocal- Ruiz, R., Daroqui, N., Maicas, M., and Flames, N. (2022). Joint actions of diverse transcription factor families establish neuron- type identities and promote enhancer selectivity. Genome Res 32, 459- 473.
+
+<|ref|>text<|/ref|><|det|>[[118, 147, 812, 181]]<|/det|>
+Kadyk, L.C., and Kimble, J. (1998). Genetic regulation of entry into meiosis in Caenorhabditis elegans. Development 125, 1803- 1813.
+
+<|ref|>text<|/ref|><|det|>[[118, 194, 870, 244]]<|/det|>
+Kamath, R.S., Fraser, A.G., Dong, Y., Poulin, G., Durbin, R., Gotta, M., Kanapin, A., Le Bot, N., Moreno, S., Sohrmann, M., et al. (2003). Systematic functional analysis of the Caenorhabditis elegans genome using RNAi. Nature 421, 231- 237.
+
+<|ref|>text<|/ref|><|det|>[[118, 257, 879, 323]]<|/det|>
+Kerins, J.A., Hanazawa, M., Dorsett, M., and Schedl, T. (2010). PRP- 17 and the pre- mRNA splicing pathway are preferentially required for the proliferation versus meiotic development decision and germline sex determination in Caenorhabditis elegans. Dev Dyn 239, 1555- 1572.
+
+<|ref|>text<|/ref|><|det|>[[118, 336, 879, 387]]<|/det|>
+Kershner, A.M., Shin, H., Hansen, T.J., and Kimble, J. (2014). Discovery of two GLP- 1/Notch target genes that account for the role of GLP- 1/Notch signaling in stem cell maintenance. Proc Natl Acad Sci U S A 111, 3739- 3744.
+
+<|ref|>text<|/ref|><|det|>[[118, 400, 820, 434]]<|/det|>
+Kumsta, C., and Hansen, M. (2012). C. elegans rrf- 1 mutations maintain RNAi efficiency in the soma in addition to the germline. PLoS One 7, e35428.
+
+<|ref|>text<|/ref|><|det|>[[118, 446, 860, 497]]<|/det|>
+Lan, H., Wang, X., Jiang, L., Wu, J., Wan, X., Zeng, L., Zhang, D., Lin, Y., Hou, C., Wu, S., et al. (2019). An extracellular matrix protein promotes anillin- dependent processes in the Caenorhabditis elegans germline. Life Sci Alliance 2.
+
+<|ref|>text<|/ref|><|det|>[[118, 510, 863, 560]]<|/det|>
+Liu, X.M., Wang, Y.K., Liu, Y.H., Yu, X.X., Wang, P.C., Li, X., Du, Z.Q., and Yang, C.X. (2018). Single- cell transcriptome sequencing reveals that cell division cycle 5- like protein is essential for porcine oocyte maturation. J Biol Chem 293, 1767- 1780.
+
+<|ref|>text<|/ref|><|det|>[[118, 574, 860, 623]]<|/det|>
+Luo, Y., Hitz, B.C., Gabdank, I., Hilton, J.A., Kagda, M.S., Lam, B., Myers, Z., Sud, P., Jou, J., Lin, K., et al. (2020). New developments on the Encyclopedia of DNA Elements (ENCODE) data portal. Nucleic Acids Res 48, D882- D889.
+
+<|ref|>text<|/ref|><|det|>[[118, 637, 880, 686]]<|/det|>
+Maeda, I., Kohara, Y., Yamamoto, M., and Sugimoto, A. (2001). Large- scale analysis of gene function in Caenorhabditis elegans by high- throughput RNAi. Curr Biol 11, 171- 176.
+
+<|ref|>text<|/ref|><|det|>[[118, 700, 858, 750]]<|/det|>
+Mainpal, R., Nance, J., and Yanowitz, J.L. (2015). A germ cell determinant reveals parallel pathways for germ line development in Caenorhabditis elegans. Development 142, 3571- 3582.
+
+<|ref|>text<|/ref|><|det|>[[118, 764, 880, 813]]<|/det|>
+Mak, W., Fang, C., Holden, T., Dratver, M.B., and Lin, H. (2016). An Important Role of Pumilio 1 in Regulating the Development of the Mammalian Female Germline. Biol Reprod 94, 134.
+
+<|ref|>text<|/ref|><|det|>[[118, 827, 840, 861]]<|/det|>
+Nayak, S., Goree, J., and Schedl, T. (2005). fog- 2 and the evolution of self- fertile hermaphroditism in Caenorhabditis. PLoS Biol 3, e6.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 84, 870, 135]]<|/det|>
+Nayak, S., Santiago, F.E., Jin, H., Lin, D., Schedl, T., and Kipreos, E.T. (2002). The Caenorhabditis elegans Skp1- related gene family: diverse functions in cell proliferation, morphogenesis, and meiosis. Curr Biol 12, 277- 287.
+
+<|ref|>text<|/ref|><|det|>[[118, 147, 877, 198]]<|/det|>
+Phillips, C.M., and Dernburg, A.F. (2006). A family of zinc- finger proteins is required for chromosome- specific pairing and synapsis during meiosis in C. elegans. Dev Cell 11, 817- 829.
+
+<|ref|>text<|/ref|><|det|>[[118, 211, 877, 261]]<|/det|>
+Raiders, S.A., Eastwood, M.D., Bacher, M., and Priess, J.R. (2018). Binucleate germ cells in Caenorhabditis elegans are removed by physiological apoptosis. PLoS Genet 14, e1007417.
+
+<|ref|>text<|/ref|><|det|>[[118, 274, 840, 324]]<|/det|>
+Rodriguez- Crespo, D., Nanchen, M., Rajopadhye, S., and Wicky, C. (2022). The zinc- finger transcription factor LSL- 1 is a major regulator of the germline transcriptional program in Caenorhabditis elegans. Genetics 221.
+
+<|ref|>text<|/ref|><|det|>[[118, 337, 850, 403]]<|/det|>
+Rual, J.F., Ceron, J., Koreth, J., Hao, T., Nicot, A.S., Hirozane- Kishikawa, T., Vandenhaute, J., Orkin, S.H., Hill, D.E., van den Heuvel, S., et al. (2004). Toward improving Caenorhabditis elegans phenome mapping with an ORFeome- based RNAi library. Genome Res 14, 2162- 2168.
+
+<|ref|>text<|/ref|><|det|>[[118, 416, 870, 451]]<|/det|>
+Seidel, H.S., and Kimble, J. (2015). Cell- cycle quiescence maintains Caenorhabditis elegans germline stem cells independent of GLP- 1/Notch. Elife 4.
+
+<|ref|>text<|/ref|><|det|>[[118, 464, 857, 514]]<|/det|>
+Serizay, J., Dong, Y., Janes, J., Chesney, M., Cerrato, C., and Ahringer, J. (2020). Distinctive regulatory architectures of germline- active and somatic genes in C. elegans. Genome Res 30, 1752- 1765.
+
+<|ref|>text<|/ref|><|det|>[[118, 527, 871, 577]]<|/det|>
+Seydoux, G., Mello, C.C., Pettitt, J., Wood, W.B., Priess, J.R., and Fire, A. (1996). Repression of gene expression in the embryonic germ lineage of C. elegans. Nature 382, 713- 716.
+
+<|ref|>text<|/ref|><|det|>[[118, 590, 870, 640]]<|/det|>
+Shin, H., Haupt, K.A., Kershner, A.M., Kroll- Conner, P., Wickens, M., and Kimble, J. (2017). SYGL- 1 and LST- 1 link niche signaling to PUF RNA repression for stem cell maintenance in Caenorhabditis elegans. Plos Genetics 13.
+
+<|ref|>text<|/ref|><|det|>[[118, 653, 850, 720]]<|/det|>
+Simmer, F., Moorman, C., Van Der Linden, A.M., Kuijk, E., Van Den Berghe, P.V., Kamath, R., Fraser, A.G., Ahringer, J., and Plasterk, R.H. (2003). Genome- Wide RNAi of C. elegans Using the Hypersensitive rrf- 3 Strain Reveals Novel Gene Functions. PLoS Biol 1, E12.
+
+<|ref|>text<|/ref|><|det|>[[118, 734, 863, 799]]<|/det|>
+Sisakhtnezhad, S., and Heshmati, P. (2018). Comparative analysis of single- cell RNA sequencing data from mouse spermatogonial and mesenchymal stem cells to identify differentially expressed genes and transcriptional regulators of germline cells. J Cell Physiol 233, 5231- 5242.
+
+<|ref|>text<|/ref|><|det|>[[118, 813, 860, 879]]<|/det|>
+Sonnichsen, B., Koski, L.B., Walsh, A., Marschall, P., Neumann, B., Brehm, M., Alleaume, A.M., Artelt, J., Bettencourt, P., Cassin, E., et al. (2005). Full- genome RNAi profiling of early embryogenesis in Caenorhabditis elegans. Nature 434, 462- 469.
+
+<|ref|>text<|/ref|><|det|>[[118, 893, 815, 911]]<|/det|>
+Starck, J. (1977). Radioautographic study of RNA synthesis in Caenorhabditis
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 661, 101]]<|/det|>
+elegans (Bergerac variety) oogenesis. Biol Cell 30, 181- 182.
+
+<|ref|>text<|/ref|><|det|>[[118, 113, 864, 181]]<|/det|>
+Sun, Y., Yang, P., Zhang, Y., Bao, X., Li, J., Hou, W., Yao, X., Han, J., and Zhang, H. (2011). A genome- wide RNAi screen identifies genes regulating the formation of P bodies in C. elegans and their functions in NMD and RNAi. Protein Cell 2, 918- 939.
+
+<|ref|>text<|/ref|><|det|>[[118, 194, 860, 244]]<|/det|>
+Tabara, H., Sarkissian, M., Kelly, W.G., Fleenor, J., Grishok, A., Timmons, L., Fire, A., and Mello, C.C. (1999). The rde- 1 gene, RNA interference, and transposon silencing in C. elegans. Cell 99, 123- 132.
+
+<|ref|>text<|/ref|><|det|>[[118, 258, 870, 307]]<|/det|>
+Tax, F.E., Yeargers, J.J., and Thomas, J.H. (1994). Sequence of C. elegans lag- 2 reveals a cell- signalling domain shared with Delta and Serrate of Drosophila. Nature 368, 150- 154.
+
+<|ref|>text<|/ref|><|det|>[[118, 321, 850, 354]]<|/det|>
+Timmons, L., and Fire, A. (1998). Specific interference by ingested dsRNA [letter]. Nature 395, 854.
+
+<|ref|>text<|/ref|><|det|>[[118, 368, 844, 417]]<|/det|>
+Tzur, Y.B., Winter, E., Gao, J., Hashimshony, T., Yanai, I., and Colaiacovo, M.P. (2018). Spatiotemporal Gene Expression Analysis of the Caenorhabditis elegans Germline Uncovers a Syncytial Expression Switch. Genetics 210, 587- 605.
+
+<|ref|>text<|/ref|><|det|>[[118, 431, 872, 496]]<|/det|>
+Wan, L.B., Pan, H., Hannenhalli, S., Cheng, Y., Ma, J., Fedorow, A., Lobanenkov, V., Latham, K.E., Schultz, R.M., and Bartolomei, M.S. (2008). Maternal depletion of CTCF reveals multiple functions during oocyte and preimplantation embryo development. Development 135, 2729- 2738.
+
+<|ref|>text<|/ref|><|det|>[[118, 510, 863, 559]]<|/det|>
+Wu, Y., Hu, X., Li, Z., Wang, M., Li, S., Wang, X., Lin, X., Liao, S., Zhang, Z., Feng, X., et al. (2016). Transcription Factor RFX2 Is a Key Regulator of Mouse Spermiogenesis. Sci Rep 6, 20435.
+
+<|ref|>text<|/ref|><|det|>[[118, 573, 866, 606]]<|/det|>
+Zou, L., Wu, D., Zang, X., Wang, Z., Wu, Z., and Chen, D. (2019). Construction of a germline- specific RNAi tool in C. elegans. Sci Rep 9, 2354.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 44, 144, 68]]<|/det|>
+## Figures
+
+<|ref|>image<|/ref|><|det|>[[60, 100, 700, 720]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[43, 852, 115, 870]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[43, 894, 585, 912]]<|/det|>
+Phenotypic Profiling of Germline Transcription Factor Function
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[40, 44, 950, 180]]<|/det|>
+(A) Schematic of the C. elegans hermaphrodite germline (left), identification of germline-expressed TFs by RNA sequencing (center), and representative images and phenotypic readouts for high-content distal and proximal germline analysis (right). The distal germ line is labelled with DAPI (nuclei), SYGL-1 (Notch target gene) and pH3 (M-phase chromosomes). PZ = progenitor zone, TZ = transition zone. The proximal germ line is marked with transgenic fluorophores: red = nuclei; green = plasma membrane. Scale bars = 20 μm.
+
+<|ref|>text<|/ref|><|det|>[[40, 196, 951, 331]]<|/det|>
+(B- D) Heatmaps showing phenotypic overview for TF silencing causing distal (B \(\geq 20\%\) change compared to control), proximal (C \(\geq 50\%\) of animals with the phenotype) or distal and proximal germline phenotypes (D). (B) TF family categories (colored boxes); progenitor zone (PZ), transition zone (TZ) and SYGL-1+ region phenotypes shown as percentage change compared to control (blue = decrease; red = increase); germline expression of each TF (grey bars = log2 CPM); mammalian ortholog associated with the reproduction GO term (blue boxes = No, black boxes = Yes).
+
+<|ref|>text<|/ref|><|det|>[[40, 347, 952, 504]]<|/det|>
+(C) Labelling as in B, except purple = proximal phenotype; blue = no phenotype detected. Phenotypes shown in this figure: small germ line, rachis defect (narrow or wide rachis), meiotic defect (multinucleated cells, abnormal meiotic progression), apoptosis, oocyte defect (delayed expansion at the turn, difference in single-array oocyte number, difference in budded oocyte number, vesiculation), sperm defect (mislocated sperm, incomplete spermatogenesis). (D) Labelling as in B and C. Note: the heatmaps do not include essential GTFs identified in the screens – this analysis is detailed in Figure 4 and Table S4.
+
+<|ref|>text<|/ref|><|det|>[[41, 521, 899, 566]]<|/det|>
+(E) TF family distribution of the 875 C. elegans TFs, 96 TFs that regulate the distal germ line or are essential for germline development, and 52 TFs that regulate the proximal germline.
+
+<|ref|>text<|/ref|><|det|>[[41, 582, 928, 650]]<|/det|>
+TF families shown in this figure: bZIP = basic leucine zipper domain, HD = homeodomain, HMG = High mobility group box domain, MYB= myeloblastosis viral oncogene homolog, NHR = nuclear hormone receptors, T-box, WH = winged helix, ZF = zinc finger.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[45, 37, 803, 780]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 800, 117, 820]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[42, 845, 384, 864]]<|/det|>
+TF Control of Distal Germ Cell Behavior
+
+(A) Quantification of nuclei number in the PZ of 3xflag::syg1-1; sun-1p::rde-1; rde-1(mkc36) one-day adults. \(\mathrm{n} = 23 - 24\) . Green dashed line = average of the control.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[41, 45, 951, 111]]<|/det|>
+(B and C) Quantification of nuclei number (B) and confocal micrographs (C) of one-day adult germline PZ of sun-1p::rde-1; rde-1(mkc36) treated with control RNAi and glp-1(ar202); sun-1p::rde-1; rde-1(mkc36) treated with control or experimental RNAi. \(n = 29 - 34\) .
+
+<|ref|>text<|/ref|><|det|>[[41, 128, 884, 150]]<|/det|>
+(D and E) Quantification of SYGL- 1+ nuclei number (D) and confocal micrographs of germline PZ
+
+<|ref|>text<|/ref|><|det|>[[41, 166, 940, 233]]<|/det|>
+(E) of 3xflag::syg1- 1; sun-1p::rde- 1; rde- 1(mkc36) one-day adults. \(n = 23 - 24\) . Green dashed line = average of the control (D); yellow dashed line = PZ/TZ boundary (E - left) and white line = SYGL- 1 boundary (E - right).
+
+<|ref|>text<|/ref|><|det|>[[41, 250, 951, 339]]<|/det|>
+(F) Proliferation rates of the C. elegans germ line after GTF RNAi. RNAi was performed from the L1 stage for 66 hrs before commencing EdU labelling, and germ lines collected and imaged after 4 and 10 hrs. The 3xflag::syg1- 1; sun-1p::rde- 1; rde- 1(mkc36) strain was used in this experiment. Results of three independent experiments were shown. \(n = 9 - 13\) for each experiment.
+
+<|ref|>text<|/ref|><|det|>[[41, 355, 844, 377]]<|/det|>
+(G) Confocal micrographs showing DAPI and EdU+ nuclei after 4 and 10 hrs of EdU labelling.
+
+<|ref|>text<|/ref|><|det|>[[41, 393, 896, 436]]<|/det|>
+(H) Heatmap showing the effect of silencing 11 GTF on proliferation rate, mitotic index, and nuclei numbers of PZ, TZ, SYGL-1+ and pH3+.
+
+<|ref|>text<|/ref|><|det|>[[41, 454, 955, 543]]<|/det|>
+RNAi was performed from the L1 stage. Data was generated from three independent experiments, and results were normalized to respective controls in (A) (B) and (D). P values assessed comparing to control RNAi by multiple unpaired t-test with no correction for multiple comparison (A, B, D and F). Error bars indicate SEM. Scale bars = 20 μm.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[60, 80, 808, 737]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 802, 117, 821]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[44, 845, 400, 864]]<|/det|>
+TF Control of Meiotic Germ Cell Behavior
+
+<|ref|>text<|/ref|><|det|>[[42, 882, 940, 925]]<|/det|>
+(A) Quantification of multinucleated germ cells of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data was generated from
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 45, 940, 88]]<|/det|>
+three independent experiments. \(n = 30 - 31\) . P values assessed by one- way ANOVA with no correction for multiple comparison.
+
+<|ref|>text<|/ref|><|det|>[[42, 105, 945, 218]]<|/det|>
+(B) Fluorescence micrographs of wild-type or ced-3(rp190) two-day adult germ lines in the pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) strain. Control RNAi and RNAi of dmd-7 and baz-2 were applied from the L1 stage in wild-type animals. Dash lines = border between the TZ (above) and pachytene region (below) of the germ line. Asterisks = multinucleated cells; triangles = apoptotic cells. Scale bar = 20 μm.
+
+<|ref|>text<|/ref|><|det|>[[42, 234, 943, 322]]<|/det|>
+(C and D) Quantification of apoptotic germ cells (C) and multinucleated germ cells (D) in two- day adults of pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) strain (wild-type and ced-3(rp190) animals). Data generated from three independent experiments. \(n = 30 - 33\) . P values assessed by unpaired t-test.
+
+<|ref|>text<|/ref|><|det|>[[42, 339, 947, 428]]<|/det|>
+(E) Quantification of multinucleated germ cells in ced-3(rp190), pie-1p::mCherry::his-58; pie-1p::GFP::PH(PLC1delta1); sun-1p::rde-1; rde-1(mkc36) two-day adults following RNAi from the L1 stage. Data generated from three independent experiments. \(n = 30\) . P values assessed by one-way ANOVA with no correction for multiple comparison.
+
+<|ref|>text<|/ref|><|det|>[[42, 444, 937, 580]]<|/det|>
+(F and G) Confocal micrographs of DAPI (white) and phalloidin (pink) staining (F) and quantification of germline folding events in the pachytene region (G) of sun-1p::rde-1; rde-1(mkc36) one-day adults. Images for control RNAi (L4440) and lin-26 RNAi are shown in F (note - only one plane is shown). Data was generated from four independent experiments. \(n = 24 - 36\) . Yellow dashed line = border between the TZ (right) and pachytene region (left) of the germ line. P values assessed by one-way ANOVA with no correction for multiple comparison.
+
+<|ref|>text<|/ref|><|det|>[[42, 597, 780, 618]]<|/det|>
+RNAi was performed from the L1 stage. Error bars indicate SEM. Scale bars = 20 μm.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[45, 30, 700, 789]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 800, 118, 819]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[44, 844, 620, 864]]<|/det|>
+Essential TFs act Late in Germline Development to Control Fertility
+
+<|ref|>text<|/ref|><|det|>[[42, 881, 930, 925]]<|/det|>
+(A) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L1 stage. Data generated from three independent experiments. \(n = 15 - 18\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 45, 949, 111]]<|/det|>
+(B) Timeline of temporal germline analysis showing the time and respective life stages when germline imaging and analysis were performed following egg-laying on control and RNAi plates (RNAi from the L1 stage).
+
+<|ref|>text<|/ref|><|det|>[[42, 128, 952, 217]]<|/det|>
+(C) Quantification of germline length of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) animals at the L4 stage following RNAi from the L1 stage. Data was generated from three independent experiments, and results normalized to respective controls. \(\mathrm{n} = 26 - 30\) . P values assessed by one-way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+<|ref|>text<|/ref|><|det|>[[42, 234, 949, 300]]<|/det|>
+(D) DIC (left) and fluorescent micrographs (right) of pie-1p::mCherry::his-58; sun-1p::rde-1; rde-1(mkc36) germ lines at the L4 stage following control, cdc-5L and znf-622 RNAi. Blue arrow = vulva. Scale bar = 20 μm.
+
+<|ref|>text<|/ref|><|det|>[[42, 317, 952, 428]]<|/det|>
+(E) Heatmap showing the percentage of germ lines producing sperm, oocytes and embryos in day 1, day 2 and day 3 of adulthood following germline-specific RNAi from the L1 stage. For day 2 and day 3 adult analysis, worms were selected from day 1 sterile animals, except for the control group, and incubated for another 48 hrs or 72hrs prior to analysis. Data was generated from three independent experiments. \(\mathrm{n} = 30\) .
+
+<|ref|>text<|/ref|><|det|>[[42, 446, 945, 512]]<|/det|>
+(F) Quantification of hatched larvae and dead eggs (brood size) following germline-specific RNAi from the L4 stage. Data generated from three independent experiments. \(\mathrm{n} = 17 - 18\) . P values assessed by one-way ANOVA with no correction for multiple comparison.
+
+<|ref|>text<|/ref|><|det|>[[42, 529, 944, 572]]<|/det|>
+(G-J) Quantification of nuclei number of PZ (G), TZ (H), pH3+ (I) and SYGL- 1+ (J) of 3xflag::syg1- 1; sun- 1p::rde- 1; rde- 1(mkc36) one-day adult germ lines following RNAi treatment from the L4 stage. \(\mathrm{n} = 22 - 24\) .
+
+<|ref|>text<|/ref|><|det|>[[42, 590, 928, 633]]<|/det|>
+P values assessed by one-way ANOVA with no correction for multiple comparison. Error bars indicate SEM.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 656, 312, 683]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 707, 768, 727]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 745, 200, 950]]<|/det|>
+- FigureS1.pdf- FigureS2.pdf- FigureS3.pdf- FigureS4.pdf- FigureS5.pdf- FigureS6.pdf- FigureS7.pdf- FigureS8.pdf
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 46, 600, 330]]<|/det|>
+- TableS1.Germlinetranscriptomeanalysis.xlsx- TableS2WormGTFexpressionandreproductivefunctions.xlsx- TableS3RNAiplasmidusedinthisstudy.xlsx- TableS4Distalgermlineanalysis.xlsx- TableS5ProximalgermlineanalysisV6.xlsx- TableS6156GTFswithgermlinefunctions.xlsx- TableS7PreviouslyreportedphenotypesinC.elegans.xlsx- TableS8GTFfunctionsinotherorganismsGOanalysis.xlsx- TableS9Strainsusedinthisstudy.xlsx- TableS10Oligosusedinthisstudy.xlsx- TableS11Sourcedata.xlsx
+
+<--- Page Split --->
diff --git a/preprint/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb/images_list.json b/preprint/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..0637a088a01e8ddab3bf3fa98dbe804cbde1a0dc
--- /dev/null
+++ b/preprint/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb/images_list.json
@@ -0,0 +1 @@
+[]
\ No newline at end of file
diff --git a/preprint/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb.mmd b/preprint/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..c1d17209418a8a937405b6a3f63ed27f6733071f
--- /dev/null
+++ b/preprint/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb/preprint__014d74e44dae70e5db80998cebc90ca95b419b71bced776056d3779c43cd19fb.mmd
@@ -0,0 +1,650 @@
+
+# Thor: a platform for cell-level investigation of spatial transcriptomics and histology
+
+Guangyu Wang gwang2@houstonmethodist.org Houston Methodist Research Institute https://orcid.org/0000- 0003- 4803- 7200
+
+Pengzhi Zhang pzhang@houstonmethodist.org Houston Methodist Research Institute https://orcid.org/0000- 0001- 6920- 1490
+
+Weiqing Chen wchen5@houstonmethodist.org Cornell University https://orcid.org/0000- 0003- 3539- 9210
+
+Tu Tran ttran7@houstonmethodist.org Houston Methodist Research Institute
+
+Minghao Zhou minghaozhou01@gmail.com University of Florida
+
+Kaylee Carter kncarter2@houstonmethodist.org Houston Methodist Research Institute https://orcid.org/0009- 0002- 8920- 3033
+
+Ibrahem Kandel ikandel@houstonmethodist.org Houston Methodist Research Institute
+
+Shengyu Li sli5@houstonmethodist.org Houston Methodist
+
+Li Lai llai@houstonmethodist.org Houston Methodist Research Institute https://orcid.org/0000- 0002- 5731- 2705
+
+Qianqian Song qianqian.song.66@gmail.com University of Florida
+
+Keith Youker kayouker@houstonmethodist.org Houston Methodist Research Institute https://orcid.org/0000- 0003- 2535- 7973
+
+Yu Yang yangyu1@ufl.edu University of Florida
+
+<--- Page Split --->
+
+Keith Syon Chan kschan@houstonmethodist.org Houston Methodist Research Institute
+
+Xen Ping Hoi xpinghoi@houstonmethodist.org Houston Methodist Research Institute https://orcid.org/0000- 0001- 7610- 7291
+
+Fotis Nikolo fnikolo@houstonmethodist.org Houston Methodist Research Institute
+
+## Article
+
+Keywords:
+
+DOI: https://doi.org/
+
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+<--- Page Split --->
+
+# Thor: a platform for cell-level investigation of spatial transcriptomics and histology
+
+Pengzhi Zhang \(^{1,2,3,4,\#}\) , Weiqing Chen \(^{5,\#}\) , Tu Nhi Tran \(^{1,2,3,4}\) , Minghao Zhou \(^{6}\) , Kaylee N. Carter \(^{2}\) , Ibrahem Kandel \(^{1,2,3,4}\) , Shengyu Li \(^{1,2,3,4}\) , Xen Ping Hoi \(^{7,8,9}\) , Keith Youker \(^{4,10}\) , Li Lai \(^{2}\) , Qianqian Song \(^{6}\) , Yu Yang \(^{11}\) , Fotis Nikolos \(^{7,8}\) , Keith Syson Chan \(^{7,8}\) , Guangyu Wang \(^{1,2,3,4}\)
+
+1. Center for Bioinformatics and Computational Biology, Houston Methodist Research Institute, Houston, TX, 77030, USA
+2. Center for Cardiovascular Regeneration, Houston Methodist Research Institute, Houston, TX, 77030, USA
+3. Center for RNA Therapeutics, Houston Methodist Research Institute, Houston, TX, 77030, USA
+4. Department of Cardiothoracic Surgery, Weill Cornell Medicine, Cornell University, New York, NY, 10065, USA
+5. Department of Physiology, Biophysics & Systems Biology, Weill Cornell Graduate School of Medical Science, Weill Cornell Medicine, Cornell University, New York, NY, 10065, USA
+6. Department of Health Outcomes and Biomedical Informatics, University of Florida, Gainesville, FL, 32610, USA
+7. Department of Urology, Houston Methodist Research Institute, Houston, TX, 77030, USA
+8. Spatial Omics Core, Neal Cancer Center, Houston Methodist Research Institute, Houston, TX, 77030, USA
+9. Graduate Program in Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA 90069, USA
+10. Department of Cardiovascular Sciences, Houston Methodist Research Institute, Houston, TX, 77030, USA
+11. Department of Pathology, Immunology and Laboratory Medicine, College of Medicine, University of Florida, Gainesville, FL, 32608, USA
+# Those authors contributed equally to the work.
+
+<--- Page Split --->
+
+## Abstract
+
+Spatial transcriptomics integrates transcriptomics data with histological tissue images, offering deeper insights into cellular organization and molecular functions. However, existing computational platforms mainly focus on genomic analysis, leaving a gap in the seamless integration of genomic and image analysis. To address this, we introduce Thor, a comprehensive computational platform for multi- modal analysis of spatial transcriptomics and histological images. Thor utilizes an anti- shrinking Markov diffusion method to infer single- cell spatial transcriptomes from spot- level data, effectively integrating cell morphology with spatial transcriptomics. The platform features 10 modules designed for cell- level genomic and image analysis. Additionally, we present Mjolnir, a web- based tool for interactive tissue analysis using vivid gigapixel images that display information on histology, gene expression, pathway enrichment, and immune response. Thor's accuracy was validated through simulations and ISH, MERFISH, Xenium, and Stereo- seq datasets. To demonstrate its versatility, we applied Thor for joint genomic- histology analysis across various datasets. In in- house heart failure patient samples, Thor identified a regenerative signature in heart failure, with protein presence confirmed in blood vessels through immunofluorescence staining. Thor also revealed the layered structure of the mouse olfactory bulb, performed unbiased screening of breast cancer hallmarks, elucidated the heterogeneity of immune responses, and annotated fibrotic regions in multiple heart failure zones using a semi- supervised approach. Furthermore, Thor imputed high- resolution spatial transcriptomics data in an in- house bladder cancer sample sequenced using Visium HD, uncovering stronger spatial patterns that align more closely with histology. Bridging the gap between genomic and image analysis in spatial biology, Thor offers a powerful tool for comprehensive cellular and molecular analysis.
+
+<--- Page Split --->
+
+## Introduction
+
+The complex organization of cells within tissues is profoundly connected to their biological function. This underpins the widespread utility of histological images in health and disease. The development of computational methods empowered by deep learning on histological images has drastically enhanced efficiency and accuracy in tissue analysis in diverse applications1, including automated cancer diagnosis2, survival prediction3, histopathology image classification and retrieval4, tissue segmentation5, 6, nucleus and cell segmentation7- 9, and in silico staining10. Furthermore, rapid advancements in high- throughput technologies such as RNA sequencing (RNA- seq) and whole genome sequencing (WGS) are transforming the landscape of conventional histological analysis, offering unprecedented insights beyond tissue images. For example, recent research has demonstrated that the integration of histological images with genomic biomarker mutations and biological pathways leads to accurate predictions of survival across diverse conditions3, 11. In the evolving landscape of biological investigation, spatially resolved molecular technologies have become a pivotal focus for unraveling cellular diversity, tissue organization, and functions. Spatial omics data have been incorporated and routinely acquired by programs such as the human cell atlas (HCA) and the human biomolecular atlas program (HuBMAP), advancing the construction of comprehensive spatial maps featuring various biomolecules, including RNA, proteins, and metabolites12, 13. A widely adopted molecular technology is spatial transcriptomics (ST), which involves slicing tissues into thin layers for hematoxylin and eosin (H&E) staining and spatial sequencing, enabling simultaneous investigation of tissue/cellular phenotype and molecular mechanism on the same slide.
+
+Recent efforts to advance ST analysis have focused on incorporating spatial neighborhood information14, or integrating histology images15- 17. However, these tools typically operate at subspot or superpixel spatial scales, which do not correspond to individual cells, hindering biologically relevant insights - particularly in contexts requiring cell- level data, such as analyzing ligand- receptor interactions. Another branch of ST analysis frameworks addresses cellular heterogeneity by resolving cell- type compositions within spatial spots18- 20. However, these approaches do not infer cell- level gene expression and are further restricted by the quality and availability of scRNA- seq reference data, especially for formalin- fixed paraffin- embedded (FFPE) tissues where transcriptomic data quality is often compromised. While emerging methods enable cellular- level histological structure analysis21, 22, similarly they do not generate single- cell resolution gene expression matrices, thereby excluding them from downstream functional or molecular analyses. Moreover, those platforms are mostly tailored to specific tasks (e.g. deconvolution), whereas comprehensive analysis platforms (e.g. Seurat) prioritize - omics analysis without deeply analyzing histopathological images23- 25.
+
+To meet the urgent need for jointly analyzing genomics and histology, we present a multi- modal platform - Thor - for bridging and exploring cellular phenotypes and molecular insights. Thor enhances the incorporation of morphology and transcriptome data of individual cells by inferring cell- resolution transcriptome from spot- level ST data using an anti- shrinking Markov graph diffusion method. Moreover, Thor features extensible modules for comprehensive genomic analyses, such as immune response, functional pathway enrichment, transcription factor (TF) activity, and copy number variation (CNV), alongside tissue analyses such as semi- supervised tissue annotation and nucleus detection. Additionally, we develop Mjolnir, a user- friendly web- based platform for interactive exploration of cellular organization and pathogenesis in tissues, on a laptop, with no coding required.
+
+We elucidated the principles of Thor and rigorously assessed its effectiveness and accuracy through simulations and various datasets, obtained from high- resolution experimental methods,
+
+<--- Page Split --->
+
+including in situ hybridization (ISH), multiplexed error- robust fluorescence in situ hybridization (MERFISH)26, spatio- temporal enhanced resolution omics- sequencing (Stereo- seq)27, and Xenium28. Thor outperformed state- of- the- art methods in predicting cell- level ST on a breast cancer dataset using Xenium data as the ground truth. We analyzed a mouse olfactory bulb (MOB) tissue, human breast cancer tissues, and multi- sample heart failure patient tissues. Thor revealed a refined layered structure in MOB and identified distinct gene modules. In heart failure, Thor quantified fibrotic regions across different heart zones. Furthermore, we collected in- house heart failure samples from patients who received a left ventricular assist device (LVAD) implantation to study the signature genes in vascular regeneration. We identified regenerative signatures in heart failure and validated them through immunofluorescence (IF) staining. In breast cancer, Thor conducted an unbiased screening of breast cancer hallmarks, uncovering the intricate heterogeneity of immune responses in tumor regions. In summary, Thor enables comprehensive interpretation of ST data at the single- cell and whole- transcriptome levels, delivering advanced functional insights, and providing an interactive interface for in- depth analyses.
+
+## Results
+
+## Thor infers cell-resolution spatial transcriptome for multi-modal analysis
+
+Histological images and high- throughput sequencing data are widely adopted for various applications2, 29- 31. Despite their significance, these two sources of information are often examined independently with separate tools. Sequencing- based ST and the paired histological whole slide image (WSI) capture inherent cellular structures in the tissue at different resolutions, providing complementary information. For example, in human heart tissues with MI, we observed that the projection of histological features onto principal components segregated tissues at cellular resolution (Figure 1a, Supplementary Note 1). Similarly, spatial patterns can be discerned through marker gene expression at a coarser resolution (spot level). Clustering results of spots by using either source of features were consistent and complementary, as demonstrated in the human MI samples, a human ductal carcinoma in situ (DCIS) sample, and a MOB sample (See details in Supplementary Note 1). Previous studies also indicated that spatial gene expression can be predicted or refined based on histological images15- 17. Therefore, we hypothesize that it is feasible to recover cell- level resolution transcriptomics data by learning shared patterns from both the histology and the transcriptome.
+
+Multi- modal analysis in Thor involves two key steps. First, elevating spot- resolution ST data to single- cell resolution (Figure 1a). Second, in- depth genomics and tissue image analyses (Figure 1b- c). In the first step, Thor (i) applies deep learning methods to segment cells/nuclei from the WSI, termed in silico cells; (ii) extracts morphological and spot- level transcriptomic features into a combinatory feature space to construct a cell- cell network; (iii) creates a Markov transition matrix, representing the probabilities of transitioning from a cell to every other cell in the system in one step; (iv) infers gene expression of the in silico cells by data diffusion with the transition matrix (Figure 1a). Thor represents the cellular patterns using a nearest neighbors graph, where cells are connected according to their distances in the combinatory feature space reflecting the physical separation, and the histological and genomic complexity. The Markov transition matrix is constructed such that information from "homogeneous" spots asymmetrically corrects information from "heterogeneous" spots, where heterogeneity of a spot is determined by the enclosed cells in the combinatory feature space (Figure 1a). In the second step, we establish a standardized genomics analysis framework for in- depth research and clinical practice. The genomics analysis encompasses a wide array of insights, including cell type annotation, immune response analysis, biological functional pathway analysis, differential gene expression analysis, spatially expressed module detection, TF activity analysis, and CNV analysis (Figure 1b). Thor also includes tissue image analysis tools including nucleus segmentation, region of
+
+<--- Page Split --->
+
+interest (ROI) selection, and semi- supervised ROI annotation. To enhance accessibility and usability, we introduce a web- based platform Mjolnir that seamlessly visualizes both histological images and genomic analyses (Figure 1c). Altogether, Thor elevates tissue analysis by integrating image analysis and genomic insights.
+
+## Thor demonstrates accuracy and robustness in simulation data
+
+We systematically evaluated Thor's accuracy and robustness under realistic experimental conditions. We simulated expression profiles for 1,000 genes in 6,579 cells, whose spatial positions were extracted from a mouse cerebellum tissue as the ground truth32; and based on those cells, we created "spots" by aggregating gene expression levels in cells covered by a spot (Figure S1a, see details in Methods: Simulation details). We assessed Thor's prediction accuracy by computing the normalized root mean squared error (NRMSE) between the predicted and the ground- truth gene expression values (see Methods for details).
+
+We first evaluated Thor's performance under suboptimal histology imaging conditions. Two primary issues can impact its accuracy: (i) missed detection of cell nuclei, which commonly occurs in out- of- focus or high- density regions, and (ii) erroneous cell- cell connections resulting from poor histological features. Under ideal conditions with neither cell dropouts nor randomized connections, Thor's predicted gene expression closely matched the ground truth, yielding a median NRMSE of 0.07 (Figures S1a and S2). Introducing random "missouts" of cells (0%- 40%) lead to a slight increase in median NRMSE from 0.07 to 0.075 (Figure S1b), while introducing randomized connections in 30% - 40% of cells modestly increased the median NRMSE to 0.08 (Figure S1b). These findings suggest that Thor maintains robust prediction accuracy even in the presence of substantial missing cells and disrupted cell connections.
+
+Next, we examined the spatial resolution, a critical factor in spatial technologies ranging from subcellular scales to \(\sim 100 \mu m\) . Larger spots lead to greater cell heterogeneity within each spot (Figure S3). When we varied the spot diameter from \(25 \mu m\) to \(150 \mu m\) , Thor accurately predicted single- cell gene expression for spots up to \(\sim 100 \mu m\) in diameter, although the median NRMSE increased to 0.08 at \(150 \mu m\) . To further highlight advantages of our algorithm, we compared Thor against three alternative methods: (a) nearest spot method – assigning gene expression based on the nearest spot; (b) k- nearest neighbors (KNN) smoothing method – assigning gene expression by averaging over the nearest twenty cells; and (c) BayesSpace – assigning gene expression based on local spatial neighborhoods of sub- spots. At \(25 \mu m\) , both the nearest spot method and Thor exhibited high accuracy (median NRMSE 0.06). The nearest spot method's performance declined sharply as spot size increased beyond \(25 \mu m\) , while Thor remained accurate with the spot size up to \(100 \mu m\) . This suggests that Thor's superior performance is not solely due to incorporating nucleus segmentation. By contrast, both the KNN smoothing method and BayesSpace performed poorly across all spot sizes, with median NRMSE values of approximately 0.2 (Figure S1c). The KNN smoothing method consistently underperformed, underscoring the benefits of Thor's shared nearest neighbors cell- cell graph and feature- preserving Markov diffusion approach.
+
+To quantitatively evaluate Thor's performance under increasing spot complexity, we plotted the mean absolute error (MAE) of each cell against the Shannon entropy of cell type proportions. As spot heterogeneity increased, the MAE for the nearest spot method rose sharply; meanwhile, Thor accurately imputed gene expression for both low (Figure S3c, A) and high (Figure S3c, B, C) heterogeneity spots. Although a subset of cells in highly heterogeneous spots showed a slight increase in MAE (Figure S3c, C), Thor's error remained much lower than that of the nearest spot method.
+
+<--- Page Split --->
+
+Finally, to evaluate Thor's imputation performance under varying dropout levels, an important challenge in high- resolution spatial transcriptomics, we simulated 15 conditions with dropout ratios ranging from \(5\%\) to \(60\%\) and categorized them into three regimes: low dropout \((< 15\%)\) , moderate dropout \((15 - 40\%)\) , and high dropout \((>40\%)\) . We then measured cluster separations in principal component analysis (PCA) space using silhouette coefficients. As shown in the PCA plots (Figure S1d), introducing dropouts severely diminished cluster separations in the ground truth data, with silhouette coefficients reduced from 0.8 to near 0. In contrast, Thor- imputed data maintained the silhouette coefficient to above 0.7- 0.8 in the low- dropout regime, outperforming the KNN smoothing method and BayesSpace. When dropout ratios rose to the moderate regime, where the ground truth data's silhouette coefficients declined to 0.1- 0.4, Thor- imputed data recovered the cluster separation successfully (silhouette coefficients 0.5- 0.6). Even under high- dropout conditions \((>40\%)\) , Thor's scores remained substantially above those of KNN smoothing and BayesSpace.
+
+Collectively, these analyses highlight Thor's accuracy and robustness in the presence of suboptimal histology or transcriptomics data, including high proportions of missed cells, disrupted cell connections, varying spot sizes, and substantial technical dropouts.
+
+## Thor infers accurate gene expression at single-cell resolution
+
+Next, we evaluated Thor on a mouse brain receptor map data acquired by MERFISH. The MERFISH data comprised 483 RNA targets from individual cells (Figure S4a). We simulated Visium- like data within the hippocampus region by creating a grid of evenly spaced "ST spots". The RNA molecule counts in a synthetic spot were aggregated over the cells covered by the "ST spot". These synthetic spots contained a mixture of cells of different cell types, particularly within the hippocampal subregions CA1/2/3 and the dentate gyrus (DG; Figure S4a). Thor connected cells of the same cell types by proximity in the morphological feature space and the spatial space, as illustrated by the cell- cell network in CA1 and DG (Figure S5a; note the cell type information was not provided to Thor). Thor successfully predicted cell- level gene expression in these heterogeneous regions evidenced by the profiles of selected marker genes (Figures S4b and S5b). For instance, Thor recovered Adra1d expression in CA1 and DG, which was missing in the spot- level data and the BayesSpace result. Furthermore, to gain a global view of the similarity between the in silico cells and the MERFISH cells, we projected the high- dimensional gene expression matrices to a joint uniform manifold approximation and projection (UMAP) embedding. The in silico cells inferred by Thor seamlessly mixed with the MERFISH cells on UMAP, and the distribution of cell type clusters of the in silico cells matched the ground- truth cell types (Figure S4c). As a baseline, mixtures of cell types were aggregated in the spot- level data, resulting in a low silhouette coefficient and Calinski- Harabasz index when mapped to the nearest cells. Thor substantially improved the cell type separation, achieving a silhouette score of 0.45 and a high Calinski- Harabasz index of 10,000, and outperformed BayesSpace by a large margin (Figure S4d).
+
+We further applied Thor to a Visium dataset of human breast cancer tissue and compared the result against a Xenium reference dataset of the adjacent tissue section28. Using transcriptome data from the Visium dataset and the post- Xenium H&E image as input, Thor successfully inferred in silico cell- level gene expression. Visually, the spatial patterns of gene expression align closely with Xenium data (Figure 2a). To gain a global view, we clustered the in silico cell- level gene expression using conventional single- cell RNA- seq (scRNA- seq) clustering. The same major cell types were identified from the in silico cells as from the Xenium data, as evidenced by the spatial distribution of the cell types and the mean expression heatmap of marker genes of each cell type (Figure 2b). Additionally, integrating the predicted in silico cells with the Xenium cells showed that cells from the same cell types colocalize from both datasets
+
+<--- Page Split --->
+
+(Figure S6), indicating Thor's ability to predict accurate and biologically meaningful cell- level gene expressions.
+
+For a quantitative evaluation, we benchmarked Thor with three state- of- the- art methods of enhancing ST to near- cell resolution14, 15, 17. The spatial units vary among those tools (Thor: cell, iStar: superpixel, BayesSpace: subspot, and TESLA: superpixel), therefore, we calculated both image- centric and cell- centric metrics to provide a more complete evaluation. On the one hand, by converting spatial profiles of gene expression data into images, we compared the similarities between the predicted spatial patterns with the Xenium spatial patterns using the metrics structural similarity index measure (SSIM) and root mean squared error (RMSE) of pixel values. On the other hand, by mapping the pixel expression data to the cells using the nearest neighbors approach, we compared the deviations between the resulted cell- level gene expression with the Xenium data using cell- wise RMSE as an additional metric. Thor achieved the highest similarity with the Xenium data on all the metrics (Figures 2c and S7). When using the cell- wise RMSE, the general trend remains, yet the difference between the four methods became less prominent. This is likely because all the gene expression levels including Thor needed to be mapped to the common cell positions (Xenium cells) using nearest neighbors before calculating cell- wise RMSE, which might have smoothed out some intricate details in the spatial pattern, as seen in Figure S7(c- d). Overall, Thor demonstrated significantly better agreement with the Xenium data.
+
+To gain more insights into Thor's unique advantage, we compared the expression profiles of representative genes with second best performing tool, iStar. Thor and iStar enhanced spatial resolution to (near) cell resolution, iStar at times introduced artifacts, including excessive fusion, for instance, at segment boundaries (Figure 2d, red arrows), and in regions with sparse cells (Figure 2d, blue arrow). For example, the spatial expression of myoepithelial marker DST inferred by Thor accurately outlined the boundaries of three DCIS regions in ROI 5 (Figure 2d), as confirmed by the Xenium data and the H&E staining image. While Thor did not maintain the spatial gradient pattern due to misdetection of flat nuclei around certain region boundaries, iStar introduced excessive fusion in the tumor regions, as indicated by the red arrows in Figure 2d. Additional examples are provided in Figures S8- 9. These artifacts are likely due to that iStar predicts the expression of super- pixel patches of the whole slide image, rather than a cell. This approach may result in the omission of valuable cellular morphology information. In contrast, Thor takes a fundamentally different approach by considering a cell as the minimum biological unit and can accurately infer single- cell gene expression via a cell- cell network constructed with the integration of transcriptomics and histology data.
+
+## Thor unveils refined tissue structure in mouse olfactory bulb
+
+Thor unveils refined tissue structure in mouse olfactory bulbWe extended our evaluation of Thor- inferred gene expression levels on a MOB dataset collected by Visium. We compared the inferred molecular patterns with those acquired from high- resolution techniques, including the ISH images33 and Stereo- seq data27. Results showed the spatial patterns of gene expression levels inferred by Thor aligned well with both ISH and Stereo- seq data (Figures S10a and S11). For example, Eomes is a marker gene of cells in the glomerular layer and mitral layer34, as observed in the ISH and Stereo- seq data. However, due to the limited spatial resolution, the spot- level Visium data failed to adequately capture the pattern in the mitral layer and exhibited discontinuities in the glomerular layer. By integrating the high- resolution H&E image with the spot- resolution ST, Thor recovered the spatial patterns marked by Eomes in glomerular and mitral layers (Figure S10a). Detailed gene expression profiles from Thor, ISH, Stereo- seq, and Visium, were provided for comparison in Figure S11.
+
+<--- Page Split --->
+
+At the whole- transcriptome level, the in silico cell clusters dissected six main layers in the MOB, the subependymal zone (SEZ), two granule layers, the mitral layer, the glomerular layer, and the olfactory nerve layer (Figure S10b). We further applied Cell- ID35 to infer cell types (see Method; Signature genes are provided in Supplementary Table S1). By integrating ST with spatial locations and histological features, Thor resolved refined neuron subtypes. For example, Thor distinguished granule cells (GCs) between GC- 1 and GC- 2 subtypes, with GC- 1 concentrated in the internal plexiform layer and GC- 2 predominantly in the granule cell layer. Additionally, Thor separated mitral cells (M/TCs) into M/TC- 1 and M/TC- 2 subtypes, with M/TC- 2 concentrated in the mitral layer and M/TC- 1 extending into the glomerular layer. These results demonstrated Thor's capability to refine cell type classification by leveraging histology and spatial transcriptomic data.
+
+Leveraging the cell- resolution spatial profiles, we next identified genes with spatially dependent activation patterns and coordinated gene modules using the package Hotspot36. The genes in the in silico cells formed 8 gene modules reflecting the primary structure of MOB (Figure S10c), with modules '2', '4', '7', and '8' capturing the glomerular layer, the mitral layer, the granule layers, and the olfactory nerve layers, respectively (Figure S10d). Remarkably, module '4' captured the thin mitral layer (thickness \(< 40 \mu m\) ), indicating successful resolution- enhancement by Thor, enriching a thin layer of the M/TC- 2 mitral cell subtype. The gene ontology (GO) pathway enrichment analysis of the layer- specific gene modules suggested a cascade of activities covering odor information sensory, processing, signal transmission, and memory formation in MOB layers. Together, Thor unveiled refined layers in the MOB tissue by accurately inferring cell- level gene expression data, aligning with various experimental measurements.
+
+## Thor supports semi-supervised annotation of fibrotic regions in human myocardial infarction tissues
+
+To better leverage the combinatory space of histological and transcriptomic features, we developed a human- in- the- loop tool for enhanced identification of tissue regions or spatial domains. The semi- supervised annotation tool operates within Mjolnir, enabling researchers to annotate small representative regions using marker gene expression and morphology of cells in gigapixel resolution images. These transcriptome- and morphology- guided annotations can then be quickly propagated across the entire tissue section based on Pearson correlation of the combinatory features, facilitating comprehensive tissue characterization.
+
+We first quantitatively evaluated Thor's semi- supervised annotation using a cohort of heart tissue samples37, which included high- resolution H&E images, high- quality ST data, and spot- level expert annotations for key tissue types in heart including vessel, node, adipose, and fibrosis. Thor's semi- supervised annotations demonstrated strong concordance with expert annotations, achieving accuracy ranges of 0.94- 0.99 for vessels, 0.92- 0.98 for nodes, 0.84- 0.92 for adipose, and 0.92- 0.93 for fibrosis (Figure S12). In contrast, spot- level clustering, even with optimized parameters, struggled to distinguish structures such as vessels (enriched with smooth muscle cells) from certain myocardium regions (Figure S13). These results suggest Thor enhances spatial tissue annotation by integrating histology with transcriptomics, surpassing spot- level clustering.
+
+Next, we applied Thor to analyze six myocardial infarction (MI) patient samples, comprising two necrotic zones (ischemic zone, IZ), two unaffected zones (remote zone, RZ), and two late- stage fibrotic zones (FZ), to enable granular characterization of these distinct tissue zones in heart failure. Using the Mjolnir platform, we first defined an ROI based on fibroblast marker gene expression (PDGFRA and FBLN2) and morphological patterns in an H&E image. Thor then automatically extended the curated ROIs by identifying similar cells in the entire tissue. The
+
+<--- Page Split --->
+
+expression profiles of representative genes, including fibroblast marker genes and cardiac muscle- associated genes, displayed coherent patterns in the curated ROIs and the discovered cells (Figures 3a and S14- 17). Such semi- supervised annotation revealed dense fibrotic areas and shallow areas which were otherwise difficult to identify manually (Figures 3b, S16). The resulting fractions of fibrotic areas in the six samples increased in the order of RZ, IZ, and FZ (Figure 3c).
+
+The precisely annotated fibrotic regions then enabled unbiased functional analysis. For each sample, we performed differential gene expression analysis between cells in the fibrotic and non- fibrotic regions (lists of differentially expressed genes are provided in Supplementary Table S2), followed by GO pathway enrichment analysis. Irrespective of sample zones, the fibrotic regions showed significant enrichment of pathways such as positive regulation of T cell proliferation, fibroblast proliferation, stress fiber assembly, and collagen fibril organization, whereas myocardium- related pathways were enriched in non- fibrotic regions (Figures 3a, d and S18a). These findings align with previous evidence of T cell proliferation and fibroblast- mediated T cell activation in cardiac settings38, 39. Interestingly, the fibrotic regions of RZ samples demonstrated more pronounced inflammation and fibrosis, likely reflecting heterogeneous progression of ischemic injury among the patient samples. After myocardial infarction, tissue in the immediate infarct area often undergoes rapid cell death and necrosis, whereas distant/remote zones may experience a delayed and prolonged inflammatory and fibrotic response40, 41. While IZ and FZ contained the largest proportions of fibrotic regions at the whole tissue level (Figure 3c), those findings demonstrate that functionally distinct fibrotic domains can exist outside necrotic regions.
+
+To identify regulatory factors influencing those fibrotic regions, we estimated TF activities by utilizing a gene regulatory network database42. Compared to non- fibrotic regions, the most prominently activated TFs induced critical pathways, such as epithelial- mesenchymal transition (TWIST2 and SNAI2) and immune response (STAT4 and MYB; Figures 3e and S18b). The detected top regulating TFs agreed with existing studies: SMAD3 has been identified as a principal mediator of the fibrotic response to activate cardiac fibroblasts43; SP1/1 has been reported as an essential orchestrator of the pro- fibrotic gene expression program in multiple human organs44.
+
+Overall, Thor's semi- supervised annotation provides a more nuanced view by integrating morphological features with transcriptomics. This approach refines fibrotic tissue boundaries, highlights subtle variations in fibrotic progression, and provides functional insights into the molecular drivers of post- infarction cardiac fibrosis.
+
+## Thor discovers regenerative signature in heart failure
+
+Spot- level spatial transcriptomics often struggles to reveal intricate patterns in small or narrow regions due to limitations in spatial resolution. One such example is to identify the regenerative signatures in vessel regions. Thor allows for the exploration of gene expression in cell- resolution spatial contexts by predicting gene expression in cells detected from the histological images, thereby enhancing the ability to uncover intricate patterns.
+
+In patients with advanced heart failure, LVADs are commonly used before heart transplantation for cardiac support which provide evident improvement in the structure and function of the heart45, 46. Thus, we applied Thor to in- house heart tissues collected from post- LVAD implantation patients to identify genes driving regenerative remodeling. As the vasculature system plays an important role in cardiac recovery47, we prioritized our analysis in the vascular regions. Blood vessels typically consist of three layers, tunica intima, tunica media, and tunica
+
+<--- Page Split --->
+
+adventitia, from inside to outside. The middle layer is mostly comprised of smooth muscle cells. In Mjolnir, based on the cell phenotypes and the expression levels of the smooth muscle marker MYH11, we annotated 29 and 11 vessel internal regions on two post- LVAD heart tissues (Figures 4a and S19a- c). We extracted highly expressed genes in these vessels, finding 56 genes common to both tissues (Figures 4b and S19d). Excluding smooth muscle markers (such as TAGLN, ACTA2, MYH11, and MYLK), PLA2G2A stood out. PLA2G2A was reported to promote cell proliferation, angiogenesis, and tissue regeneration48 in several tumor types. In the cardiovascular field, another study showed that the PLA2G2A is specifically expressed in donor heart fibroblasts compared with the failing heart fibroblasts49. Our previous work highlighted fibroblasts' role in revascularization50, 51, leading us to hypothesize that PLA2G2A expression is a signature of cardiovascular regeneration. To validate this hypothesis, we divided the vessel cells into PLA2G2A+ and PLA2G2A- groups based on the distribution of PLA2G2A expression (Figure 4c). We found that upregulated genes in PLA2G2A+ cells were enriched in pathways including tube morphogenesis and blood vessel morphogenesis and development (Figure 4d). The expression levels of PLA2G2A in the vessels across two patients exhibited an apparent pattern: high PLA2G2A expression was linked to vessels surrounded by connective or adipose tissues while low expression was associated with vessels surrounded by myocardium (Figure S19e- f). Follow- up immunofluorescence staining of tissues from two post- LVAD patients further confirmed PLA2G2A presence in vessels at the protein level, supporting its role in heart recovery (Figure 4e). Altogether, Thor's histology- transcriptome joint analysis revealed cell- resolution gene expression patterns and identified crucial molecules that may drive vascular regeneration in heart tissues.
+
+## Thor enables multi-layered investigation of hallmarks in DCIS data
+
+Thor offers rich layers of information through streamlined multi- modal analyses within a unified platform. To showcase Thor's strengths and functions, we analyzed a well- validated DCIS dataset that has been used as benchmarks widely18, 52. DCIS is a potential precursor to invasive ductal carcinoma, a condition that can progress into a form requiring surgical intervention and radiotherapy. Understanding the heterogeneity of various DCIS regions is crucial for elucidating the factors driving their diverse behavior. The DCIS dataset comprises 18 pathologist- annotated major tumor regions (T1- T18; Figure 5a). Histological features of segmented cells identified distinct clusters, underscoring their ability to distinguish between tissue regions (Figure 5b; Supplementary Note 1). Through integrated histological features and ST analyses, Thor enabled a multi- layered investigation of breast cancer hallmarks.
+
+First, Thor facilitates cell type annotation at single- cell level. The spatial distribution of annotated cell types aligned with the results from state- of- the- art methods such as CytoSPACE and RCTD18, 53 (Figures 5c and S20). The signature genes of each cell type are provided in Supplementary Table S3 for reference. While these methods require scRNA- seq reference data, Thor overcomes the limitation by integrating the underused histological features with ST. Additionally, Thor's advantage lies in providing gene expression for individual cells detected directly from the tissue image for additional analysis, maintaining cells' spatial arrangement.
+
+Second, Mjolnir enables interactive exploration of the spatial profiles of key molecules on the gigapixel histological images seamlessly at various zoom levels spanning from the whole tissue to the cellular scale. As an example, the visualization of VEGFA, a pivotal angiogenic factor influencing tumor growth and metastasis, highlighted distinct abundance levels within tumor subpopulations at the cellular resolution (Figure 5d). Additional gene expression profiles at both spot and in silico cell levels were provided in Figure S21. A closer examination of the tumor region T1 using Thor revealed the morphological features and the nuanced expression patterns of the cancer cells. VEGFA exhibited the highest expression at the center of the tumor region
+
+<--- Page Split --->
+
+T1, gradually decreasing in abundance towards the boundary; and was minimally expressed in the myeloid cell population outside of T1.
+
+Third, Thor enables efficient search of similar cells in the combinatory space of histological and transcriptomic features. We curated a small set of tumor cells in T8 based on cell morphology and the key gene expression profiles. Cells in most tumor regions were successfully identified (Figure 5e; accuracy: 0.83). Interestingly, hardly any tumor cells in T7 matched the curated set, likely due to its distinct immune microenvironment. Instead, tumor cells in T7 were effectively identified using a separate set of curated cells within T7 (Figure S22). This demonstrates Thor's precision in identifying tumor cells through integrated analysis.
+
+Using only the H&E image, the clustering- constrained- attention multiple- instance learning (CLAM) method2 identified high- attention regions (Figure 5e) that broadly overlapped with pathology- annotated tumor areas (Figure 5a). However, CLAM also identified adipose tissue as high- attention region, which was not directly relevant to cancer (black box in Figure 5e). These false positives happen for patterns which are not strongly represented in the negative samples2, and may require additional training of CLAM on curated datasets of labelled WSIs for more improved specificity. This demonstrated the value of tissue image analysis for tumor detection while highlighting the need for further multi- modal integration to reduce false positives.
+
+Fourth, Thor's cell- level molecular signature and pathway enrichment analysis provided deeper insights into the heterogeneity of tumor progression. By examining spatial patterns of oncogenes and tumor suppressors, we observed a marked contrast between ERBB2 (HER2; an oncogene) and ATM (a tumor suppressor)54: ERBB2 was highly expressed across all tumor regions, whereas ATM was upregulated exclusively in region T7 (Figure S23). An unbiased investigation of cancer hallmark pathways further highlighted their complexity across different tumor regions at the cell level, including DNA repair, a crucial process for maintaining DNA integrity and preventing mutations (Figure S24). Notably, despite the low expression of ESR1 (Figure S21), the estrogen response pathway still showed significant enrichment in tumor regions (Figure S24), emphasizing the power of pathway- based analyses to refine breast cancer classification.
+
+Lastly, genomic CNV inference from Thor's cell- level transcriptome classified tumor and normal cells. Thor successfully uncovered genome- wide CNV profiles in DCIS (Figure 5f), achieving an F1 score of 0.78 and a Jaccard index of 0.64 (Figure 5g), which closely aligned with pathology- annotated tumor regions and surpassed spot- level CNV analyses (F1 score: 0.73; Jaccard index: 0.58; Figure 5g). Unlike spot- level CNV, which averages all cells in a spot, and can misrepresent regions containing both aneuploid and diploid cells, Thor's single- cell approach accurately detected mixed populations, as exemplified by tumor region T7. Spot- level analysis labeled this entire region as aneuploid, whereas Thor- inferred and CytoSPACE- mapped single- cell data identified a mixture of aneuploid and diploid cells. Thor further revealed key copy number aberrations across all tumor cells, including gains in 1, 2q, 8q, 12p, and 18p and losses in 5, 8p, 11q, and 12q. These aberrations highlighted well- known breast cancer- associated genes, such as MDM4, ZNF595, FGFR4, HIST1H1B, TPD52, DECR1, GRB7, and JUP55. CNV analyses provide critical insights into the genomic alterations that underpin tumor heterogeneity and progression, offering potential biomarkers for prognosis and therapeutic targets. Altogether, Through Thor's unified platform of integrated analyses of histology and transcriptomics data, Thor offers an unbiased, multi- layered view of breast cancer hallmarks.
+
+Thor reveals heterogeneity of immune response in tumor regions of DCIS
+
+<--- Page Split --->
+
+We further investigated cell- level immune responses in DCIS by computing the well- established "TLS score" to quantitively capture local immune activity around the tumor regions55. For each cell, the score was calculated by comparing the averaged RNA expression levels of 29 signature genes, including key markers of immune cells such as T cells, monocytes, macrophages, and fibroblasts56, to the average expression of randomized control genes (Figure 6a, see Methods). We then ranked tumor regions based on the median TLS scores of cells residing within each region, along with those in a narrow peritumoral layer (one spot- size outward from the tumor boundary). Regions T7, T1, and T17 exhibited the highest median TLS scores, indicative of robust immune activity (Figure 6b).
+
+To gain deeper insight into the molecular distinctions of these high- and low- scoring regions, we performed differential gene expression analyses comparing tumor regions with the highest TLS scores (T7, T1, and T17) and those with the lowest (T11, T6, and T15). Several immune- related genes showed pronounced variation: for example, CD84 and SMAD3 were abundant in T7 but nearly undetectable in T15 (Figures 6c and S25), whereas KANK1, often relevant in cancer prognosis, was highly expressed in T6 and T15 but absent in T7. We further examined functional distinctions and interactions between tumor regions and their immediate peritumoral neighbors (Figure S25b). T7 was enriched for pathways linked to immune responses and T cell co- stimulation, whereas T15 was enriched for tumor- related pathways such as hypoxia response and cell adhesion.
+
+Finally, we conducted unbiased region- specific pathway enrichment analysis based on upregulated genes in each tumor region (compared to the remaining tissue). As expected from the high TLS scores, T7- specific genes were linked to immune response, T cell activation, and inflammatory response pathways, while T15- specific genes were associated with hypoxia response and cell- cell adhesion (Figure 6c). A global heatmap (Figure 6d) illustrated that other tumor regions, such as T9, T14, and T13, also displayed strong enrichment for inflammatory and immune pathways. Notably, high- scoring regions like T7 and T1 showed enrichment of B cell activation pathway, suggesting more robust immune microenvironments that may be therapeutically relevant. By mapping these immune landscapes at single- cell resolution, Thor provided valuable insights into the functional heterogeneity among tumor regions, supporting a refined understanding of immune- tumor interactions in DCIS.
+
+## Thor enhances gene expression imputation in high-resolution Visium HD data
+
+Recent advances in spatial transcriptomics technologies are pushing toward cellular or even subcellular resolution, yet these high- resolution methods still face challenges such as substantial dropout and technical noise. To demonstrate Thor's effectiveness under these conditions, we generated a high- resolution dataset from an in- house bladder cancer sample using Visium HD. In our experiment, despite the spatial resolution of up to \(2 \mu m\) square bins (aggregated into \(8 \mu m\) square bins for analyses as recommended by 10x Genomics), Visium HD data exhibited high technical noise. For example, PTPRC (a lymphoid marker) appeared sparsely distributed in immune- rich niches, while SPINK1 (a urothelium- associated gene) was erroneously detected in non- tissue regions (Figure S26a). We applied Thor to integrate the \(2 \mu m\) square bins with the histology image. Thor's cell- level imputation yielded more coherent expression patterns than \(8 \mu m\) square bins. The that correctly localized PTPRC to immune areas and SPINK1 to the tumor boundary, aligning with pathology annotations.
+
+Beyond single- gene assessments, Thor- imputed data captured distinct cell populations more accurately. For instance, cluster 7 in Thor's results precisely matched the pathology- annotated immune cell regions (Figure S26b), whereas the raw bin- level data overestimated immune cell
+
+<--- Page Split --->
+
+presence (Figure S26c). Similar overestimation of certain cell types was also reported recently in Visium HD data57. Taking together, these proof- of- concept analyses underscore Thor's ability to refine gene expression signals and enhance biological interpretability in high- resolution ST datasets.
+
+## Robustness of Thor to parameter settings
+
+Thor is designed to be highly flexible, allowing customization of various parameters that control the preprocessing of image/transcriptome data, cell- cell graph construction, and the Markov diffusion process. To evaluate Thor's robustness, we conducted a systematic sensitivity analysis of key parameters, including the diffusion step size \(t\) , the number of cell neighbors \(k\) , and the number of principal components \(nPC\) of the transcriptome data. Thor constructs a shared nearest neighbors (SNN) cell- cell graph based on the \(k\) - nearest neighbors in the combinatory space. First, we tested a range of \(k\) values on the MOB dataset while keeping other parameters fixed ( \(t = 40\) and \(nPC = 10\) ). To reduce bias from highly expressed genes, we applied z- score normalization for each gene. We then calculated the Pearson correlation coefficients ( \(r\) ) across each pair of \(k\) settings. Thor demonstrated strong robustness for \(k\) values between 4 and 10, with a mean \(r = 0.88\) and standard deviation (std) = 0.09. However, very small \(k\) values (< 3) may produce disconnected cell graphs, whereas very large \(k\) values (40- 100) may lead to over- smoothing and weaker correlations with the results of other \(k\) values (mean \(r = 0.56\) , std = 0.27). Second, we evaluated the impact of varying \(nPC\) values while fixing \(k = 5\) and \(t = 40\) . As shown in Figure S27a, Thor remains highly robust when \(nPC \geq 8\) (mean \(r = 0.94\) , std = 0.05). In contrast, \(nPC < 4\) fails to capture sufficient complexity in the data, leading to lower correlations with high \(nPC\) values. Third, we also evaluated a range of diffusion time \(t\) while keeping \(nPC = 10\) and \(k = 5\) fixed. Thor converged after approximately 10 diffusion steps, achieving a mean \(r = 0.90\) (std = 0.10) for \(t = 10\) . However, large \(t\) values (e.g. \(t > 50\) ) may notably increase run time without significant performance gains (Figure S27b). Overall, our analyses show that Thor is robust to a broad range of \(t\) , \(k\) , and \(nPC\) values. These findings indicate that minor adjustments within reasonable parameter ranges have minimal effect on Thor's results, which justifies that we kept a common set of parameters across all case studies.
+
+Moreover, variational autoencoder (VAE) is widely used for RNA- seq data analysis58- 60. Thor can utilize the latent representation in VAE for faster predictions. In the fast mode, the Markov diffusion is conducted on the VAE latent embeddings. The hyperparameter tuning, such as adjusting the input and latent dimensions of VAE can affect the results of Thor and contributes to generalizability. The input dimension should depend on the genes of interest, such as highly variable genes or spatially variable genes. Moreover, a proper latent dimension should sufficiently capture the biological complexity in the data. For instance, a latent dimension of 10 is set by default in scvi- tools59, with 20 or 30 being appropriate for more complex scRNA- seq datasets. We evaluated Thor's performance on the MOB dataset by varying the latent dimensions in separate VAE models (8, 16, 20, 32, 64, and 128), while keeping other parameters fixed (\(nPC = 10\), \(k = 5\), and \(t = 40\)). Thor- predicted gene expressions remained highly consistent with Pearson's \(r > 0.85\) across all settings (Figure S27c). These results indicate that Thor is robust to a broad range of parameter settings.
+
+## Discussion
+
+Thor is an extensible and customizable platform detailed in the following aspects.
+
+(i) The cell-level ST broadens the spectrum of downstream analyses to those originally designed for scRNA-seq data. Outputs from Thor are ready to be interfaced with a variety of existing libraries for analyses such as Squidpy24 and stLearn25 and can be easily adapted for
+
+<--- Page Split --->
+
+scRNA- seq tools. Currently, Thor has included submodules such as cell- specific pathway enrichment \(^{61}\) , inference of genomic CNV profiles \(^{62}\) , and ligand- receptor analysis \(^{63}\) .
+
+(ii) Thor supports customized cell features for building the cell-cell network. In this work, we highlight Thor's performance using intensity-based morphological features such as color intensities of the staining image patches. The inclusion of more task-relevant features elevates the quality of the cell-cell network. For example, research has shown that spatial cellular graphs built from multiplexed immunofluorescence data enable the better modeling of disease-relevant microenvironments \(^{64}\) . In addition, Thor supports direct input of a cell-cell network adjacency matrix.
+
+(iii) Beyond spatial transcriptomics, emerging omics technology such as spatial metabolomics and proteomics are increasingly adopted to capture local metabolic or protein-level processes that underlie key tissue functions and disease mechanisms. While our current work focuses on applying Thor to spatial transcriptomics, we envision that its underlying framework, which constructs a cell-cell graph from spot-level data, cell coordinates, and histological features, then refines those data through graph diffusion, could be adapted for spatial metabolomics or proteomics as well. By substituting transcriptomic values with metabolomic or proteomic intensities, Thor could enable a more comprehensive, multi-omic view of tissue biology at single-cell resolution. We anticipate that future developments will provide deeper insights into complex tissue characterizations by integrating these additional modalities.
+
+Thor integrates histological features and transcriptomic features by inferring cell- level ST. Notably, Thor does not require any additional scRNA- seq data as a reference. This not only reduces the sequencing cost but also proves practically advantageous in FFPE tissues. FFPE tissues serve as the most abundant specimens for longitudinal studies with preserved tissue morphological details, yet RNA- seq profiling encounters hurdles due to RNA crosslinking, modifications, and degradation. The Visium platform offers a solution for profiling mRNA levels in both fresh- frozen and FFPE tissues, employing a de- crosslinking process \(^{65}\) . Nevertheless, it falls short of providing cellular- level resolution. In contrast, commonly used methods like chromogenic immunohistochemistry (IHC) for assessing in situ biomarker expression in FFPE tissues are limited by the number of analytes, non- linear staining intensity, and the subjective nature of the quantitative analysis \(^{66}\) . Thor strategically leverages the advantages of Visium and overcomes these challenges by delivering cell- level whole- transcriptome analysis, reducing the cost and workload.
+
+Thor offers several advantages over existing frameworks for studying histological structures. PROST uses spatial relationships and transcriptomics data to identify spatially variable genes and to cluster spatial domains, but it does not enhance the resolution of the original ST data \(^{21}\) . Thus, with Visium data, PROST operates at the Visium- spot level and does not utilize histology images. By contrast, Thor integrates cell- level features from histology images with spot- level transcriptomics, enabling inference of gene expression at the single- cell level and providing a more granular analysis of histological structures from Visium data. METI, meanwhile, is an end- to- end framework tailored to cancer ST data, mapping tumor cells and the surrounding microenvironment primarily in oncology- focused contexts \(^{22}\) . Thor, on the other hand, was conceived as a more generalizable approach applicable across various tissues, disease states, and organisms. Moreover, neither PROST nor METI directly output single- cell gene expression. In contrast, Thor integrates histological and transcriptomic data in a task- agnostic manner to infer spatially resolved single- cell gene expression. This capability supports a broad range of downstream analyses and comes bundled with extensive analytical modules, including pathway enrichment, spatial gene module identification, differential gene expression, transcription factor activity estimation, and interactive whole- slide data visualization. Taken together, these features
+
+<--- Page Split --->
+
+allow Thor to complement and extend the capabilities of frameworks by offering deeper spatial and molecular insights into tissue architecture.
+
+Thor stands out as a comprehensive, user- friendly platform designed for multi- modal tissue analyses. As a model- based computational method, Thor operates efficiently on a laptop, presenting a practical advantage to existing deep learning- based approaches that demand abundant training data and intricate computational skills. The platform includes an interactive web- based tool Mjolnir, which enhances the analysis experience by allowing users to thoroughly investigate cell- level information through gigapixel histological images conveying various multimodal attributes. Its intuitive interface enhances accessibility to a broad user base. Mjolnir incorporates a tile server algorithm that dynamically loads gigapixel images for smooth navigation. This not only resolves computational resource demands for visualization but also significantly improves the overall usability and responsiveness of the platform during analysis sessions, even on a laptop. Furthermore, Mjolnir functions as a standalone tool, offering users the flexibility to upload their images and cell- level attributes.
+
+With rapid breakthroughs in deep- learning- based computer vision algorithms \(^{7,8,67 - 69}\) , accurately detecting cell nuclei has become increasingly viable, transforming the challenge of cell detection in high- density regions \(^{70,71}\) . As an integrative spatial transcriptomics analysis platform, Thor incorporates multiple SOTA tools for cell segmentation and also supports manually/strategically added missing cells, enabling enhanced flexibility and adaptability for diverse workflows. Thor is designed to stay aligned with ongoing advancements in cell segmentation technologies, ensuring that its methods remain cutting- edge. Thor extracts tile- based image features from an image patch centered at the segmented cell nucleus centroid to capture the local environment surrounding the nucleus. These features are not limited to the nucleus itself but include the tissue context within the image tile, providing a comprehensive representation of the cell's local environment from histology. Tile- based feature extraction is a practical strategy widely adopted in histology image analysis by deep- learning models and pathology foundation models. It facilitates a wide range of downstream tasks, including cell segmentation, cell type annotation, and tumor microenvironment profiling \(^{15,17,72 - 75}\) . We recognize that certain cell types or microstructures may require more specialized descriptors. To address this, Thor provides an API (thor.pp.image.WholeSlideImage.load_external_cell_features) that supports morphological features generated by external tools (e.g., CellProfiler or CellViT). Researchers can extract customized metrics, such as cell shape, texture, or intensity profiles, then input these features into Thor, effectively augmenting or replacing the default cell detection and tile- based features. This flexible design allows Thor to accommodate a wide spectrum of histological analyses and cellular phenotyping tasks, ensuring that users can tailor the platform to their unique research objectives.
+
+Recent advances in spatial transcriptomics technologies have pushed spatial resolution toward cellular or even subcellular level \(^{27,32,76}\) , yet each technology still faces practical hurdles that Thor can help address. For instance, although Visium HD offers sub- cellular bin sizes, it can suffer from high dropout rates, low gene coverage \(^{57}\) , and imperfect bin- to- cell alignment \(^{77}\) . Meanwhile, Slide- seq may provide sparse transcript detection and limited capture size \(^{78}\) , and image- based platforms such as Xenium and CosMX rely on predefined gene panels and may omit genes of interest. Our results show that by integrating Visium HD data with histological features, Thor reduces technical noise and reveals spatially coherent expression patterns that match pathology annotations. Beyond improving data quality, Thor functions as a comprehensive downstream analysis platform capable of handling the computational and visualization demands posed by large- scale ST datasets, where a single slide can contain millions of bins or hundreds of thousands of cells per slide. Thor's interactive visualization tool,
+
+<--- Page Split --->
+
+Mojlnir, renders gigapixel images and facilitates responsive exploration on standard computing hardware. Moreover, Thor remains a cost- effective option for achieving single- cell level analyses with standard Visium data (approximately \(70\%\) less expensive than Visium HD), benefiting labs with resource constraints or those seeking to reanalyze legacy ST datasets.
+
+Thor has several limitations. First, it relies on high- resolution histology images (typically 0.25 to \(0.5 \mu m\) per pixel) for cell detection and histological feature extraction. Real- world scenarios may introduce complexities, such as loss of focus in imaging or improper staining across large tissue regions. Such conditions may lead to missed cell detection or unrepresentative image features and Thor's performance may understandably suffer. Additionally, Thor's performance may be affected in regions where nuclei are difficult to identify, such as cells in peripheral areas with flat nuclei. Incorporating higher precision imaging techniques, such as the DAPI imaging used in the Xenium data cell detection, could help address this issue. Second, Thor does not currently support multi- sample integration, as batch effects in transcriptomics data and histological variability between tissue sections introduce biases that complicate direct comparisons and spatial alignment. These challenges also limit the applicability of semi- supervised annotation across multiple samples. Third, Thor does not operate at subcellular resolution to provide further finer level analysis. Due to the light diffraction limits in standard histology imaging and complex morphological variability of subcellular structures, robust and accurate segmentation of individual organelles or subcellular structures are highly challenging \(^{79}\) and restricted for certain organelles in restricted platforms \(^{69,80,81}\) . Thor's cell- level integrated analyses of transcriptomics and histology may complement with nanoscale spatial omics technologies. Its modular architecture could, in future work, integrate with subcellular methods like Stereo- seq to bridge tissue, cellular, and subcellular- level insights.
+
+In conclusion, Thor effectively leverages ST analysis by integrating histology and transcriptomics, refining gene expression to the single- cell level and enabling more precise characterization of tissue architecture. This approach provides a valuable foundation for future cross- modal integration, including highly multiplexed imaging techniques (e.g., CODEX or MIBI) to achieve a more comprehensive, multi- modal understanding of spatial- omics data. By enabling the exploration of cellular interactions across spatial landscapes, Thor not only facilitates discovery of biological insights but also lays the foundation for the development of novel therapeutic modalities, thereby advancing the field of precision medicine for more effective and personalized patient care.
+
+<--- Page Split --->
+
+## Methods
+
+## Overview of Thor
+
+Thor integrates transcriptomics and histological information by faithfully inferring the whole transcriptome of in silico cells. Thor does not require training for the inference of cell- level gene expression. Instead, it operates per slide through a four- step modularized workflow (see Supplementary Note 1).
+
+(i) Identify cells and extract locations and morphological features of each cell in their spatial neighborhood from the histological image. Meanwhile, the ST data is preprocessed, and the gene expression of the cells is initialized to their nearest spots.
+
+(ii) Compute multi-modal distances between cells and construct the cell-cell network based on their morphological features, geometrical locations, and the transcriptome collectively.
+
+(iii) Convert the distances to affinities using an exponential kernel, so that the similarity between two cells decreases exponentially with the multi-modal distance. (iv) Infer gene expression of the cells by transitioning information flow between similar cells and prohibiting that from cells covered by a heterogeneous spot.
+
+Then the predicted cell- level gene expression can be applied to perform downstream analyses including interactive analysis in ROIs. The modules are described in detail as follows.
+
+## Nucleus segmentation and feature extraction from histological images (reordered for its importance)
+
+Nucleus segmentation is critical in the analysis of histological images, enabling quantitative assessment of the number of nuclei, density, and morphological characteristics. Thor integrates several state- of- the- art tools \(^{6,7,67}\) for nucleus segmentation and supports user- supplied segmentation results to ensure adaptability across diverse platforms.
+
+For jointly analyzing the histological image and the transcriptomics, Thor employs two filtering processes: Thor eliminates out- of- context nuclei by superimposing segmented nuclei on the aligned spatial spots and removing nuclei whose centers are beyond a cutoff distance from the nearest spots. The default cutoff distance is the diameter of the spots. Furthermore, Thor detects and removes isolated cells or artifacts located away from the tissue boundaries.
+
+Tile- level histological features are extracted to represent the local environment surrounding each cell. This local environment is defined by extending from the nucleus centroid to a given distance, typically twice the mean distance between the nearest nuclei centroids. In this study, we included image features such as the mean and standard deviation of color intensities, as well as image entropy, within a defined radius around each nucleus on the tissue. These features have proven to be effective in constructing cell- cell networks for Thor inference across all tested datasets. Additionally, Thor supports custom functions for feature extraction and allows the integration of user- supplied nucleus or cell- specific features, as well as deep- learning- derived features, offering flexibility and extensibility in the analysis process. Thor is designed to incorporate advancements in segmentation toolkits to stay on the front of cell segmentation field.
+
+## Constructing the cell-cell network
+
+Thor infers cell- level gene expression based on the cell- cell network. Connectivity between cells is determined by their distances in the combinatory feature space, formed by morphological features, geometrical locations, and the low- dimensional representation of the transcriptomic data. The features are standardized to normal distribution \(N(0,1)\) across all the cells. Nearest
+
+<--- Page Split --->
+
+neighbors are included to construct the KNN cell- cell network based on the distance metric \(d_{ij}\) in the feature space, i.e.
+
+\[d_{ij} = \sqrt{\left(w^{gen\_m}d_{ij}^{gen}\right)^2 + \left(w^{geo\_m}d_{ij}^{geo}\right)^2 + \left(d_{ij}^{mor}\right)^2} \quad (1)\]
+
+where \(d_{ij}^{gen}, d_{ij}^{geo}, d_{ij}^{mor}\) are the dimension- normalized Euclidean distances in the transcriptomic (reduced dimension), geometrical, and morphological feature space, respectively; \(w^{gen\_m}\) and \(w^{geo\_m}\) are the respective weights in relative to the morphological feature distance. Increasing the \(w^{geo\_m}\) value leads to a more localized network and increasing the \(w^{gen\_m}\) value favors the distance in the transcriptomic space.
+
+Next, to preserve local structure and account for the non- uniform density of the cells, the KNN cell graph is converted to a shared nearest neighbors (SNN) graph. SNN prioritizes connections among cells that have multiple neighbors in common. This emphasis can unveil intricate data patterns and has demonstrated a reduced susceptibility to isolated noisy data points. Cells \(i\) and \(j\) are connected if the proportion of their shared neighbors \(w_{ij}\) is beyond a given threshold.
+
+\[w_{ij} = card(NN(i)\cap NN(j)) / k \quad (2)\]
+
+In Eqn. (2), \(NN(i)\) and \(NN(j)\) refer to the sets of nearest neighbors of cell \(i\) and cell \(j\) respectively. card refers to the cardinality of the overlap set. \(k\) is the number of nearest neighbors considered.
+
+## Feature-preserving Markov diffusion model
+
+As the ST spot data represents the aggregate expression across enclosed cells, we hypothesize that gene expression in a homogeneous spot is more accurate compared to a heterogeneous spot. The heterogeneity of a spot is quantified by the coefficient of variation in cellular features of all cells mapped to the spot or by the Shannon entropy when cell type labels are available (e.g., from spot deconvolution methods). On the SNN cell graph, Thor ensures that more accurate gene expression data corrects the less accurate ones while inhibiting the propagation of the less accurate information through modulation of node weights and edge weights.
+
+Cells mapped to a more homogenous spot carry a larger node weight \(G_{i}\) , thus more robust to variations. \(G_{i}\) is calculated as an exponential kernel on the heterogeneity of the corresponding spot.
+
+\[G_{i} = e^{-kS_{i}} \quad (3)\]
+
+where \(k\) is the inverse kernel width that controls the shape and \(S_{i}\) is the heterogeneity of the spot enclosing cell \(i\) . The edge weight \(\epsilon_{ij}\) between two cells \(i\) and \(j\) is computed as the product of the "bandwidth" \(w_{ij}\) as shown in Eqn. (5), proportion of their shared neighbors defined in Eqn. (2), and the "latency" \(L_{ij}\) defined in Eqn. (4).
+
+\[\begin{array}{l}{L_{ij} = \frac{1}{1 + e^{-\alpha (G_i - G_j)}}}\\ {\epsilon_{ij} = (1 - \delta_{ij})L_{ij}w_{ij} + \delta_{ij}G_i} \end{array} \quad (5)\]
+
+where \(\alpha\) controls the steepness of the scaled sigmoid function.
+
+The transition matrix \(F_{ij}\) is then computed as,
+
+\[F_{ij} = (1 - \lambda)\delta_{ij} + \lambda \epsilon_{ij} = \delta_{ij} - \lambda (\delta_{ij} - \epsilon_{ij}) \quad (6)\]
+
+where the constant \(1 - \lambda \in (0,1)\) is the probability of keeping the original (self) gene expression. As shown in Eqns. (4- 6), the "latency" is a key parameter that turns the symmetric SNN into an asymmetric network in favor of incoming information flow in a connection from the
+
+<--- Page Split --->
+
+cell with a lower heterogeneity score, or a larger node weight, to the cell with a higher heterogeneity score.
+
+The transition matrix takes the same form as in a Laplacian smoothing method, likewise, the diffusion causes shrinking in the transcriptome space. Therefore, we employ a well- known feature- preserving technique in the field of surface smoothing \(^{82}\) and introduce a reversed diffusion transition matrix \(R_{ij}\) after the forward diffusion to inflate the transcriptome space.
+
+\[R_{ij} = (1 - \mu)\delta_{ij} + \mu \epsilon_{ij} = \delta_{ij} - \mu (\delta_{ij} - \epsilon_{ij}) \quad (7)\]
+
+where \(\mu \in (- 1,0)\) , \(\delta_{ij}\) is the Kronecker delta. In practice, the absolute value of \(\mu\) is set marginally larger than \(\lambda\) for sufficient inflation.
+
+The feature- preserving diffusion is composed of a forward diffusion step followed by a reversed diffusion step. Therefore, the effective transition matrix is computed as the matrix multiplication of the reversed diffusion transition matrix \(R_{ik}\) and the forward diffusion transition matrix \(F_{kj}\) ,
+
+\[T_{ij} = \sum_k R_{ik} F_{kj} \quad (8)\]
+
+The resulting Markov transition matrix \(F_{ij}\) represents the probability distribution of transitioning from each cell to every other cell in a single step. The transition matrix \(T_{ij}\) is normalized by rows to ensure that the probabilities of incoming signals sum up to 1.
+
+Lastly, after obtaining the Markov transition matrix, Thor performs graph diffusion to infer the gene expression at the cellular level.
+
+\[x^{n} = (T)^{n}x^{0} \quad (9)\]
+
+where \(x^{0}\) is the input gene expression initialized by the nearest spot- level values, \(x^{n}\) is the final inferred gene expression, \(F\) is the feature- preserving Markov transition matrix, and \(n\) is the number of diffusion steps. The Markov diffusion converges rapidly, typically within 10 steps \(^{83}\) .
+
+Due to the substantial number of in silico cells, the diffusion can take hours. To speed up Thor, the Markov graph diffusion may be performed on the reduced- dimensional embedding, such as the latent variables of a variational autoencoder (VAE), and the transcriptome can be reconstructed from the latent variables. Finally, Thor rescales the gene expression to the same range as the input spot- level gene expression, and optionally samples cell- level gene expression considering stochasticity in scRNA- seq reads.
+
+## Advanced analyses and dynamic visualization
+
+Technical challenges arise when analyzing and visualizing systems containing a vast number of cells. The WSIs are gigapixel- scale and typically encompass from 10,000 to 100,000 in silico cells within a \(6.5 \text{mm} \times 6.5 \text{mm}\) tissue sample. These large- scale datasets present significant difficulties in terms of computational resources and effective data visualization. To address these challenges, we adapted existing pipelines for analysis of cell- level multi- omics and imaging data, as well as developed a dedicated tool Mjolnir for interactive visualization of large biomedical images. Details for dynamic visualization and advanced analyses are as follows,
+
+- Interactive visualization of histology and genomics. Mjolnir leverages image-tiling technologies used by Google Maps, enabling seamless navigation through gigapixel images at a range of zoom levels. Mjolnir empowers users to visualize segmented components, including spots and cells/nuclei color-coded by gene expression or additional attributes, such as copy number profiles.
+
+- ROI selection. Mjolnir supports drawing and editing regions of any shape on the staining image. A user can export the selected ROIs in common data formats such as annData for gene expression, TIFF for image patches, and JSON for polygon coordinates, facilitating further analyses.
+
+<--- Page Split --->
+
+- DEG analysis. Differentially expressed genes (DEGs) are extracted between two specified groups of cells. Thor treats individual cells in a group as replicates and assesses the significance of changes in gene expression using statistical models.- Pathway enrichment analysis. A pathway is represented by a group of specific molecules that collectively carry out vital functions within cells and organisms. Thor adapts the Python package decoupler61 to compute the cellular enrichment of pathways.- TF activity analysis. The activity of a TF is inferred by the expression levels of its regulated genes. Thor adapts decoupler61 to compute cellular TF activity.- CNV analysis. Thor integrates the R package CopyKAT62 for CNV analysis with a wrapper function. Thor expedites the calculation of CNV by parallel computing.- TLS score. The TLS score is calculated based on 29 signature genes, including markers of immune cells such as T cells, monocytes, macrophages, and fibroblasts56. The TLS score in the DCIS dataset was calculated with the scanpy.tl.score_genes function in SCANPY84, as the averaged expression of a set of genes subtracted by the averaged expression of a set of randomly sampled genes.- Cell-cell communication. Thor integrates the python package COMMOT63 to analyze cell-cell communication, which accounts for competition among different ligand and receptor species as well as spatial distances between cells. Thor boosts the calculation by implementing a more efficient function to compute the cell-cell spatial distance matrix within the interaction cutoff distance in place of the original implementation.
+
+## Post-LVAD heart failure ST data collection
+
+Sample collection and preparation Tissues were collected from patients wearing LVAD before a heart transplant. All samples were obtained under an approved IRB protocol (Pro00006097:1 Congestive Heart Failure) at Houston Methodist Hospital. FFPE heart failure tissue samples were collected using standard- of- care procedures. Tissue sections \((10\mu m)\) obtained from the FFPE tissues were mounted on Visium spatial gene expression slides (10x Genomics, 1000520). The samples were processed as described in the manufacturer's protocols.
+
+ST by 10x Genomics Visium The tissue slides were permeabilized at \(37^{\circ}C\) for 6 min, and polyadenylated mRNA was captured by oligonucleotides bound to the slides. Reverse transcription, second- strand synthesis, complementary DNA (cDNA) amplification and library preparation proceeded using the Visium Spatial Gene Expression Slide & Reagent Kit (10x Genomics, 1000520) according to the manufacturer's protocol. After evaluation by real- time PCR, cDNA amplification included 13- 14 cycles. Indexed libraries were pooled equimolarly and sequenced on a NovaSeq X Plus instrument in a PE28/150 run (Illumina). An average of 26, 011 paired reads were generated per spot and the median genes per spot were 2,277. Tissues were stained with H&E, and slides were scanned on a Pannoramic MIDI scanner (3DHISTECH) using a \(\times 20\) , 0.8- NA objective.
+
+Spatial profiling of vascular protein To capture the spatial expression of the candidate protein, we adapted an established protocol for spatial mapping using immunofluorescence staining. This technique provides detailed visualization of gene expression within tissue contexts, allowing for precise localization and analysis of the candidate gene's expression patterns across different tissue regions. First, paraffin- embedded sections were deparaffinized with xylene thrice for 5 minutes each. The sections were then rehydrated through a series of ethanol washes: twice in \(100\%\) ethanol for 2 minutes each, twice in \(95\%\) ethanol for 2 minutes each, and once in \(75\%\) ethanol for 2 minutes. The slides were then rinsed in ultra- pure water for 5 minutes, followed by Tris- buffered saline (TBS) containing \(0.0025\%\) TritonX- 100 for 5 minutes. For
+
+<--- Page Split --->
+
+antibodies recognizing surface proteins, a rinse with 1xTBS alone was used. Subsequently, the slides were subjected to antigen retrieval by placing them in a sodium citrate solution heated to \(85^{\circ}C\) on a hot plate for 10 minutes. The sections were then encircled with a pap pen, and the primary antibody was applied overnight in a dark, humidified chamber at \(4^{\circ}C\) . The following day, the slides were washed twice with either 1xTBS containing TritonX- 100 or 1xTBS alone, depending on the nature of the protein of interest. Next, the slides were incubated with the secondary antibody in a dark chamber for 30 minutes. After incubation, the slides were washed twice and mounted using a DAPI- containing mounting medium. Microscopy images were obtained using an Olympus FV3000 Confocal microscope. A negative control slide was used to establish the threshold settings, which were consistently applied to all slides for image acquisition.
+
+## Preprocessing the histology images
+
+In order to accurately detect cells/nuclei from histology images, preprocessing steps including image normalization and augmentation of the histology images in this study adhered to recommending settings the cell segmentation tools. For StarDist, pixel values were clipped at \(1\%\) and \(99.8\%\) for all the (red, green, blue) color channels, and the trained model '2D_versatile_he' was used. Cellpose internally included data normalization in the neural network. Following the recommendations in Squidpy, we inverted the color values of the H&E images and used the blue channel for nuclei segmentation24.
+
+For the MOB dataset, nuclei were segmented from the H&E staining images with Cellpose7 using the parameters (min_size = 10, flow_threshold = 0.4, channel_cellpose = 0). For the human MI datasets, the 10x Genomics human breast cancer Xenium & Visium datasets, the 10x Genomics human DCIS dataset, and the post-LVAD human heart tissues, StarDist67 was used with the default parameters (prob_thresh = 0.05, nms_thresh = 0.2). For the mouse brain MERFISH dataset, the cell segmentation downloaded along with the data was used.
+
+## Preprocessing the spatial transcriptomic data
+
+The initial preprocessing steps involved quality control and library size normalization, adhering to the SCANPY standard protocols84. Highly/spatially variable genes were identified by established protocols84- 86 for inference and following downstream analyses. A low- dimensional representation was obtained through dimension reduction methods, including PCA, UMAP, or by utilizing the latent space of a VAE.
+
+## Parameter settings in Thor inference
+
+Thor inference demonstrated robust performance to the variations in parameter settings. Therefore, in all analyses of this study, default parameters in Thor were employed, with specific configurations as outlined below. The construction of the cell neighborhood graph utilized an initial k- nearest neighbor approach, setting the number of neighbors to 5 (n_neighbors = 5). Additionally, the probability of retaining the original (self) gene expression, denoted as \(1 - \lambda\) in Eqn. (6), was set to 0.2 (equivalently in Thor, smoothing_scale = 0.8), and the total number of diffusion steps was specified as 20 (n_iters = 20).
+
+## CytoSPACE
+
+CytoSPACE was performed on the Human ductal carcinoma in situ by Visium dataset to map single cells from a reference scRNA- seq data. A breast cancer scRNA- seq atlas by Wu et al. was used as the reference87. Default parameters were used. The default cell type information from the original study87 was projected.
+
+<--- Page Split --->
+
+## RCTD
+
+RCTD was ran on the Human ductal carcinoma in situ by Visium dataset to deconvolute the cell type proportions in the spots. An annotated breast cancer scRNA- seq atlas by Wu et al. was used as the reference data87. Default parameters were used.
+
+## iStar
+
+For iStar prediction of superpixel level gene expression on the Human breast cancer by Visium data, default settings recommended in the documentation in the GitHub repository (https://github.com/daviddaiweizhang/istar) were used. We applied iStar to the post- Xenium H&E image and the paired Visium dataset. We set the desired pixel size to \(0.25 \mu m\) for high- resolution inference of the spatial gene expression.
+
+## BayesSpace
+
+For enhancing spatial features on the simulation data, we set the number of clusters to the ground truth number of clusters, number of PCA components to 10, and spatial- enhancing Markov chain Monte Carlo (MCMC) rounds to 50,000. For enhancing spatial features on the mouse MERFISH- generated spot data, we set the number of clusters to 8, number of PCA components to 10, and spatial- enhancing MCMC rounds to 50,000. For enhancing spatial features on the 10x human breast cancer by Visium dataset, we set the number of clusters to 6 (the number of major clusters identified in the reference Xenium dataset), number of PCA components to 10, and spatial- enhancing MCMC rounds to 50,000. Other parameters were set to their default values.
+
+## Cell type annotation by Cell-ID
+
+Cell- ID was used to transfer the cell type information from an annotated reference scRNA- seq data to annotate single- cell data inferred by Thor35. Cell- ID was performed by a per- cell assessment in the query dataset evaluating the replication of gene signatures extracted from the reference dataset.
+
+We followed the Cell- ID vignette and used the default parameters. For the MOB dataset from 10x Genomics, we used the cell type signatures from the scRNA- seq data88. For the human DCIS dataset from 10x Genomics, we used the cell type signatures from the scRNA- seq data (https://drive.google.com/file/d/1G8gK4MxCmRG4JZi588wloMsP8iZIQf z/view?usp=share_link) for Cell- ID annotation18. We further refined the annotations by using expression levels of key gene signatures including EPCAM and CDH1, to distinguish between normal and tumor epithelial cells. Similarly, monocytes and macrophages were separated by using marker genes VCAN (versican) and CD14, which were upregulated in circulating monocytes and reduced upon differentiation to macrophages (Figure S20a).
+
+## Pathway enrichment analysis
+
+Functional enrichment analysis was performed using the over- representation analysis (ORA) method implemented in the Python package decouple61, 89. For each cell, the top expressed genes were treated as the set of interest. For a given gene set (e.g. a GO term), a one- sided Fisher exact test was applied to test the significance of overlap between the gene sets. The resulting p values were log- transformed to yield enrichment scores, where higher scores indicate greater significance. For example, T cell proliferation score was calculated by overlapping the top expressed gene lists in each cell with the GO term positive regulation of T cell proliferation (GO:0042102).
+
+<--- Page Split --->
+
+## Transcription factor activity inference
+
+The database CollecTRI and Python package decoupler were used for the TF activity inference. CollecTRI is a comprehensive resource comprising weighted transcriptional regulatory networks of TF- target gene interactions90. TF activities were estimated using the univariate linear model method implemented in decoupler61, by predicting gene expression levels based on the TF- Gene interaction weights from CollecTRI. The resulting TF activity scores provide directional insights: positive scores indicate active TFs driving gene expression, whereas negative scores suggest inactivity or repression.
+
+## Gene module identification
+
+Hotspot36 was used for identification of informative genes in the single- cell level spatial transcriptome dataset. For the module assignment by Hotspot in the MOB dataset, the number of nearest neighbors was set to 30 for creating the KNN graph. A false discover rate (FDR) cutoff of 0.05 was applied, thereby grouping 1,688 out of all the 2,781 highly variable genes into 8 modules.
+
+## Datasets and preprocessing
+
+Human breast cancer by Xenium & Visium: The Xenium gene expression matrix and the Visium raw reads were downloaded from the 10x website (https://www.10xgenomics.com/products/xenium- in- situ/preview- dataset- human- breast). We mapped the Visium reads to the post- Xenium H&E staining image (In Situ Sample 1, Replicate 1) using 10x Space Ranger software (v2.1.0) for direct comparison between Thor- inferred result and Xenium data. The processed Visium gene expression matrix of the 306 genes, found commonly in the Xenium and the Visium datasets, and the post- Xenium H&E image were utilized as input for Thor/iStar/TESLA/BayesSpace. The Xenium data was employed as a reference for assessing the performance of Thor or iStar and was excluded during prediction.
+
+Human ductal carcinoma in situ by Visium: The gene expression matrix and the paired full- resolution H&E staining image were downloaded from the 10x website (https://www.10xgenomics.com/resources/datasets/human- breast- cancer- ductal- carcinoma- in- situ- invasive- carcinoma- ffpe- 1- standard- 1- 3- 0). The gene expression matrix was preprocessed and log- normalized expression of 2,748 highly variable genes was used to train a VAE network for accelerating Thor inference. The dimension of the latent space of VAE was set to 20.
+
+Human healthy heart sample by Visium: The full resolution H&E staining images of 12 samples were downloaded from links (https://www.heartcellatlas.org/) in the original publication37. The gene expression matrices and spot level expert annotations were provided in the annData files. The sample IDs include "HCAHeartST11702008" (vessel: S1), "HCAHeartST12992072" (vessel: S2), "HCAHeartST9383353" (vessel: S3), "HCAHeartST11290662" (node: S4), "HCAHeartST11702008" (node: S5), "HCAHeartST11702009" (node: S6), "HCAHeartST13228106" (adipose: S7), "HCAHeartST9383354" (adipose: S8), "HCAHeartST13228103" (adipose: S9), "HCAHeartST13228106" (fibrosis: S10), "HCAHeartST11350377" (fibrosis: S11), and "HCAHeartST8795936" (fibrosis: S12).
+
+Human myocardial infarction by Visium: The gene expression matrices and paired full- resolution H&E staining images of six samples were downloaded from links provided in the original publication40 (https://zenodo.org/records/6580069#.ZHYP9OzMK3I). Samples "10X0025" (RZ1), "ACH0019" (RZ2), "ACH0012" (IZ1), "ACH0014" (IZ2), "ACH008" (FZ1), "ACH006" (FZ2) were downloaded for analysis. To facilitate the comparison of tissues from ischaemic, fibrotic, and remote zones, where the expressed genes exhibited substantial variations, we aimed to
+
+<--- Page Split --->
+
+maximize the overlap of genes among the six samples. After filtering out genes not expressed in any spot, we inferred the expression of all the remaining genes.
+
+Human post- LVAD heart failure by Visium: The gene expression matrices were obtained by using Space Ranger (v2.1.0), referencing the GRCh38 human Genome. The gene expression was preprocessed following SCANPY standard protocols. Log- normalized expression of all expressed genes was used as input.
+
+Human bladder cancer by Visium HD: The gene expression matrices were obtained by using Space Ranger (v2.1.0), referencing the GRCh38 human Genome. Gene expression matrices of the \(2 \mu m\) square bins and \(8 \mu m\) square bins were preprocessed using SCANPY. Log- normalized expression of highly variable genes of \(2 \mu m\) square bins was used as input. Log- normalized expression of \(8 \mu m\) square bins were used for comparison.
+
+Mouse olfactory bulb by Visium: The gene expression matrix and paired full- resolution H&E staining image were downloaded from the 10x website (https://www.10xgenomics.com/resources/datasets/adult-mouse- olfactory- bulb- 1- standard- 1). The gene expression was preprocessed following SCANPY standard protocols. Log- normalized expression of highly variable genes was used as input. A VAE network was trained to allow inference in the latent space. For evaluation, we downloaded the ISH images of selected genes in MOB from Allen brain atlas33 and the gene expression data from the Stereo- seq study27.
+
+Mouse brain by MERFISH: We used the Vizgen MERFISH mouse brain receptor map dataset that contains a MERFISH measurement of a 483 gene panel. Sample Slice 2 Replicate 1 was used and downloaded from https://info.vizgen.com/mouse- brain- map?submissionGuid=5606514b- 5a81- 4405- 999e- 327f908281cc. The DAPI image "mosaic_DAPI_z2.tif" was used for extracting image features of single cells. 8,597 cells in the hippocampus region were extracted (Figure S4a). After preprocessing, the log- normalized expression in 535 synthetic spots and the DAPI image features were used as input for Thor.
+
+## Simulation details
+
+Thor's accuracy, sensitivity, and limitations of Thor were evaluated on simulated ST data under conditions, including diverse sources of ground truth data, variation in spot sizes, missouts in cell identification, false connections in a cell- cell network, and technical dropouts in sequencing. We extracted the positions of 6,579 cells in a mouse cerebellum Slide- seq data32, including the Granular (Cluster 1), Oligodendrocyte (Cluster 2), and Purkinje (Cluster 3) cells. Those cell locations reliably reflect the spatial distribution of cells in the real tissue and the gene counts in the single cells were simulated using Poisson distributions. We simulated a single- cell ST dataset by generating 1,000 genes of distinct spatial expression patterns, acting as markers for the three cell types. This included 350 genes for each of the first two cell types and 300 genes for the third cell type. Specifically, for the marker genes, the mean values of the Poisson distributions ( \(\lambda\) ) were randomly sampled in the range of (100, 200); and for the non- marker genes, \(\lambda\) values were randomly sampled in the range of (10, 20). Spots were then created on a grid and the spot- resolution gene expression levels are aggregated values of the enclosed cells.
+
+(i) To assess the effect of different spot sizes, we simulated a series of spot diameters ranging from 25 to \(150 \mu m\), with nearby spots separated by \(100 \mu m\). (ii) To assess the effect of cell missouts, we randomly dropped \(10\%\), \(20\%\), \(30\%\), and \(40\%\) of the cells. (iii) To assess the effect of the false connections in the cell-cell network, we added randomized connections in the cell-cell network, until \(10\%\), \(20\%\), \(30\%\), and \(40\%\) of the cells contained randomized connections. In this evaluation, we did not directly use an
+
+<--- Page Split --->
+
+image, instead, the cell positions were predefined, and the cell types were converted to one- hot vectors as image features. These features, combined with the generated spot- level gene expression, constituted the input for Thor, using default parameters to infer the cell- level ST data.
+
+Additionally, to systematically assess the effect of technical dropouts, we simulated single- cell gene expression using the R package Splatter \(^{91}\) with no dropouts and with variable levels of dropouts. Splatter models the probability of transcript dropouts using a logistic function based on the mean expression levels \(P_{\text{dropout}}(x) = 1 / (1 + e^{- k*(x - x_0)}),\) where \(x\) is the mean expression level. The probability of transcript dropouts are controlled by two parameters, the midpoint parameter \((x_0\) or dropout. mid) and the shape parameter \((k\) or dropout. shape). The former is the expression level at which \(50\%\) cells are zero, and the latter controls how quickly the probabilities change from the midpoint. To simulate a wide range of dropout conditions, we used combinations of dropout. mid values [1, 2, 3, 4, 5] and dropout. shape values [- 1, - 2, - 5], with percentages of zero reads up to \(63\%\) . This allowed comprehensive assessment of the impact of varying dropout levels on Thor's performance. Spot- level gene expressions generated from these single- cell simulations with dropout were then used as inputs for Thor.
+
+We employed the Silhouette coefficient and Calinski- Harabasz index to measure the separation of clusters. The scores were calculated on the PCA embeddings of the corresponding gene expression arrays using the functions from the library scikit- learn. We randomly sampled 3,000 cells (without replacement out of all the 6,579 cells) 10 times in the calculation of the mean Silhouette coefficients for statistical significance.
+
+The MERFISH data of the mouse brain receptor map consists of 83,538 cells and 483 genes. We simulated Visium- like spot- level data by creating a grid of evenly spaced "spots". The molecule counts in a synthetic spot were aggregated over all the cells covered by the "spot". The spot size was set to \(100 \mu m\) and a total of 4,870 spots were simulated. We focused on the hippocampus region (Figure S4a), which consists of 535 spots covering 8,597 cells. For visualization purposes, major Leiden cell clusters in the original data were annotated according to the cellular locations in the hippocampus components and a previous study \(^{19}\) . Minor cell clusters were merged and labeled as "Others". A DAPI image in the dataset and the generated spot- level gene expression were jointly analyzed by Thor. For comparison, the positions of cells segmented from the source were used as our cell positions. Image features including the mean and standard deviation of the grayness and the entropy of image patches surrounding the cells were calculated. The predicted transcriptome and the ground truth transcriptome were integrated by harmony \(^{92}\) .
+
+## Evaluating cell-level spatial gene expression prediction accuracy
+
+We used the root mean square error and structural similarity index to quantify the prediction accuracy for each gene. In the simulation datasets, NRMSE was employed to calculate the mean deviation of the predicted gene expression from the ground truth data in all cells, as defined in Eqn. 10.
+
+\[\mathrm{NRMSE}\stackrel {\mathrm{def}}{=}\frac{\sqrt{\frac{\sum_{i = 1}^{n}(x_{i}^{\mathrm{pred}} - x_{i}^{\mathrm{truth}})^{2}}{n}}}{\frac{\sum_{i = 1}^{n}x_{i}^{\mathrm{truth}}}{n}} \quad (10)\]
+
+where \(x_{i}^{\mathrm{pred}}(x_{i}^{\mathrm{truth}})\) is the predicted (ground truth) gene expression in cell \(i\) ; and \(n\) is the number of cells.
+
+<--- Page Split --->
+
+To assess the performance of predicted gene expressions by Thor and other methods, we calculated two pixel- centric metrics including SSIM, RMSE (pixels) and a cell- centric metric RMSE (cells). For pixel- centric metrics, similar to the methodology from the iStar study17, both the ground truth and predicted gene expression were treated as grayscale images. Considering spatial contexts within the images, we calculated SSIM between the spatial structures of the ground truth and predicted gene expression images. Practically, we observed slight local distortions and shifts existed between the Visium and Xenium slides. For a more reliable measure of the prediction quality prediction, we therefore calculated the Complex Wave SSIM, which is insensitive to consistent spatial translation93. SSIM values range from 0 to 1, with 1 indicating identical images and 0 indicating no similarity. For cell- centric metrics, we aggregated the nearby gene expression of super- pixels to the ground truth cells.
+
+## Comparison between Thor results and pathology annotation
+
+To quantitatively assess Thor's semi- supervised annotation function, we compared Thor against spot- level expert annotations. Because Thor assigns labels at the single- cell level, we employed majority voting to map these cell- level annotations to each spot. This allowed a direct comparison with expert- labeled spots. We report two commonly used classification metrics, accuracy, and area under the curve (AUC) as defined below. Accuracy is defined as the ratio of correct predictions to the total number of predictions. The area under the receiver operating characteristic (ROC) curve, which plots the true positive rate (sensitivity) against the false positive rate (1 - specificity) at various threshold settings. A higher AUC suggests better overall classification performance.
+
+To quantitatively assess Thor's prediction of aneuploid cells through CNV analysis, we compared against pathology- annotated tumor regions. We used two metrics F1 score and the Jaccard index. F1 score is calculated as the harmonic mean of precision and recall, and a higher F1 score indicates a better balance between precision (the proportion of predicted positives that are truly positive) and recall (the proportion of true positives that are correctly identified). Jaccard index measures the degree of overlap between predicted and reference sets by dividing the size of their intersection by the size of their union; values closer to 1 indicate a higher concordance between the two.
+
+## Human bladder cancer sample Visium HD data collection
+
+Pre- treatment formalin- fixed paraffin- embedded (FFPE) tissue blocks were obtained from patients diagnosed with muscle- invasive bladder cancer (MIBC). All samples were collected under an approved IRB protocol (PRO00037670), and written informed consent was obtained from all participants prior to tissue collection. Standard- of- care procedures were used to preserve and process the tissues. For spatial transcriptomics, \(10 \mu m\) sections were cut from the FFPE blocks and mounted onto Visium HD Spatial Gene Expression slides (10x Genomics). Sections were prepared in accordance with the manufacturer's guidelines (10x Genomics). All subsequent steps were performed following the Visium HD sample preparation protocol.
+
+## Code availability
+
+All the source codes are attached as supplementary files. We will release them on GitHub upon acceptance of the manuscript.
+
+## Acknowledgments
+
+This work was supported by Houston Methodist internal grant to G.W., National Institute of General Medical Sciences of the National Institutes of Health (1R35GM150460 to G.W., 1R35GM151089 to Q.S.), National Heart, Lung, and Blood Institute to L.L (HL169204- 01A1),
+
+<--- Page Split --->
+
+and National Cancer Institute (U54CA274375, R01CA175397 to K.S.C). This work utilized the Houston Methodist Neal Cancer Center Spatial Omics Core. The Core was funded by Cancer Prevention and Research Institute of Texas (CPRIT: RR230010). We appreciate Drs. Qin Ma and Jordan Krull from the Ohio State University for critical reading and discussion.
+
+## Contributions
+
+G.W. supervised the study. P.Z. and G.W. designed and developed the graph diffusion model. P.Z., W.C., T.N.T, I.K., and S.L. performed the data analyses. P.Z., T.N.T., and M.Z. developed the web platform. L.L. and K.N.C. prepared the post- LVAD patient tissues and performed the IF staining. Y.Y. annotated the bladder cancer tissue image. X.H., F.N., and K.S.C prepared the bladder cancer sample for Visium HD sequencing. P.Z., W.C., K.N.C., L.L., and G.W. wrote the manuscript. Q.S. helped supervise the development of the web platform. L.L. supervised the IF staining experiments. All authors contributed to writing the manuscript and provided approval for the submitted version.
+
+## Ethics declarations
+
+Competing interests The authors declare no competing interests.
+
+## References
+
+1. Bressan, D., Battistoni, G. & Hannon, G.J. The dawn of spatial omics. Science 381, eabq4964 (2023).
+2. Lu, M.Y. et al. Data-efficient and weakly supervised computational pathology on whole-slide images. Nat Biomed Eng 5, 555-570 (2021).
+3. Mobadersany, P. et al. Predicting cancer outcomes from histology and genomics using convolutional networks. Proc Natl Acad Sci U S A 115, E2970-E2979 (2018).
+4. Huang, Z., Bianchi, F., Yuksekgonul, M., Montine, T.J. & Zou, J. A visual-language foundation model for pathology image analysis using medical Twitter. Nat Med 29, 2307-2316 (2023).
+5. Nirschl, J.J. et al. in Deep Learning for Medical Image Analysis. (eds. S.K. Zhou, H. Greenspan & D. Shen) 179-195 (Academic Press, 2017).
+6. Pati, P. et al. Hierarchical graph representations in digital pathology. Medical image analysis 75, 102264 (2022).
+7. Stringer, C., Wang, T., Michaelos, M. & Pachitariu, M. Cellpose: a generalist algorithm for cellular segmentation. Nat Methods 18, 100-106 (2021).
+8. Stirling, D.R. et al. CellProfiler 4: improvements in speed, utility and usability. BMC Bioinformatics 22, 433 (2021).
+9. Greenwald, N.F. et al. Whole-cell segmentation of tissue images with human-level performance using large-scale data annotation and deep learning. Nature Biotechnology 40, 555-565 (2022).
+10. He, B. et al. AI-enabled in silico immunohistochemical characterization for Alzheimer's disease. Cell Rep Methods 2, 100191 (2022).
+11. Jaume, G. et al. Modeling Dense Multimodal Interactions Between Biological Pathways and Histology for Survival Prediction. arXiv preprint arXiv:2304.06819 (2023).
+12. Jain, S. et al. Advances and prospects for the Human BioMolecular Atlas Program (HuBMAP). Nat Cell Biol 25, 1089-1100 (2023).
+13. Zhuang, X. Spatially resolved single-cell genomics and transcriptomics by imaging. Nature Methods 18, 18-22 (2021).
+14. Zhao, E. et al. Spatial transcriptomics at subspot resolution with BayesSpace. Nat Biotechnol 39, 1375-1384 (2021).
+
+<--- Page Split --->
+
+1280 15. Hu, J. et al. Deciphering tumor ecosystems at super resolution from spatial transcriptomics with TESLA. Cell Syst 14, 404- 417 e404 (2023).1282 16. Bergenstrahle, L. et al. Super-resolved spatial transcriptomics by deep data fusion. Nat Biotechnol 40, 476- 479 (2022).1284 17. Zhang, D. et al. Inferring super-resolution tissue architecture by integrating spatial transcriptomics with histology. Nat Biotechnol (2024).1286 18. Vahid, M.R. et al. High-resolution alignment of single-cell and spatial transcriptomes with CytoSPACE. Nat Biotechnol 41, 1543- 1548 (2023).1288 19. Biancalani, T. et al. Deep learning and alignment of spatially resolved single-cell transcriptomes with Tangram. Nat Methods 18, 1352- 1362 (2021).1290 20. Kleshchevnikov, V. et al. Cell2location maps fine- grained cell types in spatial transcriptomics. Nat Biotechnol 40, 661- 671 (2022).1292 21. Liang, Y. et al. PROST: quantitative identification of spatially variable genes and domain detection in spatial transcriptomics. Nat Commun 15, 600 (2024).1294 22. Jiang, J. et al. METI: deep profiling of tumor ecosystems by integrating cell morphology and spatial transcriptomics. Nat Commun 15, 7312 (2024).1296 23. Hao, Y. et al. Dictionary learning for integrative, multimodal and scalable single-cell analysis. Nat Biotechnol 42, 293- 304 (2024).1298 24. Palla, G. et al. Squidpy: a scalable framework for spatial omics analysis. Nat Methods 19, 171- 178 (2022).1300 25. Pham, D. et al. Robust mapping of spatiotemporal trajectories and cell- cell interactions in healthy and diseased tissues. Nat Commun 14, 7739 (2023).1302 26. Chen, K.H., Boettiger, A.N., Moffitt, J.R., Wang, S. & Zhuang, X. RNA imaging. Spatially resolved, highly multiplexed RNA profiling in single cells. Science 348, aaa6090 (2015).1304 27. Chen, A. et al. Spatiotemporal transcriptomic atlas of mouse organogenesis using DNA nanoball- patterned arrays. Cell 185, 1777- 1792 e1721 (2022).1306 28. Janesick, A. et al. High resolution mapping of the tumor microenvironment using integrated single- cell, spatial and in situ analysis. Nat Commun 14, 8353 (2023).1308 29. Van de Sande, B. et al. Applications of single- cell RNA sequencing in drug discovery and development. Nat Rev Drug Discov 22, 496- 520 (2023).1310 30. Niazi, M.K.K., Parwani, A.V. & Gurcan, M.N. Digital pathology and artificial intelligence. Lancet Oncol 20, e253- e261 (2019).1312 31. Swanson, K., Wu, E., Zhang, A., Alizadeh, A.A. & Zou, J. From patterns to patients: Advances in clinical machine learning for cancer diagnosis, prognosis, and treatment. Cell 186, 1772- 1791 (2023).1315 32. Rodriques, S.G. et al. Slide- seq: A scalable technology for measuring genome- wide expression at high spatial resolution. Science 363, 1463- 1467 (2019).1317 33. Lein, E.S. et al. Genome- wide atlas of gene expression in the adult mouse brain. Nature 445, 168- 176 (2007).1319 34. Tepe, B. et al. Single- Cell RNA- Seq of Mouse Olfactory Bulb Reveals Cellular Heterogeneity and Activity- Dependent Molecular Census of Adult- Born Neurons. Cell Rep 25, 2689- 2703 e2683 (2018).1322 35. Cortal, A., Martignetti, L., Six, E. & Rausell, A. Gene signature extraction and cell identity recognition at the single- cell level with Cell- ID. Nat Biotechnol 39, 1095- 1102 (2021).1324 36. DeTomaso, D. & Yosef, N. Hotspot identifies informative gene modules across modalities of single- cell genomics. Cell Syst 12, 446- 456 e449 (2021).1326 37. Kanemaru, K. et al. Spatially resolved multiomics of human cardiac niches. Nature 619, 801- 810 (2023).1328 38. Learmonth, M., Corker, A., Dasgupta, S. & DeLeon- Pennell, K.Y. Regulation of cardiac fibroblasts by lymphocytes after a myocardial infarction: playing in the major league. Am J Physiol Heart Circ Physiol 325, H553- H561 (2023).
+
+<--- Page Split --->
+
+1331 39. Ramos, G., Hofmann, U. & Frantz, S. Myocardial fibrosis seen through the lenses of T- 1332 cell biology. J Mol Cell Cardiol 92, 41- 45 (2016). 1333 40. Kuppe, C. et al. Spatial multi- omic map of human myocardial infarction. Nature 608, 766- 1334 777 (2022). 1335 41. Frangogiannis, N.G. Cardiac fibrosis. Cardiovasc Res 117, 1450- 1488 (2021). 1336 42. Muller- Dott, S. et al. Expanding the coverage of regulons from high- confidence prior 1337 knowledge for accurate estimation of transcription factor activities. Nucleic Acids Res 1338 (2023). 1339 43. Khalil, H. et al. Fibroblast- specific TGF- beta- Smad2/3 signaling underlies cardiac 1340 fibrosis. J Clin Invest 127, 3770- 3783 (2017). 1341 44. Wohlfahrt, T. et al. PU.1 controls fibroblast polarization and tissue fibrosis. Nature 566, 1342 344- 349 (2019). 1343 45. Maybaum, S. et al. Cardiac improvement during mechanical circulatory support: a 1344 prospective multicenter study of the LVAD Working Group. Circulation 115, 2497- 2505 1345 (2007). 1346 46. Jakovljevic, D.G. et al. Left Ventricular Assist Device as a Bridge to Recovery for 1347 Patients With Advanced Heart Failure. J Am Coll Cardiol 69, 1924- 1933 (2017). 1348 47. Luxan, G. & Dimmeler, S. The vasculature: a therapeutic target in heart failure? 1349 Cardiovasc Res 118, 53- 64 (2022). 1350 48. Ge, W. et al. PLA2G2A(+) cancer- associated fibroblasts mediate pancreatic cancer 1351 immune escape via impeding antitumor immune response of CD8(+) cytotoxic T cells. 1352 Cancer Lett 558, 216095 (2023). 1353 49. Koenig, A.L. et al. Single- cell transcriptomics reveals cell- type- specific diversification in 1354 human heart failure. Nat Cardiovasc Res 1, 263- 280 (2022). 1355 50. Meng, S. et al. Reservoir of Fibroblasts Promotes Recovery From Limb Ischemia. Circulation 142, 1647- 1662 (2020). 1357 51. Lai, L., Reineke, E., Hamilton, D.J. & Cooke, J.P. Glycolytic Switch Is Required for 1358 Transdifferentiation to Endothelial Lineage. Circulation 139, 119- 133 (2019). 1359 52. Zhu, S. et al. STIE: Single- cell level deconvolution, convolution, and clustering in in situ 1360 capturing- based spatial transcriptomics. Nat Commun 15, 7559 (2024). 1361 53. Cable, D.M. et al. Robust decomposition of cell type mixtures in spatial transcriptomics. 1362 Nat Biotechnol 40, 517- 526 (2022). 1363 54. Estiar, M.A. & Mehdipour, P. ATM in breast and brain tumors: a comprehensive review. 1364 Cancer Biol Med 15, 210- 227 (2018). 1365 55. Wei, R. et al. Spatial charting of single- cell transcriptomes in tissues. Nat Biotechnol 40, 1190- 1199 (2022). 1366 56. Meylan, M. et al. Tertiary lymphoid structures generate and propagate anti- tumor 1367 antibody- producing plasma cells in renal cell cancer. Immunity 55, 527- 541 e525 (2022). 1368 57. Polanski, K. et al. Bin2cell reconstructs cells from high resolution Visium HD data. 1369 Bioinformatics 40 (2024). 1370 58. Gronbech, C.H. et al. scVAE: variational auto- encoders for single- cell gene expression 1371 data. Bioinformatics 36, 4415- 4422 (2020). 1372 59. Lopez, R., Regier, J., Cole, M.B., Jordan, M.I. & Yosef, N. Deep generative modeling for 1373 single- cell transcriptomics. Nat Methods 15, 1053- 1058 (2018). 1374 60. Xu, H. et al. SPACEL: deep learning- based characterization of spatial transcriptome 1375 architectures. Nat Commun 14, 7603 (2023). 1376 61. Badia, I.M.P. et al. decoupleR: ensemble of computational methods to infer biological 1377 activities from omics data. Bioinform Adv 2, vbac016 (2022). 1378 62. Gao, R. et al. Delineating copy number and clonal substructure in human tumors from 1380 single- cell transcriptomes. Nat Biotechnol 39, 599- 608 (2021).
+
+<--- Page Split --->
+
+1381 63. Cang, Z. et al. Screening cell-cell communication in spatial transcriptomics via collective 1382 optimal transport. Nat Methods 20, 218- 228 (2023). 1383 64. Wu, Z. et al. Graph deep learning for the characterization of tumour microenvironments 1384 from spatial protein profiles in tissue specimens. Nat Biomed Eng 6, 1435- 1448 (2022). 1385 65. Gracia Villacampa, E. et al. Genome- wide spatial expression profiling in formalin- fixed 1386 tissues. Cell Genom 1, 100065 (2021). 1387 66. Rimm, D.L. What brown cannot do for you. Nat Biotechnol 24, 914- 916 (2006). 1388 67. Schmidt, U., Weigert, M., Broaddus, C. & Myers, G. in Medical Image Computing and 1389 Computer Assisted Intervention 265- 273 (Springer, 2018). 1390 68. Horst, F. et al. Cellvit: Vision transformers for precise cell segmentation and 1391 classification. Medical Image Analysis 94, 103143 (2024). 1392 69. Ma, J. et al. Segment anything in medical images. Nat Commun 15, 654 (2024). 1393 70. Pachitariu, M. & Stringer, C. Cellpose 2.0: how to train your own model. Nat Methods 19, 1634- 1641 (2022). 1395 71. Greenwald, N.F. et al. Whole- cell segmentation of tissue images with human- level 1396 performance using large- scale data annotation and deep learning. Nat Biotechnol 40, 555- 565 (2022). 1398 72. Bannon, D. et al. DeepCell Kiosk: scaling deep learning- enabled cellular image analysis 1399 with Kubernetes. Nat Methods 18, 43- 45 (2021). 1400 73. Xu, H. et al. A whole- slide foundation model for digital pathology from real- world data. 1401 Nature 630, 181- 188 (2024). 1402 74. Chen, R.J. et al. Towards a general- purpose foundation model for computational 1403 pathology. Nat Med 30, 850- 862 (2024). 1404 75. Wang, X. et al. A pathology foundation model for cancer diagnosis and prognosis 1405 prediction. Nature 634, 970- 978 (2024). 1406 76. Oliveira, M.F. et al. Characterization of immune cell populations in the tumor 1407 microenvironment of colorectal cancer using high definition spatial profiling. bioRxiv, 2024.2006.2004.597233 (2024). 1409 77. Kamel, M. et al. ENACT: End- to- End Analysis of Visium High Definition (HD) Data. 1410 bioRxiv, 2024.2010.2017.618905 (2024). 1411 78. You, Y. et al. Systematic comparison of sequencing- based spatial transcriptomic 1412 methods. Nat Methods 21, 1743- 1754 (2024). 1413 79. Sekh, A.A. et al. Physics- based machine learning for subcellular segmentation in living 1414 cells. Nature Machine Intelligence 3, 1071- 1080 (2021). 1415 80. Glancy, B. MitoNet: A generalizable model for segmentation of individual mitochondria 1416 within electron microscopy datasets. Cell Syst 14, 7- 8 (2023). 1417 81. Lu, M. et al. ERnet: a tool for the semantic segmentation and quantitative analysis of 1418 endoplasmic reticulum topology. Nat Methods 20, 569- 579 (2023). 1419 82. Taubin, G. Curve and surface smoothing without shrinkage. Proc Ieee Int Conf Comput 1420 Vis, 852- 857 (1995). 1421 83. van Dijk, D. et al. Recovering Gene Interactions from Single- Cell Data Using Data 1422 Diffusion. Cell 174, 716- 729 e727 (2018). 1423 84. Wolf, F.A., Angerer, P. & Theis, F.J. SCANPY: large- scale single- cell gene expression 1424 data analysis. Genome Biol 19, 15 (2018). 1425 85. Zhu, J., Sun, S. & Zhou, X. SPARK- X: non- parametric modeling enables scalable and 1426 robust detection of spatial expression patterns for large spatial transcriptomic studies. Genome Biol 22, 184 (2021). 1428 86. Svensson, V., Teichmann, S.A. & Stegle, O. SpatialDE: identification of spatially variable 1429 genes. Nat Methods 15, 343- 346 (2018). 1430 87. Wu, S.Z. et al. A single- cell and spatially resolved atlas of human breast cancers. Nat 1431 Genet 53, 1334- 1347 (2021).
+
+<--- Page Split --->
+
+1432 88. Tepe, B. et al. Single-Cell RNA-Seq of Mouse Olfactory Bulb Reveals Cellular Heterogeneity and Activity-Dependent Molecular Census of Adult-Born Neurons. Cell Reports 25, 2689-2703. e2683 (2018). 1435 89. Khatri, P., Sirota, M. & Butte, A.J. Ten years of pathway analysis: current approaches and outstanding challenges. PLoS Comput Biol 8, e1002375 (2012). 1437 90. Muller-Dott, S. et al. Expanding the coverage of regulons from high-confidence prior knowledge for accurate estimation of transcription factor activities. Nucleic Acids Res 51, 10934-10949 (2023). 1439 91. Zappia, L., Phipson, B. & Oshlack, A. Splatter: simulation of single-cell RNA sequencing data. Genome Biol 18, 174 (2017). 1442 92. Korsunsky, I. et al. Fast, sensitive and accurate integration of single-cell data with Harmony. Nat Methods 16, 1289-1296 (2019). 1444 93. Zhou, W. & Simoncelli, E.P. in Proceedings. (ICASSP '05). IEEE International Conference on Acoustics, Speech, and Signal Processing, 2005., Vol. 2 ii/573-ii/576 Vol. 572 (2005).
+
+<--- Page Split --->
+
+## Figure legends
+
+Figure legendsFigure 1: Thor - a software suite for integrated analyses of histology and transcriptomics data at the in silico cell level. (a) Histological images and high- throughput sequencing data capture inherent cellular structures at different resolutions and share complementary information. The projection of the histological features to the first principal component highlights the tissue sections at cell resolution; meanwhile, expression patterns of marker genes of the cardiac smooth muscle cells (MYH11) and the fibroblast cells (RARRES2) demonstrate consistent patterns at spot resolution. The cell- cell network is constructed according to the distances in the combinatory feature space of histology (including location) and transcriptomics. In the example and illustration of cell- cell network, the nodes represent cells, edges represent connections, and the colors indicate cell types. Thor infers single- cell spatial transcriptome by utilizing an anti- shrinking Markov graph diffusion model. The expression profile of the marker gene MYH11 in smooth muscle aligns with the texture of the H&E staining image, as visualized by the Mjolnir web platform. (b) Thor adapts and implements a diversity of modules for advanced single- cell analyses around the inferred spatially resolved whole transcriptome of the in silico cells. (c) The Mjolnir platform supports interactive multi- modal tissue analysis.
+
+Figure 2: Thor accurately predicts single-cell spatial gene expression in human breast cancer. (a) Spatial gene expression of in silico cells inferred from the Visium data and the H&E staining image of a breast cancer tissue by Thor align closely with Xenium data from the adjacent tissue section. The numbers on the H&E staining image mark DCIS regions of interest. (b) Thor- inferred spatial transcriptome of in silico cells demonstrate consistent cell clusters with Xenium using scRNA- seq clustering. The cluster annotations were adapted from the original study of the dataset28. The mean expression levels of differentially expressed genes in each cluster were visualized using heatmaps. (c) Thor outperforms iStar in the prediction of spatial gene expression. (d) Spatial expression profiles of representative genes at the region of interest level are compared between Thor, iStar, and Xenium. Thor- inferred spatial gene expression closely aligns with the Xenium data, while iStar introduces artifacts at segment boundaries (the red arrows) and in regions with sparse cells (the blue arrow).
+
+Figure 3: Thor detects fibrotic regions in multiple human heart tissues with MI. (a) H&E staining images of tissues from a remote zone (RZ1), an ischaemic zone (IZ1), and a fibrotic zone (FZ1). Purple and green squares mark curated ROIs and are annotated as fibrotic and non- fibrotic regions. Close- up views of the cell morphology and inferred cellular expression of the fibroblast marker gene PDGFRA are provided for the curated ROIs. (b) Mjolnir- annotated fibrotic regions (blue) are visualized on the H&E staining images. T cell proliferation pathway enrichment scores are calculated based on the top highly expressed genes in each cell. (c) Barplot the percentages of the fibrotic regions in all six samples. (d) Heatmap of the GO pathway enrichment based on the up- regulated DEGs (fold change \(> 2\) , adjusted p_value \(< 0.01\) using t- test) in the fibrotic region compared to the non- fibrotic region in each sample, and the up- regulated DEGs (fold change \(> 2\) , adjusted p_value \(< 0.01\) using t- test) in the non- fibrotic region compared to the fibrotic region in each sample. (e) TF activity is inferred from the in silico cell spatial transcriptome. We use RTN (R package) for the transcriptional network inference and Cytoscape for network visualization.
+
+Figure 4: Thor identifies regenerative signatures in vessels in human heart failure. (a) Thor infers cell- level gene expression, expression of the smooth muscle marker MYH11 are visualized at the spot level and the cell level on sample I tissue. Utilizing Mjolnir, vessel regions are annotated. The expression of MYH11 in selected vessels (labelled 1- 4) is recovered by Thor, where there exhibits low expression of MYH11 at the spot resolution. (b) The upregulated
+
+<--- Page Split --->
+
+genes in the vessels shared by two samples are ranked according to the gene scores. (c) Cells in the vessel regions are divided into two groups according to PLA2G2A expression levels. A cutoff of 0.5 is used, where the first and the second Gaussian distributions overlap. (d) GO pathway enrichment using the top 500 upregulated DEGs (with the lowest adjusted \(p\) - values) in the PLA2G2A \(^+\) cells. (e) IF staining views of protein level PLA2G2A expression in post- LVAD patient tissues.
+
+Figure 5: Thor provides unbiased screening of hallmarks in cancer. (a) H&E staining image of the DCIS tissue. The annotation of eighteen major tumor regions (T1- T18) in the DCIS tissue is adapted from the annotation by pathology experts (Agoko NV, Belgium). (b) Leiden clusters of the segmented cells using morphological features. The list of image features and details of Leiden clustering are provided in Supplementary Note 1. Colors represent cell clusters. (c) The spatial distribution of cell types. Cell types are obtained by Cell- ID using the Thor- inferred spatial transcriptome of the in silico cells and refined with cell type markers. (d) VEGFA gene expression pattern at tissue and cell scales in tumor region T1. (e) The tumor regions identified by high attention values in CLAM and semi- supervised annotation in Mjolnir. The black dotted square marks a high- attention region where adipocytes are predominantly located. (f) Heatmap of the copy number profiles inferred by CopyKAT based on the in silico cell- level transcriptome predicted by Thor. A selected list of breast cancer- related genes is provided. (g) Aneuploid (tumor) and diploid (non- tumor) regions inferred by CopyKAT show consistent results between in silico cell- level transcriptome and spot data.
+
+Figure 6: Thor reveals mechanistic insights into the immune response of DCIS. (a) Cell- level TLS scores. The TLS score is calculated based on 29 genes. (b) Boxplot of the TLS scores in the 18 tumor regions. The tumor regions are ranked according to the median TLS score. The middle line in the box plot, median; box boundary, interquartile range; whiskers, 5- 95 percentile; minimum and maximum, not indicated in the boxplot. (c) Zoom- in view of the tumor regions with highest/lowest (T7/T15) TLS scores. The expression level of one DEG, CD84, is visualized in the inner and perimetral parts of the tumor regions. GO pathway enrichment is based on 300 up- regulated (fold change \(> 2\) , adjusted \(p\) - value \(< 0.01\) using t- test) and 300 down- regulated (fold change \(< 0.5\) , adjusted \(p\) - value \(< 0.01\) using t- test) DEGs between T7 and T15. (d) Heatmap of the GO pathway enrichment based on the up- regulated DEGs in each tumor region compared to the rest (fold change \(> 1.5\) , adjusted \(p\) - value \(< 0.05\) using t- test).
+
+Figure S1: Thor inference has a reliable performance on simulation data. (a) Expression profile of a gene in simulated spot- resolution data (spot separation: \(100 \mu m\) ), the ground truth, and Thor- predicted single- cell data. (b) Thor shows robust accuracy with cell- misouts or perturbations in the cell- cell network. NRMSE values provide a quantitative measure of the normalized deviation of Thor- inferred gene expression from the ground- truth gene expression. (c) Thor's accuracy in different spot sizes. The nearest spot method maps the expression of the closest spot to the cell; KNN smoothing takes the average of the twenty nearest neighbors; the subspot- level gene expression from BayesSpace is mapped to the identified cells using nearest cell neighbors. (d) Thor imputes gene expression with technical dropouts and recovers cluster separation. The error bars for the mean Silhouette coefficients are omitted as they are too small to visualize. The colors in the PCA plots represent the ground truth cell type information. "Drop %" in the table is calculated as the ratio of zeros in the count matrix of the simulated scRNA- seq data. For the box plots, the middle line in the box plot, median; box boundary, interquartile range; whiskers, 5- 95 percentile; minimum and maximum, not indicated in the boxplot; gray dots, individual data points.
+
+<--- Page Split --->
+
+Figure S2: Gene expression profiles in the simulated dataset. Spot-resolution data (spot separation: \(100 \mu m\) ), cell- resolution, and Thor- predicted single- cell data are visualized. Each row shows two marker genes for the same cell type.
+
+Figure S3: Visualization of cell missouts and different spot sizes. (a) In the single- cell spatial transcriptome data, the miss- detection of cells from \(10\%\) to \(40\%\) randomly leads to sparser cell distribution. (b) The proportion of homogeneous spots (characterized by low spot heterogeneity scores) decreases as spot size increases. Spot heterogeneity is quantified using the Shannon entropy of cell type proportions within a spot. (c) Thor demonstrates robust performance across varying levels of spot heterogeneity. Mean absolute error (MAE) is calculated between Thor- predicted and ground- truth gene expression levels. A, B, C mark one low- heterogeneity, and two high- heterogeneity clusters of the Thor data.
+
+Figure S4: Thor accurately predicts single- cell spatial gene expression from simulated spot- resolution gene expression in mouse hippocampus. (a) Cell- type distribution in the mouse hippocampus region from the MERFISH data (ground truth; left panel) and cell- type population in simulated spots (right panel). Spots in regions including the CA and DG, are composed of cells of diverse cell types. (b) Expression patterns of representative genes inferred by Thor (left panel), alongside the ground- truth MERFISH data (second panel), spot data (third panel), and subspot data (right panel). Pearson correlation coefficients are provided. (c) Clusters of the Thor- inferred in silico cells overlap well with the ground- truth cell clusters. (d) Quantitative evaluation of Thor clusters. The Silhouette coefficient and Calinski- Harabasz index are calculated based on the embeddings and the ground truth cell annotations. For BayesSpace, as the native output is sub- spot level gene expression, both the sub- spot level and cell- level metrics are considered (mapping the closest sub- spots to the cells).
+
+Figure S5: Visualization of cell- cell network and predicted gene expression in the simulated mouse cerebellum data. (a) In the analysis of this simulated dataset, Thor connects similar cells based on location and image features. Cells of similar types are interconnected (note: cell type information is not used in constructing the cell- cell network). (b) Thor refines gene expression in various regions of the mouse hippocampus, demonstrated by a few selected genes inferred by Thor (left panel), alongside the ground- truth MERFISH data (second panel), spot data (third panel), and subspot data (right panel). Pearson correlation coefficients are provided.
+
+Figure S6: UMAP embeddings of the Thor and Xenium integrated cells colored by modalities and by cell types. The embeddings were obtained from the PCA space by integration with harmonypy.
+
+Figure S7: Quantitative comparison between Thor and ST spatial resolution- enhancement tools. (a) Using image- level metrics, and (b) Using cell- level metrics. One- sided Mann- Whitney tests are performed between Thor and other two best- performing tools. For the box plots, the middle line in the box plot, median; box boundary, interquartile range; whiskers, 5- 95 percentile. (c) Spatial profiles of representative genes inferred by Thor and other tools. Xenium gene expression profiles are provided for reference. The CW- SSIM scores are included. (d) Spatial profiles of representative genes inferred by Thor and other tools. The RMSE of Min- Max normalized cell level expressions are provided. Nearest cell/superpixel/subspot expression levels are mapped to the Xenium cell positions.
+
+Figure S8: Expression profiles of genes in the human breast cancer tissues. Data predicted by Thor and iStar, along with Xenium and Visium measurement are compared. For
+
+<--- Page Split --->
+
+visualization, gene expression levels predicted by Thor and iStar are normalized in the whole tissue.
+
+Figure S9: Expression profiles of genes in ROIs of the human breast cancer tissues. Data predicted by Thor and iStar, along with measured by Xenium and Visium are compared in ROIs. H&E images of the ROIs are provided for reference. For visualization, gene expression levels predicted by Thor and iStar are normalized in the ROI.
+
+Figure S10: Thor reveals detailed mouse olfactory bulb layers. (a) Spatial expression profiles of genes in the mouse olfactory bulb using the ISH (first row), Stereo- seq (second row), Visium (third row), and Thor- inferred (fourth row) data. Selected regions (black boxes) are zoomed in for detailed inspection of gene expression in glomerular, mitral, and SEZ layers. (b) Spatial distribution of cell clusters and neuron subtypes based on the Thor- inferred single- cell gene expression. OSN: Olfactory sensory neuron, PGC: Periglomerular cell, GC: Granule cell, M/TC: Mitral/Tufted cell. (c) Genes are grouped into 8 modules based on pairwise local correlation using the package Hotspot. Marker genes for MOB layers are shown along corresponding gene modules. (d) Module scores of four gene modules are visualized with spatial context, as well as the Thor- inferred single- cell expression profiles of representative genes in the four modules. (e) Heatmap of the GO pathway enrichment of the four representative gene modules.
+
+Figure S11: Comparison between predicted expression profiles and gene expression patterns measured from other sources in MOB. The top row is the ISH images downloaded from Allen brain atlas; the second row is the predicted gene expression using Thor; the third row is the gene expression measured by Stereo- seq; the fourth row is the spot- level gene expression sequenced by Visium from 10x Genomics.
+
+Figure S12: Quantitative assessment of Thor's semi- supervised annotation against spot- level expert annotations. (left panel) H&E image, (second panel) spot- level pathology annotations, (third panel) Thor's cell- level annotations, and (right panel) Thor's cell- level annotation mapped to the spots using majority voting (>50%) of representative samples in each tissue type including vessel, node, adipose, and fibrosis. The metrics are calculated based on spot- level annotations.
+
+Figure S13: Comparison between Thor's semi- supervised annotation and the spot- level clustering. (a) H&E staining image and expert annotations on the heart tissue sample. (b) Cells annotated via Thor's semi- supervised annotation. Annotation of cells are mapped to corresponding spots according to majority voting for quantitative evaluation against expert annotations. (c) K- means clusters solely based on Visium ST data. Regardless of the number of clusters used, Visium ST data alone fails to accurately distinguish vessel- associated spots (enriched with smooth muscle and endothelial cells) from some myocardium spots with high TAGLN (a smooth muscle marker) expression.
+
+Figure S14: Curated fibrotic ROIs in human myocardial infarction tissues. H&E staining images of all the tissues from remote, ischaemic, and fibrotic zones. The predicted single- cell expression of the fibroblast marker gene (FBLN2) and cardiac muscle- associated gene (MEF2A) are visualized in the curated ROIs.
+
+Figure S15: DEGs between the curated fibrotic and non- fibrotic regions in the RZ1, IZ1, and FZ1 tissues. H&E staining images of RZ1, IZ1, and FZ1 tissues and Thor- predicted single- cell expression of the fibroblast marker gene (FBLN2) and cardiac muscle- associated genes
+
+<--- Page Split --->
+
+(CASQ2 and PKP2) are visualized in the curated ROIs. F and NF stand for fibrotic region and non- fibrotic region, respectively.
+
+Figure S16: Semi- supervised annotation selects fibrotic regions in shallow areas in human myocardial infarction tissues. Thor- annotated fibrotic regions (blue) are visualized on the H&E staining images of RZ2, IZ2, and FZ2 tissues. Thor- predicted cell- level expression profiles of fibroblast marker genes (PDGFRA and FBLN2) and cardiac muscle- associated genes (CASQ2 and PKP2) are visualized in the curated ROIs.
+
+Figure S17: Expression patterns of fibrotic- specific and cardiac muscle- associated genes in human myocardial infarction tissues. Fibroblast marker genes (PDGFRA and FBLN2), and cardiac muscle- associated genes (CASQ2 and PKP2) are visualized on top of the whole tissues.
+
+Figure S18: GO pathway enrichment and TF activity in human heart tissues with MI. (a) The GO pathway enrichment scores are calculated based on the gene expression in each in silico cell using the Python library decoupler. (b) The TF activity scores are calculated based on the gene expression in each in silico cell. The database CollectRI and Python library decoupler are used for inferring the TF activity.
+
+Figure S19: Gene expression patterns in vessels in human heart failure. (a) Thor infers cell- level gene expression, expression of the smooth muscle marker MYH11 are visualized at the spot level and the cell level on sample II tissue. (b) The expression profiles of MYH11 in selected vessels are visualized at the spot resolution and the cell resolution. (c) Vessel regions are annotated utilizing Mjolnir. (d) Venn diagram of the upregulated genes in the vessels from two samples. (e) Spatial context and morphology of cells with high / low PLA2G2A expression in post- LVAD patient tissues.
+
+Figure S20: The inferred cell type distribution in DCIS by (a) Thor, (b) CytoSPACE, and (c) RCTD. Expression profiles of tumor and macrophage marker genes are provided for reference. The aneuploid (tumor) and diploid (non- tumor) cell distributions inferred by CopyKAT using CytoSPACE- mapped gene expression is comparable to Thor result.
+
+Figure S21: Expression profiles of genes in DCIS. (a) Thor- predicted single- cell spatial gene expression; (b) Spot- resolution spatial gene expression from the Visium data.
+
+Figure S22: Semi- supervised annotation selects tumor cells in tumor region T7 in DCIS. The curated rectangular region is marked with a black box.
+
+Figure S23: 2D density plots of the expression of oncogene and tumor suppressor gene in DCIS. (a) Expressions of the oncogene ERBB2 and tumor suppressor gene ATM are plotted in tumor regions with highest TLS scores (T7, T1, and T14) and lowest TLS scores (T11, T6, and T15), where cells are colored according to the density. (b) The predicted spatial expression levels of the two genes by Thor and the fold changes between the oncogene and the tumor suppressor.
+
+Figure S24: Enrichment of hallmark pathways in DCIS. The hallmark pathway enrichment is performed using decoupler with Thor- predicted cell- level transcriptome and the MSigDB hallmark gene sets as input.
+
+<--- Page Split --->
+
+Figure S25: Comparison of tumor regions with highest and lowest TLS scores and their interactions with surrounding environments. (a) Zoom- in view of the tumor regions of highest (T7 and T1) and lowest (T6 and T15) TLS scores. Thor- predicted expression of DEGs is visualized in the inner and perimetral parts of the tumor regions. (b) Interaction between tumor regions and the surrounding environments. The orange dashed lines mark the pathology- annotated tumor region boundaries.
+
+Figure S26: Thor imputes Visium HD data and reconstructs gene expression patterns that align with pathology annotations in a bladder cancer sample. (a) Pathology annotations (left) highlight immune cells (ROI 1), invasive carcinoma (ROI 2), and a tumor fragment (ROI 3). Gene expression patterns inferred by Thor (middle) and from Visium HD (right). The orange arrow points to a region with no cell. (b) Cell clusters by Thor with a zoomed- in view of ROI 1. (c) Bin clusters by Visium HD 8 \(\mu m\) bin data with a zoomed- in view of ROI 1.
+
+Figure S27: Sensitivity analyses of Thor inference on (a) graph construction parameters, (b) the diffusion steps, and (c) VAE latent dimensions. Mean Pearson correlation coefficients between every pair of parameter settings for all genes are plotted. Spatial distributions of a representative gene Penk are provided to illustrate the influence of diffusion steps and latent dimension on interference.
+
+<--- Page Split --->
+
+## Figures
+
+图
+
+Figure 1
+
+Revised Figure 4
+
+Figure 2
+
+Revised Figure 6
+
+Figure 3
+
+Revised Figure 5
+
+Figure 4
+
+Revised Figure 3
+
+Figure 5
+
+Figure 1
+
+Figure 6
+
+Revised Figure 2
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- nreditorialpolicychecklist.pdf- SupplementaryTables.xlsx- SupplementaryNote1.docx- sourcecode.zip- websitehtmls.zip
+
+<--- Page Split --->
+
+- Notebooksall.zip- supplementaryfigurescombined.pdf- nrreportingsummary.pdf- NCOMMS2453068Ars.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/images_list.json b/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..da73a30cdfcb3a9b1b67826f5880669b230e63ed
--- /dev/null
+++ b/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/images_list.json
@@ -0,0 +1,62 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1. Fe monodispersion on ZnCr2O4 spinel. HADDF-STEM images of (a) 4.48% Fe-Zn/Cr and (b) 7.78% Fe-Zn/Cr and corresponding EDS mappings of Fe element. (c) HADDF intensity",
+ "footnote": [],
+ "bbox": [
+ [
+ 117,
+ 150,
+ 880,
+ 808
+ ]
+ ],
+ "page_idx": 7
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2. Catalyst evaluation of monodispersed and enriched Fe. (a) Catalyst evaluation of pristine \\(\\mathrm{ZnCr_2O_4}\\) and different Fe-Zn/Cr with H-ZSM-5; reaction conditions: \\(350^{\\circ}\\mathrm{C}\\) , 2.0 MPa, space velocity \\(= 600\\mathrm{ml}\\mathrm{h}^{-1}\\cdot \\mathrm{g}_{\\mathrm{cat}}^{-1}\\) , \\(\\mathrm{CO:H_2 = 1:1}\\) . (b) The optimal space time yield (STY) of aromatics for different catalysts (note that the STYs were obtained at the optimized reaction conditions for each catalyst and the corresponding reaction conditions are summarized in table S3). (c) TOF and aromatic selectivity as functions of Fe contents in \\(\\mathrm{ZnCr_2O_4}\\) and reaction conditions are similar as A. (d) Comparison between reported Fe-based catalysts and isolated Fe-Zn/Cr + H-ZSM-5 catalyst on syngas conversion to aromatics. (e) Stability test of \\(4.48\\%\\) Fe-Zn/Cr + H-ZSM-5 catalytic system for \\(100\\mathrm{h}\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 133,
+ 82,
+ 876,
+ 370
+ ]
+ ],
+ "page_idx": 12
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig. 3. Understanding the role of monodispersed Fe in catalytic activity. (a) Thermodynamic phase diagram of Fe-doped \\(\\mathrm{ZnCr_2O_4}\\) (111) surfaces at varying temperatures and CO partial pressures \\((P_{\\mathrm{CO}})\\) (b) iDPC-STEM images of \\(4.48\\%\\) Fe-Zn/Cr. (c) iDPC-STEM intensity profiles along the corresponding dashed lines in B. (d) O 1s XPS spectra of \\(\\mathrm{ZnCr_2O_4}\\) and different Fe-Zn/Cr samples. (e) Projected electric field strength and vector map of \\(4.48\\%\\) Fe-Zn/Cr. (f) Differential charge density (cyan and yellow represent charge depletion and accumulation, respectively; the cutoff of the density-difference isosurface is \\(0.11\\mathrm{e~Å}^{-3}\\) ).",
+ "footnote": [],
+ "bbox": [
+ [
+ 130,
+ 117,
+ 880,
+ 440
+ ]
+ ],
+ "page_idx": 15
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4. The mechanism study of monodispersed Fe & pristine \\(\\mathrm{ZnCr_2O_4}\\) in syngas conversion.",
+ "footnote": [],
+ "bbox": [
+ [
+ 149,
+ 99,
+ 819,
+ 420
+ ]
+ ],
+ "page_idx": 17
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce.mmd b/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..e8d71b75feff8d116b81940fc2e46aea375a6295
--- /dev/null
+++ b/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce.mmd
@@ -0,0 +1,196 @@
+
+# Accelerating Syngas-to-Aromatic Conversion via Spontaneously Monodispersed Fe in ZnCr2O4 Spinel
+
+Guo Tian Tsinghua University Xinyan Liu University of Electronic Science and Technology of China Chenxi Zhang ( cxzhang@mail.tsinghua.edu.cn ) Tsinghua University https://orcid.org/0000- 0002- 1708- 9449 Xiaoyu Fan Tsinghua University Hao Xiong Tsinghua University https://orcid.org/0000- 0001- 5479- 7754 Xiao Chen Tsinghua University https://orcid.org/0000- 0003- 1104- 6146 Wenzheng Li Tsinghua University Binhang Yan Tsinghua University https://orcid.org/0000- 0003- 2833- 8022 Lan Zhang Beijing University of Technology Ning Wang Beijing University of Technology Hong- Jie Peng University of Electronic Science and Technology of China https://orcid.org/0000- 0002- 4183- 703X Fei Wei Tsinghua University https://orcid.org/0000- 0002- 1422- 9784
+
+# Article
+
+# Keywords:
+
+Posted Date: May 13th, 2022
+
+DOI: https://doi.org/10.21203/rs.3.rs- 1607273/v1
+
+<--- Page Split --->
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on September 22nd, 2022. See the published version at https://doi.org/10.1038/s41467-022-33217-9.
+
+<--- Page Split --->
+
+# Title: Accelerating Syngas-to-Aromatic Conversion via Spontaneously Monodispersed Fe in ZnCr₂O₄ Spinel
+
+Authors: Guo Tian†, Xinyan Liu†, Chenxi Zhang†, Xiaoyu Fan†, Hao Xiong†, Xiao Chen†,
+
+Wenzheng Li†, Binhang Yan†, Lan Zhang3, Ning Wang3, Hong-Jie Peng2, Fei Wei1\*
+
+# Affiliations:
+
+1. Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology,
+
+Department of Chemical Engineering, Tsinghua University, Beijing, China, 100084
+
+2. Institute of Fundamental and Frontier Sciences, University of Electronic Science and
+
+Technology of China, Chengdu 611731, Sichuan, China
+
+3. Faculty of Environment and Life, Beijing University of Technology, Beijing 100124, China
+
+† These authors contributed equally to this work
+
+\* Corresponding authors Fei Wei, email: wf- dce@tsinghua.edu.cn, Chenxi Zhang, email:
+
+cxzhang@mail.tsinghua.edu.cn, Xiao Chen, email: chenx123@tsinghua.edu.cn, Hong-Jie Peng:
+
+hjpeng@uestc.edu.cn.
+
+<--- Page Split --->
+
+## Abstract:
+
+Spontaneous monodispersion of Fe species and their stabilization in reactive atmospheres remain a key challenge in catalytic syngas chemistry. In this study, we present a catalyst with spontaneously monodispersed Fe on \(\mathrm{ZnCr_2O_4}\) , which shows remarkable performance in the syngas- to- aromatic reaction when coupled with a H- ZSM- 5 zeolite. Monodispersed Fe increases the turnover frequency from 0.54 to \(2.48\mathrm{h}^{-1}\) without sacrificing the record high selectivity total aromatic ( \(80\% - 90\%\) ) at a single pass. This is enabled by the activation of CO and \(\mathrm{H}_2\) at oxygen vacancy nearest to the isolated Fe site and the prevention of carbide formation. Atomic precise characterization and theoretical calculations shed light on the origin and implications of spontaneous Fe monodispersion.
+
+One Sentence Summary: Highly monodispersed Fe is realized on a \(\mathrm{ZnCr_2O_4}\) spinel and stabilized under a highly reactive atmosphere, showing record high catalytic performance in the syngas- to- aromatic reaction.
+
+<--- Page Split --->
+
+## Main Text:
+
+## Introduction
+
+The spontaneous dispersion of catalytically active species on a support has been widely investigated in heterogeneous catalysis due to interactions between the species and support \(^{1,2}\) . Highly dispersed or, more strictly, monodispersed active sites endow the supported catalysts with unique catalytic properties. Spontaneous monodispersion can also improve atomic efficiency. Metal oxides with weak internal cohesive energy, e.g., \(\mathrm{MoO}_3\) and \(\mathrm{NiO}\) , can be easily dispersed on supports such as \(\gamma\) - \(\mathrm{Al}_2\mathrm{O}_3\) and \(\mathrm{TiO}_2\) , manifesting as prototype designs of spontaneously dispersed active sites. Such spontaneous dispersion is driven by negative Gibbs free energy \((\Delta G < 0)\) of breaking internal bonds of oxides being dispersed and forming new bonds between dispersed species and support. From this thermodynamics perspective, the monodispersion of species with strong self- interaction, such as Fe and Pt, presents a daunting challenge in heterogeneous catalysis \(^{3- 5}\) .
+
+Confining Fe and Pt precursors into the cages of nanoporous materials is an effective means of preparing monodispersed catalysts that is paramount in many sectors of heterogeneous catalysis \(^{6}\) . However, owing to the high surface energy, monodispersed Fe and Pt species tend to migrate and agglomerate under reaction conditions, especially at elevated temperatures, which inevitably cause catalyst deactivation. For instance, Han et al. \(^{7}\) found that the formation of Fe nanoclusters resulted in the deactivation of monodispersed Fe- N- C catalysts in proton exchange membrane fuel cells. Improving the metal- support interaction using an oxygen- donor support was considered an efficient method to stabilize monodispersed species \(^{8}\) . Recently, Nie et al. \(^{9}\) demonstrated how atomically dispersed ionic \(\mathrm{Pt}^{2 + }\) was stabilized by \(\mathrm{CeO}_2\) to endure steam treatment, presenting a feasible way against catalyst sintering. In addition to agglomeration, reactive atmosphere such as
+
+<--- Page Split --->
+
+syngas can induce irreversible phase transition from metal to metal carbides, e.g. Fe to \(\mathrm{Fe_xC_y}\) , and the as- generated carbides further complicate the reaction pathways of syngas conversion and result in unwanted products \(^{10,11}\) . Therefore, how to stabilize monodispersed Fe species and to avoid \(\mathrm{Fe_xC_y}\) formation in a reactive atmosphere has become a major bottleneck in catalytic syngas conversion.
+
+In this study, we rationalized \(\mathrm{ZnCr_2O_4}\) spinel with abundant oxygen vacancies (Ov) as an oxygen- donor support. Fe could be spontaneously monodispersed on \(\mathrm{ZnCr_2O_4}\) via a simple impregnation method when the content of Fe was controlled less than 5 wt%. The octahedral site preference energies from the literature \(^{12}\) are in the order of \(\mathrm{Fe^{3 + } < Fe^{2 + } < Cr^{3 + } < Zn^{2 + }}\) , indicating that \(\mathrm{Fe^{2 + }}\) or \(\mathrm{Fe^{3 + }}\) prefers to occupy the octahedral sites, whereas \(\mathrm{Zn^{2 + }}\) tends to occupy the tetrahedral sites in the spinel structure. The spontaneously monodispersed Fe was found not only thermodynamically stable at high temperature but also resistive to carbonization in a reducing atmosphere. When coupled with a H- ZSM- 5 zeolite as a test, \(\mathrm{ZnCr_2O_4}\) with monodispersed Fe showed significantly improved syngas conversion efficiency (45%) with a turnover frequency (TOF) increased from 0.54 to 2.48 h\(^{- 1}\) ; while the high selectivity towards aromatics was maintained by preventing the formation of \(\mathrm{Fe_xC_y}\) . Moreover, the composite catalyst exhibited superior stability as no sign of decay in either the activity or total aromatic selectivity was observed for more than 100 h reaction at 350°C and 2.0 MPa. Density functional theory (DFT) calculations revealed that monodispersed Fe sites in \(\mathrm{ZrCr_2O_4}\) greatly reduced energy barriers of forming formaldehyde (H\(_2\)CO) and methanol (CH\(_3\)OH) from syngas, which were previously identified as key intermediates leading to aromatics \(^{13- 15}\) . This study not only demonstrates a promising monodispersed catalyst that is highly active, selective and stable in reactive syngas atmosphere but also sheds a light on spontaneous monodispersion of catalytically active species for heterogeneous catalysis.
+
+<--- Page Split --->
+
+## Results and Discussion
+
+## Identification of spontaneously monodispersed and enriched Fe
+
+\(Z n C r_{2}O_{4}\) spinels with increasing amounts of Fe (denoted as \(X\%\) Fe- Zn/Cr where X refers to the weight percentage of Fe) were prepared for investigation (supplementary fig.1). The identical crystal structure of \(Z n F e_{2}O_{4}\) and \(Z n C r_{2}O_{4}\) , as well as the similar atomic weights of Fe and Cr, makes it very challenging to identify the state of Fe in \(Z n C r_{2}O_{4}\) 16,17. High- angle annular dark- field scanning transmission electron microscopy (HADDF- STEM) images of different Fe- Zn/Cr all show well- identified atomic lattices of the spinel [001] and [220] surfaces (Figs. 1a,b and supplementary figs.2, 3). Nevertheless, the Fe, Cr, and Zn atoms cannot be distinguished only by the contrast of images. To probe the element distribution, HADDF energy dispersive spectroscopy (EDS) mapping at the atomic scale was employed. Elemental composition through EDS analysis agrees well with the quantitative inductively coupled plasma optical emission spectroscopy results (supplementary fig.4). When the amount of Fe is less than \(4.48 \mathrm{wt}\%\) , distribution of Fe is uniform across the catalyst surface. In contrast, Fe is enriched at the catalyst edges when its amount further increases to \(7.78 \mathrm{wt}\%\) . Furthermore, the spinel structure also exist at the edges, indicating that the Fe- enriched region might be assigned to \(Z n F e_{2}O_{4}\) (supplementary fig.5). This is further verified by DFT simulation of the [220] surfaces of \(Z n C r_{2}O_{4}\) and \(Z n F e_{2}O_{4}\) , which show that the Cr (16d)- Cr (16d) distance is a \(\sim 6\%\) longer than the Fe (16d)- Fe (16d) distance (supplementary fig.6). Such a difference aligns with the analysis of HADDF intensity profiles of a Fe- enriched region (arrow 1) and a Fe- deficient region (arrow 2), respectively (Fig. 1c). Distances between two adjacent 16d sites in the two region are \(0.278 \mathrm{nm}\) and \(0.294 \mathrm{nm}\) , respectively. Therefore, it is inferred that when the Fe amount \(< 4.48 \mathrm{wt}\%\) , it is feasible to monodisperse Fe on the \(Z n C r_{2}O_{4}\) matrix spontaneously; when the Fe amount increases to \(7.78 \mathrm{wt}\%\) , Fe starts to accumulate at the edge of the catalyst surface, likely in form of \(Z n F e_{2}O_{4}\) .
+
+<--- Page Split --->
+
+
+Fig. 1. Fe monodispersion on ZnCr2O4 spinel. HADDF-STEM images of (a) 4.48% Fe-Zn/Cr and (b) 7.78% Fe-Zn/Cr and corresponding EDS mappings of Fe element. (c) HADDF intensity
+
+<--- Page Split --->
+
+profile of two lines at the selected regions shown in the inset HADDF- STEM image. Atomic structure of \(\mathrm{Zn(Cr, Fe)_2O_4}\) spinel is also shown as an inset to illustrate the distance between two adjacent (16d) sites. (d) Fe K- edge X- ray absorption near- edge structure (XANES) profiles of different Fe- Zn/Cr and some standard samples. (e) The first two shells, Fe- O and Fe- Cr/Fe- Fe fittings, of the Fe K- edge Fourier transform- extended X- ray absorption fine structure (FT- EXAFS) spectra of different Fe- Zn/Cr. (f,g) Fe K- edge wavelet transform (WT)- EXAFS spectra of \(4.48\%\) Fe- Zn/Cr and \(7.78\%\) Fe- Zn/Cr, respectively. (h) DFT calculated substitution energies of Fe in the 4a site and 16d sites (including isolated, adjacent and multiple sites) of the \(\mathrm{ZnCr_2O_4}\) matrix. (i) Structure model of pristine \(\mathrm{ZnCr_2O_4}\) showing different sites. (j) Schematic illustration showing how monodispersed Fe endures reactive atmosphere and enriched Fe suffer from phase transition to \(\mathrm{Fe_xC_y}\) during syngas conversion.
+
+Since electron microscopy analysis only reveals local structure information, XANES and EXAFS based on synchrotron radiation were performed to unveil the coordination structures more globally. The Fe XANES edges of different Fe- Zn/Cr is between those of \(\mathrm{Fe_2O_3}\) and \(\mathrm{FeO}\) , indicating that the average valence state of Fe is between \(+2\) and \(+3\) (Fig. 1d and supplementary fig. 7). FT- EXAFS spectra of different Fe- Zn/Cr reveals a Fe- O distance without phase correction \((1.62 \AA)\) similar to that of \(\mathrm{ZnFe_2O_4}\) (Fig. 1e and supplementary fig. 8a). While for the peak at around \(2.8 \AA\) , Fe- Zn/Cr samples with a Fe content \(\leq 4.48 \mathrm{wt\%}\) show a bond length closer to \(\mathrm{Fe_3O_4}\) and \(7.78\%\) Fe- Zn/Cr is closer to \(\mathrm{ZnFe_2O_4}\) . Although FT- EXAFS cannot distinguish the separate peaks with an atomic number of \(\pm 2\) , e.g. Fe- Fe and Fe- Cr, such a difference is coincided with the DFT calculations (supplementary fig.6) and HADDF- STEM observation (Fig. 1c), suggesting that only the Fe- O- Cr structure exists in spontaneously monodispersed Fe samples (<4.48 wt%),
+
+<--- Page Split --->
+
+whereas the Fe- O- Cr and Fe- O- Fe structures coexist in the enriched Fe sample (7.78 wt%). Further Fe 2p X- ray photoelectron spectroscopy (XPS) analysis shown in supplementary fig. 8b supports the above deduction from FT- EXAFS \(^{18,19}\) .
+
+The subtle difference in local coordination structures between samples with monodispersed and enriched Fe is further confirmed using WT- EXAFS (Figs. 1f, 1g and supplementary fig. 9). In general, the WT- EXAFS heat maps show two scattering centers, which are associated with Fe- O and Fe- Cr/Fe- Fe, Fe- Fe, respectively. The k- axis location of the second scattering center shifts to higher values with increasing Fe amounts (6.46 Å \(^{- 1}\) , 6.49 Å \(^{- 1}\) , 6.73 Å \(^{- 1}\) and 6.83 Å \(^{- 1}\) when the Fe amount is 2.89%, 4.48%, 7.78%, and 100% (i.e. ZnFe \(_2\) O \(_4\) )), corresponding to shortened bond lengths (supplementary fig. 10). This aligns well with the transition from longer Fe- Cr to shorter Fe- Fe. The FT- EXAFS and WT- EXAFS results were further fitted using optimized doped Fe- Zn/Cr systems (Fig. 1e and supplementary fig. 11). Fitted results show that the coordination numbers (CNs) of Fe- O (i.e. the nearest neighboring shell) are more than 4 for all Fe- Zn/Cr samples, verifying the 16d site as Fe- substitution site because 4a site’s CN is less than 4 (table S1) \(^{20}\) . All the fitting results including The CN, bond distances (R), and Debye–Waller factor (σ²) are listed in Table S1 supplementary Materials.
+
+The above electron microscopic and synchrotron radiation- based spectroscopic characterizations experimentally validates the monodispersion of Fe when the Fe content is below 4.48 wt%. We then performed DFT calculations to understand the origin of Fe monodispersion. Energies that are required for Fe substituting Cr or Zn atoms at different sites on the (111) surface of ZnCr \(_2\) O \(_4\) are shown in Fig. 1h, along with the atomic surface model of ZnCr \(_2\) O \(_4\) (111) surface shown in Fig. 1i (calculation details are presented in Supplementary Materials). Notably, substitution of Cr by Fe at the (16d) site is thermodynamically preferred (−2.43 eV) over substitution of Zn at the (4a) site (3.47 eV) (with structures shown in supplementary figs. 12a, b).
+
+<--- Page Split --->
+
+When more Cr (16d) sites are considered for Fe substitution, it is found that Fe preferrs to substitute a (16d) site far from the existing doping site rather than an adjacent one, with a substitution energy being \(0.96\mathrm{eV}\) more negative (with structures shown in supplementary fig. 12c, d). Namely, isolated (16d) sites are preferably occupied upon Fe doping. Note that calculated substitution energies at isolated (16d) sites remain negative when the doping concentration of Fe increases from \(6.25\%\) to \(25\%\) (normalized to all the surface metal atoms of spinel (111) surface), providing theoretical insights into spontaneous monodispersion of Fe on \(\mathrm{ZnCr_2O_4}\) . By using DFT calculation, we also investigated the stability of isolated Fe doping site in a reactive syngas condition. The formation energies of \(\mathrm{Fe_5C_2}\) (as a representative \(\mathrm{Fe_xC_y}\) phase) from Fe in \(\mathrm{ZnFe_2O_4}\) and monodispersed Fe in \(\mathrm{ZnCr_2O_4}\) are \(- 3.17\mathrm{eV}\) and \(1.25\mathrm{eV}\) and per Fe atom, respectively, indicating the strong tendency of \(\mathrm{ZnFe_2O_4}\) and high resistance of Fe- Zn/Cr to form carbides. Therefore, we propose a catalyst evolution scene herein (Fig. 1j). In a oxide- zeolite (OX- ZEO) tandem catalytic system for syngas conversion, the oxide catalyzes the formation of oxygenates such as \(\mathrm{H_2CO}\) and \(\mathrm{CH_3OH}\) from syngas and the zeolite further selectively catalyzes these oxygenates to produce aromatics \(^{21 - 23}\) . The Fe- enriched oxide catalysts, however, suffers from irreversible phase transition to \(\mathrm{Fe_xC_y}\) , which follows Anderson- Schulz- Flory theory and inevitably leads to alkanes with uncontrolled carbon atoms per molecule. In contrast, the monodispersed Fe with superior stability against sintering and carbonization could enable stable aromatics formation from syngas.
+
+## Catalyst performance of monodispersed and enriched Fe in \(\mathrm{ZnCr_2O_4}\) matrix coupled with H-ZSM-5 for syngas conversion
+
+To validate above prospect on the superior stability of monodispersed Fe in \(\mathrm{ZnCr_2O_4}\) through theoretical prediction, different Fe- Zn/Cr oxides were coupled with H- ZSM- 5 as tandem catalysts for selective syngas conversion to aromatics. Fig. 2a shows the catalyst evaluation of Fe- Zn/Crvs.
+
+<--- Page Split --->
+
+pristine \(\mathrm{ZnCr_2O_4}\) (denoted as \(\mathrm{Zn / Cr}\) ) at a reaction conditions of \(2.0\mathrm{MPa}\) \(\mathrm{CO:H_2 = 1:1)}\) , \(350^{\circ}\) C and \(600\mathrm{ml}\mathrm{h}^{- 1}\cdot \mathrm{g}_{\mathrm{cat}}^{- 1}\) . CO conversion increases from \(13\%\) using pristine \(\mathrm{Zn / Cr}\) to \(45\%\) using \(4.48\%\) Fe- Zn/Cr with monodispersed Fesites; meanwhile, the total aromatic selectivity remains as high as \(80\%\) with various alkanes as minor side products. Since the conversion processes in tandem, i.e. syngas to oxygenates and oxygenates to aromatics, are spatially separated, the enhanced CO conversion is attributed to the activation effect of Fe dopants on CO and \(\mathrm{H_2}\) to accelerate oxygenates formation. In situ diffuse reflectance infrared Fourier transform spectroscopy results shows that signal intensities of oxygenate intermediates are at least an order of magnitude higher on \(4.48\%\) Fe- Zn/Cr than on pristine \(\mathrm{Zn / Cr}\) , corroborating the above analysis (fig. S13). \(7.78\%\) Fe- Zn/Cr with enriched Fe increases the CO conversion to \(51\%\) but sacrifices the total aromatic selectivity from \(80\%\) to \(44\%\) , along with significantly higher yields of \(\mathrm{CH_4}\) and \(\mathrm{C_2 - C_4}\) alkanes. Since these alkanes are typical products of \(\mathrm{Fe_xC_y}\) - catalyzed syngas conversion \(^{24,25}\) , we characterized spent \(7.78\%\) Fe- Zn/Cr using HADDF- STEM and observed \(\mathrm{Fe_xC_y}\) phases (fig. S14). The \(\mathrm{Fe_xC_y}\) phases likely originated from the Fe- O- Fe structure present in the enriched Fe parts of \(7.78\%\) Fe- Zn/Cr and this is rationalized by the negative formation energy of carbides from \(\mathrm{ZnFe_2O_4}\) in former theoretical prediction \(^{24,25}\) .
+
+<--- Page Split --->
+
+
+Fig. 2. Catalyst evaluation of monodispersed and enriched Fe. (a) Catalyst evaluation of pristine \(\mathrm{ZnCr_2O_4}\) and different Fe-Zn/Cr with H-ZSM-5; reaction conditions: \(350^{\circ}\mathrm{C}\) , 2.0 MPa, space velocity \(= 600\mathrm{ml}\mathrm{h}^{-1}\cdot \mathrm{g}_{\mathrm{cat}}^{-1}\) , \(\mathrm{CO:H_2 = 1:1}\) . (b) The optimal space time yield (STY) of aromatics for different catalysts (note that the STYs were obtained at the optimized reaction conditions for each catalyst and the corresponding reaction conditions are summarized in table S3). (c) TOF and aromatic selectivity as functions of Fe contents in \(\mathrm{ZnCr_2O_4}\) and reaction conditions are similar as A. (d) Comparison between reported Fe-based catalysts and isolated Fe-Zn/Cr + H-ZSM-5 catalyst on syngas conversion to aromatics. (e) Stability test of \(4.48\%\) Fe-Zn/Cr + H-ZSM-5 catalytic system for \(100\mathrm{h}\) .
+
+As a typical tandem reaction over a bifunctional OX- ZEO catalyst, it has been reported that and low temperature and high pressure are detrimental to aromatics selectivity and CO conversion, respectively \(^{26,27}\) . In this study, these two problems were tackled by monodispersion of Fe on \(\mathrm{ZnCr_2O_4}\) . A low reaction temperature of \(275^{\circ}\mathrm{C}\) was previously found to increase the single pass
+
+<--- Page Split --->
+
+aromatic selectivity to \(\sim 82\% - 84\%\) using unmodified \(\mathrm{ZnCr_2O_4 + H - ZSM - 5}\) catalysts; while \(4.48\%\) Fe- Zn/Cr profoundly promotes the aromatic selectivity up to \(88\%\) to \(91\%\) , a value that has rarely been achieved (supplementary figs. 15a,b). It means that even at a low temperature, the monodispersed Fe is able to activate CO and \(\mathrm{H}_2\) to produce oxygenate intermediates, which further diffuse into the pores of zeolites to initiate C- C coupling and subsequent aromatics formation \(^{22,28}\) . In addition to low temperature performance, \(\mathrm{ZnCr_2O_4}\) with monodispersed Fe also exhibit outstanding high pressure performance (supplementary figs. 15c,d). The CO conversion increases remarkably from \(44\%\) to \(68\%\) , whereas selectivity towards \(\mathrm{CH_4}\) and \(\mathrm{C}_2\mathrm{- C}_4\) side products is only marginally increased by \(< 1\%\) . By analyzing the Fe contents and STYs of aromatics, it is found that STYs increase with higher Fe amounts only when Fe remains monodispersed and once Fe is further enriched to form Fe- O- Fe structure prone to carbonization, STYs of aromatics deteriorate due to the emergence of conventional Fischer- Tropsch pathways (Fig. 2b and supplementary fig. 16a) \(^{29}\) . This trend is also notable when projecting TOF and total aromatic selectivity to the Fe content; monodispersed Fe increases the TOF of syngas conversion and maintains high selectivity towards aromatics, whereas enriched Fe sacrifices the aromatic selectivity despite the higher TOF (Fig. 2c). As shown in Fig. 2d and supplementary fig. 16b, the outstanding ability of our monodispersed Fe- Zn/Cr based OX- ZEO catalysts to achieve high CO conversion and high aromatics selectivity simultaneously is further illustrated through comparison with several recently reported catalysts for syngas conversion process \(^{30 - 34}\) . Further, the long- term stability test of \(4.48\%\) Fe- Zn/Cr + H- ZSM- 5 shows no signs of decay in either the activity or total aromatic selectivity for more than \(100\mathrm{~h}\) at \(350^{\circ}\mathrm{C}\) and \(2.0\mathrm{MPa}\) and stable CO conversion of \(\sim 45\%\) is achieved (Fig. 2e).
+
+<--- Page Split --->
+
+## Mechanistic investigation of monodispersed Fe in enhanced catalytic activity
+
+The above catalysis evaluation demonstrates the unique ability of monodispersed Fe to catalyze syngas to form reactive oxygenates. To understand the origin of such enhanced activity, we further performed a series of combinatorial mechanistic investigations. Previous demonstrations have suggested surface \(\mathrm{Ov}\) as possible active sites for CO activation \(^{35,36}\) . However, there is a lack of high- precision characterization of \(\mathrm{Ov}^{37}\) . DFT calculations were firstly performed to assess the equilibrium \(\mathrm{Ov}\) concentration in monodispersed Fe- Zn/Cr samples. Using spinel (111) surface as a model surface, the formation energies of \(\mathrm{Ov}\) with different concentrations and spatial locations (i.e., surface and subsurface layer) were calculated through either CO or \(\mathrm{H}_{2}\) reduction (calculation details are presented in Supplementary Materials). Similar to a previous study, CO reduction was found to be the major driving force for \(\mathrm{Ov}\) formation \(^{13}\) (supplementary fig. 17). The phase diagram shows that \(\mathrm{Ov}\) preferably presents in the surface layer with a concentration of 0.25 monolayer (ML) under the experimental condition (Fig. 3a). The atomic evidence of surface \(\mathrm{Ov}\) was obtained by using the integrated differential phase- contrast STEM (iDPC- STEM) technique. Fig. 3b depicts the [111] surface of 4.48 % Fe- Zn/Cr and some \(\mathrm{Ov}\) can be identified with atomic precision. A microquantitative intensity statistic analysis was subsequently performed by applying line scan to the iDPC- STEM images. The non- periodic variations in image contrast relating to O demonstrate the existence of \(\mathrm{Ov}\) and its concentration is estimated to be 25%–28%, similar to the theoretically predicted \(\mathrm{Ov}\) concentration (Fig. 3c). O1s XPS spectra of different Fe- Zn/Cr samples further show that Fe doping only alters surface \(\mathrm{Ov}\) concentration by insignificant amounts (Fig. 3d). Electron paramagnetic resonance spectroscopy also quantitatively evidences the existence of \(\mathrm{Ov}\) (supplementary figs. 18a, b). It is found that there are not much changes in the \(\mathrm{Ov}\) content.
+
+<--- Page Split --->
+
+
+Fig. 3. Understanding the role of monodispersed Fe in catalytic activity. (a) Thermodynamic phase diagram of Fe-doped \(\mathrm{ZnCr_2O_4}\) (111) surfaces at varying temperatures and CO partial pressures \((P_{\mathrm{CO}})\) (b) iDPC-STEM images of \(4.48\%\) Fe-Zn/Cr. (c) iDPC-STEM intensity profiles along the corresponding dashed lines in B. (d) O 1s XPS spectra of \(\mathrm{ZnCr_2O_4}\) and different Fe-Zn/Cr samples. (e) Projected electric field strength and vector map of \(4.48\%\) Fe-Zn/Cr. (f) Differential charge density (cyan and yellow represent charge depletion and accumulation, respectively; the cutoff of the density-difference isosurface is \(0.11\mathrm{e~Å}^{-3}\) ).
+
+Since the \(\mathrm{O}_{\mathrm{V}}\) concentration remains marginally affected by Fe doping, it might not be the reason for the enhanced catalytic activity. We then focused on the effect of local electronic structures and performed a charge density analysis by combining electric field imaging and theoretical calculations. As shown in Fig. 3e and supplementary figs. 18c,d, some local bright spots (in red circle) appear despite the surrounding uniform intensity, implying the possible charge transfer between isolated Fe and surrounding O and \(\mathrm{O}_{\mathrm{V}}\) 38. This is corroborated by the theoretically
+
+<--- Page Split --->
+
+calculated charge density (Fig. 3f). Clearly, charges on Ov and O nearest to the Fe dopant increase in Fe- doped \(\mathrm{ZnCr_2O_4}\) with respect to pristine \(\mathrm{ZnCr_2O_4}\) . The locally modulated charge density could account for the difference in catalytic activity between monodispersed Fe- Zn/Cr and Zn/Cr. A series of experiments were conducted to prove the promoted activation effect of Fe dopants on CO and \(\mathrm{H}_2\) (supplementary figs. 19, 20).
+
+CO hydrogenation reaction pathways were investigated using DFT calculations. By taking the aforementioned structural characterization and theoretical analysis into consideration, undoped and isolated Fe- doped \(\mathrm{ZnCr_2O_4}\) (111) surfaces with 1/4 ML Ov on the surface were constructed for simulations. The gas phase energies of CO and \(\mathrm{H}_2\) are adjusted using the actual experimental conditions. On both surfaces, our calculations support the stepwise hydrogenation mechanism in syngas conversion (Fig. 4a) \(^{13,15}\) . In more details, the reaction starts with CO adsorption at Ov (Fig. 4b). Next, \(\mathrm{H}_2\) dissociates near the surface Ov and \(\mathrm{H}^*\) is adsorbed on top of an O near Fe (16d). Subsequently, adsorbed CO\* is stepwise hydrogenated to form formyl (CHO\*), formaldehyde (CH2O\*), methoxyl (CH3O\*), and finally CH3OH. It is found that pristine \(\mathrm{ZnCr_2O_4}\) (111) with Ov is mainly limited by the weak adsorption of \(\mathrm{H}^*\) with the presence of CHO\*, as well as strong adsorption of CH3O\*. The incorporation of isolated Fe effectively stabilizes the state of CHO\* + H\*, making the hydrogenation step to form H2CO\* energetically exothermic, while destabilizes the state of CH3O\* + H\*, thereby facilitating the formation of CH3OH. From both aspects, monodispersed Fe improves the ability of pristine \(\mathrm{ZnCr_2O_4}\) to produce key oxygenate intermediates of H2CO and CH3OH from syngas. These key intermediates further participate in complicated oxygenate- to- aromatics reactions occurring in the pores of H- ZSM- 5 \(^{39}\) .
+
+<--- Page Split --->
+
+
+Fig. 4. The mechanism study of monodispersed Fe & pristine \(\mathrm{ZnCr_2O_4}\) in syngas conversion.
+
+(a) Gibbs free energy diagrams of syngas conversion to \(\mathrm{CH_3OH}\) on pristine and Fe-doped \(\mathrm{ZnCr_2O_4}\) (111) surfaces with 1/4 ML \(\mathrm{Ov}\) . The reaction images are shown in the inset of a; Zn: green, Cr: blue, Fe: yellow, O: red, C: brown, and H: white. (b) The atomic structures of the corresponding states in a.
+
+## Conclusion
+
+In this study, we demonstrated that the spinel structure of \(\mathrm{ZnCr_2O_4}\) can disperse strong self- interaction metal, Fe, spontaneously due to the thermodynamically stable state caused by the interaction between Fe and \(\mathrm{ZnCr_2O_4}\) , showing the highest performance in syngas- to- aromatic reaction. By combining high- precision microscopic and macroscopic characterizations and theory calculations, monodispersed Fe activates the surrounding \(\mathrm{Ov}\) , thereby activating the CO and \(\mathrm{H_2}\)
+
+<--- Page Split --->
+
+while avoiding the formation of \(\mathrm{Fe_xC_y}\) and maintaining stability under a reducing atmosphere. The TOF increased from 0.54 to \(2.48 \mathrm{h}^{- 1}\) without sacrificing the aromatic selectivity in monodispersed Fe samples. Our monodispersed Fe in the \(\mathrm{ZnCr_2O_4}\) catalyst showed \(81.4\%\) aromatic selectivity at a single- pass CO conversion of \(68.4\%\) , which is the best catalyst evaluation among all Fe- based catalysts during the syngas- to- aromatic reaction. DFT calculations revealed that the monodispersion of Fe in 16d sites lowered the key determining step of \(\mathrm{HCO^* + H^* - H_2CO^*}\) , thereby accelerating the C1 oxygenate intermediates, which made them diffuse quickly into the pores of H- ZSM- 5 to initiate the C- C coupling toward the aromatics. This study provides a prototype for rationally tailoring single atom Fe in syngas chemistry to obtain targeted catalytic reactivity and avoid the formation of \(\mathrm{Fe_xC_y}\) .
+
+<--- Page Split --->
+
+Wang, X., Zhao, B., Jiang, D.- e. & Xie, Y. Monolayer dispersion of MoO3, NiO and their precursors on \(\gamma\) - Al2O3. Applied Catalysis A: General 188, 201- 209 (1999). Zhang, X., Liu, J., Jing, Y. & Xie, Y. Support effects on the catalytic behavior of NiO/Al2O3 for oxidative dehydrogenation of ethane to ethylene. Applied Catalysis A: General 240, 143- 150 (2003). Brajpuriya, R. & Shripathi, T. Investigation of Fe/Al interface as a function of annealing temperature using XPS. Applied Surface Science 255, 6149- 6154, doi:10.1016/j.apsusc.2009.01.070 (2009). Guo, Y., Fu, Y., Liu, Y. & Shen, S. Photoelectrochemical activity of ZnFe2O4modified \(\alpha\) - Fe2O3nanorod array films. RSC Advances 4, doi:10.1039/c4ra05289g (2014). Gao, R. et al. Pt/Fe2O3 with Pt- Fe pair sites as a catalyst for oxygen reduction with ultralow Pt loading. Nature Energy 6, 614- 623, doi:10.1038/s41560- 021- 00826- 5 (2021). Sun, Q., Wang, N. & Yu, J. Advances in Catalytic Applications of Zeolite- Supported Metal Catalysts. Adv Mater 33, e2104442, doi:10.1002/adma.202104442 (2021). Han, J. et al. Single- atom Fe- Nx- C as an efficient electrocatalyst for zinc- air batteries. Advanced Functional Materials 29, 1808872 (2019). Jones, J. et al. Thermally stable single- atom platinum- on- ceria catalysts via atom trapping. Science 353, 150- 154 (2016). Nie, L. et al. Activation of surface lattice oxygen in single- atom Pt/CeO2 for low- temperature CO oxidation. Science 358, 1419- 1423 (2017). Xu, Y. et al. A hydrophobic FeMn@Si catalyst increases olefins from syngas by suppressing C1 by- products. Science 371, 610- 613, doi:10.1126/science.abb3649 (2021). Cui, X. et al. Selective production of aromatics directly from carbon dioxide hydrogenation. ACS Catalysis 9, 3866- 3876 (2019). Navrotsky, A. & Kleppa, O. The thermodynamics of cation distributions in simple spinels. Journal of Inorganic and nuclear Chemistry 29, 2701- 2714 (1967). Ma, S., Huang, S.- D. & Liu, Z.- P. Dynamic coordination of cations and catalytic selectivity on zinc- chromium oxide alloys during syngas conversion. Nature Catalysis 2, 671- 677, doi:10.1038/s41929- 019- 0293- 8 (2019). Hu, J. et al. Sulfur vacancy- rich MoS2 as a catalyst for the hydrogenation of CO2 to methanol. Nature Catalysis 4, 242- 250, doi:10.1038/s41929- 021- 00584- 3 (2021). Zhang, Z. et al. The active sites of Cu- ZnO catalysts for water gas shift and CO hydrogenation reactions. Nat Commun 12, 4331, doi:10.1038/s41467- 021- 24621- 8 (2021). Guo, Y. et al. A facile spray pyrolysis method to prepare Ti- doped ZnFe2O4 for boosting photoelectrochemical water splitting. Journal of Materials Chemistry A 5, 7571- 7577, doi:10.1039/c6ta11134c (2017). Fu, Y. et al. Insights into the size effect of ZnCr2O4 spinel oxide in composite catalysts for conversion of syngas to aromatics. Green Energy & Environment, doi:10.1016/j.gee.2021.07.003 (2021).
+
+<--- Page Split --->
+
+367 18 Gao, W. et al. Capsule-like zeolite catalyst fabricated by solvent-free strategy for para- 368 Xylene formation from CO2 hydrogenation. Applied Catalysis B: Environmental 303, 369 120906 (2022). 370 19 Han, W. et al. Research progresses in the hydrogenation of carbon dioxide to certain 371 hydrocarbon products. Journal of Fuel Chemistry and Technology 49, 1609- 1619 (2021). 372 20 Li, A. et al. Enhancing the stability of cobalt spinel oxide towards sustainable oxygen 373 evolution in acid. Nature Catalysis, 1- 10 (2022). 374 21 Jiao, F. et al. Selective conversion of syngas to light olefins. Science 351, 1065- 1068 375 (2016). 376 22 Zhou, W. et al. New horizon in C1 chemistry: breaking the selectivity limitation in 377 transformation of syngas and hydrogenation of CO2 into hydrocarbon chemicals and fuels. 378 Chem Soc Rev 48, 3193- 3228, doi:10.1039/c8cs00502h (2019). 379 23 Li, Z. et al. Highly Selective Conversion of Carbon Dioxide to Aromatics over Tandem 380 Catalysts. Joule 3, 570- 583, doi:10.1016/j.joule.2018.10.027 (2019). 381 24 Song, C. et al. Photothermal conversion of CO2 with tunable selectivity using Fe- based 382 catalysts: from oxide to carbide. ACS Catalysis 10, 10364- 10374 (2020). 383 25 Li, Z. et al. Fe- Based Catalysts for the Direct Photohydrogenation of CO2 to Value- Added 384 Hydrocarbons. Advanced Energy Materials 11, 2002783 (2021). 385 26 Liu, C. et al. Constructing directional component distribution in a bifunctional catalyst to 386 boost the tandem reaction of syngas conversion. Chem Catalysis 1, 896- 907, 387 doi:10.1016/j.checat.2021.06.016 (2021). 388 27 Arslan, M. T. et al. Highly Selective Conversion of CO2 or CO into Precursors for 389 Kerosene- Based Aviation Fuel via an Aldol- Aromatic Mechanism. ACS Catalysis 12, 390 2023- 2033 (2022). 391 28 Zhou, C. et al. Highly Active ZnO- ZrO2 Aerogels Integrated with H- ZSM- 5 for Aromatics 392 Synthesis from Carbon Dioxide. ACS Catalysis 10, 302- 310, 393 doi:10.1021/acscatal.9b04309 (2019). 394 29 Zhu, J. et al. Dynamic structural evolution of iron catalysts involving competitive oxidation 395 and carburization during CO2 hydrogenation. Science Advances 8, eabm3629 (2022). 396 30 Zhao, B. et al. Direct Transformation of Syngas to Aromatics over Na- Zn- Fe 5 C 2 and 397 Hierarchical HZSM- 5 Tandem Catalysts. Chem 3, 323- 333, 398 doi:10.1016/j.chempr.2017.06.017 (2017). 399 31 Wei, J. et al. Directly converting CO2 into a gasoline fuel. Nature communications 8, 1- 9 400 (2017). 401 32 Geng, S., Jiang, F., Xu, Y. & Liu, X. iron- based Fischer- Tropsch synthesis for the efficient 402 conversion of carbon dioxide into Isoparaffins. ChemCatChem 8, 1303- 1307 (2016). 403 33 Wang, X. et al. Synthesis of isoalkanes over a core (Fe- Zn- Zr)- shell (zeolite) catalyst by 404 CO 2 hydrogenation. Chemical Communications 52, 7352- 7355 (2016). 405 34 Dai, C. et al. Hydrogenation of CO2 to Aromatics over Fe- K/Alkaline Al2O3 and P/ZSM- 406 5 Tandem Catalysts. Industrial & Engineering Chemistry Research 59, 19194- 19202 407 (2020).
+
+<--- Page Split --->
+
+408 35 Wang, Y. et al. Visualizing Element Migration over Bifunctional Metal- Zeolite Catalysts 409 and its Impact on Catalysis. Angew Chem Int Ed Engl 60, 17735- 17743, 410 doi:10.1002/anie.202107264 (2021). 411 36 Pan, X., Jiao, F., Miao, D. & Bao, X. Oxide- Zeolite- Based Composite Catalyst Concept 412 That Enables Syngas Chemistry beyond Fischer- Tropsch Synthesis. Chemical Reviews 413 121, 6588- 6609 (2021). 414 37 Wang, S. et al. Selective conversion of CO2 into propene and butene. Chem 6, 3344- 3363 415 (2020). 416 38 Shibata, N. et al. Electric field imaging of single atoms. Nature communications 8, 1- 7 417 (2017). 418 39 Arslan, M. T. et al. Selective Conversion of Syngas into Tetramethylbenzene via an Aldol- 419 Aromatic Mechanism. ACS Catalysis 10, 2477- 2488, doi:10.1021/acscatal.9b03417 420 (2020). 421
+
+## Acknowledgements:
+
+This work is supported by the National Natural Science Foundation of China (21908125 and 22005170), the National Key Research and Development Program of China (2018YFB0604801), the Key Research and Development Program of Inner Mongolia and Ordos, and CNPC Innovation Funds.
+
+Author contributions: G.T and X.L contributed equally. All the authors approved the final version of the manuscript.
+
+Competing financial interests: The authors declare no competing financial interests.
+
+Data and materials availability: All data are available in the manuscript or the supplementary materials.
+
+Supplementary Information:
+
+Materials and Methods
+
+Figs. S1 to S20
+
+Table S1 to S4
+
+References (1- 9)
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+SupplementaryInformationSubmitNatureCommunication.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce_det.mmd b/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..be01140cec423fd362389716a47cef8396672dca
--- /dev/null
+++ b/preprint/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce/preprint__014d7fcc701aeaec731ab407447a9cff88ca28668ba3db6be184e70f89ec55ce_det.mmd
@@ -0,0 +1,246 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 888, 208]]<|/det|>
+# Accelerating Syngas-to-Aromatic Conversion via Spontaneously Monodispersed Fe in ZnCr2O4 Spinel
+
+<|ref|>text<|/ref|><|det|>[[44, 230, 588, 777]]<|/det|>
+Guo Tian Tsinghua University Xinyan Liu University of Electronic Science and Technology of China Chenxi Zhang ( cxzhang@mail.tsinghua.edu.cn ) Tsinghua University https://orcid.org/0000- 0002- 1708- 9449 Xiaoyu Fan Tsinghua University Hao Xiong Tsinghua University https://orcid.org/0000- 0001- 5479- 7754 Xiao Chen Tsinghua University https://orcid.org/0000- 0003- 1104- 6146 Wenzheng Li Tsinghua University Binhang Yan Tsinghua University https://orcid.org/0000- 0003- 2833- 8022 Lan Zhang Beijing University of Technology Ning Wang Beijing University of Technology Hong- Jie Peng University of Electronic Science and Technology of China https://orcid.org/0000- 0002- 4183- 703X Fei Wei Tsinghua University https://orcid.org/0000- 0002- 1422- 9784
+
+<|ref|>title<|/ref|><|det|>[[44, 825, 100, 841]]<|/det|>
+# Article
+
+<|ref|>title<|/ref|><|det|>[[44, 862, 135, 879]]<|/det|>
+# Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 899, 297, 917]]<|/det|>
+Posted Date: May 13th, 2022
+
+<|ref|>text<|/ref|><|det|>[[44, 936, 473, 954]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 1607273/v1
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 44, 911, 87]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 123, 914, 167]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on September 22nd, 2022. See the published version at https://doi.org/10.1038/s41467-022-33217-9.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[72, 80, 875, 135]]<|/det|>
+# Title: Accelerating Syngas-to-Aromatic Conversion via Spontaneously Monodispersed Fe in ZnCr₂O₄ Spinel
+
+<|ref|>text<|/ref|><|det|>[[111, 220, 884, 243]]<|/det|>
+Authors: Guo Tian†, Xinyan Liu†, Chenxi Zhang†, Xiaoyu Fan†, Hao Xiong†, Xiao Chen†,
+
+<|ref|>text<|/ref|><|det|>[[111, 264, 779, 285]]<|/det|>
+Wenzheng Li†, Binhang Yan†, Lan Zhang3, Ning Wang3, Hong-Jie Peng2, Fei Wei1\*
+
+<|ref|>title<|/ref|><|det|>[[113, 338, 217, 355]]<|/det|>
+# Affiliations:
+
+<|ref|>text<|/ref|><|det|>[[111, 370, 812, 392]]<|/det|>
+1. Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology,
+
+<|ref|>text<|/ref|><|det|>[[111, 405, 808, 426]]<|/det|>
+Department of Chemical Engineering, Tsinghua University, Beijing, China, 100084
+
+<|ref|>text<|/ref|><|det|>[[111, 440, 815, 460]]<|/det|>
+2. Institute of Fundamental and Frontier Sciences, University of Electronic Science and
+
+<|ref|>text<|/ref|><|det|>[[111, 475, 590, 495]]<|/det|>
+Technology of China, Chengdu 611731, Sichuan, China
+
+<|ref|>text<|/ref|><|det|>[[111, 510, 869, 531]]<|/det|>
+3. Faculty of Environment and Life, Beijing University of Technology, Beijing 100124, China
+
+<|ref|>text<|/ref|><|det|>[[111, 584, 496, 604]]<|/det|>
+† These authors contributed equally to this work
+
+<|ref|>text<|/ref|><|det|>[[111, 626, 820, 647]]<|/det|>
+\* Corresponding authors Fei Wei, email: wf- dce@tsinghua.edu.cn, Chenxi Zhang, email:
+
+<|ref|>text<|/ref|><|det|>[[111, 661, 870, 682]]<|/det|>
+cxzhang@mail.tsinghua.edu.cn, Xiao Chen, email: chenx123@tsinghua.edu.cn, Hong-Jie Peng:
+
+<|ref|>text<|/ref|><|det|>[[111, 696, 290, 715]]<|/det|>
+hjpeng@uestc.edu.cn.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 81, 197, 98]]<|/det|>
+## Abstract:
+
+<|ref|>text<|/ref|><|det|>[[111, 113, 885, 415]]<|/det|>
+Spontaneous monodispersion of Fe species and their stabilization in reactive atmospheres remain a key challenge in catalytic syngas chemistry. In this study, we present a catalyst with spontaneously monodispersed Fe on \(\mathrm{ZnCr_2O_4}\) , which shows remarkable performance in the syngas- to- aromatic reaction when coupled with a H- ZSM- 5 zeolite. Monodispersed Fe increases the turnover frequency from 0.54 to \(2.48\mathrm{h}^{-1}\) without sacrificing the record high selectivity total aromatic ( \(80\% - 90\%\) ) at a single pass. This is enabled by the activation of CO and \(\mathrm{H}_2\) at oxygen vacancy nearest to the isolated Fe site and the prevention of carbide formation. Atomic precise characterization and theoretical calculations shed light on the origin and implications of spontaneous Fe monodispersion.
+
+<|ref|>text<|/ref|><|det|>[[112, 464, 884, 552]]<|/det|>
+One Sentence Summary: Highly monodispersed Fe is realized on a \(\mathrm{ZnCr_2O_4}\) spinel and stabilized under a highly reactive atmosphere, showing record high catalytic performance in the syngas- to- aromatic reaction.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 82, 211, 99]]<|/det|>
+## Main Text:
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 150, 225, 168]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[111, 184, 886, 551]]<|/det|>
+The spontaneous dispersion of catalytically active species on a support has been widely investigated in heterogeneous catalysis due to interactions between the species and support \(^{1,2}\) . Highly dispersed or, more strictly, monodispersed active sites endow the supported catalysts with unique catalytic properties. Spontaneous monodispersion can also improve atomic efficiency. Metal oxides with weak internal cohesive energy, e.g., \(\mathrm{MoO}_3\) and \(\mathrm{NiO}\) , can be easily dispersed on supports such as \(\gamma\) - \(\mathrm{Al}_2\mathrm{O}_3\) and \(\mathrm{TiO}_2\) , manifesting as prototype designs of spontaneously dispersed active sites. Such spontaneous dispersion is driven by negative Gibbs free energy \((\Delta G < 0)\) of breaking internal bonds of oxides being dispersed and forming new bonds between dispersed species and support. From this thermodynamics perspective, the monodispersion of species with strong self- interaction, such as Fe and Pt, presents a daunting challenge in heterogeneous catalysis \(^{3- 5}\) .
+
+<|ref|>text<|/ref|><|det|>[[111, 568, 886, 902]]<|/det|>
+Confining Fe and Pt precursors into the cages of nanoporous materials is an effective means of preparing monodispersed catalysts that is paramount in many sectors of heterogeneous catalysis \(^{6}\) . However, owing to the high surface energy, monodispersed Fe and Pt species tend to migrate and agglomerate under reaction conditions, especially at elevated temperatures, which inevitably cause catalyst deactivation. For instance, Han et al. \(^{7}\) found that the formation of Fe nanoclusters resulted in the deactivation of monodispersed Fe- N- C catalysts in proton exchange membrane fuel cells. Improving the metal- support interaction using an oxygen- donor support was considered an efficient method to stabilize monodispersed species \(^{8}\) . Recently, Nie et al. \(^{9}\) demonstrated how atomically dispersed ionic \(\mathrm{Pt}^{2 + }\) was stabilized by \(\mathrm{CeO}_2\) to endure steam treatment, presenting a feasible way against catalyst sintering. In addition to agglomeration, reactive atmosphere such as
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 78, 884, 239]]<|/det|>
+syngas can induce irreversible phase transition from metal to metal carbides, e.g. Fe to \(\mathrm{Fe_xC_y}\) , and the as- generated carbides further complicate the reaction pathways of syngas conversion and result in unwanted products \(^{10,11}\) . Therefore, how to stabilize monodispersed Fe species and to avoid \(\mathrm{Fe_xC_y}\) formation in a reactive atmosphere has become a major bottleneck in catalytic syngas conversion.
+
+<|ref|>text<|/ref|><|det|>[[111, 252, 886, 904]]<|/det|>
+In this study, we rationalized \(\mathrm{ZnCr_2O_4}\) spinel with abundant oxygen vacancies (Ov) as an oxygen- donor support. Fe could be spontaneously monodispersed on \(\mathrm{ZnCr_2O_4}\) via a simple impregnation method when the content of Fe was controlled less than 5 wt%. The octahedral site preference energies from the literature \(^{12}\) are in the order of \(\mathrm{Fe^{3 + } < Fe^{2 + } < Cr^{3 + } < Zn^{2 + }}\) , indicating that \(\mathrm{Fe^{2 + }}\) or \(\mathrm{Fe^{3 + }}\) prefers to occupy the octahedral sites, whereas \(\mathrm{Zn^{2 + }}\) tends to occupy the tetrahedral sites in the spinel structure. The spontaneously monodispersed Fe was found not only thermodynamically stable at high temperature but also resistive to carbonization in a reducing atmosphere. When coupled with a H- ZSM- 5 zeolite as a test, \(\mathrm{ZnCr_2O_4}\) with monodispersed Fe showed significantly improved syngas conversion efficiency (45%) with a turnover frequency (TOF) increased from 0.54 to 2.48 h\(^{- 1}\) ; while the high selectivity towards aromatics was maintained by preventing the formation of \(\mathrm{Fe_xC_y}\) . Moreover, the composite catalyst exhibited superior stability as no sign of decay in either the activity or total aromatic selectivity was observed for more than 100 h reaction at 350°C and 2.0 MPa. Density functional theory (DFT) calculations revealed that monodispersed Fe sites in \(\mathrm{ZrCr_2O_4}\) greatly reduced energy barriers of forming formaldehyde (H\(_2\)CO) and methanol (CH\(_3\)OH) from syngas, which were previously identified as key intermediates leading to aromatics \(^{13- 15}\) . This study not only demonstrates a promising monodispersed catalyst that is highly active, selective and stable in reactive syngas atmosphere but also sheds a light on spontaneous monodispersion of catalytically active species for heterogeneous catalysis.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 81, 310, 100]]<|/det|>
+## Results and Discussion
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 115, 648, 135]]<|/det|>
+## Identification of spontaneously monodispersed and enriched Fe
+
+<|ref|>text<|/ref|><|det|>[[111, 145, 886, 904]]<|/det|>
+\(Z n C r_{2}O_{4}\) spinels with increasing amounts of Fe (denoted as \(X\%\) Fe- Zn/Cr where X refers to the weight percentage of Fe) were prepared for investigation (supplementary fig.1). The identical crystal structure of \(Z n F e_{2}O_{4}\) and \(Z n C r_{2}O_{4}\) , as well as the similar atomic weights of Fe and Cr, makes it very challenging to identify the state of Fe in \(Z n C r_{2}O_{4}\) 16,17. High- angle annular dark- field scanning transmission electron microscopy (HADDF- STEM) images of different Fe- Zn/Cr all show well- identified atomic lattices of the spinel [001] and [220] surfaces (Figs. 1a,b and supplementary figs.2, 3). Nevertheless, the Fe, Cr, and Zn atoms cannot be distinguished only by the contrast of images. To probe the element distribution, HADDF energy dispersive spectroscopy (EDS) mapping at the atomic scale was employed. Elemental composition through EDS analysis agrees well with the quantitative inductively coupled plasma optical emission spectroscopy results (supplementary fig.4). When the amount of Fe is less than \(4.48 \mathrm{wt}\%\) , distribution of Fe is uniform across the catalyst surface. In contrast, Fe is enriched at the catalyst edges when its amount further increases to \(7.78 \mathrm{wt}\%\) . Furthermore, the spinel structure also exist at the edges, indicating that the Fe- enriched region might be assigned to \(Z n F e_{2}O_{4}\) (supplementary fig.5). This is further verified by DFT simulation of the [220] surfaces of \(Z n C r_{2}O_{4}\) and \(Z n F e_{2}O_{4}\) , which show that the Cr (16d)- Cr (16d) distance is a \(\sim 6\%\) longer than the Fe (16d)- Fe (16d) distance (supplementary fig.6). Such a difference aligns with the analysis of HADDF intensity profiles of a Fe- enriched region (arrow 1) and a Fe- deficient region (arrow 2), respectively (Fig. 1c). Distances between two adjacent 16d sites in the two region are \(0.278 \mathrm{nm}\) and \(0.294 \mathrm{nm}\) , respectively. Therefore, it is inferred that when the Fe amount \(< 4.48 \mathrm{wt}\%\) , it is feasible to monodisperse Fe on the \(Z n C r_{2}O_{4}\) matrix spontaneously; when the Fe amount increases to \(7.78 \mathrm{wt}\%\) , Fe starts to accumulate at the edge of the catalyst surface, likely in form of \(Z n F e_{2}O_{4}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[117, 150, 880, 808]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[111, 840, 884, 896]]<|/det|>
+Fig. 1. Fe monodispersion on ZnCr2O4 spinel. HADDF-STEM images of (a) 4.48% Fe-Zn/Cr and (b) 7.78% Fe-Zn/Cr and corresponding EDS mappings of Fe element. (c) HADDF intensity
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 80, 886, 450]]<|/det|>
+profile of two lines at the selected regions shown in the inset HADDF- STEM image. Atomic structure of \(\mathrm{Zn(Cr, Fe)_2O_4}\) spinel is also shown as an inset to illustrate the distance between two adjacent (16d) sites. (d) Fe K- edge X- ray absorption near- edge structure (XANES) profiles of different Fe- Zn/Cr and some standard samples. (e) The first two shells, Fe- O and Fe- Cr/Fe- Fe fittings, of the Fe K- edge Fourier transform- extended X- ray absorption fine structure (FT- EXAFS) spectra of different Fe- Zn/Cr. (f,g) Fe K- edge wavelet transform (WT)- EXAFS spectra of \(4.48\%\) Fe- Zn/Cr and \(7.78\%\) Fe- Zn/Cr, respectively. (h) DFT calculated substitution energies of Fe in the 4a site and 16d sites (including isolated, adjacent and multiple sites) of the \(\mathrm{ZnCr_2O_4}\) matrix. (i) Structure model of pristine \(\mathrm{ZnCr_2O_4}\) showing different sites. (j) Schematic illustration showing how monodispersed Fe endures reactive atmosphere and enriched Fe suffer from phase transition to \(\mathrm{Fe_xC_y}\) during syngas conversion.
+
+<|ref|>text<|/ref|><|det|>[[112, 531, 886, 907]]<|/det|>
+Since electron microscopy analysis only reveals local structure information, XANES and EXAFS based on synchrotron radiation were performed to unveil the coordination structures more globally. The Fe XANES edges of different Fe- Zn/Cr is between those of \(\mathrm{Fe_2O_3}\) and \(\mathrm{FeO}\) , indicating that the average valence state of Fe is between \(+2\) and \(+3\) (Fig. 1d and supplementary fig. 7). FT- EXAFS spectra of different Fe- Zn/Cr reveals a Fe- O distance without phase correction \((1.62 \AA)\) similar to that of \(\mathrm{ZnFe_2O_4}\) (Fig. 1e and supplementary fig. 8a). While for the peak at around \(2.8 \AA\) , Fe- Zn/Cr samples with a Fe content \(\leq 4.48 \mathrm{wt\%}\) show a bond length closer to \(\mathrm{Fe_3O_4}\) and \(7.78\%\) Fe- Zn/Cr is closer to \(\mathrm{ZnFe_2O_4}\) . Although FT- EXAFS cannot distinguish the separate peaks with an atomic number of \(\pm 2\) , e.g. Fe- Fe and Fe- Cr, such a difference is coincided with the DFT calculations (supplementary fig.6) and HADDF- STEM observation (Fig. 1c), suggesting that only the Fe- O- Cr structure exists in spontaneously monodispersed Fe samples (<4.48 wt%),
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 78, 884, 170]]<|/det|>
+whereas the Fe- O- Cr and Fe- O- Fe structures coexist in the enriched Fe sample (7.78 wt%). Further Fe 2p X- ray photoelectron spectroscopy (XPS) analysis shown in supplementary fig. 8b supports the above deduction from FT- EXAFS \(^{18,19}\) .
+
+<|ref|>text<|/ref|><|det|>[[111, 184, 886, 622]]<|/det|>
+The subtle difference in local coordination structures between samples with monodispersed and enriched Fe is further confirmed using WT- EXAFS (Figs. 1f, 1g and supplementary fig. 9). In general, the WT- EXAFS heat maps show two scattering centers, which are associated with Fe- O and Fe- Cr/Fe- Fe, Fe- Fe, respectively. The k- axis location of the second scattering center shifts to higher values with increasing Fe amounts (6.46 Å \(^{- 1}\) , 6.49 Å \(^{- 1}\) , 6.73 Å \(^{- 1}\) and 6.83 Å \(^{- 1}\) when the Fe amount is 2.89%, 4.48%, 7.78%, and 100% (i.e. ZnFe \(_2\) O \(_4\) )), corresponding to shortened bond lengths (supplementary fig. 10). This aligns well with the transition from longer Fe- Cr to shorter Fe- Fe. The FT- EXAFS and WT- EXAFS results were further fitted using optimized doped Fe- Zn/Cr systems (Fig. 1e and supplementary fig. 11). Fitted results show that the coordination numbers (CNs) of Fe- O (i.e. the nearest neighboring shell) are more than 4 for all Fe- Zn/Cr samples, verifying the 16d site as Fe- substitution site because 4a site’s CN is less than 4 (table S1) \(^{20}\) . All the fitting results including The CN, bond distances (R), and Debye–Waller factor (σ²) are listed in Table S1 supplementary Materials.
+
+<|ref|>text<|/ref|><|det|>[[111, 636, 886, 902]]<|/det|>
+The above electron microscopic and synchrotron radiation- based spectroscopic characterizations experimentally validates the monodispersion of Fe when the Fe content is below 4.48 wt%. We then performed DFT calculations to understand the origin of Fe monodispersion. Energies that are required for Fe substituting Cr or Zn atoms at different sites on the (111) surface of ZnCr \(_2\) O \(_4\) are shown in Fig. 1h, along with the atomic surface model of ZnCr \(_2\) O \(_4\) (111) surface shown in Fig. 1i (calculation details are presented in Supplementary Materials). Notably, substitution of Cr by Fe at the (16d) site is thermodynamically preferred (−2.43 eV) over substitution of Zn at the (4a) site (3.47 eV) (with structures shown in supplementary figs. 12a, b).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[110, 78, 886, 699]]<|/det|>
+When more Cr (16d) sites are considered for Fe substitution, it is found that Fe preferrs to substitute a (16d) site far from the existing doping site rather than an adjacent one, with a substitution energy being \(0.96\mathrm{eV}\) more negative (with structures shown in supplementary fig. 12c, d). Namely, isolated (16d) sites are preferably occupied upon Fe doping. Note that calculated substitution energies at isolated (16d) sites remain negative when the doping concentration of Fe increases from \(6.25\%\) to \(25\%\) (normalized to all the surface metal atoms of spinel (111) surface), providing theoretical insights into spontaneous monodispersion of Fe on \(\mathrm{ZnCr_2O_4}\) . By using DFT calculation, we also investigated the stability of isolated Fe doping site in a reactive syngas condition. The formation energies of \(\mathrm{Fe_5C_2}\) (as a representative \(\mathrm{Fe_xC_y}\) phase) from Fe in \(\mathrm{ZnFe_2O_4}\) and monodispersed Fe in \(\mathrm{ZnCr_2O_4}\) are \(- 3.17\mathrm{eV}\) and \(1.25\mathrm{eV}\) and per Fe atom, respectively, indicating the strong tendency of \(\mathrm{ZnFe_2O_4}\) and high resistance of Fe- Zn/Cr to form carbides. Therefore, we propose a catalyst evolution scene herein (Fig. 1j). In a oxide- zeolite (OX- ZEO) tandem catalytic system for syngas conversion, the oxide catalyzes the formation of oxygenates such as \(\mathrm{H_2CO}\) and \(\mathrm{CH_3OH}\) from syngas and the zeolite further selectively catalyzes these oxygenates to produce aromatics \(^{21 - 23}\) . The Fe- enriched oxide catalysts, however, suffers from irreversible phase transition to \(\mathrm{Fe_xC_y}\) , which follows Anderson- Schulz- Flory theory and inevitably leads to alkanes with uncontrolled carbon atoms per molecule. In contrast, the monodispersed Fe with superior stability against sintering and carbonization could enable stable aromatics formation from syngas.
+
+<|ref|>sub_title<|/ref|><|det|>[[113, 742, 883, 795]]<|/det|>
+## Catalyst performance of monodispersed and enriched Fe in \(\mathrm{ZnCr_2O_4}\) matrix coupled with H-ZSM-5 for syngas conversion
+
+<|ref|>text<|/ref|><|det|>[[113, 811, 884, 900]]<|/det|>
+To validate above prospect on the superior stability of monodispersed Fe in \(\mathrm{ZnCr_2O_4}\) through theoretical prediction, different Fe- Zn/Cr oxides were coupled with H- ZSM- 5 as tandem catalysts for selective syngas conversion to aromatics. Fig. 2a shows the catalyst evaluation of Fe- Zn/Crvs.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[110, 78, 886, 630]]<|/det|>
+pristine \(\mathrm{ZnCr_2O_4}\) (denoted as \(\mathrm{Zn / Cr}\) ) at a reaction conditions of \(2.0\mathrm{MPa}\) \(\mathrm{CO:H_2 = 1:1)}\) , \(350^{\circ}\) C and \(600\mathrm{ml}\mathrm{h}^{- 1}\cdot \mathrm{g}_{\mathrm{cat}}^{- 1}\) . CO conversion increases from \(13\%\) using pristine \(\mathrm{Zn / Cr}\) to \(45\%\) using \(4.48\%\) Fe- Zn/Cr with monodispersed Fesites; meanwhile, the total aromatic selectivity remains as high as \(80\%\) with various alkanes as minor side products. Since the conversion processes in tandem, i.e. syngas to oxygenates and oxygenates to aromatics, are spatially separated, the enhanced CO conversion is attributed to the activation effect of Fe dopants on CO and \(\mathrm{H_2}\) to accelerate oxygenates formation. In situ diffuse reflectance infrared Fourier transform spectroscopy results shows that signal intensities of oxygenate intermediates are at least an order of magnitude higher on \(4.48\%\) Fe- Zn/Cr than on pristine \(\mathrm{Zn / Cr}\) , corroborating the above analysis (fig. S13). \(7.78\%\) Fe- Zn/Cr with enriched Fe increases the CO conversion to \(51\%\) but sacrifices the total aromatic selectivity from \(80\%\) to \(44\%\) , along with significantly higher yields of \(\mathrm{CH_4}\) and \(\mathrm{C_2 - C_4}\) alkanes. Since these alkanes are typical products of \(\mathrm{Fe_xC_y}\) - catalyzed syngas conversion \(^{24,25}\) , we characterized spent \(7.78\%\) Fe- Zn/Cr using HADDF- STEM and observed \(\mathrm{Fe_xC_y}\) phases (fig. S14). The \(\mathrm{Fe_xC_y}\) phases likely originated from the Fe- O- Fe structure present in the enriched Fe parts of \(7.78\%\) Fe- Zn/Cr and this is rationalized by the negative formation energy of carbides from \(\mathrm{ZnFe_2O_4}\) in former theoretical prediction \(^{24,25}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[133, 82, 876, 370]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 416, 884, 712]]<|/det|>
+Fig. 2. Catalyst evaluation of monodispersed and enriched Fe. (a) Catalyst evaluation of pristine \(\mathrm{ZnCr_2O_4}\) and different Fe-Zn/Cr with H-ZSM-5; reaction conditions: \(350^{\circ}\mathrm{C}\) , 2.0 MPa, space velocity \(= 600\mathrm{ml}\mathrm{h}^{-1}\cdot \mathrm{g}_{\mathrm{cat}}^{-1}\) , \(\mathrm{CO:H_2 = 1:1}\) . (b) The optimal space time yield (STY) of aromatics for different catalysts (note that the STYs were obtained at the optimized reaction conditions for each catalyst and the corresponding reaction conditions are summarized in table S3). (c) TOF and aromatic selectivity as functions of Fe contents in \(\mathrm{ZnCr_2O_4}\) and reaction conditions are similar as A. (d) Comparison between reported Fe-based catalysts and isolated Fe-Zn/Cr + H-ZSM-5 catalyst on syngas conversion to aromatics. (e) Stability test of \(4.48\%\) Fe-Zn/Cr + H-ZSM-5 catalytic system for \(100\mathrm{h}\) .
+
+<|ref|>text<|/ref|><|det|>[[112, 764, 884, 890]]<|/det|>
+As a typical tandem reaction over a bifunctional OX- ZEO catalyst, it has been reported that and low temperature and high pressure are detrimental to aromatics selectivity and CO conversion, respectively \(^{26,27}\) . In this study, these two problems were tackled by monodispersion of Fe on \(\mathrm{ZnCr_2O_4}\) . A low reaction temperature of \(275^{\circ}\mathrm{C}\) was previously found to increase the single pass
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[110, 78, 886, 837]]<|/det|>
+aromatic selectivity to \(\sim 82\% - 84\%\) using unmodified \(\mathrm{ZnCr_2O_4 + H - ZSM - 5}\) catalysts; while \(4.48\%\) Fe- Zn/Cr profoundly promotes the aromatic selectivity up to \(88\%\) to \(91\%\) , a value that has rarely been achieved (supplementary figs. 15a,b). It means that even at a low temperature, the monodispersed Fe is able to activate CO and \(\mathrm{H}_2\) to produce oxygenate intermediates, which further diffuse into the pores of zeolites to initiate C- C coupling and subsequent aromatics formation \(^{22,28}\) . In addition to low temperature performance, \(\mathrm{ZnCr_2O_4}\) with monodispersed Fe also exhibit outstanding high pressure performance (supplementary figs. 15c,d). The CO conversion increases remarkably from \(44\%\) to \(68\%\) , whereas selectivity towards \(\mathrm{CH_4}\) and \(\mathrm{C}_2\mathrm{- C}_4\) side products is only marginally increased by \(< 1\%\) . By analyzing the Fe contents and STYs of aromatics, it is found that STYs increase with higher Fe amounts only when Fe remains monodispersed and once Fe is further enriched to form Fe- O- Fe structure prone to carbonization, STYs of aromatics deteriorate due to the emergence of conventional Fischer- Tropsch pathways (Fig. 2b and supplementary fig. 16a) \(^{29}\) . This trend is also notable when projecting TOF and total aromatic selectivity to the Fe content; monodispersed Fe increases the TOF of syngas conversion and maintains high selectivity towards aromatics, whereas enriched Fe sacrifices the aromatic selectivity despite the higher TOF (Fig. 2c). As shown in Fig. 2d and supplementary fig. 16b, the outstanding ability of our monodispersed Fe- Zn/Cr based OX- ZEO catalysts to achieve high CO conversion and high aromatics selectivity simultaneously is further illustrated through comparison with several recently reported catalysts for syngas conversion process \(^{30 - 34}\) . Further, the long- term stability test of \(4.48\%\) Fe- Zn/Cr + H- ZSM- 5 shows no signs of decay in either the activity or total aromatic selectivity for more than \(100\mathrm{~h}\) at \(350^{\circ}\mathrm{C}\) and \(2.0\mathrm{MPa}\) and stable CO conversion of \(\sim 45\%\) is achieved (Fig. 2e).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[113, 80, 757, 100]]<|/det|>
+## Mechanistic investigation of monodispersed Fe in enhanced catalytic activity
+
+<|ref|>text<|/ref|><|det|>[[111, 111, 886, 835]]<|/det|>
+The above catalysis evaluation demonstrates the unique ability of monodispersed Fe to catalyze syngas to form reactive oxygenates. To understand the origin of such enhanced activity, we further performed a series of combinatorial mechanistic investigations. Previous demonstrations have suggested surface \(\mathrm{Ov}\) as possible active sites for CO activation \(^{35,36}\) . However, there is a lack of high- precision characterization of \(\mathrm{Ov}^{37}\) . DFT calculations were firstly performed to assess the equilibrium \(\mathrm{Ov}\) concentration in monodispersed Fe- Zn/Cr samples. Using spinel (111) surface as a model surface, the formation energies of \(\mathrm{Ov}\) with different concentrations and spatial locations (i.e., surface and subsurface layer) were calculated through either CO or \(\mathrm{H}_{2}\) reduction (calculation details are presented in Supplementary Materials). Similar to a previous study, CO reduction was found to be the major driving force for \(\mathrm{Ov}\) formation \(^{13}\) (supplementary fig. 17). The phase diagram shows that \(\mathrm{Ov}\) preferably presents in the surface layer with a concentration of 0.25 monolayer (ML) under the experimental condition (Fig. 3a). The atomic evidence of surface \(\mathrm{Ov}\) was obtained by using the integrated differential phase- contrast STEM (iDPC- STEM) technique. Fig. 3b depicts the [111] surface of 4.48 % Fe- Zn/Cr and some \(\mathrm{Ov}\) can be identified with atomic precision. A microquantitative intensity statistic analysis was subsequently performed by applying line scan to the iDPC- STEM images. The non- periodic variations in image contrast relating to O demonstrate the existence of \(\mathrm{Ov}\) and its concentration is estimated to be 25%–28%, similar to the theoretically predicted \(\mathrm{Ov}\) concentration (Fig. 3c). O1s XPS spectra of different Fe- Zn/Cr samples further show that Fe doping only alters surface \(\mathrm{Ov}\) concentration by insignificant amounts (Fig. 3d). Electron paramagnetic resonance spectroscopy also quantitatively evidences the existence of \(\mathrm{Ov}\) (supplementary figs. 18a, b). It is found that there are not much changes in the \(\mathrm{Ov}\) content.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[130, 117, 880, 440]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[112, 454, 884, 680]]<|/det|>
+Fig. 3. Understanding the role of monodispersed Fe in catalytic activity. (a) Thermodynamic phase diagram of Fe-doped \(\mathrm{ZnCr_2O_4}\) (111) surfaces at varying temperatures and CO partial pressures \((P_{\mathrm{CO}})\) (b) iDPC-STEM images of \(4.48\%\) Fe-Zn/Cr. (c) iDPC-STEM intensity profiles along the corresponding dashed lines in B. (d) O 1s XPS spectra of \(\mathrm{ZnCr_2O_4}\) and different Fe-Zn/Cr samples. (e) Projected electric field strength and vector map of \(4.48\%\) Fe-Zn/Cr. (f) Differential charge density (cyan and yellow represent charge depletion and accumulation, respectively; the cutoff of the density-difference isosurface is \(0.11\mathrm{e~Å}^{-3}\) ).
+
+<|ref|>text<|/ref|><|det|>[[112, 696, 884, 892]]<|/det|>
+Since the \(\mathrm{O}_{\mathrm{V}}\) concentration remains marginally affected by Fe doping, it might not be the reason for the enhanced catalytic activity. We then focused on the effect of local electronic structures and performed a charge density analysis by combining electric field imaging and theoretical calculations. As shown in Fig. 3e and supplementary figs. 18c,d, some local bright spots (in red circle) appear despite the surrounding uniform intensity, implying the possible charge transfer between isolated Fe and surrounding O and \(\mathrm{O}_{\mathrm{V}}\) 38. This is corroborated by the theoretically
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 78, 884, 240]]<|/det|>
+calculated charge density (Fig. 3f). Clearly, charges on Ov and O nearest to the Fe dopant increase in Fe- doped \(\mathrm{ZnCr_2O_4}\) with respect to pristine \(\mathrm{ZnCr_2O_4}\) . The locally modulated charge density could account for the difference in catalytic activity between monodispersed Fe- Zn/Cr and Zn/Cr. A series of experiments were conducted to prove the promoted activation effect of Fe dopants on CO and \(\mathrm{H}_2\) (supplementary figs. 19, 20).
+
+<|ref|>text<|/ref|><|det|>[[111, 253, 885, 799]]<|/det|>
+CO hydrogenation reaction pathways were investigated using DFT calculations. By taking the aforementioned structural characterization and theoretical analysis into consideration, undoped and isolated Fe- doped \(\mathrm{ZnCr_2O_4}\) (111) surfaces with 1/4 ML Ov on the surface were constructed for simulations. The gas phase energies of CO and \(\mathrm{H}_2\) are adjusted using the actual experimental conditions. On both surfaces, our calculations support the stepwise hydrogenation mechanism in syngas conversion (Fig. 4a) \(^{13,15}\) . In more details, the reaction starts with CO adsorption at Ov (Fig. 4b). Next, \(\mathrm{H}_2\) dissociates near the surface Ov and \(\mathrm{H}^*\) is adsorbed on top of an O near Fe (16d). Subsequently, adsorbed CO\* is stepwise hydrogenated to form formyl (CHO\*), formaldehyde (CH2O\*), methoxyl (CH3O\*), and finally CH3OH. It is found that pristine \(\mathrm{ZnCr_2O_4}\) (111) with Ov is mainly limited by the weak adsorption of \(\mathrm{H}^*\) with the presence of CHO\*, as well as strong adsorption of CH3O\*. The incorporation of isolated Fe effectively stabilizes the state of CHO\* + H\*, making the hydrogenation step to form H2CO\* energetically exothermic, while destabilizes the state of CH3O\* + H\*, thereby facilitating the formation of CH3OH. From both aspects, monodispersed Fe improves the ability of pristine \(\mathrm{ZnCr_2O_4}\) to produce key oxygenate intermediates of H2CO and CH3OH from syngas. These key intermediates further participate in complicated oxygenate- to- aromatics reactions occurring in the pores of H- ZSM- 5 \(^{39}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[149, 99, 819, 420]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[112, 453, 884, 475]]<|/det|>
+Fig. 4. The mechanism study of monodispersed Fe & pristine \(\mathrm{ZnCr_2O_4}\) in syngas conversion.
+
+<|ref|>text<|/ref|><|det|>[[112, 487, 884, 610]]<|/det|>
+(a) Gibbs free energy diagrams of syngas conversion to \(\mathrm{CH_3OH}\) on pristine and Fe-doped \(\mathrm{ZnCr_2O_4}\) (111) surfaces with 1/4 ML \(\mathrm{Ov}\) . The reaction images are shown in the inset of a; Zn: green, Cr: blue, Fe: yellow, O: red, C: brown, and H: white. (b) The atomic structures of the corresponding states in a.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 697, 212, 714]]<|/det|>
+## Conclusion
+
+<|ref|>text<|/ref|><|det|>[[112, 730, 884, 891]]<|/det|>
+In this study, we demonstrated that the spinel structure of \(\mathrm{ZnCr_2O_4}\) can disperse strong self- interaction metal, Fe, spontaneously due to the thermodynamically stable state caused by the interaction between Fe and \(\mathrm{ZnCr_2O_4}\) , showing the highest performance in syngas- to- aromatic reaction. By combining high- precision microscopic and macroscopic characterizations and theory calculations, monodispersed Fe activates the surrounding \(\mathrm{Ov}\) , thereby activating the CO and \(\mathrm{H_2}\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 78, 886, 415]]<|/det|>
+while avoiding the formation of \(\mathrm{Fe_xC_y}\) and maintaining stability under a reducing atmosphere. The TOF increased from 0.54 to \(2.48 \mathrm{h}^{- 1}\) without sacrificing the aromatic selectivity in monodispersed Fe samples. Our monodispersed Fe in the \(\mathrm{ZnCr_2O_4}\) catalyst showed \(81.4\%\) aromatic selectivity at a single- pass CO conversion of \(68.4\%\) , which is the best catalyst evaluation among all Fe- based catalysts during the syngas- to- aromatic reaction. DFT calculations revealed that the monodispersion of Fe in 16d sites lowered the key determining step of \(\mathrm{HCO^* + H^* - H_2CO^*}\) , thereby accelerating the C1 oxygenate intermediates, which made them diffuse quickly into the pores of H- ZSM- 5 to initiate the C- C coupling toward the aromatics. This study provides a prototype for rationally tailoring single atom Fe in syngas chemistry to obtain targeted catalytic reactivity and avoid the formation of \(\mathrm{Fe_xC_y}\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[56, 88, 886, 888]]<|/det|>
+Wang, X., Zhao, B., Jiang, D.- e. & Xie, Y. Monolayer dispersion of MoO3, NiO and their precursors on \(\gamma\) - Al2O3. Applied Catalysis A: General 188, 201- 209 (1999). Zhang, X., Liu, J., Jing, Y. & Xie, Y. Support effects on the catalytic behavior of NiO/Al2O3 for oxidative dehydrogenation of ethane to ethylene. Applied Catalysis A: General 240, 143- 150 (2003). Brajpuriya, R. & Shripathi, T. Investigation of Fe/Al interface as a function of annealing temperature using XPS. Applied Surface Science 255, 6149- 6154, doi:10.1016/j.apsusc.2009.01.070 (2009). Guo, Y., Fu, Y., Liu, Y. & Shen, S. Photoelectrochemical activity of ZnFe2O4modified \(\alpha\) - Fe2O3nanorod array films. RSC Advances 4, doi:10.1039/c4ra05289g (2014). Gao, R. et al. Pt/Fe2O3 with Pt- Fe pair sites as a catalyst for oxygen reduction with ultralow Pt loading. Nature Energy 6, 614- 623, doi:10.1038/s41560- 021- 00826- 5 (2021). Sun, Q., Wang, N. & Yu, J. Advances in Catalytic Applications of Zeolite- Supported Metal Catalysts. Adv Mater 33, e2104442, doi:10.1002/adma.202104442 (2021). Han, J. et al. Single- atom Fe- Nx- C as an efficient electrocatalyst for zinc- air batteries. Advanced Functional Materials 29, 1808872 (2019). Jones, J. et al. Thermally stable single- atom platinum- on- ceria catalysts via atom trapping. Science 353, 150- 154 (2016). Nie, L. et al. Activation of surface lattice oxygen in single- atom Pt/CeO2 for low- temperature CO oxidation. Science 358, 1419- 1423 (2017). Xu, Y. et al. A hydrophobic FeMn@Si catalyst increases olefins from syngas by suppressing C1 by- products. Science 371, 610- 613, doi:10.1126/science.abb3649 (2021). Cui, X. et al. Selective production of aromatics directly from carbon dioxide hydrogenation. ACS Catalysis 9, 3866- 3876 (2019). Navrotsky, A. & Kleppa, O. The thermodynamics of cation distributions in simple spinels. Journal of Inorganic and nuclear Chemistry 29, 2701- 2714 (1967). Ma, S., Huang, S.- D. & Liu, Z.- P. Dynamic coordination of cations and catalytic selectivity on zinc- chromium oxide alloys during syngas conversion. Nature Catalysis 2, 671- 677, doi:10.1038/s41929- 019- 0293- 8 (2019). Hu, J. et al. Sulfur vacancy- rich MoS2 as a catalyst for the hydrogenation of CO2 to methanol. Nature Catalysis 4, 242- 250, doi:10.1038/s41929- 021- 00584- 3 (2021). Zhang, Z. et al. The active sites of Cu- ZnO catalysts for water gas shift and CO hydrogenation reactions. Nat Commun 12, 4331, doi:10.1038/s41467- 021- 24621- 8 (2021). Guo, Y. et al. A facile spray pyrolysis method to prepare Ti- doped ZnFe2O4 for boosting photoelectrochemical water splitting. Journal of Materials Chemistry A 5, 7571- 7577, doi:10.1039/c6ta11134c (2017). Fu, Y. et al. Insights into the size effect of ZnCr2O4 spinel oxide in composite catalysts for conversion of syngas to aromatics. Green Energy & Environment, doi:10.1016/j.gee.2021.07.003 (2021).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 78, 886, 888]]<|/det|>
+367 18 Gao, W. et al. Capsule-like zeolite catalyst fabricated by solvent-free strategy for para- 368 Xylene formation from CO2 hydrogenation. Applied Catalysis B: Environmental 303, 369 120906 (2022). 370 19 Han, W. et al. Research progresses in the hydrogenation of carbon dioxide to certain 371 hydrocarbon products. Journal of Fuel Chemistry and Technology 49, 1609- 1619 (2021). 372 20 Li, A. et al. Enhancing the stability of cobalt spinel oxide towards sustainable oxygen 373 evolution in acid. Nature Catalysis, 1- 10 (2022). 374 21 Jiao, F. et al. Selective conversion of syngas to light olefins. Science 351, 1065- 1068 375 (2016). 376 22 Zhou, W. et al. New horizon in C1 chemistry: breaking the selectivity limitation in 377 transformation of syngas and hydrogenation of CO2 into hydrocarbon chemicals and fuels. 378 Chem Soc Rev 48, 3193- 3228, doi:10.1039/c8cs00502h (2019). 379 23 Li, Z. et al. Highly Selective Conversion of Carbon Dioxide to Aromatics over Tandem 380 Catalysts. Joule 3, 570- 583, doi:10.1016/j.joule.2018.10.027 (2019). 381 24 Song, C. et al. Photothermal conversion of CO2 with tunable selectivity using Fe- based 382 catalysts: from oxide to carbide. ACS Catalysis 10, 10364- 10374 (2020). 383 25 Li, Z. et al. Fe- Based Catalysts for the Direct Photohydrogenation of CO2 to Value- Added 384 Hydrocarbons. Advanced Energy Materials 11, 2002783 (2021). 385 26 Liu, C. et al. Constructing directional component distribution in a bifunctional catalyst to 386 boost the tandem reaction of syngas conversion. Chem Catalysis 1, 896- 907, 387 doi:10.1016/j.checat.2021.06.016 (2021). 388 27 Arslan, M. T. et al. Highly Selective Conversion of CO2 or CO into Precursors for 389 Kerosene- Based Aviation Fuel via an Aldol- Aromatic Mechanism. ACS Catalysis 12, 390 2023- 2033 (2022). 391 28 Zhou, C. et al. Highly Active ZnO- ZrO2 Aerogels Integrated with H- ZSM- 5 for Aromatics 392 Synthesis from Carbon Dioxide. ACS Catalysis 10, 302- 310, 393 doi:10.1021/acscatal.9b04309 (2019). 394 29 Zhu, J. et al. Dynamic structural evolution of iron catalysts involving competitive oxidation 395 and carburization during CO2 hydrogenation. Science Advances 8, eabm3629 (2022). 396 30 Zhao, B. et al. Direct Transformation of Syngas to Aromatics over Na- Zn- Fe 5 C 2 and 397 Hierarchical HZSM- 5 Tandem Catalysts. Chem 3, 323- 333, 398 doi:10.1016/j.chempr.2017.06.017 (2017). 399 31 Wei, J. et al. Directly converting CO2 into a gasoline fuel. Nature communications 8, 1- 9 400 (2017). 401 32 Geng, S., Jiang, F., Xu, Y. & Liu, X. iron- based Fischer- Tropsch synthesis for the efficient 402 conversion of carbon dioxide into Isoparaffins. ChemCatChem 8, 1303- 1307 (2016). 403 33 Wang, X. et al. Synthesis of isoalkanes over a core (Fe- Zn- Zr)- shell (zeolite) catalyst by 404 CO 2 hydrogenation. Chemical Communications 52, 7352- 7355 (2016). 405 34 Dai, C. et al. Hydrogenation of CO2 to Aromatics over Fe- K/Alkaline Al2O3 and P/ZSM- 406 5 Tandem Catalysts. Industrial & Engineering Chemistry Research 59, 19194- 19202 407 (2020).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 80, 886, 343]]<|/det|>
+408 35 Wang, Y. et al. Visualizing Element Migration over Bifunctional Metal- Zeolite Catalysts 409 and its Impact on Catalysis. Angew Chem Int Ed Engl 60, 17735- 17743, 410 doi:10.1002/anie.202107264 (2021). 411 36 Pan, X., Jiao, F., Miao, D. & Bao, X. Oxide- Zeolite- Based Composite Catalyst Concept 412 That Enables Syngas Chemistry beyond Fischer- Tropsch Synthesis. Chemical Reviews 413 121, 6588- 6609 (2021). 414 37 Wang, S. et al. Selective conversion of CO2 into propene and butene. Chem 6, 3344- 3363 415 (2020). 416 38 Shibata, N. et al. Electric field imaging of single atoms. Nature communications 8, 1- 7 417 (2017). 418 39 Arslan, M. T. et al. Selective Conversion of Syngas into Tetramethylbenzene via an Aldol- 419 Aromatic Mechanism. ACS Catalysis 10, 2477- 2488, doi:10.1021/acscatal.9b03417 420 (2020). 421
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 408, 285, 425]]<|/det|>
+## Acknowledgements:
+
+<|ref|>text<|/ref|><|det|>[[115, 427, 883, 504]]<|/det|>
+This work is supported by the National Natural Science Foundation of China (21908125 and 22005170), the National Key Research and Development Program of China (2018YFB0604801), the Key Research and Development Program of Inner Mongolia and Ordos, and CNPC Innovation Funds.
+
+<|ref|>text<|/ref|><|det|>[[115, 525, 883, 565]]<|/det|>
+Author contributions: G.T and X.L contributed equally. All the authors approved the final version of the manuscript.
+
+<|ref|>text<|/ref|><|det|>[[115, 584, 789, 604]]<|/det|>
+Competing financial interests: The authors declare no competing financial interests.
+
+<|ref|>text<|/ref|><|det|>[[115, 623, 883, 662]]<|/det|>
+Data and materials availability: All data are available in the manuscript or the supplementary materials.
+
+<|ref|>text<|/ref|><|det|>[[115, 682, 360, 700]]<|/det|>
+Supplementary Information:
+
+<|ref|>text<|/ref|><|det|>[[115, 703, 300, 720]]<|/det|>
+Materials and Methods
+
+<|ref|>text<|/ref|><|det|>[[115, 723, 240, 739]]<|/det|>
+Figs. S1 to S20
+
+<|ref|>text<|/ref|><|det|>[[115, 743, 238, 758]]<|/det|>
+Table S1 to S4
+
+<|ref|>text<|/ref|><|det|>[[115, 763, 250, 779]]<|/det|>
+References (1- 9)
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 612, 150]]<|/det|>
+SupplementaryInformationSubmitNatureCommunication.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/images_list.json b/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..7a19c0fffc2d6956ae93214a8c0b63deea61b591
--- /dev/null
+++ b/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/images_list.json
@@ -0,0 +1,47 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. Chirality at different length scales. (a) Bright-Field STEM image showing the stack of 16 STO/16 PTO/16 STO with SRO buffer layer on DSO substrate. The red regions near the center of the PTO layer indicate the position of the vortex core approximately. (b) Vector mapping of the local displacements of A sites of highlighted region in (a) overlaid on HAADF-STEM image. The local red- and blue contrast at the center of the PTO layer indicates the local non-zero curl of displacement. The net lateral polarization resulting from vortex off-centering is indicated at the top. The dotted black line shows the center of the PTO layer. (c) Dark field TEM image along [110]o direction displaying long tubular vortex structure with domain walls shown as white dashed lines.",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 95,
+ 884,
+ 400
+ ]
+ ],
+ "page_idx": 7
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Identification of polarization using 4D-STEM mapping. (a) Schematic showing the e-beam scanned in 4D STEM mode across the vortex sample in in-plane geometry. (b) Virtual dark field image of the vortex region obtained via integrating the intensity of disk 3 from the mean diffraction pattern in (c). Zoomed-in images of the (d) dash-dot region (e) solid line region showing lateral (P [001]o) and axial (P [110]o) polarization maps in vortices. \\(\\alpha , \\beta ,\\) and \\(\\gamma\\) domain walls can be identified. \\(\\alpha\\) domain wall (magenta curve) has an anti-parallel lateral (P [001]o) component, \\(\\beta\\) (green curve) domain wall has an anti-parallel axial component (P [110]o), \\(\\gamma\\) has both axial and lateral components antiparallel across the domain wall.",
+ "footnote": [],
+ "bbox": [
+ [
+ 120,
+ 95,
+ 880,
+ 490
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Identification of triple point topologies and chiral domain walls. (a) The helicity map formed from Figure 2b shows left and right-handed domains separated by \\(\\alpha\\) (magenta) and \\(\\beta\\) (green). Additionally, achiral domain walls (black line) also coexist. The resultant triple point topologies formed due to the co-existence of chiral and achiral domain walls are shown in encircled regions. The sense of rotation of these triple point topologies is indicated in the encircled region. (b-c) Possible pairs of triple points. (b) represents triple points with opposite sense of rotation with the point of inversion along \\(\\beta\\) , \\(\\gamma\\) , and \\(\\alpha\\) (c) represents triple points with the same sense of rotation. The green ticks on the side show what has been observed in experiments.",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 90,
+ 875,
+ 288
+ ]
+ ],
+ "page_idx": 11
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18.mmd b/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..8b22d44444e8a219d0c52520b3d73309441bd8a4
--- /dev/null
+++ b/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18.mmd
@@ -0,0 +1,270 @@
+
+# The emergence of three-dimensional chiral domain walls in polar vortices
+
+Sandhya Susarla ( \(\boxed{ \begin{array}{r l} \end{array} }\) sandhya.susarla@asu.edu) Arizona State University https://orcid.org/0000- 0003- 1773- 0993
+
+Shang- Lin Hsu University of california, Berkeley
+
+Fernando Gomez- Ortiz Universidad de Cantabria https://orcid.org/0000- 0002- 7203- 8476
+
+Pablo Garcia- Fernandez Universidad de Cantabria https://orcid.org/0000- 0002- 4901- 0811
+
+Benjamin Savitzky Cornell University
+
+SUJIT DAS Indian Institute of Science, Bangalore https://orcid.org/0000- 0001- 9823- 0207
+
+Piush Behera University of California, Berkeley
+
+Javier Junquera Universidad de Cantabria, Cantabria Campus Internacional https://orcid.org/0000- 0002- 9957- 8982
+
+Peter Erucis Lawrence Berkeley National Laboratory https://orcid.org/0000- 0002- 6762- 9976
+
+Ramamoorthy Ramesh Rice University
+
+Colin Ophus National Center for Electron Microscopy Facility, Molecular Foundry, Lawrence Berkeley National Laboratory
+
+Article
+
+Keywords:
+
+Posted Date: February 8th, 2023
+
+DOI: https://doi.org/10.21203/rs.3.rs- 2551328/v1
+
+License: \(\circledcirc\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+
+Version of Record: A version of this preprint was published at Nature Communications on July 25th, 2023. See the published version at https://doi.org/10.1038/s41467-023-40009-2.
+
+<--- Page Split --->
+
+## The emergence of three-dimensional chiral domain walls in polar vortices
+
+Sandhya Susarla \(^{1,2,\mathrm{S}\# *}\) , Shanglin Hsu \(^{1,2\#}\) , Fernando Gómez- Ortiz \(^{4}\) , Pablo García- Fernández \(^{4}\) , Benjamin H. Savitzky \(^{1}\) , Sujit Das \(^{2,6}\) , Piush Behera \(^{3}\) , Javier Junquera \(^{4}\) , Peter Ercius \(^{1}\) , Ramamoorthy Ramesh \(^{1,2,5,7,8*}\) , Colin Ophus \(^{1*}\)
+
+1: National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA 94720
+2: Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley CA, USA 94720
+3: Department of Materials Science & Engineering, University of California, Berkeley, CA, USA 94720
+4: Departmento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional Santander, Spain, 39005
+5: Department of Physics, University of California, Berkeley Berkeley, CA, USA 94720
+6: Material Research Centre, Indian Institute of Science, Bangalore, 560012
+7: Department of Physics, Rice University, Houston, TX, USA, 77005
+8: Department of Materials Science and Nanoengineering, Houston, TX, USA, 77005 #Equal contribution.
+\$ Present address: School for Engineering of Matter, Transport, and Energy, Arizona State University
+
+Corresponding authors: sandhya.susarla@asu.edu, ramamoorthy.ramesh@rice.edu, and clophus@lbl.gov
+
+## Abstract
+
+Chirality or handedness of a material can be used as an order parameter to uncover emergent electronic properties for quantum information science. Conventionally, chirality is found in naturally occurring biomolecules and magnetic materials. Chirality can be engineered in a topological polar vortex ferroelectric/dielectric system via atomic- scale symmetry- breaking operations. We use four- dimensional scanning transmission electron microscopy (4D- STEM) to map out topology- driven three- dimensional domain walls, where the handedness of two neighbor topological domains change or remain the same. The nature of the domain walls is governed by the interplay of local perpendicular (lateral) and parallel (axial) polarization with respect to the tubular vortex structures. Unique symmetry- breaking operations and the finite nature of domain walls results in a triple point at the junction of chiral and achiral domain walls. The unconventional nature of the domain walls with triple point pairs may result in unique electrostatic and magnetic properties potentially useful for quantum sensing applications.
+
+<--- Page Split --->
+
+## Introduction
+
+Chirality is a unique topological feature that drives many- body interactions in naturally occurring organic molecules and proteins \(^{1}\) , subatomic particle physics \(^{2}\) , and solid- state physics \(^{3}\) . The symmetries in a chiral system are configured in such a way that its mirror image cannot be superimposed on itself, manifesting a handedness to the system as exemplified by screws and our own hands. Chirality also exists at the microscale/nanoscale level in inorganic and organic materials such as liquid crystals \(^{4}\) , spin textures in ferromagnets \(^{5,6}\) , amino acids, and D/L- glucose molecules \(^{1}\) with applications in spin selectivity- based quantum sensing \(^{7}\) , non- linear optics \(^{8}\) , and biosensing applications \(^{9}\) . However, there are very few examples of chiral inorganic ferroelectric crystals which could have fundamentally different domain textures \(^{10 - 13}\) . Over the past few years, novel polarization textures in ferroelectrics such as merons \(^{14}\) , polar flux- closure domains \(^{15,16}\) , vortices \(^{17}\) , bubble domains \(^{18,19}\) , super crystals \(^{20,21}\) and skyrmions \(^{22}\) have been engineered in oxide superlattices, emerging from the careful interplay of elastic, electrostatic and gradient energies of electric dipoles. The electric dipole arrangement and complex orbital hybridization in these systems have been probed by the x- ray scattering techniques \(^{23}\) , scanning transmission electron microscopy (STEM) \(^{17}\) - electron energy loss spectroscopy (EELS) \(^{24}\) , phase- field simulations \(^{12,14,15,17,20}\) and atomistic first- and second- principles calculations \(^{17,18,20,22,23}\) . Surprisingly, the presence of chirality has been observed in one such topological texture i.e. polar vortices in \(\mathrm{PbTiO_3 / SrTiO_3}\) superlattices from resonant soft x- ray scattering (RXS) \(^{23}\) , second harmonic generation (SHG) and second principles calculations \(^{25}\) . The presence of chirality in polar vortices is an emergent phenomenon because none of the parent compounds such as \(\mathrm{SrTiO_3}\) or \(\mathrm{PbTiO_3}\) are known to be chiral. It has been recently shown experimentally and theoretically that the presence of chirality in these systems might be due to different sources.
+
+<--- Page Split --->
+
+First, the strongest one is the coexistence of vortices with an axial component of the polarization, perpendicular to the vortex plane \(^{26}\) . The second factor is the buckling of the vortices (i.e., a staggered vortex configuration where the center of the clockwise and counterclockwise vortices are located at different heights) combined with different sizes of the up and down domains results in a chiral structure, although its strength is smaller than in the first scenario. This last source of chirality can be reversed by external electric fields. The first experimental demonstration was in \(^{25}\) , where chirality switches in a reversible, deterministic, and non- destructive fashion over mesoscale regions \(^{25}\) .
+
+Without any prior knowledge, one would expect the as- grown sample as a racemic mixture, i.e., equal amounts of left- handed and right- handed domain enantiomers, where chirality within each domain comes from a combination of the two sources described above. To have a non- destructive switchable chirality, it is essential to understand the role of the domain walls separating the enantiomers. In other words, what local physical parameters play a role when the handedness in neighboring domains changes? This includes the offset between the center of the cores, the axial component at the center of the clockwise/counterclockwise vortices, the sense of rotation of the vortices when they merge at the domain wall, the presence of dislocations, or the combined effect of all of them. A proper understanding of how the left/right- handed domains evolve at the nanoscale is crucial to design new electrically switchable chiral devices that can be measured without scientifically sophisticated techniques. Indeed, a proper answer to this question will pave the way for the use of these chiral textures in next- generation technologies.
+
+Four- dimensional (4D)- STEM can precisely measure strain, and thus spontaneous polarization in ferroelectrics due to the violation of Friedel's Law \(^{27 - 29}\) . This makes 4D- STEM a unique tool to probe polarization in three dimensions and understand emergent chirality in
+
+<--- Page Split --->
+
+polarization vortices. In the current work, we have used 4D- STEM to probe three- dimensional domain walls in polar vortices in oxide superlattices and understand the nano- scale nature of chirality. We find that both achiral and chiral domain walls coexist in the same system. The chiral to achiral domain wall transition is driven by the change in local axial and lateral polarization direction across the domain wall. We have discovered new pair of triple points with the opposite/same sense of rotation at the junction of achiral and chiral domain walls. Finally, we unravel all the possible configurations of chiral and achiral domain walls in this system through different symmetry- breaking operations.
+
+## Results
+
+Trilayer \((\mathrm{SrTiO}_3)_{16} / (\mathrm{PbTiO}_3)_{16} / (\mathrm{SrTiO}_3)_{16}\) (STO/PTO/STO) were grown on orthorhombic \(\mathrm{DyScO}_3\) (DSO) \([110]_{0}\) substrates with \(\mathrm{SrRuO}_3\) as a buffer layer using reflection high- energy electron diffraction (RHEED)- assisted pulsed- laser deposition (PLD) (Figure 1A and Supplementary Information). The polar vortex phase in this system is stabilized as a consequence of the interplay between depolarization energy at the PTO/STO interfaces, elastic energy from the tensile strain imposed by the DSO substrate, and the gradient energy in the ferroelectric \(^{17}\) .
+
+A direct way to measure the polar textures in vortex topologies is through electron microscopy using atomic resolution images. We have used different types of STEM and TEM techniques to characterize the exact positions of the vortex centers. Figure 1a shows a low- magnification bright- field STEM image of the superlattice trilayer with an SRO buffer layer along the \([1\bar{1} 0]_{0}\) zone axis. The diffraction contrast in BF- STEM allows us to directly locate the vortex center as dark contrast; marked using red circles in Figure 1a. To precisely understand the polarization or displacement texture around each vortex center, we obtained the A- site
+
+<--- Page Split --->
+
+displacement vector maps at atomic resolution via gaussian fitting at A- sites (Methods, supplementary information). Figure 1b shows the High angle annular dark field (HAADF)- STEM image of trilayer STO/PTO/STO along \([1\bar{1} 0]_{0}\) zone axis where brighter regions are PTO and darker regions are STO. Overlaid yellow arrows show clockwise and counterclockwise rotating curls in the displacement of the A- cation in PTO/STO superlattices. The coexistence of the concomitant non- zero curl of polarization (red/blue contrast) with an alternating axial component of the polarization (perpendicular to the plane defined by the vortices) is the first symmetry- breaking operation that results in emergent chirality in an otherwise non- chiral system. The non- zero curl is larger in continuously rotating polarization textures such as polar vortices \(^{25,27}\) , merons \(^{30}\) , and skyrmions \(^{22}\) than in other polarization textures such as flux closure domains \(^{15,16}\) where the curl vanished in the central regions with \(180^{0}\) domain walls. Additionally, we observe that the cores of the polarization curls (indicated as blue/red contrast) are not located exactly at the center of the PTO layer, but follow a zig- zag type pattern, giving rise to a net in- plane polarization rotation along \([001]_{0}\) (lateral component) indicated as \(\mathrm{P}_{\mathrm{x}}\) in Figure 1b. This buckling, combined with a small difference in the size of the up and down domains, is the second symmetry- breaking operation that results in net chirality; in agreement with previous observations \(^{25}\) .
+
+<--- Page Split --->
+
+
+Figure 1. Chirality at different length scales. (a) Bright-Field STEM image showing the stack of 16 STO/16 PTO/16 STO with SRO buffer layer on DSO substrate. The red regions near the center of the PTO layer indicate the position of the vortex core approximately. (b) Vector mapping of the local displacements of A sites of highlighted region in (a) overlaid on HAADF-STEM image. The local red- and blue contrast at the center of the PTO layer indicates the local non-zero curl of displacement. The net lateral polarization resulting from vortex off-centering is indicated at the top. The dotted black line shows the center of the PTO layer. (c) Dark field TEM image along [110]o direction displaying long tubular vortex structure with domain walls shown as white dashed lines.
+
+The various permutations and combinations of atomic scale symmetry- breaking operations such as a non- zero curl of polarization together with the presence of an axial component, and the buckling of the vortices that yield a non- zero polarization component along [001]o, result in different types of domains walls at the mesoscale. We can visualize the mesoscale domain walls in these topological structures by imaging the vortices along the [110]o zone axis using weak beam dark field TEM (Figure 1c). We can observe the tubular nature of vortex textures by long bright and dark stripes regions in the image. Additionally, we observe different domain wall features (indicated as white dashed lines) cutting across vortex tubes. Overall, if we combine our observations from DF- TEM and HR- STEM, we observe a three-
+
+<--- Page Split --->
+
+dimensional structure in the PbTiO₃ layer sandwiched between SrTiO₃ layers where the polarization curls follow a tubular pattern (Figure 2a). Unfortunately, the images formed by weak beam dark field, HRSTEM, and BF- STEM are merely atomic projections and cannot give us an estimate of physical quantities such as polarization and chirality. On the other hand, 4D- STEM allows us to collect a diffraction pattern at each probe position, which can then be used to create precise maps of physical quantities. For the present experiment, we performed 4D- STEM imaging on a trilayer STO/PTO/STO along the [110]₀ zone axis (Figure 2a). We used a probe size of \(\sim 7 \text{Å}\) , larger than the STO/PTO unit cell dimensions ( \(\sim 4 \text{Å}\) ) to remove the atomic- resolution signal and to estimate the polarization at unit cell resolution. The 4D- STEM analysis was carried out in open source py4DSTEM analysis package ³¹. We define the [110]₀ direction as axial and [001]₀ direction as lateral. The rotation calibration was performed between the real space and diffraction space to determine the lateral and axial axis. Details are given in the supplementary information. For initial visualization of the polar textures, we created a virtual dark field image using the [2\(\bar{1}\)0]₀ disk (disk 3) as shown in Figure 2b- c. The polarization from the PTO layer can be determined qualitatively by subtracting opposite Friedel pair disks due to the violation of Friedel’s law ²⁷-²⁹. The polarization maps corresponding to regions delimited by rectangles in Figure 2b are shown in Figure 2d- e. We observe alternate longitudinal red and blue stripes representing positive and negative polarization in both the lateral ([001]₀) and axial [110]₀ directions with domain walls as seen from the weak beam dark field images marked with green and magenta lines in Figure 2d and with a black line in Figure 2e. We observe that the axial polarization magnitude is relatively smaller than the lateral polarization in agreement with the predictions from previous second principles calculations ²³,²⁵.
+
+<--- Page Split --->
+
+
+Figure 2. Identification of polarization using 4D-STEM mapping. (a) Schematic showing the e-beam scanned in 4D STEM mode across the vortex sample in in-plane geometry. (b) Virtual dark field image of the vortex region obtained via integrating the intensity of disk 3 from the mean diffraction pattern in (c). Zoomed-in images of the (d) dash-dot region (e) solid line region showing lateral (P [001]o) and axial (P [110]o) polarization maps in vortices. \(\alpha , \beta ,\) and \(\gamma\) domain walls can be identified. \(\alpha\) domain wall (magenta curve) has an anti-parallel lateral (P [001]o) component, \(\beta\) (green curve) domain wall has an anti-parallel axial component (P [110]o), \(\gamma\) has both axial and lateral components antiparallel across the domain wall.
+
+We track the relative domain shift across the wall by the black dotted line as shown in Figure 2d- e. In Figure 2d, we observe a \(\alpha\) - domain wall (magenta line) where the lateral polarization shifts whereas the axial polarization remain the same, as shown in Figure 3. We also detect a \(\beta\) - domain wall (green line), where the axial polarization shifts, but the lateral polarization remains the same. Finally, in Figure 2e there is a third domain wall configuration i.e., a \(\gamma\) - domain wall (black line) as well where both the lateral and axial polarization shift. We verified this observation with average line profiles across the domain walls (Supplementary
+
+<--- Page Split --->
+
+information, Figure S1). To detect whether a change of chirality occurs at these domain walls, a way to quantify the chirality is required. The order parameter that best captures the breakdown of chiral symmetry is the helicity H of the chiral field. In our case, the chiral field is the polarization, and for the helicity, we borrow the definition from fluid dynamics:
+
+\[\mathcal{H} = \int \vec{p}\cdot \left(\vec{\nabla}\times \vec{p}\right)d^{3}r, \quad (1)\]
+
+where \(\vec{p}\) is the local value of polarization. Note that \(\mathcal{H}\) changes sign upon a mirror symmetry reflection \(^{32,33}\) . A nonzero helicity means chirality or lack of mirror symmetry of the polarization texture: right (left) handedness can be associated with positive (negative) values of \(\mathcal{H}\) . Assuming a vortex structure where the polarization lines in the plane defined by the vortices are closed, and that we can measure the axial and lateral components of the polarization at the topmost \(\mathrm{PbTiO_3}\) layer, then the previous equation can be estimated by
+
+\[\mathcal{H} = 2\cdot < p_{lateral} > < p_{axial} > \quad (2)\]
+
+where \(p_{lateral}\) and \(p_{axial}\) are polarization along lateral and axial directions (Supplementary information, Figure S2). Using this equation we can understand the nature of domain walls found in Figure 2d- e. For the \(\alpha /\beta\) domain wall, only one of the lateral/axial polarization sign change across the domain wall. This causes a change in the overall sign of helicity, thus making them chiral domain walls. On the other hand, the \(\gamma\) - domain wall has both a lateral and axial polarization switch, which doesn't change the overall helicity of the system, thus making it an achiral domain wall.
+
+<--- Page Split --->
+
+
+Figure 3. Identification of triple point topologies and chiral domain walls. (a) The helicity map formed from Figure 2b shows left and right-handed domains separated by \(\alpha\) (magenta) and \(\beta\) (green). Additionally, achiral domain walls (black line) also coexist. The resultant triple point topologies formed due to the co-existence of chiral and achiral domain walls are shown in encircled regions. The sense of rotation of these triple point topologies is indicated in the encircled region. (b-c) Possible pairs of triple points. (b) represents triple points with opposite sense of rotation with the point of inversion along \(\beta\) , \(\gamma\) , and \(\alpha\) (c) represents triple points with the same sense of rotation. The green ticks on the side show what has been observed in experiments.
+
+We can use the qualitative lateral and axial polarization data from 4D- STEM and create a map of the helicity over a large scale using the helicity equation as shown in Figure 3. The red and blue regions in the chirality maps indicate different signs of helicity in the system, making them left- handed and right- handed chiral domains separated by the \(\alpha\) or \(\beta\) domain walls. We find that most of these chiral and achiral domain walls were not visible in the virtual dark field images. Further, we also observe a unique triple point topology at the mesoscale whenever the two types of chiral domain walls meet an achiral domain wall as seen from black- encircled areas, thus forming a quasi- 1D defect in the network of chiral and achiral domain walls. These triple points tend to exist in pairs and exhibit a sense of rotation via the transition from \(\alpha\) to \(\beta\) to \(\gamma\) domain wall and vice- versa (Figure 3, S3- S4), similar to what has been observed previously in the trimerized domain walls in hexagonal manganates \(^{34}\) , vortex- antivortex phases in intercalated Vander- Waal ferromagnets \(^{6}\) , and ferroelectric vortex cores in BiFeO \(_{3}\) \(^{35}\) . The sense of rotation in
+
+<--- Page Split --->
+
+a triple point can be the same or opposite depending on the arrangement of \(\alpha , \beta\) or \(\gamma\) domain walls. Figure 3b,c illustrates this situation. Whenever a pair of domain walls \((\beta , \gamma\) or \(\alpha , \gamma\) or \(\alpha , \beta\) ) break inversion symmetry across \(\alpha , \beta\) or \(\gamma\) domains, we form triple point pairs with opposite sense of rotation. If the inversion symmetry across \(\alpha , \beta\) or \(\gamma\) domains is not broken, we form triple point pairs with the same sense of rotation. The origin of triple point pairs can be understood by the following hypothesis. Consider the example of the first triple point pair in Figure 3b. If this particular type of triple point has to be isolated, then \(\beta\) boundary would infinitely separate the positive and negative chirality regions. If \(\beta\) boundary is not infinite, then it has to meet somewhere an \(\alpha\) boundary to continue separating the positive and negative chirality regions. Now, if a \(\beta\) boundary (change in axial polarization) meets an \(\alpha\) boundary (change in lateral polarization), a \(\gamma\) boundary appears (change in both lateral and axial polarization). In such a scenario, we get another triple point in the vicinity of the first triple point thus explaining the origins of pairs for the majority of cases. \(\alpha / \beta\) boundary could be isolated only in very special circumstances when they are born/die at the surface or they are infinitely long.
+
+![PLACEHOLDER_12_0]
+
+
+<--- Page Split --->
+
+Figure 4. Types of chiral domain walls. (a) Four possible combinations of alternating clockwise/counterclockwise vortices are displaced, Top and bottom cartoons differ by the direction of the axial component of the polarization (red dot and blue cross). Left and right cartoons differ by the curl of the polarization. The chirality for each type of domain is indicated by a sketched hand. The possible domain walls between these configurations are marked as type \(\alpha /\alpha^{\prime}\) , \(\beta /\beta^{\prime}\) , and \(\gamma /\gamma^{\prime}\) . \(\alpha /\alpha^{\prime}\) and \(\beta /\beta^{\prime}\) domain walls change the chirality at the domain wall. \(\gamma /\gamma^{\prime}\) domains preserve the chirality. (b- d) Three- dimensional representation of three types of chiral domain walls observed by 4D- STEM measurements.
+
+From a theoretical perspective, there are three symmetry- breaking operations for the formation of domain walls, 1) Change in the lateral polarization direction, 2) Change in axial polarization direction, and 3) Change in the net lateral polarization due to the vortex core shifting away from the center. If we consider all three factors, then we expect to have six types of domain walls as shown in Figure 4. The first pair of chiral domain walls, \(\alpha /\alpha^{\prime}\) , results from a combination of factors 1 and 3. The second chiral domain wall pair, \(\beta /\beta^{\prime}\) , results from a combination of factors 2 and 3. The third achiral domain wall pair results from all three factors. Unfortunately, it is challenging to measure the quantitative net lateral component in the vortices due to the very low sensitivity of electron scattering to sample changes along the beam direction. Due to this, \(\alpha /\alpha^{\prime}\) , \(\beta /\beta^{\prime}\) , and \(\gamma /\gamma^{\prime}\) are degenerate in this 4D- STEM and thus we observe only three types of domain walls. This has been consistent in multiple such 4D STEM as observed in Figure S3- S4. Future studies, such as depth sectioning or sample tilting experiments, may be able to probe this variation \(^{36}\) .
+
+## Discussion
+
+We have unraveled the nanoscale three- dimensional domain wall network in topological polar vortices using quantitative 4D- STEM techniques. The polar vortex oxide superlattice has emergent chirality through different symmetry- breaking operations in the non- zero curl of polarization along with the alternate axial polarization component and vortex buckling- induced net- in plane rotation or lateral polarization component. The interplay of these symmetry- breaking
+
+<--- Page Split --->
+
+operations results in the formation of two types of chiral and an achiral domain wall within tubular vortex topologies. Topology- driven domain wall existence in our work is unusual in comparison to other electrostatic wall conditions- driven domain walls in the ferroic materials \(^{16,34}\) . The finite nature of chiral and achiral domain walls results in the formation of unique triple points whenever these domain walls intersect. The most probable existence of these points is in pairs with the same/different handedness, similar to multiferroic materials such as barium hexaferrite \(^{37}\) and \(\mathrm{BiFeO_3}^{35}\) . To our best understanding, such an unconventional scenario has not been seen yet in improper ferroics literature. We hope that our studies could inspire future experiments to understand the electronic and magnetic transport at these triple points within the network of chiral and achiral domain walls in polar vortices oxide superlattices.
+
+## Materials and Methods
+
+Synthesis: \([(PbTiO_3)_{16} / (SrTiO_3)_{16}]\) trilayer with \(\mathrm{SrRuO_3}\) buffer layer was synthesized on single- crystalline \(\mathrm{DyScO_3}\) (011) substrates via reflection high- energy electron diffraction (RHEED)- assisted pulsed- laser deposition (KrF laser). The \(\mathrm{PbTiO_3}\) and the \(\mathrm{SrTiO_3}\) layers were grown at \(610^{\circ}\mathrm{C}\) in \(100\mathrm{mTorr}\) oxygen pressure.
+
+HR- STEM vector mapping: The vector mapping was performed via Gaussian fitting of A site atomic positions on the drift- corrected HR- STEM images \(^{38}\) . First, all the A- sites in the drift- corrected images were identified using “Atomap” atom finding tool \(^{39}\) . Once the atoms were identified, the atomic planes were divided into different zone axis such as along \([001]_0\) and \([001]_0\) . The deviation in local A- displacement was found by taking the difference between the local A site displacement and the corresponding average displacement in the local zone axis plane. The displacement vectors were further interpolated into a grid Cartesian grid and then
+
+<--- Page Split --->
+
+differentiated to obtain strain tensor maps. The infinitesimal rotation or the curl of the displacement of vortices was calculated using the following equation:
+
+\[\theta = \frac{1}{2}\left(\frac{\partial u}{\partial y} -\frac{\partial v}{\partial x}\right)\]
+
+The color bar in the curl of displacement plot is plotted with respect to the mean intensities in the \(\mathrm{PbTiO_3}\) layer.
+
+4D STEM analysis: All 4D STEM experiments were carried out on TEAM I microscope (aberration- corrected Thermo Fisher Scientific Titan 80- 300) using a Gatan K3 direct detection camera located at the end of a Gatan Continuum imaging filter. The microscope was operated at \(300\mathrm{kV}\) with a probe current of \(100\mathrm{pA}\) . The probe semi- angle used for the measurement was 2 mrad. Diffraction patterns were collected using a step size of \(1\mathrm{nm}\) with 514 by 399 scan positions. The K3 camera was used in full- frame electron counting mode with a binning of 4 pixels by 4 pixels and a camera length of \(1.05\mathrm{mm}\) . The exposure time for each diffraction pattern was \(47\mathrm{ms}\) . The 4D STEM analysis was carried out using the py4DSTEM modules. Briefly, rotation calibration was performed between the diffraction and image plane to identify the right orientation of the zone axis. For that process, the defocused image in the Ronchigram was compared to the focused scan image and the relative orientation of the two images was compared. Once the zone axis was identified, all the disks in the diffraction pattern at each probe position were fitted using the disk fitting function. The so- called polarization maps were generated by taking the normalized intensity difference between the opposite Friedel pair disks. Subsequently, the signal- to- noise in these polarization maps was improved by using a combination of low- pass and high- pass Gaussian filters. By using a high- pass Gaussian filter, we also minimized the dominating thickness contrast.
+
+<--- Page Split --->
+
+## References:
+
+1. Sowa, W. Synthesis of L-glucurone. Conversion of D-glucose into L-glucose. Can. J. Chem. 47, 3931–3934 (1969).
+2. Nambu, Y. Spontaneous symmetry breaking in particle physics: A case of cross fertilization. Int. J. Mod. Phys. A 24, 2371–2377 (2009).
+3. Spaldin, N. A., Fiebig, M. & Mostovoy, M. The toroidal moment in condensed-matter physics and its relation to the magnetoelectric effect. J. Phys. Condens. Matter 20, 434203 (2008).
+4. Nakata, M., Shao, R.-F., Maclennan, J. E., Weissflog, W. & Clark, N. A. Electric-field-induced chirality flipping in smectic liquid crystals: the role of anisotropic viscosity. Phys. Rev. Lett. 96, 067802 (2006).
+5. Chen, G. et al. Unlocking Bloch-type chirality in ultrathin magnets through uniaxial strain. Nat. Commun. 6, 6598 (2015).
+6. Horibe, Y. et al. Color theorems, chiral domain topology, and magnetic properties of Fe(x)TaS2. J. Am. Chem. Soc. 136, 8368–8373 (2014).
+7. Qian, Q. et al. Chiral molecular intercalation superlattices. Nature 606, 902–908 (2022).
+8. Fischer, P. & Hache, F. Nonlinear optical spectroscopy of chiral molecules. Chirality 17, 421–437 (2005).
+9. Ma, W., Xu, L., Wang, L., Xu, C. & Kuang, H. Chirality-based biosensors. Adv. Funct. Mater. 29, 1805512 (2019).
+10. Cherifi-Hertel, S. et al. Non-Ising and chiral ferroelectric domain walls revealed by nonlinear optical microscopy. Nat. Commun. 8, 15768 (2017).
+11. Lee, S. et al. Single ferroelectric and chiral magnetic domain of single-crystalline BiFeO3in
+
+<--- Page Split --->
+
+an electric field. Phys. Rev. B Condens. Matter Mater. Phys. 78, (2008).
+
+12. Liu, D. et al. Phase-field simulations of vortex chirality manipulation in ferroelectric thin films. npj quantum mater. 7, (2022).
+
+13. Hu, Z.-B. et al. An effective strategy of introducing chirality to achieve multifunctionality in rare-earth double perovskite ferroelectrics. Small Methods 6, e2200421 (2022).
+
+14. Wang, Y. J. et al. Polar meron lattice in strained oxide ferroelectrics. Nat. Mater. 19, 881-886 (2020).
+
+15. Li, X. et al. Atomic-Scale Observations of Electrical and Mechanical Manipulation of Topological Polar Flux Closure. Proc. Natl. Acad. Sci. 117, 18954 (2020).
+
+16. Tang, Y. L. et al. Ferroelectrics. Observation of a periodic array of flux-closure quadrants in strained ferroelectric PbTiO₃ films. Science 348, 547-551 (2015).
+
+17. Yadav, A. K. et al. Observation of polar vortices in oxide superlattices. Nature 530, 198-201 (2016).
+
+18. Zhang, Q. et al. Nanoscale Bubble Domains and Topological Transitions in Ultrathin Ferroelectric Films. Adv. Mater. 29, 1702375 (2017).
+
+19. Zhang, Q. et al. Deterministic Switching of Ferroelectric Bubble Nanodomains. Adv. Funct. Mater 29, 1808573 (2019).
+
+20. Hadjimichael, M. et al. Metal-ferroelectric supercrystals with periodically curved metallic layers. Nat. Mater. 20, 495-502 (2021).
+
+21. Stoica, V. A. et al. Optical creation of a supercrystal with three-dimensional nanoscale periodicity. Nat. Mater. 18, 377-383 (2019).
+
+22. Das, S. et al. Observation of room-temperature polar skyrmions. Nature 568, 368-372 (2019).
+
+<--- Page Split --->
+
+23. Padraic Shafer, Pablo García-Fernández, Pablo Aguado-Puente, Anoop R. Damodaran, Ajay K. Yadav, Christopher T. Nelson, Shang-Lin Hsu, Jacek C. Wojdel, Jorge Iniguez, Lane W. Martin, Elke Arenholz, Javier Junquera, Ramamoorthy Ramesh. Emergent Chirality in the Electric Polarization Texture of Titanate Superlattices. Proc. Natl. Acad. Sci. U. S. A 115, 915–920 (2018).
+
+24. Susarla, S. et al. Atomic scale crystal field mapping of polar vortices in oxide superlattices. Nat. Commun. 12, 6273 (2021).
+
+25. Behera, P. et al. Electric field control of chirality. Sci. Adv. 8, eabj8030 (2022).
+
+26. Louis, L., Kornev, I., Geneste, G., Dkhil, B. & Bellaiche, L. Novel complex phenomena in ferroelectric nanocomposites. J. Phys. Condens. Matter 24, 402201 (2012).
+
+27. Nguyen, K. X. et al. Transferring orbital angular momentum to an electron beam reveals toroidal and chiral order. arXiv [cond-mat.mtrl-sci] (2020).
+
+28. Ophus, C. Four-dimensional scanning transmission electron microscopy (4D-STEM): From scanning nanodiffraction to ptychography and beyond. Microsc. Microanal. 25, 563–582 (2019).
+
+29. Deb, P. et al. Imaging polarity in two dimensional materials by breaking Friedel's law. Ultramicroscopy 215, 113019 (2020).
+
+30. Shao, Y.-T. et al. Emergent chirality in a polar meron to skyrmion phase transition. arXiv [cond-mat.mes-hall] (2021).
+
+31. Savitzky, B. H. et al. Py4DSTEM: Open source software for 4D-STEM data analysis. Microsc. Microanal. 25, 124–125 (2019).
+
+32. Moffatt, H. K. & Ricca, R. L. Helicity and the Cálugáreanu invariant. Proc., Math. phys. sci. 439, 411–429 (1992).
+
+<--- Page Split --->
+
+33. Moffatt, H. K. Helicity and singular structures in fluid dynamics. Proc. Natl. Acad. Sci. U. S. A. 111, 3663–3670 (2014).
+
+34. Holtz, M. E. et al. Topological defects in hexagonal manganites: Inner structure and emergent electrostatics. Nano Lett. 17, 5883–5890 (2017).
+
+35. Balke, N. et al. Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3. Nat. Phys. 8, 81–88 (2012).
+
+36. Zeltmann, S. E. et al. Uncovering polar vortex structures by inversion of multiple scattering with a stacked Bloch wave model. arXiv [cond-mat.mtrl-sci] (2022).
+
+37. Karpov, D. et al. Nanoscale topological defects and improper ferroelectric domains in multiferroic barium hexaferrite nanocrystals. Phys. Rev. B. 100, (2019).
+
+38. Ophus, C., Ciston, J. & Nelson, C. T. Correcting nonlinear drift distortion of scanning probe and scanning transmission electron microscopies from image pairs with orthogonal scan directions. Ultramicroscopy 162, 1–9 (2016).
+
+39. Nord, M., Erik Vullum, P., MacLaren, I., Tybell, T. & Holmestad, R. Atomap - automated analysis of atomic resolution STEM images. Microsc. Microanal. 23, 426–427 (2017).
+
+## Acknowledgments
+
+All the electron microscopy experiments were carried out at the National Center for Electron Microscopy (NCEM) located in the Molecular Foundry user facility at Lawrence Berkeley National Laboratory. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE- AC02- 05CH11231. S.S. and R.R. are supported by the DOE Quantum Materials Program. CO acknowledges support from a DOE Early Career Research Award. F.G.- O., P.G.- F., and J.J. acknowledge financial support from Grant No. PGC2018- 096955- B- C41 funded by
+
+<--- Page Split --->
+
+MCIN/AEI/10.13039/501100011033 and by ERDF "A way of making Europe," by the European Union. F.G.- O. acknowledges financial support from Grant No. FPU18/04661 funded by MCIN/AEI/10.13039/501100011033. BHS was supported by the Toyota Research Institute. National Institute of Health Research UK.
+
+Author contributions: S.S., R.R., and C.O. conceived the idea, and designed the experiments. S.S. analyzed the 4D STEM datasets, made the figures and wrote the initial draft of the manuscript. S.L. performed the 4D STEM experiments. B.H. provided inputs for the scripts of the 4D STEM analysis. F.G.O, P.G. F, and J.J helped in providing intellectual inputs regarding the origin of chiral domain walls and triple points. P.B. and P.E. participated in revising the manuscript. R.R. and C.O. supervised the project.
+
+Competing interests: Authors declare that they have no competing interests.
+
+Data and materials availability: All data are available in the main text or the supplementary materials.
+
+## Supplementary Materials.
+
+All the supplementary materials is available in supplemental information.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- Sl.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18_det.mmd b/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..d88a3ef84cbdb399906598678b67bab4b376b57a
--- /dev/null
+++ b/preprint/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18/preprint__015d965c0cb0c74c387f9596e3f91c0197ff39a7333b1c0b5bef96993bcbbd18_det.mmd
@@ -0,0 +1,348 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 936, 175]]<|/det|>
+# The emergence of three-dimensional chiral domain walls in polar vortices
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 621, 236]]<|/det|>
+Sandhya Susarla ( \(\boxed{ \begin{array}{r l} \end{array} }\) sandhya.susarla@asu.edu) Arizona State University https://orcid.org/0000- 0003- 1773- 0993
+
+<|ref|>text<|/ref|><|det|>[[44, 241, 336, 282]]<|/det|>
+Shang- Lin Hsu University of california, Berkeley
+
+<|ref|>text<|/ref|><|det|>[[44, 288, 633, 330]]<|/det|>
+Fernando Gomez- Ortiz Universidad de Cantabria https://orcid.org/0000- 0002- 7203- 8476
+
+<|ref|>text<|/ref|><|det|>[[44, 335, 631, 377]]<|/det|>
+Pablo Garcia- Fernandez Universidad de Cantabria https://orcid.org/0000- 0002- 4901- 0811
+
+<|ref|>text<|/ref|><|det|>[[44, 382, 209, 422]]<|/det|>
+Benjamin Savitzky Cornell University
+
+<|ref|>text<|/ref|><|det|>[[44, 428, 738, 470]]<|/det|>
+SUJIT DAS Indian Institute of Science, Bangalore https://orcid.org/0000- 0001- 9823- 0207
+
+<|ref|>text<|/ref|><|det|>[[44, 475, 336, 515]]<|/det|>
+Piush Behera University of California, Berkeley
+
+<|ref|>text<|/ref|><|det|>[[44, 521, 923, 563]]<|/det|>
+Javier Junquera Universidad de Cantabria, Cantabria Campus Internacional https://orcid.org/0000- 0002- 9957- 8982
+
+<|ref|>text<|/ref|><|det|>[[44, 568, 756, 609]]<|/det|>
+Peter Erucis Lawrence Berkeley National Laboratory https://orcid.org/0000- 0002- 6762- 9976
+
+<|ref|>text<|/ref|><|det|>[[44, 614, 247, 654]]<|/det|>
+Ramamoorthy Ramesh Rice University
+
+<|ref|>text<|/ref|><|det|>[[44, 660, 886, 723]]<|/det|>
+Colin Ophus National Center for Electron Microscopy Facility, Molecular Foundry, Lawrence Berkeley National Laboratory
+
+<|ref|>text<|/ref|><|det|>[[44, 764, 101, 782]]<|/det|>
+Article
+
+<|ref|>text<|/ref|><|det|>[[44, 802, 137, 820]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 840, 323, 860]]<|/det|>
+Posted Date: February 8th, 2023
+
+<|ref|>text<|/ref|><|det|>[[44, 879, 473, 899]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 2551328/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 916, 909, 958]]<|/det|>
+License: \(\circledcirc\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 100, 907, 142]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on July 25th, 2023. See the published version at https://doi.org/10.1038/s41467-023-40009-2.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[189, 97, 808, 116]]<|/det|>
+## The emergence of three-dimensional chiral domain walls in polar vortices
+
+<|ref|>text<|/ref|><|det|>[[175, 121, 865, 176]]<|/det|>
+Sandhya Susarla \(^{1,2,\mathrm{S}\# *}\) , Shanglin Hsu \(^{1,2\#}\) , Fernando Gómez- Ortiz \(^{4}\) , Pablo García- Fernández \(^{4}\) , Benjamin H. Savitzky \(^{1}\) , Sujit Das \(^{2,6}\) , Piush Behera \(^{3}\) , Javier Junquera \(^{4}\) , Peter Ercius \(^{1}\) , Ramamoorthy Ramesh \(^{1,2,5,7,8*}\) , Colin Ophus \(^{1*}\)
+
+<|ref|>text<|/ref|><|det|>[[173, 192, 872, 472]]<|/det|>
+1: National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA 94720
+2: Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley CA, USA 94720
+3: Department of Materials Science & Engineering, University of California, Berkeley, CA, USA 94720
+4: Departmento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional Santander, Spain, 39005
+5: Department of Physics, University of California, Berkeley Berkeley, CA, USA 94720
+6: Material Research Centre, Indian Institute of Science, Bangalore, 560012
+7: Department of Physics, Rice University, Houston, TX, USA, 77005
+8: Department of Materials Science and Nanoengineering, Houston, TX, USA, 77005 #Equal contribution.
+\$ Present address: School for Engineering of Matter, Transport, and Energy, Arizona State University
+
+<|ref|>text<|/ref|><|det|>[[115, 488, 810, 524]]<|/det|>
+Corresponding authors: sandhya.susarla@asu.edu, ramamoorthy.ramesh@rice.edu, and clophus@lbl.gov
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 549, 191, 565]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[115, 583, 883, 793]]<|/det|>
+Chirality or handedness of a material can be used as an order parameter to uncover emergent electronic properties for quantum information science. Conventionally, chirality is found in naturally occurring biomolecules and magnetic materials. Chirality can be engineered in a topological polar vortex ferroelectric/dielectric system via atomic- scale symmetry- breaking operations. We use four- dimensional scanning transmission electron microscopy (4D- STEM) to map out topology- driven three- dimensional domain walls, where the handedness of two neighbor topological domains change or remain the same. The nature of the domain walls is governed by the interplay of local perpendicular (lateral) and parallel (axial) polarization with respect to the tubular vortex structures. Unique symmetry- breaking operations and the finite nature of domain walls results in a triple point at the junction of chiral and achiral domain walls. The unconventional nature of the domain walls with triple point pairs may result in unique electrostatic and magnetic properties potentially useful for quantum sensing applications.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 91, 225, 109]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[112, 120, 886, 880]]<|/det|>
+Chirality is a unique topological feature that drives many- body interactions in naturally occurring organic molecules and proteins \(^{1}\) , subatomic particle physics \(^{2}\) , and solid- state physics \(^{3}\) . The symmetries in a chiral system are configured in such a way that its mirror image cannot be superimposed on itself, manifesting a handedness to the system as exemplified by screws and our own hands. Chirality also exists at the microscale/nanoscale level in inorganic and organic materials such as liquid crystals \(^{4}\) , spin textures in ferromagnets \(^{5,6}\) , amino acids, and D/L- glucose molecules \(^{1}\) with applications in spin selectivity- based quantum sensing \(^{7}\) , non- linear optics \(^{8}\) , and biosensing applications \(^{9}\) . However, there are very few examples of chiral inorganic ferroelectric crystals which could have fundamentally different domain textures \(^{10 - 13}\) . Over the past few years, novel polarization textures in ferroelectrics such as merons \(^{14}\) , polar flux- closure domains \(^{15,16}\) , vortices \(^{17}\) , bubble domains \(^{18,19}\) , super crystals \(^{20,21}\) and skyrmions \(^{22}\) have been engineered in oxide superlattices, emerging from the careful interplay of elastic, electrostatic and gradient energies of electric dipoles. The electric dipole arrangement and complex orbital hybridization in these systems have been probed by the x- ray scattering techniques \(^{23}\) , scanning transmission electron microscopy (STEM) \(^{17}\) - electron energy loss spectroscopy (EELS) \(^{24}\) , phase- field simulations \(^{12,14,15,17,20}\) and atomistic first- and second- principles calculations \(^{17,18,20,22,23}\) . Surprisingly, the presence of chirality has been observed in one such topological texture i.e. polar vortices in \(\mathrm{PbTiO_3 / SrTiO_3}\) superlattices from resonant soft x- ray scattering (RXS) \(^{23}\) , second harmonic generation (SHG) and second principles calculations \(^{25}\) . The presence of chirality in polar vortices is an emergent phenomenon because none of the parent compounds such as \(\mathrm{SrTiO_3}\) or \(\mathrm{PbTiO_3}\) are known to be chiral. It has been recently shown experimentally and theoretically that the presence of chirality in these systems might be due to different sources.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 879, 354]]<|/det|>
+First, the strongest one is the coexistence of vortices with an axial component of the polarization, perpendicular to the vortex plane \(^{26}\) . The second factor is the buckling of the vortices (i.e., a staggered vortex configuration where the center of the clockwise and counterclockwise vortices are located at different heights) combined with different sizes of the up and down domains results in a chiral structure, although its strength is smaller than in the first scenario. This last source of chirality can be reversed by external electric fields. The first experimental demonstration was in \(^{25}\) , where chirality switches in a reversible, deterministic, and non- destructive fashion over mesoscale regions \(^{25}\) .
+
+<|ref|>text<|/ref|><|det|>[[113, 368, 883, 771]]<|/det|>
+Without any prior knowledge, one would expect the as- grown sample as a racemic mixture, i.e., equal amounts of left- handed and right- handed domain enantiomers, where chirality within each domain comes from a combination of the two sources described above. To have a non- destructive switchable chirality, it is essential to understand the role of the domain walls separating the enantiomers. In other words, what local physical parameters play a role when the handedness in neighboring domains changes? This includes the offset between the center of the cores, the axial component at the center of the clockwise/counterclockwise vortices, the sense of rotation of the vortices when they merge at the domain wall, the presence of dislocations, or the combined effect of all of them. A proper understanding of how the left/right- handed domains evolve at the nanoscale is crucial to design new electrically switchable chiral devices that can be measured without scientifically sophisticated techniques. Indeed, a proper answer to this question will pave the way for the use of these chiral textures in next- generation technologies.
+
+<|ref|>text<|/ref|><|det|>[[114, 785, 875, 876]]<|/det|>
+Four- dimensional (4D)- STEM can precisely measure strain, and thus spontaneous polarization in ferroelectrics due to the violation of Friedel's Law \(^{27 - 29}\) . This makes 4D- STEM a unique tool to probe polarization in three dimensions and understand emergent chirality in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 881, 354]]<|/det|>
+polarization vortices. In the current work, we have used 4D- STEM to probe three- dimensional domain walls in polar vortices in oxide superlattices and understand the nano- scale nature of chirality. We find that both achiral and chiral domain walls coexist in the same system. The chiral to achiral domain wall transition is driven by the change in local axial and lateral polarization direction across the domain wall. We have discovered new pair of triple points with the opposite/same sense of rotation at the junction of achiral and chiral domain walls. Finally, we unravel all the possible configurations of chiral and achiral domain walls in this system through different symmetry- breaking operations.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 404, 180, 421]]<|/det|>
+## Results
+
+<|ref|>text<|/ref|><|det|>[[113, 437, 884, 632]]<|/det|>
+Trilayer \((\mathrm{SrTiO}_3)_{16} / (\mathrm{PbTiO}_3)_{16} / (\mathrm{SrTiO}_3)_{16}\) (STO/PTO/STO) were grown on orthorhombic \(\mathrm{DyScO}_3\) (DSO) \([110]_{0}\) substrates with \(\mathrm{SrRuO}_3\) as a buffer layer using reflection high- energy electron diffraction (RHEED)- assisted pulsed- laser deposition (PLD) (Figure 1A and Supplementary Information). The polar vortex phase in this system is stabilized as a consequence of the interplay between depolarization energy at the PTO/STO interfaces, elastic energy from the tensile strain imposed by the DSO substrate, and the gradient energy in the ferroelectric \(^{17}\) .
+
+<|ref|>text<|/ref|><|det|>[[113, 647, 880, 877]]<|/det|>
+A direct way to measure the polar textures in vortex topologies is through electron microscopy using atomic resolution images. We have used different types of STEM and TEM techniques to characterize the exact positions of the vortex centers. Figure 1a shows a low- magnification bright- field STEM image of the superlattice trilayer with an SRO buffer layer along the \([1\bar{1} 0]_{0}\) zone axis. The diffraction contrast in BF- STEM allows us to directly locate the vortex center as dark contrast; marked using red circles in Figure 1a. To precisely understand the polarization or displacement texture around each vortex center, we obtained the A- site
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 85, 876, 670]]<|/det|>
+displacement vector maps at atomic resolution via gaussian fitting at A- sites (Methods, supplementary information). Figure 1b shows the High angle annular dark field (HAADF)- STEM image of trilayer STO/PTO/STO along \([1\bar{1} 0]_{0}\) zone axis where brighter regions are PTO and darker regions are STO. Overlaid yellow arrows show clockwise and counterclockwise rotating curls in the displacement of the A- cation in PTO/STO superlattices. The coexistence of the concomitant non- zero curl of polarization (red/blue contrast) with an alternating axial component of the polarization (perpendicular to the plane defined by the vortices) is the first symmetry- breaking operation that results in emergent chirality in an otherwise non- chiral system. The non- zero curl is larger in continuously rotating polarization textures such as polar vortices \(^{25,27}\) , merons \(^{30}\) , and skyrmions \(^{22}\) than in other polarization textures such as flux closure domains \(^{15,16}\) where the curl vanished in the central regions with \(180^{0}\) domain walls. Additionally, we observe that the cores of the polarization curls (indicated as blue/red contrast) are not located exactly at the center of the PTO layer, but follow a zig- zag type pattern, giving rise to a net in- plane polarization rotation along \([001]_{0}\) (lateral component) indicated as \(\mathrm{P}_{\mathrm{x}}\) in Figure 1b. This buckling, combined with a small difference in the size of the up and down domains, is the second symmetry- breaking operation that results in net chirality; in agreement with previous observations \(^{25}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 95, 884, 400]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 414, 883, 575]]<|/det|>
+Figure 1. Chirality at different length scales. (a) Bright-Field STEM image showing the stack of 16 STO/16 PTO/16 STO with SRO buffer layer on DSO substrate. The red regions near the center of the PTO layer indicate the position of the vortex core approximately. (b) Vector mapping of the local displacements of A sites of highlighted region in (a) overlaid on HAADF-STEM image. The local red- and blue contrast at the center of the PTO layer indicates the local non-zero curl of displacement. The net lateral polarization resulting from vortex off-centering is indicated at the top. The dotted black line shows the center of the PTO layer. (c) Dark field TEM image along [110]o direction displaying long tubular vortex structure with domain walls shown as white dashed lines.
+
+<|ref|>text<|/ref|><|det|>[[113, 590, 874, 890]]<|/det|>
+The various permutations and combinations of atomic scale symmetry- breaking operations such as a non- zero curl of polarization together with the presence of an axial component, and the buckling of the vortices that yield a non- zero polarization component along [001]o, result in different types of domains walls at the mesoscale. We can visualize the mesoscale domain walls in these topological structures by imaging the vortices along the [110]o zone axis using weak beam dark field TEM (Figure 1c). We can observe the tubular nature of vortex textures by long bright and dark stripes regions in the image. Additionally, we observe different domain wall features (indicated as white dashed lines) cutting across vortex tubes. Overall, if we combine our observations from DF- TEM and HR- STEM, we observe a three-
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 84, 879, 850]]<|/det|>
+dimensional structure in the PbTiO₃ layer sandwiched between SrTiO₃ layers where the polarization curls follow a tubular pattern (Figure 2a). Unfortunately, the images formed by weak beam dark field, HRSTEM, and BF- STEM are merely atomic projections and cannot give us an estimate of physical quantities such as polarization and chirality. On the other hand, 4D- STEM allows us to collect a diffraction pattern at each probe position, which can then be used to create precise maps of physical quantities. For the present experiment, we performed 4D- STEM imaging on a trilayer STO/PTO/STO along the [110]₀ zone axis (Figure 2a). We used a probe size of \(\sim 7 \text{Å}\) , larger than the STO/PTO unit cell dimensions ( \(\sim 4 \text{Å}\) ) to remove the atomic- resolution signal and to estimate the polarization at unit cell resolution. The 4D- STEM analysis was carried out in open source py4DSTEM analysis package ³¹. We define the [110]₀ direction as axial and [001]₀ direction as lateral. The rotation calibration was performed between the real space and diffraction space to determine the lateral and axial axis. Details are given in the supplementary information. For initial visualization of the polar textures, we created a virtual dark field image using the [2\(\bar{1}\)0]₀ disk (disk 3) as shown in Figure 2b- c. The polarization from the PTO layer can be determined qualitatively by subtracting opposite Friedel pair disks due to the violation of Friedel’s law ²⁷-²⁹. The polarization maps corresponding to regions delimited by rectangles in Figure 2b are shown in Figure 2d- e. We observe alternate longitudinal red and blue stripes representing positive and negative polarization in both the lateral ([001]₀) and axial [110]₀ directions with domain walls as seen from the weak beam dark field images marked with green and magenta lines in Figure 2d and with a black line in Figure 2e. We observe that the axial polarization magnitude is relatively smaller than the lateral polarization in agreement with the predictions from previous second principles calculations ²³,²⁵.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[120, 95, 880, 490]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 509, 880, 654]]<|/det|>
+Figure 2. Identification of polarization using 4D-STEM mapping. (a) Schematic showing the e-beam scanned in 4D STEM mode across the vortex sample in in-plane geometry. (b) Virtual dark field image of the vortex region obtained via integrating the intensity of disk 3 from the mean diffraction pattern in (c). Zoomed-in images of the (d) dash-dot region (e) solid line region showing lateral (P [001]o) and axial (P [110]o) polarization maps in vortices. \(\alpha , \beta ,\) and \(\gamma\) domain walls can be identified. \(\alpha\) domain wall (magenta curve) has an anti-parallel lateral (P [001]o) component, \(\beta\) (green curve) domain wall has an anti-parallel axial component (P [110]o), \(\gamma\) has both axial and lateral components antiparallel across the domain wall.
+
+<|ref|>text<|/ref|><|det|>[[113, 668, 880, 900]]<|/det|>
+We track the relative domain shift across the wall by the black dotted line as shown in Figure 2d- e. In Figure 2d, we observe a \(\alpha\) - domain wall (magenta line) where the lateral polarization shifts whereas the axial polarization remain the same, as shown in Figure 3. We also detect a \(\beta\) - domain wall (green line), where the axial polarization shifts, but the lateral polarization remains the same. Finally, in Figure 2e there is a third domain wall configuration i.e., a \(\gamma\) - domain wall (black line) as well where both the lateral and axial polarization shift. We verified this observation with average line profiles across the domain walls (Supplementary
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 214]]<|/det|>
+information, Figure S1). To detect whether a change of chirality occurs at these domain walls, a way to quantify the chirality is required. The order parameter that best captures the breakdown of chiral symmetry is the helicity H of the chiral field. In our case, the chiral field is the polarization, and for the helicity, we borrow the definition from fluid dynamics:
+
+<|ref|>equation<|/ref|><|det|>[[172, 228, 575, 253]]<|/det|>
+\[\mathcal{H} = \int \vec{p}\cdot \left(\vec{\nabla}\times \vec{p}\right)d^{3}r, \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[113, 268, 875, 465]]<|/det|>
+where \(\vec{p}\) is the local value of polarization. Note that \(\mathcal{H}\) changes sign upon a mirror symmetry reflection \(^{32,33}\) . A nonzero helicity means chirality or lack of mirror symmetry of the polarization texture: right (left) handedness can be associated with positive (negative) values of \(\mathcal{H}\) . Assuming a vortex structure where the polarization lines in the plane defined by the vortices are closed, and that we can measure the axial and lateral components of the polarization at the topmost \(\mathrm{PbTiO_3}\) layer, then the previous equation can be estimated by
+
+<|ref|>equation<|/ref|><|det|>[[172, 479, 575, 500]]<|/det|>
+\[\mathcal{H} = 2\cdot < p_{lateral} > < p_{axial} > \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[113, 514, 880, 744]]<|/det|>
+where \(p_{lateral}\) and \(p_{axial}\) are polarization along lateral and axial directions (Supplementary information, Figure S2). Using this equation we can understand the nature of domain walls found in Figure 2d- e. For the \(\alpha /\beta\) domain wall, only one of the lateral/axial polarization sign change across the domain wall. This causes a change in the overall sign of helicity, thus making them chiral domain walls. On the other hand, the \(\gamma\) - domain wall has both a lateral and axial polarization switch, which doesn't change the overall helicity of the system, thus making it an achiral domain wall.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 90, 875, 288]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 311, 884, 455]]<|/det|>
+Figure 3. Identification of triple point topologies and chiral domain walls. (a) The helicity map formed from Figure 2b shows left and right-handed domains separated by \(\alpha\) (magenta) and \(\beta\) (green). Additionally, achiral domain walls (black line) also coexist. The resultant triple point topologies formed due to the co-existence of chiral and achiral domain walls are shown in encircled regions. The sense of rotation of these triple point topologies is indicated in the encircled region. (b-c) Possible pairs of triple points. (b) represents triple points with opposite sense of rotation with the point of inversion along \(\beta\) , \(\gamma\) , and \(\alpha\) (c) represents triple points with the same sense of rotation. The green ticks on the side show what has been observed in experiments.
+
+<|ref|>text<|/ref|><|det|>[[113, 476, 884, 884]]<|/det|>
+We can use the qualitative lateral and axial polarization data from 4D- STEM and create a map of the helicity over a large scale using the helicity equation as shown in Figure 3. The red and blue regions in the chirality maps indicate different signs of helicity in the system, making them left- handed and right- handed chiral domains separated by the \(\alpha\) or \(\beta\) domain walls. We find that most of these chiral and achiral domain walls were not visible in the virtual dark field images. Further, we also observe a unique triple point topology at the mesoscale whenever the two types of chiral domain walls meet an achiral domain wall as seen from black- encircled areas, thus forming a quasi- 1D defect in the network of chiral and achiral domain walls. These triple points tend to exist in pairs and exhibit a sense of rotation via the transition from \(\alpha\) to \(\beta\) to \(\gamma\) domain wall and vice- versa (Figure 3, S3- S4), similar to what has been observed previously in the trimerized domain walls in hexagonal manganates \(^{34}\) , vortex- antivortex phases in intercalated Vander- Waal ferromagnets \(^{6}\) , and ferroelectric vortex cores in BiFeO \(_{3}\) \(^{35}\) . The sense of rotation in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 85, 884, 570]]<|/det|>
+a triple point can be the same or opposite depending on the arrangement of \(\alpha , \beta\) or \(\gamma\) domain walls. Figure 3b,c illustrates this situation. Whenever a pair of domain walls \((\beta , \gamma\) or \(\alpha , \gamma\) or \(\alpha , \beta\) ) break inversion symmetry across \(\alpha , \beta\) or \(\gamma\) domains, we form triple point pairs with opposite sense of rotation. If the inversion symmetry across \(\alpha , \beta\) or \(\gamma\) domains is not broken, we form triple point pairs with the same sense of rotation. The origin of triple point pairs can be understood by the following hypothesis. Consider the example of the first triple point pair in Figure 3b. If this particular type of triple point has to be isolated, then \(\beta\) boundary would infinitely separate the positive and negative chirality regions. If \(\beta\) boundary is not infinite, then it has to meet somewhere an \(\alpha\) boundary to continue separating the positive and negative chirality regions. Now, if a \(\beta\) boundary (change in axial polarization) meets an \(\alpha\) boundary (change in lateral polarization), a \(\gamma\) boundary appears (change in both lateral and axial polarization). In such a scenario, we get another triple point in the vicinity of the first triple point thus explaining the origins of pairs for the majority of cases. \(\alpha / \beta\) boundary could be isolated only in very special circumstances when they are born/die at the surface or they are infinitely long.
+
+<|ref|>image<|/ref|><|det|>[[124, 593, 770, 865]]<|/det|>
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 875, 232]]<|/det|>
+Figure 4. Types of chiral domain walls. (a) Four possible combinations of alternating clockwise/counterclockwise vortices are displaced, Top and bottom cartoons differ by the direction of the axial component of the polarization (red dot and blue cross). Left and right cartoons differ by the curl of the polarization. The chirality for each type of domain is indicated by a sketched hand. The possible domain walls between these configurations are marked as type \(\alpha /\alpha^{\prime}\) , \(\beta /\beta^{\prime}\) , and \(\gamma /\gamma^{\prime}\) . \(\alpha /\alpha^{\prime}\) and \(\beta /\beta^{\prime}\) domain walls change the chirality at the domain wall. \(\gamma /\gamma^{\prime}\) domains preserve the chirality. (b- d) Three- dimensional representation of three types of chiral domain walls observed by 4D- STEM measurements.
+
+<|ref|>text<|/ref|><|det|>[[113, 253, 884, 696]]<|/det|>
+From a theoretical perspective, there are three symmetry- breaking operations for the formation of domain walls, 1) Change in the lateral polarization direction, 2) Change in axial polarization direction, and 3) Change in the net lateral polarization due to the vortex core shifting away from the center. If we consider all three factors, then we expect to have six types of domain walls as shown in Figure 4. The first pair of chiral domain walls, \(\alpha /\alpha^{\prime}\) , results from a combination of factors 1 and 3. The second chiral domain wall pair, \(\beta /\beta^{\prime}\) , results from a combination of factors 2 and 3. The third achiral domain wall pair results from all three factors. Unfortunately, it is challenging to measure the quantitative net lateral component in the vortices due to the very low sensitivity of electron scattering to sample changes along the beam direction. Due to this, \(\alpha /\alpha^{\prime}\) , \(\beta /\beta^{\prime}\) , and \(\gamma /\gamma^{\prime}\) are degenerate in this 4D- STEM and thus we observe only three types of domain walls. This has been consistent in multiple such 4D STEM as observed in Figure S3- S4. Future studies, such as depth sectioning or sample tilting experiments, may be able to probe this variation \(^{36}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 711, 207, 728]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[114, 744, 880, 905]]<|/det|>
+We have unraveled the nanoscale three- dimensional domain wall network in topological polar vortices using quantitative 4D- STEM techniques. The polar vortex oxide superlattice has emergent chirality through different symmetry- breaking operations in the non- zero curl of polarization along with the alternate axial polarization component and vortex buckling- induced net- in plane rotation or lateral polarization component. The interplay of these symmetry- breaking
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 879, 424]]<|/det|>
+operations results in the formation of two types of chiral and an achiral domain wall within tubular vortex topologies. Topology- driven domain wall existence in our work is unusual in comparison to other electrostatic wall conditions- driven domain walls in the ferroic materials \(^{16,34}\) . The finite nature of chiral and achiral domain walls results in the formation of unique triple points whenever these domain walls intersect. The most probable existence of these points is in pairs with the same/different handedness, similar to multiferroic materials such as barium hexaferrite \(^{37}\) and \(\mathrm{BiFeO_3}^{35}\) . To our best understanding, such an unconventional scenario has not been seen yet in improper ferroics literature. We hope that our studies could inspire future experiments to understand the electronic and magnetic transport at these triple points within the network of chiral and achiral domain walls in polar vortices oxide superlattices.
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 438, 314, 457]]<|/det|>
+## Materials and Methods
+
+<|ref|>text<|/ref|><|det|>[[114, 480, 867, 605]]<|/det|>
+Synthesis: \([(PbTiO_3)_{16} / (SrTiO_3)_{16}]\) trilayer with \(\mathrm{SrRuO_3}\) buffer layer was synthesized on single- crystalline \(\mathrm{DyScO_3}\) (011) substrates via reflection high- energy electron diffraction (RHEED)- assisted pulsed- laser deposition (KrF laser). The \(\mathrm{PbTiO_3}\) and the \(\mathrm{SrTiO_3}\) layers were grown at \(610^{\circ}\mathrm{C}\) in \(100\mathrm{mTorr}\) oxygen pressure.
+
+<|ref|>text<|/ref|><|det|>[[113, 626, 864, 857]]<|/det|>
+HR- STEM vector mapping: The vector mapping was performed via Gaussian fitting of A site atomic positions on the drift- corrected HR- STEM images \(^{38}\) . First, all the A- sites in the drift- corrected images were identified using “Atomap” atom finding tool \(^{39}\) . Once the atoms were identified, the atomic planes were divided into different zone axis such as along \([001]_0\) and \([001]_0\) . The deviation in local A- displacement was found by taking the difference between the local A site displacement and the corresponding average displacement in the local zone axis plane. The displacement vectors were further interpolated into a grid Cartesian grid and then
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 89, 787, 144]]<|/det|>
+differentiated to obtain strain tensor maps. The infinitesimal rotation or the curl of the displacement of vortices was calculated using the following equation:
+
+<|ref|>equation<|/ref|><|det|>[[422, 165, 568, 207]]<|/det|>
+\[\theta = \frac{1}{2}\left(\frac{\partial u}{\partial y} -\frac{\partial v}{\partial x}\right)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 229, 882, 284]]<|/det|>
+The color bar in the curl of displacement plot is plotted with respect to the mean intensities in the \(\mathrm{PbTiO_3}\) layer.
+
+<|ref|>text<|/ref|><|det|>[[112, 300, 880, 888]]<|/det|>
+4D STEM analysis: All 4D STEM experiments were carried out on TEAM I microscope (aberration- corrected Thermo Fisher Scientific Titan 80- 300) using a Gatan K3 direct detection camera located at the end of a Gatan Continuum imaging filter. The microscope was operated at \(300\mathrm{kV}\) with a probe current of \(100\mathrm{pA}\) . The probe semi- angle used for the measurement was 2 mrad. Diffraction patterns were collected using a step size of \(1\mathrm{nm}\) with 514 by 399 scan positions. The K3 camera was used in full- frame electron counting mode with a binning of 4 pixels by 4 pixels and a camera length of \(1.05\mathrm{mm}\) . The exposure time for each diffraction pattern was \(47\mathrm{ms}\) . The 4D STEM analysis was carried out using the py4DSTEM modules. Briefly, rotation calibration was performed between the diffraction and image plane to identify the right orientation of the zone axis. For that process, the defocused image in the Ronchigram was compared to the focused scan image and the relative orientation of the two images was compared. Once the zone axis was identified, all the disks in the diffraction pattern at each probe position were fitted using the disk fitting function. The so- called polarization maps were generated by taking the normalized intensity difference between the opposite Friedel pair disks. Subsequently, the signal- to- noise in these polarization maps was improved by using a combination of low- pass and high- pass Gaussian filters. By using a high- pass Gaussian filter, we also minimized the dominating thickness contrast.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 108, 216, 125]]<|/det|>
+## References:
+
+<|ref|>text<|/ref|><|det|>[[112, 140, 884, 900]]<|/det|>
+1. Sowa, W. Synthesis of L-glucurone. Conversion of D-glucose into L-glucose. Can. J. Chem. 47, 3931–3934 (1969).
+2. Nambu, Y. Spontaneous symmetry breaking in particle physics: A case of cross fertilization. Int. J. Mod. Phys. A 24, 2371–2377 (2009).
+3. Spaldin, N. A., Fiebig, M. & Mostovoy, M. The toroidal moment in condensed-matter physics and its relation to the magnetoelectric effect. J. Phys. Condens. Matter 20, 434203 (2008).
+4. Nakata, M., Shao, R.-F., Maclennan, J. E., Weissflog, W. & Clark, N. A. Electric-field-induced chirality flipping in smectic liquid crystals: the role of anisotropic viscosity. Phys. Rev. Lett. 96, 067802 (2006).
+5. Chen, G. et al. Unlocking Bloch-type chirality in ultrathin magnets through uniaxial strain. Nat. Commun. 6, 6598 (2015).
+6. Horibe, Y. et al. Color theorems, chiral domain topology, and magnetic properties of Fe(x)TaS2. J. Am. Chem. Soc. 136, 8368–8373 (2014).
+7. Qian, Q. et al. Chiral molecular intercalation superlattices. Nature 606, 902–908 (2022).
+8. Fischer, P. & Hache, F. Nonlinear optical spectroscopy of chiral molecules. Chirality 17, 421–437 (2005).
+9. Ma, W., Xu, L., Wang, L., Xu, C. & Kuang, H. Chirality-based biosensors. Adv. Funct. Mater. 29, 1805512 (2019).
+10. Cherifi-Hertel, S. et al. Non-Ising and chiral ferroelectric domain walls revealed by nonlinear optical microscopy. Nat. Commun. 8, 15768 (2017).
+11. Lee, S. et al. Single ferroelectric and chiral magnetic domain of single-crystalline BiFeO3in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[150, 90, 722, 109]]<|/det|>
+an electric field. Phys. Rev. B Condens. Matter Mater. Phys. 78, (2008).
+
+<|ref|>text<|/ref|><|det|>[[115, 124, 861, 180]]<|/det|>
+12. Liu, D. et al. Phase-field simulations of vortex chirality manipulation in ferroelectric thin films. npj quantum mater. 7, (2022).
+
+<|ref|>text<|/ref|><|det|>[[115, 194, 866, 250]]<|/det|>
+13. Hu, Z.-B. et al. An effective strategy of introducing chirality to achieve multifunctionality in rare-earth double perovskite ferroelectrics. Small Methods 6, e2200421 (2022).
+
+<|ref|>text<|/ref|><|det|>[[115, 263, 868, 319]]<|/det|>
+14. Wang, Y. J. et al. Polar meron lattice in strained oxide ferroelectrics. Nat. Mater. 19, 881-886 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 333, 836, 389]]<|/det|>
+15. Li, X. et al. Atomic-Scale Observations of Electrical and Mechanical Manipulation of Topological Polar Flux Closure. Proc. Natl. Acad. Sci. 117, 18954 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 402, 883, 458]]<|/det|>
+16. Tang, Y. L. et al. Ferroelectrics. Observation of a periodic array of flux-closure quadrants in strained ferroelectric PbTiO₃ films. Science 348, 547-551 (2015).
+
+<|ref|>text<|/ref|><|det|>[[115, 472, 861, 528]]<|/det|>
+17. Yadav, A. K. et al. Observation of polar vortices in oxide superlattices. Nature 530, 198-201 (2016).
+
+<|ref|>text<|/ref|><|det|>[[115, 542, 829, 598]]<|/det|>
+18. Zhang, Q. et al. Nanoscale Bubble Domains and Topological Transitions in Ultrathin Ferroelectric Films. Adv. Mater. 29, 1702375 (2017).
+
+<|ref|>text<|/ref|><|det|>[[115, 611, 877, 667]]<|/det|>
+19. Zhang, Q. et al. Deterministic Switching of Ferroelectric Bubble Nanodomains. Adv. Funct. Mater 29, 1808573 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 681, 866, 737]]<|/det|>
+20. Hadjimichael, M. et al. Metal-ferroelectric supercrystals with periodically curved metallic layers. Nat. Mater. 20, 495-502 (2021).
+
+<|ref|>text<|/ref|><|det|>[[115, 751, 840, 806]]<|/det|>
+21. Stoica, V. A. et al. Optical creation of a supercrystal with three-dimensional nanoscale periodicity. Nat. Mater. 18, 377-383 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 821, 837, 877]]<|/det|>
+22. Das, S. et al. Observation of room-temperature polar skyrmions. Nature 568, 368-372 (2019).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 852, 250]]<|/det|>
+23. Padraic Shafer, Pablo García-Fernández, Pablo Aguado-Puente, Anoop R. Damodaran, Ajay K. Yadav, Christopher T. Nelson, Shang-Lin Hsu, Jacek C. Wojdel, Jorge Iniguez, Lane W. Martin, Elke Arenholz, Javier Junquera, Ramamoorthy Ramesh. Emergent Chirality in the Electric Polarization Texture of Titanate Superlattices. Proc. Natl. Acad. Sci. U. S. A 115, 915–920 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 262, 874, 317]]<|/det|>
+24. Susarla, S. et al. Atomic scale crystal field mapping of polar vortices in oxide superlattices. Nat. Commun. 12, 6273 (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 331, 780, 353]]<|/det|>
+25. Behera, P. et al. Electric field control of chirality. Sci. Adv. 8, eabj8030 (2022).
+
+<|ref|>text<|/ref|><|det|>[[113, 367, 871, 422]]<|/det|>
+26. Louis, L., Kornev, I., Geneste, G., Dkhil, B. & Bellaiche, L. Novel complex phenomena in ferroelectric nanocomposites. J. Phys. Condens. Matter 24, 402201 (2012).
+
+<|ref|>text<|/ref|><|det|>[[113, 436, 856, 492]]<|/det|>
+27. Nguyen, K. X. et al. Transferring orbital angular momentum to an electron beam reveals toroidal and chiral order. arXiv [cond-mat.mtrl-sci] (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 506, 878, 597]]<|/det|>
+28. Ophus, C. Four-dimensional scanning transmission electron microscopy (4D-STEM): From scanning nanodiffraction to ptychography and beyond. Microsc. Microanal. 25, 563–582 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 611, 840, 666]]<|/det|>
+29. Deb, P. et al. Imaging polarity in two dimensional materials by breaking Friedel's law. Ultramicroscopy 215, 113019 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 681, 860, 736]]<|/det|>
+30. Shao, Y.-T. et al. Emergent chirality in a polar meron to skyrmion phase transition. arXiv [cond-mat.mes-hall] (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 750, 832, 805]]<|/det|>
+31. Savitzky, B. H. et al. Py4DSTEM: Open source software for 4D-STEM data analysis. Microsc. Microanal. 25, 124–125 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 820, 852, 875]]<|/det|>
+32. Moffatt, H. K. & Ricca, R. L. Helicity and the Cálugáreanu invariant. Proc., Math. phys. sci. 439, 411–429 (1992).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 869, 144]]<|/det|>
+33. Moffatt, H. K. Helicity and singular structures in fluid dynamics. Proc. Natl. Acad. Sci. U. S. A. 111, 3663–3670 (2014).
+
+<|ref|>text<|/ref|><|det|>[[113, 158, 821, 214]]<|/det|>
+34. Holtz, M. E. et al. Topological defects in hexagonal manganites: Inner structure and emergent electrostatics. Nano Lett. 17, 5883–5890 (2017).
+
+<|ref|>text<|/ref|><|det|>[[113, 228, 875, 283]]<|/det|>
+35. Balke, N. et al. Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3. Nat. Phys. 8, 81–88 (2012).
+
+<|ref|>text<|/ref|><|det|>[[113, 298, 879, 354]]<|/det|>
+36. Zeltmann, S. E. et al. Uncovering polar vortex structures by inversion of multiple scattering with a stacked Bloch wave model. arXiv [cond-mat.mtrl-sci] (2022).
+
+<|ref|>text<|/ref|><|det|>[[113, 368, 835, 423]]<|/det|>
+37. Karpov, D. et al. Nanoscale topological defects and improper ferroelectric domains in multiferroic barium hexaferrite nanocrystals. Phys. Rev. B. 100, (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 437, 883, 528]]<|/det|>
+38. Ophus, C., Ciston, J. & Nelson, C. T. Correcting nonlinear drift distortion of scanning probe and scanning transmission electron microscopies from image pairs with orthogonal scan directions. Ultramicroscopy 162, 1–9 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 542, 870, 597]]<|/det|>
+39. Nord, M., Erik Vullum, P., MacLaren, I., Tybell, T. & Holmestad, R. Atomap - automated analysis of atomic resolution STEM images. Microsc. Microanal. 23, 426–427 (2017).
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 630, 272, 648]]<|/det|>
+## Acknowledgments
+
+<|ref|>text<|/ref|><|det|>[[113, 663, 877, 893]]<|/det|>
+All the electron microscopy experiments were carried out at the National Center for Electron Microscopy (NCEM) located in the Molecular Foundry user facility at Lawrence Berkeley National Laboratory. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE- AC02- 05CH11231. S.S. and R.R. are supported by the DOE Quantum Materials Program. CO acknowledges support from a DOE Early Career Research Award. F.G.- O., P.G.- F., and J.J. acknowledge financial support from Grant No. PGC2018- 096955- B- C41 funded by
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 881, 214]]<|/det|>
+MCIN/AEI/10.13039/501100011033 and by ERDF "A way of making Europe," by the European Union. F.G.- O. acknowledges financial support from Grant No. FPU18/04661 funded by MCIN/AEI/10.13039/501100011033. BHS was supported by the Toyota Research Institute. National Institute of Health Research UK.
+
+<|ref|>text<|/ref|><|det|>[[172, 235, 877, 430]]<|/det|>
+Author contributions: S.S., R.R., and C.O. conceived the idea, and designed the experiments. S.S. analyzed the 4D STEM datasets, made the figures and wrote the initial draft of the manuscript. S.L. performed the 4D STEM experiments. B.H. provided inputs for the scripts of the 4D STEM analysis. F.G.O, P.G. F, and J.J helped in providing intellectual inputs regarding the origin of chiral domain walls and triple points. P.B. and P.E. participated in revising the manuscript. R.R. and C.O. supervised the project.
+
+<|ref|>text<|/ref|><|det|>[[172, 480, 785, 500]]<|/det|>
+Competing interests: Authors declare that they have no competing interests.
+
+<|ref|>text<|/ref|><|det|>[[173, 515, 794, 570]]<|/det|>
+Data and materials availability: All data are available in the main text or the supplementary materials.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 586, 336, 604]]<|/det|>
+## Supplementary Materials.
+
+<|ref|>text<|/ref|><|det|>[[115, 620, 694, 640]]<|/det|>
+All the supplementary materials is available in supplemental information.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 92, 765, 112]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 130, 137, 149]]<|/det|>
+- Sl.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/images_list.json b/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..1d68dde9df9c60e723ecb61ddad87cbfb018b393
--- /dev/null
+++ b/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/images_list.json
@@ -0,0 +1,92 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1 | Concept of optical fiber sensing for LSB. (a) Schematic of a fiber optic sensor immersed in electrolyte for in-situ detection of sulfur concentration originating from the generated dissolved polysulfide and their transport activities (i.e., shuttle effect). (b) Backward-propagation guided modes inside fiber for sensing (Supplementary information Fig. S1). (c) Experimental spectra response to polysulfide. (d) The wavelength shifts of cladding mode resonance at \\(\\sim 1560 \\mathrm{nm}\\) to \\(100 \\mathrm{mM}\\) polysulfide \\(\\mathrm{Li}_2\\mathrm{S}_x\\) ( \\(x = 1, 2, 3, \\dots , 8\\) ), shaded in green; (e) to concentration variation of \\(\\mathrm{Li}_2\\mathrm{S}_4\\) and \\(\\mathrm{Li}_2\\mathrm{S}_8\\) from \\(0 \\mathrm{mM}\\) to \\(100 \\mathrm{mM}\\) ; (f) to same sulfur concentration of polysulfide \\(\\mathrm{Li}_2\\mathrm{S}_x\\) ( \\(x = 4, 5, 6, 7, 8\\) ).",
+ "footnote": [],
+ "bbox": [
+ [
+ 163,
+ 85,
+ 838,
+ 508
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2 | Decoding electrolyte sulfur concentration dynamic of LSB. (a) Operando measurement of LSB by TFBG and XRD at C/20 (left panel: polysulfide dissolution allowed (electrolyte of 1 M LiTFSI, 0.5 M LiNO₃ in DOL/DME (1:1, v/v)); right panel: polysulfide dissolution prohibited (electrolyte of LP30: 1 M LiPF₆ in EC/DMC) of sulfur and Super P carbon composite (60/40 wt.%) cathode. (b) Morphology (SEM) and content of elemental sulfur and Super P carbon (energy-dispersive X-ray spectroscopy, EDX) of the cathode at the end of charging. (c) The quantitative analysis of sulfur before cycling, end of first plateau of discharge and end of charge. (d) The recrystallized sulfur governed by comporptionation reactions and potential voltage. The shaded region in blue stands for 15 hours of rest (OCV mode) starting at the end of charging demonstrating that the re-crystallized sulfur (marked by green asterisk “\\*”) dissolves into the electrolyte in the form of soluble polysulfide through comporptionation reactions.",
+ "footnote": [],
+ "bbox": [
+ [
+ 170,
+ 95,
+ 844,
+ 650
+ ]
+ ],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig. 3 | Decoding the disproportionation process and evolution. (a, b, c and d) The temporal voltage (black curve) and decoded electrolyte sulfur concentration (red curve) by GITT test (the capacity and optical spectra are given in supplementary Fig. S7). (a, b and c) Detailed view of electrolyte response to current pulse (kinetic process) and rest (thermodynamic process). (e) Transport flux of soluble sulfur based on current pulse (kinetics process, green triangle, \\(D_t = V_{BD} / (S \\times t)\\) and rest (thermodynamic process, blue square, \\(D_t = V_{DE} / (S \\times t)\\) , where \\(S\\) is across section area of electrolyte that sensor is immersed in, \\(t\\) is corresponding time. It indicates the slope of soluble sulfur consumption (negative) or formation (positive) in electrolyte, which is also plotted by arrows in bottom (arrow up: sulfur increasing, arrow down: sulfur decreasing). The normalized ratio (red sphere) represents the sulfur consumption of rest (thermodynamic process) by \\(Ratio = |D_t| / (|D_t| + |D_k|)\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 157,
+ 173,
+ 842,
+ 682
+ ]
+ ],
+ "page_idx": 8
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4 | Operando monitoring over cycling and cycling rate. (a) Spectra contour of TFBG cladding mode resonances response (details are given in supplementary video). (b) Temporal voltage (grey line), decoded sulfur concentration (red line), and temperature of electrolyte (blue line) over the cycling. (c) Capacity variation of (b) upon time. (d) Soluble sulfur",
+ "footnote": [],
+ "bbox": [
+ [
+ 192,
+ 412,
+ 808,
+ 813
+ ]
+ ],
+ "page_idx": 10
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Fig. 5 | Chemistry of LSB with outstanding polysulfide-trapping capability cathodes. (a) Operando measurement of LSB by TFBG and XRD at C/20 (left panel: nonpolar physical adsorption of polysulfide by KB carbon; right panel: polar adsorption of polysulfide by MOF-801(Zr)). (b) In-situ detection of polysulfide adsorption by MOF-801(Zr). (c) XRD spectra for MOF-801(Zr) before and after adsorption of \\(\\mathrm{Li}_2\\mathrm{S}_6\\) . (d) The temporal voltage (grey line), decoded sulfur concentration (red line) of cathode composite based on MOF-801(Zr), and decoded sulfur concentration (blue line) considering the cathode with KB substrate (same amount of active material) is used as a reference without showing the temporal voltage.",
+ "footnote": [],
+ "bbox": [
+ [
+ 186,
+ 90,
+ 816,
+ 595
+ ]
+ ],
+ "page_idx": 13
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Fig. 6 | The correlation between electrochemical performance and \\(\\mathrm{Li}_2\\mathrm{S}\\) nucleation, sulfur crystallization. (a) Content of \\(\\mathrm{Li}_2\\mathrm{S}\\) nucleation (h1) and solid sulfur crystallization (h2). (b) Cycling performance of cathode composite at C/15 over 30 cycles. (c and d) The corresponding ratio of \\(\\mathrm{Li}_2\\mathrm{S}\\) nucleation (c) and solid sulfur crystallization (d). (e) Cycling rate performance of cathode composite. (f and g) The corresponding ratio of \\(\\mathrm{Li}_2\\mathrm{S}\\) nucleation (f) and solid sulfur crystallization (g). Note that all the cycling cell pursed in the presence of TFBG fiber and the \\(\\mathrm{Li}_2\\mathrm{S}\\) (h1) and solid sulfur (h2) is normalized by comparing the consumption sulfur in current cycle to that of sulfur fully dissolved in first cycle.",
+ "footnote": [],
+ "bbox": [
+ [
+ 225,
+ 390,
+ 773,
+ 747
+ ]
+ ],
+ "page_idx": 14
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c.mmd b/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..b3e07e41c240f6e61b13a18967dd1affd4d60f67
--- /dev/null
+++ b/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c.mmd
@@ -0,0 +1,321 @@
+
+# Detangling electrolyte chemical dynamics and evolution in Li-S batteries by operando monitoring with optical resonance combs
+
+Jean- Marie Tarascon ( Jean- marie.tarascon@college- de- france.fr) UMR 8260 « Chimie du Solide et de l'Energie », https://orcid.org/0000- 0002- 7059- 6845
+
+Fu Liu College de France
+
+Wenqing Lu École supérieure de physique et de chimie industrielles de la Ville de Paris
+
+Jiaqiang Huang the Hong Kong University of Science and Technology (Guangzhou) https://orcid.org/0000- 0001- 8250- 228X
+
+Vanessa Pimenta École supérieure de physique et de chimie industrielles de la Ville de Paris
+
+Steven Boles NTNU - Norwegian University of Science and Technology https://orcid.org/0000- 0003- 1422- 5529
+
+Rezan Demir- Çakan Gebze Technical University
+
+Article
+
+Keywords:
+
+Posted Date: August 4th, 2023
+
+DOI: https://doi.org/10.21203/rs.3.rs- 3192096/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on November 14th, 2023. See the published version at https://doi.org/10.1038/s41467- 023- 43110- 8.
+
+<--- Page Split --->
+
+Detangling electrolyte chemical dynamics and evolution in Li- S batteries by operando monitoring with optical resonance combs
+
+Fu Liu \(^{1,2}\) , Wenqing Lu \(^{3}\) , Jiaqiang Huang \(^{4}\) , Vanessa Pimenta \(^{3}\) , Steven Boles \(^{5}\) , Rezan
+
+Demir- Cakan \(^{6,7*}\) & Jean- Marie Tarascon \(^{1,2,8*}\)
+
+\(^{1}\) Collège de France, Chimie du Solide et de l'Energie—UMR 8260 CNRS, Paris, France. \(^{2}\) Réseau sur le Stockage Electrochimique de l'Energie (RS2E)—FR, CNRS 3459, Amiens, France. \(^{3}\) Institut des Matériaux Poreux de Paris (IMAP), ESPCI Paris, Ecole Normale Supérieure, CNRS, PSL University, Paris, France \(^{4}\) The Hong Kong University of Science and Technology (Guangzhou), Sustainable Energy and Environment Thrust, Nansha, Guangzhou, Guangdong 511400, P. R. China \(^{5}\) Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway \(^{6}\) Gebze Technical University, Institute of Nanotechnology, Gebze, Kocaeli, 41400, Turkey \(^{7}\) Gebze Technical University, Department of Chemical Engineering, Kocaeli, 41400, Turkey \(^{8}\) Sorbonne Université—Université Pierre- et- Marie- Curie Paris (UPMC), Paris, France
+
+Challenges in enabling next- generation rechargeable batteries with lower cost, higher energy density, and longer cycling life stem not only from combining appropriate materials, but from optimally using cell components given their respective evolutions. One- size- fits- all approaches to operational cycling and monitoring are limited in improving sustainability if they cannot utilize and capture essential chemical dynamics and states of electrodes and electrolytes. Herein we describe and show how the use of tilted fiber Bragg grating (TFBG) sensors to track, via the monitoring of both temperature and refractive index metrics, electrolyte- electrode coupled changes that fundamentally control lithium sulfur batteries. Through quantitative sensing of the sulfur concentration in the electrolyte, we demonstrate that the nucleation pathway and crystallization of \(\mathrm{Li}_2\mathrm{S}\) and sulfur governs the cycling performance. With this technique, a critical milestone is achieved, not only towards developing chemistry- wise cells (in terms of smart battery sensing leading to improved safety and health diagnostics), but further towards demonstrating that the coupling of sensing and cycling can revitalize known cell chemistries and break open new directions for their development.
+
+## Introduction
+
+Widescale utilization of renewable energy sources is essential to supplementing and perhaps replacing the carbon- based energy supply responsible for climate change. The recent success of electric vehicles made possible by lithium- ion battery technology, attributed to both improved reliability and cost reductions, demonstrates that new breakthrough chemistries may not be necessary for a 'green transition' if known electrochemical cell pairings can be mastered. Included among these chemistries are resurgent lithium sulfur batteries (LSB), which, in spite of their appeal in terms of theoretical specific energy ( \(\sim 2600 \mathrm{Wh / kg}\) ), are still not commercialized. This can be attributed to a number of unresolved challenges, including the insulating nature of sulfur and lithium sulfides, large volume expansion (80%) of the solid sulfur cathode during the formation of \(\mathrm{Li}_2\mathrm{S}\) , and shuttle effect caused by soluble polysulfide in electrolyte \(^{1,2}\) .
+
+<--- Page Split --->
+
+Numerous characterization techniques have been deployed to clarify the underlying science of LSBs during operation, which have contributed significantly to a better understanding of the kinetics and thermodynamics of the dissolution/precipitation of polysulfides, whose critical role in LSBs has been known for nearly 50 years3. Since then, methods such as X- ray diffraction (XRD)4,5, electrochemical tests6- 8, and spectroscopic techniques9- 16 have been used to provide valuable information regarding identification of polysulfide species and reaction kinetics. However, it is experimentally challenging to isolate the individual polysulfides due to the propensity of disproportionation, and these analytical techniques rely on special equipment and cell designs that cannot be directly deployed for long cycling periods. Recently, optical fiber sensors have attracted attention in battery sensing due to their low cost, compactness, remote sensing capabilities, and simple integration into batteries without interfering with their internal chemistry17. Among the fiber sensor family, the most commercialized Fiber Bragg grating (FBG) sensors have been well integrated inside Na (Li)- ion batteries for monitoring heat and pressure18 or inside the solid- state batteries for tracking the stress dynamics19. Indeed, recently Ziyun et al. demonstrated that the cathode stress evolution of LSB can be in- situ monitored by FBG sensors for understanding the chemo- mechanics20. Nevertheless, testing polysulfides with FBGs is still limited, owing to the fact that the sensing signals are totally confined inside the fiber core and cannot sense the electrolyte surrounding the fiber surface.
+
+In order to investigate the external medium of fiber, TFBGs (same structure as FBG without physical structure modification21, but rotating the grating plane to a specific angle) have been proposed to excite hundreds of discrete cladding mode resonances that are sensitive to the external medium refractive index perturbation via evanescent fields22, hence serving as an optical 'comb'. This has led to the development of high- performance sensors used in various areas, including biomedicine23, magnetic detection24, and gas monitoring25. Recently, TFBGs have been integrated into commercial batteries to detect chemical dynamics/state of electrolytes related to chemical evolution26. Interestingly, some TFBG- assisted surface plasmon resonance (TFBG- SPR) sensors with higher sensing sensitivity have also been developed for Zn- ion batteries to offer an alternative way of probing ion transport kinetics27. Overall, TFBG sensors provide new opportunities to deal with the challenge of battery sensing as they combine direct optical sensing of the environment, as well as physio- mechanical sensing of the environment via the confined optical modes.
+
+Herein, TFBG sensors, enabling measurements with a wide array of parameters including refractive index, temperature, and strain, are proposed to operate track the chemical dynamics/states of the LSB via electrolyte sulfur concentration. We demonstrate that the capacity fading is strongly correlated with the dissolution/precipitation of polysulfides throughout the cycling and hence, with respect to cycling rates. By exploiting the kinetic and thermodynamic response of soluble sulfur in the electrolyte, the nonlinear transport flux clarifies the "invisible" disproportionation process together with their dynamic evolution. With this understanding, we show that altering the nucleation pathway of the crystalline Li2S and sulfur can be attributed to real improvements in cell cycling performance. Subsequently, it is noted that TFBGs have the ability to obtain key chemical- physical- thermal metrics in operando with notable time and spatial resolution that may extend beyond LSBs.
+
+<--- Page Split --->
+
+## Results
+
+## Characteristics of TFBG sensing
+
+Prior to in operando battery inspection, it is appropriate to first briefly visit the suitability of TFBG sensing for such chemistries, as related to fundamental principles of their operation. TFBGs, immersed in an electrolyte (Fig. 1a), were made in the core of the commercial single- mode fiber by ultraviolet pulse laser to induce periodically permanent refractive modulation. They obey a phase matching condition by enhancing the coupling between fundamental core mode and backward- propagation cladding modes22 (Fig. 1b):
+
+\[\lambda = \left(n_{11}(\lambda) + n_{lm}(\lambda)\right)\lambda /\cos \theta \quad (1)\]
+
+where \(\lambda\) is the cladding mode resonance wavelength, \(n_{11}(\lambda)\) is the effective index of core mode, and \(n_{lm}(\lambda)\) is the effective index of cladding mode with azimuthal order \(l\) and radial order \(m\) . \(\Lambda\) is the period of grating along the fiber axis, and \(\theta\) is the grating tilt angle. The experimental spectra are presented in Fig. 1c, where the core mode resonance (i.e., Bragg resonance) is located at the longest wavelength around \(1590 \mathrm{nm}\) (sensitive to temperature and strain \((T, \epsilon)\) )22. The cladding mode resonances guided by the fiber cladding (beside \(T, \epsilon\) , also sensitive to refractive index \((R)\) of the surrounding media) are shown on the left of Bragg resonances. The leaky modes are located at the region where there is a discontinuity in the cladding mode envelope and their amplitude, indicating the loss of total internal reflection at the point where the cladding mode effective index becomes equal to or smaller than the surrounding \(R\) . Therefore, with respect to soluble polysulfides which perturb electrolyte density, and hence the refractive- index, we focus on the high order guided cladding modes near the leaky mode region.
+
+<--- Page Split --->
+
+
+Fig. 1 | Concept of optical fiber sensing for LSB. (a) Schematic of a fiber optic sensor immersed in electrolyte for in-situ detection of sulfur concentration originating from the generated dissolved polysulfide and their transport activities (i.e., shuttle effect). (b) Backward-propagation guided modes inside fiber for sensing (Supplementary information Fig. S1). (c) Experimental spectra response to polysulfide. (d) The wavelength shifts of cladding mode resonance at \(\sim 1560 \mathrm{nm}\) to \(100 \mathrm{mM}\) polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 1, 2, 3, \dots , 8\) ), shaded in green; (e) to concentration variation of \(\mathrm{Li}_2\mathrm{S}_4\) and \(\mathrm{Li}_2\mathrm{S}_8\) from \(0 \mathrm{mM}\) to \(100 \mathrm{mM}\) ; (f) to same sulfur concentration of polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 4, 5, 6, 7, 8\) ).
+
+To investigate the response of our TFBG to polysulfides, depicted in Fig. 1c, the TFBG was thoroughly immersed in a series of \(100 \mathrm{mM}\) polysulfide containing electrolytes in a modified Swagelok cell. Bearing this in mind, the Bragg resonance remains stable because any strain and temperature variation were eliminated during the measurements, indicating that the cladding mode wavelength shift is only related to refractive index variation. When the chain length of polysulfides is increased while keeping the polysulfide concentration the same, the guided modes on the left side of cladding mode at \(1560 \mathrm{nm}\) becomes leaky due to the increased refractive index. This is a result of the number sulfur atoms in solution becoming larger and perturbing the corresponding mode effective refractive index, while guided modes on its right side are linearly shifted to longer wavelength (Fig. 1d,e and Supplementary Fig. S2a,b). Noteworthy is the fact that the refractive index tested by TFBG sensor is an "average effect" of all the pertinent refractive indices of lithium polysulfide solutions. Following this,
+
+<--- Page Split --->
+
+dilution of the \(100~\mathrm{mM}\) polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 4\) , 5, 6, 7, 8) to an equivalent concentration of sulfur (Supplementary Fig. S2c) yields an equivalent optical effect, stemming from the refractive index of polysulfide solutions converging to the same density, (Fig. 1f and Supplementary Fig. S2d,e). Therefore, rather than recognizing the specific species inside the electrolyte, the TFBG sensor will distinctly reveal the electrolyte sulfur concentration evolution of LSB cell (so long as temperature is kept constant).
+
+## Operando measurement of chemical dynamic state of LSB
+
+Given the promising proof- of- concept of sulfur concentration measurement in electrolyte, we explored the capability of operando chemical dynamics/states testing of LSB cell by putting a \(2\mathrm{mm}\) thick, \(12.8\mathrm{mm}\) diameter polyether ether ketone (PEEK) ring ( \(1\mathrm{cm}\) long TFBG can go through) in the middle of the Swagelok to separate the cathode (sulfur and Super P carbon composite (60/40 wt. \(\%\) )) and lithium anode so that fiber sensor would not touch any of them (Supplementary Fig. S3). Filling the PEEK ring with electrolyte (500 μL, \(1\mathrm{M}\) LiTFSI, 0.5 M LiNO3 in DOL/DME (1:1, v/v)) where the sensor is immersed, the effect of ion concentration gradient of electrolyte including \(\mathrm{Li}^+\) , TFSI- and \(\mathrm{NO}_3^-\) in DOL and DME can be safely neglected. It should be noted that prior to LSB investigations, a control experiment was executed with lithium iron phosphate (LFP) as the cathode. Here it was found that the corresponding \(R / o\) of electrolyte variation is 20 times smaller than that in LSB in which dissolved polysulfide is formed (Supplementary Fig. S4). Therefore, the use of a TFBG can provide for the possibility of measuring sulfur concentration in the electrolyte during cell operation, and to a large extent, the measurement will be irrespective of the cell's state of charge or state of health.
+
+<--- Page Split --->
+
+
+Fig. 2 | Decoding electrolyte sulfur concentration dynamic of LSB. (a) Operando measurement of LSB by TFBG and XRD at C/20 (left panel: polysulfide dissolution allowed (electrolyte of 1 M LiTFSI, 0.5 M LiNO₃ in DOL/DME (1:1, v/v)); right panel: polysulfide dissolution prohibited (electrolyte of LP30: 1 M LiPF₆ in EC/DMC) of sulfur and Super P carbon composite (60/40 wt.%) cathode. (b) Morphology (SEM) and content of elemental sulfur and Super P carbon (energy-dispersive X-ray spectroscopy, EDX) of the cathode at the end of charging. (c) The quantitative analysis of sulfur before cycling, end of first plateau of discharge and end of charge. (d) The recrystallized sulfur governed by comporptionation reactions and potential voltage. The shaded region in blue stands for 15 hours of rest (OCV mode) starting at the end of charging demonstrating that the re-crystallized sulfur (marked by green asterisk “\*”) dissolves into the electrolyte in the form of soluble polysulfide through comporptionation reactions.
+
+<--- Page Split --->
+
+Based on the aforementioned concept, we measured the electrolyte sulfur concentration variation with a TFBG sensor while simultaneously deploying in operando XRD during C/20 cycling to track phase transitions of the composite electrode (Fig. 2a,c). At the upper voltage plateau around 2.4 V, the highest sulfur concentration in the electrolyte was monitored (left panel of Fig. 2a) and found to be accompanied by a decrease in the sulfur peak intensity (XRD pattern) resulting from a series of phase transformations, i.e., from solid sulfur to soluble intermediate polysulfides. On the other hand, when the carbonate- based electrolyte was used as a reference (i.e., LP30, right panel of Fig. 2a), no concentration gradient was observed in the electrolyte and remained nearly stable due to the fact that no soluble polysulfide intermediates were formed. Instead this resulted in the formation of insoluble and undetected products, since it is known that there is a nucleophilic reaction between sulfur radical and ethylene carbonate of LP30 to form thiocarbonate- like solid electrolyte interphase28,29 (Supplementary Fig. S5). Turning to the lower voltage plateau around 2.1 V (Fig. 2a), the concentration of dissolved sulfur decreases as a result of the reduction of long- chain polysulfide into shorter chains, leading to insoluble Li2S compound in the cathode (Supplementary Fig. S6a) confirmed by XRD30,31. Upon charging, the sulfur concentration indicates reversible recovery consistent with the decay of Li2S peaks until complete disappearance at the voltage \(\sim 2.4 \text{V}\), where crystallization of sulfur starts and thus sulfur concentration in electrolyte drops again, even though the deposited solid sulfur in the cathode is featureless by XRD31. To confirm the sulfur at the end of charge, the cathode powder was recovered in the glovebox by washing and drying to remove any soluble polysulfide as well as remaining electrolyte salts (Fig.2b,c), confirming that \(1.4 \%\) sulfur was detected and its surface topography was unchanged (i.e., no formation of big crystalline particles)31. Furthermore, when setting the 15- hour open circuit voltage (OCV) after charging, the sulfur concentration increases and reaches a plateau within 9 hours (Fig.2c), whereas, on the other hand, no sulfur concentration changes were observed during rest periods applied at the end of discharge (Supplementary Fig. S6b). It is most likely explained by compropriotation reactions during the rest period when the recrystallized sulfur from the end of charging is transformed to soluble lower- order polysulfide via reacting with high- order polysulfide32. This is also supported by the beginning of 2 hours rest (first cycle before discharging) demonstrating relatively little variation of electrolyte since fresh electrolyte contains a minimum amount of high order polysulfide and the compropriotation reactions are thus not possible (Supplementary Fig. S6c). The crystalline sulfur at the end of charge is related to the cut- off potential that the sulfur recrystallization process disappears4 (disappearance of sulfur concentration valley at the end of charge in Fig.2d) if setting the potential below 2.4 V (indicated that less sulfur suppresses the related compropriotation reactions, also detailed in Supplementary Fig. S6c). Altogether, the dynamic of sulfur concentration of electrolyte decoded by TFBG sensor supports the simplified chemical reaction process: during discharging the sulfur receives electrons and transfers them first to soluble Li2S at the high voltage plateau. This is followed by formation of insoluble Li2S at the low voltage plateau and vice versa for the charging process, indicating that the consumption rate of sulfur under the galvanostatic condition can be expressed as a ratio. According to the "linear" sulfur concentration variation rate by monitoring the slope (mM/h) on each plateau tested by sensor during the discharge and charging steps (Supplementary Fig. S4a) it was
+
+<--- Page Split --->
+
+observed that the ratio on the upper and lower plateaus at the discharge step is 3.9. This is similar to the value obtained during charging (0.9), suggesting that the rate of sulfur transformation to/from soluble polysulfide is \(\sim 4.3\) times faster than that to/from insoluble Li₂S and the respective polysulfides.
+
+
+
+Fig. 3 | Decoding the disproportionation process and evolution. (a, b, c and d) The temporal voltage (black curve) and decoded electrolyte sulfur concentration (red curve) by GITT test (the capacity and optical spectra are given in supplementary Fig. S7). (a, b and c) Detailed view of electrolyte response to current pulse (kinetic process) and rest (thermodynamic process). (e) Transport flux of soluble sulfur based on current pulse (kinetics process, green triangle, \(D_t = V_{BD} / (S \times t)\) and rest (thermodynamic process, blue square, \(D_t = V_{DE} / (S \times t)\) , where \(S\) is across section area of electrolyte that sensor is immersed in, \(t\) is corresponding time. It indicates the slope of soluble sulfur consumption (negative) or formation (positive) in electrolyte, which is also plotted by arrows in bottom (arrow up: sulfur increasing, arrow down: sulfur decreasing). The normalized ratio (red sphere) represents the sulfur consumption of rest (thermodynamic process) by \(Ratio = |D_t| / (|D_t| + |D_k|)\) .
+
+<--- Page Split --->
+
+The disproportionation and association reactions of likely intermediates are mesmerizing, but despite an awareness of their existence, their mysterious dynamics make LSBs seemingly incomprehensible. Nevertheless, the real- time quantification of soluble sulfur afforded by TFBGs provides a convincing way to straighten their story when combined with GITT (Fig. 3). As depicted in Fig. 3d, the overall profile of sulfur concentration variation matches well with dissolution/precipitation of polysulfides and sulfur already confirmed in Fig.2, and we focus on the temporal response of electrolyte to the current pulse and respective rest period. According to Fig. 3a,b,c the "tiny" variation of sulfur concentration from A to B (moving from the rest to cycling mode) is the electrolyte instantaneous response to the leading edge of current pulse with strong electrical field gradient, originating from polysulfide redistribution driven by the sudden electrical field33. This effect trends in the opposite direction as polysulfide diffusion in the region from B to C, which relates to the current pulse (referred to herein as the kinetic process). The reader may note a discrepancy between voltage and concentration from C to D during rest, which is attributed to the "delay" between the electrochemical reaction at the electrode surface and the position of the sensor in the cell. Hence a small lag exists even if removing the current pulse. Regarding the OCV relaxation (3 hours rest period) and movement towards equilibrium (herein coined as the thermodynamic process) in the region from C to E, the sulfur concentration fluctuation is most likely explained by polysulfide disproportionation process (i.e. \(Li_2S_8 \leftrightarrow Li_2S_7 + 1/4S_8\) )34 since the two best- remaining hypotheses, dissociation (i.e. \(Li_2S_8 \leftrightarrow Li^+ + LiS_7\) or \(Li_2S_8 \leftrightarrow 2LiS_7\) )34 and non- uniform polysulfide distribution can be excluded: the dissociation of polysulfide including anions and radicals are rare while the neutral lithium polysulfide is dominant in electrolyte34; the polysulfide distribution reaches equilibrium within 1 min (time interval of spectra recording) that is nearly synchronous to electrochemistry (Fig. 2a), not matching the rest period situation with 3 hours of continuous soluble sulfur consumption or generation. After careful deliberation, we move forward with the idea that electrochemical and disproportionation processes can be extracted respectively by temporal response of electrolyte based on sulfur concentration decoded by TFBG sensor.
+
+Encouraged by the results mentioned above, we have next attempted to build a quantitative relation between kinetic and thermodynamic processes through a primitive estimation of transport flux of sulfur in the electrolyte (Fig. 3e). In STAGE I, on the higher voltage plateau, solid sulfur was continuously consumed upon discharge to form long chain polysulfide, \(\mathrm{Li}_2\mathrm{S}_8\) (green triangle), together with the rapid disproportionation process \(Li_2S_8 \leftrightarrow Li_2S_6 + 1/4S_8\) 35- 37 leading to soluble sulfur consumption during relaxation (blue square). At the same time the normalized ratio (red sphere) between the rest and current pulse process nearly remains the same and fixed at 0.1 (shaded in light green color), meaning that there is a competition reaction between the soluble long chain polysulfide species formation and the \(\mathrm{S}_8\) - precipitation in the beginning of the discharge step. In STAGE II, regarding the first- to- second plateau transition whereby a voltage slope forms between 2.3 and 2.1 V, the shorter chain polysulfide \(\mathrm{Li}_2\mathrm{S}_4\) is expected to be generated38,39. This is accompanied by a reduction in the rate of formation of soluble sulfur in the electrolyte and hence, the sulfur concentration during resting keeps increasing while the generation of fresh long chain polysulfides winds down and the kinetic/thermodynamic ratio can reach 0.89. This indicates that polysulfide species formation via disproportionation is dominant due to fact that dissolved sulfur
+
+<--- Page Split --->
+
+continues to react with polysulfide present in the electrolyte during rest38,41. Undoubtedly an enriched concentration of sulfur in the electrolyte contributes significantly towards driving the formation of more polysulfides. In STAGE III where the lower voltage plateau marks the conversion between \(\mathrm{Li}_2\mathrm{S}_4\) to shorter chain \(\mathrm{Li}_2\mathrm{S}_2\) and \(\mathrm{Li}_2\mathrm{S}\) forms, the potential disproportionation process \(Li_2S_2 \leftrightarrow 1 / 3Li_2S_4 + 2 / 3Li_2S^{40,41}\) is highlighted from the middle of the second plateau, and raises the sulfur concentration to about a normalized ratio of 0.2 which follows until the end of the half- cycle. Upon charging (STAGE IV and STAGE V), it is evident that the process is not a fully reversible one, as seen with STAGE IV where \(\mathrm{Li}_2\mathrm{S}_4\) and \(\mathrm{Li}_2\mathrm{S}_6\) reappear and the push towards thermodynamic equilibrium necessitates disproportionation processes leading to consumption of sulfur during rest periods, but an overall concentration increase. In STAGE V, the sulfur concentration in electrolyte drops very sharply, caused by the recrystallization of sulfur during current pulsing, even though that is not visible in the operando XRD studies shown in Fig. 2a. Interestingly, the rise of soluble sulfur during these late- stage rest periods suggests nucleation and/or growth limitations of the recrystallized sulfur, which will be addressed here later. Altogether, the quantitative disproportionation process decoupled by the fiber sensor based on GITT provides meaningful details to understand micro- mechanisms of complicated kinetics processes.
+
+
+
+Fig. 4 | Operando monitoring over cycling and cycling rate. (a) Spectra contour of TFBG cladding mode resonances response (details are given in supplementary video). (b) Temporal voltage (grey line), decoded sulfur concentration (red line), and temperature of electrolyte (blue line) over the cycling. (c) Capacity variation of (b) upon time. (d) Soluble sulfur
+
+<--- Page Split --->
+
+concentration dynamic related to cycling rate. (e) Soluble sulfur concentration dynamic related to cycling rate of first/second plateau. The concentration drop through the recrystallization of sulfur at the end of charge is marked by green asterisk \(^{**}\) . With Mode I, the cycling rate was set by upper plateau (C/20) and lower plateau (C/5); Mode II by upper plateau (C/5) and lower plateau (C/20) and Mode III by upper plateau (C/10) and lower plateau (C/10).
+
+Inspired by aforementioned exploration of internal mechanisms of LSBs, we decide to further investigate the operando monitoring over cycling and cycling rates (Fig. 4a,b). Bearing in mind that the temperature (blue curve in Fig. 4b), decoded by Bragg resonance located at \(1589 \text{nm}^{26}\) , initially rises to \(25 \text{C}^\circ\) and keeps a constant afterward due to the shipping from glovebox to oven to reach thermal equilibrium. The periodic sulfur concentration evolution (red curve in Fig. 4b), decoded by the wavelength shift of cladding mode located at \(\sim 1559.5 \text{nm}\) in Fig. 4a, indicates the reversible dissolution/precipitation of polysulfides and sulfur. Noteworthy here is the feasibility of observing the amplitude of soluble sulfur variation (supplementary Fig. S8) that matches the cycling behavior associated with capacity fading owning to less and less \(\text{Li}_2\text{S}\) and solid sulfur crystallization over cycles (Fig.4c), which could be reasonably attributed to the high electrolyte to sulfur ratio (E/S ratio, \(>100 \mu \text{L} /\text{mg}\) ), thereby inducing stronger polysulfide shuttle effect with less sulfur utilization. Regarding a sulfur concentration response to the cycling rate depicted in Fig. 4d, a lower cycling rate (C/15) leads to the largest sulfur concentration change, strongly supporting the idea that the most soluble sulfur in electrolyte is transformed to solid species ( \(\text{Li}_2\text{S}\) ) when given adequate time for completion of the redox process. Accelerating the cycling to C/10, C/5 and C/3, partially soluble sulfur transformation is seen (i.e., background of sulfur concentration rises) together with less sulfur crystallization (i.e., the "dip" of soluble concentration at the end of charge).
+
+Following the evidence thus far, it is then reasonable to conclude that regular galvanostatic operating conditions might not be perfect for LSBs, considering the various competing mechanisms explored above which are evident at different stages of charge and discharge. With this in mind, different modes of cycling protocols were also pursued to be able to tune the cycling performance. For instance, when setting a relatively low (high) cycling rate for the upper (lower) plateau depicted in Fig. 4e (Mode I), only half of the soluble sulfur inside electrolyte was transformed to \(\text{Li}_2\text{S}\) due to high cycling rate of lower plateau. On the upper voltage plateau the solid sulfur dissolution or recrystallization was \(100\%\) successful and which can be readily attributed to the low cycling rate in this voltage range. Further confirmation of the delicate cycling nature of LSBs was seen in Mode II as \(80\%\) of the soluble sulfur inside electrolyte was transformed to \(\text{Li}_2\text{S}\) due to long cycling in the lower plateau (C/20) but with less solid sulfur recrystallization at the end of charge (C/5). Overall, the quantitative relation of soluble sulfur evolution and cycling/cycling rate implies that the efficiency of solid sulfur and \(\text{Li}_2\text{S}\) formation governs the cycling performance and significant new progress might be made through cycling condition optimization alone.
+
+## High performance based on novel functional cathode
+
+Extensive work has been conducted over the years to improve the LSB performance through variety of means: the use of high- conductivity cathodes, strong polysulfide binding to
+
+<--- Page Split --->
+
+suppress the shuttling phenomenon, surface chemistry to control \(\mathrm{Li_2S}\) nucleation or dissolution, design of cathode architectures that are elastic to withstand volume expansion, and optimized electrolytes enabling high sulfur utilization42. Considering the strategy of trapping lithium polysulfides, it includes physical (spatial) entrapment by confining polysulfide in the pores of non- polar carbon materials43 or designing a sulfur host material that exhibits stronger chemical interaction such as dipolar configurations based on polar surfaces44, metal- sulfur bonding45 and surface chemistry for polysulfide grafting and catenation46, leading to long cycling without strong capacity fading. Nevertheless, the fundamental problem regardless of approach is all related to the polysulfides dissolving inside the electrolyte, thus a smart sensor that can reliably track the soluble sulfur in real time should be of particular value.
+
+In this respect, in addition to the less porous Super P carbon discussed above, the Ketjen black (KB) carbon whose BET surface area \(>1200 \text{m}^2 /\text{g}\) is utilized as physical nonpolar sulfur confinement host (KB/S, 40/60 wt.%), and the electrolyte was simultaneously monitored by a TFBG sensor together with XRD to characterize the composite cathode phase transitions (left panel of Fig. 5a). After the melt- diffusion treatment process, part of sulfur penetrates into the nanostructure of KB (Supplementary Fig. S9); however, during cycling the nonpolar physical adsorption or confinement of polysulfide is very limited and massive soluble polysulfide is dissolved and detected. Surprisingly, the capability of \(\mathrm{Li_2S}\) crystallization is enhanced since more than 91 % soluble sulfur disappears and converts to solid short chain polysulfide at second plateau as indicated by the fiber sensor. Meanwhile, unlike linearly sulfur concentration change with super P carbon (BET surface area: \(62 \text{m}^2 /\text{g}\) ) substrate cell in Fig. 2a, KB containing cell becomes "nonlinear" with a higher rate, indicating that the nucleation rate of \(\mathrm{Li_2S}\) is increasing. It could be reasonably assigned by instantaneous nucleation that depletion of the nucleation site of KB occurs at a very early stage, following the nonlinear kinetics of the nucleation pathway: \(\mathcal{N} = \mathcal{N}_c[1 - \exp (- At)]\) where \(\mathcal{N}\) is the density of nuclei, \(\mathcal{N}_c\) is the density of available nucleation site, and \(A\) is the nucleation rate47. In contrast, considering less porous Super P carbon containing cell in Fig.2a with a lower nucleation rate, the initial density of nuclei increases linearly with time: \(\mathcal{N} = \mathcal{N}_c At\) (i.e. progressive nucleation)48,49. Moreover, the porous structure of KB also accelerates the dissolution and re- crystallization of sulfur, which results in a strong sulfur concentration saturation at the transient stage relating to semisolid \(\mathrm{Li_2S_4}\) generation (keeping a balance between electrochemical and disproportionation process) and enhanced soluble sulfur reduction to solid sulfur at the end of charging (Supplementary Fig. S10). The sulfur concentration dynamic responding to potential and cycling rate is consistent with the Super P substrate, detailed in Supplementary Fig. S11.
+
+<--- Page Split --->
+
+
+Fig. 5 | Chemistry of LSB with outstanding polysulfide-trapping capability cathodes. (a) Operando measurement of LSB by TFBG and XRD at C/20 (left panel: nonpolar physical adsorption of polysulfide by KB carbon; right panel: polar adsorption of polysulfide by MOF-801(Zr)). (b) In-situ detection of polysulfide adsorption by MOF-801(Zr). (c) XRD spectra for MOF-801(Zr) before and after adsorption of \(\mathrm{Li}_2\mathrm{S}_6\) . (d) The temporal voltage (grey line), decoded sulfur concentration (red line) of cathode composite based on MOF-801(Zr), and decoded sulfur concentration (blue line) considering the cathode with KB substrate (same amount of active material) is used as a reference without showing the temporal voltage.
+
+To further extend the use of porous materials as host matrix for sulfur confinement, Metal- Organic Frameworks (MOFs) can be considered as efficient candidates for the selective adsorption of polysulfide species45,50. We have considered MOF- 801(Zr), a microporous zirconium fumarate with pores of about 5- 12 Å and a high specific surface area (1020 (±20) m2/g), to be considered as an efficient candidate for the adsorption of polysulfide species. Its 3D cubic structure is built- up from \(\mathrm{Zr_6O_4(OH)_4}\) oxo- clusters linked to fumarate ligands and exhibits abundant missing linkers defect sites and reactive terminal –OH groups. Due to the
+
+<--- Page Split --->
+
+Lewis acidic character of the Zr nodes and the reactivity of these terminal groups, the polysulfide species (soft Lewis bases) are expected to interact strongly with the framework51,52. Depicted in Fig. 5c, the \(0.5 \mathrm{ml} 100 \mathrm{mM}\) polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 4, 6, 8\) ) was monitored in real time by fiber sensor during adsorption, which is evidently finished within 1 hour ensuring efficient adsorption inside the cell. After fully adsorbing \(100 \mathrm{mM} \mathrm{Li}_2\mathrm{S}_6\) (Fig. 5d), the XRD pattern shows the appearance of new peaks in addition to the ones of MOF- 801(Zr), matching with the peaks of pure solid sulfur (Supplementary Fig. S12) consistent with the "yellow" color of the powder. This explains why the operando test starts with the peaks of sulfur (XRD pattern on the right panel of Fig. 5a). The subsequent electrochemical reaction is the same as the cathode substrate with KB including concentration saturation in the transition region between the first and the second plateau, nonlinear sulfur consumption rate with instantaneous nucleation pathway and enhanced sulfur crystallization at the end of charge. However, a key point and difference is that the sulfur concentration inside the electrolyte dramatically decreases by \(80.8\%\) with the same amount of active material due to the enhanced adsorption and localization of polysulfides through Lewis acid- base chemical interaction by MOF- 801(Zr) (Fig.5d and Support information, Fig. S13).
+
+
+
+Fig. 6 | The correlation between electrochemical performance and \(\mathrm{Li}_2\mathrm{S}\) nucleation, sulfur crystallization. (a) Content of \(\mathrm{Li}_2\mathrm{S}\) nucleation (h1) and solid sulfur crystallization (h2). (b) Cycling performance of cathode composite at C/15 over 30 cycles. (c and d) The corresponding ratio of \(\mathrm{Li}_2\mathrm{S}\) nucleation (c) and solid sulfur crystallization (d). (e) Cycling rate performance of cathode composite. (f and g) The corresponding ratio of \(\mathrm{Li}_2\mathrm{S}\) nucleation (f) and solid sulfur crystallization (g). Note that all the cycling cell pursed in the presence of TFBG fiber and the \(\mathrm{Li}_2\mathrm{S}\) (h1) and solid sulfur (h2) is normalized by comparing the consumption sulfur in current cycle to that of sulfur fully dissolved in first cycle.
+
+<--- Page Split --->
+
+To evaluate the performance of cathode considering the three S cathode composites (with Super P, KB, MOF- 801(Zr)), we decided to compare their long cycling performance together with capabilities of \(\mathsf{Li}_2\mathsf{S}\) nucleation (h1) and sulfur crystallization (h2) (Fig. 6a). Depicted in Fig. 6b, the KB and MOF- 801(Zr) cell both experienced better capacity retention over 30 cycles at C/15 with a fade rate as \(0.99\%\) , \(0.88\%\) per cycles, respectively, while the super P cell is fading with \(4.7\%\) per cycles, which is consistent with the capability of crystallization of \(\mathsf{Li}_2\mathsf{S}\) and sulfur shown in Fig. 6c,d. Surprisingly, the KB and MOF- 801(Zr) cells have the similar efficiency of solid species crystallization (also supported by Fig. 6f) by taking the merit of high surface area, whereas the MOF- 801(Zr) exhibits the best capacity retention due to its strong chemical interaction for polysulfide which also well explains the capability to trap and recrystallize sulfur(Fig. 6g). Meanwhile, less sulfur utilization will be induced as well by intrinsic adsorption together with its low conductivity nature, leading to the lower capacity of MOF- 801(Zr) than that of KB cell over cycling. On the other hand, the Super P cell is fading fast because of high electrolyte volume with the E/S ratio over \(100\mu \mathrm{L} / \mathrm{mg}\) , presumably due to shuttle phenomenon enhancement. However, this problem does not affect the performance of KB and MOF- 801(Zr) cells, revealing that perhaps the most important parameter for cycling performance is related to the capability of crystallization of \(\mathsf{Li}_2\mathsf{S}\) and sulfur, which relies on a comprehensive balance with all involved factors such as high surface area, sulfur anion bonding and conductivity, in addition to cycling conditions.
+
+## Discussions and conclusions
+
+Herein, TFBG sensors with low cost, easy integration into batteries, and long cycling capabilities during cell operation were demonstrated for operando testing of electrolyte sulfur concentration evolution of the LSB, which reveals the correlated relationship between the capacity fading and dynamic of dissolution/precipitation of polysulfides over cycling and at different cycling rates. Meanwhile, the chemical kinetics and thermodynamic response of soluble polysulfide in electrolyte were decoded with GITT experiments, with the disproportionation dynamic process linked to the transport flux of soluble species. Moreover, the cycling performance is well improved by designing the composite cathodes via porous carbon as nonpolar physical sulfur confinement and MOF- 801(Zr) as polar adsorption of polysulfide, through a host- guest chemical interaction. These substrates indicate that the nucleation kinetics and growth of \(\mathsf{Li}_2\mathsf{S}\) are changing from progressive to an instantaneous pathway due to enhanced soluble sulfur consumption rate, ultimately leading to the improvement of crystallization capability of \(\mathsf{Li}_2\mathsf{S}\) and sulfur.
+
+Despite the encouraging insights supported by TFBG technology, a limitation of our operando testing stems from the refractive index link, which as mentioned, is an "average" effect of all species inside electrolyte. Thus, somewhat complicated data inference is required with critical external inputs, as comparing to direct evidence and measurement of species by infrared fiber operando measurement53 and Raman spectroscopy based on hollow- core optical fiber54. This could might be solved in future by machine learning algorithms to simplify analysis and hence lead to more efficient 'combing' of data. Second, the optical interrogator used here is both expensive and bulky (volume), so future efforts may warrant an optimized integrator system capable of capturing a sensing signal by energy (amplitude) instead of wavelength55, but intensity- based measurements may present other technical challenges.
+
+<--- Page Split --->
+
+Finally, the cycling based on Swagelok is achieved with high E/S ratio which enhances the shuttle effect of polysulfide, leading to acceleration of capacity fading. Therefore, long- term cycling configurations such as coin or 18650 cells integrated with fiber sensors might reveal other prominent performance- governing mechanisms. Nevertheless, TFBG sensors still provide fruitful details of the chemical dynamics of polysulfide as a diagnostic technique to monitor the state of health of cells in real- time.
+
+Considering the specific properties of TFBG, including multi- resonance- peaks, high refractive index sensitivity, and ultrafast response, new opportunities of battery sensing can be envisioned, such that more than two gratings can be integrated inside the cell to map the sulfur gradient with more precision and accuracy, ultrathin solid electrolyte interphase (SEI) films could be characterized by sensitivity enhanced surface plasmon resonance based TFBG via surface and bulk refractive index discrimination56, the dynamic of electrons and phonon coupling inside cathode could be probed by ultrafast measurement through the pump- probe configuration of TFBG57. Overall, the non- disruptive diagnostic techniques based on the TFBG sensor allow us to monitor chemical- physical- thermal metrics in operando with notable time and spatial resolution. Therefore, with the use of these combs it becomes possible to detangle hidden high- value information such as states of charge, health estimations, and operational guidance along with non- electrochemical early- failure indicators, leading to increased straighter pathways to improving battery reliability, service life, and safety.
+
+## Methods
+
+## Materials and electrode preparation
+
+## Synthesis of MOF-801(Zr)
+
+10.86 mmol of \(\mathrm{ZrOCl_2\cdot 8H_2O}\) , 7.624 mmol of fumaric acid, 9 mL of formic acid and 40 mL of deionized water were mixed in the reactor58, following 5 h stirring when the solution becomes cloudy. The ultimate product was collected by centrifugation, abundantly washed with water and ethanol, and dried under vacuum.
+
+Preparation of polysulfides solutions: the \(100~\mathrm{mM}\) lithium polysulfides solution \(\mathrm{Li_2S_x}\) ( \(x = 2\) , 3, \(\dots\) , 8) were prepared by mixing lithium sulfide (99.9 % \(\mathrm{Li_2S}\) , Sigma Aldrich) and sulfur (S, Sigma Aldrich) in stoichiometric ratio to organic electrolyte (1 M LiTFSI, 0.5 M LiNO3 in DOL/DME (1:1, v/v)), and the solution was continuously stirred with additional heating process at \(55~\mathrm{C}^\circ\) for 4 days in argon filled glovebox.
+
+Preparation of sulfur composite electrodes: sulfur and Super P conductive carbon (Ketjenblack carbon) with a ratio 60/40 wt% were mixed by hand- grinding, followed by a heat- treatment (160 \(^\circ \mathrm{C}\) during 8 hours under air). The 5 wt Poly(tetrafluoroethylene) dispersion (PTFE, Alfa Aesar) is mixed with the cathode composite, rolled to a film and punched into disks with sulfur loading around \(5.3\mathrm{mg / cm}^2\) , and dried under vacuum at \(80^\circ \mathrm{C}\) overnight. To make the cathode composite with MOF- 801(Zr), the thoroughly adsorption of \(100\mathrm{mM}\mathrm{Li}_2\mathrm{S}_6\) in DOL/DME (1:1, v/v) was achieved by MOF- 801(Zr) with a stoichiometric ratio of \(1\mathrm{mL} / 40\) mg, followed by washing the powder twice by DOL and tried in vacuum overnight. The sulfur contained MOF- 801(Zr) (40% sulfur) was mixed with Super P conductive carbon with 50/50 wt% by hand- grinding without heat- treatment.
+
+<--- Page Split --->
+
+## TFBG fabrication and sensing system.
+
+Each \(10mm\) - long TFBG with \(7^{\circ}\) internal tilt angle was inscribed in hydrogen- loaded CORNING SMF- 28 fiber by laser irradiation based on phase- mask method22. Hydrogen loading of the fibers, enhancing their photosensitivity to ultraviolet light, was performed at room temperature and a pressure of 15.2 MPa for 14 days. The input light from KrF pulsed excimer laser (model PM- 848 from Light Machinery, Inc., emitting at 248 nm and 100 pulse/second) was cylindrically focused along the fiber axis with energy of \(\sim 40m\) over the grating region and also having passed through a 1078.4 nm period phase mask to produce a permanent periodic refractive index modulation in the core of the fiber. Rotating the fiber and phase mask, the tilt of grating fringes was obtained at an angle in the core as \(7^{\circ}\) .
+
+## Computational details
+
+The transmission spectra simulations were carried out based on three- layer cylindrical waveguide using analytical method57. First, the simulated spectra is calibrated by the experimental spectra in air; Second, the refractive index of electrolyte were obtained by increasing the simulation surrounding RI (third layer) manually to match the experimental spectra, which is 1.3858 at 1559 nm wavelength considering the dispersion (supplementary Fig. S2d,e), Finally, mode intensity profiles were simulated by a complex finite- difference vectoral simulation tool (FIMMWAVE, by Photon Design), consisting of a three- layer waveguide: \(8.2\mu m\) core diameter with refractive index 1.449311, \(125\mu m\) cladding diameter with refractive index 1.444078, \(80\mu m\) diameter medium of electrolyte (refractive index \(= 1.3858\) ).
+
+## Integration of TFBG sensors into modified Swagelok
+
+A ring made of PEEK (12.8 mm diameter, 2mm thick to fit 10 mm length fiber sensor) is fixed in the middle of 19 mm diameter Swagelok cell where fiber sensor can go through by drilling two holes. The Li metal foil (0.38 mm thickness, 14 mm diameter) is attached to one side of PEEK ring as anode, and on the other side of ring there is a steel grid to hold one Whatman separator beneath sulfur composite cathode. The cells were assembled in an argon- filled glovebox.
+
+## Electrochemical measurements
+
+The electrochemical performances of Swagelok cell were evaluated by BCS- 810 or MPG2 potentiostat (Biologic, France) at \(25^{\circ}C\) degree inside temperature- controlled oven (Memmert, \(\pm 0.1^{\circ}C\) ). The galvanostatic discharge- charge cycling was carried out with the voltage range of \(1.7V - 2.8V\) .
+
+## Operando measurement by TFBG sensors and XRD
+
+To achieve TFBG sensor operando measurement, the optical transmission spectra were recorded (1 min/spectra) by an optical integrator (CTP10, EXFO SOLUTIONS) with a resolution of \(1pm\) for wavelength ranging from 1500 nm to 1600 nm. Considering XRD operando measurement, it was performed on a D8 Advance diffractometer (Bruker) using a Cu Ka X- ray source \((\lambda_{\mathrm{cal}} = 1.54056\) A, \(\lambda_{\mathrm{cal}} = 1.54439\) A) and a LynxEye XE detector. The XRD pattern and electrochemical data are simultaneously recorded by a custom designed airtight cell with a beryllium window producing a full pattern every 20 min.
+
+<--- Page Split --->
+
+## Preparation of cycled electrode samples for SEM and EDX imaging
+
+The samples, at the end of charging, were prepared by washing the cathode powder twice by DOL to remove any dissolved lithium polysulfide species and lithium salt, and dried in vacuum chamber overnight. Then the powder was coated with gold (plasma sputtering coater (GSL- 1100X- SPC- 12, MTI)) for SEM (FEI Magellan) equipped with an energy- dispersive X- ray spectroscopy detector (Oxford Instruments) performed under an acceleration voltage of 20 kV.
+
+## Data availability
+
+All relevant data are included in the paper and Supplementary Information. Extra data are available on reasonable request from the corresponding author.
+
+## Reference
+
+1. Bruce, P. G., Freunberger, S. A., Hardwick, L. J. & Tarascon, J.-M. Li-O2 and Li-S batteries with high energy storage. Nat. Mater. 11, 19-29 (2012).
+2. Li, T. et al. A comprehensive understanding of lithium-sulfur battery technology. Adv. Funct. Matter. 29, 1901730 (2019).
+3. Eichinger, G. & Besenhard, J. O. High energy density lithium cells: part II. cathodes and complete cells. J. Electroanal. Chem. 72, 1-31 (1976).
+4. Nelson, J. et al. In operando X-ray diffraction and transmission X-ray microscopy of lithium sulfur batteries. J. Am. Chem. Soc. 134, 6337-6343 (2012).
+5. Conder, J., Rouchet, R., Trabesinger, S., Marino, C., Gubler, L. & Villevieille, C. Direct observation of lithium polysulfides in lithium-sulfur batteries using operando X-ray diffraction. Nat. Energy 2, 17069 (2017).
+6. Lu, Y.-C., He, Q. & Gasteiger, H. A. Probing the lithium-sulfur redox reactions: a rotation-ring disk electrode study. J. Phys. Chem. C 118, 5733-5741 (2014).
+7. Schneider, H. et al. On the electrode potentials in lithium-sulfur batteries and their solvent-dependence. J. Electrochem. Soc. 161, A1399-A1406 (2014).
+8. Deng, Z., Zhang, Z., Lai, Y., Liu, J., Li, J. & Liu, Y. Electrochemical impedance spectroscopy study of a lithium/sulfur battery: modeling and analysis of capacity fading. J. Electrochem. Soc. 160, A553-A558 (2013).
+9. Zou, Q. & Lu, Y.-C. Solvent-dictated lithium sulfur redox reactions: an operando UV-vis spectroscopic study. J. Phys. Chem. Lett. 7, 1518-1525 (2016).
+10. He, Q. et al. Operando identification of liquid intermediates in lithium-sulfur batteries via transmission UV-vis spectroscopy. J. Electrochem. Soc. 167, 080508 (2020).
+11. Patel, M. U. M. & Dominko, R. Application of in operando UV/Vis spectroscopy in lithium-sulfur batteries. ChemSusChem. 7, 2167-2175 (2014).
+
+<--- Page Split --->
+
+12. Patel, M. U. M., Demir-Cakan, R., Morcrette, M., Tarascon, J.-M., Gaberscek, M. & Dominko, R. Li-S battery analyzed by UV/Vis in operando mode. ChemSusChem. 6, 1177-1181 (2013).13. Kawase, A., Shirai, S., Yamoto, Y., Arakawa, R. & Takata, T. Electrochemical reactions of lithium-sulfur batteries: an analytical study using the organic conversion technique. Phys. Chem. Chem. Phys. 16, 9344-9350 (2014).14. Kavčič, M., Petric, M., Rajh, A., Isaković, K., Vizintin, A., Talian, S. D. & Dominko, R. Characterization of Li-S batteries using laboratory sulfur X-ray emission spectroscopy. ACS Appl. Energy Mater. 4, 2357-2364 (2021).15. Prehal, C. et al. On the nanoscale structural evolution of solid discharge products in lithium-sulfur batteries using operando scattering. Nat. Commun. 13, 6326 (2020).16. Saqib, N., Ohlhausen, G. M. & Porter, J. M. In operando infrared spectroscopy of lithium polysulfide using a novel spectro-electrochemical cell. J. Power Sources 364, 266-271 (2017).17. Huang, J., Boles, S. T. & Tarascon, J.-M. Sensing as the key to battery lifetime and sustainability. Nat. Sustain. 5, 194-204 (2022).18. Huang, J. et al. Operando decoding of chemical and thermal events in commercial Na(Li)-ion cells via optical sensors. Nat. Energy 5, 674-683 (2020).19. Blanquer, L. A., Marchini, F., Seitz, J. R., Daher, N., Bétermier, F., Huang, J., Gervillié, C. & Tarascon, J.-M. Optical sensors for operando stress monitoring in lithium-based batteries containing solid-state or liquid electrolytes. Nat. Commun. 13, 1153 (2022).20. Miao, Z. et al. Direct optical fiber monitor on stress evolution of the sulfur-based cathodes for lithium-sulfur batteries. Energy Environ. Sci. 15, 2029-2038 (2022).21. Ghannoum, A., Norris, R. C., Lyer, K., Zdravkova, L., Yu, A. & Nieva, P. Optical characterization of commercial lithiated graphite battery electrodes and in situ fiber optic evanescent wave spectroscopy. ACS Appl. Mater. Interfaces 8, 18763-18769 (2016).22. Albert, J., Shao, L. Y. & Caucheteur, C. Tilted fiber Bragg grating sensors. Laser Photonics Rev. 7, 83-108 (2013).23. Shevchenko, Y. et al. In situ biosensing with a surface plasmon resonance fiber grating aptasensor. Anal. Chem. 83, 7027-7034 (2011).24. Zhang, Z. et al. Plasmonic fiber-optic vector magnetometer. Appl. Phys. Lett. 108, 101105 (2016).25. Caucheteur, C., Guo, T., Liu, F., Guan, B.-O. & Albert, J. Ultrasensitive plasmonic sensing in air using optical fibre spectral combs. Nat. Commun. 7, 13371 (2016).26. Huang, J., Han, X., Liu, F., Gervillié, C., Blanquer, L. A., Guo, T. & Tarascon, J.-M. Monitoring battery electrolyte chemistry via in-operando tilted fiber Bragg grating sensors. Energy Environ. Sci. 14, 6464-6475 (2021).27. Wang, R. et al. Operando monitoring of ion activities in aqueous batteries with plasmonic fiber-optic sensors. Nat. Commun. 13, 547 (2022).
+
+<--- Page Split --->
+
+28. Wang, L. et al. Compositions and formation mechanisms of solid-electrolyte interphase on microporous carbon/sulfur cathodes. Chem. Mater. 32, 3765-3775 (2020).
+
+29. Xu, Y. et al. Confined sulfur in microporous carbon renders superior cycling stability in Li/S batteries. Adv. Funct. Mater. 25, 4312-4320 (2015).
+
+30. Kumaresan, K., Mikhaylik, Y. & White, R. E. A mathematical model for a lithium-sulfur cell. J. Electrochem. Soc. 155, A576-A582 (2008).
+
+31. Walus, S., Barchasz, C., Colin, J. F., Martin, J. F., Elkaim, E., Lepretre, J. C. & Alloin, F. New insight into the working mechanism of lithium-sulfur batteries: in situ and operando X-ray diffraction characterization. Chem. Commun. 49, 7899-7901 (2013).
+
+32. Shen, C. et al. Self-discharge behavior of lithium-sulfur batteries at different electrolyte/sulfur ratios. J. Electrochem. Soc. 166, A5287-A5294 (2019).
+
+33. Zugmann, S., Fleischmann, M., Amereller, M., Gschwind, R. M., Wiemhofer, H. D. & Gores, H. J. Measurement of transference numbers for lithium ion electrolytes via four different methods, a comparative study. Electrochim. Acta 56, 3926-3933 (2011).
+
+34. Zhang, B., Wu, J., Gu, J., Li, S., Yan, T. & Gao, X.-P. The fundamental understanding of lithium polysulfide in ether-based electrolyte for lithium-sulfur batteries. ACS Energy Lett. 6, 537-546 (2021).
+
+35. Cuisinier, M. et al. Sulfur speciation in Li-S batteries determined by operando X-ray absorption spectroscopy. J. Phys. Chem. Lett. 4, 3227-3232 (2013).
+
+36. Barchasz, C., Molton, F., Duboc, C., Lepretre, J. C., Patoux, S. & Alloin, F. Lithium/sulfur cell discharge mechanism: an original approach for intermediate species identification. Anal. Chem. 84, 3973-3980 (2012).
+
+37. Liu, J., Chen, H., Chen, W., Zhang, Y. & Zheng, Y. New insight into the "shuttle mechanism" of rechargeable lithium-sulfur batteries. ChemElectroChem 6, 2782-2787 (2019).
+
+38. Mikhaylik, Y. V. & Akridge, J. R. Polysulfide shuttle study in the Li/S battery system. J. Electrochem. Soc. 151, A1969-A1976 (2004).
+
+39. He, Q., Gorlin, Y., Patel, M. U. M., Gasteiger, H. A. & Lu, Y.-C. Unraveling the correlation between solvent properties and sulfur redox behavior in lithium-sulfur batteries. J. Electrochem. Soc. 165, A4027-A4033 (2018).
+
+40. Wujcik, K. H. et al. Fingerprinting lithium-sulfur battery reaction products by X-ray absorption spectroscopy. J. Electrochem. Soc. 161, A1100-A1106 (2014).
+
+41. Moy, D., Manivannan, A. & Narayanan, S. R. Direct measurement of polysulfide shuttle current: a window into understanding the performance of lithium-sulfur cells. J. Electrochem. Soc. 162, A1-A7 (2015).
+
+42. Pang, Q., Liang, X., Kwok, C. Y. & Nazar, L. F. Advances in lithium-sulfur batteries based on multifunctional cathodes and electrolytes. Nat. Energy 1, 16132 (2016).
+
+43. Ji, X., Lee, K. T. & Nazar, L. F. A highly ordered nanostructured carbon-sulphur cathode
+
+<--- Page Split --->
+
+for lithium- sulphur batteries. Nat. Mater. 8, 500- 506 (2009).
+
+44. Pang, Q., Kundu, D., Cuisinier, M. & Nazar, L. F. Surface-enhanced redox chemistry of polysulphides on a metallic and polar host for lithium-sulphur batteries. Nat. Commun. 5, 4759 (2014).
+
+45. Zheng, J. et al. Lewis acid-base interactions between polysulfide and metal organic framework in lithium sulfur batteries. Nano Lett. 14, 2345-2352 (2014).
+
+46. Liang, X., Hart, C., Pang, Q., Garsuch, A., Weiss, T. & Nazar, L. F. A highly efficient polysulfide mediator for lithium-sulfur batteries. Nat. Commun. 6, 5682 (2015).
+
+47. Hyde, M. E. & Compton, R. G. A review of the analysis of multiple nucleation with diffusion controlled growth. J. Electroanal. Chem. 549, 1-12 (2003).
+
+48. Pan, H. et al. Non-encapsulation approach for high-performance Li-S batteries through controlled nucleation and growth. Nat. Energy 2, 813-820 (2017).
+
+49. Li, Z., Zhou, Y., Wang, Y. & Lu, Y.-C. Solvent-mediated Li2S electrodeposition: a critical manipulator in lithium-sulfur batteries. Adv. Energy Mater. 8, 1802207 (2019).
+
+50. Zheng, Y., Zheng, S., Xue, H. & Pang, H. Metal-organic frameworks for lithium-sulfur batteries. J. Mater. Chem. A 7, 3469-3491 (2019).
+
+51. Feng, X. et al. Engineering a highly defective stable Uio-66 with tunable Lewis-Bronsted acidity: the role of the hemilabile linker. J. Am. Chem. Soc. 142, 3174-3183 (2020).
+
+52. Zheng, Z.-J., Ye, H. & Guo, Z.-P. Recent progress on pristine metal/covalent-organic frameworks and their composites for lithium-sulfur batteries. Energy Environ. Sci. 14, 1835-1853 (2021).
+
+53. Gervillie-Mouraveiff, C. et al. Unlocking cell chemistry evolution with operando fibre optic infrared spectroscopy in commercial Na(Li)-ion batteries. Nat. Energy 7, 1157-1169 (2022).
+
+54. Miele, E. et al. Hollow-core optical fibre sensors for operando Raman spectroscopy investigation of Li-ion battery liquid electrolytes. Nat. Commun. 13, 1651 (2022).
+
+55. Gang, T., Liu, F., Hu, M. & Albert, J. Integrated differential area method for variable sensitivity interrogation of tilted fiber Bragg grating sensors. J. Lightwave Technol. 37, 4531-4536 (2019).
+
+56. Liu, F., Zhang, X., Li, K., Guo, T., Lanoul, A. & Albert, J. Discrimination of bulk and surface refractive index change in plasmonic sensors with narrow bandwidth resonance combs. ACS Sens. 6, 3013-3023 (2021).
+
+57. Liu, F. & Albert, J. 40 GHz-rate all-optical cross-modulation of core-guided near infrared light in single mode fiber by surface plasmons on gold-coated tilted fiber Bragg gratings. APL Photonics 4, 126104 (2019).
+
+58. Dai, S., Nouar, F., Zhang, S., Tissot, A. & Serre, C. One-step room-temperature synthesis of metal (IV) carboxylate metal-organic frameworks. Angew. Chem. Int. Ed. 60, 4282-4288 (2021).
+
+<--- Page Split --->
+
+## Acknowledgements
+
+AcknowledgementsJ.- M. Tarascon acknowledges the International Balzan Prize Foundation and the LABEX STOREXII for funding. F. Liu and J.- M. Tarascon acknowledge the European Project "Innovative physical/virtual sensor platform for battery cell" (INSTABAT) (European Union's Horizon 2020 research and innovation program under grant agreement No 955930). W. Lu acknowledges the support of the CSC scholarship (201906880002). R. Demir- Cakan is thankful to the French Embassy for the Visiting Researcher Fellowship (135694V). We thank Dr. J. Forero- Saboya for his assistance of scanning electron microscopy images. We thank Prof. J. Albert from Carleton University (Ottawa, Canada) for the fabrication of fiber sensors and assistance of simulation software. Finally, we gladly thank Dr. W. He, Dr. Y. Wang, Dr. X. Gao, Dr. B. Li, Dr. C. Gervillie- Mouravieff and Mr. C. Leau for extensive and valuable discussion and comments.
+
+## Author Contributions
+
+Author ContributionsF. Liu, J. Huang, R. Demir- Cakan and J.- M. Tarascon conceived the idea and designed the experiments. F. Liu performed the experiments. F. Liu, J. Huang, R. Demir- Cakan and J.- M. Tarascon performed the data analysis. W. Lu and V. Pimenta provided the MOF- 801(Zr). Finally, F. Liu, S. Boles, R. Demir- Cakan and J.- M. Tarascon wrote the paper with contributions from all authors.
+
+## Conflicts of interest
+
+The authors declare no competing financial interests
+
+## Additional information
+
+Supplementary information: the online version contains supplementary material available at
+
+Correspondence and requests for materials should be addressed to R. Demir- Cakan or J.- M. Tarascon.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+Supportinformation.pdf LiSbatterysensing.mp4
+
+<--- Page Split --->
diff --git a/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c_det.mmd b/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..0514cf9efa139af0cec0db0792ca9c19588f434a
--- /dev/null
+++ b/preprint/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c/preprint__0179e628a853118df9da75d50a227d9cf3c9b00dfa8825f8efe5e29d0d1c5f4c_det.mmd
@@ -0,0 +1,421 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 912, 208]]<|/det|>
+# Detangling electrolyte chemical dynamics and evolution in Li-S batteries by operando monitoring with optical resonance combs
+
+<|ref|>text<|/ref|><|det|>[[44, 228, 816, 270]]<|/det|>
+Jean- Marie Tarascon ( Jean- marie.tarascon@college- de- france.fr) UMR 8260 « Chimie du Solide et de l'Energie », https://orcid.org/0000- 0002- 7059- 6845
+
+<|ref|>text<|/ref|><|det|>[[44, 276, 214, 316]]<|/det|>
+Fu Liu College de France
+
+<|ref|>text<|/ref|><|det|>[[44, 323, 692, 364]]<|/det|>
+Wenqing Lu École supérieure de physique et de chimie industrielles de la Ville de Paris
+
+<|ref|>text<|/ref|><|det|>[[44, 369, 950, 432]]<|/det|>
+Jiaqiang Huang the Hong Kong University of Science and Technology (Guangzhou) https://orcid.org/0000- 0001- 8250- 228X
+
+<|ref|>text<|/ref|><|det|>[[44, 438, 692, 479]]<|/det|>
+Vanessa Pimenta École supérieure de physique et de chimie industrielles de la Ville de Paris
+
+<|ref|>text<|/ref|><|det|>[[44, 484, 905, 526]]<|/det|>
+Steven Boles NTNU - Norwegian University of Science and Technology https://orcid.org/0000- 0003- 1422- 5529
+
+<|ref|>text<|/ref|><|det|>[[44, 531, 291, 571]]<|/det|>
+Rezan Demir- Çakan Gebze Technical University
+
+<|ref|>text<|/ref|><|det|>[[44, 613, 102, 630]]<|/det|>
+Article
+
+<|ref|>text<|/ref|><|det|>[[44, 650, 137, 669]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 689, 310, 708]]<|/det|>
+Posted Date: August 4th, 2023
+
+<|ref|>text<|/ref|><|det|>[[44, 726, 475, 746]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 3192096/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 764, 910, 807]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 824, 530, 844]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 880, 958, 924]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on November 14th, 2023. See the published version at https://doi.org/10.1038/s41467- 023- 43110- 8.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[175, 85, 822, 120]]<|/det|>
+Detangling electrolyte chemical dynamics and evolution in Li- S batteries by operando monitoring with optical resonance combs
+
+<|ref|>text<|/ref|><|det|>[[217, 124, 821, 143]]<|/det|>
+Fu Liu \(^{1,2}\) , Wenqing Lu \(^{3}\) , Jiaqiang Huang \(^{4}\) , Vanessa Pimenta \(^{3}\) , Steven Boles \(^{5}\) , Rezan
+
+<|ref|>text<|/ref|><|det|>[[342, 152, 666, 170]]<|/det|>
+Demir- Cakan \(^{6,7*}\) & Jean- Marie Tarascon \(^{1,2,8*}\)
+
+<|ref|>text<|/ref|><|det|>[[145, 177, 850, 380]]<|/det|>
+\(^{1}\) Collège de France, Chimie du Solide et de l'Energie—UMR 8260 CNRS, Paris, France. \(^{2}\) Réseau sur le Stockage Electrochimique de l'Energie (RS2E)—FR, CNRS 3459, Amiens, France. \(^{3}\) Institut des Matériaux Poreux de Paris (IMAP), ESPCI Paris, Ecole Normale Supérieure, CNRS, PSL University, Paris, France \(^{4}\) The Hong Kong University of Science and Technology (Guangzhou), Sustainable Energy and Environment Thrust, Nansha, Guangzhou, Guangdong 511400, P. R. China \(^{5}\) Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway \(^{6}\) Gebze Technical University, Institute of Nanotechnology, Gebze, Kocaeli, 41400, Turkey \(^{7}\) Gebze Technical University, Department of Chemical Engineering, Kocaeli, 41400, Turkey \(^{8}\) Sorbonne Université—Université Pierre- et- Marie- Curie Paris (UPMC), Paris, France
+
+<|ref|>text<|/ref|><|det|>[[147, 391, 852, 666]]<|/det|>
+Challenges in enabling next- generation rechargeable batteries with lower cost, higher energy density, and longer cycling life stem not only from combining appropriate materials, but from optimally using cell components given their respective evolutions. One- size- fits- all approaches to operational cycling and monitoring are limited in improving sustainability if they cannot utilize and capture essential chemical dynamics and states of electrodes and electrolytes. Herein we describe and show how the use of tilted fiber Bragg grating (TFBG) sensors to track, via the monitoring of both temperature and refractive index metrics, electrolyte- electrode coupled changes that fundamentally control lithium sulfur batteries. Through quantitative sensing of the sulfur concentration in the electrolyte, we demonstrate that the nucleation pathway and crystallization of \(\mathrm{Li}_2\mathrm{S}\) and sulfur governs the cycling performance. With this technique, a critical milestone is achieved, not only towards developing chemistry- wise cells (in terms of smart battery sensing leading to improved safety and health diagnostics), but further towards demonstrating that the coupling of sensing and cycling can revitalize known cell chemistries and break open new directions for their development.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 678, 250, 693]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[148, 705, 852, 907]]<|/det|>
+Widescale utilization of renewable energy sources is essential to supplementing and perhaps replacing the carbon- based energy supply responsible for climate change. The recent success of electric vehicles made possible by lithium- ion battery technology, attributed to both improved reliability and cost reductions, demonstrates that new breakthrough chemistries may not be necessary for a 'green transition' if known electrochemical cell pairings can be mastered. Included among these chemistries are resurgent lithium sulfur batteries (LSB), which, in spite of their appeal in terms of theoretical specific energy ( \(\sim 2600 \mathrm{Wh / kg}\) ), are still not commercialized. This can be attributed to a number of unresolved challenges, including the insulating nature of sulfur and lithium sulfides, large volume expansion (80%) of the solid sulfur cathode during the formation of \(\mathrm{Li}_2\mathrm{S}\) , and shuttle effect caused by soluble polysulfide in electrolyte \(^{1,2}\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 85, 851, 436]]<|/det|>
+Numerous characterization techniques have been deployed to clarify the underlying science of LSBs during operation, which have contributed significantly to a better understanding of the kinetics and thermodynamics of the dissolution/precipitation of polysulfides, whose critical role in LSBs has been known for nearly 50 years3. Since then, methods such as X- ray diffraction (XRD)4,5, electrochemical tests6- 8, and spectroscopic techniques9- 16 have been used to provide valuable information regarding identification of polysulfide species and reaction kinetics. However, it is experimentally challenging to isolate the individual polysulfides due to the propensity of disproportionation, and these analytical techniques rely on special equipment and cell designs that cannot be directly deployed for long cycling periods. Recently, optical fiber sensors have attracted attention in battery sensing due to their low cost, compactness, remote sensing capabilities, and simple integration into batteries without interfering with their internal chemistry17. Among the fiber sensor family, the most commercialized Fiber Bragg grating (FBG) sensors have been well integrated inside Na (Li)- ion batteries for monitoring heat and pressure18 or inside the solid- state batteries for tracking the stress dynamics19. Indeed, recently Ziyun et al. demonstrated that the cathode stress evolution of LSB can be in- situ monitored by FBG sensors for understanding the chemo- mechanics20. Nevertheless, testing polysulfides with FBGs is still limited, owing to the fact that the sensing signals are totally confined inside the fiber core and cannot sense the electrolyte surrounding the fiber surface.
+
+<|ref|>text<|/ref|><|det|>[[148, 446, 851, 686]]<|/det|>
+In order to investigate the external medium of fiber, TFBGs (same structure as FBG without physical structure modification21, but rotating the grating plane to a specific angle) have been proposed to excite hundreds of discrete cladding mode resonances that are sensitive to the external medium refractive index perturbation via evanescent fields22, hence serving as an optical 'comb'. This has led to the development of high- performance sensors used in various areas, including biomedicine23, magnetic detection24, and gas monitoring25. Recently, TFBGs have been integrated into commercial batteries to detect chemical dynamics/state of electrolytes related to chemical evolution26. Interestingly, some TFBG- assisted surface plasmon resonance (TFBG- SPR) sensors with higher sensing sensitivity have also been developed for Zn- ion batteries to offer an alternative way of probing ion transport kinetics27. Overall, TFBG sensors provide new opportunities to deal with the challenge of battery sensing as they combine direct optical sensing of the environment, as well as physio- mechanical sensing of the environment via the confined optical modes.
+
+<|ref|>text<|/ref|><|det|>[[148, 696, 851, 899]]<|/det|>
+Herein, TFBG sensors, enabling measurements with a wide array of parameters including refractive index, temperature, and strain, are proposed to operate track the chemical dynamics/states of the LSB via electrolyte sulfur concentration. We demonstrate that the capacity fading is strongly correlated with the dissolution/precipitation of polysulfides throughout the cycling and hence, with respect to cycling rates. By exploiting the kinetic and thermodynamic response of soluble sulfur in the electrolyte, the nonlinear transport flux clarifies the "invisible" disproportionation process together with their dynamic evolution. With this understanding, we show that altering the nucleation pathway of the crystalline Li2S and sulfur can be attributed to real improvements in cell cycling performance. Subsequently, it is noted that TFBGs have the ability to obtain key chemical- physical- thermal metrics in operando with notable time and spatial resolution that may extend beyond LSBs.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[148, 86, 208, 100]]<|/det|>
+## Results
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 113, 400, 129]]<|/det|>
+## Characteristics of TFBG sensing
+
+<|ref|>text<|/ref|><|det|>[[147, 140, 851, 250]]<|/det|>
+Prior to in operando battery inspection, it is appropriate to first briefly visit the suitability of TFBG sensing for such chemistries, as related to fundamental principles of their operation. TFBGs, immersed in an electrolyte (Fig. 1a), were made in the core of the commercial single- mode fiber by ultraviolet pulse laser to induce periodically permanent refractive modulation. They obey a phase matching condition by enhancing the coupling between fundamental core mode and backward- propagation cladding modes22 (Fig. 1b):
+
+<|ref|>equation<|/ref|><|det|>[[357, 255, 828, 274]]<|/det|>
+\[\lambda = \left(n_{11}(\lambda) + n_{lm}(\lambda)\right)\lambda /\cos \theta \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[147, 280, 851, 520]]<|/det|>
+where \(\lambda\) is the cladding mode resonance wavelength, \(n_{11}(\lambda)\) is the effective index of core mode, and \(n_{lm}(\lambda)\) is the effective index of cladding mode with azimuthal order \(l\) and radial order \(m\) . \(\Lambda\) is the period of grating along the fiber axis, and \(\theta\) is the grating tilt angle. The experimental spectra are presented in Fig. 1c, where the core mode resonance (i.e., Bragg resonance) is located at the longest wavelength around \(1590 \mathrm{nm}\) (sensitive to temperature and strain \((T, \epsilon)\) )22. The cladding mode resonances guided by the fiber cladding (beside \(T, \epsilon\) , also sensitive to refractive index \((R)\) of the surrounding media) are shown on the left of Bragg resonances. The leaky modes are located at the region where there is a discontinuity in the cladding mode envelope and their amplitude, indicating the loss of total internal reflection at the point where the cladding mode effective index becomes equal to or smaller than the surrounding \(R\) . Therefore, with respect to soluble polysulfides which perturb electrolyte density, and hence the refractive- index, we focus on the high order guided cladding modes near the leaky mode region.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[163, 85, 838, 508]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 520, 851, 668]]<|/det|>
+Fig. 1 | Concept of optical fiber sensing for LSB. (a) Schematic of a fiber optic sensor immersed in electrolyte for in-situ detection of sulfur concentration originating from the generated dissolved polysulfide and their transport activities (i.e., shuttle effect). (b) Backward-propagation guided modes inside fiber for sensing (Supplementary information Fig. S1). (c) Experimental spectra response to polysulfide. (d) The wavelength shifts of cladding mode resonance at \(\sim 1560 \mathrm{nm}\) to \(100 \mathrm{mM}\) polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 1, 2, 3, \dots , 8\) ), shaded in green; (e) to concentration variation of \(\mathrm{Li}_2\mathrm{S}_4\) and \(\mathrm{Li}_2\mathrm{S}_8\) from \(0 \mathrm{mM}\) to \(100 \mathrm{mM}\) ; (f) to same sulfur concentration of polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 4, 5, 6, 7, 8\) ).
+
+<|ref|>text<|/ref|><|det|>[[147, 686, 851, 907]]<|/det|>
+To investigate the response of our TFBG to polysulfides, depicted in Fig. 1c, the TFBG was thoroughly immersed in a series of \(100 \mathrm{mM}\) polysulfide containing electrolytes in a modified Swagelok cell. Bearing this in mind, the Bragg resonance remains stable because any strain and temperature variation were eliminated during the measurements, indicating that the cladding mode wavelength shift is only related to refractive index variation. When the chain length of polysulfides is increased while keeping the polysulfide concentration the same, the guided modes on the left side of cladding mode at \(1560 \mathrm{nm}\) becomes leaky due to the increased refractive index. This is a result of the number sulfur atoms in solution becoming larger and perturbing the corresponding mode effective refractive index, while guided modes on its right side are linearly shifted to longer wavelength (Fig. 1d,e and Supplementary Fig. S2a,b). Noteworthy is the fact that the refractive index tested by TFBG sensor is an "average effect" of all the pertinent refractive indices of lithium polysulfide solutions. Following this,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[148, 85, 851, 195]]<|/det|>
+dilution of the \(100~\mathrm{mM}\) polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 4\) , 5, 6, 7, 8) to an equivalent concentration of sulfur (Supplementary Fig. S2c) yields an equivalent optical effect, stemming from the refractive index of polysulfide solutions converging to the same density, (Fig. 1f and Supplementary Fig. S2d,e). Therefore, rather than recognizing the specific species inside the electrolyte, the TFBG sensor will distinctly reveal the electrolyte sulfur concentration evolution of LSB cell (so long as temperature is kept constant).
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 207, 614, 222]]<|/det|>
+## Operando measurement of chemical dynamic state of LSB
+
+<|ref|>text<|/ref|><|det|>[[147, 233, 852, 492]]<|/det|>
+Given the promising proof- of- concept of sulfur concentration measurement in electrolyte, we explored the capability of operando chemical dynamics/states testing of LSB cell by putting a \(2\mathrm{mm}\) thick, \(12.8\mathrm{mm}\) diameter polyether ether ketone (PEEK) ring ( \(1\mathrm{cm}\) long TFBG can go through) in the middle of the Swagelok to separate the cathode (sulfur and Super P carbon composite (60/40 wt. \(\%\) )) and lithium anode so that fiber sensor would not touch any of them (Supplementary Fig. S3). Filling the PEEK ring with electrolyte (500 μL, \(1\mathrm{M}\) LiTFSI, 0.5 M LiNO3 in DOL/DME (1:1, v/v)) where the sensor is immersed, the effect of ion concentration gradient of electrolyte including \(\mathrm{Li}^+\) , TFSI- and \(\mathrm{NO}_3^-\) in DOL and DME can be safely neglected. It should be noted that prior to LSB investigations, a control experiment was executed with lithium iron phosphate (LFP) as the cathode. Here it was found that the corresponding \(R / o\) of electrolyte variation is 20 times smaller than that in LSB in which dissolved polysulfide is formed (Supplementary Fig. S4). Therefore, the use of a TFBG can provide for the possibility of measuring sulfur concentration in the electrolyte during cell operation, and to a large extent, the measurement will be irrespective of the cell's state of charge or state of health.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[170, 95, 844, 650]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 668, 852, 890]]<|/det|>
+Fig. 2 | Decoding electrolyte sulfur concentration dynamic of LSB. (a) Operando measurement of LSB by TFBG and XRD at C/20 (left panel: polysulfide dissolution allowed (electrolyte of 1 M LiTFSI, 0.5 M LiNO₃ in DOL/DME (1:1, v/v)); right panel: polysulfide dissolution prohibited (electrolyte of LP30: 1 M LiPF₆ in EC/DMC) of sulfur and Super P carbon composite (60/40 wt.%) cathode. (b) Morphology (SEM) and content of elemental sulfur and Super P carbon (energy-dispersive X-ray spectroscopy, EDX) of the cathode at the end of charging. (c) The quantitative analysis of sulfur before cycling, end of first plateau of discharge and end of charge. (d) The recrystallized sulfur governed by comporptionation reactions and potential voltage. The shaded region in blue stands for 15 hours of rest (OCV mode) starting at the end of charging demonstrating that the re-crystallized sulfur (marked by green asterisk “\*”) dissolves into the electrolyte in the form of soluble polysulfide through comporptionation reactions.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 78, 852, 900]]<|/det|>
+Based on the aforementioned concept, we measured the electrolyte sulfur concentration variation with a TFBG sensor while simultaneously deploying in operando XRD during C/20 cycling to track phase transitions of the composite electrode (Fig. 2a,c). At the upper voltage plateau around 2.4 V, the highest sulfur concentration in the electrolyte was monitored (left panel of Fig. 2a) and found to be accompanied by a decrease in the sulfur peak intensity (XRD pattern) resulting from a series of phase transformations, i.e., from solid sulfur to soluble intermediate polysulfides. On the other hand, when the carbonate- based electrolyte was used as a reference (i.e., LP30, right panel of Fig. 2a), no concentration gradient was observed in the electrolyte and remained nearly stable due to the fact that no soluble polysulfide intermediates were formed. Instead this resulted in the formation of insoluble and undetected products, since it is known that there is a nucleophilic reaction between sulfur radical and ethylene carbonate of LP30 to form thiocarbonate- like solid electrolyte interphase28,29 (Supplementary Fig. S5). Turning to the lower voltage plateau around 2.1 V (Fig. 2a), the concentration of dissolved sulfur decreases as a result of the reduction of long- chain polysulfide into shorter chains, leading to insoluble Li2S compound in the cathode (Supplementary Fig. S6a) confirmed by XRD30,31. Upon charging, the sulfur concentration indicates reversible recovery consistent with the decay of Li2S peaks until complete disappearance at the voltage \(\sim 2.4 \text{V}\), where crystallization of sulfur starts and thus sulfur concentration in electrolyte drops again, even though the deposited solid sulfur in the cathode is featureless by XRD31. To confirm the sulfur at the end of charge, the cathode powder was recovered in the glovebox by washing and drying to remove any soluble polysulfide as well as remaining electrolyte salts (Fig.2b,c), confirming that \(1.4 \%\) sulfur was detected and its surface topography was unchanged (i.e., no formation of big crystalline particles)31. Furthermore, when setting the 15- hour open circuit voltage (OCV) after charging, the sulfur concentration increases and reaches a plateau within 9 hours (Fig.2c), whereas, on the other hand, no sulfur concentration changes were observed during rest periods applied at the end of discharge (Supplementary Fig. S6b). It is most likely explained by compropriotation reactions during the rest period when the recrystallized sulfur from the end of charging is transformed to soluble lower- order polysulfide via reacting with high- order polysulfide32. This is also supported by the beginning of 2 hours rest (first cycle before discharging) demonstrating relatively little variation of electrolyte since fresh electrolyte contains a minimum amount of high order polysulfide and the compropriotation reactions are thus not possible (Supplementary Fig. S6c). The crystalline sulfur at the end of charge is related to the cut- off potential that the sulfur recrystallization process disappears4 (disappearance of sulfur concentration valley at the end of charge in Fig.2d) if setting the potential below 2.4 V (indicated that less sulfur suppresses the related compropriotation reactions, also detailed in Supplementary Fig. S6c). Altogether, the dynamic of sulfur concentration of electrolyte decoded by TFBG sensor supports the simplified chemical reaction process: during discharging the sulfur receives electrons and transfers them first to soluble Li2S at the high voltage plateau. This is followed by formation of insoluble Li2S at the low voltage plateau and vice versa for the charging process, indicating that the consumption rate of sulfur under the galvanostatic condition can be expressed as a ratio. According to the "linear" sulfur concentration variation rate by monitoring the slope (mM/h) on each plateau tested by sensor during the discharge and charging steps (Supplementary Fig. S4a) it was
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 85, 851, 156]]<|/det|>
+observed that the ratio on the upper and lower plateaus at the discharge step is 3.9. This is similar to the value obtained during charging (0.9), suggesting that the rate of sulfur transformation to/from soluble polysulfide is \(\sim 4.3\) times faster than that to/from insoluble Li₂S and the respective polysulfides.
+
+<|ref|>image<|/ref|><|det|>[[157, 173, 842, 682]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 696, 851, 900]]<|/det|>
+Fig. 3 | Decoding the disproportionation process and evolution. (a, b, c and d) The temporal voltage (black curve) and decoded electrolyte sulfur concentration (red curve) by GITT test (the capacity and optical spectra are given in supplementary Fig. S7). (a, b and c) Detailed view of electrolyte response to current pulse (kinetic process) and rest (thermodynamic process). (e) Transport flux of soluble sulfur based on current pulse (kinetics process, green triangle, \(D_t = V_{BD} / (S \times t)\) and rest (thermodynamic process, blue square, \(D_t = V_{DE} / (S \times t)\) , where \(S\) is across section area of electrolyte that sensor is immersed in, \(t\) is corresponding time. It indicates the slope of soluble sulfur consumption (negative) or formation (positive) in electrolyte, which is also plotted by arrows in bottom (arrow up: sulfur increasing, arrow down: sulfur decreasing). The normalized ratio (red sphere) represents the sulfur consumption of rest (thermodynamic process) by \(Ratio = |D_t| / (|D_t| + |D_k|)\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 85, 852, 601]]<|/det|>
+The disproportionation and association reactions of likely intermediates are mesmerizing, but despite an awareness of their existence, their mysterious dynamics make LSBs seemingly incomprehensible. Nevertheless, the real- time quantification of soluble sulfur afforded by TFBGs provides a convincing way to straighten their story when combined with GITT (Fig. 3). As depicted in Fig. 3d, the overall profile of sulfur concentration variation matches well with dissolution/precipitation of polysulfides and sulfur already confirmed in Fig.2, and we focus on the temporal response of electrolyte to the current pulse and respective rest period. According to Fig. 3a,b,c the "tiny" variation of sulfur concentration from A to B (moving from the rest to cycling mode) is the electrolyte instantaneous response to the leading edge of current pulse with strong electrical field gradient, originating from polysulfide redistribution driven by the sudden electrical field33. This effect trends in the opposite direction as polysulfide diffusion in the region from B to C, which relates to the current pulse (referred to herein as the kinetic process). The reader may note a discrepancy between voltage and concentration from C to D during rest, which is attributed to the "delay" between the electrochemical reaction at the electrode surface and the position of the sensor in the cell. Hence a small lag exists even if removing the current pulse. Regarding the OCV relaxation (3 hours rest period) and movement towards equilibrium (herein coined as the thermodynamic process) in the region from C to E, the sulfur concentration fluctuation is most likely explained by polysulfide disproportionation process (i.e. \(Li_2S_8 \leftrightarrow Li_2S_7 + 1/4S_8\) )34 since the two best- remaining hypotheses, dissociation (i.e. \(Li_2S_8 \leftrightarrow Li^+ + LiS_7\) or \(Li_2S_8 \leftrightarrow 2LiS_7\) )34 and non- uniform polysulfide distribution can be excluded: the dissociation of polysulfide including anions and radicals are rare while the neutral lithium polysulfide is dominant in electrolyte34; the polysulfide distribution reaches equilibrium within 1 min (time interval of spectra recording) that is nearly synchronous to electrochemistry (Fig. 2a), not matching the rest period situation with 3 hours of continuous soluble sulfur consumption or generation. After careful deliberation, we move forward with the idea that electrochemical and disproportionation processes can be extracted respectively by temporal response of electrolyte based on sulfur concentration decoded by TFBG sensor.
+
+<|ref|>text<|/ref|><|det|>[[148, 611, 852, 907]]<|/det|>
+Encouraged by the results mentioned above, we have next attempted to build a quantitative relation between kinetic and thermodynamic processes through a primitive estimation of transport flux of sulfur in the electrolyte (Fig. 3e). In STAGE I, on the higher voltage plateau, solid sulfur was continuously consumed upon discharge to form long chain polysulfide, \(\mathrm{Li}_2\mathrm{S}_8\) (green triangle), together with the rapid disproportionation process \(Li_2S_8 \leftrightarrow Li_2S_6 + 1/4S_8\) 35- 37 leading to soluble sulfur consumption during relaxation (blue square). At the same time the normalized ratio (red sphere) between the rest and current pulse process nearly remains the same and fixed at 0.1 (shaded in light green color), meaning that there is a competition reaction between the soluble long chain polysulfide species formation and the \(\mathrm{S}_8\) - precipitation in the beginning of the discharge step. In STAGE II, regarding the first- to- second plateau transition whereby a voltage slope forms between 2.3 and 2.1 V, the shorter chain polysulfide \(\mathrm{Li}_2\mathrm{S}_4\) is expected to be generated38,39. This is accompanied by a reduction in the rate of formation of soluble sulfur in the electrolyte and hence, the sulfur concentration during resting keeps increasing while the generation of fresh long chain polysulfides winds down and the kinetic/thermodynamic ratio can reach 0.89. This indicates that polysulfide species formation via disproportionation is dominant due to fact that dissolved sulfur
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 84, 852, 399]]<|/det|>
+continues to react with polysulfide present in the electrolyte during rest38,41. Undoubtedly an enriched concentration of sulfur in the electrolyte contributes significantly towards driving the formation of more polysulfides. In STAGE III where the lower voltage plateau marks the conversion between \(\mathrm{Li}_2\mathrm{S}_4\) to shorter chain \(\mathrm{Li}_2\mathrm{S}_2\) and \(\mathrm{Li}_2\mathrm{S}\) forms, the potential disproportionation process \(Li_2S_2 \leftrightarrow 1 / 3Li_2S_4 + 2 / 3Li_2S^{40,41}\) is highlighted from the middle of the second plateau, and raises the sulfur concentration to about a normalized ratio of 0.2 which follows until the end of the half- cycle. Upon charging (STAGE IV and STAGE V), it is evident that the process is not a fully reversible one, as seen with STAGE IV where \(\mathrm{Li}_2\mathrm{S}_4\) and \(\mathrm{Li}_2\mathrm{S}_6\) reappear and the push towards thermodynamic equilibrium necessitates disproportionation processes leading to consumption of sulfur during rest periods, but an overall concentration increase. In STAGE V, the sulfur concentration in electrolyte drops very sharply, caused by the recrystallization of sulfur during current pulsing, even though that is not visible in the operando XRD studies shown in Fig. 2a. Interestingly, the rise of soluble sulfur during these late- stage rest periods suggests nucleation and/or growth limitations of the recrystallized sulfur, which will be addressed here later. Altogether, the quantitative disproportionation process decoupled by the fiber sensor based on GITT provides meaningful details to understand micro- mechanisms of complicated kinetics processes.
+
+<|ref|>image<|/ref|><|det|>[[192, 412, 808, 813]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 826, 850, 899]]<|/det|>
+Fig. 4 | Operando monitoring over cycling and cycling rate. (a) Spectra contour of TFBG cladding mode resonances response (details are given in supplementary video). (b) Temporal voltage (grey line), decoded sulfur concentration (red line), and temperature of electrolyte (blue line) over the cycling. (c) Capacity variation of (b) upon time. (d) Soluble sulfur
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[148, 84, 851, 195]]<|/det|>
+concentration dynamic related to cycling rate. (e) Soluble sulfur concentration dynamic related to cycling rate of first/second plateau. The concentration drop through the recrystallization of sulfur at the end of charge is marked by green asterisk \(^{**}\) . With Mode I, the cycling rate was set by upper plateau (C/20) and lower plateau (C/5); Mode II by upper plateau (C/5) and lower plateau (C/20) and Mode III by upper plateau (C/10) and lower plateau (C/10).
+
+<|ref|>text<|/ref|><|det|>[[148, 206, 852, 537]]<|/det|>
+Inspired by aforementioned exploration of internal mechanisms of LSBs, we decide to further investigate the operando monitoring over cycling and cycling rates (Fig. 4a,b). Bearing in mind that the temperature (blue curve in Fig. 4b), decoded by Bragg resonance located at \(1589 \text{nm}^{26}\) , initially rises to \(25 \text{C}^\circ\) and keeps a constant afterward due to the shipping from glovebox to oven to reach thermal equilibrium. The periodic sulfur concentration evolution (red curve in Fig. 4b), decoded by the wavelength shift of cladding mode located at \(\sim 1559.5 \text{nm}\) in Fig. 4a, indicates the reversible dissolution/precipitation of polysulfides and sulfur. Noteworthy here is the feasibility of observing the amplitude of soluble sulfur variation (supplementary Fig. S8) that matches the cycling behavior associated with capacity fading owning to less and less \(\text{Li}_2\text{S}\) and solid sulfur crystallization over cycles (Fig.4c), which could be reasonably attributed to the high electrolyte to sulfur ratio (E/S ratio, \(>100 \mu \text{L} /\text{mg}\) ), thereby inducing stronger polysulfide shuttle effect with less sulfur utilization. Regarding a sulfur concentration response to the cycling rate depicted in Fig. 4d, a lower cycling rate (C/15) leads to the largest sulfur concentration change, strongly supporting the idea that the most soluble sulfur in electrolyte is transformed to solid species ( \(\text{Li}_2\text{S}\) ) when given adequate time for completion of the redox process. Accelerating the cycling to C/10, C/5 and C/3, partially soluble sulfur transformation is seen (i.e., background of sulfur concentration rises) together with less sulfur crystallization (i.e., the "dip" of soluble concentration at the end of charge).
+
+<|ref|>text<|/ref|><|det|>[[148, 548, 852, 825]]<|/det|>
+Following the evidence thus far, it is then reasonable to conclude that regular galvanostatic operating conditions might not be perfect for LSBs, considering the various competing mechanisms explored above which are evident at different stages of charge and discharge. With this in mind, different modes of cycling protocols were also pursued to be able to tune the cycling performance. For instance, when setting a relatively low (high) cycling rate for the upper (lower) plateau depicted in Fig. 4e (Mode I), only half of the soluble sulfur inside electrolyte was transformed to \(\text{Li}_2\text{S}\) due to high cycling rate of lower plateau. On the upper voltage plateau the solid sulfur dissolution or recrystallization was \(100\%\) successful and which can be readily attributed to the low cycling rate in this voltage range. Further confirmation of the delicate cycling nature of LSBs was seen in Mode II as \(80\%\) of the soluble sulfur inside electrolyte was transformed to \(\text{Li}_2\text{S}\) due to long cycling in the lower plateau (C/20) but with less solid sulfur recrystallization at the end of charge (C/5). Overall, the quantitative relation of soluble sulfur evolution and cycling/cycling rate implies that the efficiency of solid sulfur and \(\text{Li}_2\text{S}\) formation governs the cycling performance and significant new progress might be made through cycling condition optimization alone.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 836, 579, 852]]<|/det|>
+## High performance based on novel functional cathode
+
+<|ref|>text<|/ref|><|det|>[[149, 864, 850, 899]]<|/det|>
+Extensive work has been conducted over the years to improve the LSB performance through variety of means: the use of high- conductivity cathodes, strong polysulfide binding to
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 84, 851, 287]]<|/det|>
+suppress the shuttling phenomenon, surface chemistry to control \(\mathrm{Li_2S}\) nucleation or dissolution, design of cathode architectures that are elastic to withstand volume expansion, and optimized electrolytes enabling high sulfur utilization42. Considering the strategy of trapping lithium polysulfides, it includes physical (spatial) entrapment by confining polysulfide in the pores of non- polar carbon materials43 or designing a sulfur host material that exhibits stronger chemical interaction such as dipolar configurations based on polar surfaces44, metal- sulfur bonding45 and surface chemistry for polysulfide grafting and catenation46, leading to long cycling without strong capacity fading. Nevertheless, the fundamental problem regardless of approach is all related to the polysulfides dissolving inside the electrolyte, thus a smart sensor that can reliably track the soluble sulfur in real time should be of particular value.
+
+<|ref|>text<|/ref|><|det|>[[147, 298, 851, 759]]<|/det|>
+In this respect, in addition to the less porous Super P carbon discussed above, the Ketjen black (KB) carbon whose BET surface area \(>1200 \text{m}^2 /\text{g}\) is utilized as physical nonpolar sulfur confinement host (KB/S, 40/60 wt.%), and the electrolyte was simultaneously monitored by a TFBG sensor together with XRD to characterize the composite cathode phase transitions (left panel of Fig. 5a). After the melt- diffusion treatment process, part of sulfur penetrates into the nanostructure of KB (Supplementary Fig. S9); however, during cycling the nonpolar physical adsorption or confinement of polysulfide is very limited and massive soluble polysulfide is dissolved and detected. Surprisingly, the capability of \(\mathrm{Li_2S}\) crystallization is enhanced since more than 91 % soluble sulfur disappears and converts to solid short chain polysulfide at second plateau as indicated by the fiber sensor. Meanwhile, unlike linearly sulfur concentration change with super P carbon (BET surface area: \(62 \text{m}^2 /\text{g}\) ) substrate cell in Fig. 2a, KB containing cell becomes "nonlinear" with a higher rate, indicating that the nucleation rate of \(\mathrm{Li_2S}\) is increasing. It could be reasonably assigned by instantaneous nucleation that depletion of the nucleation site of KB occurs at a very early stage, following the nonlinear kinetics of the nucleation pathway: \(\mathcal{N} = \mathcal{N}_c[1 - \exp (- At)]\) where \(\mathcal{N}\) is the density of nuclei, \(\mathcal{N}_c\) is the density of available nucleation site, and \(A\) is the nucleation rate47. In contrast, considering less porous Super P carbon containing cell in Fig.2a with a lower nucleation rate, the initial density of nuclei increases linearly with time: \(\mathcal{N} = \mathcal{N}_c At\) (i.e. progressive nucleation)48,49. Moreover, the porous structure of KB also accelerates the dissolution and re- crystallization of sulfur, which results in a strong sulfur concentration saturation at the transient stage relating to semisolid \(\mathrm{Li_2S_4}\) generation (keeping a balance between electrochemical and disproportionation process) and enhanced soluble sulfur reduction to solid sulfur at the end of charging (Supplementary Fig. S10). The sulfur concentration dynamic responding to potential and cycling rate is consistent with the Super P substrate, detailed in Supplementary Fig. S11.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[186, 90, 816, 595]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 612, 850, 759]]<|/det|>
+Fig. 5 | Chemistry of LSB with outstanding polysulfide-trapping capability cathodes. (a) Operando measurement of LSB by TFBG and XRD at C/20 (left panel: nonpolar physical adsorption of polysulfide by KB carbon; right panel: polar adsorption of polysulfide by MOF-801(Zr)). (b) In-situ detection of polysulfide adsorption by MOF-801(Zr). (c) XRD spectra for MOF-801(Zr) before and after adsorption of \(\mathrm{Li}_2\mathrm{S}_6\) . (d) The temporal voltage (grey line), decoded sulfur concentration (red line) of cathode composite based on MOF-801(Zr), and decoded sulfur concentration (blue line) considering the cathode with KB substrate (same amount of active material) is used as a reference without showing the temporal voltage.
+
+<|ref|>text<|/ref|><|det|>[[148, 770, 850, 898]]<|/det|>
+To further extend the use of porous materials as host matrix for sulfur confinement, Metal- Organic Frameworks (MOFs) can be considered as efficient candidates for the selective adsorption of polysulfide species45,50. We have considered MOF- 801(Zr), a microporous zirconium fumarate with pores of about 5- 12 Å and a high specific surface area (1020 (±20) m2/g), to be considered as an efficient candidate for the adsorption of polysulfide species. Its 3D cubic structure is built- up from \(\mathrm{Zr_6O_4(OH)_4}\) oxo- clusters linked to fumarate ligands and exhibits abundant missing linkers defect sites and reactive terminal –OH groups. Due to the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 85, 857, 380]]<|/det|>
+Lewis acidic character of the Zr nodes and the reactivity of these terminal groups, the polysulfide species (soft Lewis bases) are expected to interact strongly with the framework51,52. Depicted in Fig. 5c, the \(0.5 \mathrm{ml} 100 \mathrm{mM}\) polysulfide \(\mathrm{Li}_2\mathrm{S}_x\) ( \(x = 4, 6, 8\) ) was monitored in real time by fiber sensor during adsorption, which is evidently finished within 1 hour ensuring efficient adsorption inside the cell. After fully adsorbing \(100 \mathrm{mM} \mathrm{Li}_2\mathrm{S}_6\) (Fig. 5d), the XRD pattern shows the appearance of new peaks in addition to the ones of MOF- 801(Zr), matching with the peaks of pure solid sulfur (Supplementary Fig. S12) consistent with the "yellow" color of the powder. This explains why the operando test starts with the peaks of sulfur (XRD pattern on the right panel of Fig. 5a). The subsequent electrochemical reaction is the same as the cathode substrate with KB including concentration saturation in the transition region between the first and the second plateau, nonlinear sulfur consumption rate with instantaneous nucleation pathway and enhanced sulfur crystallization at the end of charge. However, a key point and difference is that the sulfur concentration inside the electrolyte dramatically decreases by \(80.8\%\) with the same amount of active material due to the enhanced adsorption and localization of polysulfides through Lewis acid- base chemical interaction by MOF- 801(Zr) (Fig.5d and Support information, Fig. S13).
+
+<|ref|>image<|/ref|><|det|>[[225, 390, 773, 747]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 761, 851, 907]]<|/det|>
+Fig. 6 | The correlation between electrochemical performance and \(\mathrm{Li}_2\mathrm{S}\) nucleation, sulfur crystallization. (a) Content of \(\mathrm{Li}_2\mathrm{S}\) nucleation (h1) and solid sulfur crystallization (h2). (b) Cycling performance of cathode composite at C/15 over 30 cycles. (c and d) The corresponding ratio of \(\mathrm{Li}_2\mathrm{S}\) nucleation (c) and solid sulfur crystallization (d). (e) Cycling rate performance of cathode composite. (f and g) The corresponding ratio of \(\mathrm{Li}_2\mathrm{S}\) nucleation (f) and solid sulfur crystallization (g). Note that all the cycling cell pursed in the presence of TFBG fiber and the \(\mathrm{Li}_2\mathrm{S}\) (h1) and solid sulfur (h2) is normalized by comparing the consumption sulfur in current cycle to that of sulfur fully dissolved in first cycle.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 85, 852, 435]]<|/det|>
+To evaluate the performance of cathode considering the three S cathode composites (with Super P, KB, MOF- 801(Zr)), we decided to compare their long cycling performance together with capabilities of \(\mathsf{Li}_2\mathsf{S}\) nucleation (h1) and sulfur crystallization (h2) (Fig. 6a). Depicted in Fig. 6b, the KB and MOF- 801(Zr) cell both experienced better capacity retention over 30 cycles at C/15 with a fade rate as \(0.99\%\) , \(0.88\%\) per cycles, respectively, while the super P cell is fading with \(4.7\%\) per cycles, which is consistent with the capability of crystallization of \(\mathsf{Li}_2\mathsf{S}\) and sulfur shown in Fig. 6c,d. Surprisingly, the KB and MOF- 801(Zr) cells have the similar efficiency of solid species crystallization (also supported by Fig. 6f) by taking the merit of high surface area, whereas the MOF- 801(Zr) exhibits the best capacity retention due to its strong chemical interaction for polysulfide which also well explains the capability to trap and recrystallize sulfur(Fig. 6g). Meanwhile, less sulfur utilization will be induced as well by intrinsic adsorption together with its low conductivity nature, leading to the lower capacity of MOF- 801(Zr) than that of KB cell over cycling. On the other hand, the Super P cell is fading fast because of high electrolyte volume with the E/S ratio over \(100\mu \mathrm{L} / \mathrm{mg}\) , presumably due to shuttle phenomenon enhancement. However, this problem does not affect the performance of KB and MOF- 801(Zr) cells, revealing that perhaps the most important parameter for cycling performance is related to the capability of crystallization of \(\mathsf{Li}_2\mathsf{S}\) and sulfur, which relies on a comprehensive balance with all involved factors such as high surface area, sulfur anion bonding and conductivity, in addition to cycling conditions.
+
+<|ref|>sub_title<|/ref|><|det|>[[150, 447, 375, 462]]<|/det|>
+## Discussions and conclusions
+
+<|ref|>text<|/ref|><|det|>[[148, 474, 852, 713]]<|/det|>
+Herein, TFBG sensors with low cost, easy integration into batteries, and long cycling capabilities during cell operation were demonstrated for operando testing of electrolyte sulfur concentration evolution of the LSB, which reveals the correlated relationship between the capacity fading and dynamic of dissolution/precipitation of polysulfides over cycling and at different cycling rates. Meanwhile, the chemical kinetics and thermodynamic response of soluble polysulfide in electrolyte were decoded with GITT experiments, with the disproportionation dynamic process linked to the transport flux of soluble species. Moreover, the cycling performance is well improved by designing the composite cathodes via porous carbon as nonpolar physical sulfur confinement and MOF- 801(Zr) as polar adsorption of polysulfide, through a host- guest chemical interaction. These substrates indicate that the nucleation kinetics and growth of \(\mathsf{Li}_2\mathsf{S}\) are changing from progressive to an instantaneous pathway due to enhanced soluble sulfur consumption rate, ultimately leading to the improvement of crystallization capability of \(\mathsf{Li}_2\mathsf{S}\) and sulfur.
+
+<|ref|>text<|/ref|><|det|>[[148, 724, 852, 907]]<|/det|>
+Despite the encouraging insights supported by TFBG technology, a limitation of our operando testing stems from the refractive index link, which as mentioned, is an "average" effect of all species inside electrolyte. Thus, somewhat complicated data inference is required with critical external inputs, as comparing to direct evidence and measurement of species by infrared fiber operando measurement53 and Raman spectroscopy based on hollow- core optical fiber54. This could might be solved in future by machine learning algorithms to simplify analysis and hence lead to more efficient 'combing' of data. Second, the optical interrogator used here is both expensive and bulky (volume), so future efforts may warrant an optimized integrator system capable of capturing a sensing signal by energy (amplitude) instead of wavelength55, but intensity- based measurements may present other technical challenges.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[148, 85, 851, 195]]<|/det|>
+Finally, the cycling based on Swagelok is achieved with high E/S ratio which enhances the shuttle effect of polysulfide, leading to acceleration of capacity fading. Therefore, long- term cycling configurations such as coin or 18650 cells integrated with fiber sensors might reveal other prominent performance- governing mechanisms. Nevertheless, TFBG sensors still provide fruitful details of the chemical dynamics of polysulfide as a diagnostic technique to monitor the state of health of cells in real- time.
+
+<|ref|>text<|/ref|><|det|>[[148, 206, 851, 445]]<|/det|>
+Considering the specific properties of TFBG, including multi- resonance- peaks, high refractive index sensitivity, and ultrafast response, new opportunities of battery sensing can be envisioned, such that more than two gratings can be integrated inside the cell to map the sulfur gradient with more precision and accuracy, ultrathin solid electrolyte interphase (SEI) films could be characterized by sensitivity enhanced surface plasmon resonance based TFBG via surface and bulk refractive index discrimination56, the dynamic of electrons and phonon coupling inside cathode could be probed by ultrafast measurement through the pump- probe configuration of TFBG57. Overall, the non- disruptive diagnostic techniques based on the TFBG sensor allow us to monitor chemical- physical- thermal metrics in operando with notable time and spatial resolution. Therefore, with the use of these combs it becomes possible to detangle hidden high- value information such as states of charge, health estimations, and operational guidance along with non- electrochemical early- failure indicators, leading to increased straighter pathways to improving battery reliability, service life, and safety.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 456, 222, 471]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[150, 483, 438, 499]]<|/det|>
+## Materials and electrode preparation
+
+<|ref|>sub_title<|/ref|><|det|>[[150, 507, 357, 523]]<|/det|>
+## Synthesis of MOF-801(Zr)
+
+<|ref|>text<|/ref|><|det|>[[149, 534, 850, 606]]<|/det|>
+10.86 mmol of \(\mathrm{ZrOCl_2\cdot 8H_2O}\) , 7.624 mmol of fumaric acid, 9 mL of formic acid and 40 mL of deionized water were mixed in the reactor58, following 5 h stirring when the solution becomes cloudy. The ultimate product was collected by centrifugation, abundantly washed with water and ethanol, and dried under vacuum.
+
+<|ref|>text<|/ref|><|det|>[[148, 617, 850, 708]]<|/det|>
+Preparation of polysulfides solutions: the \(100~\mathrm{mM}\) lithium polysulfides solution \(\mathrm{Li_2S_x}\) ( \(x = 2\) , 3, \(\dots\) , 8) were prepared by mixing lithium sulfide (99.9 % \(\mathrm{Li_2S}\) , Sigma Aldrich) and sulfur (S, Sigma Aldrich) in stoichiometric ratio to organic electrolyte (1 M LiTFSI, 0.5 M LiNO3 in DOL/DME (1:1, v/v)), and the solution was continuously stirred with additional heating process at \(55~\mathrm{C}^\circ\) for 4 days in argon filled glovebox.
+
+<|ref|>text<|/ref|><|det|>[[148, 720, 851, 903]]<|/det|>
+Preparation of sulfur composite electrodes: sulfur and Super P conductive carbon (Ketjenblack carbon) with a ratio 60/40 wt% were mixed by hand- grinding, followed by a heat- treatment (160 \(^\circ \mathrm{C}\) during 8 hours under air). The 5 wt Poly(tetrafluoroethylene) dispersion (PTFE, Alfa Aesar) is mixed with the cathode composite, rolled to a film and punched into disks with sulfur loading around \(5.3\mathrm{mg / cm}^2\) , and dried under vacuum at \(80^\circ \mathrm{C}\) overnight. To make the cathode composite with MOF- 801(Zr), the thoroughly adsorption of \(100\mathrm{mM}\mathrm{Li}_2\mathrm{S}_6\) in DOL/DME (1:1, v/v) was achieved by MOF- 801(Zr) with a stoichiometric ratio of \(1\mathrm{mL} / 40\) mg, followed by washing the powder twice by DOL and tried in vacuum overnight. The sulfur contained MOF- 801(Zr) (40% sulfur) was mixed with Super P conductive carbon with 50/50 wt% by hand- grinding without heat- treatment.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[150, 86, 446, 101]]<|/det|>
+## TFBG fabrication and sensing system.
+
+<|ref|>text<|/ref|><|det|>[[148, 108, 851, 274]]<|/det|>
+Each \(10mm\) - long TFBG with \(7^{\circ}\) internal tilt angle was inscribed in hydrogen- loaded CORNING SMF- 28 fiber by laser irradiation based on phase- mask method22. Hydrogen loading of the fibers, enhancing their photosensitivity to ultraviolet light, was performed at room temperature and a pressure of 15.2 MPa for 14 days. The input light from KrF pulsed excimer laser (model PM- 848 from Light Machinery, Inc., emitting at 248 nm and 100 pulse/second) was cylindrically focused along the fiber axis with energy of \(\sim 40m\) over the grating region and also having passed through a 1078.4 nm period phase mask to produce a permanent periodic refractive index modulation in the core of the fiber. Rotating the fiber and phase mask, the tilt of grating fringes was obtained at an angle in the core as \(7^{\circ}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 282, 327, 298]]<|/det|>
+## Computational details
+
+<|ref|>text<|/ref|><|det|>[[148, 306, 851, 489]]<|/det|>
+The transmission spectra simulations were carried out based on three- layer cylindrical waveguide using analytical method57. First, the simulated spectra is calibrated by the experimental spectra in air; Second, the refractive index of electrolyte were obtained by increasing the simulation surrounding RI (third layer) manually to match the experimental spectra, which is 1.3858 at 1559 nm wavelength considering the dispersion (supplementary Fig. S2d,e), Finally, mode intensity profiles were simulated by a complex finite- difference vectoral simulation tool (FIMMWAVE, by Photon Design), consisting of a three- layer waveguide: \(8.2\mu m\) core diameter with refractive index 1.449311, \(125\mu m\) cladding diameter with refractive index 1.444078, \(80\mu m\) diameter medium of electrolyte (refractive index \(= 1.3858\) ).
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 496, 568, 512]]<|/det|>
+## Integration of TFBG sensors into modified Swagelok
+
+<|ref|>text<|/ref|><|det|>[[148, 520, 851, 629]]<|/det|>
+A ring made of PEEK (12.8 mm diameter, 2mm thick to fit 10 mm length fiber sensor) is fixed in the middle of 19 mm diameter Swagelok cell where fiber sensor can go through by drilling two holes. The Li metal foil (0.38 mm thickness, 14 mm diameter) is attached to one side of PEEK ring as anode, and on the other side of ring there is a steel grid to hold one Whatman separator beneath sulfur composite cathode. The cells were assembled in an argon- filled glovebox.
+
+<|ref|>sub_title<|/ref|><|det|>[[150, 637, 398, 652]]<|/det|>
+## Electrochemical measurements
+
+<|ref|>text<|/ref|><|det|>[[149, 660, 851, 732]]<|/det|>
+The electrochemical performances of Swagelok cell were evaluated by BCS- 810 or MPG2 potentiostat (Biologic, France) at \(25^{\circ}C\) degree inside temperature- controlled oven (Memmert, \(\pm 0.1^{\circ}C\) ). The galvanostatic discharge- charge cycling was carried out with the voltage range of \(1.7V - 2.8V\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 740, 555, 756]]<|/det|>
+## Operando measurement by TFBG sensors and XRD
+
+<|ref|>text<|/ref|><|det|>[[148, 764, 851, 891]]<|/det|>
+To achieve TFBG sensor operando measurement, the optical transmission spectra were recorded (1 min/spectra) by an optical integrator (CTP10, EXFO SOLUTIONS) with a resolution of \(1pm\) for wavelength ranging from 1500 nm to 1600 nm. Considering XRD operando measurement, it was performed on a D8 Advance diffractometer (Bruker) using a Cu Ka X- ray source \((\lambda_{\mathrm{cal}} = 1.54056\) A, \(\lambda_{\mathrm{cal}} = 1.54439\) A) and a LynxEye XE detector. The XRD pattern and electrochemical data are simultaneously recorded by a custom designed airtight cell with a beryllium window producing a full pattern every 20 min.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[149, 85, 682, 102]]<|/det|>
+## Preparation of cycled electrode samples for SEM and EDX imaging
+
+<|ref|>text<|/ref|><|det|>[[148, 109, 851, 217]]<|/det|>
+The samples, at the end of charging, were prepared by washing the cathode powder twice by DOL to remove any dissolved lithium polysulfide species and lithium salt, and dried in vacuum chamber overnight. Then the powder was coated with gold (plasma sputtering coater (GSL- 1100X- SPC- 12, MTI)) for SEM (FEI Magellan) equipped with an energy- dispersive X- ray spectroscopy detector (Oxford Instruments) performed under an acceleration voltage of 20 kV.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 230, 279, 246]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[149, 257, 829, 293]]<|/det|>
+All relevant data are included in the paper and Supplementary Information. Extra data are available on reasonable request from the corresponding author.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 304, 231, 320]]<|/det|>
+## Reference
+
+<|ref|>text<|/ref|><|det|>[[145, 330, 852, 887]]<|/det|>
+1. Bruce, P. G., Freunberger, S. A., Hardwick, L. J. & Tarascon, J.-M. Li-O2 and Li-S batteries with high energy storage. Nat. Mater. 11, 19-29 (2012).
+2. Li, T. et al. A comprehensive understanding of lithium-sulfur battery technology. Adv. Funct. Matter. 29, 1901730 (2019).
+3. Eichinger, G. & Besenhard, J. O. High energy density lithium cells: part II. cathodes and complete cells. J. Electroanal. Chem. 72, 1-31 (1976).
+4. Nelson, J. et al. In operando X-ray diffraction and transmission X-ray microscopy of lithium sulfur batteries. J. Am. Chem. Soc. 134, 6337-6343 (2012).
+5. Conder, J., Rouchet, R., Trabesinger, S., Marino, C., Gubler, L. & Villevieille, C. Direct observation of lithium polysulfides in lithium-sulfur batteries using operando X-ray diffraction. Nat. Energy 2, 17069 (2017).
+6. Lu, Y.-C., He, Q. & Gasteiger, H. A. Probing the lithium-sulfur redox reactions: a rotation-ring disk electrode study. J. Phys. Chem. C 118, 5733-5741 (2014).
+7. Schneider, H. et al. On the electrode potentials in lithium-sulfur batteries and their solvent-dependence. J. Electrochem. Soc. 161, A1399-A1406 (2014).
+8. Deng, Z., Zhang, Z., Lai, Y., Liu, J., Li, J. & Liu, Y. Electrochemical impedance spectroscopy study of a lithium/sulfur battery: modeling and analysis of capacity fading. J. Electrochem. Soc. 160, A553-A558 (2013).
+9. Zou, Q. & Lu, Y.-C. Solvent-dictated lithium sulfur redox reactions: an operando UV-vis spectroscopic study. J. Phys. Chem. Lett. 7, 1518-1525 (2016).
+10. He, Q. et al. Operando identification of liquid intermediates in lithium-sulfur batteries via transmission UV-vis spectroscopy. J. Electrochem. Soc. 167, 080508 (2020).
+11. Patel, M. U. M. & Dominko, R. Application of in operando UV/Vis spectroscopy in lithium-sulfur batteries. ChemSusChem. 7, 2167-2175 (2014).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[140, 85, 852, 920]]<|/det|>
+12. Patel, M. U. M., Demir-Cakan, R., Morcrette, M., Tarascon, J.-M., Gaberscek, M. & Dominko, R. Li-S battery analyzed by UV/Vis in operando mode. ChemSusChem. 6, 1177-1181 (2013).13. Kawase, A., Shirai, S., Yamoto, Y., Arakawa, R. & Takata, T. Electrochemical reactions of lithium-sulfur batteries: an analytical study using the organic conversion technique. Phys. Chem. Chem. Phys. 16, 9344-9350 (2014).14. Kavčič, M., Petric, M., Rajh, A., Isaković, K., Vizintin, A., Talian, S. D. & Dominko, R. Characterization of Li-S batteries using laboratory sulfur X-ray emission spectroscopy. ACS Appl. Energy Mater. 4, 2357-2364 (2021).15. Prehal, C. et al. On the nanoscale structural evolution of solid discharge products in lithium-sulfur batteries using operando scattering. Nat. Commun. 13, 6326 (2020).16. Saqib, N., Ohlhausen, G. M. & Porter, J. M. In operando infrared spectroscopy of lithium polysulfide using a novel spectro-electrochemical cell. J. Power Sources 364, 266-271 (2017).17. Huang, J., Boles, S. T. & Tarascon, J.-M. Sensing as the key to battery lifetime and sustainability. Nat. Sustain. 5, 194-204 (2022).18. Huang, J. et al. Operando decoding of chemical and thermal events in commercial Na(Li)-ion cells via optical sensors. Nat. Energy 5, 674-683 (2020).19. Blanquer, L. A., Marchini, F., Seitz, J. R., Daher, N., Bétermier, F., Huang, J., Gervillié, C. & Tarascon, J.-M. Optical sensors for operando stress monitoring in lithium-based batteries containing solid-state or liquid electrolytes. Nat. Commun. 13, 1153 (2022).20. Miao, Z. et al. Direct optical fiber monitor on stress evolution of the sulfur-based cathodes for lithium-sulfur batteries. Energy Environ. Sci. 15, 2029-2038 (2022).21. Ghannoum, A., Norris, R. C., Lyer, K., Zdravkova, L., Yu, A. & Nieva, P. Optical characterization of commercial lithiated graphite battery electrodes and in situ fiber optic evanescent wave spectroscopy. ACS Appl. Mater. Interfaces 8, 18763-18769 (2016).22. Albert, J., Shao, L. Y. & Caucheteur, C. Tilted fiber Bragg grating sensors. Laser Photonics Rev. 7, 83-108 (2013).23. Shevchenko, Y. et al. In situ biosensing with a surface plasmon resonance fiber grating aptasensor. Anal. Chem. 83, 7027-7034 (2011).24. Zhang, Z. et al. Plasmonic fiber-optic vector magnetometer. Appl. Phys. Lett. 108, 101105 (2016).25. Caucheteur, C., Guo, T., Liu, F., Guan, B.-O. & Albert, J. Ultrasensitive plasmonic sensing in air using optical fibre spectral combs. Nat. Commun. 7, 13371 (2016).26. Huang, J., Han, X., Liu, F., Gervillié, C., Blanquer, L. A., Guo, T. & Tarascon, J.-M. Monitoring battery electrolyte chemistry via in-operando tilted fiber Bragg grating sensors. Energy Environ. Sci. 14, 6464-6475 (2021).27. Wang, R. et al. Operando monitoring of ion activities in aqueous batteries with plasmonic fiber-optic sensors. Nat. Commun. 13, 547 (2022).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 85, 852, 120]]<|/det|>
+28. Wang, L. et al. Compositions and formation mechanisms of solid-electrolyte interphase on microporous carbon/sulfur cathodes. Chem. Mater. 32, 3765-3775 (2020).
+
+<|ref|>text<|/ref|><|det|>[[147, 131, 850, 166]]<|/det|>
+29. Xu, Y. et al. Confined sulfur in microporous carbon renders superior cycling stability in Li/S batteries. Adv. Funct. Mater. 25, 4312-4320 (2015).
+
+<|ref|>text<|/ref|><|det|>[[147, 177, 848, 212]]<|/det|>
+30. Kumaresan, K., Mikhaylik, Y. & White, R. E. A mathematical model for a lithium-sulfur cell. J. Electrochem. Soc. 155, A576-A582 (2008).
+
+<|ref|>text<|/ref|><|det|>[[147, 223, 850, 277]]<|/det|>
+31. Walus, S., Barchasz, C., Colin, J. F., Martin, J. F., Elkaim, E., Lepretre, J. C. & Alloin, F. New insight into the working mechanism of lithium-sulfur batteries: in situ and operando X-ray diffraction characterization. Chem. Commun. 49, 7899-7901 (2013).
+
+<|ref|>text<|/ref|><|det|>[[147, 288, 850, 323]]<|/det|>
+32. Shen, C. et al. Self-discharge behavior of lithium-sulfur batteries at different electrolyte/sulfur ratios. J. Electrochem. Soc. 166, A5287-A5294 (2019).
+
+<|ref|>text<|/ref|><|det|>[[147, 335, 850, 388]]<|/det|>
+33. Zugmann, S., Fleischmann, M., Amereller, M., Gschwind, R. M., Wiemhofer, H. D. & Gores, H. J. Measurement of transference numbers for lithium ion electrolytes via four different methods, a comparative study. Electrochim. Acta 56, 3926-3933 (2011).
+
+<|ref|>text<|/ref|><|det|>[[147, 399, 850, 453]]<|/det|>
+34. Zhang, B., Wu, J., Gu, J., Li, S., Yan, T. & Gao, X.-P. The fundamental understanding of lithium polysulfide in ether-based electrolyte for lithium-sulfur batteries. ACS Energy Lett. 6, 537-546 (2021).
+
+<|ref|>text<|/ref|><|det|>[[147, 464, 850, 499]]<|/det|>
+35. Cuisinier, M. et al. Sulfur speciation in Li-S batteries determined by operando X-ray absorption spectroscopy. J. Phys. Chem. Lett. 4, 3227-3232 (2013).
+
+<|ref|>text<|/ref|><|det|>[[147, 510, 850, 563]]<|/det|>
+36. Barchasz, C., Molton, F., Duboc, C., Lepretre, J. C., Patoux, S. & Alloin, F. Lithium/sulfur cell discharge mechanism: an original approach for intermediate species identification. Anal. Chem. 84, 3973-3980 (2012).
+
+<|ref|>text<|/ref|><|det|>[[147, 575, 850, 610]]<|/det|>
+37. Liu, J., Chen, H., Chen, W., Zhang, Y. & Zheng, Y. New insight into the "shuttle mechanism" of rechargeable lithium-sulfur batteries. ChemElectroChem 6, 2782-2787 (2019).
+
+<|ref|>text<|/ref|><|det|>[[147, 621, 850, 656]]<|/det|>
+38. Mikhaylik, Y. V. & Akridge, J. R. Polysulfide shuttle study in the Li/S battery system. J. Electrochem. Soc. 151, A1969-A1976 (2004).
+
+<|ref|>text<|/ref|><|det|>[[147, 667, 850, 720]]<|/det|>
+39. He, Q., Gorlin, Y., Patel, M. U. M., Gasteiger, H. A. & Lu, Y.-C. Unraveling the correlation between solvent properties and sulfur redox behavior in lithium-sulfur batteries. J. Electrochem. Soc. 165, A4027-A4033 (2018).
+
+<|ref|>text<|/ref|><|det|>[[147, 732, 850, 767]]<|/det|>
+40. Wujcik, K. H. et al. Fingerprinting lithium-sulfur battery reaction products by X-ray absorption spectroscopy. J. Electrochem. Soc. 161, A1100-A1106 (2014).
+
+<|ref|>text<|/ref|><|det|>[[147, 779, 850, 832]]<|/det|>
+41. Moy, D., Manivannan, A. & Narayanan, S. R. Direct measurement of polysulfide shuttle current: a window into understanding the performance of lithium-sulfur cells. J. Electrochem. Soc. 162, A1-A7 (2015).
+
+<|ref|>text<|/ref|><|det|>[[147, 844, 850, 878]]<|/det|>
+42. Pang, Q., Liang, X., Kwok, C. Y. & Nazar, L. F. Advances in lithium-sulfur batteries based on multifunctional cathodes and electrolytes. Nat. Energy 1, 16132 (2016).
+
+<|ref|>text<|/ref|><|det|>[[147, 890, 850, 906]]<|/det|>
+43. Ji, X., Lee, K. T. & Nazar, L. F. A highly ordered nanostructured carbon-sulphur cathode
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 85, 600, 101]]<|/det|>
+for lithium- sulphur batteries. Nat. Mater. 8, 500- 506 (2009).
+
+<|ref|>text<|/ref|><|det|>[[147, 112, 850, 166]]<|/det|>
+44. Pang, Q., Kundu, D., Cuisinier, M. & Nazar, L. F. Surface-enhanced redox chemistry of polysulphides on a metallic and polar host for lithium-sulphur batteries. Nat. Commun. 5, 4759 (2014).
+
+<|ref|>text<|/ref|><|det|>[[147, 177, 850, 213]]<|/det|>
+45. Zheng, J. et al. Lewis acid-base interactions between polysulfide and metal organic framework in lithium sulfur batteries. Nano Lett. 14, 2345-2352 (2014).
+
+<|ref|>text<|/ref|><|det|>[[147, 223, 850, 259]]<|/det|>
+46. Liang, X., Hart, C., Pang, Q., Garsuch, A., Weiss, T. & Nazar, L. F. A highly efficient polysulfide mediator for lithium-sulfur batteries. Nat. Commun. 6, 5682 (2015).
+
+<|ref|>text<|/ref|><|det|>[[147, 270, 850, 305]]<|/det|>
+47. Hyde, M. E. & Compton, R. G. A review of the analysis of multiple nucleation with diffusion controlled growth. J. Electroanal. Chem. 549, 1-12 (2003).
+
+<|ref|>text<|/ref|><|det|>[[147, 316, 850, 352]]<|/det|>
+48. Pan, H. et al. Non-encapsulation approach for high-performance Li-S batteries through controlled nucleation and growth. Nat. Energy 2, 813-820 (2017).
+
+<|ref|>text<|/ref|><|det|>[[147, 362, 850, 398]]<|/det|>
+49. Li, Z., Zhou, Y., Wang, Y. & Lu, Y.-C. Solvent-mediated Li2S electrodeposition: a critical manipulator in lithium-sulfur batteries. Adv. Energy Mater. 8, 1802207 (2019).
+
+<|ref|>text<|/ref|><|det|>[[147, 408, 850, 444]]<|/det|>
+50. Zheng, Y., Zheng, S., Xue, H. & Pang, H. Metal-organic frameworks for lithium-sulfur batteries. J. Mater. Chem. A 7, 3469-3491 (2019).
+
+<|ref|>text<|/ref|><|det|>[[147, 455, 850, 490]]<|/det|>
+51. Feng, X. et al. Engineering a highly defective stable Uio-66 with tunable Lewis-Bronsted acidity: the role of the hemilabile linker. J. Am. Chem. Soc. 142, 3174-3183 (2020).
+
+<|ref|>text<|/ref|><|det|>[[147, 501, 850, 555]]<|/det|>
+52. Zheng, Z.-J., Ye, H. & Guo, Z.-P. Recent progress on pristine metal/covalent-organic frameworks and their composites for lithium-sulfur batteries. Energy Environ. Sci. 14, 1835-1853 (2021).
+
+<|ref|>text<|/ref|><|det|>[[147, 565, 850, 601]]<|/det|>
+53. Gervillie-Mouraveiff, C. et al. Unlocking cell chemistry evolution with operando fibre optic infrared spectroscopy in commercial Na(Li)-ion batteries. Nat. Energy 7, 1157-1169 (2022).
+
+<|ref|>text<|/ref|><|det|>[[147, 612, 850, 647]]<|/det|>
+54. Miele, E. et al. Hollow-core optical fibre sensors for operando Raman spectroscopy investigation of Li-ion battery liquid electrolytes. Nat. Commun. 13, 1651 (2022).
+
+<|ref|>text<|/ref|><|det|>[[147, 658, 850, 712]]<|/det|>
+55. Gang, T., Liu, F., Hu, M. & Albert, J. Integrated differential area method for variable sensitivity interrogation of tilted fiber Bragg grating sensors. J. Lightwave Technol. 37, 4531-4536 (2019).
+
+<|ref|>text<|/ref|><|det|>[[147, 723, 850, 777]]<|/det|>
+56. Liu, F., Zhang, X., Li, K., Guo, T., Lanoul, A. & Albert, J. Discrimination of bulk and surface refractive index change in plasmonic sensors with narrow bandwidth resonance combs. ACS Sens. 6, 3013-3023 (2021).
+
+<|ref|>text<|/ref|><|det|>[[147, 788, 850, 842]]<|/det|>
+57. Liu, F. & Albert, J. 40 GHz-rate all-optical cross-modulation of core-guided near infrared light in single mode fiber by surface plasmons on gold-coated tilted fiber Bragg gratings. APL Photonics 4, 126104 (2019).
+
+<|ref|>text<|/ref|><|det|>[[147, 853, 850, 907]]<|/det|>
+58. Dai, S., Nouar, F., Zhang, S., Tissot, A. & Serre, C. One-step room-temperature synthesis of metal (IV) carboxylate metal-organic frameworks. Angew. Chem. Int. Ed. 60, 4282-4288 (2021).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[149, 86, 308, 101]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[148, 113, 852, 315]]<|/det|>
+AcknowledgementsJ.- M. Tarascon acknowledges the International Balzan Prize Foundation and the LABEX STOREXII for funding. F. Liu and J.- M. Tarascon acknowledge the European Project "Innovative physical/virtual sensor platform for battery cell" (INSTABAT) (European Union's Horizon 2020 research and innovation program under grant agreement No 955930). W. Lu acknowledges the support of the CSC scholarship (201906880002). R. Demir- Cakan is thankful to the French Embassy for the Visiting Researcher Fellowship (135694V). We thank Dr. J. Forero- Saboya for his assistance of scanning electron microscopy images. We thank Prof. J. Albert from Carleton University (Ottawa, Canada) for the fabrication of fiber sensors and assistance of simulation software. Finally, we gladly thank Dr. W. He, Dr. Y. Wang, Dr. X. Gao, Dr. B. Li, Dr. C. Gervillie- Mouravieff and Mr. C. Leau for extensive and valuable discussion and comments.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 326, 321, 341]]<|/det|>
+## Author Contributions
+
+<|ref|>text<|/ref|><|det|>[[148, 353, 851, 444]]<|/det|>
+Author ContributionsF. Liu, J. Huang, R. Demir- Cakan and J.- M. Tarascon conceived the idea and designed the experiments. F. Liu performed the experiments. F. Liu, J. Huang, R. Demir- Cakan and J.- M. Tarascon performed the data analysis. W. Lu and V. Pimenta provided the MOF- 801(Zr). Finally, F. Liu, S. Boles, R. Demir- Cakan and J.- M. Tarascon wrote the paper with contributions from all authors.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 456, 307, 472]]<|/det|>
+## Conflicts of interest
+
+<|ref|>text<|/ref|><|det|>[[149, 484, 548, 500]]<|/det|>
+The authors declare no competing financial interests
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 511, 334, 526]]<|/det|>
+## Additional information
+
+<|ref|>text<|/ref|><|det|>[[148, 539, 850, 572]]<|/det|>
+Supplementary information: the online version contains supplementary material available at
+
+<|ref|>text<|/ref|><|det|>[[148, 585, 848, 619]]<|/det|>
+Correspondence and requests for materials should be addressed to R. Demir- Cakan or J.- M. Tarascon.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 43, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 131, 291, 177]]<|/det|>
+Supportinformation.pdf LiSbatterysensing.mp4
+
+<--- Page Split --->
diff --git a/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/images_list.json b/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..b3ade5bcad660a677f8fbcbf76d33fd220ac04ea
--- /dev/null
+++ b/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/images_list.json
@@ -0,0 +1,107 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1 Multiple valence bands enable high \\(ZT\\) values in p-type PbSe. a Schmatic diagram of multi-bands (L, \\(\\Sigma\\) , \\(\\Lambda\\) ) involvement in transport. The Brillouin zone shows that the degeneracies at the L, \\(\\Sigma\\) , and \\(\\Lambda\\) points are 4, 12, and 8, respectively. b The activated third band \\(\\Lambda\\) enables higher \\(ZT\\) values compared with the single-band and two-band PbSe-based materials.",
+ "footnote": [],
+ "bbox": [
+ [
+ 150,
+ 88,
+ 841,
+ 333
+ ]
+ ],
+ "page_idx": 18
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2 Crystal structure and band gap. a Schematic crystal structure of Pb0.98Na0.02Se - \\(x\\%\\) AgInSe2 (LISS). b Powder XRD patterns of LISS. c Refined lattice constants of LISS. d Room-temperature infrared spectra for PbSe - \\(x\\%\\) AgInSe2 and Pb0.98Na0.02Se - \\(x\\%\\) AgInSe2.",
+ "footnote": [],
+ "bbox": [
+ [
+ 155,
+ 95,
+ 844,
+ 515
+ ]
+ ],
+ "page_idx": 19
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig. 3 Electrical properties as a function of temperature for \\(\\mathrm{Pb_{0.98}Na_{0.02}Se - x\\%}\\) AgInSe2 (LISS) compounds. a Electrical conductivity. b Seebeck coefficient. c Power factor. d Weighted mobility. The hollow circles in d represent the weighted mobility of single-band and two-band PbSe-based materials.",
+ "footnote": [],
+ "bbox": [
+ [
+ 150,
+ 90,
+ 844,
+ 500
+ ]
+ ],
+ "page_idx": 20
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4 Pisarenko plot and Hall carrier mobility. a Pisarenko plot of Seebeck coefficients as a function of Hall carrier concentration \\((n_{\\mathrm{H}})\\) for \\(\\mathrm{Pb_{0.98}Na_{0.02}Se - x\\%}\\) AgInSe2 (LISS). The solid black line is calculated assuming \\(m^{*} = 0.44m_{\\mathrm{e}}\\) and the purple line represents the result assuming \\(m^{*} = 0.81m_{\\mathrm{e}}\\) within the SPB model. The gray circles show the Pisarenko plot for Na-doped PbSe reported by Wang et al.38 b Hall carrier mobility \\((\\mu_{\\mathrm{H}})\\) versus Hall carrier concentration \\((n_{\\mathrm{H}})\\) at 303K.",
+ "footnote": [],
+ "bbox": [
+ [
+ 150,
+ 90,
+ 847,
+ 300
+ ]
+ ],
+ "page_idx": 21
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Fig. 5 Electronic band structure. a Electronic band structure of \\(\\mathrm{Pb_27Se_27}\\) (blue) and \\(\\mathrm{Pb_{25}AgInSe_{27}}\\) (red). b Electronic density of states (DOS) near the Fermi level for \\(\\mathrm{Pb_{27}Se_{27}}\\) (black), \\(\\mathrm{Pb_{26}AgSe_{27}}\\) (green), \\(\\mathrm{Pb_{26}InSe_{27}}\\) (blue) and \\(\\mathrm{Pb_{25}AgInSe_{27}}\\) (red), respectively. c Electronic band structure of \\(\\mathrm{Pb_{25}AgInSe_{27}}\\) at \\(300\\mathrm{K}\\) and \\(873\\mathrm{K}\\) , respectively. d Temperature-dependent infrared spectra of \\(\\mathrm{PbSe - 2\\%AgInSe_2}\\) . e The experimental (red) and theoretical (blue) bandgap \\((E_{\\mathrm{g}})\\) and the theoretical energy offset between VBM1 and VBM2 \\((\\Delta E_{1 - 2})\\) and between VBM1 and VBM3 \\((\\Delta E_{1 - 3})\\) as a function of temperature. f Temperature-dependent electronic DOS of \\(\\mathrm{Pb_{25}AgInSe_{27}}\\) near the VBM.",
+ "footnote": [],
+ "bbox": [
+ [
+ 171,
+ 88,
+ 822,
+ 670
+ ]
+ ],
+ "page_idx": 22
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Fig. 6 Thermal transport properties and figure-of-merit \\(ZT\\) as a function of temperature for \\(\\mathrm{Pb_{0.98}Na_{0.02}Se - x\\%AgInSe_2}\\) (LISS) compounds. a Total thermal conductivity. b Lattice thermal conductivity. Inset shows the room-temperature lattice thermal conductivities departure from the theoretical line calculated by the Callaway model. c The average sound velocity \\(\\left(\\nu_{\\mathrm{avg}}\\right)\\) versus lattice thermal conductivity \\(\\left(\\kappa_{\\mathrm{L}}\\right)\\) for LISS compounds at room temperature. d Temperature-dependent \\(ZT\\) for LISS samples.",
+ "footnote": [],
+ "bbox": [
+ [
+ 152,
+ 88,
+ 840,
+ 500
+ ]
+ ],
+ "page_idx": 23
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_7.jpg",
+ "caption": "Fig. 7 Microstructures and local structure analysis for high-performance LISS sample. a Low magnification of bright-field TEM image for \\(\\mathrm{Pb_{0.98}Na_{0.02}Se}\\) - \\(2.05\\%\\) AgInSe2 sample. b The enlarged TEM pattern presents the nanoscale precipitates remarked by the arrows. c High resolution TEM (HRTEM) picture of a selected nanoprecipitate. d The corresponding selected area electron diffraction (SAED) pattern with cubic structure along [111]. e, f High angle annular dark field (HAADF) patterns for \\(\\mathrm{Pb_{0.98}Na_{0.02}Se}\\) - \\(2.05\\%\\) AgInSe2. g Experimental XANES spectra of In \\(K\\) -edge for \\(\\mathrm{Pb_{0.98}Na_{0.02}Se}\\) - \\(2\\%\\) AgInSe2 (red dots), and AgInSe2 (orange line), respectively. The blue line shows the theoretical XANES spectrum of In \\(K\\) -edge for In-doped PbSe assuming that In occupy the Pb site. The black line represents a linear combination fitting (LCF) result of In \\(K\\) -edge of \\(\\mathrm{Pb_{0.98}Na_{0.02}Se}\\) - \\(2\\%\\) AgInSe2 considering that the In \\(K\\) -edge of AgInSe2 and In-doped PbSe serves as standards. h Multiple scattering calculations of In \\(K\\) -edge XANES for In-doped PbSe with different atomic clusters. The inset shows the nearest-two shell of In atom when it occupies the Pb site in PbSe matrix. The \\(E_0\\) is the absorption edge energy of In \\(K\\) -edge of In foil.",
+ "footnote": [],
+ "bbox": [
+ [
+ 149,
+ 84,
+ 848,
+ 585
+ ]
+ ],
+ "page_idx": 24
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d.mmd b/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..162f3ec6002bfa3c8be37ac42135f2cb1a750ff8
--- /dev/null
+++ b/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d.mmd
@@ -0,0 +1,197 @@
+
+# Multiple valence bands convergence and strong phonon scattering lead to high thermoelectric performance in p-type PbSe
+
+Yingcai Zhu Beihang University Dongyang Wang Beihang University Tao Hong Beihang University Lei Hu Tokyo Institute of Technology https://orcid.org/0000- 0002- 4647- 1604 Toshiaki Ina Japan Synchrotron Radiation Research Institute Shaoping Zhan Beihang University Bingchao Qin Beihang University Haonan Shi Beihang University Lizhong Su Beihang University Xiang Gao Center for High Pressure Science and Technology Advanced Research Li- Dong Zhao ( zhaolidong@buaa.edu.cn ) Beihang University https://orcid.org/0000- 0003- 1247- 4345
+
+## Article
+
+# Keywords:
+
+Posted Date: April 26th, 2022
+
+DOI: https://doi.org/10.21203/rs.3.rs- 1575296/v1
+
+<--- Page Split --->
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on July 19th, 2022. See the published version at https://doi.org/10.1038/s41467-022-31939-4.
+
+<--- Page Split --->
+
+# Multiple valence bands convergence and strong phonon scattering
+
+# lead to high thermoelectric performance in p-type PbSe
+
+Yingcai Zhu,1 Dongyang Wang,1 Tao Hong,1 Lei Hu,2 Toshiaki Ina,3 Shaoping, Zhan,1 Bingchao Qin,1 Haonan Shi,1 Lizhong Su,1 Xiang Gao,4 Li- Dong Zhao1\\*
+
+1School of Materials Science and Engineering, Beihang University, Beijing 100191, China 2State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China 3Research and Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring- 8), Sayo, Hyogo, Japan 4Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing, 100094, China
+
+Thermoelectric generators enable the conversion of waste heat to electricity, which is an effective way to alleviate the global energy crisis. However, the inefficiency of thermoelectric materials is the main obstacle for realizing their widespread applications and thus developing materials with high thermoelectric performance is urgent. Here we show that multiple valence bands and strong phonon scattering can be realized simultaneously in p- type PbSe through the incorporation of AgInSe2. The multiple valleys enable large weighted mobility, indicating enhanced electrical properties. Local structure and microstructure analysis reveal that about 80 percent of Ag and In atoms form AgInSe2 as nano- scale precipitates, which result in strong phonon scattering and thus ultralow lattice thermal conductivity. Consequently, we achieve an exceptional \(ZT\) of \(\sim 2.1\) at 873 K in p- type PbSe. Our results demonstrate that a combination of band manipulation and microstructure engineering can be realized by tuning the composition. We expect our findings to be a general strategy for achieving high thermoelectric performance in bulk material, pushing the thermoelectric materials for realistic applications.
+
+<--- Page Split --->
+
+The depletion of fossil fuels and the deteriorating environment motivate the human beings to find sustainable and clean energy solutions. Thermoelectric devices can be used in energy harvesting from waste heat or be utilized in refrigeration, which is favorable for raising energy efficiency, attracting widespread attention from around the world. The efficiency of thermoelectric devices is largely determined by the figure of merit \(ZT\) of their constituent thermoelectric materials, \(ZT = \frac{S^2\sigma T}{\kappa_e + \kappa_L}\) , where \(S\) represents the Seebeck coefficient, \(\sigma\) is the electrical conductivity, \(\kappa_e\) is the electrical contribution to the thermal conductivity, \(\kappa_L\) is the lattice thermal conductivity, and \(T\) is the absolute temperature, respectively. However, decoupling the interdependence between electrical and thermal transport properties is a crucial but challenging issue for improving the thermoelectric performance of materials. To achieve good electrical properties, various strategies such as band convergence \(^{1 - 4}\) , band sharpening \(^{5}\) , band alignment \(^{6}\) , carrier mobility optimization \(^{7}\) and resonant states introduction \(^{8}\) were adopted. On the other hand, materials with disordered or complex crystal structure \(^{9,10}\) , giant anharmonicity \(^{11,12}\) , and lone pair electrons \(^{13}\) often exhibit intrinsic low lattice thermal conductivity, which are promising candidates for thermoelectric applications. Moreover, the lattice thermal conductivity can be largely suppressed by microstructural engineering, including nano-scale precipitates \(^{14,15}\) , dislocations \(^{16,17}\) , grain boundaries \(^{18}\) , and all- scale hierarchical architectures \(^{19 - 21}\) . Therefore, a synergistic combination of electronic band modulation and microstructural engineering is expected to achieve advanced thermoelectric materials.
+
+PbTe has long been used for mid- temperature power generation, whereas the scarcity of element Te make it expensive for wide applications. PbSe is a perfect substitute for expensive PbTe due to the earth- abundant element Se. Hitherto, only limited studies show that the \(ZT\) of PbSe could reach \(1.7^{22 - 24}\) , motivating us to search strategies to improve the thermoelectric properties of PbSe. The weighted mobility \((\mu w = \mu (m^* /m_e)^{3 / 2})\) is a good descriptor for the inherent electrical performance of materials \(^{25}\) . Multiple degenerate electronic bands enable large density- of- states effective mass \(m^*\)
+
+<--- Page Split --->
+
+without obvious effect on the carrier mobility \((\mu)^{1}\) , facilitating the improvement of \(\mu \mathrm{w}\) . Indeed, the interplay of multiple bands enable large power factor or \(\mu \mathrm{w}\) and thus ultrahigh \(ZT^{26,27}\) . However, the two- band convergence is much difficult to realize due to the large energy offset between the valence band maximum (L) and the secondary valence band maximum \((\Sigma)\) in PbSe and to date only limited works can promote band convergence in it \(^{23,28,29}\) . It is more challenging to achieve multiple bands convergence in PbSe.
+
+The lattice thermal conductivity is another important parameter for the thermoelectric performance indicated by the quality factor \(B\) ( \(B \propto \mu \mathrm{w} / \kappa \mathrm{L}\) ). The introduction of materials with low lattice thermal conductivity in MTe ( \(M = \mathrm{Pb}\) , Ge) matrixes was proved to be an effective method to manipulate their thermal transport properties \(^{30,31}\) . For example, the appearance of nanodots in AgPb \(_m\) SbTe \(_{2 + m}\) (LAST) system is considered as the origin of their low lattice thermal conductivity and thus the enhanced thermoelectric performance \(^{30}\) . Interestingly, the electrical properties of materials can also be optimized in similar way, such as in PbTe- AgInTe \(_2\) (LIST) \(^{32}\) and SnTe- AgInTe \(_2\) \(^{33}\) . These enhanced performances motivate us to search strategies for optimizing the \(\mu \mathrm{w}\) and \(\kappa \mathrm{L}\) simultaneously.
+
+Beyond the two- band convergence between the L and \(\Sigma\) bands, we found that a third valence band \(\Lambda\) with a degeneracy \(N_{\mathrm{v}} = 8\) could be activated (Figure 1a) through the incorporation of AgInSe \(_2\) in the PbSe matrix doped with \(2\%\) Na (LISS). These three- band convergence tendency enables large weighted mobility. Additionally, local structure analysis by the x- ray absorption fine structure (XAFS) spectra indicates that more than \(80\%\) of Ag and In atoms form AgInSe \(_2\) in the system. Interestingly, AgInSe \(_2\) is also a good thermoelectric material with intrinsic ultralow lattice thermal conductivity \(^{34 - 36}\) . The tetragonal AgInSe \(_2\) is perfect inserted in the PbSe matrix as nano- scale precipitates revealed by the transmission electron microscopy (TEM), causing strong phonon scattering and hence resulting in ultralow lattice thermal conductivity. Therefore, a synergistic optimization of \(\mu \mathrm{w}\) and \(\kappa \mathrm{L}\) is realized. As a consequence, an
+
+<--- Page Split --->
+
+exceptional high \(ZT \sim 2.1\) is achieved at 873 K, which is much better than the single- band and two- band activated p- type PbSe- based materials28,29 (Figure 1b).
+
+## Results
+
+Crystal structure. The LISS compounds crystallize in cubic structure (Space group, \(Fm - 3m\) ), which is reflected by the x- ray diffraction (XRD) measurements that the XRD patterns can be indexed on the basis of cubic PbSe and no secondary phase is observed within the instrumental detection limit (Figure 2a, 2b). The diffraction peaks tend to shift to higher angles with increment of AgInSe2. Therefore, the lattice parameter \((a)\) slightly decreases with increasing AgInSe2 content (Figure 2c), which may be attributed to the smaller atomic radius of Ag, and In compared with that of Pb. This phenomenon also demonstrates that the AgInSe2 is incorporated in the Pb0.98Na0.02Se matrix.
+
+Electronic transport properties. The continuous decrease of the electrical conductivity with increasing temperature indicates a degenerate semiconducting property for LISS samples (Figure 3a). Additionally, the electrical conductivity is suppressed significantly after the introduction of AgInSe2. The electrical conductivity of Pb0.98Na0.02Se is as large as 3848 S/cm at room temperature, which decline to 774 S/cm for Pb0.98Na0.02Se- 2.15% AgInSe2 sample. To uncover this behavior, room temperature Hall measurements were performed. Obviously, the carrier concentration is reduced largely with increasing AgInSe2 (Figure S1), explaining the depressed electrical conductivity. The reduction of carrier concentration may be due to the formation of InPb defects. These InPb defects are shallow donors in PbSe37, which will counteract with holes.
+
+The Seebeck coefficient increases with elevated temperature for all samples and no saturate peak appears (Figure 2b), demonstrating that no obvious bipolar effect occur at high temperatures. The Seebeck coefficient is largely enhanced over the whole temperature range with the increment of AgInSe2. Typically, the Seebeck coefficient of Pb0.98Na0.02Se is only 19.2 μV/K at room temperature, whereas a much larger Seebeck
+
+<--- Page Split --->
+
+coefficient value of \(116\mu \mathrm{V / K}\) is achieved for \(\mathrm{Pb_{0.98}Na_{0.02}Se - 2.15\% AgInSe_2}\) sample. This dramatically promoted Seebeck coefficients will facilitate the enhancement of power factor. Indeed, the \(PF\) have an apparent improvement especially at the 300 - 600 K temperature range for all doped samples (Figure 3c). The room temperature \(PF\) value of \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) is only \(\sim 1.4\mu \mathrm{Wcm^{- 1}K^{- 2}}\) . In sharp contrast, the room temperature \(PF\) increases to \(\sim 11.1\mu \mathrm{Wcm^{- 1}K^{- 2}}\) when \(x = 2.1\) and this value is continuously improved to \(\sim 15.6\mu \mathrm{Wcm^{- 1}K^{- 2}}\) at 423 K (Figure 3c).
+
+To understand the nature of the improvement of Seebeck coefficient, the relationship of Seebeck coefficient as a function of carrier concentration (Pisarenko curve) was compared at room temperature (Figure 4a). Generally, the Seebeck coefficient increases with decreasing carrier concentration. However, the Seebeck coefficient is largely departure from the theoretical values estimated by the single parabolic band (SPB) model, which indicate that a complex electronic band should be involved in the electrical transport properties. Accordingly, the effective mass \((m^*)\) of LISS is largely increased from \(0.44m_{\mathrm{e}}\) to \(0.81m_{\mathrm{e}}\) with the introduction of \(\mathrm{AgInSe_2}\) (Figure 4a). In contrast, the effective mass of Na- doped PbSe is only \(\sim 0.28m_{\mathrm{e}}\) (Figure 4a). The Hall carrier mobility increases with doping and a maximum value of \(\sim 125\mathrm{cm}^2\mathrm{V}^{- 1}\mathrm{s}^{- 1}\) is obtained when \(\mathrm{x} = 2\) (Figure 4b), which is largely due to the depressed carrier concentration. Consequently, the weighted mobility \((\mu \mathrm{w})\) of LISS compounds is largely enhanced especially at the 300- 600K temperature range, which is higher than that of single- band and two- band PbSe- based materials (Figure 3d).
+
+DFT calculations were also conducted to understand the origin of the enhanced Seebeck coefficients. We observed significant change of the electronic band structure with the incorporation of \(\mathrm{AgInSe_2}\) in PbSe matrix (Figure 5a). The bandgap is enlarged upon doping, which will depress the bipolar effect and facilitate the enhancement of Seebeck coefficient. These calculations are well in accordance with our experimental results. The experimental bandgap is \(\sim 0.24\mathrm{eV}\) for the pristine PbSe, while the bandgap increases obviously with the incorporation of \(\mathrm{AgInSe_2}\) and a large bandgap \(\sim 0.33\mathrm{eV}\)
+
+<--- Page Split --->
+
+is achieved for the PbSe - \(2\%\) AgInSe \(_2\) sample (Figure 2d). Interestingly, the bandgap is further enlarged to \(\sim 0.38 \mathrm{eV}\) with Na doping (Figure 2d). In addition, the L band is flattened. The sharp peaks reflected in the density of states (DOS) for valence band also reveal the band flattening character (Figure 5b). Simultaneously, the \(\Sigma\) band is elevated and hence the energy offset \((\Delta E_{1 - 2})\) between L and \(\Sigma\) band is shortened. Surprisingly, a third valence band at the \(\Lambda\) point is activated and it remains at the same energy level compared with the \(\Sigma\) band (Figure 5a). These multiple valence bands enable large effective mass without significant affect the carrier mobility, which is the origin of enhanced Seebeck coefficient and the weighted mobility \((\mu \mathrm{w})\) . The electronic band structures of Ag and In doped PbSe were also calculated (Figure S2a, S2b). The Ag- doping and In- doping reflect p- type and n- type doping effect, respectively, which are consistent with previous experimental results \(^{38,39}\) . Additionally, In- doping has a more important effect on decreasing energy offset \((\Delta E_{1 - 2})\) compared with the Ag- doping (Figure S2c), while Ag- doping plays a major role in enlarging the bandgap (Figure S2d). Both Ag and In atoms play an important role in band manipulation.
+
+Using the lattice parameters extracted from the temperature- dependent synchrotron radiation x- ray diffraction (SR- XRD) patterns (Figure S3), we calculated the band structures as a function of temperature (Figure 5c, Figure S4). Clearly, the bandgap increases with rising temperature, which is also verified experimentally (Figure 5d). However, the theoretical bandgap is smaller than the experimental result (Figure 5e), which may be attribute to the neglect of the effect of thermal disorder on the bandgap in our calculations. Moreover, the energy offset \((\Delta E_{1 - 2})\) between L and \(\Sigma\) bands decreases with increasing temperature (Figure 5e). Interestingly, the energy offset \((\Delta E_{1 - 3})\) between L and \(\Lambda\) also shows a decline tendency with rising temperature and its value is even smaller than \(\Delta E_{1 - 2}\) in the whole temperature range (Figure 5e). The convergence tendency and the involvement of the third valence band is also reflected in the DOS corresponding to the valence band increases with increasing temperature (Figure 5f). This convergence behavior is experimentally verified via Hall measurements, in which a maximum Hall coefficient \((R_{\mathrm{H}})\) is observed (Figure S5a) and it is a sign of band
+
+<--- Page Split --->
+
+convergence of the multi- valence bands \(^{20,23}\) . Consequently, the effective mass \((m^{*})\) of \(\mathrm{Pb_{0.98}Na_{0.02}Se - 2.05\%AgInSe_2}\) increases from \(0.73m_{\mathrm{e}}\) to \(2.16m_{\mathrm{e}}\) with rising temperature, which is much higher than the \(m^{*}\) of single Na- doped \(\mathrm{PbSe^{40}}\) (Figure S5b).
+
+Thermal transport properties and the figure- of- merit \(ZT\) . Thermal conductivity is another important property for thermoelectric performance. The total thermal conductivity \((\kappa_{\mathrm{tot}})\) decreases significantly with increasing \(\mathrm{AgInSe_2}\) (Figure 6a). The \(\kappa_{\mathrm{tot}}\) is a composite of lattice thermal conductivity \((\kappa_{\mathrm{L}})\) and electronic contributions to the thermal conductivity \((\kappa_{\mathrm{e}})\) . The \(\kappa_{\mathrm{e}}\) was calculated by the Wiedemann- Franz relation, \(\kappa_{\mathrm{e}} = L\sigma T\) , where \(L\) is estimated by SPB model (Figure S6a). The \(\kappa_{\mathrm{e}}\) decreases remarkably with doping due to largely depressed electrical conductivity (Figure S6b). Furthermore, the \(\kappa_{\mathrm{L}}\) is obtained by subtracting the electronic contribution from the total thermal conductivity (Figure 6b). Similarly, the \(\kappa_{\mathrm{L}}\) is largely suppressed with doping and the room- temperature \(\kappa_{\mathrm{L}}\) values are much lower than the theoretical estimation by the Callaway model (Figure 6b, inset). In addition, the \(\kappa_{\mathrm{L}}\) decreases with rising temperature and a clear departure from \(T^{- 1}\) relation is observed, demonstrating that the strong phonon scattering occurs. To further uncover the mechanism of the reduction of \(\kappa_{\mathrm{L}}\) , sound velocities were measured for all the samples at room temperature (Table S1). Interestingly, the average sound velocity \((v_{\mathrm{avg}})\) slightly increases after doping (Figure 6c). The deduced Grüneisen parameters of LISS are almost unchanged. The lattice thermal conductivity can be expressed as \(\kappa_{\mathrm{L}} = \frac{1}{3} Cv_{\mathrm{avg}}^{2}\tau\) based on the simple kinetic theory \(^{41}\) , where \(C\) is the specific heat, \(\tau\) is the phonon lifetime. Here, the \(v_{\mathrm{avg}}\) increases upon doping and thus the reduction of lattice thermal conductivity should be derived from the decrease of phonon lifetime. In another word, enhanced phonon scattering is the main origin of the largely suppressed lattice thermal conductivity.
+
+Thanks to the complex band structure behavior and strong phonon scattering with the introduction of \(\mathrm{AgInSe_2}\) , the figure- of- merit \(ZT\) is largely enhanced in the whole temperature range and a maximum \(ZT\) value of \(\sim 2.1\) is achieved at 873K for
+
+<--- Page Split --->
+
+\(\mathrm{Pb_{0.98}Na_{0.02}Se - 2.05\% AgInSe_2}\) sample (Figure 6d). Considering the correction of heat capacity, we can also obtain a large \(ZT\) of \(\sim 1.9\) at 873K (Figure 6d, Figure S7). The high thermoelectric properties of LISS samples are reproducible (Figure S8).
+
+Microstructure and local structure analysis. The TEM images of LISS sample display that abundant nanosized precipitates are embedded in PbSe matrix (Figure 7a, 7b). In addition, strip- like dislocations are also observed (circled regions in Figure 7a). Both nanoscale precipitates and multi- scale dislocations are effective phonon scattering centers. The annular dark- field (ADF) STEM image and the EDS elemental mappings exhibit obvious Ag- rich and In- rich patterns for the precipitates (Figure S9). Accordingly, the elemental distributions of Se and Na are relatively homogeneous in the entire area, whereas Pb- poor regions are observed within the precipitates (Figure S9). A more clearer microstructural features of the precipitate is revealed by performing HRTEM (Figure 7c). The corresponding SAED pattern indicate a main cubic structure along [111], whereas the precipitates shows a different crystal structure from the PbSe matrix as another series of diffraction spots are exhibited which can be indexed to AgInSe₂ (Figure 7d). The HAADF patterns show that the tetragonal AgInSe₂ is perfectly inserted in the cubic PbSe matrix as a nine- atom grid (Figure 7e). We can also observe lattice dislocation in the HAADF (Figure 7f). The lattice mismatch induced by precipitates and dislocations will introduce large strain fluctuations and thus enhance the phonon scattering \(^{42}\) . Therefore, the lattice thermal conductivity of LISS was largely reduced to its amorphous limit of 0.31 Wm⁻¹K⁻¹ at 873 K arising from the strong phonon scattering.
+
+Understanding the atomic occupation of doping elements in the lattice allow us elucidate their role on manipulating the thermal or electrical transport properties. The x- ray absorption fine structure (XAFS) spectroscopy is a powerful tool to investigate the local structure in materials \(^{43 - 48}\) . Here, we performed XAFS measurements for PbSe, AgInSe₂ and LISS, respectively. The x- ray absorption near- edge structure (XANES) of Se K- edge and Pb L₃- edge did not show any change after the introduction of AgInSe₂
+
+<--- Page Split --->
+
+in PbSe (Figure S10), demonstrating a steady PbSe cubic matrix, which is well consistent with the XRD patterns. There are four main features in the XANES of In \(K\) - edge of LISS (Figure 7g), in which 1, 3, 4 features can well reflected in the In \(K\) - edge of AgInSe \(_2\) , indicating that most of In atoms may form AgInSe \(_2\) in the system. Furthermore, we calculated the XANES spectra of In \(K\) - edge for the In- doped PbSe assuming that In occupy the Pb site, in which the peak B is well corresponding with the feature 2 of In \(K\) - edge of LISS. Moreover, after adding the second shell (twelve Pb atoms) as shown by the 19- atoms cluster calculation (Figure 7h), the feature B is well reflected and the calculation is almost convergent. Therefore, the origin of feature 2 is mainly arising from the multiple scattering of the photoelectrons by the second shell of Pb atoms in the PbSe matrix. The linear combination fitting (LCF) was used to evaluate the atomic occupied ratio of In atoms in each standards (Figure 7g). Similar analysis was performed for the XANES of Ag \(K\) - edge (Figure S11). The LCF fitting results indicate that more than \(80\%\) of Ag and In atoms form AgInSe \(_2\) in the system (Table S2), causing strong phonon scattering.
+
+## Discussion
+
+In summary, a combined effect of three activated valence bands and strong phonon scattering is realized via introducing AgInSe \(_2\) in Pb \(_{0.98}\) Na \(_{0.02}\) Se matrix. These multiple valence bands convergence enable the enhancement of thermoelectric power factor at low temperature region and maintain at a high level at elevated temperature. Interestingly, local structure studies by XANES reveal that most of Ag or In atoms form AgInSe \(_2\) secondary phase. The numerous nanoscale AgInSe \(_2\) precipitates and multiscale dislocations observed in the TEM will cause strong phonon scattering. Therefore, the lattice thermal conductivity is largely depressed. As a consequence, a distinguished figure- of- merit \(ZT\) of \(\sim 2.1\) is achieved at 873K, which is among the best bulk thermoelectric materials. This work proves that multiple valence bands could be activated in p- type PbSe and highlights the strong phonon scattering effect through the introduction of secondary phase with ultralow thermal conductivity, which guide a new route to achieve excellent thermoelectric performance in bulk materials. The
+
+<--- Page Split --->
+
+quantitative atomic occupation of doping elements provides a new perspective to understand their role on manipulating transport properties. We expect more advanced thermoelectric materials can be achieved by employing this strategy.
+
+## Methods
+
+Synthesis. High- purity starting materials, Pb (99.999%), Se (99.999%), Na (99.9%), Ag (99.99%), In (99.99 %) were weighted in stoichiometric ratio (Pb0.98Na0.02Se - x% AgInSe2) and loaded in carbon coating silica tubes under an N2- filled glove box. The silica tubes were sealed under vacuum and then slowly heated to 1423 K in 24 h, soaked at this temperature for 10 h and followed by furnace cooling down to room temperature. The obtained ingots were grounded into powders and then densified at 873 K for 6 minutes with a pressure of 50 MPa using spark plasma sintering (SPS- 211Lx). Finally, highly dense bulk samples ( \(>97\%\) of theoretical density) were obtained.
+
+Thermoelectric property measurements. The bulk samples were cut into rectangular solids ( \(3 \times 3 \times 10 \mathrm{mm}^3\) ) and square pieces ( \(10 \times 10 \times 1 \mathrm{mm}^3\) ) for electrical and thermal transport properties measurements, respectively. The Seebeck coefficients and electrical conductivities were measured using the Ulvac Riko ZEM- 3 instrument. We calculated the thermal conductivity using the equation of \(\kappa_{tot} = D \cdot C_p \cdot \rho\) , where the thermal diffusivity \((D)\) was determined using a laser flash method by the Netzsch LFA- 457 facility, the heat capacity \((C_p)\) was estimated using both the Dulong- Petit law and an empirical equation \((C_p / k_B \mathrm{atom}^{- 1} = 3.07 + 4.7 \times 10^{- 4} (T / \mathrm{K} - 300))^{29}\) , and the density is calculated by the dimensions and mass of the samples. The combined uncertainty of all measurements for determining the \(ZT\) is less than \(20\%\) .
+
+Characterizations. Room- temperature powder x- ray diffraction measurements were conducted using a D/MAX 2500 PC system with Cu \(\mathrm{K}_{\alpha}\) radiation. High- temperature synchrotron radiation x- ray diffraction (SR- XRD) patterns were performed for \(\mathrm{Pb}_{0.98}\mathrm{Na}_{0.02}\mathrm{Se} - 2\% \mathrm{AgInSe}_2\) at the BL14B1 beamline of Shanghai synchrotron radiation facility (SSRF). The wavelength of the x- ray is \(0.6887 \mathrm{\AA}\) . The sample was heated from \(300 \mathrm{K}\) to \(875 \mathrm{K}\) at a rate of \(1.5 \mathrm{K min}^{- 1}\) . The bandgap was measured using the Shimadezu
+
+<--- Page Split --->
+
+Model UV- 3600 Plus instrument and was estimated by the Kubelka- Munk equation. The Hall coefficient \((R_{\mathrm{H}})\) was conducted by the Van der Pauw method using the Lake Shore 8400 Series. Scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) were performed using a JEOL ARM200F equipped with cold field emission gun and ASCOR probe corrector. More details can be found in the Supporting Information.
+
+First- principles calculations. Density functional theory (DFT) calculations were performed using the projector- augmented wave (PAW) method49, as implemented in the Vienna Ab initio Simulation Package (VASP)50,51. We utilized the revised Perdew- Burke- Ernzerhof (PBE)52 generalized gradient approximation (GGA) to estimate the exchange- correlation interactions. A cutoff energy was set to 450 eV for the plane- wave expansion of the electron density and the Monkhorst- Pack \(k\) - point sampling 0.1 Å- 1 was used within all the calculations. The atomic positions were fully relaxed when the maximum residual ionic force and total energy difference are converged within 0.01 eV Å- 1 and 10- 7 eV, respectively. Several 3×3×3 supercells were constructed (Pb27Se27, Pb26AgSe27, Pb26InSe27, Pb25AgInSe27), avoiding the defect- defect interaction. The occupations of Ag or/and In atoms in the supercells were relaxed in our calculations. The temperature- dependent electronic band structures were performed using the experimental lattice parameters at elevated temperatures deriving from the SR- XRD data.
+
+X- ray absorption fine structure (XAFS) spectroscopy measurements. The XAFS experiments were performed at BL01B1 beamline of Spring- 8 in Japan. The electron energy of the storage ring is 8.0 GeV with a top- up filling of 99.5 mA accumulated current during the experiment. The Si (311) double- crystal monochromator was used for tuning the monochromatic beam. We measured the XAFS of Ag \(K\) - edge and In \(K\) - edge for AgInSe2 in transmission mode. The XAFS measurements of Se \(K\) - edge, and Pb \(L_{3}\) - edge for PbSe and Pb0.98Na0.02Se - 2% AgInSe2 were conducted in transmission mode, while the measurements of Ag \(K\) - edge and In \(K\) - edge for Pb0.98Na0.02Se - 2% AgInSe2 were performed in fluorescence mode using 19- element Ge solid- state detector (SSD). All experimental XAFS spectra were preprocessed using the IFFEFIT package53.
+
+<--- Page Split --->
+
+XAFS calculation and analysis. The x- ray absorption near edge structure (XANES) calculations of Ag \(K\) - edge for Ag- doped PbSe and In \(K\) - edge for In- doped PbSe were performed based on the full multiple scattering (FMS) theory using FEFF9 program \(^{54,55}\) . We use self- consistent field (SCF) method to estimate the atomic scattering potential. To investigate the doping site of Ag or In in PbSe, we simply replace the central Pb absorber with Ag or In atom while maintaining the coordinates. To achieve good convergence, the cluster radius for SCF and FMS was fixed as 8 and 10 Angstrom, respectively. Linear combination fittings (LCF) of In \(K\) - edge for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe \(_2\) was performed using the Athena software assuming that the XANES of In \(K\) - edge of AgInSe \(_2\) and In- doped PbSe as the standards. A similar LCF analysis was applied for the XANES of Ag \(K\) - edge of \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe \(_2\) . Since we cannot ensure that the Ag or In atoms totally occupy the Pb site in PbSe matrix without formation of impurity phases, we thus used the calculated XANES as one of standards in the LCF analysis.
+
+## References
+
+1 Pei, Y. et al. Convergence of electronic bands for high performance bulk thermoelectrics. Nature 473, 66- 69 (2011). 2 Tang, Y. et al. Convergence of multi- valley bands as the electronic origin of high thermoelectric performance in CoSb \(_3\) skutterudites. Nat. Mater. 14, 1223- 1228 (2015). 3 Hu, L. et al. High thermoelectric performance enabled by convergence of nested conduction bands in \(\mathrm{Pb_7Bi_4Se_{13}}\) with low thermal conductivity. Nat. Commun. 12, 4793 (2021). 4 Chang, C. et al. 3D charge and 2D phonon transports leading to high out- of- plane zT in n- type SnSe crystals. Science 360, 778- 783 (2018). 5 Xiao, Y. et al. Band Sharpening and Band Alignment Enable High Quality Factor to Enhance Thermoelectric Performance in n- Type PbS. J. Am. Chem. Soc. 142, 4051- 4060 (2020). 6 Zhao, L.- D., Dravid, V. P. & Kanatzidis, M. G. The panoscopic approach to high performance thermoelectrics. Energy Environ. Sci. 7, 251- 268 (2014). 7 Qin, B. C. & Zhao, L. D. Carriers: the less, the faster. Mat. Lab 1, 220004 (2022). 8 Zhang, Q. et al. Enhancement of Thermoelectric Figure- of- Merit by Resonant States of Aluminium Doping in Lead Selenide. Energy Environ. Sci. 5(1), 5246- 5251 (2012). 9 Snyder, G. J. & Toberer, E. S. Complex thermoelectric materials. Nat. Mater. 7,
+
+<--- Page Split --->
+
+105- 114 (2008).10 Liu, H. et al. Copper ion liquid- like thermoelectrics. Nat. Mater. 11, 422- 425 (2012).11 Zhao, L. D. et al. Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals. Nature 508, 373- 377 (2014).12 Delaire, O. et al. Giant anharmonic phonon scattering in PbTe. Nat. Mater. 10, 614- 619 (2011).13 Skoug, E. J. & Morelli, D. T. Role of Lone- Pair Electrons in Producing Minimum Thermal Conductivity in Nitrogen- Group Chalcogenide Compounds. Phys. Rev. Lett. 107, 235901 (2011).14 Pei, Y., Lensch- Falk, J., Toberer, E. S., Medlin, D. L. & Snyder, G. J. High thermoelectric performance in PbTe due to large nanoscale \(\mathrm{Ag_2Te}\) precipitates and La doping. Adv. Funct. Mater. 21, 241- 249 (2011).15 Hong, T. et al. Band convergence and nanostructure modulations lead to high thermoelectric performance in \(\mathrm{SnPb_{0.04}Te - y\%AgSbTe_2}\) . Mater. Today Phys. 21, 100505 (2021).16 Kim, S. I. et al. Dense dislocation arrays embedded in grain boundaries for high- performance bulk thermoelectrics. Science 348, 109- 114 (2015).17 Chen, Z. et al. Lattice Dislocations Enhancing Thermoelectric PbTe in Addition to Band Convergence. Adv. Mater. 29 (2017).18 Meng, X. F. et al. Grain Boundary Engineering for Achieving High Thermoelectric Performance in n- Type Skutterudites. Adv. Energy Mater. 7, 1602582 (2017).19 Biswas, K. et al. High- performance bulk thermoelectrics with all- scale hierarchical architectures. Nature 489, 414- 418 (2012).20 Zhao, L. D. et al. All- scale hierarchical thermoelectrics: MgTe in PbTe facilitates valence band convergence and suppresses bipolar thermal transport for high performance. Energy Environ. Sci. 6, 3346 (2013).21 Wang, S. et al. Hierarchical structures lead to high thermoelectric performance in \(\mathrm{Cu_{m + n}Pb_{100}Sb_{m}Te_{100}Se_{2m}}\) (CLAST). Energy Environ. Sci. 14, 451- 461 (2021).22 Jiang, B. et al. Entropy engineering promotes thermoelectric performance in p- type chalcogenides. Nat. Commun. 12, 3234 (2021).23 Tan, G. et al. All- Scale Hierarchically Structured p- Type PbSe Alloys with High Thermoelectric Performance Enabled by Improved Band Degeneracy. J. Am. Chem. Soc. 141, 4480- 4486 (2019).24 Jiang, B. et al. High- entropy- stabilized chalcogenides with high thermoelectric performance. Science 371, 830- 834 (2021).25 Snyder, G. J. et al. Weighted Mobility. Adv. Mater. 32, e2001537 (2020).26 He, W. et al. High thermoelectric performance in low- cost \(\mathrm{SnS_{0.91}Se_{0.09}}\) crystals. Science 365, 1418- 1424 (2019).27 Qin, B. et al. Power generation and thermoelectric cooling enabled by momentum and energy multiband alignments. Science 373, 556- 561 (2021).28 Hodges, J. M. et al. Chemical Insights into PbSe- x%HgSe: High Power Factor and Improved Thermoelectric Performance by Alloying with Discordant Atoms.
+
+<--- Page Split --->
+
+29 Wang, H., Gibbs, Z. M., Takagiwa, Y. & Snyder, G. J. Tuning bands of PbSe for better thermoelectric efficiency. Energy Environ. Sci. 7, 804- 811 (2014). 30 Hsu, K. F., Loo, S., Guo, F., Chen, W., Dyck, J. S., Uher, C., Hogan, T., Polychroniadis, E. K., Kanatzidis, M. G. Cubic AgPbmSbTe2+m Bulk Thermoelectric Materials with High Figure of Merit. Science, 818- 821 (2004). 31 Plachkova, S. K. Thermoelectric Figure of Merit of the System (GeTe)1-x- (AgSbTe2)x. Phys. Stat. Sol. (a) 83, 349 (1984). 32 Xiao, Y. et al. Amphoteric Indium Enables Carrier Engineering to Enhance the Power Factor and Thermoelectric Performance in n- Type AgnPb100 InnTe 100+2n (LIST). Adv. Energy Mater. 9, 1900414 (2019). 33 Banik, A., Shenoy, U. S., Saha, S., Waghmare, U. V. & Biswas, K. High Power Factor and Enhanced Thermoelectric Performance of SnTe- AgInTe2: Synergistic Effect of Resonance Level and Valence Band Convergence. J. Am. Chem. Soc. 138, 13068- 13075 (2016). 34 Zhu, Y. et al. Synergistically optimizing carrier concentration and decreasing sound velocity in n- type AgInSe2 Thermoelectrics. Chem. Mater. 31, 8182- 8190 (2019). 35 Zhu, Y. et al. Physical insights on the low lattice thermal conductivity of AgInSe2. Mater. Today Phys. 19, 100428 (2021). 36 Qiu, P. et al. Intrinsically high thermoelectric performance in AgInSe2 n- type diamond- like compounds Adv. Sci. 5, 1700727 (2018). 37 Wrasse, E. O., Baierle, R. J., Fazzio, A. & Schmidt, T. M. First- principles study of group III impurity doped PbSe: Bulk and nanowire. Phys. Rev. B 87 (2013). 38 Wang, S. et al. Exploring the doping effects of Ag in p- type PbSe compounds with enhanced thermoelectric performance. J. Phys. D: Appl. Phys. 44, 475304 (2011). 39 Androulakis, J., Lee, Y., Todorov, I., Chung, D.- Y. & Kanatzidis, M. High- temperature thermoelectric properties of n- type PbSe doped with Ga, In, and Pb. Phys. Rev. B 83 (2011). 40 Wang, H., Pei, Y., LaLonde, A. D. & Snyder, G. J. Heavily doped p- type PbSe with high thermoelectric performance: an alternative for PbTe. Adv. Mater. 23, 1366- 1370 (2011). 41 Christensen, M. et al. Avoided crossing of rattler modes in thermoelectric materials. Nat. Mater. 7, 811- 815 (2008). 42 Wu, H. J. et al. Broad temperature plateau for thermoelectric figure of merit ZT>2 in phase- separated PbTe0.7S0.3. Nat. Commun. 5, 4515 (2014). 43 Xu, W., Liu, Y., Marcelli, A., Shang, P. P. & Liu, W. S. The complexity of thermoelectric materials: why we need powerful and brilliant synchrotron radiation sources? Mater. Today Phys. 6, 68- 82 (2018). 44 Liu, Y. et al. Synergistically Optimizing Electrical and Thermal Transport Properties of BiCuSeO via a Dual- Doping Approach. Adv. Energy Mater. 6, 1502423 (2016). 45 Hu, L. et al. Localized Symmetry Breaking for Tuning Thermal Expansion in
+
+<--- Page Split --->
+
+ScF3 Nanoscale Frameworks. J. Am. Chem. Soc. 140, 4477- 4480 (2018). 46 Keiber, T., Bridges, F. & Sales, B. C. Lead is not off center in PbTe: the importance of r- space phase information in extended X- ray absorption fine structure spectroscopy. Phys. Rev. Lett. 111 (2013). 47 Zhu, Y. C. et al. Lattice dynamics and thermal conductivity in \(\mathrm{Cu_2Zn_{1 - x}Co_xSnSe_4}\) . Inorg. Chem. 57, 6051- 6056 (2018). 48 Xu, W. et al. Nanoscale heterogeneity in thermoelectrics: the occurrence of phase separation in Fe- doped \(\mathrm{Ca_3Co_4O_9}\) . Phys. Chem. Chem. Phys. 18, 14580- 14587 (2016). 49 Blöchl, P. E. Projector augmented- wave method. Phys. Rev. B 50, 17953- 17979 (1994). 50 Kresse, G. & Furthmuller, J. Efficient iterative schemes for ab initio total- energy calculations using a plane- wave basis set. Phys. Rev. B 54, 11169 (1996). 51 Kresse, G. & Furthmuller, J. Efficiency of ab- initio total energy calculations for metals and semiconductors using a plane- wave basis set. Comput. Mat. Sci. 6, 15- 50 (1996). 52 Perdew, J. P. et al. Restoring the density- gradient expansion for exchange in solids and surfaces. Phys. Rev. Lett. 100, 136406 (2008). 53 Ravel, B., Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X- ray absorption spectroscopy using IFEFFIT. J. Synchrotron Rad. 12, 537- 541 (2005). 54 J.J. Rehr, R. C. A. Modern Theory of XAFS. Rev. Mod. Phys. 72, 621 (2000). 55 Rehr, J. J., Kas, J. J., Vila, F. D., Prange, M. P. & Jorissen, K. Parameter- free calculations of X- ray spectra with FEFF9. Phys. Chem. Chem. Phys. 12, 5503- 5513 (2010).
+
+<--- Page Split --->
+
+## Acknowledgements
+
+AcknowledgementsThe authors thank BL14B1 at Shanghai synchrotron radiation facility (SSRF) for the SR- XRD measurements. We thank BL01B1 at Spring- 8 for the XAFS experiments (Proposal Number: 2021B1109). This work was supported by National Natural Science Foundation of China (51772012, 52002042 and 52002011), National Key Research and Development Program of China (2018YFA0702100 and 2018YFB0703600), National Postdoctoral Program for Innovative Talents (BX20200028), the Beijing Natural Science Foundation (JQ18004), and 111 Project (B17002). L.- D.Z. appreciates the support of the high performance computing (HPC) resources at Beihang University, the National Science Fund for Distinguished Young Scholars (51925101), and center for High Pressure Science and Technology Advanced Research (HPSTAR) for SEM and TEM measurements.
+
+## Authors contributions
+
+Y.Z. and L.- D.Z. prepared the samples, carried out the experiments, analyzed the results and wrote the paper. T.H. and X.G. performed the microscopy experiments. D.Y.W. carried out the DFT calculations. Y.Z., L.H. and T.I. conducted the XAFS measurements and analyzed the data. S.Z., B.Q., H.S. and L.S. performed the SR- XRD experiments. All authors coedited the manuscript.
+
+## Competing interests
+
+The authors declare no competing interests.
+
+## Additional information
+
+Correspondence and requests for materials should be addressed to L.- D. Zhao.
+
+<--- Page Split --->
+
+
+Fig. 1 Multiple valence bands enable high \(ZT\) values in p-type PbSe. a Schmatic diagram of multi-bands (L, \(\Sigma\) , \(\Lambda\) ) involvement in transport. The Brillouin zone shows that the degeneracies at the L, \(\Sigma\) , and \(\Lambda\) points are 4, 12, and 8, respectively. b The activated third band \(\Lambda\) enables higher \(ZT\) values compared with the single-band and two-band PbSe-based materials.
+
+<--- Page Split --->
+
+
+Fig. 2 Crystal structure and band gap. a Schematic crystal structure of Pb0.98Na0.02Se - \(x\%\) AgInSe2 (LISS). b Powder XRD patterns of LISS. c Refined lattice constants of LISS. d Room-temperature infrared spectra for PbSe - \(x\%\) AgInSe2 and Pb0.98Na0.02Se - \(x\%\) AgInSe2.
+
+<--- Page Split --->
+
+
+Fig. 3 Electrical properties as a function of temperature for \(\mathrm{Pb_{0.98}Na_{0.02}Se - x\%}\) AgInSe2 (LISS) compounds. a Electrical conductivity. b Seebeck coefficient. c Power factor. d Weighted mobility. The hollow circles in d represent the weighted mobility of single-band and two-band PbSe-based materials.
+
+<--- Page Split --->
+
+
+Fig. 4 Pisarenko plot and Hall carrier mobility. a Pisarenko plot of Seebeck coefficients as a function of Hall carrier concentration \((n_{\mathrm{H}})\) for \(\mathrm{Pb_{0.98}Na_{0.02}Se - x\%}\) AgInSe2 (LISS). The solid black line is calculated assuming \(m^{*} = 0.44m_{\mathrm{e}}\) and the purple line represents the result assuming \(m^{*} = 0.81m_{\mathrm{e}}\) within the SPB model. The gray circles show the Pisarenko plot for Na-doped PbSe reported by Wang et al.38 b Hall carrier mobility \((\mu_{\mathrm{H}})\) versus Hall carrier concentration \((n_{\mathrm{H}})\) at 303K.
+
+<--- Page Split --->
+
+
+Fig. 5 Electronic band structure. a Electronic band structure of \(\mathrm{Pb_27Se_27}\) (blue) and \(\mathrm{Pb_{25}AgInSe_{27}}\) (red). b Electronic density of states (DOS) near the Fermi level for \(\mathrm{Pb_{27}Se_{27}}\) (black), \(\mathrm{Pb_{26}AgSe_{27}}\) (green), \(\mathrm{Pb_{26}InSe_{27}}\) (blue) and \(\mathrm{Pb_{25}AgInSe_{27}}\) (red), respectively. c Electronic band structure of \(\mathrm{Pb_{25}AgInSe_{27}}\) at \(300\mathrm{K}\) and \(873\mathrm{K}\) , respectively. d Temperature-dependent infrared spectra of \(\mathrm{PbSe - 2\%AgInSe_2}\) . e The experimental (red) and theoretical (blue) bandgap \((E_{\mathrm{g}})\) and the theoretical energy offset between VBM1 and VBM2 \((\Delta E_{1 - 2})\) and between VBM1 and VBM3 \((\Delta E_{1 - 3})\) as a function of temperature. f Temperature-dependent electronic DOS of \(\mathrm{Pb_{25}AgInSe_{27}}\) near the VBM.
+
+<--- Page Split --->
+
+
+Fig. 6 Thermal transport properties and figure-of-merit \(ZT\) as a function of temperature for \(\mathrm{Pb_{0.98}Na_{0.02}Se - x\%AgInSe_2}\) (LISS) compounds. a Total thermal conductivity. b Lattice thermal conductivity. Inset shows the room-temperature lattice thermal conductivities departure from the theoretical line calculated by the Callaway model. c The average sound velocity \(\left(\nu_{\mathrm{avg}}\right)\) versus lattice thermal conductivity \(\left(\kappa_{\mathrm{L}}\right)\) for LISS compounds at room temperature. d Temperature-dependent \(ZT\) for LISS samples.
+
+<--- Page Split --->
+
+
+Fig. 7 Microstructures and local structure analysis for high-performance LISS sample. a Low magnification of bright-field TEM image for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2.05\%\) AgInSe2 sample. b The enlarged TEM pattern presents the nanoscale precipitates remarked by the arrows. c High resolution TEM (HRTEM) picture of a selected nanoprecipitate. d The corresponding selected area electron diffraction (SAED) pattern with cubic structure along [111]. e, f High angle annular dark field (HAADF) patterns for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2.05\%\) AgInSe2. g Experimental XANES spectra of In \(K\) -edge for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe2 (red dots), and AgInSe2 (orange line), respectively. The blue line shows the theoretical XANES spectrum of In \(K\) -edge for In-doped PbSe assuming that In occupy the Pb site. The black line represents a linear combination fitting (LCF) result of In \(K\) -edge of \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe2 considering that the In \(K\) -edge of AgInSe2 and In-doped PbSe serves as standards. h Multiple scattering calculations of In \(K\) -edge XANES for In-doped PbSe with different atomic clusters. The inset shows the nearest-two shell of In atom when it occupies the Pb site in PbSe matrix. The \(E_0\) is the absorption edge energy of In \(K\) -edge of In foil.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+SupplementaryInformation.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d_det.mmd b/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..ff950693a729225730480583a89c05731f04e8e7
--- /dev/null
+++ b/preprint/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d/preprint__018ea56f56282342b1a9e7b0cea3a8dc2890bbe74f3ff129238a91951bc7905d_det.mmd
@@ -0,0 +1,240 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 883, 209]]<|/det|>
+# Multiple valence bands convergence and strong phonon scattering lead to high thermoelectric performance in p-type PbSe
+
+<|ref|>text<|/ref|><|det|>[[42, 230, 675, 740]]<|/det|>
+Yingcai Zhu Beihang University Dongyang Wang Beihang University Tao Hong Beihang University Lei Hu Tokyo Institute of Technology https://orcid.org/0000- 0002- 4647- 1604 Toshiaki Ina Japan Synchrotron Radiation Research Institute Shaoping Zhan Beihang University Bingchao Qin Beihang University Haonan Shi Beihang University Lizhong Su Beihang University Xiang Gao Center for High Pressure Science and Technology Advanced Research Li- Dong Zhao ( zhaolidong@buaa.edu.cn ) Beihang University https://orcid.org/0000- 0003- 1247- 4345
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 777, 101, 794]]<|/det|>
+## Article
+
+<|ref|>title<|/ref|><|det|>[[44, 814, 135, 832]]<|/det|>
+# Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 852, 300, 870]]<|/det|>
+Posted Date: April 26th, 2022
+
+<|ref|>text<|/ref|><|det|>[[44, 890, 473, 908]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 1575296/v1
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 44, 907, 87]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 123, 905, 167]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on July 19th, 2022. See the published version at https://doi.org/10.1038/s41467-022-31939-4.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[163, 93, 833, 114]]<|/det|>
+# Multiple valence bands convergence and strong phonon scattering
+
+<|ref|>title<|/ref|><|det|>[[216, 130, 779, 151]]<|/det|>
+# lead to high thermoelectric performance in p-type PbSe
+
+<|ref|>text<|/ref|><|det|>[[148, 157, 850, 196]]<|/det|>
+Yingcai Zhu,1 Dongyang Wang,1 Tao Hong,1 Lei Hu,2 Toshiaki Ina,3 Shaoping, Zhan,1 Bingchao Qin,1 Haonan Shi,1 Lizhong Su,1 Xiang Gao,4 Li- Dong Zhao1\\*
+
+<|ref|>text<|/ref|><|det|>[[147, 215, 853, 362]]<|/det|>
+1School of Materials Science and Engineering, Beihang University, Beijing 100191, China 2State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China 3Research and Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring- 8), Sayo, Hyogo, Japan 4Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing, 100094, China
+
+<|ref|>text<|/ref|><|det|>[[147, 393, 853, 803]]<|/det|>
+Thermoelectric generators enable the conversion of waste heat to electricity, which is an effective way to alleviate the global energy crisis. However, the inefficiency of thermoelectric materials is the main obstacle for realizing their widespread applications and thus developing materials with high thermoelectric performance is urgent. Here we show that multiple valence bands and strong phonon scattering can be realized simultaneously in p- type PbSe through the incorporation of AgInSe2. The multiple valleys enable large weighted mobility, indicating enhanced electrical properties. Local structure and microstructure analysis reveal that about 80 percent of Ag and In atoms form AgInSe2 as nano- scale precipitates, which result in strong phonon scattering and thus ultralow lattice thermal conductivity. Consequently, we achieve an exceptional \(ZT\) of \(\sim 2.1\) at 873 K in p- type PbSe. Our results demonstrate that a combination of band manipulation and microstructure engineering can be realized by tuning the composition. We expect our findings to be a general strategy for achieving high thermoelectric performance in bulk material, pushing the thermoelectric materials for realistic applications.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[146, 85, 855, 677]]<|/det|>
+The depletion of fossil fuels and the deteriorating environment motivate the human beings to find sustainable and clean energy solutions. Thermoelectric devices can be used in energy harvesting from waste heat or be utilized in refrigeration, which is favorable for raising energy efficiency, attracting widespread attention from around the world. The efficiency of thermoelectric devices is largely determined by the figure of merit \(ZT\) of their constituent thermoelectric materials, \(ZT = \frac{S^2\sigma T}{\kappa_e + \kappa_L}\) , where \(S\) represents the Seebeck coefficient, \(\sigma\) is the electrical conductivity, \(\kappa_e\) is the electrical contribution to the thermal conductivity, \(\kappa_L\) is the lattice thermal conductivity, and \(T\) is the absolute temperature, respectively. However, decoupling the interdependence between electrical and thermal transport properties is a crucial but challenging issue for improving the thermoelectric performance of materials. To achieve good electrical properties, various strategies such as band convergence \(^{1 - 4}\) , band sharpening \(^{5}\) , band alignment \(^{6}\) , carrier mobility optimization \(^{7}\) and resonant states introduction \(^{8}\) were adopted. On the other hand, materials with disordered or complex crystal structure \(^{9,10}\) , giant anharmonicity \(^{11,12}\) , and lone pair electrons \(^{13}\) often exhibit intrinsic low lattice thermal conductivity, which are promising candidates for thermoelectric applications. Moreover, the lattice thermal conductivity can be largely suppressed by microstructural engineering, including nano-scale precipitates \(^{14,15}\) , dislocations \(^{16,17}\) , grain boundaries \(^{18}\) , and all- scale hierarchical architectures \(^{19 - 21}\) . Therefore, a synergistic combination of electronic band modulation and microstructural engineering is expected to achieve advanced thermoelectric materials.
+
+<|ref|>text<|/ref|><|det|>[[147, 709, 852, 896]]<|/det|>
+PbTe has long been used for mid- temperature power generation, whereas the scarcity of element Te make it expensive for wide applications. PbSe is a perfect substitute for expensive PbTe due to the earth- abundant element Se. Hitherto, only limited studies show that the \(ZT\) of PbSe could reach \(1.7^{22 - 24}\) , motivating us to search strategies to improve the thermoelectric properties of PbSe. The weighted mobility \((\mu w = \mu (m^* /m_e)^{3 / 2})\) is a good descriptor for the inherent electrical performance of materials \(^{25}\) . Multiple degenerate electronic bands enable large density- of- states effective mass \(m^*\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 852, 275]]<|/det|>
+without obvious effect on the carrier mobility \((\mu)^{1}\) , facilitating the improvement of \(\mu \mathrm{w}\) . Indeed, the interplay of multiple bands enable large power factor or \(\mu \mathrm{w}\) and thus ultrahigh \(ZT^{26,27}\) . However, the two- band convergence is much difficult to realize due to the large energy offset between the valence band maximum (L) and the secondary valence band maximum \((\Sigma)\) in PbSe and to date only limited works can promote band convergence in it \(^{23,28,29}\) . It is more challenging to achieve multiple bands convergence in PbSe.
+
+<|ref|>text<|/ref|><|det|>[[147, 311, 853, 581]]<|/det|>
+The lattice thermal conductivity is another important parameter for the thermoelectric performance indicated by the quality factor \(B\) ( \(B \propto \mu \mathrm{w} / \kappa \mathrm{L}\) ). The introduction of materials with low lattice thermal conductivity in MTe ( \(M = \mathrm{Pb}\) , Ge) matrixes was proved to be an effective method to manipulate their thermal transport properties \(^{30,31}\) . For example, the appearance of nanodots in AgPb \(_m\) SbTe \(_{2 + m}\) (LAST) system is considered as the origin of their low lattice thermal conductivity and thus the enhanced thermoelectric performance \(^{30}\) . Interestingly, the electrical properties of materials can also be optimized in similar way, such as in PbTe- AgInTe \(_2\) (LIST) \(^{32}\) and SnTe- AgInTe \(_2\) \(^{33}\) . These enhanced performances motivate us to search strategies for optimizing the \(\mu \mathrm{w}\) and \(\kappa \mathrm{L}\) simultaneously.
+
+<|ref|>text<|/ref|><|det|>[[147, 616, 852, 914]]<|/det|>
+Beyond the two- band convergence between the L and \(\Sigma\) bands, we found that a third valence band \(\Lambda\) with a degeneracy \(N_{\mathrm{v}} = 8\) could be activated (Figure 1a) through the incorporation of AgInSe \(_2\) in the PbSe matrix doped with \(2\%\) Na (LISS). These three- band convergence tendency enables large weighted mobility. Additionally, local structure analysis by the x- ray absorption fine structure (XAFS) spectra indicates that more than \(80\%\) of Ag and In atoms form AgInSe \(_2\) in the system. Interestingly, AgInSe \(_2\) is also a good thermoelectric material with intrinsic ultralow lattice thermal conductivity \(^{34 - 36}\) . The tetragonal AgInSe \(_2\) is perfect inserted in the PbSe matrix as nano- scale precipitates revealed by the transmission electron microscopy (TEM), causing strong phonon scattering and hence resulting in ultralow lattice thermal conductivity. Therefore, a synergistic optimization of \(\mu \mathrm{w}\) and \(\kappa \mathrm{L}\) is realized. As a consequence, an
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[148, 88, 850, 136]]<|/det|>
+exceptional high \(ZT \sim 2.1\) is achieved at 873 K, which is much better than the single- band and two- band activated p- type PbSe- based materials28,29 (Figure 1b).
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 174, 215, 190]]<|/det|>
+## Results
+
+<|ref|>text<|/ref|><|det|>[[147, 200, 853, 415]]<|/det|>
+Crystal structure. The LISS compounds crystallize in cubic structure (Space group, \(Fm - 3m\) ), which is reflected by the x- ray diffraction (XRD) measurements that the XRD patterns can be indexed on the basis of cubic PbSe and no secondary phase is observed within the instrumental detection limit (Figure 2a, 2b). The diffraction peaks tend to shift to higher angles with increment of AgInSe2. Therefore, the lattice parameter \((a)\) slightly decreases with increasing AgInSe2 content (Figure 2c), which may be attributed to the smaller atomic radius of Ag, and In compared with that of Pb. This phenomenon also demonstrates that the AgInSe2 is incorporated in the Pb0.98Na0.02Se matrix.
+
+<|ref|>text<|/ref|><|det|>[[147, 449, 853, 746]]<|/det|>
+Electronic transport properties. The continuous decrease of the electrical conductivity with increasing temperature indicates a degenerate semiconducting property for LISS samples (Figure 3a). Additionally, the electrical conductivity is suppressed significantly after the introduction of AgInSe2. The electrical conductivity of Pb0.98Na0.02Se is as large as 3848 S/cm at room temperature, which decline to 774 S/cm for Pb0.98Na0.02Se- 2.15% AgInSe2 sample. To uncover this behavior, room temperature Hall measurements were performed. Obviously, the carrier concentration is reduced largely with increasing AgInSe2 (Figure S1), explaining the depressed electrical conductivity. The reduction of carrier concentration may be due to the formation of InPb defects. These InPb defects are shallow donors in PbSe37, which will counteract with holes.
+
+<|ref|>text<|/ref|><|det|>[[147, 784, 853, 914]]<|/det|>
+The Seebeck coefficient increases with elevated temperature for all samples and no saturate peak appears (Figure 2b), demonstrating that no obvious bipolar effect occur at high temperatures. The Seebeck coefficient is largely enhanced over the whole temperature range with the increment of AgInSe2. Typically, the Seebeck coefficient of Pb0.98Na0.02Se is only 19.2 μV/K at room temperature, whereas a much larger Seebeck
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 853, 275]]<|/det|>
+coefficient value of \(116\mu \mathrm{V / K}\) is achieved for \(\mathrm{Pb_{0.98}Na_{0.02}Se - 2.15\% AgInSe_2}\) sample. This dramatically promoted Seebeck coefficients will facilitate the enhancement of power factor. Indeed, the \(PF\) have an apparent improvement especially at the 300 - 600 K temperature range for all doped samples (Figure 3c). The room temperature \(PF\) value of \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) is only \(\sim 1.4\mu \mathrm{Wcm^{- 1}K^{- 2}}\) . In sharp contrast, the room temperature \(PF\) increases to \(\sim 11.1\mu \mathrm{Wcm^{- 1}K^{- 2}}\) when \(x = 2.1\) and this value is continuously improved to \(\sim 15.6\mu \mathrm{Wcm^{- 1}K^{- 2}}\) at 423 K (Figure 3c).
+
+<|ref|>text<|/ref|><|det|>[[147, 310, 853, 692]]<|/det|>
+To understand the nature of the improvement of Seebeck coefficient, the relationship of Seebeck coefficient as a function of carrier concentration (Pisarenko curve) was compared at room temperature (Figure 4a). Generally, the Seebeck coefficient increases with decreasing carrier concentration. However, the Seebeck coefficient is largely departure from the theoretical values estimated by the single parabolic band (SPB) model, which indicate that a complex electronic band should be involved in the electrical transport properties. Accordingly, the effective mass \((m^*)\) of LISS is largely increased from \(0.44m_{\mathrm{e}}\) to \(0.81m_{\mathrm{e}}\) with the introduction of \(\mathrm{AgInSe_2}\) (Figure 4a). In contrast, the effective mass of Na- doped PbSe is only \(\sim 0.28m_{\mathrm{e}}\) (Figure 4a). The Hall carrier mobility increases with doping and a maximum value of \(\sim 125\mathrm{cm}^2\mathrm{V}^{- 1}\mathrm{s}^{- 1}\) is obtained when \(\mathrm{x} = 2\) (Figure 4b), which is largely due to the depressed carrier concentration. Consequently, the weighted mobility \((\mu \mathrm{w})\) of LISS compounds is largely enhanced especially at the 300- 600K temperature range, which is higher than that of single- band and two- band PbSe- based materials (Figure 3d).
+
+<|ref|>text<|/ref|><|det|>[[147, 728, 853, 914]]<|/det|>
+DFT calculations were also conducted to understand the origin of the enhanced Seebeck coefficients. We observed significant change of the electronic band structure with the incorporation of \(\mathrm{AgInSe_2}\) in PbSe matrix (Figure 5a). The bandgap is enlarged upon doping, which will depress the bipolar effect and facilitate the enhancement of Seebeck coefficient. These calculations are well in accordance with our experimental results. The experimental bandgap is \(\sim 0.24\mathrm{eV}\) for the pristine PbSe, while the bandgap increases obviously with the incorporation of \(\mathrm{AgInSe_2}\) and a large bandgap \(\sim 0.33\mathrm{eV}\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 854, 500]]<|/det|>
+is achieved for the PbSe - \(2\%\) AgInSe \(_2\) sample (Figure 2d). Interestingly, the bandgap is further enlarged to \(\sim 0.38 \mathrm{eV}\) with Na doping (Figure 2d). In addition, the L band is flattened. The sharp peaks reflected in the density of states (DOS) for valence band also reveal the band flattening character (Figure 5b). Simultaneously, the \(\Sigma\) band is elevated and hence the energy offset \((\Delta E_{1 - 2})\) between L and \(\Sigma\) band is shortened. Surprisingly, a third valence band at the \(\Lambda\) point is activated and it remains at the same energy level compared with the \(\Sigma\) band (Figure 5a). These multiple valence bands enable large effective mass without significant affect the carrier mobility, which is the origin of enhanced Seebeck coefficient and the weighted mobility \((\mu \mathrm{w})\) . The electronic band structures of Ag and In doped PbSe were also calculated (Figure S2a, S2b). The Ag- doping and In- doping reflect p- type and n- type doping effect, respectively, which are consistent with previous experimental results \(^{38,39}\) . Additionally, In- doping has a more important effect on decreasing energy offset \((\Delta E_{1 - 2})\) compared with the Ag- doping (Figure S2c), while Ag- doping plays a major role in enlarging the bandgap (Figure S2d). Both Ag and In atoms play an important role in band manipulation.
+
+<|ref|>text<|/ref|><|det|>[[147, 534, 853, 914]]<|/det|>
+Using the lattice parameters extracted from the temperature- dependent synchrotron radiation x- ray diffraction (SR- XRD) patterns (Figure S3), we calculated the band structures as a function of temperature (Figure 5c, Figure S4). Clearly, the bandgap increases with rising temperature, which is also verified experimentally (Figure 5d). However, the theoretical bandgap is smaller than the experimental result (Figure 5e), which may be attribute to the neglect of the effect of thermal disorder on the bandgap in our calculations. Moreover, the energy offset \((\Delta E_{1 - 2})\) between L and \(\Sigma\) bands decreases with increasing temperature (Figure 5e). Interestingly, the energy offset \((\Delta E_{1 - 3})\) between L and \(\Lambda\) also shows a decline tendency with rising temperature and its value is even smaller than \(\Delta E_{1 - 2}\) in the whole temperature range (Figure 5e). The convergence tendency and the involvement of the third valence band is also reflected in the DOS corresponding to the valence band increases with increasing temperature (Figure 5f). This convergence behavior is experimentally verified via Hall measurements, in which a maximum Hall coefficient \((R_{\mathrm{H}})\) is observed (Figure S5a) and it is a sign of band
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 87, 852, 164]]<|/det|>
+convergence of the multi- valence bands \(^{20,23}\) . Consequently, the effective mass \((m^{*})\) of \(\mathrm{Pb_{0.98}Na_{0.02}Se - 2.05\%AgInSe_2}\) increases from \(0.73m_{\mathrm{e}}\) to \(2.16m_{\mathrm{e}}\) with rising temperature, which is much higher than the \(m^{*}\) of single Na- doped \(\mathrm{PbSe^{40}}\) (Figure S5b).
+
+<|ref|>text<|/ref|><|det|>[[146, 199, 852, 789]]<|/det|>
+Thermal transport properties and the figure- of- merit \(ZT\) . Thermal conductivity is another important property for thermoelectric performance. The total thermal conductivity \((\kappa_{\mathrm{tot}})\) decreases significantly with increasing \(\mathrm{AgInSe_2}\) (Figure 6a). The \(\kappa_{\mathrm{tot}}\) is a composite of lattice thermal conductivity \((\kappa_{\mathrm{L}})\) and electronic contributions to the thermal conductivity \((\kappa_{\mathrm{e}})\) . The \(\kappa_{\mathrm{e}}\) was calculated by the Wiedemann- Franz relation, \(\kappa_{\mathrm{e}} = L\sigma T\) , where \(L\) is estimated by SPB model (Figure S6a). The \(\kappa_{\mathrm{e}}\) decreases remarkably with doping due to largely depressed electrical conductivity (Figure S6b). Furthermore, the \(\kappa_{\mathrm{L}}\) is obtained by subtracting the electronic contribution from the total thermal conductivity (Figure 6b). Similarly, the \(\kappa_{\mathrm{L}}\) is largely suppressed with doping and the room- temperature \(\kappa_{\mathrm{L}}\) values are much lower than the theoretical estimation by the Callaway model (Figure 6b, inset). In addition, the \(\kappa_{\mathrm{L}}\) decreases with rising temperature and a clear departure from \(T^{- 1}\) relation is observed, demonstrating that the strong phonon scattering occurs. To further uncover the mechanism of the reduction of \(\kappa_{\mathrm{L}}\) , sound velocities were measured for all the samples at room temperature (Table S1). Interestingly, the average sound velocity \((v_{\mathrm{avg}})\) slightly increases after doping (Figure 6c). The deduced Grüneisen parameters of LISS are almost unchanged. The lattice thermal conductivity can be expressed as \(\kappa_{\mathrm{L}} = \frac{1}{3} Cv_{\mathrm{avg}}^{2}\tau\) based on the simple kinetic theory \(^{41}\) , where \(C\) is the specific heat, \(\tau\) is the phonon lifetime. Here, the \(v_{\mathrm{avg}}\) increases upon doping and thus the reduction of lattice thermal conductivity should be derived from the decrease of phonon lifetime. In another word, enhanced phonon scattering is the main origin of the largely suppressed lattice thermal conductivity.
+
+<|ref|>text<|/ref|><|det|>[[147, 821, 851, 895]]<|/det|>
+Thanks to the complex band structure behavior and strong phonon scattering with the introduction of \(\mathrm{AgInSe_2}\) , the figure- of- merit \(ZT\) is largely enhanced in the whole temperature range and a maximum \(ZT\) value of \(\sim 2.1\) is achieved at 873K for
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 852, 165]]<|/det|>
+\(\mathrm{Pb_{0.98}Na_{0.02}Se - 2.05\% AgInSe_2}\) sample (Figure 6d). Considering the correction of heat capacity, we can also obtain a large \(ZT\) of \(\sim 1.9\) at 873K (Figure 6d, Figure S7). The high thermoelectric properties of LISS samples are reproducible (Figure S8).
+
+<|ref|>text<|/ref|><|det|>[[147, 199, 853, 721]]<|/det|>
+Microstructure and local structure analysis. The TEM images of LISS sample display that abundant nanosized precipitates are embedded in PbSe matrix (Figure 7a, 7b). In addition, strip- like dislocations are also observed (circled regions in Figure 7a). Both nanoscale precipitates and multi- scale dislocations are effective phonon scattering centers. The annular dark- field (ADF) STEM image and the EDS elemental mappings exhibit obvious Ag- rich and In- rich patterns for the precipitates (Figure S9). Accordingly, the elemental distributions of Se and Na are relatively homogeneous in the entire area, whereas Pb- poor regions are observed within the precipitates (Figure S9). A more clearer microstructural features of the precipitate is revealed by performing HRTEM (Figure 7c). The corresponding SAED pattern indicate a main cubic structure along [111], whereas the precipitates shows a different crystal structure from the PbSe matrix as another series of diffraction spots are exhibited which can be indexed to AgInSe₂ (Figure 7d). The HAADF patterns show that the tetragonal AgInSe₂ is perfectly inserted in the cubic PbSe matrix as a nine- atom grid (Figure 7e). We can also observe lattice dislocation in the HAADF (Figure 7f). The lattice mismatch induced by precipitates and dislocations will introduce large strain fluctuations and thus enhance the phonon scattering \(^{42}\) . Therefore, the lattice thermal conductivity of LISS was largely reduced to its amorphous limit of 0.31 Wm⁻¹K⁻¹ at 873 K arising from the strong phonon scattering.
+
+<|ref|>text<|/ref|><|det|>[[147, 755, 853, 914]]<|/det|>
+Understanding the atomic occupation of doping elements in the lattice allow us elucidate their role on manipulating the thermal or electrical transport properties. The x- ray absorption fine structure (XAFS) spectroscopy is a powerful tool to investigate the local structure in materials \(^{43 - 48}\) . Here, we performed XAFS measurements for PbSe, AgInSe₂ and LISS, respectively. The x- ray absorption near- edge structure (XANES) of Se K- edge and Pb L₃- edge did not show any change after the introduction of AgInSe₂
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 853, 499]]<|/det|>
+in PbSe (Figure S10), demonstrating a steady PbSe cubic matrix, which is well consistent with the XRD patterns. There are four main features in the XANES of In \(K\) - edge of LISS (Figure 7g), in which 1, 3, 4 features can well reflected in the In \(K\) - edge of AgInSe \(_2\) , indicating that most of In atoms may form AgInSe \(_2\) in the system. Furthermore, we calculated the XANES spectra of In \(K\) - edge for the In- doped PbSe assuming that In occupy the Pb site, in which the peak B is well corresponding with the feature 2 of In \(K\) - edge of LISS. Moreover, after adding the second shell (twelve Pb atoms) as shown by the 19- atoms cluster calculation (Figure 7h), the feature B is well reflected and the calculation is almost convergent. Therefore, the origin of feature 2 is mainly arising from the multiple scattering of the photoelectrons by the second shell of Pb atoms in the PbSe matrix. The linear combination fitting (LCF) was used to evaluate the atomic occupied ratio of In atoms in each standards (Figure 7g). Similar analysis was performed for the XANES of Ag \(K\) - edge (Figure S11). The LCF fitting results indicate that more than \(80\%\) of Ag and In atoms form AgInSe \(_2\) in the system (Table S2), causing strong phonon scattering.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 535, 242, 551]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[147, 560, 853, 914]]<|/det|>
+In summary, a combined effect of three activated valence bands and strong phonon scattering is realized via introducing AgInSe \(_2\) in Pb \(_{0.98}\) Na \(_{0.02}\) Se matrix. These multiple valence bands convergence enable the enhancement of thermoelectric power factor at low temperature region and maintain at a high level at elevated temperature. Interestingly, local structure studies by XANES reveal that most of Ag or In atoms form AgInSe \(_2\) secondary phase. The numerous nanoscale AgInSe \(_2\) precipitates and multiscale dislocations observed in the TEM will cause strong phonon scattering. Therefore, the lattice thermal conductivity is largely depressed. As a consequence, a distinguished figure- of- merit \(ZT\) of \(\sim 2.1\) is achieved at 873K, which is among the best bulk thermoelectric materials. This work proves that multiple valence bands could be activated in p- type PbSe and highlights the strong phonon scattering effect through the introduction of secondary phase with ultralow thermal conductivity, which guide a new route to achieve excellent thermoelectric performance in bulk materials. The
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[148, 89, 851, 164]]<|/det|>
+quantitative atomic occupation of doping elements provides a new perspective to understand their role on manipulating transport properties. We expect more advanced thermoelectric materials can be achieved by employing this strategy.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 201, 226, 217]]<|/det|>
+## Methods
+
+<|ref|>text<|/ref|><|det|>[[147, 228, 852, 442]]<|/det|>
+Synthesis. High- purity starting materials, Pb (99.999%), Se (99.999%), Na (99.9%), Ag (99.99%), In (99.99 %) were weighted in stoichiometric ratio (Pb0.98Na0.02Se - x% AgInSe2) and loaded in carbon coating silica tubes under an N2- filled glove box. The silica tubes were sealed under vacuum and then slowly heated to 1423 K in 24 h, soaked at this temperature for 10 h and followed by furnace cooling down to room temperature. The obtained ingots were grounded into powders and then densified at 873 K for 6 minutes with a pressure of 50 MPa using spark plasma sintering (SPS- 211Lx). Finally, highly dense bulk samples ( \(>97\%\) of theoretical density) were obtained.
+
+<|ref|>text<|/ref|><|det|>[[147, 450, 852, 737]]<|/det|>
+Thermoelectric property measurements. The bulk samples were cut into rectangular solids ( \(3 \times 3 \times 10 \mathrm{mm}^3\) ) and square pieces ( \(10 \times 10 \times 1 \mathrm{mm}^3\) ) for electrical and thermal transport properties measurements, respectively. The Seebeck coefficients and electrical conductivities were measured using the Ulvac Riko ZEM- 3 instrument. We calculated the thermal conductivity using the equation of \(\kappa_{tot} = D \cdot C_p \cdot \rho\) , where the thermal diffusivity \((D)\) was determined using a laser flash method by the Netzsch LFA- 457 facility, the heat capacity \((C_p)\) was estimated using both the Dulong- Petit law and an empirical equation \((C_p / k_B \mathrm{atom}^{- 1} = 3.07 + 4.7 \times 10^{- 4} (T / \mathrm{K} - 300))^{29}\) , and the density is calculated by the dimensions and mass of the samples. The combined uncertainty of all measurements for determining the \(ZT\) is less than \(20\%\) .
+
+<|ref|>text<|/ref|><|det|>[[147, 747, 852, 905]]<|/det|>
+Characterizations. Room- temperature powder x- ray diffraction measurements were conducted using a D/MAX 2500 PC system with Cu \(\mathrm{K}_{\alpha}\) radiation. High- temperature synchrotron radiation x- ray diffraction (SR- XRD) patterns were performed for \(\mathrm{Pb}_{0.98}\mathrm{Na}_{0.02}\mathrm{Se} - 2\% \mathrm{AgInSe}_2\) at the BL14B1 beamline of Shanghai synchrotron radiation facility (SSRF). The wavelength of the x- ray is \(0.6887 \mathrm{\AA}\) . The sample was heated from \(300 \mathrm{K}\) to \(875 \mathrm{K}\) at a rate of \(1.5 \mathrm{K min}^{- 1}\) . The bandgap was measured using the Shimadezu
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 852, 247]]<|/det|>
+Model UV- 3600 Plus instrument and was estimated by the Kubelka- Munk equation. The Hall coefficient \((R_{\mathrm{H}})\) was conducted by the Van der Pauw method using the Lake Shore 8400 Series. Scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) were performed using a JEOL ARM200F equipped with cold field emission gun and ASCOR probe corrector. More details can be found in the Supporting Information.
+
+<|ref|>text<|/ref|><|det|>[[147, 255, 853, 636]]<|/det|>
+First- principles calculations. Density functional theory (DFT) calculations were performed using the projector- augmented wave (PAW) method49, as implemented in the Vienna Ab initio Simulation Package (VASP)50,51. We utilized the revised Perdew- Burke- Ernzerhof (PBE)52 generalized gradient approximation (GGA) to estimate the exchange- correlation interactions. A cutoff energy was set to 450 eV for the plane- wave expansion of the electron density and the Monkhorst- Pack \(k\) - point sampling 0.1 Å- 1 was used within all the calculations. The atomic positions were fully relaxed when the maximum residual ionic force and total energy difference are converged within 0.01 eV Å- 1 and 10- 7 eV, respectively. Several 3×3×3 supercells were constructed (Pb27Se27, Pb26AgSe27, Pb26InSe27, Pb25AgInSe27), avoiding the defect- defect interaction. The occupations of Ag or/and In atoms in the supercells were relaxed in our calculations. The temperature- dependent electronic band structures were performed using the experimental lattice parameters at elevated temperatures deriving from the SR- XRD data.
+
+<|ref|>text<|/ref|><|det|>[[147, 644, 853, 916]]<|/det|>
+X- ray absorption fine structure (XAFS) spectroscopy measurements. The XAFS experiments were performed at BL01B1 beamline of Spring- 8 in Japan. The electron energy of the storage ring is 8.0 GeV with a top- up filling of 99.5 mA accumulated current during the experiment. The Si (311) double- crystal monochromator was used for tuning the monochromatic beam. We measured the XAFS of Ag \(K\) - edge and In \(K\) - edge for AgInSe2 in transmission mode. The XAFS measurements of Se \(K\) - edge, and Pb \(L_{3}\) - edge for PbSe and Pb0.98Na0.02Se - 2% AgInSe2 were conducted in transmission mode, while the measurements of Ag \(K\) - edge and In \(K\) - edge for Pb0.98Na0.02Se - 2% AgInSe2 were performed in fluorescence mode using 19- element Ge solid- state detector (SSD). All experimental XAFS spectra were preprocessed using the IFFEFIT package53.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 853, 470]]<|/det|>
+XAFS calculation and analysis. The x- ray absorption near edge structure (XANES) calculations of Ag \(K\) - edge for Ag- doped PbSe and In \(K\) - edge for In- doped PbSe were performed based on the full multiple scattering (FMS) theory using FEFF9 program \(^{54,55}\) . We use self- consistent field (SCF) method to estimate the atomic scattering potential. To investigate the doping site of Ag or In in PbSe, we simply replace the central Pb absorber with Ag or In atom while maintaining the coordinates. To achieve good convergence, the cluster radius for SCF and FMS was fixed as 8 and 10 Angstrom, respectively. Linear combination fittings (LCF) of In \(K\) - edge for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe \(_2\) was performed using the Athena software assuming that the XANES of In \(K\) - edge of AgInSe \(_2\) and In- doped PbSe as the standards. A similar LCF analysis was applied for the XANES of Ag \(K\) - edge of \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe \(_2\) . Since we cannot ensure that the Ag or In atoms totally occupy the Pb site in PbSe matrix without formation of impurity phases, we thus used the calculated XANES as one of standards in the LCF analysis.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 507, 245, 523]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[145, 529, 852, 902]]<|/det|>
+1 Pei, Y. et al. Convergence of electronic bands for high performance bulk thermoelectrics. Nature 473, 66- 69 (2011). 2 Tang, Y. et al. Convergence of multi- valley bands as the electronic origin of high thermoelectric performance in CoSb \(_3\) skutterudites. Nat. Mater. 14, 1223- 1228 (2015). 3 Hu, L. et al. High thermoelectric performance enabled by convergence of nested conduction bands in \(\mathrm{Pb_7Bi_4Se_{13}}\) with low thermal conductivity. Nat. Commun. 12, 4793 (2021). 4 Chang, C. et al. 3D charge and 2D phonon transports leading to high out- of- plane zT in n- type SnSe crystals. Science 360, 778- 783 (2018). 5 Xiao, Y. et al. Band Sharpening and Band Alignment Enable High Quality Factor to Enhance Thermoelectric Performance in n- Type PbS. J. Am. Chem. Soc. 142, 4051- 4060 (2020). 6 Zhao, L.- D., Dravid, V. P. & Kanatzidis, M. G. The panoscopic approach to high performance thermoelectrics. Energy Environ. Sci. 7, 251- 268 (2014). 7 Qin, B. C. & Zhao, L. D. Carriers: the less, the faster. Mat. Lab 1, 220004 (2022). 8 Zhang, Q. et al. Enhancement of Thermoelectric Figure- of- Merit by Resonant States of Aluminium Doping in Lead Selenide. Energy Environ. Sci. 5(1), 5246- 5251 (2012). 9 Snyder, G. J. & Toberer, E. S. Complex thermoelectric materials. Nat. Mater. 7,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 90, 852, 902]]<|/det|>
+105- 114 (2008).10 Liu, H. et al. Copper ion liquid- like thermoelectrics. Nat. Mater. 11, 422- 425 (2012).11 Zhao, L. D. et al. Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals. Nature 508, 373- 377 (2014).12 Delaire, O. et al. Giant anharmonic phonon scattering in PbTe. Nat. Mater. 10, 614- 619 (2011).13 Skoug, E. J. & Morelli, D. T. Role of Lone- Pair Electrons in Producing Minimum Thermal Conductivity in Nitrogen- Group Chalcogenide Compounds. Phys. Rev. Lett. 107, 235901 (2011).14 Pei, Y., Lensch- Falk, J., Toberer, E. S., Medlin, D. L. & Snyder, G. J. High thermoelectric performance in PbTe due to large nanoscale \(\mathrm{Ag_2Te}\) precipitates and La doping. Adv. Funct. Mater. 21, 241- 249 (2011).15 Hong, T. et al. Band convergence and nanostructure modulations lead to high thermoelectric performance in \(\mathrm{SnPb_{0.04}Te - y\%AgSbTe_2}\) . Mater. Today Phys. 21, 100505 (2021).16 Kim, S. I. et al. Dense dislocation arrays embedded in grain boundaries for high- performance bulk thermoelectrics. Science 348, 109- 114 (2015).17 Chen, Z. et al. Lattice Dislocations Enhancing Thermoelectric PbTe in Addition to Band Convergence. Adv. Mater. 29 (2017).18 Meng, X. F. et al. Grain Boundary Engineering for Achieving High Thermoelectric Performance in n- Type Skutterudites. Adv. Energy Mater. 7, 1602582 (2017).19 Biswas, K. et al. High- performance bulk thermoelectrics with all- scale hierarchical architectures. Nature 489, 414- 418 (2012).20 Zhao, L. D. et al. All- scale hierarchical thermoelectrics: MgTe in PbTe facilitates valence band convergence and suppresses bipolar thermal transport for high performance. Energy Environ. Sci. 6, 3346 (2013).21 Wang, S. et al. Hierarchical structures lead to high thermoelectric performance in \(\mathrm{Cu_{m + n}Pb_{100}Sb_{m}Te_{100}Se_{2m}}\) (CLAST). Energy Environ. Sci. 14, 451- 461 (2021).22 Jiang, B. et al. Entropy engineering promotes thermoelectric performance in p- type chalcogenides. Nat. Commun. 12, 3234 (2021).23 Tan, G. et al. All- Scale Hierarchically Structured p- Type PbSe Alloys with High Thermoelectric Performance Enabled by Improved Band Degeneracy. J. Am. Chem. Soc. 141, 4480- 4486 (2019).24 Jiang, B. et al. High- entropy- stabilized chalcogenides with high thermoelectric performance. Science 371, 830- 834 (2021).25 Snyder, G. J. et al. Weighted Mobility. Adv. Mater. 32, e2001537 (2020).26 He, W. et al. High thermoelectric performance in low- cost \(\mathrm{SnS_{0.91}Se_{0.09}}\) crystals. Science 365, 1418- 1424 (2019).27 Qin, B. et al. Power generation and thermoelectric cooling enabled by momentum and energy multiband alignments. Science 373, 556- 561 (2021).28 Hodges, J. M. et al. Chemical Insights into PbSe- x%HgSe: High Power Factor and Improved Thermoelectric Performance by Alloying with Discordant Atoms.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 78, 853, 900]]<|/det|>
+29 Wang, H., Gibbs, Z. M., Takagiwa, Y. & Snyder, G. J. Tuning bands of PbSe for better thermoelectric efficiency. Energy Environ. Sci. 7, 804- 811 (2014). 30 Hsu, K. F., Loo, S., Guo, F., Chen, W., Dyck, J. S., Uher, C., Hogan, T., Polychroniadis, E. K., Kanatzidis, M. G. Cubic AgPbmSbTe2+m Bulk Thermoelectric Materials with High Figure of Merit. Science, 818- 821 (2004). 31 Plachkova, S. K. Thermoelectric Figure of Merit of the System (GeTe)1-x- (AgSbTe2)x. Phys. Stat. Sol. (a) 83, 349 (1984). 32 Xiao, Y. et al. Amphoteric Indium Enables Carrier Engineering to Enhance the Power Factor and Thermoelectric Performance in n- Type AgnPb100 InnTe 100+2n (LIST). Adv. Energy Mater. 9, 1900414 (2019). 33 Banik, A., Shenoy, U. S., Saha, S., Waghmare, U. V. & Biswas, K. High Power Factor and Enhanced Thermoelectric Performance of SnTe- AgInTe2: Synergistic Effect of Resonance Level and Valence Band Convergence. J. Am. Chem. Soc. 138, 13068- 13075 (2016). 34 Zhu, Y. et al. Synergistically optimizing carrier concentration and decreasing sound velocity in n- type AgInSe2 Thermoelectrics. Chem. Mater. 31, 8182- 8190 (2019). 35 Zhu, Y. et al. Physical insights on the low lattice thermal conductivity of AgInSe2. Mater. Today Phys. 19, 100428 (2021). 36 Qiu, P. et al. Intrinsically high thermoelectric performance in AgInSe2 n- type diamond- like compounds Adv. Sci. 5, 1700727 (2018). 37 Wrasse, E. O., Baierle, R. J., Fazzio, A. & Schmidt, T. M. First- principles study of group III impurity doped PbSe: Bulk and nanowire. Phys. Rev. B 87 (2013). 38 Wang, S. et al. Exploring the doping effects of Ag in p- type PbSe compounds with enhanced thermoelectric performance. J. Phys. D: Appl. Phys. 44, 475304 (2011). 39 Androulakis, J., Lee, Y., Todorov, I., Chung, D.- Y. & Kanatzidis, M. High- temperature thermoelectric properties of n- type PbSe doped with Ga, In, and Pb. Phys. Rev. B 83 (2011). 40 Wang, H., Pei, Y., LaLonde, A. D. & Snyder, G. J. Heavily doped p- type PbSe with high thermoelectric performance: an alternative for PbTe. Adv. Mater. 23, 1366- 1370 (2011). 41 Christensen, M. et al. Avoided crossing of rattler modes in thermoelectric materials. Nat. Mater. 7, 811- 815 (2008). 42 Wu, H. J. et al. Broad temperature plateau for thermoelectric figure of merit ZT>2 in phase- separated PbTe0.7S0.3. Nat. Commun. 5, 4515 (2014). 43 Xu, W., Liu, Y., Marcelli, A., Shang, P. P. & Liu, W. S. The complexity of thermoelectric materials: why we need powerful and brilliant synchrotron radiation sources? Mater. Today Phys. 6, 68- 82 (2018). 44 Liu, Y. et al. Synergistically Optimizing Electrical and Thermal Transport Properties of BiCuSeO via a Dual- Doping Approach. Adv. Energy Mater. 6, 1502423 (2016). 45 Hu, L. et al. Localized Symmetry Breaking for Tuning Thermal Expansion in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 83, 852, 551]]<|/det|>
+ScF3 Nanoscale Frameworks. J. Am. Chem. Soc. 140, 4477- 4480 (2018). 46 Keiber, T., Bridges, F. & Sales, B. C. Lead is not off center in PbTe: the importance of r- space phase information in extended X- ray absorption fine structure spectroscopy. Phys. Rev. Lett. 111 (2013). 47 Zhu, Y. C. et al. Lattice dynamics and thermal conductivity in \(\mathrm{Cu_2Zn_{1 - x}Co_xSnSe_4}\) . Inorg. Chem. 57, 6051- 6056 (2018). 48 Xu, W. et al. Nanoscale heterogeneity in thermoelectrics: the occurrence of phase separation in Fe- doped \(\mathrm{Ca_3Co_4O_9}\) . Phys. Chem. Chem. Phys. 18, 14580- 14587 (2016). 49 Blöchl, P. E. Projector augmented- wave method. Phys. Rev. B 50, 17953- 17979 (1994). 50 Kresse, G. & Furthmuller, J. Efficient iterative schemes for ab initio total- energy calculations using a plane- wave basis set. Phys. Rev. B 54, 11169 (1996). 51 Kresse, G. & Furthmuller, J. Efficiency of ab- initio total energy calculations for metals and semiconductors using a plane- wave basis set. Comput. Mat. Sci. 6, 15- 50 (1996). 52 Perdew, J. P. et al. Restoring the density- gradient expansion for exchange in solids and surfaces. Phys. Rev. Lett. 100, 136406 (2008). 53 Ravel, B., Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X- ray absorption spectroscopy using IFEFFIT. J. Synchrotron Rad. 12, 537- 541 (2005). 54 J.J. Rehr, R. C. A. Modern Theory of XAFS. Rev. Mod. Phys. 72, 621 (2000). 55 Rehr, J. J., Kas, J. J., Vila, F. D., Prange, M. P. & Jorissen, K. Parameter- free calculations of X- ray spectra with FEFF9. Phys. Chem. Chem. Phys. 12, 5503- 5513 (2010).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[149, 91, 318, 107]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[147, 117, 853, 412]]<|/det|>
+AcknowledgementsThe authors thank BL14B1 at Shanghai synchrotron radiation facility (SSRF) for the SR- XRD measurements. We thank BL01B1 at Spring- 8 for the XAFS experiments (Proposal Number: 2021B1109). This work was supported by National Natural Science Foundation of China (51772012, 52002042 and 52002011), National Key Research and Development Program of China (2018YFA0702100 and 2018YFB0703600), National Postdoctoral Program for Innovative Talents (BX20200028), the Beijing Natural Science Foundation (JQ18004), and 111 Project (B17002). L.- D.Z. appreciates the support of the high performance computing (HPC) resources at Beihang University, the National Science Fund for Distinguished Young Scholars (51925101), and center for High Pressure Science and Technology Advanced Research (HPSTAR) for SEM and TEM measurements.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 450, 343, 467]]<|/det|>
+## Authors contributions
+
+<|ref|>text<|/ref|><|det|>[[147, 477, 852, 608]]<|/det|>
+Y.Z. and L.- D.Z. prepared the samples, carried out the experiments, analyzed the results and wrote the paper. T.H. and X.G. performed the microscopy experiments. D.Y.W. carried out the DFT calculations. Y.Z., L.H. and T.I. conducted the XAFS measurements and analyzed the data. S.Z., B.Q., H.S. and L.S. performed the SR- XRD experiments. All authors coedited the manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 647, 323, 664]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[149, 674, 503, 691]]<|/det|>
+The authors declare no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 729, 351, 745]]<|/det|>
+## Additional information
+
+<|ref|>text<|/ref|><|det|>[[147, 756, 782, 774]]<|/det|>
+Correspondence and requests for materials should be addressed to L.- D. Zhao.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[150, 88, 841, 333]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 344, 850, 436]]<|/det|>
+Fig. 1 Multiple valence bands enable high \(ZT\) values in p-type PbSe. a Schmatic diagram of multi-bands (L, \(\Sigma\) , \(\Lambda\) ) involvement in transport. The Brillouin zone shows that the degeneracies at the L, \(\Sigma\) , and \(\Lambda\) points are 4, 12, and 8, respectively. b The activated third band \(\Lambda\) enables higher \(ZT\) values compared with the single-band and two-band PbSe-based materials.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[155, 95, 844, 515]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 530, 852, 603]]<|/det|>
+Fig. 2 Crystal structure and band gap. a Schematic crystal structure of Pb0.98Na0.02Se - \(x\%\) AgInSe2 (LISS). b Powder XRD patterns of LISS. c Refined lattice constants of LISS. d Room-temperature infrared spectra for PbSe - \(x\%\) AgInSe2 and Pb0.98Na0.02Se - \(x\%\) AgInSe2.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[150, 90, 844, 500]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 511, 851, 585]]<|/det|>
+Fig. 3 Electrical properties as a function of temperature for \(\mathrm{Pb_{0.98}Na_{0.02}Se - x\%}\) AgInSe2 (LISS) compounds. a Electrical conductivity. b Seebeck coefficient. c Power factor. d Weighted mobility. The hollow circles in d represent the weighted mobility of single-band and two-band PbSe-based materials.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[150, 90, 847, 300]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 308, 850, 418]]<|/det|>
+Fig. 4 Pisarenko plot and Hall carrier mobility. a Pisarenko plot of Seebeck coefficients as a function of Hall carrier concentration \((n_{\mathrm{H}})\) for \(\mathrm{Pb_{0.98}Na_{0.02}Se - x\%}\) AgInSe2 (LISS). The solid black line is calculated assuming \(m^{*} = 0.44m_{\mathrm{e}}\) and the purple line represents the result assuming \(m^{*} = 0.81m_{\mathrm{e}}\) within the SPB model. The gray circles show the Pisarenko plot for Na-doped PbSe reported by Wang et al.38 b Hall carrier mobility \((\mu_{\mathrm{H}})\) versus Hall carrier concentration \((n_{\mathrm{H}})\) at 303K.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[171, 88, 822, 670]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 678, 850, 844]]<|/det|>
+Fig. 5 Electronic band structure. a Electronic band structure of \(\mathrm{Pb_27Se_27}\) (blue) and \(\mathrm{Pb_{25}AgInSe_{27}}\) (red). b Electronic density of states (DOS) near the Fermi level for \(\mathrm{Pb_{27}Se_{27}}\) (black), \(\mathrm{Pb_{26}AgSe_{27}}\) (green), \(\mathrm{Pb_{26}InSe_{27}}\) (blue) and \(\mathrm{Pb_{25}AgInSe_{27}}\) (red), respectively. c Electronic band structure of \(\mathrm{Pb_{25}AgInSe_{27}}\) at \(300\mathrm{K}\) and \(873\mathrm{K}\) , respectively. d Temperature-dependent infrared spectra of \(\mathrm{PbSe - 2\%AgInSe_2}\) . e The experimental (red) and theoretical (blue) bandgap \((E_{\mathrm{g}})\) and the theoretical energy offset between VBM1 and VBM2 \((\Delta E_{1 - 2})\) and between VBM1 and VBM3 \((\Delta E_{1 - 3})\) as a function of temperature. f Temperature-dependent electronic DOS of \(\mathrm{Pb_{25}AgInSe_{27}}\) near the VBM.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[152, 88, 840, 500]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 510, 851, 621]]<|/det|>
+Fig. 6 Thermal transport properties and figure-of-merit \(ZT\) as a function of temperature for \(\mathrm{Pb_{0.98}Na_{0.02}Se - x\%AgInSe_2}\) (LISS) compounds. a Total thermal conductivity. b Lattice thermal conductivity. Inset shows the room-temperature lattice thermal conductivities departure from the theoretical line calculated by the Callaway model. c The average sound velocity \(\left(\nu_{\mathrm{avg}}\right)\) versus lattice thermal conductivity \(\left(\kappa_{\mathrm{L}}\right)\) for LISS compounds at room temperature. d Temperature-dependent \(ZT\) for LISS samples.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[149, 84, 848, 585]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 587, 850, 864]]<|/det|>
+Fig. 7 Microstructures and local structure analysis for high-performance LISS sample. a Low magnification of bright-field TEM image for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2.05\%\) AgInSe2 sample. b The enlarged TEM pattern presents the nanoscale precipitates remarked by the arrows. c High resolution TEM (HRTEM) picture of a selected nanoprecipitate. d The corresponding selected area electron diffraction (SAED) pattern with cubic structure along [111]. e, f High angle annular dark field (HAADF) patterns for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2.05\%\) AgInSe2. g Experimental XANES spectra of In \(K\) -edge for \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe2 (red dots), and AgInSe2 (orange line), respectively. The blue line shows the theoretical XANES spectrum of In \(K\) -edge for In-doped PbSe assuming that In occupy the Pb site. The black line represents a linear combination fitting (LCF) result of In \(K\) -edge of \(\mathrm{Pb_{0.98}Na_{0.02}Se}\) - \(2\%\) AgInSe2 considering that the In \(K\) -edge of AgInSe2 and In-doped PbSe serves as standards. h Multiple scattering calculations of In \(K\) -edge XANES for In-doped PbSe with different atomic clusters. The inset shows the nearest-two shell of In atom when it occupies the Pb site in PbSe matrix. The \(E_0\) is the absorption edge energy of In \(K\) -edge of In foil.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 131, 366, 150]]<|/det|>
+SupplementaryInformation.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/images_list.json b/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..48ab997191b4c9706396e94fcda135023730f11b
--- /dev/null
+++ b/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/images_list.json
@@ -0,0 +1,100 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. MR-EILLS model. MR-EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR-EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A-C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) in different populations, and larger point means the larger value of \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) . As the pleiotropic effect larger, the \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) is larger, thus the first part of MR-EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) and \\(\\hat{\\theta}_{p^{\\prime}}^{(\\ell)}\\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR-EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \\(\\hat{\\theta}_{p^{\\prime}}^{(\\ell)}\\) and \\(\\epsilon_{j}^{(\\ell)}\\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \\(\\sum_{n\\in \\mathbb{J}}\\hat{\\epsilon}_{j}^{(\\ell)}| + \\sum_{p\\in \\mathbb{P}}\\sum_{n\\in \\mathbb{J}}\\hat{\\theta}_{p^{\\prime}}^{(\\ell)}\\epsilon_{j}^{(\\ell)}|\\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \\(\\lambda\\) . The third part of MR-EILLS model is removing the invalid IVs by \\(\\lambda\\) .",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 24
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. MR-EILLS model. MR-EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR-EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A-C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) in different populations, and larger point means the larger value of \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) . As the pleiotropic effect larger, the \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) is larger, thus the first part of MR-EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \\(\\hat{\\epsilon}_{j}^{(\\ell)}\\) and \\(\\hat{\\theta}_{p^{\\prime}}^{(\\ell)}\\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR-EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \\(\\hat{\\theta}_{p^{\\prime}}^{(\\ell)}\\) and \\(\\epsilon_{j}^{(\\ell)}\\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \\(\\sum_{n\\in \\mathbb{J}}\\hat{\\epsilon}_{j}^{(\\ell)}| + \\sum_{p\\in \\mathbb{P}}\\sum_{n\\in \\mathbb{J}}\\hat{\\theta}_{p^{\\prime}}^{(\\ell)}\\epsilon_{j}^{(\\ell)}|\\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \\(\\lambda\\) . The third part of MR-EILLS model is removing the invalid IVs by \\(\\lambda\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 50,
+ 303,
+ 530,
+ 530
+ ]
+ ],
+ "page_idx": 24
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 45,
+ 949,
+ 352
+ ]
+ ],
+ "page_idx": 24
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 44,
+ 45,
+ 866,
+ 789
+ ]
+ ],
+ "page_idx": 25
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 44,
+ 45,
+ 870,
+ 789
+ ]
+ ],
+ "page_idx": 26
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5",
+ "footnote": [],
+ "bbox": [
+ [
+ 44,
+ 48,
+ 950,
+ 280
+ ]
+ ],
+ "page_idx": 27
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6",
+ "footnote": [],
+ "bbox": [
+ [
+ 45,
+ 406,
+ 950,
+ 742
+ ]
+ ],
+ "page_idx": 28
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10.mmd b/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..c92ca235703e88d240523a622f6b1517aaf85850
--- /dev/null
+++ b/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10.mmd
@@ -0,0 +1,375 @@
+
+# Invariance-based Mendelian Randomization Method Integrating Multiple Heterogeneous GWAS Summary Datasets
+
+Xiaohua Zhou
+
+azhou@bicmr.pku.edu.cn
+
+Beijing International Center for Mathematical Research, Peking University Lei Hou
+
+Peking University
+
+Hao Chen Institute for Medical Dataology, Cheeloo College of Medicine, Shandong University
+
+## Article
+
+Keywords: univariate mendelian randomization, multivariate mendelian randomization, GWAS summary datasets, heterogeneous populations, multiple ancestries
+
+Posted Date: December 17th, 2024
+
+DOI: https://doi.org/10.21203/rs.3.rs- 5602368/v1
+
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on August 18th, 2025. See the published version at https://doi.org/10.1038/s41467- 025- 62823- 6.
+
+<--- Page Split --->
+
+# Invariance-based Mendelian Randomization Method Integrating Multiple Heterogeneous GWAS Summary Datasets
+
+3 Lei Hou \(^{1}\) , Hao Chen \(^{4}\) , Xiao- Hua Zhou \(^{1,2,3*}\)
+
+# 4 Author affiliations:
+
+5 1. Beijing International Center for Mathematical Research, Peking University, 6 Beijing, P.R.China, 100871 7 2. Department of Biostatistics, Peking University, Beijing, P.R.China, 100871 8 3. Chongqing Big Data Research Institute, Peking University, Chongqing, P.R.China, 9 401333 10 4. Department of biostatistics, School of Public Health, Cheeloo College of Medicine, 11 Shandong University, Shandong, Beijing, P.R.China, 250000
+
+# \*Corresponding author:
+
+14 Xiao- Hua Zhou, 15 E- mail: azhou@bicmr.pku.edu.cn, 16 Telephone: +86 18910208518, 17 Address: Peking University, No.5 Yiheyuan Road Haidian District, Beijing, P.R.China
+
+<--- Page Split --->
+
+## Abstract
+
+Various geographical landscapes, diverse lifestyles and genetic structures may lead the heterogeneity among the GWAS summary datasets from distinct populations, especially different ethnic groups. This increases the difficulty in inferring global causal relationships from exposures on the outcome when integrating multiple GWAS summary datasets. We proposed a mendelian randomization (MR) method called MR- EILLS, which leverages the Environment Invariant Linear Least Squares (EILLS) to deduce the global causal relationship that invariant in all heterogeneous populations. The MR- EILLS model works in both univariate and multivariate scenarios, and allows the invalid instrumental variables (IVs) violating exchangeability and exclusion restriction assumptions. In addition, MR- EILLS shows the unbiased causal effect estimations of one or multiple exposures on the outcome, whether there are valid or invalid IVs. Comparing with traditional MR and meta methods, MR- EILLS demonstrates the highest estimation accuracy, the most stable type I error rates, and the highest statistical power. Finally, MR- EILLS is applied to explore the independent causal relationships between 11 blood cells and lung function, using GWAS summary statistics from five ancestries (African, East Asian, South Asian, Hispanics Latinos and European). The results cover most of the expected causal links which have biological interpretations and several new links supported by previous observational literatures.
+
+Keywords: univariate mendelian randomization, multivariate mendelian randomization, GWAS summary datasets, heterogeneous populations, multiple ancestries
+
+<--- Page Split --->
+
+## Introduction
+
+In recent years, with the rising number of Genome- Wide Association Study (GWAS) investigations, there has been a notable increase in the public availability and utilization of GWAS summary data by researchers [1- 2]. This inclusive dataset encompasses information from diverse populations and ethnic backgrounds [3- 6], a development that researchers find valuable, thus making it a current focal point of research interest. Owing to a range of influences including geographical landscapes and varied lifestyles, genetic structures exhibit significant diversity among distinct populations [7- 8], also we called population stratification, potentially leading to heterogeneity in GWAS summary data across different ethnic groups, such as those of European, Asian, and American descent. Mendelian randomization (MR) [2, 9] is a methodology that relies on the utilization of publicly available GWAS summary data for causal inference. It uses genetic variants as instrumental variables (IVs) to infer the causal effect of one or multiple exposures on an outcome, that is, univariable or multivariable MR [10- 11], respectively. A valid IV must satisfy the flowing three assumptions: relevance, exchangeability and exclusion restriction [9]. When we consider heterogeneous populations, one valid IV in a population may be an invalid IV in another population due to various genetic structures. For example, \(G_{1}\) is a valid IV in population I, it may be correlated with the confounder \(U\) between exposure and outcome in the population II, while \(U\) is not the confounder in the population I. In this case, \(G_{1}\) violates the exchangeability in population II. In addition, \(G_{1}\) may be correlated (linkage disequilibrium (LD)) [12] with another SNP \(G_{2}\) which directly affect the outcome in the population II, but \(G_{1}\) is independent with \(G_{2}\) in the population I. In this case, \(G_{1}\) violates the exclusion restriction in population II and this is due to the LD references in different populations are different. This complexity amplifies the difficulty of deducing the global causal relationship by integrating multiple heterogeneous GWAS summary datasets.
+
+One straightforward idea to infer global causal relationships using MR is that, first conduct MR analysis separately using valid IVs in different populations and obtain the causal effect estimations in each population, then combine all estimations by meta- analysis [13- 14]. Even there may be invalid IVs in the first step, lots of MR methods [15- 18] are proposed to remove the influence of invalid IVs on the causal effect estimation.
+
+<--- Page Split --->
+
+However, the accuracy of meta-analysis results depends on the robustness of different MR methods, while these MR methods require different assumptions [15- 18], which may be difficult to satisfy or even cannot be tested. This may induce the inconsistent causal effect estimation in different populations, and bring difficulties for inferring global causal relationships (see section Application). Another idea is that first conduct GWAS meta- analysis for heterogeneous populations, then select valid IVs to infer causal relationship using MR. The difficulty for this strategy is that only a short number of independent SNPs (no LD) can be selected because the LD reference panels in different populations are different [8,19]. These two strategies are both two- step process, and bring the doubled statistical errors, which yields the lower accuracy of causal effect estimation. Besides, meta- analysis is a statistical technique used to combine and analyze results from multiple studies [20], if one result is inaccurate, the results of meta- analysis is also incorrect. It is not a causal method in itself and does not necessarily provide causal evidence that holds true in every population included in the analysis. Therefore, following we proposed a one- step method which integrating all information but not only MR results in each population, and provide the causal evidence that holds true (also called invariant) in each population.
+
+In this paper, we provide a MR method called MR- EILLS, which utilizes the Environment Invariant Linear Least Squares (EILLS) [21] to integrating multiple heterogeneous GWAS summary datasets, then infer global causal relationship. The MR- EILLS model works in both univariate and multivariate scenarios, and allows the invalid IVs violating exchangeability and exclusion restriction assumptions. In addition, MR- EILLS shows the unbiased causal effect estimation of one or multiple exposures on the outcome, whether there are valid or invalid IVs. Comparing with traditional MR and Meta methods, MR- EILLS demonstrates the highest estimation accuracy, the most stable type I error rates, and higher statistical power. Finally, MR- EILLS is applied to explore the independent causal relationships between 11 blood cells and 4 lung function indexes, using GWAS summary statistics from 5 ancestries: African, East Asian, South Asian, Hispanics Latinos and European.
+
+## Results
+
+## Method overview
+
+[please insert the Figure 1 here]
+
+<--- Page Split --->
+
+MR- EILLS model integrating the GWAS summary statistics from multiple heterogeneous populations, and find the causal exposures which have invariant effects with outcome in heterogeneous populations. GWAS summary statistics in \(E\) heterogeneous populations include \(G_{j} - X\) association \(\hat{\theta}_{p,j}^{(e)}\) and its standard error \(\sigma_{G_jX_p}^{(e)^2}\) , as well as \(G_{j} - Y\) association \(\hat{\Gamma}_{y,j}^{(e)}\) and its standard error \(\sigma_{y,j}^{(e)^2}\) for \(E = e\) . We assume that the causal effects of causal exposures on \(Y\) is invariant in different populations, that is \(\beta_{0p}^{(1)} = \beta_{0p}^{(2)} = \ldots = \beta_{0p}^{(E)} = \beta_{0p}^{*}\) for \(p\in P^{*}\) , while the genetic associations between SNPs and exposures/outcome/confounders may be different, and confounders between exposures and the outcome are also different. MR- EILLS model (Figure 1) aims to explore the global causal effect estimation by minimizing the following objective function
+
+\[\begin{array}{rl} & {\mathcal{Q}(\beta_{0p}^{*};\hat{\theta}_{p,j}^{(e)},\hat{\Gamma}_{y,j}^{(e)},\sigma_{y,j}^{(e)^2})}\\ & {= \sum_{e\in E}w^{(e)}\mathrm{E}_{j\in S^{*}}[|w_{j}^{(e)}\hat{\mathcal{E}}_{j}^{(e)}|^2 ] + \gamma \sum_{p\in P}\sum_{e\in E}w^{(e)}|\mathrm{E}_{j\in S^{*}}[\hat{\theta}_{p,j}^{(e)}\cdot w_{j}^{(e)}\hat{\mathcal{E}}_{j}^{(e)}]|^2} \end{array} \quad (1)\]
+
+where \(w_{j}^{(e)}\) is the weight of IV \(G_{j}\) on the causal effect estimation in population \(E = e\) , and \(w^{(e)}\) is the weight of population \(E = e\) on the global causal effect estimation. The first part of objective function (1) is the empirical \(L_{2}\) loss, which is the multiple populations version of objective function (6) in one population (see Method section), and \(\hat{\mathcal{E}}_{j}^{(e)} = \hat{\Gamma}_{y,j}^{(e)} - \sum_{p}\hat{\theta}_{p,j}^{(e)}\beta_{0p}^{(e)}\) also denotes the pleiotropic effect. Motivating simulation (Figure 1A, Figure S1A) demonstrates that as the pleiotropic effect (no matter correlated or uncorrelated) increasing, the absolute value of \(\hat{\mathcal{E}}_{j}^{(e)}\) is larger. The second part of objective function (1) is the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) in some populations because this correlation would distort the causal effect estimation (see Method section). Motivating simulation (Figure 1B, Figure S1B) demonstrates that as correlated pleiotropic effect increasing, the correlation between \(\hat{\mathcal{E}}_{j}^{(e)}\) and \(\hat{\theta}_{p,j}^{(e)}\) is larger, and this means the violation of the InSIDE assumption [18] is more severe. \(\gamma > 0\) is the hyper parameter. In addition, we add the restriction
+
+\[S^{*} = \{j:\sum_{e\in E}|\epsilon_{j}^{(e)}| + \sum_{p\in P}\sum_{e\in E}|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}|< \lambda \} \quad (2)\]
+
+<--- Page Split --->
+
+to select the valid IVs. The first part in equation (2) represents the total pleiotropic effect for \(j - th\) IV, and the second part in equation (2) represents the correlation between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) for \(j - th\) IV. \(\lambda >0\) is the hyper parameter controlling the strictness of filtering IVs. When there are invalid IVs, the ridge plot of \(\sum_{e\in E}\left|\epsilon_{j}^{(e)}\right| + \sum_{p\in P}\sum_{e\in E}\left|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}\right|\) has at least two peaks (Figure 1C, Method section), while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . Thus equation (2) removes the invalid IVs with pleiotropic effects are larger than \(\lambda\) .
+
+## Simulation
+
+We generated the GWAS summary statistics of \(E\) heterogeneous populations with different edges' effects, IV strength and pleiotropy in the cases of UVMR and MVMR, respectively. And we compared MR- EILLS with six published methods includes IVW, MR- Egger, MR- Lasso, MR- Median, MR- cML and MR- BMA, and all of them had the UVMR and MVMR version except MR- BMA. For these MR methods, we consider two strategies: metaMR: first meta all the GWAS summary statistics of multiple datasets for each variable then conduct the MR analysis; mrMeta: first conduct the MR analysis in multiple datasets separately then meta all the MR results. Meta methods include the random- effect and fixed- effect meta- analysis.
+
+[please insert the Figure 2 here]
+
+For UVMR, in case (a), when there is correlated and uncorrelated pleiotropy (30% invalid IVs), MR- EILLS and MR- cML with metaMR show the unbiased causal effect estimation, while other methods are biased (Figure 2). MR- EILLS exhibits the higher accuracy, more stable type I error rates when causal effect is 0, and higher statistical power when causal effect isn't zero, than MR- cML with metaMR. When the proportion of invalid IVs is 80%, causal effect estimation using all MR methods including MR- cML are all biased, while MR- EILLS shows the unbiased causal effect estimation. MR- EILLS also exhibits the stable type I error rate when causal effect is 0 and statistical power is above 90% when the number of IVs is 300 in the case of causal effect is not zero. For the case (b), simulation results are similar as that in case (c). For the case (c), when there is no pleiotropy, all the methods show the unbiased causal effect estimation, stable type I error rate when causal effect is zero and high statistical power when causal effect isn't zero. Simulation results are shown in Figure S2- S21.
+
+<--- Page Split --->
+
+[please insert the Figure 3 here]
+
+[please insert the Figure 4 here]
+
+For MVMR, Figure 3 shows the causal effect estimation when there are 8 exposures, and \(30\%\) IVs have correlated or uncorrelated pleiotropy (case(a)). MR- EILLS shows unbiased causal effect estimations for all exposures, while other methods show the biased causal effect estimation, and MR- cML with metaMR also exhibits sightly biased causal effect estimations for some exposures. MR- EILLS also shows the highest accuracy among all methods. Figure 4 shows the type I error rate when causal effect is zero and statistical power when causal effect isn't zero. MR- EILLS shows the highest statistical power when causal effect isn't zero, and the most stable type I error rate while it is slightly lower than 0.05 for several exposures, but this phenomenon disappears when the number of populations is larger, e.g. \(E = 8\) (Figure S2- S3). When \(P = 3\) , the results of simulation are similar as above. When the proportion of invalid IVs is \(80\%\) , causal effect estimation using all MR methods are biased, while MR- EILLS shows the unbiased causal effect estimation. MR- EILLS also exhibits the stable type I error rate when causal effect is 0 and statistical power is above \(90\%\) when the number of IVs is 300 in the case of causal effect is not zero. For the case (b), simulation results are similar as that in case (c). For the case (c), when there is no pleiotropy, all the methods show the unbiased causal effect estimation, stable type I error rate when causal effect is zero and high statistical power when causal effect isn't zero. Simulation results are shown in Figure S22- S43. When \(P = 15\) , we calculate the mean of F1 score, recall and precision for each method in Figure 5. MR- EILLS shows the highest F1 score, recall and precision among all methods.
+
+[please insert the Figure 5 here]
+
+We also demonstrate the heterogeneity of causal effect estimations among different populations. The summary of \(I^2\) for all simulation are shown in Table S1- S3. We randomly select one simulation and demonstrate its causal effects' estimation for each MR methods and each dataset in Figure S31, S37 and S43, which show the forest plot of causal effect estimation in different populations for different methods. The \(I^2\) in case (a) is higher than case (c), that is, the pleiotropy improve the heterogeneity between populations. The causal effect estimation in different populations show the inconsistent causal effect estimation.
+
+<--- Page Split --->
+
+## Application
+
+We explore the causal relationships between total 11 blood cells (5 red blood cells: hemoglobin concentration (HGB), hematocrit (HCT), mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC); 5 white blood cells: white blood cell count (WBC), neutrophil count (Neutro), monocyte count (Mono), basophil count (Baso), eosinophil counts (Eosin); 1 platelets: platelet count (PLT)) and 4 lung function indexes (forced expiratory volume (FEV), vital capacity (FVC), FEV/FVC ratio, peak expiratory flow (PEF)) using GWAS summary statistics from 5 ancestries: African, East Asian, South Asian, Hispanics Latinos and European. Details for GWAS summary statistics were shown in Method section and Table S4.
+
+Firstly, we conducted traditional MR analysis in 5 ancestries, respectively, and performed the heterogeneous analysis for each MR method. Results were shown in Figure 6A. We found that there were large heterogeneities ( \(I^2 > 0.75\) ) for a number of blood cells in 5 ancestries. Then we conducted MR- EILLS analysis to explore independent causal effect from 11 blood cells on each lung function index. We plot ridge plots for each outcome in 5 ancestries and results were shown in Figure S44. Based on the ridge plot, we set the \(\lambda\) for MR- EILLS (Table S5). Results of MR- EILLS revealed that 3 blood cells (2 white blood cells: WBC and Neutro; 1 red blood cells: HGB) were causally associated with FEV; 1 blood cell (white blood cells: WBC) was causally associated with FVC; 3 blood cells (1 platelets: PLT; 2 red blood cells: HGB and HCT) was causally associated with FEV/FVC; 1 blood cell (red blood cells: HGB) was causally associated with PEF.
+
+[please insert the Figure 6 here]
+
+We found that the higher counts of some white blood cells, red blood cells or platelets would independently reduce the levels of lung function. For FEV, higher counts of WBC, Neutro and HGB would causally induce the lower level of FEV (WBC: \(\mathrm{beta} = - 0.14\) , \(95\% \mathrm{CI}\) : [- 0.24, - 0.04]; Neutro: \(\mathrm{beta} = - 0.17\) , \(95\% \mathrm{CI}\) : [- 0.24, - 0.04]; HGB: \(\mathrm{beta} = - 0.29\) , \(95\% \mathrm{CI}\) : [- 0.54, - 0.03]). The counts of Neutro and HCT were negatively associated with the level of FVC (Neutro: \(\mathrm{beta} = - 0.09\) , \(95\% \mathrm{CI}\) : [- 0.18, - 0.01]; HCT: \(\mathrm{beta} = - 0.06\) , \(95\% \mathrm{CI}\) : [- 0.13, - 0.002]). Besides, elevation in the levels of PLT and Neutro were associated with a decreased FEV/FVC ratio (PLT: \(\mathrm{beta} = - 0.26\) , \(95\% \mathrm{CI}\) : [- 0.49, - 0.02]; Neutro: \(\mathrm{beta} = - 0.16\) , \(95\% \mathrm{CI}\) : [- 0.30, - 0.02]). Higher concentrations of MCH
+
+<--- Page Split --->
+
+might result in a lower PEF level (beta=- 0.08, 95%CI: [- 0.16, - 0.004]). James et al. validated that an increased WBC count has been associated with lower levels of lung function and provided the biological explanations [22]. A 15- year longitudinal study demonstrated that higher blood neutrophil concentrations was associated with accelerated FEV decline [23]. The inverse relations between FEV, FVC and red blood cell counts were also supported by observational studies [24- 25]. A prospectively Longitudinal analyses revealed that higher baseline neutrophil count predicted lower serially obtained FVC [26]. A retrospective study found that there is a strong correlation between PLT and FEV/FVC ratio [27]. The results cover most of the expected causal links which have biological interpretations and several new links supported by previous observational literatures. Details of results were shown in Table S6- S11.
+
+## Discussion
+
+In this paper, we proposed a MR method MR- EILLS, which works in both univariable and multivariable framework, and it outputted the global causal effect estimation of multiple heterogeneous populations using only GWAS summary statistics. Results of simulation exhibited the superior performance of MR- EILLS and its application in exploring causal relationships from 11 blood cells to lung function covered most of the expected causal links.
+
+MR- EILLS integrates the GWAS summary datasets from heterogeneous populations, and for each population, GWAS summary datasets for exposure and outcome can be from either the same individuals or the different but heterogeneous individuals. Actually, this assumption is the same as that in traditional two- sample MR analysis, which require two homogeneous but non- overlap samples. MR- EILLS assumes that the GWAS summary datasets for each population are from homogeneous but non- overlap samples. In the application, we assume that the individuals in each ancestry are homogeneous, and the genetic diversity in different ancestries lead the heterogeneous among ancestries (different IV strength and pleiotropy).
+
+MR- EILLS allows different IV set in different populations. However, the strategy for metaMR, that is, first conduct GWAS meta- analysis then perform MR analysis, require the SNPs that are independent (no LD) in all populations, this reduces a large number of IVs, although GWAS meta- analysis helps researchers obtain more significant SNPs with \(P< 5\times 10^{- 8}\) . Besides, only a few MR methods allow the SNP set
+
+<--- Page Split --->
+
+with large LD. MR- EILLS solved this tricky issue and it only requires that IV set in each population are independent without LD.
+
+MR- EILLS model has two hyper- parameters, which need researchers to set appropriate value to estimate causal effects of exposures on the outcome. For \(\gamma\) , we recommend \(\gamma > 0.4\) in UVMR, and \(\gamma > 0\) in MVMR. The larger \(\gamma\) , the stronger the role of empirical focused linear invariance regularizer. For \(\lambda\) , we suggest the researchers plot the ridge plot to find the optimal value. In model (2), we keep the SNP, for which the pleiotropic effect in all populations is lower than \(\lambda\) . When the scales of different populations are different, the model (2) can be modified as the following model (2- 1)
+
+\[S^{*} = \{j:\left|\epsilon_{j}^{(e)}\right| + \sum_{p\in P}\left|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}\right|< \lambda_{e}\text{for any} e\} . \quad (2-1)\]
+
+The researchers can set different \(\lambda_{e}\) for different populations. For example, in our applications, we set different \(\lambda_{e}\) for five ancestries, respectively, and five ridge plots are plotted for each outcome. MR- EILLS works if and only if there are at least \(J \geq P\) valid IVs in the IV set and this assumption is less strict than the plurality assumption [17], which requires the valid IVs form the largest group of IVs sharing the same causal parameter value.
+
+There are several limitations for MR- EILLS. The first is that MR- EILLS doesn't work in the high- dimensional case yet. One future key research direction is to extend MR- EILLS to high- dimensional exposure scenarios, especially for the high- dimensional- omics biomarkers, for this, correlated IVs is also an important issue to be solved. Another point is that inappropriate settings of hyper parameters may induce the incorrect inference of causal relationships between exposures and outcome. It is important to choose the appropriate for hyper parameters, especially for \(\lambda\) . The value of \(\lambda\) determined that whether the invalid IVs are removed, and if \(\lambda\) is too large, the causal effect estimation would be distorted. If \(\lambda\) is too small, the number of remaining IVs is small, thus in the future it is necessary to extend MR- EILLS to correlated IVs scenarios.
+
+In conclusion, we proposed a MR method MR- EILLS, which integrate multiple heterogeneous GWAS summary datasets to infer the global causal relationships between exposures and outcome. This study has important guiding significance for the discovery of new disease- related factors. We look forward to offering constructive
+
+<--- Page Split --->
+
+suggestions for disease diagnosis and applying our method beyond the scope considered here.
+
+## Methods
+
+## MR-EILLS model: MR integrating multiple heterogeneous populations
+
+For one population, assume \(P\) exposures \(X_{p}, p \in \{1, \ldots , P\}\) and one outcome \(Y\) . The \(J\) independent IVs \(G_{j}, j \in \{1, \ldots , J\}\) satisfy the following three assumptions:
+
+A1. \(G_{j}\) is associated with at least one of \(P\) exposures;
+
+A2. \(G_{j}\) is not associated with the confounder between \(P\) exposures and the outcome;
+
+A3. \(G_{j}\) affects the outcome only through exposures.
+
+Then the MR model based on the individual data is:
+
+\[\begin{array}{l}{{U=\sum_{j}\omega_{j}G_{j}+\epsilon_{X_{U}}}}\\ {{X_{p}=\sum_{j}\alpha_{p j}G_{j}+\sum_{X_{k}\in p a(X_{p})}\beta_{X_{k}X_{p}}X_{k}+\beta_{1p}U+\epsilon_{X_{p}}}}\\ {{Y=\sum_{j}\gamma_{j}G_{j}+\sum_{p}\beta_{0p}X_{p}+\beta_{2}U+\epsilon_{Y}}}\end{array} \quad (3)\]
+
+where \(\epsilon_{X_{U}}, \epsilon_{X_{p}}, \epsilon_{Y} \sim N(0,1)\) . \(\gamma_{j}\) represents the uncorrelated pleiotropic effect and \(\omega_{j}\) represents the correlated pleiotropy. \(\beta_{0p}\) denote the causal effect of \(X_{p}\) on \(Y\) . We call the exposures with \(\beta_{0p} \neq 0\) are the causal exposures, which we want to discover, while the exposures with \(\beta_{0p} = 0\) are the spurious exposures, which are not the true cause of outcome. We define the set of causal exposures is \(\{X_{p}\} , p \in P^{*} \subseteq \{1, \ldots , P\}\) . When \(P = 1\) , above model is called UVMR, while when \(P > 1\) , it is called MVMR. To simplify the expression, our model below uniformly uses \(P\) exposures, both applicable to UVMR and MVMR.
+
+GWAS summary statistics including \(G_{j} - X_{p}\) association \(\hat{\theta}_{p,j}\) and its variance \(\sigma_{p,j}^{2}\) , as well as \(G_{j} - Y\) association \(\hat{\Gamma}_{y,j}\) and its variance \(\sigma_{y,j}^{2}\) . Based on model (3), we have
+
+\[\begin{array}{l}{\theta_{p,j} = \alpha_{p,j} + \omega_{j}\beta_{1p} + \sum_{X_{k}\in p a(X_{p})}\theta_{k,j}\beta_{X_{k}X_{p}}}\\ {\Gamma_{y,j} = \omega_{j}\beta_{2} + \gamma_{j} + \sum_{p}\theta_{p,j}\beta_{0p}} \end{array} \quad (4)\]
+
+<--- Page Split --->
+
+When \(G_{j}\) is a valid IV (no pleiotropy), that is \(\gamma_{j} = \omega_{j} = 0\) , then \(\epsilon_{j} = \Gamma_{y,j} - \sum_{p}\theta_{p,j}\beta_{0p}\) is zero and it is dependent with \(\theta_{p,j}\) . For \(j\in \{1,\dots,J\}\) , we can identify \(\beta_{0p}\) \((p\in \{1,\dots,P\})\) by the system of linear equations \(\Gamma_{y,j} = \sum_{p}\theta_{p,j}\beta_{0p}\) if and only if \(J\geq P\) . The causal effects of exposures on the outcome \(\beta_{0p}\) can be estimated by weighted version of ordinary least squares (OLS), that is, the IVW regression
+
+\[\hat{\Gamma}_{y,j} = \sum_{p}\hat{\theta}_{p,j}\beta_{0p} + \zeta_{j},\zeta_{j}\sim N(0,\sigma_{y,j}^{2}), \quad (5)\]
+
+which set the intercept is zero. This model minimizes the empirical \(L_{2}\) loss objective function
+
+\[\begin{array}{rl} & Q(\beta_{0p};\hat{\theta}_{p,j},\hat{\Gamma}_{y,j},\sigma_{y,j}^{2})\\ & = \mathrm{E}[|w_{j}\epsilon_{j}|^{2}]\\ & = \mathrm{E}[|w_{j}(\hat{\Gamma}_{y,j} - \sum_{p}\hat{\theta}_{p,j}\beta_{0p})|^{2}] \end{array} \quad (6)\]
+
+where \(w_{j}\) represents the weight of IV \(G_{j}\) on the casual effect estimation. If \(G_{j}\) have uncorrelated pleiotropy \((\gamma_{j}\neq 0)\) , that is, \(G_{j}\) is causally associated with \(Y\) not through any \(X_{p}\) , then the \(\epsilon_{j} = \gamma_{j}\) is no more equal to zero, and it represents the uncorrelated pleiotropic effect. MR- Egger regression [18] is proposed to solved this problem by allowing the intercept term in model (5), and the intercept represent the pleiotropic effect. MR- Egger regression requires the InSIDE assumption, which means the pleiotropic effect is independent with \(\theta_{p,j}\) . If \(G_{j}\) have correlated pleiotropy \((\omega_{j}\neq 0)\) , that is, \(G_{j}\) is causally associated with the unmeasured confounding \(U\) between \(X_{p}\) and \(Y\) , then pleiotropic effect \(\epsilon_{j} = \omega_{j}\beta_{2} + \gamma_{j}\) is not independent with \(\theta_{p,j}\) because of the common term \(\omega_{j}\) . This is the violation of the InSIDE assumption. Equation (5- 6) and MR- Egger require that \(\epsilon_{j}\) is independent with \(\theta_{p,j}\) because the correlation between intercept term and independent variables would distort the causal effect estimation. Results of motivating simulation for correlated and uncorrelated pleiotropy are shown in Figure S1.
+
+When there are \(E\) heterogeneous populations, GWAS summary statistics include \(\hat{\theta}_{p,j}^{(e)}\) , \(\sigma_{G_jX_p}^{(e)2}\) , \(\hat{\Gamma}_{y,j}^{(e)}\) and \(\sigma_{y,j}^{(e)2}\) for \(E = e\) . We define \(\epsilon_{j}^{(e)} = \Gamma_{y,j}^{(e)} - \sum_{p}\theta_{p,j}^{(e)}\beta_{0p}^{(e)}\) and \(\hat{\epsilon}_{j}^{(e)} = \hat{\Gamma}_{y,j}^{(e)} - \sum_{p}\hat{\theta}_{p,j}^{(e)}\beta_{0p}^{(e)}\) in the version of multiple populations. We use superscript \((e)\)
+
+<--- Page Split --->
+
+to denote the \(e\) - th population. We assume that the pleiotropic effect, IV strength and the relationships among exposures are different in heterogeneous populations, while the causal effects of causal exposures on \(Y\) is invariant, that is \(\beta_{0p}^{(1)} = \beta_{0p}^{(2)} = \ldots = \beta_{0p}^{(E)} = \beta_{0p}^{*}\) for \(p \in P^{*}\) , this assumption called the structure assumption [21]. These assumptions are rational because the IV satisfying A1- A3 only control the unmeasured confounders between \(X_{p}\) and \(Y\) , while other unmeasured confounders between IV and exposure, or between IV and outcome, or between exposures, are not controlled, and these unmeasured confounders also the reason for heterogeneity between populations.
+
+Note that one valid IV in one population may be the invalid IV in the other heterogeneous populations. On the other hand, an IV may be associated with the exposures in all heterogeneous populations, while it may have different uncorrelated or correlated pleiotropy in the different populations. This leads to inconsistent independence relationships between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) across different populations and inconsistent causal effect estimation of exposures on the outcome in different heterogeneous populations. Therefore, we leverage the Environment Invariant Linear Least Squares (EILLS) [21], the multiple heterogeneous populations version of OLS, to construct the MR- EILLS model. MR- EILLS model integrating the GWAS summary statistics from multiple heterogeneous populations, and find the causal exposures which have invariant effects with outcome in heterogeneous populations. MR- EILLS model aims to minimize the following objective function
+
+\[\begin{array}{rl} & {\mathcal{Q}(\beta_{0p}^{*};\hat{\theta}_{p,j}^{(e)},\hat{\Gamma}_{y,j}^{(e)},\sigma_{y,j}^{(e)2})}\\ & {= \sum_{e\in E}w^{(e)}\mathrm{E}_{j\in S^{*}}\{\mid w_{j}^{(e)}\hat{\xi}_{j}^{(e)}\mid^{2}\} +\gamma \sum_{e\in E}w^{(e)}\sum_{p\in P}\mid \mathrm{E}_{j\in S^{*}}[\hat{\theta}_{p,j}^{(e)}\cdot w_{j}^{(e)}\hat{\xi}_{j}^{(e)}]\mid^{2}} \end{array} \quad (1)\]
+
+where
+
+\[w_{j}^{(e)} = \frac{\sigma_{y,j}^{(e) - 2}}{\sum_{j\in S^{*}}\sigma_{y,j}^{(e) - 2}}\mathrm{and}w^{(e)} = \frac{N_{e}}{N} \quad (7)\]
+
+\(w_{j}^{(e)}\) is the weight of IV \(G_{j}\) on the casual effect estimation in population \(E = e\) , and \(w^{(e)}\) is the weight of population \(E = e\) on the final casual effect estimation. The first part of objective function (1) is the empirical \(L_{2}\) loss, which is the multiple populations version of objective function (6) in one population. The second part of objective function (1) is the empirical focused linear invariance regularizer, which discourages
+
+<--- Page Split --->
+
+selecting exposures with strong correlation between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) in some populations because this will distort the causal effect estimation. \(\gamma >0\) is the hyper parameter. In addition, we add the restriction
+
+\[S^{*} = \{j:\sum_{e\in E}\left|\epsilon_{j}^{(e)}\right| + \sum_{p\in P}\sum_{e\in E}\left|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}\right|< \lambda \} \quad (2)\]
+
+to select the valid IVs. The first part in equation (2) represents the uncorrelated pleiotropic effect for \(j - th\) IV, and the second part in equation (2) represents the correlated pleiotropic effect for \(j - th\) IV. \(\lambda >0\) is the hyper parameter controlling the strictness of filtering IVs. Equation (2) removes the invalid IVs with pleiotropic effect above \(\lambda\) .
+
+The causal effects \(\beta_{0p}^{*}\) can be identified under the assumption [21] that there are at least \(P\) valid IVs in the IV set, that is \(J\geq P\) . We use the a limited- memory modification of the BFGS quasi- Newton method [28] to find the optimal solution \(\beta_{0p}^{*}\) of objective function (1) under the restriction of equation (2). The confidence interval is estimated by Bootstrap method.
+
+## Simulation
+
+We generate the GWAS summary statistics of \(E\) heterogeneous populations by following process:
+
+\[\theta_{p,j}^{(e)} = \alpha_{p,j}^{(e)} + \omega_{j}^{(e)}\beta_{1p}^{(e)} + \sum_{X_{k}\in pa(X_{p})}\theta_{k,j}^{(e)}\beta_{X_{k}X_{p}}^{(e)} + \xi_{p,j}^{(e)}\] \[\Gamma_{y,j}^{(e)} = \omega_{j}^{(e)}\beta_{2}^{(e)} + \gamma_{j}^{(e)} + \sum_{p}\theta_{p,j}^{(e)}\beta_{0p}^{(e)} + \xi_{y,j}^{(e)}\]
+
+Totally \(P\) exposures, the causal exposures are the top \(30\%\) of all exposures (e.g. \(P = 8\) , floor( \(P\times 30\% = 2\) , then the top two ( \(X_{1}\) and \(X_{2}\) ) are the causal exposures). The effect of causal exposure on \(Y\) ( \(\beta_{0p}^{(e)}\) , \(p\in P^{*}\) ) is 0.2 for MVMR ( \(P > 1\) ) and 0.1 for UVMR ( \(P = 1\) ), and the effect of other spurious exposure on \(Y\) ( \(\beta_{0p}^{(e)}\) , \(p\notin P^{*}\) ) is 0. \(\beta_{X_{k}X_{p}}^{(e)}\sim U(- 1,1)\) for the effect of edge \(X_{k}\to X_{p}\) . We set IV strength \(\alpha_{p,j}^{(e)}\sim U(0.05,0.2)\) for \(E = e\) and \(X_{p}\) ; \(\xi_{p,j}^{(e)}\sim N(0,\sigma_{p,j}^{(e)2})\) for \(E = e\) and \(X_{p}\) , \(\sigma_{p,j}^{(e)2}\sim U(0.01,0.05)\) for \(X_{p}\) ; \(\xi_{y,j}^{(e)}\sim N(0,\sigma_{y,j}^{(e)2})\) for \(E = e\) , \(\sigma_{y,j}^{(e)2}\sim U(0.05,0.1)\) and different variances represent different sample sizes; \(\beta_{1p}^{(e)}\sim U(0.5,0.8)\) for \(X_{p}\) ; \(\beta_{2}^{(e)}\sim U(0.5,0.8)\) . We consider three scenarios:
+
+<--- Page Split --->
+
+(a) No pleiotropy;
+
+(b) uncorrelated pleiotropy effect \(\gamma_{j}^{(e)} \sim U(0,0.5)\) .
+
+(c) uncorrelated and correlated pleiotropy effect, \(\gamma_{j}^{(e)} \sim U(0,0.5)\) and \(\omega_{j}^{(e)} \sim U(0,0.5)\) .
+
+The parameters of edges' effects, IV strength and pleiotropy are random select from uniform distribution, thus they are different in different datasets and these represent the heterogeneous datasets. We vary the number of populations are \(E = 3\) or 8; the number of IVs is 100 or 300; the number of exposures is \(P = 1, 3, 8\) or 15, which include the cases of univariable and multivariable MR.
+
+We conduct 200 repeated simulations to evaluate the performance of MR- EILLS. We also compare six methods includes IVW, MR- Egger, MR- Lasso, MR- Median, MR- cML and MR- BMA. For \(P = 1\) , we compare five methods in the UVMR version except MR- BMA; for \(P = 3, 8\) and 15, we compare all six methods in the MVMR version. For these MR methods, we consider two strategies: (1) first meta all the GWAS summary statistics of \(E\) datasets for each variable then conduct the MR analysis; (2) first conduct the MR analysis in \(E\) datasets separately then meta all the MR results. Meta methods include the random- effect and fixed- effect meta- analysis.
+
+We evaluate the performance of all methods by box- violin plot for causal effect estimation, histogram for type I error when causal effect is zero and statistical power when causal effect isn't zero. Besides, we calculate the \(I^{2}\) statistics in each simulation, to evaluate the heterogeneity of causal effect estimation among different datasets, for each MR method. We plot the violin plot of \(I^{2}\) statistics for the estimations of each variable, and we random select six simulations to demonstrate the quartiles of estimation, then plot the forest plot of estimations for each method and each variable. For \(P = 15\) , we calculate the mean of F1 score, recall and precision for each method. Recall (i.e. power, or sensitivity) measures how many relationships a method can recover from the true causal relationships, whereas precision (i.e., 1- FDR) measures how many correct relationships are recovered in the inferred relationships. The F1 score is a combined index of recall and precision.
+
+## Setting of hyper parameters \(\gamma\) and \(\lambda\)
+
+We recommend that the practitioners determine the value of \(\lambda\) by plotting a ridge plot. The abscissa is the value of \(\sum_{e \in E} | e_{j}^{(e)} | + \sum_{p \in P} \sum_{e \in E} | \hat{\theta}_{p,j}^{(e)} e_{j}^{(e)} |\) for each IV in equation (8). We plot the ridge plot in simulations in Figure S45- S49. These plots demonstrates
+
+<--- Page Split --->
+
+that when there is no pleiotropy, the figure has only one peak, and the \(\lambda\) just takes the value of the abscission after the first peak. When there is pleiotropy, the figure has two peaks, and the corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . We provide the function of ridge plot in R package MREILLS.
+
+In addition, we evaluate the root mean square error (RMSE) of causal effect estimation using a grid search: \(\gamma\) ranges from 0.1 to 200 and \(\lambda\) ranges from 0.1 to 1. Results are shown in the Figure S50- 58. We conclude the ranges of hyper parameters when RMSE<0.1 in Table S12. For UVMR, we recommend \(\gamma >0.4\) . When \(\gamma >0.4\) , the RMSE is less than 0.1, especially for the case of correlated and uncorrelated pleiotropy, while in other cases, RMSE is less than 0.05. For MVMR, \(\gamma >0\) is recommended. Comparing with all valid IVs, invalid IVs increased the RMSE of causal effect estimation, no matter correlated or uncorrelated pleiotropy. Therefore, \(\gamma\) is loosely valued, especially when \(P > 1\) . The larger \(\gamma\) , the stronger the role of empirical focused linear invariance regularizer.
+
+## Application
+
+We explored the causal effect of 11 blood cells on 4 lung function indexes using GWAS summary statistics from 5 ancestries: African, East Asian, South Asian, Hispanics Latinos and European. GWAS summary statistics for blood cells were extracted from Chen et al. [29], which conducted trans- ethnic and ancestry- specific GWAS in 746,667 individuals from 5 global populations (15,171, 151,807, 8,189, 9,368 and 563,947 individuals for 5 ancestries, respectively). GWAS summary statistics for lung function were extracted from Shrine et al. [30], which conducted trans- ethnic GWAS analysis in 49 cohorts from 5 populations (8,590, 85,279, 4,270, 14,668 and 475,645 individuals for 5 ancestries, respectively). Details are shown in Table S4.
+
+Firstly, we select IVs for MR analysis. For MR- EILLS and mrMeta analysis, we separately select SNPs with \(P< 5\times 10^{- 8}\) and clump the LD with \(r^2 >0.01\) in each population (Table S9). For metaMR analysis, we select SNPs with \(P< 5\times 10^{- 8}\) in each population then clump the union set of above SNPs with \(r^2 >0.01\) (Table S10). Then we extract the summary statistics for IVs and conduct the MR- EILLS, mrMeta and metaMR analysis. We also calculate the \(I^2\) statistics to evaluate the heterogeneity of causal effect estimation among different populations, for each MR method. For MR
+
+<--- Page Split --->
+
+467 EILLS, we plot the ridge plot in each population, and set \(\gamma = 0.5\) . The setting of \(\lambda\) are shown in the Table S5.
+
+<--- Page Split --->
+
+## Acknowledgements
+
+None.
+
+## Author Contributions
+
+LH and ZX conceived the study. LH contributed to theoretical derivation with assistance from ZX. LH and HC contributed to the data simulation and application. LH and ZX wrote the manuscript with input from all other authors. All authors reviewed and approved the final manuscript.
+
+## Competing Interests statement
+
+The authors declare no competing interests.
+
+## Data and code availability
+
+GWAS summary statistics for blood cells are publicly available at http://www.mhi- humangenetics.org/en/resources/. The GWAS summary data for lung function are publicly available at GWAS catalog. All the analysis in our article were implemented by R software (version 4.3.2). R packages used in our analysis include TwoSampleMR, MendelianRandomization, and ggplot2. MREILLS model can be implemented by R package https://github.com/hhoulei/ MREILLS. All the codes for simulation are uploaded in https://github.com/hhoulei/MREILLS_Simul.
+
+## Ethics approval and consent to participate
+
+The data used in our study was all publicly available and obtained written informed consent from all participants.
+
+## Source of Funding
+
+This work was supported by the National Natural Science Foundation of China (Grant 82404378, T2341018), China Postdoctoral Science Foundation (Grant GZB20230011, 2024M750115, 2024T170014).
+
+<--- Page Split --->
+
+## Reference
+
+[1]. Zhu, Z., Zhang, F., Hu, H., Bakshi, A., Robinson, M. R., Powell, J. E., Montgomery, G. W., Goddard, M. E., Wray, N. R., Visscher, P. M., & Yang, J. (2016). Integration of summary data from GWAS and eQTL studies predicts complex trait gene targets. Nature genetics, 48(5), 481–487. [2]. Emdin, C. A., Khera, A. V., & Kathiresan, S. (2017). Mendelian randomization. Jama, 318(19), 5521925-1926. [3]. Bycroft, C., Freeman, C., Petkova, D., Band, G., Elliott, L. T., Sharp, K., ... & Marchini, J. (2018). The UK Biobank resource with deep phenotype and genomic data. Nature, 562(7726), 203-209. [4]. Kubo, M. (2017). BioBank Japan project: epidemiological study. Journal of epidemiology, 27(3Suppl), S1. [5]. Zhao, H., Rasheed, H., Nöst, T. H., Cho, Y., Liu, Y., Bhatta, L., ... & Zheng, J. (2022). Proteome-wide Mendelian randomization in global biobank meta-analysis reveals multi-ancestry drug targets for common diseases. Cell Genomics, 2(11).[6]. Feng, Y. A., Chen, C. Y., Chen, T. T., Kuo, P. H., Hsu, Y. H., Yang, H. I., Chen, W. J., Su, M. W., Chu, H. W., Shen, C. Y., Ge, T., Huang, H., & Lin, Y. F. (2022). Taiwan Biobank: A rich biomedical research database of the Taiwanese population. Cell genomics, 2(11), 100197. [7]. Lewis, A. C., Molina, S. J., Appelbaum, P. S., Dauda, B., Di Rienzo, A., Fuentes, A., ... & Allen, D. S. (2022). Getting genetic ancestry right for science and society. Science, 376(6590), 250-252. [8]. Petrovski, S., & Goldstein, D. B. (2016). Unequal representation of genetic variation across ancestry groups creates healthcare inequality in the application of precision medicine. Genome biology, 17, 1-3. [9]. Sanderson, E., Glymour, M. M., Holmes, M. V., Kang, H., Morrison, J., Munafò, M. R., ... & Davey Smith, G. (2022). Mendelian randomization. Nature Reviews Methods Primers, 2(1), 6. [10]. Sanderson, E., Davey Smith, G., Windmeijer, F., & Bowden, J. (2019). An examination of multivariable Mendelian randomization in the single-sample and two-sample summary data settings. International journal of epidemiology, 48(3), 713-727. [11]. Burgess, S., & Thompson, S. G. (2015). Multivariable Mendelian randomization: the use of pleiotropic genetic variants to estimate causal effects. American journal of epidemiology, 181(4), 251-260. https://doi.org/10.1093/aje/kwu283[12]. Slatkin M. (2008). Linkage disequilibrium--understanding the evolutionary past and mapping the medical future. Nature reviews. Genetics, 9(6), 477-485. [13]. Fang, A., Zhao, Y., Yang, P., Zhang, X., & Giovannucci, E. L. (2024). Vitamin D and human health: evidence from Mendelian randomization studies. European journal of epidemiology, 39(5), 467-490. https://doi.org/10.1007/s10654-023-01075-4
+
+<--- Page Split --->
+
+[14]. Bowden, J., & Holmes, M. V. (2019). Meta-analysis and Mendelian randomization: A review. Research synthesis methods, 10(4), 486-496. https://doi.org/10.1002/jrsm.1346[15]. Bowden J, Davey Smith G, Haycock PC, et al. Consistent estimation in mendelian randomization with some invalid instruments using a weighted median estimator. Genet Epidemiol, 2016, 40(4):304-314. [16]. Hartwig FP, Davey Smith G, Bowden J. Robust inference in summary data Mendelian randomization via the zero modal pleiotropy assumption. Int J Epidemiol 2017;46:1985-98. [17]. Burgess S, Zuber V, Gkatzionis A, Foley CN. Modal-based estimation via heterogeneity- penalized weighting: model averaging for consistent and efficient estimation in Mendelian randomization when a plurality of candidate instruments are valid. Int J Epidemiol. 2018 Aug 1;47(4):1242-1254. [18]. Bowden J, Davey Smith G, Burgess S. Mendelian randomization with invalid instruments: effect estimation and bias detection through Egger regression. Int J Epidemiol. 2015 Apr;44(2):512-25. [19]. Ellegren, H., & Galtier, N. (2016). Determinants of genetic diversity. Nature reviews. Genetics, 17(7), 422-433. [20]. Stroup, D. F., Berlin, J. A., Morton, S. C., Olkin, I., Williamson, G. D., Rennie, D., Moher, D., Becker, B. J., Sipe, T. A., & Thacker, S. B. (2000). Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA, 283(15), 2008-2012. https://doi.org/10.1001/jama.283.15.2008[21]. Fan, J., Fang, C., Gu, Y., & Zhang, T. (2023). Environment invariant linear least squares. arXiv preprint arXiv:2303.03092. [22]. James, A. L., Knuiman, M. W., Divitini, M. L., Musk, A. W., Ryan, G., & Bartholomew, H. C. (1999). Associations between white blood cell count, lung function, respiratory illness and mortality: the Busselton Health Study. The European respiratory journal, 13(5), 1115-1119. [23]. Zeig-Owens, R., Singh, A., Aldrich, T. K., Hall, C. B., Schwartz, T., Webber, M. P., Cohen, H. W., Kelly, K. J., Nolan, A., Prezant, D. J., & Weiden, M. D. (2018). Blood Leukocyte Concentrations, FEV1 Decline, and Airflow Limitation. A 15-Year Longitudinal Study of World Trade Center-exposed Firefighters. Annals of the American Thoracic Society, 15(2), 173-183. [24]. Grant, B. J., Kudalkar, D. P., Muti, P., McCann, S. E., Trevisan, M., Freudenheim, J. L., & Schünemann, H. J. (2003). Relation between lung function and RBC distribution width in a population-based study. Chest, 124(2), 494-500. [25]. Huang, Y., Wang, J., Shen, J., Ma, J., Miao, X., Ding, K., Jiang, B., Hu, B., Fu, F., Huang, L., Cao, M., & Zhang, X. (2021). Relationship of Red Cell Index with the Severity of Chronic Obstructive Pulmonary Disease. International journal of chronic obstructive pulmonary disease, 16, 825-834. https://doi.org/10.2147/COPD.S292666[26]. Wareing, N., Mohan, V., Taherian, R., Volkmann, E. R., Lyons, M. A., Wilhalme, H., Roth, M. D., Estrada-Y-Martin, R. M., Skaug, B., Mayes, M. D., Tashkin, D. P., & Assassi, S. (2023). Blood Neutrophil Count and Neutrophil-to-Lymphocyte Ratio for Prediction of Disease
+
+<--- Page Split --->
+
+572 Progression and Mortality in Two Independent Systemic Sclerosis Cohorts. Arthritis care & 573 research, 75(3), 648- 656. https://doi.org/10.1002/acr.24880 574 [27]. Ulasli, S. S., Ozyurek, B. A., Yilmaz, E. B., & Ulubay, G. (2012). Mean platelet volume 575 as an inflammatory marker in acute exacerbation of chronic obstructive pulmonary disease. 576 Polskie Archiwum Medycyny Wewnetrznej, 122(6), 284- 290. 577 [28]. Eisen, M., Mokhtari, A., & Ribeiro, A. (2017). Decentralized quasi- Newton methods. 578 IEEE Transactions on Signal Processing, 65(10), 2613- 2628. 579 [29]. Chen, M. H., Raffield, L. M., Mousas, A., Sakaue, S., Huffman, J. E., Moscati, A., Trivedi, 580 B., Jiang, T., Akbari, P., Vuckovic, D., Bao, E. L., Zhong, X., Manansala, R., Laplante, V., Chen, 581 M., Lo, K. S., Qian, H., Lareau, C. A., Beaudoin, M., Hunt, K. A., ... Lettre, G. (2020). Trans- 582 ethnic and Ancestry- Specific Blood- Cell Genetics in 746,667 Individuals from 5 Global 583 Populations. Cell, 182(5), 1198- 1213. e14. 584 [30]. Shrine, N., Izquierdo, A. G., Chen, J., Packer, R., Hall, R. J., Guyatt, A. L., Batini, C., 585 Thompson, R. J., Pavuluri, C., Malik, V., Hobbs, B. D., Moll, M., Kim, W., Tal- Singer, R., 586 Bakke, P., Fawcett, K. A., John, C., Coley, K., Piga, N. N., Pozarickij, A., ... Tobin, M. D. 587 (2023). Multi- ancestry genome- wide association analyses improve resolution of genes and 588 pathways influencing lung function and chronic obstructive pulmonary disease risk. Nature 589 genetics, 55(3), 410- 422. 590
+
+<--- Page Split --->
+
+## Figure Legends
+
+Figure 1. MR- EILLS model. MR- EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR- EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A- C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \(\hat{\mathcal{E}}_j^{(e)}\) in different populations, and larger point means the larger value of \(|\hat{\mathcal{E}}_j^{(e)}|\) . As the pleiotropic effect larger, the \(|\hat{\mathcal{E}}_j^{(e)}|\) is larger, thus the first part of MR- EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \(\hat{\mathcal{E}}_j^{(e)}\) and \(\hat{\theta}_{p,j}^{(e)}\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR- EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\theta_{p,j}^{(e)}\) and \(\mathcal{E}_j^{(e)}\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \(\sum_{e\in E}|\mathcal{E}_j^{(e)}| + \sum_{p\in P}\sum_{e\in E}|\hat{\theta}_{p,j}^{(e)}\mathcal{E}_j^{(e)}|\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . The third part of MR- EILLS model is removing the invalid IVs by \(\lambda\) .
+
+Figure 2. Simulation results when \(P = 1\) (UVMR). (A- B) Results of causal effect estimation and type I error rate when the causal effect is zero. (C- D) Results of causal effect estimation and type I error rate when the causal effect is 0.1. The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+Figure 3. Simulation results of causal effect estimation when \(P = 8\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+Figure 4. Simulation results of type I error rate for spurious exposures and statistical power for causal exposures when \(P = 8\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+<--- Page Split --->
+
+Figure 5. Simulation results of F1 score, precision and recall when \(P = 15\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+Figure 6. Results in application. (A) the heterogeneity among different populations; (B) the causal effect estimations of 11 blood cells on lung function.
+
+<--- Page Split --->
+
+## Figures
+
+
+
+
+Summary statistics:
+
+\(G - X_{p}\) association \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) \(\sigma_{p^{\prime}}^{(\ell)}\) \(G - Y\) association \(\hat{\Gamma}_{p^{\prime}}^{(\ell)}\) \(\sigma_{p^{\prime}}^{(\ell)}\)
+
+MR- EILLS Model:
+
+
+
+Figure 1. MR-EILLS model. MR-EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR-EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A-C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \(\hat{\epsilon}_{j}^{(\ell)}\) in different populations, and larger point means the larger value of \(\hat{\epsilon}_{j}^{(\ell)}\) . As the pleiotropic effect larger, the \(\hat{\epsilon}_{j}^{(\ell)}\) is larger, thus the first part of MR-EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \(\hat{\epsilon}_{j}^{(\ell)}\) and \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR-EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) and \(\epsilon_{j}^{(\ell)}\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \(\sum_{n\in \mathbb{J}}\hat{\epsilon}_{j}^{(\ell)}| + \sum_{p\in \mathbb{P}}\sum_{n\in \mathbb{J}}\hat{\theta}_{p^{\prime}}^{(\ell)}\epsilon_{j}^{(\ell)}|\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . The third part of MR-EILLS model is removing the invalid IVs by \(\lambda\) .
+
+Question: How to infer global causal relationships by integrating multiple heterogeneous GWAS summary datasets?
+
+
+
+Figure 1. MR-EILLS model. MR-EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR-EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A-C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \(\hat{\epsilon}_{j}^{(\ell)}\) in different populations, and larger point means the larger value of \(\hat{\epsilon}_{j}^{(\ell)}\) . As the pleiotropic effect larger, the \(\hat{\epsilon}_{j}^{(\ell)}\) is larger, thus the first part of MR-EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \(\hat{\epsilon}_{j}^{(\ell)}\) and \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR-EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) and \(\epsilon_{j}^{(\ell)}\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \(\sum_{n\in \mathbb{J}}\hat{\epsilon}_{j}^{(\ell)}| + \sum_{p\in \mathbb{P}}\sum_{n\in \mathbb{J}}\hat{\theta}_{p^{\prime}}^{(\ell)}\epsilon_{j}^{(\ell)}|\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . The third part of MR-EILLS model is removing the invalid IVs by \(\lambda\) .
+
+## Figure 1
+
+See image above for figure legend.
+
+<--- Page Split --->
+
+
+Figure 2
+
+Simulation results when \(\mathrm{P} = 1\) (UVMR). (A- B) Results of causal effect estimation and type I error rate when the causal effect is zero. (C- D) Results of causal effect estimation and type I error rate when the causal effect is 0.1. The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+<--- Page Split --->
+
+
+Figure 3
+
+Simulation results of causal effect estimation when \(\mathbf{P} = \mathbf{8}\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+<--- Page Split --->
+
+
+Figure 4
+
+Simulation results of type I error rate for spurious exposures and statistical power for causal exposures when \(\mathbf{P} = \mathbf{8}\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+<--- Page Split --->
+
+
+Figure 5
+
+Simulation results of F1 score, precision and recall when \(\mathbf{P} = 15\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+![PLACEHOLDER_28_1]
+
+Figure 6
+
+Results in application.(A) the heterogeneity among different populations; (B) the causal effect estimations of 11 blood cells on lung function.
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<--- Page Split --->
+
+SupplementaryTable.xlsxSupplementaryMaterials1208.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10_det.mmd b/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..db1c35edbe8b7a11f0fa3aed4b5b3e7d072c4136
--- /dev/null
+++ b/preprint/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10/preprint__019a1322a4a18120bcf8546c95c7927691c4f4ceee9e4ba840a419b80a2ebe10_det.mmd
@@ -0,0 +1,492 @@
+<|ref|>title<|/ref|><|det|>[[44, 106, 950, 208]]<|/det|>
+# Invariance-based Mendelian Randomization Method Integrating Multiple Heterogeneous GWAS Summary Datasets
+
+<|ref|>text<|/ref|><|det|>[[44, 229, 150, 247]]<|/det|>
+Xiaohua Zhou
+
+<|ref|>text<|/ref|><|det|>[[54, 256, 300, 273]]<|/det|>
+azhou@bicmr.pku.edu.cn
+
+<|ref|>text<|/ref|><|det|>[[50, 302, 730, 343]]<|/det|>
+Beijing International Center for Mathematical Research, Peking University Lei Hou
+
+<|ref|>text<|/ref|><|det|>[[52, 348, 208, 366]]<|/det|>
+Peking University
+
+<|ref|>text<|/ref|><|det|>[[44, 373, 770, 415]]<|/det|>
+Hao Chen Institute for Medical Dataology, Cheeloo College of Medicine, Shandong University
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 456, 103, 473]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 493, 940, 536]]<|/det|>
+Keywords: univariate mendelian randomization, multivariate mendelian randomization, GWAS summary datasets, heterogeneous populations, multiple ancestries
+
+<|ref|>text<|/ref|><|det|>[[44, 553, 350, 572]]<|/det|>
+Posted Date: December 17th, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 591, 475, 611]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 5602368/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 629, 916, 672]]<|/det|>
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 690, 535, 710]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 745, 936, 789]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on August 18th, 2025. See the published version at https://doi.org/10.1038/s41467- 025- 62823- 6.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[117, 98, 828, 149]]<|/det|>
+# Invariance-based Mendelian Randomization Method Integrating Multiple Heterogeneous GWAS Summary Datasets
+
+<|ref|>text<|/ref|><|det|>[[108, 172, 495, 192]]<|/det|>
+3 Lei Hou \(^{1}\) , Hao Chen \(^{4}\) , Xiao- Hua Zhou \(^{1,2,3*}\)
+
+<|ref|>title<|/ref|><|det|>[[108, 220, 316, 237]]<|/det|>
+# 4 Author affiliations:
+
+<|ref|>text<|/ref|><|det|>[[108, 243, 852, 412]]<|/det|>
+5 1. Beijing International Center for Mathematical Research, Peking University, 6 Beijing, P.R.China, 100871 7 2. Department of Biostatistics, Peking University, Beijing, P.R.China, 100871 8 3. Chongqing Big Data Research Institute, Peking University, Chongqing, P.R.China, 9 401333 10 4. Department of biostatistics, School of Public Health, Cheeloo College of Medicine, 11 Shandong University, Shandong, Beijing, P.R.China, 250000
+
+<|ref|>title<|/ref|><|det|>[[148, 460, 360, 478]]<|/det|>
+# \*Corresponding author:
+
+<|ref|>text<|/ref|><|det|>[[108, 485, 850, 640]]<|/det|>
+14 Xiao- Hua Zhou, 15 E- mail: azhou@bicmr.pku.edu.cn, 16 Telephone: +86 18910208518, 17 Address: Peking University, No.5 Yiheyuan Road Haidian District, Beijing, P.R.China
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[148, 85, 240, 103]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[144, 123, 852, 563]]<|/det|>
+Various geographical landscapes, diverse lifestyles and genetic structures may lead the heterogeneity among the GWAS summary datasets from distinct populations, especially different ethnic groups. This increases the difficulty in inferring global causal relationships from exposures on the outcome when integrating multiple GWAS summary datasets. We proposed a mendelian randomization (MR) method called MR- EILLS, which leverages the Environment Invariant Linear Least Squares (EILLS) to deduce the global causal relationship that invariant in all heterogeneous populations. The MR- EILLS model works in both univariate and multivariate scenarios, and allows the invalid instrumental variables (IVs) violating exchangeability and exclusion restriction assumptions. In addition, MR- EILLS shows the unbiased causal effect estimations of one or multiple exposures on the outcome, whether there are valid or invalid IVs. Comparing with traditional MR and meta methods, MR- EILLS demonstrates the highest estimation accuracy, the most stable type I error rates, and the highest statistical power. Finally, MR- EILLS is applied to explore the independent causal relationships between 11 blood cells and lung function, using GWAS summary statistics from five ancestries (African, East Asian, South Asian, Hispanics Latinos and European). The results cover most of the expected causal links which have biological interpretations and several new links supported by previous observational literatures.
+
+<|ref|>text<|/ref|><|det|>[[147, 590, 850, 656]]<|/det|>
+Keywords: univariate mendelian randomization, multivariate mendelian randomization, GWAS summary datasets, heterogeneous populations, multiple ancestries
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 85, 279, 103]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[144, 120, 852, 789]]<|/det|>
+In recent years, with the rising number of Genome- Wide Association Study (GWAS) investigations, there has been a notable increase in the public availability and utilization of GWAS summary data by researchers [1- 2]. This inclusive dataset encompasses information from diverse populations and ethnic backgrounds [3- 6], a development that researchers find valuable, thus making it a current focal point of research interest. Owing to a range of influences including geographical landscapes and varied lifestyles, genetic structures exhibit significant diversity among distinct populations [7- 8], also we called population stratification, potentially leading to heterogeneity in GWAS summary data across different ethnic groups, such as those of European, Asian, and American descent. Mendelian randomization (MR) [2, 9] is a methodology that relies on the utilization of publicly available GWAS summary data for causal inference. It uses genetic variants as instrumental variables (IVs) to infer the causal effect of one or multiple exposures on an outcome, that is, univariable or multivariable MR [10- 11], respectively. A valid IV must satisfy the flowing three assumptions: relevance, exchangeability and exclusion restriction [9]. When we consider heterogeneous populations, one valid IV in a population may be an invalid IV in another population due to various genetic structures. For example, \(G_{1}\) is a valid IV in population I, it may be correlated with the confounder \(U\) between exposure and outcome in the population II, while \(U\) is not the confounder in the population I. In this case, \(G_{1}\) violates the exchangeability in population II. In addition, \(G_{1}\) may be correlated (linkage disequilibrium (LD)) [12] with another SNP \(G_{2}\) which directly affect the outcome in the population II, but \(G_{1}\) is independent with \(G_{2}\) in the population I. In this case, \(G_{1}\) violates the exclusion restriction in population II and this is due to the LD references in different populations are different. This complexity amplifies the difficulty of deducing the global causal relationship by integrating multiple heterogeneous GWAS summary datasets.
+
+<|ref|>text<|/ref|><|det|>[[147, 791, 851, 907]]<|/det|>
+One straightforward idea to infer global causal relationships using MR is that, first conduct MR analysis separately using valid IVs in different populations and obtain the causal effect estimations in each population, then combine all estimations by meta- analysis [13- 14]. Even there may be invalid IVs in the first step, lots of MR methods [15- 18] are proposed to remove the influence of invalid IVs on the causal effect estimation.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 82, 852, 496]]<|/det|>
+However, the accuracy of meta-analysis results depends on the robustness of different MR methods, while these MR methods require different assumptions [15- 18], which may be difficult to satisfy or even cannot be tested. This may induce the inconsistent causal effect estimation in different populations, and bring difficulties for inferring global causal relationships (see section Application). Another idea is that first conduct GWAS meta- analysis for heterogeneous populations, then select valid IVs to infer causal relationship using MR. The difficulty for this strategy is that only a short number of independent SNPs (no LD) can be selected because the LD reference panels in different populations are different [8,19]. These two strategies are both two- step process, and bring the doubled statistical errors, which yields the lower accuracy of causal effect estimation. Besides, meta- analysis is a statistical technique used to combine and analyze results from multiple studies [20], if one result is inaccurate, the results of meta- analysis is also incorrect. It is not a causal method in itself and does not necessarily provide causal evidence that holds true in every population included in the analysis. Therefore, following we proposed a one- step method which integrating all information but not only MR results in each population, and provide the causal evidence that holds true (also called invariant) in each population.
+
+<|ref|>text<|/ref|><|det|>[[144, 502, 853, 791]]<|/det|>
+In this paper, we provide a MR method called MR- EILLS, which utilizes the Environment Invariant Linear Least Squares (EILLS) [21] to integrating multiple heterogeneous GWAS summary datasets, then infer global causal relationship. The MR- EILLS model works in both univariate and multivariate scenarios, and allows the invalid IVs violating exchangeability and exclusion restriction assumptions. In addition, MR- EILLS shows the unbiased causal effect estimation of one or multiple exposures on the outcome, whether there are valid or invalid IVs. Comparing with traditional MR and Meta methods, MR- EILLS demonstrates the highest estimation accuracy, the most stable type I error rates, and higher statistical power. Finally, MR- EILLS is applied to explore the independent causal relationships between 11 blood cells and 4 lung function indexes, using GWAS summary statistics from 5 ancestries: African, East Asian, South Asian, Hispanics Latinos and European.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 810, 225, 828]]<|/det|>
+## Results
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 850, 293, 866]]<|/det|>
+## Method overview
+
+<|ref|>text<|/ref|><|det|>[[368, 874, 628, 891]]<|/det|>
+[please insert the Figure 1 here]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 82, 852, 375]]<|/det|>
+MR- EILLS model integrating the GWAS summary statistics from multiple heterogeneous populations, and find the causal exposures which have invariant effects with outcome in heterogeneous populations. GWAS summary statistics in \(E\) heterogeneous populations include \(G_{j} - X\) association \(\hat{\theta}_{p,j}^{(e)}\) and its standard error \(\sigma_{G_jX_p}^{(e)^2}\) , as well as \(G_{j} - Y\) association \(\hat{\Gamma}_{y,j}^{(e)}\) and its standard error \(\sigma_{y,j}^{(e)^2}\) for \(E = e\) . We assume that the causal effects of causal exposures on \(Y\) is invariant in different populations, that is \(\beta_{0p}^{(1)} = \beta_{0p}^{(2)} = \ldots = \beta_{0p}^{(E)} = \beta_{0p}^{*}\) for \(p\in P^{*}\) , while the genetic associations between SNPs and exposures/outcome/confounders may be different, and confounders between exposures and the outcome are also different. MR- EILLS model (Figure 1) aims to explore the global causal effect estimation by minimizing the following objective function
+
+<|ref|>equation<|/ref|><|det|>[[245, 380, 848, 450]]<|/det|>
+\[\begin{array}{rl} & {\mathcal{Q}(\beta_{0p}^{*};\hat{\theta}_{p,j}^{(e)},\hat{\Gamma}_{y,j}^{(e)},\sigma_{y,j}^{(e)^2})}\\ & {= \sum_{e\in E}w^{(e)}\mathrm{E}_{j\in S^{*}}[|w_{j}^{(e)}\hat{\mathcal{E}}_{j}^{(e)}|^2 ] + \gamma \sum_{p\in P}\sum_{e\in E}w^{(e)}|\mathrm{E}_{j\in S^{*}}[\hat{\theta}_{p,j}^{(e)}\cdot w_{j}^{(e)}\hat{\mathcal{E}}_{j}^{(e)}]|^2} \end{array} \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[144, 458, 852, 850]]<|/det|>
+where \(w_{j}^{(e)}\) is the weight of IV \(G_{j}\) on the causal effect estimation in population \(E = e\) , and \(w^{(e)}\) is the weight of population \(E = e\) on the global causal effect estimation. The first part of objective function (1) is the empirical \(L_{2}\) loss, which is the multiple populations version of objective function (6) in one population (see Method section), and \(\hat{\mathcal{E}}_{j}^{(e)} = \hat{\Gamma}_{y,j}^{(e)} - \sum_{p}\hat{\theta}_{p,j}^{(e)}\beta_{0p}^{(e)}\) also denotes the pleiotropic effect. Motivating simulation (Figure 1A, Figure S1A) demonstrates that as the pleiotropic effect (no matter correlated or uncorrelated) increasing, the absolute value of \(\hat{\mathcal{E}}_{j}^{(e)}\) is larger. The second part of objective function (1) is the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) in some populations because this correlation would distort the causal effect estimation (see Method section). Motivating simulation (Figure 1B, Figure S1B) demonstrates that as correlated pleiotropic effect increasing, the correlation between \(\hat{\mathcal{E}}_{j}^{(e)}\) and \(\hat{\theta}_{p,j}^{(e)}\) is larger, and this means the violation of the InSIDE assumption [18] is more severe. \(\gamma > 0\) is the hyper parameter. In addition, we add the restriction
+
+<|ref|>equation<|/ref|><|det|>[[309, 860, 848, 896]]<|/det|>
+\[S^{*} = \{j:\sum_{e\in E}|\epsilon_{j}^{(e)}| + \sum_{p\in P}\sum_{e\in E}|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}|< \lambda \} \quad (2)\]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 83, 852, 298]]<|/det|>
+to select the valid IVs. The first part in equation (2) represents the total pleiotropic effect for \(j - th\) IV, and the second part in equation (2) represents the correlation between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) for \(j - th\) IV. \(\lambda >0\) is the hyper parameter controlling the strictness of filtering IVs. When there are invalid IVs, the ridge plot of \(\sum_{e\in E}\left|\epsilon_{j}^{(e)}\right| + \sum_{p\in P}\sum_{e\in E}\left|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}\right|\) has at least two peaks (Figure 1C, Method section), while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . Thus equation (2) removes the invalid IVs with pleiotropic effects are larger than \(\lambda\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 315, 244, 331]]<|/det|>
+## Simulation
+
+<|ref|>text<|/ref|><|det|>[[147, 339, 852, 554]]<|/det|>
+We generated the GWAS summary statistics of \(E\) heterogeneous populations with different edges' effects, IV strength and pleiotropy in the cases of UVMR and MVMR, respectively. And we compared MR- EILLS with six published methods includes IVW, MR- Egger, MR- Lasso, MR- Median, MR- cML and MR- BMA, and all of them had the UVMR and MVMR version except MR- BMA. For these MR methods, we consider two strategies: metaMR: first meta all the GWAS summary statistics of multiple datasets for each variable then conduct the MR analysis; mrMeta: first conduct the MR analysis in multiple datasets separately then meta all the MR results. Meta methods include the random- effect and fixed- effect meta- analysis.
+
+<|ref|>text<|/ref|><|det|>[[368, 560, 629, 578]]<|/det|>
+[please insert the Figure 2 here]
+
+<|ref|>text<|/ref|><|det|>[[147, 584, 852, 899]]<|/det|>
+For UVMR, in case (a), when there is correlated and uncorrelated pleiotropy (30% invalid IVs), MR- EILLS and MR- cML with metaMR show the unbiased causal effect estimation, while other methods are biased (Figure 2). MR- EILLS exhibits the higher accuracy, more stable type I error rates when causal effect is 0, and higher statistical power when causal effect isn't zero, than MR- cML with metaMR. When the proportion of invalid IVs is 80%, causal effect estimation using all MR methods including MR- cML are all biased, while MR- EILLS shows the unbiased causal effect estimation. MR- EILLS also exhibits the stable type I error rate when causal effect is 0 and statistical power is above 90% when the number of IVs is 300 in the case of causal effect is not zero. For the case (b), simulation results are similar as that in case (c). For the case (c), when there is no pleiotropy, all the methods show the unbiased causal effect estimation, stable type I error rate when causal effect is zero and high statistical power when causal effect isn't zero. Simulation results are shown in Figure S2- S21.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[366, 84, 629, 101]]<|/det|>
+[please insert the Figure 3 here]
+
+<|ref|>text<|/ref|><|det|>[[368, 108, 629, 126]]<|/det|>
+[please insert the Figure 4 here]
+
+<|ref|>text<|/ref|><|det|>[[145, 131, 852, 644]]<|/det|>
+For MVMR, Figure 3 shows the causal effect estimation when there are 8 exposures, and \(30\%\) IVs have correlated or uncorrelated pleiotropy (case(a)). MR- EILLS shows unbiased causal effect estimations for all exposures, while other methods show the biased causal effect estimation, and MR- cML with metaMR also exhibits sightly biased causal effect estimations for some exposures. MR- EILLS also shows the highest accuracy among all methods. Figure 4 shows the type I error rate when causal effect is zero and statistical power when causal effect isn't zero. MR- EILLS shows the highest statistical power when causal effect isn't zero, and the most stable type I error rate while it is slightly lower than 0.05 for several exposures, but this phenomenon disappears when the number of populations is larger, e.g. \(E = 8\) (Figure S2- S3). When \(P = 3\) , the results of simulation are similar as above. When the proportion of invalid IVs is \(80\%\) , causal effect estimation using all MR methods are biased, while MR- EILLS shows the unbiased causal effect estimation. MR- EILLS also exhibits the stable type I error rate when causal effect is 0 and statistical power is above \(90\%\) when the number of IVs is 300 in the case of causal effect is not zero. For the case (b), simulation results are similar as that in case (c). For the case (c), when there is no pleiotropy, all the methods show the unbiased causal effect estimation, stable type I error rate when causal effect is zero and high statistical power when causal effect isn't zero. Simulation results are shown in Figure S22- S43. When \(P = 15\) , we calculate the mean of F1 score, recall and precision for each method in Figure 5. MR- EILLS shows the highest F1 score, recall and precision among all methods.
+
+<|ref|>text<|/ref|><|det|>[[368, 650, 629, 668]]<|/det|>
+[please insert the Figure 5 here]
+
+<|ref|>text<|/ref|><|det|>[[145, 675, 852, 870]]<|/det|>
+We also demonstrate the heterogeneity of causal effect estimations among different populations. The summary of \(I^2\) for all simulation are shown in Table S1- S3. We randomly select one simulation and demonstrate its causal effects' estimation for each MR methods and each dataset in Figure S31, S37 and S43, which show the forest plot of causal effect estimation in different populations for different methods. The \(I^2\) in case (a) is higher than case (c), that is, the pleiotropy improve the heterogeneity between populations. The causal effect estimation in different populations show the inconsistent causal effect estimation.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 85, 248, 101]]<|/det|>
+## Application
+
+<|ref|>text<|/ref|><|det|>[[145, 108, 852, 348]]<|/det|>
+We explore the causal relationships between total 11 blood cells (5 red blood cells: hemoglobin concentration (HGB), hematocrit (HCT), mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC); 5 white blood cells: white blood cell count (WBC), neutrophil count (Neutro), monocyte count (Mono), basophil count (Baso), eosinophil counts (Eosin); 1 platelets: platelet count (PLT)) and 4 lung function indexes (forced expiratory volume (FEV), vital capacity (FVC), FEV/FVC ratio, peak expiratory flow (PEF)) using GWAS summary statistics from 5 ancestries: African, East Asian, South Asian, Hispanics Latinos and European. Details for GWAS summary statistics were shown in Method section and Table S4.
+
+<|ref|>text<|/ref|><|det|>[[145, 354, 852, 644]]<|/det|>
+Firstly, we conducted traditional MR analysis in 5 ancestries, respectively, and performed the heterogeneous analysis for each MR method. Results were shown in Figure 6A. We found that there were large heterogeneities ( \(I^2 > 0.75\) ) for a number of blood cells in 5 ancestries. Then we conducted MR- EILLS analysis to explore independent causal effect from 11 blood cells on each lung function index. We plot ridge plots for each outcome in 5 ancestries and results were shown in Figure S44. Based on the ridge plot, we set the \(\lambda\) for MR- EILLS (Table S5). Results of MR- EILLS revealed that 3 blood cells (2 white blood cells: WBC and Neutro; 1 red blood cells: HGB) were causally associated with FEV; 1 blood cell (white blood cells: WBC) was causally associated with FVC; 3 blood cells (1 platelets: PLT; 2 red blood cells: HGB and HCT) was causally associated with FEV/FVC; 1 blood cell (red blood cells: HGB) was causally associated with PEF.
+
+<|ref|>text<|/ref|><|det|>[[369, 652, 629, 670]]<|/det|>
+[please insert the Figure 6 here]
+
+<|ref|>text<|/ref|><|det|>[[145, 676, 852, 892]]<|/det|>
+We found that the higher counts of some white blood cells, red blood cells or platelets would independently reduce the levels of lung function. For FEV, higher counts of WBC, Neutro and HGB would causally induce the lower level of FEV (WBC: \(\mathrm{beta} = - 0.14\) , \(95\% \mathrm{CI}\) : [- 0.24, - 0.04]; Neutro: \(\mathrm{beta} = - 0.17\) , \(95\% \mathrm{CI}\) : [- 0.24, - 0.04]; HGB: \(\mathrm{beta} = - 0.29\) , \(95\% \mathrm{CI}\) : [- 0.54, - 0.03]). The counts of Neutro and HCT were negatively associated with the level of FVC (Neutro: \(\mathrm{beta} = - 0.09\) , \(95\% \mathrm{CI}\) : [- 0.18, - 0.01]; HCT: \(\mathrm{beta} = - 0.06\) , \(95\% \mathrm{CI}\) : [- 0.13, - 0.002]). Besides, elevation in the levels of PLT and Neutro were associated with a decreased FEV/FVC ratio (PLT: \(\mathrm{beta} = - 0.26\) , \(95\% \mathrm{CI}\) : [- 0.49, - 0.02]; Neutro: \(\mathrm{beta} = - 0.16\) , \(95\% \mathrm{CI}\) : [- 0.30, - 0.02]). Higher concentrations of MCH
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 83, 852, 348]]<|/det|>
+might result in a lower PEF level (beta=- 0.08, 95%CI: [- 0.16, - 0.004]). James et al. validated that an increased WBC count has been associated with lower levels of lung function and provided the biological explanations [22]. A 15- year longitudinal study demonstrated that higher blood neutrophil concentrations was associated with accelerated FEV decline [23]. The inverse relations between FEV, FVC and red blood cell counts were also supported by observational studies [24- 25]. A prospectively Longitudinal analyses revealed that higher baseline neutrophil count predicted lower serially obtained FVC [26]. A retrospective study found that there is a strong correlation between PLT and FEV/FVC ratio [27]. The results cover most of the expected causal links which have biological interpretations and several new links supported by previous observational literatures. Details of results were shown in Table S6- S11.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 367, 256, 386]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[147, 406, 852, 547]]<|/det|>
+In this paper, we proposed a MR method MR- EILLS, which works in both univariable and multivariable framework, and it outputted the global causal effect estimation of multiple heterogeneous populations using only GWAS summary statistics. Results of simulation exhibited the superior performance of MR- EILLS and its application in exploring causal relationships from 11 blood cells to lung function covered most of the expected causal links.
+
+<|ref|>text<|/ref|><|det|>[[147, 553, 852, 769]]<|/det|>
+MR- EILLS integrates the GWAS summary datasets from heterogeneous populations, and for each population, GWAS summary datasets for exposure and outcome can be from either the same individuals or the different but heterogeneous individuals. Actually, this assumption is the same as that in traditional two- sample MR analysis, which require two homogeneous but non- overlap samples. MR- EILLS assumes that the GWAS summary datasets for each population are from homogeneous but non- overlap samples. In the application, we assume that the individuals in each ancestry are homogeneous, and the genetic diversity in different ancestries lead the heterogeneous among ancestries (different IV strength and pleiotropy).
+
+<|ref|>text<|/ref|><|det|>[[147, 775, 852, 895]]<|/det|>
+MR- EILLS allows different IV set in different populations. However, the strategy for metaMR, that is, first conduct GWAS meta- analysis then perform MR analysis, require the SNPs that are independent (no LD) in all populations, this reduces a large number of IVs, although GWAS meta- analysis helps researchers obtain more significant SNPs with \(P< 5\times 10^{- 8}\) . Besides, only a few MR methods allow the SNP set
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 83, 850, 127]]<|/det|>
+with large LD. MR- EILLS solved this tricky issue and it only requires that IV set in each population are independent without LD.
+
+<|ref|>text<|/ref|><|det|>[[147, 133, 852, 333]]<|/det|>
+MR- EILLS model has two hyper- parameters, which need researchers to set appropriate value to estimate causal effects of exposures on the outcome. For \(\gamma\) , we recommend \(\gamma > 0.4\) in UVMR, and \(\gamma > 0\) in MVMR. The larger \(\gamma\) , the stronger the role of empirical focused linear invariance regularizer. For \(\lambda\) , we suggest the researchers plot the ridge plot to find the optimal value. In model (2), we keep the SNP, for which the pleiotropic effect in all populations is lower than \(\lambda\) . When the scales of different populations are different, the model (2) can be modified as the following model (2- 1)
+
+<|ref|>equation<|/ref|><|det|>[[312, 345, 848, 380]]<|/det|>
+\[S^{*} = \{j:\left|\epsilon_{j}^{(e)}\right| + \sum_{p\in P}\left|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}\right|< \lambda_{e}\text{for any} e\} . \quad (2-1)\]
+
+<|ref|>text<|/ref|><|det|>[[147, 388, 852, 540]]<|/det|>
+The researchers can set different \(\lambda_{e}\) for different populations. For example, in our applications, we set different \(\lambda_{e}\) for five ancestries, respectively, and five ridge plots are plotted for each outcome. MR- EILLS works if and only if there are at least \(J \geq P\) valid IVs in the IV set and this assumption is less strict than the plurality assumption [17], which requires the valid IVs form the largest group of IVs sharing the same causal parameter value.
+
+<|ref|>text<|/ref|><|det|>[[147, 546, 852, 812]]<|/det|>
+There are several limitations for MR- EILLS. The first is that MR- EILLS doesn't work in the high- dimensional case yet. One future key research direction is to extend MR- EILLS to high- dimensional exposure scenarios, especially for the high- dimensional- omics biomarkers, for this, correlated IVs is also an important issue to be solved. Another point is that inappropriate settings of hyper parameters may induce the incorrect inference of causal relationships between exposures and outcome. It is important to choose the appropriate for hyper parameters, especially for \(\lambda\) . The value of \(\lambda\) determined that whether the invalid IVs are removed, and if \(\lambda\) is too large, the causal effect estimation would be distorted. If \(\lambda\) is too small, the number of remaining IVs is small, thus in the future it is necessary to extend MR- EILLS to correlated IVs scenarios.
+
+<|ref|>text<|/ref|><|det|>[[147, 818, 852, 911]]<|/det|>
+In conclusion, we proposed a MR method MR- EILLS, which integrate multiple heterogeneous GWAS summary datasets to infer the global causal relationships between exposures and outcome. This study has important guiding significance for the discovery of new disease- related factors. We look forward to offering constructive
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 83, 850, 127]]<|/det|>
+suggestions for disease diagnosis and applying our method beyond the scope considered here.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 145, 240, 164]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 184, 745, 204]]<|/det|>
+## MR-EILLS model: MR integrating multiple heterogeneous populations
+
+<|ref|>text<|/ref|><|det|>[[147, 211, 847, 261]]<|/det|>
+For one population, assume \(P\) exposures \(X_{p}, p \in \{1, \ldots , P\}\) and one outcome \(Y\) . The \(J\) independent IVs \(G_{j}, j \in \{1, \ldots , J\}\) satisfy the following three assumptions:
+
+<|ref|>text<|/ref|><|det|>[[187, 273, 631, 293]]<|/det|>
+A1. \(G_{j}\) is associated with at least one of \(P\) exposures;
+
+<|ref|>text<|/ref|><|det|>[[147, 305, 850, 353]]<|/det|>
+A2. \(G_{j}\) is not associated with the confounder between \(P\) exposures and the outcome;
+
+<|ref|>text<|/ref|><|det|>[[187, 361, 615, 380]]<|/det|>
+A3. \(G_{j}\) affects the outcome only through exposures.
+
+<|ref|>text<|/ref|><|det|>[[147, 390, 570, 409]]<|/det|>
+Then the MR model based on the individual data is:
+
+<|ref|>equation<|/ref|><|det|>[[315, 415, 848, 500]]<|/det|>
+\[\begin{array}{l}{{U=\sum_{j}\omega_{j}G_{j}+\epsilon_{X_{U}}}}\\ {{X_{p}=\sum_{j}\alpha_{p j}G_{j}+\sum_{X_{k}\in p a(X_{p})}\beta_{X_{k}X_{p}}X_{k}+\beta_{1p}U+\epsilon_{X_{p}}}}\\ {{Y=\sum_{j}\gamma_{j}G_{j}+\sum_{p}\beta_{0p}X_{p}+\beta_{2}U+\epsilon_{Y}}}\end{array} \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[147, 508, 851, 732]]<|/det|>
+where \(\epsilon_{X_{U}}, \epsilon_{X_{p}}, \epsilon_{Y} \sim N(0,1)\) . \(\gamma_{j}\) represents the uncorrelated pleiotropic effect and \(\omega_{j}\) represents the correlated pleiotropy. \(\beta_{0p}\) denote the causal effect of \(X_{p}\) on \(Y\) . We call the exposures with \(\beta_{0p} \neq 0\) are the causal exposures, which we want to discover, while the exposures with \(\beta_{0p} = 0\) are the spurious exposures, which are not the true cause of outcome. We define the set of causal exposures is \(\{X_{p}\} , p \in P^{*} \subseteq \{1, \ldots , P\}\) . When \(P = 1\) , above model is called UVMR, while when \(P > 1\) , it is called MVMR. To simplify the expression, our model below uniformly uses \(P\) exposures, both applicable to UVMR and MVMR.
+
+<|ref|>text<|/ref|><|det|>[[147, 741, 850, 823]]<|/det|>
+GWAS summary statistics including \(G_{j} - X_{p}\) association \(\hat{\theta}_{p,j}\) and its variance \(\sigma_{p,j}^{2}\) , as well as \(G_{j} - Y\) association \(\hat{\Gamma}_{y,j}\) and its variance \(\sigma_{y,j}^{2}\) . Based on model (3), we have
+
+<|ref|>equation<|/ref|><|det|>[[310, 830, 848, 888]]<|/det|>
+\[\begin{array}{l}{\theta_{p,j} = \alpha_{p,j} + \omega_{j}\beta_{1p} + \sum_{X_{k}\in p a(X_{p})}\theta_{k,j}\beta_{X_{k}X_{p}}}\\ {\Gamma_{y,j} = \omega_{j}\beta_{2} + \gamma_{j} + \sum_{p}\theta_{p,j}\beta_{0p}} \end{array} \quad (4)\]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 83, 850, 230]]<|/det|>
+When \(G_{j}\) is a valid IV (no pleiotropy), that is \(\gamma_{j} = \omega_{j} = 0\) , then \(\epsilon_{j} = \Gamma_{y,j} - \sum_{p}\theta_{p,j}\beta_{0p}\) is zero and it is dependent with \(\theta_{p,j}\) . For \(j\in \{1,\dots,J\}\) , we can identify \(\beta_{0p}\) \((p\in \{1,\dots,P\})\) by the system of linear equations \(\Gamma_{y,j} = \sum_{p}\theta_{p,j}\beta_{0p}\) if and only if \(J\geq P\) . The causal effects of exposures on the outcome \(\beta_{0p}\) can be estimated by weighted version of ordinary least squares (OLS), that is, the IVW regression
+
+<|ref|>equation<|/ref|><|det|>[[312, 234, 848, 264]]<|/det|>
+\[\hat{\Gamma}_{y,j} = \sum_{p}\hat{\theta}_{p,j}\beta_{0p} + \zeta_{j},\zeta_{j}\sim N(0,\sigma_{y,j}^{2}), \quad (5)\]
+
+<|ref|>text<|/ref|><|det|>[[145, 273, 850, 321]]<|/det|>
+which set the intercept is zero. This model minimizes the empirical \(L_{2}\) loss objective function
+
+<|ref|>equation<|/ref|><|det|>[[320, 328, 848, 412]]<|/det|>
+\[\begin{array}{rl} & Q(\beta_{0p};\hat{\theta}_{p,j},\hat{\Gamma}_{y,j},\sigma_{y,j}^{2})\\ & = \mathrm{E}[|w_{j}\epsilon_{j}|^{2}]\\ & = \mathrm{E}[|w_{j}(\hat{\Gamma}_{y,j} - \sum_{p}\hat{\theta}_{p,j}\beta_{0p})|^{2}] \end{array} \quad (6)\]
+
+<|ref|>text<|/ref|><|det|>[[145, 419, 852, 815]]<|/det|>
+where \(w_{j}\) represents the weight of IV \(G_{j}\) on the casual effect estimation. If \(G_{j}\) have uncorrelated pleiotropy \((\gamma_{j}\neq 0)\) , that is, \(G_{j}\) is causally associated with \(Y\) not through any \(X_{p}\) , then the \(\epsilon_{j} = \gamma_{j}\) is no more equal to zero, and it represents the uncorrelated pleiotropic effect. MR- Egger regression [18] is proposed to solved this problem by allowing the intercept term in model (5), and the intercept represent the pleiotropic effect. MR- Egger regression requires the InSIDE assumption, which means the pleiotropic effect is independent with \(\theta_{p,j}\) . If \(G_{j}\) have correlated pleiotropy \((\omega_{j}\neq 0)\) , that is, \(G_{j}\) is causally associated with the unmeasured confounding \(U\) between \(X_{p}\) and \(Y\) , then pleiotropic effect \(\epsilon_{j} = \omega_{j}\beta_{2} + \gamma_{j}\) is not independent with \(\theta_{p,j}\) because of the common term \(\omega_{j}\) . This is the violation of the InSIDE assumption. Equation (5- 6) and MR- Egger require that \(\epsilon_{j}\) is independent with \(\theta_{p,j}\) because the correlation between intercept term and independent variables would distort the causal effect estimation. Results of motivating simulation for correlated and uncorrelated pleiotropy are shown in Figure S1.
+
+<|ref|>text<|/ref|><|det|>[[147, 819, 850, 905]]<|/det|>
+When there are \(E\) heterogeneous populations, GWAS summary statistics include \(\hat{\theta}_{p,j}^{(e)}\) , \(\sigma_{G_jX_p}^{(e)2}\) , \(\hat{\Gamma}_{y,j}^{(e)}\) and \(\sigma_{y,j}^{(e)2}\) for \(E = e\) . We define \(\epsilon_{j}^{(e)} = \Gamma_{y,j}^{(e)} - \sum_{p}\theta_{p,j}^{(e)}\beta_{0p}^{(e)}\) and \(\hat{\epsilon}_{j}^{(e)} = \hat{\Gamma}_{y,j}^{(e)} - \sum_{p}\hat{\theta}_{p,j}^{(e)}\beta_{0p}^{(e)}\) in the version of multiple populations. We use superscript \((e)\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 82, 852, 292]]<|/det|>
+to denote the \(e\) - th population. We assume that the pleiotropic effect, IV strength and the relationships among exposures are different in heterogeneous populations, while the causal effects of causal exposures on \(Y\) is invariant, that is \(\beta_{0p}^{(1)} = \beta_{0p}^{(2)} = \ldots = \beta_{0p}^{(E)} = \beta_{0p}^{*}\) for \(p \in P^{*}\) , this assumption called the structure assumption [21]. These assumptions are rational because the IV satisfying A1- A3 only control the unmeasured confounders between \(X_{p}\) and \(Y\) , while other unmeasured confounders between IV and exposure, or between IV and outcome, or between exposures, are not controlled, and these unmeasured confounders also the reason for heterogeneity between populations.
+
+<|ref|>text<|/ref|><|det|>[[144, 297, 852, 594]]<|/det|>
+Note that one valid IV in one population may be the invalid IV in the other heterogeneous populations. On the other hand, an IV may be associated with the exposures in all heterogeneous populations, while it may have different uncorrelated or correlated pleiotropy in the different populations. This leads to inconsistent independence relationships between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) across different populations and inconsistent causal effect estimation of exposures on the outcome in different heterogeneous populations. Therefore, we leverage the Environment Invariant Linear Least Squares (EILLS) [21], the multiple heterogeneous populations version of OLS, to construct the MR- EILLS model. MR- EILLS model integrating the GWAS summary statistics from multiple heterogeneous populations, and find the causal exposures which have invariant effects with outcome in heterogeneous populations. MR- EILLS model aims to minimize the following objective function
+
+<|ref|>equation<|/ref|><|det|>[[248, 599, 848, 666]]<|/det|>
+\[\begin{array}{rl} & {\mathcal{Q}(\beta_{0p}^{*};\hat{\theta}_{p,j}^{(e)},\hat{\Gamma}_{y,j}^{(e)},\sigma_{y,j}^{(e)2})}\\ & {= \sum_{e\in E}w^{(e)}\mathrm{E}_{j\in S^{*}}\{\mid w_{j}^{(e)}\hat{\xi}_{j}^{(e)}\mid^{2}\} +\gamma \sum_{e\in E}w^{(e)}\sum_{p\in P}\mid \mathrm{E}_{j\in S^{*}}[\hat{\theta}_{p,j}^{(e)}\cdot w_{j}^{(e)}\hat{\xi}_{j}^{(e)}]\mid^{2}} \end{array} \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[145, 697, 202, 712]]<|/det|>
+where
+
+<|ref|>equation<|/ref|><|det|>[[350, 718, 848, 770]]<|/det|>
+\[w_{j}^{(e)} = \frac{\sigma_{y,j}^{(e) - 2}}{\sum_{j\in S^{*}}\sigma_{y,j}^{(e) - 2}}\mathrm{and}w^{(e)} = \frac{N_{e}}{N} \quad (7)\]
+
+<|ref|>text<|/ref|><|det|>[[144, 777, 852, 914]]<|/det|>
+\(w_{j}^{(e)}\) is the weight of IV \(G_{j}\) on the casual effect estimation in population \(E = e\) , and \(w^{(e)}\) is the weight of population \(E = e\) on the final casual effect estimation. The first part of objective function (1) is the empirical \(L_{2}\) loss, which is the multiple populations version of objective function (6) in one population. The second part of objective function (1) is the empirical focused linear invariance regularizer, which discourages
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[146, 84, 850, 160]]<|/det|>
+selecting exposures with strong correlation between \(\theta_{p,j}^{(e)}\) and \(\epsilon_{j}^{(e)}\) in some populations because this will distort the causal effect estimation. \(\gamma >0\) is the hyper parameter. In addition, we add the restriction
+
+<|ref|>equation<|/ref|><|det|>[[339, 172, 848, 208]]<|/det|>
+\[S^{*} = \{j:\sum_{e\in E}\left|\epsilon_{j}^{(e)}\right| + \sum_{p\in P}\sum_{e\in E}\left|\hat{\theta}_{p,j}^{(e)}\epsilon_{j}^{(e)}\right|< \lambda \} \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[146, 216, 851, 341]]<|/det|>
+to select the valid IVs. The first part in equation (2) represents the uncorrelated pleiotropic effect for \(j - th\) IV, and the second part in equation (2) represents the correlated pleiotropic effect for \(j - th\) IV. \(\lambda >0\) is the hyper parameter controlling the strictness of filtering IVs. Equation (2) removes the invalid IVs with pleiotropic effect above \(\lambda\) .
+
+<|ref|>text<|/ref|><|det|>[[146, 348, 851, 477]]<|/det|>
+The causal effects \(\beta_{0p}^{*}\) can be identified under the assumption [21] that there are at least \(P\) valid IVs in the IV set, that is \(J\geq P\) . We use the a limited- memory modification of the BFGS quasi- Newton method [28] to find the optimal solution \(\beta_{0p}^{*}\) of objective function (1) under the restriction of equation (2). The confidence interval is estimated by Bootstrap method.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 494, 245, 510]]<|/det|>
+## Simulation
+
+<|ref|>text<|/ref|><|det|>[[147, 517, 850, 561]]<|/det|>
+We generate the GWAS summary statistics of \(E\) heterogeneous populations by following process:
+
+<|ref|>equation<|/ref|><|det|>[[301, 567, 695, 622]]<|/det|>
+\[\theta_{p,j}^{(e)} = \alpha_{p,j}^{(e)} + \omega_{j}^{(e)}\beta_{1p}^{(e)} + \sum_{X_{k}\in pa(X_{p})}\theta_{k,j}^{(e)}\beta_{X_{k}X_{p}}^{(e)} + \xi_{p,j}^{(e)}\] \[\Gamma_{y,j}^{(e)} = \omega_{j}^{(e)}\beta_{2}^{(e)} + \gamma_{j}^{(e)} + \sum_{p}\theta_{p,j}^{(e)}\beta_{0p}^{(e)} + \xi_{y,j}^{(e)}\]
+
+<|ref|>text<|/ref|><|det|>[[146, 630, 851, 900]]<|/det|>
+Totally \(P\) exposures, the causal exposures are the top \(30\%\) of all exposures (e.g. \(P = 8\) , floor( \(P\times 30\% = 2\) , then the top two ( \(X_{1}\) and \(X_{2}\) ) are the causal exposures). The effect of causal exposure on \(Y\) ( \(\beta_{0p}^{(e)}\) , \(p\in P^{*}\) ) is 0.2 for MVMR ( \(P > 1\) ) and 0.1 for UVMR ( \(P = 1\) ), and the effect of other spurious exposure on \(Y\) ( \(\beta_{0p}^{(e)}\) , \(p\notin P^{*}\) ) is 0. \(\beta_{X_{k}X_{p}}^{(e)}\sim U(- 1,1)\) for the effect of edge \(X_{k}\to X_{p}\) . We set IV strength \(\alpha_{p,j}^{(e)}\sim U(0.05,0.2)\) for \(E = e\) and \(X_{p}\) ; \(\xi_{p,j}^{(e)}\sim N(0,\sigma_{p,j}^{(e)2})\) for \(E = e\) and \(X_{p}\) , \(\sigma_{p,j}^{(e)2}\sim U(0.01,0.05)\) for \(X_{p}\) ; \(\xi_{y,j}^{(e)}\sim N(0,\sigma_{y,j}^{(e)2})\) for \(E = e\) , \(\sigma_{y,j}^{(e)2}\sim U(0.05,0.1)\) and different variances represent different sample sizes; \(\beta_{1p}^{(e)}\sim U(0.5,0.8)\) for \(X_{p}\) ; \(\beta_{2}^{(e)}\sim U(0.5,0.8)\) . We consider three scenarios:
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 85, 300, 102]]<|/det|>
+(a) No pleiotropy;
+
+<|ref|>text<|/ref|><|det|>[[145, 110, 555, 131]]<|/det|>
+(b) uncorrelated pleiotropy effect \(\gamma_{j}^{(e)} \sim U(0,0.5)\) .
+
+<|ref|>text<|/ref|><|det|>[[145, 140, 848, 163]]<|/det|>
+(c) uncorrelated and correlated pleiotropy effect, \(\gamma_{j}^{(e)} \sim U(0,0.5)\) and \(\omega_{j}^{(e)} \sim U(0,0.5)\) .
+
+<|ref|>text<|/ref|><|det|>[[145, 171, 852, 290]]<|/det|>
+The parameters of edges' effects, IV strength and pleiotropy are random select from uniform distribution, thus they are different in different datasets and these represent the heterogeneous datasets. We vary the number of populations are \(E = 3\) or 8; the number of IVs is 100 or 300; the number of exposures is \(P = 1, 3, 8\) or 15, which include the cases of univariable and multivariable MR.
+
+<|ref|>text<|/ref|><|det|>[[145, 296, 852, 488]]<|/det|>
+We conduct 200 repeated simulations to evaluate the performance of MR- EILLS. We also compare six methods includes IVW, MR- Egger, MR- Lasso, MR- Median, MR- cML and MR- BMA. For \(P = 1\) , we compare five methods in the UVMR version except MR- BMA; for \(P = 3, 8\) and 15, we compare all six methods in the MVMR version. For these MR methods, we consider two strategies: (1) first meta all the GWAS summary statistics of \(E\) datasets for each variable then conduct the MR analysis; (2) first conduct the MR analysis in \(E\) datasets separately then meta all the MR results. Meta methods include the random- effect and fixed- effect meta- analysis.
+
+<|ref|>text<|/ref|><|det|>[[145, 494, 852, 788]]<|/det|>
+We evaluate the performance of all methods by box- violin plot for causal effect estimation, histogram for type I error when causal effect is zero and statistical power when causal effect isn't zero. Besides, we calculate the \(I^{2}\) statistics in each simulation, to evaluate the heterogeneity of causal effect estimation among different datasets, for each MR method. We plot the violin plot of \(I^{2}\) statistics for the estimations of each variable, and we random select six simulations to demonstrate the quartiles of estimation, then plot the forest plot of estimations for each method and each variable. For \(P = 15\) , we calculate the mean of F1 score, recall and precision for each method. Recall (i.e. power, or sensitivity) measures how many relationships a method can recover from the true causal relationships, whereas precision (i.e., 1- FDR) measures how many correct relationships are recovered in the inferred relationships. The F1 score is a combined index of recall and precision.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 805, 460, 824]]<|/det|>
+## Setting of hyper parameters \(\gamma\) and \(\lambda\)
+
+<|ref|>text<|/ref|><|det|>[[145, 832, 850, 912]]<|/det|>
+We recommend that the practitioners determine the value of \(\lambda\) by plotting a ridge plot. The abscissa is the value of \(\sum_{e \in E} | e_{j}^{(e)} | + \sum_{p \in P} \sum_{e \in E} | \hat{\theta}_{p,j}^{(e)} e_{j}^{(e)} |\) for each IV in equation (8). We plot the ridge plot in simulations in Figure S45- S49. These plots demonstrates
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 84, 851, 179]]<|/det|>
+that when there is no pleiotropy, the figure has only one peak, and the \(\lambda\) just takes the value of the abscission after the first peak. When there is pleiotropy, the figure has two peaks, and the corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . We provide the function of ridge plot in R package MREILLS.
+
+<|ref|>text<|/ref|><|det|>[[145, 185, 852, 444]]<|/det|>
+In addition, we evaluate the root mean square error (RMSE) of causal effect estimation using a grid search: \(\gamma\) ranges from 0.1 to 200 and \(\lambda\) ranges from 0.1 to 1. Results are shown in the Figure S50- 58. We conclude the ranges of hyper parameters when RMSE<0.1 in Table S12. For UVMR, we recommend \(\gamma >0.4\) . When \(\gamma >0.4\) , the RMSE is less than 0.1, especially for the case of correlated and uncorrelated pleiotropy, while in other cases, RMSE is less than 0.05. For MVMR, \(\gamma >0\) is recommended. Comparing with all valid IVs, invalid IVs increased the RMSE of causal effect estimation, no matter correlated or uncorrelated pleiotropy. Therefore, \(\gamma\) is loosely valued, especially when \(P > 1\) . The larger \(\gamma\) , the stronger the role of empirical focused linear invariance regularizer.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 460, 248, 477]]<|/det|>
+## Application
+
+<|ref|>text<|/ref|><|det|>[[145, 483, 852, 696]]<|/det|>
+We explored the causal effect of 11 blood cells on 4 lung function indexes using GWAS summary statistics from 5 ancestries: African, East Asian, South Asian, Hispanics Latinos and European. GWAS summary statistics for blood cells were extracted from Chen et al. [29], which conducted trans- ethnic and ancestry- specific GWAS in 746,667 individuals from 5 global populations (15,171, 151,807, 8,189, 9,368 and 563,947 individuals for 5 ancestries, respectively). GWAS summary statistics for lung function were extracted from Shrine et al. [30], which conducted trans- ethnic GWAS analysis in 49 cohorts from 5 populations (8,590, 85,279, 4,270, 14,668 and 475,645 individuals for 5 ancestries, respectively). Details are shown in Table S4.
+
+<|ref|>text<|/ref|><|det|>[[145, 703, 852, 881]]<|/det|>
+Firstly, we select IVs for MR analysis. For MR- EILLS and mrMeta analysis, we separately select SNPs with \(P< 5\times 10^{- 8}\) and clump the LD with \(r^2 >0.01\) in each population (Table S9). For metaMR analysis, we select SNPs with \(P< 5\times 10^{- 8}\) in each population then clump the union set of above SNPs with \(r^2 >0.01\) (Table S10). Then we extract the summary statistics for IVs and conduct the MR- EILLS, mrMeta and metaMR analysis. We also calculate the \(I^2\) statistics to evaluate the heterogeneity of causal effect estimation among different populations, for each MR method. For MR
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[87, 84, 850, 131]]<|/det|>
+467 EILLS, we plot the ridge plot in each population, and set \(\gamma = 0.5\) . The setting of \(\lambda\) are shown in the Table S5.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[148, 85, 347, 104]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[148, 125, 200, 141]]<|/det|>
+None.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 162, 373, 181]]<|/det|>
+## Author Contributions
+
+<|ref|>text<|/ref|><|det|>[[147, 201, 822, 293]]<|/det|>
+LH and ZX conceived the study. LH contributed to theoretical derivation with assistance from ZX. LH and HC contributed to the data simulation and application. LH and ZX wrote the manuscript with input from all other authors. All authors reviewed and approved the final manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 313, 460, 333]]<|/det|>
+## Competing Interests statement
+
+<|ref|>text<|/ref|><|det|>[[148, 352, 503, 370]]<|/det|>
+The authors declare no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 390, 413, 410]]<|/det|>
+## Data and code availability
+
+<|ref|>text<|/ref|><|det|>[[147, 428, 838, 595]]<|/det|>
+GWAS summary statistics for blood cells are publicly available at http://www.mhi- humangenetics.org/en/resources/. The GWAS summary data for lung function are publicly available at GWAS catalog. All the analysis in our article were implemented by R software (version 4.3.2). R packages used in our analysis include TwoSampleMR, MendelianRandomization, and ggplot2. MREILLS model can be implemented by R package https://github.com/hhoulei/ MREILLS. All the codes for simulation are uploaded in https://github.com/hhoulei/MREILLS_Simul.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 614, 576, 634]]<|/det|>
+## Ethics approval and consent to participate
+
+<|ref|>text<|/ref|><|det|>[[147, 653, 825, 696]]<|/det|>
+The data used in our study was all publicly available and obtained written informed consent from all participants.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 716, 338, 736]]<|/det|>
+## Source of Funding
+
+<|ref|>text<|/ref|><|det|>[[147, 755, 851, 823]]<|/det|>
+This work was supported by the National Natural Science Foundation of China (Grant 82404378, T2341018), China Postdoctoral Science Foundation (Grant GZB20230011, 2024M750115, 2024T170014).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[144, 84, 252, 103]]<|/det|>
+## Reference
+
+<|ref|>text<|/ref|><|det|>[[140, 120, 852, 888]]<|/det|>
+[1]. Zhu, Z., Zhang, F., Hu, H., Bakshi, A., Robinson, M. R., Powell, J. E., Montgomery, G. W., Goddard, M. E., Wray, N. R., Visscher, P. M., & Yang, J. (2016). Integration of summary data from GWAS and eQTL studies predicts complex trait gene targets. Nature genetics, 48(5), 481–487. [2]. Emdin, C. A., Khera, A. V., & Kathiresan, S. (2017). Mendelian randomization. Jama, 318(19), 5521925-1926. [3]. Bycroft, C., Freeman, C., Petkova, D., Band, G., Elliott, L. T., Sharp, K., ... & Marchini, J. (2018). The UK Biobank resource with deep phenotype and genomic data. Nature, 562(7726), 203-209. [4]. Kubo, M. (2017). BioBank Japan project: epidemiological study. Journal of epidemiology, 27(3Suppl), S1. [5]. Zhao, H., Rasheed, H., Nöst, T. H., Cho, Y., Liu, Y., Bhatta, L., ... & Zheng, J. (2022). Proteome-wide Mendelian randomization in global biobank meta-analysis reveals multi-ancestry drug targets for common diseases. Cell Genomics, 2(11).[6]. Feng, Y. A., Chen, C. Y., Chen, T. T., Kuo, P. H., Hsu, Y. H., Yang, H. I., Chen, W. J., Su, M. W., Chu, H. W., Shen, C. Y., Ge, T., Huang, H., & Lin, Y. F. (2022). Taiwan Biobank: A rich biomedical research database of the Taiwanese population. Cell genomics, 2(11), 100197. [7]. Lewis, A. C., Molina, S. J., Appelbaum, P. S., Dauda, B., Di Rienzo, A., Fuentes, A., ... & Allen, D. S. (2022). Getting genetic ancestry right for science and society. Science, 376(6590), 250-252. [8]. Petrovski, S., & Goldstein, D. B. (2016). Unequal representation of genetic variation across ancestry groups creates healthcare inequality in the application of precision medicine. Genome biology, 17, 1-3. [9]. Sanderson, E., Glymour, M. M., Holmes, M. V., Kang, H., Morrison, J., Munafò, M. R., ... & Davey Smith, G. (2022). Mendelian randomization. Nature Reviews Methods Primers, 2(1), 6. [10]. Sanderson, E., Davey Smith, G., Windmeijer, F., & Bowden, J. (2019). An examination of multivariable Mendelian randomization in the single-sample and two-sample summary data settings. International journal of epidemiology, 48(3), 713-727. [11]. Burgess, S., & Thompson, S. G. (2015). Multivariable Mendelian randomization: the use of pleiotropic genetic variants to estimate causal effects. American journal of epidemiology, 181(4), 251-260. https://doi.org/10.1093/aje/kwu283[12]. Slatkin M. (2008). Linkage disequilibrium--understanding the evolutionary past and mapping the medical future. Nature reviews. Genetics, 9(6), 477-485. [13]. Fang, A., Zhao, Y., Yang, P., Zhang, X., & Giovannucci, E. L. (2024). Vitamin D and human health: evidence from Mendelian randomization studies. European journal of epidemiology, 39(5), 467-490. https://doi.org/10.1007/s10654-023-01075-4
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 75, 855, 905]]<|/det|>
+[14]. Bowden, J., & Holmes, M. V. (2019). Meta-analysis and Mendelian randomization: A review. Research synthesis methods, 10(4), 486-496. https://doi.org/10.1002/jrsm.1346[15]. Bowden J, Davey Smith G, Haycock PC, et al. Consistent estimation in mendelian randomization with some invalid instruments using a weighted median estimator. Genet Epidemiol, 2016, 40(4):304-314. [16]. Hartwig FP, Davey Smith G, Bowden J. Robust inference in summary data Mendelian randomization via the zero modal pleiotropy assumption. Int J Epidemiol 2017;46:1985-98. [17]. Burgess S, Zuber V, Gkatzionis A, Foley CN. Modal-based estimation via heterogeneity- penalized weighting: model averaging for consistent and efficient estimation in Mendelian randomization when a plurality of candidate instruments are valid. Int J Epidemiol. 2018 Aug 1;47(4):1242-1254. [18]. Bowden J, Davey Smith G, Burgess S. Mendelian randomization with invalid instruments: effect estimation and bias detection through Egger regression. Int J Epidemiol. 2015 Apr;44(2):512-25. [19]. Ellegren, H., & Galtier, N. (2016). Determinants of genetic diversity. Nature reviews. Genetics, 17(7), 422-433. [20]. Stroup, D. F., Berlin, J. A., Morton, S. C., Olkin, I., Williamson, G. D., Rennie, D., Moher, D., Becker, B. J., Sipe, T. A., & Thacker, S. B. (2000). Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA, 283(15), 2008-2012. https://doi.org/10.1001/jama.283.15.2008[21]. Fan, J., Fang, C., Gu, Y., & Zhang, T. (2023). Environment invariant linear least squares. arXiv preprint arXiv:2303.03092. [22]. James, A. L., Knuiman, M. W., Divitini, M. L., Musk, A. W., Ryan, G., & Bartholomew, H. C. (1999). Associations between white blood cell count, lung function, respiratory illness and mortality: the Busselton Health Study. The European respiratory journal, 13(5), 1115-1119. [23]. Zeig-Owens, R., Singh, A., Aldrich, T. K., Hall, C. B., Schwartz, T., Webber, M. P., Cohen, H. W., Kelly, K. J., Nolan, A., Prezant, D. J., & Weiden, M. D. (2018). Blood Leukocyte Concentrations, FEV1 Decline, and Airflow Limitation. A 15-Year Longitudinal Study of World Trade Center-exposed Firefighters. Annals of the American Thoracic Society, 15(2), 173-183. [24]. Grant, B. J., Kudalkar, D. P., Muti, P., McCann, S. E., Trevisan, M., Freudenheim, J. L., & Schünemann, H. J. (2003). Relation between lung function and RBC distribution width in a population-based study. Chest, 124(2), 494-500. [25]. Huang, Y., Wang, J., Shen, J., Ma, J., Miao, X., Ding, K., Jiang, B., Hu, B., Fu, F., Huang, L., Cao, M., & Zhang, X. (2021). Relationship of Red Cell Index with the Severity of Chronic Obstructive Pulmonary Disease. International journal of chronic obstructive pulmonary disease, 16, 825-834. https://doi.org/10.2147/COPD.S292666[26]. Wareing, N., Mohan, V., Taherian, R., Volkmann, E. R., Lyons, M. A., Wilhalme, H., Roth, M. D., Estrada-Y-Martin, R. M., Skaug, B., Mayes, M. D., Tashkin, D. P., & Assassi, S. (2023). Blood Neutrophil Count and Neutrophil-to-Lymphocyte Ratio for Prediction of Disease
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 82, 852, 459]]<|/det|>
+572 Progression and Mortality in Two Independent Systemic Sclerosis Cohorts. Arthritis care & 573 research, 75(3), 648- 656. https://doi.org/10.1002/acr.24880 574 [27]. Ulasli, S. S., Ozyurek, B. A., Yilmaz, E. B., & Ulubay, G. (2012). Mean platelet volume 575 as an inflammatory marker in acute exacerbation of chronic obstructive pulmonary disease. 576 Polskie Archiwum Medycyny Wewnetrznej, 122(6), 284- 290. 577 [28]. Eisen, M., Mokhtari, A., & Ribeiro, A. (2017). Decentralized quasi- Newton methods. 578 IEEE Transactions on Signal Processing, 65(10), 2613- 2628. 579 [29]. Chen, M. H., Raffield, L. M., Mousas, A., Sakaue, S., Huffman, J. E., Moscati, A., Trivedi, 580 B., Jiang, T., Akbari, P., Vuckovic, D., Bao, E. L., Zhong, X., Manansala, R., Laplante, V., Chen, 581 M., Lo, K. S., Qian, H., Lareau, C. A., Beaudoin, M., Hunt, K. A., ... Lettre, G. (2020). Trans- 582 ethnic and Ancestry- Specific Blood- Cell Genetics in 746,667 Individuals from 5 Global 583 Populations. Cell, 182(5), 1198- 1213. e14. 584 [30]. Shrine, N., Izquierdo, A. G., Chen, J., Packer, R., Hall, R. J., Guyatt, A. L., Batini, C., 585 Thompson, R. J., Pavuluri, C., Malik, V., Hobbs, B. D., Moll, M., Kim, W., Tal- Singer, R., 586 Bakke, P., Fawcett, K. A., John, C., Coley, K., Piga, N. N., Pozarickij, A., ... Tobin, M. D. 587 (2023). Multi- ancestry genome- wide association analyses improve resolution of genes and 588 pathways influencing lung function and chronic obstructive pulmonary disease risk. Nature 589 genetics, 55(3), 410- 422. 590
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 85, 308, 105]]<|/det|>
+## Figure Legends
+
+<|ref|>text<|/ref|><|det|>[[145, 123, 852, 655]]<|/det|>
+Figure 1. MR- EILLS model. MR- EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR- EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A- C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \(\hat{\mathcal{E}}_j^{(e)}\) in different populations, and larger point means the larger value of \(|\hat{\mathcal{E}}_j^{(e)}|\) . As the pleiotropic effect larger, the \(|\hat{\mathcal{E}}_j^{(e)}|\) is larger, thus the first part of MR- EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \(\hat{\mathcal{E}}_j^{(e)}\) and \(\hat{\theta}_{p,j}^{(e)}\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR- EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\theta_{p,j}^{(e)}\) and \(\mathcal{E}_j^{(e)}\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \(\sum_{e\in E}|\mathcal{E}_j^{(e)}| + \sum_{p\in P}\sum_{e\in E}|\hat{\theta}_{p,j}^{(e)}\mathcal{E}_j^{(e)}|\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . The third part of MR- EILLS model is removing the invalid IVs by \(\lambda\) .
+
+<|ref|>text<|/ref|><|det|>[[145, 657, 852, 770]]<|/det|>
+Figure 2. Simulation results when \(P = 1\) (UVMR). (A- B) Results of causal effect estimation and type I error rate when the causal effect is zero. (C- D) Results of causal effect estimation and type I error rate when the causal effect is 0.1. The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+<|ref|>text<|/ref|><|det|>[[145, 756, 852, 825]]<|/det|>
+Figure 3. Simulation results of causal effect estimation when \(P = 8\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+<|ref|>text<|/ref|><|det|>[[145, 831, 852, 902]]<|/det|>
+Figure 4. Simulation results of type I error rate for spurious exposures and statistical power for causal exposures when \(P = 8\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 83, 854, 152]]<|/det|>
+Figure 5. Simulation results of F1 score, precision and recall when \(P = 15\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(E = 3\) .
+
+<|ref|>text<|/ref|><|det|>[[145, 158, 850, 202]]<|/det|>
+Figure 6. Results in application. (A) the heterogeneity among different populations; (B) the causal effect estimations of 11 blood cells on lung function.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[45, 43, 143, 68]]<|/det|>
+## Figures
+
+<|ref|>image<|/ref|><|det|>[[45, 92, 536, 235]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[45, 250, 130, 259]]<|/det|>
+Summary statistics:
+
+<|ref|>text<|/ref|><|det|>[[48, 260, 161, 281]]<|/det|>
+\(G - X_{p}\) association \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) \(\sigma_{p^{\prime}}^{(\ell)}\) \(G - Y\) association \(\hat{\Gamma}_{p^{\prime}}^{(\ell)}\) \(\sigma_{p^{\prime}}^{(\ell)}\)
+
+<|ref|>text<|/ref|><|det|>[[48, 291, 130, 300]]<|/det|>
+MR- EILLS Model:
+
+<|ref|>image<|/ref|><|det|>[[50, 303, 530, 530]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[68, 551, 483, 810]]<|/det|>
+Figure 1. MR-EILLS model. MR-EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR-EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A-C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \(\hat{\epsilon}_{j}^{(\ell)}\) in different populations, and larger point means the larger value of \(\hat{\epsilon}_{j}^{(\ell)}\) . As the pleiotropic effect larger, the \(\hat{\epsilon}_{j}^{(\ell)}\) is larger, thus the first part of MR-EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \(\hat{\epsilon}_{j}^{(\ell)}\) and \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR-EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) and \(\epsilon_{j}^{(\ell)}\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \(\sum_{n\in \mathbb{J}}\hat{\epsilon}_{j}^{(\ell)}| + \sum_{p\in \mathbb{P}}\sum_{n\in \mathbb{J}}\hat{\theta}_{p^{\prime}}^{(\ell)}\epsilon_{j}^{(\ell)}|\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . The third part of MR-EILLS model is removing the invalid IVs by \(\lambda\) .
+
+<|ref|>text<|/ref|><|det|>[[360, 250, 535, 281]]<|/det|>
+Question: How to infer global causal relationships by integrating multiple heterogeneous GWAS summary datasets?
+
+<|ref|>image<|/ref|><|det|>[[50, 303, 530, 530]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[48, 551, 483, 810]]<|/det|>
+Figure 1. MR-EILLS model. MR-EILLS model aims to infer the causal relationships between one or multiple exposures and one outcome, integrating multiple GWAS summary datasets from heterogeneous populations. There are different pleiotropic effects and IV strengths for the same IVs in heterogeneous populations. The objective function of MR-EILLS model considers the both correlated and uncorrelated pleiotropy and remove the invalid IVs. Figure (A-C) are the results of motivating simulation. Figure (A) shows the point plot for absolute value of \(\hat{\epsilon}_{j}^{(\ell)}\) in different populations, and larger point means the larger value of \(\hat{\epsilon}_{j}^{(\ell)}\) . As the pleiotropic effect larger, the \(\hat{\epsilon}_{j}^{(\ell)}\) is larger, thus the first part of MR-EILLS model minimize pleiotropic effect between different populations. Figure (B) shows the correlation between \(\hat{\epsilon}_{j}^{(\ell)}\) and \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) , which representing the correlated pleiotropic effect or the violation of InSIDE assumption. As the correlated pleiotropic effect increasing, this correlation is larger. This corresponding to the second part of MR-EILLS, the empirical focused linear invariance regularizer, which discourages selecting exposures with strong correlation between \(\hat{\theta}_{p^{\prime}}^{(\ell)}\) and \(\epsilon_{j}^{(\ell)}\) in some populations because this correlation would distort the causal effect estimation. Figure (C) shows the ridge plot of \(\sum_{n\in \mathbb{J}}\hat{\epsilon}_{j}^{(\ell)}| + \sum_{p\in \mathbb{P}}\sum_{n\in \mathbb{J}}\hat{\theta}_{p^{\prime}}^{(\ell)}\epsilon_{j}^{(\ell)}|\) when there are different proportion of invalid IVs. When there are invalid IVs, the ridge plot has two peaks, while the ridge plot has only one peak when there is no invalid IV. The corresponding abscission value at the lowest point between the two peaks is the optimal \(\lambda\) . The third part of MR-EILLS model is removing the invalid IVs by \(\lambda\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[45, 850, 113, 867]]<|/det|>
+## Figure 1
+
+<|ref|>text<|/ref|><|det|>[[45, 892, 345, 910]]<|/det|>
+See image above for figure legend.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[40, 45, 949, 352]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 372, 117, 392]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[41, 414, 928, 504]]<|/det|>
+Simulation results when \(\mathrm{P} = 1\) (UVMR). (A- B) Results of causal effect estimation and type I error rate when the causal effect is zero. (C- D) Results of causal effect estimation and type I error rate when the causal effect is 0.1. The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[44, 45, 866, 789]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 802, 116, 821]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[42, 842, 907, 888]]<|/det|>
+Simulation results of causal effect estimation when \(\mathbf{P} = \mathbf{8}\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[44, 45, 870, 789]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 802, 117, 820]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[42, 843, 940, 909]]<|/det|>
+Simulation results of type I error rate for spurious exposures and statistical power for causal exposures when \(\mathbf{P} = \mathbf{8}\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[44, 48, 950, 280]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 301, 118, 320]]<|/det|>
+Figure 5
+
+<|ref|>text<|/ref|><|det|>[[42, 342, 930, 386]]<|/det|>
+Simulation results of F1 score, precision and recall when \(\mathbf{P} = 15\) (MVMR). The number of IVs is 100 and the proportion of invalid IVs is \(30\%\) . The number of populations is \(\mathrm{E} = 3\) .
+
+<|ref|>image<|/ref|><|det|>[[45, 406, 950, 742]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 765, 116, 784]]<|/det|>
+Figure 6
+
+<|ref|>text<|/ref|><|det|>[[42, 806, 858, 849]]<|/det|>
+Results in application.(A) the heterogeneity among different populations; (B) the causal effect estimations of 11 blood cells on lung function.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 873, 312, 900]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 923, 768, 942]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 46, 390, 92]]<|/det|>
+SupplementaryTable.xlsxSupplementaryMaterials1208.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/images_list.json b/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..46b974b84b5d5d57711985e352f7e845541fe9f8
--- /dev/null
+++ b/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/images_list.json
@@ -0,0 +1,152 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1: Ternary complex of SMARCA2 and VHL/ElonginC/ElonginB (VCB) induced by ACBI1 shows structural similarities with PROTAC 1 and PROTAC 2: a Overall perspective of SMARCA2 Isoform 2 (green) and VCB (grey) induced by degrader molecule ACBI1 (bright orange). b ACBI1-induced interface contacts between SMARCA2 and VCB. The proteins are shown in space-filling, the colors are as in a, annotated residues are among those that make the highest number of contacts (see c). c A contact map for the interface of the crystal structure. The circle size reflects the number of atoms (including hydrogen atoms) participating in interactions. d Superposition of 6HAY (purple), 6HAX (salmon), 7S4E (green) by aligning VHL (grey) shows varied conformations of the warheads of the three degraders PROTAC 1, PROTAC 2, or ACBI1 (up to 1.7 Å) resulting in alterations of SMARCA2 within the ternary complex.",
+ "footnote": [],
+ "bbox": [
+ [
+ 195,
+ 184,
+ 808,
+ 579
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2: ACBI1-induced ternary complex formation of SMC2:VCB leads to protection of specific sites:a-d, SMARCA2 isoform 2(a), VHL(b), Elongin C(c), and Elongin B(d) monitored for hydrogen-deuterium exchange over time. The difference plots of each protein in the binary and ternary states are generated by subtracting the deuterium exchange of like peptides of the APO or binary from the binary or ternary states (defined as Binary \\(\\Delta\\) APO and Ternary \\(\\Delta\\) Binary), respectively. Regions that exchange significantly less than the comparative state are depicted in blue (negative), whereas regions that exchange significantly more appear in red (positive). The resultant difference plots of the binary (e), or ternary complex (f) were mapped onto the structure 7S4E. The experiments were repeated on 2 separate days. All raw relative uptake plots of the deuterium exchange for each state and experiment can be found in the supplementary material (Supplementary Figures 38–88).",
+ "footnote": [],
+ "bbox": [
+ [
+ 240,
+ 120,
+ 757,
+ 660
+ ]
+ ],
+ "page_idx": 12
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3: Comparison of WESTPA simulations with and without data from HDX-MS experiments. I-RMSD probability densities are shown for ternary complexes with a warhead RMSD \\(< 2 \\text{Å}\\) and \\(> 30\\) contacts between protected residues. Structures sampled by WES+HDX (red) have almost exclusively an I-RMSD value \\(< 2 \\text{Å}\\) , whereas those from WE simulations without any information from HDX (blue) are widely distributed.",
+ "footnote": [],
+ "bbox": [
+ [
+ 150,
+ 364,
+ 852,
+ 672
+ ]
+ ],
+ "page_idx": 17
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4: Illustration of the representative prediction produced by REVO simulation and its comparison to the co-crystallized structure (PDB ID: 6HAX) (a) predicted ternary structure with I-RMSD=1.1 Å; (b) detail of the binding interface; (c) contact maps for the interfaces of co-crystallized and predicted structures. The circle size reflects the number of atoms (including hydrogens) participating in interactions; (d) structurally aligned prediction (green) and co-crystallized structure (pink) with a detailed PROTAC 2 comparison shown.",
+ "footnote": [],
+ "bbox": [
+ [
+ 130,
+ 150,
+ 888,
+ 730
+ ]
+ ],
+ "page_idx": 18
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5: Assessing ternary complex formation. (a) The minimum I-RMSD over time during the simulation for the REVO simulations of the PROTAC2 system. Each green line indicates one replica and the black line is the average between all runs. The blue line indicates the I-RMSD for a vanilla molecular dynamics simulation. (b) A scatter plot of the free energy vs the I-RMSD of each of the 500 clusters from the PROTAC 2 simulations. The circles are colored by w-RMSD. (c) The predicted binding rates for PROTAC 1 system (purple) and the ACBI1 system (green). The black line is the experimental on rate determined via SPR.",
+ "footnote": [],
+ "bbox": [
+ [
+ 315,
+ 110,
+ 662,
+ 744
+ ]
+ ],
+ "page_idx": 19
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6: Comparing the bound ensembles determined by docking and REVO simulations with information from HDX-MS for the PDB ID 6HAX ternary complex. The REVO bound ensemble is defined as structures below a warhead RMSD of 2 Å and more than 30 contacts between the target and ligase interface. The docking bound basin is defined as the top-100 structures as determined by Rosetta-scoring. (a) Probability density function distributions of I-RMSD values for the bound ensembles. (b) The percent of structures in the predicted bound ensembles below specific I-RMSD thresholds (2 Å, 2.5 Å, and 3 Å).",
+ "footnote": [],
+ "bbox": [
+ [
+ 250,
+ 145,
+ 723,
+ 712
+ ]
+ ],
+ "page_idx": 22
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_7.jpg",
+ "caption": "Figure 7: SAXS profiles and structural ensembles of SMC2-isoform1/isoform2:ACBI1:VCB complexes. (a) Comparison of theoretical and experimental SAXS profiles, SAXS intensity vs. \\(q\\) . (b) The histograms of \\(\\mathrm{R}_g\\) of SMC2-isoform1:ACBI1:VCB (red) and SMC2-isoform2:ACBI1:VCB (blue) complexes calculated from HREMD simulations. The inverted red and blue triangles are the \\(\\mathrm{R}_g\\) values of starting structures of SMC2-isoform1/isoform2:ACBI1:VCB from homology model and crystallography respectively.",
+ "footnote": [],
+ "bbox": [
+ [
+ 220,
+ 101,
+ 770,
+ 777
+ ]
+ ],
+ "page_idx": 24
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_15.jpg",
+ "caption": "Figure 8: Most populated structures of SMARCA2 bound to VHL with different degrader molecules, identified by dimension reduction and clustering of HREMD simulation data. (a-d) Colors of VHL and SMARCA2 represent HDX-MS protection in the presence of the degrader molecules relative to the situation in the absence of the degrader. The second ranked structures of c PROTAC 2 and d isoform 1 SMARCA2 are displayed and support our HDX-MS data, whereas the top three structures are included in Supplementary Figure 15. Elongin B and Elongin C are also included in panel d. e The top structures of ternary complexes are compared after aligning VHL to illustrate conformational differences among top structures of ternary complexes.",
+ "footnote": [],
+ "bbox": [
+ [
+ 137,
+ 103,
+ 870,
+ 728
+ ]
+ ],
+ "page_idx": 25
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_9.jpg",
+ "caption": "Figure 9: a Conformational free energy landscape as a function of the first two tICA features of SMARCA2-PROTAC2-VHL ternary complex inferred from a Markov state model (MSM). The ensemble of bound states from REVO simulations is shown as blue points; the crystal structure (PDB ID 6HAX) is shown as a red X. In this projection, states II and V are close to state I. b Network diagram of the coarse-grained MSM calculated using a lag time of 50 ns, with the stationary probabilities associated with each state indicated. c Mean first-passage times to transition (MFPT) from one state in the MSM to another. Numbers indicate predicted MFPTs in \\(\\mu \\mathrm{s}\\) . d-e Comparison of the crystal structure (gray) with the lowest free energy state (cyan) and a metastable state (orange) predicted by the MSM. Arrows indicate a change of orientation relative to d.",
+ "footnote": [],
+ "bbox": [
+ [
+ 313,
+ 116,
+ 685,
+ 666
+ ]
+ ],
+ "page_idx": 26
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_10.jpg",
+ "caption": "Figure 10: Degrader dependent SMARCA2 Lys densities in the CRL-VHL ubiquitination zone. a. Active form of CRL-VHL with bound SMARCA2 and E2-ubiquitin with open CRL conformation. b. same as a with a closed conformation of CRL generated by meta-eABF simulations. c. Distance of Lys residues (side-chain nitrogen atom) from SMARCA2 to the C-terminus glycine C atom of ubiquitin for three different degraders. d. Density of Lys residues in 3D space near ubiquitination zone of CRL-VHL.",
+ "footnote": [],
+ "bbox": [
+ [
+ 197,
+ 110,
+ 820,
+ 773
+ ]
+ ],
+ "page_idx": 30
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182.mmd b/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..6fe2b682b3ee63d44ae995b62e385bebd33c1dda
--- /dev/null
+++ b/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182.mmd
@@ -0,0 +1,729 @@
+
+# Atomic-Resolution Prediction of Degrader-mediated Ternary Complex Structures by Combining Molecular Simulations with Hydrogen Deuterium Exchange
+
+Tom Dixon Michigan State University https://orcid.org/0000- 0002- 4520- 3894
+
+Derek MacPherson Roivant Discovery https://orcid.org/0000- 0003- 2006- 1620
+
+Barmak Mostofian Roivant Discovery https://orcid.org/0000- 0003- 0568- 9866
+
+Taras Dauzhenka Roivant Discovery
+
+Samuel Lotz Roivant Discovery
+
+Dwight McGee Roivant Discovery
+
+Sharon Shechter Roivant Discovery
+
+Utsab Shrestha Roivant Discovery
+
+Rafal Wiewiora Roivant Discovery
+
+Zachary McDargh Roivant Discovery
+
+Fen Pei Roivant Discovery
+
+Rajat Pal Roivant Discovery
+
+Joao Vieira Ribeiro Roivant Discovery https://orcid.org/0000- 0002- 0353- 4126
+
+Tanner Wilkerson Roivant Discovery
+
+Vipin Sachdeva Roivant Discovery
+
+<--- Page Split --->
+
+Ning Gao Roivant Discovery Shouya Jain Roivant Discovery Samuel Sparks Roivant Discovery Yunxing Li Roivant Discovery Alexander Vinitsky Roivant Discovery Xin Zhang Roivant Discovery Asghar Razavi Roivant Discovery István Kolossváry Roivant Discovery Jason Imbriglio Roivant Discovery Artem Evdokimov Roivant Discovery Louise Bergeron Roivant Discovery Alex Dickson Michigan State University Huafeng Xu Michigan State University Woody Sherman Michigan State University Jesus Izaguirre ( Jesus.izaguirre@roivant.com ) Roivant Discovery https://orcid.org/0000-0002-4687-4884
+
+## Article
+
+Keywords:
+
+Posted Date: February 15th, 2022
+
+DOI: https://doi.org/10.21203/rs.3.rs-1318882/v1
+
+<--- Page Split --->
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on October 6th, 2022. See the published version at https://doi.org/10.1038/s41467-022-33575-4.
+
+<--- Page Split --->
+
+# Atomic-Resolution Prediction of Degrader-mediated Ternary Complex Structures by Combining Molecular Simulations with Hydrogen Deuterium Exchange
+
+Tom Dixon, \(^{1, \bullet}\) Derek MacPherson, \(^{1, \bullet}\) Barmak Mostofian, \(^{1, \bullet}\) Taras Dauzhenka, \(^{1}\) Samuel Lotz, \(^{1}\) Dwight McGee, \(^{1}\) Sharon Shechter, \(^{1}\) Utsab R. Shrestha, \(^{1}\) Rafal Wiewiora, \(^{1}\) Zachary A. McDargh, \(^{1}\) Fen Pei, \(^{1}\) Rajat Pal, \(^{1}\) João V. Ribeiro, \(^{1}\) Tanner Wilkerson, \(^{1}\) Vipin Sachdeva, \(^{1}\) Ning Gao, \(^{1}\) Shourya Jain, \(^{1}\) Samuel Sparks, \(^{1}\) Yunxing Li, \(^{1}\) Alexander Vinitsky, \(^{1}\) Xin Zhang, \(^{1}\) Asghar M. Razavi, \(^{1}\) István Kolossváry, \(^{1}\) Jason Imbriglio, \(^{1}\) Artem Evdokimov, \(^{1}\) Louise Bergeron, \(^{1}\) Alex Dickson, \(^{*, \dagger}\) Huafeng Xu, \(^{*, \dagger}\) Woody Sherman, \(^{*, \dagger}\) and Jesus A. Izaguirre \(^{*, \dagger}\)
+
+\(^{1}\) Department of Biochemistry and Molecular Biology, Michigan State University, USA \(^{1}\) Roviant Discovery, New York, USA
+
+\(^{1}\) These authors contributed equally
+
+E- mail: alexrd@msu.edu; huafeng.xu@roivant.com; woody.sherman@roivant.com; jesus.izaguirre@roivant.com
+
+## Abstract
+
+Targeted protein degradation (TPD) has emerged as a powerful approach for removing (rather than inhibiting) proteins implicated in diseases. A key step in TPD
+
+<--- Page Split --->
+
+is the formation of an induced proximity complex where a degrader molecule recruits an E3 ligase to the protein of interest (POI), facilitating the transfer of ubiquitin to the POI and initiating the proteasomal degradation process. Here, we address three critical aspects of the TPD process using atomistic simulations: 1) formation of the ternary complex induced by a degrader molecule, 2) conformational heterogeneity of the ternary complex, and 3) degradation efficiency via the full Cullin Ring Ligase (CRL) macromolecular assembly. The novel approach described here combines experimental biophysical data with molecular dynamics (MD) simulations to accurately predict ternary complex structures at atomic resolution. We integrate hydrogen-deuterium exchange mass spectrometry (HDX-MS, which measures the solvent exposure of protein residues) with MD to improve the efficiency and accuracy of the ternary structure predictions of the bromodomain of the cancer target SMARCA2 with the E3 ligase VHL, as mediated by three different degrader molecules. The simulations accurately reproduce X- ray crystal structures – including a new structure that we determined in this work (PDB ID: 7S4E) – with root mean square deviations (RMSD) of 1.1 to 1.6 Å. The simulations also reveal a structural ensemble of low- energy conformations of the ternary complex. Snapshots from these simulations are used as seeds for additional simulations, where we perform 7.1 milliseconds of aggregate simulation time using Folding@home. The detailed free energy surface captures the crystal structure conformation within a low- energy basin and is consistent with solution- phase experimental data (HDX- MS and SAXS). Finally, we graft a structural ensemble of the ternary complexes onto the full CRL and perform enhanced sampling simulations, which suggest that differences in degradation efficiency may be related to the proximity distribution of lysine residues on the POI relative to the E2- loaded ubiquitin.
+
+## 1 Introduction
+
+Heterobifunctional degraders are a class of ligands that induce proximity between a target protein of interest (POI) and a E3 ubiquitin ligase, which can ultimately lead
+
+<--- Page Split --->
+
+to ubiquitination of the POI and its subsequent proteosomal degradation through a complex machinery of proteins. \(^{1}\) These degraders provide the opportunity of a novel therapeutic modality – single molecules induce catalytic turnover of the POI – and potentially offer an avenue for modulation of targets traditionally labeled as “undruggable” by classical therapeutic strategies. \(^{2 - 4}\) The subset of degraders classified as hetero- bifunctionals consists of two separate moieties, the “warhead” and the “ligand”, joined by a “linker”; the warhead binds to the POI and the ligand binds to an E3 ligase such as Cereblon (CRBN), \(^{5 - 7}\) cIAP, \(^{8}\) KEAP1, \(^{9}\) and von Hippel- Lindau protein (VHL). \(^{10 - 12}\) In each case it is the ability of the warhead- linker- ligand degrader molecule to induce a ternary complex that is critical for bridging the interaction between the POI and an E3 ligase (which can be the native or non- native degradation partner of the POI). Often key to the function of these molecules, cooperativity, i.e., the difference between the binding affinity of the ternary complex and those of its binary components, is a complex descriptor of these non- native interactions bridging the induced interface of the POI- E3 pair and it has strong correlation to degradation efficiency.
+
+The formation of the POI- degrader- E3 ternary complex is central to the targeted protein degradation (TPD) process, but how the formation of the ternary structure impacts protein degradation is still poorly understood, especially given the dynamic nature of the non- native induced proximity complex. \(^{13}\) X- ray crystallography – the primary experimental technique for determining 3- dimensional structures of the ternary complex \(^{14}\) – provides a high resolution structure of a single conformational state, but a growing body of evidence suggests that the dynamic nature of the ternary structure may not accurately represented by this lowest energy crystallization snapshot. For instance, a study of several heterobifunctional degraders, that induce proximity between VHL and SMARCA2, a BAF ATPase subunit, found that a positive cooperativity upon ternary complex formation leads to higher degradation efficiency. \(^{15}\) Furthermore, despite the fact that the different SMARCA2 degraders displayed different degrees of efficiency, \(^{15}\) the formed ternary complexes are nearly structurally identical, raising questions about the relationship between static structural representations of the
+
+<--- Page Split --->
+
+ternary complex and degradation efficiency. Moreover, further complicating the relationship of cooperativity, structure and degradation, studies targeting the degradation of Burton Tyrosine Kinase (BTK) by CRBN or cIAP found that high degradation efficiencies can also be achieved through degrader molecules that induce a non- cooperative ternary complex, demonstrating a disconnect between binding affinity and degradation efficiency. \(^{16,17}\)
+
+This and other findings \(^{18 - 20}\) suggest that degradation efficiency is more complex than can be understood through the thermodynamics of binding or through the analysis of static structures. As such, determining the dynamic ensemble of the ternary complex may reveal mechanistic insights to facilitate the design of more effective degrader molecules. \(^{14,21 - 24}\)
+
+Our ultimate goal is to understand the structural and dynamic basis for differences in degradation among a set of degrader molecules. Here, we specifically focus on three different VHL- recruiting degraders of SMARCA2 isoform 2, for which crystal structures already exist, i.e., PROTAC 1 (PDB ID: 6HAY) and PROTAC 2 (PDB ID: 6HAX), or have been obtained as part of this study, namely ACBI1 (PDB ID: 7S4E), with cooperativity and degradation efficiency summarized in Table 1. To this end, we carry out MD simulations in combination with hydrogen- deuterium exchange mass- spectrometry (HDX- MS), shedding light on the dynamics of the ternary complexes beyond what is provided by static crystal structures. Specifically, we use “protection data” derived from HDX- MS as collective variables in weighted- ensemble MD simulations, enhancing both the speed and accuracy of the computational predictions. We also show the usefulness of HDX- MS data as constraints for protein- protein docking when higher throughput and lower resolution models are sought, such as when screening many degrader molecules. Furthermore, we introduce methodology, that includes long- timescale MD simulations augmented with small- angle X- ray scattering (SAXS) data and Markov state modeling, to determine the conformational free energy landscapes of the ternary complexes, which is the foundation for quantifying the populations of different conformational states. Finally, as an example of downstream use of these models,
+
+<--- Page Split --->
+
+we also model the entire cullin- RING ligase (CRL) assembly to explore structural and dynamic factors that may be associated with ubiquitination.
+
+Previous work to computationally predict ternary structures mostly consisted of protein- protein docking protocols, possibly followed by refinement of the initial structures with molecular dynamics (MD) simulations to assess the stability of the predicted models. \(^{23 - 29}\) However, these docking protocols fail to predict high- resolution structures (sub- 2.0 Å) with high fidelity, demonstrating the challenge associated with the generation and selection of high- accuracy ternary structure models.
+
+Recently, Eron et al. demonstrated how ternary complex structures of BRD4 do not represent the biologically relevant conformer of the ternary complex induced with CRBN. These studies demonstrated the merit of HDX- MS and modeling revealed the dynamic nature and alternative conformations that helped explain the dramatically increased cooperativity, ternary complex formation and degradation of their molecule CFT- 1297 compared to the literary standard, dBET6. \(^{30}\) The authors used the experimental data to improve protein- protein docking predictions, but they admit that the high flexibility of degrader- induced ternary complexes impedes a complete description of the bound conformations.
+
+This work offers unique insights into the dynamic nature of the ternary structure ensemble and that of the full CRL macromolecular assembly that could explain ubiquitination and downstream protein degradation. Our results can be used to guide the design of novel degrader molecules that induce a productive ternary complex ensemble. In particular, having a small set of high population ternary complex structures can provide an avenue for structure- based degrader design, particularly focused on linker design to improve different properties of the degrader. We make the simulation and experimental results available to the research community, including source codes and the release of a new X- ray crystal structure of ACBI1 with SMARCA2:VHL that has been deposited into the Protein Data Bank (PDB ID: 7S4E).
+
+<--- Page Split --->
+
+Table 1: Binding affinity \((K_{d})\) , efficiencies (IC50, DC50), and cooperativity \((\alpha)\) of PROTAC 1, PROTAC 2, and ACBI1 degraders. Ternary IC50 and binary (SMARCA2) DC50 values are reported; the cooperativity is the ratio of binary over ternary IC50. Table adapted from Farnaby et al. \(^{15}\)
+
+ | Kd, VHL(nM) | Kd, SMARCA2(nM) | IC50 (nM) | DC50 (nM) | α |
| PROTAC 1 | 98 ± 26 | 4500 ± 480 | 205 ± 15 | 300 | 12 |
| PROTAC 2 | 100 ± 10 | 770 ± 51 | 45 ± 9 | N/A | 18 |
| ACBI1 | 250 ± 64 | 1800 ± 980 | 26 ± 3 | 6/3.3 | 30 |
+
+## 2 Results
+
+### 2.1 Degraders with different efficiency induce similar ternary complex structures in X-ray crystallography.
+
+The ternary complexes of SMARCA2 isoform 2 (SMC2) and the VHL/ElonginC/ElonginB (VCB) complex induced by different heterobifunctional degraders have been studied extensively. \(^{23,31}\) In particular, PROTAC 1, PROTAC 2, and ACBI1 are three prominent degrader molecules that induce a ternary SMC2:VCB complex with quite different degradation efficiencies (see Table 1). Whereas crystal structures of the ternary complexes induced by PROTAC 1 (PDB ID: 6HAY) and PROTAC 2 (PDB ID: 6HAX) exist, none has been reported to date for ACBI1, the most potent degrader among them. Thus, we determined the structure of SMC2:VHL liganded by ACBI1 via X- ray crystallography. The structure was obtained by hanging drop vapor diffusion (see Methods) \(^{23}\) and solved by molecular replacement to 2.25 Å in the highest resolution shell (Supplementary Figure 20), using the PROTAC 2 (PDB ID:6HAX) crystal structure as the search model (Figure 1a).
+
+ACBI1 bridges the induced interface, forming contacts with both proteins. Importantly, the ligand induces favorable contacts across the non- native interface, such as VCB:ARG69 and SMC2:PHE1463 (Figure 1 b,c). SMC2:ASN1464 maintains critical bivalent contacts to the aminopyridazine group of ACBI1, positioning the terminal phenol group for pi stacking interactions with residues PHE1409 and TYR1421 (Figure
+
+<--- Page Split --->
+
+1b,c). On the VHL side of the interface, the interactions between TYR98 and ACBI1 are consistent with those between the same residue and PROTAC 1 or PROTAC 2 (Figure 1b,c). \(^{23}\)
+
+
+
+Figure 1: Ternary complex of SMARCA2 and VHL/ElonginC/ElonginB (VCB) induced by ACBI1 shows structural similarities with PROTAC 1 and PROTAC 2: a Overall perspective of SMARCA2 Isoform 2 (green) and VCB (grey) induced by degrader molecule ACBI1 (bright orange). b ACBI1-induced interface contacts between SMARCA2 and VCB. The proteins are shown in space-filling, the colors are as in a, annotated residues are among those that make the highest number of contacts (see c). c A contact map for the interface of the crystal structure. The circle size reflects the number of atoms (including hydrogen atoms) participating in interactions. d Superposition of 6HAY (purple), 6HAX (salmon), 7S4E (green) by aligning VHL (grey) shows varied conformations of the warheads of the three degraders PROTAC 1, PROTAC 2, or ACBI1 (up to 1.7 Å) resulting in alterations of SMARCA2 within the ternary complex.
+
+Despite differences in the linker compositions, the protein- protein interface induced by ACBI1 is structurally similar to that induced by PROTACs 1 or \(2^{23}\) (see Figure 1d). There are more distal changes in the orientation of SMARCA2 with respect to
+
+<--- Page Split --->
+
+VCB due to the minor differences in the linker compositions, e.g. the ACBI1 linker has one additional ether group compared to the PROTAC 2 linker, which yields a slight 1.7 Å twist of ACBI1 compared to the other two degraders, resulting in a subtle 5 Å “swing” of the protein in the crystal structure (Figure 1d).
+
+Overall, the structural similarity of the protein- protein interface does not align with the markedly different degradation efficiency obtained \(^{15}\) suggesting that the (dynamic) ensemble of ternary complex structures may be fairly different among them. Consistent with other studies, \(^{17,32}\) this implies that “crystallographic snapshots” are not suitable to provide a holistic view of the ensemble of all possible ternary complex structures in solution, but merely represent a subset of the relevant conformations favored by crystallization. \(^{33}\) Consequently, such X- ray structures cannot fully capture the dynamic nature of the degrader- induced ternary complexes, which play a pivotal role in biological activity and degradation efficiencies. \(^{17,32}\)
+
+### 2.2 Hydrogen Deuterium Exchange Reveals Extended Protein-Protein Interfaces
+
+In order to assess the impact of different degrader molecules on the dynamic nature of the SMC2:VCB interactions, we performed hydrogen- deuterium exchange of the respective APO, binary and ternary (complex) species, thus characterizing the induced protein- protein interface in solution. \(^{30}\) This approach is a promising alternative to previous attempts at characterizing degrader ternary complexes that employed multiple crystal structures, \(^{32}\) NMR, \(^{17}\) and SAXS coupled with various forms of modeling. Based on previously established protocols, \(^{34 - 36}\) and with the knowledge of binding constants for each of the three degraders, the assay was designed to optimize the complex formation of 80% or greater to obtain maximal exchange of the ternary complexes. The complexes were subsequently subjected to on- line pepsin digestion and optimized for 100% sequence coverage (see supplementary Fig. 22) of each protein within the complex and stable deuterium exchange (see supplementary Figs. 23- 26). To ascertain the changes in
+
+<--- Page Split --->
+
+solvent protection in the binary or ternary complex, the peptide- specific uptake of the APO or binary species was subtracted from that of the corresponding like peptides in the binary or ternary state (referred to as Binary \(\Delta\) APO and Ternary \(\Delta\) Binary), respectively. The results are summarized in difference plots that highlight the statistically significant (95% or 98% confidence interval) changes in D2O uptake (see Figure 2a- d for the SMC2:VCB complex induced by ACBI). Importantly, protection during HDX- MS arises due to changes in the environment around the observed residues, which could be a result of direct occlusion of solvent or conformational changes. \(^{37}\)
+
+Figure 2a reveals that large regions of SMC2 become protected upon ternary complex formation (see Ternary \(\Delta\) Binary difference plot). These stretches of protected residues, e.g. amino acids 1409- 1422 and 1456- 1470, overlap with the ligand binding site based on the ternary complex structure published in this work (7S4E) and those published previously (6HAY, 6HAX), which confirms the similarity of the ternary complex interface among the three degrader molecules discussed above. Additionally, there are also stretches of protected amino acids, 1394- 1407, that are too distant from the established binding interface to result from complex formation (Figure 2a and f). Interestingly, the Binary \(\Delta\) APO difference plot shows that under our experimental conditions the ligand concentration is close to the dissociation constant \(\mathrm{KD} = 10\mu \mathrm{M}^{23}\) ), as there is minimal difference between the exchange of SMC2 in presence and in absence of the ligand (Figure 2a and e).
+
+Large regions of VHL are protected in the presence of the ligand as indicated by the Binary \(\Delta\) APO difference plot (Figure 2b and e). The most protected residues in the binary state are centered around amino acids 87- 116, which include all 9 residues in the ligand binding site of VHL. In the presence of SMC2 (see Figure 2b, Ternary \(\Delta\) Binary difference plot), much of the allosteric network due to ligand binding can be subtracted away leaving only the most significantly protected residues induced by ternary complex formation (Figure 2b and f). In particular, residues 60- 72, which house the critical interaction of ARG69 show significant protection due to ternary complex formation (Figure 2b and f). Taken together, this data underscores the importance of
+
+<--- Page Split --->
+
+
+Figure 2: ACBI1-induced ternary complex formation of SMC2:VCB leads to protection of specific sites:a-d, SMARCA2 isoform 2(a), VHL(b), Elongin C(c), and Elongin B(d) monitored for hydrogen-deuterium exchange over time. The difference plots of each protein in the binary and ternary states are generated by subtracting the deuterium exchange of like peptides of the APO or binary from the binary or ternary states (defined as Binary \(\Delta\) APO and Ternary \(\Delta\) Binary), respectively. Regions that exchange significantly less than the comparative state are depicted in blue (negative), whereas regions that exchange significantly more appear in red (positive). The resultant difference plots of the binary (e), or ternary complex (f) were mapped onto the structure 7S4E. The experiments were repeated on 2 separate days. All raw relative uptake plots of the deuterium exchange for each state and experiment can be found in the supplementary material (Supplementary Figures 38–88).
+
+<--- Page Split --->
+
+cooperativity driving the formation of the ternary complex for molecules with poor binding affinity to the POI. Under the same conditions as the binary SMC2 experiments, ligand binding and resultant changes in deuterium exchange are only observed on SMC2 in the presence of the E3 VHL.
+
+Additionally, we observe protection of residues 166- 176 and residues 187- 201 on VHL (Figure 2b and f) as well as some regions on Elongin B and C that show protection upon ternary complex formation (see Figure 2c and d). Although these sites are distal from the binding interface, they spatially align with one another when mapped onto the structure (Figure 2c) potentially uncovering a critical network of allosteric changes38 induced by ACBI1 that may play a role in downstream positioning of SMARCA2 to the E2 in the CRL complex.
+
+Studying the solution state dynamics of the protein and protein complexes uncovers key details that are missed by crystallographic snap shots. As many of the crystallographic contacts are nearly identical between the different degrader molecules, there must be critical interactions being underrepresented in this way. Utilizing HDX- MS or other solution state derived data as restraints in modeling and simulation opens a pathway from a single accepted protein conformer to a vast ensemble of protein complexes. Production of high accuracy protein ensembles enables alternative routes for design, optimization and mechanism of action studies for degrader and molecular glues.
+
+### 2.3 HDX data enhance weighted ensemble simulations of ternary complex formation
+
+We simulate the formation of SMC2:VHL degrader ternary complexes using weighted ensemble simulations (WES), where a set of weighted trajectories (called "walkers") are evolved in parallel providing a means to compute non- equilibrium properties and predict likely binding pathways. Specifically, we apply the WESTPA software, which discretizes sampling space into bins along pre- defined collective variables (CVs). While this path sampling strategy has been employed before for tasks such as protein- protein
+
+<--- Page Split --->
+
+binding, \(^{39}\) it is noteworthy that the current simulations are not informed by any structural data about the ternary complex interface from X- ray crystallography experiments.
+
+Starting from a dissociated configuration, in which the degrader molecule (e.g., PROTAC 2) is bound to VHL, yet both are clearly apart from SMC2 (initial separation distance \(\sim 20 \mathrm{\AA}\) ), the formation of ternary aggregates is simulated yielding complexes with interface structures well comparable to that obtained experimentally (PDB ID: 6HAX). For this simulation, we used observables such as the number of atomic contacts or the distance between the target (SMC2) and ligase (VHL) proteins or the warhead- RMSD (w- RMSD) with respect to the crystal structure of the target- warhead complex as CVs and we assessed the quality of bound complexes by a different metric, namely the interface- RMSD (I- RMSD) \(^{40}\) of each walker with respect to a reference ternary structure (see Methods for all simulation details).
+
+An ensemble of bound ternary complexes with I- RMSD \(< 2 \mathrm{\AA}\) can be simulated within an aggregate simulation time of \(\sim 5 \mu \mathrm{s}\) . Remarkably, when introducing as a CV the number of contacts formed by the protected residues, as determined by the HDX- MS experiments described above, the fraction of ternary complexes with an I- RMSD \(< 2 \mathrm{\AA}\) is markedly higher compared to simulations, in which any protein- protein contacts were considered (see Figure 3). Movie S1 shows the continuous trajectory of one such ternary complex binding event. This improvement illustrates the significance of merging high- performance computer simulations, that generate a wealth of molecular structures, with solution- phase experimental methods, that capture the inherently dynamic nature of degrader ternary complexes. In this regard, the synergy of WE simulations with HDX- MS is a particularly interesting example where the path sampling algorithm is furnished with a fairly simple parameter, derived from experimental measurements. We call this integrated approach WES+HDX throughout this work.
+
+While the WES discussed above reliably produce the ternary complex, the algorithm is expensive due to the use of two CVs and an increasing number of walkers. Therefore, to more systematically study the formation of ternary complexes with all three degraders, i.e., ACBI1, PROTAC 1 and PROTAC 2, we employ the bin- less WE
+
+<--- Page Split --->
+
+variant 'Resampling of Ensembles by Variation Optimization' (or REVO), \(^{41}\) which maximizes an objective function called the trajectory variation, defined using a sum of walker- walker distances (see Methods). Specifically, we simulate the ternary complex formation using a distance metric composed of a weighted combination of w- RMSD, differences in contacts between the target and ligase protected residues, and the differences in contacts between the target and the PROTAC.
+
+We ran seven independent REVO simulations to predict the ternary complex of PROTAC 2 for an aggregate simulation time of \(12.5\mu s\) and three such simulations totaling \(\sim 6\mu s\) for both PROTAC 1 and ACBI1. These simulations had 48 walkers each and were run for 2000 cycles at 20 ps per cycle. In all simulations, bound ternary complexes were formed with minimum I- RMSDs of \(0.5\mathrm{\AA}\) for ACBI1, \(0.7\mathrm{\AA}\) for PROTAC 1, and \(1.1\mathrm{\AA}\) for PROTAC 2, respectively.
+
+To highlight the sampling ability of WE simulations, Figure 5a compares the minimum I- RMSD of the SMC2:PROTAC2:VHL simulation with that from vanilla MD simulations of the same system as a function of aggregate simulation time. While the minimum I- RMSD converges to \(2.5\mathrm{\AA}\) across the 7 REVO simulations within \(0.2\mu s\) of aggregate simulation time (Fig. 5 A). In comparison, the I- RMSD for vanilla MD remains as high as \(10\mathrm{\AA}\) after \(1.4\mu s\) of simulation.
+
+The very high prediction accuracy of the WES+HDX simulations is illustrated for the SMC2:PROTAC2:VHL system in Figure 4. Examples of predicted structures are visualized in Figure 4a,b. The contact maps presented in Figure 4c have been obtained by the Arpeggio software \(^{42}\) applied to the ternary interfaces of the experimental cocrystal structure (top panel) and to the lowest I- RMSD structure produced by the WES+HDX simulations (bottom panel). Each point reflects the degree of interaction, revealing an interaction pattern from the WES+HDX simulations that is comparable to that from experiment. The near- perfect alignment (I- RMSD = \(1.1\mathrm{\AA}\) ) of one sampled conformation with the co- crystallized structure shown in Figure 4d further emphasizes that the interactions of ternary degrader complexes observed experimentally can be recaptured by WES+HDX.
+
+<--- Page Split --->
+
+Six out of seven of the SMC2:PROTAC2:VHL simulations observed binding events for a total of 3278 unique observations. In order to assess the degree of heterogeneity within this ensemble, we clustered the WE results into 500 macrostates with a k- means algorithm using the \(C\alpha - C\alpha\) distances between the ligase and target protected residues. As expected, all low I- RMSD states have low values of w- RMSD (Figure 5b). States with high free energies, i.e., above 1.5 kcal/mol, have large I- RMSDs, ranging from 1.5 to 30 Å. However, the I- RMSD distribution among the 20 low free energy states below 0.5 kcal/mol is significantly tighter, ranging from 1.1 to 9.2Å with an average value of 3.7 Å and 12 out of 20 states even having an I- RMSD below 3 Å.
+
+We predict binding rate constants for the three different PROTACs directly from WES+HDX simulations using the probability flux into a bound state (I- RMSD < 2 Å). While the predicted rates for PROTAC 1 and ACBI1 are on the same order of magnitude as in experiments (Figure 5c), we predict a significantly slower binding rate for PROTAC 2, which is not yet determined experimentally. However, for all three rates there are large uncertainties, as has previously been observed in WE rate calculations. \(^{43,44}\) Better statistics can be achieved by longer simulation times or the use of recently proposed algorithms that converge these rates more efficiently, \(^{45,46}\) which is beyond the scope of this work.
+
+In most of the analysis above, we have used the I- RMSD with respect to a reference structure as an observable to assess the quality of structures obtained from WES+HDX simulations. However, such reference structures, usually obtained from experiment, may not be readily available. Thus, it is desirable to determine the usefulness of other features to predict the ternary complex formation. To this end, we filtered the ensemble of simulated SMC2:PROTAC2:VHL structures for bound complexes with w- RMSD < 2 Å and > 30 contacts between protected residues (see Figure 6a). Among these, the bulk of the density was limited to I- RMSD values between 1 and 4 Å, with 90% below 3 Å and 43% even below 2 Å (Figure 6b), indicating that parameters such as the warhead- RMSD and the number of contacts between protected residues may well aid in characterizing bound ternary complexes.
+
+<--- Page Split --->
+
+The simulations presented above stem from the physics- based formulation of molecular dynamics, which comes with an elevated computational cost (e.g. three REVO simulation replicas required around 300 A40 GPU hours). As the WES+HDX results reveal, the associated level of detail allows an entire ensemble of ternary complexes, including many conformations with a pronounced protein interface, to be generated ab initio, i.e., from a fairly dissociated state and with no additional information on the protein- protein binding pose. Such unbiased simulations of ternary complex formation are key to understanding important interactions underlying degrader selectivity and cooperativity.
+
+
+
+Figure 3: Comparison of WESTPA simulations with and without data from HDX-MS experiments. I-RMSD probability densities are shown for ternary complexes with a warhead RMSD \(< 2 \text{Å}\) and \(> 30\) contacts between protected residues. Structures sampled by WES+HDX (red) have almost exclusively an I-RMSD value \(< 2 \text{Å}\) , whereas those from WE simulations without any information from HDX (blue) are widely distributed.
+
+<--- Page Split --->
+
+
+Figure 4: Illustration of the representative prediction produced by REVO simulation and its comparison to the co-crystallized structure (PDB ID: 6HAX) (a) predicted ternary structure with I-RMSD=1.1 Å; (b) detail of the binding interface; (c) contact maps for the interfaces of co-crystallized and predicted structures. The circle size reflects the number of atoms (including hydrogens) participating in interactions; (d) structurally aligned prediction (green) and co-crystallized structure (pink) with a detailed PROTAC 2 comparison shown.
+
+<--- Page Split --->
+
+
+Figure 5: Assessing ternary complex formation. (a) The minimum I-RMSD over time during the simulation for the REVO simulations of the PROTAC2 system. Each green line indicates one replica and the black line is the average between all runs. The blue line indicates the I-RMSD for a vanilla molecular dynamics simulation. (b) A scatter plot of the free energy vs the I-RMSD of each of the 500 clusters from the PROTAC 2 simulations. The circles are colored by w-RMSD. (c) The predicted binding rates for PROTAC 1 system (purple) and the ACBI1 system (green). The black line is the experimental on rate determined via SPR.
+
+<--- Page Split --->
+
+
+Table 2: Comparison of \(k_{on}\) rates between simulation and experiment for the ACBI1 PROTAC 1, and PROTAC 2 systems. The experimental rate for PROTAC 2 has not been determined yet.
+
+| PROTAC | Predicted Rate (M-1s-1) | Experimental Rate (M-1s-1) |
| ACBI1 | 3 * 105 ± 2 * 105 | 2.4 * 105 |
| PROTAC 1 | 10 * 105 ± 8 * 105 | 2.9 * 105 |
| PROTAC 2 | 2.2 * 102 ± 1.7 * 102 | N/A |
+
+### 2.4 HDX-MS improves prediction of ternary complex using docking
+
+Molecular docking is a very popular method for high- throughput predictions of binding poses, that follows a protocol of sampling, searching, and scoring these predictions. Considering the computational cost of the WES+HDX method described above, docking is a viable alternative to the simulation approach in obtaining different conformations of the flexible degrader ternary complexes in a less resource- intensive and more timely fashion.
+
+To demonstrate the usefulness of HDX- MS data for more accurate structural predictions, we show that incorporating experimentally retrieved distance restraints into the docking protocol significantly improves its ability to predict ternary complexes of high quality (see detailed comparisons in Supplementary Figures 1 and 2)). In particular, it is striking how strongly the incorporation of HDX- MS data can boost the accuracy of the docking protocol among the highest- ranked docking poses.
+
+In contrast to recent work, \(^{30}\) our docking method uses HDX- MS data to impose additional distance restraints at the sampling stage (instead of post- sampling scoring). Also, differently from the distance restraints derived from chemical cross- linking experiments, \(^{47}\) our approach is based on the statistics of the length of the linker in a degrader molecule. Application of the HDX- MS data for re- ranking of the docking predictions, as described by Eron et al., \(^{30}\) may lead to a more quantitative assessment of structures. Discussion of the interplay of HDX- MS- derived restraints and HDX- MS- based re- rankings in docking is beyond the scope of the present work.
+
+<--- Page Split --->
+
+Although WES+HDX consistently outperforms the HDX- enhanced docking routine (see Figure 6), docking, in combination with HDX- MS, is a useful tool for the quick filtering of a large number of degrader designs considering the significantly less computational cost of this approach (75 CPU hours for 3 independent replicas compared to 300 A40 GPU hours for the WES method).
+
+### 2.5 Flexibility of Ternary Complex Revealed by HREMD Simulations and Validation by SAXS Experiments
+
+HDX- MS measurements revealed substantial flexibility of the ternary protein complexes studied here. To further study their conformational heterogeneity, we performed atomistic Hamiltonian replica- exchange MD (HREMD) simulations to augment the experiments and explore the structural diversity of multiple SMC2:VHL ternary degrader- protein complexes (see Supplementary Table 2). HREMD is a parallel tempering simulation method that efficiently samples large conformational changes of proteins in aqueous solution and, therefore, is a promising strategy to study the protein- protein interactions and the flexibility of degraders in ternary complexes (see Methods 4.10). To ensure the HREMD- generated ensembles are accurate and reliable, we validate simulations of two large complexes (SMC2- isoform1/isoform2:ACBI1:VCB) by directly comparing against the size exclusion chromatography coupled to small- angle X- ray scattering (SEC- SAXS) data, see Figure 7a.
+
+The excellent agreement ( \(\chi^{2} = 1.55\) and \(\chi^{2} = 1.23\) for SMC2- isoform1/isoform2:ACBI1:VCB respectively, where \(\chi^{2}\) is defined in Eq. 11) between SAXS profiles obtained from experiment and such calculated from simulations shows that the HREMD simulations captured the long timescale conformational ensembles to experimental accuracy. Furthermore, the ensemble- averaged \(R_{g}\) of two complexes from simulations are in excellent agreement to \(R_{g}\) values obtained using Guinier approximation (Eq. 1) to the experimental SAXS data (Supplementary Figure 12), \(R_{g} = 33.4\pm 0.4\) Å and \(32.3\pm 0.3\) Å for SMC2- isoform1/isoform2:ACBI1:VCB, respectively. The histograms
+
+<--- Page Split --->
+
+
+Figure 6: Comparing the bound ensembles determined by docking and REVO simulations with information from HDX-MS for the PDB ID 6HAX ternary complex. The REVO bound ensemble is defined as structures below a warhead RMSD of 2 Å and more than 30 contacts between the target and ligase interface. The docking bound basin is defined as the top-100 structures as determined by Rosetta-scoring. (a) Probability density function distributions of I-RMSD values for the bound ensembles. (b) The percent of structures in the predicted bound ensembles below specific I-RMSD thresholds (2 Å, 2.5 Å, and 3 Å).
+
+<--- Page Split --->
+
+of \(R_{g}\) (calculated from atomic coordinates using Eq. 2) suggest that ternary complexes are flexible in solution leading to a change in overall conformation compared to their simulation starting structures (homology model and crystal structure of SMC2- isoform1/isoform2:ACBI1:VCB, respectively), see Figure 7b. These results illustrate the need for an enhanced sampling method, such as HREMD, to rigorously probe the conformational changes of the inherently flexible ternary degrader complexes
+
+### 2.6 Conformational sampling of ternary complexes
+
+We quantify the free energy landscape of the ternary complexes using data from our HREMD simulations. We use principle component analysis (PCA) of the distances between interface residues observed in our HREMD simulations to identify high- variance collective variables (see Methods). The probability distribution of these high- variance features allows us to determine a more easily interpretable free energy landscape from our simulation data than would be possible otherwise. We find that the landscape of each protein complex contained several local minima differing by only a few kcal/mol.
+
+Using \(k\) - means clustering in the PCA feature space, we then identify distinct clusters of conformations. Cluster centers roughly correspond to local minima in the free energy landscape, see Supplementary Figure 14. The clusters identified by \(k\) - means are consistent with our HDX- MS protection data: Figure 8 shows that interface residues that were found to be protected in HDX- MS experiments are observed to interact in either the most populated or second most populated cluster identified by \(k\) - means. Notably, this analysis shows that in the second most populated structure of Iso1- ACBI1- VCB, the helix formed by the 17 residue extension of isoform 1- SMARCA2 interacts with a beta sheet of VHL, Figure 8d, in accordance with HDX- MS experiments that found this beta sheet to be protected in presence of Iso1, but not in the presence of Iso2. Similarly, highly populated structures of Iso2- ACBI1- VHL and Iso2- PROTAC2- VHL show contact between residues that were observed to be protected in HDX- MS experiments with these PROTACs, but not with PROTAC 1, while the most populated structure of PROTAC 1 does not show these contacts.
+
+<--- Page Split --->
+
+
+Figure 7: SAXS profiles and structural ensembles of SMC2-isoform1/isoform2:ACBI1:VCB complexes. (a) Comparison of theoretical and experimental SAXS profiles, SAXS intensity vs. \(q\) . (b) The histograms of \(\mathrm{R}_g\) of SMC2-isoform1:ACBI1:VCB (red) and SMC2-isoform2:ACBI1:VCB (blue) complexes calculated from HREMD simulations. The inverted red and blue triangles are the \(\mathrm{R}_g\) values of starting structures of SMC2-isoform1/isoform2:ACBI1:VCB from homology model and crystallography respectively.
+
+<--- Page Split --->
+
+
+Figure 8: Most populated structures of SMARCA2 bound to VHL with different degrader molecules, identified by dimension reduction and clustering of HREMD simulation data. (a-d) Colors of VHL and SMARCA2 represent HDX-MS protection in the presence of the degrader molecules relative to the situation in the absence of the degrader. The second ranked structures of c PROTAC 2 and d isoform 1 SMARCA2 are displayed and support our HDX-MS data, whereas the top three structures are included in Supplementary Figure 15. Elongin B and Elongin C are also included in panel d. e The top structures of ternary complexes are compared after aligning VHL to illustrate conformational differences among top structures of ternary complexes.
+
+<--- Page Split --->
+
+
+Figure 9: a Conformational free energy landscape as a function of the first two tICA features of SMARCA2-PROTAC2-VHL ternary complex inferred from a Markov state model (MSM). The ensemble of bound states from REVO simulations is shown as blue points; the crystal structure (PDB ID 6HAX) is shown as a red X. In this projection, states II and V are close to state I. b Network diagram of the coarse-grained MSM calculated using a lag time of 50 ns, with the stationary probabilities associated with each state indicated. c Mean first-passage times to transition (MFPT) from one state in the MSM to another. Numbers indicate predicted MFPTs in \(\mu \mathrm{s}\) . d-e Comparison of the crystal structure (gray) with the lowest free energy state (cyan) and a metastable state (orange) predicted by the MSM. Arrows indicate a change of orientation relative to d.
+
+<--- Page Split --->
+
+We selected 98 representative structures from HREMD data to use as initial configurations for Folding@home (F@H) simulations of SMC2 Iso2- PROTAC2- VHL. Each initial condition was cloned 100 times and run for \(\sim 650 \mathrm{ns}\) , for a total of \(\sim 6 \mathrm{ms}\) of simulation data. These independent MD trajectories provide the basis for fitting a Markov state model (MSM), \(^{48}\) which provides a full thermodynamic and kinetic description of the system and allow for the prediction of experimental observables of interest. \(^{49}\) We used time- lagged independent component analysis (tICA) \(^{50}\) to determine the collective variables with the slowest dynamics. The distance between points in the tICA feature space corresponds roughly to kinetic distance.
+
+The MSM predicts a stationary probability distribution on tICA space that is in general different from the empirical distribution of our simulation data. Interestingly, the MSM predicts that the the crystal structure of PROTAC 2 is 1.5 kcal/mol higher in free energy than the global free energy minimum, while the bound structures obtained from our REVO simulations are \(\sim 1.5 - 3.5 \mathrm{kcal / mol}\) above the global minimum, Figure 9a- c. The model also predicts a metastable state with free energy 2.2 kcal/mol (Figure 9e).
+
+This model is coarse- grained to obtain a five- state MSM, of which the following three states are of particular interest: the global minimum state (or state I) with a stationary probability of 0.63, the metastable state III with 0.10 probability, and state IV, to which the experimental crystal structure can be assigned and which has a stationary probability of 0.05. The global minimum state differs from the crystal structure 6HAX by an I- RMSD of 3.6 Å, while the metastable state has an I- RMSD of 4.4 Å relative to the crystal structure. The global minimum state is stabilized by a large number of protein- protein contacts (Supplementary Figure 16). Contacts between VHL and PROTAC 2 are largely unchanged between the metastable and global minimum states, likely due to the tight interaction between VHL and the PROTAC. On the other hand, the metastable state lacks contacts between PROTAC 2 and ARG29, ASN90, and ILE96 of SMARCA2. The area of the binding interface was substantially increased in both the metastable and global minimum states relative to the crystal structure: the
+
+<--- Page Split --->
+
+global minimum state had a buried surface area of \(2962 \mathrm{\AA}^{2}\) , compared to \(2800 \mathrm{\AA}^{2}\) for the metastable state and \(2369 \mathrm{\AA}^{2}\) for the crystal structure.
+
+We repeated this procedure with \(900 \mu s\) of \(\mathrm{F}@\mathrm{H}\) data of SMC2 Iso2- PROTAC 1- VHL and \(500 \mu s\) of \(\mathrm{F}@\mathrm{H}\) data of SMC2 Iso2- ACBI1- VHL (Supplementary Figures 17 and 18). The resultant MSMs predicted that the crystal structure of the SMC2 Iso2- PROTAC 1- VHL system is \(2.2 \mathrm{kcal / mol}\) higher than the free energy minimum, while the crystal structure of the Iso2- ACBI1- VHL system is only \(0.7 \mathrm{kcal / mol}\) higher in energy than the ground state. Coarse- graining the PROTAC 1 model yielded a two- state MSM, while a three- state MSM was obtained for the ACBI1 system. In both cases, the crystal structure falls into the most probable macro- state. Interestingly, in the ground state predicted by the PROTAC 1 MSM, SMARCA2 is rotated relative to VHL, similar to the PROTAC 2 ground state, while in the ground state of the ACBI1 system, the position of SMARCA2 is similar to that in the crystal structure for all three ternary complexes.
+
+### 2.7 Identifying the ubiquitination zone for Cullin-RING Ligase with VHL and SMARCA2
+
+In addition to simulating the ternary complex formation and associated dynamics, a more complete understanding of the ubiquitination process should involve the full Cullin- RING E3 ubiquitin ligase (CRL). To do this, we study different degrader molecules in the context of the full Cullin- RING E3 ubiquitin ligase (CRL) along with the POI. Here, we study the position different solvent- exposed lysine residues from the POI relative to the ubiquitination zone of the CRL macromolecular assembly, specifically focusing on the probability of POI lysine residue density within this zone. The hypothesis is that the ubiquitination rate depends on the probability of finding a lysine residue in the ubiquitination zone. As such, this analysis can provide insights on the degradation potency of degrader molecules. First, we built an entire E2- E3 complex for CRL- VHL in its activated form using a recently obtained structure of the active form of the closely
+
+<--- Page Split --->
+
+related CRL- \(\beta\) TrCP as reference \(^{51}\) (see Methods). Second, we used the meta- eABF simulation approach (see Methods) to sample CRL open- closed conformations in the presence of SMARCA2. These conformations were then used as reference states to superimpose structures from HREMD simulations of VHL:degrader:SMARCA2 on the active state of the CRL- VHL, allowing us to obtain Lys densities from SMARCA2 in the ubiquitination zone of the CRL- VHL. Comparing the Lys densities of the three degraders (10), we observe that ACBI1 places the most Lys density in the ubiquitination zone of CRL- VHL, followed by PROTAC 2 and PROTAC 1. This order of Lys density in the ubiquitination zone agrees with the experimentally observed degradation data. \(^{15}\)
+
+## 3 Discussion
+
+The formation of a ternary complex via a degrader molecule is a critical step in targeted protein degradation. However, accurately predicting ternary complexes has posed challenges to the field due to the size of the system, the conformational flexibility, the timescales for biological motions, and the limited understanding of the solution- phase structural ensemble. The ability to accurately predict the formation of ternary complexes and the corresponding structural ensembles would enable more precise optimization of degrader molecules (e.g. linkers and attachment points) and facilitate structure activity relationship studies, thus improving rational degrader design.
+
+Here, we studied three different degrader molecules of SMARCA2 with VHL that have similar thermodynamic binding profiles and crystal structure conformations but different degradation efficiencies. Consistent with previous observations, the crystal structure of ACBI1 determined in this work (PDB ID: 7S4E) revealed a conformation nearly identical to its two closest analogs PROTAC 1 (PDB: 6HAY) and PROTAC 2 (PDB: 6HAX). The overall structural similarity of these complexes, yet different degradation profiles, highlights one of the critical challenges in degrader optimization. The approach we describe here combines MD simulations with biophysical experiments, leading to accurate dynamic ternary structure predictions and a detailed mechanistic
+
+<--- Page Split --->
+
+
+Figure 10: Degrader dependent SMARCA2 Lys densities in the CRL-VHL ubiquitination zone. a. Active form of CRL-VHL with bound SMARCA2 and E2-ubiquitin with open CRL conformation. b. same as a with a closed conformation of CRL generated by meta-eABF simulations. c. Distance of Lys residues (side-chain nitrogen atom) from SMARCA2 to the C-terminus glycine C atom of ubiquitin for three different degraders. d. Density of Lys residues in 3D space near ubiquitination zone of CRL-VHL.
+
+<--- Page Split --->
+
+understanding of the characteristics that impact binding selectivity, cooperativity, and degrader efficiency. We show that hydrogen deuterium mass spectrometry (HDX- MS) and small- angle X- ray scattering (SAXS) provide a dynamic description of the ternary complex, in contrast to static x- ray crystal structures, leading to insights regarding the solution state ensemble of ternary degrader complexes. This novel approach, where we integrate data from the biophysical experiments with weighted ensemble (WE) MD simulations, uncovered atomic level differences among distinct conformations adopted by the ternary complexes. For example, we found that the X- ray structures represent only one of many low energy conformations within the dynamic ternary structural ensemble: the crystal structures of ACBI1, PROTAC 2 and PROTAC 1 are 0.9 kcal/mol, 1.5 kcal/mol and 2.0 kcal/mol higher in energy than their corresponding global minima conformation, respectively. Other low- energy structures found on the free energy landscapes can be used as starting points for degrader design or for more sophisticated analyses, such as predicting ubiquitination probability of a particular degrader molecule state.
+
+The data from HDX- MS experiments is used as collective variables for weighted ensemble (WE) simulations, which provide atomic level resolution of the binding process and of the ternary complex conformational ensemble ( \(< 2 \text{Å I- RMSD}\) ). Different WE resampling algorithms (i.e., WESTPA, that uses bins along CVs, and the binless REVO method) can efficiently simulate the binding of ternary degrader complexes when augmented with information on distinct solvent- protected residues from HDX- MS. This novel combination of simulation and experiment leads to improved predictions of ternary degrader complexes (see Supplementary Figure 10 for a comparison of the simulation and docking methods with and without information from HDX- MS experiments). Further improvements being explored in our group include optimizing parameters for the WE simulations and using the HDX- MS data for scoring structures, similar to recent work by Eron and coworkers. \(^{30}\) We are also working on ubiquitination mapping experiments to validate the ubiquitination probability predictions.
+
+The methodology described here relies on advanced physics- based simulations and
+
+<--- Page Split --->
+
+solution- phase biophysical experiments. Because the methodology is based on physical principles without the need for training data, we expect the approach to be transferable to other POI- E3 ligase ternary complexes with induced proximity degrader molecules. Efforts in our group are underway to expand the application to more ligands in the SMARCA2/VLH system and to other POI/E3 combinations. We believe that the predictive simulations described here will increase the efficiency of molecular design for TPD.
+
+We make source code, simulation results, and experimental data from this work publicly available for researchers to further advance the field of induced proximity modulation.
+
+## 4 Methods
+
+### 4.1 Cloning, expression and purification of SMARCA2 and VHL/EloB/C
+
+The SMARCA2 gene from Homo sapiens was custom- synthesized at Genscript with N- terminal GST tag (Ciulli 2019 Nature ChemBio) and thrombin protease cleavage site. The synthetic gene comprising the SMARCA2 (UniProt accession number P51531- 1; residues 1373- 1511) was cloned into pET28 vector to create plasmid pL- 477. The second construct of SMARCA2 with deletion 1400- 1417 (UniProt accession number P51531- 2) was created as pL- 478. For biotinylated SMARCA2, AVI- tag was gene synthesized at C- terminus of pL- 478 to create pL- 479. The VHL gene from Homo sapiens was custom- synthesized with N- terminal His6 tag \(^{15}\) and thrombin protease cleavage site. The synthetic gene comprising the VHL (UniProt accession number P40337; residues 54- 213) was cloned into pET28 vector to create plasmid pL- 476. ElonginB and ElonginC gene from Homo sapiens was custom- synthesized with AVI- tag at C- terminus of EloB. \(^{22}\) The synthetic genes comprising the EloB (UniProt accession number Q15370; residues 1- 104) and EloC (UniProt accession number Q15369; residues 17- 112) were cloned into
+
+<--- Page Split --->
+
+pCDFDuet vector to create plasmid pL- 474. For protein structural study, AVI- tag was deleted in pL- 474 to create pL- 524.
+
+For SMARCA2 protein expression, the plasmid was transformed into BL21(DE3) and plated on Luria- Bertani (LB) medium containing 50 \(\mu \mathrm{g / ml}\) kanamycin at \(37^{\circ}\mathrm{C}\) overnight. A single colony of BL21(DE3)/pL- 477 or BL21(DE3)/pL- 478 was inoculated into a 100- ml culture of LB containing 50 \(\mu \mathrm{g / ml}\) kanamycin and grown overnight at \(37^{\circ}\mathrm{C}\) . The overnight culture was diluted to OD600=0.1 in 2 x 1- liter of Terrific Broth medium containing 50 \(\mu \mathrm{g / ml}\) kanamycin and grown at \(37^{\circ}\mathrm{C}\) with aeration to mid- logarithmic phase (OD600 = 1). The culture was incubated on ice for 30 minutes and transferred to \(16^{\circ}\mathrm{C}\) . IPTG was then added to a final concentration in each culture of \(0.3\mathrm{mM}\) . After overnight induction at \(16^{\circ}\mathrm{C}\) , the cells were harvested by centrifugation at 5,000 xg for 15 min at \(4^{\circ}\mathrm{C}\) . The frozen cell paste from 2 L of cell culture was suspended in 50 ml of Buffer A consisting of 50 mM HEPES (pH 7.5), 0.5 M NaCl, 5 mM DTT, \(5\%\) (v/v) glycerol, supplemented with 1 protease inhibitor cocktail tablet (Roche Molecular Biochemical) per 50 ml buffer. Cells were disrupted by Avestin C3 at 20,000 psi twice at \(4^{\circ}\mathrm{C}\) , and the crude extract was centrifuged at 39,000 xg (JA- 17 rotor, Beckman- Coulter) for 30 min at \(4^{\circ}\mathrm{C}\) . Two ml Glutathione Sepharose 4 B (Cytiva) was added into the supernatant and mixed at \(4^{\circ}\mathrm{C}\) for 1 hour, washed with Buffer A and eluted with 20 mM reduced glutathione (Sigma). The protein concentration was measured by Bradford assay, and GST- tag was cleaved by thrombin (1:100) at \(4^{\circ}\mathrm{C}\) overnight during dialysis against 1 L of Buffer B (20 mM HEPES, pH 7.5, 150 mM NaCl, 1mM DTT). The sample was concentrated to 3 ml and applied at a flow rate of 1.0 ml/min to a 120- ml Superdex 75 (HR 16/60) (Cytiva) pre- equilibrated with Buffer B. The fractions containing SMARCA2 were pooled and concentrated by Amicon® Ultracel- 3K (Millipore). The protein concentration was determined by OD280 and characterized by SDS- PAGE analysis and analytical LC- MS. The protein was stored at \(- 80^{\circ}\mathrm{C}\) .
+
+For VHL/Elob/C protein expression, the plasmids were co- transformed into BL21(DE3) and plated on Luria- Bertani (LB) medium containing 50 \(\mu \mathrm{g / ml}\) kanamycin and 50
+
+<--- Page Split --->
+
+\(\mu \mathrm{g / ml}\) streptomycin at \(37^{\circ}\mathrm{C}\) overnight. A single colony of BL21(DE3)/pL- 476/474 or BL21(DE3)/pL- 476/524 was inoculated into a 100- ml culture of LB containing 50 \(\mu \mathrm{g / ml}\) kanamycin and \(50\mu \mathrm{g / ml}\) streptomycin and grown overnight at \(37^{\circ}\mathrm{C}\) . The overnight culture was diluted to OD600=0.1 in \(6\mathrm{x}1\) - liter of Terrific Broth medium containing \(50\mu \mathrm{g / ml}\) kanamycin and \(50\mu \mathrm{g / ml}\) streptomycin and grown at \(37^{\circ}\mathrm{C}\) with aeration to mid- logarithmic phase (OD600 = 1). The culture was incubated on ice for 30 minutes and transferred to \(18^{\circ}\mathrm{C}\) . IPTG was then added to a final concentration of \(0.3\mathrm{mM}\) in each culture. After overnight induction at \(18^{\circ}\mathrm{C}\) , the cells were harvested by centrifugation at 5,000 g for 15 min at \(4^{\circ}\mathrm{C}\) . The frozen cell paste from \(6\mathrm{L}\) of cell culture was suspended in \(150\mathrm{ml}\) of Buffer C consisting of \(50\mathrm{mM}\) HEPES (pH 7.5), \(0.5\mathrm{M}\) NaCl, \(10\mathrm{mM}\) imidazole, \(1\mathrm{mM}\) TCEP, \(5\%\) (v/v) glycerol, supplemented with 1 protease inhibitor cocktail tablet (Roche Molecular Biochemical) per \(50\mathrm{ml}\) buffer. Cells were disrupted by Avestin C3 at 20,000 psi twice at \(4^{\circ}\mathrm{C}\) , and the crude extract was centrifuged at \(17000\mathrm{g}\) (JA- 17 rotor, Beckman- Coulter) for \(30\mathrm{min}\) at \(4^{\circ}\mathrm{C}\) . Ten ml Ni Sepharose 6 FastFlow (Cytiva) was added into the supernatant and mixed at \(4^{\circ}\mathrm{C}\) for 1 hour, washed with Buffer C containing \(25\mathrm{mM}\) imidazole and eluted with \(300\mathrm{mM}\) imidazole. The protein concentration was measured by Bradford assay. For protein crystallization, His- tag was cleaved by thrombin (1:100) at \(4^{\circ}\mathrm{C}\) overnight during dialysis against \(1\mathrm{L}\) of Buffer D ( \(20\mathrm{mM}\) HEPES, pH 7.5, \(150\mathrm{mM}\) NaCl, 1 mM DTT). The sample was concentrated to \(3\mathrm{ml}\) and applied at a flow rate of 1.0 ml/min to a 120- ml Superdex 75 (HR 16/60) (Cytiva) pre- equilibrated with Buffer D. The fractions containing VHL/EloB/C were pooled and concentrated by Amicon® Ultracel- 10K (Millipore). The protein concentration was determined by OD280 and characterized by SDS- PAGE analysis and analytical LC- MS. The protein was stored at \(- 80^{\circ}\mathrm{C}\) . For SPR assay, \(10\mathrm{mg}\) VHL/EloB/C protein complex was incubated with BirA (1:20), \(1\mathrm{mM}\) ATP and \(0.5\mathrm{mM}\) Biotin and \(10\mathrm{mM}\) MgCl2 at \(4^{\circ}\mathrm{C}\) overnight, removed free ATP and Biotin by 120- ml Superdex 75 (HR 16/60) with the same procedure as above, and confirmed the biotinylation by LC/MS.
+
+<--- Page Split --->
+
+### 4.2 Hydrogen Deuterium Exchange Mass Spectrometry
+
+Our HDX analyses were performed as reported previously with minor modifications. \(^{34,36,52}\) HDX experiments were performed using a protein stock at the initial concentration of 200 \(\mu \mathrm{M}\) of SMARCA2, VCB in the APO, binary (200 \(\mu \mathrm{M}\) PROTAC ACBI1) and ternary (200 \(\mu \mathrm{M}\) PROTAC ACBI1) states in 50 mM HEPES, pH 7.4, 150 mM NaCl, 1 mM TCEP, 2% DMSO in H2O. The protein samples were injected into the nanoAC- QUITY system equipped with HDX technology for UPLC separation (Waters Corp. \(^{53}\) ) to generate mapping experiments used to assess sequence coverage. Generated maps were used for all subsequent exchange experiments. HDX was performed by diluting the initial 200 \(\mu \mathrm{M}\) protein stock 13- fold with D2O (Cambridge Isotopes) containing buffer (10 mM phosphate, pD 7.4, 150 mM NaCl) and incubated at 10 °C for various time points (0.5, 5, 30 min). At the designated time point, an aliquot from the exchanging experiment was sampled and diluted 1:13 into D2O quenching buffer containing (100 mM phosphate, pH 2.1, 50 mM NaCl, 3M GuHCl) at 1 °C. The process was repeated at all time points, including for non- deuterated samples in H2O- containing buffers. Quenched samples were injected into a 5- \(\mu \mathrm{m}\) BEH 2.1 X 30- mm Enzymate- immobilized pepsin column (Waters Corp.) at 100 \(\mu \mathrm{l} / \mathrm{min}\) in 0.1% formic acid at 10 °C and then incubated for 4.5 min for on- column digestion. Peptides were collected at 0 °C on a C18 VanGuard trap column (1.7 \(\mu \mathrm{m}\) X 30 mm) (Waters Corp.) for desalting with 0.1% formic acid in H2O and then subsequently separated with an in- line 1.8μMHsS T3 C18 2.1 X 30- mm nanoACQUITY UPLC column (Waters Corp.) for a 10- min gradient ranging from 0.1% formic acid to acetonitrile (7 min, 5- 35%; 1 min, 35- 85%; 2 min hold 85% acetonitrile) at 40 \(\mu \mathrm{l} / \mathrm{min}\) at 0 °C. Fragments were mass- analyzed using the Synapt G2Si ESL- Q- ToF mass spectrometer (Waters Corp.). Between injections, a pepsin- wash step was performed to minimize peptide carryover. Mass and collision- induced dissociation in data- independent acquisition mode (MSE) and ProteinLynx Global Server (PLGS) version 3.0 software (Waters Corp.) were used to identify the peptides in the non- deuterated mapping experiments and analyzed in the same fashion as HDX experiments. Mapping experiments generated from PLGS were imported
+
+<--- Page Split --->
+
+into the DynamX version 3.0 (Waters Corp.) with quality thresholds of MS1 signal intensity of 5000, maximum sequence length of 25 amino acids, minimum products 2.0, minimum products per amino acid of 0.3, minimum PLGS score of 6.0. Automated results were inspected manually to ensure the corresponding m/z and isotopic distributions at various charge states were assigned to the corresponding peptides in all proteins (SMARCA2, VHL, ElonC, ElonB). DynamX was utilized to generate the relative deuterium incorporation plots and HDX heat map for each peptide. The relative deuterium uptake of common peptides was determined by subtracting the weighted-average mass of the centroid of the non-deuterated control samples from the deuterated samples at each time point. All experiments were made under the same experimental conditions negating the need for back-exchange calculations but therefore are reported as relative. \(^{37}\) All HDX experiments were performed twice, on 2 separate days, and a 98 and 95% confidence limit of uncertainty was applied to calculate the mean relative deuterium uptake of each data set. Mean relative deuterium uptake thresholds were calculated as described previously. \(^{34,36,52}\) Differences in deuterium uptake that exceeded the error of the datasets were considered significant.
+
+### 4.3 SEC-SAXS experiments
+
+SAXS data were collected with an AKTAmicro (GE Healthcare) FPLC coupled to a BioXolver L SAXS system (Xenocs) that utilized an Excilium MetalJet D2+ X- ray source operating at a wavelength of 1.34 Å. We measured two protein complex samples,
+
+(i) SMARCA2-isoform1:ACBI1:VCB, and
+
+(ii) SMARCA2-isoform2:ACBI1:VCB.
+
+The scattering data was detected on PILATUS3 300 K (Dectris) detector with a resulting \(q\) range of 0.0134 – 0.5793 Å\(^{-1}\). To ensure the resulting scattering profile is solely due to complexes with all four protein chains and a degrader, and devoid of contributions from binary or uncomplexed proteins, size exclusion chromatography is coupled to SAXS (SEC-SAXS). The elution peak 1 of the SEC profile is assigned to the
+
+<--- Page Split --->
+
+ternary complexes, whereas peak 2 is attributed to binary or uncomplexed proteins, respectively (Supplementary Figure 11). The SEC- SAXS data for each sample was collected by loading \(500~\mu \mathrm{L}\) of the ternary complex formed by addition of equimolar concentrations (275 \(\mu \mathrm{M}\) ) of SMARCA2, VCB and ACBI1, onto a Superdex 200 Increase \(10 / 30\) equilibrated with \(20~\mathrm{mM}\) HEPES pH 7.5, \(150~\mathrm{mM}\) NaCl and \(1~\mathrm{mM}\) DTT at \(20^{\circ}\mathrm{C}\) . The solution scattering data was collected as a continuous 60 second data- frame measurements with a flow rate of \(0.05~\mathrm{mL / min}\) . The average scattering profile of all frames within the elution peak 1 was calculated and subtracted from the average buffer scattering to yield the scattering data of the protein complex. The final SAXS profile of each ternary complex (Figure 7a) was determined from the average scattering signal from the sample in the elution peak 1, where the relatively large variability in the calculated radius of gyration, \(R_{g}\) (red solid/open circles in Supplementary Figure 11). This indicates that complexes are dynamic or flexible. Data reduction was performed using the BioXTAS RAW 2.0.3 software. \(^{54}\) \(R_{g}\) was estimated from experimental an SAXS curve using the Guinier approximation,
+
+\[I(q)\approx I(0)e^{\frac{-q^{2}R_{g}^{2}}{3}},f o r q\to 0 \quad (1)\]
+
+where \(I(q)\) and \(I(0)\) are the measured SAXS intensity and forward scattering intensity at \(q = 0\) , respectively. \(q\) is the magnitude of scattering vector given by, \(q = 4\pi \sin \theta /\lambda\) , where \(2\theta\) is the scattering angle and \(\lambda\) is the wavelength of incident beam. The linear region in \(ln(I(q))\) vs. \(q^{2}\) was fitted at low- \(q\) values such that \(q_{max}R_{g}\leq 1.3\) to estimate \(R_{g}\) , where \(q_{max}\) is the maximum \(q\) - value in the Guinier fit (Supplementary Figure 12). On the other hand, \(R_{g}\) of the protein complex in simulation was directly calculated from atomic coordinates using following relation,
+
+\[R_{g} = \sqrt{\frac{\sum_{i}m_{i}\left\Vert\mathbf{r_{i}}\right\Vert^{2}}{\sum_{i}m_{i}}} \quad (2)\]
+
+where \(m_{i}\) is the mass of \(i^{t h}\) atom and \(\mathbf{r_{i}}\) is the position of \(i^{t h}\) atom with respect to the center of mass of the molecule.
+
+<--- Page Split --->
+
+### 4.4 Molecular dynamics simulations
+
+The initial coordinates of the system were obtained from X- ray crystal structures PDB ID 6HAX, 6HAY, or 7S4E, respectively. The missing atoms were added using the LEaP module in AMBER20. The AMBER ff14SB force field \(^{55}\) was employed for the protein and the PROTAC force field parameters were generated using in- house programs for all MD simulations in this study. The explicit solvent was modeled using TIP3P water encapsulating the solute in a rectangular box. Counter ions were added to the system to enforce neutrality. Langevin dynamics was used to maintain the temperature at \(300\mathrm{K}\) and the collision frequency was set to \(2.0\mathrm{ps}^{- 1}\) . The SHAKE algorithm was utilized so that 2 fs time step could be achieved.
+
+A step- wise equilibration protocol was used prior to running the production phase of the Molecular Dynamics simulations. First, a minimization was performed with a positional restraint of 5 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) applied to all solute heavy atoms followed by a fully unrestrained minimization. Each minimization was composed of 500 steps of the steepest decent followed by 2000 steps of conjugate gradient. Using 5 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) positional restraint on the heavy atoms of the solute, the system was linearly heated from 50 to 300 K for a duration of 500 ps (NVT ensemble) followed by a density equilibration of 750 ps (NPT ensemble). Over the course of five 250 ps simulations, the restraints on the heavy atoms of the systems were reduced from 5 to 0.1 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) . Then, a 500 ps simulation was run with a positional restraint of 0.1 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) on the backbone atoms followed by a fully unrestrained 5 ns simulation.
+
+Three independent regular MD simulations were performed for each of the three bound degrader complexes for up 1 \(\mu \mathrm{s}\) . Structures obtained from these simulations were clustered into 25 groups based on their structural similarity. One representative structure from each cluster (along with the experimentally obtained crystal structure) were used as the set of reference ternary complexes for the evaluation of bound complex predictions by WE simulations or docking.
+
+<--- Page Split --->
+
+### 4.5 Isoform 1 homology model
+
+4.5 Isoform 1 homology modelSince no suitable X- ray structure for SMARCA2 isoform 1 BRD domain is available in the PDB, we have used the YASARA (Yet Another Scientific Artificial Reality Application) homology modeling module (YASARA Biosciences GmbH) to build a high- resolution model of SMARCA2 isoform 1 from its amino acid sequence. This was used as a model for the binding of the warhead to SMARCA2 isoform1, although the final prediction reported here came from our simulations. The sequence that was used is Uniprot P51531- 1 (residues 1373- 1493) has an additional 17 aa loop compared to P51531- 2 (missing loop at 1400- 1417). As a template for homology modeling, we used the structure from the PDB ID 6HAY. Once the model was completed, an Amber minimization, which restrained all heavy atoms except the loop residues, was run. This ensured that the residues in the loop do not overlap and assume a stable secondary structure conformation. Minimization did not show major side- chain movements in the final minimized output which further suggested that the structure was stable
+
+### 4.6 Unbound System Preparation
+
+4.6 Unbound System PreparationThe ternary complexes were unbound "manually" by separating the corresponding VHL- PROTAC complex from SMARCA2 by \(20 - 40\mathring{\mathrm{A}}\) (depending on the system). The simulation box of these unbound systems were then solvated with explicit waters and counter ions were added to neutralize their net charge. The ACBI1 system has 24,093 water molecules, 9 chlorine ions. The PROTAC 1 system has 21191 water molecules and 10 chlorine ions. The PROTAC 2 simulations has 31,567 water atoms and 9 chlorine ions. All systems were placed in rectangular boxes, with dimensions: \(123\mathring{\mathrm{A}}\times 76\mathring{\mathrm{A}}\times 98\mathring{\mathrm{A}}\) for the ACBI1 system \(131\mathring{\mathrm{A}}\times 84\mathring{\mathrm{A}}\times 84\mathring{\mathrm{A}}\) for the PROTAC 1 system and \(144\mathring{\mathrm{A}}\times 89\mathring{\mathrm{A}}\times 91\mathring{\mathrm{A}}\) for the PROTAC 2 system.
+
+<--- Page Split --->
+
+### 4.7 WESTPA simulations
+
+The binding of ternary complexes was simulated using weighted ensemble methods. With WESTPA, short simulations sample in parallel a conformational space divided into bins based on pre- defined collective variables (CVs). Each bin may contain a number ( \(M\) ) of trajectory "walkers", \(i\) , that carry a certain weight \((w_{i})\) . The simulations run for a relatively short time ( \(\tau = 50ps\) ), after which trajectories are either replicated, if their number per bin is \(< M\) , or they are merged, if there are \(>M\) trajectories per bin. Importantly, the sum of all \(w_{i}\) equals 1 in any iteration, i.e., the trajectory replication and merging operations correspond to an unbiased statistical resampling of the underlying distribution. \(^{56}\) Detailed description about the WE path sampling algorithms and the WESTPA software can be found elsewhere. \(^{57 - 59}\)
+
+The unbound systems described above were taken as the starting configuration for each binding simulation with the GPU- accelerated version of the AMBER molecular dynamics package. \(^{60}\) To ensure the PROTAC remains bound to the VHL protein during these simulations, a modest (1 kcal mol \(^{- 1}\) Å \(^{- 2}\) ) flat- bottom position restraint was enforced between the center of masses of the ligand and protein binding site heavy atoms. All other MD simulation parameters were as described above
+
+For each of the three systems, two WESTPA simulations were performed: one for the initial formation of the ternary complex and one for the refinement of the binding interactions. In each case, \(M\) was set to 5 and two collective variables (CV1 and CV2) were defined to assess progress.
+
+In the first set of simulations, CV1 was defined as the warhead- RMSD, or w- RMSD, of the PROTAC warhead with respect to the corresponding crystal structure of the bound complex. CV2 was a combination of two observables; it was either defined to be the number of native atomic contacts between the warhead and the SMARCA2 binding interface or, if the binding sites were so distant that no contacts were formed, it was defined as the distance of the binding partners, i.e., SMARCA2 and the VHL- PROTAC binary complex. Contacts were counted between non- hydrogen atoms within a radius of 4.5 Å and, to ensure that CV2 is defined along one linear dimension, the contact
+
+<--- Page Split --->
+
+counts were scaled by - 1. This selection of CV1 and CV2 with an appropriate binning allowed the separated binding partners to assemble, during the WESTPA simulations, into ternary complexes that are similar to the corresponding crystal structures, which were used for w- RMSD and native contact calculations.
+
+In the refinement simulations, both CV1 and CV2 were contact counts. CV1 was the number of heavy- atom contacts between two proteins, whereas CV2 was the number of heavy- atom contacts between both proteins and the PROTAC. When augmenting the WE simulations with HDX- MS data, only the protected residues of the two proteins, as informed by the corresponding experiments, were taken into consideration for the contact counts of both CVs.
+
+The ensemble of predicted bound structures was evaluated by comparing the distributions of minimum interface- RMSDs (I- RMSDs) with respect to the set of reference ternary complexes, where the interface is defined by SMC2 and VHL residues within \(10\mathring{A}\) . Furthermore, to obtain a subset of reliable predictions, these I- RMSD distributions only contain structures with w- RMSD \(< 2\mathring{A}\) and \(>30\) contacts between any residues of the two proteins or, in the case of employing HDX data, between the protected residues of the two proteins.
+
+### 4.8 REVO-epsilon Weighted Ensemble method
+
+We also applied a variant of the weighted ensemble algorithm, REVO. We will describe the application of the REVO algorithm as it pertains to this study, but a more detailed explanation can be found in previous works. The goal of the REVO resampling algorithm is to maximize the variation function defined as:
+
+\[V = \sum_{i}V_{i} = \sum_{i}\sum_{j}\left(\frac{d_{ij}}{d_{0}}\right)^{\alpha}\phi_{i}\phi_{j} \quad (3)\]
+
+where \(V_{i}\) is the walker variation, \(d_{ij}\) is the distance between walkers i and j determined using a specific distance metric, \(d_{0}\) is the characteristic distance used to make the distance term dimensionless, set to 0.148 for all simulations, the \(\alpha\) is used to deter
+
+<--- Page Split --->
+
+mine how influential the distances are to the walker variation and was set to 6 for all the simulations. The novelty terms \(\phi_{i}\) and \(\phi_{j}\) are defined as: \(\phi_{i} = \log (w_{i}) - \log \left(\frac{p_{min}}{100}\right)\) . The minimum weight, \(p_{min}\) , allowed during the simulation was \(10^{- 50}\) . Cloning was attempted for the walker with the highest variance, \(V_{i}\) when the weights of the resultant clones would be larger than \(p_{min}\) , provided it is within distance \(\epsilon\) of the walker with the maximal progress towards binding of the ternary complex. The two walkers selected for merging were within a distance of 2 (A) and have a combined weight larger than the maximal weight allowed, \(p_{max}\) , which was set to 0.1 for all REVO simulations. The merge pair also needed to minimize:
+
+\[\frac{V_{j}w_{i} - V_{i}w_{j}}{w_{i} + w_{j}} \quad (4)\]
+
+If the proposed merging and cloning operations increase the total variance of the simulation, the operations are performed and we repeat this process until the variation can no longer be increased.
+
+Three different distance metrics were used while simulating the PROTAC 2 system: Using the warhead RMSD to the crystal structure, maximizing the contact strength (defined below) between protected residues identified by HDX data, and a linear combination of the warhead RMSD, contact strength between HDX- protected residues, and the contact strength between SMARCA2 and the degrader. The simulations for the other systems used the last distance metric exclusively. To compute the warhead RMSD distance metric, we aligned to the binding site atoms on SMARCA2, defined as atoms that were within 8 Å of the warhead in the crystal structure. Then the RMSD was calculated between the warhead in each frame and the crystal structure. The distance between a set of walkers i and j is defined as: \(d = |\frac{1}{RMSD_{i}} - \frac{1}{RMSD_{j}}|\) . The contact strength is defined by determining the distances between residues. We calculate the minimum distance between the residues and use the following to determine the contact strength:
+
+<--- Page Split --->
+
+\[strength = \frac{1}{1 + e^{-k(r - r_0)}} \quad (5)\]
+
+where k is the steepness of the curve, \(r\) is the minimum distance between any 2 residues and \(r_0\) is the distance we want a contact strength of 0.5. We used 10 for k and 5 Å for \(r_0\) . The total contact strength was the sum of all residue- residue contact strengths. The distance between walkers i and j was calculated by: \(d = |cs_i - cs_j|\) where cs is the contact strength of a given walker.
+
+All REVO simulations were run using OpenMM v.7.5.0. Simulation details are as described above. The degrader- VHL interface was restrained to maintain the complex during the simulation by using a OpenMM custom centroid force defined as:
+
+\[CentroidForce = k*(dist - edist)^2 \quad (6)\]
+
+where the dist is the distance between the center of mass of PROTAC and the center of mass of VHL and the edit is the distance between the center of mass of PROTAC and center of mass of VHL of the crystal structure, and k is a constant set to 2 kcal/mol \* Ų.
+
+### 4.9 Ternary complex docking protocol
+
+Following \(^{27,29}\) (Methods 4 and 4b) and, \(^{26}\) we assume that high fidelity structures of SMC2:warhead and VHL:ligand are known and available to be used in protein- protein docking. This docking of two proteins with bound PROTAC moieties is performed in the absence of the linker. The conformations of linker are sampled independently with an in- house developed protocol that uses implementation of fast quantum mechanical methods, CREST. \(^{61 - 63}\) Differently from the docking protocols described in, \(^{26,27,29}\) we make use of distance restraints derived either from the end- to- end distances of the sampled conformations of linker, or from the HDX- MS data. Thus, before running the protein- protein docking, we generate an ensemble of conformers for linkers and calculate the mean \((x_0)\) and standard deviation \((sd)\) for the end- to- end distance. This
+
+<--- Page Split --->
+
+information is then used to set the distance restraints in the RosettaDock software: \(^{64,65}\)
+
+\[f_{1}(x) = (\frac{x - x_{0}}{sd})^{2}, \quad (7)\]
+
+where \(x\) is the distance between a pair of atoms in a candidate docking pose (the pair of atoms is specified as the attachment points of the linker to warhead and ligand).
+
+When information about the protected residues is available from HDX- MS experiments, we used them to set up a set of additional distance restraints:
+
+\[f_{2,i}(x) = \frac{1}{1 + \exp(-m\cdot(x - x0))} -0.5, \quad (8)\]
+
+where \(i\) is the index of a protected residue, \(x0\) is the center of the sigmoid function and \(m\) is its slope. As above, \(x0\) value was set to be the mean end- to- end distance calculated over the ensemble of linker conformers. The value of \(m\) was set to be 2.0 in all the performed docking experiments. The type of RosettaDock- restraint is SiteConstraint, with specification of \(\mathrm{C}\alpha\) atom for each protected residue and the chain- ID of partnering protein (i.e., \(x\) in Eq.(8) is the distance of \(\mathrm{C}\alpha\) atom from the partnering protein). Thus, the total restraint- term used in docking takes the form:
+
+\[f_{restr.}(x) = w\cdot (f_{1}(x) + \sum_{i}f_{2,i}(x)), \quad (9)\]
+
+where \(w = 10\) is the weight of this additional score function term.
+
+RosettaDock implements a Monte Carlo- based multi- scale docking algorithm that samples both rigid- body orientation and side- chain conformations. The distance- based scoring terms, Eq. (9), bias sampling towards those docking poses that are compatible with specified restraints. This limits the number of output docking structures, as only those ones that pass the Metropolis criterion with the additional term of Eq. (9) will be considered.
+
+Once the docking poses are generated with RosettaDock, all the pre- generated conformations of the linker are structurally aligned onto each of the docking predictions. \(^{26}\)
+
+<--- Page Split --->
+
+Only those structures that satisfy the RMS- threshold value of \(\leq 0.3 \mathrm{\AA}\) are saved as PDB files. All the docking predictions are re- ranked by the values of Rosetta Interface score \((I_{sc})\) . The produced ternary structures are examined for clashes, minimized and submitted for further investigations with Molecular Dynamics methods. Details about running the described docking protocol can be found in Supplementary Material.
+
+### 4.10 HREMD simulation
+
+The details of Hamiltonian replica- exchange MD (HREMD) \(^{66,67}\) can be found in the Supplementary Material (Supplementary Figures 13 and 14, and Table 2). For all HREMD simulations, we chose the effective temperatures, \(T_{0} = 300 \mathrm{K}\) and \(T_{max} = 425 \mathrm{K}\) such that the Hamiltonian scaling parameter, \(\lambda_{0} = 1.00\) and \(\lambda_{min} = 0.71\) for the lowest and the highest rank replicas respectively. We estimated the number of replicas \((n)\) in such a way that the average exchange probabilities \((p)\) between neighboring replicas were in the range of 0.3 to 0.4. We used \(n = 20\) and \(n = 24\) for SMC2:degrader:VHL and SMC2:degrader:VCB respectively. Each simulation was run for \(0.5 \mu \mathrm{s}\) /replica, and a snapshot of a complex was saved every 5 ps (total 100,001 frames per replica). Finally, we performed all the analyses on only the lowest rank replica that ran with original/unscaled Hamiltonian.
+
+We assessed the efficiency of sampling by observing (i) the values of \(p\) , (ii) a good overlap of histograms of potential energy between adjacent replicas (Supplementary Figure 13), and (iii) a mixing of exchange of coordinates across all the replicas (Supplementary Figure 14).
+
+### 4.11 Conformational free energy landscape determination
+
+In order to quantify to the conformational free energy landscape, we performed dimension reduction of our simulation trajectories using principle component analysis (PCA). First, the simulation trajectories were featurized by calculating interfacial residue contact distances. Pairs of residues were identified as part of the interface if they passed
+
+<--- Page Split --->
+
+within 5 Å of each other during the simulation trajectory, where the distance between two residues was defined as the distance between their closest heavy atoms. PCA was then used to identify the features that contributed most to the variance by diagonalizing the covariance matrix; for each simulated system, the number of features used in our analysis was chosen as that which explained at least 95% of the variance.
+
+After projecting the simulation data onto the resultant feature space, snapshots were clustered using the \(k\) - means algorithm. The number of clusters \(k\) was chosen using the "elbow- method", i.e. by visually identifying the point at which the marginal effect of an additional cluster was significantly reduced. In cases where no "elbow" could be unambiguously identified, \(k\) was chosen to be the number of local maxima of the probability distribution in the PCA feature space. Interestingly, the centroids determined by \(k\) - means approximately coincided with such local maxima, consistent with the interpretation of the centroids as local minima in the free energy landscape.
+
+To prepare the Folding@home simulations, HREMD data were featurized with interface distances and its dimensionality reduced with PCA as described above. The trajectory was then clustered into 98 k- means states, whose cluster centers were selected as 'seeds' for Folding@home massively parallel simulations. The simulation systems and parameters were kept the same as for HREMD and loaded into OpenMM where they were energy minimized and equilibrated for 5 ns in the NPT ensemble (T = 310 K, p = 1 atm) using the openmmtools Langevin BAOAB integrator with 2 fs timestep. 100 trajectories with random starting velocities were then initialized on Folding@home for each of the seeds. The final dataset consists of 9800 trajectories, 5.7 milliseconds of aggregate simulation time, and 650 ns median trajectory length. This dataset is made publicly available at:
+
+https://console.cloud.google.com/storage/browser/paperdata.
+
+For computational efficiency, the data was strided to 5 ns/frame, featurized with closest heavy atom interface distances (as described above), and projected into tICA space at lag time 5 ns using commute mapping. The dimensionality of the dataset was reduced to 339 dimensions, keeping the number of tICs necessary to explain 95%
+
+<--- Page Split --->
+
+of kinetic variance. The resulting tICA space was discretized into 1000 microstates using k- means. The Markov state model (MSM) was then estimated from the resulting discretized trajectories at lag time 50 ns using a minimum number of counts for ergodic trimming (i.e. the 'mincount_connectivity' argument in PyEMMA) of 4, as the default setting resulted in a trapped state whose connectivity between simulation sub- ensembles starting from two different seeds was observed only due to clustering noise. The validity of the MSM was confirmed by plotting the populations from raw MD counts vs. equilibrium populations from the MSM, which is a useful test, especially when multiple seeds are used and the issue of connectivity is paramount. A hidden Markov model (HMM) was then computed using 5 macrostates to coarse- grain the transition matrix.
+
+### 4.12 Comparison of HREMD to SAXS experiment
+
+We validated the HREMD- generated ensembles of SMC2- isoform1/isoform2:ACBI1:VCB complexes by directly comparing to the experimental SAXS data. The theoretical SAXS profile was computed from each snapshot from the HREMD simulation trajectory using CRYSOL \(^{68}\) available in a software package ATSAS. \(^{69}\) The following CRYSOL command was used: \(crysol < filename.pdb > - lm 20 - sm 0.5 - ns 201 - un 1 - eh - dro 0.03\) . To expedite the writing of PDBs from HREMD trajectory and calculation of SAXS profiles, we used the multiprocessing functionality implemented in a Python package \(idpflex^{70}\) The ensemble- averaged theoretical SAXS profile was determined as below,
+
+\[< I(q) > = \frac{1}{n}\sum_{i = 1}^{n}I_{i}(q) \quad (10)\]
+
+where \(n = 100,001\) is the total number of frames in HREMD trajectory of each complex. The ensemble- averaged theoretical SAXS profile was compared to experiment (Figure 7c) by minimizing chi- square ( \(\chi^{2}\) ) given by,
+
+<--- Page Split --->
+
+\[\chi^{2} = \frac{1}{(m - 1)}\sum_{i = 1}^{m}\left\{\frac{\left[< I_{expt}(q_{i}) > -(c< I_{calc}(q_{i}) > +b)\right]}{\sigma_{expt}(q_{i})}\right\}^{2} \quad (11)\]
+
+where \(< I_{expt}(q) >\) and \(< I_{calc}(q) >\) are the ensemble- averaged experimental and theoretical SAXS intensities respectively, \(m\) is the number of experimental \(q\) points, \(c\) is a scaling factor, \(b\) is a constant background, and \(\sigma_{expt}\) is the error in \(I_{expt}(q)\) .
+
+### 4.13 Cullin-RING E3 ubiquitin ligase (CRL) simulations to explore activation
+
+To study the impact of different bifunctional molecules on ubiquitination, first we constructed an active form of the Cullin- RING E3 ubiquitin ligase (CRL) with VHL and grafted it onto the ternary structures from the VHL- degrader- SMARCA2 simulations described above. We used targeted MD simulations (TMD) \(^{71}\) to drive the activation of the CLR based on the active structure of a homologous E3 ligase, CRL- \(\beta\) TrCP (PDB ID 6TTU). \(^{51}\) The full CRL- VHL system was built using PDB IDs 1LQB and 5N4W including VHL, ElonginB, ElonginC, Cullin2, and RBX1. \(^{11,72}\) NEDD8 was placed near residue Lys689 of the CRL where neddylation occurs.
+
+As the collective variable for TMD, we used the residue- based RMSD of the last \(\sim 70\) Cα atoms of the Cullin C- terminus (where neddylation and subsequent activation occur) of Cullin1 from the 6TTU structure \(^{51}\) as the reference state and modeled Cullin2 from its inactive form in the 5N4W structure to this reference state. In addition, the Cα atoms of the entire NEDD8 protein from the 6TTU structure was also used as a reference structure during TMD. Residues 135 to 425 from Cullin2 and corresponding residues from Cullin1 were used for alignment during TMD. The force constant for TMD was set to 30 kJ/mol/\(\mathrm{nm}^{2}\) . The system in a rectangular simulation box with a total number of \(\sim 500\mathrm{K}\) atoms and an ionic concentration of 0.120 M using KCl. Hydrogen mass repartitioning (HMR) was used to enable 4 fs timestep simulations using the the AMBER ff14SB force field parameters. The TMD structure was then
+
+<--- Page Split --->
+
+used to build the entire complex for CRL- VHL- Degrader- SMARCA2. The system also included E2 and ubiquitin from the 6TTU structure. This system was solvated in a truncated octahedral box to avoid protein rotation during simulation and it was equilibrated for about 30 ns before subsequent meta- eABF simulations for identifying the ubiquitination zone.
+
+### 4.14 Meta-eABF simulations on full Cullin-RING E3 ubiquitin ligases (CRL) complex
+
+We employ an advanced path- based simulation method that combines metadynamics with extended adaptive biasing force (meta- eABF) to study the dynamic nature of the full CRL- VHL- degrader- SMARCA2 complex and generate a diverse set of putative closed conformations that place the E2- loaded ubiquitin close to lysine residues on SMARCA2. The results from the meta- eABF simulation are used to seed additional simulations for unbiased ensemble- scale sampling.
+
+Detailed description of the meta- eABF algorithm and its variants can be found elsewhere, \(^{73 - 76}\) but for clarity we present a brief account here. Similar to adaptive biasing force (ABF) methods, meta- eABF simulations also utilize adaptive free energy biasing force to enhance sampling along one or more collective variables (CVs), but the practical implementation is different. Meta- eABF evokes the extended Lagrangian formalism of ABF whereby an auxiliary simulation is introduced with a small number of degrees of freedom equal to the number of CVs, and each real CV is associated with its so- called fictitious counterpart in the low- dimensional auxiliary simulation. The real CV is tethered to its fictitious CV via a stiff spring with a large force constant and the adaptive biasing force is equal to the running average of the negative of the spring force. The biasing force is only applied to the fictitious CV, which in turn “drags” the real simulation along the real CV via the spring by periodically injecting the instantaneous spring force back into the real simulation. Moreover, the main tenet of the meta- eABF method is employing metadynamics (MtD) or well- tempered metadynamics.
+
+<--- Page Split --->
+
+ics (WTM) to enhance sampling of the fictitious CV itself. The combined approach provides advantages from both MtD/WTM and eABF.
+
+For CRL- VHL closure we chose a single CV, the center- of- mass (COM) distance between SMARCA2 and E2 ligase- ubiquitin (E2- Ub) complex. The initial COM distance after relaxation was \(\sim 65\) Å, and we ran 40 ns of meta- eABF simulation biasing the COM distance between 25- 75 Å. During this simulation we saw multiple ring closing- opening events with the last frame representing a slightly open conformation with COM distance \(\sim 36\) Å. We then continued the meta- eABF simulation for another 80 ns but narrowing the bias range on the COM distance to 25- 40 Å in order to focus the sampling on closed or nearly closed conformations. The simulations were run using OpenMM 7.5 \(^{77}\) interfaced with PLUMED 2.7. \(^{78}\)
+
+## Acknowledgement
+
+This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE- AC05- 00OR22725.
+
+We thank the University of Massachusetts Institute of Applied Life Sciences Mass Spectrometry Core ( RRID:SCR_019063) and Stephen J. Eyles for their support and mentorship during the collection, and processing of all Hydrogen Deuterium Exchange Data. We thank Helix Biostructures LLC for their assistance with X- Ray data collection and raw data reduction. SAXS measurements were based upon research conducted at the Structural Biology Platform of the Université de Montréal, which is supported by the Canadian Foundation for Innovation award #30574.
+
+We are grateful to all the citizen scientists who contributed their compute power to make parts of this work possible, and members of the Folding@home community who volunteered to help with technical support to run these simulations.
+
+<--- Page Split --->
+
+## 5 Author contributions
+
+TDi and BM ran and analyzed WES+HDX simulations. DMa performed crystallography and HDX- MS experiments. TDa ran docking simulations. SL wrote software to support simulations and analysis. DMc ran MD simulations and analyses. SSh and RP performed homology modeling and analyzed data. URS ran HREMD simulations and compared to SAXS. RW and ZAM ran FAH simulations and performed conformational landscape analyses. FP analyzed HDX data. JVR assisted with visualization and analyses. TW and VS helped scale WESTPA in Summit and to run all simulations efficiently in our HPC cluster. NG and SJ performed protein production. SSp performed SAXS analyses. YL and AV performed SPR experiments. XZ oversaw synthesis of PROTAC molecules. AMR and IK performed CRL simulations and ubiquitination analyses. JIm, AE, and LB helped edit the paper. AD, HX, WS and JAI directed the research presented in this paper. All authors wrote the paper.
+
+## Supporting Information Available
+
+We make all experimental data used in this study available, including HDX- MS and a crystal structure of SMARCA2:ACBI1:VHL- Elongin C- Elongin B (PDB ID 7S4E). We also make available trajectory data for the conformational sampling of the crystal structures and the ternary complex formation simulations at https://console.cloud.google.com/storage/browser/paperdata. We have created a repository information about the format of the WES+HDX trajectory data, and source code needed to run WES+HDX at https://github.com/stxinsite/degrader- ternary- complex- prediction.
+
+## References
+
+(1) Wu, T.; Yoon, H.; Xiong, Y.; Dixon-Clarke, S. E.; Nowak, R. P.; Fischer, E. S. Targeted protein degradation as a powerful research tool in basic biology and
+
+<--- Page Split --->
+
+drug target discovery. NAT STRUCT MOL BIOL 2020, 27, 605- 614.
+
+(2) Schneider, M.; Radoux, C. J.; Hercules, A.; Ochoa, D.; Dunham, I.; Zalmas, L.-P.; Hessler, G.; Ruf, S.; Shanmugasundaram, V.; Hann, M. M.; Thomas, P. J.; Queisser, M. A.; Benowitz, A. B.; Brown, K.; Leach, A. R. The PROTACtable genome. NAT REV DRUG DISCOV 2021, 1-9.
+
+(3) Schapira, M.; Calabrese, M. F.; Bullock, A. N.; Crews, C. M. Targeted protein degradation: expanding the toolbox. NAT REV DRUG DISCOV 2019, 18, 949-963.
+
+(4) Coleman, K. G.; Crews, C. M. Proteolysis-Targeting Chimeras: Harnessing the Ubiquitin-Proteasome System to Induce Degradation of Specific Target Proteins. Annual Review of Cancer Biology 2017, 2, 1-18.
+
+(5) Matyskiela, M. E. et al. A Cereblon Modulator (CC-220) with Improved Degradation of Ikaros and Aiolos. Journal of Medicinal Chemistry 2018, 61, 535-542.
+
+(6) Chamberlain, P. P. et al. Structure of the human Cereblon-DDB1-lenalidomide complex reveals basis for responsiveness to thalidomide analogs. Nature Structural & Molecular Biology 2014, 21, 803-809.
+
+(7) Krönke, J. et al. Lenalidomide Causes Selective Degradation of IKZF1 and IKZF3 in Multiple Myeloma Cells. Science 343, 301-305.
+
+(8) Ohoka, N. et al. In Vivo Knockdown of Pathogenic Proteins via Specific and Nongenetic Inhibitor of Apoptosis Protein (IAP)-dependent Protein Erasers (SNIPERs)*. Journal of Biological Chemistry 2017, 292, 4556-4570.
+
+(9) Wei, J. et al. Harnessing the E3 Ligase KEAP1 for Targeted Protein Degradation. Journal of the American Chemical Society 2021, 143, 15073-15083.
+
+(10) Rodriguez-Gonzalez, A.; Cyrus, K.; Salcius, M.; Kim, K.; Crews, C. M.; Deshaies, R. J.; Sakamoto, K. M. Targeting steroid hormone receptors for ubiqu
+
+<--- Page Split --->
+
+uitination and degradation in breast and prostate cancer. Oncogene 2008, 27, 7201–7211.
+
+(11) Hon, W.-C.; Wilson, M. I.; Harlos, K.; Claridge, T. D.; Schofield, C. J.; Pugh, C. W.; Maxwell, P. H.; Ratcliffe, P. J.; Stuart, D. I.; Jones, E. Y. Structural basis for the recognition of hydroxyproline in HIF-1α by pVHL. Nature 2002, 417, 975–978.
+
+(12) Sakamoto, K. M.; Kim, K. B.; Kumagai, A.; Mercurio, F.; Crews, C. M.; Deshaies, R. J. Protacs: Chimeric molecules that target proteins to the Skp1-Cullin-F box complex for ubiquitination and degradation. Proceedings of the National Academy of Sciences 2001, 98, 8554–8559.
+
+(13) Roy, M. J.; Winkler, S.; Hughes, S. J.; Whitworth, C.; Galant, M.; Farnaby, W. l.; Rumpel, K.; Ciulli, A. SPR-Measured Dissociation Kinetics of PROTAC Ternary Complexes Influence Target Degradation Rate. ACS CHEM BIOL 2019, 14, 361–368.
+
+(14) Hughes, S.; Ciulli, A. Molecular recognition of ternary complexes: a new dimension in the structure-guided design of chemical degraders. ESSAYS BIOCHEM 2017, 61, 505–516.
+
+(15) Farnaby, W.; Koegl, M.; Roy, M. J.; Whitworth, C.; Diers, E.; Trainor, N.; Zollman, D.; Steurer, S.; Karolyi-Oezguer, J.; Riedmueller, C., et al. BAF complex vulnerabilities in cancer demonstrated via structure-based PROTAC design. Nature chemical biology 2019, 15, 672–680.
+
+(16) Zorba, A. et al. Delineating the role of cooperativity in the design of potent PROTACs for BTK. Proceedings of the National Academy of Sciences 2018, 115, 201803662.
+
+(17) Schiemer, J. et al. Snapshots and ensembles of BTK and cIAP1 protein degrader ternary complexes. NAT CHEM BIOL 2021, 17, 152–160.
+
+<--- Page Split --->
+
+(18) Huang, H.-T.; Dobrovolsky, D.; Paulk, J.; Yang, G.; Weisberg, E. L.; Doctor, Z. M.; Buckley, D. L.; Cho, J.-H.; Ko, E.; Jang, J., et al. A chemoproteomic approach to query the degradable kinome using a multi-kinase degrader. Cell chemical biology 2018, 25, 88–99.
+
+(19) Bondeson, D. P.; Smith, B. E.; Burslem, G. M.; Buhimschi, A. D.; Hines, J.; Jaime-Figueroa, S.; Wang, J.; Hamman, B. D.; Ishchenko, A.; Crews, C. M. Lessons in PROTAC design from selective degradation with a promiscuous warhead. Cell chemical biology 2018, 25, 78–87.
+
+(20) Ward, C. C.; Kleinman, J. I.; Brittain, S. M.; Lee, P. S.; Chung, C. Y. S.; Kim, K.; Petri, Y.; Thomas, J. R.; Tallarico, J. A.; McKenna, J. M., et al. Covalent ligand screening uncovers a RNF4 E3 ligase recruiter for targeted protein degradation applications. ACS chemical biology 2019, 14, 2430–2440.
+
+(21) Zengerle, M.; Chan, K.-H.; Ciulli, A. Selective Small Molecule Induced Degradation of the BET Bromodomain Protein BRD4. ACS CHEM BIOL 2015, 10, 1770–1777.
+
+(22) Gadd, M. S.; Testa, A.; Lucas, X.; Chan, K.-H.; Chen, W.; Lamont, D. J.; Zengerle, M.; Ciulli, A. Structural basis of PROTAC cooperative recognition for selective protein degradation. NAT CHEM BIOL 2017, 13, 514–521.
+
+(23) Farnaby, W. et al. BAF complex vulnerabilities in cancer demonstrated via structure-based PROTAC design. NAT CHEM BIOL 2019, 15, 672–680.
+
+(24) Testa, A.; Hughes, S. J.; Lucas, X.; Wright, J. E.; Ciulli, A. Structure-Based Design of a Macrocyclic PROTAC. Angewandte Chemie International Edition 2020, 59, 1727–1734.
+
+(25) Zaidman, D.; Prilusky, J.; London, N. PRosettaC: Rosetta Based Modeling of PROTAC Mediated Ternary Complexes. J CHEM INF MODEL 2020, 60, 4894–4903.
+
+<--- Page Split --->
+
+(26) Bai, N.; Kirubakaran, P.; Karanicolas, J. Rationalizing PROTAC-mediated ternary complex formation using Rosetta. J. Chem. Inf. Model. 2021, 61, 1368–1382.
+
+(27) Drummond, M. L.; Henry, A.; Li, H.; Williams, C. I. Improved Accuracy for Modeling PROTAC-Mediated Ternary Complex Formation and Targeted Protein Degradation via New In Silico Methodologies. J CHEM INF MODEL 2020, 60, 5234–5254.
+
+(28) Shaheer, M.; Singh, R.; Sobhia, M. E. Protein degradation: a novel computational approach to design protein degrader probes for main protease of SARS-CoV-2. J BIOMOL STRUCT DYN 2021, 1–13.
+
+(29) Drummond, M. L.; Henry, A.; Li, H.; Williams, C. I. Improved Accuracy for Modeling PROTAC-Mediated Ternary Complex Formation and Targeted Protein Degradation via New In Silico Methodologies. J CHEM INF MODEL 2020, 60, 5234–5254.
+
+(30) Eron, S. J.; Huang, H.; Agafonov, R. V.; Fitzgerald, M. E.; Patel, J.; Michael, R. E.; Lee, T. D.; Hart, A. A.; Shaulsky, J.; Nasveschuk, C. G.; Phillips, A. J.; Fisher, S. L.; Good, A. Structural Characterization of Degrader-Induced Ternary Complexes Using Hydrogen–Deuterium Exchange Mass Spectrometry and Computational Modeling: Implications for Structure-Based Design. ACS Chemical Biology 2021,
+
+(31) Liu, X.; Zhang, X.; Lv, D.; Yuan, Y.; Zheng, G.; Zhou, D. Assays and technologies for developing proteolysis targeting chimera degraders. Future Medicinal Chemistry 2020, 12, 1155–1179.
+
+(32) Nowak, R. P.; DeAngelo, S. L.; Buckley, D.; He, Z.; Donovan, K. A.; An, J.; Safaee, N.; Jedrychowski, M. P.; Ponthier, C. M.; Ishoey, M.; Zhang, T.; Mancias, J. D.; Gray, N. S.; Bradner, E. S., J. E. Fischer Plasticity in binding confers
+
+<--- Page Split --->
+
+selectivity in ligand- induced protein degradation. Nature Chemical Biology 2018, 14, 706–714.
+
+(33) Deller, M. C.; Kong, L.; Rupp, B. Protein stability: A crystallographer’s perspective. Acta Crystallogr F Struct Biol Commun 2016, 72, 72–95.
+
+(34) Dagbay, K. B.; Bolik-Coulon, N.; Savinov, S. N.; Hardy, J. A. Caspase-6 undergoes a Distinct Helix-Strand Interconversion upon Substrate Binding\*. J BIOL CHEM 2017, 292, 4885–4897.
+
+(35) Dagbay, K. B.; Hardy, J. A. Multiple proteolytic events in caspase-6 self-activation impact conformations of discrete structural regions. Proceedings of the National Academy of Sciences of the United States of America 2017, 114, E7977–E7986.
+
+(36) MacPherson, D. J.; Mills, C. L.; Ondrechen, M. J.; Hardy, J. A. Tri-arginine exosite patch of caspase-6 recruits substrates for hydrolysis. J BIOL CHEM 2019, 294, 71–88.
+
+(37) Wales, T. E.; Engen, J. R. Hydrogen exchange mass spectrometry for the analysis of protein dynamics. MASS SPECTROM REV 2006, 25, 158–170.
+
+(38) Gallagher, E. S.; Hudgens, J. W. Mapping Protein-Ligand Interactions with Proteolytic Fragmentation, Hydrogen/Deuterium Exchange-Mass Spectrometry. Methods in Enzymology 2016, 566.
+
+(39) Saglam, A. S.; Chong, L. T. Protein-protein binding pathways and calculations of rate constants using fully-continuous, explicit-solvent simulations. Chemical Science 2018, 10, 2360–2372.
+
+(40) Méndez, R.; Leplae, R.; De Maria, L.; Wodak, S. J. Assessment of blind predictions of protein–protein interactions: Current status of docking methods. PROTEINS 2003, 52, 51–67.
+
+(41) Donyapour, N.; Roussev, N. M.; Dickson, A. REVO: Resampling of ensembles by variation optimization. J. Chem. Phys. 2019, 150.
+
+<--- Page Split --->
+
+(42) Jubb, H. C.; Higueruelo, A. P.; Ochoa-Montaño, B.; Pitt, W. R.; Ascher, D. B.; Blundell, T. L. Arpeggio: A Web Server for Calculating and Visualising Interatomic Interactions in Protein Structures. Journal of Molecular Biology 2017, 429, 365-371.
+
+(43) Lotz, S. D.; Dickson, A. Wepy: A Flexible Software Framework for Simulating Rare Events with Weighted Ensemble Resampling. ACS Omega 2020, 5, 31608-31623.
+
+(44) Dixon, T.; Uyar, A.; Ferguson-Miller, S.; Dickson, A. Membrane-Mediated Ligand Unbinding of the PK-11195 Ligand from TSPO. Biophysical Journal 2021, 120, 158-167.
+
+(45) Copperman, J.; Zuckerman, D. M. Accelerated Estimation of Long-Timescale Kinetics from Weighted Ensemble Simulation via Non-Markovian "Microbin" Analysis. Journal of Chemical Theory and Computation 2020, 16, 6763-6775.
+
+(46) DeGrave, A. J.; Bogetti, A. T.; Chong, L. T. The RED scheme: Rate-constant estimation from pre-steady state weighted ensemble simulations. The Journal of Chemical Physics 2021, 154, 114111.
+
+(47) Zhang, M. M.; Beno, B. R.; Huang, R. Y.-C.; Adhikari, J.; Deyanova, E. G.; Li, J.; Chen, G.; Gross, M. L. An Integrated Approach for Determining a Protein-Protein Binding Interface in Solution and an Evaluation of Hydrogen-Deuterium Exchange Kinetics for Adjudicating Candidate Docking Models. Anal. Chem. 2019, 91, 15709-15717.
+
+(48) Scherer, M. K.; Trendelkamp-Schroer, B.; Paul, F.; Pérez-Hernández, G.; Hoffmann, M.; Plattner, N.; Wehmeyer, C.; Prinz, J.-H.; Noé, F. PyEMMA 2: A Software Package for Estimation, Validation, and Analysis of Markov Models. Journal of Chemical Theory and Computation 2015, 11, 5525-5542.
+
+<--- Page Split --->
+
+(49) Husic, B. E.; Pande, V. S. Markov state models: From an art to a science. Journal of the American Chemical Society 2018, 140, 2386-2396.
+
+(50) Molgedey, L.; Schuster, H. G. Separation of a mixture of independent signals using time delayed correlations. Phys. Rev. Lett. 1994, 72, 3634-3637.
+
+(51) Baek, K.; Krist, D. T.; Prabu, J. R.; Hill, S.; Klügel, M.; Neumaier, L.-M.; von Gronau, S.; Kleiger, G.; Schulman, B. A. NEDD8 nucleates a multivalent cullin–RING–UBE2D ubiquitin ligation assembly. Nature 2020, 578, 461-466.
+
+(52) Dagbay, K. B.; Hardy, J. A. Multiple proteolytic events in caspase-6 self-activation impact conformations of discrete structural regions. P NATL ACAD SCI USA 2017, 114, E7977-E7986.
+
+(53) Wales, T. E.; Fadgen, K. E.; Gerhardt, G. C.; Engen, J. R. High-Speed and High-Resolution UPLC Separation at Zero Degrees Celsius. AANAL BIOANAL CHEM 2008, 80, 6815-6820.
+
+(54) Hopkins, J. B.; Gillilan, R. E.; Skou, S. BioXTAS RAW: improvements to a free open-source program for small-angle X-ray scattering data reduction and analysis. J APPL CRYSTALLOGR 2017, 50, 1545-1553.
+
+(55) Maier, J. A.; Martinez, C.; Kasavajhala, K.; Wickstrom, L.; Hauser, K. E.; Simmerling, C. ff14SB: Improving the Accuracy of Protein Side Chain and Backbone Parameters from ff99SB. J CHEM THEORY COMPUT 2015, 11, 3696-3713, PMID: 26574453.
+
+(56) Zhang, B. W.; Jasnow, D.; Zuckerman, D. M. The "weighted ensemble" path sampling method is statistically exact for a broad class of stochastic processes and binning procedures. J CHEM PHYS 2010, 132, 054107.
+
+(57) Huber, G. A.; Kim, S. Weighted-ensemble Brownian dynamics simulations for protein association reactions. BIOPHYS J 1996, 70, 97-110.
+
+<--- Page Split --->
+
+(58) Zuckerman, D. M.; Chong, L. T. Weighted Ensemble Simulation: Review of Methodology, Applications, and Software. ANN REV BIOPHYS 2017, 46, 43–57.
+
+(59) Zwier, M. C.; Adelman, J. L.; Kaus, J. W.; Pratt, A. J.; Wong, K. F.; Rego, N. B.; Suarez, E.; Lettieri, S.; Wang, D. W.; Grabe, M.; Zuckerman, D. M.; Chong, L. T. WESTPA: An Interoperable, Highly Scalable Software Package for Weighted Ensemble Simulation and Analysis. J CHEM THEORY COMPUT 2015, 11, 800–809.
+
+(60) Pearlman, D. A.; Case, D. A.; Caldwell, J. W.; Ross, W. S.; Cheatham III, T. E.; DeBolt, S.; Ferguson, D.; Seibel, G.; Kollman, P. AMBER, a package of computer programs for applying molecular mechanics, normal mode analysis, molecular dynamics and free energy calculations to simulate the structural and energetic properties of molecules. COMPUT PHYS COMMUN 1995, 91, 1–41.
+
+(61) Pracht, P.; Bohle, F.; Grimme, S. Automated exploration of the low-energy chemical space with fast quantum chemical methods. Phys. Chem. Chem. Phys. 2020, 22, 7169–7192.
+
+(62) Grimme, S. Exploration of Chemical Compound, Conformer, and Reaction Space with Meta-Dynamics Simulations Based on Tight-Binding Quantum Chemical Calculations. J. Chem. Theory Comput. 2019, 15, 2847–2862.
+
+(63) Bannwarth, C.; Ehlert, S.; Grimme, S. GFN2-xTB—An Accurate and Broadly Parametrized Self-Consistent Tight-Binding Quantum Chemical Method with Multipole Electrostatics and Density-Dependent Dispersion Contributions. J. Chem. Theory Comput. 2019, 15, 1652–1671.
+
+(64) Gray, J. J.; Moughon, S.; Wang, C.; Schueler-Furman, O.; Kuhlman, B.; Rohl, C. A.; Baker, D. Protein–Protein Docking with Simultaneous Optimization of Rigid-body Displacement and Side-chain Conformations. J. Mol. Biol. 2003, 331, 281–299.
+
+<--- Page Split --->
+
+(65) Marze, N. A.; Roy Burman, S. S.; Sheffler, W.; Gray, J. J. Efficient flexible backbone protein–protein docking for challenging targets. Bioinformatics 2018, 34, 3461–3469.
+
+(66) Bussi, G. Hamiltonian replica exchange in GROMACS: a flexible implementation. MOL PHYS 2014, 112, 379–384.
+
+(67) Wang, L.; Friesner, R. A.; Berne, B. J. Replica exchange with solute scaling: a more efficient version of replica exchange with solute tempering (REST2). J PHYS CHEM B 2011, 115, 9431–9438.
+
+(68) Svergun, D.; Barberato, C.; Koch, M. H. J. CRYSOL – a Program to Evaluate X-ray Solution Scattering of Biological Macromolecules from Atomic Coordinates. J APPL CRYSTALLOGR 1995, 28, 768–773.
+
+(69) Manalastas-Cantos, K.; Konarev, P. V.; Hajizadeh, N. R.; Kikhney, A. G.; Petoukhov, M. V.; Molodenskiy, D. S.; Panjkovich, A.; Mertens, H. D. T.; Gruzinov, A.; Borges, C.; Jeffries, C. M.; Svergun, D. I.; Franke, D. ATSAS 3.0: expanded functionality and new tools for small-angle scattering data analysis. J APPL CRYSTALLOGR 2021, 54, 343–355.
+
+(70) Borreguero, J. M.; Islam, F. F.; Shrestha, U. R.; Petridis, L. idpflex: Analysis of Intrinsically Disordered Proteins by Comparing Simulations to Small Angle Scattering Experiments. Journal of Open Source Software 2018, 3.
+
+(71) Cheng, X.; Wang, H.; Grant, B.; Sine, S. M.; McCammon, J. A. Targeted molecular dynamics study of C-loop closure and channel gating in nicotinic receptors. PLoS computational biology 2006, 2, e134.
+
+(72) Edmondson, S. D.; Yang, B.; Fallan, C. Proteolysis Targeting Chimeras (PROTACs) in ‘Beyond Rule-of-Five’ Chemical Space: Recent Progress and Future Challenges. BIOORG MED CHEM LETT 2019, 29, 1555–1564.
+
+<--- Page Split --->
+
+(73) Comer, J.; Gumbart, J. C.; Hénin, J.; Lelièvre, T.; Pohorille, A.; Chipot, C. The adaptive biasing force method: Everything you always wanted to know but were afraid to ask. The Journal of Physical Chemistry B 2015, 119, 1129–1151.
+
+(74) Lesage, A.; Lelièvre, T.; Stoltz, G.; Hénin, J. Smoothed biasing forces yield unbiased free energies with the extended-system adaptive biasing force method. The Journal of Physical Chemistry B 2017, 121, 3676–3685.
+
+(75) Fu, H.; Zhang, H.; Chen, H.; Shao, X.; Chipot, C.; Cai, W. Zooming across the free-energy landscape: shaving barriers, and flooding valleys. The journal of physical chemistry letters 2018, 9, 4738–4745.
+
+(76) Fu, H.; Shao, X.; Cai, W.; Chipot, C. Taming rugged free energy landscapes using an average force. Accounts of chemical research 2019, 52, 3254–3264.
+
+(77) Eastman, P.; Swails, J.; Chodera, J. D.; McGibbon, R. T.; Zhao, Y.; Beauchamp, K. A.; Wang, L.-P.; Simmonett, A. C.; Harrigan, M. P.; Stern, C. D., et al. OpenMM 7: Rapid development of high performance algorithms for molecular dynamics. PLoS computational biology 2017, 13, e1005659.
+
+(78) Bonomi, M. Promoting transparency and reproducibility in enhanced molecular simulations. Nature methods 2019, 16, 670–673.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+ternarycomplexpredictionsicompr.pdf protacnrreportingsummary2. pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182_det.mmd b/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..40937e79d63e3fb0a3762fc211a6a22fa686f775
--- /dev/null
+++ b/preprint/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182/preprint__01cb486613d82fb6bd28494662843f5e750475d21b9066890284fd7c62002182_det.mmd
@@ -0,0 +1,959 @@
+<|ref|>title<|/ref|><|det|>[[44, 106, 944, 245]]<|/det|>
+# Atomic-Resolution Prediction of Degrader-mediated Ternary Complex Structures by Combining Molecular Simulations with Hydrogen Deuterium Exchange
+
+<|ref|>text<|/ref|><|det|>[[44, 264, 636, 331]]<|/det|>
+Tom Dixon Michigan State University https://orcid.org/0000- 0002- 4520- 3894
+
+<|ref|>text<|/ref|><|det|>[[44, 316, 575, 360]]<|/det|>
+Derek MacPherson Roivant Discovery https://orcid.org/0000- 0003- 2006- 1620
+
+<|ref|>text<|/ref|><|det|>[[44, 357, 575, 400]]<|/det|>
+Barmak Mostofian Roivant Discovery https://orcid.org/0000- 0003- 0568- 9866
+
+<|ref|>text<|/ref|><|det|>[[44, 405, 214, 446]]<|/det|>
+Taras Dauzhenka Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 452, 214, 492]]<|/det|>
+Samuel Lotz Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 498, 214, 538]]<|/det|>
+Dwight McGee Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 544, 214, 584]]<|/det|>
+Sharon Shechter Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 590, 214, 630]]<|/det|>
+Utsab Shrestha Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 636, 214, 676]]<|/det|>
+Rafal Wiewiora Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 682, 214, 722]]<|/det|>
+Zachary McDargh Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 728, 214, 768]]<|/det|>
+Fen Pei Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 774, 214, 814]]<|/det|>
+Rajat Pal Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 820, 214, 860]]<|/det|>
+Joao Vieira Ribeiro Roivant Discovery https://orcid.org/0000- 0002- 0353- 4126
+
+<|ref|>text<|/ref|><|det|>[[44, 866, 214, 906]]<|/det|>
+Tanner Wilkerson Roivant Discovery
+
+<|ref|>text<|/ref|><|det|>[[44, 912, 214, 953]]<|/det|>
+Vipin Sachdeva Roivant Discovery
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 42, 576, 739]]<|/det|>
+Ning Gao Roivant Discovery Shouya Jain Roivant Discovery Samuel Sparks Roivant Discovery Yunxing Li Roivant Discovery Alexander Vinitsky Roivant Discovery Xin Zhang Roivant Discovery Asghar Razavi Roivant Discovery István Kolossváry Roivant Discovery Jason Imbriglio Roivant Discovery Artem Evdokimov Roivant Discovery Louise Bergeron Roivant Discovery Alex Dickson Michigan State University Huafeng Xu Michigan State University Woody Sherman Michigan State University Jesus Izaguirre ( Jesus.izaguirre@roivant.com ) Roivant Discovery https://orcid.org/0000-0002-4687-4884
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 777, 102, 794]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 815, 137, 832]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 853, 335, 870]]<|/det|>
+Posted Date: February 15th, 2022
+
+<|ref|>text<|/ref|><|det|>[[44, 891, 473, 908]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs-1318882/v1
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 44, 911, 87]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 123, 925, 167]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on October 6th, 2022. See the published version at https://doi.org/10.1038/s41467-022-33575-4.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[115, 144, 872, 333]]<|/det|>
+# Atomic-Resolution Prediction of Degrader-mediated Ternary Complex Structures by Combining Molecular Simulations with Hydrogen Deuterium Exchange
+
+<|ref|>text<|/ref|><|det|>[[115, 364, 881, 616]]<|/det|>
+Tom Dixon, \(^{1, \bullet}\) Derek MacPherson, \(^{1, \bullet}\) Barmak Mostofian, \(^{1, \bullet}\) Taras Dauzhenka, \(^{1}\) Samuel Lotz, \(^{1}\) Dwight McGee, \(^{1}\) Sharon Shechter, \(^{1}\) Utsab R. Shrestha, \(^{1}\) Rafal Wiewiora, \(^{1}\) Zachary A. McDargh, \(^{1}\) Fen Pei, \(^{1}\) Rajat Pal, \(^{1}\) João V. Ribeiro, \(^{1}\) Tanner Wilkerson, \(^{1}\) Vipin Sachdeva, \(^{1}\) Ning Gao, \(^{1}\) Shourya Jain, \(^{1}\) Samuel Sparks, \(^{1}\) Yunxing Li, \(^{1}\) Alexander Vinitsky, \(^{1}\) Xin Zhang, \(^{1}\) Asghar M. Razavi, \(^{1}\) István Kolossváry, \(^{1}\) Jason Imbriglio, \(^{1}\) Artem Evdokimov, \(^{1}\) Louise Bergeron, \(^{1}\) Alex Dickson, \(^{*, \dagger}\) Huafeng Xu, \(^{*, \dagger}\) Woody Sherman, \(^{*, \dagger}\) and Jesus A. Izaguirre \(^{*, \dagger}\)
+
+<|ref|>text<|/ref|><|det|>[[135, 639, 861, 691]]<|/det|>
+\(^{1}\) Department of Biochemistry and Molecular Biology, Michigan State University, USA \(^{1}\) Roviant Discovery, New York, USA
+
+<|ref|>text<|/ref|><|det|>[[350, 701, 648, 720]]<|/det|>
+\(^{1}\) These authors contributed equally
+
+<|ref|>text<|/ref|><|det|>[[175, 744, 820, 794]]<|/det|>
+E- mail: alexrd@msu.edu; huafeng.xu@roivant.com; woody.sherman@roivant.com; jesus.izaguirre@roivant.com
+
+<|ref|>sub_title<|/ref|><|det|>[[458, 828, 539, 846]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[160, 864, 835, 912]]<|/det|>
+Targeted protein degradation (TPD) has emerged as a powerful approach for removing (rather than inhibiting) proteins implicated in diseases. A key step in TPD
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[158, 87, 839, 763]]<|/det|>
+is the formation of an induced proximity complex where a degrader molecule recruits an E3 ligase to the protein of interest (POI), facilitating the transfer of ubiquitin to the POI and initiating the proteasomal degradation process. Here, we address three critical aspects of the TPD process using atomistic simulations: 1) formation of the ternary complex induced by a degrader molecule, 2) conformational heterogeneity of the ternary complex, and 3) degradation efficiency via the full Cullin Ring Ligase (CRL) macromolecular assembly. The novel approach described here combines experimental biophysical data with molecular dynamics (MD) simulations to accurately predict ternary complex structures at atomic resolution. We integrate hydrogen-deuterium exchange mass spectrometry (HDX-MS, which measures the solvent exposure of protein residues) with MD to improve the efficiency and accuracy of the ternary structure predictions of the bromodomain of the cancer target SMARCA2 with the E3 ligase VHL, as mediated by three different degrader molecules. The simulations accurately reproduce X- ray crystal structures – including a new structure that we determined in this work (PDB ID: 7S4E) – with root mean square deviations (RMSD) of 1.1 to 1.6 Å. The simulations also reveal a structural ensemble of low- energy conformations of the ternary complex. Snapshots from these simulations are used as seeds for additional simulations, where we perform 7.1 milliseconds of aggregate simulation time using Folding@home. The detailed free energy surface captures the crystal structure conformation within a low- energy basin and is consistent with solution- phase experimental data (HDX- MS and SAXS). Finally, we graft a structural ensemble of the ternary complexes onto the full CRL and perform enhanced sampling simulations, which suggest that differences in degradation efficiency may be related to the proximity distribution of lysine residues on the POI relative to the E2- loaded ubiquitin.
+
+<|ref|>sub_title<|/ref|><|det|>[[163, 804, 387, 828]]<|/det|>
+## 1 Introduction
+
+<|ref|>text<|/ref|><|det|>[[161, 850, 837, 898]]<|/det|>
+Heterobifunctional degraders are a class of ligands that induce proximity between a target protein of interest (POI) and a E3 ubiquitin ligase, which can ultimately lead
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[159, 90, 839, 508]]<|/det|>
+to ubiquitination of the POI and its subsequent proteosomal degradation through a complex machinery of proteins. \(^{1}\) These degraders provide the opportunity of a novel therapeutic modality – single molecules induce catalytic turnover of the POI – and potentially offer an avenue for modulation of targets traditionally labeled as “undruggable” by classical therapeutic strategies. \(^{2 - 4}\) The subset of degraders classified as hetero- bifunctionals consists of two separate moieties, the “warhead” and the “ligand”, joined by a “linker”; the warhead binds to the POI and the ligand binds to an E3 ligase such as Cereblon (CRBN), \(^{5 - 7}\) cIAP, \(^{8}\) KEAP1, \(^{9}\) and von Hippel- Lindau protein (VHL). \(^{10 - 12}\) In each case it is the ability of the warhead- linker- ligand degrader molecule to induce a ternary complex that is critical for bridging the interaction between the POI and an E3 ligase (which can be the native or non- native degradation partner of the POI). Often key to the function of these molecules, cooperativity, i.e., the difference between the binding affinity of the ternary complex and those of its binary components, is a complex descriptor of these non- native interactions bridging the induced interface of the POI- E3 pair and it has strong correlation to degradation efficiency.
+
+<|ref|>text<|/ref|><|det|>[[160, 516, 839, 904]]<|/det|>
+The formation of the POI- degrader- E3 ternary complex is central to the targeted protein degradation (TPD) process, but how the formation of the ternary structure impacts protein degradation is still poorly understood, especially given the dynamic nature of the non- native induced proximity complex. \(^{13}\) X- ray crystallography – the primary experimental technique for determining 3- dimensional structures of the ternary complex \(^{14}\) – provides a high resolution structure of a single conformational state, but a growing body of evidence suggests that the dynamic nature of the ternary structure may not accurately represented by this lowest energy crystallization snapshot. For instance, a study of several heterobifunctional degraders, that induce proximity between VHL and SMARCA2, a BAF ATPase subunit, found that a positive cooperativity upon ternary complex formation leads to higher degradation efficiency. \(^{15}\) Furthermore, despite the fact that the different SMARCA2 degraders displayed different degrees of efficiency, \(^{15}\) the formed ternary complexes are nearly structurally identical, raising questions about the relationship between static structural representations of the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 837, 250]]<|/det|>
+ternary complex and degradation efficiency. Moreover, further complicating the relationship of cooperativity, structure and degradation, studies targeting the degradation of Burton Tyrosine Kinase (BTK) by CRBN or cIAP found that high degradation efficiencies can also be achieved through degrader molecules that induce a non- cooperative ternary complex, demonstrating a disconnect between binding affinity and degradation efficiency. \(^{16,17}\)
+
+<|ref|>text<|/ref|><|det|>[[160, 260, 837, 392]]<|/det|>
+This and other findings \(^{18 - 20}\) suggest that degradation efficiency is more complex than can be understood through the thermodynamics of binding or through the analysis of static structures. As such, determining the dynamic ensemble of the ternary complex may reveal mechanistic insights to facilitate the design of more effective degrader molecules. \(^{14,21 - 24}\)
+
+<|ref|>text<|/ref|><|det|>[[160, 401, 838, 904]]<|/det|>
+Our ultimate goal is to understand the structural and dynamic basis for differences in degradation among a set of degrader molecules. Here, we specifically focus on three different VHL- recruiting degraders of SMARCA2 isoform 2, for which crystal structures already exist, i.e., PROTAC 1 (PDB ID: 6HAY) and PROTAC 2 (PDB ID: 6HAX), or have been obtained as part of this study, namely ACBI1 (PDB ID: 7S4E), with cooperativity and degradation efficiency summarized in Table 1. To this end, we carry out MD simulations in combination with hydrogen- deuterium exchange mass- spectrometry (HDX- MS), shedding light on the dynamics of the ternary complexes beyond what is provided by static crystal structures. Specifically, we use “protection data” derived from HDX- MS as collective variables in weighted- ensemble MD simulations, enhancing both the speed and accuracy of the computational predictions. We also show the usefulness of HDX- MS data as constraints for protein- protein docking when higher throughput and lower resolution models are sought, such as when screening many degrader molecules. Furthermore, we introduce methodology, that includes long- timescale MD simulations augmented with small- angle X- ray scattering (SAXS) data and Markov state modeling, to determine the conformational free energy landscapes of the ternary complexes, which is the foundation for quantifying the populations of different conformational states. Finally, as an example of downstream use of these models,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[161, 90, 836, 138]]<|/det|>
+we also model the entire cullin- RING ligase (CRL) assembly to explore structural and dynamic factors that may be associated with ubiquitination.
+
+<|ref|>text<|/ref|><|det|>[[161, 147, 838, 308]]<|/det|>
+Previous work to computationally predict ternary structures mostly consisted of protein- protein docking protocols, possibly followed by refinement of the initial structures with molecular dynamics (MD) simulations to assess the stability of the predicted models. \(^{23 - 29}\) However, these docking protocols fail to predict high- resolution structures (sub- 2.0 Å) with high fidelity, demonstrating the challenge associated with the generation and selection of high- accuracy ternary structure models.
+
+<|ref|>text<|/ref|><|det|>[[160, 316, 838, 563]]<|/det|>
+Recently, Eron et al. demonstrated how ternary complex structures of BRD4 do not represent the biologically relevant conformer of the ternary complex induced with CRBN. These studies demonstrated the merit of HDX- MS and modeling revealed the dynamic nature and alternative conformations that helped explain the dramatically increased cooperativity, ternary complex formation and degradation of their molecule CFT- 1297 compared to the literary standard, dBET6. \(^{30}\) The authors used the experimental data to improve protein- protein docking predictions, but they admit that the high flexibility of degrader- induced ternary complexes impedes a complete description of the bound conformations.
+
+<|ref|>text<|/ref|><|det|>[[160, 572, 838, 847]]<|/det|>
+This work offers unique insights into the dynamic nature of the ternary structure ensemble and that of the full CRL macromolecular assembly that could explain ubiquitination and downstream protein degradation. Our results can be used to guide the design of novel degrader molecules that induce a productive ternary complex ensemble. In particular, having a small set of high population ternary complex structures can provide an avenue for structure- based degrader design, particularly focused on linker design to improve different properties of the degrader. We make the simulation and experimental results available to the research community, including source codes and the release of a new X- ray crystal structure of ACBI1 with SMARCA2:VHL that has been deposited into the Protein Data Bank (PDB ID: 7S4E).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 884, 160]]<|/det|>
+Table 1: Binding affinity \((K_{d})\) , efficiencies (IC50, DC50), and cooperativity \((\alpha)\) of PROTAC 1, PROTAC 2, and ACBI1 degraders. Ternary IC50 and binary (SMARCA2) DC50 values are reported; the cooperativity is the ratio of binary over ternary IC50. Table adapted from Farnaby et al. \(^{15}\)
+
+<|ref|>table<|/ref|><|det|>[[114, 187, 901, 267]]<|/det|>
+
+ | Kd, VHL(nM) | Kd, SMARCA2(nM) | IC50 (nM) | DC50 (nM) | α |
| PROTAC 1 | 98 ± 26 | 4500 ± 480 | 205 ± 15 | 300 | 12 |
| PROTAC 2 | 100 ± 10 | 770 ± 51 | 45 ± 9 | N/A | 18 |
| ACBI1 | 250 ± 64 | 1800 ± 980 | 26 ± 3 | 6/3.3 | 30 |
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 302, 315, 325]]<|/det|>
+## 2 Results
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 354, 868, 415]]<|/det|>
+### 2.1 Degraders with different efficiency induce similar ternary complex structures in X-ray crystallography.
+
+<|ref|>text<|/ref|><|det|>[[160, 431, 857, 763]]<|/det|>
+The ternary complexes of SMARCA2 isoform 2 (SMC2) and the VHL/ElonginC/ElonginB (VCB) complex induced by different heterobifunctional degraders have been studied extensively. \(^{23,31}\) In particular, PROTAC 1, PROTAC 2, and ACBI1 are three prominent degrader molecules that induce a ternary SMC2:VCB complex with quite different degradation efficiencies (see Table 1). Whereas crystal structures of the ternary complexes induced by PROTAC 1 (PDB ID: 6HAY) and PROTAC 2 (PDB ID: 6HAX) exist, none has been reported to date for ACBI1, the most potent degrader among them. Thus, we determined the structure of SMC2:VHL liganded by ACBI1 via X- ray crystallography. The structure was obtained by hanging drop vapor diffusion (see Methods) \(^{23}\) and solved by molecular replacement to 2.25 Å in the highest resolution shell (Supplementary Figure 20), using the PROTAC 2 (PDB ID:6HAX) crystal structure as the search model (Figure 1a).
+
+<|ref|>text<|/ref|><|det|>[[160, 773, 836, 905]]<|/det|>
+ACBI1 bridges the induced interface, forming contacts with both proteins. Importantly, the ligand induces favorable contacts across the non- native interface, such as VCB:ARG69 and SMC2:PHE1463 (Figure 1 b,c). SMC2:ASN1464 maintains critical bivalent contacts to the aminopyridazine group of ACBI1, positioning the terminal phenol group for pi stacking interactions with residues PHE1409 and TYR1421 (Figure
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 91, 835, 166]]<|/det|>
+1b,c). On the VHL side of the interface, the interactions between TYR98 and ACBI1 are consistent with those between the same residue and PROTAC 1 or PROTAC 2 (Figure 1b,c). \(^{23}\)
+
+<|ref|>image<|/ref|><|det|>[[195, 184, 808, 579]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 597, 883, 800]]<|/det|>
+Figure 1: Ternary complex of SMARCA2 and VHL/ElonginC/ElonginB (VCB) induced by ACBI1 shows structural similarities with PROTAC 1 and PROTAC 2: a Overall perspective of SMARCA2 Isoform 2 (green) and VCB (grey) induced by degrader molecule ACBI1 (bright orange). b ACBI1-induced interface contacts between SMARCA2 and VCB. The proteins are shown in space-filling, the colors are as in a, annotated residues are among those that make the highest number of contacts (see c). c A contact map for the interface of the crystal structure. The circle size reflects the number of atoms (including hydrogen atoms) participating in interactions. d Superposition of 6HAY (purple), 6HAX (salmon), 7S4E (green) by aligning VHL (grey) shows varied conformations of the warheads of the three degraders PROTAC 1, PROTAC 2, or ACBI1 (up to 1.7 Å) resulting in alterations of SMARCA2 within the ternary complex.
+
+<|ref|>text<|/ref|><|det|>[[160, 829, 836, 904]]<|/det|>
+Despite differences in the linker compositions, the protein- protein interface induced by ACBI1 is structurally similar to that induced by PROTACs 1 or \(2^{23}\) (see Figure 1d). There are more distal changes in the orientation of SMARCA2 with respect to
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[161, 90, 836, 195]]<|/det|>
+VCB due to the minor differences in the linker compositions, e.g. the ACBI1 linker has one additional ether group compared to the PROTAC 2 linker, which yields a slight 1.7 Å twist of ACBI1 compared to the other two degraders, resulting in a subtle 5 Å “swing” of the protein in the crystal structure (Figure 1d).
+
+<|ref|>text<|/ref|><|det|>[[160, 204, 838, 450]]<|/det|>
+Overall, the structural similarity of the protein- protein interface does not align with the markedly different degradation efficiency obtained \(^{15}\) suggesting that the (dynamic) ensemble of ternary complex structures may be fairly different among them. Consistent with other studies, \(^{17,32}\) this implies that “crystallographic snapshots” are not suitable to provide a holistic view of the ensemble of all possible ternary complex structures in solution, but merely represent a subset of the relevant conformations favored by crystallization. \(^{33}\) Consequently, such X- ray structures cannot fully capture the dynamic nature of the degrader- induced ternary complexes, which play a pivotal role in biological activity and degradation efficiencies. \(^{17,32}\)
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 483, 891, 543]]<|/det|>
+### 2.2 Hydrogen Deuterium Exchange Reveals Extended Protein-Protein Interfaces
+
+<|ref|>text<|/ref|><|det|>[[160, 560, 838, 893]]<|/det|>
+In order to assess the impact of different degrader molecules on the dynamic nature of the SMC2:VCB interactions, we performed hydrogen- deuterium exchange of the respective APO, binary and ternary (complex) species, thus characterizing the induced protein- protein interface in solution. \(^{30}\) This approach is a promising alternative to previous attempts at characterizing degrader ternary complexes that employed multiple crystal structures, \(^{32}\) NMR, \(^{17}\) and SAXS coupled with various forms of modeling. Based on previously established protocols, \(^{34 - 36}\) and with the knowledge of binding constants for each of the three degraders, the assay was designed to optimize the complex formation of 80% or greater to obtain maximal exchange of the ternary complexes. The complexes were subsequently subjected to on- line pepsin digestion and optimized for 100% sequence coverage (see supplementary Fig. 22) of each protein within the complex and stable deuterium exchange (see supplementary Figs. 23- 26). To ascertain the changes in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 839, 308]]<|/det|>
+solvent protection in the binary or ternary complex, the peptide- specific uptake of the APO or binary species was subtracted from that of the corresponding like peptides in the binary or ternary state (referred to as Binary \(\Delta\) APO and Ternary \(\Delta\) Binary), respectively. The results are summarized in difference plots that highlight the statistically significant (95% or 98% confidence interval) changes in D2O uptake (see Figure 2a- d for the SMC2:VCB complex induced by ACBI). Importantly, protection during HDX- MS arises due to changes in the environment around the observed residues, which could be a result of direct occlusion of solvent or conformational changes. \(^{37}\)
+
+<|ref|>text<|/ref|><|det|>[[160, 317, 839, 648]]<|/det|>
+Figure 2a reveals that large regions of SMC2 become protected upon ternary complex formation (see Ternary \(\Delta\) Binary difference plot). These stretches of protected residues, e.g. amino acids 1409- 1422 and 1456- 1470, overlap with the ligand binding site based on the ternary complex structure published in this work (7S4E) and those published previously (6HAY, 6HAX), which confirms the similarity of the ternary complex interface among the three degrader molecules discussed above. Additionally, there are also stretches of protected amino acids, 1394- 1407, that are too distant from the established binding interface to result from complex formation (Figure 2a and f). Interestingly, the Binary \(\Delta\) APO difference plot shows that under our experimental conditions the ligand concentration is close to the dissociation constant \(\mathrm{KD} = 10\mu \mathrm{M}^{23}\) ), as there is minimal difference between the exchange of SMC2 in presence and in absence of the ligand (Figure 2a and e).
+
+<|ref|>text<|/ref|><|det|>[[160, 657, 839, 902]]<|/det|>
+Large regions of VHL are protected in the presence of the ligand as indicated by the Binary \(\Delta\) APO difference plot (Figure 2b and e). The most protected residues in the binary state are centered around amino acids 87- 116, which include all 9 residues in the ligand binding site of VHL. In the presence of SMC2 (see Figure 2b, Ternary \(\Delta\) Binary difference plot), much of the allosteric network due to ligand binding can be subtracted away leaving only the most significantly protected residues induced by ternary complex formation (Figure 2b and f). In particular, residues 60- 72, which house the critical interaction of ARG69 show significant protection due to ternary complex formation (Figure 2b and f). Taken together, this data underscores the importance of
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[240, 120, 757, 660]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 668, 883, 870]]<|/det|>
+Figure 2: ACBI1-induced ternary complex formation of SMC2:VCB leads to protection of specific sites:a-d, SMARCA2 isoform 2(a), VHL(b), Elongin C(c), and Elongin B(d) monitored for hydrogen-deuterium exchange over time. The difference plots of each protein in the binary and ternary states are generated by subtracting the deuterium exchange of like peptides of the APO or binary from the binary or ternary states (defined as Binary \(\Delta\) APO and Ternary \(\Delta\) Binary), respectively. Regions that exchange significantly less than the comparative state are depicted in blue (negative), whereas regions that exchange significantly more appear in red (positive). The resultant difference plots of the binary (e), or ternary complex (f) were mapped onto the structure 7S4E. The experiments were repeated on 2 separate days. All raw relative uptake plots of the deuterium exchange for each state and experiment can be found in the supplementary material (Supplementary Figures 38–88).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 836, 194]]<|/det|>
+cooperativity driving the formation of the ternary complex for molecules with poor binding affinity to the POI. Under the same conditions as the binary SMC2 experiments, ligand binding and resultant changes in deuterium exchange are only observed on SMC2 in the presence of the E3 VHL.
+
+<|ref|>text<|/ref|><|det|>[[160, 203, 838, 393]]<|/det|>
+Additionally, we observe protection of residues 166- 176 and residues 187- 201 on VHL (Figure 2b and f) as well as some regions on Elongin B and C that show protection upon ternary complex formation (see Figure 2c and d). Although these sites are distal from the binding interface, they spatially align with one another when mapped onto the structure (Figure 2c) potentially uncovering a critical network of allosteric changes38 induced by ACBI1 that may play a role in downstream positioning of SMARCA2 to the E2 in the CRL complex.
+
+<|ref|>text<|/ref|><|det|>[[160, 402, 838, 620]]<|/det|>
+Studying the solution state dynamics of the protein and protein complexes uncovers key details that are missed by crystallographic snap shots. As many of the crystallographic contacts are nearly identical between the different degrader molecules, there must be critical interactions being underrepresented in this way. Utilizing HDX- MS or other solution state derived data as restraints in modeling and simulation opens a pathway from a single accepted protein conformer to a vast ensemble of protein complexes. Production of high accuracy protein ensembles enables alternative routes for design, optimization and mechanism of action studies for degrader and molecular glues.
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 653, 836, 712]]<|/det|>
+### 2.3 HDX data enhance weighted ensemble simulations of ternary complex formation
+
+<|ref|>text<|/ref|><|det|>[[160, 730, 838, 893]]<|/det|>
+We simulate the formation of SMC2:VHL degrader ternary complexes using weighted ensemble simulations (WES), where a set of weighted trajectories (called "walkers") are evolved in parallel providing a means to compute non- equilibrium properties and predict likely binding pathways. Specifically, we apply the WESTPA software, which discretizes sampling space into bins along pre- defined collective variables (CVs). While this path sampling strategy has been employed before for tasks such as protein- protein
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 836, 140]]<|/det|>
+binding, \(^{39}\) it is noteworthy that the current simulations are not informed by any structural data about the ternary complex interface from X- ray crystallography experiments.
+
+<|ref|>text<|/ref|><|det|>[[160, 147, 838, 421]]<|/det|>
+Starting from a dissociated configuration, in which the degrader molecule (e.g., PROTAC 2) is bound to VHL, yet both are clearly apart from SMC2 (initial separation distance \(\sim 20 \mathrm{\AA}\) ), the formation of ternary aggregates is simulated yielding complexes with interface structures well comparable to that obtained experimentally (PDB ID: 6HAX). For this simulation, we used observables such as the number of atomic contacts or the distance between the target (SMC2) and ligase (VHL) proteins or the warhead- RMSD (w- RMSD) with respect to the crystal structure of the target- warhead complex as CVs and we assessed the quality of bound complexes by a different metric, namely the interface- RMSD (I- RMSD) \(^{40}\) of each walker with respect to a reference ternary structure (see Methods for all simulation details).
+
+<|ref|>text<|/ref|><|det|>[[160, 428, 839, 790]]<|/det|>
+An ensemble of bound ternary complexes with I- RMSD \(< 2 \mathrm{\AA}\) can be simulated within an aggregate simulation time of \(\sim 5 \mu \mathrm{s}\) . Remarkably, when introducing as a CV the number of contacts formed by the protected residues, as determined by the HDX- MS experiments described above, the fraction of ternary complexes with an I- RMSD \(< 2 \mathrm{\AA}\) is markedly higher compared to simulations, in which any protein- protein contacts were considered (see Figure 3). Movie S1 shows the continuous trajectory of one such ternary complex binding event. This improvement illustrates the significance of merging high- performance computer simulations, that generate a wealth of molecular structures, with solution- phase experimental methods, that capture the inherently dynamic nature of degrader ternary complexes. In this regard, the synergy of WE simulations with HDX- MS is a particularly interesting example where the path sampling algorithm is furnished with a fairly simple parameter, derived from experimental measurements. We call this integrated approach WES+HDX throughout this work.
+
+<|ref|>text<|/ref|><|det|>[[161, 798, 838, 903]]<|/det|>
+While the WES discussed above reliably produce the ternary complex, the algorithm is expensive due to the use of two CVs and an increasing number of walkers. Therefore, to more systematically study the formation of ternary complexes with all three degraders, i.e., ACBI1, PROTAC 1 and PROTAC 2, we employ the bin- less WE
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 251]]<|/det|>
+variant 'Resampling of Ensembles by Variation Optimization' (or REVO), \(^{41}\) which maximizes an objective function called the trajectory variation, defined using a sum of walker- walker distances (see Methods). Specifically, we simulate the ternary complex formation using a distance metric composed of a weighted combination of w- RMSD, differences in contacts between the target and ligase protected residues, and the differences in contacts between the target and the PROTAC.
+
+<|ref|>text<|/ref|><|det|>[[160, 260, 838, 421]]<|/det|>
+We ran seven independent REVO simulations to predict the ternary complex of PROTAC 2 for an aggregate simulation time of \(12.5\mu s\) and three such simulations totaling \(\sim 6\mu s\) for both PROTAC 1 and ACBI1. These simulations had 48 walkers each and were run for 2000 cycles at 20 ps per cycle. In all simulations, bound ternary complexes were formed with minimum I- RMSDs of \(0.5\mathrm{\AA}\) for ACBI1, \(0.7\mathrm{\AA}\) for PROTAC 1, and \(1.1\mathrm{\AA}\) for PROTAC 2, respectively.
+
+<|ref|>text<|/ref|><|det|>[[160, 430, 838, 590]]<|/det|>
+To highlight the sampling ability of WE simulations, Figure 5a compares the minimum I- RMSD of the SMC2:PROTAC2:VHL simulation with that from vanilla MD simulations of the same system as a function of aggregate simulation time. While the minimum I- RMSD converges to \(2.5\mathrm{\AA}\) across the 7 REVO simulations within \(0.2\mu s\) of aggregate simulation time (Fig. 5 A). In comparison, the I- RMSD for vanilla MD remains as high as \(10\mathrm{\AA}\) after \(1.4\mu s\) of simulation.
+
+<|ref|>text<|/ref|><|det|>[[160, 599, 838, 902]]<|/det|>
+The very high prediction accuracy of the WES+HDX simulations is illustrated for the SMC2:PROTAC2:VHL system in Figure 4. Examples of predicted structures are visualized in Figure 4a,b. The contact maps presented in Figure 4c have been obtained by the Arpeggio software \(^{42}\) applied to the ternary interfaces of the experimental cocrystal structure (top panel) and to the lowest I- RMSD structure produced by the WES+HDX simulations (bottom panel). Each point reflects the degree of interaction, revealing an interaction pattern from the WES+HDX simulations that is comparable to that from experiment. The near- perfect alignment (I- RMSD = \(1.1\mathrm{\AA}\) ) of one sampled conformation with the co- crystallized structure shown in Figure 4d further emphasizes that the interactions of ternary degrader complexes observed experimentally can be recaptured by WES+HDX.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 839, 336]]<|/det|>
+Six out of seven of the SMC2:PROTAC2:VHL simulations observed binding events for a total of 3278 unique observations. In order to assess the degree of heterogeneity within this ensemble, we clustered the WE results into 500 macrostates with a k- means algorithm using the \(C\alpha - C\alpha\) distances between the ligase and target protected residues. As expected, all low I- RMSD states have low values of w- RMSD (Figure 5b). States with high free energies, i.e., above 1.5 kcal/mol, have large I- RMSDs, ranging from 1.5 to 30 Å. However, the I- RMSD distribution among the 20 low free energy states below 0.5 kcal/mol is significantly tighter, ranging from 1.1 to 9.2Å with an average value of 3.7 Å and 12 out of 20 states even having an I- RMSD below 3 Å.
+
+<|ref|>text<|/ref|><|det|>[[160, 345, 839, 590]]<|/det|>
+We predict binding rate constants for the three different PROTACs directly from WES+HDX simulations using the probability flux into a bound state (I- RMSD < 2 Å). While the predicted rates for PROTAC 1 and ACBI1 are on the same order of magnitude as in experiments (Figure 5c), we predict a significantly slower binding rate for PROTAC 2, which is not yet determined experimentally. However, for all three rates there are large uncertainties, as has previously been observed in WE rate calculations. \(^{43,44}\) Better statistics can be achieved by longer simulation times or the use of recently proposed algorithms that converge these rates more efficiently, \(^{45,46}\) which is beyond the scope of this work.
+
+<|ref|>text<|/ref|><|det|>[[160, 599, 839, 902]]<|/det|>
+In most of the analysis above, we have used the I- RMSD with respect to a reference structure as an observable to assess the quality of structures obtained from WES+HDX simulations. However, such reference structures, usually obtained from experiment, may not be readily available. Thus, it is desirable to determine the usefulness of other features to predict the ternary complex formation. To this end, we filtered the ensemble of simulated SMC2:PROTAC2:VHL structures for bound complexes with w- RMSD < 2 Å and > 30 contacts between protected residues (see Figure 6a). Among these, the bulk of the density was limited to I- RMSD values between 1 and 4 Å, with 90% below 3 Å and 43% even below 2 Å (Figure 6b), indicating that parameters such as the warhead- RMSD and the number of contacts between protected residues may well aid in characterizing bound ternary complexes.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[159, 90, 839, 337]]<|/det|>
+The simulations presented above stem from the physics- based formulation of molecular dynamics, which comes with an elevated computational cost (e.g. three REVO simulation replicas required around 300 A40 GPU hours). As the WES+HDX results reveal, the associated level of detail allows an entire ensemble of ternary complexes, including many conformations with a pronounced protein interface, to be generated ab initio, i.e., from a fairly dissociated state and with no additional information on the protein- protein binding pose. Such unbiased simulations of ternary complex formation are key to understanding important interactions underlying degrader selectivity and cooperativity.
+
+<|ref|>image<|/ref|><|det|>[[150, 364, 852, 672]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 712, 884, 806]]<|/det|>
+Figure 3: Comparison of WESTPA simulations with and without data from HDX-MS experiments. I-RMSD probability densities are shown for ternary complexes with a warhead RMSD \(< 2 \text{Å}\) and \(> 30\) contacts between protected residues. Structures sampled by WES+HDX (red) have almost exclusively an I-RMSD value \(< 2 \text{Å}\) , whereas those from WE simulations without any information from HDX (blue) are widely distributed.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[130, 150, 888, 730]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 737, 883, 848]]<|/det|>
+Figure 4: Illustration of the representative prediction produced by REVO simulation and its comparison to the co-crystallized structure (PDB ID: 6HAX) (a) predicted ternary structure with I-RMSD=1.1 Å; (b) detail of the binding interface; (c) contact maps for the interfaces of co-crystallized and predicted structures. The circle size reflects the number of atoms (including hydrogens) participating in interactions; (d) structurally aligned prediction (green) and co-crystallized structure (pink) with a detailed PROTAC 2 comparison shown.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[315, 110, 662, 744]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 757, 883, 887]]<|/det|>
+Figure 5: Assessing ternary complex formation. (a) The minimum I-RMSD over time during the simulation for the REVO simulations of the PROTAC2 system. Each green line indicates one replica and the black line is the average between all runs. The blue line indicates the I-RMSD for a vanilla molecular dynamics simulation. (b) A scatter plot of the free energy vs the I-RMSD of each of the 500 clusters from the PROTAC 2 simulations. The circles are colored by w-RMSD. (c) The predicted binding rates for PROTAC 1 system (purple) and the ACBI1 system (green). The black line is the experimental on rate determined via SPR.
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[194, 152, 808, 232]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[114, 87, 883, 144]]<|/det|>
+Table 2: Comparison of \(k_{on}\) rates between simulation and experiment for the ACBI1 PROTAC 1, and PROTAC 2 systems. The experimental rate for PROTAC 2 has not been determined yet.
+
+| PROTAC | Predicted Rate (M-1s-1) | Experimental Rate (M-1s-1) |
| ACBI1 | 3 * 105 ± 2 * 105 | 2.4 * 105 |
| PROTAC 1 | 10 * 105 ± 8 * 105 | 2.9 * 105 |
| PROTAC 2 | 2.2 * 102 ± 1.7 * 102 | N/A |
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 270, 834, 330]]<|/det|>
+### 2.4 HDX-MS improves prediction of ternary complex using docking
+
+<|ref|>text<|/ref|><|det|>[[161, 345, 836, 508]]<|/det|>
+Molecular docking is a very popular method for high- throughput predictions of binding poses, that follows a protocol of sampling, searching, and scoring these predictions. Considering the computational cost of the WES+HDX method described above, docking is a viable alternative to the simulation approach in obtaining different conformations of the flexible degrader ternary complexes in a less resource- intensive and more timely fashion.
+
+<|ref|>text<|/ref|><|det|>[[161, 516, 838, 678]]<|/det|>
+To demonstrate the usefulness of HDX- MS data for more accurate structural predictions, we show that incorporating experimentally retrieved distance restraints into the docking protocol significantly improves its ability to predict ternary complexes of high quality (see detailed comparisons in Supplementary Figures 1 and 2)). In particular, it is striking how strongly the incorporation of HDX- MS data can boost the accuracy of the docking protocol among the highest- ranked docking poses.
+
+<|ref|>text<|/ref|><|det|>[[161, 686, 838, 905]]<|/det|>
+In contrast to recent work, \(^{30}\) our docking method uses HDX- MS data to impose additional distance restraints at the sampling stage (instead of post- sampling scoring). Also, differently from the distance restraints derived from chemical cross- linking experiments, \(^{47}\) our approach is based on the statistics of the length of the linker in a degrader molecule. Application of the HDX- MS data for re- ranking of the docking predictions, as described by Eron et al., \(^{30}\) may lead to a more quantitative assessment of structures. Discussion of the interplay of HDX- MS- derived restraints and HDX- MS- based re- rankings in docking is beyond the scope of the present work.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 222]]<|/det|>
+Although WES+HDX consistently outperforms the HDX- enhanced docking routine (see Figure 6), docking, in combination with HDX- MS, is a useful tool for the quick filtering of a large number of degrader designs considering the significantly less computational cost of this approach (75 CPU hours for 3 independent replicas compared to 300 A40 GPU hours for the WES method).
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 256, 835, 317]]<|/det|>
+### 2.5 Flexibility of Ternary Complex Revealed by HREMD Simulations and Validation by SAXS Experiments
+
+<|ref|>text<|/ref|><|det|>[[160, 333, 838, 666]]<|/det|>
+HDX- MS measurements revealed substantial flexibility of the ternary protein complexes studied here. To further study their conformational heterogeneity, we performed atomistic Hamiltonian replica- exchange MD (HREMD) simulations to augment the experiments and explore the structural diversity of multiple SMC2:VHL ternary degrader- protein complexes (see Supplementary Table 2). HREMD is a parallel tempering simulation method that efficiently samples large conformational changes of proteins in aqueous solution and, therefore, is a promising strategy to study the protein- protein interactions and the flexibility of degraders in ternary complexes (see Methods 4.10). To ensure the HREMD- generated ensembles are accurate and reliable, we validate simulations of two large complexes (SMC2- isoform1/isoform2:ACBI1:VCB) by directly comparing against the size exclusion chromatography coupled to small- angle X- ray scattering (SEC- SAXS) data, see Figure 7a.
+
+<|ref|>text<|/ref|><|det|>[[160, 674, 896, 892]]<|/det|>
+The excellent agreement ( \(\chi^{2} = 1.55\) and \(\chi^{2} = 1.23\) for SMC2- isoform1/isoform2:ACBI1:VCB respectively, where \(\chi^{2}\) is defined in Eq. 11) between SAXS profiles obtained from experiment and such calculated from simulations shows that the HREMD simulations captured the long timescale conformational ensembles to experimental accuracy. Furthermore, the ensemble- averaged \(R_{g}\) of two complexes from simulations are in excellent agreement to \(R_{g}\) values obtained using Guinier approximation (Eq. 1) to the experimental SAXS data (Supplementary Figure 12), \(R_{g} = 33.4\pm 0.4\) Å and \(32.3\pm 0.3\) Å for SMC2- isoform1/isoform2:ACBI1:VCB, respectively. The histograms
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[250, 145, 723, 712]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 723, 883, 852]]<|/det|>
+Figure 6: Comparing the bound ensembles determined by docking and REVO simulations with information from HDX-MS for the PDB ID 6HAX ternary complex. The REVO bound ensemble is defined as structures below a warhead RMSD of 2 Å and more than 30 contacts between the target and ligase interface. The docking bound basin is defined as the top-100 structures as determined by Rosetta-scoring. (a) Probability density function distributions of I-RMSD values for the bound ensembles. (b) The percent of structures in the predicted bound ensembles below specific I-RMSD thresholds (2 Å, 2.5 Å, and 3 Å).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 252]]<|/det|>
+of \(R_{g}\) (calculated from atomic coordinates using Eq. 2) suggest that ternary complexes are flexible in solution leading to a change in overall conformation compared to their simulation starting structures (homology model and crystal structure of SMC2- isoform1/isoform2:ACBI1:VCB, respectively), see Figure 7b. These results illustrate the need for an enhanced sampling method, such as HREMD, to rigorously probe the conformational changes of the inherently flexible ternary degrader complexes
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 286, 766, 309]]<|/det|>
+### 2.6 Conformational sampling of ternary complexes
+
+<|ref|>text<|/ref|><|det|>[[160, 325, 839, 512]]<|/det|>
+We quantify the free energy landscape of the ternary complexes using data from our HREMD simulations. We use principle component analysis (PCA) of the distances between interface residues observed in our HREMD simulations to identify high- variance collective variables (see Methods). The probability distribution of these high- variance features allows us to determine a more easily interpretable free energy landscape from our simulation data than would be possible otherwise. We find that the landscape of each protein complex contained several local minima differing by only a few kcal/mol.
+
+<|ref|>text<|/ref|><|det|>[[160, 525, 839, 911]]<|/det|>
+Using \(k\) - means clustering in the PCA feature space, we then identify distinct clusters of conformations. Cluster centers roughly correspond to local minima in the free energy landscape, see Supplementary Figure 14. The clusters identified by \(k\) - means are consistent with our HDX- MS protection data: Figure 8 shows that interface residues that were found to be protected in HDX- MS experiments are observed to interact in either the most populated or second most populated cluster identified by \(k\) - means. Notably, this analysis shows that in the second most populated structure of Iso1- ACBI1- VCB, the helix formed by the 17 residue extension of isoform 1- SMARCA2 interacts with a beta sheet of VHL, Figure 8d, in accordance with HDX- MS experiments that found this beta sheet to be protected in presence of Iso1, but not in the presence of Iso2. Similarly, highly populated structures of Iso2- ACBI1- VHL and Iso2- PROTAC2- VHL show contact between residues that were observed to be protected in HDX- MS experiments with these PROTACs, but not with PROTAC 1, while the most populated structure of PROTAC 1 does not show these contacts.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[220, 101, 770, 777]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 789, 883, 901]]<|/det|>
+Figure 7: SAXS profiles and structural ensembles of SMC2-isoform1/isoform2:ACBI1:VCB complexes. (a) Comparison of theoretical and experimental SAXS profiles, SAXS intensity vs. \(q\) . (b) The histograms of \(\mathrm{R}_g\) of SMC2-isoform1:ACBI1:VCB (red) and SMC2-isoform2:ACBI1:VCB (blue) complexes calculated from HREMD simulations. The inverted red and blue triangles are the \(\mathrm{R}_g\) values of starting structures of SMC2-isoform1/isoform2:ACBI1:VCB from homology model and crystallography respectively.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[137, 103, 870, 728]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 737, 883, 903]]<|/det|>
+Figure 8: Most populated structures of SMARCA2 bound to VHL with different degrader molecules, identified by dimension reduction and clustering of HREMD simulation data. (a-d) Colors of VHL and SMARCA2 represent HDX-MS protection in the presence of the degrader molecules relative to the situation in the absence of the degrader. The second ranked structures of c PROTAC 2 and d isoform 1 SMARCA2 are displayed and support our HDX-MS data, whereas the top three structures are included in Supplementary Figure 15. Elongin B and Elongin C are also included in panel d. e The top structures of ternary complexes are compared after aligning VHL to illustrate conformational differences among top structures of ternary complexes.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[313, 116, 685, 666]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 694, 883, 876]]<|/det|>
+Figure 9: a Conformational free energy landscape as a function of the first two tICA features of SMARCA2-PROTAC2-VHL ternary complex inferred from a Markov state model (MSM). The ensemble of bound states from REVO simulations is shown as blue points; the crystal structure (PDB ID 6HAX) is shown as a red X. In this projection, states II and V are close to state I. b Network diagram of the coarse-grained MSM calculated using a lag time of 50 ns, with the stationary probabilities associated with each state indicated. c Mean first-passage times to transition (MFPT) from one state in the MSM to another. Numbers indicate predicted MFPTs in \(\mu \mathrm{s}\) . d-e Comparison of the crystal structure (gray) with the lowest free energy state (cyan) and a metastable state (orange) predicted by the MSM. Arrows indicate a change of orientation relative to d.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 839, 336]]<|/det|>
+We selected 98 representative structures from HREMD data to use as initial configurations for Folding@home (F@H) simulations of SMC2 Iso2- PROTAC2- VHL. Each initial condition was cloned 100 times and run for \(\sim 650 \mathrm{ns}\) , for a total of \(\sim 6 \mathrm{ms}\) of simulation data. These independent MD trajectories provide the basis for fitting a Markov state model (MSM), \(^{48}\) which provides a full thermodynamic and kinetic description of the system and allow for the prediction of experimental observables of interest. \(^{49}\) We used time- lagged independent component analysis (tICA) \(^{50}\) to determine the collective variables with the slowest dynamics. The distance between points in the tICA feature space corresponds roughly to kinetic distance.
+
+<|ref|>text<|/ref|><|det|>[[160, 345, 839, 534]]<|/det|>
+The MSM predicts a stationary probability distribution on tICA space that is in general different from the empirical distribution of our simulation data. Interestingly, the MSM predicts that the the crystal structure of PROTAC 2 is 1.5 kcal/mol higher in free energy than the global free energy minimum, while the bound structures obtained from our REVO simulations are \(\sim 1.5 - 3.5 \mathrm{kcal / mol}\) above the global minimum, Figure 9a- c. The model also predicts a metastable state with free energy 2.2 kcal/mol (Figure 9e).
+
+<|ref|>text<|/ref|><|det|>[[160, 542, 839, 902]]<|/det|>
+This model is coarse- grained to obtain a five- state MSM, of which the following three states are of particular interest: the global minimum state (or state I) with a stationary probability of 0.63, the metastable state III with 0.10 probability, and state IV, to which the experimental crystal structure can be assigned and which has a stationary probability of 0.05. The global minimum state differs from the crystal structure 6HAX by an I- RMSD of 3.6 Å, while the metastable state has an I- RMSD of 4.4 Å relative to the crystal structure. The global minimum state is stabilized by a large number of protein- protein contacts (Supplementary Figure 16). Contacts between VHL and PROTAC 2 are largely unchanged between the metastable and global minimum states, likely due to the tight interaction between VHL and the PROTAC. On the other hand, the metastable state lacks contacts between PROTAC 2 and ARG29, ASN90, and ILE96 of SMARCA2. The area of the binding interface was substantially increased in both the metastable and global minimum states relative to the crystal structure: the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 86, 835, 139]]<|/det|>
+global minimum state had a buried surface area of \(2962 \mathrm{\AA}^{2}\) , compared to \(2800 \mathrm{\AA}^{2}\) for the metastable state and \(2369 \mathrm{\AA}^{2}\) for the crystal structure.
+
+<|ref|>text<|/ref|><|det|>[[160, 147, 838, 477]]<|/det|>
+We repeated this procedure with \(900 \mu s\) of \(\mathrm{F}@\mathrm{H}\) data of SMC2 Iso2- PROTAC 1- VHL and \(500 \mu s\) of \(\mathrm{F}@\mathrm{H}\) data of SMC2 Iso2- ACBI1- VHL (Supplementary Figures 17 and 18). The resultant MSMs predicted that the crystal structure of the SMC2 Iso2- PROTAC 1- VHL system is \(2.2 \mathrm{kcal / mol}\) higher than the free energy minimum, while the crystal structure of the Iso2- ACBI1- VHL system is only \(0.7 \mathrm{kcal / mol}\) higher in energy than the ground state. Coarse- graining the PROTAC 1 model yielded a two- state MSM, while a three- state MSM was obtained for the ACBI1 system. In both cases, the crystal structure falls into the most probable macro- state. Interestingly, in the ground state predicted by the PROTAC 1 MSM, SMARCA2 is rotated relative to VHL, similar to the PROTAC 2 ground state, while in the ground state of the ACBI1 system, the position of SMARCA2 is similar to that in the crystal structure for all three ternary complexes.
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 512, 835, 571]]<|/det|>
+### 2.7 Identifying the ubiquitination zone for Cullin-RING Ligase with VHL and SMARCA2
+
+<|ref|>text<|/ref|><|det|>[[160, 588, 847, 893]]<|/det|>
+In addition to simulating the ternary complex formation and associated dynamics, a more complete understanding of the ubiquitination process should involve the full Cullin- RING E3 ubiquitin ligase (CRL). To do this, we study different degrader molecules in the context of the full Cullin- RING E3 ubiquitin ligase (CRL) along with the POI. Here, we study the position different solvent- exposed lysine residues from the POI relative to the ubiquitination zone of the CRL macromolecular assembly, specifically focusing on the probability of POI lysine residue density within this zone. The hypothesis is that the ubiquitination rate depends on the probability of finding a lysine residue in the ubiquitination zone. As such, this analysis can provide insights on the degradation potency of degrader molecules. First, we built an entire E2- E3 complex for CRL- VHL in its activated form using a recently obtained structure of the active form of the closely
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 338]]<|/det|>
+related CRL- \(\beta\) TrCP as reference \(^{51}\) (see Methods). Second, we used the meta- eABF simulation approach (see Methods) to sample CRL open- closed conformations in the presence of SMARCA2. These conformations were then used as reference states to superimpose structures from HREMD simulations of VHL:degrader:SMARCA2 on the active state of the CRL- VHL, allowing us to obtain Lys densities from SMARCA2 in the ubiquitination zone of the CRL- VHL. Comparing the Lys densities of the three degraders (10), we observe that ACBI1 places the most Lys density in the ubiquitination zone of CRL- VHL, followed by PROTAC 2 and PROTAC 1. This order of Lys density in the ubiquitination zone agrees with the experimentally observed degradation data. \(^{15}\)
+
+<|ref|>sub_title<|/ref|><|det|>[[162, 378, 357, 402]]<|/det|>
+## 3 Discussion
+
+<|ref|>text<|/ref|><|det|>[[160, 424, 838, 644]]<|/det|>
+The formation of a ternary complex via a degrader molecule is a critical step in targeted protein degradation. However, accurately predicting ternary complexes has posed challenges to the field due to the size of the system, the conformational flexibility, the timescales for biological motions, and the limited understanding of the solution- phase structural ensemble. The ability to accurately predict the formation of ternary complexes and the corresponding structural ensembles would enable more precise optimization of degrader molecules (e.g. linkers and attachment points) and facilitate structure activity relationship studies, thus improving rational degrader design.
+
+<|ref|>text<|/ref|><|det|>[[160, 652, 838, 898]]<|/det|>
+Here, we studied three different degrader molecules of SMARCA2 with VHL that have similar thermodynamic binding profiles and crystal structure conformations but different degradation efficiencies. Consistent with previous observations, the crystal structure of ACBI1 determined in this work (PDB ID: 7S4E) revealed a conformation nearly identical to its two closest analogs PROTAC 1 (PDB: 6HAY) and PROTAC 2 (PDB: 6HAX). The overall structural similarity of these complexes, yet different degradation profiles, highlights one of the critical challenges in degrader optimization. The approach we describe here combines MD simulations with biophysical experiments, leading to accurate dynamic ternary structure predictions and a detailed mechanistic
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[197, 110, 820, 773]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 782, 883, 893]]<|/det|>
+Figure 10: Degrader dependent SMARCA2 Lys densities in the CRL-VHL ubiquitination zone. a. Active form of CRL-VHL with bound SMARCA2 and E2-ubiquitin with open CRL conformation. b. same as a with a closed conformation of CRL generated by meta-eABF simulations. c. Distance of Lys residues (side-chain nitrogen atom) from SMARCA2 to the C-terminus glycine C atom of ubiquitin for three different degraders. d. Density of Lys residues in 3D space near ubiquitination zone of CRL-VHL.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 839, 507]]<|/det|>
+understanding of the characteristics that impact binding selectivity, cooperativity, and degrader efficiency. We show that hydrogen deuterium mass spectrometry (HDX- MS) and small- angle X- ray scattering (SAXS) provide a dynamic description of the ternary complex, in contrast to static x- ray crystal structures, leading to insights regarding the solution state ensemble of ternary degrader complexes. This novel approach, where we integrate data from the biophysical experiments with weighted ensemble (WE) MD simulations, uncovered atomic level differences among distinct conformations adopted by the ternary complexes. For example, we found that the X- ray structures represent only one of many low energy conformations within the dynamic ternary structural ensemble: the crystal structures of ACBI1, PROTAC 2 and PROTAC 1 are 0.9 kcal/mol, 1.5 kcal/mol and 2.0 kcal/mol higher in energy than their corresponding global minima conformation, respectively. Other low- energy structures found on the free energy landscapes can be used as starting points for degrader design or for more sophisticated analyses, such as predicting ubiquitination probability of a particular degrader molecule state.
+
+<|ref|>text<|/ref|><|det|>[[160, 515, 839, 875]]<|/det|>
+The data from HDX- MS experiments is used as collective variables for weighted ensemble (WE) simulations, which provide atomic level resolution of the binding process and of the ternary complex conformational ensemble ( \(< 2 \text{Å I- RMSD}\) ). Different WE resampling algorithms (i.e., WESTPA, that uses bins along CVs, and the binless REVO method) can efficiently simulate the binding of ternary degrader complexes when augmented with information on distinct solvent- protected residues from HDX- MS. This novel combination of simulation and experiment leads to improved predictions of ternary degrader complexes (see Supplementary Figure 10 for a comparison of the simulation and docking methods with and without information from HDX- MS experiments). Further improvements being explored in our group include optimizing parameters for the WE simulations and using the HDX- MS data for scoring structures, similar to recent work by Eron and coworkers. \(^{30}\) We are also working on ubiquitination mapping experiments to validate the ubiquitination probability predictions.
+
+<|ref|>text<|/ref|><|det|>[[187, 883, 835, 902]]<|/det|>
+The methodology described here relies on advanced physics- based simulations and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 279]]<|/det|>
+solution- phase biophysical experiments. Because the methodology is based on physical principles without the need for training data, we expect the approach to be transferable to other POI- E3 ligase ternary complexes with induced proximity degrader molecules. Efforts in our group are underway to expand the application to more ligands in the SMARCA2/VLH system and to other POI/E3 combinations. We believe that the predictive simulations described here will increase the efficiency of molecular design for TPD.
+
+<|ref|>text<|/ref|><|det|>[[160, 290, 837, 364]]<|/det|>
+We make source code, simulation results, and experimental data from this work publicly available for researchers to further advance the field of induced proximity modulation.
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 406, 335, 431]]<|/det|>
+## 4 Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 459, 836, 520]]<|/det|>
+### 4.1 Cloning, expression and purification of SMARCA2 and VHL/EloB/C
+
+<|ref|>text<|/ref|><|det|>[[160, 536, 838, 897]]<|/det|>
+The SMARCA2 gene from Homo sapiens was custom- synthesized at Genscript with N- terminal GST tag (Ciulli 2019 Nature ChemBio) and thrombin protease cleavage site. The synthetic gene comprising the SMARCA2 (UniProt accession number P51531- 1; residues 1373- 1511) was cloned into pET28 vector to create plasmid pL- 477. The second construct of SMARCA2 with deletion 1400- 1417 (UniProt accession number P51531- 2) was created as pL- 478. For biotinylated SMARCA2, AVI- tag was gene synthesized at C- terminus of pL- 478 to create pL- 479. The VHL gene from Homo sapiens was custom- synthesized with N- terminal His6 tag \(^{15}\) and thrombin protease cleavage site. The synthetic gene comprising the VHL (UniProt accession number P40337; residues 54- 213) was cloned into pET28 vector to create plasmid pL- 476. ElonginB and ElonginC gene from Homo sapiens was custom- synthesized with AVI- tag at C- terminus of EloB. \(^{22}\) The synthetic genes comprising the EloB (UniProt accession number Q15370; residues 1- 104) and EloC (UniProt accession number Q15369; residues 17- 112) were cloned into
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 91, 835, 138]]<|/det|>
+pCDFDuet vector to create plasmid pL- 474. For protein structural study, AVI- tag was deleted in pL- 474 to create pL- 524.
+
+<|ref|>text<|/ref|><|det|>[[160, 145, 839, 848]]<|/det|>
+For SMARCA2 protein expression, the plasmid was transformed into BL21(DE3) and plated on Luria- Bertani (LB) medium containing 50 \(\mu \mathrm{g / ml}\) kanamycin at \(37^{\circ}\mathrm{C}\) overnight. A single colony of BL21(DE3)/pL- 477 or BL21(DE3)/pL- 478 was inoculated into a 100- ml culture of LB containing 50 \(\mu \mathrm{g / ml}\) kanamycin and grown overnight at \(37^{\circ}\mathrm{C}\) . The overnight culture was diluted to OD600=0.1 in 2 x 1- liter of Terrific Broth medium containing 50 \(\mu \mathrm{g / ml}\) kanamycin and grown at \(37^{\circ}\mathrm{C}\) with aeration to mid- logarithmic phase (OD600 = 1). The culture was incubated on ice for 30 minutes and transferred to \(16^{\circ}\mathrm{C}\) . IPTG was then added to a final concentration in each culture of \(0.3\mathrm{mM}\) . After overnight induction at \(16^{\circ}\mathrm{C}\) , the cells were harvested by centrifugation at 5,000 xg for 15 min at \(4^{\circ}\mathrm{C}\) . The frozen cell paste from 2 L of cell culture was suspended in 50 ml of Buffer A consisting of 50 mM HEPES (pH 7.5), 0.5 M NaCl, 5 mM DTT, \(5\%\) (v/v) glycerol, supplemented with 1 protease inhibitor cocktail tablet (Roche Molecular Biochemical) per 50 ml buffer. Cells were disrupted by Avestin C3 at 20,000 psi twice at \(4^{\circ}\mathrm{C}\) , and the crude extract was centrifuged at 39,000 xg (JA- 17 rotor, Beckman- Coulter) for 30 min at \(4^{\circ}\mathrm{C}\) . Two ml Glutathione Sepharose 4 B (Cytiva) was added into the supernatant and mixed at \(4^{\circ}\mathrm{C}\) for 1 hour, washed with Buffer A and eluted with 20 mM reduced glutathione (Sigma). The protein concentration was measured by Bradford assay, and GST- tag was cleaved by thrombin (1:100) at \(4^{\circ}\mathrm{C}\) overnight during dialysis against 1 L of Buffer B (20 mM HEPES, pH 7.5, 150 mM NaCl, 1mM DTT). The sample was concentrated to 3 ml and applied at a flow rate of 1.0 ml/min to a 120- ml Superdex 75 (HR 16/60) (Cytiva) pre- equilibrated with Buffer B. The fractions containing SMARCA2 were pooled and concentrated by Amicon® Ultracel- 3K (Millipore). The protein concentration was determined by OD280 and characterized by SDS- PAGE analysis and analytical LC- MS. The protein was stored at \(- 80^{\circ}\mathrm{C}\) .
+
+<|ref|>text<|/ref|><|det|>[[161, 855, 866, 903]]<|/det|>
+For VHL/Elob/C protein expression, the plasmids were co- transformed into BL21(DE3) and plated on Luria- Bertani (LB) medium containing 50 \(\mu \mathrm{g / ml}\) kanamycin and 50
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[159, 87, 839, 876]]<|/det|>
+\(\mu \mathrm{g / ml}\) streptomycin at \(37^{\circ}\mathrm{C}\) overnight. A single colony of BL21(DE3)/pL- 476/474 or BL21(DE3)/pL- 476/524 was inoculated into a 100- ml culture of LB containing 50 \(\mu \mathrm{g / ml}\) kanamycin and \(50\mu \mathrm{g / ml}\) streptomycin and grown overnight at \(37^{\circ}\mathrm{C}\) . The overnight culture was diluted to OD600=0.1 in \(6\mathrm{x}1\) - liter of Terrific Broth medium containing \(50\mu \mathrm{g / ml}\) kanamycin and \(50\mu \mathrm{g / ml}\) streptomycin and grown at \(37^{\circ}\mathrm{C}\) with aeration to mid- logarithmic phase (OD600 = 1). The culture was incubated on ice for 30 minutes and transferred to \(18^{\circ}\mathrm{C}\) . IPTG was then added to a final concentration of \(0.3\mathrm{mM}\) in each culture. After overnight induction at \(18^{\circ}\mathrm{C}\) , the cells were harvested by centrifugation at 5,000 g for 15 min at \(4^{\circ}\mathrm{C}\) . The frozen cell paste from \(6\mathrm{L}\) of cell culture was suspended in \(150\mathrm{ml}\) of Buffer C consisting of \(50\mathrm{mM}\) HEPES (pH 7.5), \(0.5\mathrm{M}\) NaCl, \(10\mathrm{mM}\) imidazole, \(1\mathrm{mM}\) TCEP, \(5\%\) (v/v) glycerol, supplemented with 1 protease inhibitor cocktail tablet (Roche Molecular Biochemical) per \(50\mathrm{ml}\) buffer. Cells were disrupted by Avestin C3 at 20,000 psi twice at \(4^{\circ}\mathrm{C}\) , and the crude extract was centrifuged at \(17000\mathrm{g}\) (JA- 17 rotor, Beckman- Coulter) for \(30\mathrm{min}\) at \(4^{\circ}\mathrm{C}\) . Ten ml Ni Sepharose 6 FastFlow (Cytiva) was added into the supernatant and mixed at \(4^{\circ}\mathrm{C}\) for 1 hour, washed with Buffer C containing \(25\mathrm{mM}\) imidazole and eluted with \(300\mathrm{mM}\) imidazole. The protein concentration was measured by Bradford assay. For protein crystallization, His- tag was cleaved by thrombin (1:100) at \(4^{\circ}\mathrm{C}\) overnight during dialysis against \(1\mathrm{L}\) of Buffer D ( \(20\mathrm{mM}\) HEPES, pH 7.5, \(150\mathrm{mM}\) NaCl, 1 mM DTT). The sample was concentrated to \(3\mathrm{ml}\) and applied at a flow rate of 1.0 ml/min to a 120- ml Superdex 75 (HR 16/60) (Cytiva) pre- equilibrated with Buffer D. The fractions containing VHL/EloB/C were pooled and concentrated by Amicon® Ultracel- 10K (Millipore). The protein concentration was determined by OD280 and characterized by SDS- PAGE analysis and analytical LC- MS. The protein was stored at \(- 80^{\circ}\mathrm{C}\) . For SPR assay, \(10\mathrm{mg}\) VHL/EloB/C protein complex was incubated with BirA (1:20), \(1\mathrm{mM}\) ATP and \(0.5\mathrm{mM}\) Biotin and \(10\mathrm{mM}\) MgCl2 at \(4^{\circ}\mathrm{C}\) overnight, removed free ATP and Biotin by 120- ml Superdex 75 (HR 16/60) with the same procedure as above, and confirmed the biotinylation by LC/MS.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[161, 88, 822, 112]]<|/det|>
+### 4.2 Hydrogen Deuterium Exchange Mass Spectrometry
+
+<|ref|>text<|/ref|><|det|>[[159, 120, 840, 916]]<|/det|>
+Our HDX analyses were performed as reported previously with minor modifications. \(^{34,36,52}\) HDX experiments were performed using a protein stock at the initial concentration of 200 \(\mu \mathrm{M}\) of SMARCA2, VCB in the APO, binary (200 \(\mu \mathrm{M}\) PROTAC ACBI1) and ternary (200 \(\mu \mathrm{M}\) PROTAC ACBI1) states in 50 mM HEPES, pH 7.4, 150 mM NaCl, 1 mM TCEP, 2% DMSO in H2O. The protein samples were injected into the nanoAC- QUITY system equipped with HDX technology for UPLC separation (Waters Corp. \(^{53}\) ) to generate mapping experiments used to assess sequence coverage. Generated maps were used for all subsequent exchange experiments. HDX was performed by diluting the initial 200 \(\mu \mathrm{M}\) protein stock 13- fold with D2O (Cambridge Isotopes) containing buffer (10 mM phosphate, pD 7.4, 150 mM NaCl) and incubated at 10 °C for various time points (0.5, 5, 30 min). At the designated time point, an aliquot from the exchanging experiment was sampled and diluted 1:13 into D2O quenching buffer containing (100 mM phosphate, pH 2.1, 50 mM NaCl, 3M GuHCl) at 1 °C. The process was repeated at all time points, including for non- deuterated samples in H2O- containing buffers. Quenched samples were injected into a 5- \(\mu \mathrm{m}\) BEH 2.1 X 30- mm Enzymate- immobilized pepsin column (Waters Corp.) at 100 \(\mu \mathrm{l} / \mathrm{min}\) in 0.1% formic acid at 10 °C and then incubated for 4.5 min for on- column digestion. Peptides were collected at 0 °C on a C18 VanGuard trap column (1.7 \(\mu \mathrm{m}\) X 30 mm) (Waters Corp.) for desalting with 0.1% formic acid in H2O and then subsequently separated with an in- line 1.8μMHsS T3 C18 2.1 X 30- mm nanoACQUITY UPLC column (Waters Corp.) for a 10- min gradient ranging from 0.1% formic acid to acetonitrile (7 min, 5- 35%; 1 min, 35- 85%; 2 min hold 85% acetonitrile) at 40 \(\mu \mathrm{l} / \mathrm{min}\) at 0 °C. Fragments were mass- analyzed using the Synapt G2Si ESL- Q- ToF mass spectrometer (Waters Corp.). Between injections, a pepsin- wash step was performed to minimize peptide carryover. Mass and collision- induced dissociation in data- independent acquisition mode (MSE) and ProteinLynx Global Server (PLGS) version 3.0 software (Waters Corp.) were used to identify the peptides in the non- deuterated mapping experiments and analyzed in the same fashion as HDX experiments. Mapping experiments generated from PLGS were imported
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[159, 90, 839, 536]]<|/det|>
+into the DynamX version 3.0 (Waters Corp.) with quality thresholds of MS1 signal intensity of 5000, maximum sequence length of 25 amino acids, minimum products 2.0, minimum products per amino acid of 0.3, minimum PLGS score of 6.0. Automated results were inspected manually to ensure the corresponding m/z and isotopic distributions at various charge states were assigned to the corresponding peptides in all proteins (SMARCA2, VHL, ElonC, ElonB). DynamX was utilized to generate the relative deuterium incorporation plots and HDX heat map for each peptide. The relative deuterium uptake of common peptides was determined by subtracting the weighted-average mass of the centroid of the non-deuterated control samples from the deuterated samples at each time point. All experiments were made under the same experimental conditions negating the need for back-exchange calculations but therefore are reported as relative. \(^{37}\) All HDX experiments were performed twice, on 2 separate days, and a 98 and 95% confidence limit of uncertainty was applied to calculate the mean relative deuterium uptake of each data set. Mean relative deuterium uptake thresholds were calculated as described previously. \(^{34,36,52}\) Differences in deuterium uptake that exceeded the error of the datasets were considered significant.
+
+<|ref|>sub_title<|/ref|><|det|>[[162, 570, 504, 591]]<|/det|>
+### 4.3 SEC-SAXS experiments
+
+<|ref|>text<|/ref|><|det|>[[161, 608, 838, 712]]<|/det|>
+SAXS data were collected with an AKTAmicro (GE Healthcare) FPLC coupled to a BioXolver L SAXS system (Xenocs) that utilized an Excilium MetalJet D2+ X- ray source operating at a wavelength of 1.34 Å. We measured two protein complex samples,
+
+<|ref|>text<|/ref|><|det|>[[161, 722, 494, 740]]<|/det|>
+(i) SMARCA2-isoform1:ACBI1:VCB, and
+
+<|ref|>text<|/ref|><|det|>[[162, 751, 460, 768]]<|/det|>
+(ii) SMARCA2-isoform2:ACBI1:VCB.
+
+<|ref|>text<|/ref|><|det|>[[161, 779, 838, 911]]<|/det|>
+The scattering data was detected on PILATUS3 300 K (Dectris) detector with a resulting \(q\) range of 0.0134 – 0.5793 Å\(^{-1}\). To ensure the resulting scattering profile is solely due to complexes with all four protein chains and a degrader, and devoid of contributions from binary or uncomplexed proteins, size exclusion chromatography is coupled to SAXS (SEC-SAXS). The elution peak 1 of the SEC profile is assigned to the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[159, 90, 839, 508]]<|/det|>
+ternary complexes, whereas peak 2 is attributed to binary or uncomplexed proteins, respectively (Supplementary Figure 11). The SEC- SAXS data for each sample was collected by loading \(500~\mu \mathrm{L}\) of the ternary complex formed by addition of equimolar concentrations (275 \(\mu \mathrm{M}\) ) of SMARCA2, VCB and ACBI1, onto a Superdex 200 Increase \(10 / 30\) equilibrated with \(20~\mathrm{mM}\) HEPES pH 7.5, \(150~\mathrm{mM}\) NaCl and \(1~\mathrm{mM}\) DTT at \(20^{\circ}\mathrm{C}\) . The solution scattering data was collected as a continuous 60 second data- frame measurements with a flow rate of \(0.05~\mathrm{mL / min}\) . The average scattering profile of all frames within the elution peak 1 was calculated and subtracted from the average buffer scattering to yield the scattering data of the protein complex. The final SAXS profile of each ternary complex (Figure 7a) was determined from the average scattering signal from the sample in the elution peak 1, where the relatively large variability in the calculated radius of gyration, \(R_{g}\) (red solid/open circles in Supplementary Figure 11). This indicates that complexes are dynamic or flexible. Data reduction was performed using the BioXTAS RAW 2.0.3 software. \(^{54}\) \(R_{g}\) was estimated from experimental an SAXS curve using the Guinier approximation,
+
+<|ref|>equation<|/ref|><|det|>[[380, 528, 833, 560]]<|/det|>
+\[I(q)\approx I(0)e^{\frac{-q^{2}R_{g}^{2}}{3}},f o r q\to 0 \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 588, 839, 778]]<|/det|>
+where \(I(q)\) and \(I(0)\) are the measured SAXS intensity and forward scattering intensity at \(q = 0\) , respectively. \(q\) is the magnitude of scattering vector given by, \(q = 4\pi \sin \theta /\lambda\) , where \(2\theta\) is the scattering angle and \(\lambda\) is the wavelength of incident beam. The linear region in \(ln(I(q))\) vs. \(q^{2}\) was fitted at low- \(q\) values such that \(q_{max}R_{g}\leq 1.3\) to estimate \(R_{g}\) , where \(q_{max}\) is the maximum \(q\) - value in the Guinier fit (Supplementary Figure 12). On the other hand, \(R_{g}\) of the protein complex in simulation was directly calculated from atomic coordinates using following relation,
+
+<|ref|>equation<|/ref|><|det|>[[417, 799, 833, 843]]<|/det|>
+\[R_{g} = \sqrt{\frac{\sum_{i}m_{i}\left\Vert\mathbf{r_{i}}\right\Vert^{2}}{\sum_{i}m_{i}}} \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 863, 836, 910]]<|/det|>
+where \(m_{i}\) is the mass of \(i^{t h}\) atom and \(\mathbf{r_{i}}\) is the position of \(i^{t h}\) atom with respect to the center of mass of the molecule.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[162, 88, 595, 110]]<|/det|>
+### 4.4 Molecular dynamics simulations
+
+<|ref|>text<|/ref|><|det|>[[161, 127, 838, 374]]<|/det|>
+The initial coordinates of the system were obtained from X- ray crystal structures PDB ID 6HAX, 6HAY, or 7S4E, respectively. The missing atoms were added using the LEaP module in AMBER20. The AMBER ff14SB force field \(^{55}\) was employed for the protein and the PROTAC force field parameters were generated using in- house programs for all MD simulations in this study. The explicit solvent was modeled using TIP3P water encapsulating the solute in a rectangular box. Counter ions were added to the system to enforce neutrality. Langevin dynamics was used to maintain the temperature at \(300\mathrm{K}\) and the collision frequency was set to \(2.0\mathrm{ps}^{- 1}\) . The SHAKE algorithm was utilized so that 2 fs time step could be achieved.
+
+<|ref|>text<|/ref|><|det|>[[160, 382, 838, 684]]<|/det|>
+A step- wise equilibration protocol was used prior to running the production phase of the Molecular Dynamics simulations. First, a minimization was performed with a positional restraint of 5 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) applied to all solute heavy atoms followed by a fully unrestrained minimization. Each minimization was composed of 500 steps of the steepest decent followed by 2000 steps of conjugate gradient. Using 5 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) positional restraint on the heavy atoms of the solute, the system was linearly heated from 50 to 300 K for a duration of 500 ps (NVT ensemble) followed by a density equilibration of 750 ps (NPT ensemble). Over the course of five 250 ps simulations, the restraints on the heavy atoms of the systems were reduced from 5 to 0.1 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) . Then, a 500 ps simulation was run with a positional restraint of 0.1 kcal mol \(^{- 1}\) \(\mathrm{\AA}^{- 2}\) on the backbone atoms followed by a fully unrestrained 5 ns simulation.
+
+<|ref|>text<|/ref|><|det|>[[160, 694, 838, 854]]<|/det|>
+Three independent regular MD simulations were performed for each of the three bound degrader complexes for up 1 \(\mu \mathrm{s}\) . Structures obtained from these simulations were clustered into 25 groups based on their structural similarity. One representative structure from each cluster (along with the experimentally obtained crystal structure) were used as the set of reference ternary complexes for the evaluation of bound complex predictions by WE simulations or docking.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[161, 88, 533, 111]]<|/det|>
+### 4.5 Isoform 1 homology model
+
+<|ref|>text<|/ref|><|det|>[[160, 127, 839, 489]]<|/det|>
+4.5 Isoform 1 homology modelSince no suitable X- ray structure for SMARCA2 isoform 1 BRD domain is available in the PDB, we have used the YASARA (Yet Another Scientific Artificial Reality Application) homology modeling module (YASARA Biosciences GmbH) to build a high- resolution model of SMARCA2 isoform 1 from its amino acid sequence. This was used as a model for the binding of the warhead to SMARCA2 isoform1, although the final prediction reported here came from our simulations. The sequence that was used is Uniprot P51531- 1 (residues 1373- 1493) has an additional 17 aa loop compared to P51531- 2 (missing loop at 1400- 1417). As a template for homology modeling, we used the structure from the PDB ID 6HAY. Once the model was completed, an Amber minimization, which restrained all heavy atoms except the loop residues, was run. This ensured that the residues in the loop do not overlap and assume a stable secondary structure conformation. Minimization did not show major side- chain movements in the final minimized output which further suggested that the structure was stable
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 521, 570, 545]]<|/det|>
+### 4.6 Unbound System Preparation
+
+<|ref|>text<|/ref|><|det|>[[160, 561, 839, 807]]<|/det|>
+4.6 Unbound System PreparationThe ternary complexes were unbound "manually" by separating the corresponding VHL- PROTAC complex from SMARCA2 by \(20 - 40\mathring{\mathrm{A}}\) (depending on the system). The simulation box of these unbound systems were then solvated with explicit waters and counter ions were added to neutralize their net charge. The ACBI1 system has 24,093 water molecules, 9 chlorine ions. The PROTAC 1 system has 21191 water molecules and 10 chlorine ions. The PROTAC 2 simulations has 31,567 water atoms and 9 chlorine ions. All systems were placed in rectangular boxes, with dimensions: \(123\mathring{\mathrm{A}}\times 76\mathring{\mathrm{A}}\times 98\mathring{\mathrm{A}}\) for the ACBI1 system \(131\mathring{\mathrm{A}}\times 84\mathring{\mathrm{A}}\times 84\mathring{\mathrm{A}}\) for the PROTAC 1 system and \(144\mathring{\mathrm{A}}\times 89\mathring{\mathrm{A}}\times 91\mathring{\mathrm{A}}\) for the PROTAC 2 system.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[162, 88, 478, 110]]<|/det|>
+### 4.7 WESTPA simulations
+
+<|ref|>text<|/ref|><|det|>[[161, 127, 838, 401]]<|/det|>
+The binding of ternary complexes was simulated using weighted ensemble methods. With WESTPA, short simulations sample in parallel a conformational space divided into bins based on pre- defined collective variables (CVs). Each bin may contain a number ( \(M\) ) of trajectory "walkers", \(i\) , that carry a certain weight \((w_{i})\) . The simulations run for a relatively short time ( \(\tau = 50ps\) ), after which trajectories are either replicated, if their number per bin is \(< M\) , or they are merged, if there are \(>M\) trajectories per bin. Importantly, the sum of all \(w_{i}\) equals 1 in any iteration, i.e., the trajectory replication and merging operations correspond to an unbiased statistical resampling of the underlying distribution. \(^{56}\) Detailed description about the WE path sampling algorithms and the WESTPA software can be found elsewhere. \(^{57 - 59}\)
+
+<|ref|>text<|/ref|><|det|>[[161, 410, 838, 572]]<|/det|>
+The unbound systems described above were taken as the starting configuration for each binding simulation with the GPU- accelerated version of the AMBER molecular dynamics package. \(^{60}\) To ensure the PROTAC remains bound to the VHL protein during these simulations, a modest (1 kcal mol \(^{- 1}\) Å \(^{- 2}\) ) flat- bottom position restraint was enforced between the center of masses of the ligand and protein binding site heavy atoms. All other MD simulation parameters were as described above
+
+<|ref|>text<|/ref|><|det|>[[161, 581, 838, 684]]<|/det|>
+For each of the three systems, two WESTPA simulations were performed: one for the initial formation of the ternary complex and one for the refinement of the binding interactions. In each case, \(M\) was set to 5 and two collective variables (CV1 and CV2) were defined to assess progress.
+
+<|ref|>text<|/ref|><|det|>[[161, 694, 838, 910]]<|/det|>
+In the first set of simulations, CV1 was defined as the warhead- RMSD, or w- RMSD, of the PROTAC warhead with respect to the corresponding crystal structure of the bound complex. CV2 was a combination of two observables; it was either defined to be the number of native atomic contacts between the warhead and the SMARCA2 binding interface or, if the binding sites were so distant that no contacts were formed, it was defined as the distance of the binding partners, i.e., SMARCA2 and the VHL- PROTAC binary complex. Contacts were counted between non- hydrogen atoms within a radius of 4.5 Å and, to ensure that CV2 is defined along one linear dimension, the contact
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 194]]<|/det|>
+counts were scaled by - 1. This selection of CV1 and CV2 with an appropriate binning allowed the separated binding partners to assemble, during the WESTPA simulations, into ternary complexes that are similar to the corresponding crystal structures, which were used for w- RMSD and native contact calculations.
+
+<|ref|>text<|/ref|><|det|>[[160, 203, 838, 365]]<|/det|>
+In the refinement simulations, both CV1 and CV2 were contact counts. CV1 was the number of heavy- atom contacts between two proteins, whereas CV2 was the number of heavy- atom contacts between both proteins and the PROTAC. When augmenting the WE simulations with HDX- MS data, only the protected residues of the two proteins, as informed by the corresponding experiments, were taken into consideration for the contact counts of both CVs.
+
+<|ref|>text<|/ref|><|det|>[[160, 373, 838, 562]]<|/det|>
+The ensemble of predicted bound structures was evaluated by comparing the distributions of minimum interface- RMSDs (I- RMSDs) with respect to the set of reference ternary complexes, where the interface is defined by SMC2 and VHL residues within \(10\mathring{A}\) . Furthermore, to obtain a subset of reliable predictions, these I- RMSD distributions only contain structures with w- RMSD \(< 2\mathring{A}\) and \(>30\) contacts between any residues of the two proteins or, in the case of employing HDX data, between the protected residues of the two proteins.
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 596, 722, 620]]<|/det|>
+### 4.8 REVO-epsilon Weighted Ensemble method
+
+<|ref|>text<|/ref|><|det|>[[160, 636, 838, 742]]<|/det|>
+We also applied a variant of the weighted ensemble algorithm, REVO. We will describe the application of the REVO algorithm as it pertains to this study, but a more detailed explanation can be found in previous works. The goal of the REVO resampling algorithm is to maximize the variation function defined as:
+
+<|ref|>equation<|/ref|><|det|>[[365, 768, 832, 815]]<|/det|>
+\[V = \sum_{i}V_{i} = \sum_{i}\sum_{j}\left(\frac{d_{ij}}{d_{0}}\right)^{\alpha}\phi_{i}\phi_{j} \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 823, 836, 899]]<|/det|>
+where \(V_{i}\) is the walker variation, \(d_{ij}\) is the distance between walkers i and j determined using a specific distance metric, \(d_{0}\) is the characteristic distance used to make the distance term dimensionless, set to 0.148 for all simulations, the \(\alpha\) is used to deter
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 89, 838, 338]]<|/det|>
+mine how influential the distances are to the walker variation and was set to 6 for all the simulations. The novelty terms \(\phi_{i}\) and \(\phi_{j}\) are defined as: \(\phi_{i} = \log (w_{i}) - \log \left(\frac{p_{min}}{100}\right)\) . The minimum weight, \(p_{min}\) , allowed during the simulation was \(10^{- 50}\) . Cloning was attempted for the walker with the highest variance, \(V_{i}\) when the weights of the resultant clones would be larger than \(p_{min}\) , provided it is within distance \(\epsilon\) of the walker with the maximal progress towards binding of the ternary complex. The two walkers selected for merging were within a distance of 2 (A) and have a combined weight larger than the maximal weight allowed, \(p_{max}\) , which was set to 0.1 for all REVO simulations. The merge pair also needed to minimize:
+
+<|ref|>equation<|/ref|><|det|>[[448, 360, 833, 397]]<|/det|>
+\[\frac{V_{j}w_{i} - V_{i}w_{j}}{w_{i} + w_{j}} \quad (4)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 419, 837, 495]]<|/det|>
+If the proposed merging and cloning operations increase the total variance of the simulation, the operations are performed and we repeat this process until the variation can no longer be increased.
+
+<|ref|>text<|/ref|><|det|>[[160, 504, 838, 864]]<|/det|>
+Three different distance metrics were used while simulating the PROTAC 2 system: Using the warhead RMSD to the crystal structure, maximizing the contact strength (defined below) between protected residues identified by HDX data, and a linear combination of the warhead RMSD, contact strength between HDX- protected residues, and the contact strength between SMARCA2 and the degrader. The simulations for the other systems used the last distance metric exclusively. To compute the warhead RMSD distance metric, we aligned to the binding site atoms on SMARCA2, defined as atoms that were within 8 Å of the warhead in the crystal structure. Then the RMSD was calculated between the warhead in each frame and the crystal structure. The distance between a set of walkers i and j is defined as: \(d = |\frac{1}{RMSD_{i}} - \frac{1}{RMSD_{j}}|\) . The contact strength is defined by determining the distances between residues. We calculate the minimum distance between the residues and use the following to determine the contact strength:
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[398, 110, 833, 145]]<|/det|>
+\[strength = \frac{1}{1 + e^{-k(r - r_0)}} \quad (5)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 160, 837, 293]]<|/det|>
+where k is the steepness of the curve, \(r\) is the minimum distance between any 2 residues and \(r_0\) is the distance we want a contact strength of 0.5. We used 10 for k and 5 Å for \(r_0\) . The total contact strength was the sum of all residue- residue contact strengths. The distance between walkers i and j was calculated by: \(d = |cs_i - cs_j|\) where cs is the contact strength of a given walker.
+
+<|ref|>text<|/ref|><|det|>[[160, 302, 837, 378]]<|/det|>
+All REVO simulations were run using OpenMM v.7.5.0. Simulation details are as described above. The degrader- VHL interface was restrained to maintain the complex during the simulation by using a OpenMM custom centroid force defined as:
+
+<|ref|>equation<|/ref|><|det|>[[354, 413, 833, 434]]<|/det|>
+\[CentroidForce = k*(dist - edist)^2 \quad (6)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 455, 837, 560]]<|/det|>
+where the dist is the distance between the center of mass of PROTAC and the center of mass of VHL and the edit is the distance between the center of mass of PROTAC and center of mass of VHL of the crystal structure, and k is a constant set to 2 kcal/mol \* Ų.
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 595, 622, 618]]<|/det|>
+### 4.9 Ternary complex docking protocol
+
+<|ref|>text<|/ref|><|det|>[[160, 634, 838, 911]]<|/det|>
+Following \(^{27,29}\) (Methods 4 and 4b) and, \(^{26}\) we assume that high fidelity structures of SMC2:warhead and VHL:ligand are known and available to be used in protein- protein docking. This docking of two proteins with bound PROTAC moieties is performed in the absence of the linker. The conformations of linker are sampled independently with an in- house developed protocol that uses implementation of fast quantum mechanical methods, CREST. \(^{61 - 63}\) Differently from the docking protocols described in, \(^{26,27,29}\) we make use of distance restraints derived either from the end- to- end distances of the sampled conformations of linker, or from the HDX- MS data. Thus, before running the protein- protein docking, we generate an ensemble of conformers for linkers and calculate the mean \((x_0)\) and standard deviation \((sd)\) for the end- to- end distance. This
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 835, 110]]<|/det|>
+information is then used to set the distance restraints in the RosettaDock software: \(^{64,65}\)
+
+<|ref|>equation<|/ref|><|det|>[[424, 140, 833, 174]]<|/det|>
+\[f_{1}(x) = (\frac{x - x_{0}}{sd})^{2}, \quad (7)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 189, 836, 236]]<|/det|>
+where \(x\) is the distance between a pair of atoms in a candidate docking pose (the pair of atoms is specified as the attachment points of the linker to warhead and ligand).
+
+<|ref|>text<|/ref|><|det|>[[160, 245, 835, 292]]<|/det|>
+When information about the protected residues is available from HDX- MS experiments, we used them to set up a set of additional distance restraints:
+
+<|ref|>equation<|/ref|><|det|>[[343, 321, 833, 358]]<|/det|>
+\[f_{2,i}(x) = \frac{1}{1 + \exp(-m\cdot(x - x0))} -0.5, \quad (8)\]
+
+<|ref|>text<|/ref|><|det|>[[160, 371, 838, 561]]<|/det|>
+where \(i\) is the index of a protected residue, \(x0\) is the center of the sigmoid function and \(m\) is its slope. As above, \(x0\) value was set to be the mean end- to- end distance calculated over the ensemble of linker conformers. The value of \(m\) was set to be 2.0 in all the performed docking experiments. The type of RosettaDock- restraint is SiteConstraint, with specification of \(\mathrm{C}\alpha\) atom for each protected residue and the chain- ID of partnering protein (i.e., \(x\) in Eq.(8) is the distance of \(\mathrm{C}\alpha\) atom from the partnering protein). Thus, the total restraint- term used in docking takes the form:
+
+<|ref|>equation<|/ref|><|det|>[[358, 594, 833, 630]]<|/det|>
+\[f_{restr.}(x) = w\cdot (f_{1}(x) + \sum_{i}f_{2,i}(x)), \quad (9)\]
+
+<|ref|>text<|/ref|><|det|>[[161, 640, 678, 659]]<|/det|>
+where \(w = 10\) is the weight of this additional score function term.
+
+<|ref|>text<|/ref|><|det|>[[160, 668, 838, 829]]<|/det|>
+RosettaDock implements a Monte Carlo- based multi- scale docking algorithm that samples both rigid- body orientation and side- chain conformations. The distance- based scoring terms, Eq. (9), bias sampling towards those docking poses that are compatible with specified restraints. This limits the number of output docking structures, as only those ones that pass the Metropolis criterion with the additional term of Eq. (9) will be considered.
+
+<|ref|>text<|/ref|><|det|>[[160, 838, 836, 885]]<|/det|>
+Once the docking poses are generated with RosettaDock, all the pre- generated conformations of the linker are structurally aligned onto each of the docking predictions. \(^{26}\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 88, 838, 223]]<|/det|>
+Only those structures that satisfy the RMS- threshold value of \(\leq 0.3 \mathrm{\AA}\) are saved as PDB files. All the docking predictions are re- ranked by the values of Rosetta Interface score \((I_{sc})\) . The produced ternary structures are examined for clashes, minimized and submitted for further investigations with Molecular Dynamics methods. Details about running the described docking protocol can be found in Supplementary Material.
+
+<|ref|>sub_title<|/ref|><|det|>[[162, 257, 470, 280]]<|/det|>
+### 4.10 HREMD simulation
+
+<|ref|>text<|/ref|><|det|>[[160, 297, 839, 600]]<|/det|>
+The details of Hamiltonian replica- exchange MD (HREMD) \(^{66,67}\) can be found in the Supplementary Material (Supplementary Figures 13 and 14, and Table 2). For all HREMD simulations, we chose the effective temperatures, \(T_{0} = 300 \mathrm{K}\) and \(T_{max} = 425 \mathrm{K}\) such that the Hamiltonian scaling parameter, \(\lambda_{0} = 1.00\) and \(\lambda_{min} = 0.71\) for the lowest and the highest rank replicas respectively. We estimated the number of replicas \((n)\) in such a way that the average exchange probabilities \((p)\) between neighboring replicas were in the range of 0.3 to 0.4. We used \(n = 20\) and \(n = 24\) for SMC2:degrader:VHL and SMC2:degrader:VCB respectively. Each simulation was run for \(0.5 \mu \mathrm{s}\) /replica, and a snapshot of a complex was saved every 5 ps (total 100,001 frames per replica). Finally, we performed all the analyses on only the lowest rank replica that ran with original/unscaled Hamiltonian.
+
+<|ref|>text<|/ref|><|det|>[[160, 608, 837, 714]]<|/det|>
+We assessed the efficiency of sampling by observing (i) the values of \(p\) , (ii) a good overlap of histograms of potential energy between adjacent replicas (Supplementary Figure 13), and (iii) a mixing of exchange of coordinates across all the replicas (Supplementary Figure 14).
+
+<|ref|>sub_title<|/ref|><|det|>[[160, 747, 835, 771]]<|/det|>
+### 4.11 Conformational free energy landscape determination
+
+<|ref|>text<|/ref|><|det|>[[160, 789, 837, 891]]<|/det|>
+In order to quantify to the conformational free energy landscape, we performed dimension reduction of our simulation trajectories using principle component analysis (PCA). First, the simulation trajectories were featurized by calculating interfacial residue contact distances. Pairs of residues were identified as part of the interface if they passed
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 837, 222]]<|/det|>
+within 5 Å of each other during the simulation trajectory, where the distance between two residues was defined as the distance between their closest heavy atoms. PCA was then used to identify the features that contributed most to the variance by diagonalizing the covariance matrix; for each simulated system, the number of features used in our analysis was chosen as that which explained at least 95% of the variance.
+
+<|ref|>text<|/ref|><|det|>[[160, 232, 838, 450]]<|/det|>
+After projecting the simulation data onto the resultant feature space, snapshots were clustered using the \(k\) - means algorithm. The number of clusters \(k\) was chosen using the "elbow- method", i.e. by visually identifying the point at which the marginal effect of an additional cluster was significantly reduced. In cases where no "elbow" could be unambiguously identified, \(k\) was chosen to be the number of local maxima of the probability distribution in the PCA feature space. Interestingly, the centroids determined by \(k\) - means approximately coincided with such local maxima, consistent with the interpretation of the centroids as local minima in the free energy landscape.
+
+<|ref|>text<|/ref|><|det|>[[160, 458, 839, 760]]<|/det|>
+To prepare the Folding@home simulations, HREMD data were featurized with interface distances and its dimensionality reduced with PCA as described above. The trajectory was then clustered into 98 k- means states, whose cluster centers were selected as 'seeds' for Folding@home massively parallel simulations. The simulation systems and parameters were kept the same as for HREMD and loaded into OpenMM where they were energy minimized and equilibrated for 5 ns in the NPT ensemble (T = 310 K, p = 1 atm) using the openmmtools Langevin BAOAB integrator with 2 fs timestep. 100 trajectories with random starting velocities were then initialized on Folding@home for each of the seeds. The final dataset consists of 9800 trajectories, 5.7 milliseconds of aggregate simulation time, and 650 ns median trajectory length. This dataset is made publicly available at:
+
+<|ref|>text<|/ref|><|det|>[[170, 770, 655, 788]]<|/det|>
+https://console.cloud.google.com/storage/browser/paperdata.
+
+<|ref|>text<|/ref|><|det|>[[160, 798, 837, 902]]<|/det|>
+For computational efficiency, the data was strided to 5 ns/frame, featurized with closest heavy atom interface distances (as described above), and projected into tICA space at lag time 5 ns using commute mapping. The dimensionality of the dataset was reduced to 339 dimensions, keeping the number of tICs necessary to explain 95%
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[159, 90, 839, 393]]<|/det|>
+of kinetic variance. The resulting tICA space was discretized into 1000 microstates using k- means. The Markov state model (MSM) was then estimated from the resulting discretized trajectories at lag time 50 ns using a minimum number of counts for ergodic trimming (i.e. the 'mincount_connectivity' argument in PyEMMA) of 4, as the default setting resulted in a trapped state whose connectivity between simulation sub- ensembles starting from two different seeds was observed only due to clustering noise. The validity of the MSM was confirmed by plotting the populations from raw MD counts vs. equilibrium populations from the MSM, which is a useful test, especially when multiple seeds are used and the issue of connectivity is paramount. A hidden Markov model (HMM) was then computed using 5 macrostates to coarse- grain the transition matrix.
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 426, 767, 450]]<|/det|>
+### 4.12 Comparison of HREMD to SAXS experiment
+
+<|ref|>text<|/ref|><|det|>[[160, 466, 847, 713]]<|/det|>
+We validated the HREMD- generated ensembles of SMC2- isoform1/isoform2:ACBI1:VCB complexes by directly comparing to the experimental SAXS data. The theoretical SAXS profile was computed from each snapshot from the HREMD simulation trajectory using CRYSOL \(^{68}\) available in a software package ATSAS. \(^{69}\) The following CRYSOL command was used: \(crysol < filename.pdb > - lm 20 - sm 0.5 - ns 201 - un 1 - eh - dro 0.03\) . To expedite the writing of PDBs from HREMD trajectory and calculation of SAXS profiles, we used the multiprocessing functionality implemented in a Python package \(idpflex^{70}\) The ensemble- averaged theoretical SAXS profile was determined as below,
+
+<|ref|>equation<|/ref|><|det|>[[413, 712, 832, 755]]<|/det|>
+\[< I(q) > = \frac{1}{n}\sum_{i = 1}^{n}I_{i}(q) \quad (10)\]
+
+<|ref|>text<|/ref|><|det|>[[161, 763, 836, 840]]<|/det|>
+where \(n = 100,001\) is the total number of frames in HREMD trajectory of each complex. The ensemble- averaged theoretical SAXS profile was compared to experiment (Figure 7c) by minimizing chi- square ( \(\chi^{2}\) ) given by,
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[259, 100, 833, 157]]<|/det|>
+\[\chi^{2} = \frac{1}{(m - 1)}\sum_{i = 1}^{m}\left\{\frac{\left[< I_{expt}(q_{i}) > -(c< I_{calc}(q_{i}) > +b)\right]}{\sigma_{expt}(q_{i})}\right\}^{2} \quad (11)\]
+
+<|ref|>text<|/ref|><|det|>[[161, 168, 837, 247]]<|/det|>
+where \(< I_{expt}(q) >\) and \(< I_{calc}(q) >\) are the ensemble- averaged experimental and theoretical SAXS intensities respectively, \(m\) is the number of experimental \(q\) points, \(c\) is a scaling factor, \(b\) is a constant background, and \(\sigma_{expt}\) is the error in \(I_{expt}(q)\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 279, 835, 339]]<|/det|>
+### 4.13 Cullin-RING E3 ubiquitin ligase (CRL) simulations to explore activation
+
+<|ref|>text<|/ref|><|det|>[[160, 356, 839, 576]]<|/det|>
+To study the impact of different bifunctional molecules on ubiquitination, first we constructed an active form of the Cullin- RING E3 ubiquitin ligase (CRL) with VHL and grafted it onto the ternary structures from the VHL- degrader- SMARCA2 simulations described above. We used targeted MD simulations (TMD) \(^{71}\) to drive the activation of the CLR based on the active structure of a homologous E3 ligase, CRL- \(\beta\) TrCP (PDB ID 6TTU). \(^{51}\) The full CRL- VHL system was built using PDB IDs 1LQB and 5N4W including VHL, ElonginB, ElonginC, Cullin2, and RBX1. \(^{11,72}\) NEDD8 was placed near residue Lys689 of the CRL where neddylation occurs.
+
+<|ref|>text<|/ref|><|det|>[[160, 584, 839, 888]]<|/det|>
+As the collective variable for TMD, we used the residue- based RMSD of the last \(\sim 70\) Cα atoms of the Cullin C- terminus (where neddylation and subsequent activation occur) of Cullin1 from the 6TTU structure \(^{51}\) as the reference state and modeled Cullin2 from its inactive form in the 5N4W structure to this reference state. In addition, the Cα atoms of the entire NEDD8 protein from the 6TTU structure was also used as a reference structure during TMD. Residues 135 to 425 from Cullin2 and corresponding residues from Cullin1 were used for alignment during TMD. The force constant for TMD was set to 30 kJ/mol/\(\mathrm{nm}^{2}\) . The system in a rectangular simulation box with a total number of \(\sim 500\mathrm{K}\) atoms and an ionic concentration of 0.120 M using KCl. Hydrogen mass repartitioning (HMR) was used to enable 4 fs timestep simulations using the the AMBER ff14SB force field parameters. The TMD structure was then
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 222]]<|/det|>
+used to build the entire complex for CRL- VHL- Degrader- SMARCA2. The system also included E2 and ubiquitin from the 6TTU structure. This system was solvated in a truncated octahedral box to avoid protein rotation during simulation and it was equilibrated for about 30 ns before subsequent meta- eABF simulations for identifying the ubiquitination zone.
+
+<|ref|>sub_title<|/ref|><|det|>[[161, 256, 843, 319]]<|/det|>
+### 4.14 Meta-eABF simulations on full Cullin-RING E3 ubiquitin ligases (CRL) complex
+
+<|ref|>text<|/ref|><|det|>[[160, 333, 839, 496]]<|/det|>
+We employ an advanced path- based simulation method that combines metadynamics with extended adaptive biasing force (meta- eABF) to study the dynamic nature of the full CRL- VHL- degrader- SMARCA2 complex and generate a diverse set of putative closed conformations that place the E2- loaded ubiquitin close to lysine residues on SMARCA2. The results from the meta- eABF simulation are used to seed additional simulations for unbiased ensemble- scale sampling.
+
+<|ref|>text<|/ref|><|det|>[[159, 504, 839, 893]]<|/det|>
+Detailed description of the meta- eABF algorithm and its variants can be found elsewhere, \(^{73 - 76}\) but for clarity we present a brief account here. Similar to adaptive biasing force (ABF) methods, meta- eABF simulations also utilize adaptive free energy biasing force to enhance sampling along one or more collective variables (CVs), but the practical implementation is different. Meta- eABF evokes the extended Lagrangian formalism of ABF whereby an auxiliary simulation is introduced with a small number of degrees of freedom equal to the number of CVs, and each real CV is associated with its so- called fictitious counterpart in the low- dimensional auxiliary simulation. The real CV is tethered to its fictitious CV via a stiff spring with a large force constant and the adaptive biasing force is equal to the running average of the negative of the spring force. The biasing force is only applied to the fictitious CV, which in turn “drags” the real simulation along the real CV via the spring by periodically injecting the instantaneous spring force back into the real simulation. Moreover, the main tenet of the meta- eABF method is employing metadynamics (MtD) or well- tempered metadynamics.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 835, 138]]<|/det|>
+ics (WTM) to enhance sampling of the fictitious CV itself. The combined approach provides advantages from both MtD/WTM and eABF.
+
+<|ref|>text<|/ref|><|det|>[[160, 147, 838, 394]]<|/det|>
+For CRL- VHL closure we chose a single CV, the center- of- mass (COM) distance between SMARCA2 and E2 ligase- ubiquitin (E2- Ub) complex. The initial COM distance after relaxation was \(\sim 65\) Å, and we ran 40 ns of meta- eABF simulation biasing the COM distance between 25- 75 Å. During this simulation we saw multiple ring closing- opening events with the last frame representing a slightly open conformation with COM distance \(\sim 36\) Å. We then continued the meta- eABF simulation for another 80 ns but narrowing the bias range on the COM distance to 25- 40 Å in order to focus the sampling on closed or nearly closed conformations. The simulations were run using OpenMM 7.5 \(^{77}\) interfaced with PLUMED 2.7. \(^{78}\)
+
+<|ref|>sub_title<|/ref|><|det|>[[164, 435, 415, 460]]<|/det|>
+## Acknowledgement
+
+<|ref|>text<|/ref|><|det|>[[161, 481, 836, 558]]<|/det|>
+This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE- AC05- 00OR22725.
+
+<|ref|>text<|/ref|><|det|>[[160, 567, 838, 756]]<|/det|>
+We thank the University of Massachusetts Institute of Applied Life Sciences Mass Spectrometry Core ( RRID:SCR_019063) and Stephen J. Eyles for their support and mentorship during the collection, and processing of all Hydrogen Deuterium Exchange Data. We thank Helix Biostructures LLC for their assistance with X- Ray data collection and raw data reduction. SAXS measurements were based upon research conducted at the Structural Biology Platform of the Université de Montréal, which is supported by the Canadian Foundation for Innovation award #30574.
+
+<|ref|>text<|/ref|><|det|>[[160, 765, 837, 841]]<|/det|>
+We are grateful to all the citizen scientists who contributed their compute power to make parts of this work possible, and members of the Folding@home community who volunteered to help with technical support to run these simulations.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[162, 85, 507, 110]]<|/det|>
+## 5 Author contributions
+
+<|ref|>text<|/ref|><|det|>[[160, 131, 839, 465]]<|/det|>
+TDi and BM ran and analyzed WES+HDX simulations. DMa performed crystallography and HDX- MS experiments. TDa ran docking simulations. SL wrote software to support simulations and analysis. DMc ran MD simulations and analyses. SSh and RP performed homology modeling and analyzed data. URS ran HREMD simulations and compared to SAXS. RW and ZAM ran FAH simulations and performed conformational landscape analyses. FP analyzed HDX data. JVR assisted with visualization and analyses. TW and VS helped scale WESTPA in Summit and to run all simulations efficiently in our HPC cluster. NG and SJ performed protein production. SSp performed SAXS analyses. YL and AV performed SPR experiments. XZ oversaw synthesis of PROTAC molecules. AMR and IK performed CRL simulations and ubiquitination analyses. JIm, AE, and LB helped edit the paper. AD, HX, WS and JAI directed the research presented in this paper. All authors wrote the paper.
+
+<|ref|>sub_title<|/ref|><|det|>[[162, 504, 633, 531]]<|/det|>
+## Supporting Information Available
+
+<|ref|>text<|/ref|><|det|>[[160, 551, 839, 771]]<|/det|>
+We make all experimental data used in this study available, including HDX- MS and a crystal structure of SMARCA2:ACBI1:VHL- Elongin C- Elongin B (PDB ID 7S4E). We also make available trajectory data for the conformational sampling of the crystal structures and the ternary complex formation simulations at https://console.cloud.google.com/storage/browser/paperdata. We have created a repository information about the format of the WES+HDX trajectory data, and source code needed to run WES+HDX at https://github.com/stxinsite/degrader- ternary- complex- prediction.
+
+<|ref|>sub_title<|/ref|><|det|>[[162, 812, 313, 835]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[170, 858, 836, 906]]<|/det|>
+(1) Wu, T.; Yoon, H.; Xiong, Y.; Dixon-Clarke, S. E.; Nowak, R. P.; Fischer, E. S. Targeted protein degradation as a powerful research tool in basic biology and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[202, 90, 751, 110]]<|/det|>
+drug target discovery. NAT STRUCT MOL BIOL 2020, 27, 605- 614.
+
+<|ref|>text<|/ref|><|det|>[[170, 130, 836, 234]]<|/det|>
+(2) Schneider, M.; Radoux, C. J.; Hercules, A.; Ochoa, D.; Dunham, I.; Zalmas, L.-P.; Hessler, G.; Ruf, S.; Shanmugasundaram, V.; Hann, M. M.; Thomas, P. J.; Queisser, M. A.; Benowitz, A. B.; Brown, K.; Leach, A. R. The PROTACtable genome. NAT REV DRUG DISCOV 2021, 1-9.
+
+<|ref|>text<|/ref|><|det|>[[170, 256, 836, 330]]<|/det|>
+(3) Schapira, M.; Calabrese, M. F.; Bullock, A. N.; Crews, C. M. Targeted protein degradation: expanding the toolbox. NAT REV DRUG DISCOV 2019, 18, 949-963.
+
+<|ref|>text<|/ref|><|det|>[[170, 353, 836, 430]]<|/det|>
+(4) Coleman, K. G.; Crews, C. M. Proteolysis-Targeting Chimeras: Harnessing the Ubiquitin-Proteasome System to Induce Degradation of Specific Target Proteins. Annual Review of Cancer Biology 2017, 2, 1-18.
+
+<|ref|>text<|/ref|><|det|>[[170, 451, 836, 500]]<|/det|>
+(5) Matyskiela, M. E. et al. A Cereblon Modulator (CC-220) with Improved Degradation of Ikaros and Aiolos. Journal of Medicinal Chemistry 2018, 61, 535-542.
+
+<|ref|>text<|/ref|><|det|>[[170, 520, 836, 597]]<|/det|>
+(6) Chamberlain, P. P. et al. Structure of the human Cereblon-DDB1-lenalidomide complex reveals basis for responsiveness to thalidomide analogs. Nature Structural & Molecular Biology 2014, 21, 803-809.
+
+<|ref|>text<|/ref|><|det|>[[170, 618, 836, 666]]<|/det|>
+(7) Krönke, J. et al. Lenalidomide Causes Selective Degradation of IKZF1 and IKZF3 in Multiple Myeloma Cells. Science 343, 301-305.
+
+<|ref|>text<|/ref|><|det|>[[170, 687, 836, 763]]<|/det|>
+(8) Ohoka, N. et al. In Vivo Knockdown of Pathogenic Proteins via Specific and Nongenetic Inhibitor of Apoptosis Protein (IAP)-dependent Protein Erasers (SNIPERs)*. Journal of Biological Chemistry 2017, 292, 4556-4570.
+
+<|ref|>text<|/ref|><|det|>[[170, 784, 835, 832]]<|/det|>
+(9) Wei, J. et al. Harnessing the E3 Ligase KEAP1 for Targeted Protein Degradation. Journal of the American Chemical Society 2021, 143, 15073-15083.
+
+<|ref|>text<|/ref|><|det|>[[160, 854, 835, 902]]<|/det|>
+(10) Rodriguez-Gonzalez, A.; Cyrus, K.; Salcius, M.; Kim, K.; Crews, C. M.; Deshaies, R. J.; Sakamoto, K. M. Targeting steroid hormone receptors for ubiqu
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[201, 90, 836, 137]]<|/det|>
+uitination and degradation in breast and prostate cancer. Oncogene 2008, 27, 7201–7211.
+
+<|ref|>text<|/ref|><|det|>[[161, 158, 836, 264]]<|/det|>
+(11) Hon, W.-C.; Wilson, M. I.; Harlos, K.; Claridge, T. D.; Schofield, C. J.; Pugh, C. W.; Maxwell, P. H.; Ratcliffe, P. J.; Stuart, D. I.; Jones, E. Y. Structural basis for the recognition of hydroxyproline in HIF-1α by pVHL. Nature 2002, 417, 975–978.
+
+<|ref|>text<|/ref|><|det|>[[161, 284, 837, 390]]<|/det|>
+(12) Sakamoto, K. M.; Kim, K. B.; Kumagai, A.; Mercurio, F.; Crews, C. M.; Deshaies, R. J. Protacs: Chimeric molecules that target proteins to the Skp1-Cullin-F box complex for ubiquitination and degradation. Proceedings of the National Academy of Sciences 2001, 98, 8554–8559.
+
+<|ref|>text<|/ref|><|det|>[[161, 410, 836, 514]]<|/det|>
+(13) Roy, M. J.; Winkler, S.; Hughes, S. J.; Whitworth, C.; Galant, M.; Farnaby, W. l.; Rumpel, K.; Ciulli, A. SPR-Measured Dissociation Kinetics of PROTAC Ternary Complexes Influence Target Degradation Rate. ACS CHEM BIOL 2019, 14, 361–368.
+
+<|ref|>text<|/ref|><|det|>[[161, 536, 836, 611]]<|/det|>
+(14) Hughes, S.; Ciulli, A. Molecular recognition of ternary complexes: a new dimension in the structure-guided design of chemical degraders. ESSAYS BIOCHEM 2017, 61, 505–516.
+
+<|ref|>text<|/ref|><|det|>[[161, 633, 836, 738]]<|/det|>
+(15) Farnaby, W.; Koegl, M.; Roy, M. J.; Whitworth, C.; Diers, E.; Trainor, N.; Zollman, D.; Steurer, S.; Karolyi-Oezguer, J.; Riedmueller, C., et al. BAF complex vulnerabilities in cancer demonstrated via structure-based PROTAC design. Nature chemical biology 2019, 15, 672–680.
+
+<|ref|>text<|/ref|><|det|>[[161, 760, 836, 835]]<|/det|>
+(16) Zorba, A. et al. Delineating the role of cooperativity in the design of potent PROTACs for BTK. Proceedings of the National Academy of Sciences 2018, 115, 201803662.
+
+<|ref|>text<|/ref|><|det|>[[161, 857, 836, 905]]<|/det|>
+(17) Schiemer, J. et al. Snapshots and ensembles of BTK and cIAP1 protein degrader ternary complexes. NAT CHEM BIOL 2021, 17, 152–160.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 195]]<|/det|>
+(18) Huang, H.-T.; Dobrovolsky, D.; Paulk, J.; Yang, G.; Weisberg, E. L.; Doctor, Z. M.; Buckley, D. L.; Cho, J.-H.; Ko, E.; Jang, J., et al. A chemoproteomic approach to query the degradable kinome using a multi-kinase degrader. Cell chemical biology 2018, 25, 88–99.
+
+<|ref|>text<|/ref|><|det|>[[160, 215, 837, 320]]<|/det|>
+(19) Bondeson, D. P.; Smith, B. E.; Burslem, G. M.; Buhimschi, A. D.; Hines, J.; Jaime-Figueroa, S.; Wang, J.; Hamman, B. D.; Ishchenko, A.; Crews, C. M. Lessons in PROTAC design from selective degradation with a promiscuous warhead. Cell chemical biology 2018, 25, 78–87.
+
+<|ref|>text<|/ref|><|det|>[[160, 341, 837, 446]]<|/det|>
+(20) Ward, C. C.; Kleinman, J. I.; Brittain, S. M.; Lee, P. S.; Chung, C. Y. S.; Kim, K.; Petri, Y.; Thomas, J. R.; Tallarico, J. A.; McKenna, J. M., et al. Covalent ligand screening uncovers a RNF4 E3 ligase recruiter for targeted protein degradation applications. ACS chemical biology 2019, 14, 2430–2440.
+
+<|ref|>text<|/ref|><|det|>[[160, 466, 837, 545]]<|/det|>
+(21) Zengerle, M.; Chan, K.-H.; Ciulli, A. Selective Small Molecule Induced Degradation of the BET Bromodomain Protein BRD4. ACS CHEM BIOL 2015, 10, 1770–1777.
+
+<|ref|>text<|/ref|><|det|>[[160, 565, 837, 641]]<|/det|>
+(22) Gadd, M. S.; Testa, A.; Lucas, X.; Chan, K.-H.; Chen, W.; Lamont, D. J.; Zengerle, M.; Ciulli, A. Structural basis of PROTAC cooperative recognition for selective protein degradation. NAT CHEM BIOL 2017, 13, 514–521.
+
+<|ref|>text<|/ref|><|det|>[[160, 662, 837, 711]]<|/det|>
+(23) Farnaby, W. et al. BAF complex vulnerabilities in cancer demonstrated via structure-based PROTAC design. NAT CHEM BIOL 2019, 15, 672–680.
+
+<|ref|>text<|/ref|><|det|>[[160, 731, 837, 808]]<|/det|>
+(24) Testa, A.; Hughes, S. J.; Lucas, X.; Wright, J. E.; Ciulli, A. Structure-Based Design of a Macrocyclic PROTAC. Angewandte Chemie International Edition 2020, 59, 1727–1734.
+
+<|ref|>text<|/ref|><|det|>[[160, 829, 837, 905]]<|/det|>
+(25) Zaidman, D.; Prilusky, J.; London, N. PRosettaC: Rosetta Based Modeling of PROTAC Mediated Ternary Complexes. J CHEM INF MODEL 2020, 60, 4894–4903.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 836, 165]]<|/det|>
+(26) Bai, N.; Kirubakaran, P.; Karanicolas, J. Rationalizing PROTAC-mediated ternary complex formation using Rosetta. J. Chem. Inf. Model. 2021, 61, 1368–1382.
+
+<|ref|>text<|/ref|><|det|>[[160, 186, 836, 291]]<|/det|>
+(27) Drummond, M. L.; Henry, A.; Li, H.; Williams, C. I. Improved Accuracy for Modeling PROTAC-Mediated Ternary Complex Formation and Targeted Protein Degradation via New In Silico Methodologies. J CHEM INF MODEL 2020, 60, 5234–5254.
+
+<|ref|>text<|/ref|><|det|>[[160, 313, 836, 389]]<|/det|>
+(28) Shaheer, M.; Singh, R.; Sobhia, M. E. Protein degradation: a novel computational approach to design protein degrader probes for main protease of SARS-CoV-2. J BIOMOL STRUCT DYN 2021, 1–13.
+
+<|ref|>text<|/ref|><|det|>[[160, 410, 836, 515]]<|/det|>
+(29) Drummond, M. L.; Henry, A.; Li, H.; Williams, C. I. Improved Accuracy for Modeling PROTAC-Mediated Ternary Complex Formation and Targeted Protein Degradation via New In Silico Methodologies. J CHEM INF MODEL 2020, 60, 5234–5254.
+
+<|ref|>text<|/ref|><|det|>[[160, 536, 836, 699]]<|/det|>
+(30) Eron, S. J.; Huang, H.; Agafonov, R. V.; Fitzgerald, M. E.; Patel, J.; Michael, R. E.; Lee, T. D.; Hart, A. A.; Shaulsky, J.; Nasveschuk, C. G.; Phillips, A. J.; Fisher, S. L.; Good, A. Structural Characterization of Degrader-Induced Ternary Complexes Using Hydrogen–Deuterium Exchange Mass Spectrometry and Computational Modeling: Implications for Structure-Based Design. ACS Chemical Biology 2021,
+
+<|ref|>text<|/ref|><|det|>[[160, 719, 836, 796]]<|/det|>
+(31) Liu, X.; Zhang, X.; Lv, D.; Yuan, Y.; Zheng, G.; Zhou, D. Assays and technologies for developing proteolysis targeting chimera degraders. Future Medicinal Chemistry 2020, 12, 1155–1179.
+
+<|ref|>text<|/ref|><|det|>[[160, 817, 836, 895]]<|/det|>
+(32) Nowak, R. P.; DeAngelo, S. L.; Buckley, D.; He, Z.; Donovan, K. A.; An, J.; Safaee, N.; Jedrychowski, M. P.; Ponthier, C. M.; Ishoey, M.; Zhang, T.; Mancias, J. D.; Gray, N. S.; Bradner, E. S., J. E. Fischer Plasticity in binding confers
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[201, 90, 835, 137]]<|/det|>
+selectivity in ligand- induced protein degradation. Nature Chemical Biology 2018, 14, 706–714.
+
+<|ref|>text<|/ref|><|det|>[[161, 156, 835, 205]]<|/det|>
+(33) Deller, M. C.; Kong, L.; Rupp, B. Protein stability: A crystallographer’s perspective. Acta Crystallogr F Struct Biol Commun 2016, 72, 72–95.
+
+<|ref|>text<|/ref|><|det|>[[161, 223, 836, 301]]<|/det|>
+(34) Dagbay, K. B.; Bolik-Coulon, N.; Savinov, S. N.; Hardy, J. A. Caspase-6 undergoes a Distinct Helix-Strand Interconversion upon Substrate Binding\*. J BIOL CHEM 2017, 292, 4885–4897.
+
+<|ref|>text<|/ref|><|det|>[[161, 320, 836, 397]]<|/det|>
+(35) Dagbay, K. B.; Hardy, J. A. Multiple proteolytic events in caspase-6 self-activation impact conformations of discrete structural regions. Proceedings of the National Academy of Sciences of the United States of America 2017, 114, E7977–E7986.
+
+<|ref|>text<|/ref|><|det|>[[161, 415, 836, 491]]<|/det|>
+(36) MacPherson, D. J.; Mills, C. L.; Ondrechen, M. J.; Hardy, J. A. Tri-arginine exosite patch of caspase-6 recruits substrates for hydrolysis. J BIOL CHEM 2019, 294, 71–88.
+
+<|ref|>text<|/ref|><|det|>[[161, 511, 836, 560]]<|/det|>
+(37) Wales, T. E.; Engen, J. R. Hydrogen exchange mass spectrometry for the analysis of protein dynamics. MASS SPECTROM REV 2006, 25, 158–170.
+
+<|ref|>text<|/ref|><|det|>[[161, 578, 836, 655]]<|/det|>
+(38) Gallagher, E. S.; Hudgens, J. W. Mapping Protein-Ligand Interactions with Proteolytic Fragmentation, Hydrogen/Deuterium Exchange-Mass Spectrometry. Methods in Enzymology 2016, 566.
+
+<|ref|>text<|/ref|><|det|>[[161, 673, 836, 750]]<|/det|>
+(39) Saglam, A. S.; Chong, L. T. Protein-protein binding pathways and calculations of rate constants using fully-continuous, explicit-solvent simulations. Chemical Science 2018, 10, 2360–2372.
+
+<|ref|>text<|/ref|><|det|>[[161, 769, 836, 845]]<|/det|>
+(40) Méndez, R.; Leplae, R.; De Maria, L.; Wodak, S. J. Assessment of blind predictions of protein–protein interactions: Current status of docking methods. PROTEINS 2003, 52, 51–67.
+
+<|ref|>text<|/ref|><|det|>[[161, 864, 836, 912]]<|/det|>
+(41) Donyapour, N.; Roussev, N. M.; Dickson, A. REVO: Resampling of ensembles by variation optimization. J. Chem. Phys. 2019, 150.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 836, 195]]<|/det|>
+(42) Jubb, H. C.; Higueruelo, A. P.; Ochoa-Montaño, B.; Pitt, W. R.; Ascher, D. B.; Blundell, T. L. Arpeggio: A Web Server for Calculating and Visualising Interatomic Interactions in Protein Structures. Journal of Molecular Biology 2017, 429, 365-371.
+
+<|ref|>text<|/ref|><|det|>[[160, 215, 836, 290]]<|/det|>
+(43) Lotz, S. D.; Dickson, A. Wepy: A Flexible Software Framework for Simulating Rare Events with Weighted Ensemble Resampling. ACS Omega 2020, 5, 31608-31623.
+
+<|ref|>text<|/ref|><|det|>[[160, 312, 836, 388]]<|/det|>
+(44) Dixon, T.; Uyar, A.; Ferguson-Miller, S.; Dickson, A. Membrane-Mediated Ligand Unbinding of the PK-11195 Ligand from TSPO. Biophysical Journal 2021, 120, 158-167.
+
+<|ref|>text<|/ref|><|det|>[[160, 409, 836, 488]]<|/det|>
+(45) Copperman, J.; Zuckerman, D. M. Accelerated Estimation of Long-Timescale Kinetics from Weighted Ensemble Simulation via Non-Markovian "Microbin" Analysis. Journal of Chemical Theory and Computation 2020, 16, 6763-6775.
+
+<|ref|>text<|/ref|><|det|>[[160, 508, 836, 585]]<|/det|>
+(46) DeGrave, A. J.; Bogetti, A. T.; Chong, L. T. The RED scheme: Rate-constant estimation from pre-steady state weighted ensemble simulations. The Journal of Chemical Physics 2021, 154, 114111.
+
+<|ref|>text<|/ref|><|det|>[[160, 605, 836, 738]]<|/det|>
+(47) Zhang, M. M.; Beno, B. R.; Huang, R. Y.-C.; Adhikari, J.; Deyanova, E. G.; Li, J.; Chen, G.; Gross, M. L. An Integrated Approach for Determining a Protein-Protein Binding Interface in Solution and an Evaluation of Hydrogen-Deuterium Exchange Kinetics for Adjudicating Candidate Docking Models. Anal. Chem. 2019, 91, 15709-15717.
+
+<|ref|>text<|/ref|><|det|>[[160, 759, 836, 864]]<|/det|>
+(48) Scherer, M. K.; Trendelkamp-Schroer, B.; Paul, F.; Pérez-Hernández, G.; Hoffmann, M.; Plattner, N.; Wehmeyer, C.; Prinz, J.-H.; Noé, F. PyEMMA 2: A Software Package for Estimation, Validation, and Analysis of Markov Models. Journal of Chemical Theory and Computation 2015, 11, 5525-5542.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 836, 140]]<|/det|>
+(49) Husic, B. E.; Pande, V. S. Markov state models: From an art to a science. Journal of the American Chemical Society 2018, 140, 2386-2396.
+
+<|ref|>text<|/ref|><|det|>[[160, 159, 836, 208]]<|/det|>
+(50) Molgedey, L.; Schuster, H. G. Separation of a mixture of independent signals using time delayed correlations. Phys. Rev. Lett. 1994, 72, 3634-3637.
+
+<|ref|>text<|/ref|><|det|>[[160, 228, 836, 305]]<|/det|>
+(51) Baek, K.; Krist, D. T.; Prabu, J. R.; Hill, S.; Klügel, M.; Neumaier, L.-M.; von Gronau, S.; Kleiger, G.; Schulman, B. A. NEDD8 nucleates a multivalent cullin–RING–UBE2D ubiquitin ligation assembly. Nature 2020, 578, 461-466.
+
+<|ref|>text<|/ref|><|det|>[[160, 325, 836, 402]]<|/det|>
+(52) Dagbay, K. B.; Hardy, J. A. Multiple proteolytic events in caspase-6 self-activation impact conformations of discrete structural regions. P NATL ACAD SCI USA 2017, 114, E7977-E7986.
+
+<|ref|>text<|/ref|><|det|>[[160, 421, 836, 500]]<|/det|>
+(53) Wales, T. E.; Fadgen, K. E.; Gerhardt, G. C.; Engen, J. R. High-Speed and High-Resolution UPLC Separation at Zero Degrees Celsius. AANAL BIOANAL CHEM 2008, 80, 6815-6820.
+
+<|ref|>text<|/ref|><|det|>[[160, 520, 836, 597]]<|/det|>
+(54) Hopkins, J. B.; Gillilan, R. E.; Skou, S. BioXTAS RAW: improvements to a free open-source program for small-angle X-ray scattering data reduction and analysis. J APPL CRYSTALLOGR 2017, 50, 1545-1553.
+
+<|ref|>text<|/ref|><|det|>[[160, 617, 836, 722]]<|/det|>
+(55) Maier, J. A.; Martinez, C.; Kasavajhala, K.; Wickstrom, L.; Hauser, K. E.; Simmerling, C. ff14SB: Improving the Accuracy of Protein Side Chain and Backbone Parameters from ff99SB. J CHEM THEORY COMPUT 2015, 11, 3696-3713, PMID: 26574453.
+
+<|ref|>text<|/ref|><|det|>[[160, 742, 836, 820]]<|/det|>
+(56) Zhang, B. W.; Jasnow, D.; Zuckerman, D. M. The "weighted ensemble" path sampling method is statistically exact for a broad class of stochastic processes and binning procedures. J CHEM PHYS 2010, 132, 054107.
+
+<|ref|>text<|/ref|><|det|>[[160, 841, 836, 890]]<|/det|>
+(57) Huber, G. A.; Kim, S. Weighted-ensemble Brownian dynamics simulations for protein association reactions. BIOPHYS J 1996, 70, 97-110.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 837, 140]]<|/det|>
+(58) Zuckerman, D. M.; Chong, L. T. Weighted Ensemble Simulation: Review of Methodology, Applications, and Software. ANN REV BIOPHYS 2017, 46, 43–57.
+
+<|ref|>text<|/ref|><|det|>[[160, 159, 837, 291]]<|/det|>
+(59) Zwier, M. C.; Adelman, J. L.; Kaus, J. W.; Pratt, A. J.; Wong, K. F.; Rego, N. B.; Suarez, E.; Lettieri, S.; Wang, D. W.; Grabe, M.; Zuckerman, D. M.; Chong, L. T. WESTPA: An Interoperable, Highly Scalable Software Package for Weighted Ensemble Simulation and Analysis. J CHEM THEORY COMPUT 2015, 11, 800–809.
+
+<|ref|>text<|/ref|><|det|>[[160, 313, 837, 446]]<|/det|>
+(60) Pearlman, D. A.; Case, D. A.; Caldwell, J. W.; Ross, W. S.; Cheatham III, T. E.; DeBolt, S.; Ferguson, D.; Seibel, G.; Kollman, P. AMBER, a package of computer programs for applying molecular mechanics, normal mode analysis, molecular dynamics and free energy calculations to simulate the structural and energetic properties of molecules. COMPUT PHYS COMMUN 1995, 91, 1–41.
+
+<|ref|>text<|/ref|><|det|>[[160, 467, 836, 545]]<|/det|>
+(61) Pracht, P.; Bohle, F.; Grimme, S. Automated exploration of the low-energy chemical space with fast quantum chemical methods. Phys. Chem. Chem. Phys. 2020, 22, 7169–7192.
+
+<|ref|>text<|/ref|><|det|>[[160, 565, 837, 642]]<|/det|>
+(62) Grimme, S. Exploration of Chemical Compound, Conformer, and Reaction Space with Meta-Dynamics Simulations Based on Tight-Binding Quantum Chemical Calculations. J. Chem. Theory Comput. 2019, 15, 2847–2862.
+
+<|ref|>text<|/ref|><|det|>[[160, 663, 837, 769]]<|/det|>
+(63) Bannwarth, C.; Ehlert, S.; Grimme, S. GFN2-xTB—An Accurate and Broadly Parametrized Self-Consistent Tight-Binding Quantum Chemical Method with Multipole Electrostatics and Density-Dependent Dispersion Contributions. J. Chem. Theory Comput. 2019, 15, 1652–1671.
+
+<|ref|>text<|/ref|><|det|>[[160, 789, 837, 893]]<|/det|>
+(64) Gray, J. J.; Moughon, S.; Wang, C.; Schueler-Furman, O.; Kuhlman, B.; Rohl, C. A.; Baker, D. Protein–Protein Docking with Simultaneous Optimization of Rigid-body Displacement and Side-chain Conformations. J. Mol. Biol. 2003, 331, 281–299.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[161, 90, 836, 165]]<|/det|>
+(65) Marze, N. A.; Roy Burman, S. S.; Sheffler, W.; Gray, J. J. Efficient flexible backbone protein–protein docking for challenging targets. Bioinformatics 2018, 34, 3461–3469.
+
+<|ref|>text<|/ref|><|det|>[[161, 187, 835, 236]]<|/det|>
+(66) Bussi, G. Hamiltonian replica exchange in GROMACS: a flexible implementation. MOL PHYS 2014, 112, 379–384.
+
+<|ref|>text<|/ref|><|det|>[[161, 257, 836, 333]]<|/det|>
+(67) Wang, L.; Friesner, R. A.; Berne, B. J. Replica exchange with solute scaling: a more efficient version of replica exchange with solute tempering (REST2). J PHYS CHEM B 2011, 115, 9431–9438.
+
+<|ref|>text<|/ref|><|det|>[[161, 354, 836, 430]]<|/det|>
+(68) Svergun, D.; Barberato, C.; Koch, M. H. J. CRYSOL – a Program to Evaluate X-ray Solution Scattering of Biological Macromolecules from Atomic Coordinates. J APPL CRYSTALLOGR 1995, 28, 768–773.
+
+<|ref|>text<|/ref|><|det|>[[161, 451, 836, 584]]<|/det|>
+(69) Manalastas-Cantos, K.; Konarev, P. V.; Hajizadeh, N. R.; Kikhney, A. G.; Petoukhov, M. V.; Molodenskiy, D. S.; Panjkovich, A.; Mertens, H. D. T.; Gruzinov, A.; Borges, C.; Jeffries, C. M.; Svergun, D. I.; Franke, D. ATSAS 3.0: expanded functionality and new tools for small-angle scattering data analysis. J APPL CRYSTALLOGR 2021, 54, 343–355.
+
+<|ref|>text<|/ref|><|det|>[[161, 606, 836, 682]]<|/det|>
+(70) Borreguero, J. M.; Islam, F. F.; Shrestha, U. R.; Petridis, L. idpflex: Analysis of Intrinsically Disordered Proteins by Comparing Simulations to Small Angle Scattering Experiments. Journal of Open Source Software 2018, 3.
+
+<|ref|>text<|/ref|><|det|>[[161, 704, 836, 780]]<|/det|>
+(71) Cheng, X.; Wang, H.; Grant, B.; Sine, S. M.; McCammon, J. A. Targeted molecular dynamics study of C-loop closure and channel gating in nicotinic receptors. PLoS computational biology 2006, 2, e134.
+
+<|ref|>text<|/ref|><|det|>[[161, 802, 836, 877]]<|/det|>
+(72) Edmondson, S. D.; Yang, B.; Fallan, C. Proteolysis Targeting Chimeras (PROTACs) in ‘Beyond Rule-of-Five’ Chemical Space: Recent Progress and Future Challenges. BIOORG MED CHEM LETT 2019, 29, 1555–1564.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[160, 90, 838, 167]]<|/det|>
+(73) Comer, J.; Gumbart, J. C.; Hénin, J.; Lelièvre, T.; Pohorille, A.; Chipot, C. The adaptive biasing force method: Everything you always wanted to know but were afraid to ask. The Journal of Physical Chemistry B 2015, 119, 1129–1151.
+
+<|ref|>text<|/ref|><|det|>[[160, 187, 838, 264]]<|/det|>
+(74) Lesage, A.; Lelièvre, T.; Stoltz, G.; Hénin, J. Smoothed biasing forces yield unbiased free energies with the extended-system adaptive biasing force method. The Journal of Physical Chemistry B 2017, 121, 3676–3685.
+
+<|ref|>text<|/ref|><|det|>[[160, 285, 838, 362]]<|/det|>
+(75) Fu, H.; Zhang, H.; Chen, H.; Shao, X.; Chipot, C.; Cai, W. Zooming across the free-energy landscape: shaving barriers, and flooding valleys. The journal of physical chemistry letters 2018, 9, 4738–4745.
+
+<|ref|>text<|/ref|><|det|>[[160, 382, 838, 430]]<|/det|>
+(76) Fu, H.; Shao, X.; Cai, W.; Chipot, C. Taming rugged free energy landscapes using an average force. Accounts of chemical research 2019, 52, 3254–3264.
+
+<|ref|>text<|/ref|><|det|>[[160, 450, 838, 555]]<|/det|>
+(77) Eastman, P.; Swails, J.; Chodera, J. D.; McGibbon, R. T.; Zhao, Y.; Beauchamp, K. A.; Wang, L.-P.; Simmonett, A. C.; Harrigan, M. P.; Stern, C. D., et al. OpenMM 7: Rapid development of high performance algorithms for molecular dynamics. PLoS computational biology 2017, 13, e1005659.
+
+<|ref|>text<|/ref|><|det|>[[160, 577, 836, 625]]<|/det|>
+(78) Bonomi, M. Promoting transparency and reproducibility in enhanced molecular simulations. Nature methods 2019, 16, 670–673.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 410, 177]]<|/det|>
+ternarycomplexpredictionsicompr.pdf protacnrreportingsummary2. pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/images_list.json b/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..21f8bba976cc6965d530c3d6f3409449553fb9bc
--- /dev/null
+++ b/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/images_list.json
@@ -0,0 +1,77 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1: Scalable production of UFPFs. a Schematic of the good solvent exchange strategy to prepare UFPFs in a modified wet spinning protocol. In the case of poor solvent exchange (light orange region, upper panel), PANi molecules are rapidly solidified into thick gels and protofibres with rough crystallized particles. In the case of good solvent exchange (light blue region, lower panel), the formed gels with low viscosity occur an impressive gel extension and are slenderized into ultrafine fibres. b Schematic of the modified wet spinning process. c Scanning electron microscope (SEM) image of the marked region in b, showing the sharp necking behavior of gel PANi fibres. The close observation to region 1 (d), region 2 (e), and region 3 (f) in the marked zone of c, illustrating the sharply necking process of PANi gels. g Photograph of a 5.4-kilometres-long UFPF collected in two hours. Scale bars: c 20 μm, d 2 μm, e 10 μm, g 150 mm.",
+ "footnote": [],
+ "bbox": [
+ [
+ 152,
+ 85,
+ 848,
+ 617
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2: Mechanism and mechanical properties of UFPPs. a SEM images of the PAni fibres produced in different solvating species. Specifically, the upper four panels showing the fibres prepared from poor solvents, and the lower two panels showing the fibres fabricated from good solvents. b Raman spectra of PAni fibres after placing in air for four weeks. c The diffusivity from PAni dispersions (in m-cresol) to various solvating species. d The viscosity of PAni gels formed in various solvating species. e Mechanics simulation results of extension behaviors of PAni gel fibres at different interfacial pressure. f Typical tensile stress-strain curves of UFPPs. g Ashby plot comparing the mechanical strength of UFPPs to previously reported CPFs. Scale bars in a: Water, Ethanol, EA, Acetone \\(20\\mu \\mathrm{m}\\) (left) \\(10\\mu \\mathrm{m}\\) (right); NMP \\(20\\mu \\mathrm{m}\\) (left) \\(5\\mu \\mathrm{m}\\) (right), DMF \\(20\\mu \\mathrm{m}\\) (left) \\(2\\mu \\mathrm{m}\\) (right).",
+ "footnote": [],
+ "bbox": [
+ [
+ 157,
+ 90,
+ 849,
+ 455
+ ]
+ ],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig. 3: Energy and charge storage capacities of UFPFs. a Schematic of a micro capacitor constructed using two UFPF electrodes on a substrate. b Cyclic voltammetry curves with the increasing scan rates from 10 to 20, 50, 80 and \\(100\\mathrm{mV}\\mathrm{s}^{-1}\\) . c Galvanostatic charge/discharge curves at various current densities increasing from 0.32 to 0.63, 1.59 and \\(3.18\\mathrm{mA}\\mathrm{cm}^{-2}\\) . d The area capacitance of UFPFs comparing to previous reported electrodes. e Cycle galvanostatic charge/discharge curves during 120 cycles between 0 and \\(0.6\\mathrm{V}\\) at \\(1.59\\mathrm{mA}\\mathrm{cm}^{-2}\\) . f. The relationship between current and voltage at a slow rate of \\(10\\mathrm{mV}\\mathrm{s}^{-1}\\) . g The charge storage capacity of UFPFs comparing to other charge storage materials.",
+ "footnote": [],
+ "bbox": [
+ [
+ 150,
+ 90,
+ 850,
+ 451
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4: Demonstration and characterization of all-solid organic electrochemical transistor based on UFPFs. a Schematic of the all-solid OECT composed of three polymer layers, one silver wire as the gate electrode, and one UFPF as the drain-source channel. b Cross-section SEM image and schematic of OECT. The yellow break lines direct the charge flow along the fibre chains (green solid lines). c Transmittance of the OECT in the region of visible light. A typical output curve (d), transfer curve (e), and power consumption in operation (f) of OECT. Scale bars: b 20 μm.",
+ "footnote": [],
+ "bbox": [
+ [
+ 156,
+ 85,
+ 848,
+ 547
+ ]
+ ],
+ "page_idx": 11
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Fig. 5: Electrical response of the all-solid OECT to mechanical deformations. a Schematic of the mechanism explaining the response to the action of external pressure. b Relative drain-source change \\((\\Delta \\mathrm{I}_{\\mathrm{DS}} / \\mathrm{I}_{\\mathrm{DS0}})\\) and sensitivity as a function of pressure. c Response time of the all-solid OECT when pressing (rising edge) and releasing (falling part) under the instantaneous pressure of 17.8 KPa. d Cyclic response at three different pressure levels (0.92, 6.8, and 22.2 KPa). e, Schematic of the working principle of the response to friction. f Cyclic response at three different frictions (1.84, 4.69, and 5.55 KPa). g An enlarged curve of the marked part in (f). h Cyclic response at different friction speeds from 4, 6, 8, 10, 15, to \\(20\\mathrm{mm}\\mathrm{s}^{-1}\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 151,
+ 85,
+ 841,
+ 402
+ ]
+ ],
+ "page_idx": 13
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e.mmd b/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..0b5b8f9cc6a02cbbbbd6c7dfe63ae11ccaa0742b
--- /dev/null
+++ b/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e.mmd
@@ -0,0 +1,258 @@
+
+# Scalable production of ultrafine polyaniline fibres for tactile organic electrochemical transistors
+
+Bo Fang Hong Kong Polytechnic University
+
+Jianmin Yan Hong Kong Polytechnic University
+
+Dan Chang Zhejiang University
+
+Jinli Piao Hong Kong Polytechnic University
+
+Kit Ming Ma Hong Kong Polytechnic University
+
+Qiao Du Hong Kong University of Science and Technology
+
+Ping Gao Hong Kong University of Science and Technology
+
+Yang Chai Hong Kong Polytechnic University https://orcid.org/0000- 0002- 8943- 0861
+
+Xiaoming Tao ( \(\boxed{\times}\) xiao- ming.tao@polyu.edu.hk) Hong Kong Polytechnic University https://orcid.org/0000- 0002- 2406- 0695
+
+## Article
+
+# Keywords:
+
+Posted Date: December 8th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 1126903/v1
+
+License: \(\circledcirc\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on April 19th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 29773- 9.
+
+<--- Page Split --->
+
+# Scalable production of ultrafine polyaniline fibres for tactile organic electrochemical transistors
+
+Bo Fang1,2, Jianmin Yan1,3, Dan Chang4, Jinli Piao1,2, Kit Ming Ma1,2, Qiao Gu5, Ping Gao5, Yang Chai1,3\* Xiaoming Tao1,2\*
+
+1Research Institute for Intelligent Wearable Systems, Hong Kong Polytechnic University, Hong Kong, 999077 China
+
+2Institute of Textiles and Clothing, Hong Kong Polytechnic University, Hong Kong, 999077 China
+
+3Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong, 999077 China
+
+4Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027 China
+
+5Department of Chemical and Biological Engineering, The Hong Kong University of Science and Technology, Hong Kong, 999077 China
+
+Email: ychai@polyu.edu.hk; xiao- ming.tao@polyu.edu.hk
+
+The development of continuous conducting polymer fibres is essential for applications ranging from advanced fibrous devices to frontier fabric electronics. The use of continuous conducting polymer fibres requires a small diameter to maximize their electroactive surfaces, microstructural orientations, and mechanical strengths. However, regularly used wet spinning techniques have rarely achieved this goal due primarily to the insufficient slenderization of rapidly solidified conducting polymer molecules in poor solvents. Here we report a good solvent exchange strategy to wet spin the ultrafine polyaniline fibres at the large scale. The slow diffusion between good solvents distinctly decreases the viscosity of gel protofibers, which undergo an impressive drawing ratio. The continuously collected polyaniline fibres have a previously unattained diameter below \(5 \mu \mathrm{m}\) , high energy and charge storage capacities, and favorable mechanical performance. We demonstrated an ultrathin all- solid organic electrochemical transistor based
+
+<--- Page Split --->
+
+on ultrafine polyaniline fibres, which substantially amplified microampere drain- source electrical signals with less one volt driving voltage and effectively operated as a tactile sensor detecting pressure and friction forces at different levels. The aggressive electronical and electrochemical merits of ultrafine polyaniline fibres and their great potentials to prepare on industrial scale offer new opportunities for high- performance soft electronics and large- area electronic textiles.
+
+The extended conjugated and easily doped \(\pi\) - system along the backbone enables conducting polymers to possess intriguing transport, optical, and electrochemical properties, which have rarely been found in conventional polymers and metal conductors \(^{1 - 3}\) . Processing conducting polymers into macroscopically fibrous materials makes it possible to translate their nano- object features to human- friendly products in a continuous manner. The combined merits, including but not limited to mechanical flexibility, intrinsic conductivity, and electrochemical activity, of conducting polymer fibres (CPFs) have introduced a new era of “electronic textiles” \(^{4}\) . For instance, highly conductive and electrochemically active poly(3- methylthiophene) fibres have been achieved by in situ electrochemical oxidation of monomers \(^{5}\) . Fast ion transport between CPFs and ionic liquids has given birth to long- term operation actuators, electrochromic windows, and numeric displays \(^{6}\) . In recent studies, the wet- spun poly (3,4- ethylene dioxythiophene) (PEDOT) fibres have been widely used in various frontier fields, such as flexible energy storage electrodes, implantable bioelectronics, and organic transistors \(^{7,8}\) .
+
+Unfortunately, due primarily to the large diameters, the performance and expectations of most achieved continuous CPFs have been limited by their insufficient electroactive surfaces and weak breaking strengths. Electropinning and wet spinning are two mainstream strategies to produce continuous CPFs. In the case of electrospinning, the fairly rigid backbone due to the high aromaticity results into an insufficient elasticity of conducting polymer solutions, which fails to be solely electrospun into fine fibres \(^{9}\) . Although a two- fluid electrospinning technique has been proposed by coating a soluble and electrospinable fluid on the conducting polymer cores, the complex procedures
+
+<--- Page Split --->
+
+involving the addition and removal of second components defy the mass production of electrospun CPFs10,11. In the case of conventional wet spinning, conducting polymer dopes tend to occur a transient solidification in poor solvents, induced by the strong interactions of conducting polymer chains. The rapidly hardened gels suppress the post- stretching and slenderizing procedures, and cause the wet- spun CPFs to show a large diameter, generally beyond \(10 \mu \mathrm{m}^{12 - 14}\) . The large diameters largely discount the mechanical properties and electrochemical activities of CPFs4,15. Thus, there is an urgent need to realize the mass production of ultrafine CPFs, which remains challenging. In this work, we report a good solvent exchange strategy in a modified wet spinning technique to prepare the ultrafine polyaniline (PAni) fibres (UFPFs) at the large scale. Beyond conventional wet spinning protocol, we replaced poor solvents by good solvents as the coagulation bath to decrease the viscosity of gel protofibres, which were subject to an ultrahigh drawing ratio and reduced to an ultrafine morphology. The obtained UFPFs own a small diameter below \(5 \mu \mathrm{m}\) , an unprecedented mechanical strength of \(1080 \pm 71 \mathrm{MPa}\) , a high area capacitance beyond \(1008 \mathrm{mF} \mathrm{cm}^{- 2}\) , and an enormous charge storage capacity of \(5.25 \times 10^{4} \mathrm{mC} \mathrm{cm}^{- 2}\) . Based on the structural and electrochemical merits of UFPFs, we demonstrated an ultrathin all- solid organic electrochemical transistor (OECT) with less one volt driving voltage, which substantially amplified drain- source electrical signals with a low power- consumption and responded to vertical pressure and horizontal friction forces at different levels. Our work opens an avenue to prepare continuous ultrafine CPFs and high- performance soft electronics.
+
+<--- Page Split --->
+
+
+Fig. 1: Scalable production of UFPFs. a Schematic of the good solvent exchange strategy to prepare UFPFs in a modified wet spinning protocol. In the case of poor solvent exchange (light orange region, upper panel), PANi molecules are rapidly solidified into thick gels and protofibres with rough crystallized particles. In the case of good solvent exchange (light blue region, lower panel), the formed gels with low viscosity occur an impressive gel extension and are slenderized into ultrafine fibres. b Schematic of the modified wet spinning process. c Scanning electron microscope (SEM) image of the marked region in b, showing the sharp necking behavior of gel PANi fibres. The close observation to region 1 (d), region 2 (e), and region 3 (f) in the marked zone of c, illustrating the sharply necking process of PANi gels. g Photograph of a 5.4-kilometres-long UFPF collected in two hours. Scale bars: c 20 μm, d 2 μm, e 10 μm, g 150 mm.
+
+<--- Page Split --->
+
+## Results
+
+Preparation and characterization of UFPFs. In the modified one- step wet spinning process, we used good solvents as the coagulation bath to realize the mass production of UFPFs (Fig. 1a- b and Supplementary Fig. 1). After doping PANi power (emeraldine base) with camphor sulfonic acid (CSA) at a molar ratio of 2:1, we dispersed fully doped PANi into m- cresol as the raw spinning dopes (see the Methods section) \(^{16}\) . Significantly, the direct use of doped PANi solutions as the dopes saves the trouble of conventional post- doping procedures, and further permits the uniform charge distribution throughout the fibre length \(^{17}\) . A good solvent, dimethyl formamide (DMF), of PANi operated as the coagulation bath. A slow solvent exchange between m- cresol and DMF facilitated the formation of PANi gel protofibres with a quite low viscosity below 3000 cP. Subsequently, we observed a sharp decrease of diameter from \(\sim 0.1 \mathrm{mm}\) to \(\sim 4.7 \mu \mathrm{m}\) when stretching the gel fibres in bath (Fig. 1c- f), which, to our knowledge, is a record small value in the achieved wet- spun CPFs \(^{4}\) . The ultrafine fibre shows a smooth surface (Fig. 1f and Supplementary Fig. 2) and highly crystallized microstructures (Supplementary Fig.3). Moreover, such an impressive drawing ratio enables a very high production efficiency of UFPFs beyond 40 meters per minute. For example, we prepared a 5.4- kilometres- long UFPF in two hours (Fig. 1e).
+
+<--- Page Split --->
+
+
+Fig. 2: Mechanism and mechanical properties of UFPPs. a SEM images of the PAni fibres produced in different solvating species. Specifically, the upper four panels showing the fibres prepared from poor solvents, and the lower two panels showing the fibres fabricated from good solvents. b Raman spectra of PAni fibres after placing in air for four weeks. c The diffusivity from PAni dispersions (in m-cresol) to various solvating species. d The viscosity of PAni gels formed in various solvating species. e Mechanics simulation results of extension behaviors of PAni gel fibres at different interfacial pressure. f Typical tensile stress-strain curves of UFPPs. g Ashby plot comparing the mechanical strength of UFPPs to previously reported CPFs. Scale bars in a: Water, Ethanol, EA, Acetone \(20\mu \mathrm{m}\) (left) \(10\mu \mathrm{m}\) (right); NMP \(20\mu \mathrm{m}\) (left) \(5\mu \mathrm{m}\) (right), DMF \(20\mu \mathrm{m}\) (left) \(2\mu \mathrm{m}\) (right).
+
+The sharp necking behaviors of gel protofibres are highly related to the use of good solvents as the coagulation bath. We recorded the evolution of surface morphologies of PAni fibres collected from different solvating species. As shown in Fig. 2a, the obtained fibres in poor solvating species, i.e., water, ethanol, ethyl acetate (EA), and acetone, generally present coarse surfaces and large diameters around \(20\mu \mathrm{m}\) . By comparison,
+
+<--- Page Split --->
+
+we clearly observed a necking phenomenon in both cases of good solvents, i.e., N- methyl- 2- pyrrolidone (NMP) and DMF. Such necking effects promoted the finally produced fibres to behave ultrafine morphologies, which assists PAni fibres to behave better structure and performance stabilities due to the higher degree of orientation and crystallization (see the X- ray diffraction analysis in Supplementary Fig. 3). We used Raman spectra to evaluate their structural evolution after placing fibres in air for four weeks. As shown in Fig. 2b, we did not find obvious de- doping signals in Raman spectra of the PAni fibres from good solvents, whereas various de- doping peaks (1223 \(\mathrm{cm^{- 1}}\) and \(1462\mathrm{cm^{- 1}}\) ) appeared in the cases of poor solvents.
+
+We speculate that this sharp necking phenomenon may be caused by two factors: diffusion difference and interfacial pressure. In the conventional wet spinning protocol, the diffusion from good solvents to poor solvents occurs quickly to solidify dope fluids into gel fibres18,19. The rapid diffusion could be aggravated in the system of conducting polymers due to the strong interactions of rigid chains. Thus, PAni molecules tend to bond into irregularly crystallized particles prior to undergoing extensive drawing, as present in the upper panels of Fig. 1a. In previous reports using poor solvents as coagulation bath, although CPFs with a smooth surface could be collected by enhanced shear flow and strong stretching12,14, diameters are unable to be decreased to the ideal level due to the insufficient stretching slenderization of solidified gels. In contrast, the diffusion from dope fluids to good solvents is quite slow. Such slow diffusion allows the formation of fibrous gels with a low viscosity and the following high drawing ratios. Note that most conventional polymers are incapable of gelling in good solvents due to the poor chain interactions20,21.
+
+We calculated the diffusivities between various solvents and measured the viscosity of corresponding formed gels to support our explanations. The diffusivity from A molecules to B molecules, \(D_{AB}^{0}\) , is determined by the equation
+
+\[\frac{D_{AB}^{0}\mu_{B}}{T} = 8.52\times 10^{-8}V_{bB}^{-1 / 3}\left[1.40\left(\frac{V_{bB}}{V_{bA}}\right)^{1 / 3} + \frac{V_{bB}}{V_{bA}}\right]\]
+
+<--- Page Split --->
+
+, where \(\mu_{B}\) is the solvent viscosity, T is the temperature, and \(V_{b}\) is the molar volume of solvent at its normal boiling temperature \(^{22}\) . As displayed in Fig. 2c, the diffusivities from m- cresol to DMF \((7.5\times 10^{- 6} \mathrm{cm}^{2}\mathrm{s}^{- 1})\) and NMP \((7.71\times 10^{- 6} \mathrm{cm}^{2}\mathrm{s}^{- 1}\) ) are generally lower than that of poor solvents. Diffusion in bath further dominates the viscosity of protofibres. To monitor the viscosity of gel fibres in practical conditions, we conducted the viscometer tests at a low revolution (e.g., 10 Rev.). As summarized in Fig. 2d, the formed PANi gels in good solvents show a viscosity below \(3000\mathrm{cP}\) , much lower than that of poor solvents ( \(>4000\mathrm{cP}\) ). The established solvating specific- diffusivity- viscosity formula accords well with our proposed explanations.
+
+Interfacial pressure during solvent exchange is another major factor relating to the necking behavior of PANi protofibres. In a two fluid system, the interfacial pressure between two kind of solvents is inclined to decrease with the improved solvent diffusion \(^{23}\) . Based on the slow diffusion from m- cresol to good solvents (Fig. 2c), the interfacial pressure between gel fibres and coagulation bath is considerable, which further induces the necking of protofibres. To understand this, we conducted a mechanic simulation to the stretching behavior of gel fibres at different interfacial pressure (see the progressive results in Supplementary Fig.4 and Method section). According to the simulation results in Fig. 2e, the higher interfacial pressure drives gel fibres to occur the sharper necking and thinning effects at a given tensile stress. This probably explains the formation of UFPFs in DMF bath.
+
+UFPFs show impressive mechanical performance. Different from that of conventional polymer fibres, the typical linear strain- stress curves of UFPFs demonstrate a brittle fracture behavior with a small tensile strain of \(3.67\pm 0.64\%\) (Fig. 2f). It is reasonable if considering the rigid backbone of PANi chains, which likely gather and condense into fragile fibrous assemblies after undergoing strong shear flow in spinning microtubes. According to classical Griffith theory on brittle fracture, fibres' strength generally improves with the decrease of diameter due to the depressed structural defects \(^{24}\) . We compared the mechanical performance of UFPFs with previously reported CPFs.
+
+<--- Page Split --->
+
+
+Fig. 3: Energy and charge storage capacities of UFPFs. a Schematic of a micro capacitor constructed using two UFPF electrodes on a substrate. b Cyclic voltammetry curves with the increasing scan rates from 10 to 20, 50, 80 and \(100\mathrm{mV}\mathrm{s}^{-1}\) . c Galvanostatic charge/discharge curves at various current densities increasing from 0.32 to 0.63, 1.59 and \(3.18\mathrm{mA}\mathrm{cm}^{-2}\) . d The area capacitance of UFPFs comparing to previous reported electrodes. e Cycle galvanostatic charge/discharge curves during 120 cycles between 0 and \(0.6\mathrm{V}\) at \(1.59\mathrm{mA}\mathrm{cm}^{-2}\) . f. The relationship between current and voltage at a slow rate of \(10\mathrm{mV}\mathrm{s}^{-1}\) . g The charge storage capacity of UFPFs comparing to other charge storage materials.
+
+Derived from the strain- stress curves, we concluded that UFPFs have a modulus of \(29.89 \pm 5.6\%\) GPa, and a strength of \(1080 \pm 71\) MPa, at least one order of magnitude higher than that of CPFs with larger diameters (Fig. 2g), mainly including PEDOT fibres (<450 MPa) \(^{7,25 - 29}\) and PAni fibres (<400 MPa) \(^{30 - 33}\) .
+
+Energy and charge storage capacities. Ultrafine morphology optimizes the
+
+<--- Page Split --->
+
+electroactive surfaces, which enables UFPFs to exhibit superb energy and charge storage capacities. To evaluate the electrochemical activity of UFPFs, we constructed a micro capacitor using polyvinyl alcohol (PVA)- \(\mathrm{H}_3\mathrm{PO}_4\) gel electrolyte and two UFPF electrodes (Fig. 3a). The electrochemical properties were checked by cyclic voltammetry (CV) and galvanostatic charge- discharge (GCD) measurements. At different scan rates, the nearly rectangular shape of CV curves and instantaneous current response to voltage reversal at each end potential suggest the good electrochemical activity of UFPFs34 (Fig. 3b). The nearly triangular shape of GCD curves at different current densities illustrates the formation of efficient electric double layers and charge propagation across the UFPF electrodes35 (Fig. 3c). According to the GCD results, we determined the electrochemical properties of UFPFs. Among of them, the area capacitance, \(\mathrm{C_A}\) , is between 1008 and 1666 mF cm- 2 at the current densities between 0.32 and 3.18 mA cm- 2, outperforming previously reported thick CPFs29 and other electrodes, such as carbon nanomaterials3434,36, metal oxides37 and conducting polymers38- 41, and approaching to that of PANi nanowires42 (Fig. 3d). The volumetric capacitance, power density and energy density reach 83.8 F cm- 3, 0.96 W cm- 3 and 4.19 mWh cm- 3, respectively (Supplementary Fig. 5). In lifetime tests of UFPF- based capacitor, both the potential and capacitance continued without significant decrease for 120 charge/discharge cycles at a low current density of 1.59 mA cm- 2, indicating the reliable electrochemical performance stability of UFPFs (Fig. 3e).
+
+We were able to confirm the amount of transported charge per unit area to UFPF during the charge/discharge cycle. The charge during a triangular wave potential between - 0.9 V and 1.0 V (water window, see the Supplementary Fig. 6) was calculated by integrating the measured current with respect to the time of period at a low scan rate of 10 mV s- 1 (Fig. 3f)6. We determined that the charge storage capacity of UFPF was \(5.25 \times 10^{4}\) mC cm- 2, a value at least two orders of magnitude higher than that of noble metals43, carbon bulk44 - 46 and previously reported conducting polymers47 (Fig. 3g). This value decreases slightly to \(2.015 \times 10^{4}\) mC cm- 2 at a tenfold scan rate of 100 mV s- 1 (Supplementary Fig. 7).
+
+<--- Page Split --->
+
+
+Fig. 4: Demonstration and characterization of all-solid organic electrochemical transistor based on UFPFs. a Schematic of the all-solid OECT composed of three polymer layers, one silver wire as the gate electrode, and one UFPF as the drain-source channel. b Cross-section SEM image and schematic of OECT. The yellow break lines direct the charge flow along the fibre chains (green solid lines). c Transmittance of the OECT in the region of visible light. A typical output curve (d), transfer curve (e), and power consumption in operation (f) of OECT. Scale bars: b 20 μm.
+
+Structure and performance of all- solid OECT. Benefitting from the favorable energy and charge storage performance of UFPFs, we demonstrated a high- performance all- solid OECT. OECT amplifies drain- source current intensities at low operating voltages by ion penetration into the organic mixed ionic- electronic conductors, i.e., conducting
+
+<--- Page Split --->
+
+polymers48,49. This process is controlled by the gate bias, and, to date, has generally conducted in aqueous electrolytes. To preclude the interference of external environment, we promoted the working conditions of OECT from aqueous environments to all- solid state by using gel electrolytes as the ion matrix. As shown in Fig. 4a- b, our OECT is mainly constructed by three polymer layers. The upper layer is the cured polyurethane (PU) working as the dielectric coating and also protecting the device from the invasion of external action50. A fibrous silver gate electrode with a diameter of \(7 \mu \mathrm{m}\) is fixed in PU. Since UFPFs have demonstrated reliable electrochemical activities in PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel, we used PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel as the middle layer to inject ions to or uptake ions from the drain- source channel materials. A UFPF right below the silver gate is fused in the ion gel, and operates as the channel material. The bottom layer is also pure PU acting as the supporter of the whole device. Due to the remarkable flexibility and transparency of PVA and PU, the all- solid OECT is very soft, and shows a transmittance beyond \(80\%\) in the region of visible light (Fig. 4c), and a small thickness below \(300 \mu \mathrm{m}\) .
+
+Despite the long channel length ( \(\sim 0.48 \mathrm{cm}\) ), much larger than of conventional micrometer- scale device, the all- solid OECT showed favorable amplification performance with a high on- off current ratio ( \(>10^3\) , Fig. 4e) at low voltages ( \(< 1 \mathrm{V}\) , Fig. 4d). The relatively fair transconductance ( \(\mathrm{g}_{\mathrm{m}} < 60 \mu \mathrm{S}\) ) is probably ascribed to the small cross- sectional area, which dramatically magnifies the resistance of fibrillar channel. Note that the all- solid OECT is an energy saving device with extremely low power consumptions. For example, at a given drain- source voltage of \(0.6 \mathrm{V}\) , the consumed power is below \(18 \mu \mathrm{W}\) (Fig. 4f).
+
+<--- Page Split --->
+
+
+Fig. 5: Electrical response of the all-solid OECT to mechanical deformations. a Schematic of the mechanism explaining the response to the action of external pressure. b Relative drain-source change \((\Delta \mathrm{I}_{\mathrm{DS}} / \mathrm{I}_{\mathrm{DS0}})\) and sensitivity as a function of pressure. c Response time of the all-solid OECT when pressing (rising edge) and releasing (falling part) under the instantaneous pressure of 17.8 KPa. d Cyclic response at three different pressure levels (0.92, 6.8, and 22.2 KPa). e, Schematic of the working principle of the response to friction. f Cyclic response at three different frictions (1.84, 4.69, and 5.55 KPa). g An enlarged curve of the marked part in (f). h Cyclic response at different friction speeds from 4, 6, 8, 10, 15, to \(20\mathrm{mm}\mathrm{s}^{-1}\) .
+
+We proved that the all- solid OECT functioned to amplify small electrical signals in gel environments and respond to mechanical deformation as a tactile sensor. As illustrated in Fig. 5a, the applied vertical pressure on the surface of the all- solid OECT adjusted the ion penetration due to the improved gate- source electric field and the redistribution of intrinsic capacitance51. At a \(\mathrm{V}_{\mathrm{G}}\) of - 0.1 V and a \(\mathrm{V}_{\mathrm{D}}\) of 0.35 V, we observed a stable increase of drain- source current, \(\mathrm{I}_{\mathrm{DS}}\) , with the increasing pressure, up to a 92% amplification from 0 to 40 KPa (Fig. 5b). The sensitivity is at the level of 0.01- 0.1 KPa1 in this process (dark cyan dots in Fig. 5b). As shown in Fig. 5c, the average rising time and falling time under instantaneous pressure of 17.8 KPa is \(\sim 536\) ms and \(\sim 698\) ms,
+
+<--- Page Split --->
+
+respectively. Such integrated parameters facilitated the all- solid OECT to respond to different pressure levels from 0.92 to \(22.2\mathrm{KPa}\) (Fig. 5d). In addition to the response to pressure at the vertical direction, the all- solid OECT also reacted to friction at the horizontal direction (Fig. 5e and Supplementary Fig. 8). The forward and backward friction of a load on the surface changed the real- time distance between silver gate and UFPP channel repeatedly, thus producing a bimodal response curve (Fig. 5g). Note that, to enable the enlargement of \(\mathrm{I_{DS}}\) with the increasing gate- channel distance under the repeated friction, we applied a positive \(\mathrm{V_G}\) of \(0.1\mathrm{V}\) at a \(\mathrm{V_D}\) of \(0.55\mathrm{V}\) . The all- solid OECT responded stably to friction at different magnitudes (Fig. 5f, from 1.84 to 5.55 \(\mathrm{KPa}\) ) and different speeds (Fig. 5h, from 4 to \(20\mathrm{mm}\mathrm{s}^{- 1}\) ) during our cyclic tests. For example, \(\mathrm{I_{DS}}\) increased \(\sim 86\%\) at \(5.55\mathrm{KPa}\) .
+
+## Discussion
+
+The past decades have witnessed great achievements in preparing high- performance CPFs, which made a vast difference to the rapid development of advanced electronics. However, due to the limitations of both technology and strategy, it is still difficult to produce ultrafine CPFs at the large scale. We proposed a good solvents strategy in a modified wet spinning technology. With a principle of diffusion- controlled slow gelation of protofibres, the new system successfully downsized the diameter of PANi fibres to below \(5\mu \mathrm{m}\) , a value smaller than that of most previous work. Furthermore, the ultrafine morphology with highly improved electroactive surfaces promotes UFPPs to behave superb electrochemical activities and mechanical performance.
+
+It is of great importance to realize the mass production of ultrafine CPFs. We constructed an all- solid OECT to employ the impressive energy and charge storage capacities of UFPPs. A handful of fibres are robust enough to satisfy the operation as the tactile sensor. In view of the ability to produce on the industrial scale, UFPPs are promised to be extended to large- area electronics, such as textile- scale numeric displays, soft electrochromic windows, and wearable energy harvesting systems.
+
+<--- Page Split --->
+
+## Methods
+
+Characteristics. All the SEM images were collected on a tungsten thermionic emission SEM system (the Tescan VEGA3). XRD spectra were obtained from XRD system (Rigaku SmartLab) equipped with \(9\mathrm{kW}\) rotating anode X- ray source ( \(\lambda \sim 1.54\mathrm{\AA}\) ) coupling with high- quality semiconductor detector that supports 0D, 1D or 2D x- ray diffraction measurement. Raman spectra were recorded from Renishaw Micro- Raman Spectroscopy system fully integrated with confocal microscope spectrometer and a \(785\mathrm{nm}\) laser source. Mechanical tests were conducted on an advanced rheometric expansion system at the Hong Kong University of Science and Technology. All the electrochemical tests were processed on an electrochemical workstation (VersaSTAT3). The measurements of OECT were conducted on probe station (Micromanipulator) with Keithley 4200A- SCS parameter analyzer.
+
+The fabrication of UFPFs. PAni power (emeraldine base, purchased from Sigma- Aldrich) was mixed with CSA at a molar ratio of 2:1. After being milled for 15 minutes, the uniform doped PAni was dispersed in m- cresol (after degassing) at a concentration of \(0.05\mathrm{gmL^{- 1}}\) . The dispersions were used as spinning dopes after blending in air for 8 hours, and extruded through a PEEK microtube with an inner diameter of \(100\mu \mathrm{m}\) at a rate of \(1\mathrm{mL}\mathrm{min}^{- 1}\) . Coagulation bath was chosen according to the experimental requirements. PAni fibres were directly drawn out from bath and collected on a graphite roller continuously.
+
+Numerical method. The experimental result is verified by numerical method using commercial software ANSYS. The simulation is performed using workbench 18.0. In the simplified computational model, a geometric model of gel tube is developed, in which the ratio of diameter to length is chosen as 1:18, and the mechanical properties, density, Young's modulus and Poisson's ratio are selected as \(300\mathrm{kg / m3}\) , \(1000\mathrm{Pa}\) and 0.01, respectively. For the boundary conditions, one end of the gel model set as fixed support, and another end applies extend displacement to mimic the stretching effect in the actual situation. Meanwhile, the corresponding pressure is applied on the outer surface of the gel model to account for the function of the impressive interfacial pressure on the surface of gel fibres. To ensure the convergence of the result, a grid independence test is conducted by refining mesh size sequentially, and the finite element mesh with 162641 nodes and 37128 hexahedral elements are adopted finally.
+
+The fabrication of micro capacitor. Micro capacitor composed of two UFPF electrodes and the
+
+<--- Page Split --->
+
+gel electrolyte was constructed on a glass substrate. To prepare the gel electrolyte, PVA power was dispersed into deionized water at a mass ratio of 9:1. PVA was dissolved after being heated for 5 hours at \(85^{\circ}\mathrm{C}\) . Then phosphoric acid was added at a mass ratio of 1:10 with deionized water. The mixture cooled at room temperature and were ready for use. Two UFPFs were placed in parallel on the glass slide. The transparent PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel was dropped between UFPFs. Two cooper wires connected to the UPPFs with silver paste worked as the conductor lines. After condensing for 10 minutes at \(40^{\circ}\mathrm{C}\) , the whole device was subject to electrochemical tests.
+
+The fabrication of all- solid OECT. The OECT was built from three layers: two PU layers and one ion gel layer. PU dispersion in DMF was casted on a PVDF substrate. After being treated in oven at \(60^{\circ}\mathrm{C}\) , a thin and transparent layer of pure PU was obtained. One drop of PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel electrolyte was added on the surface of solidified PU. An UFPF was immersed into gel. After been dried at \(45^{\circ}\mathrm{C}\) for 15 minutes, a UFPF channel locked in PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel was obtained. Afterwards, another drop of PU was added and a silver wire operation as the gate electrode was putted in PU at the liquid state. After being dried at \(60^{\circ}\mathrm{C}\) , an all- solid OECT was prepared. Note that all the three electrodes were connected to cooper electrodes for following measurements.
+
+## Data availability
+
+The data that support the findings of this study are available from the corresponding author upon reasonable request. Correspondence and requests for materials should be addressed to Y.C. and X.T.
+
+## Acknowledgements
+
+This work is supported by the Research Grants Council of Hong Kong (No. 15201419), Hong Kong Polytechnic University Postdoctoral Fellowship and Endowed Professorship Fund (No. 847A).
+
+## Author contributions
+
+X. T. supervised this study. B. F. designed and conducted the main experiments. J. Y., Y. C. and B. F. constructed and characterized the transistor. D. C. helped to build the wet spinning equipment and discussed the results. J. P. did the mechanic simulations. K. M. M. helped to draw a part of schematics. Q. G. and P. G. helped to conduct the mechanical tests. B.F., X. T. and Y. C. wrote the manuscript.
+
+## Competing interests
+
+The authors declare no competing interests.
+
+## References
+
+<--- Page Split --->
+
+1. Sariciftci, N. S., Smilowitz, L., Heeger, A. J. & Wudl, F. Photoinduced electron transfer from a conducting polymer to buckminsterfullerene. Science 258, 1474-1476 (1992).
+2. Frommer, J. E. Conducting polymer solutions. Acc. Chem. Res. 19, 2-9 (1986).
+3. Shi, G., Jin, S., Xue, G. & Li, C. A conducting polymer film stronger than aluminum. Science 267, 994-996 (1995).
+4. Mirabedini, A., Foroughi, J. & Wallace, G. G. Developments in conducting polymer fibres: from established spinning methods toward advanced applications. RSC Adv. 6, 44687-44716 (2016).
+5. Li, S., Macosko, C. W. & White, H. S. Electrochemical processing of conducting polymer fibers. Science 259, 957-960 (1993).
+6. Lu, W. et al. Use of ionic liquids for \(\pi\) -conjugated polymer electrochemical devices. Science 297, 983-987 (2002).
+7. Kim, Y. et al. Strain-engineering induced anisotropic crystallite orientation and maximized carrier mobility for high-performance microfiber-based organic bioelectronic devices. Adv. Mater. 33, 2007550 (2021).
+8. Koizumi, Y. et al. Electropolymerization on wireless electrodes towards conducting polymer microfiber networks. Nat. Commun. 7, 1-6 (2016).
+9. Jian, H. Y., Fridrikh, S. V. & Rutledge, G. C. The role of elasticity in the formation of electrospun fibers. Polymer 47, 4789-4797 (2006).
+10. Zhang, Y. & Rutledge, G. C. Electrical conductivity of electrospun polyaniline and polyaniline-blend fibers and mats. Macromolecules 45, 4238-4246 (2012).
+11. Zhang, Y. et al. Electrospun polyaniline fibers as highly sensitive room temperature chemiresistive sensors for ammonia and nitrogen dioxide gases. Adv. Funct. Mater. 24, 4005-4014 (2014).
+12. Hsu, C. H., Cohen, J. D. & Tietz, R. F. Polyaniline spinning solutions and fibers. Synth. Met. 59, 37-41 (1993).
+13. Pomfret, S. J., Adams, P. N., Comfort, N. P. & Monkman, A. P. Inherently electrically conductive fibers wet spun from a sulfonic acid-doped polyaniline solution. Adv. Mater. 10, 1351-1353 (1998).
+14. Mottaghtialab, V., Xi, B., Spinks, G. M. & Wallace, G. G. Polyaniline fibres containing single walled carbon nanotubes: Enhanced performance artificial muscles. Synth. Met. 156, 796-803 (2006).
+15. Park, J. H., & Rutledge, G. C. 50th anniversary perspective: advanced polymer fibers: high performance and ultrafine. Macromolecules 50, 5627-5642 (2017).
+16. Jiang, H., Geng, Y., Li, J., Jing, X. & Wang, F. Organic acid doped polyaniline derivatives. Synth. Met. 84, 125-126 (1997).
+
+<--- Page Split --->
+
+17. Wang, H. L., Romero, R. J., Mattes, B. R., Zhu, Y. & Winokur, M. J. Effect of processing conditions on the properties of high molecular weight conductive polyaniline fiber. J. Polym. Sci. Pol. Phys. 38, 194-204 (2000).
+
+18. Fang, B., Peng, L., Xu, Z. & Gao, C. Wet-spinning of continuous montmorillonite-graphene fibers for fire-resistant lightweight conductors. ACS Nano 9, 5214-5222 (2015).
+
+19. Paul, D. R. Diffusion during the coagulation step of wet-spinning. J. Appl. Polym. Sci. 12, 383-402 (1968).
+
+20. Fang, B., Chang, D., Xu, Z. & Gao, C. A review on graphene fibers: expectations, advances, and prospects. Adv. Mater. 32, 1902664 (2020).
+
+21. Chang, D. et al. Reversible fusion and fission of graphene oxide-based fibers. Science 372, 614-617 (2021).
+
+22. Yang, D., Fadeev, A., Adams, P. N. & Mattes, B. R. Controlling macrovoid formation in wet-spun polyaniline fibers. Smart Structures and Materials 2001: Electroactive Polymer Actuators and Devices. 4329, 59-71 (2001).
+
+23. Wijmans, J. G. & Baker, R. W. The solution-diffusion model: a review. J. Membr. Sci. 107, 1-21 (1995).
+
+24. Lajtai, E. Z. A theoretical and experimental evaluation of the Griffith theory of brittle fracture. Tectonophysics 11, 129-156 (1971).
+
+25. Okuzaki, H. & Ishihara, M. Spinning and characterization of conducting microfibers. Macromol. Rapid Commun. 24, 261-264 (2003). (PEDOT 17.2 MPa)
+
+26. Okuzaki, H., Harashina, Y. & Yan, H. Highly conductive PEDOT/PSS microfibers fabricated by wet-spinning and dip-treatment in ethylene glycol. Eur. Polym. J. 45, 256-261 (2009). (PEDOT 130 MPa)
+
+27. Jalili, R., Razal, J. M., Innis, P. C. & Wallace, G. G. One-step wet-spinning process of poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) fibers and the origin of higher electrical conductivity. Adv. Funct. Mater. 21, 3363-3370. (2011). (PEDOT 125 MPa)
+
+28. Zhang, J. et al. Fast and scalable wet-spinning of highly conductive PEDOT: PSS fibers enables versatile applications. J. Mater. Chem. A. 7, 6401-6410 (2019). (PEDOT 435 MPa).
+
+29. Wang, Z. et al. All-in-one fiber for stretchable fiber-shaped tandem supercapacitors. Nano Energy 45, 210-219 (2018). (PEDOT 112.7 MPa) (PEDOT/PSS fibers)
+
+30. Andreatta, A., Cao, Y., Chiang, J. C., Heeger, A. J. & Smith, P. Electrically-conductive fibers of polyaniline spun from solutions in concentrated sulfuric acid. Synth. Met. 26, 383-389 (1988). (PAni 20 MPa)
+
+31. Pomfret, S. J., Adams, P. N., Comfort, N. P. & Monkman, A. P. Electrical and mechanical properties of polyaniline fibres produced by a one-step wet spinning process. Polymer 41, 2265-2269 (2000). (PAni 97 MPa)
+
+32. Pomfret, S. J., Adams, P. N., Comfort, N. P. & Monkman, A. P. Advances in processing routes
+
+<--- Page Split --->
+
+for conductive polyaniline fibres. Synth. Met. 101, 724- 725 (1999). (PAni 100 MPa)33. Hsu, C. H., Cohen, J. D. & Tietz, R. F. Polyaniline spinning solutions and fibers. Synth. Met. 59, 37- 41 (1993). (PAni 400 MPa)34. Kou, L. et al. Coaxial wet- spun yarn supercapacitors for high- energy density and safe wearable electronics. Nat. Commun. 5, 1- 10. (2014). (RGO/CNT fibers)35. Yoo, J. J. et al. Ultrathin planar graphene supercapacitors. Nano Lett. 11, 1423- 1427 (2011).36. Yu, D. et al. Scalable synthesis of hierarchically structured carbon nanotube- graphene fibres for capacitive energy storage. Nat. Nanotechnol. 9, 555- 562 (2014). (RGO/SWCNT fiber)37. Lu, X. et al. Oxygen- deficient hematite nanorods as high- performance and novel negative electrodes for flexible asymmetric supercapacitors. Adv. Mater. 26, 3148- 3155 (2014).38. Zheng, Y. et al. Thermally- treated and acid- etched carbon fiber cloth based on pre- oxidized polyacrylonitrile as self- standing and high area- capacitance electrodes for flexible supercapacitors. Chem. Eng. J. 364, 70- 78 (2019). (PAN clothes)39. Zeng, S. et al. Electrochemical fabrication of carbon nanotube/polyaniline hydrogel film for all- solid- state flexible supercapacitor with high areal capacitance. J. Mater. Chem. A 3, 23864- 23870 (2015). (PAni/CNT)40. Yuan, L. et al. Polypyrrole- coated paper for flexible solid- state energy storage. Energ. Environ. Sci. 6, 470- 476 (2013). (PPy)41. Chi, K. et al. Freestanding graphene paper supported three- dimensional porous graphene- polyaniline nanocomposite synthesized by inkjet printing and in flexible all- solid- state supercapacitor. ACS Appl. Mater. Inter. 6, 16312- 16319 (2014). (PAni/graphene)42. Horng, Y. Y. et al. Flexible supercapacitor based on polyaniline nanowires/carbon cloth with both high gravimetric and area- normalized capacitance. J. Power Sources 195, 4418- 4422 (2010).43. Lu, Y. et al. Electrodeposited polypyrrole/carbon nanotubes composite films electrodes for neural interfaces. Biomaterials 31, 5169- 5181 (2010). (Pt, PPy/Cl)44. Gerwig, R. et al. PEDOT- CNT composite microelectrodes for recording and electrostimulation applications: fabrication, morphology, and electrical properties. Front. Neuroeng. 5, 8 (2012). (PEDOT/CNT, PEDOT/CI04)45. Vitale, F., Summerson, S. R., Aazhang, B., Kemere, C. & Pasquali, M. Neural stimulation and recording with bidirectional, soft carbon nanotube fiber microelectrodes. ACS Nano 9, 4465- 4474 (2015). (CNT fiber)46. Wang, K. et al. High- performance graphene- fiber- based neural recording microelectrodes. Adv. Mater. 31, 1805867 (2019). (Graphene/Pt)47. Venkatraman, S. et al. In vitro and in vivo evaluation of PEDOT microelectrodes for neural stimulation and recording. IEEE T. Neur. Sys. Reh. 19, 307- 316 (2011). (PEDOT/PSS, PPy/CNT, PPy/PSS)48. Inal, S., Malliaras, G. G. & Rivnay, J. Benchmarking organic mixed conductors for transistors.
+
+<--- Page Split --->
+
+Nat. Commun. 8, 1- 7 (2017).
+
+49. Rivnay, J. et al. Structural control of mixed ionic and electronic transport in conducting polymers. Nat. Commun. 7, 1-9 (2016).
+
+50. Lee, S. et al. Nanomesh pressure sensor for monitoring finger manipulation without sensory interference. Science 370, 966-970 (2020).
+
+51. Wang, X. et al. A Sub-1-V, microwatt power-consumption iontronic pressure sensor based on organic electrochemical transistors. IEEE Electron Device Lett. 42, 46-49 (2020).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+Supplementaryinformation1130. pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e_det.mmd b/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..84d17fe6a3ecac016975b4315cef9545fa403487
--- /dev/null
+++ b/preprint/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e/preprint__01cfd239b63d0b5b3bd8fba2f46c4523116e4ea7471e771fa2f189c14b26428e_det.mmd
@@ -0,0 +1,333 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 955, 175]]<|/det|>
+# Scalable production of ultrafine polyaniline fibres for tactile organic electrochemical transistors
+
+<|ref|>text<|/ref|><|det|>[[44, 196, 352, 238]]<|/det|>
+Bo Fang Hong Kong Polytechnic University
+
+<|ref|>text<|/ref|><|det|>[[44, 243, 350, 284]]<|/det|>
+Jianmin Yan Hong Kong Polytechnic University
+
+<|ref|>text<|/ref|><|det|>[[44, 290, 225, 330]]<|/det|>
+Dan Chang Zhejiang University
+
+<|ref|>text<|/ref|><|det|>[[44, 336, 350, 377]]<|/det|>
+Jinli Piao Hong Kong Polytechnic University
+
+<|ref|>text<|/ref|><|det|>[[44, 382, 350, 423]]<|/det|>
+Kit Ming Ma Hong Kong Polytechnic University
+
+<|ref|>text<|/ref|><|det|>[[44, 429, 484, 470]]<|/det|>
+Qiao Du Hong Kong University of Science and Technology
+
+<|ref|>text<|/ref|><|det|>[[44, 475, 484, 516]]<|/det|>
+Ping Gao Hong Kong University of Science and Technology
+
+<|ref|>text<|/ref|><|det|>[[44, 521, 707, 562]]<|/det|>
+Yang Chai Hong Kong Polytechnic University https://orcid.org/0000- 0002- 8943- 0861
+
+<|ref|>text<|/ref|><|det|>[[44, 566, 707, 608]]<|/det|>
+Xiaoming Tao ( \(\boxed{\times}\) xiao- ming.tao@polyu.edu.hk) Hong Kong Polytechnic University https://orcid.org/0000- 0002- 2406- 0695
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 650, 102, 667]]<|/det|>
+## Article
+
+<|ref|>title<|/ref|><|det|>[[44, 688, 135, 706]]<|/det|>
+# Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 725, 333, 744]]<|/det|>
+Posted Date: December 8th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 763, 473, 782]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 1126903/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 800, 909, 844]]<|/det|>
+License: \(\circledcirc\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 879, 909, 921]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on April 19th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 29773- 9.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[147, 92, 850, 151]]<|/det|>
+# Scalable production of ultrafine polyaniline fibres for tactile organic electrochemical transistors
+
+<|ref|>text<|/ref|><|det|>[[147, 161, 852, 210]]<|/det|>
+Bo Fang1,2, Jianmin Yan1,3, Dan Chang4, Jinli Piao1,2, Kit Ming Ma1,2, Qiao Gu5, Ping Gao5, Yang Chai1,3\* Xiaoming Tao1,2\*
+
+<|ref|>text<|/ref|><|det|>[[147, 218, 850, 266]]<|/det|>
+1Research Institute for Intelligent Wearable Systems, Hong Kong Polytechnic University, Hong Kong, 999077 China
+
+<|ref|>text<|/ref|><|det|>[[147, 275, 853, 321]]<|/det|>
+2Institute of Textiles and Clothing, Hong Kong Polytechnic University, Hong Kong, 999077 China
+
+<|ref|>text<|/ref|><|det|>[[147, 330, 850, 377]]<|/det|>
+3Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong, 999077 China
+
+<|ref|>text<|/ref|><|det|>[[147, 386, 853, 433]]<|/det|>
+4Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027 China
+
+<|ref|>text<|/ref|><|det|>[[147, 441, 850, 488]]<|/det|>
+5Department of Chemical and Biological Engineering, The Hong Kong University of Science and Technology, Hong Kong, 999077 China
+
+<|ref|>text<|/ref|><|det|>[[147, 496, 653, 515]]<|/det|>
+Email: ychai@polyu.edu.hk; xiao- ming.tao@polyu.edu.hk
+
+<|ref|>text<|/ref|><|det|>[[147, 551, 853, 905]]<|/det|>
+The development of continuous conducting polymer fibres is essential for applications ranging from advanced fibrous devices to frontier fabric electronics. The use of continuous conducting polymer fibres requires a small diameter to maximize their electroactive surfaces, microstructural orientations, and mechanical strengths. However, regularly used wet spinning techniques have rarely achieved this goal due primarily to the insufficient slenderization of rapidly solidified conducting polymer molecules in poor solvents. Here we report a good solvent exchange strategy to wet spin the ultrafine polyaniline fibres at the large scale. The slow diffusion between good solvents distinctly decreases the viscosity of gel protofibers, which undergo an impressive drawing ratio. The continuously collected polyaniline fibres have a previously unattained diameter below \(5 \mu \mathrm{m}\) , high energy and charge storage capacities, and favorable mechanical performance. We demonstrated an ultrathin all- solid organic electrochemical transistor based
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 852, 247]]<|/det|>
+on ultrafine polyaniline fibres, which substantially amplified microampere drain- source electrical signals with less one volt driving voltage and effectively operated as a tactile sensor detecting pressure and friction forces at different levels. The aggressive electronical and electrochemical merits of ultrafine polyaniline fibres and their great potentials to prepare on industrial scale offer new opportunities for high- performance soft electronics and large- area electronic textiles.
+
+<|ref|>text<|/ref|><|det|>[[147, 282, 852, 692]]<|/det|>
+The extended conjugated and easily doped \(\pi\) - system along the backbone enables conducting polymers to possess intriguing transport, optical, and electrochemical properties, which have rarely been found in conventional polymers and metal conductors \(^{1 - 3}\) . Processing conducting polymers into macroscopically fibrous materials makes it possible to translate their nano- object features to human- friendly products in a continuous manner. The combined merits, including but not limited to mechanical flexibility, intrinsic conductivity, and electrochemical activity, of conducting polymer fibres (CPFs) have introduced a new era of “electronic textiles” \(^{4}\) . For instance, highly conductive and electrochemically active poly(3- methylthiophene) fibres have been achieved by in situ electrochemical oxidation of monomers \(^{5}\) . Fast ion transport between CPFs and ionic liquids has given birth to long- term operation actuators, electrochromic windows, and numeric displays \(^{6}\) . In recent studies, the wet- spun poly (3,4- ethylene dioxythiophene) (PEDOT) fibres have been widely used in various frontier fields, such as flexible energy storage electrodes, implantable bioelectronics, and organic transistors \(^{7,8}\) .
+
+<|ref|>text<|/ref|><|det|>[[147, 700, 852, 914]]<|/det|>
+Unfortunately, due primarily to the large diameters, the performance and expectations of most achieved continuous CPFs have been limited by their insufficient electroactive surfaces and weak breaking strengths. Electropinning and wet spinning are two mainstream strategies to produce continuous CPFs. In the case of electrospinning, the fairly rigid backbone due to the high aromaticity results into an insufficient elasticity of conducting polymer solutions, which fails to be solely electrospun into fine fibres \(^{9}\) . Although a two- fluid electrospinning technique has been proposed by coating a soluble and electrospinable fluid on the conducting polymer cores, the complex procedures
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 81, 853, 696]]<|/det|>
+involving the addition and removal of second components defy the mass production of electrospun CPFs10,11. In the case of conventional wet spinning, conducting polymer dopes tend to occur a transient solidification in poor solvents, induced by the strong interactions of conducting polymer chains. The rapidly hardened gels suppress the post- stretching and slenderizing procedures, and cause the wet- spun CPFs to show a large diameter, generally beyond \(10 \mu \mathrm{m}^{12 - 14}\) . The large diameters largely discount the mechanical properties and electrochemical activities of CPFs4,15. Thus, there is an urgent need to realize the mass production of ultrafine CPFs, which remains challenging. In this work, we report a good solvent exchange strategy in a modified wet spinning technique to prepare the ultrafine polyaniline (PAni) fibres (UFPFs) at the large scale. Beyond conventional wet spinning protocol, we replaced poor solvents by good solvents as the coagulation bath to decrease the viscosity of gel protofibres, which were subject to an ultrahigh drawing ratio and reduced to an ultrafine morphology. The obtained UFPFs own a small diameter below \(5 \mu \mathrm{m}\) , an unprecedented mechanical strength of \(1080 \pm 71 \mathrm{MPa}\) , a high area capacitance beyond \(1008 \mathrm{mF} \mathrm{cm}^{- 2}\) , and an enormous charge storage capacity of \(5.25 \times 10^{4} \mathrm{mC} \mathrm{cm}^{- 2}\) . Based on the structural and electrochemical merits of UFPFs, we demonstrated an ultrathin all- solid organic electrochemical transistor (OECT) with less one volt driving voltage, which substantially amplified drain- source electrical signals with a low power- consumption and responded to vertical pressure and horizontal friction forces at different levels. Our work opens an avenue to prepare continuous ultrafine CPFs and high- performance soft electronics.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[152, 85, 848, 617]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 624, 852, 891]]<|/det|>
+Fig. 1: Scalable production of UFPFs. a Schematic of the good solvent exchange strategy to prepare UFPFs in a modified wet spinning protocol. In the case of poor solvent exchange (light orange region, upper panel), PANi molecules are rapidly solidified into thick gels and protofibres with rough crystallized particles. In the case of good solvent exchange (light blue region, lower panel), the formed gels with low viscosity occur an impressive gel extension and are slenderized into ultrafine fibres. b Schematic of the modified wet spinning process. c Scanning electron microscope (SEM) image of the marked region in b, showing the sharp necking behavior of gel PANi fibres. The close observation to region 1 (d), region 2 (e), and region 3 (f) in the marked zone of c, illustrating the sharply necking process of PANi gels. g Photograph of a 5.4-kilometres-long UFPF collected in two hours. Scale bars: c 20 μm, d 2 μm, e 10 μm, g 150 mm.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[148, 91, 214, 107]]<|/det|>
+## Results
+
+<|ref|>text<|/ref|><|det|>[[147, 115, 854, 584]]<|/det|>
+Preparation and characterization of UFPFs. In the modified one- step wet spinning process, we used good solvents as the coagulation bath to realize the mass production of UFPFs (Fig. 1a- b and Supplementary Fig. 1). After doping PANi power (emeraldine base) with camphor sulfonic acid (CSA) at a molar ratio of 2:1, we dispersed fully doped PANi into m- cresol as the raw spinning dopes (see the Methods section) \(^{16}\) . Significantly, the direct use of doped PANi solutions as the dopes saves the trouble of conventional post- doping procedures, and further permits the uniform charge distribution throughout the fibre length \(^{17}\) . A good solvent, dimethyl formamide (DMF), of PANi operated as the coagulation bath. A slow solvent exchange between m- cresol and DMF facilitated the formation of PANi gel protofibres with a quite low viscosity below 3000 cP. Subsequently, we observed a sharp decrease of diameter from \(\sim 0.1 \mathrm{mm}\) to \(\sim 4.7 \mu \mathrm{m}\) when stretching the gel fibres in bath (Fig. 1c- f), which, to our knowledge, is a record small value in the achieved wet- spun CPFs \(^{4}\) . The ultrafine fibre shows a smooth surface (Fig. 1f and Supplementary Fig. 2) and highly crystallized microstructures (Supplementary Fig.3). Moreover, such an impressive drawing ratio enables a very high production efficiency of UFPFs beyond 40 meters per minute. For example, we prepared a 5.4- kilometres- long UFPF in two hours (Fig. 1e).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[157, 90, 849, 455]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 460, 852, 728]]<|/det|>
+Fig. 2: Mechanism and mechanical properties of UFPPs. a SEM images of the PAni fibres produced in different solvating species. Specifically, the upper four panels showing the fibres prepared from poor solvents, and the lower two panels showing the fibres fabricated from good solvents. b Raman spectra of PAni fibres after placing in air for four weeks. c The diffusivity from PAni dispersions (in m-cresol) to various solvating species. d The viscosity of PAni gels formed in various solvating species. e Mechanics simulation results of extension behaviors of PAni gel fibres at different interfacial pressure. f Typical tensile stress-strain curves of UFPPs. g Ashby plot comparing the mechanical strength of UFPPs to previously reported CPFs. Scale bars in a: Water, Ethanol, EA, Acetone \(20\mu \mathrm{m}\) (left) \(10\mu \mathrm{m}\) (right); NMP \(20\mu \mathrm{m}\) (left) \(5\mu \mathrm{m}\) (right), DMF \(20\mu \mathrm{m}\) (left) \(2\mu \mathrm{m}\) (right).
+
+<|ref|>text<|/ref|><|det|>[[147, 760, 852, 891]]<|/det|>
+The sharp necking behaviors of gel protofibres are highly related to the use of good solvents as the coagulation bath. We recorded the evolution of surface morphologies of PAni fibres collected from different solvating species. As shown in Fig. 2a, the obtained fibres in poor solvating species, i.e., water, ethanol, ethyl acetate (EA), and acetone, generally present coarse surfaces and large diameters around \(20\mu \mathrm{m}\) . By comparison,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 852, 330]]<|/det|>
+we clearly observed a necking phenomenon in both cases of good solvents, i.e., N- methyl- 2- pyrrolidone (NMP) and DMF. Such necking effects promoted the finally produced fibres to behave ultrafine morphologies, which assists PAni fibres to behave better structure and performance stabilities due to the higher degree of orientation and crystallization (see the X- ray diffraction analysis in Supplementary Fig. 3). We used Raman spectra to evaluate their structural evolution after placing fibres in air for four weeks. As shown in Fig. 2b, we did not find obvious de- doping signals in Raman spectra of the PAni fibres from good solvents, whereas various de- doping peaks (1223 \(\mathrm{cm^{- 1}}\) and \(1462\mathrm{cm^{- 1}}\) ) appeared in the cases of poor solvents.
+
+<|ref|>text<|/ref|><|det|>[[147, 366, 852, 748]]<|/det|>
+We speculate that this sharp necking phenomenon may be caused by two factors: diffusion difference and interfacial pressure. In the conventional wet spinning protocol, the diffusion from good solvents to poor solvents occurs quickly to solidify dope fluids into gel fibres18,19. The rapid diffusion could be aggravated in the system of conducting polymers due to the strong interactions of rigid chains. Thus, PAni molecules tend to bond into irregularly crystallized particles prior to undergoing extensive drawing, as present in the upper panels of Fig. 1a. In previous reports using poor solvents as coagulation bath, although CPFs with a smooth surface could be collected by enhanced shear flow and strong stretching12,14, diameters are unable to be decreased to the ideal level due to the insufficient stretching slenderization of solidified gels. In contrast, the diffusion from dope fluids to good solvents is quite slow. Such slow diffusion allows the formation of fibrous gels with a low viscosity and the following high drawing ratios. Note that most conventional polymers are incapable of gelling in good solvents due to the poor chain interactions20,21.
+
+<|ref|>text<|/ref|><|det|>[[148, 783, 852, 857]]<|/det|>
+We calculated the diffusivities between various solvents and measured the viscosity of corresponding formed gels to support our explanations. The diffusivity from A molecules to B molecules, \(D_{AB}^{0}\) , is determined by the equation
+
+<|ref|>equation<|/ref|><|det|>[[283, 867, 711, 911]]<|/det|>
+\[\frac{D_{AB}^{0}\mu_{B}}{T} = 8.52\times 10^{-8}V_{bB}^{-1 / 3}\left[1.40\left(\frac{V_{bB}}{V_{bA}}\right)^{1 / 3} + \frac{V_{bB}}{V_{bA}}\right]\]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 852, 331]]<|/det|>
+, where \(\mu_{B}\) is the solvent viscosity, T is the temperature, and \(V_{b}\) is the molar volume of solvent at its normal boiling temperature \(^{22}\) . As displayed in Fig. 2c, the diffusivities from m- cresol to DMF \((7.5\times 10^{- 6} \mathrm{cm}^{2}\mathrm{s}^{- 1})\) and NMP \((7.71\times 10^{- 6} \mathrm{cm}^{2}\mathrm{s}^{- 1}\) ) are generally lower than that of poor solvents. Diffusion in bath further dominates the viscosity of protofibres. To monitor the viscosity of gel fibres in practical conditions, we conducted the viscometer tests at a low revolution (e.g., 10 Rev.). As summarized in Fig. 2d, the formed PANi gels in good solvents show a viscosity below \(3000\mathrm{cP}\) , much lower than that of poor solvents ( \(>4000\mathrm{cP}\) ). The established solvating specific- diffusivity- viscosity formula accords well with our proposed explanations.
+
+<|ref|>text<|/ref|><|det|>[[147, 366, 852, 664]]<|/det|>
+Interfacial pressure during solvent exchange is another major factor relating to the necking behavior of PANi protofibres. In a two fluid system, the interfacial pressure between two kind of solvents is inclined to decrease with the improved solvent diffusion \(^{23}\) . Based on the slow diffusion from m- cresol to good solvents (Fig. 2c), the interfacial pressure between gel fibres and coagulation bath is considerable, which further induces the necking of protofibres. To understand this, we conducted a mechanic simulation to the stretching behavior of gel fibres at different interfacial pressure (see the progressive results in Supplementary Fig.4 and Method section). According to the simulation results in Fig. 2e, the higher interfacial pressure drives gel fibres to occur the sharper necking and thinning effects at a given tensile stress. This probably explains the formation of UFPFs in DMF bath.
+
+<|ref|>text<|/ref|><|det|>[[147, 700, 852, 912]]<|/det|>
+UFPFs show impressive mechanical performance. Different from that of conventional polymer fibres, the typical linear strain- stress curves of UFPFs demonstrate a brittle fracture behavior with a small tensile strain of \(3.67\pm 0.64\%\) (Fig. 2f). It is reasonable if considering the rigid backbone of PANi chains, which likely gather and condense into fragile fibrous assemblies after undergoing strong shear flow in spinning microtubes. According to classical Griffith theory on brittle fracture, fibres' strength generally improves with the decrease of diameter due to the depressed structural defects \(^{24}\) . We compared the mechanical performance of UFPFs with previously reported CPFs.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[150, 90, 850, 451]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 480, 852, 693]]<|/det|>
+Fig. 3: Energy and charge storage capacities of UFPFs. a Schematic of a micro capacitor constructed using two UFPF electrodes on a substrate. b Cyclic voltammetry curves with the increasing scan rates from 10 to 20, 50, 80 and \(100\mathrm{mV}\mathrm{s}^{-1}\) . c Galvanostatic charge/discharge curves at various current densities increasing from 0.32 to 0.63, 1.59 and \(3.18\mathrm{mA}\mathrm{cm}^{-2}\) . d The area capacitance of UFPFs comparing to previous reported electrodes. e Cycle galvanostatic charge/discharge curves during 120 cycles between 0 and \(0.6\mathrm{V}\) at \(1.59\mathrm{mA}\mathrm{cm}^{-2}\) . f. The relationship between current and voltage at a slow rate of \(10\mathrm{mV}\mathrm{s}^{-1}\) . g The charge storage capacity of UFPFs comparing to other charge storage materials.
+
+<|ref|>text<|/ref|><|det|>[[147, 729, 852, 833]]<|/det|>
+Derived from the strain- stress curves, we concluded that UFPFs have a modulus of \(29.89 \pm 5.6\%\) GPa, and a strength of \(1080 \pm 71\) MPa, at least one order of magnitude higher than that of CPFs with larger diameters (Fig. 2g), mainly including PEDOT fibres (<450 MPa) \(^{7,25 - 29}\) and PAni fibres (<400 MPa) \(^{30 - 33}\) .
+
+<|ref|>text<|/ref|><|det|>[[147, 869, 850, 888]]<|/det|>
+Energy and charge storage capacities. Ultrafine morphology optimizes the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 80, 853, 640]]<|/det|>
+electroactive surfaces, which enables UFPFs to exhibit superb energy and charge storage capacities. To evaluate the electrochemical activity of UFPFs, we constructed a micro capacitor using polyvinyl alcohol (PVA)- \(\mathrm{H}_3\mathrm{PO}_4\) gel electrolyte and two UFPF electrodes (Fig. 3a). The electrochemical properties were checked by cyclic voltammetry (CV) and galvanostatic charge- discharge (GCD) measurements. At different scan rates, the nearly rectangular shape of CV curves and instantaneous current response to voltage reversal at each end potential suggest the good electrochemical activity of UFPFs34 (Fig. 3b). The nearly triangular shape of GCD curves at different current densities illustrates the formation of efficient electric double layers and charge propagation across the UFPF electrodes35 (Fig. 3c). According to the GCD results, we determined the electrochemical properties of UFPFs. Among of them, the area capacitance, \(\mathrm{C_A}\) , is between 1008 and 1666 mF cm- 2 at the current densities between 0.32 and 3.18 mA cm- 2, outperforming previously reported thick CPFs29 and other electrodes, such as carbon nanomaterials3434,36, metal oxides37 and conducting polymers38- 41, and approaching to that of PANi nanowires42 (Fig. 3d). The volumetric capacitance, power density and energy density reach 83.8 F cm- 3, 0.96 W cm- 3 and 4.19 mWh cm- 3, respectively (Supplementary Fig. 5). In lifetime tests of UFPF- based capacitor, both the potential and capacitance continued without significant decrease for 120 charge/discharge cycles at a low current density of 1.59 mA cm- 2, indicating the reliable electrochemical performance stability of UFPFs (Fig. 3e).
+
+<|ref|>text<|/ref|><|det|>[[147, 672, 853, 915]]<|/det|>
+We were able to confirm the amount of transported charge per unit area to UFPF during the charge/discharge cycle. The charge during a triangular wave potential between - 0.9 V and 1.0 V (water window, see the Supplementary Fig. 6) was calculated by integrating the measured current with respect to the time of period at a low scan rate of 10 mV s- 1 (Fig. 3f)6. We determined that the charge storage capacity of UFPF was \(5.25 \times 10^{4}\) mC cm- 2, a value at least two orders of magnitude higher than that of noble metals43, carbon bulk44 - 46 and previously reported conducting polymers47 (Fig. 3g). This value decreases slightly to \(2.015 \times 10^{4}\) mC cm- 2 at a tenfold scan rate of 100 mV s- 1 (Supplementary Fig. 7).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[156, 85, 848, 547]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 604, 852, 760]]<|/det|>
+Fig. 4: Demonstration and characterization of all-solid organic electrochemical transistor based on UFPFs. a Schematic of the all-solid OECT composed of three polymer layers, one silver wire as the gate electrode, and one UFPF as the drain-source channel. b Cross-section SEM image and schematic of OECT. The yellow break lines direct the charge flow along the fibre chains (green solid lines). c Transmittance of the OECT in the region of visible light. A typical output curve (d), transfer curve (e), and power consumption in operation (f) of OECT. Scale bars: b 20 μm.
+
+<|ref|>text<|/ref|><|det|>[[147, 797, 852, 900]]<|/det|>
+Structure and performance of all- solid OECT. Benefitting from the favorable energy and charge storage performance of UFPFs, we demonstrated a high- performance all- solid OECT. OECT amplifies drain- source current intensities at low operating voltages by ion penetration into the organic mixed ionic- electronic conductors, i.e., conducting
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[146, 87, 855, 470]]<|/det|>
+polymers48,49. This process is controlled by the gate bias, and, to date, has generally conducted in aqueous electrolytes. To preclude the interference of external environment, we promoted the working conditions of OECT from aqueous environments to all- solid state by using gel electrolytes as the ion matrix. As shown in Fig. 4a- b, our OECT is mainly constructed by three polymer layers. The upper layer is the cured polyurethane (PU) working as the dielectric coating and also protecting the device from the invasion of external action50. A fibrous silver gate electrode with a diameter of \(7 \mu \mathrm{m}\) is fixed in PU. Since UFPFs have demonstrated reliable electrochemical activities in PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel, we used PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel as the middle layer to inject ions to or uptake ions from the drain- source channel materials. A UFPF right below the silver gate is fused in the ion gel, and operates as the channel material. The bottom layer is also pure PU acting as the supporter of the whole device. Due to the remarkable flexibility and transparency of PVA and PU, the all- solid OECT is very soft, and shows a transmittance beyond \(80\%\) in the region of visible light (Fig. 4c), and a small thickness below \(300 \mu \mathrm{m}\) .
+
+<|ref|>text<|/ref|><|det|>[[147, 504, 853, 721]]<|/det|>
+Despite the long channel length ( \(\sim 0.48 \mathrm{cm}\) ), much larger than of conventional micrometer- scale device, the all- solid OECT showed favorable amplification performance with a high on- off current ratio ( \(>10^3\) , Fig. 4e) at low voltages ( \(< 1 \mathrm{V}\) , Fig. 4d). The relatively fair transconductance ( \(\mathrm{g}_{\mathrm{m}} < 60 \mu \mathrm{S}\) ) is probably ascribed to the small cross- sectional area, which dramatically magnifies the resistance of fibrillar channel. Note that the all- solid OECT is an energy saving device with extremely low power consumptions. For example, at a given drain- source voltage of \(0.6 \mathrm{V}\) , the consumed power is below \(18 \mu \mathrm{W}\) (Fig. 4f).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[151, 85, 841, 402]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 409, 852, 620]]<|/det|>
+Fig. 5: Electrical response of the all-solid OECT to mechanical deformations. a Schematic of the mechanism explaining the response to the action of external pressure. b Relative drain-source change \((\Delta \mathrm{I}_{\mathrm{DS}} / \mathrm{I}_{\mathrm{DS0}})\) and sensitivity as a function of pressure. c Response time of the all-solid OECT when pressing (rising edge) and releasing (falling part) under the instantaneous pressure of 17.8 KPa. d Cyclic response at three different pressure levels (0.92, 6.8, and 22.2 KPa). e, Schematic of the working principle of the response to friction. f Cyclic response at three different frictions (1.84, 4.69, and 5.55 KPa). g An enlarged curve of the marked part in (f). h Cyclic response at different friction speeds from 4, 6, 8, 10, 15, to \(20\mathrm{mm}\mathrm{s}^{-1}\) .
+
+<|ref|>text<|/ref|><|det|>[[147, 657, 852, 900]]<|/det|>
+We proved that the all- solid OECT functioned to amplify small electrical signals in gel environments and respond to mechanical deformation as a tactile sensor. As illustrated in Fig. 5a, the applied vertical pressure on the surface of the all- solid OECT adjusted the ion penetration due to the improved gate- source electric field and the redistribution of intrinsic capacitance51. At a \(\mathrm{V}_{\mathrm{G}}\) of - 0.1 V and a \(\mathrm{V}_{\mathrm{D}}\) of 0.35 V, we observed a stable increase of drain- source current, \(\mathrm{I}_{\mathrm{DS}}\) , with the increasing pressure, up to a 92% amplification from 0 to 40 KPa (Fig. 5b). The sensitivity is at the level of 0.01- 0.1 KPa1 in this process (dark cyan dots in Fig. 5b). As shown in Fig. 5c, the average rising time and falling time under instantaneous pressure of 17.8 KPa is \(\sim 536\) ms and \(\sim 698\) ms,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 853, 388]]<|/det|>
+respectively. Such integrated parameters facilitated the all- solid OECT to respond to different pressure levels from 0.92 to \(22.2\mathrm{KPa}\) (Fig. 5d). In addition to the response to pressure at the vertical direction, the all- solid OECT also reacted to friction at the horizontal direction (Fig. 5e and Supplementary Fig. 8). The forward and backward friction of a load on the surface changed the real- time distance between silver gate and UFPP channel repeatedly, thus producing a bimodal response curve (Fig. 5g). Note that, to enable the enlargement of \(\mathrm{I_{DS}}\) with the increasing gate- channel distance under the repeated friction, we applied a positive \(\mathrm{V_G}\) of \(0.1\mathrm{V}\) at a \(\mathrm{V_D}\) of \(0.55\mathrm{V}\) . The all- solid OECT responded stably to friction at different magnitudes (Fig. 5f, from 1.84 to 5.55 \(\mathrm{KPa}\) ) and different speeds (Fig. 5h, from 4 to \(20\mathrm{mm}\mathrm{s}^{- 1}\) ) during our cyclic tests. For example, \(\mathrm{I_{DS}}\) increased \(\sim 86\%\) at \(5.55\mathrm{KPa}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 424, 242, 441]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[147, 450, 853, 693]]<|/det|>
+The past decades have witnessed great achievements in preparing high- performance CPFs, which made a vast difference to the rapid development of advanced electronics. However, due to the limitations of both technology and strategy, it is still difficult to produce ultrafine CPFs at the large scale. We proposed a good solvents strategy in a modified wet spinning technology. With a principle of diffusion- controlled slow gelation of protofibres, the new system successfully downsized the diameter of PANi fibres to below \(5\mu \mathrm{m}\) , a value smaller than that of most previous work. Furthermore, the ultrafine morphology with highly improved electroactive surfaces promotes UFPPs to behave superb electrochemical activities and mechanical performance.
+
+<|ref|>text<|/ref|><|det|>[[147, 700, 855, 858]]<|/det|>
+It is of great importance to realize the mass production of ultrafine CPFs. We constructed an all- solid OECT to employ the impressive energy and charge storage capacities of UFPPs. A handful of fibres are robust enough to satisfy the operation as the tactile sensor. In view of the ability to produce on the industrial scale, UFPPs are promised to be extended to large- area electronics, such as textile- scale numeric displays, soft electrochromic windows, and wearable energy harvesting systems.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[148, 91, 226, 107]]<|/det|>
+## Methods
+
+<|ref|>text<|/ref|><|det|>[[147, 117, 853, 386]]<|/det|>
+Characteristics. All the SEM images were collected on a tungsten thermionic emission SEM system (the Tescan VEGA3). XRD spectra were obtained from XRD system (Rigaku SmartLab) equipped with \(9\mathrm{kW}\) rotating anode X- ray source ( \(\lambda \sim 1.54\mathrm{\AA}\) ) coupling with high- quality semiconductor detector that supports 0D, 1D or 2D x- ray diffraction measurement. Raman spectra were recorded from Renishaw Micro- Raman Spectroscopy system fully integrated with confocal microscope spectrometer and a \(785\mathrm{nm}\) laser source. Mechanical tests were conducted on an advanced rheometric expansion system at the Hong Kong University of Science and Technology. All the electrochemical tests were processed on an electrochemical workstation (VersaSTAT3). The measurements of OECT were conducted on probe station (Micromanipulator) with Keithley 4200A- SCS parameter analyzer.
+
+<|ref|>text<|/ref|><|det|>[[147, 396, 853, 580]]<|/det|>
+The fabrication of UFPFs. PAni power (emeraldine base, purchased from Sigma- Aldrich) was mixed with CSA at a molar ratio of 2:1. After being milled for 15 minutes, the uniform doped PAni was dispersed in m- cresol (after degassing) at a concentration of \(0.05\mathrm{gmL^{- 1}}\) . The dispersions were used as spinning dopes after blending in air for 8 hours, and extruded through a PEEK microtube with an inner diameter of \(100\mu \mathrm{m}\) at a rate of \(1\mathrm{mL}\mathrm{min}^{- 1}\) . Coagulation bath was chosen according to the experimental requirements. PAni fibres were directly drawn out from bath and collected on a graphite roller continuously.
+
+<|ref|>text<|/ref|><|det|>[[147, 589, 853, 886]]<|/det|>
+Numerical method. The experimental result is verified by numerical method using commercial software ANSYS. The simulation is performed using workbench 18.0. In the simplified computational model, a geometric model of gel tube is developed, in which the ratio of diameter to length is chosen as 1:18, and the mechanical properties, density, Young's modulus and Poisson's ratio are selected as \(300\mathrm{kg / m3}\) , \(1000\mathrm{Pa}\) and 0.01, respectively. For the boundary conditions, one end of the gel model set as fixed support, and another end applies extend displacement to mimic the stretching effect in the actual situation. Meanwhile, the corresponding pressure is applied on the outer surface of the gel model to account for the function of the impressive interfacial pressure on the surface of gel fibres. To ensure the convergence of the result, a grid independence test is conducted by refining mesh size sequentially, and the finite element mesh with 162641 nodes and 37128 hexahedral elements are adopted finally.
+
+<|ref|>text<|/ref|><|det|>[[147, 896, 850, 913]]<|/det|>
+The fabrication of micro capacitor. Micro capacitor composed of two UFPF electrodes and the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 89, 853, 274]]<|/det|>
+gel electrolyte was constructed on a glass substrate. To prepare the gel electrolyte, PVA power was dispersed into deionized water at a mass ratio of 9:1. PVA was dissolved after being heated for 5 hours at \(85^{\circ}\mathrm{C}\) . Then phosphoric acid was added at a mass ratio of 1:10 with deionized water. The mixture cooled at room temperature and were ready for use. Two UFPFs were placed in parallel on the glass slide. The transparent PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel was dropped between UFPFs. Two cooper wires connected to the UPPFs with silver paste worked as the conductor lines. After condensing for 10 minutes at \(40^{\circ}\mathrm{C}\) , the whole device was subject to electrochemical tests.
+
+<|ref|>text<|/ref|><|det|>[[147, 283, 868, 496]]<|/det|>
+The fabrication of all- solid OECT. The OECT was built from three layers: two PU layers and one ion gel layer. PU dispersion in DMF was casted on a PVDF substrate. After being treated in oven at \(60^{\circ}\mathrm{C}\) , a thin and transparent layer of pure PU was obtained. One drop of PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel electrolyte was added on the surface of solidified PU. An UFPF was immersed into gel. After been dried at \(45^{\circ}\mathrm{C}\) for 15 minutes, a UFPF channel locked in PVA- \(\mathrm{H}_3\mathrm{PO}_4\) gel was obtained. Afterwards, another drop of PU was added and a silver wire operation as the gate electrode was putted in PU at the liquid state. After being dried at \(60^{\circ}\mathrm{C}\) , an all- solid OECT was prepared. Note that all the three electrodes were connected to cooper electrodes for following measurements.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 508, 275, 523]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[148, 535, 850, 580]]<|/det|>
+The data that support the findings of this study are available from the corresponding author upon reasonable request. Correspondence and requests for materials should be addressed to Y.C. and X.T.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 592, 296, 607]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[149, 618, 850, 662]]<|/det|>
+This work is supported by the Research Grants Council of Hong Kong (No. 15201419), Hong Kong Polytechnic University Postdoctoral Fellowship and Endowed Professorship Fund (No. 847A).
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 674, 312, 689]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[147, 700, 852, 828]]<|/det|>
+X. T. supervised this study. B. F. designed and conducted the main experiments. J. Y., Y. C. and B. F. constructed and characterized the transistor. D. C. helped to build the wet spinning equipment and discussed the results. J. P. did the mechanic simulations. K. M. M. helped to draw a part of schematics. Q. G. and P. G. helped to conduct the mechanical tests. B.F., X. T. and Y. C. wrote the manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 841, 302, 856]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[150, 868, 458, 884]]<|/det|>
+The authors declare no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 895, 245, 911]]<|/det|>
+## References
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 102, 852, 895]]<|/det|>
+1. Sariciftci, N. S., Smilowitz, L., Heeger, A. J. & Wudl, F. Photoinduced electron transfer from a conducting polymer to buckminsterfullerene. Science 258, 1474-1476 (1992).
+2. Frommer, J. E. Conducting polymer solutions. Acc. Chem. Res. 19, 2-9 (1986).
+3. Shi, G., Jin, S., Xue, G. & Li, C. A conducting polymer film stronger than aluminum. Science 267, 994-996 (1995).
+4. Mirabedini, A., Foroughi, J. & Wallace, G. G. Developments in conducting polymer fibres: from established spinning methods toward advanced applications. RSC Adv. 6, 44687-44716 (2016).
+5. Li, S., Macosko, C. W. & White, H. S. Electrochemical processing of conducting polymer fibers. Science 259, 957-960 (1993).
+6. Lu, W. et al. Use of ionic liquids for \(\pi\) -conjugated polymer electrochemical devices. Science 297, 983-987 (2002).
+7. Kim, Y. et al. Strain-engineering induced anisotropic crystallite orientation and maximized carrier mobility for high-performance microfiber-based organic bioelectronic devices. Adv. Mater. 33, 2007550 (2021).
+8. Koizumi, Y. et al. Electropolymerization on wireless electrodes towards conducting polymer microfiber networks. Nat. Commun. 7, 1-6 (2016).
+9. Jian, H. Y., Fridrikh, S. V. & Rutledge, G. C. The role of elasticity in the formation of electrospun fibers. Polymer 47, 4789-4797 (2006).
+10. Zhang, Y. & Rutledge, G. C. Electrical conductivity of electrospun polyaniline and polyaniline-blend fibers and mats. Macromolecules 45, 4238-4246 (2012).
+11. Zhang, Y. et al. Electrospun polyaniline fibers as highly sensitive room temperature chemiresistive sensors for ammonia and nitrogen dioxide gases. Adv. Funct. Mater. 24, 4005-4014 (2014).
+12. Hsu, C. H., Cohen, J. D. & Tietz, R. F. Polyaniline spinning solutions and fibers. Synth. Met. 59, 37-41 (1993).
+13. Pomfret, S. J., Adams, P. N., Comfort, N. P. & Monkman, A. P. Inherently electrically conductive fibers wet spun from a sulfonic acid-doped polyaniline solution. Adv. Mater. 10, 1351-1353 (1998).
+14. Mottaghtialab, V., Xi, B., Spinks, G. M. & Wallace, G. G. Polyaniline fibres containing single walled carbon nanotubes: Enhanced performance artificial muscles. Synth. Met. 156, 796-803 (2006).
+15. Park, J. H., & Rutledge, G. C. 50th anniversary perspective: advanced polymer fibers: high performance and ultrafine. Macromolecules 50, 5627-5642 (2017).
+16. Jiang, H., Geng, Y., Li, J., Jing, X. & Wang, F. Organic acid doped polyaniline derivatives. Synth. Met. 84, 125-126 (1997).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 95, 852, 161]]<|/det|>
+17. Wang, H. L., Romero, R. J., Mattes, B. R., Zhu, Y. & Winokur, M. J. Effect of processing conditions on the properties of high molecular weight conductive polyaniline fiber. J. Polym. Sci. Pol. Phys. 38, 194-204 (2000).
+
+<|ref|>text<|/ref|><|det|>[[145, 163, 850, 202]]<|/det|>
+18. Fang, B., Peng, L., Xu, Z. & Gao, C. Wet-spinning of continuous montmorillonite-graphene fibers for fire-resistant lightweight conductors. ACS Nano 9, 5214-5222 (2015).
+
+<|ref|>text<|/ref|><|det|>[[145, 205, 850, 243]]<|/det|>
+19. Paul, D. R. Diffusion during the coagulation step of wet-spinning. J. Appl. Polym. Sci. 12, 383-402 (1968).
+
+<|ref|>text<|/ref|><|det|>[[145, 247, 850, 286]]<|/det|>
+20. Fang, B., Chang, D., Xu, Z. & Gao, C. A review on graphene fibers: expectations, advances, and prospects. Adv. Mater. 32, 1902664 (2020).
+
+<|ref|>text<|/ref|><|det|>[[145, 290, 850, 328]]<|/det|>
+21. Chang, D. et al. Reversible fusion and fission of graphene oxide-based fibers. Science 372, 614-617 (2021).
+
+<|ref|>text<|/ref|><|det|>[[145, 332, 850, 393]]<|/det|>
+22. Yang, D., Fadeev, A., Adams, P. N. & Mattes, B. R. Controlling macrovoid formation in wet-spun polyaniline fibers. Smart Structures and Materials 2001: Electroactive Polymer Actuators and Devices. 4329, 59-71 (2001).
+
+<|ref|>text<|/ref|><|det|>[[145, 397, 850, 436]]<|/det|>
+23. Wijmans, J. G. & Baker, R. W. The solution-diffusion model: a review. J. Membr. Sci. 107, 1-21 (1995).
+
+<|ref|>text<|/ref|><|det|>[[145, 440, 850, 479]]<|/det|>
+24. Lajtai, E. Z. A theoretical and experimental evaluation of the Griffith theory of brittle fracture. Tectonophysics 11, 129-156 (1971).
+
+<|ref|>text<|/ref|><|det|>[[145, 483, 850, 522]]<|/det|>
+25. Okuzaki, H. & Ishihara, M. Spinning and characterization of conducting microfibers. Macromol. Rapid Commun. 24, 261-264 (2003). (PEDOT 17.2 MPa)
+
+<|ref|>text<|/ref|><|det|>[[145, 526, 850, 586]]<|/det|>
+26. Okuzaki, H., Harashina, Y. & Yan, H. Highly conductive PEDOT/PSS microfibers fabricated by wet-spinning and dip-treatment in ethylene glycol. Eur. Polym. J. 45, 256-261 (2009). (PEDOT 130 MPa)
+
+<|ref|>text<|/ref|><|det|>[[145, 590, 850, 652]]<|/det|>
+27. Jalili, R., Razal, J. M., Innis, P. C. & Wallace, G. G. One-step wet-spinning process of poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) fibers and the origin of higher electrical conductivity. Adv. Funct. Mater. 21, 3363-3370. (2011). (PEDOT 125 MPa)
+
+<|ref|>text<|/ref|><|det|>[[145, 656, 850, 695]]<|/det|>
+28. Zhang, J. et al. Fast and scalable wet-spinning of highly conductive PEDOT: PSS fibers enables versatile applications. J. Mater. Chem. A. 7, 6401-6410 (2019). (PEDOT 435 MPa).
+
+<|ref|>text<|/ref|><|det|>[[145, 699, 850, 738]]<|/det|>
+29. Wang, Z. et al. All-in-one fiber for stretchable fiber-shaped tandem supercapacitors. Nano Energy 45, 210-219 (2018). (PEDOT 112.7 MPa) (PEDOT/PSS fibers)
+
+<|ref|>text<|/ref|><|det|>[[145, 742, 850, 802]]<|/det|>
+30. Andreatta, A., Cao, Y., Chiang, J. C., Heeger, A. J. & Smith, P. Electrically-conductive fibers of polyaniline spun from solutions in concentrated sulfuric acid. Synth. Met. 26, 383-389 (1988). (PAni 20 MPa)
+
+<|ref|>text<|/ref|><|det|>[[145, 806, 850, 866]]<|/det|>
+31. Pomfret, S. J., Adams, P. N., Comfort, N. P. & Monkman, A. P. Electrical and mechanical properties of polyaniline fibres produced by a one-step wet spinning process. Polymer 41, 2265-2269 (2000). (PAni 97 MPa)
+
+<|ref|>text<|/ref|><|det|>[[144, 870, 850, 889]]<|/det|>
+32. Pomfret, S. J., Adams, P. N., Comfort, N. P. & Monkman, A. P. Advances in processing routes
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[150, 98, 850, 895]]<|/det|>
+for conductive polyaniline fibres. Synth. Met. 101, 724- 725 (1999). (PAni 100 MPa)33. Hsu, C. H., Cohen, J. D. & Tietz, R. F. Polyaniline spinning solutions and fibers. Synth. Met. 59, 37- 41 (1993). (PAni 400 MPa)34. Kou, L. et al. Coaxial wet- spun yarn supercapacitors for high- energy density and safe wearable electronics. Nat. Commun. 5, 1- 10. (2014). (RGO/CNT fibers)35. Yoo, J. J. et al. Ultrathin planar graphene supercapacitors. Nano Lett. 11, 1423- 1427 (2011).36. Yu, D. et al. Scalable synthesis of hierarchically structured carbon nanotube- graphene fibres for capacitive energy storage. Nat. Nanotechnol. 9, 555- 562 (2014). (RGO/SWCNT fiber)37. Lu, X. et al. Oxygen- deficient hematite nanorods as high- performance and novel negative electrodes for flexible asymmetric supercapacitors. Adv. Mater. 26, 3148- 3155 (2014).38. Zheng, Y. et al. Thermally- treated and acid- etched carbon fiber cloth based on pre- oxidized polyacrylonitrile as self- standing and high area- capacitance electrodes for flexible supercapacitors. Chem. Eng. J. 364, 70- 78 (2019). (PAN clothes)39. Zeng, S. et al. Electrochemical fabrication of carbon nanotube/polyaniline hydrogel film for all- solid- state flexible supercapacitor with high areal capacitance. J. Mater. Chem. A 3, 23864- 23870 (2015). (PAni/CNT)40. Yuan, L. et al. Polypyrrole- coated paper for flexible solid- state energy storage. Energ. Environ. Sci. 6, 470- 476 (2013). (PPy)41. Chi, K. et al. Freestanding graphene paper supported three- dimensional porous graphene- polyaniline nanocomposite synthesized by inkjet printing and in flexible all- solid- state supercapacitor. ACS Appl. Mater. Inter. 6, 16312- 16319 (2014). (PAni/graphene)42. Horng, Y. Y. et al. Flexible supercapacitor based on polyaniline nanowires/carbon cloth with both high gravimetric and area- normalized capacitance. J. Power Sources 195, 4418- 4422 (2010).43. Lu, Y. et al. Electrodeposited polypyrrole/carbon nanotubes composite films electrodes for neural interfaces. Biomaterials 31, 5169- 5181 (2010). (Pt, PPy/Cl)44. Gerwig, R. et al. PEDOT- CNT composite microelectrodes for recording and electrostimulation applications: fabrication, morphology, and electrical properties. Front. Neuroeng. 5, 8 (2012). (PEDOT/CNT, PEDOT/CI04)45. Vitale, F., Summerson, S. R., Aazhang, B., Kemere, C. & Pasquali, M. Neural stimulation and recording with bidirectional, soft carbon nanotube fiber microelectrodes. ACS Nano 9, 4465- 4474 (2015). (CNT fiber)46. Wang, K. et al. High- performance graphene- fiber- based neural recording microelectrodes. Adv. Mater. 31, 1805867 (2019). (Graphene/Pt)47. Venkatraman, S. et al. In vitro and in vivo evaluation of PEDOT microelectrodes for neural stimulation and recording. IEEE T. Neur. Sys. Reh. 19, 307- 316 (2011). (PEDOT/PSS, PPy/CNT, PPy/PSS)48. Inal, S., Malliaras, G. G. & Rivnay, J. Benchmarking organic mixed conductors for transistors.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[163, 99, 373, 113]]<|/det|>
+Nat. Commun. 8, 1- 7 (2017).
+
+<|ref|>text<|/ref|><|det|>[[147, 120, 852, 156]]<|/det|>
+49. Rivnay, J. et al. Structural control of mixed ionic and electronic transport in conducting polymers. Nat. Commun. 7, 1-9 (2016).
+
+<|ref|>text<|/ref|><|det|>[[147, 163, 850, 200]]<|/det|>
+50. Lee, S. et al. Nanomesh pressure sensor for monitoring finger manipulation without sensory interference. Science 370, 966-970 (2020).
+
+<|ref|>text<|/ref|><|det|>[[147, 207, 850, 243]]<|/det|>
+51. Wang, X. et al. A Sub-1-V, microwatt power-consumption iontronic pressure sensor based on organic electrochemical transistors. IEEE Electron Device Lett. 42, 46-49 (2020).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 397, 150]]<|/det|>
+Supplementaryinformation1130. pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/images_list.json b/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..d8f8ae26e489a8d70077acf9283188ffcad13784
--- /dev/null
+++ b/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/images_list.json
@@ -0,0 +1,168 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. On-chip micro-vascularization enabled by soft microfluidics. (a) 3D printed tissue culture chip designed for eight multiplexed soft 3D soft microfluidic capillary grids. Inset: microfluidic capillary grid fabricated on a plastic baseplate and diagram of working principle. (b) of microfluidic capillary grid (left) and the close up image of the same grid showing individual hydrogel capillaries (right). (c) Microvessel 3D printing by 3D printing of microfluidic grid using high-resolution 2-photon stereo-lithography with non-swelling photo-polymerizable hydrogel precursors enables reproduction of features as small as \\(10\\mu \\mathrm{m}\\) . The top view photograph demonstrates an array of cylinders of various outer diameter in micrometers (top row) and wall thickness in micrometers (columns). (d) CAD image of microfluidic grid (left) with capillaries shown in red and the structural components shown in grey. The fence at the circumference of the structure makes",
+ "footnote": [],
+ "bbox": [
+ [
+ 171,
+ 110,
+ 825,
+ 744
+ ]
+ ],
+ "page_idx": 33
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Transcriptomic changes upon perfusion. (a) Combined dataset UMAP (control, non-perfused and perfused samples). (b) Combined dataset UMAP with neuroepithelial cells (NE), pluripotent-neuroepithelial transitioning cells (P-NE), proliferating cells with medium mitochondrial (mito.) content, pluripotent cells (P) with low glycolysis (glyc.) and medium mitochondrial content, glycolytic pluripotent cells with low mitochondrial content, highly glycolytic pluripotent cells, a highly glycolytic hypoxic (hypo.) identity and a stressed cluster. (c) Pseudotime trajectory on combined dataset UMAP. (d) Cluster specific expressions of selected marker genes. Expression values are normalized and centered. Sample fractions for each identified cluster. (e) GO enrichment analysis for key processes upregulated in perfused and non-perfused samples.",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 240,
+ 899,
+ 565
+ ]
+ ],
+ "page_idx": 35
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Changes in proliferation mediated by hypoxia. a) Representative experimental results demonstrating differences in proliferation and viability between standard organoid culture(left column) and the tissue constructs without (middle column) and with perfusion (right column). Top row: bright field images of organoids, non-perfused and perfused constructs correspondingly. Middle row: immunofluorescent images of apoptotic marker cleaved Caspase 3 (green) expressed in the three conditions. Bottom row: immunofluorescent images of hypoxia marker HIF1a (green). Hoechst staining of nuclei shown in blue. The images represent transverse cross-sections of the tissue constructs. (b) Top: average proportion of the number of live cells in perfused and non-perfused constructs quantified by flow cytometry (90.95.1% in perfused vs 89.2±4.4% in non-perfused tissue, n.s., n=4). Middle: average expression of cleaved Caspase 3 in control organoids (8±1% area, n=7), non-perfused(35.7±5%, pControl=0.02, n=4) and perfused tissue constructs (5.1±1% of total area, pControl=0.02, n=9). Bottom: average expression of hypoxia marker HIF-1a in control organoids (100±3%, n=4), non-perfused (55±3%, pControl=0.0003, n=3) and perfused constructs (26±2%, pControl=0.0004, n=2). Control organoids, non-perfused and perfused constructs are denoted as Ctrl, NP and P correspondingly, data are represented as mean ± SEM, asterisks (*) denote statistical significance of the difference between control organoids and the tissue constructs (unpaired two-tailed Student's t-test, 95% confidence interval). (c) Representative fluo-cytometry data, demonstrating the difference in total number of cells between perfused and non-perfused constructs. (d) Distribution of gene expression levels across the single cell population for hypoxia (left), G2M cell cycle (middle) and S cell cycle (right) associated gene sets. Scale bar: 1mm",
+ "footnote": [],
+ "bbox": [
+ [
+ 115,
+ 105,
+ 901,
+ 420
+ ]
+ ],
+ "page_idx": 36
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4. Rapid neural differentiation in perfused systems. (a) Representative experimental results demonstrating the result of 2 days of neuronal induction in control organoids(left column), non-perfused (middle column) and perfused (right column) tissue constructs. Top, middle and bottom row: immunofluorescent images of stem cell marker NANOG, early neural marker PAX6 and cell adhesion proteins N-Cadherin (green) and E-Cadherin (red) correspondingly. The images represent transverse cross-sections of the tissue constructs. In most cases, the cross-sections of capillaries are visible as circular structures (marked by triangles) (b) Average expression of PAX6(Ctrl: Not detected; NP: \\(0.2\\% \\pm 0.2\\%\\) , pControl \\(= 0.35(n.s.)\\) , \\(n = 9\\) ; P: \\(21.5 \\pm 2\\%\\) , pControl \\(= 0.00002\\) , \\(n = 12\\) ), NANOG(Ctrl: \\(73.6 \\pm 8\\%\\) , \\(n = 9\\) ; NP: \\(16.1 \\pm 2\\%\\) , pControl \\(= 0.00007\\) , \\(n = 11\\) ; P: not detected), NCad(CDH2) (Ctrl: \\(100 \\pm 1\\%\\) , \\(n = 8\\) ; NP: \\(7.6 \\pm 1\\%\\) , pControl \\(= 4e - 13\\) , \\(n = 3\\) ; P: \\(55.7 \\pm 9\\%\\) (pControl \\(= 0.009\\) , \\(n = 5\\) ) and ECad(CDH1) (Ctrl: \\(99 \\pm 2\\%\\) , \\(n = 12\\) ; NP: \\(26.6 \\pm 7\\%\\) , pControl \\(= 0.0001\\) , \\(n = 6\\) ; P: \\(4.5 \\pm 2\\%\\) , pControl \\(= 2e - 10\\) , \\(n = 5\\) ) markers in control organoids (Ctrl), non-perfused(NP) and perfused(P) constructs. Data are represented as mean \\(\\pm\\) SEM, asterisks (*) denote statistical significance of the difference between control organoids and the tissue constructs (unpaired two-tailed Student's \\(t\\) -test, \\(95\\%\\) confidence interval) (c) UMAP plot of the combined dataset showing the localization of cells from control organoids, non-perfused and perfused constructs in the UMAP space. (d) UMAP plot of the combined dataset highlighting locations of PAX6, NANOG, NCad (CDH2) and ECad(CDH1) expressing cells in the UMAP space. Scale bar: \\(250 \\mu m\\)",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 155,
+ 876,
+ 570
+ ]
+ ],
+ "page_idx": 37
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5. Functional improvement in perfused liver microtissues. (a) Hematoxylin and eosin of a transverse section of liver tissue construct with hepatocyte-like morphology and no visible indication of apoptosis. (b) Immunofluorescence images showing presence of AFP and CYP3A4, (c) Alpha-1 antitrypsin (AAT) and Cytokeratin 19 (KRT19), and (d) basic hepatic markers albumin (ALB) and hepatic nuclear factor HNF4α expression (f) Heatmap representation of fold change gene expression levels normalized to control 2D cell culture and compared to standard hepatic organoids and perfused liver constructs; rows are centered and scaled. Gene expression data for hepatic 2D culture and hepatic organoids are from Kumar et al74. Scale bar: \\(50\\mu \\mathrm{m}\\)",
+ "footnote": [],
+ "bbox": [
+ [
+ 128,
+ 140,
+ 888,
+ 457
+ ]
+ ],
+ "page_idx": 38
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_3.jpg",
+ "caption": "Supplementary Figure 3. Two-photon stereo-lithography enables precision fabrication in a wide range of scales. Microfluidic grids of different dimensions (in mm): 1.2mm x 1.2mm x 1.2mm (left), 2.6mm x 2.6 mm x 1.5mm (middle), 6.5mm x 6.5mm x 5mm (right). Perfusion vessels in each grid have identical 50μm diameter and inter-vessel distance of 250μm. Scale bar 5 mm.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 40
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_4.jpg",
+ "caption": "Supplementary Figure 4. Daily brightfield imaging of neural tissue in perfused and non-perfused chips. (a) Bright field images of the perfused (top) and non-perfused (bottom) tissue constructs taken every 2 days during the culturing protocol. (b) Live sections of perfused (left) and non-perfused (right) tissue constructs taken at the end of the culturing protocol. Scale bar 500μm.",
+ "footnote": [],
+ "bbox": [
+ [
+ 130,
+ 240,
+ 840,
+ 744
+ ]
+ ],
+ "page_idx": 41
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_6.jpg",
+ "caption": "Supplementary Figure 6. Gene-set analysis for various processes. Combined dataset UMAP with scores for pluripotent, glycolysis and neural progenitor gene-set as well as the \\(\\%\\) mitochondrial genes. Hierarchical clustering of gene-set scores and \\(\\%\\) mitochondrial genes. Score is column scaled.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 41
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_7.jpg",
+ "caption": "Supplementary Figure 7. Gene expression for unannotated hNTO clusters with the top 25 marker genes for each cluster.",
+ "footnote": [],
+ "bbox": [
+ [
+ 260,
+ 90,
+ 732,
+ 830
+ ]
+ ],
+ "page_idx": 42
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_8.jpg",
+ "caption": "Supplementary Figure 8. Cluster-specific analysis of scRNAseq dataset. Dot-plot heatmap of hypoxia and cell cycle markers for each identified cluster. The average gene expression is represented by the color intensity of each dot, whereas the dot size represents the percentage of the gene-expressing cells for each sample within each cluster.",
+ "footnote": [],
+ "bbox": [
+ [
+ 115,
+ 168,
+ 856,
+ 455
+ ]
+ ],
+ "page_idx": 43
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_9.jpg",
+ "caption": "Supplementary Figure 9. Difference in localized expression of hypoxia marker HIF1α and apoptosis marker cleaved Caspase-3. (a) HIF1α expression is localized to regions containing intact cell bodies (middle), evidenced by intact nuclei in the outlined region (left) as well as well-defined cytoplasmic regions stained with E-Cad antibody (right). (b) Cleaved Caspase-3 expression (middle) is localized to regions with apoptotic cell bodies evidenced by Hoechst stain of fragmented nuclei (outside of the outlined live region on the left image). Scale bar 100μm.",
+ "footnote": [],
+ "bbox": [
+ [
+ 232,
+ 216,
+ 760,
+ 488
+ ]
+ ],
+ "page_idx": 44
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_10.jpg",
+ "caption": "Supplementary Figure 10. Brightfield images of perfused liver cultures. Bright field images of the perfused liver-like tissue constructs taken during tissue culturing. Scale bar 500μm.",
+ "footnote": [],
+ "bbox": [
+ [
+ 113,
+ 94,
+ 928,
+ 310
+ ]
+ ],
+ "page_idx": 45
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345.mmd b/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..c09aa8b26d58818c70c241b9d308de757086e01a
--- /dev/null
+++ b/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345.mmd
@@ -0,0 +1,515 @@
+
+# Engineering large-scale perfused tissues via synthetic 3D soft microfluidics
+
+Sergei Grebenyuk KU Leuven
+
+Abdel Rahman Abdel Fattah KU Leuven https://orcid.org/0000- 0002- 7817- 5586
+
+Gregorius Rustandi KU Leuven
+
+Manoj Kumar KU Leuven https://orcid.org/0000- 0002- 0572- 5786
+
+Burak Toprakhisar
+
+Stem Cell Institute, Department of Stem Cell and Developmental Biology, KU Leuven, Leuven, Belgium
+
+Idris Salmon KU Leuven
+
+Catherine Verfaillie
+
+KU Leuven https://orcid.org/0000- 0001- 7564- 4079
+
+Adrian Ranga ( adrian.ranga@kuleuven.be )
+
+adrian.ranga@kuleuven.be https://orcid.org/0000- 0002- 6400- 9472
+
+Article
+
+Keywords:
+
+Posted Date: September 8th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 867063/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+
+# Engineering large-scale perfused tissues via synthetic 3D soft microfluidics
+
+Sergei Grebenyuk \(^{1}\) , Abdel Rahman Abdel Fattah \(^{1}\) , Gregorius Rustandi \(^{1}\) , Manoj Kumar \(^{2}\) , Burak Toprakhisar \(^{2}\) , Idris Salmon \(^{1}\) , Catherine Verfaillie \(^{2}\) , Adrian Ranga \(^{1*}\)
+
+\(^{1}\) Laboratory of Bioengineering and Morphogenesis, Biomechanics Section, Department of Mechanical Engineering, KU Leuven, Leuven, Belgium
+
+\(^{2}\) Stem Cell Institute Leuven and Department of Development and Regeneration, Faculty of Medicine, KU Leuven, Leuven, Belgium
+
+\* email: adrian.ranga@kuleuven.be
+
+## Abstract
+
+The vascularization of engineered tissues and organoids has remained a major unresolved challenge in regenerative medicine. While multiple approaches have been developed to vascularize in vitro tissues, it has thus far not been possible to generate sufficiently dense networks of small- scale vessels to perfuse large de novo tissues. Here, we achieve the perfusion of multi- mm \(^{3}\) tissue constructs by generating networks of synthetic capillary- scale 3D vessels. Our 3D soft microfluidic strategy is uniquely enabled by a 3D- printable 2- photon- polymerizable hydrogel formulation, which allows for precise microvessel printing at scales below the diffusion limit of living tissues. We demonstrate that these large- scale engineered tissues are viable, proliferative and exhibit complex morphogenesis during long- term in- vitro culture, while avoiding hypoxia and necrosis. We show by scRNAseq and immunohistochemistry that neural differentiation is significantly accelerated in perfused neural constructs. Additionally, we illustrate the versatility of this platform by demonstrating long- term perfusion of developing liver tissue. This fully synthetic vascularization platform opens the door to the generation of human tissue models at unprecedented scale and complexity.
+
+<--- Page Split --->
+
+## Introduction
+
+Human engineered tissue and organoids are potentially transformational model systems, which could create dramatic efficiencies in the drug discovery process and function as key building blocks for regenerative medicine applications. In particular, larger- scale tissues have the possibility to recapitulate complex functional and organizational characteristics of their in vivo counterparts, and could therefore become a long- sought alternative to animal models \(^{1 - 3}\) . However, the poorly defined structural organization, small size and slow maturation of these tissues have remained major limitations in engineering fully functional and reproducible organoids and tissues.
+
+In vivo, the development of tissues is supported by a complex network of blood vessels which provide oxygen, nutrients and waste exchange and mediate paracrine interactions via growth and differentiation factors \(^{4}\) . The size of the microvasculature is a critical parameter for local tissue perfusion: to maintain sufficient diffusion of oxygen, nutrients, and waste products most cells in vivo lie within \(200 \mu \mathrm{m}\) of a capillary. In the absence of vascular support, normal physiological conditions can be maintained only within this narrow range. Similar to the diffusion limits in normal tissue, the generation of solid tissue in vitro requires both vascularization and flow to maintain cell viability throughout the entire construct \(^{1}\) . The lack of vascularization in engineered tissues therefore prevents oxygen and nutrient exchange, which is thought to be the main reason for the commonly observed development of a necrotic core within organoids once they reach a critical size, as well as for apoptosis within engineered tissues. These issues have been widely recognized, and various approaches have been reported in order to overcome them \(^{5}\) .
+
+The extrinsic induction of angiogenesis has been frequently used in the context of organoid vascularization. Vessel sprouts have been shown to infiltrate organoids maintained with endothelial cells in separate compartments of microfluidic culture devices \(^{6,7}\) , or co- cultured with pre- established microvascular beds \(^{8,9}\) . These results have suggested that the presence of a perfusable vasculature can enhance organoid growth \(^{8}\) , confirming the importance of systemic cross- talk between vasculature and organoids in the developmental process. The resulting organoids have nonetheless been limited in size, and to date, functional organoid vascularization has only been achieved by grafting organoids into host animals \(^{10,11}\) .
+
+A number of studies have focused on creating artificial vessels though the use of templating approaches based on patterned layer- by- layer deposition of gelled material, in the form of thin filaments \(^{12}\) ,
+
+<--- Page Split --->
+
+droplets \(^{13 - 18}\) or layer- by- layer polymerization by stereolithography \(^{19 - 21}\) . Large tissue constructs have been generated by bioprinting of bioinks comprised of gels carrying different cell types \(^{12,22,23}\) , with vascular templates generated by depositing endothelial cells interleaved with tissue- specific cells using filament extrusion \(^{24 - 28}\) or stereolithography \(^{19,21}\) . While multiphoton lithography has been used to fabricate capillary- sized tubular fragments \(^{29}\) and vascular mimics \(^{30}\) , these vessels have thus far not been successfully perfused. The dissolution of sacrificial networks to form lumenized vessels has been proposed as an alternative strategy, with resorbable gel filaments being created via stereolithography \(^{31}\) , pre- polymer extrusion \(^{32 - 38}\) or molding \(^{39}\) . Artificial vessels have also been formed by the direct removal of diverse hydrogel material such as silk fibroin and PEG hydrogels using laser photo- ablation \(^{40 - 44}\) including in the presence of cells \(^{45 - 47}\) .
+
+Despite the versatility of these vessel templating approaches, the minimal diameter of perfusable engineered vessels reported thus far has been limited to \(150\mu \mathrm{m}^{33,39}\) and, in parallel with strategies based on extrinsic angiogenesis in organ- on- chip implementations \(^{48}\) , the size of generated tissues has been limited to \(400 - 500\mu \mathrm{m}\) in at least one dimension \(^{49 - 53}\) . Because of their small size, engineered tissues which have been implemented thus far do not preserve a physiologically relevant signaling context within the tissue, nor do they develop to a level of complexity comparable to in vivo organs.
+
+## Photo-polymerizable non-swelling hydrogels enable 3D soft microfluidics
+
+In order to vascularize tissue at large scale, we hypothesized that a microfluidic approach which could bridge the capillary to tissue scale would be necessary to enable the perfusion of thick three- dimensional tissue constructs. We therefore designed a dense, regularly spaced capillary network whose tubular walls were made of a hydrogel allowing diffusion (Fig. 1a). Tissues growing within this soft grid- like hydrated network would interface with an external perfusion pumping system, circulating cell culture medium throughout the volume of the tissue (Fig. 1a and Supplementary Fig. 1). We developed an approach whereby the perfusable grid would be printed directly on a hard plastic base (Fig. 1a), thereby forming a tight seal. This base, which contains perfusion holes, would then be incorporated into a perfusion chip linked to a peristaltic pump circulating cell culture medium (Supplementary Fig. 1)
+
+<--- Page Split --->
+
+An important requirement of this platform was the need to have capillary- like tubing at scales of a few \(\mu \mathrm{m}\) in diameter and thickness, while perfusing across a large, multi- \(\mathrm{mm}^3\) three- dimensional space. The geometrical complexity of the design, properties of the biopolymer and fabrication scale ranging from \(10\mu \mathrm{m}\) to \(2000\mu \mathrm{m}\) featured by our design made two- photon laser scanning photo- polymerization the ideal technology for this purpose. Initial 3D prints with the 2- photon Nanoscribe printer using commonly used photopolymerizable materials, including gelatin and PEG diacrylate, resulted in significant swelling of the material upon polymerization and hydration, which disrupted the seal between the soft microfluidic grid and the rigid plastic plate, and generated mismatched tubular segments (Supplementary Fig. 2).
+
+To overcome this post- printing distortion, we developed a custom formulated hydrophilic photopolymer based on polyethylene glycol diacrylate (PEGDA). While PEGDA exhibits cell- repelling surface properties, the polymer surface could be rendered cell- binding by the addition of the photocrosslinker pentaerythritol triacrylate (PETA)54. We reasoned that the addition of a significant amount of PETA as a crosslinker would increase the toughness of the polymer, and balanced with the addition of an inert "filler" component (Triton- X 100) would on the other hand retain sufficient porosity of the polymer to enable rapid diffusion.
+
+The combination of 2- photon printing with this non- swelling hydrogel material allowed printing of a variety of microfluidic grids, ranging in size from \(1.2 \times 1.2 \times 1.2\mathrm{mm}\) up to \(6.5 \times 6.5 \times 5\mathrm{mm}\) (Fig. 1b and Supplementary Fig. 3) with vessel diameters from \(10\mu \mathrm{m}\) to \(>70\mu \mathrm{m}\) and vessel wall thickness from \(2\mu \mathrm{m}\) to \(10\mu \mathrm{m}\) (Fig. 1c). Importantly, the printing with our novel formulation resin resulted in a 1:1 fidelity between the generated CAD geometry and the printed parts, thereby ensuring no distortion and a tight seal (Supplementary Fig. 2). The standard size used for most of the subsequent experiments was \(2.6\mathrm{mm} \times 2.6\mathrm{mm} \times 1.5\mathrm{mm}\) , with an inter- vessel distance of \(250\mu \mathrm{m}\) (Fig. 1b). These grids could be incorporated into a multi- plexed perfusion chip allowing up to 8 grids to be perfused simultaneously (Fig. 1a). Single cells or organoids smaller than the \(250\mu \mathrm{m}\) inter- capillary distance, previously mixed within a liquid hydrogel (eg. Matrigel) precursor solution, could be seeded into the platform, yielding a "gel- in- gel" 3- dimensional construct (Fig. 1d). Vessel permeability to water- soluble molecules within the chips overlayed with Matrigel was verified using fluorescein, with diffusion throughout the three- dimensional space seen in less than 10 minutes (Fig. 1e).
+
+<--- Page Split --->
+
+To perform a biological proof of concept experiment, we generated hundreds of organoids of less than \(200 \mu m\) diameter by aggregating human pluripotent stem cells (hPSCs) in microwells in pluripotency medium over 24 hours. We collected these aggregates in cold liquid Matrigel, which were then pipetted into the grids. Initial seeding demonstrated that these aggregates filled the grids and, over a period of 8 days of growth and neural differentiation, merged and filled the whole volume (Fig. 1f and Supplementary Fig. 4).
+
+## scRNAseq reveals changes in differentiation, hypoxia, cell cycle regulation and differentiation upon perfusion
+
+To assess how perfusion affected cellular processes and differentiation in large- scale in- vitro tissue, we dissociated cells from tissue constructs in a perfused and a non- perfused grid, as well as from organoids in conventional suspension culture after the 8- day culture period, and performed single cell RNA sequencing. Graph- based clustering and Uniform Manifold Approximation and Projection (UMAP) dimensionality reduction technique on the 8,625 total cells retained after QC revealed significant transcriptomic differences between the tissue constructs (perfused and non- perfused) and the control organoids as evidenced by largely separated clustering of these cell populations (Fig. 2a). Correlation analysis using the 100 most differentially expressed marker genes revealed the most difference between perfused tissue and conventional organoid culture, with non- perfused tissue sharing gene expression profiles with the other two conditions (Supplementary Fig. 5). Differential gene expression analysis was then used to annotate eight clusters, which were largely differentiated by fate, as well as by metabolic, hypoxia and cell cycle regulation (Fig. 2b, Fig. 2d, Supplementary Fig. 6, Supplementary Fig. 7). Cells from control organoids were found in clusters with low, medium and high glycolytic processes marked by a pluripotent identity, including highly expressed markers such as NANOG and OCT4 (POUF5F1). Both perfused and non- perfused tissues expressed varying degrees of hypoxia, proliferation, mitochondrial gene expression and neuroepithelial markers. The non- perfused tissue made up the largest proportion of the hypoxic and stressed clusters (HIF1α, FOS) while the perfused tissue represented the majority of the neuroepithelial cluster (PAX6).
+
+In particular, control organoids had lower expression of mitochondrial genes (Supplementary Fig. 7, Supplementary Fig. 8) compared to the tissue constructs. This is in line with previous reports of lower
+
+<--- Page Split --->
+
+mitochondrial activity in human embryonic stem cells that increase upon differentiation to fit the energy needs of resultant cell identities55. Indeed, differentiation towards the neuroepithelial fates from pluripotent cells was characterized by an increase in mitochondrial activity, and a simultaneous decrease in glycolysis (Supplementary Fig. 8). These results suggest a metabolic switch from anaerobic glycolysis to oxidative phosphorylation in the tissue constructs, as has been reported to occur during cell differentiation after exit from pluripotency56,57. Such transitions, which were additionally evidenced in pseudotime analysis (Fig. 2c) distinguished the control organoids from the tissue constructs in the microfluidic grids, and further characterized differences between non- perfused and perfused tissues.
+
+The perfused tissue was also characterized by the expression of the neuroepithelial markers PAX6, PAX7, PAX3, and CDH2, while sharing IRX1 and IRX2 markers with non- perfused tissue (Fig. 2d). Moreover, while non- perfused and perfused tissues represented similar proportions of the pluripotent proliferating cluster, the perfused tissue expressed the highest proliferation markers such as CDC6 (Supplementary Fig. 7). Additionally, the high expression of proliferation markers such MKi67 and TOP2A in the neuroepithelial cluster suggested the retained proliferative capacity of perfused tissues after neuroepithelial differentiation, while maintaining overall minimal hypoxic/stress response markers VEGF, FOS, HIF1a (Supplementary Fig. 8). By contrast, non- perfused tissue was distinguished by significant presence of pluripotency (NANOG, POU5F1/OCT- 4) (Fig. 2d) and hypoxia/stress markers (Fig. 2d, Supplementary Fig. 8). The control organoids, on the other hand, were mostly represented by pluripotent and hypoxic cells with complete absence of neuroepithelial identity (Fig. 2d and Supplementary Fig. 8), likely due to the short time in neural differentiation conditions.
+
+To investigate transcriptional changes and associated cellular processes upon perfusion in a systematic manner, we performed differential gene expression analysis between perfused and non- perfused tissue constructs followed by Gene Ontology (GO) enrichment analysis (Fig. 2e). This analysis confirmed up- regulation of processes related to cell division and proliferation in the perfused sample, as well as regulation of neural precursors and neural precursor cell proliferation. By contrast, cell stress, hypoxia and cellular death processes were upregulated in non- perfused samples. Taken together our analysis of the transcriptomic data suggested that perfusion of large tissue constructs dramatically decreased apoptosis and hypoxia, and accelerated the process of neural differentiation.
+
+<--- Page Split --->
+
+## Perfusion rescues hypoxia and necrotic core in large tissue constructs
+
+To further investigate how perfusion modulates the spatial distribution of hypoxia and apoptosis, we imaged the constructs in bright field microscopy and sectioned whole samples transversely, perpendicular to the direction of grid perfusion, followed by immunohistochemistry (Fig. 3a and associated quantification in Fig. 3b). Control organoids demonstrated a characteristic dark dense tissue core with occasional lighter voidlike structures, surrounded by more translucent peripheral tissue. In non- perfused samples, tissue growth was restricted to the internal volume of the microfluidic grid, with generally dense central tissue interspersed with patchy lighter areas. Strikingly, perfused tissue covered the entire volume of the grid in a uniformly dense manner, with bulging epithelial outgrowths characteristic of cerebral organoids at the periphery. These observations suggested that cell proliferation was much higher in the perfused grids, compared to the non- perfused samples. To confirm this observation quantitatively, we dissociated the tissue constructs into single cells, stained with calcein- AM and ethidium homodimer to label live and dead cells respectively, followed by quantitative flow cytometry (Fig. 3b and Fig. 3c). Our analysis revealed a 5- fold difference in total cell number in the perfused tissue constructs over the non- perfused ones, while the proportion of live cells was similar (90.9±5.1% in perfused vs 89.2±4.4% in non- perfused tissue) (Fig. 3a and Fig. 3b).
+
+To determine whether these changes in viability and proliferation were due to apoptosis, we stained sections of the grids for cleaved Caspase 3, an active form of the Caspase- 3 enzyme responsible for the degradation of multiple cellular proteins and ultimately for cell fragmentation into apoptotic bodies. Upon sectioning, the control organoids were empty in the center, suggesting, as has previously been reported58, the loss of apoptotic cells during the sectioning process. Closer to this inner core, signs of apoptosis were evident (8±1% of total area), (Fig. 3a,b), consistent with the large size of these organoids. Tissue in the non- perfused grids exhibited a clear inner core of apoptotic cellular fragments (35.7±5% of total section area) (Fig. 3a) along with empty regions completely lacking cells, with some analogous features to control organoids. Strikingly, nearly the entire perfused tissue did not show signs of cleaved Caspase 3 (5.1±1% of total area), indicating that perfusion successfully prevented cell apoptosis throughout the course of differentiation.
+
+<--- Page Split --->
+
+To verify whether hypoxia could be involved in initiating the observed apoptosis in the non- perfused samples, we next stained for HIF1α, a heterodimer protein complex playing a key role in oxygen homeostasis59,60. The rapid buildup of HIF- 1α in low- oxygen conditions is known to trigger a hypoxic response ultimately leading to apoptosis61,62. In line with scRNA analysis data (Fig. 3d), high HIF1α expression levels were detected in the control organoids (100±3% mean fluorescent intensity), as well as in the non- perfused samples (55±3% of organoid control). Conversely, low levels of HIF1α expression were observed in the perfused samples (26±2% of organoid control) (Fig. 3a), associated with a higher proportion of cycling G2, M and S phase cells (Fig. 3d).
+
+The patterns of HIF- 1α and cleaved Caspase3 expression in non- perfused tissue sections therefore suggest that in these samples, cells in the center of the construct were in a transient hypoxic state ultimately leading to apoptotic cell death. This transition from hypoxic to apoptotic cell state continued until the volume of the tissue was small enough to allow sufficient oxygen supply by a passive diffusion, with the accumulation of apoptotic bodies and cellular debris preserving the cleaved Caspase 3 expression in the bulk of the non- perfused tissue (Supplementary Fig. 9). Conversely, this phenomenon was completely absent in the perfused samples, clearly confirming that thick tissues at multi- mm3 scale could be grown with high viability, and with little to no apoptosis or hypoxia within this platform.
+
+## Accelerated neural differentiation in perfused tissue constructs
+
+Our scRNAseq data suggested that perfusion not only improved proliferation, prevented apoptosis and hypoxia, but could also direct fate specification. To confirm these findings, we analyzed specific markers of pluripotency and neural differentiation by immunohistochemistry (Fig. 3a and associated image quantification in Fig. 3b). NANOG, a canonical marker of pluripotency was abundantly expressed in organoids (73.6±8% of cells) and significantly expressed in non- perfused constructs (16.1±2%) at the protein level, but was completely missing in perfused samples. Conversely, PAX6, the earliest marker of neural differentiation was clearly evidenced in the perfused samples (21.5±2%), but not in organoid controls and non- perfused samples. These results were in line with the scRNAseq data, which indicated that NANOG- expressing cells were present in the control and non- perfused samples, while PAX6 was largely expressed in the perfused sample (Fig. 4c). The transition of stem cells from pluripotency to neural identity
+
+<--- Page Split --->
+
+is regulated by a loss of cellular expression of E- CADHERIN (CDH1) and a gain of N- CADHERIN (CDH2) expression which drives neural differentiation by inhibiting FGF- mediated pathways63. In order to assess whether perfusion enhanced this transition, we stained for E- CADHERIN to evidence the epithelial state associated with pluripotency, and for N- CADHERIN to confirm the transition to early neuro- epithelial identity. Perfused samples were indeed largely N- CADHERIN positive (55.7±9% vs 7.6±1% in non- perfused samples), while more cells in the non- perfused samples maintained E- CADHERIN+ identity (26.6±7% vs 4.5±2% in perfused samples). These results were confirmed by the scRNA data (Fig. 4c), indicating the predominant expression of N- CADHERIN in cells from perfused tissue, and E- CADHERIN in non- perfused and control tissue. Taken together, these results demonstrate that perfusion rapidly accelerates the transition from pluripotency to early neuroepithelial identity, while cells which lack perfusion remain in a state of pluripotency.
+
+## Long-term perfusion of liver tissue constructs
+
+To demonstrate the versatility of this platform, we went on to assess the differentiation of PSC- derived liver progenitors in perfused grids. hPSC were differentiated for 8 days in conventional 2D culture, followed by spheroid generation, seeding into the chip and perfusion for an additional 32 days. As was the case with neural differentiation, cells merged over time into a continuous tissue (Supplementary Fig. 10), with histological analysis identifying tightly packed cells with an eosinophilic and clear vacuolated cytoplasm reminiscent of hepatocytes, with no evidence of apoptotic bodies or necrosis throughout the tissue (Fig. 5a). The expression of many hepatocyte- specific genes was upregulated in perfused tissue constructs compared to both control hepatic organoids and 2D hepatocyte differentiation, including hepatocyte nuclear factor 6 (HNF6), Na+/taurocholate co- transporting polypeptide (NTCP), albumin (ALB), alpha1- antitrypsin (AAT) and two major cytochrome P450 enzymes CYP2C9 and CYP3A4 (Fig. 5f). The presence of CYP3A4 as well as of the hepatocyte progenitor marker AFP were confirmed at the protein level in the perfused sample by immunohistochemistry (Fig. 5b). Interestingly, the two major gluconeogenesis enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6- phosphatase alpha (G6PC) were also expressed at higher levels in the perfused constructs, compared to control organoids (1.6- and 1.3- fold higher expression, respectively) (Fig. 5f).
+
+<--- Page Split --->
+
+We next assessed whether non- parenchymal cells in the developing liver, such as cytokeratin 19 (KRT19)- expressing cholangiocytes, which contribute to bile secretion and hepatocyte survival64, were also present in our perfused culture system. These cells are generated in- vivo from hepatoblasts surrounding the portal veins, while hepatoblasts located away from portal vein areas differentiate into hepatocytes65. We observed a similar localization pattern of KRT19+ cells, with such cells tightly surrounding every vessel in the microfluidic grid (Fig. 5c), while the hepatocytic markers HNF4α66 was expressed in cells scattered in the inter- vessel space (Fig. 5d). Additionally, the functional production of albumin (ALB) was confirmed by staining (Fig. 5d).
+
+Taken together, our results confirmed the feasibility of using this synthetic micro- vascularization approach as a generic strategy to building large, viable, perfused in- vitro tissues.
+
+## Discussion
+
+Here, we demonstrated for the first time an integrated3D culture platform which provides a physiologically relevant micro- perfusion for engineered tissues, resulting in enhanced tissue growth and differentiation compared to previously reported in- vitro tissue vascularization strategies.
+
+We showed that microvascular networks could be created using 2- photon hydrogel polymerization, demonstrating that this technology can be used to achieve micro- vasculature with previously unreported accuracy, resolution and scale. A significant limitation of current photo- polymerizable hydrogel materials is the significant swelling of the material, which prevents the robust, leak- free interface between printed structures and microfluidic perfusion systems. Our development of a non- swelling photo- polymerizable material formulation was a critical component to overcome this limitation, and enabled the printing of 3D soft microfluidic systems which could be reliably perfused over multiple weeks. The exchange of nutrients and oxygen as well as the removal of waste products was achieved via simple diffusion as the printed vascular network is permeable to water- soluble molecules and gases. The direct fabrication of capillaries of a defined topology delivers an unprecedented control over tissue perfusion parameters, and the design of the vascular network is highly flexible and can be adapted to more complex geometrical and structural requirements. To provide a complete extracellular milieu with structural 3D support to the growing engineered tissue, the space around the perfused vessels was filled with hydrogel. In the experiments
+
+<--- Page Split --->
+
+presented here, the hydrogel component consisted of the commonly used proteinaceous matrix Matrigel, however the platform can also readily accommodate without any additional modifications the use of other naturally derived matrices such as collagen, as well as synthetic artificial extracellular matrices such as poly(ethylene) glycol PEG \(^{67}\) or alginate \(^{68}\) . This technology provides a reliable fluidic coupling between the microfluidic grid and the host perfusion device, such that a continuous peristaltic pump driven perfusion is possible. By integrating these printed microfluidic grids into a perfusion system, we were able to demonstrate that that large- scale (>15mm \(^{3}\) ) fully perfused neural and liver tissues could be generated with this platform.
+
+Our experiments with neural tissue demonstrate that the differentiation trajectory of cells in this perfused system is significantly enhanced. While control organoids remained largely in a pluripotent state, scRNAseq analysis revealed that perfused tissue rapidly differentiated towards the neural fate, together with a switch from glycolysis to oxidative phosphorylation. Imaging and flow cytometry confirmed that this tissue was highly viable, and immunohistochemistry showed markers of neural differentiation, which were absent in the non- perfused sample, as well as hallmarks of epithelial to mesenchymal transition. This was underscored by our observations that the lack of active micro- perfusion of the engineered tissue construct triggered a stress response in the cells within the inner core of the tissue. The accelerated differentiation of tissues upon perfusion is thought to be due not only to increased availability of nutrients and oxygen but also to the rapid diffusion of differentiation factors within the tissue via the tightly spaced capillary network.
+
+The possibility of long- term perfusion within this platform was demonstrated by the maintenance of viable engineered liver tissue demonstrating enhanced phenotypic and functional features compared to standard 2D and 3D organoid culture. As cells in our current capillary design were not sufficiently distant from the source of oxygen to generate an oxygen gradient, we did not observe a clear spatial segregation of hepatocytic markers, known as zonation, in the perfused liver tissue, however this feature could be engineered by wider inter- vessel distance.
+
+Overall, the 3D soft microfluidic technology presented here overcomes one of the major challenge in engineering tissues and organoids: the lack of tissue perfusion from the initiation of tissue growth, and enables the generation of large engineered tissues which are vascularized from within and their maintenance over long periods of time. In applications such as disease modeling and drug development,
+
+<--- Page Split --->
+
+such a highly defined synthetic perfusion system would be beneficial in avoiding the complexity and variability introduced by exogenous angiogenesis- driven vascularization. While the current implementation of the platform does not recapitulate features of in vivo vascular networks such as adaptive vascular remodeling or selective blood brain barrier interactions, it addresses the major problem of oxygen, nutrient and growth factor and small molecule supply as well as of waste removal, allowing to generate viable tissues beyond currently available dimensions. The incorporating of endothelial vasculature with this synthetic capillaries could be implemented, where the hydrogel micro- vascularization could provide a temporary tissue support during the time required for angiogenesis- driven capillarization to establish a perfusable network. We expect that this approach is widely applicable in overcoming the current size limitations of bio- printed tissues and provides a technological foundation for the development of perfusable in vitro models of increased complexity and scale.
+
+## Acknowledgements
+
+This work was supported by FWO grant G087018N, Interreg Biomat- on- Chip grant and Vlaams- Brabant and Flemish Government co- financing, KU Leuven grants C14/17/111 and C32/17/027.
+
+<--- Page Split --->
+
+## Materials and Methods
+
+Human PSC culture. Human PSCs were cultured in Matrigel (356277, Becton Dickinson) coated 6 well plates up to \(60 - 70\%\) confluency. Passages were performed by a 3 min treatment of Dispase II (D4693, Sigma) at \(37^{\circ}C\) , followed by 2- 3 PBS washings at RT. 1 mL of E8- Flex medium (A2858501, Thermo Scientific) was added and the colonies were scraped and gently pipetted 4- 5 times through 1ml plastic tip to break the colonies. The colony suspension was then diluted at 1:5 ratio and plated to a Matrigel coated wells in \(2\mathsf{mL}\) of E8Flex medium supplemented with \(10\mu \mathsf{M}\) Rock inhibitor(Y- 27632, Hellobio) for \(24h\) . The medium was then replaced by \(2\mathsf{mL}\) of fresh E8- Flex medium and incubation was continued for \(48h\) , at which point the colonies usually reached \(60 - 70\%\) confluency and were ready for next passage.
+
+Human PSC- derived cerebral organoids and perfused cerebral tissue. We adapted the protocol by Lancaster et al. \(^{69}\) to our experimental conditions. Upon reaching a confluency of \(60 - 70\%\) hPSCs were dissociated by treatment the colonies with \(250\mu \mathsf{I}\) Accutase (A1110501, Gibco) for 7 min at \(37^{\circ}C\) and resuspended in E8Flex medium containing \(10\mu \mathsf{M}\) Rock inhibitor.
+
+Organoids were generated in U- bottom 96- well plates (#351177, Falcon). The plates were rinsed with Anti- Adherence Solution (#07010, Stemcell Technologies) and cells were plated at 9000cells/well density. Plates were spun at 300rcf at RT and left in CO2 incubator for 24 hours for hPSC spheroid aggregation, after which culture medium was replaced by fresh E8- Flex medium, without Rock inhibitor and changed afterwards every 2 days. At day 2, the spheroids were embedded in growth factor reduced (GFR) Matrigel (354230, Becton Dickinson) and kept in 6- well plates, pre- rinsed with Anti Adherence Solution in CO2 incubator. At day 6, neuronal induction was started by replacing E8- Flex medium with DMEM/F12 medium (31330038, Gibco) containing \(1\%\) MEM- NEAA (11140035, Gibco), \(1\%\) Glutamax (35050038, Gibco), \(1\%\) Pen- Strep (15140122, Gibco), \(0.5\%\) N2 supplement (17502048, Gibco) and \(1\mathsf{ug / ml}\) Heparin (H3149, Sigma) (neural induction medium). Day 8 spheroids were used for characterization.
+
+For the formation of perfused tissue, at day 0, we first generated micro- hPSC spheroids using 24- well Aggrewell plates (34411, Stemcell Technologies) following a protocol supplied by the manufacturer. Specifically, we seeded Aggrewells with hPSCs to obtain 350- 400 cells per micro- well. After 24 hours,
+
+<--- Page Split --->
+
+spheroids formed and the medium was replaced by fresh E8- Flex without Rock inhibitor. At day 2, the spheroids typically reached a diameter of 180- 200um, and were harvested and resuspended in ice cold GFR Matrigel at a density of 3500 spheroids per 200- 250ul GFR Matrigel. The grids were placed under stereomicroscope in a 35mm petri dish on ice and seeded with the spheroid suspension at final density of \(\sim 1800\) spheroids per grid. \(200\mu l\) plastic tips pre- chilled on ice were used to dispense the suspension under stereomicroscope. Seeding was performed in several stages in order to allow dispensed spheroids to settle into the grids. After seeding, the grids were kept in a CO2 incubator for 40- 50 min to allow Matrigel polymerization, after which the grids where placed in a perfusion chip and perfusion was started. E8- Flex/PenStrep medium was changed every 2 days (3- 4ml per grid). At day 6, E8- Flex medium was replaced by neural induction medium for 2 days. At day 8, the grids were extracted and the tissue used for characterizations.
+
+Immunofluorescence analysis of cerebral tissue samples. Samples were fixed with \(4\%\) paraformaldehyde (158127, Sigma- Aldrich) for 24- 36 hours at \(4^{\circ}C\) and washed by 3 incubations in PBS for 15- 20 min at room temperature. Fixed tissue was sectioned either by embedding in low melting point agarose and sectioning on vibratome (Leica VT1000S) into 100- 150um sections or cryopreserved in OCT(6502, Thermo APD Consumables) overnight at \(4^{\circ}C\) , re- embedded into fresh OCT, frozen in isopropanol/dry ice slurry, cut into 50um sections on cryotome (Leica CM1850) and affixed on SuperFrost Plus (10019419, Thermo Scientific) microscope glass slides.
+
+Sections were incubated in a permeabilization and blocking solution of \(0.3\%\) Triton X (A4975, PanREAC Applichem) and \(3\%\) BSA (A7906, Sigma) in PBS for 24 hours at \(4^{\circ}C\) . Primary antibodies were diluted in the permeabilization and blocking solution and applied to sections for 24h at \(4^{\circ}C\) , after which three PBS washes were performed over another 24h period. Secondary antibodies and Hoechst were also diluted in the permeabilization and blocking solution and applied to sections overnight at \(4^{\circ}C\) , followed by washing in PBS 3- 4 times over another 24 hours. Antibodies used in this study are listed in Table 1. Stained agarose- embedded sections were stored in 2mM sodium azide solution in PBS. Cryosections were mounted in Fluoromount- G medium and stored at \(4^{\circ}C\) .
+
+<--- Page Split --->
+
+
+Table 1. List of antibodies used in this study
+
+| Primary | Host | Dilution | Manufacturer |
| Pax6, monoclonal | Mouse | 1:200 | DSHB |
| Nanog | Goat | 1:200 | R&D Systems, AF1997 |
| ECad | Mouse | 1:500 | Abcam, ab76055 |
| NCad | Rat | 1:200 | DSHB |
| Cleaved Caspase3 | Rabbit | 1:400 | Cell Signaling Technology, 9661 |
| HIF1a | Rabbit | 1:500 | Abcam, ab51608 |
| HNF4α | Mouse | 1:200 | Abcam, ab41898 |
| Alpha-1-Antitrypsin | Rabbit | 1:200 | DAKO, A0012 (00092029) |
| PEPCK | Mouse | 1/1000 | Santa Cruz, sc-271204 |
| MRP2 | Mouse | 1/500 | Abcam, ab3373 |
| KRT19 | goat | 1/500 | Santa Cruz, sc-33120 |
| ALB | Rabbit | 1/500 | Abcam, ab207327 |
| Secondary | | | |
| Hoechst | | | Sigma-Aldrich, 14533 |
| Anti-mouse Alexa 647 | Donkey | 1:500 | Invitrogen, A31571 |
| Anti-goat Alexa 647 | Donkey | 1:500 | Invitrogen, A21447 |
| Anti-rat Alexa 555 | Goat | 1:500 | Invitrogen, A21434 |
| Anti-goat Alexa 555 | Donkey | 1:500 | Invitrogen, A21432 |
| Anti-rabbit Alexa 555 | Donkey | 1:500 | Invitrogen, A31572 |
| Anti-mouse Alexa 488 | Donky | 1:500 | Invitrogen, A11029 |
+
+Human PSC- derived perfused hepatic tissue. All liver differentiation experiments were performed with the H3CX hiPSC line previously generated 70. H3CX is a hiPSC line (Sigma 0028, Sigma- Aldrich) genetically engineered to overexpress 3 transcription factors HNF1A, FOXA3 and PROX1 upon Doxycycline induction, which allows for rapid generation of hepatocyte- like progeny. H3CX cells were
+
+<--- Page Split --->
+
+expanded feeder- free on Matrigel (BD Biosciences)- coated plates in E8 or E8 Flex (Thermo Fisher Scientific). HC3X cells were differentiated towards HLCs as previously described71. Briefly, HC3X cells were dissociated to single cells using StemPro™Accutase™ Cell dissociation Reagent (Thermo Fisher Scientific) and plated on Matrigel- coated plates at \(\pm 8.75 \times 10^{4}\) cells/cm² in mTeSR medium (Stem Cell Technologies) supplemented with RevitaCell (Thermo Fisher Scientific). When cells reached 70- 80% confluence, differentiation was performed during 40 days in liver differentiation medium (LDM) containing to comprise 500ml total volume: 285 ml of DMEM low glucose (Invitrogen 31885023), 200 ml of MCDB- 201 solution in water (Sigma M- 6770) adjusted to pH 7.2, \(0.25 \times\) of Linoleic acid—Bovine serum albumin (LA- BSA, Sigma L- 9530), \(0.25 \times\) of Insulin- transferrin- selenium (ITS, Sigma I- 3146), 50 U of Penicillin/Streptomycin (Invitrogen 15140122), 100 nM of I- ascorbic acid (Sigma A8960), 1 μM dexamethasone (Sigma D2915) and 50 μM of \(\beta\) - mercaptoethanol (Invitrogen 31350010). Differentiation medium was supplemented with \(0.6\%\) dimethylsulfoxide (DMSO) during the first 12 days of the culture. \(2.0\%\) DMSO and 3x concentrate of non- essential amino- acids (NEAA) was added to LDM medium between days 12- 13, and from day 14 until the end of differentiation 20g/L glycine was added to LDM medium supplemented with NEAA. Differentiation was performed in presence of the following factors: day 0- 1: 100ng/ml Activin- A and 50ng/ml Wnt3a, day 2- 3: 100ng/ml Activin- A, day 4- 7: 50ng/ml BMP4, day 8- 11: 20ng/ml FGF1, and 20ng/ml HGF during the rest of differentiation. Doxycycline (5ug/ml) was applied from day 4 until the end of differentiation. All cytokines were purchased from Peprotech.
+
+RNA extraction and quantitative reverse- transcription PCR. RNA extraction was performed using TR1zol reagent (Invitrogen) following manufacturer's instructions. At least 1μg of RNA was transcribed to cDNA using the Superscript III First- Strand synthesis (Invitrogen). Gene expression analysis was performed using the Platinum SYBR green qPCR supermix- UDG kit (Invitrogen) in a ViiA 7 Real- Time PCR instrument (Thermo Fisher Scientific). The sequences of all used RT- qPCR primers are listed in Table 2. The ribosomal protein L19 transcript (RPL19) was used as a housekeeping gene for normalization.
+
+| RPL19 | ATTGGTCTCATTGGGGTCTAAC AGTATGCTCAGGCTTCAGAAGA |
| AAT | AGGGCCGGAAGCTAGTGAGT TCCTCGGTGTTCCTTGACTTC |
+
+<--- Page Split --->
+
+
+Table 2. List of primers used in this study
+
+| NTCP | ATGCTGAGGCAAGGATGTTC AGCAGCAGCACGACAGAGTA |
| G6PC | GTGTCCGTGATCGCAAGCC GACGAGGTTGAGCCAGTCTC |
| CYP3A4 | TTCCTCCCTGAAAGATTCAGC GTTGAAGAAGTCTCCTAAGCT |
| PEPCK | AAGAAGTGCTTTGCTCTCAG CCTTAAATGACCTTGTCGT |
| CYP2D6 | CATACCTGCCCTACTACCAAA TGTCTGCCTGGTCCTC |
| PGC1α | CCTTCGAGCACAAGAAAACA TGCTTCGTCGTCAAAAACAG |
| HNF6 | AAATCACCATTTCCCAGCAG ACTCCTCCTTCTTGCGTCA |
| ALB | ATGCTGAGGCAAGGATGTTC AGCAGCAGCACGACAGAGTA |
| AAT | AGGGGCTGAAGCTAGTGGAT TCCTCGGTGTCCTTGACTTC |
+
+Histology. Samples were fixed with \(4\%\) (w/v) paraformaldehyde (PFA, Sigma- Aldrich) overnight at \(4^{\circ}\mathrm{C}\) washed 3 times with PBS and submerged in PBS- sodium azide ( \(0.01\%\) v/v) solution at \(4^{\circ}\mathrm{C}\) until embedded in paraffin. Hydrogel sections (5 \(\mu \mathrm{m}\) ) were prepared using a microtome (Microm HM 360, Marshall Scientific.) For Hematoxylin and Eosin (H&E) staining, sections were treated with xylene solution to remove the paraffin, and gradually rehydrated in ethanol (100 to \(70\%\) , v/v). H&E staining was performed by submerging rehydrated hydrogel sections in Harris Hematoxylin solution, acid alcohol, bluing reagent and Eosin- Y solution by order. Stained samples were dehydrated with ascending alcohol series, washed in xylene solution, and mounted with DPX mountant (Sigma- Aldrich).
+
+Immunofluorescence analysis of liver tissue samples. Following deparaffinization in xylene and rehydration in descending alcohol series, heat- mediated antigen retrieval was performed by incubating hydrogel sections in Dako antigen retrieval solution (Dako) for 20 min at \(98^{\circ}\mathrm{C}\) . This step was followed by cell permeabilization with \(0.01\%\) (v/v) Triton- X (Sigma- Aldrich) solution in PBS, for 20 minutes. Samples
+
+<--- Page Split --->
+
+were then incubated with \(5\%\) (v/v) Goat or Donkey Serum (Dako) for 30 min. Primary antibodies diluted in Dako antibody diluent solution, were incubated overnight at \(4^{\circ}C\) , followed by washing steps and incubation with Alexa- coupled secondary antibody (1:500) and Hoechst 33412 (1:500) solution for 1 hour at room temperature. Finally, samples were washed in PBS, and mounted with Vectashield antifade mounting medium (Vector Laboratories). Stained sections were imaged using laser scanning confocal microscope (LSM 880, Zeiss, Germany), and image processing were performed on ZEN Blue software (Zeiss, Germany).
+
+Image acquisition and analysis of cerebral tissue samples. Fluorescence images were obtained using a confocal microscope (Leica SP8 DIVE, Leica Microsystems) equipped with 10x NA0.4 dry objective. Acquisition parameters were kept constant for all samples obtained in the same experiment. Image processing was performed using Fiji/ImageJ (NIH) and custom- written ImageJ Java plugin. At the data preprocessing stage, image stacks were collapsed by maximum intensity projection. Resulting images were translated to 8- bit lookup table representation, manually cleaned from grid structure elements and thresholded by replacing all sub- threshold pixels with black (zero value) pixels. Lookup tables of the images were then remapped from [Threshold..255] back to full [0..255] range. Threshold values were chosen manually for Hoechst and marker channels for each image in order to remove background from the images. For all markers except HIF1α, total protein expression levels in a tissue were quantified as a relative number of cells expressing the protein, i.e.
+
+\[Protein expression = \frac{Marker^{+}cellnumber}{Totalcellnumber} \times 100\%\]
+
+On the assumption that cell size is constant across the samples, the relative number of cells was estimated as a ratio of areas occupied by cells on marker and Hoechst channels. Corresponding areas were calculated by counting all non- zero pixels on marker and Hoechst channels. For statistical comparison, results for each marker were pooled from all experiments.
+
+As HIF1α marker is constitutively expressed in cells under normoxic conditions, its expression level in a tissue was estimated as the average fluorescence intensity on the marker channel. Threshold values were kept constant for organoids, non- perfused and perfused samples obtained in the same experiment;
+
+<--- Page Split --->
+
+expression values obtained in the experiment were normalized to organoid value and normalized data from different experiments were averaged.
+
+All results are expressed as mean \(\pm\) SEM. Statistical comparisons between two data groups were analyzed using unpaired two- tailed Student's \(t\) - test with a \(95\%\) confidence interval (Origin Pro v9.5, OriginLab Inc.). Significance was marked on plots by \*, \*\* and \*\*\* for \(p< 0.05\) , \(p< 0.01\) , and \(p< 0.001\) correspondingly. If not stated otherwise, the statistical significance was assessed for comparisons of perfused and non- perfused samples to organoid control samples and denoted by "pControl".
+
+Organoid dissociation and single- cell RNA sequencing. For dissociation, the microfluidic grids of non- perfused and perfused samples were removed from the perfusion chips and, along with the control organoids, placed temporarily in DMEM/F12 media in independent \(15 \text{mL}\) Falcon tubes until all 3 samples were ready for the next step (time \(< 5 \text{min}\) ). The DMEM was then replaced with \(1 \text{mL}\) of pre- warmed TrypLE Express (12605010, Gibco) at \(37^{\circ} \text{C}\) . The samples were transferred to a warm water bath at \(37^{\circ} \text{C}\) for 7.5 minutes with gentle agitation every 1 minute after the first 3 minutes. A visual inspection was performed using an inverted microscope to ensure complete dissociation of tissues and the presence of single cells. The \(1 \text{mL}\) solution was introduced to \(9 \text{mL}\) of DMEM supplemented with \(20\%\) FBS for TrypLE Express neutralization, and centrifuged at \(500 \text{rcf}\) for 5 minutes. The pellet was resuspended in \(200 \text{uL}\) of N2B27 media and put on ice. This dissociation protocol yielded an average viability of above \(80\%\) across all samples.
+
+Library preparations for the scRNAseq was performed using 10X Genomics Chromium Single Cell 3' Kit, v3 (10X Genomics, Pleasanton, CA, USA). The cell count and the viability of the samples were accessed using LUNA dual fluorescence cell counter (Logos Biosystems) and a targeted cell recovery of 6000 cells was aimed for all the samples. Post cell count and QC, the samples were immediately loaded onto the Chromium Controller. Single cell RNAseq libraries were prepared using manufacturers recommendations (Single cell 3' reagent kits v3 user guide; CG00052 Rev B), and at the different check points, the library quality was accessed using Qubit (ThermoFisher) and Bioanalyzer (Agilent). Single cell libraries were sequenced using paired- end sequencing workflow and with recommended 10X; v3 read
+
+<--- Page Split --->
+
+parameters (28- 8- 0- 91 cycles). The data generated from sequencing was de- multiplexed and mapped against human genome reference using CellRanger v3.0.2.
+
+Single Cell RNA sequencing Data Processing. We have sequenced 4,818, 5,453, and 2,804 cells for non- perfused, perfused and control organoids samples respectively for a total of 13,075 cells, which were reduced after QC steps to 8,625 cells with an average of 1,852 detected genes per cell. Data processing and subsequent steps were performed using the Seurat72 tool for single cell genomics version 3 in R version 4.0.3. A filtering step was performed to ensure the quality of the data, where the counts of mitochondrial reads and total genes reads were assessed. Cells with more than \(15\%\) of identifiable genes rising from the mitochondrial genome were filtered out. Similarly, cells having fewer identifiable genes than 200 (low quality) and above 7,500 (probable doublets) were filtered out. Data normalization was performed, followed by the identification of 2,000 highly variable genes using the FindVariableFeatures(). S- phase and G2M- phase cell cycle regression was performed to allow cell clustering purely on cell identity and fate, which otherwise was biased by cell cycle phases. Auto scaling of the data was performed and described using principal component analysis (PCA) using the RunPCA() function.
+
+Correlation analysis. Correlation heatmap between samples was performed in R using the top 100 marker genes for each sample using the FindAllMarkers() function followed by the selection of the top 100 marker genes using the top_n() function with \(n = 100\) and wt = avg.logFC. The correlation analysis was generated using the cor() function using the Pearson method and the heatmap using the heatmap.2() function in R.
+
+Data Clustering. Graph- based clustering using the FindNeighbors() function (using top 15 principal components (PCs)) and FindCluster() function (resolution = 0.5) was performed to group cells based on their transcriptional profiles. No batch correction was performed on the data set. Data visualization was performed using the Uniform Manifold Approximation and Projection (UMAP) dimensionality reduction technique using the RunUMAP package while employing the top 15 PCs identified in the previous PCA step. Cluster annotation was based on hallmark genes to identify Neuroepithelial cluster (PAX6, PAX7, PAX3), Pluripotent- Neuroepithelial transitioning (P- NE) cells (WNT4, IRX1, IRX2), Proliferating cells
+
+<--- Page Split --->
+
+(CDC6, PTN, MK167, TOP2A), medium mitochondrial gene content and low glycolysis pluripotent cells (MK167, TOP2A, with the expression of NANOG, POU5F1, DPPA4), Pluripotent cells (NANOG, POU5F1, DPPA4), highly glycolytic pluripotent cells that link to the Cycling pluripotent and Pluripotent cells but include the expressions (LDHA, ENO1, HK2), a cluster undergoing EMT/migration with hypoxic markers (EPCAM, VIM, TWIST2, VEGFA) and finally a stressed cluster (FOS, HIF1A, JUN). One cluster was manually removed due to very low unique molecular identifier (UMI) count, after which the data was reprocessed to account for the removal of the cluster.
+
+Pseudotime trajectories. Trajectory analysis was performed using Monocle \(3^{73}\) on R by employing the monocole3 and SeuratWrappers libraries. The Seurat obtained object containing all combined samples was passed to the Monocle 3 pipeline using the as.cell_data_set() function followed by processing using the cluster_cells() function. The pseudotime trajectory was inferred by first using the subset function on the only partition detected, followed by the learn_graph() function. Cells were colored in their inferred pseudotime using the which.max() function with the FetchData() (AVP) function, followed by the order_cells() function with the root_cell = max.avp. The UMAP superimposed with inferred pseudotime trajectory was generated using the plot_cells() function.
+
+Gene- set analysis and hierarchical clustering. Gene- sets were created using the AddModuleScore() function in R. three gene- set were created to explore the dataset, pluripotency gene- set (POU5F1, NANOG, CDH1), glycolysis gene- set (ALDOA, BPGM, ENO1, ENO2, GPI, HK1, HK2, PFKL, PFKM, PGAM1, PGK1, PKM, TP11), and a neural progenitor gene- set (PAX3, PAX6, PAX7, OTX2, CDH2). The % mitochondrial genes were obtain as evaluated by the Seurat pipeline. Each cell was evaluated and scored and its expression plotted on UMAPS. Cluster level hierarchical clustering of the gene- set scores and % mitochondrial genes was employed using R package heatmap.2 after scaling the expression across rows (clusters).
+
+Design and fabrication of soft micro- fluidic grids. The microfluidic grids were designed as a multitude of parallel capillaries stemming from a common reservoir. The dimensions of the grid (2.6x2.6x1.5mm) were
+
+<--- Page Split --->
+
+chosen as a compromise between size and the fabrication time. The grids were micro- fabricated on custom baseplates using high- resolution 3D printer (Photonic Professional GT2, Nanoscribe GmbH) equipped with 2- photon femtosecond laser. CAD model of the capillary grid was pre- processed by DeScribe software (Nanoscribe GmbH) to produce a printing job with defined printing parameters. A custom- formulation photopolymerizable resin was used to print microfluidic grids which contained \(2\%\) 2- Benzyl- 2- (dimethylamino)- 4'- morpholinobutyrophenone (lrgacure 369), \(7\%\) propylene glycol methyl ether acetate (PGMEA), \(36\%\) poly(ethylene glycol) diacrylate, MW700 (PEGDA 700), \(25\%\) pentaerythritol triacrylate (PETA), \(20\%\) Triton X- 100 and \(10\%\) water. lrgacure 369 was purchased from Tokyo Chemical Industry Ltd, the other components were from Sigma- Aldrich.
+
+The microfluidic grids were printed on custom plates 3D printed on Formlabs Form 2 printer from a biocompatible resin (Dental SG, Formlabs Inc), post- cured by UV light (Formcure station, Formlabs Inc) for 2h at \(80^{\circ}C\) and washed in 2- propanol for 3- 4 days with daily change of the solvent. The plates had 1mm thickness and 10mm diameter, with 0.5mm perfusion holes. The grid printing process was set up such that the inlets in the microfluidic grid were aligned with the perfusion holes in a baseplate. After fabrication, baseplate- grid assemblies were washed during 2 days in PGMEA, 12 days in 2- propanol and then kept in PBS until use. The solvents were refreshed every 1- 2 days and PBS was refreshed daily for the first week and every 2- 3 days afterwards.
+
+Fabrication of perfusion chips and setting up perfusion. The perfusion chips were implemented as an assembly as shown in Supplementary Fig. 1. Two microfluidic grids were sandwiched between two polydimethylsiloxane (PDMS) custom- profiled blocks. Two metal plates clamped with screws provided a tight junction between PDMS blocks and cover slips, thereby forming fluidic channels within the chip. The chips were designed to only allow contact of the medium with PDMS blocks and cover slips, thereby isolating the flow from contact with other materials of the chip. Guiding frames were used to simplify the alignment of the PDMS blocks during the chip assembly process.
+
+The PDMS blocks were made by casting liquid PDMS compound into custom- designed plastic molds and curing overnight at \(80^{\circ}C\) . The plastic molds were fabricated by stereo- lithography (SLA) 3D printer Form 2 (Formlabs Inc.) using a bio- compatible Formlabs Dental SG resin. The printed molds were
+
+<--- Page Split --->
+
+post- processed by thorough washing in 2- propanol and post- cured for 90 min at \(80^{\circ}C\) (Formcure, Formlabs Inc.). Metal plates were made from 1mm stainless steel sheet by laser cutting and stainless steel screws were used for clamping the assembly. The guiding frames were 3D printed and cover slips were glued to the metal plates with a bio- compatible UV/heat curable epoxy (NOA 86H, Norland) to provide a final two- part setup shown in Supplementary Fig. 1d.
+
+Two chambers of the chip, containing perfused and non- perfused grids, a peristaltic pump and a medium reservoir (50ml Falcon tube) were connected by flexible PVC tubing (ID/OD 0.8/1.6mm) in series (Supplementary Fig. 1e). The medium was taken from the reservoir by the pump and fed through chambers containing the non- perfused and then the perfused grid, after which the medium was sent back to the reservoir for \(\mathrm{CO_2 / O_2}\) equilibration. A 0.22um filter was connected between the two chambers of the chip to protect capillaries of the perfused grid from potential clogging with tissue debris. The medium reservoir and the chip were kept in a CO2 incubator, while the peristaltic pump remained outside to protect electronics from humidity and to ensure proper cooling. The medium reservoir and the chip were installed on a custom made 3D printed holder (Supplementary Fig. 1f) to simplify transitions between a CO2 incubator and a laminar hood. At day 0 of an experiment, all parts of the perfusion were sterilized by ethanol and UV light in a laminar hood, connected together and filled with equilibrated medium. The microfluidic grids, seeded with hPSC spheroids, were installed in the chip (Supplementary Fig. 1d) and the chip was clamped by screws (Supplementary Fig. 1f- i). Air bubbles were removed from the system and the perfusion started at approx. \(400\mu \mathrm{L} / \mathrm{min}\) flow rate (Supplementary Fig. 1, f- iii).
+
+Multi- grid perfusion chips were designed to provide an equal multiplexed perfusion for all microfluidic grids. The fluidic inlet of the chip, via three steps of bifurcations, was split into eight fluidic channels feeding eight wells. All fluidic channels had equal length and cross- section and, therefore, equal hydraulic resistance. The multi- grid chip were fabricated by stereo- lithography (SLA) 3D printer Form 2 (Formlabs Inc.) using Formlabs Dental SG resin. The printed chips were post- processed by thorough washing in 2- propanol and post- cured for 90 min at \(60^{\circ}C\) . 7- 8mm pieces of syringe needles (0.9mm) were cut by hand drill/cutter (Precision drill, Proxxon Inc.) and glued into chip inlets by a biocompatible UV/heat curable epoxy glue to serve as connectors for flexible tubing. This assembly was again post- cured in FormCure station for 120 min at \(80^{\circ}C\) to achieve complete hardening of the glue. To integrate microfluidic
+
+<--- Page Split --->
+
+grids, a custom profile gaskets, cut from 0.5mm PDMS sheet by a laser cutter, were placed under the grid substrates to provide a liquid- tight contact and the substrates were fixed in place by 3D printed fasteners.
+
+Data availability. All raw sequencing data, and the combined processed and metadata files generated in this study are available at GEO. The accession number for the reported data is GSE181290. This study did not generate any unique code. For review purposes please use the following token (ybchyyqofpejzgv) to access the sequencing data at: https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE181290. The ImageJ Java code used for analysis of the image data are available upon request.
+
+<--- Page Split --->
+
+## References
+
+1. Kaushik, G., Ponnusamy, M. P. & Batra, S. K. Concise Review: Current Status of Three-Dimensional Organoids as Preclinical Models: 3D Organoid Culture as a Tool for Research. Stem Cells 36, 1329–1340 (2018).
+2. Ollé-Vila, A., Duran-Nebreda, S., Conde-Pueyo, N., Montañez, R. & Solé, R. A morphospace for synthetic organs and organoids: the possible and the actual. Integr. Biol. 8, 485–503 (2016).
+3. Van Norman, G. A. Limitations of Animal Studies for Predicting Toxicity in Clinical Trials. JACC: Basic to Translational Science 4, 845–854 (2019).
+4. Gilbert, S. F. Developmental biology. (Sinauer Associates, 2000).
+5. Grebenyuk, S. & Ranga, A. Engineering Organoid Vascularization. Front. Bioeng. Biotechnol. 7, 39 (2019).
+6. Nashimoto, Y. et al. Integrating perfusable vascular networks with a three-dimensional tissue in a microfluidic device. Integrative Biology 9, 506–518 (2017).
+7. Salmon, I. et al. Engineering neurovascular organoids with 3D printed microfluidic chips. http://biorxiv.org/lookup/doi/10.1101/2021.01.09.425975 (2021) doi:10.1101/2021.01.09.425975.
+8. Rajasekar, S. et al. IFlowPlate—A Customized 384-Well Plate for the Culture of Perfusable Vascularized Colon Organoids. Adv. Mater. 32, 2002974 (2020).
+9. Sugihara, K. et al. A new perfusion culture method with a self-organized capillary network. PLoS ONE 15, e0240552 (2020).
+10. Takebe, T. et al. Vascularized and functional human liver from an iPSC-derived organ bud transplant. Nature 499, 481–484 (2013).
+11. Mansour, A. A. et al. An in vivo model of functional and vascularized human brain organoids. Nature Biotechnology 36, 432–441 (2018).
+12. Zhu, W. et al. 3D printing of functional biomaterials for tissue engineering. Current Opinion in Biotechnology 40, 103–112 (2016).
+13. Xie, M. et al. Electro-Assisted Bioprinting of Low-Concentration GelMA Microdroplets. Small 15, 1804216 (2019).
+
+<--- Page Split --->
+
+14. Cui, X., Boland, T., D.D'Lima, D. & K. Lotz, M. Thermal Inkjet Printing in Tissue Engineering and Regenerative Medicine. Recent Patents on Drug Delivery & Formulation 6, 149–155 (2012).
+
+15. Dababneh, A. B. & Ozbolat, I. T. Bioprinting Technology: A Current State-of-the-Art Review. Journal of Manufacturing Science and Engineering 136, 061016 (2014).
+
+16. Gudapati, H., Dey, M. & Ozbolat, I. A comprehensive review on droplet-based bioprinting: Past, present and future. Biomaterials 102, 20–42 (2016).
+
+17. Christensen, K. et al. Freeform inkjet printing of cellular structures with bifurcations: Approach Freeform Fabrication of Bifurcated Cellular Structures by Using a Liquid Support-Based Inkjet Printing Approach. Biotechnology and Bioengineering 112, 1047–1055 (2015).
+
+18. Nakamura, M. et al. Ink Jet Three-Dimensional Digital Fabrication for Biological Tissue Manufacturing: Analysis of Alginate Microgel Beads Produced by Ink Jet Droplets for Three Dimensional Tissue Fabrication. Journal of Imaging Science and Technology 52, 060201 (2008).
+
+19. Zhu, W. et al. Direct 3D bioprinting of prevascularized tissue constructs with complex microarchitecture. Biomaterials 124, 106–115 (2017).
+
+20. Ma, X. et al. Deterministically patterned biomimetic human iPSC-derived hepatic model via rapid 3D bioprinting. Proceedings of the National Academy of Sciences 113, 2206–2211 (2016).
+
+21. Huang, T. Q., Qu, X., Liu, J. & Chen, S. 3D printing of biomimetic microstructures for cancer cell migration. Biomedical Microdevices 16, 127–132 (2014).
+
+22. Singh, N. K. et al. Three-dimensional cell-printing of advanced renal tubular tissue analogue. Biomaterials 232, 119734 (2020).
+
+23. Gao, Q. et al. 3D printing of complex GelMA-based scaffolds with nanoclay. Biofabrication 11, 035006 (2019).
+
+24. Jia, W. et al. Direct 3D bioprinting of perfusable vascular constructs using a blend bioink. Biomaterials 106, 58–68 (2016).
+
+25. Xu, C., Chai, W., Huang, Y. & Markwald, R. R. Scaffold-free inkjet printing of three-dimensional zigzag cellular tubes. Biotechnology and Bioengineering 109, 3152–3160 (2012).
+
+<--- Page Split --->
+
+26. Kinoshita, K., Iwase, M., Yamada, M., Yajima, Y. & Seki, M. Fabrication of multilayered vascular tissues using microfluidic agarose hydrogel platforms. Biotechnology Journal (2016) doi:10.1002/biot.201600083.
+
+27. Roudsari, L. C., Jeffs, S. E., Witt, A. S., Gill, B. J. & West, J. L. A 3D Poly(ethylene glycol)-based Tumor Angiogenesis Model to Study the Influence of Vascular Cells on Lung Tumor Cell Behavior. Scientific Reports 6, 32726 (2016).
+
+28. Zhang, Y. S. et al. Bioprinting 3D microfibrous scaffolds for engineering endothelialized myocardium and heart-on-a-chip. Biomaterials 110, 45-59 (2016).
+
+29. Meyer, W. et al. Soft Polymers for Building up Small and Smallest Blood Supplying Systems by Stereolithography. Journal of Functional Biomaterials 3, 257-268 (2012).
+
+30. Huber, B. et al. Blood-Vessel Mimicking Structures by Stereolithographic Fabrication of Small Porous Tubes Using Cytocompatible Polyacrylate Elastomers, Biofunctionalization and Endothelialization. Journal of Functional Biomaterials 7, 11 (2016).
+
+31. Kang, H.-W. et al. A 3D bioprinting system to produce human-scale tissue constructs with structural integrity. Nature Biotechnology 34, 312-319 (2016).
+
+32. Compaan, A. M., Song, K., Chai, W. & Huang, Y. Cross-Linkable Microgel Composite Matrix Bath for Embedded Bioprinting of Perfusable Tissue Constructs and Sculpting of Solid Objects. ACS Appl. Mater. Interfaces 12, 7855-7868 (2020).
+
+33. Miller, J. S. et al. Rapid casting of patterned vascular networks for perfusable engineered three-dimensional tissues. Nature Materials 11, 768-774 (2012).
+
+34. Kolesky, D. B., Homan, K. A., Skylar-Scott, M. A. & Lewis, J. A. Three-dimensional bioprinting of thick vascularized tissues. Proceedings of the National Academy of Sciences 113, 3179-3184 (2016).
+
+35. Wu, W., DeConinck, A. & Lewis, J. A. Omnidirectional Printing of 3D Microvascular Networks. Advanced Materials 23, H178-H183 (2011).
+
+36. Bertassoni, L. E. et al. Hydrogel bioprinted microchannel networks for vascularization of tissue engineering constructs. Lab Chip 14, 2202-2211 (2014).
+
+<--- Page Split --->
+
+37. Subbiah, R. et al. Prevascularized hydrogels with mature vascular networks promote the regeneration of critical-size calvarial bone defects in vivo A short running title: Prevascularized hydrogels repair bone defects. J Tissue Eng Regen Med (2021) doi:10.1002/term.3166.
+
+38. Skylar-Scott, M. A. et al. Biomanufacturing of organ-specific tissues with high cellular density and embedded vascular channels. Sci. Adv. 5, eaaw2459 (2019).
+
+39. Silvestri, V. L. et al. A Tissue-Engineered 3D Microvessel Model Reveals the Dynamics of Mosaic Vessel Formation in Breast Cancer. Cancer Res 80, 4288-4301 (2020).
+
+40. Applegate, M. B. et al. Laser-based three-dimensional multiscale micropatterning of biocompatible hydrogels for customized tissue engineering scaffolds. Proceedings of the National Academy of Sciences 112, 12052-12057 (2015).
+
+41. Ouija, M. et al. Three dimensional microstructuring of biopolymers by femtosecond laser irradiation. Applied Physics Letters 95, 263703 (2009).
+
+42. Sarig-Nadir, O., Livnat, N., Zajdman, R., Shoham, S. & Seliktar, D. Laser Photoablation of Guidance Microchannels into Hydrogels Directs Cell Growth in Three Dimensions. Biophysical Journal 96, 4743-4752 (2009).
+
+43. Brandenberg, N. & Lutolf, M. P. In Situ Patterning of Microfluidic Networks in 3D Cell-Laden Hydrogels. Advanced Materials 28, 7450-7456 (2016).
+
+44. Skylar-Scott, M. A., Liu, M.-C., Wu, Y. & Yanik, M. F. Multi-photon microfabrication of three-dimensional capillary-scale vascular networks. in (eds. von Freymann, G., Schoenfeld, W. V. & Rumpf, R. C.) 101150L (2017). doi:10.1117/12.2253520.
+
+45. Kloxin, A. M., Kasko, A. M., Salinas, C. N. & Anseth, K. S. Photodegradable Hydrogels for Dynamic Tuning of Physical and Chemical Properties. Science 324, 59-63 (2009).
+
+46. Kloxin, A. M., Tibbitt, M. W., Kasko, A. M., Fairbairn, J. A. & Anseth, K. S. Tunable Hydrogels for External Manipulation of Cellular Microenvironments through Controlled Photodegradation. Advanced Materials 22, 61-66 (2010).
+
+47. Tibbitt, M. W., Kloxin, A. M., Dyamenahalli, K. U. & Anseth, K. S. Controlled two-photon photodegradation of PEG hydrogels to study and manipulate subcellular interactions on soft materials. Soft Matter 6, 5100 (2010).
+
+<--- Page Split --->
+
+48. Kim, J., Kong, J. S., Han, W., Kim, B. S. & Cho, D.-W. 3D Cell Printing of Tissue/Organ-Mimicking Constructs for Therapeutic and Drug Testing Applications. IJMS 21, 7757 (2020).
+
+49. Ahadian, S. et al. Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies. Advanced Healthcare Materials 1700506 (2017) doi:10.1002/adhm.201700506.
+
+50. Mittal, R. et al. Organ-on-chip models: Implications in drug discovery and clinical applications. J Cell Physiol 234, 8352-8380 (2019).
+
+51. Van Norman, G. A. Limitations of Animal Studies for Predicting Toxicity in Clinical Trials. JACC: Basic to Translational Science 5, 387-397 (2020).
+
+52. Gaetani, R. et al. Epicardial application of cardiac progenitor cells in a 3D-printed gelatin/hyaluronic acid patch preserves cardiac function after myocardial infarction. Biomaterials 61, 339-348 (2015).
+
+53. Norona, L. M., Nguyen, D. G., Gerber, D. A., Presnell, S. C. & LeCluyse, E. L. Editor's Highlight: Modeling Compound-Induced Fibrogenesis In Vitro Using Three-Dimensional Bioprinted Human Liver Tissues. Toxicol. Sci. 154, 354-367 (2016).
+
+54. Klein, F. et al. Two-Component Polymer Scaffolds for Controlled Three-Dimensional Cell Culture. Advanced Materials 23, 1341-1345 (2011).
+
+55. St. John, J. C. et al. The Analysis of Mitochondria and Mitochondrial DNA in Human Embryonic Stem Cells. in Human Embryonic Stem Cell Protocols vol. 331 347-374 (Humana Press, 2006).
+
+56. Prigione, A., Fauler, B., Lurz, R., Lehrach, H. & Adjaye, J. The Senescence-Related Mitochondrial/Oxidative Stress Pathway is Repressed in Human Induced Pluripotent Stem Cells. STEM CELLS 28, 721-733 (2010).
+
+57. Wu, J., Ocampo, A. & Belmonte, J. C. I. Cellular Metabolism and Induced Pluripotency. Cell 166, 1371-1385 (2016).
+
+58. Berger, E. et al. Millifluidic culture improves human midbrain organoid vitality and differentiation. Lab Chip 18, 3172-3183 (2018).
+
+59. Jiang, B. H., Semenza, G. L., Bauer, C. & Marti, H. H. Hypoxia-inducible factor 1 levels vary exponentially over a physiologically relevant range of O2 tension. American Journal of Physiology-Cell Physiology 271, C1172-C1180 (1996).
+
+<--- Page Split --->
+
+60. Huang, L. E., Gu, J., Schau, M. & Bunn, H. F. Regulation of hypoxia-inducible factor 1 is mediated by an O2-dependent degradation domain via the ubiquitin-proteasome pathway. Proceedings of the National Academy of Sciences 95, 7987-7992 (1998).
+
+61. Greijer, A. E. The role of hypoxia inducible factor 1 (HIF-1) in hypoxia induced apoptosis. Journal of Clinical Pathology 57, 1009-1014 (2004).
+
+62. Wang, M., Tan, J., Miao, Y., Li, M. & Zhang, Q. Role of \(\mathrm{Ca^{2 + }}\) and ion channels in the regulation of apoptosis under hypoxia. Histol Histopathol 33, 237-246 (2018).
+
+63. Punovuori, K. et al. N-cadherin stabilises neural identity by dampening anti-neural signals. Development 146, dev183269 (2019).
+
+64. Tietz, P. S. & Larusso, N. F. Cholangiocyte biology. Curr Opin Gastroenterol 22, 279-287 (2006).
+
+65. Ruebner, B. H., Blankenberg, T. A., Burrows, D. A., Soohoo, W. & Lund, J. K. Development and Transformation of the Ductal Plate in the Developing Human Liver. Pediatric Pathology 10, 55-68 (1990).
+
+66. Limaye, P. B. et al. Expression of specific hepatocyte and cholangiocyte transcription factors in human liver disease and embryonic development. Lab Invest 88, 865-872 (2008).
+
+67. Ranga, A. et al. Neural tube morphogenesis in synthetic 3D microenvironments. Proc Natl Acad Sci USA 113, E6831-E6839 (2016).
+
+68. Medina, J. D. et al. Functionalization of Alginate with Extracellular Matrix Peptides Enhances Viability and Function of Encapsulated Porcine Islets. Adv. Healthcare Mater. 9, 2000102 (2020).
+
+69. Lancaster, M. A. & Knoblich, J. A. Generation of cerebral organoids from human pluripotent stem cells. Nature Protocols 9, 2329-2340 (2014).
+
+70. Boon, R. et al. Amino acid levels determine metabolism and CYP450 function of hepatocytes and hepatoma cell lines. Nat Commun 11, 1393 (2020).
+
+71. Roelandt, P., Vanhove, J. & Verfaillie, C. Directed Differentiation of Pluripotent Stem Cells to Functional Hepatocytes. in Pluripotent Stem Cells (eds. Lakshmipathy, U. & Vemuri, M. C.) vol. 997 141-147 (Humana Press, 2013).
+
+72. Stuart, T. et al. Comprehensive Integration of Single-Cell Data. Cell 177, 1888-1902.e21 (2019).
+
+<--- Page Split --->
+
+73. Cao, J. et al. The single-cell transcriptional landscape of mammalian organogenesis. Nature 566, 496–502 (2019).
+
+74. Kumar, M. et al. A fully defined matrix to support a pluripotent stem cell derived multi-cell-liver steatohepatitis and fibrosis model. Biomaterials 276, 121006 (2021).
+
+<--- Page Split --->
+
+Figures
+
+<--- Page Split --->
+
+
+Figure 1. On-chip micro-vascularization enabled by soft microfluidics. (a) 3D printed tissue culture chip designed for eight multiplexed soft 3D soft microfluidic capillary grids. Inset: microfluidic capillary grid fabricated on a plastic baseplate and diagram of working principle. (b) of microfluidic capillary grid (left) and the close up image of the same grid showing individual hydrogel capillaries (right). (c) Microvessel 3D printing by 3D printing of microfluidic grid using high-resolution 2-photon stereo-lithography with non-swelling photo-polymerizable hydrogel precursors enables reproduction of features as small as \(10\mu \mathrm{m}\) . The top view photograph demonstrates an array of cylinders of various outer diameter in micrometers (top row) and wall thickness in micrometers (columns). (d) CAD image of microfluidic grid (left) with capillaries shown in red and the structural components shown in grey. The fence at the circumference of the structure makes
+
+<--- Page Split --->
+
+up a "basket" that can be filled (right) with cell aggregates (spheroids) which merge and produce a solid tissue incorporating hydrogel capillaries. (e) Hydrogel capillaries are readily permeable. \(25\mu \mathrm{M}\) of Fluorescein, perfused through the microfluidic grid, embedded in Matrigel, passes across capillary walls and saturates the gel within several minutes. (f) Process of tissue generation. Photograph of an empty capillary grid with the tip of \(200\mu \mathrm{l}\) pipette tip visible above the grid (left), close up image of the greed seeded with hIPSC spheroids (middle) manually dispensed from the pipette shown on the left image, image of the spheroids fused into a solid tissue after 24- 36 hours of culturing on chip. The top row schematically represents the same process, where spheroids and the resulting tissue are shown in blue.
+
+<--- Page Split --->
+
+
+Figure 2. Transcriptomic changes upon perfusion. (a) Combined dataset UMAP (control, non-perfused and perfused samples). (b) Combined dataset UMAP with neuroepithelial cells (NE), pluripotent-neuroepithelial transitioning cells (P-NE), proliferating cells with medium mitochondrial (mito.) content, pluripotent cells (P) with low glycolysis (glyc.) and medium mitochondrial content, glycolytic pluripotent cells with low mitochondrial content, highly glycolytic pluripotent cells, a highly glycolytic hypoxic (hypo.) identity and a stressed cluster. (c) Pseudotime trajectory on combined dataset UMAP. (d) Cluster specific expressions of selected marker genes. Expression values are normalized and centered. Sample fractions for each identified cluster. (e) GO enrichment analysis for key processes upregulated in perfused and non-perfused samples.
+
+<--- Page Split --->
+
+
+Figure 3. Changes in proliferation mediated by hypoxia. a) Representative experimental results demonstrating differences in proliferation and viability between standard organoid culture(left column) and the tissue constructs without (middle column) and with perfusion (right column). Top row: bright field images of organoids, non-perfused and perfused constructs correspondingly. Middle row: immunofluorescent images of apoptotic marker cleaved Caspase 3 (green) expressed in the three conditions. Bottom row: immunofluorescent images of hypoxia marker HIF1a (green). Hoechst staining of nuclei shown in blue. The images represent transverse cross-sections of the tissue constructs. (b) Top: average proportion of the number of live cells in perfused and non-perfused constructs quantified by flow cytometry (90.95.1% in perfused vs 89.2±4.4% in non-perfused tissue, n.s., n=4). Middle: average expression of cleaved Caspase 3 in control organoids (8±1% area, n=7), non-perfused(35.7±5%, pControl=0.02, n=4) and perfused tissue constructs (5.1±1% of total area, pControl=0.02, n=9). Bottom: average expression of hypoxia marker HIF-1a in control organoids (100±3%, n=4), non-perfused (55±3%, pControl=0.0003, n=3) and perfused constructs (26±2%, pControl=0.0004, n=2). Control organoids, non-perfused and perfused constructs are denoted as Ctrl, NP and P correspondingly, data are represented as mean ± SEM, asterisks (*) denote statistical significance of the difference between control organoids and the tissue constructs (unpaired two-tailed Student's t-test, 95% confidence interval). (c) Representative fluo-cytometry data, demonstrating the difference in total number of cells between perfused and non-perfused constructs. (d) Distribution of gene expression levels across the single cell population for hypoxia (left), G2M cell cycle (middle) and S cell cycle (right) associated gene sets. Scale bar: 1mm
+
+<--- Page Split --->
+
+
+Figure 4. Rapid neural differentiation in perfused systems. (a) Representative experimental results demonstrating the result of 2 days of neuronal induction in control organoids(left column), non-perfused (middle column) and perfused (right column) tissue constructs. Top, middle and bottom row: immunofluorescent images of stem cell marker NANOG, early neural marker PAX6 and cell adhesion proteins N-Cadherin (green) and E-Cadherin (red) correspondingly. The images represent transverse cross-sections of the tissue constructs. In most cases, the cross-sections of capillaries are visible as circular structures (marked by triangles) (b) Average expression of PAX6(Ctrl: Not detected; NP: \(0.2\% \pm 0.2\%\) , pControl \(= 0.35(n.s.)\) , \(n = 9\) ; P: \(21.5 \pm 2\%\) , pControl \(= 0.00002\) , \(n = 12\) ), NANOG(Ctrl: \(73.6 \pm 8\%\) , \(n = 9\) ; NP: \(16.1 \pm 2\%\) , pControl \(= 0.00007\) , \(n = 11\) ; P: not detected), NCad(CDH2) (Ctrl: \(100 \pm 1\%\) , \(n = 8\) ; NP: \(7.6 \pm 1\%\) , pControl \(= 4e - 13\) , \(n = 3\) ; P: \(55.7 \pm 9\%\) (pControl \(= 0.009\) , \(n = 5\) ) and ECad(CDH1) (Ctrl: \(99 \pm 2\%\) , \(n = 12\) ; NP: \(26.6 \pm 7\%\) , pControl \(= 0.0001\) , \(n = 6\) ; P: \(4.5 \pm 2\%\) , pControl \(= 2e - 10\) , \(n = 5\) ) markers in control organoids (Ctrl), non-perfused(NP) and perfused(P) constructs. Data are represented as mean \(\pm\) SEM, asterisks (*) denote statistical significance of the difference between control organoids and the tissue constructs (unpaired two-tailed Student's \(t\) -test, \(95\%\) confidence interval) (c) UMAP plot of the combined dataset showing the localization of cells from control organoids, non-perfused and perfused constructs in the UMAP space. (d) UMAP plot of the combined dataset highlighting locations of PAX6, NANOG, NCad (CDH2) and ECad(CDH1) expressing cells in the UMAP space. Scale bar: \(250 \mu m\)
+
+<--- Page Split --->
+
+
+Figure 5. Functional improvement in perfused liver microtissues. (a) Hematoxylin and eosin of a transverse section of liver tissue construct with hepatocyte-like morphology and no visible indication of apoptosis. (b) Immunofluorescence images showing presence of AFP and CYP3A4, (c) Alpha-1 antitrypsin (AAT) and Cytokeratin 19 (KRT19), and (d) basic hepatic markers albumin (ALB) and hepatic nuclear factor HNF4α expression (f) Heatmap representation of fold change gene expression levels normalized to control 2D cell culture and compared to standard hepatic organoids and perfused liver constructs; rows are centered and scaled. Gene expression data for hepatic 2D culture and hepatic organoids are from Kumar et al74. Scale bar: \(50\mu \mathrm{m}\)
+
+<--- Page Split --->
+
+Supplementary Figures
+
+<--- Page Split --->
+
+
+
+Supplementary Figure 1. Assembly and operation of the chip device. (a) Cutaway view of the fully assembled culture chip, the chamber with perfused capillary grid is shown. Cell culture medium enters the culture chamber through the inlet (1mm syringe needle, cut into 15mm pieces), passes through the capillary grid and leaves the chamber through outlet (not shown). (b) Exploded view of the chip. (c) Side view cross section of the chip. Tissue constructs can be observed through the glass windows with inverted or upright microscopes. The view also demonstrates that the cell culture medium only comes into contact with PDMS(pink) and glass(blue) parts of the chip. (d) During the assembly, a user needs to handle only two pre- assembled "halves" of the chip. (e) Schematic representation of the perfusion system driven by a peristaltic pump, with culture medium circulating between the perfusion chip and the medium reservoir. Here, the grid in the right chamber is surrounded by a constant medium flow but the flow through its capillaries is absent, while in the downstream grid (left chamber) the flow passes through the capillaries and diffuses across the walls into the tissue. (f) Photographs of fully assembled chip and perfusion system. The non-perfused and perfused chambers are connected by external tubing (left), with \(0.22\mu m\) filter connected inline between the chambers. The chip and the medium reservoir resides in a custom 3D-printed holder (middle) and connected to a peristaltic pump installed outside of \(\mathrm{CO_2}\) incubator (right). The image shows three experiments running in parallel.
+
+<--- Page Split --->
+
+
+
+
+
+
+Supplementary Figure 2. Optimization of printable material properties. (a) Test structure printed from PEGDA or PEGDA \(90\% /\) PETA \(10\%\) mixture. Both ends of the part are connected to a baseplate. When submerged to cell culture medium, swelling of the material leads to a breakage of the part. (b) Our custom formulation resin effectively prevents swelling in aqueous media and preserves the geometry of the microfabricated structures. Scale bar \(100\mu \mathrm{m}\) .
+
+<--- Page Split --->
+
+
+Supplementary Figure 3. Two-photon stereo-lithography enables precision fabrication in a wide range of scales. Microfluidic grids of different dimensions (in mm): 1.2mm x 1.2mm x 1.2mm (left), 2.6mm x 2.6 mm x 1.5mm (middle), 6.5mm x 6.5mm x 5mm (right). Perfusion vessels in each grid have identical 50μm diameter and inter-vessel distance of 250μm. Scale bar 5 mm.
+
+<--- Page Split --->
+
+
+Supplementary Figure 4. Daily brightfield imaging of neural tissue in perfused and non-perfused chips. (a) Bright field images of the perfused (top) and non-perfused (bottom) tissue constructs taken every 2 days during the culturing protocol. (b) Live sections of perfused (left) and non-perfused (right) tissue constructs taken at the end of the culturing protocol. Scale bar 500μm.
+
+<--- Page Split --->
+
+
+
+Supplementary Figure 5. Correlation analysis between perfused-, non-perfused neural tissue constructs and conventional neural organoid culture. Correlation analysis using the top 100 differentially expressed marker genes for each of the three experimental conditions.
+
+<--- Page Split --->
+
+
+Supplementary Figure 6. Gene-set analysis for various processes. Combined dataset UMAP with scores for pluripotent, glycolysis and neural progenitor gene-set as well as the \(\%\) mitochondrial genes. Hierarchical clustering of gene-set scores and \(\%\) mitochondrial genes. Score is column scaled.
+
+<--- Page Split --->
+![PLACEHOLDER_46_0]
+
+Supplementary Figure 7. Gene expression for unannotated hNTO clusters with the top 25 marker genes for each cluster.
+
+<--- Page Split --->
+![PLACEHOLDER_47_0]
+
+Supplementary Figure 8. Cluster-specific analysis of scRNAseq dataset. Dot-plot heatmap of hypoxia and cell cycle markers for each identified cluster. The average gene expression is represented by the color intensity of each dot, whereas the dot size represents the percentage of the gene-expressing cells for each sample within each cluster.
+
+<--- Page Split --->
+![PLACEHOLDER_48_0]
+
+Supplementary Figure 9. Difference in localized expression of hypoxia marker HIF1α and apoptosis marker cleaved Caspase-3. (a) HIF1α expression is localized to regions containing intact cell bodies (middle), evidenced by intact nuclei in the outlined region (left) as well as well-defined cytoplasmic regions stained with E-Cad antibody (right). (b) Cleaved Caspase-3 expression (middle) is localized to regions with apoptotic cell bodies evidenced by Hoechst stain of fragmented nuclei (outside of the outlined live region on the left image). Scale bar 100μm.
+
+<--- Page Split --->
+![PLACEHOLDER_49_0]
+
+Supplementary Figure 10. Brightfield images of perfused liver cultures. Bright field images of the perfused liver-like tissue constructs taken during tissue culturing. Scale bar 500μm.
+
+<--- Page Split --->
diff --git a/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345_det.mmd b/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..84caf6036574e063a1b834633ec9a023d0dd04df
--- /dev/null
+++ b/preprint/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345/preprint__01e7a1078c78ab368216c5666b306391adfa28f34c3a711786fcea2c12e51345_det.mmd
@@ -0,0 +1,653 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 820, 175]]<|/det|>
+# Engineering large-scale perfused tissues via synthetic 3D soft microfluidics
+
+<|ref|>text<|/ref|><|det|>[[44, 196, 197, 234]]<|/det|>
+Sergei Grebenyuk KU Leuven
+
+<|ref|>text<|/ref|><|det|>[[44, 241, 508, 283]]<|/det|>
+Abdel Rahman Abdel Fattah KU Leuven https://orcid.org/0000- 0002- 7817- 5586
+
+<|ref|>text<|/ref|><|det|>[[44, 289, 212, 328]]<|/det|>
+Gregorius Rustandi KU Leuven
+
+<|ref|>text<|/ref|><|det|>[[44, 335, 508, 377]]<|/det|>
+Manoj Kumar KU Leuven https://orcid.org/0000- 0002- 0572- 5786
+
+<|ref|>text<|/ref|><|det|>[[44, 382, 208, 400]]<|/det|>
+Burak Toprakhisar
+
+<|ref|>text<|/ref|><|det|>[[44, 403, 931, 423]]<|/det|>
+Stem Cell Institute, Department of Stem Cell and Developmental Biology, KU Leuven, Leuven, Belgium
+
+<|ref|>text<|/ref|><|det|>[[44, 428, 155, 465]]<|/det|>
+Idris Salmon KU Leuven
+
+<|ref|>text<|/ref|><|det|>[[44, 472, 212, 490]]<|/det|>
+Catherine Verfaillie
+
+<|ref|>text<|/ref|><|det|>[[44, 494, 508, 513]]<|/det|>
+KU Leuven https://orcid.org/0000- 0001- 7564- 4079
+
+<|ref|>text<|/ref|><|det|>[[44, 519, 452, 539]]<|/det|>
+Adrian Ranga ( adrian.ranga@kuleuven.be )
+
+<|ref|>text<|/ref|><|det|>[[50, 541, 647, 560]]<|/det|>
+adrian.ranga@kuleuven.be https://orcid.org/0000- 0002- 6400- 9472
+
+<|ref|>text<|/ref|><|det|>[[44, 603, 102, 620]]<|/det|>
+Article
+
+<|ref|>text<|/ref|><|det|>[[44, 641, 135, 660]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 678, 340, 698]]<|/det|>
+Posted Date: September 8th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 716, 463, 736]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 867063/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 753, 910, 797]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[115, 88, 705, 106]]<|/det|>
+# Engineering large-scale perfused tissues via synthetic 3D soft microfluidics
+
+<|ref|>text<|/ref|><|det|>[[115, 145, 884, 194]]<|/det|>
+Sergei Grebenyuk \(^{1}\) , Abdel Rahman Abdel Fattah \(^{1}\) , Gregorius Rustandi \(^{1}\) , Manoj Kumar \(^{2}\) , Burak Toprakhisar \(^{2}\) , Idris Salmon \(^{1}\) , Catherine Verfaillie \(^{2}\) , Adrian Ranga \(^{1*}\)
+
+<|ref|>text<|/ref|><|det|>[[115, 233, 884, 281]]<|/det|>
+\(^{1}\) Laboratory of Bioengineering and Morphogenesis, Biomechanics Section, Department of Mechanical Engineering, KU Leuven, Leuven, Belgium
+
+<|ref|>text<|/ref|><|det|>[[115, 291, 884, 339]]<|/det|>
+\(^{2}\) Stem Cell Institute Leuven and Department of Development and Regeneration, Faculty of Medicine, KU Leuven, Leuven, Belgium
+
+<|ref|>text<|/ref|><|det|>[[117, 350, 375, 367]]<|/det|>
+\* email: adrian.ranga@kuleuven.be
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 437, 184, 453]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[113, 492, 885, 833]]<|/det|>
+The vascularization of engineered tissues and organoids has remained a major unresolved challenge in regenerative medicine. While multiple approaches have been developed to vascularize in vitro tissues, it has thus far not been possible to generate sufficiently dense networks of small- scale vessels to perfuse large de novo tissues. Here, we achieve the perfusion of multi- mm \(^{3}\) tissue constructs by generating networks of synthetic capillary- scale 3D vessels. Our 3D soft microfluidic strategy is uniquely enabled by a 3D- printable 2- photon- polymerizable hydrogel formulation, which allows for precise microvessel printing at scales below the diffusion limit of living tissues. We demonstrate that these large- scale engineered tissues are viable, proliferative and exhibit complex morphogenesis during long- term in- vitro culture, while avoiding hypoxia and necrosis. We show by scRNAseq and immunohistochemistry that neural differentiation is significantly accelerated in perfused neural constructs. Additionally, we illustrate the versatility of this platform by demonstrating long- term perfusion of developing liver tissue. This fully synthetic vascularization platform opens the door to the generation of human tissue models at unprecedented scale and complexity.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 89, 213, 105]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[113, 116, 885, 310]]<|/det|>
+Human engineered tissue and organoids are potentially transformational model systems, which could create dramatic efficiencies in the drug discovery process and function as key building blocks for regenerative medicine applications. In particular, larger- scale tissues have the possibility to recapitulate complex functional and organizational characteristics of their in vivo counterparts, and could therefore become a long- sought alternative to animal models \(^{1 - 3}\) . However, the poorly defined structural organization, small size and slow maturation of these tissues have remained major limitations in engineering fully functional and reproducible organoids and tissues.
+
+<|ref|>text<|/ref|><|det|>[[113, 320, 886, 629]]<|/det|>
+In vivo, the development of tissues is supported by a complex network of blood vessels which provide oxygen, nutrients and waste exchange and mediate paracrine interactions via growth and differentiation factors \(^{4}\) . The size of the microvasculature is a critical parameter for local tissue perfusion: to maintain sufficient diffusion of oxygen, nutrients, and waste products most cells in vivo lie within \(200 \mu \mathrm{m}\) of a capillary. In the absence of vascular support, normal physiological conditions can be maintained only within this narrow range. Similar to the diffusion limits in normal tissue, the generation of solid tissue in vitro requires both vascularization and flow to maintain cell viability throughout the entire construct \(^{1}\) . The lack of vascularization in engineered tissues therefore prevents oxygen and nutrient exchange, which is thought to be the main reason for the commonly observed development of a necrotic core within organoids once they reach a critical size, as well as for apoptosis within engineered tissues. These issues have been widely recognized, and various approaches have been reported in order to overcome them \(^{5}\) .
+
+<|ref|>text<|/ref|><|det|>[[113, 639, 885, 833]]<|/det|>
+The extrinsic induction of angiogenesis has been frequently used in the context of organoid vascularization. Vessel sprouts have been shown to infiltrate organoids maintained with endothelial cells in separate compartments of microfluidic culture devices \(^{6,7}\) , or co- cultured with pre- established microvascular beds \(^{8,9}\) . These results have suggested that the presence of a perfusable vasculature can enhance organoid growth \(^{8}\) , confirming the importance of systemic cross- talk between vasculature and organoids in the developmental process. The resulting organoids have nonetheless been limited in size, and to date, functional organoid vascularization has only been achieved by grafting organoids into host animals \(^{10,11}\) .
+
+<|ref|>text<|/ref|><|det|>[[115, 843, 884, 890]]<|/det|>
+A number of studies have focused on creating artificial vessels though the use of templating approaches based on patterned layer- by- layer deposition of gelled material, in the form of thin filaments \(^{12}\) ,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 885, 367]]<|/det|>
+droplets \(^{13 - 18}\) or layer- by- layer polymerization by stereolithography \(^{19 - 21}\) . Large tissue constructs have been generated by bioprinting of bioinks comprised of gels carrying different cell types \(^{12,22,23}\) , with vascular templates generated by depositing endothelial cells interleaved with tissue- specific cells using filament extrusion \(^{24 - 28}\) or stereolithography \(^{19,21}\) . While multiphoton lithography has been used to fabricate capillary- sized tubular fragments \(^{29}\) and vascular mimics \(^{30}\) , these vessels have thus far not been successfully perfused. The dissolution of sacrificial networks to form lumenized vessels has been proposed as an alternative strategy, with resorbable gel filaments being created via stereolithography \(^{31}\) , pre- polymer extrusion \(^{32 - 38}\) or molding \(^{39}\) . Artificial vessels have also been formed by the direct removal of diverse hydrogel material such as silk fibroin and PEG hydrogels using laser photo- ablation \(^{40 - 44}\) including in the presence of cells \(^{45 - 47}\) .
+
+<|ref|>text<|/ref|><|det|>[[113, 378, 885, 542]]<|/det|>
+Despite the versatility of these vessel templating approaches, the minimal diameter of perfusable engineered vessels reported thus far has been limited to \(150\mu \mathrm{m}^{33,39}\) and, in parallel with strategies based on extrinsic angiogenesis in organ- on- chip implementations \(^{48}\) , the size of generated tissues has been limited to \(400 - 500\mu \mathrm{m}\) in at least one dimension \(^{49 - 53}\) . Because of their small size, engineered tissues which have been implemented thus far do not preserve a physiologically relevant signaling context within the tissue, nor do they develop to a level of complexity comparable to in vivo organs.
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 581, 688, 599]]<|/det|>
+## Photo-polymerizable non-swelling hydrogels enable 3D soft microfluidics
+
+<|ref|>text<|/ref|><|det|>[[113, 609, 885, 861]]<|/det|>
+In order to vascularize tissue at large scale, we hypothesized that a microfluidic approach which could bridge the capillary to tissue scale would be necessary to enable the perfusion of thick three- dimensional tissue constructs. We therefore designed a dense, regularly spaced capillary network whose tubular walls were made of a hydrogel allowing diffusion (Fig. 1a). Tissues growing within this soft grid- like hydrated network would interface with an external perfusion pumping system, circulating cell culture medium throughout the volume of the tissue (Fig. 1a and Supplementary Fig. 1). We developed an approach whereby the perfusable grid would be printed directly on a hard plastic base (Fig. 1a), thereby forming a tight seal. This base, which contains perfusion holes, would then be incorporated into a perfusion chip linked to a peristaltic pump circulating cell culture medium (Supplementary Fig. 1)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 885, 310]]<|/det|>
+An important requirement of this platform was the need to have capillary- like tubing at scales of a few \(\mu \mathrm{m}\) in diameter and thickness, while perfusing across a large, multi- \(\mathrm{mm}^3\) three- dimensional space. The geometrical complexity of the design, properties of the biopolymer and fabrication scale ranging from \(10\mu \mathrm{m}\) to \(2000\mu \mathrm{m}\) featured by our design made two- photon laser scanning photo- polymerization the ideal technology for this purpose. Initial 3D prints with the 2- photon Nanoscribe printer using commonly used photopolymerizable materials, including gelatin and PEG diacrylate, resulted in significant swelling of the material upon polymerization and hydration, which disrupted the seal between the soft microfluidic grid and the rigid plastic plate, and generated mismatched tubular segments (Supplementary Fig. 2).
+
+<|ref|>text<|/ref|><|det|>[[113, 320, 885, 513]]<|/det|>
+To overcome this post- printing distortion, we developed a custom formulated hydrophilic photopolymer based on polyethylene glycol diacrylate (PEGDA). While PEGDA exhibits cell- repelling surface properties, the polymer surface could be rendered cell- binding by the addition of the photocrosslinker pentaerythritol triacrylate (PETA)54. We reasoned that the addition of a significant amount of PETA as a crosslinker would increase the toughness of the polymer, and balanced with the addition of an inert "filler" component (Triton- X 100) would on the other hand retain sufficient porosity of the polymer to enable rapid diffusion.
+
+<|ref|>text<|/ref|><|det|>[[113, 523, 886, 892]]<|/det|>
+The combination of 2- photon printing with this non- swelling hydrogel material allowed printing of a variety of microfluidic grids, ranging in size from \(1.2 \times 1.2 \times 1.2\mathrm{mm}\) up to \(6.5 \times 6.5 \times 5\mathrm{mm}\) (Fig. 1b and Supplementary Fig. 3) with vessel diameters from \(10\mu \mathrm{m}\) to \(>70\mu \mathrm{m}\) and vessel wall thickness from \(2\mu \mathrm{m}\) to \(10\mu \mathrm{m}\) (Fig. 1c). Importantly, the printing with our novel formulation resin resulted in a 1:1 fidelity between the generated CAD geometry and the printed parts, thereby ensuring no distortion and a tight seal (Supplementary Fig. 2). The standard size used for most of the subsequent experiments was \(2.6\mathrm{mm} \times 2.6\mathrm{mm} \times 1.5\mathrm{mm}\) , with an inter- vessel distance of \(250\mu \mathrm{m}\) (Fig. 1b). These grids could be incorporated into a multi- plexed perfusion chip allowing up to 8 grids to be perfused simultaneously (Fig. 1a). Single cells or organoids smaller than the \(250\mu \mathrm{m}\) inter- capillary distance, previously mixed within a liquid hydrogel (eg. Matrigel) precursor solution, could be seeded into the platform, yielding a "gel- in- gel" 3- dimensional construct (Fig. 1d). Vessel permeability to water- soluble molecules within the chips overlayed with Matrigel was verified using fluorescein, with diffusion throughout the three- dimensional space seen in less than 10 minutes (Fig. 1e).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 223]]<|/det|>
+To perform a biological proof of concept experiment, we generated hundreds of organoids of less than \(200 \mu m\) diameter by aggregating human pluripotent stem cells (hPSCs) in microwells in pluripotency medium over 24 hours. We collected these aggregates in cold liquid Matrigel, which were then pipetted into the grids. Initial seeding demonstrated that these aggregates filled the grids and, over a period of 8 days of growth and neural differentiation, merged and filled the whole volume (Fig. 1f and Supplementary Fig. 4).
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 262, 883, 309]]<|/det|>
+## scRNAseq reveals changes in differentiation, hypoxia, cell cycle regulation and differentiation upon perfusion
+
+<|ref|>text<|/ref|><|det|>[[112, 317, 885, 833]]<|/det|>
+To assess how perfusion affected cellular processes and differentiation in large- scale in- vitro tissue, we dissociated cells from tissue constructs in a perfused and a non- perfused grid, as well as from organoids in conventional suspension culture after the 8- day culture period, and performed single cell RNA sequencing. Graph- based clustering and Uniform Manifold Approximation and Projection (UMAP) dimensionality reduction technique on the 8,625 total cells retained after QC revealed significant transcriptomic differences between the tissue constructs (perfused and non- perfused) and the control organoids as evidenced by largely separated clustering of these cell populations (Fig. 2a). Correlation analysis using the 100 most differentially expressed marker genes revealed the most difference between perfused tissue and conventional organoid culture, with non- perfused tissue sharing gene expression profiles with the other two conditions (Supplementary Fig. 5). Differential gene expression analysis was then used to annotate eight clusters, which were largely differentiated by fate, as well as by metabolic, hypoxia and cell cycle regulation (Fig. 2b, Fig. 2d, Supplementary Fig. 6, Supplementary Fig. 7). Cells from control organoids were found in clusters with low, medium and high glycolytic processes marked by a pluripotent identity, including highly expressed markers such as NANOG and OCT4 (POUF5F1). Both perfused and non- perfused tissues expressed varying degrees of hypoxia, proliferation, mitochondrial gene expression and neuroepithelial markers. The non- perfused tissue made up the largest proportion of the hypoxic and stressed clusters (HIF1α, FOS) while the perfused tissue represented the majority of the neuroepithelial cluster (PAX6).
+
+<|ref|>text<|/ref|><|det|>[[113, 843, 883, 890]]<|/det|>
+In particular, control organoids had lower expression of mitochondrial genes (Supplementary Fig. 7, Supplementary Fig. 8) compared to the tissue constructs. This is in line with previous reports of lower
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 885, 309]]<|/det|>
+mitochondrial activity in human embryonic stem cells that increase upon differentiation to fit the energy needs of resultant cell identities55. Indeed, differentiation towards the neuroepithelial fates from pluripotent cells was characterized by an increase in mitochondrial activity, and a simultaneous decrease in glycolysis (Supplementary Fig. 8). These results suggest a metabolic switch from anaerobic glycolysis to oxidative phosphorylation in the tissue constructs, as has been reported to occur during cell differentiation after exit from pluripotency56,57. Such transitions, which were additionally evidenced in pseudotime analysis (Fig. 2c) distinguished the control organoids from the tissue constructs in the microfluidic grids, and further characterized differences between non- perfused and perfused tissues.
+
+<|ref|>text<|/ref|><|det|>[[112, 319, 886, 659]]<|/det|>
+The perfused tissue was also characterized by the expression of the neuroepithelial markers PAX6, PAX7, PAX3, and CDH2, while sharing IRX1 and IRX2 markers with non- perfused tissue (Fig. 2d). Moreover, while non- perfused and perfused tissues represented similar proportions of the pluripotent proliferating cluster, the perfused tissue expressed the highest proliferation markers such as CDC6 (Supplementary Fig. 7). Additionally, the high expression of proliferation markers such MKi67 and TOP2A in the neuroepithelial cluster suggested the retained proliferative capacity of perfused tissues after neuroepithelial differentiation, while maintaining overall minimal hypoxic/stress response markers VEGF, FOS, HIF1a (Supplementary Fig. 8). By contrast, non- perfused tissue was distinguished by significant presence of pluripotency (NANOG, POU5F1/OCT- 4) (Fig. 2d) and hypoxia/stress markers (Fig. 2d, Supplementary Fig. 8). The control organoids, on the other hand, were mostly represented by pluripotent and hypoxic cells with complete absence of neuroepithelial identity (Fig. 2d and Supplementary Fig. 8), likely due to the short time in neural differentiation conditions.
+
+<|ref|>text<|/ref|><|det|>[[113, 668, 885, 891]]<|/det|>
+To investigate transcriptional changes and associated cellular processes upon perfusion in a systematic manner, we performed differential gene expression analysis between perfused and non- perfused tissue constructs followed by Gene Ontology (GO) enrichment analysis (Fig. 2e). This analysis confirmed up- regulation of processes related to cell division and proliferation in the perfused sample, as well as regulation of neural precursors and neural precursor cell proliferation. By contrast, cell stress, hypoxia and cellular death processes were upregulated in non- perfused samples. Taken together our analysis of the transcriptomic data suggested that perfusion of large tissue constructs dramatically decreased apoptosis and hypoxia, and accelerated the process of neural differentiation.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 117, 668, 136]]<|/det|>
+## Perfusion rescues hypoxia and necrotic core in large tissue constructs
+
+<|ref|>text<|/ref|><|det|>[[112, 145, 886, 545]]<|/det|>
+To further investigate how perfusion modulates the spatial distribution of hypoxia and apoptosis, we imaged the constructs in bright field microscopy and sectioned whole samples transversely, perpendicular to the direction of grid perfusion, followed by immunohistochemistry (Fig. 3a and associated quantification in Fig. 3b). Control organoids demonstrated a characteristic dark dense tissue core with occasional lighter voidlike structures, surrounded by more translucent peripheral tissue. In non- perfused samples, tissue growth was restricted to the internal volume of the microfluidic grid, with generally dense central tissue interspersed with patchy lighter areas. Strikingly, perfused tissue covered the entire volume of the grid in a uniformly dense manner, with bulging epithelial outgrowths characteristic of cerebral organoids at the periphery. These observations suggested that cell proliferation was much higher in the perfused grids, compared to the non- perfused samples. To confirm this observation quantitatively, we dissociated the tissue constructs into single cells, stained with calcein- AM and ethidium homodimer to label live and dead cells respectively, followed by quantitative flow cytometry (Fig. 3b and Fig. 3c). Our analysis revealed a 5- fold difference in total cell number in the perfused tissue constructs over the non- perfused ones, while the proportion of live cells was similar (90.9±5.1% in perfused vs 89.2±4.4% in non- perfused tissue) (Fig. 3a and Fig. 3b).
+
+<|ref|>text<|/ref|><|det|>[[112, 553, 886, 860]]<|/det|>
+To determine whether these changes in viability and proliferation were due to apoptosis, we stained sections of the grids for cleaved Caspase 3, an active form of the Caspase- 3 enzyme responsible for the degradation of multiple cellular proteins and ultimately for cell fragmentation into apoptotic bodies. Upon sectioning, the control organoids were empty in the center, suggesting, as has previously been reported58, the loss of apoptotic cells during the sectioning process. Closer to this inner core, signs of apoptosis were evident (8±1% of total area), (Fig. 3a,b), consistent with the large size of these organoids. Tissue in the non- perfused grids exhibited a clear inner core of apoptotic cellular fragments (35.7±5% of total section area) (Fig. 3a) along with empty regions completely lacking cells, with some analogous features to control organoids. Strikingly, nearly the entire perfused tissue did not show signs of cleaved Caspase 3 (5.1±1% of total area), indicating that perfusion successfully prevented cell apoptosis throughout the course of differentiation.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 885, 310]]<|/det|>
+To verify whether hypoxia could be involved in initiating the observed apoptosis in the non- perfused samples, we next stained for HIF1α, a heterodimer protein complex playing a key role in oxygen homeostasis59,60. The rapid buildup of HIF- 1α in low- oxygen conditions is known to trigger a hypoxic response ultimately leading to apoptosis61,62. In line with scRNA analysis data (Fig. 3d), high HIF1α expression levels were detected in the control organoids (100±3% mean fluorescent intensity), as well as in the non- perfused samples (55±3% of organoid control). Conversely, low levels of HIF1α expression were observed in the perfused samples (26±2% of organoid control) (Fig. 3a), associated with a higher proportion of cycling G2, M and S phase cells (Fig. 3d).
+
+<|ref|>text<|/ref|><|det|>[[113, 320, 885, 543]]<|/det|>
+The patterns of HIF- 1α and cleaved Caspase3 expression in non- perfused tissue sections therefore suggest that in these samples, cells in the center of the construct were in a transient hypoxic state ultimately leading to apoptotic cell death. This transition from hypoxic to apoptotic cell state continued until the volume of the tissue was small enough to allow sufficient oxygen supply by a passive diffusion, with the accumulation of apoptotic bodies and cellular debris preserving the cleaved Caspase 3 expression in the bulk of the non- perfused tissue (Supplementary Fig. 9). Conversely, this phenomenon was completely absent in the perfused samples, clearly confirming that thick tissues at multi- mm3 scale could be grown with high viability, and with little to no apoptosis or hypoxia within this platform.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 581, 610, 599]]<|/det|>
+## Accelerated neural differentiation in perfused tissue constructs
+
+<|ref|>text<|/ref|><|det|>[[113, 608, 886, 890]]<|/det|>
+Our scRNAseq data suggested that perfusion not only improved proliferation, prevented apoptosis and hypoxia, but could also direct fate specification. To confirm these findings, we analyzed specific markers of pluripotency and neural differentiation by immunohistochemistry (Fig. 3a and associated image quantification in Fig. 3b). NANOG, a canonical marker of pluripotency was abundantly expressed in organoids (73.6±8% of cells) and significantly expressed in non- perfused constructs (16.1±2%) at the protein level, but was completely missing in perfused samples. Conversely, PAX6, the earliest marker of neural differentiation was clearly evidenced in the perfused samples (21.5±2%), but not in organoid controls and non- perfused samples. These results were in line with the scRNAseq data, which indicated that NANOG- expressing cells were present in the control and non- perfused samples, while PAX6 was largely expressed in the perfused sample (Fig. 4c). The transition of stem cells from pluripotency to neural identity
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 886, 398]]<|/det|>
+is regulated by a loss of cellular expression of E- CADHERIN (CDH1) and a gain of N- CADHERIN (CDH2) expression which drives neural differentiation by inhibiting FGF- mediated pathways63. In order to assess whether perfusion enhanced this transition, we stained for E- CADHERIN to evidence the epithelial state associated with pluripotency, and for N- CADHERIN to confirm the transition to early neuro- epithelial identity. Perfused samples were indeed largely N- CADHERIN positive (55.7±9% vs 7.6±1% in non- perfused samples), while more cells in the non- perfused samples maintained E- CADHERIN+ identity (26.6±7% vs 4.5±2% in perfused samples). These results were confirmed by the scRNA data (Fig. 4c), indicating the predominant expression of N- CADHERIN in cells from perfused tissue, and E- CADHERIN in non- perfused and control tissue. Taken together, these results demonstrate that perfusion rapidly accelerates the transition from pluripotency to early neuroepithelial identity, while cells which lack perfusion remain in a state of pluripotency.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 437, 475, 454]]<|/det|>
+## Long-term perfusion of liver tissue constructs
+
+<|ref|>text<|/ref|><|det|>[[112, 465, 886, 891]]<|/det|>
+To demonstrate the versatility of this platform, we went on to assess the differentiation of PSC- derived liver progenitors in perfused grids. hPSC were differentiated for 8 days in conventional 2D culture, followed by spheroid generation, seeding into the chip and perfusion for an additional 32 days. As was the case with neural differentiation, cells merged over time into a continuous tissue (Supplementary Fig. 10), with histological analysis identifying tightly packed cells with an eosinophilic and clear vacuolated cytoplasm reminiscent of hepatocytes, with no evidence of apoptotic bodies or necrosis throughout the tissue (Fig. 5a). The expression of many hepatocyte- specific genes was upregulated in perfused tissue constructs compared to both control hepatic organoids and 2D hepatocyte differentiation, including hepatocyte nuclear factor 6 (HNF6), Na+/taurocholate co- transporting polypeptide (NTCP), albumin (ALB), alpha1- antitrypsin (AAT) and two major cytochrome P450 enzymes CYP2C9 and CYP3A4 (Fig. 5f). The presence of CYP3A4 as well as of the hepatocyte progenitor marker AFP were confirmed at the protein level in the perfused sample by immunohistochemistry (Fig. 5b). Interestingly, the two major gluconeogenesis enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6- phosphatase alpha (G6PC) were also expressed at higher levels in the perfused constructs, compared to control organoids (1.6- and 1.3- fold higher expression, respectively) (Fig. 5f).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 885, 310]]<|/det|>
+We next assessed whether non- parenchymal cells in the developing liver, such as cytokeratin 19 (KRT19)- expressing cholangiocytes, which contribute to bile secretion and hepatocyte survival64, were also present in our perfused culture system. These cells are generated in- vivo from hepatoblasts surrounding the portal veins, while hepatoblasts located away from portal vein areas differentiate into hepatocytes65. We observed a similar localization pattern of KRT19+ cells, with such cells tightly surrounding every vessel in the microfluidic grid (Fig. 5c), while the hepatocytic markers HNF4α66 was expressed in cells scattered in the inter- vessel space (Fig. 5d). Additionally, the functional production of albumin (ALB) was confirmed by staining (Fig. 5d).
+
+<|ref|>text<|/ref|><|det|>[[115, 321, 883, 368]]<|/det|>
+Taken together, our results confirmed the feasibility of using this synthetic micro- vascularization approach as a generic strategy to building large, viable, perfused in- vitro tissues.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 407, 205, 423]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[114, 436, 884, 514]]<|/det|>
+Here, we demonstrated for the first time an integrated3D culture platform which provides a physiologically relevant micro- perfusion for engineered tissues, resulting in enhanced tissue growth and differentiation compared to previously reported in- vitro tissue vascularization strategies.
+
+<|ref|>text<|/ref|><|det|>[[113, 525, 885, 891]]<|/det|>
+We showed that microvascular networks could be created using 2- photon hydrogel polymerization, demonstrating that this technology can be used to achieve micro- vasculature with previously unreported accuracy, resolution and scale. A significant limitation of current photo- polymerizable hydrogel materials is the significant swelling of the material, which prevents the robust, leak- free interface between printed structures and microfluidic perfusion systems. Our development of a non- swelling photo- polymerizable material formulation was a critical component to overcome this limitation, and enabled the printing of 3D soft microfluidic systems which could be reliably perfused over multiple weeks. The exchange of nutrients and oxygen as well as the removal of waste products was achieved via simple diffusion as the printed vascular network is permeable to water- soluble molecules and gases. The direct fabrication of capillaries of a defined topology delivers an unprecedented control over tissue perfusion parameters, and the design of the vascular network is highly flexible and can be adapted to more complex geometrical and structural requirements. To provide a complete extracellular milieu with structural 3D support to the growing engineered tissue, the space around the perfused vessels was filled with hydrogel. In the experiments
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 885, 310]]<|/det|>
+presented here, the hydrogel component consisted of the commonly used proteinaceous matrix Matrigel, however the platform can also readily accommodate without any additional modifications the use of other naturally derived matrices such as collagen, as well as synthetic artificial extracellular matrices such as poly(ethylene) glycol PEG \(^{67}\) or alginate \(^{68}\) . This technology provides a reliable fluidic coupling between the microfluidic grid and the host perfusion device, such that a continuous peristaltic pump driven perfusion is possible. By integrating these printed microfluidic grids into a perfusion system, we were able to demonstrate that that large- scale (>15mm \(^{3}\) ) fully perfused neural and liver tissues could be generated with this platform.
+
+<|ref|>text<|/ref|><|det|>[[113, 321, 886, 602]]<|/det|>
+Our experiments with neural tissue demonstrate that the differentiation trajectory of cells in this perfused system is significantly enhanced. While control organoids remained largely in a pluripotent state, scRNAseq analysis revealed that perfused tissue rapidly differentiated towards the neural fate, together with a switch from glycolysis to oxidative phosphorylation. Imaging and flow cytometry confirmed that this tissue was highly viable, and immunohistochemistry showed markers of neural differentiation, which were absent in the non- perfused sample, as well as hallmarks of epithelial to mesenchymal transition. This was underscored by our observations that the lack of active micro- perfusion of the engineered tissue construct triggered a stress response in the cells within the inner core of the tissue. The accelerated differentiation of tissues upon perfusion is thought to be due not only to increased availability of nutrients and oxygen but also to the rapid diffusion of differentiation factors within the tissue via the tightly spaced capillary network.
+
+<|ref|>text<|/ref|><|det|>[[113, 611, 885, 775]]<|/det|>
+The possibility of long- term perfusion within this platform was demonstrated by the maintenance of viable engineered liver tissue demonstrating enhanced phenotypic and functional features compared to standard 2D and 3D organoid culture. As cells in our current capillary design were not sufficiently distant from the source of oxygen to generate an oxygen gradient, we did not observe a clear spatial segregation of hepatocytic markers, known as zonation, in the perfused liver tissue, however this feature could be engineered by wider inter- vessel distance.
+
+<|ref|>text<|/ref|><|det|>[[113, 785, 884, 891]]<|/det|>
+Overall, the 3D soft microfluidic technology presented here overcomes one of the major challenge in engineering tissues and organoids: the lack of tissue perfusion from the initiation of tissue growth, and enables the generation of large engineered tissues which are vascularized from within and their maintenance over long periods of time. In applications such as disease modeling and drug development,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 886, 398]]<|/det|>
+such a highly defined synthetic perfusion system would be beneficial in avoiding the complexity and variability introduced by exogenous angiogenesis- driven vascularization. While the current implementation of the platform does not recapitulate features of in vivo vascular networks such as adaptive vascular remodeling or selective blood brain barrier interactions, it addresses the major problem of oxygen, nutrient and growth factor and small molecule supply as well as of waste removal, allowing to generate viable tissues beyond currently available dimensions. The incorporating of endothelial vasculature with this synthetic capillaries could be implemented, where the hydrogel micro- vascularization could provide a temporary tissue support during the time required for angiogenesis- driven capillarization to establish a perfusable network. We expect that this approach is widely applicable in overcoming the current size limitations of bio- printed tissues and provides a technological foundation for the development of perfusable in vitro models of increased complexity and scale.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 466, 271, 483]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[115, 494, 884, 541]]<|/det|>
+This work was supported by FWO grant G087018N, Interreg Biomat- on- Chip grant and Vlaams- Brabant and Flemish Government co- financing, KU Leuven grants C14/17/111 and C32/17/027.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 89, 294, 105]]<|/det|>
+## Materials and Methods
+
+<|ref|>text<|/ref|><|det|>[[113, 144, 885, 368]]<|/det|>
+Human PSC culture. Human PSCs were cultured in Matrigel (356277, Becton Dickinson) coated 6 well plates up to \(60 - 70\%\) confluency. Passages were performed by a 3 min treatment of Dispase II (D4693, Sigma) at \(37^{\circ}C\) , followed by 2- 3 PBS washings at RT. 1 mL of E8- Flex medium (A2858501, Thermo Scientific) was added and the colonies were scraped and gently pipetted 4- 5 times through 1ml plastic tip to break the colonies. The colony suspension was then diluted at 1:5 ratio and plated to a Matrigel coated wells in \(2\mathsf{mL}\) of E8Flex medium supplemented with \(10\mu \mathsf{M}\) Rock inhibitor(Y- 27632, Hellobio) for \(24h\) . The medium was then replaced by \(2\mathsf{mL}\) of fresh E8- Flex medium and incubation was continued for \(48h\) , at which point the colonies usually reached \(60 - 70\%\) confluency and were ready for next passage.
+
+<|ref|>text<|/ref|><|det|>[[113, 408, 884, 515]]<|/det|>
+Human PSC- derived cerebral organoids and perfused cerebral tissue. We adapted the protocol by Lancaster et al. \(^{69}\) to our experimental conditions. Upon reaching a confluency of \(60 - 70\%\) hPSCs were dissociated by treatment the colonies with \(250\mu \mathsf{I}\) Accutase (A1110501, Gibco) for 7 min at \(37^{\circ}C\) and resuspended in E8Flex medium containing \(10\mu \mathsf{M}\) Rock inhibitor.
+
+<|ref|>text<|/ref|><|det|>[[113, 525, 885, 806]]<|/det|>
+Organoids were generated in U- bottom 96- well plates (#351177, Falcon). The plates were rinsed with Anti- Adherence Solution (#07010, Stemcell Technologies) and cells were plated at 9000cells/well density. Plates were spun at 300rcf at RT and left in CO2 incubator for 24 hours for hPSC spheroid aggregation, after which culture medium was replaced by fresh E8- Flex medium, without Rock inhibitor and changed afterwards every 2 days. At day 2, the spheroids were embedded in growth factor reduced (GFR) Matrigel (354230, Becton Dickinson) and kept in 6- well plates, pre- rinsed with Anti Adherence Solution in CO2 incubator. At day 6, neuronal induction was started by replacing E8- Flex medium with DMEM/F12 medium (31330038, Gibco) containing \(1\%\) MEM- NEAA (11140035, Gibco), \(1\%\) Glutamax (35050038, Gibco), \(1\%\) Pen- Strep (15140122, Gibco), \(0.5\%\) N2 supplement (17502048, Gibco) and \(1\mathsf{ug / ml}\) Heparin (H3149, Sigma) (neural induction medium). Day 8 spheroids were used for characterization.
+
+<|ref|>text<|/ref|><|det|>[[113, 816, 884, 892]]<|/det|>
+For the formation of perfused tissue, at day 0, we first generated micro- hPSC spheroids using 24- well Aggrewell plates (34411, Stemcell Technologies) following a protocol supplied by the manufacturer. Specifically, we seeded Aggrewells with hPSCs to obtain 350- 400 cells per micro- well. After 24 hours,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 886, 397]]<|/det|>
+spheroids formed and the medium was replaced by fresh E8- Flex without Rock inhibitor. At day 2, the spheroids typically reached a diameter of 180- 200um, and were harvested and resuspended in ice cold GFR Matrigel at a density of 3500 spheroids per 200- 250ul GFR Matrigel. The grids were placed under stereomicroscope in a 35mm petri dish on ice and seeded with the spheroid suspension at final density of \(\sim 1800\) spheroids per grid. \(200\mu l\) plastic tips pre- chilled on ice were used to dispense the suspension under stereomicroscope. Seeding was performed in several stages in order to allow dispensed spheroids to settle into the grids. After seeding, the grids were kept in a CO2 incubator for 40- 50 min to allow Matrigel polymerization, after which the grids where placed in a perfusion chip and perfusion was started. E8- Flex/PenStrep medium was changed every 2 days (3- 4ml per grid). At day 6, E8- Flex medium was replaced by neural induction medium for 2 days. At day 8, the grids were extracted and the tissue used for characterizations.
+
+<|ref|>text<|/ref|><|det|>[[113, 435, 886, 628]]<|/det|>
+Immunofluorescence analysis of cerebral tissue samples. Samples were fixed with \(4\%\) paraformaldehyde (158127, Sigma- Aldrich) for 24- 36 hours at \(4^{\circ}C\) and washed by 3 incubations in PBS for 15- 20 min at room temperature. Fixed tissue was sectioned either by embedding in low melting point agarose and sectioning on vibratome (Leica VT1000S) into 100- 150um sections or cryopreserved in OCT(6502, Thermo APD Consumables) overnight at \(4^{\circ}C\) , re- embedded into fresh OCT, frozen in isopropanol/dry ice slurry, cut into 50um sections on cryotome (Leica CM1850) and affixed on SuperFrost Plus (10019419, Thermo Scientific) microscope glass slides.
+
+<|ref|>text<|/ref|><|det|>[[113, 639, 886, 860]]<|/det|>
+Sections were incubated in a permeabilization and blocking solution of \(0.3\%\) Triton X (A4975, PanREAC Applichem) and \(3\%\) BSA (A7906, Sigma) in PBS for 24 hours at \(4^{\circ}C\) . Primary antibodies were diluted in the permeabilization and blocking solution and applied to sections for 24h at \(4^{\circ}C\) , after which three PBS washes were performed over another 24h period. Secondary antibodies and Hoechst were also diluted in the permeabilization and blocking solution and applied to sections overnight at \(4^{\circ}C\) , followed by washing in PBS 3- 4 times over another 24 hours. Antibodies used in this study are listed in Table 1. Stained agarose- embedded sections were stored in 2mM sodium azide solution in PBS. Cryosections were mounted in Fluoromount- G medium and stored at \(4^{\circ}C\) .
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[114, 112, 710, 744]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[115, 742, 462, 758]]<|/det|>
+Table 1. List of antibodies used in this study
+
+| Primary | Host | Dilution | Manufacturer |
| Pax6, monoclonal | Mouse | 1:200 | DSHB |
| Nanog | Goat | 1:200 | R&D Systems, AF1997 |
| ECad | Mouse | 1:500 | Abcam, ab76055 |
| NCad | Rat | 1:200 | DSHB |
| Cleaved Caspase3 | Rabbit | 1:400 | Cell Signaling Technology, 9661 |
| HIF1a | Rabbit | 1:500 | Abcam, ab51608 |
| HNF4α | Mouse | 1:200 | Abcam, ab41898 |
| Alpha-1-Antitrypsin | Rabbit | 1:200 | DAKO, A0012 (00092029) |
| PEPCK | Mouse | 1/1000 | Santa Cruz, sc-271204 |
| MRP2 | Mouse | 1/500 | Abcam, ab3373 |
| KRT19 | goat | 1/500 | Santa Cruz, sc-33120 |
| ALB | Rabbit | 1/500 | Abcam, ab207327 |
| Secondary | | | |
| Hoechst | | | Sigma-Aldrich, 14533 |
| Anti-mouse Alexa 647 | Donkey | 1:500 | Invitrogen, A31571 |
| Anti-goat Alexa 647 | Donkey | 1:500 | Invitrogen, A21447 |
| Anti-rat Alexa 555 | Goat | 1:500 | Invitrogen, A21434 |
| Anti-goat Alexa 555 | Donkey | 1:500 | Invitrogen, A21432 |
| Anti-rabbit Alexa 555 | Donkey | 1:500 | Invitrogen, A31572 |
| Anti-mouse Alexa 488 | Donky | 1:500 | Invitrogen, A11029 |
+
+<|ref|>text<|/ref|><|det|>[[113, 781, 884, 888]]<|/det|>
+Human PSC- derived perfused hepatic tissue. All liver differentiation experiments were performed with the H3CX hiPSC line previously generated 70. H3CX is a hiPSC line (Sigma 0028, Sigma- Aldrich) genetically engineered to overexpress 3 transcription factors HNF1A, FOXA3 and PROX1 upon Doxycycline induction, which allows for rapid generation of hepatocyte- like progeny. H3CX cells were
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 85, 886, 600]]<|/det|>
+expanded feeder- free on Matrigel (BD Biosciences)- coated plates in E8 or E8 Flex (Thermo Fisher Scientific). HC3X cells were differentiated towards HLCs as previously described71. Briefly, HC3X cells were dissociated to single cells using StemPro™Accutase™ Cell dissociation Reagent (Thermo Fisher Scientific) and plated on Matrigel- coated plates at \(\pm 8.75 \times 10^{4}\) cells/cm² in mTeSR medium (Stem Cell Technologies) supplemented with RevitaCell (Thermo Fisher Scientific). When cells reached 70- 80% confluence, differentiation was performed during 40 days in liver differentiation medium (LDM) containing to comprise 500ml total volume: 285 ml of DMEM low glucose (Invitrogen 31885023), 200 ml of MCDB- 201 solution in water (Sigma M- 6770) adjusted to pH 7.2, \(0.25 \times\) of Linoleic acid—Bovine serum albumin (LA- BSA, Sigma L- 9530), \(0.25 \times\) of Insulin- transferrin- selenium (ITS, Sigma I- 3146), 50 U of Penicillin/Streptomycin (Invitrogen 15140122), 100 nM of I- ascorbic acid (Sigma A8960), 1 μM dexamethasone (Sigma D2915) and 50 μM of \(\beta\) - mercaptoethanol (Invitrogen 31350010). Differentiation medium was supplemented with \(0.6\%\) dimethylsulfoxide (DMSO) during the first 12 days of the culture. \(2.0\%\) DMSO and 3x concentrate of non- essential amino- acids (NEAA) was added to LDM medium between days 12- 13, and from day 14 until the end of differentiation 20g/L glycine was added to LDM medium supplemented with NEAA. Differentiation was performed in presence of the following factors: day 0- 1: 100ng/ml Activin- A and 50ng/ml Wnt3a, day 2- 3: 100ng/ml Activin- A, day 4- 7: 50ng/ml BMP4, day 8- 11: 20ng/ml FGF1, and 20ng/ml HGF during the rest of differentiation. Doxycycline (5ug/ml) was applied from day 4 until the end of differentiation. All cytokines were purchased from Peprotech.
+
+<|ref|>text<|/ref|><|det|>[[113, 637, 886, 802]]<|/det|>
+RNA extraction and quantitative reverse- transcription PCR. RNA extraction was performed using TR1zol reagent (Invitrogen) following manufacturer's instructions. At least 1μg of RNA was transcribed to cDNA using the Superscript III First- Strand synthesis (Invitrogen). Gene expression analysis was performed using the Platinum SYBR green qPCR supermix- UDG kit (Invitrogen) in a ViiA 7 Real- Time PCR instrument (Thermo Fisher Scientific). The sequences of all used RT- qPCR primers are listed in Table 2. The ribosomal protein L19 transcript (RPL19) was used as a housekeeping gene for normalization.
+
+<|ref|>table<|/ref|><|det|>[[114, 812, 457, 897]]<|/det|>
+
+| RPL19 | ATTGGTCTCATTGGGGTCTAAC AGTATGCTCAGGCTTCAGAAGA |
| AAT | AGGGCCGGAAGCTAGTGAGT TCCTCGGTGTTCCTTGACTTC |
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[114, 88, 459, 461]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[115, 461, 441, 478]]<|/det|>
+Table 2. List of primers used in this study
+
+| NTCP | ATGCTGAGGCAAGGATGTTC AGCAGCAGCACGACAGAGTA |
| G6PC | GTGTCCGTGATCGCAAGCC GACGAGGTTGAGCCAGTCTC |
| CYP3A4 | TTCCTCCCTGAAAGATTCAGC GTTGAAGAAGTCTCCTAAGCT |
| PEPCK | AAGAAGTGCTTTGCTCTCAG CCTTAAATGACCTTGTCGT |
| CYP2D6 | CATACCTGCCCTACTACCAAA TGTCTGCCTGGTCCTC |
| PGC1α | CCTTCGAGCACAAGAAAACA TGCTTCGTCGTCAAAAACAG |
| HNF6 | AAATCACCATTTCCCAGCAG ACTCCTCCTTCTTGCGTCA |
| ALB | ATGCTGAGGCAAGGATGTTC AGCAGCAGCACGACAGAGTA |
| AAT | AGGGGCTGAAGCTAGTGGAT TCCTCGGTGTCCTTGACTTC |
+
+<|ref|>text<|/ref|><|det|>[[113, 529, 886, 754]]<|/det|>
+Histology. Samples were fixed with \(4\%\) (w/v) paraformaldehyde (PFA, Sigma- Aldrich) overnight at \(4^{\circ}\mathrm{C}\) washed 3 times with PBS and submerged in PBS- sodium azide ( \(0.01\%\) v/v) solution at \(4^{\circ}\mathrm{C}\) until embedded in paraffin. Hydrogel sections (5 \(\mu \mathrm{m}\) ) were prepared using a microtome (Microm HM 360, Marshall Scientific.) For Hematoxylin and Eosin (H&E) staining, sections were treated with xylene solution to remove the paraffin, and gradually rehydrated in ethanol (100 to \(70\%\) , v/v). H&E staining was performed by submerging rehydrated hydrogel sections in Harris Hematoxylin solution, acid alcohol, bluing reagent and Eosin- Y solution by order. Stained samples were dehydrated with ascending alcohol series, washed in xylene solution, and mounted with DPX mountant (Sigma- Aldrich).
+
+<|ref|>text<|/ref|><|det|>[[113, 792, 884, 900]]<|/det|>
+Immunofluorescence analysis of liver tissue samples. Following deparaffinization in xylene and rehydration in descending alcohol series, heat- mediated antigen retrieval was performed by incubating hydrogel sections in Dako antigen retrieval solution (Dako) for 20 min at \(98^{\circ}\mathrm{C}\) . This step was followed by cell permeabilization with \(0.01\%\) (v/v) Triton- X (Sigma- Aldrich) solution in PBS, for 20 minutes. Samples
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 884, 282]]<|/det|>
+were then incubated with \(5\%\) (v/v) Goat or Donkey Serum (Dako) for 30 min. Primary antibodies diluted in Dako antibody diluent solution, were incubated overnight at \(4^{\circ}C\) , followed by washing steps and incubation with Alexa- coupled secondary antibody (1:500) and Hoechst 33412 (1:500) solution for 1 hour at room temperature. Finally, samples were washed in PBS, and mounted with Vectashield antifade mounting medium (Vector Laboratories). Stained sections were imaged using laser scanning confocal microscope (LSM 880, Zeiss, Germany), and image processing were performed on ZEN Blue software (Zeiss, Germany).
+
+<|ref|>text<|/ref|><|det|>[[112, 320, 885, 630]]<|/det|>
+Image acquisition and analysis of cerebral tissue samples. Fluorescence images were obtained using a confocal microscope (Leica SP8 DIVE, Leica Microsystems) equipped with 10x NA0.4 dry objective. Acquisition parameters were kept constant for all samples obtained in the same experiment. Image processing was performed using Fiji/ImageJ (NIH) and custom- written ImageJ Java plugin. At the data preprocessing stage, image stacks were collapsed by maximum intensity projection. Resulting images were translated to 8- bit lookup table representation, manually cleaned from grid structure elements and thresholded by replacing all sub- threshold pixels with black (zero value) pixels. Lookup tables of the images were then remapped from [Threshold..255] back to full [0..255] range. Threshold values were chosen manually for Hoechst and marker channels for each image in order to remove background from the images. For all markers except HIF1α, total protein expression levels in a tissue were quantified as a relative number of cells expressing the protein, i.e.
+
+<|ref|>equation<|/ref|><|det|>[[310, 655, 685, 688]]<|/det|>
+\[Protein expression = \frac{Marker^{+}cellnumber}{Totalcellnumber} \times 100\%\]
+
+<|ref|>text<|/ref|><|det|>[[113, 713, 884, 820]]<|/det|>
+On the assumption that cell size is constant across the samples, the relative number of cells was estimated as a ratio of areas occupied by cells on marker and Hoechst channels. Corresponding areas were calculated by counting all non- zero pixels on marker and Hoechst channels. For statistical comparison, results for each marker were pooled from all experiments.
+
+<|ref|>text<|/ref|><|det|>[[113, 830, 884, 907]]<|/det|>
+As HIF1α marker is constitutively expressed in cells under normoxic conditions, its expression level in a tissue was estimated as the average fluorescence intensity on the marker channel. Threshold values were kept constant for organoids, non- perfused and perfused samples obtained in the same experiment;
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 883, 135]]<|/det|>
+expression values obtained in the experiment were normalized to organoid value and normalized data from different experiments were averaged.
+
+<|ref|>text<|/ref|><|det|>[[113, 146, 884, 282]]<|/det|>
+All results are expressed as mean \(\pm\) SEM. Statistical comparisons between two data groups were analyzed using unpaired two- tailed Student's \(t\) - test with a \(95\%\) confidence interval (Origin Pro v9.5, OriginLab Inc.). Significance was marked on plots by \*, \*\* and \*\*\* for \(p< 0.05\) , \(p< 0.01\) , and \(p< 0.001\) correspondingly. If not stated otherwise, the statistical significance was assessed for comparisons of perfused and non- perfused samples to organoid control samples and denoted by "pControl".
+
+<|ref|>text<|/ref|><|det|>[[112, 319, 885, 629]]<|/det|>
+Organoid dissociation and single- cell RNA sequencing. For dissociation, the microfluidic grids of non- perfused and perfused samples were removed from the perfusion chips and, along with the control organoids, placed temporarily in DMEM/F12 media in independent \(15 \text{mL}\) Falcon tubes until all 3 samples were ready for the next step (time \(< 5 \text{min}\) ). The DMEM was then replaced with \(1 \text{mL}\) of pre- warmed TrypLE Express (12605010, Gibco) at \(37^{\circ} \text{C}\) . The samples were transferred to a warm water bath at \(37^{\circ} \text{C}\) for 7.5 minutes with gentle agitation every 1 minute after the first 3 minutes. A visual inspection was performed using an inverted microscope to ensure complete dissociation of tissues and the presence of single cells. The \(1 \text{mL}\) solution was introduced to \(9 \text{mL}\) of DMEM supplemented with \(20\%\) FBS for TrypLE Express neutralization, and centrifuged at \(500 \text{rcf}\) for 5 minutes. The pellet was resuspended in \(200 \text{uL}\) of N2B27 media and put on ice. This dissociation protocol yielded an average viability of above \(80\%\) across all samples.
+
+<|ref|>text<|/ref|><|det|>[[112, 639, 885, 861]]<|/det|>
+Library preparations for the scRNAseq was performed using 10X Genomics Chromium Single Cell 3' Kit, v3 (10X Genomics, Pleasanton, CA, USA). The cell count and the viability of the samples were accessed using LUNA dual fluorescence cell counter (Logos Biosystems) and a targeted cell recovery of 6000 cells was aimed for all the samples. Post cell count and QC, the samples were immediately loaded onto the Chromium Controller. Single cell RNAseq libraries were prepared using manufacturers recommendations (Single cell 3' reagent kits v3 user guide; CG00052 Rev B), and at the different check points, the library quality was accessed using Qubit (ThermoFisher) and Bioanalyzer (Agilent). Single cell libraries were sequenced using paired- end sequencing workflow and with recommended 10X; v3 read
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 883, 136]]<|/det|>
+parameters (28- 8- 0- 91 cycles). The data generated from sequencing was de- multiplexed and mapped against human genome reference using CellRanger v3.0.2.
+
+<|ref|>text<|/ref|><|det|>[[112, 174, 885, 516]]<|/det|>
+Single Cell RNA sequencing Data Processing. We have sequenced 4,818, 5,453, and 2,804 cells for non- perfused, perfused and control organoids samples respectively for a total of 13,075 cells, which were reduced after QC steps to 8,625 cells with an average of 1,852 detected genes per cell. Data processing and subsequent steps were performed using the Seurat72 tool for single cell genomics version 3 in R version 4.0.3. A filtering step was performed to ensure the quality of the data, where the counts of mitochondrial reads and total genes reads were assessed. Cells with more than \(15\%\) of identifiable genes rising from the mitochondrial genome were filtered out. Similarly, cells having fewer identifiable genes than 200 (low quality) and above 7,500 (probable doublets) were filtered out. Data normalization was performed, followed by the identification of 2,000 highly variable genes using the FindVariableFeatures(). S- phase and G2M- phase cell cycle regression was performed to allow cell clustering purely on cell identity and fate, which otherwise was biased by cell cycle phases. Auto scaling of the data was performed and described using principal component analysis (PCA) using the RunPCA() function.
+
+<|ref|>text<|/ref|><|det|>[[113, 551, 884, 660]]<|/det|>
+Correlation analysis. Correlation heatmap between samples was performed in R using the top 100 marker genes for each sample using the FindAllMarkers() function followed by the selection of the top 100 marker genes using the top_n() function with \(n = 100\) and wt = avg.logFC. The correlation analysis was generated using the cor() function using the Pearson method and the heatmap using the heatmap.2() function in R.
+
+<|ref|>text<|/ref|><|det|>[[113, 697, 885, 891]]<|/det|>
+Data Clustering. Graph- based clustering using the FindNeighbors() function (using top 15 principal components (PCs)) and FindCluster() function (resolution = 0.5) was performed to group cells based on their transcriptional profiles. No batch correction was performed on the data set. Data visualization was performed using the Uniform Manifold Approximation and Projection (UMAP) dimensionality reduction technique using the RunUMAP package while employing the top 15 PCs identified in the previous PCA step. Cluster annotation was based on hallmark genes to identify Neuroepithelial cluster (PAX6, PAX7, PAX3), Pluripotent- Neuroepithelial transitioning (P- NE) cells (WNT4, IRX1, IRX2), Proliferating cells
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 885, 280]]<|/det|>
+(CDC6, PTN, MK167, TOP2A), medium mitochondrial gene content and low glycolysis pluripotent cells (MK167, TOP2A, with the expression of NANOG, POU5F1, DPPA4), Pluripotent cells (NANOG, POU5F1, DPPA4), highly glycolytic pluripotent cells that link to the Cycling pluripotent and Pluripotent cells but include the expressions (LDHA, ENO1, HK2), a cluster undergoing EMT/migration with hypoxic markers (EPCAM, VIM, TWIST2, VEGFA) and finally a stressed cluster (FOS, HIF1A, JUN). One cluster was manually removed due to very low unique molecular identifier (UMI) count, after which the data was reprocessed to account for the removal of the cluster.
+
+<|ref|>text<|/ref|><|det|>[[113, 320, 885, 543]]<|/det|>
+Pseudotime trajectories. Trajectory analysis was performed using Monocle \(3^{73}\) on R by employing the monocole3 and SeuratWrappers libraries. The Seurat obtained object containing all combined samples was passed to the Monocle 3 pipeline using the as.cell_data_set() function followed by processing using the cluster_cells() function. The pseudotime trajectory was inferred by first using the subset function on the only partition detected, followed by the learn_graph() function. Cells were colored in their inferred pseudotime using the which.max() function with the FetchData() (AVP) function, followed by the order_cells() function with the root_cell = max.avp. The UMAP superimposed with inferred pseudotime trajectory was generated using the plot_cells() function.
+
+<|ref|>text<|/ref|><|det|>[[113, 580, 885, 802]]<|/det|>
+Gene- set analysis and hierarchical clustering. Gene- sets were created using the AddModuleScore() function in R. three gene- set were created to explore the dataset, pluripotency gene- set (POU5F1, NANOG, CDH1), glycolysis gene- set (ALDOA, BPGM, ENO1, ENO2, GPI, HK1, HK2, PFKL, PFKM, PGAM1, PGK1, PKM, TP11), and a neural progenitor gene- set (PAX3, PAX6, PAX7, OTX2, CDH2). The % mitochondrial genes were obtain as evaluated by the Seurat pipeline. Each cell was evaluated and scored and its expression plotted on UMAPS. Cluster level hierarchical clustering of the gene- set scores and % mitochondrial genes was employed using R package heatmap.2 after scaling the expression across rows (clusters).
+
+<|ref|>text<|/ref|><|det|>[[113, 842, 883, 890]]<|/det|>
+Design and fabrication of soft micro- fluidic grids. The microfluidic grids were designed as a multitude of parallel capillaries stemming from a common reservoir. The dimensions of the grid (2.6x2.6x1.5mm) were
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 885, 339]]<|/det|>
+chosen as a compromise between size and the fabrication time. The grids were micro- fabricated on custom baseplates using high- resolution 3D printer (Photonic Professional GT2, Nanoscribe GmbH) equipped with 2- photon femtosecond laser. CAD model of the capillary grid was pre- processed by DeScribe software (Nanoscribe GmbH) to produce a printing job with defined printing parameters. A custom- formulation photopolymerizable resin was used to print microfluidic grids which contained \(2\%\) 2- Benzyl- 2- (dimethylamino)- 4'- morpholinobutyrophenone (lrgacure 369), \(7\%\) propylene glycol methyl ether acetate (PGMEA), \(36\%\) poly(ethylene glycol) diacrylate, MW700 (PEGDA 700), \(25\%\) pentaerythritol triacrylate (PETA), \(20\%\) Triton X- 100 and \(10\%\) water. lrgacure 369 was purchased from Tokyo Chemical Industry Ltd, the other components were from Sigma- Aldrich.
+
+<|ref|>text<|/ref|><|det|>[[113, 349, 886, 570]]<|/det|>
+The microfluidic grids were printed on custom plates 3D printed on Formlabs Form 2 printer from a biocompatible resin (Dental SG, Formlabs Inc), post- cured by UV light (Formcure station, Formlabs Inc) for 2h at \(80^{\circ}C\) and washed in 2- propanol for 3- 4 days with daily change of the solvent. The plates had 1mm thickness and 10mm diameter, with 0.5mm perfusion holes. The grid printing process was set up such that the inlets in the microfluidic grid were aligned with the perfusion holes in a baseplate. After fabrication, baseplate- grid assemblies were washed during 2 days in PGMEA, 12 days in 2- propanol and then kept in PBS until use. The solvents were refreshed every 1- 2 days and PBS was refreshed daily for the first week and every 2- 3 days afterwards.
+
+<|ref|>text<|/ref|><|det|>[[113, 608, 885, 803]]<|/det|>
+Fabrication of perfusion chips and setting up perfusion. The perfusion chips were implemented as an assembly as shown in Supplementary Fig. 1. Two microfluidic grids were sandwiched between two polydimethylsiloxane (PDMS) custom- profiled blocks. Two metal plates clamped with screws provided a tight junction between PDMS blocks and cover slips, thereby forming fluidic channels within the chip. The chips were designed to only allow contact of the medium with PDMS blocks and cover slips, thereby isolating the flow from contact with other materials of the chip. Guiding frames were used to simplify the alignment of the PDMS blocks during the chip assembly process.
+
+<|ref|>text<|/ref|><|det|>[[113, 813, 884, 890]]<|/det|>
+The PDMS blocks were made by casting liquid PDMS compound into custom- designed plastic molds and curing overnight at \(80^{\circ}C\) . The plastic molds were fabricated by stereo- lithography (SLA) 3D printer Form 2 (Formlabs Inc.) using a bio- compatible Formlabs Dental SG resin. The printed molds were
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 223]]<|/det|>
+post- processed by thorough washing in 2- propanol and post- cured for 90 min at \(80^{\circ}C\) (Formcure, Formlabs Inc.). Metal plates were made from 1mm stainless steel sheet by laser cutting and stainless steel screws were used for clamping the assembly. The guiding frames were 3D printed and cover slips were glued to the metal plates with a bio- compatible UV/heat curable epoxy (NOA 86H, Norland) to provide a final two- part setup shown in Supplementary Fig. 1d.
+
+<|ref|>text<|/ref|><|det|>[[112, 233, 885, 630]]<|/det|>
+Two chambers of the chip, containing perfused and non- perfused grids, a peristaltic pump and a medium reservoir (50ml Falcon tube) were connected by flexible PVC tubing (ID/OD 0.8/1.6mm) in series (Supplementary Fig. 1e). The medium was taken from the reservoir by the pump and fed through chambers containing the non- perfused and then the perfused grid, after which the medium was sent back to the reservoir for \(\mathrm{CO_2 / O_2}\) equilibration. A 0.22um filter was connected between the two chambers of the chip to protect capillaries of the perfused grid from potential clogging with tissue debris. The medium reservoir and the chip were kept in a CO2 incubator, while the peristaltic pump remained outside to protect electronics from humidity and to ensure proper cooling. The medium reservoir and the chip were installed on a custom made 3D printed holder (Supplementary Fig. 1f) to simplify transitions between a CO2 incubator and a laminar hood. At day 0 of an experiment, all parts of the perfusion were sterilized by ethanol and UV light in a laminar hood, connected together and filled with equilibrated medium. The microfluidic grids, seeded with hPSC spheroids, were installed in the chip (Supplementary Fig. 1d) and the chip was clamped by screws (Supplementary Fig. 1f- i). Air bubbles were removed from the system and the perfusion started at approx. \(400\mu \mathrm{L} / \mathrm{min}\) flow rate (Supplementary Fig. 1, f- iii).
+
+<|ref|>text<|/ref|><|det|>[[113, 639, 885, 890]]<|/det|>
+Multi- grid perfusion chips were designed to provide an equal multiplexed perfusion for all microfluidic grids. The fluidic inlet of the chip, via three steps of bifurcations, was split into eight fluidic channels feeding eight wells. All fluidic channels had equal length and cross- section and, therefore, equal hydraulic resistance. The multi- grid chip were fabricated by stereo- lithography (SLA) 3D printer Form 2 (Formlabs Inc.) using Formlabs Dental SG resin. The printed chips were post- processed by thorough washing in 2- propanol and post- cured for 90 min at \(60^{\circ}C\) . 7- 8mm pieces of syringe needles (0.9mm) were cut by hand drill/cutter (Precision drill, Proxxon Inc.) and glued into chip inlets by a biocompatible UV/heat curable epoxy glue to serve as connectors for flexible tubing. This assembly was again post- cured in FormCure station for 120 min at \(80^{\circ}C\) to achieve complete hardening of the glue. To integrate microfluidic
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 883, 136]]<|/det|>
+grids, a custom profile gaskets, cut from 0.5mm PDMS sheet by a laser cutter, were placed under the grid substrates to provide a liquid- tight contact and the substrates were fixed in place by 3D printed fasteners.
+
+<|ref|>text<|/ref|><|det|>[[113, 175, 884, 309]]<|/det|>
+Data availability. All raw sequencing data, and the combined processed and metadata files generated in this study are available at GEO. The accession number for the reported data is GSE181290. This study did not generate any unique code. For review purposes please use the following token (ybchyyqofpejzgv) to access the sequencing data at: https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE181290. The ImageJ Java code used for analysis of the image data are available upon request.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 89, 206, 105]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[110, 140, 884, 900]]<|/det|>
+1. Kaushik, G., Ponnusamy, M. P. & Batra, S. K. Concise Review: Current Status of Three-Dimensional Organoids as Preclinical Models: 3D Organoid Culture as a Tool for Research. Stem Cells 36, 1329–1340 (2018).
+2. Ollé-Vila, A., Duran-Nebreda, S., Conde-Pueyo, N., Montañez, R. & Solé, R. A morphospace for synthetic organs and organoids: the possible and the actual. Integr. Biol. 8, 485–503 (2016).
+3. Van Norman, G. A. Limitations of Animal Studies for Predicting Toxicity in Clinical Trials. JACC: Basic to Translational Science 4, 845–854 (2019).
+4. Gilbert, S. F. Developmental biology. (Sinauer Associates, 2000).
+5. Grebenyuk, S. & Ranga, A. Engineering Organoid Vascularization. Front. Bioeng. Biotechnol. 7, 39 (2019).
+6. Nashimoto, Y. et al. Integrating perfusable vascular networks with a three-dimensional tissue in a microfluidic device. Integrative Biology 9, 506–518 (2017).
+7. Salmon, I. et al. Engineering neurovascular organoids with 3D printed microfluidic chips. http://biorxiv.org/lookup/doi/10.1101/2021.01.09.425975 (2021) doi:10.1101/2021.01.09.425975.
+8. Rajasekar, S. et al. IFlowPlate—A Customized 384-Well Plate for the Culture of Perfusable Vascularized Colon Organoids. Adv. Mater. 32, 2002974 (2020).
+9. Sugihara, K. et al. A new perfusion culture method with a self-organized capillary network. PLoS ONE 15, e0240552 (2020).
+10. Takebe, T. et al. Vascularized and functional human liver from an iPSC-derived organ bud transplant. Nature 499, 481–484 (2013).
+11. Mansour, A. A. et al. An in vivo model of functional and vascularized human brain organoids. Nature Biotechnology 36, 432–441 (2018).
+12. Zhu, W. et al. 3D printing of functional biomaterials for tissue engineering. Current Opinion in Biotechnology 40, 103–112 (2016).
+13. Xie, M. et al. Electro-Assisted Bioprinting of Low-Concentration GelMA Microdroplets. Small 15, 1804216 (2019).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 849, 135]]<|/det|>
+14. Cui, X., Boland, T., D.D'Lima, D. & K. Lotz, M. Thermal Inkjet Printing in Tissue Engineering and Regenerative Medicine. Recent Patents on Drug Delivery & Formulation 6, 149–155 (2012).
+
+<|ref|>text<|/ref|><|det|>[[115, 145, 872, 193]]<|/det|>
+15. Dababneh, A. B. & Ozbolat, I. T. Bioprinting Technology: A Current State-of-the-Art Review. Journal of Manufacturing Science and Engineering 136, 061016 (2014).
+
+<|ref|>text<|/ref|><|det|>[[115, 204, 839, 251]]<|/det|>
+16. Gudapati, H., Dey, M. & Ozbolat, I. A comprehensive review on droplet-based bioprinting: Past, present and future. Biomaterials 102, 20–42 (2016).
+
+<|ref|>text<|/ref|><|det|>[[115, 261, 829, 339]]<|/det|>
+17. Christensen, K. et al. Freeform inkjet printing of cellular structures with bifurcations: Approach Freeform Fabrication of Bifurcated Cellular Structures by Using a Liquid Support-Based Inkjet Printing Approach. Biotechnology and Bioengineering 112, 1047–1055 (2015).
+
+<|ref|>text<|/ref|><|det|>[[115, 349, 847, 426]]<|/det|>
+18. Nakamura, M. et al. Ink Jet Three-Dimensional Digital Fabrication for Biological Tissue Manufacturing: Analysis of Alginate Microgel Beads Produced by Ink Jet Droplets for Three Dimensional Tissue Fabrication. Journal of Imaging Science and Technology 52, 060201 (2008).
+
+<|ref|>text<|/ref|><|det|>[[115, 436, 763, 483]]<|/det|>
+19. Zhu, W. et al. Direct 3D bioprinting of prevascularized tissue constructs with complex microarchitecture. Biomaterials 124, 106–115 (2017).
+
+<|ref|>text<|/ref|><|det|>[[115, 494, 870, 542]]<|/det|>
+20. Ma, X. et al. Deterministically patterned biomimetic human iPSC-derived hepatic model via rapid 3D bioprinting. Proceedings of the National Academy of Sciences 113, 2206–2211 (2016).
+
+<|ref|>text<|/ref|><|det|>[[115, 552, 844, 600]]<|/det|>
+21. Huang, T. Q., Qu, X., Liu, J. & Chen, S. 3D printing of biomimetic microstructures for cancer cell migration. Biomedical Microdevices 16, 127–132 (2014).
+
+<|ref|>text<|/ref|><|det|>[[115, 610, 817, 657]]<|/det|>
+22. Singh, N. K. et al. Three-dimensional cell-printing of advanced renal tubular tissue analogue. Biomaterials 232, 119734 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 668, 827, 715]]<|/det|>
+23. Gao, Q. et al. 3D printing of complex GelMA-based scaffolds with nanoclay. Biofabrication 11, 035006 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 726, 789, 773]]<|/det|>
+24. Jia, W. et al. Direct 3D bioprinting of perfusable vascular constructs using a blend bioink. Biomaterials 106, 58–68 (2016).
+
+<|ref|>text<|/ref|><|det|>[[115, 784, 836, 832]]<|/det|>
+25. Xu, C., Chai, W., Huang, Y. & Markwald, R. R. Scaffold-free inkjet printing of three-dimensional zigzag cellular tubes. Biotechnology and Bioengineering 109, 3152–3160 (2012).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 844, 163]]<|/det|>
+26. Kinoshita, K., Iwase, M., Yamada, M., Yajima, Y. & Seki, M. Fabrication of multilayered vascular tissues using microfluidic agarose hydrogel platforms. Biotechnology Journal (2016) doi:10.1002/biot.201600083.
+
+<|ref|>text<|/ref|><|det|>[[113, 174, 860, 252]]<|/det|>
+27. Roudsari, L. C., Jeffs, S. E., Witt, A. S., Gill, B. J. & West, J. L. A 3D Poly(ethylene glycol)-based Tumor Angiogenesis Model to Study the Influence of Vascular Cells on Lung Tumor Cell Behavior. Scientific Reports 6, 32726 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 262, 870, 310]]<|/det|>
+28. Zhang, Y. S. et al. Bioprinting 3D microfibrous scaffolds for engineering endothelialized myocardium and heart-on-a-chip. Biomaterials 110, 45-59 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 320, 840, 368]]<|/det|>
+29. Meyer, W. et al. Soft Polymers for Building up Small and Smallest Blood Supplying Systems by Stereolithography. Journal of Functional Biomaterials 3, 257-268 (2012).
+
+<|ref|>text<|/ref|><|det|>[[113, 378, 878, 455]]<|/det|>
+30. Huber, B. et al. Blood-Vessel Mimicking Structures by Stereolithographic Fabrication of Small Porous Tubes Using Cytocompatible Polyacrylate Elastomers, Biofunctionalization and Endothelialization. Journal of Functional Biomaterials 7, 11 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 465, 870, 512]]<|/det|>
+31. Kang, H.-W. et al. A 3D bioprinting system to produce human-scale tissue constructs with structural integrity. Nature Biotechnology 34, 312-319 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 523, 877, 599]]<|/det|>
+32. Compaan, A. M., Song, K., Chai, W. & Huang, Y. Cross-Linkable Microgel Composite Matrix Bath for Embedded Bioprinting of Perfusable Tissue Constructs and Sculpting of Solid Objects. ACS Appl. Mater. Interfaces 12, 7855-7868 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 610, 840, 657]]<|/det|>
+33. Miller, J. S. et al. Rapid casting of patterned vascular networks for perfusable engineered three-dimensional tissues. Nature Materials 11, 768-774 (2012).
+
+<|ref|>text<|/ref|><|det|>[[113, 668, 883, 715]]<|/det|>
+34. Kolesky, D. B., Homan, K. A., Skylar-Scott, M. A. & Lewis, J. A. Three-dimensional bioprinting of thick vascularized tissues. Proceedings of the National Academy of Sciences 113, 3179-3184 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 726, 825, 773]]<|/det|>
+35. Wu, W., DeConinck, A. & Lewis, J. A. Omnidirectional Printing of 3D Microvascular Networks. Advanced Materials 23, H178-H183 (2011).
+
+<|ref|>text<|/ref|><|det|>[[113, 784, 830, 832]]<|/det|>
+36. Bertassoni, L. E. et al. Hydrogel bioprinted microchannel networks for vascularization of tissue engineering constructs. Lab Chip 14, 2202-2211 (2014).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 833, 164]]<|/det|>
+37. Subbiah, R. et al. Prevascularized hydrogels with mature vascular networks promote the regeneration of critical-size calvarial bone defects in vivo A short running title: Prevascularized hydrogels repair bone defects. J Tissue Eng Regen Med (2021) doi:10.1002/term.3166.
+
+<|ref|>text<|/ref|><|det|>[[112, 175, 852, 222]]<|/det|>
+38. Skylar-Scott, M. A. et al. Biomanufacturing of organ-specific tissues with high cellular density and embedded vascular channels. Sci. Adv. 5, eaaw2459 (2019).
+
+<|ref|>text<|/ref|><|det|>[[112, 233, 856, 280]]<|/det|>
+39. Silvestri, V. L. et al. A Tissue-Engineered 3D Microvessel Model Reveals the Dynamics of Mosaic Vessel Formation in Breast Cancer. Cancer Res 80, 4288-4301 (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 291, 860, 367]]<|/det|>
+40. Applegate, M. B. et al. Laser-based three-dimensional multiscale micropatterning of biocompatible hydrogels for customized tissue engineering scaffolds. Proceedings of the National Academy of Sciences 112, 12052-12057 (2015).
+
+<|ref|>text<|/ref|><|det|>[[112, 378, 866, 425]]<|/det|>
+41. Ouija, M. et al. Three dimensional microstructuring of biopolymers by femtosecond laser irradiation. Applied Physics Letters 95, 263703 (2009).
+
+<|ref|>text<|/ref|><|det|>[[112, 436, 871, 511]]<|/det|>
+42. Sarig-Nadir, O., Livnat, N., Zajdman, R., Shoham, S. & Seliktar, D. Laser Photoablation of Guidance Microchannels into Hydrogels Directs Cell Growth in Three Dimensions. Biophysical Journal 96, 4743-4752 (2009).
+
+<|ref|>text<|/ref|><|det|>[[112, 523, 811, 570]]<|/det|>
+43. Brandenberg, N. & Lutolf, M. P. In Situ Patterning of Microfluidic Networks in 3D Cell-Laden Hydrogels. Advanced Materials 28, 7450-7456 (2016).
+
+<|ref|>text<|/ref|><|det|>[[112, 581, 835, 658]]<|/det|>
+44. Skylar-Scott, M. A., Liu, M.-C., Wu, Y. & Yanik, M. F. Multi-photon microfabrication of three-dimensional capillary-scale vascular networks. in (eds. von Freymann, G., Schoenfeld, W. V. & Rumpf, R. C.) 101150L (2017). doi:10.1117/12.2253520.
+
+<|ref|>text<|/ref|><|det|>[[112, 669, 872, 715]]<|/det|>
+45. Kloxin, A. M., Kasko, A. M., Salinas, C. N. & Anseth, K. S. Photodegradable Hydrogels for Dynamic Tuning of Physical and Chemical Properties. Science 324, 59-63 (2009).
+
+<|ref|>text<|/ref|><|det|>[[112, 726, 884, 802]]<|/det|>
+46. Kloxin, A. M., Tibbitt, M. W., Kasko, A. M., Fairbairn, J. A. & Anseth, K. S. Tunable Hydrogels for External Manipulation of Cellular Microenvironments through Controlled Photodegradation. Advanced Materials 22, 61-66 (2010).
+
+<|ref|>text<|/ref|><|det|>[[112, 813, 813, 889]]<|/det|>
+47. Tibbitt, M. W., Kloxin, A. M., Dyamenahalli, K. U. & Anseth, K. S. Controlled two-photon photodegradation of PEG hydrogels to study and manipulate subcellular interactions on soft materials. Soft Matter 6, 5100 (2010).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 88, 860, 135]]<|/det|>
+48. Kim, J., Kong, J. S., Han, W., Kim, B. S. & Cho, D.-W. 3D Cell Printing of Tissue/Organ-Mimicking Constructs for Therapeutic and Drug Testing Applications. IJMS 21, 7757 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 145, 853, 220]]<|/det|>
+49. Ahadian, S. et al. Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies. Advanced Healthcare Materials 1700506 (2017) doi:10.1002/adhm.201700506.
+
+<|ref|>text<|/ref|><|det|>[[113, 232, 874, 280]]<|/det|>
+50. Mittal, R. et al. Organ-on-chip models: Implications in drug discovery and clinical applications. J Cell Physiol 234, 8352-8380 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 290, 883, 338]]<|/det|>
+51. Van Norman, G. A. Limitations of Animal Studies for Predicting Toxicity in Clinical Trials. JACC: Basic to Translational Science 5, 387-397 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 349, 868, 397]]<|/det|>
+52. Gaetani, R. et al. Epicardial application of cardiac progenitor cells in a 3D-printed gelatin/hyaluronic acid patch preserves cardiac function after myocardial infarction. Biomaterials 61, 339-348 (2015).
+
+<|ref|>text<|/ref|><|det|>[[113, 407, 883, 483]]<|/det|>
+53. Norona, L. M., Nguyen, D. G., Gerber, D. A., Presnell, S. C. & LeCluyse, E. L. Editor's Highlight: Modeling Compound-Induced Fibrogenesis In Vitro Using Three-Dimensional Bioprinted Human Liver Tissues. Toxicol. Sci. 154, 354-367 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 494, 852, 541]]<|/det|>
+54. Klein, F. et al. Two-Component Polymer Scaffolds for Controlled Three-Dimensional Cell Culture. Advanced Materials 23, 1341-1345 (2011).
+
+<|ref|>text<|/ref|><|det|>[[113, 552, 876, 600]]<|/det|>
+55. St. John, J. C. et al. The Analysis of Mitochondria and Mitochondrial DNA in Human Embryonic Stem Cells. in Human Embryonic Stem Cell Protocols vol. 331 347-374 (Humana Press, 2006).
+
+<|ref|>text<|/ref|><|det|>[[113, 611, 844, 686]]<|/det|>
+56. Prigione, A., Fauler, B., Lurz, R., Lehrach, H. & Adjaye, J. The Senescence-Related Mitochondrial/Oxidative Stress Pathway is Repressed in Human Induced Pluripotent Stem Cells. STEM CELLS 28, 721-733 (2010).
+
+<|ref|>text<|/ref|><|det|>[[113, 697, 848, 744]]<|/det|>
+57. Wu, J., Ocampo, A. & Belmonte, J. C. I. Cellular Metabolism and Induced Pluripotency. Cell 166, 1371-1385 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 756, 872, 803]]<|/det|>
+58. Berger, E. et al. Millifluidic culture improves human midbrain organoid vitality and differentiation. Lab Chip 18, 3172-3183 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 814, 861, 890]]<|/det|>
+59. Jiang, B. H., Semenza, G. L., Bauer, C. & Marti, H. H. Hypoxia-inducible factor 1 levels vary exponentially over a physiologically relevant range of O2 tension. American Journal of Physiology-Cell Physiology 271, C1172-C1180 (1996).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 88, 880, 163]]<|/det|>
+60. Huang, L. E., Gu, J., Schau, M. & Bunn, H. F. Regulation of hypoxia-inducible factor 1 is mediated by an O2-dependent degradation domain via the ubiquitin-proteasome pathway. Proceedings of the National Academy of Sciences 95, 7987-7992 (1998).
+
+<|ref|>text<|/ref|><|det|>[[112, 175, 870, 222]]<|/det|>
+61. Greijer, A. E. The role of hypoxia inducible factor 1 (HIF-1) in hypoxia induced apoptosis. Journal of Clinical Pathology 57, 1009-1014 (2004).
+
+<|ref|>text<|/ref|><|det|>[[112, 233, 852, 280]]<|/det|>
+62. Wang, M., Tan, J., Miao, Y., Li, M. & Zhang, Q. Role of \(\mathrm{Ca^{2 + }}\) and ion channels in the regulation of apoptosis under hypoxia. Histol Histopathol 33, 237-246 (2018).
+
+<|ref|>text<|/ref|><|det|>[[112, 291, 800, 337]]<|/det|>
+63. Punovuori, K. et al. N-cadherin stabilises neural identity by dampening anti-neural signals. Development 146, dev183269 (2019).
+
+<|ref|>text<|/ref|><|det|>[[112, 348, 850, 367]]<|/det|>
+64. Tietz, P. S. & Larusso, N. F. Cholangiocyte biology. Curr Opin Gastroenterol 22, 279-287 (2006).
+
+<|ref|>text<|/ref|><|det|>[[112, 378, 855, 455]]<|/det|>
+65. Ruebner, B. H., Blankenberg, T. A., Burrows, D. A., Soohoo, W. & Lund, J. K. Development and Transformation of the Ductal Plate in the Developing Human Liver. Pediatric Pathology 10, 55-68 (1990).
+
+<|ref|>text<|/ref|><|det|>[[112, 466, 837, 512]]<|/det|>
+66. Limaye, P. B. et al. Expression of specific hepatocyte and cholangiocyte transcription factors in human liver disease and embryonic development. Lab Invest 88, 865-872 (2008).
+
+<|ref|>text<|/ref|><|det|>[[112, 523, 870, 570]]<|/det|>
+67. Ranga, A. et al. Neural tube morphogenesis in synthetic 3D microenvironments. Proc Natl Acad Sci USA 113, E6831-E6839 (2016).
+
+<|ref|>text<|/ref|><|det|>[[112, 581, 876, 628]]<|/det|>
+68. Medina, J. D. et al. Functionalization of Alginate with Extracellular Matrix Peptides Enhances Viability and Function of Encapsulated Porcine Islets. Adv. Healthcare Mater. 9, 2000102 (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 639, 850, 685]]<|/det|>
+69. Lancaster, M. A. & Knoblich, J. A. Generation of cerebral organoids from human pluripotent stem cells. Nature Protocols 9, 2329-2340 (2014).
+
+<|ref|>text<|/ref|><|det|>[[112, 697, 852, 743]]<|/det|>
+70. Boon, R. et al. Amino acid levels determine metabolism and CYP450 function of hepatocytes and hepatoma cell lines. Nat Commun 11, 1393 (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 755, 866, 830]]<|/det|>
+71. Roelandt, P., Vanhove, J. & Verfaillie, C. Directed Differentiation of Pluripotent Stem Cells to Functional Hepatocytes. in Pluripotent Stem Cells (eds. Lakshmipathy, U. & Vemuri, M. C.) vol. 997 141-147 (Humana Press, 2013).
+
+<|ref|>text<|/ref|><|det|>[[112, 842, 841, 860]]<|/det|>
+72. Stuart, T. et al. Comprehensive Integration of Single-Cell Data. Cell 177, 1888-1902.e21 (2019).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 850, 135]]<|/det|>
+73. Cao, J. et al. The single-cell transcriptional landscape of mammalian organogenesis. Nature 566, 496–502 (2019).
+
+<|ref|>text<|/ref|><|det|>[[114, 146, 825, 194]]<|/det|>
+74. Kumar, M. et al. A fully defined matrix to support a pluripotent stem cell derived multi-cell-liver steatohepatitis and fibrosis model. Biomaterials 276, 121006 (2021).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 395, 177, 411]]<|/det|>
+Figures
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[171, 110, 825, 744]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 770, 883, 904]]<|/det|>
+Figure 1. On-chip micro-vascularization enabled by soft microfluidics. (a) 3D printed tissue culture chip designed for eight multiplexed soft 3D soft microfluidic capillary grids. Inset: microfluidic capillary grid fabricated on a plastic baseplate and diagram of working principle. (b) of microfluidic capillary grid (left) and the close up image of the same grid showing individual hydrogel capillaries (right). (c) Microvessel 3D printing by 3D printing of microfluidic grid using high-resolution 2-photon stereo-lithography with non-swelling photo-polymerizable hydrogel precursors enables reproduction of features as small as \(10\mu \mathrm{m}\) . The top view photograph demonstrates an array of cylinders of various outer diameter in micrometers (top row) and wall thickness in micrometers (columns). (d) CAD image of microfluidic grid (left) with capillaries shown in red and the structural components shown in grey. The fence at the circumference of the structure makes
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 89, 882, 207]]<|/det|>
+up a "basket" that can be filled (right) with cell aggregates (spheroids) which merge and produce a solid tissue incorporating hydrogel capillaries. (e) Hydrogel capillaries are readily permeable. \(25\mu \mathrm{M}\) of Fluorescein, perfused through the microfluidic grid, embedded in Matrigel, passes across capillary walls and saturates the gel within several minutes. (f) Process of tissue generation. Photograph of an empty capillary grid with the tip of \(200\mu \mathrm{l}\) pipette tip visible above the grid (left), close up image of the greed seeded with hIPSC spheroids (middle) manually dispensed from the pipette shown on the left image, image of the spheroids fused into a solid tissue after 24- 36 hours of culturing on chip. The top row schematically represents the same process, where spheroids and the resulting tissue are shown in blue.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 240, 899, 565]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 628, 882, 761]]<|/det|>
+Figure 2. Transcriptomic changes upon perfusion. (a) Combined dataset UMAP (control, non-perfused and perfused samples). (b) Combined dataset UMAP with neuroepithelial cells (NE), pluripotent-neuroepithelial transitioning cells (P-NE), proliferating cells with medium mitochondrial (mito.) content, pluripotent cells (P) with low glycolysis (glyc.) and medium mitochondrial content, glycolytic pluripotent cells with low mitochondrial content, highly glycolytic pluripotent cells, a highly glycolytic hypoxic (hypo.) identity and a stressed cluster. (c) Pseudotime trajectory on combined dataset UMAP. (d) Cluster specific expressions of selected marker genes. Expression values are normalized and centered. Sample fractions for each identified cluster. (e) GO enrichment analysis for key processes upregulated in perfused and non-perfused samples.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[115, 105, 901, 420]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 450, 882, 730]]<|/det|>
+Figure 3. Changes in proliferation mediated by hypoxia. a) Representative experimental results demonstrating differences in proliferation and viability between standard organoid culture(left column) and the tissue constructs without (middle column) and with perfusion (right column). Top row: bright field images of organoids, non-perfused and perfused constructs correspondingly. Middle row: immunofluorescent images of apoptotic marker cleaved Caspase 3 (green) expressed in the three conditions. Bottom row: immunofluorescent images of hypoxia marker HIF1a (green). Hoechst staining of nuclei shown in blue. The images represent transverse cross-sections of the tissue constructs. (b) Top: average proportion of the number of live cells in perfused and non-perfused constructs quantified by flow cytometry (90.95.1% in perfused vs 89.2±4.4% in non-perfused tissue, n.s., n=4). Middle: average expression of cleaved Caspase 3 in control organoids (8±1% area, n=7), non-perfused(35.7±5%, pControl=0.02, n=4) and perfused tissue constructs (5.1±1% of total area, pControl=0.02, n=9). Bottom: average expression of hypoxia marker HIF-1a in control organoids (100±3%, n=4), non-perfused (55±3%, pControl=0.0003, n=3) and perfused constructs (26±2%, pControl=0.0004, n=2). Control organoids, non-perfused and perfused constructs are denoted as Ctrl, NP and P correspondingly, data are represented as mean ± SEM, asterisks (*) denote statistical significance of the difference between control organoids and the tissue constructs (unpaired two-tailed Student's t-test, 95% confidence interval). (c) Representative fluo-cytometry data, demonstrating the difference in total number of cells between perfused and non-perfused constructs. (d) Distribution of gene expression levels across the single cell population for hypoxia (left), G2M cell cycle (middle) and S cell cycle (right) associated gene sets. Scale bar: 1mm
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 155, 876, 570]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 606, 883, 856]]<|/det|>
+Figure 4. Rapid neural differentiation in perfused systems. (a) Representative experimental results demonstrating the result of 2 days of neuronal induction in control organoids(left column), non-perfused (middle column) and perfused (right column) tissue constructs. Top, middle and bottom row: immunofluorescent images of stem cell marker NANOG, early neural marker PAX6 and cell adhesion proteins N-Cadherin (green) and E-Cadherin (red) correspondingly. The images represent transverse cross-sections of the tissue constructs. In most cases, the cross-sections of capillaries are visible as circular structures (marked by triangles) (b) Average expression of PAX6(Ctrl: Not detected; NP: \(0.2\% \pm 0.2\%\) , pControl \(= 0.35(n.s.)\) , \(n = 9\) ; P: \(21.5 \pm 2\%\) , pControl \(= 0.00002\) , \(n = 12\) ), NANOG(Ctrl: \(73.6 \pm 8\%\) , \(n = 9\) ; NP: \(16.1 \pm 2\%\) , pControl \(= 0.00007\) , \(n = 11\) ; P: not detected), NCad(CDH2) (Ctrl: \(100 \pm 1\%\) , \(n = 8\) ; NP: \(7.6 \pm 1\%\) , pControl \(= 4e - 13\) , \(n = 3\) ; P: \(55.7 \pm 9\%\) (pControl \(= 0.009\) , \(n = 5\) ) and ECad(CDH1) (Ctrl: \(99 \pm 2\%\) , \(n = 12\) ; NP: \(26.6 \pm 7\%\) , pControl \(= 0.0001\) , \(n = 6\) ; P: \(4.5 \pm 2\%\) , pControl \(= 2e - 10\) , \(n = 5\) ) markers in control organoids (Ctrl), non-perfused(NP) and perfused(P) constructs. Data are represented as mean \(\pm\) SEM, asterisks (*) denote statistical significance of the difference between control organoids and the tissue constructs (unpaired two-tailed Student's \(t\) -test, \(95\%\) confidence interval) (c) UMAP plot of the combined dataset showing the localization of cells from control organoids, non-perfused and perfused constructs in the UMAP space. (d) UMAP plot of the combined dataset highlighting locations of PAX6, NANOG, NCad (CDH2) and ECad(CDH1) expressing cells in the UMAP space. Scale bar: \(250 \mu m\)
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[128, 140, 888, 457]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 477, 883, 595]]<|/det|>
+Figure 5. Functional improvement in perfused liver microtissues. (a) Hematoxylin and eosin of a transverse section of liver tissue construct with hepatocyte-like morphology and no visible indication of apoptosis. (b) Immunofluorescence images showing presence of AFP and CYP3A4, (c) Alpha-1 antitrypsin (AAT) and Cytokeratin 19 (KRT19), and (d) basic hepatic markers albumin (ALB) and hepatic nuclear factor HNF4α expression (f) Heatmap representation of fold change gene expression levels normalized to control 2D cell culture and compared to standard hepatic organoids and perfused liver constructs; rows are centered and scaled. Gene expression data for hepatic 2D culture and hepatic organoids are from Kumar et al74. Scale bar: \(50\mu \mathrm{m}\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 442, 300, 459]]<|/det|>
+Supplementary Figures
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[238, 108, 763, 544]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[114, 574, 882, 812]]<|/det|>
+Supplementary Figure 1. Assembly and operation of the chip device. (a) Cutaway view of the fully assembled culture chip, the chamber with perfused capillary grid is shown. Cell culture medium enters the culture chamber through the inlet (1mm syringe needle, cut into 15mm pieces), passes through the capillary grid and leaves the chamber through outlet (not shown). (b) Exploded view of the chip. (c) Side view cross section of the chip. Tissue constructs can be observed through the glass windows with inverted or upright microscopes. The view also demonstrates that the cell culture medium only comes into contact with PDMS(pink) and glass(blue) parts of the chip. (d) During the assembly, a user needs to handle only two pre- assembled "halves" of the chip. (e) Schematic representation of the perfusion system driven by a peristaltic pump, with culture medium circulating between the perfusion chip and the medium reservoir. Here, the grid in the right chamber is surrounded by a constant medium flow but the flow through its capillaries is absent, while in the downstream grid (left chamber) the flow passes through the capillaries and diffuses across the walls into the tissue. (f) Photographs of fully assembled chip and perfusion system. The non-perfused and perfused chambers are connected by external tubing (left), with \(0.22\mu m\) filter connected inline between the chambers. The chip and the medium reservoir resides in a custom 3D-printed holder (middle) and connected to a peristaltic pump installed outside of \(\mathrm{CO_2}\) incubator (right). The image shows three experiments running in parallel.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 123, 824, 339]]<|/det|>
+
+<|ref|>image<|/ref|><|det|>[[125, 375, 825, 620]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[114, 647, 882, 722]]<|/det|>
+Supplementary Figure 2. Optimization of printable material properties. (a) Test structure printed from PEGDA or PEGDA \(90\% /\) PETA \(10\%\) mixture. Both ends of the part are connected to a baseplate. When submerged to cell culture medium, swelling of the material leads to a breakage of the part. (b) Our custom formulation resin effectively prevents swelling in aqueous media and preserves the geometry of the microfabricated structures. Scale bar \(100\mu \mathrm{m}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 180, 904, 425]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 453, 883, 513]]<|/det|>
+Supplementary Figure 3. Two-photon stereo-lithography enables precision fabrication in a wide range of scales. Microfluidic grids of different dimensions (in mm): 1.2mm x 1.2mm x 1.2mm (left), 2.6mm x 2.6 mm x 1.5mm (middle), 6.5mm x 6.5mm x 5mm (right). Perfusion vessels in each grid have identical 50μm diameter and inter-vessel distance of 250μm. Scale bar 5 mm.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[130, 240, 840, 744]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 761, 883, 821]]<|/det|>
+Supplementary Figure 4. Daily brightfield imaging of neural tissue in perfused and non-perfused chips. (a) Bright field images of the perfused (top) and non-perfused (bottom) tissue constructs taken every 2 days during the culturing protocol. (b) Live sections of perfused (left) and non-perfused (right) tissue constructs taken at the end of the culturing protocol. Scale bar 500μm.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[339, 195, 652, 407]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[114, 439, 883, 485]]<|/det|>
+Supplementary Figure 5. Correlation analysis between perfused-, non-perfused neural tissue constructs and conventional neural organoid culture. Correlation analysis using the top 100 differentially expressed marker genes for each of the three experimental conditions.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[112, 87, 880, 480]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 506, 883, 553]]<|/det|>
+Supplementary Figure 6. Gene-set analysis for various processes. Combined dataset UMAP with scores for pluripotent, glycolysis and neural progenitor gene-set as well as the \(\%\) mitochondrial genes. Hierarchical clustering of gene-set scores and \(\%\) mitochondrial genes. Score is column scaled.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[260, 90, 732, 830]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[112, 840, 880, 870]]<|/det|>
+Supplementary Figure 7. Gene expression for unannotated hNTO clusters with the top 25 marker genes for each cluster.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[115, 168, 856, 455]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 475, 882, 536]]<|/det|>
+Supplementary Figure 8. Cluster-specific analysis of scRNAseq dataset. Dot-plot heatmap of hypoxia and cell cycle markers for each identified cluster. The average gene expression is represented by the color intensity of each dot, whereas the dot size represents the percentage of the gene-expressing cells for each sample within each cluster.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[232, 216, 760, 488]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 531, 882, 619]]<|/det|>
+Supplementary Figure 9. Difference in localized expression of hypoxia marker HIF1α and apoptosis marker cleaved Caspase-3. (a) HIF1α expression is localized to regions containing intact cell bodies (middle), evidenced by intact nuclei in the outlined region (left) as well as well-defined cytoplasmic regions stained with E-Cad antibody (right). (b) Cleaved Caspase-3 expression (middle) is localized to regions with apoptotic cell bodies evidenced by Hoechst stain of fragmented nuclei (outside of the outlined live region on the left image). Scale bar 100μm.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[113, 94, 928, 310]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 320, 884, 354]]<|/det|>
+Supplementary Figure 10. Brightfield images of perfused liver cultures. Bright field images of the perfused liver-like tissue constructs taken during tissue culturing. Scale bar 500μm.
+
+<--- Page Split --->
diff --git a/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/images_list.json b/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..50b9fd27e33c0325ac7e7a81100746ce3114d2f2
--- /dev/null
+++ b/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/images_list.json
@@ -0,0 +1,33 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1 | Study site and double approach for iron export estimation. a). Sentinel-2 10 m resolution image of Deception Island (South Shetland Islands) – Vapour Col (magenta square), where the data for this study were collected form, is the second largest chinstrap penguin rookery on Deception Island, gathering more than 19,000 breeding pairs37. b). Chinstrap penguins feeding on krill, which is their main food source28. c). Chinstrap population census estimated by the deep learning model. Despite certain limitations of the inference over areas with Cp-like artifacts, such as the rocky coastal areas, the model succeeded in accurately detecting the individuals in relevant, high density Cp areas (Extended Data in supplementary Table 1). d) Vapour Col photographically available extension. The northern tip of Vapour Col is outlined in yellow and correspond to the terrain of the panel e. Blue and green patches correspond to the output of the non-supervised classification for guano areas36. e). Northern tip of Vapour Col – penguin density is shown as a heatmap, the brightest areas correspond to the breeding zones where the penguins are tightly clustered, matching with the guano accumulation zones.",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 100,
+ 904,
+ 468
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig. 3 | Iron recycling and net primary production stimulation in the Southern Ocean pelagic areas. A perspective of Chinstrap penguins relative Fe input and net primary production stimulation compared to post-whaling Mysticeti38 and Antarctic krill39,40 Fe fertilizing rates, estimated in this study from a literature model10 (see Methods). Carbon assimilation associated with primary production (2 g C m-2 day-1, here expressed as annual assimilated C)41 refers to the Southern Ocean coastal areas, such as polynyas, marginal ice zones and the continental shelf. Despite the lower penguin Fe contribution compared to that from baleen whales, this number accounts for only one species in contrast with the Mysticeti genus, with Chinstrap numbers being 50% lower than four decades ago15, when whales were already subjected to whaling pressure. Solid arrows indicate energy fluxes within the ecosystem. Dashed arrows indicate Fe input and primary production stimulation.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Extended_Data_Figure_2.jpg",
+ "caption": "Extended Data Fig. 2 | Photographic available data of Vapour Col colony and Regions of Interest for deep learning model",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 8
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289.mmd b/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..bfa83526a325dd58bbcbe273b7662aafc53c99d1
--- /dev/null
+++ b/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289.mmd
@@ -0,0 +1,439 @@
+
+# The contribution of penguin guano to the Southern Ocean iron pool
+
+Oleg Korolev ( \(\boxed{\infty}\) o.belyaev@csic.es) Institute of Marine Sciences of Andalusia, Spanish National Research Council https://orcid.org/0000- 0002- 8851- 2996
+
+Erica Sparaventi Institute of Marine Sciences of Andalusia, Spanish National Research Council Gabriel Navarro Consejo Superior de Investigaciones Cientificas (CSIC) https://orcid.org/0000- 0002- 8919- 0060
+
+Article
+
+Keywords:
+
+Posted Date: July 22nd, 2022
+
+DOI: https://doi.org/10.21203/rs.3.rs- 1804836/v1
+
+License: © \(\circledast\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+
+## The contribution of penguin guano to the Southern Ocean iron pool
+
+Oleg B. Korolev\*,1, Erica Sparaventi1, Gabriel Navarro1, Araceli Rodríguez-Romero2, Antonio Tovar- Sánchez1
+
+1 Department of Ecology and Coastal Management, Institute of Marine Sciences of Andalusia
+
+(ICMAN), Spanish National Research Council (CSIC), 11510 Puerto Real, Cádiz, Spain.
+
+2 Department of Analytical Chemistry. Faculty of Marine and Environmental Sciences, Marine
+
+Research Institute (INMAR), University of Cádiz, Campus Río San Pedro, 11510 Puerto Real,
+
+Cádiz, Spain.
+
+Iron plays a crucial role in the high- nutrient, low- chlorophyll Southern Ocean regions, promoting phytoplankton growth and enhancing atmospheric carbon sequestration1- 5. In this area, the recycling of biogenic iron is partially driven by the iron- rich Antarctic krill (Euphausia superba), and baleen whale species as one of their main predators6- 10. However, although oceanic iron fertilization by Antarctic seabirds has been addressed by previous studies11- 13, penguins have received limited attention, despite their representing the largest seabird biomass in the southern polar region14. Here, we use breeding site guano volumes estimated from drone images and cross- validated with deep learning- powered penguin census, in combination with guano chemical composition to assess the relative iron export to the Antarctic waters from one the most abundant penguin species, the Chinstrap penguin (Pygoscelis antarcticus). Our results show that these seabirds are a relevant but previously ignored contributor to the iron remobilization pool in the Southern Ocean. With an average guano concentration of 3 mg iron g- 1, we estimate that the Chinstrap penguin population is recycling 514 tonnes iron yr- 1. The current iron contribution represents half of the input these penguins were able to recycle four decades ago, as they have declined in more than 50% since then15. Our results evidence the need for in- depth
+
+<--- Page Split --->
+
+understanding how these seabirds' population dynamics impact the surrounding Antarctic marine ecosystems.
+
+Areas of the Southern Ocean are considered high- nutrient, low- chlorophyll regions1, where photosynthetic biota is limited by iron availability16- 19. Despite that limitation, this oceanic region is one of the major sinks of anthropogenic carbon dioxide2,4,5, removing about \(5.5 \times 10^{11}\) kg C from the pelagic zone each year20- 24. Contrary to the well understood physical processes that mediate carbon acquisition, the biological pump remains poorly described due to the high spatial and temporal availability of mechanisms such as uptake, remineralization, or export of key elements. However, these Fe inputs are known to have physical source- like contribution magnitude for Fe enrichment of the southern pelagic regions6,7,25.
+
+Surface exchange of recycled biogenic Fe has previously shown to be driven by Antarctic krill (Euphausia superba), a key Fe rich species in the Southern Ocean ecosystem6,7, and several whale species mainly via excretion products6,8,10,26. However, information about the role of seabirds, especially penguins, as a source of Fe, remains limited. Unlike whales, that roam free in northern latitude waters throughout their life stages, Antarctic penguins, especially the Pygoscelis genus (i.e., Chinstrap, Adélie and Papua), are restricted to the Southern Ocean27; they feed almost exclusively (> 90% of their diet) on krill28,29; and this feeding takes place within the upper 100 m of the water column, where primary production and photosynthetic fixation of carbon by phytoplankton occurs30. Furthermore, their significant abundance leads to the accumulation of high densities of Fe- containing guano in the coastal ecosystem, reaching concentrations of up to \(3 \times 10^{3}\) times higher over the background in the waters surrounding the rookeries31. Therefore, penguins play a fundamental role in the Southern Ocean through Fe recycling11- 13,32. Their role in the local ecosystem is even more relevant when overall declining trends in specific Antarctic penguin species populations have been shown during the last four decades15,33- 35.
+
+<--- Page Split --->
+
+To analyse the relative Fe input of these seabirds into the marine environment, we have applied a holistic approach which addresses both penguin population dynamics and the amount of Fe exported through their excretion products in relation to penguin biomass. Using Deception Island's Vapour Col rookery (Fig. 1a, d, e) as a case study, we focused on one of the most abundant Antarctic penguin species, the Chinstrap penguin (Cp) (Pygoscelis antarcticus) (Fig. 1b). We assessed the Cp relative population status by collecting drone images of the breeding site, data which served as an input for a deep learning model trained to detect penguin individuals (Fig. 1c). With unsupervised classification from drone imagery36 (Fig. 1d), we estimated the amount of guano present in the colony, which we cross- validated with the Cp census- based guano accumulation (Fig. 1e). We quantified the Fe contents of guano and calculated the relative guano discharge, based on the Fe concentrations measured in the waters surrounding the rookery and the areas away from it. Subsequently, we extrapolated the input of Fe for the global population of the Cp and estimated the magnitude of its contribution to yearly carbon accumulation in the Southern Ocean. These calculations serve as an empirical basis to highlight the role of these penguins as one of the major vertebrate mediators in the pelagic Fe recycling system, prompting a possible ecosystem imbalance caused by their significant population decrease.
+
+<--- Page Split --->
+
+
+Fig. 1 | Study site and double approach for iron export estimation. a). Sentinel-2 10 m resolution image of Deception Island (South Shetland Islands) – Vapour Col (magenta square), where the data for this study were collected form, is the second largest chinstrap penguin rookery on Deception Island, gathering more than 19,000 breeding pairs37. b). Chinstrap penguins feeding on krill, which is their main food source28. c). Chinstrap population census estimated by the deep learning model. Despite certain limitations of the inference over areas with Cp-like artifacts, such as the rocky coastal areas, the model succeeded in accurately detecting the individuals in relevant, high density Cp areas (Extended Data in supplementary Table 1). d) Vapour Col photographically available extension. The northern tip of Vapour Col is outlined in yellow and correspond to the terrain of the panel e. Blue and green patches correspond to the output of the non-supervised classification for guano areas36. e). Northern tip of Vapour Col – penguin density is shown as a heatmap, the brightest areas correspond to the breeding zones where the penguins are tightly clustered, matching with the guano accumulation zones.
+
+## Results and discussion
+
+## Water iron enrichment through penguin guano
+
+To evaluate the magnitude of the Cp contribution to the Fe pool in the surrounding waters, we analysed its relative accumulation in the colony and further discharge to the seawater. We examined three guano
+
+<--- Page Split --->
+
+sample types collected on: ice, soil and from a specific collector designed for sampling uncontaminated soil- free guano (see Methods). Among all guano types, Fe exhibited the highest concentration of 3.0 \(\pm 1.4\mathrm{mg}\mathrm{g}^{- 1}\) guano, ranging from \(2.3 - 4.0\mathrm{mg}\mathrm{g}^{- 1}\) in the guano collector, with a peak reaching \(5.8\mathrm{mg}\) \(\mathrm{g}^{- 1}\) in the soil, likely reflecting a certain degree of influence from soil sources. These Fe concentrations of guano samples are consistent with the Cp main food source, the Antarctic krill, where the high content of Fe might reflect the geothermal activity of the region7. To assess the amount of guano excreted in the colony and subsequently obtain its Fe content, we volumetrically characterized, using unsupervised classification36, the nesting areas where the majority of the penguins are clustered, i.e. guano- rich zones (GRZs, Fig. 1d, e), resulting in 165.5 tonnes of dry weight guano containing \(500\pm 241\mathrm{kg}\) Fe (see Methods). To cross- check this estimation, we examined an individual- level approximation32 using the Cp census as estimated by the deep learning model to produce an output based on the mean excretion rate of each individual per day and its Fe content. We found that according to the \(16,725\pm 907\) penguins censored by the model, a total of \(169.4\mathrm{t}\) of dry weight guano can be expected in the breeding site considering 120 days as breeding season duration, containing \(512\pm 246\mathrm{kg}\) Fe (see Methods). The survey (February 8, 2021) coincided with the end of the breeding season, when penguins tend to leave the colony and therefore the deep learning census corresponded to the lower limit of the whole nesting period. Subsequently, considering the Fe concentration (0.324 mg L- 1) in the coastal water at the specific time of study, we obtained an approximate Fe content of 26 kg in \(8\times 10^{4}\mathrm{m}^{3}\) of water under the influence of the Cp plume (Fig. 2a, b). Thus, considering the accumulated amount of Fe in the GRZs of the Vapour Col colony using the mean between GRZ volumes and deep learning census, at a certain time, \(6.8\pm 4.2\%\) of the Fe content is drained into the surrounding waters.
+
+In order to quantify the fraction of guano Fe that reaches the Antarctic waters, it is necessary to consider multiple inherent climatic, terrain and biological factors. We consider that guano accumulation and washing responds to a dynamic interaction between factors, including penguin movement, in- situ snow
+
+<--- Page Split --->
+
+accumulation or melting runoff from surrounding elevated terrain. Therefore, guano can be stored in and released from the colony at any given time, depending on specific environmental conditions, consequently varying the amount of Fe released. Furthermore, terrain geomorphology highly conditions the flow of guano towards the ocean, with higher rates in steep terrains such as Vapour Col. Although we estimated close to \(7\%\) Fe discharge from the colony (see Methods), this fraction can be significantly higher if areas of guano accumulation are located near terrain with sufficient inclination and exposed to climate events. For instance, if we consider the northern tip of the Vapour Col colony, the only contributor to the Fe pool in the surrounding waters, as an example of a steep terrain, we estimate that the amount of Fe released from this zone oscillates between 20 and \(30\%\) of the total accumulated Fe. Furthermore, considering the seasonal stage at the time of the survey, our guano discharge estimates probably represent a minimal fraction of what is actually being released during the breeding peak.
+
+
+
+
+<--- Page Split --->
+
+Fig. 2 | Deception Island coastal high turbidity waters and considered volume for iron discharge estimation from Vapour Col. a). Sentinel- 2 3- D composition of Deception Island, where areas of high turbidity can be seen flowing westwards, next to the Vapour Col colony. b). Volume section of coastal water under the influence of the penguin colony. The white dot is the surface water sampling location (62°59'29" S, 60°43'32" W) for Fe analysis. To estimate the relative discharge of Fe to the Antarctic waters we consider a calculated seawater volume of \(8 \times 10^{4} \mathrm{~m}^{3}\) with a \(2 \mathrm{~m}\) average depth near-shore region of \(4 \times 10^{4} \mathrm{~m}^{2}\) (white cuboid). TP: Turbidity Plumes originating from Vapour Col breeding site. VC: Vapour Col colony.
+
+## Chinstrap penguin global iron input
+
+Iron raises special attention when its concentration in the Cp guano is compared to other krill- feeding Antarctic species. For example, in baleen whales, who currently recycle up to \(1.2 \times 10^{3}\) tonnes Fe \(\mathrm{yr}^{- 1}\) (38), Fe content in depositions range between \(145.9 \pm 133.7 \mathrm{mg} \mathrm{kg}^{- 1}\) (42), being at its most more than ten times lower than the Fe content in Cp guano found in the present study. However, penguin populations potentially gain importance because of the number and distribution of their individuals, making them important ocean fertilizers. It is complex to evaluate the Fe contribution of the global population of Cp due to its seasonal life cycle; however, once the estimate of the relative Fe input from the breeding season period is assessed, we suggest that this input corresponds to a minimal fraction of what in reality is exported to the ocean when the breeding season is over, and the population migrates to the pack ice. If we assume the same guano production rates and that the deposited guano on the ice shelves would be almost entirely washed into the ocean during the summer season, we estimate that the current population of Cp is able to produce up to \(514 \pm 248\) tonnes Fe \(\mathrm{yr}^{- 1}\) (see Methods) (Fig. 3), considering a minimum of \(10\%\) average efficiency of Fe export during the breeding season. Therefore, this Fe input to the Southern Ocean represents close to half of the input produced by baleen whales, which highlights the evident environmental relevance of Cp populations.
+
+We further explored the yearly net primary productivity (NPP) that is stimulated by Cp input of Fe in the Antarctic waters. Using a Fe recycling model proposed for baleen whales (10), we first calculated the bioavailable Fe, to then estimate total NPP in \(\mathrm{g} \mathrm{C} \mathrm{m}^{- 2} \mathrm{yr}^{- 1}\) for the extension of the Southern Ocean \((2 \times 10^{7} \mathrm{~km}^{2})\) . We found that considering the 514 tonnes Fe \(\mathrm{yr}^{- 1}\) exported by the global Cp population,
+
+<--- Page Split --->
+
+
+Fig. 3 | Iron recycling and net primary production stimulation in the Southern Ocean pelagic areas. A perspective of Chinstrap penguins relative Fe input and net primary production stimulation compared to post-whaling Mysticeti38 and Antarctic krill39,40 Fe fertilizing rates, estimated in this study from a literature model10 (see Methods). Carbon assimilation associated with primary production (2 g C m-2 day-1, here expressed as annual assimilated C)41 refers to the Southern Ocean coastal areas, such as polynyas, marginal ice zones and the continental shelf. Despite the lower penguin Fe contribution compared to that from baleen whales, this number accounts for only one species in contrast with the Mysticeti genus, with Chinstrap numbers being 50% lower than four decades ago15, when whales were already subjected to whaling pressure. Solid arrows indicate energy fluxes within the ecosystem. Dashed arrows indicate Fe input and primary production stimulation.
+
+Cp can be contributing with \(0.11 \pm 0.05\) to \(1.04 \pm 0.5 \mathrm{g C m^{- 2} y r^{- 1}}\) , with an estimated base rate of 0.46 \(\pm 0.22 \mathrm{g C m^{- 2} y r^{- 1}}\) (see Methods). These values are of the same magnitude range as the NPP driven by the entire Mysticeti genus' Fe input38, which currently represents an estimated average of \(1.08 \mathrm{g C m^{- 2} y r^{- 1}}\) NPP stimulation, highlighting the significance of Cp when comparing single to multi- species Fe export to the Antarctic waters.
+
+Although fluctuating patterns are appreciated among the Cp populations, mainly due to the complexity of spatial distribution, an overall decrease in their numbers is evident, especially in the South Shetland Islands, where various studies showed significant drops in the number of individuals33,34,43,44. Similar to the rest of the regions inhabited by Cp, Vapour Col presented a similar negative fluctuation, where a decrease in population of 36% between 1991 and 2008 has been reported35. This decrease of Cp
+
+<--- Page Split --->
+
+numbers however is common to almost all the breeding sites on the Antarctic Peninsula, possibly leading to a similar situation as that experienced by baleen whales, where its Fe recycling is now up to ten times less than in the pre- whaling period42. Overall, a global decline of >50% in Cp numbers has been reported since the 1980s15, therefore suggesting that only four decades ago, Fe recycling by these seabirds had approximately the same magnitude as the one produced by baleen whales subjected to current whaling pressure.
+
+## Conclusion
+
+Here we show that the Cp can be considered one of the biological pillars upon which Fe is being recycled in the Southern Ocean. Furthermore, if we include the Adélie penguin (Pygoscelis adeliae) as the other widely distributed Pygoscelid species, with increasing population numbers reaching \(10^{7}\) individuals45 with a mainly krill- based diet29, Pygoscelid Fe input to the Southern Ocean could potentially reach the amount that baleen whales are currently recycling. The current maximum guano Fe concentration values known for this species32 are an order of magnitude lower than those found in this study for the Cp. However, as measured here, these Fe concentrations could be even greater, leading to a significance increase of recycled Fe by these seabirds.
+
+The effect that Cp have as ocean fertilizers has been decreasing as a consequence of rapid populational decline. This general negative population trend in the Antarctic Peninsula and, by default, in the rest of their breeding sites, can be related to the environmental changes faced by the Southern Ocean region mainly due to climate change effects46. However, several hypotheses are currently considered as a possible explanation of the decline of Cp populations, arguing possible krill biomass related causes, where a decoupling between krill concentrations and nonbreeding winter season is responsible for the dropping Cp numbers15. Thus, a deeper understanding of Cp life and prey- consumption cycles would help improve their conservation status and their impact on Fe recycling in the Antarctic marine ecosystem.
+
+<--- Page Split --->
+
+196 1. Longhurst, A., Sathyendranath, S., Platt, T. & Caverhill, C. An estimate of global primary production in the ocean from satellite radiometer data. J Plankton Res 17, 1245–1271 (1995).
+
+198 2. Sabine, C. L. et al. The Oceanic Sink for Anthropogenic CO₂. Science 305, 367–371 (2004).
+
+199 3. Sagarin, R. et al. Iron fertilization in the ocean for climate mitigation: Legal, economic, and environmental challenges. Nichols School of the Environment, Duke University. (2007).
+
+201 4. Arrigo, K. R., van Dijken, G. & Long, M. Coastal Southern Ocean: A strong anthropogenic CO₂ sink. Geophys. Res. Lett. 35, L21602 (2008).
+
+203 5. Frölicher, T. L. et al. Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models. Journal of Climate 28, 862–886 (2015).
+
+205 6. Tovar-Sanchez, A., Duarte, C. M., Hernández-León, S. & Sañudo-Wilhelmy, S. A. Krill as a central node for iron cycling in the Southern Ocean. Geophys. Res. Lett. 32, L11601 (2007).
+
+207 7. Tovar-Sanchez, A., Duarte, C. M., Hernández-León, S. & Sañudo-Wilhelmy, S. A. Impact of submarine hydrothermal vents on the metal composition of krill and its excretion products. Marine Chemistry 113, 129–136 (2009).
+
+210 8. Lavery, T. J. et al. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean. Proc. R. Soc. B. 277, 3527–3531 (2010).
+
+212 9. Ratnarajah, L., Bowie, A. R., Lannuzel, D., Meiners, K. M. & Nicol, S. The Biogeochemical Role of Baleen Whales and Krill in Southern Ocean Nutrient Cycling. PLoS ONE 9, e114067 (2014).
+
+214 10. Ratnarajah, L. et al. A preliminary model of iron fertilisation by baleen whales and Antarctic krill in the Southern Ocean: Sensitivity of primary productivity estimates to parameter uncertainty. Ecological Modelling 320, 203–212 (2016).
+
+217 11. Wing, S. et al. Seabirds and marine mammals redistribute bioavailable iron in the Southern Ocean. Mar. Ecol. Prog. Ser. 510, 1–13 (2014).
+
+219 12. Shatova, O., Wing, S. R., Gault-Ringold, M., Wing, L. & Hoffmann, L. J. Seabird guano enhances phytoplankton production in the Southern Ocean. Journal of Experimental Marine Biology and Ecology 483, 74–87 (2016).
+
+222 13. Shatova, O. A., Wing, S. R., Hoffmann, L. J., Wing, L. C. & Gault-Ringold, M. Phytoplankton community structure is influenced by seabird guano enrichment in the Southern Ocean. Estuarine, Coastal and Shelf Science 191, 125–135 (2017).
+
+<--- Page Split --->
+
+14. Woehler, E. J., International Council of Scientific Unions, & Scientific Committee on Antarctic Research. A statistical assessment of the status and trends of Antarctic and Subantarctic seabirds. (Scientific Committee on Antarctic Research, 2002).
+
+15. Strycker, N. et al. A global population assessment of the Chinstrap penguin (Pygoscelis antarctica). Sci Rep 10, 19474 (2020).
+
+16. Martin, J. H., Fitzwater, S. E. & Gordon, R. M. Iron deficiency limits phytoplankton growth in Antarctic waters. Global Biogeochem. Cycles 4, 5-12 (1990).
+
+17. Geider, R. J. & La Roche, J. The role of iron in phytoplankton photosynthesis, and the potential for iron-limitation of primary productivity in the sea. Photosynth Res 39, 275-301 (1994).
+
+18. de Baar, H. J. W. Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment. J. Geophys. Res. 110, C09S16 (2005).
+
+19. Shaked, Y. & Lis, H. Disassembling Iron Availability to Phytoplankton. Front. Microbiol. 3, (2012).
+
+20. Falkowski, P. G., Barber, R. T. & Smetacek, V. Biogeochemical Controls and Feedbacks on Ocean Primary Production. Science 281, 200-206 (1998).
+
+21. Buesseler, K. O. & Boyd, P. W. Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean. Limnol. Oceanogr. 54, 1210-1232 (2009).
+
+22. DeVries, T., Primeau, F. & Deutsch, C. The sequestration efficiency of the biological pump: BIOLOGICAL PUMP SEQUESTRATION EFFICIENCY. Geophys. Res. Lett. 39, n/a-n/a (2012).
+
+23. Hauck, J. et al. On the Southern Ocean CO₂ uptake and the role of the biological carbon pump in the 21st century. Global Biogeochem. Cycles 29, 1451-1470 (2015).
+
+24. Long, M. C. et al. Strong Southern Ocean carbon uptake evident in airborne observations. Science 374, 1275-1280 (2021).
+
+25. Ratnarajah, L., Nicol, S. & Bowie, A. R. Pelagic Iron Recycling in the Southern Ocean: Exploring the Contribution of Marine Animals. Front. Mar. Sci. 5, 109 (2018).
+
+26. Schmidt, K. et al. Seabed foraging by Antarctic krill: Implications for stock assessment, bentho-pelagic coupling, and the vertical transfer of iron. Limnol. Oceanogr. 56, 1411-1428 (2011).
+
+27. Ballard, G. et al. Responding to climate change: Adélie Penguins confront astronomical and ocean boundaries. Ecology 91, 2056-2069 (2010).
+
+<--- Page Split --->
+
+28. Lynnes, A. S., Reid, K. & Croxall, J. P. Diet and reproductive success of Adélie and chinstrap penguins: linking response of predators to prey population dynamics. Polar Biol 27, (2004).
+
+29. Juáres, M. A. et al. Diet of Adélie penguins (Pygoscelis adeliae) at Stranger Point (25 de Mayo/King George Island, Antarctica) over a 13-year period (2003–2015). Polar Biol 41, 303–311 (2018).
+
+30. Mahadevan, A. The Impact of Submesoscale Physics on Primary Productivity of Plankton. Annu. Rev. Mar. Sci. 8, 161–184 (2016).
+
+31. Sparaventi, E., Rodríguez-Romero, A., Navarro, G. & Tovar-Sánchez, A. A Novel Automatic Water Autosampler Operated From UAVs for Determining Dissolved Trace Elements. Front. Mar. Sci. 9, 879953 (2022).
+
+32. Sparaventi, E., Rodríguez-Romero, A., Barbosa, A., Ramajo, L. & Tovar-Sánchez, A. Trace elements in Antarctic penguins and the potential role of guano as source of recycled metals in the Southern Ocean. Chemosphere 285, 131423 (2021).
+
+33. Ciaputa, P. & Sierakowski, K. Long-term population changes of Adelie, chinstrap, and gentoo penguins in the regions of SSSI No.8 and SSSI No.34, King George Island, Antarctica. Polish Polar Research 20, 355–365 (1999).
+
+34. Sander, M., Balbão, T. C., Polito, M. J., Costa, E. S. & Carneiro, A. P. B. Recent decrease in chinstrap penguin (Pygoscelis antarctica) populations at two of Admiralty Bay’s islets on King George Island, South Shetland Islands, Antarctica. Polar Biol 30, 659–661 (2007).
+
+35. Barbosa, A., Benzal, J., De León, A. & Moreno, J. Population decline of chinstrap penguins (Pygoscelis antarctica) on Deception Island, South Shetlands, Antarctica. Polar Biol 35, 1453–1457 (2012).
+
+36. Tovar-Sánchez, A., Román, A., Roque-Atienza, D. & Navarro, G. Applications of unmanned aerial vehicles in Antarctic environmental research. Sci Rep 11, 21717 (2021).
+
+37. Naveen, R., Lynch, H. J., Forrest, S., Mueller, T. & Polito, M. First direct, site-wide penguin survey at Deception Island, Antarctica, suggests significant declines in breeding chinstrap penguins. Polar Biol (2012) doi:10.1007/s00300-012-1230-3.
+
+38. Savoca, M. S. et al. Baleen whale prey consumption based on high-resolution foraging measurements. Nature 599, 85–90 (2021).
+
+39. Maldonado, M. T., Surma, S. & Pakhomov, E. A. Southern Ocean biological iron cycling in the prewhaling and present ecosystems. Phil. Trans. R. Soc. A. 374, 20150292 (2016).
+
+40. Böckmann, S. et al. Salp fecal pellets release more bioavailable iron to Southern Ocean phytoplankton than krill fecal pellets. Current Biology 31, 2737-2746.e3 (2021).
+
+<--- Page Split --->
+
+41. Arrigo, K. R., van Dijken, G. L. & Bushinsky, S. Primary production in the Southern Ocean, 1997–2006. J. Geophys. Res. 113, C08004 (2008).
+
+42. Nicol, S. et al. Southern Ocean iron fertilization by baleen whales and Antarctic krill: Whales, Antarctic krill and iron fertilization. Fish and Fisheries 11, 203–209 (2010).
+
+43. Lynch, H. J., Naveen, R. & Fagan, W. Censuses of penguin, Blue-eyed Shag Phalacrocorax atriceps and Southern Giant Petrel Macronectes giganteus populations on the Antarctic Peninsula, 2001-2007. Marine Ornithology 36, 83–97 (2008).
+
+44. Lynch, H. J. et al. In stark contrast to widespread declines along the Scotia Arc, a survey of the South Sandwich Islands finds a robust seabird community. Polar Biol 39, 1615–1625 (2016).
+
+45. BirdLife International (2022) Species factsheet: Pygoscelis adeliae. BirdLife International http://www.birdlife.org/ (2022).
+
+46. Forcada, J. & Trathan, P. N. Penguin responses to climate change in the Southern Ocean. Global Change Biology 15, 1618–1630 (2009).
+
+## Methods
+
+## Guano sample collection and chemical analysis
+
+During January and February, 2021, fresh guano samples were collected at the Vapour Col (VC) breeding site. The samples have been differentiated according to the collection substrate, since three types of samples have been analysed: soil, ice and guano collected in a “trap”. The traps consist of a polyethylene plastic plate with a PVC frame (40×30 cm long), placed in the colony 24 hours prior to sampling, to guarantee the collection of fresh samples, avoiding possible contamination from the soil. Fresh guano samples were collected in VC \((n = 23)\) , and placed manually using a plastic spoon in polyethylene bags or in acid-cleaned vials and stored frozen at - 20 °C until analysis. Fe was later extracted with a microwave acid digestion system (MARS-V, CEM) in accordance with the SW- 846 EPA Method 3051A⁴⁷. Approximately 0.2 g of guano sample were digested with 10 mL of nitric acid (65%, Suprapur quality) in Teflon vessels, in triplicate. After digestion, Fe contents were analysed (see Fe concentrations in Extended Data Fig. 1) using an inductively coupled plasma-mass spectrometry
+
+<--- Page Split --->
+
+(ICP- MS, iCAP Thermo). Blanks and certified material for digestion and analysis were treated like the samples. The accuracy of the analytical methods was checked using a certified reference material (Lobster hepatopancreas TORT- 2), with Fe concentration of \(109.0 \pm 5.3 \mu \mathrm{g} \mathrm{g}^{- 1}\) , and a recovery of 103.8 \(\pm 5.0\%\) . The Detection Limit calculated as three times the standard deviation of the blank values was \(0.43 \mu \mathrm{g} \mathrm{g}^{- 1}\) .
+
+## Identification of guano-rich zones
+
+To identify the regions of the colony that have the greatest accumulation of guano, i.e. GRZ, the result of a non- supervised classification36 over the VC colony terrain was used (Fig. 1d). Then, the total area of the GRZ predicted by the classification was calculated, representing a time- specific guano layer within VC. The area of these regions served as a baseline for subsequent guano volume and Cp population estimation in VC, as it is considered that the greatest percentage of the Fe export is derived from these zones.
+
+## Chinstrap penguin deep learning-powered census
+
+On February 8, 2021, Deception Island Cp rookeries were photographed during the PiMetAn Project XXXIV Spanish Antarctic campaign48 using unmanned aerial vehicles (UAV), commonly known as drones. The photographic dataset used here does not cover the entire extension of VC but only the northern tip of it (NTvc) (Extended Data Fig. 2a), and the rest of VC was photographed at a height of 150 m (Extended Data Fig. 2a), thus not suitable for penguin detection due to their small body size. Subsequently, 377 RGB images of NTvc were selected with a resolution of 3,000x4,000 pixels, captured from a flight height of 30 m and 4.9 m s- 1. The photographic data has been obtained using the DJI Mavic 2 Pro UAV equipped with an RGB sensor (Hasselblad Camera) and flights were configured using DJI's Ground Station Pro photogrammetric flight planning software. The 377 photographs were used to generate an orthomosaic using Agisoft Metashape photogrammetric software.
+
+The model Faster R- CNN49 (FRCNN) was used to perform object detection tasks. In the present research FRCNN with ResNet- 101 backbone. Training and evaluation tasks were performed using the
+
+<--- Page Split --->
+
+TensorFlow 2.0 machine learning platform by Google. The model performance was later evaluated by analysing the resulting detection metrics of three regions of interest (RoI) selected within the orthomosaic: RoI 1 and RoI 3, corresponding to a non- coastal area and RoI 2, corresponding to a representative region of a coastal area (Extended Data Fig. 2b, Table 1).
+
+Deep learning- powered census set the number of Cp in \(\mathrm{NT_{VC}}\) 's GRZ at \(2,265 \pm 159\) . The number of individuals located in outer zones (OZ, i.e. those that are not GRZ) of \(\mathrm{NT_{VC}}\) was estimated at \(1,853 \pm 130\) . The previous data were used to calculate the density of penguins for both zones, obtaining \(0.52 \pm 0.03\) ind. \(\mathrm{m}^{- 2}\) for the GRZ and \(0.028 \pm 0.01\) ind. \(\mathrm{m}^{- 2}\) for the OZ. Subsequently, the density extrapolation for the highly overflown ( \(150 \mathrm{~m}\) ) rest of VC was carried out, using the densities obtained for \(\mathrm{NT_{VC}}\) and applying them to these new GRZ and OZ. A final number of \(7,611 \pm 439\) individuals were found grouped in GRZs and \(4,996 \pm 179\) in the OZs. Finally, the total number of Cp in the entire VC colony was obtained by adding the output for both zones (Extended Data Table 2).
+
+## Vapour Col Fe accumulation and export dynamics
+
+Two approaches were explored to quantitatively assess the total Fe abundance at a given time in the studied region of the colony (see calculations in Extended Data Table 3). Firstly, the GRZ volumes were calculated to obtain an estimate of the amount of Cp deposition accumulated in the area. Determining an exact thickness of the guano layer for volume calculation was challenging, mainly due to the irregularity of the terrain, varying substrates, accumulation and discharge dynamics, and the scarcity of supporting references for this specific region. As a result, only a thin layer of \(2 \mathrm{~cm}\) as a representative thickness of fresh guano accumulation was taken into account. Then, the volume was used to estimate the total Fe content for each of GRZ, following the next equation:
+
+\[g_{Fe} = w[Fe]a_{GRZ}t d_{guano}\]
+
+where \(g_{Fe}\) is the total Fe in \(\mathrm{g}\) , \(w\) is the dry weight guano fraction, which for seabirds has been estimated at \(0.4 \mathrm{~g}^{50}\) ; \([Fe]\) is the Fe concentration in \(\mu \mathrm{g}\) per \(\mathrm{g}\) of dry guano, \(a_{GRZ}\) is the area in \(\mathrm{m}^2\) as determined
+
+<--- Page Split --->
+
+using the non- supervised classification36, \(t\) is the guano layer thickness and \(d_{\text{guano}}\) is the density of the guano obtained in Vapour Col (1,088.6 kg m- 3).
+
+To cross- check the output of the Fe content estimation using the GRZ volumes, an individual- level approach presented by Sparaventi et al.32, was used according to the following equation:
+
+\[g_{Fe} = C_p[Fe]e d\]
+
+where \(C_p\) is the deep learning- based chinstrap census, \(e\) is the penguin excretion as g of dry guano per day, estimated at \(84.4 \mathrm{g}^{51}\) ; \(d\) is the number of days a certain number of penguins remain in the area. As the breeding season begins when \(C_p\) arrive at their colonies in early October through to November until the abandon them at the end of February, 120 days were used as the guano production period in the above equation. Comparatively, the total number of \(C_p\) present in the colony and not only in its GRZ was considered, as it was assumed that each individual must spend time within the nesting areas, thus contributing to guano accumulation.
+
+## Primary production from iron fertilization
+
+The NPP stimulated by CP Fe input in the Southern Ocean was calculated using a model for Fe cycling proposed by Ratnarajah et al.10. In this way, varying Fe retention in the photic zone and phytoplankton Fe assimilation between assumed fractions 0.25 (min), 0.5 (base) and 0.75 (max.) and considering a 3 \(\mu \mathrm{mol Fe}:\mathrm{mol C}\) phytoplankton ratio52,53, an estimate of NPP was obtained for the extension of the Southern Ocean (South of \(60^{\circ}\mathrm{S}\) ). In the same way, to obtain a comparative perspective, NPP was calculated for the current Fe input estimation for baleen whales38 and krill40 (see calculations in Extended Data Table 4).
+
+## Reporting summary
+
+Extra information about this study design is available on the Nature Research Reporting Summary file attached to this article.
+
+<--- Page Split --->
+
+## Data availability
+
+The datasets generated during the current study and the code used to reproduce the results are available on https://github.com/obkorolev/penguin_iron_paper.
+
+47. Lyman, W. J., Glazer, A. E., Ong, J. H. & Coons, S. F. Overview of sediment quality in the United States. Final report. (1987).
+
+48. Navarro, G., Román, A., Roque, D. & Tovar-Sánchez, A. UAV imagery in Deception Island (Antarctica): PiMetAn Antarctic campaign 2020-2021. (2021) doi:10.20350/DIGITALCSIC/13850.
+
+49. Ren, S., He, K., Girshick, R. & Sun, J. Faster R-CNN: Towards Real-Time Object Detection with Region Proposal Networks. (2015) doi:10.48550/ARXIV.1506.01497.
+
+50. De La Peña-Lastra, S. Seabird droppings: Effects on a global and local level. Science of The Total Environment 754, 142148 (2021).
+
+51. Sun, L. & Xie, Z. Relics: Penguin Population Programs. Science Progress 84, 31-44 (2001).
+
+52. Strzepek, R. F., Maldonado, M. T., Hunter, K. A., Frew, R. D. & Boyd, P. W. Adaptive strategies by Southern Ocean phytoplankton to lessen iron limitation: Uptake of organically complexed iron and reduced cellular iron requirements. Limnol. Oceanogr. 56, 1983-2002 (2011).
+
+53. Twining, B. S., Baines, S. B. & Fisher, N. S. Element stoichiometries of individual plankton cells collected during the Southern Ocean Iron Experiment (SOFeX). Limnol. Oceanogr. 49, 2115-2128 (2004).
+
+## Acknowledgements
+
+This research has been funded by the Spanish Government projects PIMETAN (ref. RTI2018- 098048- B- I00), EQC2018- 004275- P and EQC2019- 005721- P. E. Sparaventi is supported by the Spanish FPI grant (Ref: PRE2019- 089679) and A. Rodríguez- Romero is supported by the Spanish grant, Juan de la Cierva Incorporación (Ref: IJC2018- 037545- I). We thank to D. Roque for supporting flight operations. This research is part of the POLARCSIC research initiative. Permissions to work and collect guano samples in the study area were granted by the Spanish Polar Committee. We thank the military staff of the Spanish Antarctic Base Gabriel de Castilla, the crew of the Sarmiento de Gamboa oceanographic vessel and the Marine Technology Unit (UTM- CSIC) for their logistic support, for making the XXXIV Spanish Antarctic campaign possible. We thank M. B. Dunbar, from the Institute of Marine Science of Andalusia, Spanish National Research Council
+
+<--- Page Split --->
+
+(ICMAN- CSIC), for the English language revision and M. Roca for advice on the quality of the illustrations.
+
+## Author contributions
+
+A.T.- S., A.R. and G.B. designed the research; A.T.- S., and G.B. participated in the Antarctic campaign flying unoccupied aerial vehicles and collecting data and samples; O.B.K. and E.S. performed the chemical analysis, aerial data processing and deep learning model implementation; O.B.K, E.S, G.N, A.R. and A.T.- S. wrote the manuscript.
+
+## Inclusion & ethics
+
+This study was designed and developed by a multicultural research team, with gender, nationality and religion diversity, where all members and external participants were treated with equity and respect.
+
+## Competing interests
+
+The authors declare no competing interests.
+
+Correspondence and requests for materials should be addressed to Oleg B. Korolev.
+
+<--- Page Split --->
+
+# Extended Data
+
+![PLACEHOLDER_19_0]
+
+
+Extended Data Fig. 1 | Iron concentration in fresh guano samples collected at Vapour Col. Twelve samples from 10 to \(500\mathrm{g}\) directly from the soil, six samples from 35 to \(450\mathrm{g}\) from the ice and five samples from 13 to \(50\mathrm{g}\) from the guano collectors or "traps". a). Soil, ice and trap Fe concentrations. Displaying median, Q1 and Q3, 25th and 75th percentile. b). Mean and standard deviation of \(n = 23\) guano samples, \(3.0 \pm 1.4\mathrm{mg}\mathrm{g}^{- 1}\) guano.
+
+<--- Page Split --->
+![PLACEHOLDER_20_0]
+
+Extended Data Fig. 2 | Photographic available data of Vapour Col colony and Regions of Interest for deep learning model
+
+evaluation. a). Vapour Col breeding site. Outlined in yellow, is the northern tip of Vapour Col, NTvc, which was captured 30 m above the ground, yielding an optimum quality for penguin detection. The rest of the colony outside NTvc was captured at a height of 150 m. b). Close-up look of NTvc, where the RoIs were selected for deep learning model evaluation. RoI 1 and 3 correspond to a plain, artifact- free area, where the detection had optimum results. RoI 2 correspond to a rocky coast, with many similar features that compromised the performance of the model. However, this coastal area did not account for a large number of Chinstrap individuals in a visual examination of the terrain in the orthomosaic.
+
+<--- Page Split --->
+
+482
+
+483
+
+484
+
+485
+
+486
+
+487
+
+488
+
+489
+
+490
+
+491
+
+**Extended Data Table 1 | Detection metric yielded by the deep learning model for Chinstrap census.** For RoI 1 and 2, the ability of the model to find the maximum number of penguin individuals (recall) and the confidence that they were actually penguins (precision) is very high (max=1), mainly due to the relatively plain terrain and scarcity of penguin-like objects. RoI 2 showed good precision but a low recall, due to a relatively high confidence threshold (0.6) and the presence of rocks and white water foam.
+
+| Precision (P) | Equation | RoI 1 | RoI 2 | RoI 3 |
| true positives / (true positives + false positives) | 0.98 | 0.9 | 0.97 |
| Recall (R) | true positives / (true positives + false negatives) | 0.89 | 0.31 | 0.92 |
| \(2\times P\times R/(P+R)\) | 0.93 | 0.47 | 0.94 |
+
+496
+
+497
+
+498
+
+499
+
+500
+
+501
+
+502
+
+503
+
+504
+
+505
+
+506
+
+507
+
+508
+
+<--- Page Split --->
+
+509
+
+510
+
+511
+
+512
+
+513
+
+514
+
+515
+
+516
+
+517
+
+518
+
+519
+
+520 **Extended Data Table 2 | Detected Chinstrap penguins, areas and penguin densities.** To calculate their abundance in the highly
+
+521 overflow area (150 m) density extrapolation was performed for GRZ and for the outer guano-free zones (OZ).
+
+ | GRZ(m²) | OZ(m²) | Individuals in GRZ | Individuals in OZ | Density GRZ (ind.m-2) | Density OZ (ind.m-2) | Total individuals |
| NTVC | 4,370 | 66,216 | 2,265±159 | 1,853±130 | 0.52±0.03 | 0.028±0.01 | 4,118±289 |
Rest of Vapour Col overflow at 150 m | 14,636 | 178,400 | 7,611±439 | 4,996±179 | 0.52±0.03 | 0.028±0.01 | 12,607±618 |
| | | | | | | 16,725±907 |
+
+<--- Page Split --->
+
+538
+
+539
+
+540
+
+541
+
+542
+
+543
+
+544
+
+545
+
+546
+
+547
+
+548
+
+**Extended Data Table 3 | Calculations of the relative Fe content in Vapour Col.** Two methods were proposed to cross-validate the amount of Fe present in the colony at a certain time. The first accounts for Fe obtained using guano-rich zone volumes from non-supervised classification36, and the second uses the estimated deposition per penguin individual, whose total number is obtained from the deep-learning census of the present study. Referenced parameters50,51.
+
+| Parameter | Reference | Value | Equation | Result | Uncertainty |
| Fe calculation based on unsupervised guano rich zone classification |
W \([Fe]\) | 50 | 0.4 | | | |
| \(a_{GRZ}\) | Present study | 3.02 mg g-1 | \(kgFe=0.4\times 3.02\times\) | 500 kg Fe | 268-732 kg Fe |
| \(d_{guano}\) | Present study \(Present\ study\) | 19,006 \(m^{3}\) \(1.0886\times 10^{6}g\ m^{3}\) | 19,006x1.0886x0.02 |
| t | Assumed, present study | 0.02 m | |
| Fe calculation based on deep learning Chinstrap penguin census |
Cp \([Fe]\) | Present study | 16,725 | \(kgFe=(16,725\times 3,02\) | 512 kg Fe | 266-758 kg Fe |
| e | 51 | 84.4 g | x84.4x120) |
| d | Assumed, present study | 120 days | |
+
+<--- Page Split --->
+
+**Extended Data Table 4 | Calculations for net primary production stimulated by Chinstrap penguin Fe input.** In the same way as calculated here for the Chinstrap penguin, NPP was also obtained for krill, based on ref.39,40 and for baleen whales, based on ref.38.
+
+Referenced parameters10,38,52,53. * Refers to the selected parameter of retained Fe in the photic zone and the bioavailable Fe for the
+
+phytoplankton, as the model proposed by Ratnarajah et al.10 assumed values of 0.25 and 0.75 as max. and min.
+
+| Step / Parameter | Reference | Value | Equation | Result | Uncertainty |
| Chinstrap penguin annual Fe input in the Southern Ocean | Present study | 514 tonnes Fe yr-1 | | | 266 - 762 tonnes Fe yr-1 |
| Fraction of Fe retained in the photic zone | 10 | 0.25/0.5*/0.75 | 5.14x108 g Fe yr-1 x 0.5 | 2.57x108 g Fe yr-1 retained in the photic zone | 1.33 - 3.81 x108 g Fe yr-1 |
| Fraction of Fe bioavailable for phytoplankton | 10 | 0.25/0.5*/0.75 | 2.57x108 g Fe yr-1 x 0.5 | 1.28 x108 g Fe yr-1 bioavailable for phyto. | 0.66 - 1.9 x108 g Fe yr-1 |
| Fe : C ratio of phytoplankton in the Southern Ocean | 38,52,53 | 3 μmol Fe : mol C | | | 1 - 6 μmol Fe : mol C |
| Fe molecular weight | | 55.845 g mol-1 | | | |
| g of carbon incorporated into phytoplankton biomass (NPP) | Present study | | (1.28 x108 g Fe yr-1 x 0.018 mol Fe x 106 μmol Fe x mol C x 12.01 g C) / (g Fe x mol Fe x 3 μmol Fe x mol C) | 9.22 x1012 g C yr-1 incorporated into phyto. | 4.75 - 13.7 x1012 g C yr-1 |
| Southern Ocean area (South of 60°S) | | 2 x1013 m2 | | | |
| Rate of NPP stimulation by Cp guano input | Present study | | (9.22 x1012 g C yr-1 incorporated into phyto.) / (2 x1013 m2) | 0.46 g C m-2 yr-1 incorporated into phyto. | 0.24 - 0.68 g C m-2 yr-1 |
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+NCOMMS2226937Trs.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289_det.mmd b/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..77ef81985b07c08aa049146817cf7796c8f2b9c3
--- /dev/null
+++ b/preprint/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289/preprint__01f0e3bff18307bf43bc81d95d1730c9c3bec79b418b6773f6d9e518508e2289_det.mmd
@@ -0,0 +1,603 @@
+<|ref|>title<|/ref|><|det|>[[44, 106, 927, 175]]<|/det|>
+# The contribution of penguin guano to the Southern Ocean iron pool
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 940, 260]]<|/det|>
+Oleg Korolev ( \(\boxed{\infty}\) o.belyaev@csic.es) Institute of Marine Sciences of Andalusia, Spanish National Research Council https://orcid.org/0000- 0002- 8851- 2996
+
+<|ref|>text<|/ref|><|det|>[[44, 265, 930, 450]]<|/det|>
+Erica Sparaventi Institute of Marine Sciences of Andalusia, Spanish National Research Council Gabriel Navarro Consejo Superior de Investigaciones Cientificas (CSIC) https://orcid.org/0000- 0002- 8919- 0060
+
+<|ref|>text<|/ref|><|det|>[[44, 487, 101, 504]]<|/det|>
+Article
+
+<|ref|>text<|/ref|><|det|>[[44, 524, 137, 542]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 561, 300, 580]]<|/det|>
+Posted Date: July 22nd, 2022
+
+<|ref|>text<|/ref|><|det|>[[44, 600, 475, 619]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 1804836/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 636, 910, 680]]<|/det|>
+License: © \(\circledast\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[85, 85, 770, 106]]<|/det|>
+## The contribution of penguin guano to the Southern Ocean iron pool
+
+<|ref|>text<|/ref|><|det|>[[85, 132, 910, 184]]<|/det|>
+Oleg B. Korolev\*,1, Erica Sparaventi1, Gabriel Navarro1, Araceli Rodríguez-Romero2, Antonio Tovar- Sánchez1
+
+<|ref|>text<|/ref|><|det|>[[85, 207, 853, 228]]<|/det|>
+1 Department of Ecology and Coastal Management, Institute of Marine Sciences of Andalusia
+
+<|ref|>text<|/ref|><|det|>[[85, 240, 808, 260]]<|/det|>
+(ICMAN), Spanish National Research Council (CSIC), 11510 Puerto Real, Cádiz, Spain.
+
+<|ref|>text<|/ref|><|det|>[[85, 283, 860, 303]]<|/det|>
+2 Department of Analytical Chemistry. Faculty of Marine and Environmental Sciences, Marine
+
+<|ref|>text<|/ref|><|det|>[[85, 315, 856, 335]]<|/det|>
+Research Institute (INMAR), University of Cádiz, Campus Río San Pedro, 11510 Puerto Real,
+
+<|ref|>text<|/ref|><|det|>[[85, 348, 198, 367]]<|/det|>
+Cádiz, Spain.
+
+<|ref|>text<|/ref|><|det|>[[82, 390, 913, 870]]<|/det|>
+Iron plays a crucial role in the high- nutrient, low- chlorophyll Southern Ocean regions, promoting phytoplankton growth and enhancing atmospheric carbon sequestration1- 5. In this area, the recycling of biogenic iron is partially driven by the iron- rich Antarctic krill (Euphausia superba), and baleen whale species as one of their main predators6- 10. However, although oceanic iron fertilization by Antarctic seabirds has been addressed by previous studies11- 13, penguins have received limited attention, despite their representing the largest seabird biomass in the southern polar region14. Here, we use breeding site guano volumes estimated from drone images and cross- validated with deep learning- powered penguin census, in combination with guano chemical composition to assess the relative iron export to the Antarctic waters from one the most abundant penguin species, the Chinstrap penguin (Pygoscelis antarcticus). Our results show that these seabirds are a relevant but previously ignored contributor to the iron remobilization pool in the Southern Ocean. With an average guano concentration of 3 mg iron g- 1, we estimate that the Chinstrap penguin population is recycling 514 tonnes iron yr- 1. The current iron contribution represents half of the input these penguins were able to recycle four decades ago, as they have declined in more than 50% since then15. Our results evidence the need for in- depth
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 84, 911, 135]]<|/det|>
+understanding how these seabirds' population dynamics impact the surrounding Antarctic marine ecosystems.
+
+<|ref|>text<|/ref|><|det|>[[83, 156, 913, 406]]<|/det|>
+Areas of the Southern Ocean are considered high- nutrient, low- chlorophyll regions1, where photosynthetic biota is limited by iron availability16- 19. Despite that limitation, this oceanic region is one of the major sinks of anthropogenic carbon dioxide2,4,5, removing about \(5.5 \times 10^{11}\) kg C from the pelagic zone each year20- 24. Contrary to the well understood physical processes that mediate carbon acquisition, the biological pump remains poorly described due to the high spatial and temporal availability of mechanisms such as uptake, remineralization, or export of key elements. However, these Fe inputs are known to have physical source- like contribution magnitude for Fe enrichment of the southern pelagic regions6,7,25.
+
+<|ref|>text<|/ref|><|det|>[[83, 416, 913, 867]]<|/det|>
+Surface exchange of recycled biogenic Fe has previously shown to be driven by Antarctic krill (Euphausia superba), a key Fe rich species in the Southern Ocean ecosystem6,7, and several whale species mainly via excretion products6,8,10,26. However, information about the role of seabirds, especially penguins, as a source of Fe, remains limited. Unlike whales, that roam free in northern latitude waters throughout their life stages, Antarctic penguins, especially the Pygoscelis genus (i.e., Chinstrap, Adélie and Papua), are restricted to the Southern Ocean27; they feed almost exclusively (> 90% of their diet) on krill28,29; and this feeding takes place within the upper 100 m of the water column, where primary production and photosynthetic fixation of carbon by phytoplankton occurs30. Furthermore, their significant abundance leads to the accumulation of high densities of Fe- containing guano in the coastal ecosystem, reaching concentrations of up to \(3 \times 10^{3}\) times higher over the background in the waters surrounding the rookeries31. Therefore, penguins play a fundamental role in the Southern Ocean through Fe recycling11- 13,32. Their role in the local ecosystem is even more relevant when overall declining trends in specific Antarctic penguin species populations have been shown during the last four decades15,33- 35.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[82, 81, 914, 564]]<|/det|>
+To analyse the relative Fe input of these seabirds into the marine environment, we have applied a holistic approach which addresses both penguin population dynamics and the amount of Fe exported through their excretion products in relation to penguin biomass. Using Deception Island's Vapour Col rookery (Fig. 1a, d, e) as a case study, we focused on one of the most abundant Antarctic penguin species, the Chinstrap penguin (Cp) (Pygoscelis antarcticus) (Fig. 1b). We assessed the Cp relative population status by collecting drone images of the breeding site, data which served as an input for a deep learning model trained to detect penguin individuals (Fig. 1c). With unsupervised classification from drone imagery36 (Fig. 1d), we estimated the amount of guano present in the colony, which we cross- validated with the Cp census- based guano accumulation (Fig. 1e). We quantified the Fe contents of guano and calculated the relative guano discharge, based on the Fe concentrations measured in the waters surrounding the rookery and the areas away from it. Subsequently, we extrapolated the input of Fe for the global population of the Cp and estimated the magnitude of its contribution to yearly carbon accumulation in the Southern Ocean. These calculations serve as an empirical basis to highlight the role of these penguins as one of the major vertebrate mediators in the pelagic Fe recycling system, prompting a possible ecosystem imbalance caused by their significant population decrease.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[100, 100, 904, 468]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 483, 911, 718]]<|/det|>
+Fig. 1 | Study site and double approach for iron export estimation. a). Sentinel-2 10 m resolution image of Deception Island (South Shetland Islands) – Vapour Col (magenta square), where the data for this study were collected form, is the second largest chinstrap penguin rookery on Deception Island, gathering more than 19,000 breeding pairs37. b). Chinstrap penguins feeding on krill, which is their main food source28. c). Chinstrap population census estimated by the deep learning model. Despite certain limitations of the inference over areas with Cp-like artifacts, such as the rocky coastal areas, the model succeeded in accurately detecting the individuals in relevant, high density Cp areas (Extended Data in supplementary Table 1). d) Vapour Col photographically available extension. The northern tip of Vapour Col is outlined in yellow and correspond to the terrain of the panel e. Blue and green patches correspond to the output of the non-supervised classification for guano areas36. e). Northern tip of Vapour Col – penguin density is shown as a heatmap, the brightest areas correspond to the breeding zones where the penguins are tightly clustered, matching with the guano accumulation zones.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 768, 315, 787]]<|/det|>
+## Results and discussion
+
+<|ref|>sub_title<|/ref|><|det|>[[87, 806, 496, 825]]<|/det|>
+## Water iron enrichment through penguin guano
+
+<|ref|>text<|/ref|><|det|>[[85, 838, 911, 889]]<|/det|>
+To evaluate the magnitude of the Cp contribution to the Fe pool in the surrounding waters, we analysed its relative accumulation in the colony and further discharge to the seawater. We examined three guano
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[82, 78, 914, 800]]<|/det|>
+sample types collected on: ice, soil and from a specific collector designed for sampling uncontaminated soil- free guano (see Methods). Among all guano types, Fe exhibited the highest concentration of 3.0 \(\pm 1.4\mathrm{mg}\mathrm{g}^{- 1}\) guano, ranging from \(2.3 - 4.0\mathrm{mg}\mathrm{g}^{- 1}\) in the guano collector, with a peak reaching \(5.8\mathrm{mg}\) \(\mathrm{g}^{- 1}\) in the soil, likely reflecting a certain degree of influence from soil sources. These Fe concentrations of guano samples are consistent with the Cp main food source, the Antarctic krill, where the high content of Fe might reflect the geothermal activity of the region7. To assess the amount of guano excreted in the colony and subsequently obtain its Fe content, we volumetrically characterized, using unsupervised classification36, the nesting areas where the majority of the penguins are clustered, i.e. guano- rich zones (GRZs, Fig. 1d, e), resulting in 165.5 tonnes of dry weight guano containing \(500\pm 241\mathrm{kg}\) Fe (see Methods). To cross- check this estimation, we examined an individual- level approximation32 using the Cp census as estimated by the deep learning model to produce an output based on the mean excretion rate of each individual per day and its Fe content. We found that according to the \(16,725\pm 907\) penguins censored by the model, a total of \(169.4\mathrm{t}\) of dry weight guano can be expected in the breeding site considering 120 days as breeding season duration, containing \(512\pm 246\mathrm{kg}\) Fe (see Methods). The survey (February 8, 2021) coincided with the end of the breeding season, when penguins tend to leave the colony and therefore the deep learning census corresponded to the lower limit of the whole nesting period. Subsequently, considering the Fe concentration (0.324 mg L- 1) in the coastal water at the specific time of study, we obtained an approximate Fe content of 26 kg in \(8\times 10^{4}\mathrm{m}^{3}\) of water under the influence of the Cp plume (Fig. 2a, b). Thus, considering the accumulated amount of Fe in the GRZs of the Vapour Col colony using the mean between GRZ volumes and deep learning census, at a certain time, \(6.8\pm 4.2\%\) of the Fe content is drained into the surrounding waters.
+
+<|ref|>text<|/ref|><|det|>[[85, 805, 912, 888]]<|/det|>
+In order to quantify the fraction of guano Fe that reaches the Antarctic waters, it is necessary to consider multiple inherent climatic, terrain and biological factors. We consider that guano accumulation and washing responds to a dynamic interaction between factors, including penguin movement, in- situ snow
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 82, 913, 465]]<|/det|>
+accumulation or melting runoff from surrounding elevated terrain. Therefore, guano can be stored in and released from the colony at any given time, depending on specific environmental conditions, consequently varying the amount of Fe released. Furthermore, terrain geomorphology highly conditions the flow of guano towards the ocean, with higher rates in steep terrains such as Vapour Col. Although we estimated close to \(7\%\) Fe discharge from the colony (see Methods), this fraction can be significantly higher if areas of guano accumulation are located near terrain with sufficient inclination and exposed to climate events. For instance, if we consider the northern tip of the Vapour Col colony, the only contributor to the Fe pool in the surrounding waters, as an example of a steep terrain, we estimate that the amount of Fe released from this zone oscillates between 20 and \(30\%\) of the total accumulated Fe. Furthermore, considering the seasonal stage at the time of the survey, our guano discharge estimates probably represent a minimal fraction of what is actually being released during the breeding peak.
+
+<|ref|>image<|/ref|><|det|>[[87, 518, 515, 884]]<|/det|>
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 83, 910, 222]]<|/det|>
+Fig. 2 | Deception Island coastal high turbidity waters and considered volume for iron discharge estimation from Vapour Col. a). Sentinel- 2 3- D composition of Deception Island, where areas of high turbidity can be seen flowing westwards, next to the Vapour Col colony. b). Volume section of coastal water under the influence of the penguin colony. The white dot is the surface water sampling location (62°59'29" S, 60°43'32" W) for Fe analysis. To estimate the relative discharge of Fe to the Antarctic waters we consider a calculated seawater volume of \(8 \times 10^{4} \mathrm{~m}^{3}\) with a \(2 \mathrm{~m}\) average depth near-shore region of \(4 \times 10^{4} \mathrm{~m}^{2}\) (white cuboid). TP: Turbidity Plumes originating from Vapour Col breeding site. VC: Vapour Col colony.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 264, 403, 283]]<|/det|>
+## Chinstrap penguin global iron input
+
+<|ref|>text<|/ref|><|det|>[[85, 293, 912, 775]]<|/det|>
+Iron raises special attention when its concentration in the Cp guano is compared to other krill- feeding Antarctic species. For example, in baleen whales, who currently recycle up to \(1.2 \times 10^{3}\) tonnes Fe \(\mathrm{yr}^{- 1}\) (38), Fe content in depositions range between \(145.9 \pm 133.7 \mathrm{mg} \mathrm{kg}^{- 1}\) (42), being at its most more than ten times lower than the Fe content in Cp guano found in the present study. However, penguin populations potentially gain importance because of the number and distribution of their individuals, making them important ocean fertilizers. It is complex to evaluate the Fe contribution of the global population of Cp due to its seasonal life cycle; however, once the estimate of the relative Fe input from the breeding season period is assessed, we suggest that this input corresponds to a minimal fraction of what in reality is exported to the ocean when the breeding season is over, and the population migrates to the pack ice. If we assume the same guano production rates and that the deposited guano on the ice shelves would be almost entirely washed into the ocean during the summer season, we estimate that the current population of Cp is able to produce up to \(514 \pm 248\) tonnes Fe \(\mathrm{yr}^{- 1}\) (see Methods) (Fig. 3), considering a minimum of \(10\%\) average efficiency of Fe export during the breeding season. Therefore, this Fe input to the Southern Ocean represents close to half of the input produced by baleen whales, which highlights the evident environmental relevance of Cp populations.
+
+<|ref|>text<|/ref|><|det|>[[85, 788, 912, 905]]<|/det|>
+We further explored the yearly net primary productivity (NPP) that is stimulated by Cp input of Fe in the Antarctic waters. Using a Fe recycling model proposed for baleen whales (10), we first calculated the bioavailable Fe, to then estimate total NPP in \(\mathrm{g} \mathrm{C} \mathrm{m}^{- 2} \mathrm{yr}^{- 1}\) for the extension of the Southern Ocean \((2 \times 10^{7} \mathrm{~km}^{2})\) . We found that considering the 514 tonnes Fe \(\mathrm{yr}^{- 1}\) exported by the global Cp population,
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[88, 85, 909, 380]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[87, 383, 911, 570]]<|/det|>
+Fig. 3 | Iron recycling and net primary production stimulation in the Southern Ocean pelagic areas. A perspective of Chinstrap penguins relative Fe input and net primary production stimulation compared to post-whaling Mysticeti38 and Antarctic krill39,40 Fe fertilizing rates, estimated in this study from a literature model10 (see Methods). Carbon assimilation associated with primary production (2 g C m-2 day-1, here expressed as annual assimilated C)41 refers to the Southern Ocean coastal areas, such as polynyas, marginal ice zones and the continental shelf. Despite the lower penguin Fe contribution compared to that from baleen whales, this number accounts for only one species in contrast with the Mysticeti genus, with Chinstrap numbers being 50% lower than four decades ago15, when whales were already subjected to whaling pressure. Solid arrows indicate energy fluxes within the ecosystem. Dashed arrows indicate Fe input and primary production stimulation.
+
+<|ref|>text<|/ref|><|det|>[[87, 591, 911, 740]]<|/det|>
+Cp can be contributing with \(0.11 \pm 0.05\) to \(1.04 \pm 0.5 \mathrm{g C m^{- 2} y r^{- 1}}\) , with an estimated base rate of 0.46 \(\pm 0.22 \mathrm{g C m^{- 2} y r^{- 1}}\) (see Methods). These values are of the same magnitude range as the NPP driven by the entire Mysticeti genus' Fe input38, which currently represents an estimated average of \(1.08 \mathrm{g C m^{- 2} y r^{- 1}}\) NPP stimulation, highlighting the significance of Cp when comparing single to multi- species Fe export to the Antarctic waters.
+
+<|ref|>text<|/ref|><|det|>[[87, 755, 911, 905]]<|/det|>
+Although fluctuating patterns are appreciated among the Cp populations, mainly due to the complexity of spatial distribution, an overall decrease in their numbers is evident, especially in the South Shetland Islands, where various studies showed significant drops in the number of individuals33,34,43,44. Similar to the rest of the regions inhabited by Cp, Vapour Col presented a similar negative fluctuation, where a decrease in population of 36% between 1991 and 2008 has been reported35. This decrease of Cp
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 83, 912, 266]]<|/det|>
+numbers however is common to almost all the breeding sites on the Antarctic Peninsula, possibly leading to a similar situation as that experienced by baleen whales, where its Fe recycling is now up to ten times less than in the pre- whaling period42. Overall, a global decline of >50% in Cp numbers has been reported since the 1980s15, therefore suggesting that only four decades ago, Fe recycling by these seabirds had approximately the same magnitude as the one produced by baleen whales subjected to current whaling pressure.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 293, 203, 312]]<|/det|>
+## Conclusion
+
+<|ref|>text<|/ref|><|det|>[[85, 330, 912, 579]]<|/det|>
+Here we show that the Cp can be considered one of the biological pillars upon which Fe is being recycled in the Southern Ocean. Furthermore, if we include the Adélie penguin (Pygoscelis adeliae) as the other widely distributed Pygoscelid species, with increasing population numbers reaching \(10^{7}\) individuals45 with a mainly krill- based diet29, Pygoscelid Fe input to the Southern Ocean could potentially reach the amount that baleen whales are currently recycling. The current maximum guano Fe concentration values known for this species32 are an order of magnitude lower than those found in this study for the Cp. However, as measured here, these Fe concentrations could be even greater, leading to a significance increase of recycled Fe by these seabirds.
+
+<|ref|>text<|/ref|><|det|>[[85, 592, 913, 872]]<|/det|>
+The effect that Cp have as ocean fertilizers has been decreasing as a consequence of rapid populational decline. This general negative population trend in the Antarctic Peninsula and, by default, in the rest of their breeding sites, can be related to the environmental changes faced by the Southern Ocean region mainly due to climate change effects46. However, several hypotheses are currently considered as a possible explanation of the decline of Cp populations, arguing possible krill biomass related causes, where a decoupling between krill concentrations and nonbreeding winter season is responsible for the dropping Cp numbers15. Thus, a deeper understanding of Cp life and prey- consumption cycles would help improve their conservation status and their impact on Fe recycling in the Antarctic marine ecosystem.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[30, 85, 911, 124]]<|/det|>
+196 1. Longhurst, A., Sathyendranath, S., Platt, T. & Caverhill, C. An estimate of global primary production in the ocean from satellite radiometer data. J Plankton Res 17, 1245–1271 (1995).
+
+<|ref|>text<|/ref|><|det|>[[30, 142, 840, 161]]<|/det|>
+198 2. Sabine, C. L. et al. The Oceanic Sink for Anthropogenic CO₂. Science 305, 367–371 (2004).
+
+<|ref|>text<|/ref|><|det|>[[30, 180, 911, 220]]<|/det|>
+199 3. Sagarin, R. et al. Iron fertilization in the ocean for climate mitigation: Legal, economic, and environmental challenges. Nichols School of the Environment, Duke University. (2007).
+
+<|ref|>text<|/ref|><|det|>[[30, 238, 911, 278]]<|/det|>
+201 4. Arrigo, K. R., van Dijken, G. & Long, M. Coastal Southern Ocean: A strong anthropogenic CO₂ sink. Geophys. Res. Lett. 35, L21602 (2008).
+
+<|ref|>text<|/ref|><|det|>[[30, 296, 911, 336]]<|/det|>
+203 5. Frölicher, T. L. et al. Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models. Journal of Climate 28, 862–886 (2015).
+
+<|ref|>text<|/ref|><|det|>[[30, 355, 911, 396]]<|/det|>
+205 6. Tovar-Sanchez, A., Duarte, C. M., Hernández-León, S. & Sañudo-Wilhelmy, S. A. Krill as a central node for iron cycling in the Southern Ocean. Geophys. Res. Lett. 32, L11601 (2007).
+
+<|ref|>text<|/ref|><|det|>[[30, 414, 911, 476]]<|/det|>
+207 7. Tovar-Sanchez, A., Duarte, C. M., Hernández-León, S. & Sañudo-Wilhelmy, S. A. Impact of submarine hydrothermal vents on the metal composition of krill and its excretion products. Marine Chemistry 113, 129–136 (2009).
+
+<|ref|>text<|/ref|><|det|>[[30, 496, 911, 536]]<|/det|>
+210 8. Lavery, T. J. et al. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean. Proc. R. Soc. B. 277, 3527–3531 (2010).
+
+<|ref|>text<|/ref|><|det|>[[30, 555, 911, 596]]<|/det|>
+212 9. Ratnarajah, L., Bowie, A. R., Lannuzel, D., Meiners, K. M. & Nicol, S. The Biogeochemical Role of Baleen Whales and Krill in Southern Ocean Nutrient Cycling. PLoS ONE 9, e114067 (2014).
+
+<|ref|>text<|/ref|><|det|>[[30, 614, 911, 676]]<|/det|>
+214 10. Ratnarajah, L. et al. A preliminary model of iron fertilisation by baleen whales and Antarctic krill in the Southern Ocean: Sensitivity of primary productivity estimates to parameter uncertainty. Ecological Modelling 320, 203–212 (2016).
+
+<|ref|>text<|/ref|><|det|>[[30, 696, 911, 736]]<|/det|>
+217 11. Wing, S. et al. Seabirds and marine mammals redistribute bioavailable iron in the Southern Ocean. Mar. Ecol. Prog. Ser. 510, 1–13 (2014).
+
+<|ref|>text<|/ref|><|det|>[[30, 755, 911, 817]]<|/det|>
+219 12. Shatova, O., Wing, S. R., Gault-Ringold, M., Wing, L. & Hoffmann, L. J. Seabird guano enhances phytoplankton production in the Southern Ocean. Journal of Experimental Marine Biology and Ecology 483, 74–87 (2016).
+
+<|ref|>text<|/ref|><|det|>[[30, 836, 911, 899]]<|/det|>
+222 13. Shatova, O. A., Wing, S. R., Hoffmann, L. J., Wing, L. C. & Gault-Ringold, M. Phytoplankton community structure is influenced by seabird guano enrichment in the Southern Ocean. Estuarine, Coastal and Shelf Science 191, 125–135 (2017).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[30, 85, 911, 149]]<|/det|>
+14. Woehler, E. J., International Council of Scientific Unions, & Scientific Committee on Antarctic Research. A statistical assessment of the status and trends of Antarctic and Subantarctic seabirds. (Scientific Committee on Antarctic Research, 2002).
+
+<|ref|>text<|/ref|><|det|>[[30, 165, 911, 207]]<|/det|>
+15. Strycker, N. et al. A global population assessment of the Chinstrap penguin (Pygoscelis antarctica). Sci Rep 10, 19474 (2020).
+
+<|ref|>text<|/ref|><|det|>[[30, 223, 911, 265]]<|/det|>
+16. Martin, J. H., Fitzwater, S. E. & Gordon, R. M. Iron deficiency limits phytoplankton growth in Antarctic waters. Global Biogeochem. Cycles 4, 5-12 (1990).
+
+<|ref|>text<|/ref|><|det|>[[30, 281, 911, 324]]<|/det|>
+17. Geider, R. J. & La Roche, J. The role of iron in phytoplankton photosynthesis, and the potential for iron-limitation of primary productivity in the sea. Photosynth Res 39, 275-301 (1994).
+
+<|ref|>text<|/ref|><|det|>[[30, 340, 911, 383]]<|/det|>
+18. de Baar, H. J. W. Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment. J. Geophys. Res. 110, C09S16 (2005).
+
+<|ref|>text<|/ref|><|det|>[[30, 400, 893, 420]]<|/det|>
+19. Shaked, Y. & Lis, H. Disassembling Iron Availability to Phytoplankton. Front. Microbiol. 3, (2012).
+
+<|ref|>text<|/ref|><|det|>[[30, 437, 911, 479]]<|/det|>
+20. Falkowski, P. G., Barber, R. T. & Smetacek, V. Biogeochemical Controls and Feedbacks on Ocean Primary Production. Science 281, 200-206 (1998).
+
+<|ref|>text<|/ref|><|det|>[[30, 495, 911, 538]]<|/det|>
+21. Buesseler, K. O. & Boyd, P. W. Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean. Limnol. Oceanogr. 54, 1210-1232 (2009).
+
+<|ref|>text<|/ref|><|det|>[[30, 554, 911, 597]]<|/det|>
+22. DeVries, T., Primeau, F. & Deutsch, C. The sequestration efficiency of the biological pump: BIOLOGICAL PUMP SEQUESTRATION EFFICIENCY. Geophys. Res. Lett. 39, n/a-n/a (2012).
+
+<|ref|>text<|/ref|><|det|>[[30, 613, 911, 656]]<|/det|>
+23. Hauck, J. et al. On the Southern Ocean CO₂ uptake and the role of the biological carbon pump in the 21st century. Global Biogeochem. Cycles 29, 1451-1470 (2015).
+
+<|ref|>text<|/ref|><|det|>[[30, 672, 911, 715]]<|/det|>
+24. Long, M. C. et al. Strong Southern Ocean carbon uptake evident in airborne observations. Science 374, 1275-1280 (2021).
+
+<|ref|>text<|/ref|><|det|>[[30, 732, 911, 775]]<|/det|>
+25. Ratnarajah, L., Nicol, S. & Bowie, A. R. Pelagic Iron Recycling in the Southern Ocean: Exploring the Contribution of Marine Animals. Front. Mar. Sci. 5, 109 (2018).
+
+<|ref|>text<|/ref|><|det|>[[30, 792, 911, 835]]<|/det|>
+26. Schmidt, K. et al. Seabed foraging by Antarctic krill: Implications for stock assessment, bentho-pelagic coupling, and the vertical transfer of iron. Limnol. Oceanogr. 56, 1411-1428 (2011).
+
+<|ref|>text<|/ref|><|det|>[[30, 851, 911, 894]]<|/det|>
+27. Ballard, G. et al. Responding to climate change: Adélie Penguins confront astronomical and ocean boundaries. Ecology 91, 2056-2069 (2010).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[30, 85, 911, 125]]<|/det|>
+28. Lynnes, A. S., Reid, K. & Croxall, J. P. Diet and reproductive success of Adélie and chinstrap penguins: linking response of predators to prey population dynamics. Polar Biol 27, (2004).
+
+<|ref|>text<|/ref|><|det|>[[30, 142, 911, 182]]<|/det|>
+29. Juáres, M. A. et al. Diet of Adélie penguins (Pygoscelis adeliae) at Stranger Point (25 de Mayo/King George Island, Antarctica) over a 13-year period (2003–2015). Polar Biol 41, 303–311 (2018).
+
+<|ref|>text<|/ref|><|det|>[[30, 210, 908, 249]]<|/det|>
+30. Mahadevan, A. The Impact of Submesoscale Physics on Primary Productivity of Plankton. Annu. Rev. Mar. Sci. 8, 161–184 (2016).
+
+<|ref|>text<|/ref|><|det|>[[30, 264, 899, 327]]<|/det|>
+31. Sparaventi, E., Rodríguez-Romero, A., Navarro, G. & Tovar-Sánchez, A. A Novel Automatic Water Autosampler Operated From UAVs for Determining Dissolved Trace Elements. Front. Mar. Sci. 9, 879953 (2022).
+
+<|ref|>text<|/ref|><|det|>[[30, 343, 905, 404]]<|/det|>
+32. Sparaventi, E., Rodríguez-Romero, A., Barbosa, A., Ramajo, L. & Tovar-Sánchez, A. Trace elements in Antarctic penguins and the potential role of guano as source of recycled metals in the Southern Ocean. Chemosphere 285, 131423 (2021).
+
+<|ref|>text<|/ref|><|det|>[[30, 419, 910, 481]]<|/det|>
+33. Ciaputa, P. & Sierakowski, K. Long-term population changes of Adelie, chinstrap, and gentoo penguins in the regions of SSSI No.8 and SSSI No.34, King George Island, Antarctica. Polish Polar Research 20, 355–365 (1999).
+
+<|ref|>text<|/ref|><|det|>[[30, 496, 910, 558]]<|/det|>
+34. Sander, M., Balbão, T. C., Polito, M. J., Costa, E. S. & Carneiro, A. P. B. Recent decrease in chinstrap penguin (Pygoscelis antarctica) populations at two of Admiralty Bay’s islets on King George Island, South Shetland Islands, Antarctica. Polar Biol 30, 659–661 (2007).
+
+<|ref|>text<|/ref|><|det|>[[30, 573, 890, 614]]<|/det|>
+35. Barbosa, A., Benzal, J., De León, A. & Moreno, J. Population decline of chinstrap penguins (Pygoscelis antarctica) on Deception Island, South Shetlands, Antarctica. Polar Biol 35, 1453–1457 (2012).
+
+<|ref|>text<|/ref|><|det|>[[30, 629, 890, 669]]<|/det|>
+36. Tovar-Sánchez, A., Román, A., Roque-Atienza, D. & Navarro, G. Applications of unmanned aerial vehicles in Antarctic environmental research. Sci Rep 11, 21717 (2021).
+
+<|ref|>text<|/ref|><|det|>[[30, 684, 910, 745]]<|/det|>
+37. Naveen, R., Lynch, H. J., Forrest, S., Mueller, T. & Polito, M. First direct, site-wide penguin survey at Deception Island, Antarctica, suggests significant declines in breeding chinstrap penguins. Polar Biol (2012) doi:10.1007/s00300-012-1230-3.
+
+<|ref|>text<|/ref|><|det|>[[30, 760, 907, 800]]<|/det|>
+38. Savoca, M. S. et al. Baleen whale prey consumption based on high-resolution foraging measurements. Nature 599, 85–90 (2021).
+
+<|ref|>text<|/ref|><|det|>[[30, 815, 896, 855]]<|/det|>
+39. Maldonado, M. T., Surma, S. & Pakhomov, E. A. Southern Ocean biological iron cycling in the prewhaling and present ecosystems. Phil. Trans. R. Soc. A. 374, 20150292 (2016).
+
+<|ref|>text<|/ref|><|det|>[[30, 870, 910, 910]]<|/det|>
+40. Böckmann, S. et al. Salp fecal pellets release more bioavailable iron to Southern Ocean phytoplankton than krill fecal pellets. Current Biology 31, 2737-2746.e3 (2021).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 84, 890, 123]]<|/det|>
+41. Arrigo, K. R., van Dijken, G. L. & Bushinsky, S. Primary production in the Southern Ocean, 1997–2006. J. Geophys. Res. 113, C08004 (2008).
+
+<|ref|>text<|/ref|><|det|>[[85, 137, 849, 177]]<|/det|>
+42. Nicol, S. et al. Southern Ocean iron fertilization by baleen whales and Antarctic krill: Whales, Antarctic krill and iron fertilization. Fish and Fisheries 11, 203–209 (2010).
+
+<|ref|>text<|/ref|><|det|>[[85, 191, 900, 254]]<|/det|>
+43. Lynch, H. J., Naveen, R. & Fagan, W. Censuses of penguin, Blue-eyed Shag Phalacrocorax atriceps and Southern Giant Petrel Macronectes giganteus populations on the Antarctic Peninsula, 2001-2007. Marine Ornithology 36, 83–97 (2008).
+
+<|ref|>text<|/ref|><|det|>[[85, 270, 904, 309]]<|/det|>
+44. Lynch, H. J. et al. In stark contrast to widespread declines along the Scotia Arc, a survey of the South Sandwich Islands finds a robust seabird community. Polar Biol 39, 1615–1625 (2016).
+
+<|ref|>text<|/ref|><|det|>[[85, 323, 820, 363]]<|/det|>
+45. BirdLife International (2022) Species factsheet: Pygoscelis adeliae. BirdLife International http://www.birdlife.org/ (2022).
+
+<|ref|>text<|/ref|><|det|>[[85, 378, 870, 418]]<|/det|>
+46. Forcada, J. & Trathan, P. N. Penguin responses to climate change in the Southern Ocean. Global Change Biology 15, 1618–1630 (2009).
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 483, 179, 501]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 529, 495, 547]]<|/det|>
+## Guano sample collection and chemical analysis
+
+<|ref|>text<|/ref|><|det|>[[85, 561, 912, 908]]<|/det|>
+During January and February, 2021, fresh guano samples were collected at the Vapour Col (VC) breeding site. The samples have been differentiated according to the collection substrate, since three types of samples have been analysed: soil, ice and guano collected in a “trap”. The traps consist of a polyethylene plastic plate with a PVC frame (40×30 cm long), placed in the colony 24 hours prior to sampling, to guarantee the collection of fresh samples, avoiding possible contamination from the soil. Fresh guano samples were collected in VC \((n = 23)\) , and placed manually using a plastic spoon in polyethylene bags or in acid-cleaned vials and stored frozen at - 20 °C until analysis. Fe was later extracted with a microwave acid digestion system (MARS-V, CEM) in accordance with the SW- 846 EPA Method 3051A⁴⁷. Approximately 0.2 g of guano sample were digested with 10 mL of nitric acid (65%, Suprapur quality) in Teflon vessels, in triplicate. After digestion, Fe contents were analysed (see Fe concentrations in Extended Data Fig. 1) using an inductively coupled plasma-mass spectrometry
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 82, 912, 235]]<|/det|>
+(ICP- MS, iCAP Thermo). Blanks and certified material for digestion and analysis were treated like the samples. The accuracy of the analytical methods was checked using a certified reference material (Lobster hepatopancreas TORT- 2), with Fe concentration of \(109.0 \pm 5.3 \mu \mathrm{g} \mathrm{g}^{- 1}\) , and a recovery of 103.8 \(\pm 5.0\%\) . The Detection Limit calculated as three times the standard deviation of the blank values was \(0.43 \mu \mathrm{g} \mathrm{g}^{- 1}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 258, 380, 276]]<|/det|>
+## Identification of guano-rich zones
+
+<|ref|>text<|/ref|><|det|>[[85, 289, 913, 473]]<|/det|>
+To identify the regions of the colony that have the greatest accumulation of guano, i.e. GRZ, the result of a non- supervised classification36 over the VC colony terrain was used (Fig. 1d). Then, the total area of the GRZ predicted by the classification was calculated, representing a time- specific guano layer within VC. The area of these regions served as a baseline for subsequent guano volume and Cp population estimation in VC, as it is considered that the greatest percentage of the Fe export is derived from these zones.
+
+<|ref|>sub_title<|/ref|><|det|>[[87, 496, 518, 515]]<|/det|>
+## Chinstrap penguin deep learning-powered census
+
+<|ref|>text<|/ref|><|det|>[[85, 526, 913, 846]]<|/det|>
+On February 8, 2021, Deception Island Cp rookeries were photographed during the PiMetAn Project XXXIV Spanish Antarctic campaign48 using unmanned aerial vehicles (UAV), commonly known as drones. The photographic dataset used here does not cover the entire extension of VC but only the northern tip of it (NTvc) (Extended Data Fig. 2a), and the rest of VC was photographed at a height of 150 m (Extended Data Fig. 2a), thus not suitable for penguin detection due to their small body size. Subsequently, 377 RGB images of NTvc were selected with a resolution of 3,000x4,000 pixels, captured from a flight height of 30 m and 4.9 m s- 1. The photographic data has been obtained using the DJI Mavic 2 Pro UAV equipped with an RGB sensor (Hasselblad Camera) and flights were configured using DJI's Ground Station Pro photogrammetric flight planning software. The 377 photographs were used to generate an orthomosaic using Agisoft Metashape photogrammetric software.
+
+<|ref|>text<|/ref|><|det|>[[85, 857, 912, 906]]<|/det|>
+The model Faster R- CNN49 (FRCNN) was used to perform object detection tasks. In the present research FRCNN with ResNet- 101 backbone. Training and evaluation tasks were performed using the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 83, 912, 201]]<|/det|>
+TensorFlow 2.0 machine learning platform by Google. The model performance was later evaluated by analysing the resulting detection metrics of three regions of interest (RoI) selected within the orthomosaic: RoI 1 and RoI 3, corresponding to a non- coastal area and RoI 2, corresponding to a representative region of a coastal area (Extended Data Fig. 2b, Table 1).
+
+<|ref|>text<|/ref|><|det|>[[85, 214, 912, 465]]<|/det|>
+Deep learning- powered census set the number of Cp in \(\mathrm{NT_{VC}}\) 's GRZ at \(2,265 \pm 159\) . The number of individuals located in outer zones (OZ, i.e. those that are not GRZ) of \(\mathrm{NT_{VC}}\) was estimated at \(1,853 \pm 130\) . The previous data were used to calculate the density of penguins for both zones, obtaining \(0.52 \pm 0.03\) ind. \(\mathrm{m}^{- 2}\) for the GRZ and \(0.028 \pm 0.01\) ind. \(\mathrm{m}^{- 2}\) for the OZ. Subsequently, the density extrapolation for the highly overflown ( \(150 \mathrm{~m}\) ) rest of VC was carried out, using the densities obtained for \(\mathrm{NT_{VC}}\) and applying them to these new GRZ and OZ. A final number of \(7,611 \pm 439\) individuals were found grouped in GRZs and \(4,996 \pm 179\) in the OZs. Finally, the total number of Cp in the entire VC colony was obtained by adding the output for both zones (Extended Data Table 2).
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 487, 526, 506]]<|/det|>
+## Vapour Col Fe accumulation and export dynamics
+
+<|ref|>text<|/ref|><|det|>[[85, 518, 912, 767]]<|/det|>
+Two approaches were explored to quantitatively assess the total Fe abundance at a given time in the studied region of the colony (see calculations in Extended Data Table 3). Firstly, the GRZ volumes were calculated to obtain an estimate of the amount of Cp deposition accumulated in the area. Determining an exact thickness of the guano layer for volume calculation was challenging, mainly due to the irregularity of the terrain, varying substrates, accumulation and discharge dynamics, and the scarcity of supporting references for this specific region. As a result, only a thin layer of \(2 \mathrm{~cm}\) as a representative thickness of fresh guano accumulation was taken into account. Then, the volume was used to estimate the total Fe content for each of GRZ, following the next equation:
+
+<|ref|>equation<|/ref|><|det|>[[395, 791, 602, 810]]<|/det|>
+\[g_{Fe} = w[Fe]a_{GRZ}t d_{guano}\]
+
+<|ref|>text<|/ref|><|det|>[[85, 832, 911, 885]]<|/det|>
+where \(g_{Fe}\) is the total Fe in \(\mathrm{g}\) , \(w\) is the dry weight guano fraction, which for seabirds has been estimated at \(0.4 \mathrm{~g}^{50}\) ; \([Fe]\) is the Fe concentration in \(\mu \mathrm{g}\) per \(\mathrm{g}\) of dry guano, \(a_{GRZ}\) is the area in \(\mathrm{m}^2\) as determined
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 82, 911, 135]]<|/det|>
+using the non- supervised classification36, \(t\) is the guano layer thickness and \(d_{\text{guano}}\) is the density of the guano obtained in Vapour Col (1,088.6 kg m- 3).
+
+<|ref|>text<|/ref|><|det|>[[85, 149, 911, 202]]<|/det|>
+To cross- check the output of the Fe content estimation using the GRZ volumes, an individual- level approach presented by Sparaventi et al.32, was used according to the following equation:
+
+<|ref|>equation<|/ref|><|det|>[[425, 223, 573, 243]]<|/det|>
+\[g_{Fe} = C_p[Fe]e d\]
+
+<|ref|>text<|/ref|><|det|>[[85, 264, 913, 483]]<|/det|>
+where \(C_p\) is the deep learning- based chinstrap census, \(e\) is the penguin excretion as g of dry guano per day, estimated at \(84.4 \mathrm{g}^{51}\) ; \(d\) is the number of days a certain number of penguins remain in the area. As the breeding season begins when \(C_p\) arrive at their colonies in early October through to November until the abandon them at the end of February, 120 days were used as the guano production period in the above equation. Comparatively, the total number of \(C_p\) present in the colony and not only in its GRZ was considered, as it was assumed that each individual must spend time within the nesting areas, thus contributing to guano accumulation.
+
+<|ref|>sub_title<|/ref|><|det|>[[85, 505, 459, 524]]<|/det|>
+## Primary production from iron fertilization
+
+<|ref|>text<|/ref|><|det|>[[85, 536, 913, 753]]<|/det|>
+The NPP stimulated by CP Fe input in the Southern Ocean was calculated using a model for Fe cycling proposed by Ratnarajah et al.10. In this way, varying Fe retention in the photic zone and phytoplankton Fe assimilation between assumed fractions 0.25 (min), 0.5 (base) and 0.75 (max.) and considering a 3 \(\mu \mathrm{mol Fe}:\mathrm{mol C}\) phytoplankton ratio52,53, an estimate of NPP was obtained for the extension of the Southern Ocean (South of \(60^{\circ}\mathrm{S}\) ). In the same way, to obtain a comparative perspective, NPP was calculated for the current Fe input estimation for baleen whales38 and krill40 (see calculations in Extended Data Table 4).
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 802, 293, 822]]<|/det|>
+## Reporting summary
+
+<|ref|>text<|/ref|><|det|>[[85, 837, 911, 889]]<|/det|>
+Extra information about this study design is available on the Nature Research Reporting Summary file attached to this article.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[88, 85, 257, 105]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[88, 122, 911, 175]]<|/det|>
+The datasets generated during the current study and the code used to reproduce the results are available on https://github.com/obkorolev/penguin_iron_paper.
+
+<|ref|>text<|/ref|><|det|>[[88, 185, 890, 202]]<|/det|>
+47. Lyman, W. J., Glazer, A. E., Ong, J. H. & Coons, S. F. Overview of sediment quality in the United States. Final report. (1987).
+
+<|ref|>text<|/ref|><|det|>[[88, 210, 886, 250]]<|/det|>
+48. Navarro, G., Román, A., Roque, D. & Tovar-Sánchez, A. UAV imagery in Deception Island (Antarctica): PiMetAn Antarctic campaign 2020-2021. (2021) doi:10.20350/DIGITALCSIC/13850.
+
+<|ref|>text<|/ref|><|det|>[[88, 258, 886, 299]]<|/det|>
+49. Ren, S., He, K., Girshick, R. & Sun, J. Faster R-CNN: Towards Real-Time Object Detection with Region Proposal Networks. (2015) doi:10.48550/ARXIV.1506.01497.
+
+<|ref|>text<|/ref|><|det|>[[88, 308, 880, 348]]<|/det|>
+50. De La Peña-Lastra, S. Seabird droppings: Effects on a global and local level. Science of The Total Environment 754, 142148 (2021).
+
+<|ref|>text<|/ref|><|det|>[[88, 357, 683, 373]]<|/det|>
+51. Sun, L. & Xie, Z. Relics: Penguin Population Programs. Science Progress 84, 31-44 (2001).
+
+<|ref|>text<|/ref|><|det|>[[88, 381, 886, 446]]<|/det|>
+52. Strzepek, R. F., Maldonado, M. T., Hunter, K. A., Frew, R. D. & Boyd, P. W. Adaptive strategies by Southern Ocean phytoplankton to lessen iron limitation: Uptake of organically complexed iron and reduced cellular iron requirements. Limnol. Oceanogr. 56, 1983-2002 (2011).
+
+<|ref|>text<|/ref|><|det|>[[88, 455, 896, 496]]<|/det|>
+53. Twining, B. S., Baines, S. B. & Fisher, N. S. Element stoichiometries of individual plankton cells collected during the Southern Ocean Iron Experiment (SOFeX). Limnol. Oceanogr. 49, 2115-2128 (2004).
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 536, 285, 556]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[87, 565, 884, 905]]<|/det|>
+This research has been funded by the Spanish Government projects PIMETAN (ref. RTI2018- 098048- B- I00), EQC2018- 004275- P and EQC2019- 005721- P. E. Sparaventi is supported by the Spanish FPI grant (Ref: PRE2019- 089679) and A. Rodríguez- Romero is supported by the Spanish grant, Juan de la Cierva Incorporación (Ref: IJC2018- 037545- I). We thank to D. Roque for supporting flight operations. This research is part of the POLARCSIC research initiative. Permissions to work and collect guano samples in the study area were granted by the Spanish Polar Committee. We thank the military staff of the Spanish Antarctic Base Gabriel de Castilla, the crew of the Sarmiento de Gamboa oceanographic vessel and the Marine Technology Unit (UTM- CSIC) for their logistic support, for making the XXXIV Spanish Antarctic campaign possible. We thank M. B. Dunbar, from the Institute of Marine Science of Andalusia, Spanish National Research Council
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 83, 864, 135]]<|/det|>
+(ICMAN- CSIC), for the English language revision and M. Roca for advice on the quality of the illustrations.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 160, 305, 180]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[85, 196, 912, 315]]<|/det|>
+A.T.- S., A.R. and G.B. designed the research; A.T.- S., and G.B. participated in the Antarctic campaign flying unoccupied aerial vehicles and collecting data and samples; O.B.K. and E.S. performed the chemical analysis, aerial data processing and deep learning model implementation; O.B.K, E.S, G.N, A.R. and A.T.- S. wrote the manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 362, 273, 381]]<|/det|>
+## Inclusion & ethics
+
+<|ref|>text<|/ref|><|det|>[[85, 398, 878, 485]]<|/det|>
+This study was designed and developed by a multicultural research team, with gender, nationality and religion diversity, where all members and external participants were treated with equity and respect.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 498, 264, 516]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[88, 531, 442, 549]]<|/det|>
+The authors declare no competing interests.
+
+<|ref|>text<|/ref|><|det|>[[88, 563, 794, 583]]<|/det|>
+Correspondence and requests for materials should be addressed to Oleg B. Korolev.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[88, 85, 241, 103]]<|/det|>
+# Extended Data
+
+<|ref|>image<|/ref|><|det|>[[225, 368, 770, 625]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[85, 647, 907, 737]]<|/det|>
+Extended Data Fig. 1 | Iron concentration in fresh guano samples collected at Vapour Col. Twelve samples from 10 to \(500\mathrm{g}\) directly from the soil, six samples from 35 to \(450\mathrm{g}\) from the ice and five samples from 13 to \(50\mathrm{g}\) from the guano collectors or "traps". a). Soil, ice and trap Fe concentrations. Displaying median, Q1 and Q3, 25th and 75th percentile. b). Mean and standard deviation of \(n = 23\) guano samples, \(3.0 \pm 1.4\mathrm{mg}\mathrm{g}^{- 1}\) guano.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[100, 333, 895, 660]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 670, 875, 686]]<|/det|>
+Extended Data Fig. 2 | Photographic available data of Vapour Col colony and Regions of Interest for deep learning model
+
+<|ref|>text<|/ref|><|det|>[[85, 694, 910, 833]]<|/det|>
+evaluation. a). Vapour Col breeding site. Outlined in yellow, is the northern tip of Vapour Col, NTvc, which was captured 30 m above the ground, yielding an optimum quality for penguin detection. The rest of the colony outside NTvc was captured at a height of 150 m. b). Close-up look of NTvc, where the RoIs were selected for deep learning model evaluation. RoI 1 and 3 correspond to a plain, artifact- free area, where the detection had optimum results. RoI 2 correspond to a rocky coast, with many similar features that compromised the performance of the model. However, this coastal area did not account for a large number of Chinstrap individuals in a visual examination of the terrain in the orthomosaic.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[30, 85, 60, 95]]<|/det|>
+482
+
+<|ref|>text<|/ref|><|det|>[[30, 125, 60, 134]]<|/det|>
+483
+
+<|ref|>text<|/ref|><|det|>[[30, 148, 60, 157]]<|/det|>
+484
+
+<|ref|>text<|/ref|><|det|>[[30, 187, 60, 196]]<|/det|>
+485
+
+<|ref|>text<|/ref|><|det|>[[30, 216, 60, 225]]<|/det|>
+486
+
+<|ref|>text<|/ref|><|det|>[[30, 244, 60, 253]]<|/det|>
+487
+
+<|ref|>text<|/ref|><|det|>[[30, 272, 60, 281]]<|/det|>
+488
+
+<|ref|>text<|/ref|><|det|>[[30, 300, 60, 309]]<|/det|>
+489
+
+<|ref|>text<|/ref|><|det|>[[30, 328, 60, 337]]<|/det|>
+490
+
+<|ref|>text<|/ref|><|det|>[[30, 355, 60, 365]]<|/det|>
+491
+
+<|ref|>text<|/ref|><|det|>[[30, 384, 896, 468]]<|/det|>
+**Extended Data Table 1 | Detection metric yielded by the deep learning model for Chinstrap census.** For RoI 1 and 2, the ability of the model to find the maximum number of penguin individuals (recall) and the confidence that they were actually penguins (precision) is very high (max=1), mainly due to the relatively plain terrain and scarcity of penguin-like objects. RoI 2 showed good precision but a low recall, due to a relatively high confidence threshold (0.6) and the presence of rocks and white water foam.
+
+<|ref|>table<|/ref|><|det|>[[92, 488, 910, 554]]<|/det|>
+
+| Precision (P) | Equation | RoI 1 | RoI 2 | RoI 3 |
| true positives / (true positives + false positives) | 0.98 | 0.9 | 0.97 |
| Recall (R) | true positives / (true positives + false negatives) | 0.89 | 0.31 | 0.92 |
| \(2\times P\times R/(P+R)\) | 0.93 | 0.47 | 0.94 |
+
+<|ref|>text<|/ref|><|det|>[[30, 560, 60, 569]]<|/det|>
+496
+
+<|ref|>text<|/ref|><|det|>[[30, 589, 60, 598]]<|/det|>
+497
+
+<|ref|>text<|/ref|><|det|>[[30, 626, 60, 635]]<|/det|>
+498
+
+<|ref|>text<|/ref|><|det|>[[30, 663, 60, 672]]<|/det|>
+499
+
+<|ref|>text<|/ref|><|det|>[[30, 680, 60, 690]]<|/det|>
+500
+
+<|ref|>text<|/ref|><|det|>[[30, 708, 60, 717]]<|/det|>
+501
+
+<|ref|>text<|/ref|><|det|>[[30, 735, 60, 744]]<|/det|>
+502
+
+<|ref|>text<|/ref|><|det|>[[30, 762, 60, 771]]<|/det|>
+503
+
+<|ref|>text<|/ref|><|det|>[[30, 789, 60, 798]]<|/det|>
+504
+
+<|ref|>text<|/ref|><|det|>[[30, 816, 60, 825]]<|/det|>
+505
+
+<|ref|>text<|/ref|><|det|>[[30, 843, 60, 852]]<|/det|>
+506
+
+<|ref|>text<|/ref|><|det|>[[30, 870, 60, 879]]<|/det|>
+507
+
+<|ref|>text<|/ref|><|det|>[[30, 897, 60, 906]]<|/det|>
+508
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[33, 87, 60, 99]]<|/det|>
+509
+
+<|ref|>text<|/ref|><|det|>[[33, 115, 60, 125]]<|/det|>
+510
+
+<|ref|>text<|/ref|><|det|>[[33, 140, 60, 152]]<|/det|>
+511
+
+<|ref|>text<|/ref|><|det|>[[33, 167, 60, 178]]<|/det|>
+512
+
+<|ref|>text<|/ref|><|det|>[[33, 193, 60, 204]]<|/det|>
+513
+
+<|ref|>text<|/ref|><|det|>[[33, 220, 60, 231]]<|/det|>
+514
+
+<|ref|>text<|/ref|><|det|>[[33, 246, 60, 257]]<|/det|>
+515
+
+<|ref|>text<|/ref|><|det|>[[33, 272, 60, 283]]<|/det|>
+516
+
+<|ref|>text<|/ref|><|det|>[[33, 298, 60, 309]]<|/det|>
+517
+
+<|ref|>text<|/ref|><|det|>[[33, 324, 60, 335]]<|/det|>
+518
+
+<|ref|>text<|/ref|><|det|>[[33, 350, 60, 361]]<|/det|>
+519
+
+<|ref|>text<|/ref|><|det|>[[33, 376, 884, 390]]<|/det|>
+520 **Extended Data Table 2 | Detected Chinstrap penguins, areas and penguin densities.** To calculate their abundance in the highly
+
+<|ref|>text<|/ref|><|det|>[[33, 404, 763, 415]]<|/det|>
+521 overflow area (150 m) density extrapolation was performed for GRZ and for the outer guano-free zones (OZ).
+
+<|ref|>table<|/ref|><|det|>[[90, 437, 907, 500]]<|/det|>
+
+ | GRZ(m²) | OZ(m²) | Individuals in GRZ | Individuals in OZ | Density GRZ (ind.m-2) | Density OZ (ind.m-2) | Total individuals |
| NTVC | 4,370 | 66,216 | 2,265±159 | 1,853±130 | 0.52±0.03 | 0.028±0.01 | 4,118±289 |
Rest of Vapour Col overflow at 150 m | 14,636 | 178,400 | 7,611±439 | 4,996±179 | 0.52±0.03 | 0.028±0.01 | 12,607±618 |
| | | | | | | 16,725±907 |
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[30, 88, 61, 99]]<|/det|>
+538
+
+<|ref|>text<|/ref|><|det|>[[30, 115, 61, 125]]<|/det|>
+539
+
+<|ref|>text<|/ref|><|det|>[[30, 141, 61, 152]]<|/det|>
+540
+
+<|ref|>text<|/ref|><|det|>[[30, 167, 61, 178]]<|/det|>
+541
+
+<|ref|>text<|/ref|><|det|>[[30, 194, 61, 204]]<|/det|>
+542
+
+<|ref|>text<|/ref|><|det|>[[30, 220, 61, 231]]<|/det|>
+543
+
+<|ref|>text<|/ref|><|det|>[[30, 247, 61, 257]]<|/det|>
+544
+
+<|ref|>text<|/ref|><|det|>[[30, 273, 61, 284]]<|/det|>
+545
+
+<|ref|>text<|/ref|><|det|>[[30, 300, 61, 310]]<|/det|>
+546
+
+<|ref|>text<|/ref|><|det|>[[30, 326, 61, 337]]<|/det|>
+547
+
+<|ref|>text<|/ref|><|det|>[[30, 353, 61, 363]]<|/det|>
+548
+
+<|ref|>text<|/ref|><|det|>[[30, 379, 901, 464]]<|/det|>
+**Extended Data Table 3 | Calculations of the relative Fe content in Vapour Col.** Two methods were proposed to cross-validate the amount of Fe present in the colony at a certain time. The first accounts for Fe obtained using guano-rich zone volumes from non-supervised classification36, and the second uses the estimated deposition per penguin individual, whose total number is obtained from the deep-learning census of the present study. Referenced parameters50,51.
+
+<|ref|>table<|/ref|><|det|>[[88, 486, 907, 610]]<|/det|>
+
+| Parameter | Reference | Value | Equation | Result | Uncertainty |
| Fe calculation based on unsupervised guano rich zone classification |
W \([Fe]\) | 50 | 0.4 | | | |
| \(a_{GRZ}\) | Present study | 3.02 mg g-1 | \(kgFe=0.4\times 3.02\times\) | 500 kg Fe | 268-732 kg Fe |
| \(d_{guano}\) | Present study \(Present\ study\) | 19,006 \(m^{3}\) \(1.0886\times 10^{6}g\ m^{3}\) | 19,006x1.0886x0.02 |
| t | Assumed, present study | 0.02 m | |
| Fe calculation based on deep learning Chinstrap penguin census |
Cp \([Fe]\) | Present study | 16,725 | \(kgFe=(16,725\times 3,02\) | 512 kg Fe | 266-758 kg Fe |
| e | 51 | 84.4 g | x84.4x120) |
| d | Assumed, present study | 120 days | |
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[88, 245, 908, 280]]<|/det|>
+**Extended Data Table 4 | Calculations for net primary production stimulated by Chinstrap penguin Fe input.** In the same way as calculated here for the Chinstrap penguin, NPP was also obtained for krill, based on ref.39,40 and for baleen whales, based on ref.38.
+
+<|ref|>text<|/ref|><|det|>[[88, 292, 880, 308]]<|/det|>
+Referenced parameters10,38,52,53. * Refers to the selected parameter of retained Fe in the photic zone and the bioavailable Fe for the
+
+<|ref|>text<|/ref|><|det|>[[88, 319, 760, 333]]<|/det|>
+phytoplankton, as the model proposed by Ratnarajah et al.10 assumed values of 0.25 and 0.75 as max. and min.
+
+<|ref|>table<|/ref|><|det|>[[78, 352, 920, 696]]<|/det|>
+| Step / Parameter | Reference | Value | Equation | Result | Uncertainty |
| Chinstrap penguin annual Fe input in the Southern Ocean | Present study | 514 tonnes Fe yr-1 | | | 266 - 762 tonnes Fe yr-1 |
| Fraction of Fe retained in the photic zone | 10 | 0.25/0.5*/0.75 | 5.14x108 g Fe yr-1 x 0.5 | 2.57x108 g Fe yr-1 retained in the photic zone | 1.33 - 3.81 x108 g Fe yr-1 |
| Fraction of Fe bioavailable for phytoplankton | 10 | 0.25/0.5*/0.75 | 2.57x108 g Fe yr-1 x 0.5 | 1.28 x108 g Fe yr-1 bioavailable for phyto. | 0.66 - 1.9 x108 g Fe yr-1 |
| Fe : C ratio of phytoplankton in the Southern Ocean | 38,52,53 | 3 μmol Fe : mol C | | | 1 - 6 μmol Fe : mol C |
| Fe molecular weight | | 55.845 g mol-1 | | | |
| g of carbon incorporated into phytoplankton biomass (NPP) | Present study | | (1.28 x108 g Fe yr-1 x 0.018 mol Fe x 106 μmol Fe x mol C x 12.01 g C) / (g Fe x mol Fe x 3 μmol Fe x mol C) | 9.22 x1012 g C yr-1 incorporated into phyto. | 4.75 - 13.7 x1012 g C yr-1 |
| Southern Ocean area (South of 60°S) | | 2 x1013 m2 | | | |
| Rate of NPP stimulation by Cp guano input | Present study | | (9.22 x1012 g C yr-1 incorporated into phyto.) / (2 x1013 m2) | 0.46 g C m-2 yr-1 incorporated into phyto. | 0.24 - 0.68 g C m-2 yr-1 |
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 130, 311, 150]]<|/det|>
+NCOMMS2226937Trs.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65/images_list.json b/preprint/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..eadc805d004186658e720963b85599b80615cb44
--- /dev/null
+++ b/preprint/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65/images_list.json
@@ -0,0 +1,62 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1: (a) Log-scale global map of grid cell mean ‘average edge distance’ (AED, m), as used as model input in this study and interpretable as the average Euclidian distance from an average patch edge to its interior and calculated as described (Methods, Fig. S1) to remove the urban proportion of road area. (b) System diagram of fragmentation-fire relations implemented within the ORCHIDEE model structure, where fragmentation is affecting fire size, spread, number and propensity/rate of spread (ROS)/intensity, with counteracting effects with respect to BA. Green boxes denote where AED impinges on individual fire variables (blue boxes), given modulating factors (orange) that result in emergent grid-scale fire tendencies (red). Arrows denote positive (red) and negative (blue) relationships. FDI=Fire Danger Index; ECO2=Fire CO2 emissions.",
+ "footnote": [],
+ "bbox": [
+ [
+ 120,
+ 149,
+ 545,
+ 555
+ ]
+ ],
+ "page_idx": 3
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2: (a,b): Gross fractional increase (a) and decrease (b) in simulated mean annual BA \\((f(\\Delta BA_{Frag.}))\\) versus a control simulation without fragmentation (log-scale). Grid cells where the absolute change in area burned \\(< 0.2\\%\\) of a grid cell \\((-5\\mathrm{km}^2\\mathrm{yr}^{-1})\\) were masked out. Aggregate annual increases and decreases in BA (Ha \\(\\mathrm{yr}^{-1}\\) ) due to fragmentation are included in million hectares (Mha). (c) Regression of logit link-transformed monthly mean BA against the square root of RD \\((\\mathrm{mkm}^2)\\) . Dashed black line: Observation-based regression model between BA and road density from ref. (Haas et al., 2022 71). Grey line: all simulated grid cells. Blue line and circles: only the simulated grids where fragmentation explicitly decreases mean fire size, plotted against the original road density data used in Haas et al. Red line and circles: same but plotted against the road density used in our simulations where the urban fraction of roads is removed. (d) Frequency counts of grid cells across bins of mean fragmented vegetation patch size (Ha) aggregated from the global AED map in Fig. 1a (red bars), with observed maximum (blue/purple), mean (green) and minimum (orange) observed fire patch size frequencies averaged from 2001-2020 for each grid cell, across the observed range of fire patch size using data from refs (85-88). The overlap between maximum obs. fire size (blue) and fragment size (red) is shaded purple to highlight their statistical overlap. This Figure facilitates interpretation of the fire size range and grid cell quantity affected (C,B) or unaffected (A,D) by fragmentation (see Fig. 2c).",
+ "footnote": [],
+ "bbox": [
+ [
+ 120,
+ 355,
+ 868,
+ 652
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3: (a) Simulated fractional changes in BA due to fragmentation in northern S. America \\((f(\\Delta BA_{Frag.}),\\) colour-bar), overlaid with BA and fragmentation-proxy trend data from Rosan et al. (2022)102, which were",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 75,
+ 744,
+ 860
+ ]
+ ],
+ "page_idx": 7
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4: (a) Time-averaged map showing where fragmentation relative to the control simulation without fragmentation leads to coupled (increasing or decreasing in the same direction) changes in BA \\((\\Delta \\mathrm{BA}_{\\mathrm{Frag}}\\) , Ha yr \\(^{-1}\\) ) and fire \\(\\mathrm{CO}_2\\) emissions intensity \\((\\Delta \\mathrm{ECO}_{2\\mathrm{Frag}}\\) , gC \\(\\mathrm{m}^{-2}\\) yr \\(^{-1}\\) ), shown in light colours, or decoupled changes (one increasing, the other decreasing), in dark colours. Blue depicts areas where \\(\\Delta \\mathrm{BA}_{\\mathrm{Frag}}\\) is negative, and red where it is positive. (b) Global spatial sensitivity of fire to hypothetical fragmentation levels: \\(\\mathrm{AED}_{\\mathrm{F2}}\\) simulation ensemble-averaged spatial distribution of fragmentation-doubling effects on fire burned area (unitless colour scale). All grid cells show a mean decrease in BA over the 9 simulations, but because of differential direction of change between simulations, we show in dark colours those grid cells where the average \\(\\mathrm{AED}_{\\mathrm{F2}}\\) impact is most likely to increase BA (highest fire susceptibility) and in light colours where it is most likely to decrease BA.",
+ "footnote": [],
+ "bbox": [
+ [
+ 120,
+ 129,
+ 878,
+ 290
+ ]
+ ],
+ "page_idx": 9
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65_det.mmd b/preprint/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..0daf860020b3b4f6fbba882aaebf2277a058e7d0
--- /dev/null
+++ b/preprint/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65/preprint__0207534b48d5dc7f202715e97467615fe845cf6d2005bff553f5b155b496fd65_det.mmd
@@ -0,0 +1,639 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 883, 175]]<|/det|>
+# Human land fragmentation drives tropical forest fires but dampens global burned area
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 178, 214]]<|/det|>
+Simon Bowring
+
+<|ref|>text<|/ref|><|det|>[[52, 222, 333, 240]]<|/det|>
+simon_bowring@hotmail.com
+
+<|ref|>text<|/ref|><|det|>[[44, 268, 940, 308]]<|/det|>
+Laboratoire des Sciences du Climat et de l'Environnement (LSCE), https://orcid.org/0000- 0002- 0041- 0937
+
+<|ref|>text<|/ref|><|det|>[[44, 316, 590, 356]]<|/det|>
+Wei Li Tsinghua University https://orcid.org/0000- 0003- 2543- 2558
+
+<|ref|>text<|/ref|><|det|>[[44, 362, 330, 402]]<|/det|>
+Florent Mouillot CEFE, Université de Montpellier
+
+<|ref|>text<|/ref|><|det|>[[44, 408, 950, 470]]<|/det|>
+Thais Rosan Faculty of Environment, Science and Economy, University of Exeter https://orcid.org/0000- 0003- 0155- 1739
+
+<|ref|>text<|/ref|><|det|>[[44, 477, 916, 520]]<|/det|>
+Philippe Ciais Laboratoire des Sciences du Climat et de l'Environnement https://orcid.org/0000- 0001- 8560- 4943
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 560, 103, 577]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 597, 137, 616]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 635, 318, 654]]<|/det|>
+Posted Date: October 3rd, 2023
+
+<|ref|>text<|/ref|><|det|>[[44, 674, 475, 693]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 3337266/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 711, 914, 753]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 772, 534, 791]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 827, 941, 870]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on October 24th, 2024. See the published version at https://doi.org/10.1038/s41467- 024- 53460- 6.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[117, 83, 804, 99]]<|/det|>
+# Human land fragmentation drives tropical forest fires but dampens global burned area
+
+<|ref|>text<|/ref|><|det|>[[116, 125, 758, 143]]<|/det|>
+\(^{1,2}\) Simon P.K. Bowring\*, \(^{3}\) Wei Li, \(^{4}\) Florent Mouillot, \(^{5}\) Thais M. Rosan, \(^{1}\) Philippe Ciais.
+
+<|ref|>text<|/ref|><|det|>[[115, 157, 881, 293]]<|/det|>
+\(^{1}\) Laboratoire des Sciences du Climat et de l'Environnement (LSCE), IPSL- CEA- CNRS- UVSQ, Université Paris- Saclay, Gif- sur- Yvette, France. \(^{2}\) Laboratoire de Géologie, Département de Géosciences, Ecole normale supérieure (ENS), 24 rue Lhomond, 75231 Paris Cedex 05, France \(^{3}\) Department of Earth System Science, Ministry of Education Key Laboratory for Earth System Modeling, Institute for Global Change Studies, Tsinghua University, Beijing, China. \(^{4}\) UMR 5175 CEFE, Université de Montpellier, CNRS, IRD, 1919 Route de Mende, 34293 Montpellier, France \(^{5}\) Faculty of Environment, Science and Economy, University of Exeter, Exeter, United Kingdom
+
+<|ref|>text<|/ref|><|det|>[[117, 308, 504, 323]]<|/det|>
+\*Corresponding author: simon.bowring@lsec.ipsl.fr
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 354, 187, 367]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[116, 368, 881, 549]]<|/det|>
+Landscape fragmentation has been correlated with either increases or decreases in burned area (BA), but their causal mechanisms remain elusive. Here, road density, a fragmentation proxy, is implemented in a CMIP6 coupled land- fire model, enabling dynamic representation of bottom- up processes affecting fragment edges. Over 2000- 2013, fragmentation altered BA by \(>10\%\) in \(16\%\) of burned \([0.5^{\circ}]\) grid- cells and caused gross changes of \(- 6.5\%\) to \(+5.5\%\) in global BA. Model output mimicked the global satellite- observed negative relationship between fragmentation and BA, although some regional BA decreases were matched by fire intensity increases. In recently- deforested tropical areas, however, fragmentation drove significant, observationally- consistent increases in BA \((- 1 / 4\) of Brazilian, Indonesian total BA). Fragmentation BA's relationship with population density is negative globally- averaged, but hump- shaped and largely positive in tropical and temperate forests. We suggest fragmentation could 'tip' toward net BA- amplification with future tropical forest degradation and fire- activity, providing policymakers a first quantification of fragmentation- fire risks.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 593, 217, 608]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[116, 622, 881, 834]]<|/det|>
+Human land use change (LUC) affects a third of the terrestrial surface \(^{1}\) , and the fragmentation of natural land \(^{2}\) results in large- scale biodiversity loss \(^{3,4}\) , habitat degradation \(^{5}\) , changes to the surface energy balance \(^{6 - 10}\) and biogeochemical cycling \(^{11}\) , leading to around one- third of global carbon (C) emissions \(^{12,13}\) . LUC is forecast to increase substantially by 2100, with expansions in agricultural and settlement area across all future climate- SSP scenarios of \(+12 - 83\%\) \(^{14}\) and \(+54 - 111\%\) \(^{15}\) , respectively forecast over a 2015 baseline. Concurrently, C emissions and attendant increases in global temperatures will perturb atmospheric and hydrologic circulations, combining to increase the future frequency and severity of fire events \(^{16 - 21}\) , the global area prone to frequent fire \((+ - 30\%)^{22}\) , and population- exposure to their immense socioeconomic cost \(^{23}\) . Context- specific studies have demonstrated both negative and positive interactions of LUC with fire probability without determining their drivers \(^{18,24 - 27}\) . Yet to date, no mechanistic representation of the link between the two has been developed. This restricts the capacity of a sustainable economic and infrastructural policy to consider the implications of LUC and fragmentation \(^{28}\) for fire risk, and hampers understanding and forecasting of fire behaviour, the role of human in altering prehistoric fire regimes \(^{29}\) .
+
+<|ref|>text<|/ref|><|det|>[[117, 848, 880, 909]]<|/det|>
+Fire and LUC interact via weather and vegetation through landscape fragmentation, the natural or manmade spatial discontinuity of vegetation due to ecological and economic transitions such as roads, breaks in topography and parent material, disease outbreaks, and fire itself \(^{30}\) . The fragment concept conceives of isolated vegetation patches, each with an interior and an 'edge' that is subject to a diverse range of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 83, 881, 203]]<|/det|>
+'edge effects' due to contact with a non- vegetated space. The 'edge limit' represents the point where the thinning of interior vegetation is at a maximum, whereas the 'edge area' represents the area between fragment limit and interior that is subject to a gradient of 'edge effects' such as soil and fuel drying. This conception of fragmentation has been deployed for studying edge impacts on ecology, land use dynamics and spatial planning31- 35; and more recently for a host of ecosystem properties, including air temperature36, soil moisture, microclimate9,37- 42, vegetation growth7 and phenology43. Fragmentation today is predominantly driven by large- scale investment in LUC and access infrastructure (i.e. roads)1,44- 46 - the latter the direct cause of many of the LUC effects described28,47,48.
+
+<|ref|>text<|/ref|><|det|>[[117, 218, 880, 280]]<|/det|>
+Fragmentation is difficult to measure empirically because: (1) Its definition is normative; what is fragmented and what makes it fragmented vary according to contextual lens49. (2) It isn't readily amenable to numerical reduction. Fragments have different sizes, shapes and properties50,51. (3) Different climate- vegetation and shape- size pairings may have different fire responses to fragmentation.
+
+<|ref|>text<|/ref|><|det|>[[116, 293, 881, 429]]<|/det|>
+Extant empirical studies suggest that fragmentation tends to decrease landscape- scale BA in grassland- savannahs52,53, and increase it in forest ecosystems24,53,54, however these are limited in scope, scale and number. Empirical studies of fire- fragmentation effects are scarce24 primarily because measurement is an exercise in the counterfactual, asking: what would fire outcomes be if fragmentation was/wasn't here given that it isn't/is here? Addressing this under controlled unfragmented plot- scale conditions is possible, but would likely require removing key processes e.g., potential dependency of human ignitions on degree of fragmentation. Finally, fragmentation's impact on fire takes one away from BA aggregated at annualised scales towards individual fire phenomena, with potentially opposing interpretations: Fragmentation may produce smaller/bigger individual fires while causing higher/lower annual BA.
+
+<|ref|>text<|/ref|><|det|>[[116, 442, 881, 580]]<|/det|>
+Land surface modelling is a powerful tool in this context for handling future emissions- based climate scenarios, sensitivity experiments, the integration of fragmentation- fire feedbacks and experimentation with worlds where fragmentation does and doesn't affect fire. This enables isolation of these effects in a way that is effectively impossible at in situ scales and conditions. Here, we represent fire- fragmentation dynamics in the global land surface model ORCHIDEE- MICT- SPITFIRE55- 57, a commonly- used and fire- enabled63,64 terrestrial branch of the [CMIP6] IPSL earth system model. ORCHIDEE- MICT- SPITFIRE (hereafter ORCHIDEE) integrates dynamic vegetation/fuel with climate, ignitions and fire physics65- 67 and is a participant in the Global Fire Model Intercomparison Project (FireMIP68- 70).
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 594, 440, 609]]<|/det|>
+## Conceptual Treatment of Fragmentation
+
+<|ref|>text<|/ref|><|det|>[[116, 623, 881, 730]]<|/det|>
+Model representation of fragmentation- fire must overcome three problems. First, fragments occupy a vast array of morphologies which cannot be represented explicitly at the sub- grid scales required by existing model resolutions. Second, although lack of an extant fragmentation metric might be overcome through a proxy, this proxy must be continuous and operable at sub- grid scale. Third, the edge- interior characterisation of fragments requires that gradients exist between these two states, raising the problem of how to represent such gradients given patch shape- size heterogeneity, for which predictive relationships with fire do not exist.
+
+<|ref|>text<|/ref|><|det|>[[116, 744, 881, 910]]<|/det|>
+In order of the problems outlined above, we proxy fragmentation as follows: First, fragmentation extent is proxied through road density. This is the only available satellite- derived data available that might capture fragmentation- fire effects, and simplifies analysis because roads are a fixed infrastructural feature in the medium term: Their existence is a state that changes far less than the patch interiors which they demarcate. Dirt, local, state and national summed roads are conceived of as defining the edges of fragments, because LUC and subsequent fragments require overland access, and hence the construction of roads (fragment boundaries). Roads may act as a physical barrier to fire spread, imposing limitations on individual fire size and aggregate BA71- 73, yet simultaneously expose vegetation to increased human contact, edge effects and potential fire74- 77. Second, vegetation patches arising from fragmentation are reduced to a single shape and size in a grid cell, given that the sub- grid scale is definitionally an average value. Third, this uniform patch shape is assumed to be circular, such that all patches in a grid can be
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 881, 129]]<|/det|>
+reduced to an average size that is defined by total road length. This enables conversion of empirical data to probabilistic representation of fires through ‘edge effects’ as a function of the patch radius, facilitating a ‘bottom-up’ approach to representing fragmentation-fire phenomena (Fig. S1).
+
+<|ref|>image<|/ref|><|det|>[[120, 149, 545, 555]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 562, 881, 672]]<|/det|>
+Figure 1: (a) Log-scale global map of grid cell mean ‘average edge distance’ (AED, m), as used as model input in this study and interpretable as the average Euclidian distance from an average patch edge to its interior and calculated as described (Methods, Fig. S1) to remove the urban proportion of road area. (b) System diagram of fragmentation-fire relations implemented within the ORCHIDEE model structure, where fragmentation is affecting fire size, spread, number and propensity/rate of spread (ROS)/intensity, with counteracting effects with respect to BA. Green boxes denote where AED impinges on individual fire variables (blue boxes), given modulating factors (orange) that result in emergent grid-scale fire tendencies (red). Arrows denote positive (red) and negative (blue) relationships. FDI=Fire Danger Index; ECO2=Fire CO2 emissions.
+
+<|ref|>text<|/ref|><|det|>[[115, 690, 881, 826]]<|/det|>
+We calculate satellite- estimated per- grid cell total road length (RL) globally from ref. \(^{46}\) and convert this to a number of circles (‘fragment patches’) of equal area per grid- cell, whose summed circumferences satisfy both RL and grid area (Fig. S1, Methods). Patch radii provide the average Euclidean distance from patch interior to edge, or average edge distance (AED, Fig. 1a). This enables reduction of patch edge- interior gradients to a single distance, as used in other studies \(^{31}\) , greatly simplifying conversion of observational edge effect data to model- relevant code. To calculate AED from RL, we removed the urban component (Methods) of RL for each grid cell \(^{44,45}\) , given large fires don’t occur in urban areas (Methods). Remaining RL was doubled to account for miscellaneous vegetation breaks and because the original road dataset exhibits a significant low bias (Methods, Table 1) \(^{78 - 80}\) .
+
+<|ref|>text<|/ref|><|det|>[[115, 846, 880, 906]]<|/det|>
+AED then defines the relationships between land surface variables and fire phenomena (Fig. 1b, Methods, Table 1). As fragmentation increases and AED decreases: (1) Individual fire size is restricted by patch size unless threshold conditions for crown fire spread and fuel bulk density limitation in forests and grasslands \(^{81}\) , respectively, are surpassed. This was implemented because recent statistical evidence
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 81, 880, 220]]<|/det|>
+suggests that road density \((\mathrm{mkm}^2)\) is the strongest predictor for decreases in annual BA at global scale71. (2) Vegetation is more exposed to human contact and hence ignitions- potential through machinery, smoking, trash burning, etc., proportionately increasing human ignition probability66,82 (Methods). (3) Fuel moisture and threshold fuel ignition moisture at the patch edge decreases due to edge drying37- 41, increasing fire risk and propagation potential; (4) Wind infiltration and hence speed at patch edges increases of forests only81 due to decreased surface roughness83,84 (Methods, Table 1). Thus, fragmentation potentially decouples fire rate of spread and fire intensity from BA (Figs.1,S2, Methods). We stress that this study does not seek to account for land use impacts of fragmentation (e.g. deforestation, plantation), but the impact of the fragment edge in isolation.
+
+<|ref|>text<|/ref|><|det|>[[115, 235, 880, 341]]<|/det|>
+Global- scale ORCHIDEE fire simulations were conducted at \(0.5^{\circ}\) grid- resolution over 2000- 2013 with all fragmentation functions activated, in addition to a 'control' ('CTRL') simulation, with fragmentation deactivated (Methods). A separate suite of ten sensitivity simulations, in which fragmentation was arbitrarily varied globally for all grid cells at decreasing two- fold increments of AED of \(10000\mathrm{m}\) , \(5000\mathrm{m}\) ... \(\sim 39\mathrm{m}\) (AEDF2) were performed to study the incremental effects of fragmentation- doubling on burned area at global and biome scale. These simulations were run from 2001- 2003, straddling weak or neutral El Niño/La Niña years to dampen their signal.
+
+<|ref|>image<|/ref|><|det|>[[120, 355, 868, 652]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 664, 881, 871]]<|/det|>
+Figure 2: (a,b): Gross fractional increase (a) and decrease (b) in simulated mean annual BA \((f(\Delta BA_{Frag.}))\) versus a control simulation without fragmentation (log-scale). Grid cells where the absolute change in area burned \(< 0.2\%\) of a grid cell \((-5\mathrm{km}^2\mathrm{yr}^{-1})\) were masked out. Aggregate annual increases and decreases in BA (Ha \(\mathrm{yr}^{-1}\) ) due to fragmentation are included in million hectares (Mha). (c) Regression of logit link-transformed monthly mean BA against the square root of RD \((\mathrm{mkm}^2)\) . Dashed black line: Observation-based regression model between BA and road density from ref. (Haas et al., 2022 71). Grey line: all simulated grid cells. Blue line and circles: only the simulated grids where fragmentation explicitly decreases mean fire size, plotted against the original road density data used in Haas et al. Red line and circles: same but plotted against the road density used in our simulations where the urban fraction of roads is removed. (d) Frequency counts of grid cells across bins of mean fragmented vegetation patch size (Ha) aggregated from the global AED map in Fig. 1a (red bars), with observed maximum (blue/purple), mean (green) and minimum (orange) observed fire patch size frequencies averaged from 2001-2020 for each grid cell, across the observed range of fire patch size using data from refs (85-88). The overlap between maximum obs. fire size (blue) and fragment size (red) is shaded purple to highlight their statistical overlap. This Figure facilitates interpretation of the fire size range and grid cell quantity affected (C,B) or unaffected (A,D) by fragmentation (see Fig. 2c).
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 887, 176, 900]]<|/det|>
+## Results
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 82, 365, 98]]<|/det|>
+## Global scale fire-fragmentation
+
+<|ref|>text<|/ref|><|det|>[[115, 108, 881, 281]]<|/det|>
+Global time- averaged change in BA due to fragmentation with respect to the CTRL simulation (BAFrag- \(\mathrm{BA_{CTRL}} = \Delta \mathrm{BA_{Frag}}\) ) caused both gross BA decreases and increases, depending upon the region considered. The global sum of gross \((\Delta BA_{Frag})\) decreases amounted to - 30 \(\mathrm{MHz}\mathrm{yr}^{- 1}\) and the sum of gross increases \((\Delta BA_{Frag}^{+})\) were \(+25.6\mathrm{MHz}\mathrm{yr}^{- 1}\) , equivalent to \(- 6.5\%\) and \(+5.5\%\) of 2001- 2019 averaged satellite- observed \(\mathrm{BA}^{89}\) , respectively (Fig. 2a,b). Fragmentation altered mean annual BA by more than \(\pm 10\%\) in \(17\%\) , and by more than \(25\%\) in \(7\%\) , of burned grid cells, respectively. Generally, in areas with high levels of both fragmentation (Fig.1a) and population density (Fig. 2a,b), simulated fire activity saw the largest significant proportionate BA decreases, e.g. north- west Europe, California and northeast- USA. Conversely, significant increases in BA and combustion are simulated in areas with low to moderate fragmentation and population densities (Fig. S3, S4), e.g., Indonesia, eastern Brazil and the north Mediterranean.
+
+<|ref|>text<|/ref|><|det|>[[115, 295, 881, 420]]<|/det|>
+We evaluated the statistical relationship between BA and road density (RD) emerging from our simulations, to compare with the satellite- observation- based global logit- transformed relationship of \((BA) = - 0.05*(RD) - 6.5\) (dashed black line) in ref. (1) (Fig. 2c). While the overall simulated regression models closely replicate the observed slopes and intercept, the \(\mathrm{R}^2\) coefficient is low when (i) considering all grid cells (black line, Spearman's rho \((\rho) = - 0.07\) , \(\mathrm{R}^2 = 0.05\) , \(\mathrm{p}< 0.001\) ), but it is improved in (ii) grid cells where road- fragmentation actively decreases individual fire sizes, using the same RD as employed in ref. 71 (blue line, \(\rho = - 0.46\) , \(\mathrm{R}^2 = 0.21\) , \(\mathrm{p}< 0.001\) ), and (iii) same as (ii) but RD has urban roads removed, as applied in these simulations (red line, \(\rho = - 0.66\) , \(\mathrm{R}^2 = 0.41\) , \(\mathrm{p}< 0.001\) ).
+
+<|ref|>text<|/ref|><|det|>[[115, 433, 881, 571]]<|/det|>
+The low \(\mathrm{R}^2\) in (i) is due to: First, ORCHIDEE- SPITFIRE simulates large numbers of very small fires that aggregate to low levels of annual BA (bottom- left grey dots in Fig. 2c). Where realistic, these are generally not picked up by existing satellite (MODIS) BA retrieval/processing mechanisms. Second, removal of urban roads in the AED calculation (Methods) was not performed in [71], whose regression may reflect factors that correlate with RD that would strengthen its correlation coefficient (e.g. fire suppression in urban areas, large fire- retardant surface areas, population density). Third, counts of small patch sizes calculated by the model are about two orders of magnitude lower than counts of observed mean fire sizes, meaning that fragmentation extent can only feasibly constrain fire size in a limited number of grid cells (Fig. 2d).
+
+<|ref|>text<|/ref|><|det|>[[115, 584, 881, 691]]<|/det|>
+The probability of patch size constraining fire size is high for medium- large fire sizes (area C in Fig 2d), but low for small fires, because small patch size counts are about two orders of magnitude lower than those of small fire size counts (areas A vs. B, Fig.2d). As a result, fragmentation by roads cannot on average directly decrease fire size over a broad swath of areas where fires occur (Areas A and D, Fig. 2d). This exposes the limits of fragmentation as a physical constraint to fire size, although there may be other nonphysical constraints that we exclude. The red line in Fig. 2c therefore represents the areas B and C of Fig. 2d, giving the 'effective' fragmentation- fire relation with respect to model output.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 705, 544, 721]]<|/det|>
+## Regional scale and population fragmentation impacts
+
+<|ref|>text<|/ref|><|det|>[[115, 735, 881, 902]]<|/det|>
+General patterns in regional \(\Delta \mathrm{BA_{Frag}}\) are discernible in Fig. 2a,b, but precision evaluation requires an observational dataset that removes and adds fragmentation while holding population density, vegetation and climate constant - which is implausible. However, we can compare observed and modelled fire activity in areas over which large- scale increases in fragmentation have occurred during the period for which global satellite observations of fire are available (post- 2000). This coincides with the 'boom' years of globalisation, in which lowered regulatory power and multinational corporate demand incentivised large- scale supply of cheap commodities for global markets. Large swathes of the largely- tropical global South, most notably in Indonesia and Brazil, were given over to clearing, selective logging and plantation/mining establishment over the last two decades that were associated with systematic increases in fire activity, and provides a 'before- after' comparison of fire behaviour with fragmentation. Fig. 3a plots \(f(\Delta BA_{Frag})\) in northern S. America, overlaid with data from ref. that
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 881, 283]]<|/det|>
+identified where the running mean of BA and a fragmentation proxy experienced significant \([+ / - ]\) trends over 2003- 2018. That study suggested Amazon rainforest- interior BA rose with fragmentation, but either fell or was unresponsive to fragmentation increases in the cerrado. Model output replicates the same dynamic, where large \(\Delta BA_{Frag}^{+}\) values follow the Trans- Amazonian highway \(^{103}\) into the Amazon rainforest interior (Figs. 3a, S7), while the cerrado region tends to experience decreasing BA with fragmentation. Fig. 3a's model- data comparison is not entirely commensurate as ref. \(^{102}\) ) identify temporal trends in fragmentation and total BA to approximate if and where they are correlated, whereas our fragmentation input is static and outputs only changes in the fragmentation component of BA. Thus, in cerrado areas that are subject to large climate- driven interannual variation in drought and fire extent, aggregate BA trends may subsume fragmentation BA effects. The inverse may be the case in the wet Amazon, where fragmentation can dominate fire causation \(^{54,104}\) . Large simulated \(\Delta BA_{Frag}^{+}\) in the deep interior Amazon where ref. \(^{102}\) ) find no significant trends (no data points) reflect large fractional increases in simulated fire over a miniscule baseline - fires not visible to MODIS sensor detection.
+
+<|ref|>text<|/ref|><|det|>[[115, 296, 881, 464]]<|/det|>
+In Fig. 3b, we compared grid cells where average simulated BA increased in Indonesia and Malaysia, against satellite- based grids where BA increased between 2000- 2019 over a 1982- 1999 baseline \(^{105,106}\) . We overlaid these with grid cells that experienced significant deforestation \(^{107}\) and tree plantation inception \(^{108}\) since 2000 (Fig. 3a, S5,S6). In Borneo/Kalimantan and Sumatra, where the majority of recent fragmentation and fire activity has occurred, the results from our fragmentation- fire model agreed with \(58\%\) of grid cells that experienced an observed increased of BA, of which \(67\%\) were areas of known significant deforestation and/or plantation establishment. This broadly agrees with ref. \(^{109}\) , which found that human activity had amplified (but may not dominate) drought- related fires in Sumatra and Kalimantan since 1960. The model failed to reproduce large fire anomalies in southern Borneo/Kalimantan resulting from drained peatland- vegetation burning \(^{110,111}\) , which is expected since this version of ORCHIDEE does not represent peat or soil burning.
+
+<|ref|>text<|/ref|><|det|>[[116, 477, 881, 541]]<|/det|>
+Simulated average gross \(\Delta BA_{Frag}^{+}\) values in the Amazon and Indonesia are equivalent to \(\sim 27\%\) and \(24\%\) of observed average annual BA \(^{112}\) , respectively, suggesting fragmentation is a significant driver of fire activity in tropical regions, describing the linkage between initial deforestation and dry season severity \(^{113}\) to promote fires that would otherwise not have spread.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 75, 744, 860]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 876, 880, 907]]<|/det|>
+Figure 3: (a) Simulated fractional changes in BA due to fragmentation in northern S. America \((f(\Delta BA_{Frag.}),\) colour-bar), overlaid with BA and fragmentation-proxy trend data from Rosan et al. (2022)102, which were
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 881, 306]]<|/det|>
+aggregated for Brazil's Amazonian (circular points) and Cerrado regions (triangles), as comparison. Where both BA and fragmentation increased \((+BA / + \mathrm{frag})\) over 2003- 2018, points are coloured red and \([(+BA / - \mathrm{frag}) =\) orange; \((- \mathrm{BA} / + \mathrm{frag}) =\) light blue; \((- \mathrm{BA} / = \mathrm{frag}) =\) dark blue]. Note the comparison is not entirely commensurate (see text). Simulated gross BA changes due to fragmentation over the Figure region are shown inset. (b) Comparing \(f(\Delta BA_{Frag})\) with observed (FireCCI) BA anomalies from a 1982- 1999 baseline, over areas of known large- scale fragmentation in Indonesia and Malaysia, during the period for which satellite- based fire data are available (post- 2000). Simulation- observation agreement (yellow- red) and observation- only fire anomaly grid cells (green- blue) are shaded darker along a gradient of increasing observed fire anomaly (Methods). Dots correspond to areas of significant deforestation activity(ref) and/or plantation establishment (ref) since the year 2000 (black, green), or preceding it (pink). Dot size is proportional to deforestation severity where applicable. The dotted grid highlights Borneo and Sumatra, where recent regional fragmentation is concentrated. (c) Binned frequency density scatter of fractional mean changes in BA per grid cell due to fragmentation relative to the Control \((f(\Delta BA_{Frag})\) , y- axis) where this was \(\geq \pm 1\%\) , against the logarithm of population density (x- axis) of that grid cell, plotted globally across five biome types. A generalised additive model (GAM, black line) is included for interpretation. Asterisk(\*) mark the PopD level at which \(f(\Delta BA_{Frag})\) is maximum in tropical and temperate biomes ( \(\sim 0.5\) and \(\sim 50\) individuals \(\mathrm{km}^{- 2}\) , respectively).
+
+<|ref|>text<|/ref|><|det|>[[115, 321, 881, 505]]<|/det|>
+How fire behaviour in different biomes may respond to fragmentation as population density (PopD) levels change provides insight into fire regime evolution with increasing human landscape encroachment. The per- grid relationship of \(f(\Delta BA_{Frag})\) with population density for each global biome, as well as the generalised additive model (GAM) trend for each is shown in Fig. 3b. Tropical forests simulated a clear increase in BA at low population levels (max \(\Delta BA_{Frag}\) at a population density of \(\sim 0.5\) individuals per \(\mathrm{km}^{- 2}\) , (\* in Fig. 3c)), and is the only biome where a fragmentation- related decrease in BA is less important than an increase. Temperate forest fragmentation drives a decrease in BA above low to moderate PopD and increases BA at moderately high PopD of 50 individuals \(\mathrm{km}^{- 2}\) . Boreal forests appear relatively unaffected by changes in population, although this may reflect a low statistical spread of population density114. Temperate grasslands fragmentation correlated with increased BA at low population densities, and decreased dramatically at high levels, presumably because of fragmentation limitations to fire spread.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 520, 636, 536]]<|/det|>
+## Susceptibility of \(\mathbf{CO}_2\) emissions and burned area to fragmentation
+
+<|ref|>text<|/ref|><|det|>[[115, 550, 881, 685]]<|/det|>
+Globally, the impact of fragmentation on fire C- emissions is similar to that of BA, with a net reduction of \(- 1\%\) ( \(- 0.02\mathrm{PgC}\mathrm{yr}^{- 1}\) ) of global emissions. Conversely, the spatially disaggregated fragmentation- emission impact on specific biomes (Fig. S4) suggests that its relative effect in tropical, temperate and boreal forests is largely positive, despite being negative globally. This is highlighted in Figure 4a, which shows large areas of the world overal in for forest biomes in which the direction of change of C- emissions due to fragmentation is decoupled from that of BA. This is particularly true of boreal (per ref.77) and to a lesser extent, tropical forests. This implies that fragmentation can reduce total BA while increasing the emissions- intensity of fires that do burn. This is relevant to observed increases in global fire intensity over the last twenty years115.
+
+<|ref|>text<|/ref|><|det|>[[115, 700, 881, 851]]<|/det|>
+Ten global sensitivity simulations were run, in which the AED across grid cells is synthetically varied globally at 9 factor- of- two values (F2) of AED from 10000m to \(39\mathrm{m}\) (AEDF2, see Methods). We compared the fractional change in BA of grid cells between each sequential level of applied fragmentation \(f(\Delta BA_{\Delta F2})\) as a measure of biome- scale fire sensitivity to fragmentation. BA declined everywhere as fragmentation increased when averaged over all AEDF2 levels (Fig. S9), however BA decreases were lowest in tropical and boreal forest regions of the world (Figs. 4b, S9). We aggregated grid cell \(f(\Delta BA_{\Delta F2})\) to a biome- scale average for each simulation to study how BA was altered by fragmentation as it increased. Fragmentation doubling caused biome- specific BA decreases \(f(\Delta BA_{\Delta F2})\) of \(- 7.5\%\) (Tropical forest); \(- 15\%\) (Temperate forest); \(- 19\%\) (Boreal forest); \(- 30\%\) (C3 grasslands); \(- 22\%\) (C4 grasslands). On average, BA decreased monotonically for almost all biomes (Fig. S9, S10).
+
+<|ref|>text<|/ref|><|det|>[[117, 866, 881, 911]]<|/det|>
+Simulated BA begins to decrease at different AED levels for different biomes (Fig. S9), implying differential biome- average fire sensitivities to land fragmentation. For example, to reach the same fractional decrease in BA \((- 5\%)\) due to fragmentation, an average tropical forest grid cell requires an
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 880, 114]]<|/det|>
+additional road length of \(2.5 \mathrm{km} \mathrm{km}^{- 2}\) (\~6000 km grid \(^{- 1}\) ), highlighting the higher resistance of the tropical biome to fragmentation- associated BA reductions (Fig. 4b).
+
+<|ref|>image<|/ref|><|det|>[[120, 129, 878, 290]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 295, 881, 422]]<|/det|>
+Figure 4: (a) Time-averaged map showing where fragmentation relative to the control simulation without fragmentation leads to coupled (increasing or decreasing in the same direction) changes in BA \((\Delta \mathrm{BA}_{\mathrm{Frag}}\) , Ha yr \(^{-1}\) ) and fire \(\mathrm{CO}_2\) emissions intensity \((\Delta \mathrm{ECO}_{2\mathrm{Frag}}\) , gC \(\mathrm{m}^{-2}\) yr \(^{-1}\) ), shown in light colours, or decoupled changes (one increasing, the other decreasing), in dark colours. Blue depicts areas where \(\Delta \mathrm{BA}_{\mathrm{Frag}}\) is negative, and red where it is positive. (b) Global spatial sensitivity of fire to hypothetical fragmentation levels: \(\mathrm{AED}_{\mathrm{F2}}\) simulation ensemble-averaged spatial distribution of fragmentation-doubling effects on fire burned area (unitless colour scale). All grid cells show a mean decrease in BA over the 9 simulations, but because of differential direction of change between simulations, we show in dark colours those grid cells where the average \(\mathrm{AED}_{\mathrm{F2}}\) impact is most likely to increase BA (highest fire susceptibility) and in light colours where it is most likely to decrease BA.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 436, 328, 451]]<|/det|>
+## Discussion and Conclusion
+
+<|ref|>text<|/ref|><|det|>[[116, 465, 881, 616]]<|/det|>
+By generating a parsimonious representation for land fragmentation based on observed road density, we enable the simple representation of its impacts on fire probability and behaviour in a land surface model. This reproduces observed relationships between land fragmentation and fire probability, at globally- aggregated and regional scales. We show that fragmentation has globally- significant impacts on BA, and may be a principal driver of fire activity regionally. Our grid- average approximation of vegetation fragment size as a directly- proportional barrier to fire spread appears sufficient to reproduce the relationship of BA decreasing with road density in observations, but also highlights that this physical constraint to size remains limited by the observed fire size distribution (Fig. 2d), and may be most effective at dampening larger fires. Conversely, model output reproduced large increases in BA in tropical regions where deforestation and plantation expansion are rampant,
+
+<|ref|>text<|/ref|><|det|>[[116, 630, 881, 753]]<|/det|>
+Broadly, our results mirror what is known anecdotally, but provides explanatory quantification and future projection potential for these small- scale or statistical relationships at global scale. This allows: (1) Identifying how and which edge effects may increase fire behaviour in specific locations/biomes, facilitating remediating action; (2) Dynamic forecasting of how projected changes in fragmentation/RD may impact fire behaviour in the future; (3) A first step towards policy assessment of fire risk and social welfare when considering fragmentation- relevant policy directives (e.g. Fig. S8). The methodology applied here also provides a route for large- scale modelling of other fragmentation effects in earth, ecological \(^{47,104,116,117}\) and epidemiological sciences \(^{18,119}\) .
+
+<|ref|>text<|/ref|><|det|>[[116, 767, 881, 902]]<|/det|>
+We believe that our fire model representation would be improved by discriminating between road- types, although the empirical impact of these on edge effects is for now largely unknown. Further, our results suggest that fragmentation's effect size on BA, where non- zero, varies hugely across space and time, and may only be a reflection of pre- existing model bias where modelled BA is otherwise low. Because the AED input map is static, year- by- year interpretation of output is problematic, and provides impetus for the production of higher resolution and better- identified gridded RL timeseries maps. This data shortcoming explains why we aggregate all output to simulation period average, interpretable as the probabilistic change in BA due to \(\sim 2014\) road density, which we believe reasonably retains fragmentation- fire effects given a short simulation timespan. The model appears to fail in areas of very
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 880, 113]]<|/det|>
+high soil moisture such as southern Kalimantan and the Pantanal (Fig.3a,b respectively), and peat fires/drainage should be included in future model iterations.
+
+<|ref|>text<|/ref|><|det|>[[116, 128, 881, 234]]<|/det|>
+Climate warming, population density and LUC will increase in the future, with socioeconomic effects of greatest magnitude forecast in the tropics120. Fragmentation largely increases fire in the tropics, meaning it may become a major driver of burned area there in the future, and suggests fragmentation could eventually 'tip' towards a global net- positive BA phenomenon with future tropical forest degradation and fire- activity, in a potential feedback loop. This may place greater burden on countries in these regions to balance economic policy with the environmental and welfare consequences of fire risk those policies may entail.
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 263, 187, 278]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 293, 264, 308]]<|/det|>
+## Model Description
+
+<|ref|>text<|/ref|><|det|>[[115, 323, 881, 654]]<|/det|>
+ORCHIDEE- MICT is a global- scale, grid- resolution model generally employed at 0.5 to 2 degrees, with boreal and permafrost - specific adaptations for high latitude biomes that affect soil, vegetation, hydrological and thermal processes specific to those latitudes. These process representations are particularly important in the context of this study for the modelling of future fire- vegetation- hydrological interactions. The model is carbon- based, in that it ultimately denominates earth system dynamics through their impacts on the C cycle, by which energy, soil, water and climate drive fluxes of C through the system via vegetation and associated biological and ecological processes. Thus, photosynthetic C is fixed by 11 plant functional types (PFTs), doing so differentially as each PFT is subject to specific primary production, senescence and C dynamics. The spatial distinction between PFTs can either be forced through an input vegetation map, defining the fractions of each grid cell covered by each PFT, or through the dynamic global vegetation model in ORCHIDEE, which predicts PFT type and allocation according to the biophysical suitability of each PFT to primarily climatic input variables. Fixed C is then allocated to foliage, fruit, roots, above/below - ground sapwood, heartwood and C reserves, that upon death or senescence are shunted to two reactivity- differentiated litter pools. ORCHIDEE- MICT is hard- coded with an adaptation of the SPITFIRE fire module63,66,121,122, which divides the aboveground vegetation components described above and apportions them to potential fuel type categories differentiated by their potential time to oxidation. Fire ignitions are controlled by a positive linear function of lightning flash density and a positive logistic function of human population density to represent human ignitions. Vegetation flammability is determined by fuel and climatic conditions (Nesterov Index and Fire Danger Index). The area burned in an individual fire event is determined by the rate of fire spread and fire duration, as influenced by vegetation flammability. Fire \(\mathrm{CO}_2\) emissions depend on vegetation biomass, fire intensity and duration.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 668, 360, 684]]<|/det|>
+## Fragmentation Representation
+
+<|ref|>text<|/ref|><|det|>[[115, 702, 880, 734]]<|/det|>
+The average edge distance (AED) per grid \((AED_G)\) given per- grid road length sum \((RL_G)\) was solved analytically and is given by the following:
+
+<|ref|>equation<|/ref|><|det|>[[115, 752, 504, 770]]<|/det|>
+\[AED_G = (2*Area_G*f(Cont)) / \Sigma (RL_G)) \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 782, 881, 904]]<|/det|>
+Where \(Area_G\) is the grid area in \(\mathrm{m}^2\) , and \(f(Cont)\) the fraction of each grid cell area taken up by the continental landmass. The gridded RL dataset in Meijer et al. (2018) gives a global road length estimate that is about \(50\%\) lower than that estimated by the World Road Statistics database ( \(\sim 30\) million km), and about \(300\%\) lower than the estimate provided by the CIA World Factbook. Furthermore, a recent report78 showed that the Global Roads Inventory Project (GRIP) database consistently and strongly under- predicted the existence of small roads, leading to large low biases against manually- observed road data in the report's two case study sites in the Congo and Canada. The primary reason hypothesised for these mismatches, which are acknowledged in the46 paper, is the under- representation of unofficial
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 880, 249]]<|/det|>
+and unpaved roads in their source database. GRIP was shown to under- represent total manually- measured road length in a grid cell by a factor of over 8 in one area (Fig. 19 of \(^{78}\) ). For this reason, in Eq. 1, which generates the AED map used as input to ORCHIDEE, we make the assumption that the gridded road length data underrepresent actual road length by a factor of 2, which implies a total global road length roughly in between the WRS and CIA estimates. Further, as river and stream length as well as large topographic discontinuities can reasonably be expected to act as fire breaks in most circumstances, and given that these are excluded from the input data, we take these to be potentially integrated into the factorial AED map. We acknowledge that multiplying RL uniformly by a single factor masks the likely spatial distribution of bias inherent to the GRIP database, however given that the source bias has not been assessed or quantified, we retain this spatial uniformity assumption for simplicity in this study.
+
+<|ref|>text<|/ref|><|det|>[[115, 262, 881, 460]]<|/det|>
+In order to modulate the effects of fire by fragmentation, ORCHIDEE must first be fed a gridded input map containing the AED data. This is derived from \(^{46}\) , which gives global gridded road length in m km \(^{2}\) at 5 arc- minute ( \(\sim 8\mathrm{km}\) ) resolution for a single time period ( \(\sim 2017\) ), downloaded from (https://zenodo.org/record/6420961, accessed 20/11/2022), converted to netcdf format and regridded to this study's simulation resolution of \(0.5^{\circ}\) ( \(\sim 50\mathrm{km}\) ) using the conservative interpolation function in the Climate Data Operator (CDO) package \(^{123}\) . The raw data were provided in five classes of road type: highway, primary, secondary, tertiary and local. Although we can reasonably expect each of these road classes to represent different scales of fragmentation, each conferring differential effects in their relation with fire phenomena, the paucity of empirical data on what these might be, coupled with the range of impacts that may, as mentioned be contradictory, mean that for the moment we take all road classes to be equal in effect, and as such sum them to a single road length density (RL) variable. Equation 1 is then applied to the dataset to generate a global gridded map of the average circular patch radius associated with each grid cell (AED \(G\) ).
+
+<|ref|>text<|/ref|><|det|>[[115, 472, 881, 687]]<|/det|>
+Next, we assume that spatially extensive fires do not occur on land that can be considered 'urban'. This assumption is made on the basis that urban areas are characterised by very low fuel densities (compared to, say, a pine forest), large areas of concrete, asphalt and steel, which do not burn easily, and high population densities that strongly increase the probability of successful human fire suppression. Because road density in urban areas is very high, this assumption should also require that the urban proportion of road density in each grid cell is removed from the original RL data, and a corresponding AED map generated. To do so, we download the output data from [ref. \(^{45}\) ] which gives the urban area fraction (UAF) of grid cells at global \(0.125^{\circ}\) resolution, and projects this variable globally to 2100 under the Shared Socioeconomic Pathways (SSP) scenario suite: (https://dataverse.harvard.edu/dataverse/geospatial human dimensions_data, accessed January 12, 2023). We then plotted a simple linear regression between the 2018 UAF data and the original RL, giving a relationship between the fraction of urban area in a grid cell and the road density of that grid cell ( \(\mathrm{RL} = ((2.68*10^{4})*\mathrm{UAF}) + 292\) ; \(\mathrm{R}^2 = 0.43\) ), where \(2.68*10^{4} =\) is the regression coefficient ( \(\alpha_{\mathrm{UAF}}\) , Table 1).
+
+<|ref|>text<|/ref|><|det|>[[115, 700, 881, 911]]<|/det|>
+The RL data were split into categories of urban fraction, whereby each grid cell was allocated to one of twelve UAF bins, corresponding to [0- 1, 1- 5, 5- 10, 10- 20, 20- 30...90- 100 percent] and the equation was used to estimate the implied RD at the numerical midpoint of each bin. Thus, on the basis of the RL/UAF regression, a road length per unit UAF was allocated to each of the UAF- based classes, multiplied by the actual UAF of each grid cell given its UAF, and the resulting 'excess' road length subtracted from the original RL data, to give an 'effective' road density and AED value. The resulting AED 'fragmentation' map can be compared to the original, and shows that in removing the impact of urban area roads on the representation of fragmentation, the world's most fragmented landscapes are no longer found in north- west Europe but in the north- eastern United States and e.g. Bangladesh. This is likely indicative of extensive non- urban infrastructural sprawl in the former, and a symptom of uniformly high population density and low to medium intensity and highly- extensive agricultural land use in the latter, meaning that roads criss- cross large parts of the country (see Fig. 1a). We chose to use UAF bins and calculate the RD at their midpoint instead of direct application of the regression equation because the latter's scatter is substantial, with binning more closely approximating the statistical value envelope.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 98, 473, 113]]<|/det|>
+## Description of Fire-Fragmentation Dynamics
+
+<|ref|>text<|/ref|><|det|>[[115, 131, 881, 435]]<|/det|>
+Fire size: In ORCHIDEE, total burned area per timestep is given by the product of average individual fire size in a given grid cell, and fire number. Because it has been shown in an anecdotal number of studies \(^{53}\) that for forests, fragmentation leads to decreases in fire size, and at the same time, ref. \(^{71}\) showed that the single strongest negative determinant of burned area at global scale is road density, we first approach fragmentation representation by decreasing the potential size of an individual fire as fragmentation increases. This is done first by assuming that the maximum individual fire size is a multiple \((n_{pat})\) of a grid cell's AED- determined mean patch area. This is because fragmentation may delimit the boundaries of fire spread in many circumstances, the circular AED- derived patch area is itself only an average, and large variations in patch size will be the reality, with some patches much larger than others. In addition, it lends a lower degree of restriction of fragmentation on fire size, allowing for the real- world possibility that fires can spread beyond the borders of the original vegetated patch. \(n_{pat}\) allows for future refinement of model representation when empirical relations between subgrid- scale fragment size distribution and propensity for spread become known. In the absence of such data, we set \(n_{pat}(forest) = 1\) and \(n_{pat}(grass) = 1.25\) (Table 1). We reason this because the observed individual fire size distribution is highly skewed towards small fires when compared to the fragment sizes defined by AED (see Fig. 2d), and because statistical treatment of observations suggests road fragmentation is a strong determinant of lower aggregate \(\mathrm{BA}^{71}\) . Without any empirical data to work with, a multiplier of unity appeared the most reasonable choice. We shunted grassland fire size limitation by AED by \(25\%\) above unity due to the relative ease of ignition of fine fuels in grasslands that may both more easily ignite and be carried over road barriers by wind.
+
+<|ref|>text<|/ref|><|det|>[[116, 452, 881, 544]]<|/det|>
+Fire Spread Thresholds: To introduce added realism and further reduce the restrictiveness of the fragmentation representation, the AED- denominated limit on individual fire size is only applied when separate conditions are met for forests and grasslands. For forests, if the simulated fire intensity and flame height exceed canopy base height, which is the pre- existing condition for canopy scorch in the original version of SPITFIRE \(^{63}\) , and the condition for crown fire spread in an upcoming version (Bowring et al., in prep.) then no size limitation is imposed:
+
+<|ref|>equation<|/ref|><|det|>[[115, 560, 565, 579]]<|/det|>
+\[\mathrm{FST}_{\mathrm{TREE}} = \mathrm{True}.\mathrm{IF}.:\mathrm{SH} > (\mathrm{H}_{\mathrm{TREE}} - (\mathrm{H}_{\mathrm{TREE}}*\mathrm{CL}_{\mathrm{TREE}})) \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 595, 881, 761]]<|/det|>
+Where \(\mathrm{FST}_{\mathrm{TREE}}\) is the fire spread threshold (Table 1), SH is the mean fire scorch height, \(\mathrm{H}_{\mathrm{TREE}}\) the mean tree height, \(\mathrm{CL}_{\mathrm{TREE}}\) the mean crown length. This is done to account for the possibility that high- intensity forest fires can't jump' over roads through crown spread, particularly if meteorological conditions for doing so are favourable. When this condition is met, fire spread and fire size are calculated as in the original SPITFIRE formulation. Second, over grasslands, ref. \(^{81}\) found that a critical threshold limiting fire spread ( \(\mathrm{FST}_{\mathrm{GRASS}}\) ), and hence fire patch size, exists in grasslands, which results from grassland fuel connectivity as given by area- specific fuel mass (tons \(\mathrm{Ha}^{- 1}\) ). They showed that if this 2.4 tons \(\mathrm{Ha}^{- 1}\) grass wet mass threshold is reached, even fuel at \(100\%\) moisture was able to burn. Thus, individual fire size limitation due to fragmentation on ORCHIDEE grasslands applies only to instances where the simulated grass fuel mass is below this biomass threshold, and are otherwise allowed to spread freely, as in the original SPITFIRE formulation:
+
+<|ref|>equation<|/ref|><|det|>[[115, 778, 625, 797]]<|/det|>
+\[\mathrm{fGrass}_{\mathrm{WW}} = \Sigma (\mathrm{F}_{1\mathrm{hr}} + \mathrm{F}_{10\mathrm{hr}} + \mathrm{F}_{100\mathrm{hr}} + \mathrm{F}_{1000\mathrm{hr}} + \mathrm{F}_{\mathrm{Live}})*(1 / 0.45) \quad (3)\]
+
+<|ref|>equation<|/ref|><|det|>[[115, 812, 625, 831]]<|/det|>
+\[\mathrm{FST}_{\mathrm{GRASS}} = \mathrm{True}.\mathrm{IF}.\mathrm{fGrass}_{\mathrm{WW}} > 2.5\mathrm{th}\mathrm{Ha}^{-1} \quad (4)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 848, 881, 911]]<|/det|>
+Where \(\mathrm{fGrass}_{\mathrm{WW}}\) is the summed weight of grass and grass fuel, \(\mathrm{F}_{\mathrm{hr}}\) refers to the different 'hour' fuel classes in ORCHIDEE, \(\mathrm{F}_{\mathrm{Live}}\) is live grass and (1/0.45) is the conversion of dry biomass to wet weight. Note that this ensures that the fragmentation model is able to account for the likely increases in extreme fire weather projected by future scenarios of climatic change. In a hot and dry season, a combination of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 881, 173]]<|/det|>
+fuel availability, low fuel moisture and high heat will enable an ignited fire to reach fire high reaction intensities, allowing high fuel consumption and flame heights to exceed those of the canopy and permit crown fire spread between forested patches. Likewise, fuel- limited grassland fires will, in dry seasons preceded by high pre- fire- season grass growth rates, spread when the medium of connectivity (fuel) is sufficient. Conversely, if there is insufficient fuel (i.e., prolonged drought), fire will not be able to spread between patches.
+
+<|ref|>text<|/ref|><|det|>[[115, 191, 881, 314]]<|/det|>
+Human Ignitions: Because the characterisation of fragmentation applied here is definitionally anthropogenic, it follows logically that an increment increase in road length in a given area exposes that length to human contact. Human contact in turn increases the risk of human ignitions, either through intentional (e.g., arson) or unintentional action (e.g., discarded cigarette butts, machinery, power lines, sunlit beer bottles, etc). In ORCHIDEE, human ignitions are controlled as a non- linear increasing then decreasing function of human population density, to reflect the fact that ignitions are more probable, and suppression less likely, when population density is low but not extremely sparse, such that the number of human ignitions \((IG_{H}\) , \(\mathrm{Ha^{- 1}d^{- 1}}\) ) is given by:
+
+<|ref|>equation<|/ref|><|det|>[[115, 330, 504, 384]]<|/det|>
+\[I G_{H} = P o p D* k(P o p D)* a(N d) / 10000\qquad (5)\] \[k(P o p D) = 30* e^{-0.5*\sqrt{(P o p D)}}\qquad (6)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 395, 881, 427]]<|/det|>
+Where \(PopD\) is population density and \(a(Nd)\) an observationally- estimated parameter representing ignitions per person per day, set at \(0.01^{63,66}\) .
+
+<|ref|>text<|/ref|><|det|>[[115, 444, 881, 566]]<|/det|>
+Here, we assume that an increase in fragmentation causes an increase in the probability of ignitions in direct proportion to the ratio of edge area: patch area, assuming conservatively that the human interaction with an edge can be characterised by a 1m edge depth \((\mathrm{ED}_{\mathrm{Humig}}\) , i.e. a 1m increment into the radius of the assumed circle). This 1m edge depth assumption is equivalent to the depth from the patch edge (i.e., road) which is potentially subject to increased fire ignitions due to human contact (potentially resulting in fires through arson, cigarettes, machinery, etc). The 1m edge is assumed and low, because although human effects on ignition may be occur deeper into a patch, the time averaged edge depth that they do so along the length of fragment edges is likely small, so we hold this parameter at unity.
+
+<|ref|>text<|/ref|><|det|>[[115, 583, 881, 678]]<|/det|>
+This transforms the perimeter from a length to an area, allowing us to probabilistically modulate the ignition function directly by the area represented by the total fragmentation edge area present in the grid. We then adjust the human fire ignition function \((IG_{H})\) in SPITFIRE \(^{66}\) by the product of the number of patches that fit into a grid's area \((Area_{G})\) and the cumulative fractional grid area of the ignition surface as defined by the assumed 1m ignition edge depth to arrive at a fragmentation- affected ignition function \((IG_{HFRag})\) , as illustrated in Fig. 1d.:
+
+<|ref|>equation<|/ref|><|det|>[[115, 695, 805, 713]]<|/det|>
+\[IG_{HFRag} = IG_{H} + ((Area_{G} / (\pi * A E D^{2})) * ((2\pi * A E D * 1) / Area_{G}) / 10000) \quad (7)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 717, 881, 794]]<|/det|>
+Thus, an AED of \(20\mathrm{m}\) yields a potentially increased ignition surface amounting to \(\sim 10\%\) of a grid cell. This probability is scaled to the ignitions person \(\mathrm{1km^{- 2}d^{- 1}}\) as a constant \((1 / 1000)\) , and results in significantly increased ignitions at low and high population density when fragmentation is high, which decreases exponentially as fragmentation decreases (AED increases). This is clearest at high population densities, where the suppression effect of high population is counteracted by fragmentation (Fig 1d).
+
+<|ref|>text<|/ref|><|det|>[[115, 811, 881, 902]]<|/det|>
+Fuel Wetness: Landscape fragmentation studies across many forested biomes have found that soil temperature and moisture was significantly higher and lower, respectively, at forest patch edge than in the patch interior \(^{37 - 41}\) , with subsequent impacts on fuel moisture and fire ignition and spread probabilities. We represent this by simply using the relative areas of patch area and edge area to define the proportion of a grid cell made subject to edge drying. Thus, we calculate the ratio of the edge area to patch area (the edge- to- patch ratio, EPR), and assuming conservatively that the 'edge- to- interior'
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[116, 82, 881, 144]]<|/det|>
+gradient through which temperature and soil effects are significant can be defined as the \(15\mathrm{m}\) from the edge inwards (this is the distance to which edge- interior soil moisture and temperature gradient in the above studies falls to approximately zero). This is then the area subject to increased drying and higher temperatures owing to fragmentation:
+
+<|ref|>equation<|/ref|><|det|>[[116, 160, 625, 179]]<|/det|>
+\[EPR = ((\pi *AED^2) - (\pi *(AED - 10)^2)) / (\pi *AED^2) \quad (8)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 195, 881, 321]]<|/det|>
+In ORCHIDEE- SPITFIRE, each fuel class in each grid cell is allocated a simulated fuel moisture content \((Wet_{FC})\) . In addition, there is a moisture threshold for each fuel class above which fuel consumption by fire no longer occurs \((Thresh_{FC_{1,2}})\) , where the subscripts refer to the \(1\mathrm{hr}\) and \(10\mathrm{hr}\) fuel classes subjected to edge drying. The \(100\mathrm{hr}\) fuel class is not affected in this scheme, as we assume that the diameter of \(100\mathrm{hr}\) fuel is sufficiently high to preclude edge drying from affecting its sensitivity to ignition. Here, both the calculated wetness and the ignition threshold were used to proxy edge fuel drying, and are both lowered by the product of the fractional edge- to interior moisture gradient with EPR.
+
+<|ref|>equation<|/ref|><|det|>[[115, 338, 500, 357]]<|/det|>
+\[Wet_{FC} = Wet_{FC} - ((0.25 / 2)*Wet_{FC}*EPR)(9)\]
+
+<|ref|>equation<|/ref|><|det|>[[115, 373, 694, 393]]<|/det|>
+\[Thresh_{FC_{1,2}} = Thresh_{FC_{1,2}} - ((0.25 / 2)*Thresh_{FC_{1,2}}*EPR) \quad (10)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 409, 881, 487]]<|/det|>
+Whereby 0.25 is the approximate \(25\%\) fractional soil moisture gradient difference between edge and interior (0- 20m) found across the field studies cited above. Since we take the edge depth \((\mathrm{ED}_{\mathrm{M oisture}})\) to be \(20\mathrm{m}\) , and assume a linear moisture gradient from 0- 20m, half of the maximum gradient is taken as the average decrease in soil moisture owing to fragmentation over the length of the edge, and total grid fuel wetness is then affected by the fractional area occupied by this edge.
+
+<|ref|>text<|/ref|><|det|>[[115, 504, 881, 688]]<|/det|>
+Wind Speed and Rate of Spread: Increasing fragmentation results in an increasing proportion of the landscape subject to a perimeter through which wind can travel with relatively less interruption. In other words, there is less of a barrier to wind at the patch edge and local surface roughness is lower, wind speeds are higher, and a larger proportion of the landscape is subject to these higher winds as fragmentation increases (e.g., 9). We treat this in ORCHIDEE by reducing the pre- existing model wind speed reduction factors at atmospheric versus ground level by an analytically- resolved factor derived from the implicit amount of fragment edge derived from AED. Specifically, we reduce the pre- existing reduction in windspeed due forest coverage in ORCHIDEE by the grid- areal proportion given by an assumed \(16\mathrm{m}\) mean edge depth \((ED_{WIND})\) . Effective \(ED_{WIND}\) is actually \(4\mathrm{m}\) , since at any time in any patch, we assume the wind can only come from a single direction so that \(ED_{WIND}\) is divided by 4 in model implementation. We then reduce the fixed forest wind reduction factor \((WRF = 0.4)\) in SPITFIRE proportional to the areal coverage of the fragment perimeter given by effective \(ED_{WIND}\) .
+
+<|ref|>equation<|/ref|><|det|>[[115, 704, 455, 723]]<|/det|>
+\[f_{EDGE} = Area_{patch} / Area_{edge} \quad (11)\]
+
+<|ref|>equation<|/ref|><|det|>[[115, 740, 512, 757]]<|/det|>
+\[WRF = WRF - ED_{WIND} \quad (12)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 775, 881, 882]]<|/det|>
+Increases in windspeed due to fragmentation in turn affects the fire ROS in areas that are considered substantially fragmented, leading in principle to increased BA within the patch area and (with the increase in fuel combustibility as a function of dryness and Fire Danger Index), potentially greater area- specific total combustion, fire intensity, and C emissions, potentially decoupling BA from ECO2 (Fig.1b). The fragmentation- wind relation was not applied to grasslands, because, firstly, wind has been shown to not increase grassland ROS and BA 81, and secondly, because the relative exposure differential of grass height and ground height compared to forest areas was assessed to be minimal.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[116, 83, 277, 97]]<|/det|>
+## Simulation Protocol
+
+<|ref|>text<|/ref|><|det|>[[116, 98, 882, 220]]<|/det|>
+The resulting model was spun up for 40 years to allow for vegetation to reach a quasi- equilibrium biomass state. This was done by forcing the model with the vegetation, climate and atmospheric \(\mathrm{CO_2}\) of 1901- 1910, looped over that period of time, then looped again for 40 years over 1990- 2000 forcing data, to bring the model to an equilibrium consistent with the near- present day. Principal and 'control' simulations were run over the period 2000- 2013. Vegetation was imposed and not predicted using ORCHIDE's dynamic global vegetation model to reduce uncertainties associated with its output. Climate forcing data for all runs came from the CRU- NCEP v8 dataset \(^{124}\) , and vegetation imposed on the model from the ESA- LUH2 suite of projections with 13 plant functional types \(^{14}\) .
+
+<|ref|>text<|/ref|><|det|>[[116, 233, 882, 368]]<|/det|>
+A number of additional output variables were also implemented to ease assessment of the effects of fragmentation on fire behaviour. Thus, a 'counterfactual' burned area variable, giving the burned area that would have been simulated without the fragmentation code, is written to history along with fragmentation- affected burned area, to enable tracking of fragmentation's effects. Likewise, differential burned area between the fire size and human ignitions fragmentation functions, assuming they are both activated, allows the user to track the relative burned area if either only the human ignitions or fire size - fragmentation flags were activated. This could not be done across all fragmentation- fire adaptations because of a necessarily large duplication of code and simulation runtime inefficiencies that would result.
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 383, 271, 398]]<|/det|>
+## Sensitivity Analysis
+
+<|ref|>text<|/ref|><|det|>[[116, 412, 882, 625]]<|/det|>
+We created synthetic maps of factor- two levels of homogenous global AED levels to assess the global change in burned area for each biome type (tropical, temperate, boreal) resulting from a factor- 2 change in fragmentation level. AED (not road density, which would cause differential AED because of grid area heterogeneity) was homogenised globally at 2- factor levels [of AED \(_{F2} = 39.0625\) , 78.125, 156.25, 312.5, 625, 1250, 2500, 5000, 10000, 20000 metres], permitting analysis of the biome- scale effects of fragmentation on fire independent of historical fragmentation trajectory, by calculating the global average change in burned area for each homogenised AED bin and biome. The model was run over a three- year period (2001- 2003 inclusive) for each \(\mathrm{RD}_{F2}\) level. This period was chosen because it incorporates a mixture of moderate El Niño and La Niña years, to limit its signal in simulated fire behaviour to be averaged out in annualised postprocessing. We initially maintained the existing global population distribution for the simulated years to gauge whether population density may cause a change in sign of sensitivity, and hence warrant further factorial analysis. Sensitivity was evaluated as the fractional change in BA \((\Delta fBA_{F2})\) per grid cell due to a two- fold increase in fragmentation (halving of AED):
+
+<|ref|>equation<|/ref|><|det|>[[116, 638, 694, 658]]<|/det|>
+\[\Delta fBA_{F2} = ((BA_{AEDF2[1 / 2]}) - (BA_{AEDF2[1]}) / (BA_{AEDF2[1]})GRID \quad (13)\]
+
+<|ref|>text<|/ref|><|det|>[[116, 671, 882, 872]]<|/det|>
+Where \(BA_{AED1 / 2}\) is the burned area at an AED of half the value of \(BA_{AEDF2[1]}\) . For each of the ten sensitivity simulations, biomes were assigned to each grid cell by identifying the PFT in each grid that contributed the maximum amount of simulated fire \(\mathrm{CO_2}\) emissions within that grid cell. This was done to identify the actual vegetation that burned in a grid cell, and hence the fire- relevant vegetation type, as opposed to using the maximum value between vegetation fractions of each PFT assigned to a grid cell, given that within a grid, certain vegetation types may have a fractionally higher propensity to burning than their areal coverage. At global scale, the individual PFTs were then aggregated to tropical, temperate, boreal, C3 and C4 grassland/ savannah bins. BA in ORCHIDEE- SPITFIRE is not PFT- disaggregated. However, \(\mathrm{CO_2}\) emissions from burning are. This gives a reasonable proxy of what vegetation is burning in a grid cell. Each grid cell was assigned a PFT identity according to that PFT which produced the highest fire \(\mathrm{CO_2}\) emissions over the course of each sensitivity simulation; global biome- specific masks were then created by aggregating boreal tropical and temperate forest types, and \(\Delta fBA_{F2}\) calculated for biome.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 888, 185, 902]]<|/det|>
+## Analysis
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 881, 175]]<|/det|>
+RD was recently estimated in a statistical generalised linear modelling study to be a strong negative predictor for BA globally71. We evaluated the statistical relationship between BA and road density that emerges from our simulations to compare with the same regression performed by ref. (71). We transform these two variables by taking the square root of road density and the applying the logit- link function to monthly burned area. The latter requires reducing a variable (burned area) to a probabilistic value, which in this case means a conversion to fraction of grid cell area \((p)\) . The logit function is then given by:
+
+<|ref|>equation<|/ref|><|det|>[[115, 202, 633, 227]]<|/det|>
+\[Logit(BA) = Ln\left(\frac{p}{1 - p}\right) \quad (14)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 240, 881, 377]]<|/det|>
+To estimate fragmentation- fire behaviour at biome scale, we found the maximum PFT- type that burned the most in carbon terms over the simulation period in each grid cell, by iteratively searching out the maximum value of time- aggregated \(\mathrm{CO_2}\) emissions per PFT in each grid. This was done because burned area in SPITFIRE is not output in PFT- specific fractions, while \(\mathrm{CO_2}\) emissions are, and informs us of what biome fire activity is most prevalent over time in each grid cell, such that these grid cells are collectively used to characterise global biome (PFT) - scale fire behaviour. All tropical, temperate and boreal PFTs were bundled into single biome bins to simplify explanation and analysis. Fig. 4a was produced by assigning Boolean numeric values to simulation average changes in BA and ECO2, then combining these to assign coupled/decoupled direction- of- change.
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 392, 156, 406]]<|/det|>
+## Data
+
+<|ref|>text<|/ref|><|det|>[[115, 420, 881, 573]]<|/det|>
+UAF was obtained from ref. (44). Fire size data used in Fig. 3c is sourced from FRYv2.087, updated from FRYv1.088 with single ignition point polygons delineation from ref. (86), based on pixel information MCD64A1 and FireCC151, as recently used in ref. (85). Long- term BA data for South- east Asia from105,106 was obtained from https://climate.esa.int/es/odp/#/project/fire (accessed 05/06/2023), while deforestation and pre- and post 2000 average tree plantation grid data were obtained from refs. (107,108). Fragmentation and fire data for Brazil in Fig. 3a were provided by ref. (102) and upscaled using CDO's conservative remapping function from 10km to 0.5 degree grid resolution. All other datasets above were interpolated bilinearly in CDO to 0.5 degree resolution. Postprocessing was performed using NCL, Panoply, CDO and R, with R maps created including the following packages: ncdf4, ggplot2, raster, maptools, rgdal, rgeos, maps, ggplot, sp, geosphere, rColorBrewer, ggplot, lattice, dplyr, tidyr, plyr.
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[115, 81, 595, 420]]<|/det|>
+
+| Variable | Value | Description | Rationale |
| auAF | 2.68*104 | Urban area RL removal regression coefficient (RL/Urban Area Fraction). | High RL urban areas unlikely to have significant BA removed to isolate 'fragmentation' versus 'urban' effect. |
| n pat forest | 1 | Parameter multiplier allowing individual forest fire size to exceed patch size by this factor, otherwise limited by it. | No data to suggest that this size can or cannot be exceeded given patch size unless extreme/crown fire |
| n pat grass | 1.25 | Parameter multiplier allowing individual grass fire size to exceed patch size by this factor, otherwise limited by it. | Value over unity based on assumption that some proportion of fragmented grasslands may allow spread beyond patch due to proportion of fine fuel |
| FSTTREE | conditional, empirically derived | Tree fire spread threshold, a flame height, tree height, canopy width dependent 'crown fire' condition | Allows fire to spread beyond patch size when fuel dryness, wind speed and allow flame height to exceed canopy |
| FSTGRASS | conditional, empirical | Grass fire spread threshold, based on areal fuel density | Allows fire to spread beyond patch size when fuel density exceeds threshold. |
| EDwind | 16m | Edge depth through which wind infiltration is altered by fragment edge | Assumes wind comes from a 1 direction in a given patch, patch average edge depth is approx. to 4m (16/4) in a given fire. |
| EDMoisture | 20m | Edge depth through which fuel moisture affected by fragment edge | Empirically-derived (Methods), assumes linear gradient of drying, and fuel drying itself is scaled quadratically downward with fuel type to reflect radial thickness of model fuel classes. |
| EDhumid. | 1m | Average depth through which human activities there affect ignition probability | This is assumed because although effects may be deeper, the time averaged edge depth along fragment edges is likely small. |
+
+<|ref|>table_caption<|/ref|><|det|>[[115, 442, 881, 468]]<|/det|>
+Table 1: Key components of the fragmentation module, their value, description and rationale. See Methods for detailed description and calibration of each parameter.
+
+<|ref|>title<|/ref|><|det|>[[115, 491, 281, 502]]<|/det|>
+# Competing Interests
+
+<|ref|>text<|/ref|><|det|>[[115, 506, 441, 518]]<|/det|>
+The authors declare no competing interests.
+
+<|ref|>title<|/ref|><|det|>[[115, 536, 255, 547]]<|/det|>
+# Data Availability
+
+<|ref|>text<|/ref|><|det|>[[115, 551, 768, 563]]<|/det|>
+The data presented in this study are available on request from the corresponding author.
+
+<|ref|>title<|/ref|><|det|>[[115, 581, 258, 592]]<|/det|>
+# Code Availability
+
+<|ref|>text<|/ref|><|det|>[[115, 596, 881, 623]]<|/det|>
+The version of ORCHIDEE-MICT-SPITFIRE developed here is published (DOI: ) and can be downloaded at the request of the corresponding author.
+
+<|ref|>title<|/ref|><|det|>[[115, 642, 273, 652]]<|/det|>
+# Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[115, 657, 881, 684]]<|/det|>
+SPKB was funded by research project FirEUrisk, a European Union Horizon 2020 research and innovation program under Grant Agreement No. 101003890.
+
+<|ref|>title<|/ref|><|det|>[[115, 732, 206, 742]]<|/det|>
+# References
+
+<|ref|>text<|/ref|><|det|>[[63, 761, 870, 790]]<|/det|>
+1. Winkler, K., Fuchs, R., Rounsevell, M. & Herold, M. Global land use changes are four times greater than previously estimated. Nat Commun 12, 1-10 (2021).
+
+<|ref|>text<|/ref|><|det|>[[61, 794, 857, 822]]<|/det|>
+2. Albert, J. S. et al. Human impacts outpace natural processes in the Amazon. Science (1979) **379**, (2023).
+
+<|ref|>text<|/ref|><|det|>[[61, 826, 832, 854]]<|/det|>
+3. Millard, J. et al. Global effects of land-use intensity on local pollinator biodiversity. Nat Commun 12, (2021).
+
+<|ref|>text<|/ref|><|det|>[[61, 858, 881, 888]]<|/det|>
+4. Powers, R. P. & Jetz, W. Global habitat loss and extinction risk of terrestrial vertebrates under future land-use-change scenarios. Nat Clim Chang 9, 323-329 (2019).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 85, 875, 110]]<|/det|>
+5. Matricardi, E. A. T. et al. Long-term forest degradation surpasses deforestation in the Brazilian Amazon. Science (1979) (2020) doi:10.1126/SCIENCE.ABB3021.
+
+<|ref|>text<|/ref|><|det|>[[60, 113, 870, 146]]<|/det|>
+6. Zellweger, F. et al. Forest microclimate dynamics drive plant responses to warming. Science (1979) 368, 772-775 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 148, 872, 197]]<|/det|>
+7. Reinmann, A. B. & Hutyra, L. R. Edge effects enhance carbon uptake and its vulnerability to climate change in temperate broadleaf forests. Proc Natl Acad Sci U S A 114, 107-112 (2017).
+
+<|ref|>text<|/ref|><|det|>[[60, 199, 875, 247]]<|/det|>
+8. Smith, I. A., Hutyra, L. R., Reinmann, A. B. & Thompson, J. R. Evidence for Edge Enhancements of Soil Respiration in Temperate Forests Geophysical Research Letters. 4278-4287 (2019) doi:10.1029/2019GL082459.
+
+<|ref|>text<|/ref|><|det|>[[60, 249, 870, 281]]<|/det|>
+9. De Frenne, P. et al. Forest microclimates and climate change: Importance, drivers and future research agenda. Glob Chang Biol 27, 2279-2297 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 283, 864, 315]]<|/det|>
+10. Smith, C., Baker, J. C. A. & Spracklen, D. V. Tropical deforestation causes large reductions in observed precipitation. Nature 615, 270-275 (2023).
+
+<|ref|>text<|/ref|><|det|>[[60, 316, 826, 348]]<|/det|>
+11. Zhu, L. et al. Comparable biophysical and biogeochemical feedbacks on warming from tropical moist forest degradation. Nat Geosci 16, 244-249 (2023).
+
+<|ref|>text<|/ref|><|det|>[[60, 349, 828, 381]]<|/det|>
+12. Crippa, M. et al. Food systems are responsible for a third of global anthropogenic GHG emissions. Nat Food 2, 198-209 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 382, 870, 414]]<|/det|>
+13. Hong, C. et al. Global and regional drivers of land-use emissions in 1961-2017. Nature 589, 554-561 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 415, 880, 463]]<|/det|>
+14. Hurtt, G. C. et al. Harmonization of land-use scenarios for the period 1500-2100: 600 years of global gridded annual land-use transitions, wood harvest, and resulting secondary lands. Clim Change 109, 117-161 (2011).
+
+<|ref|>text<|/ref|><|det|>[[60, 465, 863, 496]]<|/det|>
+15. Li, G. et al. Global impacts of future urban expansion on terrestrial vertebrate diversity. Nat Commun 13, (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 497, 857, 529]]<|/det|>
+16. Jolly, W. M. et al. Climate-induced variations in global wildfire danger from 1979 to 2013. Nat Commun (2015) doi:10.1038/ncomms8537.
+
+<|ref|>text<|/ref|><|det|>[[60, 531, 692, 562]]<|/det|>
+17. Bowman, D. M. J. S. et al. Fire in the earth system. Science Preprint at https://doi.org/10.1126/science.1163886 (2009).
+
+<|ref|>text<|/ref|><|det|>[[60, 564, 858, 595]]<|/det|>
+18. Brando, P. M. et al. The gathering firestorm in southern Amazonia. Sci Adv 6, 1-10 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 597, 854, 629]]<|/det|>
+19. Bowman, D. M. J. S. et al. Vegetation fires in the Anthropocene. Nat Rev Earth Environ 1, 500-515 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 630, 848, 663]]<|/det|>
+20. Ruffault, J. et al. Increased likelihood of heat-induced large wildfires in the Mediterranean Basin. Sci Rep 10, 1-9 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 664, 870, 696]]<|/det|>
+21. Clarke, H. et al. Forest fire threatens global carbon sinks and population centres under rising atmospheric water demand. Nat Commun 13, (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 697, 870, 730]]<|/det|>
+22. Senande-Rivera, M., Insua-Costa, D. & Miguez-Macho, G. Spatial and temporal expansion of global wildland fire activity in response to climate change. Nat Commun 13, (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 731, 880, 779]]<|/det|>
+23. Yu, Y. et al. Machine learning-based observation-constrained projections reveal elevated global socioeconomic risks from wildfire. Nat Commun 13, (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 781, 870, 813]]<|/det|>
+24. Armenteras, D., González, T. M. & Retana, J. Forest fragmentation and edge influence on fire occurrence and intensity under different management types in Amazon forests. Biol Conserv 159, 73-79 (2013).
+
+<|ref|>text<|/ref|><|det|>[[60, 815, 856, 847]]<|/det|>
+25. Lapola, D. M. et al. The drivers and impacts of Amazon forest degradation. Science (1979) 379, (2023).
+
+<|ref|>text<|/ref|><|det|>[[60, 849, 830, 881]]<|/det|>
+26. Laurance, W. F., Sayer, J. & Cassman, K. G. Agricultural expansion and its impacts on tropical nature. Trends Ecol Evol 29, 107-116 (2014).
+
+<|ref|>text<|/ref|><|det|>[[60, 882, 850, 915]]<|/det|>
+27. Kumar, S. et al. Changes in land use enhance the sensitivity of tropical ecosystems to fire-climate extremes. Sci Rep 12, 964 (2022).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 85, 875, 101]]<|/det|>
+29. Ellis, E. C. Ecology in an anthropogenic biosphere. Ecol Monogr 85, 287-331 (2015).
+
+<|ref|>text<|/ref|><|det|>[[60, 101, 870, 134]]<|/det|>
+30. Jacobson, A. P., Riggio, J., M. Tait, A. & E. M. Baillie, J. Global areas of low human impact ('Low Impact Areas') and fragmentation of the natural world. Sci Rep 9, (2019).
+
+<|ref|>text<|/ref|><|det|>[[60, 134, 802, 166]]<|/det|>
+31. Crooks, K. R. et al. Quantification of habitat fragmentation reveals extinction risk in terrestrial mammals. Proc Natl Acad Sci U S A 114, 7635-7640 (2017).
+
+<|ref|>text<|/ref|><|det|>[[60, 167, 855, 215]]<|/det|>
+32. McGuire, J. L., Lawler, J. J., McRae, B. H., Nuñez, T. A. & Theobald, D. M. Achieving climate connectivity in a fragmented landscape. Proc Natl Acad Sci U S A 113, 7195-7200 (2016).
+
+<|ref|>text<|/ref|><|det|>[[60, 216, 844, 281]]<|/det|>
+33. Teshome, A., de Graaff, J., Ritsema, C. & Kassie, M. Farmers' Perceptions about the Influence of Land Quality, Land Fragmentation and Tenure Systems on Sustainable Land Management in the North Western Ethiopian Highlands. Land Degrad Dev 27, 884-898 (2016).
+
+<|ref|>text<|/ref|><|det|>[[60, 281, 822, 330]]<|/det|>
+34. Manjunatha, A. V., Anik, A. R., Speelman, S. & Nuppenau, E. A. Impact of land fragmentation, farm size, land ownership and crop diversity on profit and efficiency of irrigated farms in India. Land use policy 31, 397-405 (2013).
+
+<|ref|>text<|/ref|><|det|>[[60, 331, 856, 363]]<|/det|>
+35. Gomes, E. et al. Agricultural land fragmentation analysis in a peri-urban context: From the past into the future. Ecol Indic 97, 380-388 (2019).
+
+<|ref|>text<|/ref|><|det|>[[60, 364, 802, 396]]<|/det|>
+36. Mendes, C. B. & Prevedello, J. A. Does habitat fragmentation affect landscape-level temperatures? A global analysis. Landsc Ecol 35, 1743-1756 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 396, 870, 428]]<|/det|>
+37. Meeussen, C. et al. Structural variation of forest edges across Europe. For Ecol Manage 462, 117929 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 429, 860, 461]]<|/det|>
+38. Meeussen, C. et al. Microclimatic edge-to-interior gradients of European deciduous forests. Agric For Meteorol 311, (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 462, 875, 494]]<|/det|>
+39. Crockatt, M. E. & Bebber, D. P. Edge effects on moisture reduce wood decomposition rate in a temperate forest. Glob Chang Biol 21, 698-707 (2015).
+
+<|ref|>text<|/ref|><|det|>[[60, 495, 824, 527]]<|/det|>
+40. Morreale, L. L., Thompson, J. R., Tang, X., Reinmann, A. B. & Hutyra, L. R. Elevated growth and biomass along temperate forest edges. Nat Commun 12, (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 528, 875, 576]]<|/det|>
+41. Garvey, S. M., Templer, P. H., Pierce, E. A., Reinmann, A. B. & Hutyra, L. R. Diverging patterns at the forest edge: Soil respiration dynamics of fragmented forests in urban and rural areas. 3094-3109 (2022) doi:10.1111/gcb.16099.
+
+<|ref|>text<|/ref|><|det|>[[60, 577, 870, 625]]<|/det|>
+42. Keppel, G., Anderson, S., Williams, C., Kleindorfer, S. & O'Connell, C. Microhabitats and canopy cover moderate high summer temperatures in a fragmented Mediterranean landscape. PLoS One 12, 1-18 (2017).
+
+<|ref|>text<|/ref|><|det|>[[60, 626, 844, 658]]<|/det|>
+43. Nunes, M. H. et al. Forest fragmentation impacts the seasonality of Amazonian evergreen canopies. Nat Commun 13, 1-10 (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 659, 822, 691]]<|/det|>
+44. Gao, J. & Pesaresi, M. Downscaling SSP-consistent global spatial urban land projections from 1/8-degree to 1-km resolution 2000-2100. Sci Data 8, 1-9 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 692, 820, 723]]<|/det|>
+45. Gao, J. & O'Neill, B. C. Mapping global urban land for the 21st century with data-driven simulations and Shared Socioeconomic Pathways. Nat Commun 11, 1-12 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 724, 875, 756]]<|/det|>
+46. Meijer, J. R., Huijbregts, M. A. J., Schotten, K. C. G. J. & Schipper, A. M. Global patterns of current and future road infrastructure. Environmental Research Letters 13, (2018).
+
+<|ref|>text<|/ref|><|det|>[[60, 757, 866, 789]]<|/det|>
+47. Haddad, N. M. et al. Habitat fragmentation and its lasting impact on Earth's ecosystems. Sci Adv 1, 1-10 (2015).
+
+<|ref|>text<|/ref|><|det|>[[60, 790, 870, 822]]<|/det|>
+48. Archibald, S., Staver, A. C. & Levin, S. A. Evolution of human-driven fire regimes in Africa. Proc Natl Acad Sci U S A (2012) doi:10.1073/pnas.1118648109.
+
+<|ref|>text<|/ref|><|det|>[[60, 823, 816, 855]]<|/det|>
+49. Lauss, A. & Nogue, J. Indicators of landscape fragmentation: The case for combining ecological indices and the perceptive approach. Ecol Indic 15, 85-91 (2012).
+
+<|ref|>text<|/ref|><|det|>[[60, 856, 814, 888]]<|/det|>
+50. Uuemaa, E., Mander, Ü. & Marja, R. Trends in the use of landscape spatial metrics as landscape indicators: A review. Ecol Indic 28, 100-106 (2013).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 78, 880, 905]]<|/det|>
+51. Demetriou, D., Stillwell, J. & See, L. A new methodology for measuring land fragmentation. Comput Environ Urban Syst 39, 71–80 (2013).52. Archibald, S. et al. Biological and geophysical feedbacks with fire in the Earth system. Environmental Research Letters Preprint at https://doi.org/10.1088/1748-9326/aa9ead (2018).53. Driscoll, D. A. et al. How fire interacts with habitat loss and fragmentation. Biological Reviews 96, 976–998 (2021).54. Silva, C. H. L. et al. Deforestation-induced fragmentation increases forest fire occurrence in central Brazilian Amazonia. Forests 9, (2018).55. Guimberteau, M. et al. ORCHIDEE-MICT (v8.4.1), a land surface model for the high latitudes: model description and validation. Geosci Model Dev 11, 121–163 (2018).56. Qiu, C. et al. ORCHIDEE-PEAT (revision 4596), a model for northern peatland CO2, water, and energy fluxes on daily to annual scales. Geosci Model Dev 11, 497–497 (2018).57. Bowring, S. P. K. et al. ORCHIDEE MICT-LEAK (r5459), a global model for the production, transport and transformation of dissolved organic carbon from Arctic permafrost regions, Part 2: Model evaluation over the Lena River basin. Geoscientific Model Development Discussions 1–45 (2019) doi:10.5194/gmd-2018-322.58. D’Orgeval, T., Polcher, J. & De Rosnay, P. Sensitivity of the West African hydrological cycle in ORCHIDEE to infiltration processes. Hydrol Earth Syst Sci 12, 1387–1401 (2008).59. Guimberteau, M. et al. Discharge simulation in the sub-basins of the Amazon using ORCHIDEE forced by new datasets. Hydrol Earth Syst Sci 16, 911–935 (2012).60. Thurner, M. et al. Evaluation of climate-related carbon turnover processes in global vegetation models for boreal and temperate forests. Glob Chang Biol (2017) doi:10.1111/gcb.13660.61. Lange, S. EartH2Observe, WFDEI and ERA-Interim data Merged and Bias-corrected for ISIMIP (EWEMBI). GFZ Data Services (2016) doi:10.5880/pik.2016.004.62. Lauerwald, R. et al. ORCHILEAK (revision 3875): A new model branch to simulate carbon transfers along the terrestrial-aquatic continuum of the Amazon basin. Geosci Model Dev 10, 3821–3859 (2017).63. Yue, C., Ciais, P., Cadule, P., Thonicke, K. & Van Leeuwen, T. T. Modelling the role of fires in the terrestrial carbon balance by incorporating SPITFIRE into the global vegetation model ORCHIDEE - Part 2: Carbon emissions and the role of fires in the global carbon balance. Geosci Model Dev 8, 1321–1338 (2015).64. Yue, C. et al. Modelling the role of fires in the terrestrial carbon balance by incorporating SPITFIRE into the global vegetation model ORCHIDEE - Part 1: Simulating historical global burned area and fire regimes. Geosci Model Dev (2014) doi:10.5194/gmd-7-2747-2014.65. Rothermel, R. C. Predicting behavior and size of crown fires in the northern Rocky Mountains. USDA Forest Service, Intermountain Research Station, Research Paper 46 (1991).66. Thonicke, K. et al. The influence of vegetation, fire spread and fire behaviour on biomass burning and trace gas emissions: Results from a process-based model. Biogeosciences (2010) doi:10.5194/bg-7-1991-2010.67. Albini, F. A. Estimating wildfire behavior and effects. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station 30, 1–22 (1976).68. Hartson, S. et al. The status and challenge of global fire modelling. Biogeosciences (2016) doi:10.5194/bg-13-3359-2016.69. Hartson, S. et al. Quantitative assessment of fire and vegetation properties in simulations with fire-enabled vegetation models from the Fire Model Intercomparison Project. Geosci Model Dev (2020) doi:10.5194/gmd-13-3299-2020.70. Van Marle, M. J. E. et al. Historic global biomass burning emissions for CMIP6 (BB4CMIP) based on merging satellite observations with proxies and fire models (1750-2015).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 75, 870, 870]]<|/det|>
+Geoscientific Model Development Preprint at https://doi.org/10.5194/gmd- 10- 3329- 2017 (2017). 71. Haas, O., Prentice, I. C. & Harrison, S. P. Global environmental controls on wildfire burnt area, size, and intensity. Environmental Research Letters 17, 065004 (2022). 72. Narayanaraj, G. & Wimberly, M. C. Influences of forest roads on the spatial pattern of wildfire boundaries. Int J Wildland Fire 20, 792- 803 (2011). 73. Fisher, R., Lewis, B., Price, O. & Pickford, A. Barriers to fire spread in northern Australian tropical savannas, deriving fire edge metrics from long term high- frequency fire histories. J Environ Manage 301, 113864 (2022). 74. Stolle, F., Chomitz, K. M., Lambin, E. F. & Tomich, T. P. Land use and vegetation fires in Jambi Province, Sumatra, Indonesia. For Ecol Manage 179, 277- 292 (2003). 75. Sze, J. S., Jefferson & Lee, J. S. H. Evaluating the social and environmental factors behind the 2015 extreme fire event in Sumatra, Indonesia. Environmental Research Letters 14, 015001 (2019). 76. Barni, P. E. et al. Logging Amazon forest increased the severity and spread of fires during the 2015- 2016 El Niño. For Ecol Manage 500, 119652 (2021). 77. Arienti, M. C., Cumming, S. G., Krawchuk, M. A. & Boutin, S. Road network density correlated with increased lightning fire incidence in the Canadian western boreal forest. Int J Wildland Fire 18, 970- 982 (2009). 78. Keijzer, T., Schipper, A., Meijer, J. & Nijland, W. Detecting roads from space: testing the potential of Sentinel- 1 SAR imagery and deep learning for automated road mapping. PBL Netherlands Environmental Assessment Agency (2022). 79. CIA, C. I. A. Roadways, The World Factbook 2021. https://www.cia.gov/the-world- factbook/field/roadways/ (2021). 80. IRF. World Road Statistics 2016. (2017). 81. Cardoso, A. W. et al. Quantifying the environmental limits to fire spread in grassy ecosystems. Proc Natl Acad Sci U S A 119, 1- 7 (2022). 82. ARCHIBALD, S., ROY, D. P., Van WILGEN, B. W. & SCHOLES, R. J. What limits fire? An examination of drivers of burnt area in Southern Africa. Glob Chang Biol 15, 613- 630 (2009). 83. Baker, J. C. A. & Spracklen, D. V. Climate Benefits of Intact Amazon Forests and the Biophysical Consequences of Disturbance. Frontiers in Forests and Global Change 2, (2019). 84. Trancoso, R. et al. Converting tropical forests to agriculture increases fire risk by fourfold. Environmental Research Letters 17, 104019 (2022). 85. García, M. et al. Characterizing global fire regimes from satellite- derived products. Forests 13, 699 (2022). 86. Oom, D., Silva, P. C., Bistinas, I. & Pereira, J. M. C. Highlighting biome- specific sensitivity of fire size distributions to time- gap parameter using a new algorithm for fire event individuation. Remote Sens (Basel) 8, 663 (2016). 87. Mouillot, F., Chen, W., Campagnolo, M. & Ciais, P. FRYv2.0 : a global fire patch morphology database from FireCCI51 and MCD64A1. in EGU General Assembly 2023 - EGU23- 9575 (EGU23- 9575, 2023). 88. Laurent, P. et al. FRY, a global database of fire patch functional traits derived from space- borne burned area products. Sci Data 5, 180132 (2018). 89. Giglio, L., Boschetti, L., Roy, D. P., Humber, M. L. & Justice, C. O. The Collection 6 MODIS burned area mapping algorithm and product. Remote Sens Environ 217, 72- 85 (2018).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[59, 85, 875, 135]]<|/det|>
+90. Gaveau, D. L. A., Descalas, A., Salim, M. A., Sheil, D. & Sloan, S. Refined burned-area mapping protocol using Sentinel-2 data increases estimate of 2019 Indonesian burning. Earth Syst Sci Data 13, 5353–5368 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 135, 870, 168]]<|/det|>
+91. Subramanian, A. & Kessler, M. The hyperglobalization of trade and its future. Towards a better global economy: Policy implications for citizens worldwide in the 21st century (2013).
+
+<|ref|>text<|/ref|><|det|>[[60, 168, 870, 199]]<|/det|>
+92. Stiglitz, J. E. Where modern macroeconomics went wrong. Oxf Rev Econ Policy 34, 70–106 (2018).
+
+<|ref|>text<|/ref|><|det|>[[60, 199, 875, 232]]<|/det|>
+93. Hoang, N. T. & Kanemoto, K. Mapping the deforestation footprint of nations reveals growing threat to tropical forests. Nat Ecol Evol 5, 845–853 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 232, 856, 265]]<|/det|>
+94. Pendrill, F. et al. Agricultural and forestry trade drives large share of tropical deforestation emissions. Global Environmental Change 56, 1–10 (2019).
+
+<|ref|>text<|/ref|><|det|>[[60, 265, 870, 313]]<|/det|>
+95. Lambin, E. F. & Meyfroidt, P. Global land use change, economic globalization, and the looming land scarcity. Proceedings of the National Academy of Sciences of the United States of America vol. 108 3465–3472 Preprint at https://doi.org/10.1073/pnas.1100480108 (2011).
+
+<|ref|>text<|/ref|><|det|>[[60, 313, 860, 345]]<|/det|>
+96. Byerlee, D. Globalized agriculture and tropical deforestation. Population, Agriculture, and Biodiversity 123–148 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 345, 855, 378]]<|/det|>
+97. Wolf, C., Levi, T., Ripple, W. J., Zárrate-Charry, D. A. & Betts, M. G. A forest loss report card for the world’s protected areas. Nat Ecol Evol 5, 520–529 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 378, 825, 411]]<|/det|>
+98. Giljum, S. et al. A pantropical assessment of deforestation caused by industrial mining. Proceedings of the National Academy of Sciences 119, e2118273119 (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 411, 866, 443]]<|/det|>
+99. Maxwell, S. L. et al. Degradation and forgone removals increase the carbon impact of intact forest loss by 626%. Sci Adv 5, eaax2546 (2023).
+
+<|ref|>text<|/ref|><|det|>[[60, 443, 825, 475]]<|/det|>
+100. Taubert, F. et al. Global patterns of tropical forest fragmentation. Nature 554, 519–522 (2018).
+
+<|ref|>text<|/ref|><|det|>[[60, 476, 875, 524]]<|/det|>
+101. Turubanova, S., Potapov, P. V., Tyukavina, A. & Hansen, M. C. Ongoing primary forest loss in Brazil, Democratic Republic of the Congo, and Indonesia. Environmental Research Letters 13, 074028 (2018).
+
+<|ref|>text<|/ref|><|det|>[[60, 525, 875, 558]]<|/det|>
+102. Rosan, T. M. et al. Fragmentation-Driven Divergent Trends in Burned Area in Amazonia and Cerrado. Frontiers in Forests and Global Change 5, (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 558, 860, 606]]<|/det|>
+103. Walker, R., Perz, S., Arima, E. & Simmons, C. The Transamazon Highway: Past, Present, Future. in Engineering Earth: The Impacts of Megaeengineering Projects (ed. Brunn, S. D.) 569–599 (Springer Netherlands, 2011). doi:10.1007/978-90-481-9920-4_33.
+
+<|ref|>text<|/ref|><|det|>[[60, 607, 860, 639]]<|/det|>
+104. Lapola, D. M. et al. The drivers and impacts of Amazon forest degradation. Science (1979) 379, eab9622 (2023).
+
+<|ref|>text<|/ref|><|det|>[[60, 640, 877, 688]]<|/det|>
+105. Lizundia-Loiola, J., Oton, G., Ramo, R. & Chuvieco, E. A spatio-temporal active-fire clustering approach for global burned area mapping at 250 m from MODIS data. Remote Sens Environ 236, 111493 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 689, 875, 737]]<|/det|>
+106. Oton, G., Lizundia-Loiola, J., Pettinari, M. L. & Chuvieco, E. Development of a consistent global long-term burned area product (1982–2018) based on AVHRR-LTDR data. International Journal of Applied Earth Observation and Geoinformation 103, 102473 (2021).
+
+<|ref|>text<|/ref|><|det|>[[60, 738, 870, 770]]<|/det|>
+107. Curtis, P. G., Slay, C. M., Harris, N. L., Tyukavina, A. & Hansen, M. C. Classifying drivers of global forest loss. Science (1979) 361, 1108–1111 (2018).
+
+<|ref|>text<|/ref|><|det|>[[60, 771, 785, 787]]<|/det|>
+108. Du, Z. et al. A global map of planting years of plantations. Sci Data 9, 141 (2022).
+
+<|ref|>text<|/ref|><|det|>[[60, 787, 860, 820]]<|/det|>
+109. Field, R. D., van der Werf, G. R. & Shen, S. S. P. Human amplification of drought-induced biomass burning in Indonesia since 1960. Nat Geosci 2, 185–188 (2009).
+
+<|ref|>text<|/ref|><|det|>[[60, 821, 866, 868]]<|/det|>
+110. Nikonovas, T., Spessa, A., Doerr, S. H., Clay, G. D. & Mezbahuddin, S. Near-complete loss of fire-resistant primary tropical forest cover in Sumatra and Kalimantan. Commun Earth Environ 1, 65 (2020).
+
+<|ref|>text<|/ref|><|det|>[[60, 870, 850, 902]]<|/det|>
+111. Krasovskii, A. et al. Modeling burned areas in Indonesia: The FLAM approach. Forests 9, 437 (2018).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 81, 870, 578]]<|/det|>
+112. Van Der Werf, G. R. et al. Global fire emissions estimates during 1997–2016. Earth Syst Sci Data 9, 697–720 (2017).113. Aragão, L. E. O. C. et al. 21st Century drought-related fires counteract the decline of Amazon deforestation carbon emissions. Nat Commun 9, 536 (2018).114. Mollicone, D., Eva, H. D. & Achard, F. Human role in Russian wild fires. Nature 440, 436–437 (2006).115. Zheng, B. et al. Increasing forest fire emissions despite the decline in global burned area. Sci Adv 7, (2021).116. Laurance, W. F. et al. A global strategy for road building. Nature 513, 229–232 (2014).117. Laurance, W. F. et al. Ecosystem Decay of Amazonian Forest Fragments: a 22-Year Investigation. Conservation Biology 16, 605–618 (2002).118. Plowright, R. K. et al. Land use-induced spillover: a call to action to safeguard environmental, animal, and human health. The Lancet Planetary Health vol. 5 e237–e245 Preprint at https://doi.org/10.1016/S2542-5196(21)00031-0 (2021).119. Skinner, E. B., Glidden, C. K., MacDonald, A. J. & Mordecai, E. A. Human footprint is associated with shifts in the assemblages of major vector-borne diseases. Nat Sustain 6, 652–661 (2023).120. Kemp, L. et al. Climate Endgame: Exploring catastrophic climate change scenarios. Proceedings of the National Academy of Sciences 119, e2108146119 (2022).121. Yue, C. et al. How have past fire disturbances contributed to the current carbon balance of boreal ecosystems? Biogeosciences 13, 675–675 (2016).122. Bowring, S. P. K., Jones, M. W., Ciais, P., Guenet, B. & Abiven, S. Pyrogenic carbon decomposition critical to resolving fire’s role in the Earth system. Nat Geosci 15, 135–142 (2022).123. Schulzweida, U. CDO User Guide. Preprint at https://doi.org/10.5281/zenodo.7112925 (2022).124. Viovy, N. CRUNCEP Version 7 - Atmospheric Forcing Data for the Community Land Model. Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory https://doi.org/10.5065/PZ8F-F017 (2018) doi:https://doi.org/10.5065/PZ8F-F017.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 92, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 253, 150]]<|/det|>
+MSSupplement.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/images_list.json b/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..833dbbedd539e45dcb71af172c08f48498b29323
--- /dev/null
+++ b/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/images_list.json
@@ -0,0 +1,77 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 133,
+ 90,
+ 850,
+ 304
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 131,
+ 359,
+ 880,
+ 544
+ ]
+ ],
+ "page_idx": 5
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 170,
+ 130,
+ 781,
+ 350
+ ]
+ ],
+ "page_idx": 7
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 173,
+ 88,
+ 832,
+ 364
+ ]
+ ],
+ "page_idx": 8
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5.",
+ "footnote": [],
+ "bbox": [
+ [
+ 133,
+ 319,
+ 880,
+ 500
+ ]
+ ],
+ "page_idx": 9
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3.mmd b/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..76ce7b138f770d112e8a746877f8c8dab60f519c
--- /dev/null
+++ b/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3.mmd
@@ -0,0 +1,305 @@
+
+# Crowding results from optimal integration of visual targets with contextual information
+
+Guido Marco CicchiniConsiglio Nazionale delle Ricerche https://orcid.org/0000- 0002- 3303- 0420
+
+Giovanni D'ErricoCNR Neuroscience Institute https://orcid.org/0000- 0002- 0491- 581XDavid Burr (Dave@in.cnr.it)University of Florence https://orcid.org/0000- 0003- 1541- 8832
+
+## Article
+
+# Keywords:
+
+Posted Date: March 1st, 2022
+
+DOI: https://doi.org/10.21203/rs.3.rs- 1296243/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on September 30th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 33508- 1.
+
+<--- Page Split --->
+
+# Crowding results from optimal integration of visual targets with contextual information
+
+Guido Marco Cicchini1, Giovanni D'Errico1 and David C. Burr1,2
+
+1. Institute of Neuroscience, CNR, via Moruzzi, 1, 56124 – Pisa (ITALY)
+2. Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, viale Pieraccini, 6 – 50139 Firenze (ITALY)
+
+## ABSTRACT
+
+Crowding is the inability to recognize peripheral objects in clutter, usually considered a fundamental low- level bottleneck to object recognition. Here we advance and test an alternative hypothesis, that crowding, like “serial dependence”, results from optimizing strategies that exploit redundancies in natural scenes. This notion leads to several testable predictions: (1) crowding should be greatest for unreliable targets and reliable flankers; (2) crowding- induced biases should be maximal when target and flankers have similar orientations, falling off for differences around \(20^{\circ}\) ; (3) flanker interference should be associated with higher precision in orientation judgements, leading to lower overall error rate; (4) effects should be maximal when the orientation of the target is near that of the average of the flankers, rather than to that of individual flankers. All these effects were verified, and well simulated with ideal- observer models that maximize performance. The results suggest that while crowding can impact strongly on object recognition, it is best understood not as a processing bottleneck, but as a consequence of efficient exploitation of the spatial redundancies of the natural world.
+
+<--- Page Split --->
+
+## INTRODUCTION
+
+Crowding is the inability to recognize and identify objects in clutter, despite their being clearly visible, and recognizable when presented in isolation1 (see examples in Figure 1A). It is particularly elevated in the periphery, scaling linearly with eccentricity, such that the minimal spacing between targets and flanking elements for uncrowded vision is equal to about half the eccentricity (Bouma's law2). Crowding impacts on many important daily tasks, such as face recognition and reading (for reviews see3,4,5), to the extent it has been considered a major bottleneck to object recognition.
+
+Most popular current models of crowding involve some form of compulsory pooling (or substitution) of targets with flankers. For example, Parkes and colleagues6 showed that while the orientation of a single line cannot be determined when embedded in flankers, it does influence the perceived orientation of the ensemble: hence it is merged with the flankers, rather than suppressed. This is reinforced by several studies showing that the targets can take on characteristics of the flanker stimuli7- 9. Pelli and Tillmann3 suggest that the compulsory integration occurs in higher cortical areas, such as V4, which have large receptive fields, appropriately sized to account for Bouma's law (see also10).
+
+However, compulsory integration does not explain all the known facts about crowding. For example, flankers that are similar in size, colour or orientation cause more crowding than dissimilar ones11- 13. More difficult to explain are the recent demonstrations of Herzog and colleagues14 of "uncrowding", where the addition of extra flanking stimuli around the flankers can reduce drastically their crowding effect, particularly if the extra flankers group with the original flankers to form coherent objects. These data do not fit easily with compulsory integration, even with appropriate linear filtering, which could in principle account for other effects, such as orientation or size selectivity.
+
+Crowding has been studied for decades, and usually considered to be a defect in the system, "an essential bottleneck to object perception"15. Certainly, it impacts heavily on object recognition in tasks like or face recognition: but is it possible that it may reflect processes that are in principle advantageous to perception? Perception is strongly affected by contextual information, particularly temporal context, where recent and longer term perceptual history has been shown to exert a major influence on current perception16- 19. While the role of context and experience has been appreciated for some time20,21, it has
+
+<--- Page Split --->
+
+become particularly topical in recent years within the framework of Bayesian analysis. This approach has revealed an interesting phenomenon termed "serial dependence", where the appearance of many important attributes of a stimulus (including orientation, numerosity, facial identity, beauty etc) are biased towards previously viewed stimuli17,18,22,23. Counterintuitively, these consistent biases in perception have been shown to reflect an efficient perceptual strategy, exploiting temporal redundancies in natural viewing to reduce overall reproduction errors, despite the biases24,17,25.
+
+Could crowding also be a consequence of efficient integration processes that exploit spatial (rather than temporal) redundancies to improve performance? We investigate this possibility by studying crowding with a similar paradigm used for serial dependence studies. If, like serial dependence, crowding is a by- product of efficient redundancy- reducing mechanisms, it should display several specific signature characteristics. One is that crowding- induced biases should be stronger for targets that are unreliably perceived, and for flankers that are reliably perceived. In addition, crowding should follow the signature pattern seen in serial dependence, highest when the orientations of target and flankers are similar, then steadily falling off. We verify these characteristics qualitatively and qualitatively, and show that crowding, while leading to biases, also improves overall performance. The results fit well with models simulating intelligent combination of signals from a small receptive field centred on the target with signals from a much larger integration region, following the same rules that govern serial dependence. On this view crowding should not be considered a defect, or bottleneck, in the system, but the unavoidable consequence of efficient exploitation of spatial redundancies of the natural world.
+
+<--- Page Split --->
+
+
+Figure 1
+
+a) Crowding is a visual phenomenon where items that can be easily identified in isolation are not identifiable if surrounded by similar items. The P and hand symbol on the right are difficult to recognize, while fixating the central red dots.
+
+b) Stimuli employed in this experiment. Observers judged the orientation of a peripheral target (the central oval), which was flanked above and below by oval stimuli. Two conditions were tested: a rounded target with elongated flankers (Low reliability target, high reliability flankers, at left) or an elongated target with rounded ovals (at right). In the main condition the centre-to-centre distance of flankers and targets was 5.5 deg, and eccentricity 26 degrees, leading to a Bouma ratio of 0.21.
+
+## RESULTS
+
+To test if visual crowding follows the rules of optimal integration, which well describe serial dependence \(^{18,25}\) , we measured crowding with an orientation reproduction task. Participants reproduced the orientation of oval stimuli, which were either elongated (aspect ratio 1: 2.8) or rounded (aspect 1: 1.4). Targets were presented \(26^{\circ}\) to the right of fixation, and vertically flanked by similar oval stimuli, elongated if the target was rounded, and vice versa (see Fig. 1B). The orientation of the target was either \(35^{\circ}\) or \(55^{\circ}\) (at random). The orientations of the two flankers were yoked together, and varied randomly over a range of \(\pm 45^{\circ}\) from target orientation. The clear prediction from the efficient integration model \(^{24}\) (see Eqn 10) is that the effects of crowding will be far stronger for the rounded targets and elongated flankers than vice versa. The reasons are explained formally the modelling section, but the intuition is that the rounded stimuli have less reliable orientation signals and therefore benefit more from integration with contextual information, especially if it is reliable.
+
+Figure 2A shows the bias in target reproduction as a function of difference in flanker orientation. Clearly, the rounded targets show the strongest contextual effects of crowding,
+
+<--- Page Split --->
+
+with peak biases varying by up to \(\pm 5.1^{\circ}\) , compared with \(\pm 1.9^{\circ}\) for the elongated targets. Furthermore, the pattern of bias follows closely that predicted and observed in serial dependence studies \(^{25}\) , varying non- linearly with difference between target and flanker orientation, increasing to a maximum around \(\pm 20^{\circ}\) , then decreasing. These data are well fit by derivative of gaussian functions (eqn. 15, light- coloured lines), commonly used in serial dependence studies \(^{18}\) , and expected from a causal inference model (see modelling section \(^{26}\) ). The dark lines show the predictions of another Bayesian model (eqn. 10), which has also proven successful with serial dependence data \(^{17,25}\) . While the models are detailed later, it is worth noting that they are almost entirely anchored by data, down to a simple scaling factor, suggesting that the data are consistent with ideal behaviour.
+
+
+
+Figure 2
+
+a) Average response bias (response minus target orientation) as a function of the orientation of two identical flankers. Low reliability (rounded) targets in blue, high reliability (elongated) in red. Error bars show \(\pm 1\) SEM. Dark lines show predictions from an ideal-observer Bayesian model which scales the action of flankers according to their reliability and orientation difference (Eqn 10 of model section). Light blue and red curves show predictions for the causal inference model that doses flanker and target information according to their reliability and the probability of originating from a common cause (Eqn 15 of model section).
+b) Response scatter as a function of the orientation of two identical flankers, together with model predictions. Colour coding as in A.
+c) Response Scatter error plotted against bias errors for the two conditions. Dashed circles indicate regions with identical RMSE error (given by the Pythagorean sum of the two types of error). RMSE varies with orientation, and is least around \(0^{\circ}\) , when target and flankers coincide.
+
+Another important prediction is that the contextual effects should improve performance. Figure 2B plots reproduction scatter (root- variance of reproduction trials) as a function of orientation difference. As expected, at all orientation differences, these are lower for the elongated than the rounded targets. However, for both targets, particularly the rounded
+
+<--- Page Split --->
+
+targets, the scatter decreased as the difference between target and flanker orientation decreased. Figure 2C plots scatter against bias, with points connected to follow the change in orientation. On this plot, total error (the Pythagorean sum of scatter and bias) is the radial distance from the origin. For the points with flanker orientation most distant from the target (near \(\pm 45^{\circ}\) ), the total error is around \(15^{\circ}\) . Between these extremes, total error falls off, despite the constant bias. When the flankers and targets have similar orientations, the error falls to around \(11^{\circ}\) , evidence that “crowding” improves overall performance.
+
+If the effects shown in Figure 2 represent visual crowding, they should depend on critical spacing between target and flankers, and follow Bouma's law1. We therefore measured the effects as a function of target- flanker spacing, for 5 participants. Figure 3 shows the data for the rounded targets with elongated flankers (which show the strongest effects). For the two smallest spacings (5.5 and 7.5 deg), bias showed the characteristic S- shaped dependency on the orientation of the flankers. For the larger spacings (11.0 and 16.6 deg), however, the effect was much reduced and even inverted at 11 deg. As before, the curves are fit by a derivative of gaussian function (eqn 18), which is the product of a linear regression (illustrated by dashed line in Figure 3A) and a gaussian. The best fitting slope of this regression is an estimate of the weight given to the flankers when judging orientation. Figure 3B plots the fitted weight as a function of target- flanker spacing (lower abscissa), with the upper abscissa showing the Bouma constant, the distance between target and flanker centres divided by the eccentricity (26 deg). The weight drops from 0.5 to 0 for Bouma constants between 0.3 and 0.4, broadly in line with the literature, suggesting that the effects observed here relate to crowding.
+
+<--- Page Split --->
+
+
+Figure 3
+
+a) Response bias as function of flanker orientation for various target-flanker distances leading to four different Bouma ratios (distance between flanker and target centres divided by eccentricity. Data are fit with a derivative of gaussian function with free parameters (Eqn 18).
+b) Weight of the flankers (maximal slope of the curves in panel A) as a function of the Bouma ratio (colour-code as before). Error bars show ±1 SEM.
+
+The results so far show that integration is not obligatory, but depends on the reliability of both target and flankers, and on their orientation similarity. A remaining question is how the flankers integrate with the target: each separately, or after combination with each other. Figure 4 illustrates two possibilities (see also modelling section). One is feedforward model where the target integrates independently with low- level, high- resolution neural representations of each of the flankers. The other depicts integration with a broader representation including both flankers, potentially implemented through recurrent feedback.
+
+<--- Page Split --->
+
+
+Figure 4
+
+a) Rationale of Experiment 2. Flankers could either act independently on the target (as illustrated by purple arrows in top left panel), or first pooled into a larger RF, which in turn biases the target (illustrated by the large yellow circle and arrow in bottom left panel).
+b) Predictions for the two hypotheses. If the flankers act independently, when one flanker is locked at \(+15^{\circ}\) and the other free to vary, the pattern should be similar to that of the main experiment (centre close to \(0^{\circ}\) ), but raised because of the action of the locked flanker (purple curve). If flankers are first integrated at a more global stage, maximal effect is expected when all the elements in the larger operator average \(0^{\circ}\) . Since one of the flankers is locked at \(+15^{\circ}\) , this occurs when the other flanker is \(-15^{\circ}\) , leading to a leftward shift of the curve of the main experiment (yellow curve)
+
+To distinguish between these two plausible possibilities, we measured target bias with the orientation of the two flankers varying independently. Specifically, one flanker (randomly top or bottom) was always oriented \(+15^{\circ}\) from the target, while the other varied randomly over the range. The logic is that the gaussian function windowing the contextual effect should be centred where the orientations of target and context coincide. If the integration occurs directly between the target and individual flankers, then the maximum effects should occur when the variable flanker coincides with the target; on the other hand, if the integration is with a broader representation including both flankers, maximum integration should occur when the flanker mean is zero, which occurs when the variable flanker is \(-15^{\circ}\) . These predictions are illustrated in Figure 4B: note that the individual flanker effect also predicts the curve to be higher at all flanker orientations, as the fixed flanker will exert a constant effect at all orientations of the variable flanker.
+
+<--- Page Split --->
+
+The results for the rounded targets with elongated flankers are shown figure 5A. The biases clearly follow the signature pattern, well fit by a derivative of gaussian function. The centre of the function is \(- 12.1^{\circ}\) , closer to the \(15^{\circ}\) predicted by integration with the average orientation of the flankers, than \(0^{\circ}\) predicted by the individual flanker model. The mean height of the function is \(0.5^{\circ}\) , close to that observed in the previous experiment \((- 0.9^{\circ})\) , while the individual-flanker integration model predicts a constant average bias \(4.7^{\circ}\) . Figure 5B shows the scatter for this experiment, which was reduced over the region of bias, well described by an inverted Gaussian.
+
+
+
+Figure 5.
+
+a) Biasing errors as function of a single flanker orientation, while the other flanker was locked at \(+15^{\circ}\) . Colours and conventions as for Figure 2. Thick dark lines refer to the ideal observer model (Eqn 10), thick light blue lines to the causal inference model (Eqn 15). Thin dashed lines show best-fitting derivative of gaussian, with all parameters free to vary (Eqn 18).
+b) Response Scatter as a function of the variable flanker orientation. Conventions as in panel a.
+c) Histogram of the centres of the gaussian derivative for 1000 bootstrap fits.
+
+To test significance, we bootstrapped the data 1000 times (sampling with replacement) and measured the centre of the gaussian derivative on each iteration. The results plotted in the histogram of Figure 5C show that on only 16 out of 1000 iterations (1.6%) was the centre closer to \(0^{\circ}\) (individual flanker prediction) than to \(- 15^{\circ}\) (joint-flanker prediction). This leads to a likelihood ratio (Bayes factor) of \(984 / 16 = 61.5\) , strong evidence in favour of the joint-flanker- integration model.
+
+<--- Page Split --->
+
+## MODELLING
+
+We propose two plausible models to explain the pattern of data. Both are motivated by principles of "optimal cue integration" commonly used in multi- sensory perception \(^{27,28}\) , which predict optimal combination of information from multiple sources after appropriate weighting to minimize overall root- mean- square error. The first is based on an ideal- observer model successfully used to model serial dependence \(^{17}\) , the second on a "causal- inference" model of multi- sensory integration \(^{26}\) . Both models predict well the data.
+
+## Ideal Observer
+
+Total RMS error \((E)\) can be decomposed into bias \((B)\) and precision (scatter standard deviation: \(S\) ), whose squares sum to give total squared error:
+
+\[E = \sqrt{B^{2} + S^{2}} \quad (eq.1)\]
+
+The ideal responses \((R)\) in a pooling model can be expressed as a linear weighted combination of internal representation of target \((T)\) and flankers \((F_{1}\) and \(F_{2}\) ), each weighted by \(w_{1}\) and \(w_{2}\) .
+
+\[R = w_{1}F_{1} + w_{2}F_{2} + (1 - w_{1} - w_{2})T \quad (eq.2)\]
+
+As the two flankers of this study had the same aspect ratio they should be weighted equally, \((w_{1} = w_{2} = w)\) , so Eqn. 2 simplifies to:
+
+\[R = wF_{1} + wF_{2} + (1 - 2w)T \quad (eq.3)\]
+
+The mean of the responses \((\mu_{R})\) is a simple linear combination of the means of flankers and target \((\mu_{1}, \mu_{2}\) and \(\mu_{T}\) ).
+
+\[\mu_{R} = w\mu_{1} + w\mu_{2} + (1 - 2w)\mu_{T} = w(\mu_{1} + \mu_{2}) + (1 - 2w)\mu_{T} \quad (eq.4)\]
+
+Bias is the difference between the mean estimated response \((\mu_{R})\) and real orientation, \(x_{T}\) ; \(B = \mu_{R} - x_{T}\) . Using equation 4 and considering that the average target representation \((\mu_{T})\) should be unbiased and coincide with target \((\mu_{T} = x_{T})\) it follows that:
+
+\[B = \mu_{R} - x_{T} = w(\mu_{1} + \mu_{2}) + \mu_{T} - 2w\mu_{T} - x_{T} = w(\mu_{1} + \mu_{2} - 2\mu_{T}) \quad (eq.5)\]
+
+<--- Page Split --->
+
+The term \(\mu_{1} + \mu_{2} - 2\mu_{T}\) can be rearranged as \(2((\mu_{1} + \mu_{2}) / 2 - \mu_{T})\) which is twice the distance between the average of the flanker representations, \((\mu_{1} + \mu_{2}) / 2\) , and the target representation \(\mu_{T}\) . For convenience we define:
+
+\[d = (\mu_{1} + \mu_{2}) / 2 - \mu_{T} \quad (eq. 6)\]
+
+so that Eqn. 5 becomes:
+
+\[B = w(\mu_{1} + \mu_{2} - 2\mu_{T}) = 2wd \quad (eq. 7)\]
+
+Variance of the linear combination of the flankers and target is itself a linear combination of the flanker and target variances \((\sigma_{F}^{2}\) and \(\sigma_{T}^{2}\) ) with the squared coefficients
+
+\[S^{2} = w^{2}\sigma_{F}^{2} + w^{2}\sigma_{F}^{2} + (1 - 2w)^{2}\sigma_{T}^{2} \quad (eq. 8)\]
+
+From Eqn 1, 7 and 8 it follows that RMSE can be written as:
+
+\[\begin{array}{l}{E = 4w^{2}d^{2} + w^{2}\sigma_{F}^{2} + w^{2}\sigma_{F}^{2} + (1 - 2w)^{2}\sigma_{T}^{2}}\\ {= 4w^{2}d^{2} + w^{2}\sigma_{F}^{2} + w^{2}\sigma_{F}^{2} + (1 - 4w + 4w^{2})\sigma_{T}^{2}} \end{array} \quad (eq. 9)\]
+
+Since RMSE is a function of second order of \(w\) , it is minimized when \(w = \frac{- b}{2a}\) , so the optimal weight \((w_{opt})\) is obtained at:
+
+\[w_{opt} = -\frac{1}{2}\frac{-4\sigma_{T}^{2}}{4\sigma_{F}^{2} + 2\sigma_{F}^{2} + 4d^{2}} = \frac{\sigma_{T}^{2}}{2\sigma_{F}^{2} + \sigma_{F}^{2} + 2d^{2}} \quad (eq. 10)\]
+
+This equation has much in common with that of all Bayesian- like integrations used in multisensory research and serial dependence: the weight depends directly on target variance \(\sigma_{T}^{2}\) , so targets of low reliability (inverse variance) benefit more from integration, resulting in higher weighting to the flankers. Increase in flanker variance \((\sigma_{F}^{2})\) has the opposite effect.
+
+The term \(2d^{2}\) is fundamental for the signature function, as the weight of the flankers will decrease with angular difference between target and average flanker orientation. This is reminiscent of serial dependence effects, and ensures that contextual cues are used only if they are plausibly similar to the target \(^{24,17,25}\) . Importantly, the point that will ensure maximal weight of the flankers is when the target coincides with the average of the flankers (i.e. \(d^{2} = 0\) ).
+
+<--- Page Split --->
+
+Together the behaviour of Eqns 3 and 10 define the ideal observer behaviour. In order to accommodate suboptimal behaviour we introduce a scaling factor \((\alpha)\) which multiplies \(w_{opt}\) and sets the actual weight of the flankers:
+
+\[R = \alpha w_{opt}F_1 + \alpha w_{opt}F_2 + (1 - 2\alpha w_{opt})T \quad [eq. 11]\]
+
+## Causal Inference Model
+
+An alternative model prescribes that the optimal blend of information can be obtained behaving as if the sources of information originated form one cause times the probability that two sources of information originate from the same cause26. Within this framework the maximal interaction between cues occurs when the two sources coincide, where the weight assigned of is the well known result known in sensory integration literature27,28 (see also eq. 10):
+
+\[w_{A}^{max} = \frac{\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}} \quad [eq. 12]\]
+
+The probability of the two sources originating from a common cause can be calculated using Bayes' Theorem as demonstrated in26. Assuming gaussian probability distribution functions (with centres at \(\mu_{A}\) and \(\mu_{B}\) and variances \(\sigma_{A}^{2}\) and \(\sigma_{B}^{2}\) ), the solution is soluable analytically26:
+
+\[p(A,B|C = 1)\propto \exp \left(-\frac{1}{2}\frac{(\mu_{A} - \mu_{B})^{2}\sigma_{B}^{2} + (\mu_{A} - \mu_{P})^{2}\sigma_{B}^{2} + (\mu_{B} - \mu_{P})^{2}\sigma_{A}^{2}}{\sigma_{A}^{2}\sigma_{B}^{2} + \sigma_{A}^{2}\sigma_{P}^{2} + \sigma_{B}^{2}\sigma_{P}^{2}}\right) \quad [eq. 13]\]
+
+This is function of the variances of the two sources \((\sigma_{A}^{2}\) and \(\sigma_{B}^{2}\) ), the centres of the representations \((\mu_{A}\) and \(\mu_{B}\) ) and their distance, and the a- prior likelihood of there being one cause (itself gaussian and characterized by mean and variance \(\mu_{P}\) and \(\sigma_{P}^{2}\) ). If no prior knowledge is available \((\sigma_{P}^{2} \to \infty)\) Eqn 13 simplifies to
+
+\[p(A,B|C = 1)\propto \exp \left(-\frac{1}{2}\frac{(\mu_{A} - \mu_{B})^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}}\right) \quad [eq. 14]\]
+
+This is a gaussian peaking when the distribution of the two cues coincide \((\mu_{A} = \mu_{B})\) and falling off with a space constant related to the sum of their variances \((\sigma_{A}^{2} + \sigma_{B}^{2})\) .
+
+In the specific case of our experiment we can map the two sources of information to the flanker compound (a gaussian with centre at \(\mu_{F} = (\mu_{1} + \mu_{2}) / 2\) , variance \(\sigma_{F}^{2} / 2\) ) and the
+
+<--- Page Split --->
+
+target (assumed gaussian with centre \(\mu_{T}\) , and variance \(\sigma_{T}^{2}\) . Putting together Eqns 12 and 14, the bias (difference between the response and the target) is given by:
+
+\[B = w_{F}^{max}p(F,T|C = 1)(\mu_{F} - \mu_{T}) = \frac{\sigma_{F}^{2}}{\sigma_{F}^{2} + \sigma_{T}^{2}}\exp \left(-\frac{1}{2}\frac{(\mu_{F} - \mu_{T})^{2}}{\sigma_{F}^{2} + \sigma_{T}^{2}}\right)(\mu_{F} - \mu_{T}) \quad [eq 15]\]
+
+Which is a derivative of gaussian as a function of flanker orientation \(\mu_{F}\)
+
+It also follows that response scatter is minimized only when the system considers a common cause likely (Eqn 14), predicting U- shaped (gaussian) plots of Figures 2B and 5B.
+
+Again, to allow for suboptimal behaviour we introduced two free parameters that regulate the amplitude of the dependency on the flankers \((\beta)\) and the breadth of the region of interaction \((y)\) so that the bias is:
+
+\[B = \beta \frac{\sigma_{T}^{2}}{\sigma_{F}^{2} + \sigma_{T}^{2}}\exp \left(-\frac{1}{2}\frac{(\mu_{F} - \mu_{T})^{2}}{\gamma^{2}(\sigma_{F}^{2} + \sigma_{T}^{2})}\right)(\mu_{F} - \mu_{T}) \quad [eq 16]\]
+
+Interestingly, comparable behaviour is obtained if, instead of constructing a system which multiplies probabilities as in \(^{26}\) , one considers a system that measures the similarity between two distributions via their point- by- point product of the distributions and takes either the peak or area under the distribution.
+
+The product of gaussians is itself a gaussian, is centred at \((\frac{\mu_{B}\sigma_{A}^{2} + \mu_{A}\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}})\) , has variance \((\frac{\sigma_{A}^{2}\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}})\) and peak at:
+
+\[\frac{1}{2\pi\sigma_{A}\sigma_{B}}\exp \left(-\frac{(\mu_{A} - \mu_{B})^{2}}{2(\sigma_{A}^{2} + \sigma_{B}^{2})}\right) \quad [eq. 17]\]
+
+So the peak embeds the same behaviour of Eqn. 14. It is easy to demonstrate that also the area under the curve follows the same gaussian dependency on the distance between cues as the area of a gaussian is equivalent to the peak (Eqn. 16) times the standard deviation of the curve \((\sqrt{\frac{\sigma_{A}^{2}\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}}})\) and a constant factor \(1 / \sqrt{2\pi}\) all of which are constant once the distributions have known width and thus reduce to a scaling factor.
+
+## Model Fitting
+
+The predictions of the two modelling approaches are overlayed on the data of Figures 2 and 5 with dark and light colours. To minimize degrees of freedom we derived the values of
+
+<--- Page Split --->
+
+sensory reliability from the data of Figure 2b, assuming that the extreme points \((\pm 30^{\circ}\) and \(\pm 45^{\circ}\) ) give baseline data, not influenced by flanker integration: this is 17.1 for rounded targets (blue symbols), and 11.7 for elongated targets (red symbols).
+
+We implemented the ideal observer model (Eqn. 11) with only a scaling constant \((\alpha)\) , which allows for sub- optimal behaviour. These fits are particularly good for the rounded targets (with largest effects), with \(\mathbb{R}^2\) of 0.97 and 0.74 (for bias and scatter), and 0.24 and 0.60 for elongated targets) and come about assuming \(\alpha = 0.57\) . One of the key features of the ideal observer model is that it reduces RMSE by leveraging on all available information. Thus it predicts the Global Integration of Figure 4, with centres of the Gaussian derivatives close to \(- 15^{\circ}\) . Besides capturing this key feature, the model also provides good quantitative fits to the data of Figure 5a with \(\mathbb{R}^2\) of 0.76 and average fits to those of Figure 5b 0.23 for bias and scatter respectively \((\alpha = 0.32)\) .
+
+We used the same reliability values from Figure 2b to implement the "optimal causality gating model" \(^{26}\) , the derivative of gaussian function plotted with light colours in Figures 2 and 5. The sensory reliabilities fix both the maximal slope of the curve (see Eqn 12) and the width of the region of interaction (see Eqn 14). Assuming the same sensory precisions as above (17.1 and 11.7 for the two types of stimuli) maximal slopes should be 0.81 and 0.48 for the two conditions, larger than the real data. Also the widths (27.8 and 33.2) are larger than those predicted by Eqn 14 (19 and 16.8). For this reason we allowed two scaling factors, one enabling lower weighting of the context \((\beta)\) and the other modulating the width \((\gamma)\) . Setting \(\beta = 0.54\) and \(\gamma = 1.46\) led to good fits with \(\mathbb{R}^2 = 0.97\) and 0.89 for the low reliability target (bias and scatter curves), and 0.67 and 0.79 for the high reliability target \((\beta = 0.26\) and \(\gamma = 1.97\) ). As with the other model, the prediction in Experiment 2 is for large pooling of all available cues, thus the prediction is that of a centre at \(- 15^{\circ}\) . This model also provides good fits for response bias \((R^2 = 0.89)\) and acceptable fits for response scatter \((R^2 = 0.38, \beta = 0.62\) and \(\gamma = 1.37\) ).
+
+<--- Page Split --->
+
+## DISCUSSION
+
+The results of this study suggest a novel interpretation of visual crowding: that it is a byproduct of efficient Bayesian processes, which lead to improved perceptual performance, minimizing production error. We tested and validated several key predictions of this idea. Firstly, crowding, measured as flanker- induced orientation bias, was greatest when targets had the weakest orientation signals (least reliability) and flankers had the strongest signals, as predicted from most models of optimal cue combination \(^{27,28}\) . The magnitude of the bias varied with the difference of target and flanker orientation, following the predicted nonlinear pattern, increasing to a maximum of around \(15^{\circ}\) , then falling off for larger orientation differences. Importantly, the interaction of the flankers and target was associated with a reduction in response scatter, which led to a reduction in total RMS error, an index of improved performance. Finally, the results suggest that the bias does not result from direct interactions with individual flankers, but from interaction with a representation of the average orientations of the two flankers. All these results were predicted by optimal feature combination principles, and quantitatively well modelled an ideal- observer model that minimizes reproduction errors.
+
+These results are clearly difficult to reconcile with standard models of obligatory integration \(^{6,29}\) . Passive integration systems may be tweaked to explain the stronger effects for more elongated flankers (such as having more Fourier energy at that orientation), but cannot explain the fall off in crowding effects when the difference exceeds \(15^{\circ}\) . Any basic integrator would necessarily combine orientation energy of all angles, not only similar angles. On the other hand, the flexible integrator models proposed here (Eqns 10 and 15) predict both the pattern and the magnitude of the results. Furthermore, the final experiment suggests that this intelligent orientation- dependent integration is unlikely to occur directly within a higher order cell itself, as the orientation- dependent integration function aligns with the average of two disparate flankers, rather than with each individual flanker. This suggests that the integration is between the target and a broad representation that includes both flankers. Mechanisms operating directly between target and individual flankers (such as the proposed “local association field” \(^{30}\) ) are not consistent with the results of Figure 5, which shows that flankers are first combined with each other before exerting their effects on the target.
+
+<--- Page Split --->
+
+Combination of target and a broad representation of both flankers could be implemented in several ways. One physiologically plausible mechanism would be feedback from mid- level areas, such as V4, which have large receptive fields, integrating over a wide area. These cells could contain information of both flankers (as well as the target), which could be fed back to low levels (eg V1) to integrate flexibly with finer representations of the target. Within this framework the fine- grain target information is not lost, but combined with broad contextual information in an optimal manner to improve performance. This is analogous to the process of serial dependence, where representations of perceptual history (often termed Bayesian priors) are generated at mid- to high- levels of analysis, but feed back onto fairly low processing levels31. Similar processes could evoke crowding, integrating over space rather than time.
+
+The predictions of the crowding behaviour derive from theoretical minimization of total RMS errors, explained in detail in the modelling section, but readily understood intuitively. There are two orthogonal sources of error, bias (average accuracy) and response scatter (precision), which combine by Pythagorean sum to yield total error. Thus although the contextual effects do lead to inaccuracies (biases), these are more than offset by the decrease in response scatter (Fig. 2C). Clearly, if the effects were to increase continuously with orientation, then the bias would become large, and offset the reduction in scatter, leading to increased error: integration is therefore efficient only over a limited range. Note that the efficiency- driven ideal model gives good fits simultaneous to both bias and scatter data with only one free parameter, a scaling factor. This comes out at around 0.57 for the main data and probably reflects other processes in orientation judgements that we did not control for, such as regression to the mean32,33.
+
+The current experiment shows that under conditions of crowding, information about the target is not necessarily lost. This is consistent with a good deal of previous evidence (see reference34 for review), including studies showing that it can affect the ensemble judgment5, can cause adaptation35 and that crowding induced biases may not affect grasping36. Even more dramatic are the demonstrations that increasing flanker length37 or adding additional flankers14 can decrease or eliminate crowding. Our study employed simple well controlled stimuli to allow quantitative prediction and measurement of crowding- effects, similar to the studies with serial dependence studies. Thus they do not readily relate
+
+<--- Page Split --->
+
+to the clever uncrowding studies of Herzog and colleagues. However, it is not difficult to envisage extensions to the model incorporating grouping principles within the rules of integration, in the spirit of the general principles of our model: flexible, "intelligent" combination of signals, rather than a rigid integration via "rectify and sum" or similar rules10.
+
+In summary, the current study suggests that crowding may be analogous to serial dependence, pointing to similar function and mechanisms. As serial dependence has been shown to exploit temporal redundancies to maximize performance, crowding may also reflect similar exploitation of redundancies over space. It is worth noting that while the rules governing crowding are flexible, leading to improved performance, crowding remains completely obligatory: no effort of will or deployment of attention can allow us to resolve the crowded objects, or to ignore the contextual effects of the orientated flankers. Indeed, while our proposed pooling process is flexible and "intelligent", it remains automatic, not subject to voluntary control. This is similar to many of the experience- driven perceptual illusions, such as the "hollow mask illusion"21: no effort of will can cause us to see the inside of a hollow mask as concave, we always see the convex face. However, while visual crowding remains an obligatory limitation to object recognition, we conclude that like the effects of temporal context and experience, it is best understood not as a defect or bottleneck of the system, but the consequence of efficient exploitation of spatial redundancies of the natural world.
+
+## METHODS
+
+## Participants
+
+Fifteen healthy participants with normal or corrected- to- normal vision were recruited (aged 18- 55 years, mean age = 36, 7 females). Experimental procedures are in line with the declaration of Helsinki and approved by the local ethics committee (Commissione per l'Etica della Ricerca, University of Florence, 7 July 2020). Written informed consent was obtained from each participant, which included consent to process, preserve and publish the data in anonymous form.
+
+<--- Page Split --->
+
+## Stimuli
+
+The stimuli, illustrated in Fig. 1A, were generated with Psychtoolbox for MATLAB (R2016b; MathWorks). They comprised an oval- shaped visual target flanked by oval- shaped upper and lower visual flankers, displayed 26 deg eccentric from the fixation point, with the target close to the horizontal meridian (vertical position was slightly varied from trial to trial to avoid pre- allocation of attention to the target) and flankers 5.5 deg away from the target. Both target and flankers were sketches of oval shapes, defined by 12 dark grey dots (diameter 0.3 deg, 1.4 deg inter- dots distant, 16.8 deg perimeter), presented against a uniform grey background. The target was orientated either \(+35^{\circ}\) or \(+55^{\circ}\) (clockwise) from the vertical, and flanker orientation randomly chosen in steps of \(5^{\circ}\) from \(- 45^{\circ}\) to \(+45^{\circ}\) with respect to the target orientation. The two flankers were 5.5 deg from target, leading to a Bouma ratio of 0.2. We manipulated the reliability of orientation information of target and flanker stimuli by using two different aspect ratios, 2.8 (axes 3.48 and 1.23 deg) and 1.4 (axes 3.19 and 2.28 deg), illustrated in Fig. 1A. The more elongated target was always associated with more rounded flankers, and vice versa. In each experimental session of the three experiments, the two target- flanker combinations were shown both kinds of stimuli in random order.
+
+## Procedure
+
+Stimuli were displayed on a linearized \(22^{\prime \prime}\) LCD monitor (resolution \(1920\times 1080\) pixels, refresh rate \(60\mathrm{Hz}\) ). Observers were positioned \(57~\mathrm{cm}\) from the monitor, in a quiet room with dim lighting, and maintained fixation on a small (0.35 deg) black central dot. After a random delay from the observer initiating the trial, the stimulus was displayed for \(167~\mathrm{ms}\) . Then a thin rotatable white bar \((0.05\times 5\) deg with a gaussian profile) was presented at the fixation point with random orientation, and observers matched its orientation to that of the target by mouse control. In the first two experiments, the orientation of the two flankers was yoked, while in the third, one flanker was always \(+15^{\circ}\) (clockwise) while the other varied from \(- 45^{\circ}\) to \(+45^{\circ}\) . In the second experiment, the target- flanker distance varied, being 5.5, 7.5, 11.0 and 16.6 deg, leading to Bouma ratios of 0.21, 0.27, 0.4, 0.6.
+
+Ten observers participated in the first experiment, five in the second, thirteen in the third. They contributed for a total of 10699 trials for the first experiment, 14377 for the second (spread across the four flanker- target distances) and 16574 for the last.
+
+<--- Page Split --->
+
+## Data analysis
+
+Responses occurred out from the range between 0.5 and 3 seconds after the stimulus offset were removed (for a total of \(15.9\%\) trials across the 3 experiments), as were responses with reproduction error greater than \(35^{\circ}\) ( \(6.9\%\) of trials).
+
+For each target and relative orientation of the flanker, we calculated the average constant error (bias, positive meaning clockwise) and scatter. We then averaged the values for the two targets. Bias functions were fitted by a derivative of gaussian function, which can be considered to be a gaussian of width \(s\) multiplied by a straight line of slope a [or w], which can be considered the weighting given to the flankers: 1 means the flankers are weighted equally to the target. Bias is given by:
+
+\[B = a\cdot (\theta -m)\exp \Big(-\frac{(\theta -m)^2}{s^2}\Big) + b \quad (eq. 18)\]
+
+Where \(\theta\) is orientation difference, \(m\) the centre, and \(b\) the vertical offset of the function. \(a\) , \(b\) and \(m\) were free to vary.
+
+Scatter \((S)\) was defined as the average root variance in each condition. The variation with orientation a gaussian function in the form:
+
+\[S = a\cdot \exp \Big(-\frac{(\theta - m)^2}{s^2}\Big) + b \quad (eq. 19)\]
+
+Where \(b\) is the baseline at high orientation differences and \(a\) is the amplitude of the Gaussian. As Bias and Scatter likely originate from the same process, we yoked the parameter \(s\) to best fit both curves.
+
+## REFERENCES
+
+1 Bouma, H. Interaction effects in parafoveal letter recognition. Nature 226, 177- 178, doi:10.1038/226177a0 (1970).
+2 Bouma, H. Visual interference in the parafoveal recognition of initial and final letters of words. Vision Res 13, 767- 782, doi:10.1016/0042- 6989(73)90041- 2 (1973).
+3 Pelli, D. G. & Tillman, K. A. The uncrowded window of object recognition. Nat Neurosci 11, 1129- 1135, doi:10.1038/nn.2187 (2008).
+4 Strasburger, H., Rentschler, I. & Juttner, M. Peripheral vision and pattern recognition: a review. J Vis 11, 13, doi:10.1167/11.5.13 (2011).
+
+<--- Page Split --->
+
+5 Whitney, D. & Levi, D. M. Visual crowding: a fundamental limit on conscious perception and object recognition. Trends Cogn Sci 15, 160- 168, doi:10.1016/j.tics.2011.02.005 (2011).6 Parkes, L., Lund, J., Angelucci, A., Solomon, J. A. & Morgan, M. Compulsory averaging of crowded orientation signals in human vision. Nat Neurosci 4, 739- 744, doi:10.1038/89532 (2001).7 Balas, B., Nakano, L. & Rosenholtz, R. A summary- statistic representation in peripheral vision explains visual crowding. J Vis 9, 13 11- 18, doi:10.1167/9.12.13 (2009).8 Levi, D. M. & Carney, T. Crowding in peripheral vision: why bigger is better. Curr Biol 19, 1988- 1993, doi:10.1016/j.cub.2009.09.056 (2009).9 Greenwood, J. A., Bex, P. J. & Dakin, S. C. Crowding changes appearance. Curr Biol 20, 496- 501, doi:10.1016/j.cub.2010.01.023 (2010).10 Freeman, J. & Simoncelli, E. P. Metamers of the ventral stream. Nat Neurosci 14, 1195- 1201, doi:10.1038/nn.2889 (2011).11 Nazir, T. A. Effects of lateral masking and spatial precueing on gap- resolution in central and peripheral vision. Vision Res 32, 771- 777, doi:10.1016/0042- 6989(92)90192- I (1992).12 Kooi, F. L., Toet, A., Tripathy, S. P. & Levi, D. M. The effect of similarity and duration on spatial interaction in peripheral vision. Spat Vis 8, 255- 279, doi:10.1163/156856894x00350 (1994).13 Kennedy, G. J. & Whitaker, D. The chromatic selectivity of visual crowding. J Vis 10, 15, doi:10.1167/10.6.15 (2010).14 Manassi, M., Sayim, B. & Herzog, M. H. When crowding of crowding leads to uncrowding. J Vis 13, 10, doi:10.1167/13.13.10 (2013).15 Levi, D. M. Crowding- an essential bottleneck for object recognition: a mini- review. Vision Res 48, 635- 654, doi:10.1016/j.visres.2007.12.009 (2008).16 Chopin, A. & Mamassian, P. Predictive properties of visual adaptation. Curr Biol 22, 622- 626, doi:10.1016/j.cub.2012.02.021 (2012).17 Cicchini, G. M., Anobile, G. & Burr, D. C. Compressive mapping of number to space reflects dynamic encoding mechanisms, not static logarithmic transform. Proc Natl Acad Sci U S A 111, 7867- 7872, doi:10.1073/pnas.1402785111 (2014).18 Fischer, J. & Whitney, D. Serial dependence in visual perception. Nat Neurosci 17, 738- 743, doi:10.1038/nn.3689 (2014).19 Pascucci, D. et al. Laws of concatenated perception: Vision goes for novelty, decisions for perseverance. PLoS Biol 17, e3000144, doi:10.1371/journal.pbio.3000144 (2019).20 Helmholtz, H. v. Handbuch der physiologischen Optik. (Voss, 1867).21 Gregory, R. L. Eye and brain; the psychology of seeing. (McGraw- Hill, 1966).22 Liberman, A., Fischer, J. & Whitney, D. Serial dependence in the perception of faces. Curr Biol 24, 2569- 2574, doi:10.1016/j.cub.2014.09.025 (2014).23 Taubert, J., Van der Burg, E. & Alais, D. Love at second sight: Sequential dependence of facial attractiveness in an on- line dating paradigm. Sci Rep 6, 22740, doi:10.1038/srep22740 (2016).24 Burr, D. & Cicchini, G. M. Vision: efficient adaptive coding. Curr Biol 24, R1096- 1098, doi:10.1016/j.cub.2014.10.002 (2014).
+
+<--- Page Split --->
+
+25 Cicchini, G. M., Mikellidou, K. & Burr, D. C. The functional role of serial dependence. Proc Biol Sci 285, doi:10.1098/rspb.2018.1722 (2018).26 Kording, K. P. et al. Causal inference in multisensory perception. PLoS One 2, e943, doi:10.1371/journal.pone.0000943 (2007).27 Ernst, M. O. & Banks, M. S. Humans integrate visual and haptic information in a statistically optimal fashion. Nature 415, 429- 433, doi:10.1038/415429a (2002).28 Alais, D. & Burr, D. The ventriloquist effect results from near- optimal bimodal integration. Curr Biol 14, 257- 262, doi:10.1016/j.cub.2004.01.029 (2004).29 Rosenholtz, R., Yu, D. & Keshvari, S. Challenges to pooling models of crowding: Implications for visual mechanisms. J Vis 19, 15, doi:10.1167/19.7.15 (2019).30 Field, D. J., Hayes, A. & Hess, R. F. Contour integration by the human visual system: evidence for a local "association field". Vision Res 33, 173- 193, doi:10.1016/0042- 6989(93)90156- q (1993).31 Cicchini, G. M., Benedetto, A. & Burr, D. C. Perceptual history propagates down to early levels of sensory analysis. Curr Biol 31, 1245- 1250 e1242, doi:10.1016/j.cub.2020.12.004 (2021).32 Jazayeri, M. & Shadlen, M. N. Temporal context calibrates interval timing. Nat Neurosci 13, 1020- 1026, doi:10.1038/nn.2590 (2010).33 Cicchini, G. M., Arrighi, R., Cecchetti, L., Giusti, M. & Burr, D. C. Optimal encoding of interval timing in expert percussionists. J Neurosci 32, 1056- 1060, doi:10.1523/JNEUROSCI.3411- 11.2012 (2012).34 Manassi, M. & Whitney, D. Multi- level Crowding and the Paradox of Object Recognition in Clutter. Curr Biol 28, R127- R133, doi:10.1016/j.cub.2017.12.051 (2018).35 He, S., Cavanagh, P. & Intriligator, J. Attentional resolution and the locus of visual awareness. Nature 383, 334- 337, doi:10.1038/383334a0 (1996).36 Bulakowski, P. F., Post, R. B. & Whitney, D. Visuomotor crowding: the resolution of grasping in cluttered scenes. Front Behav Neurosci 3, 49, doi:10.3389/neuro.08.049.2009 (2009).37 Banks, W. P., Larson, D. W. & Prinzmetal, W. Asymmetry of visual interference. Percept Psychophys 25, 447- 456, doi:10.3758/bf03213822 (1979).
+
+<--- Page Split --->
diff --git a/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3_det.mmd b/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..7946f66f1299f646e7a1226db3837ab158c453ee
--- /dev/null
+++ b/preprint/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3/preprint__022065845b0149dd1bde836e14da3448f70c4603767a53533c6448baf134c8c3_det.mmd
@@ -0,0 +1,403 @@
+<|ref|>title<|/ref|><|det|>[[44, 106, 933, 175]]<|/det|>
+# Crowding results from optimal integration of visual targets with contextual information
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 712, 260]]<|/det|>
+Guido Marco CicchiniConsiglio Nazionale delle Ricerche https://orcid.org/0000- 0002- 3303- 0420
+
+<|ref|>text<|/ref|><|det|>[[44, 263, 652, 330]]<|/det|>
+Giovanni D'ErricoCNR Neuroscience Institute https://orcid.org/0000- 0002- 0491- 581XDavid Burr (Dave@in.cnr.it)University of Florence https://orcid.org/0000- 0003- 1541- 8832
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 371, 101, 388]]<|/det|>
+## Article
+
+<|ref|>title<|/ref|><|det|>[[44, 409, 135, 427]]<|/det|>
+# Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 446, 301, 465]]<|/det|>
+Posted Date: March 1st, 2022
+
+<|ref|>text<|/ref|><|det|>[[44, 485, 473, 504]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 1296243/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 521, 910, 565]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 600, 914, 644]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on September 30th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 33508- 1.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[155, 88, 847, 164]]<|/det|>
+# Crowding results from optimal integration of visual targets with contextual information
+
+<|ref|>text<|/ref|><|det|>[[153, 221, 844, 244]]<|/det|>
+Guido Marco Cicchini1, Giovanni D'Errico1 and David C. Burr1,2
+
+<|ref|>text<|/ref|><|det|>[[150, 262, 805, 333]]<|/det|>
+1. Institute of Neuroscience, CNR, via Moruzzi, 1, 56124 – Pisa (ITALY)
+2. Department of Neurosciences, Psychology, Drug Research and Child Health, University of Florence, viale Pieraccini, 6 – 50139 Firenze (ITALY)
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 376, 210, 392]]<|/det|>
+## ABSTRACT
+
+<|ref|>text<|/ref|><|det|>[[118, 407, 870, 767]]<|/det|>
+Crowding is the inability to recognize peripheral objects in clutter, usually considered a fundamental low- level bottleneck to object recognition. Here we advance and test an alternative hypothesis, that crowding, like “serial dependence”, results from optimizing strategies that exploit redundancies in natural scenes. This notion leads to several testable predictions: (1) crowding should be greatest for unreliable targets and reliable flankers; (2) crowding- induced biases should be maximal when target and flankers have similar orientations, falling off for differences around \(20^{\circ}\) ; (3) flanker interference should be associated with higher precision in orientation judgements, leading to lower overall error rate; (4) effects should be maximal when the orientation of the target is near that of the average of the flankers, rather than to that of individual flankers. All these effects were verified, and well simulated with ideal- observer models that maximize performance. The results suggest that while crowding can impact strongly on object recognition, it is best understood not as a processing bottleneck, but as a consequence of efficient exploitation of the spatial redundancies of the natural world.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[120, 86, 255, 102]]<|/det|>
+## INTRODUCTION
+
+<|ref|>text<|/ref|><|det|>[[118, 117, 874, 294]]<|/det|>
+Crowding is the inability to recognize and identify objects in clutter, despite their being clearly visible, and recognizable when presented in isolation1 (see examples in Figure 1A). It is particularly elevated in the periphery, scaling linearly with eccentricity, such that the minimal spacing between targets and flanking elements for uncrowded vision is equal to about half the eccentricity (Bouma's law2). Crowding impacts on many important daily tasks, such as face recognition and reading (for reviews see3,4,5), to the extent it has been considered a major bottleneck to object recognition.
+
+<|ref|>text<|/ref|><|det|>[[118, 307, 866, 510]]<|/det|>
+Most popular current models of crowding involve some form of compulsory pooling (or substitution) of targets with flankers. For example, Parkes and colleagues6 showed that while the orientation of a single line cannot be determined when embedded in flankers, it does influence the perceived orientation of the ensemble: hence it is merged with the flankers, rather than suppressed. This is reinforced by several studies showing that the targets can take on characteristics of the flanker stimuli7- 9. Pelli and Tillmann3 suggest that the compulsory integration occurs in higher cortical areas, such as V4, which have large receptive fields, appropriately sized to account for Bouma's law (see also10).
+
+<|ref|>text<|/ref|><|det|>[[118, 523, 870, 727]]<|/det|>
+However, compulsory integration does not explain all the known facts about crowding. For example, flankers that are similar in size, colour or orientation cause more crowding than dissimilar ones11- 13. More difficult to explain are the recent demonstrations of Herzog and colleagues14 of "uncrowding", where the addition of extra flanking stimuli around the flankers can reduce drastically their crowding effect, particularly if the extra flankers group with the original flankers to form coherent objects. These data do not fit easily with compulsory integration, even with appropriate linear filtering, which could in principle account for other effects, such as orientation or size selectivity.
+
+<|ref|>text<|/ref|><|det|>[[118, 740, 877, 915]]<|/det|>
+Crowding has been studied for decades, and usually considered to be a defect in the system, "an essential bottleneck to object perception"15. Certainly, it impacts heavily on object recognition in tasks like or face recognition: but is it possible that it may reflect processes that are in principle advantageous to perception? Perception is strongly affected by contextual information, particularly temporal context, where recent and longer term perceptual history has been shown to exert a major influence on current perception16- 19. While the role of context and experience has been appreciated for some time20,21, it has
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 84, 877, 260]]<|/det|>
+become particularly topical in recent years within the framework of Bayesian analysis. This approach has revealed an interesting phenomenon termed "serial dependence", where the appearance of many important attributes of a stimulus (including orientation, numerosity, facial identity, beauty etc) are biased towards previously viewed stimuli17,18,22,23. Counterintuitively, these consistent biases in perception have been shown to reflect an efficient perceptual strategy, exploiting temporal redundancies in natural viewing to reduce overall reproduction errors, despite the biases24,17,25.
+
+<|ref|>text<|/ref|><|det|>[[117, 275, 875, 686]]<|/det|>
+Could crowding also be a consequence of efficient integration processes that exploit spatial (rather than temporal) redundancies to improve performance? We investigate this possibility by studying crowding with a similar paradigm used for serial dependence studies. If, like serial dependence, crowding is a by- product of efficient redundancy- reducing mechanisms, it should display several specific signature characteristics. One is that crowding- induced biases should be stronger for targets that are unreliably perceived, and for flankers that are reliably perceived. In addition, crowding should follow the signature pattern seen in serial dependence, highest when the orientations of target and flankers are similar, then steadily falling off. We verify these characteristics qualitatively and qualitatively, and show that crowding, while leading to biases, also improves overall performance. The results fit well with models simulating intelligent combination of signals from a small receptive field centred on the target with signals from a much larger integration region, following the same rules that govern serial dependence. On this view crowding should not be considered a defect, or bottleneck, in the system, but the unavoidable consequence of efficient exploitation of spatial redundancies of the natural world.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[133, 90, 850, 304]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[118, 333, 179, 346]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[118, 347, 878, 400]]<|/det|>
+a) Crowding is a visual phenomenon where items that can be easily identified in isolation are not identifiable if surrounded by similar items. The P and hand symbol on the right are difficult to recognize, while fixating the central red dots.
+
+<|ref|>text<|/ref|><|det|>[[118, 393, 873, 473]]<|/det|>
+b) Stimuli employed in this experiment. Observers judged the orientation of a peripheral target (the central oval), which was flanked above and below by oval stimuli. Two conditions were tested: a rounded target with elongated flankers (Low reliability target, high reliability flankers, at left) or an elongated target with rounded ovals (at right). In the main condition the centre-to-centre distance of flankers and targets was 5.5 deg, and eccentricity 26 degrees, leading to a Bouma ratio of 0.21.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 515, 195, 531]]<|/det|>
+## RESULTS
+
+<|ref|>text<|/ref|><|det|>[[117, 546, 881, 855]]<|/det|>
+To test if visual crowding follows the rules of optimal integration, which well describe serial dependence \(^{18,25}\) , we measured crowding with an orientation reproduction task. Participants reproduced the orientation of oval stimuli, which were either elongated (aspect ratio 1: 2.8) or rounded (aspect 1: 1.4). Targets were presented \(26^{\circ}\) to the right of fixation, and vertically flanked by similar oval stimuli, elongated if the target was rounded, and vice versa (see Fig. 1B). The orientation of the target was either \(35^{\circ}\) or \(55^{\circ}\) (at random). The orientations of the two flankers were yoked together, and varied randomly over a range of \(\pm 45^{\circ}\) from target orientation. The clear prediction from the efficient integration model \(^{24}\) (see Eqn 10) is that the effects of crowding will be far stronger for the rounded targets and elongated flankers than vice versa. The reasons are explained formally the modelling section, but the intuition is that the rounded stimuli have less reliable orientation signals and therefore benefit more from integration with contextual information, especially if it is reliable.
+
+<|ref|>text<|/ref|><|det|>[[119, 868, 875, 913]]<|/det|>
+Figure 2A shows the bias in target reproduction as a function of difference in flanker orientation. Clearly, the rounded targets show the strongest contextual effects of crowding,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 85, 870, 338]]<|/det|>
+with peak biases varying by up to \(\pm 5.1^{\circ}\) , compared with \(\pm 1.9^{\circ}\) for the elongated targets. Furthermore, the pattern of bias follows closely that predicted and observed in serial dependence studies \(^{25}\) , varying non- linearly with difference between target and flanker orientation, increasing to a maximum around \(\pm 20^{\circ}\) , then decreasing. These data are well fit by derivative of gaussian functions (eqn. 15, light- coloured lines), commonly used in serial dependence studies \(^{18}\) , and expected from a causal inference model (see modelling section \(^{26}\) ). The dark lines show the predictions of another Bayesian model (eqn. 10), which has also proven successful with serial dependence data \(^{17,25}\) . While the models are detailed later, it is worth noting that they are almost entirely anchored by data, down to a simple scaling factor, suggesting that the data are consistent with ideal behaviour.
+
+<|ref|>image<|/ref|><|det|>[[131, 359, 880, 544]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[119, 569, 180, 582]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[118, 583, 880, 770]]<|/det|>
+a) Average response bias (response minus target orientation) as a function of the orientation of two identical flankers. Low reliability (rounded) targets in blue, high reliability (elongated) in red. Error bars show \(\pm 1\) SEM. Dark lines show predictions from an ideal-observer Bayesian model which scales the action of flankers according to their reliability and orientation difference (Eqn 10 of model section). Light blue and red curves show predictions for the causal inference model that doses flanker and target information according to their reliability and the probability of originating from a common cause (Eqn 15 of model section).
+b) Response scatter as a function of the orientation of two identical flankers, together with model predictions. Colour coding as in A.
+c) Response Scatter error plotted against bias errors for the two conditions. Dashed circles indicate regions with identical RMSE error (given by the Pythagorean sum of the two types of error). RMSE varies with orientation, and is least around \(0^{\circ}\) , when target and flankers coincide.
+
+<|ref|>text<|/ref|><|det|>[[118, 808, 857, 905]]<|/det|>
+Another important prediction is that the contextual effects should improve performance. Figure 2B plots reproduction scatter (root- variance of reproduction trials) as a function of orientation difference. As expected, at all orientation differences, these are lower for the elongated than the rounded targets. However, for both targets, particularly the rounded
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 879, 261]]<|/det|>
+targets, the scatter decreased as the difference between target and flanker orientation decreased. Figure 2C plots scatter against bias, with points connected to follow the change in orientation. On this plot, total error (the Pythagorean sum of scatter and bias) is the radial distance from the origin. For the points with flanker orientation most distant from the target (near \(\pm 45^{\circ}\) ), the total error is around \(15^{\circ}\) . Between these extremes, total error falls off, despite the constant bias. When the flankers and targets have similar orientations, the error falls to around \(11^{\circ}\) , evidence that “crowding” improves overall performance.
+
+<|ref|>text<|/ref|><|det|>[[117, 275, 880, 660]]<|/det|>
+If the effects shown in Figure 2 represent visual crowding, they should depend on critical spacing between target and flankers, and follow Bouma's law1. We therefore measured the effects as a function of target- flanker spacing, for 5 participants. Figure 3 shows the data for the rounded targets with elongated flankers (which show the strongest effects). For the two smallest spacings (5.5 and 7.5 deg), bias showed the characteristic S- shaped dependency on the orientation of the flankers. For the larger spacings (11.0 and 16.6 deg), however, the effect was much reduced and even inverted at 11 deg. As before, the curves are fit by a derivative of gaussian function (eqn 18), which is the product of a linear regression (illustrated by dashed line in Figure 3A) and a gaussian. The best fitting slope of this regression is an estimate of the weight given to the flankers when judging orientation. Figure 3B plots the fitted weight as a function of target- flanker spacing (lower abscissa), with the upper abscissa showing the Bouma constant, the distance between target and flanker centres divided by the eccentricity (26 deg). The weight drops from 0.5 to 0 for Bouma constants between 0.3 and 0.4, broadly in line with the literature, suggesting that the effects observed here relate to crowding.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[170, 130, 781, 350]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[119, 382, 179, 395]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[118, 395, 863, 475]]<|/det|>
+a) Response bias as function of flanker orientation for various target-flanker distances leading to four different Bouma ratios (distance between flanker and target centres divided by eccentricity. Data are fit with a derivative of gaussian function with free parameters (Eqn 18).
+b) Weight of the flankers (maximal slope of the curves in panel A) as a function of the Bouma ratio (colour-code as before). Error bars show ±1 SEM.
+
+<|ref|>text<|/ref|><|det|>[[118, 549, 866, 750]]<|/det|>
+The results so far show that integration is not obligatory, but depends on the reliability of both target and flankers, and on their orientation similarity. A remaining question is how the flankers integrate with the target: each separately, or after combination with each other. Figure 4 illustrates two possibilities (see also modelling section). One is feedforward model where the target integrates independently with low- level, high- resolution neural representations of each of the flankers. The other depicts integration with a broader representation including both flankers, potentially implemented through recurrent feedback.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[173, 88, 832, 364]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[119, 386, 180, 399]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[118, 400, 876, 540]]<|/det|>
+a) Rationale of Experiment 2. Flankers could either act independently on the target (as illustrated by purple arrows in top left panel), or first pooled into a larger RF, which in turn biases the target (illustrated by the large yellow circle and arrow in bottom left panel).
+b) Predictions for the two hypotheses. If the flankers act independently, when one flanker is locked at \(+15^{\circ}\) and the other free to vary, the pattern should be similar to that of the main experiment (centre close to \(0^{\circ}\) ), but raised because of the action of the locked flanker (purple curve). If flankers are first integrated at a more global stage, maximal effect is expected when all the elements in the larger operator average \(0^{\circ}\) . Since one of the flankers is locked at \(+15^{\circ}\) , this occurs when the other flanker is \(-15^{\circ}\) , leading to a leftward shift of the curve of the main experiment (yellow curve)
+
+<|ref|>text<|/ref|><|det|>[[118, 577, 881, 884]]<|/det|>
+To distinguish between these two plausible possibilities, we measured target bias with the orientation of the two flankers varying independently. Specifically, one flanker (randomly top or bottom) was always oriented \(+15^{\circ}\) from the target, while the other varied randomly over the range. The logic is that the gaussian function windowing the contextual effect should be centred where the orientations of target and context coincide. If the integration occurs directly between the target and individual flankers, then the maximum effects should occur when the variable flanker coincides with the target; on the other hand, if the integration is with a broader representation including both flankers, maximum integration should occur when the flanker mean is zero, which occurs when the variable flanker is \(-15^{\circ}\) . These predictions are illustrated in Figure 4B: note that the individual flanker effect also predicts the curve to be higher at all flanker orientations, as the fixed flanker will exert a constant effect at all orientations of the variable flanker.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 85, 872, 288]]<|/det|>
+The results for the rounded targets with elongated flankers are shown figure 5A. The biases clearly follow the signature pattern, well fit by a derivative of gaussian function. The centre of the function is \(- 12.1^{\circ}\) , closer to the \(15^{\circ}\) predicted by integration with the average orientation of the flankers, than \(0^{\circ}\) predicted by the individual flanker model. The mean height of the function is \(0.5^{\circ}\) , close to that observed in the previous experiment \((- 0.9^{\circ})\) , while the individual-flanker integration model predicts a constant average bias \(4.7^{\circ}\) . Figure 5B shows the scatter for this experiment, which was reduced over the region of bias, well described by an inverted Gaussian.
+
+<|ref|>image<|/ref|><|det|>[[133, 319, 880, 500]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[120, 535, 181, 549]]<|/det|>
+Figure 5.
+
+<|ref|>text<|/ref|><|det|>[[118, 555, 870, 653]]<|/det|>
+a) Biasing errors as function of a single flanker orientation, while the other flanker was locked at \(+15^{\circ}\) . Colours and conventions as for Figure 2. Thick dark lines refer to the ideal observer model (Eqn 10), thick light blue lines to the causal inference model (Eqn 15). Thin dashed lines show best-fitting derivative of gaussian, with all parameters free to vary (Eqn 18).
+b) Response Scatter as a function of the variable flanker orientation. Conventions as in panel a.
+c) Histogram of the centres of the gaussian derivative for 1000 bootstrap fits.
+
+<|ref|>text<|/ref|><|det|>[[118, 693, 875, 842]]<|/det|>
+To test significance, we bootstrapped the data 1000 times (sampling with replacement) and measured the centre of the gaussian derivative on each iteration. The results plotted in the histogram of Figure 5C show that on only 16 out of 1000 iterations (1.6%) was the centre closer to \(0^{\circ}\) (individual flanker prediction) than to \(- 15^{\circ}\) (joint-flanker prediction). This leads to a likelihood ratio (Bayes factor) of \(984 / 16 = 61.5\) , strong evidence in favour of the joint-flanker- integration model.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[119, 86, 225, 102]]<|/det|>
+## MODELLING
+
+<|ref|>text<|/ref|><|det|>[[118, 117, 864, 268]]<|/det|>
+We propose two plausible models to explain the pattern of data. Both are motivated by principles of "optimal cue integration" commonly used in multi- sensory perception \(^{27,28}\) , which predict optimal combination of information from multiple sources after appropriate weighting to minimize overall root- mean- square error. The first is based on an ideal- observer model successfully used to model serial dependence \(^{17}\) , the second on a "causal- inference" model of multi- sensory integration \(^{26}\) . Both models predict well the data.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 315, 245, 332]]<|/det|>
+## Ideal Observer
+
+<|ref|>text<|/ref|><|det|>[[119, 347, 810, 393]]<|/det|>
+Total RMS error \((E)\) can be decomposed into bias \((B)\) and precision (scatter standard deviation: \(S\) ), whose squares sum to give total squared error:
+
+<|ref|>equation<|/ref|><|det|>[[178, 405, 840, 428]]<|/det|>
+\[E = \sqrt{B^{2} + S^{2}} \quad (eq.1)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 442, 870, 514]]<|/det|>
+The ideal responses \((R)\) in a pooling model can be expressed as a linear weighted combination of internal representation of target \((T)\) and flankers \((F_{1}\) and \(F_{2}\) ), each weighted by \(w_{1}\) and \(w_{2}\) .
+
+<|ref|>equation<|/ref|><|det|>[[178, 527, 840, 548]]<|/det|>
+\[R = w_{1}F_{1} + w_{2}F_{2} + (1 - w_{1} - w_{2})T \quad (eq.2)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 561, 877, 606]]<|/det|>
+As the two flankers of this study had the same aspect ratio they should be weighted equally, \((w_{1} = w_{2} = w)\) , so Eqn. 2 simplifies to:
+
+<|ref|>equation<|/ref|><|det|>[[178, 620, 840, 641]]<|/det|>
+\[R = wF_{1} + wF_{2} + (1 - 2w)T \quad (eq.3)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 647, 872, 692]]<|/det|>
+The mean of the responses \((\mu_{R})\) is a simple linear combination of the means of flankers and target \((\mu_{1}, \mu_{2}\) and \(\mu_{T}\) ).
+
+<|ref|>equation<|/ref|><|det|>[[178, 705, 840, 726]]<|/det|>
+\[\mu_{R} = w\mu_{1} + w\mu_{2} + (1 - 2w)\mu_{T} = w(\mu_{1} + \mu_{2}) + (1 - 2w)\mu_{T} \quad (eq.4)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 732, 872, 804]]<|/det|>
+Bias is the difference between the mean estimated response \((\mu_{R})\) and real orientation, \(x_{T}\) ; \(B = \mu_{R} - x_{T}\) . Using equation 4 and considering that the average target representation \((\mu_{T})\) should be unbiased and coincide with target \((\mu_{T} = x_{T})\) it follows that:
+
+<|ref|>equation<|/ref|><|det|>[[178, 817, 840, 839]]<|/det|>
+\[B = \mu_{R} - x_{T} = w(\mu_{1} + \mu_{2}) + \mu_{T} - 2w\mu_{T} - x_{T} = w(\mu_{1} + \mu_{2} - 2\mu_{T}) \quad (eq.5)\]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 866, 156]]<|/det|>
+The term \(\mu_{1} + \mu_{2} - 2\mu_{T}\) can be rearranged as \(2((\mu_{1} + \mu_{2}) / 2 - \mu_{T})\) which is twice the distance between the average of the flanker representations, \((\mu_{1} + \mu_{2}) / 2\) , and the target representation \(\mu_{T}\) . For convenience we define:
+
+<|ref|>equation<|/ref|><|det|>[[179, 170, 840, 191]]<|/det|>
+\[d = (\mu_{1} + \mu_{2}) / 2 - \mu_{T} \quad (eq. 6)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 205, 320, 222]]<|/det|>
+so that Eqn. 5 becomes:
+
+<|ref|>equation<|/ref|><|det|>[[179, 237, 840, 258]]<|/det|>
+\[B = w(\mu_{1} + \mu_{2} - 2\mu_{T}) = 2wd \quad (eq. 7)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 270, 877, 315]]<|/det|>
+Variance of the linear combination of the flankers and target is itself a linear combination of the flanker and target variances \((\sigma_{F}^{2}\) and \(\sigma_{T}^{2}\) ) with the squared coefficients
+
+<|ref|>equation<|/ref|><|det|>[[179, 328, 840, 350]]<|/det|>
+\[S^{2} = w^{2}\sigma_{F}^{2} + w^{2}\sigma_{F}^{2} + (1 - 2w)^{2}\sigma_{T}^{2} \quad (eq. 8)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 363, 614, 382]]<|/det|>
+From Eqn 1, 7 and 8 it follows that RMSE can be written as:
+
+<|ref|>equation<|/ref|><|det|>[[179, 394, 840, 450]]<|/det|>
+\[\begin{array}{l}{E = 4w^{2}d^{2} + w^{2}\sigma_{F}^{2} + w^{2}\sigma_{F}^{2} + (1 - 2w)^{2}\sigma_{T}^{2}}\\ {= 4w^{2}d^{2} + w^{2}\sigma_{F}^{2} + w^{2}\sigma_{F}^{2} + (1 - 4w + 4w^{2})\sigma_{T}^{2}} \end{array} \quad (eq. 9)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 462, 870, 514]]<|/det|>
+Since RMSE is a function of second order of \(w\) , it is minimized when \(w = \frac{- b}{2a}\) , so the optimal weight \((w_{opt})\) is obtained at:
+
+<|ref|>equation<|/ref|><|det|>[[179, 528, 850, 561]]<|/det|>
+\[w_{opt} = -\frac{1}{2}\frac{-4\sigma_{T}^{2}}{4\sigma_{F}^{2} + 2\sigma_{F}^{2} + 4d^{2}} = \frac{\sigma_{T}^{2}}{2\sigma_{F}^{2} + \sigma_{F}^{2} + 2d^{2}} \quad (eq. 10)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 575, 877, 675]]<|/det|>
+This equation has much in common with that of all Bayesian- like integrations used in multisensory research and serial dependence: the weight depends directly on target variance \(\sigma_{T}^{2}\) , so targets of low reliability (inverse variance) benefit more from integration, resulting in higher weighting to the flankers. Increase in flanker variance \((\sigma_{F}^{2})\) has the opposite effect.
+
+<|ref|>text<|/ref|><|det|>[[118, 686, 880, 837]]<|/det|>
+The term \(2d^{2}\) is fundamental for the signature function, as the weight of the flankers will decrease with angular difference between target and average flanker orientation. This is reminiscent of serial dependence effects, and ensures that contextual cues are used only if they are plausibly similar to the target \(^{24,17,25}\) . Importantly, the point that will ensure maximal weight of the flankers is when the target coincides with the average of the flankers (i.e. \(d^{2} = 0\) ).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 875, 157]]<|/det|>
+Together the behaviour of Eqns 3 and 10 define the ideal observer behaviour. In order to accommodate suboptimal behaviour we introduce a scaling factor \((\alpha)\) which multiplies \(w_{opt}\) and sets the actual weight of the flankers:
+
+<|ref|>equation<|/ref|><|det|>[[178, 171, 850, 192]]<|/det|>
+\[R = \alpha w_{opt}F_1 + \alpha w_{opt}F_2 + (1 - 2\alpha w_{opt})T \quad [eq. 11]\]
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 239, 320, 256]]<|/det|>
+## Causal Inference Model
+
+<|ref|>text<|/ref|><|det|>[[117, 271, 880, 420]]<|/det|>
+An alternative model prescribes that the optimal blend of information can be obtained behaving as if the sources of information originated form one cause times the probability that two sources of information originate from the same cause26. Within this framework the maximal interaction between cues occurs when the two sources coincide, where the weight assigned of is the well known result known in sensory integration literature27,28 (see also eq. 10):
+
+<|ref|>equation<|/ref|><|det|>[[178, 433, 850, 469]]<|/det|>
+\[w_{A}^{max} = \frac{\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}} \quad [eq. 12]\]
+
+<|ref|>text<|/ref|><|det|>[[118, 481, 880, 556]]<|/det|>
+The probability of the two sources originating from a common cause can be calculated using Bayes' Theorem as demonstrated in26. Assuming gaussian probability distribution functions (with centres at \(\mu_{A}\) and \(\mu_{B}\) and variances \(\sigma_{A}^{2}\) and \(\sigma_{B}^{2}\) ), the solution is soluable analytically26:
+
+<|ref|>equation<|/ref|><|det|>[[178, 567, 850, 602]]<|/det|>
+\[p(A,B|C = 1)\propto \exp \left(-\frac{1}{2}\frac{(\mu_{A} - \mu_{B})^{2}\sigma_{B}^{2} + (\mu_{A} - \mu_{P})^{2}\sigma_{B}^{2} + (\mu_{B} - \mu_{P})^{2}\sigma_{A}^{2}}{\sigma_{A}^{2}\sigma_{B}^{2} + \sigma_{A}^{2}\sigma_{P}^{2} + \sigma_{B}^{2}\sigma_{P}^{2}}\right) \quad [eq. 13]\]
+
+<|ref|>text<|/ref|><|det|>[[118, 614, 853, 715]]<|/det|>
+This is function of the variances of the two sources \((\sigma_{A}^{2}\) and \(\sigma_{B}^{2}\) ), the centres of the representations \((\mu_{A}\) and \(\mu_{B}\) ) and their distance, and the a- prior likelihood of there being one cause (itself gaussian and characterized by mean and variance \(\mu_{P}\) and \(\sigma_{P}^{2}\) ). If no prior knowledge is available \((\sigma_{P}^{2} \to \infty)\) Eqn 13 simplifies to
+
+<|ref|>equation<|/ref|><|det|>[[178, 727, 850, 762]]<|/det|>
+\[p(A,B|C = 1)\propto \exp \left(-\frac{1}{2}\frac{(\mu_{A} - \mu_{B})^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}}\right) \quad [eq. 14]\]
+
+<|ref|>text<|/ref|><|det|>[[118, 807, 846, 854]]<|/det|>
+This is a gaussian peaking when the distribution of the two cues coincide \((\mu_{A} = \mu_{B})\) and falling off with a space constant related to the sum of their variances \((\sigma_{A}^{2} + \sigma_{B}^{2})\) .
+
+<|ref|>text<|/ref|><|det|>[[118, 867, 855, 913]]<|/det|>
+In the specific case of our experiment we can map the two sources of information to the flanker compound (a gaussian with centre at \(\mu_{F} = (\mu_{1} + \mu_{2}) / 2\) , variance \(\sigma_{F}^{2} / 2\) ) and the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 875, 131]]<|/det|>
+target (assumed gaussian with centre \(\mu_{T}\) , and variance \(\sigma_{T}^{2}\) . Putting together Eqns 12 and 14, the bias (difference between the response and the target) is given by:
+
+<|ref|>equation<|/ref|><|det|>[[120, 141, 848, 179]]<|/det|>
+\[B = w_{F}^{max}p(F,T|C = 1)(\mu_{F} - \mu_{T}) = \frac{\sigma_{F}^{2}}{\sigma_{F}^{2} + \sigma_{T}^{2}}\exp \left(-\frac{1}{2}\frac{(\mu_{F} - \mu_{T})^{2}}{\sigma_{F}^{2} + \sigma_{T}^{2}}\right)(\mu_{F} - \mu_{T}) \quad [eq 15]\]
+
+<|ref|>text<|/ref|><|det|>[[118, 191, 703, 209]]<|/det|>
+Which is a derivative of gaussian as a function of flanker orientation \(\mu_{F}\)
+
+<|ref|>text<|/ref|><|det|>[[118, 223, 880, 269]]<|/det|>
+It also follows that response scatter is minimized only when the system considers a common cause likely (Eqn 14), predicting U- shaped (gaussian) plots of Figures 2B and 5B.
+
+<|ref|>text<|/ref|><|det|>[[118, 283, 867, 355]]<|/det|>
+Again, to allow for suboptimal behaviour we introduced two free parameters that regulate the amplitude of the dependency on the flankers \((\beta)\) and the breadth of the region of interaction \((y)\) so that the bias is:
+
+<|ref|>equation<|/ref|><|det|>[[177, 366, 845, 402]]<|/det|>
+\[B = \beta \frac{\sigma_{T}^{2}}{\sigma_{F}^{2} + \sigma_{T}^{2}}\exp \left(-\frac{1}{2}\frac{(\mu_{F} - \mu_{T})^{2}}{\gamma^{2}(\sigma_{F}^{2} + \sigma_{T}^{2})}\right)(\mu_{F} - \mu_{T}) \quad [eq 16]\]
+
+<|ref|>text<|/ref|><|det|>[[118, 414, 860, 511]]<|/det|>
+Interestingly, comparable behaviour is obtained if, instead of constructing a system which multiplies probabilities as in \(^{26}\) , one considers a system that measures the similarity between two distributions via their point- by- point product of the distributions and takes either the peak or area under the distribution.
+
+<|ref|>text<|/ref|><|det|>[[118, 528, 868, 582]]<|/det|>
+The product of gaussians is itself a gaussian, is centred at \((\frac{\mu_{B}\sigma_{A}^{2} + \mu_{A}\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}})\) , has variance \((\frac{\sigma_{A}^{2}\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}})\) and peak at:
+
+<|ref|>equation<|/ref|><|det|>[[177, 597, 850, 631]]<|/det|>
+\[\frac{1}{2\pi\sigma_{A}\sigma_{B}}\exp \left(-\frac{(\mu_{A} - \mu_{B})^{2}}{2(\sigma_{A}^{2} + \sigma_{B}^{2})}\right) \quad [eq. 17]\]
+
+<|ref|>text<|/ref|><|det|>[[118, 644, 872, 789]]<|/det|>
+So the peak embeds the same behaviour of Eqn. 14. It is easy to demonstrate that also the area under the curve follows the same gaussian dependency on the distance between cues as the area of a gaussian is equivalent to the peak (Eqn. 16) times the standard deviation of the curve \((\sqrt{\frac{\sigma_{A}^{2}\sigma_{B}^{2}}{\sigma_{A}^{2} + \sigma_{B}^{2}}})\) and a constant factor \(1 / \sqrt{2\pi}\) all of which are constant once the distributions have known width and thus reduce to a scaling factor.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 833, 236, 850]]<|/det|>
+## Model Fitting
+
+<|ref|>text<|/ref|><|det|>[[118, 866, 877, 911]]<|/det|>
+The predictions of the two modelling approaches are overlayed on the data of Figures 2 and 5 with dark and light colours. To minimize degrees of freedom we derived the values of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[119, 85, 860, 157]]<|/det|>
+sensory reliability from the data of Figure 2b, assuming that the extreme points \((\pm 30^{\circ}\) and \(\pm 45^{\circ}\) ) give baseline data, not influenced by flanker integration: this is 17.1 for rounded targets (blue symbols), and 11.7 for elongated targets (red symbols).
+
+<|ref|>text<|/ref|><|det|>[[118, 170, 875, 399]]<|/det|>
+We implemented the ideal observer model (Eqn. 11) with only a scaling constant \((\alpha)\) , which allows for sub- optimal behaviour. These fits are particularly good for the rounded targets (with largest effects), with \(\mathbb{R}^2\) of 0.97 and 0.74 (for bias and scatter), and 0.24 and 0.60 for elongated targets) and come about assuming \(\alpha = 0.57\) . One of the key features of the ideal observer model is that it reduces RMSE by leveraging on all available information. Thus it predicts the Global Integration of Figure 4, with centres of the Gaussian derivatives close to \(- 15^{\circ}\) . Besides capturing this key feature, the model also provides good quantitative fits to the data of Figure 5a with \(\mathbb{R}^2\) of 0.76 and average fits to those of Figure 5b 0.23 for bias and scatter respectively \((\alpha = 0.32)\) .
+
+<|ref|>text<|/ref|><|det|>[[117, 411, 880, 772]]<|/det|>
+We used the same reliability values from Figure 2b to implement the "optimal causality gating model" \(^{26}\) , the derivative of gaussian function plotted with light colours in Figures 2 and 5. The sensory reliabilities fix both the maximal slope of the curve (see Eqn 12) and the width of the region of interaction (see Eqn 14). Assuming the same sensory precisions as above (17.1 and 11.7 for the two types of stimuli) maximal slopes should be 0.81 and 0.48 for the two conditions, larger than the real data. Also the widths (27.8 and 33.2) are larger than those predicted by Eqn 14 (19 and 16.8). For this reason we allowed two scaling factors, one enabling lower weighting of the context \((\beta)\) and the other modulating the width \((\gamma)\) . Setting \(\beta = 0.54\) and \(\gamma = 1.46\) led to good fits with \(\mathbb{R}^2 = 0.97\) and 0.89 for the low reliability target (bias and scatter curves), and 0.67 and 0.79 for the high reliability target \((\beta = 0.26\) and \(\gamma = 1.97\) ). As with the other model, the prediction in Experiment 2 is for large pooling of all available cues, thus the prediction is that of a centre at \(- 15^{\circ}\) . This model also provides good fits for response bias \((R^2 = 0.89)\) and acceptable fits for response scatter \((R^2 = 0.38, \beta = 0.62\) and \(\gamma = 1.37\) ).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[120, 87, 225, 103]]<|/det|>
+## DISCUSSION
+
+<|ref|>text<|/ref|><|det|>[[118, 118, 878, 503]]<|/det|>
+The results of this study suggest a novel interpretation of visual crowding: that it is a byproduct of efficient Bayesian processes, which lead to improved perceptual performance, minimizing production error. We tested and validated several key predictions of this idea. Firstly, crowding, measured as flanker- induced orientation bias, was greatest when targets had the weakest orientation signals (least reliability) and flankers had the strongest signals, as predicted from most models of optimal cue combination \(^{27,28}\) . The magnitude of the bias varied with the difference of target and flanker orientation, following the predicted nonlinear pattern, increasing to a maximum of around \(15^{\circ}\) , then falling off for larger orientation differences. Importantly, the interaction of the flankers and target was associated with a reduction in response scatter, which led to a reduction in total RMS error, an index of improved performance. Finally, the results suggest that the bias does not result from direct interactions with individual flankers, but from interaction with a representation of the average orientations of the two flankers. All these results were predicted by optimal feature combination principles, and quantitatively well modelled an ideal- observer model that minimizes reproduction errors.
+
+<|ref|>text<|/ref|><|det|>[[117, 515, 875, 902]]<|/det|>
+These results are clearly difficult to reconcile with standard models of obligatory integration \(^{6,29}\) . Passive integration systems may be tweaked to explain the stronger effects for more elongated flankers (such as having more Fourier energy at that orientation), but cannot explain the fall off in crowding effects when the difference exceeds \(15^{\circ}\) . Any basic integrator would necessarily combine orientation energy of all angles, not only similar angles. On the other hand, the flexible integrator models proposed here (Eqns 10 and 15) predict both the pattern and the magnitude of the results. Furthermore, the final experiment suggests that this intelligent orientation- dependent integration is unlikely to occur directly within a higher order cell itself, as the orientation- dependent integration function aligns with the average of two disparate flankers, rather than with each individual flanker. This suggests that the integration is between the target and a broad representation that includes both flankers. Mechanisms operating directly between target and individual flankers (such as the proposed “local association field” \(^{30}\) ) are not consistent with the results of Figure 5, which shows that flankers are first combined with each other before exerting their effects on the target.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 883, 365]]<|/det|>
+Combination of target and a broad representation of both flankers could be implemented in several ways. One physiologically plausible mechanism would be feedback from mid- level areas, such as V4, which have large receptive fields, integrating over a wide area. These cells could contain information of both flankers (as well as the target), which could be fed back to low levels (eg V1) to integrate flexibly with finer representations of the target. Within this framework the fine- grain target information is not lost, but combined with broad contextual information in an optimal manner to improve performance. This is analogous to the process of serial dependence, where representations of perceptual history (often termed Bayesian priors) are generated at mid- to high- levels of analysis, but feed back onto fairly low processing levels31. Similar processes could evoke crowding, integrating over space rather than time.
+
+<|ref|>text<|/ref|><|det|>[[118, 378, 870, 686]]<|/det|>
+The predictions of the crowding behaviour derive from theoretical minimization of total RMS errors, explained in detail in the modelling section, but readily understood intuitively. There are two orthogonal sources of error, bias (average accuracy) and response scatter (precision), which combine by Pythagorean sum to yield total error. Thus although the contextual effects do lead to inaccuracies (biases), these are more than offset by the decrease in response scatter (Fig. 2C). Clearly, if the effects were to increase continuously with orientation, then the bias would become large, and offset the reduction in scatter, leading to increased error: integration is therefore efficient only over a limited range. Note that the efficiency- driven ideal model gives good fits simultaneous to both bias and scatter data with only one free parameter, a scaling factor. This comes out at around 0.57 for the main data and probably reflects other processes in orientation judgements that we did not control for, such as regression to the mean32,33.
+
+<|ref|>text<|/ref|><|det|>[[118, 700, 881, 901]]<|/det|>
+The current experiment shows that under conditions of crowding, information about the target is not necessarily lost. This is consistent with a good deal of previous evidence (see reference34 for review), including studies showing that it can affect the ensemble judgment5, can cause adaptation35 and that crowding induced biases may not affect grasping36. Even more dramatic are the demonstrations that increasing flanker length37 or adding additional flankers14 can decrease or eliminate crowding. Our study employed simple well controlled stimuli to allow quantitative prediction and measurement of crowding- effects, similar to the studies with serial dependence studies. Thus they do not readily relate
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 84, 844, 207]]<|/det|>
+to the clever uncrowding studies of Herzog and colleagues. However, it is not difficult to envisage extensions to the model incorporating grouping principles within the rules of integration, in the spirit of the general principles of our model: flexible, "intelligent" combination of signals, rather than a rigid integration via "rectify and sum" or similar rules10.
+
+<|ref|>text<|/ref|><|det|>[[117, 223, 875, 606]]<|/det|>
+In summary, the current study suggests that crowding may be analogous to serial dependence, pointing to similar function and mechanisms. As serial dependence has been shown to exploit temporal redundancies to maximize performance, crowding may also reflect similar exploitation of redundancies over space. It is worth noting that while the rules governing crowding are flexible, leading to improved performance, crowding remains completely obligatory: no effort of will or deployment of attention can allow us to resolve the crowded objects, or to ignore the contextual effects of the orientated flankers. Indeed, while our proposed pooling process is flexible and "intelligent", it remains automatic, not subject to voluntary control. This is similar to many of the experience- driven perceptual illusions, such as the "hollow mask illusion"21: no effort of will can cause us to see the inside of a hollow mask as concave, we always see the convex face. However, while visual crowding remains an obligatory limitation to object recognition, we conclude that like the effects of temporal context and experience, it is best understood not as a defect or bottleneck of the system, but the consequence of efficient exploitation of spatial redundancies of the natural world.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 690, 209, 705]]<|/det|>
+## METHODS
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 723, 223, 739]]<|/det|>
+## Participants
+
+<|ref|>text<|/ref|><|det|>[[118, 754, 879, 903]]<|/det|>
+Fifteen healthy participants with normal or corrected- to- normal vision were recruited (aged 18- 55 years, mean age = 36, 7 females). Experimental procedures are in line with the declaration of Helsinki and approved by the local ethics committee (Commissione per l'Etica della Ricerca, University of Florence, 7 July 2020). Written informed consent was obtained from each participant, which included consent to process, preserve and publish the data in anonymous form.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[119, 87, 182, 102]]<|/det|>
+## Stimuli
+
+<|ref|>text<|/ref|><|det|>[[117, 118, 876, 528]]<|/det|>
+The stimuli, illustrated in Fig. 1A, were generated with Psychtoolbox for MATLAB (R2016b; MathWorks). They comprised an oval- shaped visual target flanked by oval- shaped upper and lower visual flankers, displayed 26 deg eccentric from the fixation point, with the target close to the horizontal meridian (vertical position was slightly varied from trial to trial to avoid pre- allocation of attention to the target) and flankers 5.5 deg away from the target. Both target and flankers were sketches of oval shapes, defined by 12 dark grey dots (diameter 0.3 deg, 1.4 deg inter- dots distant, 16.8 deg perimeter), presented against a uniform grey background. The target was orientated either \(+35^{\circ}\) or \(+55^{\circ}\) (clockwise) from the vertical, and flanker orientation randomly chosen in steps of \(5^{\circ}\) from \(- 45^{\circ}\) to \(+45^{\circ}\) with respect to the target orientation. The two flankers were 5.5 deg from target, leading to a Bouma ratio of 0.2. We manipulated the reliability of orientation information of target and flanker stimuli by using two different aspect ratios, 2.8 (axes 3.48 and 1.23 deg) and 1.4 (axes 3.19 and 2.28 deg), illustrated in Fig. 1A. The more elongated target was always associated with more rounded flankers, and vice versa. In each experimental session of the three experiments, the two target- flanker combinations were shown both kinds of stimuli in random order.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 544, 207, 559]]<|/det|>
+## Procedure
+
+<|ref|>text<|/ref|><|det|>[[117, 575, 880, 830]]<|/det|>
+Stimuli were displayed on a linearized \(22^{\prime \prime}\) LCD monitor (resolution \(1920\times 1080\) pixels, refresh rate \(60\mathrm{Hz}\) ). Observers were positioned \(57~\mathrm{cm}\) from the monitor, in a quiet room with dim lighting, and maintained fixation on a small (0.35 deg) black central dot. After a random delay from the observer initiating the trial, the stimulus was displayed for \(167~\mathrm{ms}\) . Then a thin rotatable white bar \((0.05\times 5\) deg with a gaussian profile) was presented at the fixation point with random orientation, and observers matched its orientation to that of the target by mouse control. In the first two experiments, the orientation of the two flankers was yoked, while in the third, one flanker was always \(+15^{\circ}\) (clockwise) while the other varied from \(- 45^{\circ}\) to \(+45^{\circ}\) . In the second experiment, the target- flanker distance varied, being 5.5, 7.5, 11.0 and 16.6 deg, leading to Bouma ratios of 0.21, 0.27, 0.4, 0.6.
+
+<|ref|>text<|/ref|><|det|>[[119, 844, 861, 915]]<|/det|>
+Ten observers participated in the first experiment, five in the second, thirteen in the third. They contributed for a total of 10699 trials for the first experiment, 14377 for the second (spread across the four flanker- target distances) and 16574 for the last.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[120, 87, 235, 103]]<|/det|>
+## Data analysis
+
+<|ref|>text<|/ref|><|det|>[[119, 118, 878, 190]]<|/det|>
+Responses occurred out from the range between 0.5 and 3 seconds after the stimulus offset were removed (for a total of \(15.9\%\) trials across the 3 experiments), as were responses with reproduction error greater than \(35^{\circ}\) ( \(6.9\%\) of trials).
+
+<|ref|>text<|/ref|><|det|>[[118, 204, 864, 352]]<|/det|>
+For each target and relative orientation of the flanker, we calculated the average constant error (bias, positive meaning clockwise) and scatter. We then averaged the values for the two targets. Bias functions were fitted by a derivative of gaussian function, which can be considered to be a gaussian of width \(s\) multiplied by a straight line of slope a [or w], which can be considered the weighting given to the flankers: 1 means the flankers are weighted equally to the target. Bias is given by:
+
+<|ref|>equation<|/ref|><|det|>[[177, 366, 850, 399]]<|/det|>
+\[B = a\cdot (\theta -m)\exp \Big(-\frac{(\theta -m)^2}{s^2}\Big) + b \quad (eq. 18)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 410, 870, 455]]<|/det|>
+Where \(\theta\) is orientation difference, \(m\) the centre, and \(b\) the vertical offset of the function. \(a\) , \(b\) and \(m\) were free to vary.
+
+<|ref|>text<|/ref|><|det|>[[118, 469, 855, 514]]<|/det|>
+Scatter \((S)\) was defined as the average root variance in each condition. The variation with orientation a gaussian function in the form:
+
+<|ref|>equation<|/ref|><|det|>[[177, 527, 850, 559]]<|/det|>
+\[S = a\cdot \exp \Big(-\frac{(\theta - m)^2}{s^2}\Big) + b \quad (eq. 19)\]
+
+<|ref|>text<|/ref|><|det|>[[118, 570, 812, 642]]<|/det|>
+Where \(b\) is the baseline at high orientation differences and \(a\) is the amplitude of the Gaussian. As Bias and Scatter likely originate from the same process, we yoked the parameter \(s\) to best fit both curves.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 691, 228, 707]]<|/det|>
+## REFERENCES
+
+<|ref|>text<|/ref|><|det|>[[118, 723, 875, 863]]<|/det|>
+1 Bouma, H. Interaction effects in parafoveal letter recognition. Nature 226, 177- 178, doi:10.1038/226177a0 (1970).
+2 Bouma, H. Visual interference in the parafoveal recognition of initial and final letters of words. Vision Res 13, 767- 782, doi:10.1016/0042- 6989(73)90041- 2 (1973).
+3 Pelli, D. G. & Tillman, K. A. The uncrowded window of object recognition. Nat Neurosci 11, 1129- 1135, doi:10.1038/nn.2187 (2008).
+4 Strasburger, H., Rentschler, I. & Juttner, M. Peripheral vision and pattern recognition: a review. J Vis 11, 13, doi:10.1167/11.5.13 (2011).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 87, 870, 884]]<|/det|>
+5 Whitney, D. & Levi, D. M. Visual crowding: a fundamental limit on conscious perception and object recognition. Trends Cogn Sci 15, 160- 168, doi:10.1016/j.tics.2011.02.005 (2011).6 Parkes, L., Lund, J., Angelucci, A., Solomon, J. A. & Morgan, M. Compulsory averaging of crowded orientation signals in human vision. Nat Neurosci 4, 739- 744, doi:10.1038/89532 (2001).7 Balas, B., Nakano, L. & Rosenholtz, R. A summary- statistic representation in peripheral vision explains visual crowding. J Vis 9, 13 11- 18, doi:10.1167/9.12.13 (2009).8 Levi, D. M. & Carney, T. Crowding in peripheral vision: why bigger is better. Curr Biol 19, 1988- 1993, doi:10.1016/j.cub.2009.09.056 (2009).9 Greenwood, J. A., Bex, P. J. & Dakin, S. C. Crowding changes appearance. Curr Biol 20, 496- 501, doi:10.1016/j.cub.2010.01.023 (2010).10 Freeman, J. & Simoncelli, E. P. Metamers of the ventral stream. Nat Neurosci 14, 1195- 1201, doi:10.1038/nn.2889 (2011).11 Nazir, T. A. Effects of lateral masking and spatial precueing on gap- resolution in central and peripheral vision. Vision Res 32, 771- 777, doi:10.1016/0042- 6989(92)90192- I (1992).12 Kooi, F. L., Toet, A., Tripathy, S. P. & Levi, D. M. The effect of similarity and duration on spatial interaction in peripheral vision. Spat Vis 8, 255- 279, doi:10.1163/156856894x00350 (1994).13 Kennedy, G. J. & Whitaker, D. The chromatic selectivity of visual crowding. J Vis 10, 15, doi:10.1167/10.6.15 (2010).14 Manassi, M., Sayim, B. & Herzog, M. H. When crowding of crowding leads to uncrowding. J Vis 13, 10, doi:10.1167/13.13.10 (2013).15 Levi, D. M. Crowding- an essential bottleneck for object recognition: a mini- review. Vision Res 48, 635- 654, doi:10.1016/j.visres.2007.12.009 (2008).16 Chopin, A. & Mamassian, P. Predictive properties of visual adaptation. Curr Biol 22, 622- 626, doi:10.1016/j.cub.2012.02.021 (2012).17 Cicchini, G. M., Anobile, G. & Burr, D. C. Compressive mapping of number to space reflects dynamic encoding mechanisms, not static logarithmic transform. Proc Natl Acad Sci U S A 111, 7867- 7872, doi:10.1073/pnas.1402785111 (2014).18 Fischer, J. & Whitney, D. Serial dependence in visual perception. Nat Neurosci 17, 738- 743, doi:10.1038/nn.3689 (2014).19 Pascucci, D. et al. Laws of concatenated perception: Vision goes for novelty, decisions for perseverance. PLoS Biol 17, e3000144, doi:10.1371/journal.pbio.3000144 (2019).20 Helmholtz, H. v. Handbuch der physiologischen Optik. (Voss, 1867).21 Gregory, R. L. Eye and brain; the psychology of seeing. (McGraw- Hill, 1966).22 Liberman, A., Fischer, J. & Whitney, D. Serial dependence in the perception of faces. Curr Biol 24, 2569- 2574, doi:10.1016/j.cub.2014.09.025 (2014).23 Taubert, J., Van der Burg, E. & Alais, D. Love at second sight: Sequential dependence of facial attractiveness in an on- line dating paradigm. Sci Rep 6, 22740, doi:10.1038/srep22740 (2016).24 Burr, D. & Cicchini, G. M. Vision: efficient adaptive coding. Curr Biol 24, R1096- 1098, doi:10.1016/j.cub.2014.10.002 (2014).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 85, 868, 632]]<|/det|>
+25 Cicchini, G. M., Mikellidou, K. & Burr, D. C. The functional role of serial dependence. Proc Biol Sci 285, doi:10.1098/rspb.2018.1722 (2018).26 Kording, K. P. et al. Causal inference in multisensory perception. PLoS One 2, e943, doi:10.1371/journal.pone.0000943 (2007).27 Ernst, M. O. & Banks, M. S. Humans integrate visual and haptic information in a statistically optimal fashion. Nature 415, 429- 433, doi:10.1038/415429a (2002).28 Alais, D. & Burr, D. The ventriloquist effect results from near- optimal bimodal integration. Curr Biol 14, 257- 262, doi:10.1016/j.cub.2004.01.029 (2004).29 Rosenholtz, R., Yu, D. & Keshvari, S. Challenges to pooling models of crowding: Implications for visual mechanisms. J Vis 19, 15, doi:10.1167/19.7.15 (2019).30 Field, D. J., Hayes, A. & Hess, R. F. Contour integration by the human visual system: evidence for a local "association field". Vision Res 33, 173- 193, doi:10.1016/0042- 6989(93)90156- q (1993).31 Cicchini, G. M., Benedetto, A. & Burr, D. C. Perceptual history propagates down to early levels of sensory analysis. Curr Biol 31, 1245- 1250 e1242, doi:10.1016/j.cub.2020.12.004 (2021).32 Jazayeri, M. & Shadlen, M. N. Temporal context calibrates interval timing. Nat Neurosci 13, 1020- 1026, doi:10.1038/nn.2590 (2010).33 Cicchini, G. M., Arrighi, R., Cecchetti, L., Giusti, M. & Burr, D. C. Optimal encoding of interval timing in expert percussionists. J Neurosci 32, 1056- 1060, doi:10.1523/JNEUROSCI.3411- 11.2012 (2012).34 Manassi, M. & Whitney, D. Multi- level Crowding and the Paradox of Object Recognition in Clutter. Curr Biol 28, R127- R133, doi:10.1016/j.cub.2017.12.051 (2018).35 He, S., Cavanagh, P. & Intriligator, J. Attentional resolution and the locus of visual awareness. Nature 383, 334- 337, doi:10.1038/383334a0 (1996).36 Bulakowski, P. F., Post, R. B. & Whitney, D. Visuomotor crowding: the resolution of grasping in cluttered scenes. Front Behav Neurosci 3, 49, doi:10.3389/neuro.08.049.2009 (2009).37 Banks, W. P., Larson, D. W. & Prinzmetal, W. Asymmetry of visual interference. Percept Psychophys 25, 447- 456, doi:10.3758/bf03213822 (1979).
+
+<--- Page Split --->
diff --git a/preprint/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b/images_list.json b/preprint/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..59a863d636d2243abe7099db773ee375f43e4034
--- /dev/null
+++ b/preprint/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b/images_list.json
@@ -0,0 +1,85 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. Quantile Generalised Additive Models (qGAM) describing the relation between environmental factors and population density for 10-percentiles (dashed lines), 50-percentiles (solid lines), and 90-percentiles (doted lines). Here, only the six most limiting factors during the 22kaBP to 8kaBP are presented. Full explorations of evaluated variables presented in Supplementary material S1.",
+ "footnote": [],
+ "bbox": [
+ [
+ 232,
+ 85,
+ 750,
+ 581
+ ]
+ ],
+ "page_idx": 21
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Convergence between current climatic conditions (hashed density plots) and paleoclimatic conditions at four different periods (coloured density plots). Paleoclimatic periods are Greenland Stadial 2, Greenland Interstadial 1, Greenland Stadial 1, and Holocene. As in Figure 1, only the six most limiting factors during the 22kaBP to 8kaBP are presented. Full explorations of evaluated variables presented in Supplementary material S2.",
+ "footnote": [],
+ "bbox": [
+ [
+ 140,
+ 90,
+ 860,
+ 722
+ ]
+ ],
+ "page_idx": 22
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Contrast between Europe wide mean population density (top panel), and trends in key environmental variables (bottom). Estimated average population density for all Europe based on a randomization approach (top panel) are compared to archaeological population proxy based on number of calibrated radiocarbon dates for Europe between 21 and 11kyBP based on \\(^{12}\\) summaries of the Radiocarbon Palaeolithic Europe Database v28 \\(^{86}\\) (red), and core area (cf. \\(^{23}\\) population density mean and upper/lower estimates based on the Cologne Protocol (blue). On the bottom panel, plotted variables are: Effective temperature, Minimum temperature of the Coldest Month, and Maximum temperature of the Warmest Month.",
+ "footnote": [],
+ "bbox": [
+ [
+ 196,
+ 87,
+ 790,
+ 736
+ ]
+ ],
+ "page_idx": 23
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4. Estimated human population density and range (areas where population density \\(> 1\\) individual per \\(100\\mathrm{km}^2\\) ) (A-E) and factors limiting population density (F-J) across Europe for selected times during the 22ky to 8kyBP period. (A, F) Greenland Stadial 2; (B, G) Greenland Interstadial 1; (C, H) Greenland Stadial 1 warming terminations (D, I) Holocene initiation; (E, J) Mid-Holocene. Areas in grey scale represent the glacier extent as derived by PaleoMIST 85.",
+ "footnote": [],
+ "bbox": [
+ [
+ 133,
+ 90,
+ 820,
+ 690
+ ]
+ ],
+ "page_idx": 24
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5. Proportion of the ice-free area of Europe where each variable was estimated to be the factor limiting population density (A); and estimated population size based on the mean environmental conditions for each century (B). In both panels, only the six variables with the highest percentages of cells where the variable is the limiting factor are presented.",
+ "footnote": [],
+ "bbox": [
+ [
+ 137,
+ 108,
+ 884,
+ 650
+ ]
+ ],
+ "page_idx": 25
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_0.jpg",
+ "caption": "Supplementary material S2. Overlap between current climatic conditions (hashed density plots) used for model building and paleoclimatic databases (coloured density plots) used to hindcast human population density for all 19-climatic variables used. Title acronyms as in Table 1.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 26
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b.mmd b/preprint/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..8b970721cccf9b4212801e30a606dae64ea49bea
--- /dev/null
+++ b/preprint/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b/preprint__0226534d35058c645a89e4e44377c8b2e4f25f5dddefbf9c78c868b60659db7b.mmd
@@ -0,0 +1,270 @@
+
+# Changes in limiting factors for forager population dynamics in Europe across the Last Glacial-Interglacial Transition
+
+Alejandro Ordonez ( \(\boxed{ \begin{array}{r l} \end{array} }\) alejandro.ordonez@bio.au.dk) Aarhus University Felix Riede Aarhus University
+
+Article
+
+Keywords:
+
+Posted Date: December 22nd, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 1173690/v1
+
+License: © \(\circledast\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on September 6th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 32750- x.
+
+<--- Page Split --->
+
+# Changes in limiting factors for forager population dynamics in Europe across the Last Glacial-Interglacial Transition
+
+Alejandro Ordonez \(^{1,2,4}\) & Felix Riedel \(^{1,3}\)
+
+1, Center for Biodiversity Dynamics in a Changing World, Aarhus University
+
+2, Department of Biology, Aarhus University
+
+3, Department of Archaeology and Heritage Studies, Aarhus University
+
+4, Center for Sustainable Landscapes under Global Change, Aarhus University
+
+## 8 Abstract
+
+Population dynamics set the framework for human genetic and cultural evolution. For foragers, demographic and environmental changes correlate strongly, although the causal relations between different environmental variables and human responses through time and space likely varied. Building on the notion of limiting factors, namely that the scarcest resource regulates population size, we present a statistical approach to identify the dominant climatic constraints for hunter- gatherer population densities and then hindcast their changing dynamics in Europe for the period between 20kyBP to 8kyBP. Limiting factors shifted from temperature- related variables during the Pleistocene to a regional mosaic of limiting factors in the Holocene. This spatiotemporal variation suggests that hunter- gatherers needed to overcome very different adaptive challenges in different parts of Europe, and that these challenges vary over time. The signatures of these changing adaptations may be visible archaeologically. In addition, the spatial disaggregation of limiting factors from the Pleistocene to the Holocene coincides with and may partly explain the diversification of the cultural geography at this time.
+
+## 23 Introduction
+
+As the link between exogenous environmental factors and organismal physiology, demography is vital for understanding evolution, including cultural evolution \(^{1}\) . The relevance of past demography for understanding culture change in prehistory specifically has long been recognised \(^{2,3}\) . Demographic conditions impinge on cultural transmission \(^{4- 6}\) but are also clearly implicated in the boom- and- bust patterns of population fluctuations – including periodic
+
+<--- Page Split --->
+
+extirpations – suggested to have characterised the demographic histories of prehistoric foragers and incipient farmers in many regions \(^{7 - 10}\) . Numerous recent studies have focused on the drivers of population expansion to explain the pattern and timing of human colonisation using a variety of ecological comparative approaches \(^{11,12}\) (but see ref. \(^{13}\) for a discussion of points of concern of such approaches). Yet, as foragers have a high intrinsic growth rate, population increase is, in the absence of cultural or environmental constraints, the default demographic trajectory. Evidently, however, past populations did not grow substantially, making it particularly germane to understand the factors that curtailed population growth \(^{14,15}\) . The approach adopted here builds on the central theorem that population sizes would always be regulated by the scarcest resource: the limiting factor \(^{16}\) .
+
+Foragers of the recent past persisted in a wide variety of environments, from the frigid Arctic to tropical rainforests. Each environment offered particular opportunities but also posed particular challenges. While several earlier studies have pointed at temperature or seasonality as key drivers of forager demography at global or continental scales \(^{17,18}\) , the specific factors that would have capped or even depressed population size are likely to have varied in both space and time. Only in understanding these limiting factors can we begin to conduct targeted investigations of how specific forager populations may have overcome them via either population- specific genetic adaptations or the sort of ‘extra- somatic adaptions’ \(^{19}\) that are so characteristic of human culture.
+
+In this study, we focus specifically on forager palaeodemography in Europe from the Last Glacial Maximum (Greenland Stadial 2, GS2) to 8000 years before present (BP), a climatically volatile period also known as the Last Glacial- Interglacial Transition \(^{20}\) . Previous studies have identified broad patterns of population growth and expansion using different methods commonly used in ecological analyses \(^{12,21 - 23}\) . Correlations between temperature and overall population density have been identified, suggesting overall increases in energy availability as the key driver of the increase in human population size following the end of GS2 \(^{17}\) . However, regional population collapses have been suggested to have occurred asynchronously and in different places \(^{9,24}\) . This raises the question of which specific limiting factors acted on forager populations and how these limiting factors varied over space and time.
+
+Like many related studies, we begin with the global ethnographic hunter- gatherer dataset originally assembled by Binford and now digitally available \(^{25,26}\) . We couple this to a suite of quantile Generalised Additive Models (qGAMs) to describe changes in maximum (90-
+
+<--- Page Split --->
+
+percentile) population density as a univariate function of environmental variables related to the effect of temperature and precipitation on available energy, annual variability, and productivity. We then use the downscaled centennial average- conditions of each predictor derived from a transient climatic simulation (CCSM3 SynTrace- 21 \(^{27}\) ) and the best performing univariate qGAM models to hindcast hunter- gatherer population densities between 20ky to 8kyBP. We define the limiting environmental factor as the variable predicting the lowest population density at a given place and time. This approach allows us to query the spatial dynamics of forager limiting factors across the Last Glacial- Interglacial Transition and derive specific hypotheses as to which selection pressures acted most strongly on different forager communities in Late Pleistocene and Early Holocene Europe.
+
+Our analysis demonstrates that the dynamics on limiting factors for forager population densities showed marked differences in space and time. Temperature- related variables were the main limiting factors during the Pleistocene, whereas the Early Holocene was characterised by a regional mosaic of limiting factors. Furthermore, our model reveals geographic differences in the limiting factors between Fennoscandia, Southern, Central, and Eastern Europe. The spatiotemporal variation in limiting factors suggests that hunter- gatherers needed to overcome very different adaptive challenges in different parts of Europe across this period of climatic and environmental change.
+
+## Results and discussion
+
+The relation between the environmental factors explored here and population density assessed using qGAMs (Fig. 1) was negative for temperature seasonality, positive for effective temperature, winter/fall temperature, and unimodal for the warmest temperature. Seasonal, monthly, and extreme precipitation, and topographic heterogeneity showed an overall flat trend (supplementary figure S1), yet these also differed from a mean model as determined by the high deviance explained (Table 1).
+
+No single environmental variable explained more than \(81\%\) of the population density variation among ethnographic foraging societies (Table 1). However, the performance of more complex multivariate models using machine learning approaches \(^{12}\) or Structural Equation Models \(^{11}\) that combine three or more variables perform only marginally better. The five environmental variables with the highest predictive accuracies (based on the deviance explained; Table 1) were Temperature of the Coldest Month; Temperature Seasonality; Winter Mean Temperature;
+
+<--- Page Split --->
+
+Effective Temperature and Mean Annual Temperature. These variables display high collinearity (Pearson correlations range between 0.83 and 0.96), suggesting that temperature overall best captures the effect of temperature minima and energy availability in relation to forager demography. Two of the variables (Temperature of the Coldest Month and Winter Mean Temperature) represent the effect of extreme cold conditions (= winter mortality) on demographic trends and/or ecological performance \(^{28,29}\) . The other two (Mean Annual Temperature, Effective Temperature, Temperature Seasonality) relate to overall energy availability \(^{28}\) . These factors are linked to higher environmental productivity and are expected to increase available resources, leading to higher population densities, as already suggested by a plethora of earlier studies \(^{30 - 32}\) . Other variables related to environmental productivity have lower predictive accuracy (explained deviances \(< 0.79\) , see Table 1) and lower collinearity with other variables related to energy availability.
+
+Most seasonal temperature and precipitation variables showed some of the lowest explained deviances (Table 1), indicating that seasonal climatology most likely did not impose a direct limit on past forager populations densities in Late Pleistocene/Early Holocene Europe (contra \(^{18}\) ). Topographic complexity, a variable shown to influence population density in other studies \(^{11}\) , showed only above- average predictive accuracy (Table 1). Like seasonal temperature and precipitation, the topographic complexity effect on population density may be indirect and mediated by variables describing available resources or climate extremes.
+
+Besides the well- known limitations of using foragers of the recent past for reconstructing prehistoric social and demographic conditions \(^{13}\) , the issue of model truncation and non- analogy of climatic conditions present themselves as major potential caveats. Climatic non- analogy here refers to the problem of projecting models beyond the domain for which they have been calibrated \(^{33 - 35}\) . Model truncation refers to the incomplete characterisation of hunter- gatherer populations' total climate space \(^{36 - 38}\) and has been a long noted limitation of ethnographic analogies for prehistoric foragers \(^{39}\) . However, it has also been shown that the dataset assembled by Binford is not critically biased in terms of forager niche space \(^{25}\) . Likewise, we do not see either truncation or severe non- analogy in a temporal context, as the climate space observed at different moments during the 21- to- 8kyBP period show broad overlaps with the climate space used to develop our qGAMs (Fig. 2; supplementary figure S2). This means that our models are not unduly extrapolating into environmental regions where there is no clear indication of how population density changes as a function of evaluated
+
+<--- Page Split --->
+
+climatic variables. By the same token, it is necessary to highlight that the distributions of some paleoclimatic conditions – including all those with the highest predictive values in our models – are skewed towards the lower end of contemporary values. This is especially pronounced for the Pleistocene and variables such as maximum temperatures (Fig. 2), affecting our inference power on changes in population densities at these extremes.
+
+Our models indicate that the estimated human population size in Europe was the lowest at \(22\mathrm{kyBP}\) (\~294,000 individuals) and largest at \(8\mathrm{kyBP}\) (\~706,000 individuals). Also, based on our model, we show that at the warmest point of the Greenland Interstadial 1 (\~14.7kyBP; GI1), Europe's human population size estimated by our model was \~617,000 individuals; a number that decreased to \~607,000 individuals at the coldest point of the Greenland Stadial 1 (\~11.7kyBP; GS1). Overall occupied area (number of inhabited cells) was \(62.4\%\) of the region at the end of the GS2 (\~22kyBP). This number increased to \~98.8% during GI 1, decreased to \~97.7% during the GS 1, and reached the highest point (\~99.8%) by the mid- Holocene (\~8kyBP). Taken at face value, these values are gross overestimation of actual sustained forager land- use at this time. Forager land- use was evidently extensive, including largely empty spaces \(^{40}\) . By the same token, these numbers are in line with archaeologically derived trends of overall population growth and expansion during this time (red lines; Fig. 3A).
+
+During the evaluated period, the mean population density in the inhabited area varied between 2.6 and 6.2 persons per \(100\mathrm{km}^2\) ( \(\mathrm{GS2} = 2.7\mathrm{p} / 100\mathrm{km}^2\) ; \(\mathrm{GI1} = 5.25\mathrm{p} / 100\mathrm{km}^2\) ; \(\mathrm{GS1} = 5.17\mathrm{p} / 100\mathrm{km}^2\) ; \(\mathrm{mHol} = 6\mathrm{p} / 100\mathrm{km}^2\) ; Fig. 3A). Although the temporal patterns in average population density derived from our limiting- factor analysis are similar to those of core area estimates by Bocquet- Appel, et al. \(^{21}\) (blue areas, Fig. 3A), these do not match numerically due to our focus on maximum population densities. Moreover, our population density estimates are consistent with those suggested by Tallavaara, et al. \(^{12}\) , and more recently Kavanagh, et al. \(^{11}\) .
+
+The estimated pattern of human population density (Fig. 3) indicates a population expansion starting almost 3ky after the ice sheet began to recede from its maximum extent 22kabP. Evaluating the spatially explicit predictions of our model, we find that at the end of the GS2, hunter- gatherer societies in Europe extended as far north as central France, southern Germany and southern parts of modern- day Ukraine (Fig. 4A), a pattern that is consistent with archaeological evidence for the recolonisation of Europe \(^{41 - 44}\) . Our models also suggest that by the end of the GS2, a relatively large proportion of the European continent may have been at least sporadically inhabited (\~62%; Fig. 4A- B), with the Mediterranean region up to the north
+
+<--- Page Split --->
+
+of the Alps showing population densities up to 12 individuals/100 km \(^2\) . This restricted occurrence pattern is supported by the archaeological record \(^{40}\) . Furthermore, our model indicates a persistent southwest-northeast gradient of decreasing population densities in this southern region, with the most populated areas occurring in the Iberian Peninsula and the Mediterranean region (Fig. 4A- B). From this point, the recolonisation of the continent began at \(\sim 17\mathrm{kyBP}\) (Fig. 3), reaching almost all the way to Scandinavia by the start of GI1 \(\sim 14.7\mathrm{kyBP}\) , Fig. 4c). Earlier archaeological \(^{45,46}\) and modelling studies \(^{22}\) have already suggested that this colonisation was rapid but also that it proceeded in several steps where both climate and landforms served as barriers to expansion \(^{47}\) . Our results expand on this discussion by highlighting that different climate variables limited human dispersal for a given location and that these limits changed over time.
+
+Using our limiting- factor approach, we improve our understanding of demographic mechanisms in Late Pleistocene and Early Holocene European hunter- gatherer societies by highlighting the spatiotemporal changes in the main factor restricting population density (Fig. 4F- T; and Fig. 5). Our modelled population density estimates can be linked to regional or local narratives or empirical tests of changes in occurrences and population sizes (e.g., refs. \(^{25,48}\) ). The changes in limiting factors suggested in our models can be divided into three periods. The first period spans from the termination of GS2 to the onset of interstadial warming at around \(15\mathrm{kyBP}\) . During this period, energy availability measured as effective temperature (ET) was the main factor limiting population density across most of the continent ( \(\sim 50\%\) of cells; Fig. 5A). Mean temperature of the warmest month (MWM) was also a strong limiting factor ( \(\sim 30\%\) of cells; Fig. 5). However, limitations imposed by winter temperatures, could be also considered as likely limiting factors based on estimates of average conditions at a continental scale (Fig. 5B). The range of experienced temperature conditions, represented by ET, can thus be seen as the major limiting factor shaping human population density in Europe between GS2 and the initiation of warming associated with GI1 (Fig. 5A). With temperature related variables as the overwhelming limiting factor during this period (Fig. 5B), it is likely that the emergence of sophisticated sewing techniques and pyrotechnology \(^{49}\) facilitated the persistence and even moderate expansion of populations at this time.
+
+The second period covers the rapid warming (GI1) as well as cooling (GS1) events between \(14.7\mathrm{kyBP}\) to \(11.7\mathrm{kyBP}\) . During this period, the importance of ET steadily decreased, and mean temperature of the warmest month ( \(\sim 27\%\) of cells) and temperature seasonality ( \(\sim 23\%\) of cells)
+
+<--- Page Split --->
+
+became the main factors limiting population density (Fig. 5A). The decrease of ET as a limiting factor indicates that during this period of rapid change, it was not temperature but energy availability (due to the link between MWM and productivity) what determined human population density in Europe (Fig. 5B). Our models suggest that overall population densities increased (Fig. 3), although a temporary reduction associated with GS1 cooling is also clear.
+
+The last period encompasses the Early Holocene from its onset at 11.7ky to 8kyBP. Here, temperature of the warmest month increased in importance as the main limiting factor ( \(\sim 50\%\) of cells; Fig. 5A), while the effect of ET became marginal (Fig. 5B). Also, temperature seasonality became a critical limiting factor in many regions (Fig. 4I, J). These patterns indicate a complete shift from experienced temperature conditions to available resources as the main limiting factor of European forager population densities during the Holocene. Such a shift is interesting as the Early Holocene also witnessed a significant reorganisation of forager socio- ecological systems towards more varied use of resources and more pronounced territoriality focused on spatial circumscribed and regionally available resources, and a widespread shift from immediate- return to delayed- return economies. This also aligns with the idea that decreasing territory sizes and more marked boundary formation directly relate to the spatiotemporal dynamics of resource availability \(^{50}\) .
+
+The regional disaggregation of patterns in limiting factors shows strong differences between Fennoscandia, Southern, Central, and Eastern Europe (Fig. 4F- J). These patterns are persistent over time, with regional shifts linked to the main feature of temperature change. In Fennoscandia and the British Isles, effective temperature was the main limiting factor for most of the Late Pleistocene. This changed after the onset of the Holocene when seasonal temperatures and precipitation became the dominant limiting factor. In Eastern and Western Europe, effective temperature was the main limiting factor at the end of the GS2 but were replaced by Winter temperature and MWM at the onset of the GI1. During the GS1 and the early Holocene, the main limiting factors where MWM and TS. In southern Europe and especially in the Mediterranean, MWM was the main limiting factor throughout most of the GS2, after which precipitation became the dominant limiting factor.
+
+Our analyses show that the main limiting factors that limited forager population densities across the Last Glacial- Interglacial Transition in Europe changed markedly over time (Fig. 5) and space (Fig. 4F- J). We can now return to the archaeological record with these insights, searching for material culture proxies that may have allowed these past communities to
+
+<--- Page Split --->
+
+overcome these particular limiting factors \(^{51 - 53}\) . While these may have related to water availability (= containers) in the Mediterranean, they are predicted to relate to temperature (= clothing or pyrotechnology) in higher latitudes. Where such technologies are absent in the archaeological record, we can also begin to think about population vulnerability to climatic factors at regional levels. Especially in higher latitudes, population fluctuations may have been pronounced at the sub- centennial scale, to the point of local population extirpations \(^{9,54}\) .
+
+Finally, the marked shift in limiting factors at the onset of the Holocene may be indicative of a greater focus on resource access at a regional scale. The spatiotemporal dynamics of resource availability have a direct impact on land- use, mobility, territoriality, and the formation of information networks in foragers \(^{50,55}\) . In the Holocene, regional cultural signatures became more pronounced and borders between different cultural zones more strongly articulated. This itself may be seen as a response to the fundamental shift in limiting factors we have identified in our models.
+
+Seeking correlations between environmental variables and past human population densities is not a new endeavour. Following recent calls for more theoretically- informed rather than mere statistical explorations of this relationship \(^{13}\) , we highlight that while the environment can be said to strongly constrain forager lifeways, precisely which aspects of the environment do so at any one place and time vary. Our approach offers a robust way to infer the hierarchy of limiting factors and hence provide a spatiotemporal hypothesis for major selection pressures acting on forager populations in the past.
+
+Independent palaeodemographic estimates broadly support our models, but many questions remain. Climate models, for instance, only indirectly capture the interaction of human population dynamics with changes in biodiversity and ecosystem compositions. In addition, the match between modelled population densities and the field- validated presence of Late Pleistocene/Early Holocene populations is not equally robust everywhere. These deviations may stimulate targeted field- testing with the aim of assessing whether and why population densities periodically fell short of or exceeded modelled values. In conjunction with legacy data derived from archives and the literature, such fieldwork can also shed light on the specific strategies these past foragers employed to mitigate the risks posed by specific limiting factors.
+
+Small- scale societies have a variety of adaptive options at their disposal (see ref. \(^{56}\) ), most of which can be captured through archaeological proxies \(^{57 - 59}\) . Our limiting factor model here
+
+<--- Page Split --->
+
+serves as an explicit spatiotemporal hypothesis of which risk mitigation measures should be in use at which time and place. The successful identification of these would throw significant new light on the resilience and adaptation – or lack of it – during this climatically and environmentally tumultuous time. Finally, the marked shifts in dominant limiting factors identified in our models map into the results of Late Pleistocene/Early Holocene Earth System tipping points recently discussed by ref. \(^{60}\) . It is likely that, just like analogues anthropogenic warming in the present, these periods of rapid and substantive climatic change would have created challenges for contemporaneous forager populations. In an effort to align archaeological perspectives on climate change with the quandaries of our time (cf. \(^{61}\) ), future research would be well- advised to focus on such periods of major systemic transitions.
+
+## Methods
+
+## Models of hunter-gatherers' population density
+
+We use ethnographic data on terrestrially adapted mobile hunter- gatherers and their climatic space \(^{25}\) to construct a series of statistical models that predict hunter- gatherer population density based on one of 16 climatic predictors (see Table 1 for rezoning and source). While there are important caveats \(^{13}\) , this approach builds on multiple ethnographic studies showing a link between climate on the one hand and hunter- gatherer diet, mobility, and demography on the other \(^{55,62- 66}\) . This statistical connection is the basis of recent studies focused on building complex multivariate models of population dynamics \(^{11,12,67}\) . A benefit of our statistical approach is that it overcomes some significant limitations, such as lack of quantitative population size data based on the archaeological record itself or genetic data, each associated with their own limitations (as reviewed in refs. \(^{2,12}\) ).
+
+We omitted four observation classes in the original ethnographic dataset in defining the association between hunter- gatherer population density and climatic predictors. First, we removed observations associated with food producers. Second, sedentary populations or those that reside at a single location for \(>1\) year. Third, populations using aquatic resources ( \(>30\%\) of their dietary protein comes from aquatic environments, as defined in \(^{68,69}\) ). Forth, we excluded all observations related to horse- riding populations. The filters employed here correspond to those used by Tallavaara, et al. \(^{12}\) to maximise the match between ethnographic data and the current knowledge of the highly mobile and overwhelmingly terrestrially oriented lifestyles of Late Pleistocene/early Holocene hunter- gatherers in Europe. The implemented
+
+<--- Page Split --->
+
+filters are less restrictive than those used by other studies that have sought to reconstruct forager population dynamics during this time \(^{70}\) and thus allow for a relatively large degree of behavioural variation. This is important given that increasing evidence of marine and lacustrine resource use is emerging for at least certain times and regions in Late Pleistocene Europe \(^{71- 73}\) , and that a marked diversification characterises the resource base of early Holocene foragers. Finally, these filters remove any population using external supplements to their hunter- gatherer lifestyle, resulting in a database including information on 127 populations.
+
+We used climate data on historical averages (1970- 2000) for 19- climate variables (Table 1) to build our ethnography- based population density models. These were obtained from the Worldclim version 2.1 \(^{74}\) at a 10- ArcMin resolution. Importantly, we used Worldclim data instead of climatic variables directly available from the ethnographic dataset to ensure comparability between climatic variables not in the database (i.e., seasonal means). Equally importantly, this approach prevents any estimation biases due to differences between the data used to define climate- density relations and paleoclimatic surfaces (see the section estimating human populations density across the Pleistocene- Holocene transition below) used to estimate population density changes and limiting factors over time.
+
+Initially, we model how population densities of hunter- gatherer communities change along current environmental gradients using Quantile Generalised Additive Models (qGAMS). Modelling such dynamics using qGAMs offers a transparent way to determine the non- linear changes in different percentiles of a response variable (= population densities) to one or multiple environmental variables. This approach is commonly used in the ecological literature to determine the likelihood of occurrence or abundance of a given species under a particular environmental regime \(^{75- 79}\) but has never before been applied to human palaeodemography. In contrast to previous studies evaluating past human population density changes, we do not consider the synergies between multiple climatic variables when describing the relation between population densities and climate. Instead, we focus on the individual effects of evaluated variables on the top 90- percentile of population densities to identify the most pronounced limiting factor that acted on palaeodemographic growth. The tendencies in population densities as a function of environmental variables were consistent for different percentiles (see supplementary figures S1).
+
+The population density derived from the ethnographic data followed a log- normal distribution, so these were log- transformed for subsequent analyses, and a gaussian response distribution
+
+<--- Page Split --->
+
+was used in our qGAMs models. Annual, monthly, and seasonal precipitation variables were similarly transformed. The ability of each of the evaluated variables to predict hunter- gatherer population densities was determined using the mean deviance explained (1 - (Residual Deviance/Null Deviance)). These were calculated both for the whole dataset, and using a 1000- fold cross- validation approach (70% random sample for calibration and 30% for validation). All models and prediction accuracy estimates were implemented in R (version 3.6; 80) using the mgcv (version 1.8.24; 81) and qgam (version 1.3.2; 82) packages.
+
+Estimating human populations density across the Pleistocene- Holocene transition
+
+The monthly average temperature and annual precipitation values for Europe for the 21ky to 8kyBP period come from the CCSM3 SynTrace paleoclimate simulations 83. These were biased- corrected and downscaled to \(0.5^{\circ} \times 0.5^{\circ}\) following the methods described by Lorenz, et al. 84. The paleoclimatic simulation data used here was originally generated to evaluate changes in European and North American fossil pollen data and vegetation novelty since the Last Glacial Maximum 27. Source climate surfaces were aggregated to centennial means from the original decadal averages of monthly values.
+
+Past hunter- gatherer population densities were then predicted for every 30ArcMin cell above sea level. For visualization we also show the areas covered by glaciers using the glacier extent shapefiles derived by PaleoMIST 85. To generate 90% percentile population density estimates for each variable/century combination, only those qGAM models parametrised using the ethnographic data and current climatic conditions with cross- validated deviances above 70% were projected into past climatic conditions. As our objective was to establish the climatic variable that imposed the strongest constraints on hunter- gatherer population density at any one time, we determined the variable estimating the lowest 90%- percentile population density for a given cell at each evaluated time- period to be the limiting factor (the scarcest resource that would then limit population size cf. 16). For each evaluated time- period, we summarised the proportion of the available land area (i.e., land area not covered by ice) where each of the assessed variables was determined to be the limiting factor.
+
+We calculated the changes in the percentage of inhabited land area in Europe during the evaluated period by estimating the proportion of the inhabited area, here defined as the region where population densities were above 1 individual per \(100\mathrm{km}^2\) . To calculate human- population size in Europe during every century, we multiplied the predicted population density
+
+<--- Page Split --->
+
+in each cell by the land area of the corresponding cell to arrive at per cell population size. We then and summed these values to arrive at the total population size for each century.
+
+Uncertainties in population density, size, occupied area, and limiting factor estimates were determined using a cross- validation approach, where model fitting was iterated 1000 times using a random sample (70%) of the ethnographic and climate data at each time step. Each model was used to hindcast populations densities, estimate the percentage of inhabited land area and human population size, and define the relevant limiting factor. Uncertainty in continental- scale estimates of population densities, occupied area and population size was determined using 95% confidence intervals. The variable selected as the limiting factor in most cross- validation folds was selected as the limiting factor.
+
+## Validation of population density estimates
+
+To assess the validity of our population density estimations, we use the International Union for Quaternary Science (INQUA) Radiocarbon Palaeolithic Europe Database v28 \(^{86}\) . Changes in the density of records are a useful continental- scale proxy- measurement of prehistoric population size changes and are increasingly used to describe prehistoric human population dynamics trends \(^{87 - 92}\) . We extracted proxy dates (based on \(^{14}\mathrm{C}\) dates) from the INQUA Radiocarbon Palaeolithic Europe Database, aggregating these to the closest 1000 years. Our goal is to determine the match between our qGAM derived populations densities and prehistoric population occupation derived from the frequencies of radiocarbon dates between 20kaBP and 10kaBP as done by Tallavaara, et al. \(^{12}\) . This approach allowed validating our hindcasted estimates of absolute prehistoric population density since our model is not archaeologically informed, avoiding any possible circularity between model development and validation.
+
+We also used site- based estimates of population density as derived using the Cologne Protocol by Schmidt, et al. \(^{23}\) . We focus on estimates of extended interconnected socio- economic areas (Core Areas) for five unequal time bands between 25kaBP and 11.7KaBP. Although ultimately also based on Binford \(^{25}\) , these estimates present independently derived spatially implicit estimates of population density for the Late Palaeolithic in Europe.
+
+## Data availability
+
+<--- Page Split --->
+
+375 The 'Binford' ethnographic database \(^{25}\) is available from the Database of Places, Language, Culture, and Environment (D- PLACE; https://d- place.org/about). Current and Late Quaternary environmental datasets are publicly available from the associated references. International Union for Quaternary Science (INQUA) Radiocarbon Palaeolithic Europe Database v28 is available from https://pandoradata.earth/am/dataset/radiocarbon-palaeolithic-europe-database-v28. Contemporary climate databases are available form the WorldClim project (https://www.worldclim.org), and late-Pleistocene climate sources are available at https://doi.org/10.6084/m9.figshare.c.4673120.v2.
+
+## References
+
+385 1 Metcalf, C. J. E. & Pavard, S. Why evolutionary biologists should be demographers. Trends Ecol Evol 22, 205- 212, doi:10.1016/j.tree.2006.12.001 (2007). 387 2 French, J. C., Riris, P., de Pablo, J. F. L., Lozano, S. & Silva, F. A manifesto for palaeodemography in the twenty- first century. Philos T R Soc B 376, doi:ARTN 20190707 390 10.1098/rstb.2019.0707 (2021). 391 3 French, J. C. Demography and the Palaeolithic Archaeological Record. J Archaeol Method Th 23, 150- 199, doi:10.1007/s10816- 014- 9237- 4 (2016). 393 4 Henrich, J. Demography and cultural evolution: How adaptive cultural processes can produce maladaptive losses - The Tasmanian case. Am Antiquity 69, 197- 214, doi:Doi 10.2307/4128416 (2004). 395 5 Powell, A., Shennan, S. & Thomas, M. G. Late Pleistocene Demography and the Appearance of Modern Human Behavior. Science 324, 1298- 1301, doi:10.1126/science.1170165 (2009). 396 6 Shennan, S. Demography and cultural innovation: A model and its implications for the emergence of modern human culture. Cambridge Archaeological Journal 11, 5- 16, doi:Doi 10.1017/S0959774301000014 (2001). 402 7 Jorgensen, E. K. The palaeodemographic and environmental dynamics of prehistoric Arctic Norway: An overview of human- climate covariation. Quatern Int 549, 36- 51, doi:10.1016/j.quaint.2018.05.014 (2020). 405 8 Jorgensen, E. K. & Riede, F. Convergent catastrophes and the termination of the Arctic Norwegian Stone Age: A multi- proxy assessment of the demographic and adaptive responses of mid- Holocene collectors to biophysical forcing. Holocene 29, 1782- 1800, doi:Artn 0959683619862036 409 10.1177/0959683619862036 (2019). 410 9 Riede, F. Success and failure during the Late Glacial pioneer human re- colonisation of southern Scandinavia. Lateglacial and postglacial pioneers in northern Europe, 33- 52 (2014). 413 10 Tallavaara, M. & Seppa, H. Did the mid- Holocene environmental changes cause the boom and bust of hunter- gatherer population size in eastern Fennoscandia? Holocene 22, 215- 225, doi:10.1177/0959683611414937 (2012).
+
+<--- Page Split --->
+
+416 11 Kavanagh, P. H. et al. Hindcasting global population densities reveals forces enabling the origin of agriculture. Nat Hum Behav 2, 478- +, doi:10.1038/s41562- 018- 0358- 8 (2018).
+
+419 12 Tallavaara, M., Luoto, M., Korhonen, N., Jarvinen, H. & Seppa, H. Human population dynamics in Europe over the Last Glacial Maximum. P Natl Acad Sci USA 112, 8232- 8237, doi:10.1073/pnas.1503784112 (2015). 423 13 Bliege Bird, R. & Codding, B. F. Promise and peril of ecological and evolutionary modelling using cross- cultural datasets. Nature Ecology & Evolution, 1- 3 (2021). 424 14 Gurven, M. D. & Davison, R. J. Periodic catastrophes over human evolutionary history are necessary to explain the forager population paradox. P Natl Acad Sci USA 116, 12758- 12766, doi:10.1073/pnas.1902406116 (2019). 425 15 Tallavaara, M. & Jorgensen, E. K. Why are population growth rate estimates of past and present hunter- gatherers so different? Philos T R Soc B 376, doi:ARTN 20190708 429 10.1098/rstb.2019.0708 (2021). 430 16 Blackman, F. F. Optima and limiting factors. With two diagrams in the text. Ann Bot- London 19, 281- 296, doi:DOI 10.1093/oxfordjournals.aob.a089000 (1905). 431 17 Maier, A. et al. Cultural evolution and environmental change in Central Europe between 40 and 15 ka. Quatern Int 581- 582, 225- 240, doi:10.1016/j.quaint.2020.09.049 (2021). 432 18 Zhu, D., Galbraith, E. D., Reyes- Garcia, V. & Ciais, P. Global hunter- gatherer population densities constrained by influence of seasonality on diet composition. Nat Ecol Evol 5, 1536- +, doi:10.1038/s41559- 021- 01548- 3 (2021). 433 19 Binford, L. R. Archaeology as Anthropology. Am Antiquity 28, 217- 225, doi:Doi 10.2307/278380 (1962). 440 20 Lowe, J. J. et al. Synchronisation of palaeoenvironmental events in the North Atlantic region during the Last Termination: a revised protocol recommended by the INTIMATE group. Quaternary Sci Rev 27, 6- 17 (2008). 441 21 Bocquet- Appel, J. P., Demars, P. Y., Noiret, L. & Dobrowsky, D. Estimates of Upper Palaeolithic meta- population size in Europe from archaeological data. J Archaeol Sci 32, 1656- 1668, doi:10.1016/j.jas.2005.05.006 (2005). 442 22 Fort, J., Pujol, T. & Cavalli- Sforza, L. L. Palaeolithic populations and waves of advance (Human range expansions). Cambridge Archaeological Journal 14, 53- 61, doi:Doi 10.1017/S0959774304000046 (2004). 443 23 Schmidt, I. et al. Approaching prehistoric demography: proxies, scales and scope of the Cologne Protocol in European contexts. Philos T R Soc B 376, doi:ARTN 20190714 452 10.1098/rstb.2019.0714 (2021). 453 24 de Pablo, J. F. L. et al. Palaeodemographic modelling supports a population bottleneck during the Pleistocene- Holocene transition in Iberia. Nat Commun 10, doi:ARTN 1872 456 10.1038/s41467- 019- 09833- 3 (2019). 457 25 Binford, L. R. Constructing frames of reference: an analytical method for archaeological theory building using ethnographic and environmental data sets. (University of California Press, 2019). 458 26 Johnson, A. L. Exploring adaptive variation among hunter- gatherers with Binford’s frames of reference. Journal of Archaeological Research 22, 1- 42 (2014).
+
+<--- Page Split --->
+
+462 27 Burke, K. D. et al. Differing climatic mechanisms control transient and accumulated vegetation novelty in Europe and eastern North America. Philos T R Soc B 374, doi:ARTN 20190218
+465 10.1098/rstb.2019.0218 (2019).
+466 28 Currie, D. J. Energy and Large-Scale Patterns of Animal-Species and Plant-Species Richness. Am Nat 137, 27-49, doi:Doi 10.1086/285144 (1991).
+468 29 Franklin, J. Mapping species distributions: spatial inference and prediction. (Cambridge University Press, 2010).
+470 30 Harcourt, A. Human biogeography. (Univ of California Press, 2012).
+471 31 Marlowe, F. W. Hunter-gatherers and human evolution. Evol Anthropol 14, 54-67, doi:10.1002/evan.20046 (2005).
+473 32 Belovsky, G. E. An Optimal Foraging-Based Model of Hunter-Gatherer Population-Dynamics. J Anthropol Archaeol 7, 329-372, doi:Doi 10.1016/0278-4165(88)90002-5 (1988).
+476 33 Williams, J. W. & Jackson, S. T. Novel climates, no-analog communities, and ecological surprises. Front Ecol Environ 5, 475-482, doi:10.1890/070037 (2007).
+477 34 Ohlemuller, R. Running Out of Climate Space. Science 334, 613-614, doi:10.1126/science.1214215 (2011).
+480 35 Williams, J. W., Jackson, S. T. & Kutzbacht, J. E. Projected distributions of novel and disappearing climates by 2100 AD. P Natl Acad Sci USA 104, 5738-5742, doi:10.1073/pnas.0606292104 (2007).
+483 36 Warren, D. L., Glor, R. E. & Turelli, M. Environmental Niche Equivalency Versus Conservatism: Quantitative Approaches to Niche Evolution. Evolution 62, 2868-2883, doi:10.1111/j.1558-5646.2008.00482.x (2008).
+486 37 Broennimann, O. et al. Measuring ecological niche overlap from occurrence and spatial environmental data. Global Ecol Biogeogr 21, 481-497, doi:10.1111/j.1466-8238.2011.00698.x (2012).
+488 38 Warren, D. L., Cardillo, M., Rosauer, D. F. & Bolnick, D. I. Mistaking geography for biology: inferring processes from species distributions. Trends Ecol Evol 29, 572-580, doi:10.1016/j.tree.2014.08.003 (2014).
+492 39 Wobst, H. M. The archaeo-ethnology of hunter-gatherers or the tyranny of the ethnographic record in archaeology. Am Antiquity, 303-309 (1978).
+494 40 Maier, A. et al. Demographic estimates of hunter-gatherers during the Last Glacial Maximum in Europe against the background of palaeoenvironmental data. Quatern Int 425, 49-61, doi:10.1016/j.quaint.2016.04.009 (2016).
+497 41 Riede, F. The resettlement of northern Europe. Oxford Handbook of the Archaeology and Anthropology of Hunter-Gatherers, 556-581 (2014).
+499 42 Jochim, M., Herhahn, C. & Starr, H. The Magdalenian colonization of southern Germany. Am Anthropol 101, 129-142, doi:DOI 10.1525/aa.1999.101.1.129 (1999).
+501 43 Arts, N. & Deeben, J. On the northwestern border of Late Magdalenian territory. Ecology and archaeology of early Late Glacial band societies in northwestern Europe. Late Glacial in Central Europe. Culture and environment, Wroclaw, 25-66 (1987).
+504 44 Maier, A. Population and settlement dynamics from the Gravettian to the Magdalenian. Mitteilungen der Gesellschaft für Urgeschichte 26, 83-101 (2017).
+506 45 Gamble, C., Davies, W., Pettitt, P. & Richards, M. Climate change and evolving human diversity in Europe during the last glacial. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 359, 243-254 (2004).
+508 46 Housley, R. A., Gamble, C. S., Street, M. & Pettitt, P. in Proceedings of the Prehistoric Society. 25-54 (Cambridge University Press).
+
+<--- Page Split --->
+
+Fort, J., Pujol, T. & Cavalli- Sforza, L. L. Palaeolithic populations and waves of advance. Cambridge Archaeological Journal 14, 53- 61 (2004). 48 Bellwood, P. et al. First Farmers: the Origins of Agricultural Societies, by Peter Bellwood. Malden (MA): Blackwell, 2005; ISBN 0- 631- 20565- 9 hardback £ 60; ISBN 0- 631- 20566- 7 paperback £ 17.99, xix+ 360 pp., 59 figs., 3 tables. Cambridge archaeological journal 17, 87- 109 (2007). 49 d'Errico, F. et al. The origin and evolution of sewing technologies in Eurasia and North America. J Hum Evol 125, 71- 86, doi:10.1016/j.jhevol.2018.10.004 (2018). 50 Dyson- Hudson, R. & Smith, E. A. Human territoriality: an ecological reassessment. Am Anthropol 80, 21- 41 (1978). 51 Laland, K. N. & Brown, G. R. Niche construction, human behavior, and the adaptive- lag hypothesis. Evol Anthropol 15, 95- 104, doi:10.1002/evan.20093 (2006). 52 Laland, K. N. & O'Brien, M. J. Niche Construction Theory and Archaeology. J Archaeol Method Th 17, 303- 322, doi:10.1007/s10816- 010- 9096- 6 (2010). 53 Riede, F. in Handbook of evolutionary research in archaeology 337- 358 (Springer, 2019). 54 Pedersen, J., Maier, A. & Riede, F. A punctuated model for the colonisation of the Late Glacial margins of northern Europe by Hamburgian hunter- gatherers. Quartär 65, 85- 104 (2018). 55 Whallon, R. Social networks and information: Non- "utilitarian" mobility among hunter- gatherers. J Anthropol Archaeol 25, 259- 270, doi:10.1016/j.jaa.2005.11.004 (2006). 56 Leal Filho, W. et al. Impacts of climate change to African indigenous communities and examples of adaptation responses. Nat Commun 12, 1- 4 (2021). 57 Heitz, C. F., Hinz, M., Laabs, J. & Hafner, A. Mobility as resilience capacity in northern Alpine Neolithic settlement communities. Archaeological review from cambridge 36, 75- 106 (2021). 58 Riede, F., Oetelaar, G. A. & VanderHoek, R. From crisis to collapse in hunter- gatherer societies. A comparative investigation of the cultural impacts of three large volcanic eruptions on past hunter- gatherers. Crisis to Collapse- The Archaeology of Social Breakdown. Louvain- la- Neuve: UCL Presses Universitaires De Louvain, 23- 39 (2017). 59 Halstead, P., O'Shea, J. & O'Shea, J. M. Bad year economics: cultural responses to risk and uncertainty. (Cambridge University Press, 2004). 60 Brovkin, V. et al. Past abrupt changes, tipping points and cascading impacts in the Earth system. Nature Geoscience, 1- 9 (2021). 61 Burke, A. et al. The archaeology of climate change: The case for cultural diversity. Proceedings of the National Academy of Sciences 118 (2021). 62 Binford, L. R. Willow Smoke and Dogs Tails - Hunter- Gatherer Settlement Systems and Archaeological Site Formation. Am Antiquity 45, 4- 20, doi:Doi 10.2307/279653 (1980). 63 Birdsell, J. B. Some Environmental and Cultural Factors Influencing the Structuring of Australian Aboriginal Populations. Am Nat 87, 171- 207, doi:Doi 10.1086/281776 (1953). 64 Kelly, R. L. The lifeways of hunter- gatherers: the foraging spectrum. (Cambridge University Press, 2013). 65 Pennington, R. (Cambridge, Cambridge University Press, 2001). 66 Wobst, H. M. Locational Relationships in Paleolithic Society. J Hum Evol 5, 49- 58, doi:Doi 10.1016/0047- 2484(76)90099- 3 (1976).
+
+<--- Page Split --->
+
+560 67 Tallavaara, M., Eronen, J. T. & Luoto, M. Productivity, biodiversity, and pathogens 561 influence the global hunter- gatherer population density. P Natl Acad Sci USA 115, 562 1232- 1237, doi:10.1073/pnas.1715638115 (2018). 563 68 Richards, M. P., Pettitt, P. B., Stiner, M. C. & Trinkaus, E. Stable isotope evidence for 564 increasing dietary breadth in the European mid- Upper Paleolithic. Proceedings of the 565 National Academy of Sciences 98, 6528- 6532 (2001). 566 69 Drucker, D. & Bocherens, H. Carbon and nitrogen stable isotopes as tracers of change 567 in diet breadth during Middle and Upper Palaeolithic in Europe. Int J Osteoarchaeol 568 14, 162- 177, doi:10.1002/oa.753 (2004). 569 70 Kretschmer, I. Demographische Untersuchungen zu Bevölkerungsdichten, Mobilität 570 und Landnutzungsmustern im späten Jungpaläolithikum. (Verlag Marie Leidorf 571 GmbH, 2015). 572 71 Langley, M. C. & Street, M. Long range inland- coastal networks during the Late 573 Magdalenian: Evidence for individual acquisition of marine resources at Andernach- 574 Martinsberg, German Central Rhineland. J Hum Evol 64, 457- 465, 575 doi:10.1016/j.jhevol.2013.01.015 (2013). 576 72 Lanczont, M. et al. Late Glacial environment and human settlement of the Central 577 Western Carpathians: A case study of the Nowa Biala 1 open- air site (Podhale 578 Region, southern Poland). Quatern Int 512, 113- 132, 579 doi:10.1016/j.quaint.2019.02.036 (2019). 580 73 Cziésla, E. Robbenjagd in Brandenburg? Gedanken zur Verwendung großer 581 Widerhakenspitzen. Ethnographisch- archaologische Zeitschrift 48, 1- 48 (2007). 582 74 Fick, S. E. & Hijmans, R. J. WorldClim 2: new 1- km spatial resolution climate 583 surfaces for global land areas. International journal of climatology 37, 4302- 4315 584 (2017). 585 75 Yee, T. W. & Mitchell, N. D. Generalized Additive- Models in Plant Ecology. J Veg 586 Sci 2, 587- 602, doi:10.2307/3236170 (1991). 587 76 Guisan, A., Edwards, T. C. & Hastie, T. Generalized linear and generalized additive 588 models in studies of species distributions: setting the scene. Ecol Model 157, 89- 100, 589 doi:Pii S0304- 3800(02)00204- 1 590 Doi 10.1016/S0304- 3800(02)00204- 1 (2002). 591 77 Fewster, R. M., Buckland, S. T., Siriwardena, G. M., Baillie, S. R. & Wilson, J. D. 592 Analysis of population trends for farmland birds using generalized additive models. 593 Ecology 81, 1970- 1984, doi:Doi 10.1890/0012- 9658(2000)081[1970:Aoptff]2.0. Co;2 594 (2000). 595 78 Drexler, M. & Ainsworth, C. H. Generalized Additive Models Used to Predict 596 Species Abundance in the Gulf of Mexico: An Ecosystem Modeling Tool. Plos One 597 8, doi:ARTN e64458 598 10.1371/journal.pone.0064458 (2013). 599 79 Moisen, G. G. & Frescino, T. S. Comparing five modelling techniques for predicting 600 forest characteristics. Ecol Model 157, 209- 225, doi:Pii S0304- 3800(02)00197- 7 601 Doi 10.1016/S0304- 3800(02)00197- 7 (2002). 602 80 Team, R. C. R: A language and environment for statistical computing. (2013). 603 81 Wood, S. N. Generalized additive models: an introduction with R. (CRC press, 604 2017). 605 82 Fasiolo, M., Wood, S. N., Zaffran, M., Nedellec, R. & Goude, Y. Fast Calibrated 606 Additive Quantile Regression. J Am Stat Assoc, doi:10.1080/01621459.2020.1725521 607 (2020).
+
+<--- Page Split --->
+
+608 83 Liu, Z. et al. Transient Simulation of Last Deglaciation with a New Mechanism for Bolling- Allerod Warming. Science 325, 310- 314, doi:10.1126/science.1171041 (2009).
+
+611 84 Lorenz, D. J., Nieto- Lugilde, D., Blois, J. L., Fitzpatrick, M. C. & Williams, J. W. Downscaled and debiased climate simulations for North America from 21,000 years ago to 2100AD. Sci Data 3, doi:ARTN 160048
+
+614 10.1038/sdata.2016.48 (2016). 615 85 Gowan, E. J. et al. A new global ice sheet reconstruction for the past 80000 years. Nat Commun 12, doi:ARTN 1199
+
+617 10.1038/s41467- 021- 21469- w (2021). 618 86 Vermeersch, P. M. European population changes during the Marine Isotope Stages 2 and 3. Quatern Int 137, 77- 85, doi:10.1016/j.quaint.2004.11.021 (2005). 619 87 Gamble, C., Davies, W., Pettitt, P., Hazelwood, L. & Richards, M. The archaeological and genetic foundations of the European population during the late glacial: Implications for 'agricultural thinking'. Cambridge Archaeological Journal 15, 193- 223, doi:10.1017/S0959774305000107 (2005). 620 88 Steele, J. Radiocarbon dates as data: quantitative strategies for estimating colonization front speeds and event densities. J Archaeol Sci 37, 2017- 2030, doi:10.1016/j.jas.2010.03.007 (2010). 621 89 Shennan, S. et al. Regional population collapse followed initial agriculture booms in mid- Holocene Europe. Nat Commun 4, doi:ARTN 2486
+
+629 10.1038/ncomms3486 (2013). 630 90 Surovell, T. A., Finley, J. B., Smith, G. M., Brantingham, P. J. & Kelly, R. Correcting temporal frequency distributions for taphonomic bias. J Archaeol Sci 36, 1715- 1724, doi:10.1016/j.jas.2009.03.029 (2009). 631 91 Williams, A. N. The use of summed radiocarbon probability distributions in archaeology: a review of methods. J Archaeol Sci 39, 578- 589, doi:10.1016/j.jas.2011.07.014 (2012). 632 92 Kelly, R. L., Surovell, T. A., Shuman, B. N. & Smith, G. M. A continuous climatic impact on Holocene human population in the Rocky Mountains. P Natl Acad Sci USA 110, 443- 447, doi:10.1073/pnas.1201341110 (2013). 633 93 Thornthwaite, C. W. An approach toward a rational classification of climate. Geographical review 38, 55- 94 (1948). 634 94 Riley, S. J., DeGloria, S. D. & Elliot, R. Index that quantifies topographic heterogeneity. intermountain Journal of sciences 5, 23- 27 (1999).
+
+## Acknowledgements
+
+645 AO was supported by the AUFF Starting Grant (AUFF- F- 2018- 7- 8). FR's contribution is part of CLIOARCH, an ERC Consolidator Grant project that has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 817564).
+
+<--- Page Split --->
+
+## 649 Author contributions
+
+650 AO: Conceptualization; Methodology; Formal analysis; Resources; writing - original draft, 651 writing - review & editing; Visualization.
+
+652 FR: Conceptualization; Methodology; writing - original draft, writing - review & editing.
+
+<--- Page Split --->
+
+Table 1. Variables used to generate ethnographic based models of the effect of climate on hunter-gatherer population density and summary of cross-validated deviance explained for the evaluated variables. Estimates correspond to those of a 1000-fold cross-validation approach (1000 samples of 70% training and 30% testing observations) or the full dataset
+
+| Variable name | Acronym | Units | How does the variable determine population density? | Cross-validated Deviance explained. Mean [95% CI] | Full-dataset Deviance explained |
| Effective Temperature* | ET | C | Energy availability | 0.774 [0.8-0.826] | 0.792 |
Potential Evapotranspiration** | PET | mm/yr | Energy availability | 0.751 [0.8-0.81] | 0.774 |
Mean Annual Temperature | MAT | C | Energy availability | 0.733 [0.7-0.777] | 0.757 |
Mean temperature of the Coldest Month | MCM | C | Extreme Events | 0.798 [0.8-0.839] | 0.812 |
Mean temperature of the Warmest Month | MWM | C | Extreme Events | 0.705 [0.7-0.762] | 0.737 |
| Temperature Seasonality | TSeson | C | Annual Variability | 0.777 [0.8-0.839] | 0.811 |
Spring Mean Temperature | SpMT | C | Seasonal trends | 0.789 [0.8-0.828] | 0.804 |
Summer Mean Temperature | SmMT | C | Seasonal trends | 0.773 [0.8-0.817] | 0.786 |
| Fall Mean Temperature | FMT | C | Seasonal trends | 0.725 [0.7-0.786] | 0.750 |
Winter Mean Temperature | WMT | C | Seasonal trends | 0.765 [0.8-0.808] | 0.782 |
| Annual precipitation | PREC | mm/yr | Energy availability | 0.701 [0.7-0.757] | 0.712 |
Precipitation of the Driest Month | PDM | mm/m onth | Extreme Events | 0.746 [0.7-0.793] | 0.760 |
Precipitation of the Wettest Month | PDM | mm/m onth | Extreme Events | 0.77 [0.8-0.804] | 0.784 |
| Precipitation Seasonality | PSeson | mm/m onth | Annual Variability | 0.737 [0.7-0.772] | 0.748 |
| Spring Precipitation | SpPREC | mm/m onth | Seasonal trends | 0.773 [0.8-0.814] | 0.788 |
| Summer Precipitation | SmPREC | mm/m onth | Seasonal trends | 0.753 [0.8-0.8] | 0.779 |
| Fall Precipitation | FPREC | mm/m onth | Seasonal trends | 0.7 [0.7-0.772] | 0.711 |
| Winter Precipitation | TPREC | mm/m onth | Seasonal trends | 0.774 [0.8-0.826] | 0.792 |
Topographic Ruggedness Index*** | | m | Habitat Heterogeneity | 0.751 [0.8-0.81] | 0.774 |
| 654 | * Calculated following 25 |
| 655 | ** Calculated following on 93. |
| 656 | *** Calculated following 94 |
+
+<--- Page Split --->
+
+
+Figure 1. Quantile Generalised Additive Models (qGAM) describing the relation between environmental factors and population density for 10-percentiles (dashed lines), 50-percentiles (solid lines), and 90-percentiles (doted lines). Here, only the six most limiting factors during the 22kaBP to 8kaBP are presented. Full explorations of evaluated variables presented in Supplementary material S1.
+
+<--- Page Split --->
+
+
+Figure 2. Convergence between current climatic conditions (hashed density plots) and paleoclimatic conditions at four different periods (coloured density plots). Paleoclimatic periods are Greenland Stadial 2, Greenland Interstadial 1, Greenland Stadial 1, and Holocene. As in Figure 1, only the six most limiting factors during the 22kaBP to 8kaBP are presented. Full explorations of evaluated variables presented in Supplementary material S2.
+
+<--- Page Split --->
+
+
+Figure 3. Contrast between Europe wide mean population density (top panel), and trends in key environmental variables (bottom). Estimated average population density for all Europe based on a randomization approach (top panel) are compared to archaeological population proxy based on number of calibrated radiocarbon dates for Europe between 21 and 11kyBP based on \(^{12}\) summaries of the Radiocarbon Palaeolithic Europe Database v28 \(^{86}\) (red), and core area (cf. \(^{23}\) population density mean and upper/lower estimates based on the Cologne Protocol (blue). On the bottom panel, plotted variables are: Effective temperature, Minimum temperature of the Coldest Month, and Maximum temperature of the Warmest Month.
+
+<--- Page Split --->
+
+
+Figure 4. Estimated human population density and range (areas where population density \(> 1\) individual per \(100\mathrm{km}^2\) ) (A-E) and factors limiting population density (F-J) across Europe for selected times during the 22ky to 8kyBP period. (A, F) Greenland Stadial 2; (B, G) Greenland Interstadial 1; (C, H) Greenland Stadial 1 warming terminations (D, I) Holocene initiation; (E, J) Mid-Holocene. Areas in grey scale represent the glacier extent as derived by PaleoMIST 85.
+
+<--- Page Split --->
+
+
+Figure 5. Proportion of the ice-free area of Europe where each variable was estimated to be the factor limiting population density (A); and estimated population size based on the mean environmental conditions for each century (B). In both panels, only the six variables with the highest percentages of cells where the variable is the limiting factor are presented.
+
+<--- Page Split --->
+
+
+
+Supplementary material S1 Quantile Generalised Additive Models (qGAM) describing the relation between the six most important environmental factors explored and population density for 10- percentiles (dashed lines), 50- percentiles (solid lines), and 90- percentiles (doted lines). Title acronyms as in Table 1.
+
+<--- Page Split --->
+![PLACEHOLDER_27_0]
+
+Supplementary material S2. Overlap between current climatic conditions (hashed density plots) used for model building and paleoclimatic databases (coloured density plots) used to hindcast human population density for all 19-climatic variables used. Title acronyms as in Table 1.
+
+<--- Page Split --->
diff --git a/preprint/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a.mmd b/preprint/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..84ac7388ff532826e07606b403054ff86af5a520
--- /dev/null
+++ b/preprint/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a.mmd
@@ -0,0 +1,164 @@
+
+# Reference-free and cost-effective automated cell type annotation with GPT-4 in single-cell RNA-seq analysis
+
+Zhicheng Ji zhicheng.ji@duke.edu
+
+Duke University https://orcid.org/0000- 0002- 9457- 4704 Wenpin Hou Columbia University https://orcid.org/0000- 0003- 0972- 2192
+
+Brief Communication
+
+Keywords:
+
+Posted Date: May 2nd, 2023
+
+DOI: https://doi.org/10.21203/rs.3.rs- 2824971/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Methods on March 25th, 2024. See the published version at https://doi.org/10.1038/s41592- 024- 02235- 4.
+
+<--- Page Split --->
+
+# Reference-free and cost-effective automated cell type annotation with GPT-4 in single-cell RNA-seq analysis
+
+Wenpin Hou \(^{1,\dagger}\) and Zhicheng Ji \(^{2,\dagger}\)
+
+\(^{1}\) Department of Biostatistics, The Mailman School of Public Health, Columbia University, New York City, NY, USA \(^{2}\) Department of Biostatistics and Bioinformatics, Duke University School of Medicine, Durham, NC, USA. \(^{\dagger}\) Corresponding author. E- mail: wh2526@cumc.columbia.edu; zhicheng.ji@duke.edu
+
+## ABSTRACT
+
+Cell type annotation is an essential step in single- cell RNA- seq analysis. However, it is a time- consuming process that often requires expertise in collecting canonical marker genes and manually annotating cell types. Automated cell type annotation methods typically require the acquisition of high- quality reference datasets and the development of additional pipelines. We demonstrate that GPT- 4, a highly potent large language model, can automatically and accurately annotate cell types by utilizing marker gene information generated from standard single- cell RNA- seq analysis pipelines. Evaluated across hundreds of tissue types and cell types, GPT- 4 generates cell type annotations exhibiting strong concordance with manual annotations, and has the potential to considerably reduce the effort and expertise needed in cell type annotation.
+
+## Main
+
+In single- cell RNA- sequencing (scRNA- seq) analysis \(^{1,2}\) , cell type annotation is a fundamental step to elucidate cell population heterogeneity and understand the diverse functions of different cell populations within complex tissues. Standard single- cell analysis software, such as Seurat \(^{3}\) and Scanpy \(^{4}\) , routinely employ manual cell type annotation. These software tools assign single cells into clusters by cell clustering and conduct differential analysis to identify differentially expressed genes across cell clusters. Subsequently, a human expert compares canonical cell type markers with differential gene information to assign a cell type annotation to each cell cluster. This manual annotation approach requires prior knowledge of canonical cell type markers in the given tissues and is often laborious and time- consuming. Although several automated cell type annotation methods have been developed \(^{5 - 13}\) , manual cell type annotation using marker gene information remains widely used in scRNA- seq analysis \(^{14 - 28}\) .
+
+Generative Pre- trained Transformers (GPT), including GPT- 3, ChatGPT, and GPT- 4, are large language models trained on massive amounts of data and capable of generating human- like text based on user- provided contexts. Recent studies have demonstrated the competitive performance of GPT models in answering biomedical questions \(^{29 - 32}\) . Thus, we hypothesize that GPT- 4, one of the most advanced GPT models, has the ability to accurately identify cell types using marker gene information. GPT- 4 will potentially transform the manual cell type annotation process into a semi- automated procedure, with optional help from human experts to fine- tune GPT- 4- generated annotations (Figure 1a). Compared to other automated cell type annotation methods that require building additional pipelines and collecting high- quality reference datasets, GPT- 4 offers cost- efficiency and seamless integration into existing single- cell analysis pipelines, such as Seurat \(^{3}\) and Scanpy \(^{4}\) . The vast amount of training data enables GPT- 4 to be applied across a wide variety of tissues and cell types, overcoming the limitations of other automated cell type annotation methods restricted to specific reference datasets. Additionally, the chatbot- like nature of GPT- 4 allows users to easily adjust annotation granularity and provide feedback for iterative answer improvement (Figure 1a- b) \(^{31}\) .
+
+To validate the hypothesis, we systematically assessed GPT- 4's cell type annotation performance across five datasets, hundreds of tissue types and cell types, and in both human and mouse (Figure 2a). Computationally identified differential genes in four scRNA- seq datasets (Azimuth by HuBMAP \(^{22}\) , Human Cell Atlas (HCA) \(^{17}\) , Human Cell Landscape (HCL) \(^{19}\) , and Mouse Cell Atlas (MCA) \(^{18}\) ), and canonical marker genes identified through literature search in one dataset (literature) \(^{17}\) , were used as inputs to GPT- 4. Cell type annotation for HCL and MCA was performed and evaluated once by aggregating all tissues, similar to the original studies. In other studies, cell type annotation was performed and evaluated within each tissue. GPT- 4 was queried using prompts similar to Figure 1b, and its cell type annotations were compared to those provided by the original studies. The comparison results were classified as “fully match” if GPT- 4 and manual annotations refer to the same cell type, “partially match” if the two annotations refer to similar but distinct cell types (e.g., monocyte and macrophage), and “mismatch” if the two annotations refer to different cell types (e.g., T cell and macrophage). If the granularity of the manual annotation
+
+<--- Page Split --->
+
+exceeded GPT- 4 annotation, GPT- 4 was asked to give more specific annotations (Figure 1b). Figure 2b shows an example of evaluating GPT- 4 cell type annotations in a human prostate tissue literature search dataset. Supplementary Table 1 contains all cell type annotations generated manually or by GPT- 4 across different tissue types and datasets, as well as agreement between manual and GPT- 4 annotations.
+
+The performance of cell type annotation can be affected by the number of top differential genes used as reference. So we first assessed whether the number of top differential genes would affect the performance of GPT- 4 cell type annotation. To facilitate comparison, we assigned agreement scores of 1, 0.5, and 0 to cases of "fully match", "partially match", and "mismatch" respectively, and calculated the average scores across cell types within a tissue or dataset. The comparison was only performed in HCA, HCL, and MCA datasets, as full lists of differential genes were available. Figure 2c shows that GPT- 4 has the best agreement with human annotation when using the top 10 differential genes, and using more differential genes may reduce agreement. A plausible explanation is that human experts may only rely on a small number of top differential genes if they already provide a clear cell type annotation. In subsequent analyses, we used GPT- 4 cell type annotation with the top 10 differential genes for HCA, HCL, and MCA datasets.
+
+In almost all studies and tissues, GPT- 4 annotations fully or partially match manual annotations for at least \(75\%\) of cell types (Figure 2d), demonstrating GPT- 4's ability to generate cell type annotations comparable to those of human experts. The agreement is highest for marker genes identified through literature search, with GPT- 4 annotations fully matching manual annotations for approximately \(75\%\) of cell types. The agreement decreases in marker genes identified by differential analysis, which may be attributable to a lower proportion of canonical marker genes being identified as top differential genes. We then grouped cell types into major cell categories according to the manual cell type annotations (Figure 2e, Supplementary Table 1). The agreement between GPT- 4 and manual annotations is highest among cell categories that are more homogeneous (e.g., erythroid cells and adipocytes), and lowest among cell categories that are more heterogeneous (e.g., stromal cells).
+
+The low agreement between GPT- 4 and manual annotations in some cell types does not necessarily imply that GPT- 4 annotation is incorrect. For instance, cell types classified as stromal cells include fibroblasts and osteoblasts, which express type I collagen genes, as well as chondrocytes, which express type II collagen genes. For cells manually annotated as stromal cells, GPT- 4 assigns cell type annotations with higher granularity (e.g., fibroblasts, osteoblasts, and chondrocytes), resulting in partial matches and a lower agreement. For cell types manually annotated as stromal cells, the type I collagen genes appear in the differential gene lists in \(80\%\) of cases annotated as fibroblast or osteoblast by GPT- 4 and in \(0\%\) of cases annotated as chondrocyte by GPT- 4 (Figure 2f). This agrees with prior knowledge and the pattern observed in cell types manually annotated as chondrocyte, fibroblast, and osteoblast (Figure 2f), suggesting that GPT- 4 provides more accurate cell type annotations than manual annotations for stromal cells.
+
+We further tested the performance of GPT- 4 when dealing with more complicated situations in real data analysis (Figure 1c). We first tested GPT- 4's ability to identify a cell cluster representing a mixture of cell types, which may occur when a cluster contains a large number of doublets or has low- resolution cell clustering. We generated simulated datasets by combining canonical markers from two distinct cell types in half of the instances and using canonical markers from a single cell type in the other half (Methods). GPT- 4 discriminated between single and mixed cell types with an average accuracy of \(94\%\) (Figure 2g). We then tested GPT- 4's ability to identify new cell types with marker genes not documented by existing literature. We created simulation datasets using randomly selected genes as cell type markers in half of the cases and canonical markers from a single cell type in the other half (Methods). GPT- 4 is able to differentiate known and unknown cell types with an average accuracy of \(100\%\) (Figure 2h). We also tested the reproducibility of GPT- 4 annotations leveraging results in previous simulation studies (Methods). On average, GPT- 4 generated identical annotations for the same cell type markers in \(91.2\%\) of cases (Figure 2i), showing a high level of reproducibility. In conclusion, GPT- 4 exhibits robust performance across various scenarios encountered in real data analysis.
+
+In conclusion, our findings demonstrate a high level of agreement between cell type annotations generated by GPT- 4 and by human experts. Remarkably, GPT- 4 exhibits higher accuracy in annotating specific cell types. GPT- 4 can be employed as a dependable tool for automated cell type annotation of single- cell RNA- seq data, substantially reducing the time and effort required for manual annotation.
+
+## Methods
+
+## Dataset collection
+
+For the HuBMAP Azimuth project, manually annotated cell types and their marker genes were downloaded from the Azimuth website (https://azimuth.hubmapconsortium.org/). Azimuth provides cell type annotations for each tissue at different granularity levels. We selected the level of granularity with the fewest number of cell types, provided that there were more than 10 cell types within that level.
+
+For HCA \(^{17}\) , HCL \(^{19}\) , and MCA \(^{18}\) , manually annotated cell types and corresponding differential gene lists were downloaded directly from the original studies. Lists of marker genes through literature search and the corresponding cell types were
+
+<--- Page Split --->
+
+downloaded from the HCA study \(^{17}\) , and only cell types with at least 5 marker genes were used.
+
+## Gene set preparation and GPT-4 prompts
+
+Before using GPT- 4 to identify cell types, one needs to first prepare a list of top differential genes for each cell cluster. For example, one can use the following R code to extract gene lists of top 10 differential genes obtained from the standard Seurat pipeline. In the extracted results, each row is a list of differential genes for one cell cluster, separated by '
+
+# d is the differential gene table generated by Seurat ordered by p- values cat(tapply(d$gene,list(d$cluster),function(i) paste0(i[1:10],collapse='','))sep='\n')
+
+The gene lists used in this study were prepared using customized code.
+
+GPT- 4 was accessed by visiting the ChatGPT website (https://chat.openai.com/). The "Mar 23" version of GPT- 4 was used for this study. The following words were pasted on top of the differential gene lists and used as the initial prompt for GPT- 4. The word "prostate" in the following prompt was replaced with the appropriate tissue names when annotating cell types for each tissue.
+
+Identify cell types of human prostate cells using the following markers. Identify one cell type for each row. Only provide the cell type name.
+
+GPT- 4 returned a list of cell type names for each query. The following prompt was used to increase the granularity of cell type annotations when needed.
+
+Be more specific
+
+To annotate cell clusters that could be a mixture of multiple cell types, the following words are added to the prompt.
+
+Some could be a mixture of multiple cell types.
+
+To annotate cell clusters that cannot be characterized by known cell type markers and are potentially new cell types, the following words are added to the prompt
+
+Some could be unknown cell types.
+
+Finally, the following prompt can be used to convert the list of cell type annotations generated by GPT- 4 into R code that directly creates a vector of cell type names in R.
+
+Use "', " to concatenate all results into a single sentence. Put "c(" in front of the sentence and "')" after the sentence
+
+## Simulation studies and reproducibility
+
+To generate simulation datasets of unknown cell types, we compiled a list of all human genes using the Bioconductor org.Hs.eg.db package \(^{33}\) . In each simulation iteration, ten simulated unknown cell types were generated. The marker genes for each unknown cell type were produced by combining ten randomly selected human genes. Additionally, we included the literature- based cell type markers of ten randomly chosen human breast cell types as negative controls of known cell types, similar to the previous simulation study. This entire simulation process was repeated five times. Subsequently, GPT- 4 was queried using these simulated marker gene lists, and its performance in differentiating between mixed and single cell types was assessed.
+
+To generate simulation datasets of unknown cell types, we compiled a list of all human genes using the Bioconductor org.Hs.eg.db package \(^{33}\) . In each simulation iteration, ten simulated unknown cell types were generated. The marker genes for each unknown cell type were produced by combining ten randomly selected human genes. Additionally, we included the literature- based cell type markers of ten randomly chosen human breast cell types as negative controls of known cell types, similar to the previous simulation study. This entire simulation process was repeated five times. Subsequently, GPT- 4 was queried using these simulated marker gene lists, and its performance in distinguishing between known and unknown cell types was assessed.
+
+We assessed the reproducibility of GPT- 4 responses by leveraging the repeated querying of GPT- 4 with identical marker gene lists of the same negative control cell types in both simulation studies. For each cell type, reproducibility is defined as the proportion of instances in which GPT- 4 generates the most prevalent cell type annotation. For instance, in the case of vascular endothelial cells, GPT- 4 produces "endothelial cells" 8 times and "blood vascular endothelial cells" once. Consequently, the most prevalent cell type annotation is "endothelial cells," and the reproducibility is calculated as \(\frac{8}{9} = 0.89\) .
+
+<--- Page Split --->
+
+## Acknowledgments
+
+Z.J. was supported by the National Institutes of Health under Award Number 1U54AG075936- 01. The manuscript was polished by GPT- 4.
+
+## Author contributions
+
+All authors conceived the study, conducted the analysis, and wrote the manuscript.
+
+## Competing interests
+
+All authors declare no competing interests.
+
+<--- Page Split --->
+
+
+Figure 1. a, Diagram comparing cell type annotations by human experts, GPT-4, and other automated methods. b, An example showing GPT-4 prompts and answers for annotating human prostate cells with increasing granularity. c, An example showing GPT-4 prompts and answers for annotating single cell types (first two cell types), mixed cell types (third cell type), and new cell types (fourth cell type).
+
+<--- Page Split --->
+
+
+| a | Dataset | Species | Number of tissues | Number of cell types | Gene list source |
| Azimuth | Human | 11 | 276 | Differential analysis |
| Human Cell Atlas (HCA) | Human | 7 | 72 | Differential analysis |
| Human Cell Landscape (HCL) | Human | 60* | 101 | Differential analysis |
| literature (from HCA) | Human | 7 | 30 | Literature search |
| Mouse Cell Atlas (MCA) | Mouse | 51* | 65 | Differential analysis |
+
+\\* Cell type annotations were done by aggregating across tissues in the original studies
+
+| Manual annotation | GPT-4 answer | Agreement |
| Adipocyte | Adipocytes | Full |
| B cell_memory | B cells | Partial |
| Fibroblast | Fibroblasts | Full |
| Luminal Epithelial | Luminal epithelial cells | Full |
| Lymphatic Endothelial | Lymphatic endothelial | Full |
| Macrophage | Macrophages | Full |
| Mast Cell | Mast cells | Full |
| Pericyte | Pericytes | Full |
| Smooth Muscle | Smooth muscle cells | Full |
| T cell | T cells | Full |
| Vascular Endothelial | Endothelial cells | Partial |
+
+
+
+Figure 2. Evaluation of cell type annotation by GPT-4. a, Datasets included in this study b, Agreement between original and GPT-4 annotations in identifying cell types of human prostate cells. c, Averaged agreement score (y-axis) and the number of top differential genes (x-axis) in HCA, HCL, and MCA datasets. d, Proportion of cell types with different levels of agreement in each study and tissue. Averaged agreement scores are shown as black dots. e, Proportion of cell types with different levels of agreement in each cell category. Averaged agreement scores are shown as black dots. f, Proportion of cell types that include type I collagen gene in the differential gene lists. The cell types are either classified as stromal cells by manual annotations and fibroblast, osteoblast, or chondrocyte by GPT-4 annotations, or classified as fibroblast, osteoblast, or chondrocyte by manual annotations. g, Proportion of cases where GPT-4 correctly identifies mixed and single cell types. Each dot represents one round of simulation. h, Proportion of cases where GPT-4 correctly identifies known and unknown cell types. Each dot represents one round of simulation. i, Reproducibility of GPT-4 annotations. Each dot represents one cell type.
+
+<--- Page Split --->
+
+## References
+
+<--- Page Split --->
+
+27. Zeisel, A. et al. Cell types in the mouse cortex and hippocampus revealed by single-cell rna-seq. Science 347, 1138–1142 (2015).
+
+28. Zou, Z. et al. A single-cell transcriptomic atlas of human skin aging. Dev. cell 56, 383–397 (2021).
+
+29. Kung, T. H. et al. Performance of chatgpt on usmle: Potential for ai-assisted medical education using large language models. PLoS digital health 2, e0000198 (2023).
+
+30. Hou, W. & Ji, Z. Geneturing tests gpt models in genomics. bioRxiv 2023–03 (2023).
+
+31. Shue, E. et al. Empowering beginners in bioinformatics with chatgpt. bioRxiv 2023–03 (2023).
+
+32. Duong, D. & Solomon, B. D. Analysis of large-language model versus human performance for genetics questions. medRxiv 2023–01 (2023).
+
+33. Gentleman, R. C. et al. Bioconductor: open software development for computational biology and bioinformatics. Genome biology 5, 1–16 (2004).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- supptable1.csv
+
+<--- Page Split --->
diff --git a/preprint/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a_det.mmd b/preprint/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..e09932c66f48bda5e5c71fb3f8e6dbbf02a514a6
--- /dev/null
+++ b/preprint/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a/preprint__02381398ad3c168dad4fb3121959ba38b9f694fc8f5d7aeae79ef0842f4b081a_det.mmd
@@ -0,0 +1,224 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 904, 209]]<|/det|>
+# Reference-free and cost-effective automated cell type annotation with GPT-4 in single-cell RNA-seq analysis
+
+<|ref|>text<|/ref|><|det|>[[44, 230, 280, 277]]<|/det|>
+Zhicheng Ji zhicheng.ji@duke.edu
+
+<|ref|>text<|/ref|><|det|>[[44, 303, 590, 370]]<|/det|>
+Duke University https://orcid.org/0000- 0002- 9457- 4704 Wenpin Hou Columbia University https://orcid.org/0000- 0003- 0972- 2192
+
+<|ref|>text<|/ref|><|det|>[[44, 410, 230, 429]]<|/det|>
+Brief Communication
+
+<|ref|>text<|/ref|><|det|>[[44, 448, 136, 466]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 486, 291, 505]]<|/det|>
+Posted Date: May 2nd, 2023
+
+<|ref|>text<|/ref|><|det|>[[44, 524, 475, 544]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 2824971/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 561, 910, 604]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 622, 530, 642]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 678, 943, 721]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Methods on March 25th, 2024. See the published version at https://doi.org/10.1038/s41592- 024- 02235- 4.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[90, 74, 907, 137]]<|/det|>
+# Reference-free and cost-effective automated cell type annotation with GPT-4 in single-cell RNA-seq analysis
+
+<|ref|>text<|/ref|><|det|>[[90, 147, 395, 168]]<|/det|>
+Wenpin Hou \(^{1,\dagger}\) and Zhicheng Ji \(^{2,\dagger}\)
+
+<|ref|>text<|/ref|><|det|>[[90, 183, 901, 231]]<|/det|>
+\(^{1}\) Department of Biostatistics, The Mailman School of Public Health, Columbia University, New York City, NY, USA \(^{2}\) Department of Biostatistics and Bioinformatics, Duke University School of Medicine, Durham, NC, USA. \(^{\dagger}\) Corresponding author. E- mail: wh2526@cumc.columbia.edu; zhicheng.ji@duke.edu
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 254, 198, 272]]<|/det|>
+## ABSTRACT
+
+<|ref|>text<|/ref|><|det|>[[94, 303, 904, 401]]<|/det|>
+Cell type annotation is an essential step in single- cell RNA- seq analysis. However, it is a time- consuming process that often requires expertise in collecting canonical marker genes and manually annotating cell types. Automated cell type annotation methods typically require the acquisition of high- quality reference datasets and the development of additional pipelines. We demonstrate that GPT- 4, a highly potent large language model, can automatically and accurately annotate cell types by utilizing marker gene information generated from standard single- cell RNA- seq analysis pipelines. Evaluated across hundreds of tissue types and cell types, GPT- 4 generates cell type annotations exhibiting strong concordance with manual annotations, and has the potential to considerably reduce the effort and expertise needed in cell type annotation.
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 437, 137, 454]]<|/det|>
+## Main
+
+<|ref|>text<|/ref|><|det|>[[90, 463, 908, 600]]<|/det|>
+In single- cell RNA- sequencing (scRNA- seq) analysis \(^{1,2}\) , cell type annotation is a fundamental step to elucidate cell population heterogeneity and understand the diverse functions of different cell populations within complex tissues. Standard single- cell analysis software, such as Seurat \(^{3}\) and Scanpy \(^{4}\) , routinely employ manual cell type annotation. These software tools assign single cells into clusters by cell clustering and conduct differential analysis to identify differentially expressed genes across cell clusters. Subsequently, a human expert compares canonical cell type markers with differential gene information to assign a cell type annotation to each cell cluster. This manual annotation approach requires prior knowledge of canonical cell type markers in the given tissues and is often laborious and time- consuming. Although several automated cell type annotation methods have been developed \(^{5 - 13}\) , manual cell type annotation using marker gene information remains widely used in scRNA- seq analysis \(^{14 - 28}\) .
+
+<|ref|>text<|/ref|><|det|>[[90, 601, 908, 770]]<|/det|>
+Generative Pre- trained Transformers (GPT), including GPT- 3, ChatGPT, and GPT- 4, are large language models trained on massive amounts of data and capable of generating human- like text based on user- provided contexts. Recent studies have demonstrated the competitive performance of GPT models in answering biomedical questions \(^{29 - 32}\) . Thus, we hypothesize that GPT- 4, one of the most advanced GPT models, has the ability to accurately identify cell types using marker gene information. GPT- 4 will potentially transform the manual cell type annotation process into a semi- automated procedure, with optional help from human experts to fine- tune GPT- 4- generated annotations (Figure 1a). Compared to other automated cell type annotation methods that require building additional pipelines and collecting high- quality reference datasets, GPT- 4 offers cost- efficiency and seamless integration into existing single- cell analysis pipelines, such as Seurat \(^{3}\) and Scanpy \(^{4}\) . The vast amount of training data enables GPT- 4 to be applied across a wide variety of tissues and cell types, overcoming the limitations of other automated cell type annotation methods restricted to specific reference datasets. Additionally, the chatbot- like nature of GPT- 4 allows users to easily adjust annotation granularity and provide feedback for iterative answer improvement (Figure 1a- b) \(^{31}\) .
+
+<|ref|>text<|/ref|><|det|>[[90, 770, 908, 921]]<|/det|>
+To validate the hypothesis, we systematically assessed GPT- 4's cell type annotation performance across five datasets, hundreds of tissue types and cell types, and in both human and mouse (Figure 2a). Computationally identified differential genes in four scRNA- seq datasets (Azimuth by HuBMAP \(^{22}\) , Human Cell Atlas (HCA) \(^{17}\) , Human Cell Landscape (HCL) \(^{19}\) , and Mouse Cell Atlas (MCA) \(^{18}\) ), and canonical marker genes identified through literature search in one dataset (literature) \(^{17}\) , were used as inputs to GPT- 4. Cell type annotation for HCL and MCA was performed and evaluated once by aggregating all tissues, similar to the original studies. In other studies, cell type annotation was performed and evaluated within each tissue. GPT- 4 was queried using prompts similar to Figure 1b, and its cell type annotations were compared to those provided by the original studies. The comparison results were classified as “fully match” if GPT- 4 and manual annotations refer to the same cell type, “partially match” if the two annotations refer to similar but distinct cell types (e.g., monocyte and macrophage), and “mismatch” if the two annotations refer to different cell types (e.g., T cell and macrophage). If the granularity of the manual annotation
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 79, 908, 140]]<|/det|>
+exceeded GPT- 4 annotation, GPT- 4 was asked to give more specific annotations (Figure 1b). Figure 2b shows an example of evaluating GPT- 4 cell type annotations in a human prostate tissue literature search dataset. Supplementary Table 1 contains all cell type annotations generated manually or by GPT- 4 across different tissue types and datasets, as well as agreement between manual and GPT- 4 annotations.
+
+<|ref|>text<|/ref|><|det|>[[90, 141, 908, 276]]<|/det|>
+The performance of cell type annotation can be affected by the number of top differential genes used as reference. So we first assessed whether the number of top differential genes would affect the performance of GPT- 4 cell type annotation. To facilitate comparison, we assigned agreement scores of 1, 0.5, and 0 to cases of "fully match", "partially match", and "mismatch" respectively, and calculated the average scores across cell types within a tissue or dataset. The comparison was only performed in HCA, HCL, and MCA datasets, as full lists of differential genes were available. Figure 2c shows that GPT- 4 has the best agreement with human annotation when using the top 10 differential genes, and using more differential genes may reduce agreement. A plausible explanation is that human experts may only rely on a small number of top differential genes if they already provide a clear cell type annotation. In subsequent analyses, we used GPT- 4 cell type annotation with the top 10 differential genes for HCA, HCL, and MCA datasets.
+
+<|ref|>text<|/ref|><|det|>[[90, 276, 908, 397]]<|/det|>
+In almost all studies and tissues, GPT- 4 annotations fully or partially match manual annotations for at least \(75\%\) of cell types (Figure 2d), demonstrating GPT- 4's ability to generate cell type annotations comparable to those of human experts. The agreement is highest for marker genes identified through literature search, with GPT- 4 annotations fully matching manual annotations for approximately \(75\%\) of cell types. The agreement decreases in marker genes identified by differential analysis, which may be attributable to a lower proportion of canonical marker genes being identified as top differential genes. We then grouped cell types into major cell categories according to the manual cell type annotations (Figure 2e, Supplementary Table 1). The agreement between GPT- 4 and manual annotations is highest among cell categories that are more homogeneous (e.g., erythroid cells and adipocytes), and lowest among cell categories that are more heterogeneous (e.g., stromal cells).
+
+<|ref|>text<|/ref|><|det|>[[90, 397, 908, 533]]<|/det|>
+The low agreement between GPT- 4 and manual annotations in some cell types does not necessarily imply that GPT- 4 annotation is incorrect. For instance, cell types classified as stromal cells include fibroblasts and osteoblasts, which express type I collagen genes, as well as chondrocytes, which express type II collagen genes. For cells manually annotated as stromal cells, GPT- 4 assigns cell type annotations with higher granularity (e.g., fibroblasts, osteoblasts, and chondrocytes), resulting in partial matches and a lower agreement. For cell types manually annotated as stromal cells, the type I collagen genes appear in the differential gene lists in \(80\%\) of cases annotated as fibroblast or osteoblast by GPT- 4 and in \(0\%\) of cases annotated as chondrocyte by GPT- 4 (Figure 2f). This agrees with prior knowledge and the pattern observed in cell types manually annotated as chondrocyte, fibroblast, and osteoblast (Figure 2f), suggesting that GPT- 4 provides more accurate cell type annotations than manual annotations for stromal cells.
+
+<|ref|>text<|/ref|><|det|>[[90, 533, 908, 713]]<|/det|>
+We further tested the performance of GPT- 4 when dealing with more complicated situations in real data analysis (Figure 1c). We first tested GPT- 4's ability to identify a cell cluster representing a mixture of cell types, which may occur when a cluster contains a large number of doublets or has low- resolution cell clustering. We generated simulated datasets by combining canonical markers from two distinct cell types in half of the instances and using canonical markers from a single cell type in the other half (Methods). GPT- 4 discriminated between single and mixed cell types with an average accuracy of \(94\%\) (Figure 2g). We then tested GPT- 4's ability to identify new cell types with marker genes not documented by existing literature. We created simulation datasets using randomly selected genes as cell type markers in half of the cases and canonical markers from a single cell type in the other half (Methods). GPT- 4 is able to differentiate known and unknown cell types with an average accuracy of \(100\%\) (Figure 2h). We also tested the reproducibility of GPT- 4 annotations leveraging results in previous simulation studies (Methods). On average, GPT- 4 generated identical annotations for the same cell type markers in \(91.2\%\) of cases (Figure 2i), showing a high level of reproducibility. In conclusion, GPT- 4 exhibits robust performance across various scenarios encountered in real data analysis.
+
+<|ref|>text<|/ref|><|det|>[[90, 714, 907, 774]]<|/det|>
+In conclusion, our findings demonstrate a high level of agreement between cell type annotations generated by GPT- 4 and by human experts. Remarkably, GPT- 4 exhibits higher accuracy in annotating specific cell types. GPT- 4 can be employed as a dependable tool for automated cell type annotation of single- cell RNA- seq data, substantially reducing the time and effort required for manual annotation.
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 789, 172, 806]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 815, 232, 829]]<|/det|>
+## Dataset collection
+
+<|ref|>text<|/ref|><|det|>[[90, 831, 907, 891]]<|/det|>
+For the HuBMAP Azimuth project, manually annotated cell types and their marker genes were downloaded from the Azimuth website (https://azimuth.hubmapconsortium.org/). Azimuth provides cell type annotations for each tissue at different granularity levels. We selected the level of granularity with the fewest number of cell types, provided that there were more than 10 cell types within that level.
+
+<|ref|>text<|/ref|><|det|>[[90, 891, 904, 921]]<|/det|>
+For HCA \(^{17}\) , HCL \(^{19}\) , and MCA \(^{18}\) , manually annotated cell types and corresponding differential gene lists were downloaded directly from the original studies. Lists of marker genes through literature search and the corresponding cell types were
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 78, 711, 95]]<|/det|>
+downloaded from the HCA study \(^{17}\) , and only cell types with at least 5 marker genes were used.
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 110, 409, 126]]<|/det|>
+## Gene set preparation and GPT-4 prompts
+
+<|ref|>text<|/ref|><|det|>[[90, 127, 910, 173]]<|/det|>
+Before using GPT- 4 to identify cell types, one needs to first prepare a list of top differential genes for each cell cluster. For example, one can use the following R code to extract gene lists of top 10 differential genes obtained from the standard Seurat pipeline. In the extracted results, each row is a list of differential genes for one cell cluster, separated by '
+
+<|ref|>text<|/ref|><|det|>[[90, 185, 919, 216]]<|/det|>
+# d is the differential gene table generated by Seurat ordered by p- values cat(tapply(d$gene,list(d$cluster),function(i) paste0(i[1:10],collapse='','))sep='\n')
+
+<|ref|>text<|/ref|><|det|>[[110, 226, 577, 241]]<|/det|>
+The gene lists used in this study were prepared using customized code.
+
+<|ref|>text<|/ref|><|det|>[[90, 241, 910, 301]]<|/det|>
+GPT- 4 was accessed by visiting the ChatGPT website (https://chat.openai.com/). The "Mar 23" version of GPT- 4 was used for this study. The following words were pasted on top of the differential gene lists and used as the initial prompt for GPT- 4. The word "prostate" in the following prompt was replaced with the appropriate tissue names when annotating cell types for each tissue.
+
+<|ref|>text<|/ref|><|det|>[[90, 314, 792, 344]]<|/det|>
+Identify cell types of human prostate cells using the following markers. Identify one cell type for each row. Only provide the cell type name.
+
+<|ref|>text<|/ref|><|det|>[[90, 354, 907, 385]]<|/det|>
+GPT- 4 returned a list of cell type names for each query. The following prompt was used to increase the granularity of cell type annotations when needed.
+
+<|ref|>text<|/ref|><|det|>[[90, 397, 249, 411]]<|/det|>
+Be more specific
+
+<|ref|>text<|/ref|><|det|>[[101, 422, 870, 438]]<|/det|>
+To annotate cell clusters that could be a mixture of multiple cell types, the following words are added to the prompt.
+
+<|ref|>text<|/ref|><|det|>[[90, 451, 549, 466]]<|/det|>
+Some could be a mixture of multiple cell types.
+
+<|ref|>text<|/ref|><|det|>[[90, 477, 907, 508]]<|/det|>
+To annotate cell clusters that cannot be characterized by known cell type markers and are potentially new cell types, the following words are added to the prompt
+
+<|ref|>text<|/ref|><|det|>[[90, 520, 411, 535]]<|/det|>
+Some could be unknown cell types.
+
+<|ref|>text<|/ref|><|det|>[[90, 545, 907, 576]]<|/det|>
+Finally, the following prompt can be used to convert the list of cell type annotations generated by GPT- 4 into R code that directly creates a vector of cell type names in R.
+
+<|ref|>text<|/ref|><|det|>[[90, 588, 697, 618]]<|/det|>
+Use "', " to concatenate all results into a single sentence. Put "c(" in front of the sentence and "')" after the sentence
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 632, 387, 648]]<|/det|>
+## Simulation studies and reproducibility
+
+<|ref|>text<|/ref|><|det|>[[90, 649, 909, 740]]<|/det|>
+To generate simulation datasets of unknown cell types, we compiled a list of all human genes using the Bioconductor org.Hs.eg.db package \(^{33}\) . In each simulation iteration, ten simulated unknown cell types were generated. The marker genes for each unknown cell type were produced by combining ten randomly selected human genes. Additionally, we included the literature- based cell type markers of ten randomly chosen human breast cell types as negative controls of known cell types, similar to the previous simulation study. This entire simulation process was repeated five times. Subsequently, GPT- 4 was queried using these simulated marker gene lists, and its performance in differentiating between mixed and single cell types was assessed.
+
+<|ref|>text<|/ref|><|det|>[[90, 741, 909, 845]]<|/det|>
+To generate simulation datasets of unknown cell types, we compiled a list of all human genes using the Bioconductor org.Hs.eg.db package \(^{33}\) . In each simulation iteration, ten simulated unknown cell types were generated. The marker genes for each unknown cell type were produced by combining ten randomly selected human genes. Additionally, we included the literature- based cell type markers of ten randomly chosen human breast cell types as negative controls of known cell types, similar to the previous simulation study. This entire simulation process was repeated five times. Subsequently, GPT- 4 was queried using these simulated marker gene lists, and its performance in distinguishing between known and unknown cell types was assessed.
+
+<|ref|>text<|/ref|><|det|>[[90, 846, 909, 922]]<|/det|>
+We assessed the reproducibility of GPT- 4 responses by leveraging the repeated querying of GPT- 4 with identical marker gene lists of the same negative control cell types in both simulation studies. For each cell type, reproducibility is defined as the proportion of instances in which GPT- 4 generates the most prevalent cell type annotation. For instance, in the case of vascular endothelial cells, GPT- 4 produces "endothelial cells" 8 times and "blood vascular endothelial cells" once. Consequently, the most prevalent cell type annotation is "endothelial cells," and the reproducibility is calculated as \(\frac{8}{9} = 0.89\) .
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[90, 77, 264, 95]]<|/det|>
+## Acknowledgments
+
+<|ref|>text<|/ref|><|det|>[[90, 101, 905, 131]]<|/det|>
+Z.J. was supported by the National Institutes of Health under Award Number 1U54AG075936- 01. The manuscript was polished by GPT- 4.
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 148, 285, 166]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[90, 173, 628, 188]]<|/det|>
+All authors conceived the study, conducted the analysis, and wrote the manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 205, 281, 222]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[90, 230, 370, 244]]<|/det|>
+All authors declare no competing interests.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[98, 270, 900, 690]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 703, 896, 746]]<|/det|>
+Figure 1. a, Diagram comparing cell type annotations by human experts, GPT-4, and other automated methods. b, An example showing GPT-4 prompts and answers for annotating human prostate cells with increasing granularity. c, An example showing GPT-4 prompts and answers for annotating single cell types (first two cell types), mixed cell types (third cell type), and new cell types (fourth cell type).
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[115, 115, 900, 234]]<|/det|>
+
+| a | Dataset | Species | Number of tissues | Number of cell types | Gene list source |
| Azimuth | Human | 11 | 276 | Differential analysis |
| Human Cell Atlas (HCA) | Human | 7 | 72 | Differential analysis |
| Human Cell Landscape (HCL) | Human | 60* | 101 | Differential analysis |
| literature (from HCA) | Human | 7 | 30 | Literature search |
| Mouse Cell Atlas (MCA) | Mouse | 51* | 65 | Differential analysis |
+
+<|ref|>table_footnote<|/ref|><|det|>[[198, 235, 806, 250]]<|/det|>
+\\* Cell type annotations were done by aggregating across tissues in the original studies
+
+<|ref|>table<|/ref|><|det|>[[115, 258, 530, 437]]<|/det|>
+
+| Manual annotation | GPT-4 answer | Agreement |
| Adipocyte | Adipocytes | Full |
| B cell_memory | B cells | Partial |
| Fibroblast | Fibroblasts | Full |
| Luminal Epithelial | Luminal epithelial cells | Full |
| Lymphatic Endothelial | Lymphatic endothelial | Full |
| Macrophage | Macrophages | Full |
| Mast Cell | Mast cells | Full |
| Pericyte | Pericytes | Full |
| Smooth Muscle | Smooth muscle cells | Full |
| T cell | T cells | Full |
| Vascular Endothelial | Endothelial cells | Partial |
+
+<|ref|>image<|/ref|><|det|>[[114, 440, 911, 765]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 775, 911, 903]]<|/det|>
+Figure 2. Evaluation of cell type annotation by GPT-4. a, Datasets included in this study b, Agreement between original and GPT-4 annotations in identifying cell types of human prostate cells. c, Averaged agreement score (y-axis) and the number of top differential genes (x-axis) in HCA, HCL, and MCA datasets. d, Proportion of cell types with different levels of agreement in each study and tissue. Averaged agreement scores are shown as black dots. e, Proportion of cell types with different levels of agreement in each cell category. Averaged agreement scores are shown as black dots. f, Proportion of cell types that include type I collagen gene in the differential gene lists. The cell types are either classified as stromal cells by manual annotations and fibroblast, osteoblast, or chondrocyte by GPT-4 annotations, or classified as fibroblast, osteoblast, or chondrocyte by manual annotations. g, Proportion of cases where GPT-4 correctly identifies mixed and single cell types. Each dot represents one round of simulation. h, Proportion of cases where GPT-4 correctly identifies known and unknown cell types. Each dot represents one round of simulation. i, Reproducibility of GPT-4 annotations. Each dot represents one cell type.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[92, 77, 199, 95]]<|/det|>
+## References
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[87, 78, 909, 110]]<|/det|>
+27. Zeisel, A. et al. Cell types in the mouse cortex and hippocampus revealed by single-cell rna-seq. Science 347, 1138–1142 (2015).
+
+<|ref|>text<|/ref|><|det|>[[90, 113, 770, 130]]<|/det|>
+28. Zou, Z. et al. A single-cell transcriptomic atlas of human skin aging. Dev. cell 56, 383–397 (2021).
+
+<|ref|>text<|/ref|><|det|>[[88, 133, 904, 165]]<|/det|>
+29. Kung, T. H. et al. Performance of chatgpt on usmle: Potential for ai-assisted medical education using large language models. PLoS digital health 2, e0000198 (2023).
+
+<|ref|>text<|/ref|><|det|>[[88, 169, 671, 186]]<|/det|>
+30. Hou, W. & Ji, Z. Geneturing tests gpt models in genomics. bioRxiv 2023–03 (2023).
+
+<|ref|>text<|/ref|><|det|>[[88, 189, 742, 206]]<|/det|>
+31. Shue, E. et al. Empowering beginners in bioinformatics with chatgpt. bioRxiv 2023–03 (2023).
+
+<|ref|>text<|/ref|><|det|>[[88, 210, 905, 241]]<|/det|>
+32. Duong, D. & Solomon, B. D. Analysis of large-language model versus human performance for genetics questions. medRxiv 2023–01 (2023).
+
+<|ref|>text<|/ref|><|det|>[[88, 245, 905, 277]]<|/det|>
+33. Gentleman, R. C. et al. Bioconductor: open software development for computational biology and bioinformatics. Genome biology 5, 1–16 (2004).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 43, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 112]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 131, 216, 150]]<|/det|>
+- supptable1.csv
+
+<--- Page Split --->
diff --git a/preprint/preprint__025de565043ff8e7db332a9d49b5794afb4f1a967efe3413a21f6a9dbeddf7e4/preprint__025de565043ff8e7db332a9d49b5794afb4f1a967efe3413a21f6a9dbeddf7e4_det.mmd b/preprint/preprint__025de565043ff8e7db332a9d49b5794afb4f1a967efe3413a21f6a9dbeddf7e4/preprint__025de565043ff8e7db332a9d49b5794afb4f1a967efe3413a21f6a9dbeddf7e4_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..e63c19d50c45e7e67b17cd59741d14812c36a3c4
--- /dev/null
+++ b/preprint/preprint__025de565043ff8e7db332a9d49b5794afb4f1a967efe3413a21f6a9dbeddf7e4/preprint__025de565043ff8e7db332a9d49b5794afb4f1a967efe3413a21f6a9dbeddf7e4_det.mmd
@@ -0,0 +1,336 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 890, 208]]<|/det|>
+# Unequal Emissions, Unequal Impacts: How High-Income Groups Disproportionately Contribute to Climate Extremes Worldwide
+
+<|ref|>text<|/ref|><|det|>[[44, 230, 377, 276]]<|/det|>
+Sarah Schoengart sarah.schoengart@hu- berlin.de
+
+<|ref|>text<|/ref|><|det|>[[44, 304, 925, 512]]<|/det|>
+HU Berlin Zebedee Nicholls University of Melbourne https://orcid.org/0000- 0002- 4767- 2723 Roman Hoffmann International Institute for Applied Systems Analysis (IIASA) https://orcid.org/0000- 0003- 3512- 1737 Setu Pelz International Institute for Applied Systems Analysis https://orcid.org/0000- 0002- 3528- 8679 Carl- Friedrich Schleussner IIASA https://orcid.org/0000- 0001- 8471- 848X
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 550, 103, 567]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 587, 497, 606]]<|/det|>
+Keywords: Attribution, Inequality, Injustice, Extremes
+
+<|ref|>text<|/ref|><|det|>[[44, 625, 350, 644]]<|/det|>
+Posted Date: November 27th, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 663, 475, 682]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 5417521/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 700, 914, 742]]<|/det|>
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 761, 535, 780]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 816, 940, 858]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Climate Change on May 7th, 2025. See the published version at https://doi.org/10.1038/s41558- 025- 02325- x.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[92, 85, 787, 111]]<|/det|>
+# Unequal Emissions, Unequal Impacts: How
+
+<|ref|>title<|/ref|><|det|>[[92, 115, 737, 142]]<|/det|>
+# High-Income Groups Disproportionately
+
+<|ref|>title<|/ref|><|det|>[[92, 147, 775, 174]]<|/det|>
+# Contribute to Climate Extremes Worldwide
+
+<|ref|>text<|/ref|><|det|>[[92, 183, 830, 220]]<|/det|>
+Sarah Schöngart1,2, Zebedee Nicholls1,3,4, Roman Hoffmann1, Setu Pelz1, and Carl- Friedrich Schleussner1,2
+
+<|ref|>text<|/ref|><|det|>[[92, 231, 883, 312]]<|/det|>
+1International Institute for Applied Systems Analysis (IIASA), Schloβplatz 1, 2361 Laxenburg, Austria 2IRIThesys, Humboldt- Universität zu Berlin, Friedrichstrasse 191, 10117 Berlin, Germany 3Climate Resource, Melbourne, Australia 4School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, Australia
+
+<|ref|>text<|/ref|><|det|>[[92, 323, 280, 355]]<|/det|>
+Corresponding author: Sarah Schöngart1
+
+<|ref|>text<|/ref|><|det|>[[92, 360, 516, 376]]<|/det|>
+Email address: sarah.schoengart@climateanalytics.org
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 397, 222, 415]]<|/det|>
+## ABSTRACT
+
+<|ref|>text<|/ref|><|det|>[[114, 428, 875, 624]]<|/det|>
+One of the fundamental injustices of climate change is that those least responsible often bear the brunt of its impacts. This injustice persists not only between countries but also on the individual level within societies. Here, we assess how greenhouse gas emissions from consumption and investments attributable to the wealthiest population groups from 1990 to 2019 have influenced present- day (2020) global mean temperature levels as well as monthly temperature and potential drought extremes. We combine emission inequality data with an emulator- based modelling framework, enabling a systematic attribution of changes in regional extremes worldwide. We find that the top \(10\%\) wealthiest individuals globally contributed about 6.5 times the global average to global warming \((0.40^{\circ}\mathrm{C} \pm 0.16^{\circ}\mathrm{C})\) , the top \(1\%\) even 20 times the average \((0.12^{\circ}\mathrm{C} \pm 0.05^{\circ}\mathrm{C})\) . These disproportionate contributions further amplify for extreme events, with the top \(10\%\) contributing about 7 times more to the emergence of 1- in- 100 year heat and potential drought events than the global average \((11.5 \pm 3.9\) and \(4.7 \pm 2.8\) additional occurrences), the top \(1\%\) 25 times more \((4.0 \pm 1.3\) and \(1.7 \pm 0.9\) additional occurrences). Emissions from the wealthiest \(10\%\) in the United States and China, the two largest greenhouse gas emitters, are associated with a two- to three- fold increase in the frequency of heat and drought extremes across vulnerable regions. Quantifying the relationship between wealth disparities and climate change impacts can assist the discourse on climate equity and justice.
+
+<|ref|>text<|/ref|><|det|>[[115, 643, 488, 658]]<|/det|>
+Keywords: Attribution; Inequality; Injustice; Extremes
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 690, 287, 707]]<|/det|>
+## 1 INTRODUCTION
+
+<|ref|>text<|/ref|><|det|>[[92, 714, 884, 880]]<|/det|>
+Over the past two decades, extreme events attributable to climate change led to an annual average of 143 billion USD in damages[1]. How these costs could and should be covered - both between and within countries - is subject to debate[2]. Central to this debate is the stark disparity between those responsible for emissions and those affected by their impacts. The wealthiest \(10\%\) of the global population accounted for nearly half of global emissions in 2019 through private consumption and investments, whereas the poorest \(50\%\) contributed only one- tenth of global emissions[3]. At the same time, regions with low historic emissions and income levels are typically more frequently and severely exposed to climate impacts[4,5] with limited resources for adaptation[6]. This cause- and- effect injustice is widely acknowledged[7], yet, an quantification of how carbon inequality translates into unequal accountability for the resulting global temperature levels and extreme climate events is missing. Given the role of non- \(\mathrm{CO}_{2}\) greenhouse gases (GHGs), such as methane, in recent warming, a modelling rather than a metric- based approach is required to accurately assess the warming contributions of different emitters[8].
+
+<|ref|>text<|/ref|><|det|>[[92, 896, 884, 912]]<|/det|>
+In this study, we combine wealth- based carbon inequality assessments[3], with an emulator- based climate mod
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[115, 88, 880, 269]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 279, 876, 355]]<|/det|>
+Figure 1. |Overview modelling framework. Counterfactual emissions are converted into GMT using the simple climate model MAGICC and subsequently translated into grid-point level realisations of climatic variables using the ESM emulator MESMER-M-TP. a, Counterfactual CO2 emission pathways. Historic emissions (blue) without contribution of a selected emitter group post 1990 (orange). b, GMT levels for historic and counterfactual emission pathways. c, Reference, present-day and counterfactual temperature distributions at a single grid-cell.
+
+<|ref|>text<|/ref|><|det|>[[88, 380, 883, 472]]<|/det|>
+29 elling framework[9] to systematically attribute changes in global mean temperature (GMT) levels and grid- point- level climate extremes to emissions from different wealth groups. We use the Model for the Assessment of the Greenhouse Gas Induced Climate Change (MAGICC)[10], a simple climate model, in conjunction with the Modular Earth System Model Emulator for Monthly Temperature and Precipitation (MESMER- M- TP)[11], a model that is able to generate large ensembles of spatially explicit monthly temperature and precipitation data which closely resembles that of complex Earth System Models (ESMs) at a fraction of the cost.
+
+<|ref|>text<|/ref|><|det|>[[88, 485, 884, 578]]<|/det|>
+We use attribution science frameworks to link human- induced GHG emissions to changes in the frequency and intensity of individual extreme events[12]. Originally, these frameworks were developed to attribute changes to total human emissions[13,14], but they are increasingly applied to individual emitters, such as companies or countries[15,16]. When attributing impacts among multiple emitters, various approaches exist, each yielding different outcomes and being equally justifiable[17,18]. Here, we assess the changes in the characteristics of extreme events but for the emissions of a specific emitter group[15,18].
+
+<|ref|>text<|/ref|><|det|>[[88, 592, 884, 760]]<|/det|>
+We generate counterfactual emission pathways by subtracting the 1990- 2019 emissions of specific emitter groups, namely the wealthiest \(10\% /1\% /0.1\%\) globally, as well as in the US, the EU27, India, and China (Fig. 1 Panel b). Emissions data, drawn from[3], include emissions from domestic consumption, public and private investments, and trade; emissions are attributed to consumers, except, emissions from capital formation in production sectors are attributed to firm owners[19]. Emissions are reported as a basket of GHGs, aggregated with Global Warming Potential 100. We then convert these counterfactual pathways into GMT levels and gridded climatic variables (panel a in Fig. 1), allowing us to compare the 2020 climate against the hypothetical 2020 climate state that we would observe, if these groups had not emitted. Specifically, we attribute GMT levels and changes in the probability and intensity of monthly temperature and potential drought extremes (Fig. 1 Panel c), using the Standardised Precipitation Evapotranspiration Index computed over 3 month periods (SPEI- 3)[20]. For illustration, we also assess counterfactual warming outcomes based on rescaling global emissions according to the per capita profile of individual income percentiles.
+
+<|ref|>text<|/ref|><|det|>[[88, 774, 883, 820]]<|/det|>
+Our analysis attributes climate impacts to wealthy emitters and compares these to impacts from global average per capita emissions. However, we do not assess what would constitute fair or just emissions for these groups, nor do we assign direct responsibility for the resulting impacts.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 838, 227, 855]]<|/det|>
+## 2 RESULTS
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 864, 564, 880]]<|/det|>
+### 2.1 Inequality in Attributed Global Warming Contributions
+
+<|ref|>text<|/ref|><|det|>[[88, 881, 883, 911]]<|/det|>
+Our modelling framework depicts natural variability and uncertainty in the global response to emission changes (see Methods). Unless mentioned otherwise, we provide median results and the \((5^{\mathrm{th}} - 95^{\mathrm{th}})\) confidence interval. As
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[118, 88, 883, 578]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 585, 884, 800]]<|/det|>
+Figure 2. |Attributed 1990-2020 GMT increase by emitter group. a, GMT increase attributed to global top \(10\% /1\% /0.1\%\) (orange/teal/pink) and actual GMT increase over 1990-2020 (grey). Hatched areas indicate the warming for each group based on an equal per capita contribution to warming. Climate Inequality Factors (CIFs) indicating the group's contribution to global warming relative to the average contribution are given above the bars. Vertical lines represent \(5^{\mathrm{th}}\) - \(95^{\mathrm{th}}\) quantile ranges from natural variability and uncertainty in the global temperature response to emission changes. Circles highlight median values from sensitivity analysis, see Methods (lower circle: \(\mathrm{CO_2}\) -based emissions; upper circle: non- \(\mathrm{CO_2}\) -based emissions). b, Hypothetical GMT increase from 1990-2020 if everyone emitted like the given income groups, with \(5^{\mathrm{th}}\) - \(95^{\mathrm{th}}\) uncertainty ranges shown by vertical lines. c-d, Regional breakdown of the global top \(10\% /1\%\) over time. e, Same as Panel a but for the regional top \(10\% /1\% /0.1\%\) (orange, teal, pink) in the US, the EU27, India and China. Grey bar highlights the GMT increase attributable to the region as a whole. Two CIFs are given: the lighter (darker and lower) value is relative to the country's equal share (actual emissions) and measures global (regional) inequality. f-g, Income thresholds of the regional top \(10\% /1\%\) ranked against global income levels. Values below (above) bold grey line indicate regional top \(10\% /1\%\) are wealthier (poorer) than global top \(10\% /1\%\) .
+
+<|ref|>text<|/ref|><|det|>[[90, 832, 883, 878]]<|/det|>
+our database provides only basket emissions, we derived the main results assuming emissions for each GHG scale proportionally with the globally aggregated emissions (see Methods). We explore the sensitivity to this assumption in the Supplementary 5.2.
+
+<|ref|>text<|/ref|><|det|>[[90, 880, 883, 911]]<|/det|>
+GMT has risen by \(0.61^{\circ}\mathrm{C}(\pm 0.24^{\circ}\mathrm{C})\) between 1990 and 2020. We find that about \(65\% (0.40^{\circ}\mathrm{C}\pm 0.16^{\circ}\mathrm{C})\) of this increase is attributable to the global top \(10\%\) , \(20\% (0.12^{\circ}\mathrm{C}\pm 0.05^{\circ}\mathrm{C})\) to the top 1 and \(8\% (0.05^{\circ}\mathrm{C}\pm 0.02^{\circ}\mathrm{C})\) to the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 90, 883, 152]]<|/det|>
+67 top \(0.1\%\) (see Fig. 2 Panel a and Table S2). These warming responsibilities are higher (by about one fifth) than the respective group's contributions to aggregated GHG basket emissions (see Table S1), underscoring the importance of using a climate model to assess warming contributions and the potential for non- linearities in such attribution [21] (see also Supplementary Material 5.2).
+
+<|ref|>text<|/ref|><|det|>[[112, 152, 883, 227]]<|/det|>
+To put these numbers into perspective, we compute equal shares by scaling the total GMT increase according to the group's share of the global population (e.g. the global top \(10\%\) 's equal share are \(10\%\) of the full \(0.61^{\circ}\mathrm{C}\) increase). We then derive Climate Inequality Factors (CIFs) as the group's actual contribution to global warming relative to their equal share. CIFs increase from 6.5 for the top 10 to 20 (77) for the top 1 (0.1), indicating an amplification of climate inequality with increasing wealth.
+
+<|ref|>text<|/ref|><|det|>[[112, 227, 883, 289]]<|/det|>
+The full depth of the disproportion in contributions to GMT level becomes tangible when rescaling global emissions according to the per capita profile of global income groups (Fig. 2 Panel b). If the entire world population had emitted like the bottom \(50\%\) , there would have been minimal additional warming since 1990. However, if the entire world population had emitted like the top \(10\% /1\% /0.1\%\) , the GMT increase since 1990 would have been \(2.9 / 6.7 / 12.2^{\circ}\mathrm{C}\) .
+
+<|ref|>text<|/ref|><|det|>[[112, 289, 883, 395]]<|/det|>
+Accounting from 1990, the top emitters primarily come from the world's highest emitting countries: the US, China, India and the EU27 (Fig. 2 Panels c- d). Shares of the wealthy have been shifting over the past 30 years: while more than \(27\%\) of the global top \(10\%\) were European in 1990, this number has dropped to \(19\%\) in 2019; and while less than \(1\%\) of the global top \(10\%\) came from China in 1990, the share has grown to \(13\%\) in 2019. While our focus is on wealthy individuals from the world's largest economies, we note that those from smaller countries also contribute disproportionately, with within country inequalities being even more pronounced in countries in Sub- Saharan Africa and the Middle East and North Africa (MENA) region [3].
+
+<|ref|>text<|/ref|><|det|>[[112, 408, 883, 484]]<|/det|>
+We also assess contributions of emitters from selected regions (US, EU27, China, India). Income levels from regional top emitters deviate from their global counter parts, i.e. the top \(10\% /1\%\) in the US and the EU27 (India and China) are wealthier (poorer) than the globally wealthiest \(10\% /1\%\) (Fig. 2 f and g). In the US, the regional top \(10\% /1\%\) belong to the globally wealthiest \(1 - 2\% /0.1 - 0.2\%\) . In China, the top \(10\%\) were among the globally wealthiest \(37\%\) (13%) in 1990 (2019).
+
+<|ref|>text<|/ref|><|det|>[[112, 485, 883, 606]]<|/det|>
+Attributed GMT shares by regional emitter groups combine within- and between- region inequality. In the US/EU27, the top \(10\%\) contribute 3.1/2.8 times more to global warming than the average citizen, but 17/8 times more than the global average. For the US, the top \(10\%\) 's contribution alone exceeds the entire country's equal share. This relative inequality increases with increasing wealth: the top \(1\%\) in the US/EU27 contribute 53/21 times their equal shares, and the top \(0.1\%\) contribute 190/64 times their equal shares. In China, where the overall CIF is near 1, the top \(10\% /1\% /0.1\%\) emit 4, 13, and 50 times their equal shares, showing even greater regional influence from societal elites. Similarly, in India, where the national CIF is 0.3 - implying the countries per capita average emissions are below the global average -, the top \(10\% /1\% /0.1\%\) emit 1.2, 4 and 10 times above the global average.
+
+<|ref|>sub_title<|/ref|><|det|>[[112, 621, 557, 637]]<|/det|>
+### 2.2 Major Disparities in Attributable Extremes Worldwide
+
+<|ref|>text<|/ref|><|det|>[[112, 638, 883, 745]]<|/det|>
+Throughout the year, regional increases in the occurrence frequency of 1- in- 100 year heat and potential drought extremes are attributable to the emissions of the global top \(10\%\) (Fig 3 Panel a). For heat extremes, changes are most (least) pronounced in August (February), where \(11.5 \pm 3.9\) ( \(3.5 \pm 1.2\) ) additional events are attributable to the global top \(10\%\) . Similarly, attributable potential drought extremes are highest in August and September ( \(4.7 \pm 2.8\) and \(4.8 \pm 2.4\) ) additional events) and lowest in February (negligible increases). These changes refer to the global median over land that is predominantly located on the Northern Hemisphere, and Southern Hemisphere locations may see up to 30 addition attributable events in February (see also Supplementary Fig. S3).
+
+<|ref|>text<|/ref|><|det|>[[112, 745, 882, 775]]<|/det|>
+Given the intra- annual distribution of impacts, we focus on extremes in August and present results for other months in Supplementary 5.4.
+
+<|ref|>text<|/ref|><|det|>[[112, 776, 883, 866]]<|/det|>
+In August, the total increase in heat (potential droughts) events since 1990 is \(15.7 \pm 5.8\) ( \(6.5 \pm 4.1\) ). The top \(10\%\) contribute 7.3 (7.0) times the global average to this, while the top \(1\%\) contribute 25.5 (25.6) times the average (see Fig. 3 Panel c and d). In addition, the intensities of 1- in- 100 year August extreme heat (potential drought) events increased by \(0.86^{\circ}\mathrm{C} \pm 0.16^{\circ}\mathrm{C}\) ( \(0.21 \pm 0.54\) ) since 1990. \(0.56^{\circ}\mathrm{C} \pm 0.08^{\circ}\mathrm{C}\) ( \(0.13 \pm 0.06\) ) of this increase is attributable to the top \(10\%\) suggesting their contribution is 6.7 (6.3) times higher than global average S6- S10. Similarly, \(0.18^{\circ}\mathrm{C} \pm 0.02^{\circ}\mathrm{C}\) ( \(0.03 \pm 0.02\) ) are attributable to the top \(1\%\) which represents 21.0 (16.4) times the global average.
+
+<|ref|>text<|/ref|><|det|>[[112, 880, 883, 911]]<|/det|>
+While these results hold true for the global median, there is a strong spatial disparity in attributable changes at the grid- cell level with some regions being more severely impacted (see Fig. 3 and Supplementary Fig. S3- S10). For
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[118, 170, 880, 686]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 703, 884, 823]]<|/det|>
+Figure 3. | Frequency change of 1-in-100 year heat and drought events attributable to global top 10. a, Distribution of attributed extreme events across grid-cells (boxes: median and inter-quartile range, whiskers: min-max range over inliers, circles: outliers). Heat (potential drought) highlighted in red (blue) with qualitative colour shades. b, Spatial distribution attributed extreme events in August. Red (blue) areas are dominated by heat (drought) events, purple nuances indicate increases in both. c, Additional occurrences of August heat extremes by region (highlighted on map). Total increase in events between 1990 and 2020 (grey) and shares attributable to top 10 (1) in orange (teal). Climate Inequality Factors indicating the group’s contribution to extremes relative to the average contribution are given above the bars. Vertical lines correspond to \(5^{\text{th}}\) - \(95^{\text{th}}\) uncertainty ranges. d, Same as c but for potential drought conditions.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 90, 882, 166]]<|/det|>
+example, in South East Asia \(28.7(\pm 5.8)\) heat events and in West Southern Africa \(18.0(\pm 8.5)\) potential drought events are attributable to the top \(10\%\) . In particular, regions that have disproportionately contributed to the emissions of the top \(10\%\) , for example the EU27 and the US (see Fig. 2), face relatively smaller increases compared to regions that have contributed very little (e.g., Western North America and West&Central Europe compared to Northern South America in Fig. 3 Panels b and c).
+
+<|ref|>text<|/ref|><|det|>[[115, 167, 882, 226]]<|/det|>
+Notable are the relatively small (attributable) impacts over India and parts of China and the simultaneously high inter- model disagreement. This is inconsistent with the increasing number of climate- related disasters India is already facing [22]. We attribute this behaviour to the effects of air pollution in our training dataset and discuss this in the Supplementary 5.3.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 239, 784, 255]]<|/det|>
+### 2.3 Transboundary Impacts Attributable to Affluent Groups in High-emitting Countries
+
+<|ref|>text<|/ref|><|det|>[[115, 255, 882, 435]]<|/det|>
+The inequality in warming contributions from affluent groups in high- emitting regions exceed the inequality in their global counter- parts (see Fig. 2). This disparity also appears at the grid- cell level: for example, in the global median, emissions from the top \(10\%\) ( \(1\%\) ) in the US are associated with \(1.5 \pm 0.46\) ( \(0.5 \pm 0.17\) ) additional 1- in- 100 year heat events in August. This impact represents 21 (70) times the global average contribution and about three times the global top \(10\%\) 's ( \(1\%\) 's) relative contribution (see Fig. 3). For potential droughts, the top \(10\%\) ( \(1\%\) ) in the US contribute \(0.7 \pm 0.31\) ( \(0.17 \pm 0.08\) ) additional extreme events, which equates to 33 (88) times the global average. These effects are unevenly distributed across regions. For instance, in heat- vulnerable areas such as Northern South America and South East Africa, emissions from the top \(10\%\) in China (the US) are linked to \(3.0 \pm 1.0\) ( \(2.7 \pm 1.0\) ) additional occurrences of extreme heat (Fig. 4). Similarly, in drought- prone areas like Northeastern South America and West and Central Asia, \(2.7 \pm 1.0\) additional events are attributable to the top \(10\%\) in both China and the US. In most regions (we highlight Southeastern Africa and West and Central Asia in Fig. 4), emissions from regional top emitters significantly elevate risks of both heat and drought extremes.
+
+<|ref|>text<|/ref|><|det|>[[115, 437, 882, 676]]<|/det|>
+Attributing changes in extreme events to country specific wealthy emitter groups becomes increasingly challenging as emitter groups decrease in per capita size, meaning their cumulative emissions decrease even if their relative emission contributions increase. The lower bound ( \(5^{\text{th}}\) quantile) of changes in the frequency of extreme heat and drought events attributable to the global top \(10\%\) is greater than zero at \(94\%\) of locations. This numbers drops to \(62\%\) for the top \(10\%\) in China with an additional \(34\%\) ( \(2\%\) ) of locations where only changes in heat (potential drought) are robust; and it further drops to \(18\%\) for the top \(10\%\) in India with an additional \(39\%\) ( \(6\%\) ) of locations where only changes in heat (potential drought) are robust. For small cumulative emissions, robust signals extend mainly from the equatorial zone to the subtropics and are less robust from the temperate zone polewards. This implies changes in the global median of 1- in- 100 year potential drought events attributable to the top \(10\%\) in India are largely obscured by natural variability (even within our emulator framework that allows far bigger ensembles than traditional methods), while there is still a robust signal in vulnerable regions. For example, in South Eastern Africa and West and Central Asia even the lower bound estimate for additional potential heat and drought events attributable to the top \(10\%\) in India entails a \(50\%\) increase in occurrence frequency compared to pre- industrial. This again highlights the spatial disparity in attributable impacts and shows that for vulnerable areas even seemingly small increments in emissions result in considerable impacts. The induced risks depend on the definition of extremes, with tail risks becoming increasingly pronounced as event rarity increases (see Supplementary Fig. S11- S14).
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 690, 444, 707]]<|/det|>
+## 3 DISCUSSION AND CONCLUSION
+
+<|ref|>text<|/ref|><|det|>[[115, 714, 882, 880]]<|/det|>
+This study introduces a framework to attribute local extreme events to individual emitters, linking wealth- based emissions to shifts in global mean temperature (GMT) and regional extremes in heat and potential drought. We find that the globally wealthiest \(10\%\) contributed 6.5 times more to global warming than the average, with the top \(1\%\) and \(0.1\%\) contributing 20 and 76 times more, respectively. This imbalance is more pronounced at the grid- cell level: the globally wealthiest \(10\%\) and \(1\%\) contributed more than 7 and 25 times to the frequency increase of pre- industrial 1- in- 100 year heat and potential drought extremes in August than the global average. These wealthiest groups are mostly located in high- emitting countries like the US, the EU27, and China, which are less affected by local climate impacts. Therefore, their emissions are associated with significant transboundary effects, with the wealthiest \(10\%\) within the US and China contributing to at least two additional extreme heat and drought events in vulnerable regions, such as South East Asia, South East Africa, and Northern South America. This climate injustice underscores the need for addressing inequality in policy discussions [23].
+
+<|ref|>text<|/ref|><|det|>[[115, 897, 882, 911]]<|/det|>
+From a mitigation perspective, our findings suggest affluent groups are crucial in reducing their own carbon footprints
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[130, 95, 860, 319]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 348, 882, 424]]<|/det|>
+Figure 4. |Frequency increase of 1-in-100 year August extremes in selected regions attributable to regional top 10. Left: additional number of additional occurrences of heat extremes in selected regions that are attributable to the top \(10\%\) of emitters in China (dark red), US (light red), EU27 (gold) and India (blue). Right: Same as on the left but for potential droughts. Wider bars indicate more events are attributable to a given emitter group. Value on bar indicates additional number of events over the course of 100 years.
+
+<|ref|>text<|/ref|><|det|>[[113, 456, 882, 563]]<|/det|>
+and in supporting global climate action [24]. International climate agreements are typically based on production- side accounting, while our findings reinforce the need to explore mitigation strategies that also target consumption- side emissions [25,26], in particular those related to wealth, as proposed for example in ref. [3]. Additionally, our sensitivity analysis underscores the critical role of methane \((\mathrm{CH}_4)\) emissions in near- term warming and calls for new research to disentangle emissions from different wealth groups at the level of individual gases. Reducing \(\mathrm{CH}_4\) emissions in line with Paris Agreement compatible pathways can yield immediate reductions in global temperatures and climate extremes [27].
+
+<|ref|>text<|/ref|><|det|>[[112, 577, 882, 805]]<|/det|>
+From an adaptation and loss- and- damage perspective, quantifying individual contributions to climate impacts can inform financial mechanisms such as the Loss and Damage fund and domestic climate financing structures [28]. Although our framework could, in theory, aid in estimating emissions- based financial obligations, it is bound by conceptual challenges and value judgments in approach and implementation. First, our attribution relies on consumption- based carbon data, allocating emissions between consumers and shareholders through shared ownership; second, we employ the but for attribution method. All quantitative estimates are therefore tied to these assumptions. For instance, our focus on consumption- based emissions contrasts with production- based approaches [15,29]. Additionally, there are various ways to attribute capital- related emissions between consumers and shareholders [19]. Balancing these methods is essential to avoid double- counting and to address ethical and legal issues around responsibility. Additionally, the non- linear relationship between global and local emission responses complicates attribution, as emission removal sequences can lead to varying outcomes [18]. Addressing these challenges is key to developing a unified approach to attribution, which can support robust policy decisions. Accordingly, our analysis does not assign responsibility for resulting climate impacts, nor does it determine fair emission levels for any income group. Such determinations require an integrated view of fairness, justice, and socio- economic factors [23,30], with different reference points for societies at varying levels of development.
+
+<|ref|>text<|/ref|><|det|>[[112, 819, 882, 895]]<|/det|>
+From a technical viewpoint, our analysis is limited by the lack of data on how GHG emission composition varies with income and wealth. This limits the accuracy of our results, as emission composition strongly affects attribution. In addition, our drought indicator is based solely on temperature and precipitation, which may lead to overestimations in drought risks [31]. Finally, since our analysis is based on modelled data, it is subject to errors due to computational deviations from observations [32,33].
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 90, 883, 136]]<|/det|>
+In conclusion, our findings underscore the contribution of seemingly small amounts of emissions to changes in regional extremes. Advancing frameworks for attributing emissions to individual emitters can inform global climate action and address climate inequalities.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 161, 400, 179]]<|/det|>
+## 4 MATERIALS AND METHODS
+
+<|ref|>text<|/ref|><|det|>[[115, 187, 883, 383]]<|/det|>
+We quantify intensity and frequency changes in temperature and potential drought extremes attributable to specific emitter groups. The methodological framework relies on three steps (Fig. 1): first, we construct counterfactual emissions pathways, i.e. emission pathways with and without the emissions of selected population groups; second, we translate emissions into gridded temperature, precipitation and potential drought data via a chain of computationally efficient emulators; and third, we build on the framework of extreme event attribution to quantify changes in the grid- point level distributions of the climatic variables. We rely on the Standardised Precipitation Evapotranspiration Index computed over a 3 month period (SPEI- 3) to identify potential droughts [20]. The SPEI- 3 can be computed from precipitation and potential evapotranspiration (PET) data. Ideally, PET is estimated via the Penman- Monteith equation [34,35] which takes temperatures, radiation, wind speed and humidity into account. Given our emulation framework only depicts temperature and precipitation, we rely on the Thornthwaite method to compute PET from temperature data only [36]. However, PET estimates via Thornthwaite are prone to overestimations in terms of magnitude and temporal trends [31]. While this approach is practical, it is only an approximation of true drought conditions, which is why we refer to our drought indicator as potential droughts.
+
+<|ref|>text<|/ref|><|det|>[[113, 396, 883, 760]]<|/det|>
+Counterfactual emission pathways. We assess what our climate today would look like if the wealthiest \(10\% /1\% /0.1\%\) globally, as well as in the US, EU27, India and China had not contributed to global emissions between 1990 and 2019. We follow Nicholls et al. [37] to construct a timeseries of historic baseline emissions from 1850- 2019 resolved by gas. Next, we remove emitter- specific contributions from these baseline emissions (Fig. 1). To this end, we rely on a dataset of consumption- based carbon dioxide equivalent \(\mathrm{CO_2 - e}\) ) emissions by country and income decile between 1990- 2019 [3]. The estimates relate to all emissions except emissions from agriculture, forestry and other land- use (AFOLU). Our analysis requires us to make assumptions about how to disaggregate the reported basket emissions into individual gases. We focus on decomposing emissions into \(\mathrm{CO_2}\) , nitrogen oxide \(\mathrm{(N_2O)}\) and methane \(\mathrm{(CH_4)}\) . These three gases make up \(98.7\%\) of total global greenhouse gas emissions (excluding AFOLU) [38]. The composition of production- side GHG emissions varies strongly by country, ranging from primarily \(\mathrm{CO_2}\) - based emissions (e.g. Singapore), to almost equal shares between \(\mathrm{CO_2}\) and \(\mathrm{CH_4 / N_2O}\) (e.g. Qatar) and, particularly in least developed countries, primarily \(\mathrm{CH_4 / N_2O}\) (e.g. Chad) [39]. The carbon inequality dataset from [3] employs input- output tables that re- distribute production- side emissions to consumers across countries. About half of global methane emissions are embodied in global trade with household consumption dominating the final demand category [40]. Given these considerations and a lack of alternative data, we chose to apply the same decomposition assumptions across countries and emitter groups. For our central estimate, we assume that emissions for each GHG scale proportionally with the globally aggregated emissions. To test the sensitivity to this assumption we provide two extreme cases in which the wealthy emitters 1) solely emit carbon \(\mathrm{CO_2}\) - case) or 2) solely emit \(\mathrm{CH_4}\) and \(\mathrm{N_2O}\) (non- \(\mathrm{CO_2}\) - case). Note that in the \(2^{\mathrm{nd}}\) case, the emissions associated with the global top \(10\%\) are larger than the total global \(\mathrm{CH_4}\) and \(\mathrm{N_2O}\) emissions combined and we remove the excessive emissions from the \(\mathrm{CO_2}\) timeseries (converting to \(\mathrm{CO_2}\) - e using GWP100). We find that the disaggregation into dominant non- \(\mathrm{CO_2}\) GHGs, \(\mathrm{CH_4}\) and \(\mathrm{N_2O}\) , has a strong impact on the results (Fig. 2 Panels a&e). In the \(\mathrm{CO_2}\) - case the inequality in contributions to GMT levels persists, but is slightly below the inequality in GHG basket emissions. For the non- \(\mathrm{CO_2}\) - case, warming inequality is strongly amplified. This is expected given the near- term warming potential of non- \(\mathrm{CO_2}\) GHGs (see Supplementary 5.2).
+
+<|ref|>text<|/ref|><|det|>[[115, 775, 883, 911]]<|/det|>
+Emulator- based Modelling Approach. We transform counterfactual emissions into grid- point level distributions of temperature and precipitation and subsequently compute the SPEI- 3 indicator as a potential drought measure from the emulated data. The emulation consists of two steps: first, converting emissions into GMT; and second translating GMT into grid- point level monthly mean temperature and precipitation distributions (Fig. 1). The first translation step is carried out with the Model for the Assessment of the Greenhouse Gas induced Climate Change (MAGICC) [10,41,41]. MAGICC is a simple, computationally efficient climate model for global climate indicators. Our temperature outcomes are calculated with MAGICC v7.5 in a probabilistic setting that reflects the assessed uncertainty ranges from the IPCC's Sixth Assessment Report see [42]. We generate 600 GMT trajectories for each scenario. The second translation steps is carried out using the Modular Earth System Model Emulator for Monthly Temperature and Precipitation
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[86, 90, 883, 211]]<|/det|>
+(MESMER- M- TP)[111]. MESMER- M- TP combines parametric approaches and stochastic sampling to approximate the behaviour of individual climate models. For any climate model, the emulator can be calibrated on a small set of actual climate model data and then generates gridded temperature and precipitation data that statistically resemble the climate model data. Here, we calibrate MESMER- M- TP on 24 different models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) (see Supplementary Table S3). Subsequently, we convert each GMT trajectory into a single gridded timeseries of temperature and precipitation. We compute the SPEI- 3 indicator following[20] and rely on the gamma distribution for normalisation. This leaves us with a dataset containing 3 variables x 600 realisations x 2,652 grid- points x 170 years x 12 months for each scenario.
+
+<|ref|>text<|/ref|><|det|>[[86, 225, 883, 347]]<|/det|>
+Attribution Framework. Traditional attribution studies typically aim at understanding how climate change altered the statistics of a specified observed extreme. Our study deviates from this approach. We are interested in understanding the extent to which changes in a broad class of historic extremes can be related to emissions from specific emitter groups. Therefore, we use the framework for event attribution (EA) as a guideline[14] but modify it according to our research questions. Most importantly, our analysis fully relies on modelled data meaning we are not taking observational data into account. Hence, the EA framework reduces to three essential steps: first, we define extreme events; second, we perform an analysis using emulated (climate model) data and last, we synthesise the hazards into an attribution statement.
+
+<|ref|>text<|/ref|><|det|>[[86, 347, 883, 377]]<|/det|>
+Extreme event definition. We define extreme events relative to the reference period 1850- 1900 and focus on 1- in- 50, 1- in- 100 and 1- in- 10,000 year (unprecedented) events.
+
+<|ref|>text<|/ref|><|det|>[[86, 377, 883, 468]]<|/det|>
+Climate model analysis and Hazard synthesis. We use the modelled distribution of climatic variables over the reference period at each grid- point to derive grid- point specific intensity thresholds for our defined events. To assess frequency changes, we count how many times the reference intensity threshold is exceeded in a present- day (2020) climate and in a counterfactual 2020 climate and attribute the difference to a specific emitter group. Similarly, to quantify intensity changes, we assess how hot (dry) a specific extreme event would be in present- day climate and in the counterfactual climate and attribute the difference in thresholds.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 483, 367, 500]]<|/det|>
+## AUTHOR CONTRIBUTIONS
+
+<|ref|>text<|/ref|><|det|>[[86, 507, 883, 537]]<|/det|>
+All authors conceived the study. S.S. performed the data analysis and wrote the manuscript with contributions from all authors. All authors have read and agreed to the published version of the manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 552, 303, 569]]<|/det|>
+## DATA AVAILABILITY
+
+<|ref|>text<|/ref|><|det|>[[86, 577, 883, 653]]<|/det|>
+The data generated for this study is available at[43]. The results can be reproduced using public data records. The starting point of our analysis are timeseries of \(\mathrm{CO_2}\) - e per capita emissions from[3]. We further use historic emissions available through[37] compiled from[39,44- 52]. We rely on MAGICC v7.5[10,41,41] to translate our input data into GMT levels. We then rely on MESMER- M- TPv0.1.0[53,54] to generate a large- ensemble of temperature and precipitation data.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 669, 328, 686]]<|/det|>
+## ACKNOWLEDGMENTS
+
+<|ref|>text<|/ref|><|det|>[[86, 693, 883, 785]]<|/det|>
+S.S. acknowledges support by the German Federal Environmental Foundation (DBU). S.S. and C.F.S. acknowledge funds by European Union's Horizon 2020 Research and Innovation Programme under Grant No. 101003687 (PROVIDE). Z.N. acknowledges support from the European Union's Horizon 2020 Research and Innovation Funding Programme (Grant No. 101003536, Earth System Models for the Future, ESM2025). R.H. acknowledges funding by the European Union's Horizon Europe Programme under Grant Agreement No. 101094551 (SPES). The authors furthermore gratefully acknowledge funding from IIASA and the National Member Organizations that support the institute.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 799, 363, 816]]<|/det|>
+## CONFLICTS OF INTEREST
+
+<|ref|>text<|/ref|><|det|>[[86, 824, 390, 838]]<|/det|>
+The authors declare no conflict of interest.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 853, 250, 870]]<|/det|>
+## REFERENCES
+
+<|ref|>text<|/ref|><|det|>[[86, 880, 883, 910]]<|/det|>
+[1] Rebecca Newman and Ilan Noy. The global costs of extreme weather that are attributable to climate change. Nature Communications, 14(1):6103, 2023.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 90, 886, 137]]<|/det|>
+[2] Koko Warner and Michael Weisberg. A funding mosaic for loss and damage. Science, 379(6629):219- 219, 2023. doi: 10.1126/science.agd5740. URL https://www.science.org/doi/abs/10.1126/science.agd5740.
+
+<|ref|>text<|/ref|><|det|>[[111, 135, 886, 180]]<|/det|>
+[3] Lucas Chancel. Global carbon inequality over 1990- 2019. Nature Sustainability, 5(11):931- 938, 2022. [4] Pauline Wallemacq, Regina Below, and Denis McClen. Economic losses, poverty and disasters: 1998- 2017. United Nations Office for Disaster Risk Reduction.
+
+<|ref|>text<|/ref|><|det|>[[111, 180, 886, 226]]<|/det|>
+[5] Noah S. Diffenbaugh and Marshall Burke. Global warming has increased global economic inequality. 116(20): 9808- 9813. ISSN 0027- 8424, 1091- 6490. doi: 10.1073/pnas.1816020116. URL https://pnas.org/doi/full/10.1073/pnas.1816020116.
+
+<|ref|>text<|/ref|><|det|>[[111, 225, 886, 255]]<|/det|>
+[6] Stephane Hallegatte and Julie Rozenberg. Climate change through a poverty lens. Nature Climate Change, 7(4): 250- 256, 2017.
+
+<|ref|>text<|/ref|><|det|>[[111, 255, 886, 316]]<|/det|>
+[7] Emissions trends and drivers. In Intergovernmental Panel On Climate Change (Ipcc), editor, Climate Change 2022 - Mitigation of Climate Change, pages 215- 294. Cambridge University Press, 1 edition. ISBN 978- 1- 00- 915792- 6. doi: 10.1017/9781009157926.004. URL https://www.cambridge.org/core/product/identifier/9781009157926%23c2/type/book_part.
+
+<|ref|>text<|/ref|><|det|>[[111, 315, 886, 346]]<|/det|>
+[8] Kathleen A Mar, Charlotte Unger, Ludmila Walderdorff, and Tim Butler. Beyond co2 equivalence: The impacts of methane on climate, ecosystems, and health. Environmental science & policy, 134:127- 136, 2022.
+
+<|ref|>text<|/ref|><|det|>[[111, 345, 886, 390]]<|/det|>
+[9] Lea Beusch, Lukas Gudmundsson, and Sonia I Seneviratne. Emulating earth system model temperatures with mesmer: from global mean temperature trajectories to grid- point- level realizations on land. Earth System Dynamics, 11(1):139- 159, 2020.
+
+<|ref|>text<|/ref|><|det|>[[111, 390, 886, 436]]<|/det|>
+[10] Malte Meinshausen, Sarah CB Raper, and Tom ML Wigley. Emulating coupled atmosphere- ocean and carbon cycle models with a simpler model, magicc6- part 1: Model description and calibration. Atmospheric Chemistry and Physics, 11(4):1417- 1456, 2011.
+
+<|ref|>text<|/ref|><|det|>[[111, 435, 886, 481]]<|/det|>
+[11] Sarah Schongart, Peter Pfleiderer, and Carl- Friedrich SchleuBner. Exploring variability and uncertainty in precipitation within earth system models using parametric estimates from the precipitation emulator mesmer- m- tp. Technical report, Copernicus Meetings, 2024.
+
+<|ref|>text<|/ref|><|det|>[[111, 481, 886, 526]]<|/det|>
+[12] Friederike E.L. Otto. Attribution of extreme events to climate change. 48(1):813- 828. ISSN 1543- 5938, 1545- 2050. doi: 10.1146/annurev- environ- 112621- 083538. URL https://www.annualreviews.org/doi/10.1146/annurev- environ- 112621- 083538.
+
+<|ref|>text<|/ref|><|det|>[[111, 526, 886, 556]]<|/det|>
+[13] Peter A Stott, Daithi A Stone, and Myles R Allen. Human contribution to the european heatwave of 2003. Nature, 432(7017):610- 614, 2004.
+
+<|ref|>text<|/ref|><|det|>[[111, 556, 886, 601]]<|/det|>
+[14] Geert Jan Van Oldenborgh, Karin van Der Wiel, Sarah Kew, Sjoukje Philip, Friederike Otto, Robert Vautard, Andrew King, Fraser Lott, Julie Arrighi, Roop Singh, et al. Pathways and pitfalls in extreme event attribution. Climatic Change, 166(1):13, 2021.
+
+<|ref|>text<|/ref|><|det|>[[111, 601, 886, 647]]<|/det|>
+[15] Lea Beusch, Alexander Nauels, Lukas Gudmundsson, Johannes Gutschow, Carl- Friedrich Schleussner, and Sonia I Seneviratne. Responsibility of major emitters for country- level warming and extreme hot years. Communications Earth & Environment, 3(1):7, 2022.
+
+<|ref|>text<|/ref|><|det|>[[111, 647, 886, 692]]<|/det|>
+[16] Christopher W. Callahan and Justin S. Mankin. National attribution of historical climate damages. 172(3):40. ISSN 0165- 0009, 1573- 1480. doi: 10.1007/s10584- 022- 03387- y. URL https://link.springer.com/10.1007/s10584- 022- 03387- y.
+
+<|ref|>text<|/ref|><|det|>[[111, 692, 886, 722]]<|/det|>
+[17] Cathy Trudinger and Ian Enting. Comparison of formalisms for attributing responsibility for climate change: Non- linearities in the brazilian proposal approach. Climatic Change, 68(1):67- 99, 2005.
+
+<|ref|>text<|/ref|><|det|>[[111, 722, 886, 752]]<|/det|>
+[18] Friederike EL Otto, Ragnhild B Skeie, Jan S Fuglestvedt, Terje Berntsen, and Myles R Allen. Assigning historic responsibility for extreme weather events. Nature Climate Change, 7(11):757- 759, 2017.
+
+<|ref|>text<|/ref|><|det|>[[111, 752, 886, 782]]<|/det|>
+[19] Lucas Chancel and Yannic Rehm. The carbon footprint of capital: Evidence from france, germany and the us based on distributional environmental accounts. 2023.
+
+<|ref|>text<|/ref|><|det|>[[111, 782, 886, 826]]<|/det|>
+[20] SODE Tirivarombo, D Ospuile, and Peter Eliasson. Drought monitoring and analysis: standardised precipitation evapotranspiration index (spei) and standardised precipitation index (spi). Physics and Chemistry of the Earth, Parts A/B/C, 106:1- 10, 2018.
+
+<|ref|>text<|/ref|><|det|>[[111, 826, 886, 904]]<|/det|>
+[21] Myles R. Allen, Glen P. Peters, Keith P. Shine, Christian Azar, Paul Balcombe, Olivier Boucher, Michelle Cain, Philippe Ciais, William Collins, Piers M. Forster, Dave J. Frame, Pierre Friedlingstein, Claire Fyson, Thomas Gasser, Bill Hare, Stuart Jenkins, Steven P. Hamburg, Daniel J. A. Johansson, John Lynch, Adrian Macey, Johannes Morfeldt, Alexander Nauels, Ilissa Ocko, Michael Oppenheimer, Stephen W. Pacala, Raymond Pierrehumbert, Joeri Rogelj, Michiel Schaeffer, Carl F. Schleussner, Drew Shindell, Ragnhild B. Skeie, Stephen M.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 90, 888, 905]]<|/det|>
+Smith, and Katsumasa Tanaka. Indicate separate contributions of long- lived and short- lived greenhouse gases in emission targets. npj Climate and Atmospheric Science, 5(1):5, December 2022. ISSN 2397- 3722. doi: 10.1038/s41612- 021- 00226- 2. URL https://www.nature.com/articles/s41612- 021- 00226- 2. Publisher: Springer US. [22] Nikhil Kumar, Manish Kumar Goyal, Anil Kumar Gupta, Srinidhi Jha, Jew Das, and Chandra A Madramootoo. Joint behaviour of climate extremes across india: Past and future. Journal of Hydrology, 597:126185, 2021. [23] Caroline Zimm, Kian Mintz- Woo, Elina Brutschin, Susanne Hanger- Kopp, Roman Hoffmann, Jarmo S Kikstra, Michael Kuhn, Jihoon Min, Raya Muttarak, Shonali Pachauri, et al. Justice considerations in climate research. Nature Climate Change, 14(1):22- 30, 2024. [24] Shonali Pachauri, Setu Pelz, Christoph Bertram, Silvie Kreibiehl, Narasimha D. Rao, Youba Sokona, and Keywan Riahi. Fairness considerations in global mitigation investments. Science, 378(6624):1057- 1059, December 2022. doi: 10.1126/science.adf0067. URL https://www.science.org/doi/10.1126/science.adf0067. Publisher: American Association for the Advancement of Science. [25] Steven J Davis and Ken Caldeira. Consumption- based accounting of co2 emissions. Proceedings of the national academy of sciences, 107(12):5687- 5692, 2010. [26] Etern Karakaya, Burcu Yilmaz, and Sedat Alataş. How production- based and consumption- based emissions accounting systems change climate policy analysis: the case of co 2 convergence. Environmental Science and Pollution Research, 26:16682- 16694, 2019. [27] Christine M. McKenna, Amanda C. Maycock, Piers M. Forster, Christopher J. Smith, and Katarzyna B. Tokarska. Stringent mitigation substantially reduces risk of unprecedented near- term warming rates. Nature Climate Change, 11(2):126- 131, February 2021. ISSN 1758- 6798. doi: 10.1038/s41558- 020- 00957- 9. URL https://www.nature.com/articles/s41558- 020- 00957- 9. Publisher: Nature Publishing Group. [28] Olivia Serdeczny and Tabea Lissner. Research agenda for the loss and damage fund. Nature Climate Change, 13 (5):412- 412, May 2023. ISSN 1758- 6798. doi: 10.1038/s41558- 023- 01648- x. URL https://www.nature.com/articles/s41558- 023- 01648- x. Publisher: Nature Publishing Group. [29] Yann Quilcaile, Lukas Gudmundsson, Dominik Schumacher, Thomas Gasser, Richard Heede, Corina Heri, Quentin Lejeune, Shruti Nath, Wim Thiery, Carl- Friedrich Schleiussner, et al. Systematic attribution of heatwaves to the emissions of carbon majors. 2024. [30] Jarmo S. Kikstra, Alessio Mastrucci, Jihoon Min, Keywan Riahi, and Narasimha D. Rao. Decent living gaps and energy needs around the world. Environmental Research Letters, 16(9):095006, September 2021. ISSN 1748- 9326. doi: 10.1088/1748- 9326/ac1c27. URL https://dx.doi.org/10.1088/1748- 9326/ac1c27. Publisher: IOP Publishing. [31] Justin Sheffield, Eric F Wood, and Michael L Roderick. Little change in global drought over the past 60 years. Nature, 491(7424):435- 438, 2012. [32] Laura Jensen, Helena Genderer, Annette Eicker, Jürgen Kusche, and Stephanie Fiedler. Observations indicate regionally misleading wetting and drying trends in cimip6. npj Climate and Atmospheric Science, 7(1):249, 2024. [33] Yeon- Hee Kim, Seung- Ki Min, Xuebin Zhang, Jana Sillmann, and Marit Sandstad. Evaluation of the cimip6 multi- model ensemble for climate extreme indices. Weather and Climate Extremes, 29:100269, 2020. [34] Sergio M Vicente- Serrano, Gerard Van der Schrier, Santiago Beguería, Cesar Azorin- Molina, and Juan- I Lopez- Moreno. Contribution of precipitation and reference evapotranspiration to drought indices under different climates. Journal of Hydrology, 526:42- 54, 2015. [35] SI Seneviratne, X Zhang, M Adnan, W Badi, C Dereczynski, A Di Luca, SM Vicente- Serrano, M Wehner, and B Zhou. Chapter 11: weather and climate extreme events in a changing climate. 2021. [36] Christiane Nascimento Santos, Anderson Amorim Rocha Santos, Marcel Carvalho Abreu, Fabrina Bolzan Martins, Guilherme Bastos Lyra, José Leonardo de Souza, and Gustavo Bastos Lyra. Monthly potential evapotranspiration estimated using the thornthwaite method with gridded climate datasets in southeastern brazil. Theoretical and Applied Climatology, pages 1- 18, 2024. [37] Z. R. J. Nicholls, M. Meinshausen, J. Lewis, R. Gieseke, D. Dommenget, K. Dorheim, C.- S. Fan, J. S. Fuglestvedt, T. Gasser, U. Goluke, P. Goodwin, C. Hartin, A. P. Hope, E. Kriegler, N. J. Leach, D. Marchegiani, L. A. McBride, Y. Quilcaille, J. Rogelj, R. J. Salawitch, B. H. Samset, M. Sandstad, A. N. Shiklomanov, R. B. Skeie, C. J. Smith, S. Smith, K. Tanaka, J. Tsutsui, and Z. Xie. Reduced complexity model intercomparison project phase 1: introduction and evaluation of global- mean temperature response. Geoscientific Model Development, 13(11): 5175- 5190, 2020. doi: 10.5194/gmd- 13- 5175- 2020. URL https://gmd.copernicus.org/articles/13/5175/2020/.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[78, 90, 888, 910]]<|/det|>
+[38] AR Shukla, Jim Skea, A Reisinger, R Slade, R Fradera, M Pathak, A Al Khourdajie, M Belkacemi, R Van Diemen, A Hasija, et al. Summary for policymakers. Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, 2022. [39] Johannes Gutschow, M Louise Jeffery, Robert Gieseke, Ronja Gebel, David Stevens, Mario Krapp, and Marcia Rocha. The primap- hist national historical emissions time series. Earth System Science Data, 8(2):571- 603, 2016. [40] Bo Zhang, Xueli Zhao, Xiaofang Wu, Mengyao Han, Cheng He Guan, and Shaojie Song. Consumption- based accounting of global anthropogenic ch4 emissions. Earth's Future, 6(9):1349- 1363, 2018. doi: https://doi.org/10.1029/2018EF000917. URL https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018EF000917. [41] Malte Meinshausen, Nicolai Meinshausen, William Hare, Sarah C. B. Raper, Katja Frieler, Reto Knutti, David J. Frame, and Myles R. Allen. Greenhouse- gas emission targets for limiting global warming to \(2^{\circ}\mathrm{C}\) . Nature, 458 (7242):1158- 1162, apr 2009. doi: 10.1038/nature08017. [42] D. Chen, M. Rojas, B.H. Samset, K. Cobb, A. Diongue Niang, P. Edwards, S. Emori, S.H. Faria, E. Hawkins, P. Hope, P. Huybrechts, M. Meinshausen, S.K. Mustafa, G.- K. Plattner, and A.- M. Tréguier. Framing, context, and methods. In V. Masson- Delmotte, P. Zhai, A. Pirani, S. L. Connors, C. Pean, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou, editors, Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, book section 1, pages 147- 286. Cambridge University Press, Cambridge, UK and New York, NY, USA, 2021. doi: 10.1017/9781009157896.003. URL https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter01. pdf. [43] Sarah Schöngart. Income- based attribution of extrema events (v0.0.1), 2024. URL https://doi.org/10.5281/zenodo.11086168. [44] Matthew J. Gidden, Keywan Riahi, Steven J. Smith, Shinichiro Fujimori, Gunnar Luderer, Elmar Kriegler, Detlef P. van Vuuren, Maarten van den Berg, Leyang Feng, David Klein, Katherine Calvin, Jonathan C. Doelman, Stefan Frank, Oliver Fricko, Mathijs Harmsen, Tomoko Hasegawa, Petr Havlik, Jérôme Hilaire, Rachel Hoesly, Jill Horing, Alexander Popp, Elke Stehfest, and Kiyoshi Takahashi. Global emissions pathways under different socioeconomic scenarios for use in CMIP6: a dataset of harmonized emissions trajectories through the end of the century. Geoscientific Model Development, 12(4):1443- 1475, apr 2019. doi: 10.5194/gmd- 12- 1443- 2019. [45] M. Meinshausen, Z. R. J. Nicholls, J. Lewis, M. J. Gidden, E. Vogel, M. Freund, U. Beyerle, C. Gessner, A. Nauels, N. Bauer, J. G. Canadell, J. S. Daniel, A. John, P. B. Krummel, G. Luderer, N. Meinshausen, S. A. Montzka, P. J. Rayner, S. Reimann, S. J. Smith, M. van den Berg, G. J. M. Velders, M. K. Vollmer, and R. H. J. Wang. The shared socio- economic pathway (ssp) greenhouse gas concentrations and their extensions to 2500. Geoscientific Model Development, 13(8):3571- 3605, 2020. doi: 10.5194/gmd- 13- 3571- 2020. URL https://gmd.copernicus.org/articles/13/3571/2020/. [46] Guus JM Velders, David W Fahey, John S Daniel, Stephen O Andersen, and Mack McFarland. Future atmospheric abundances and climate forcings from scenarios of global and regional hydrofluorocarbon (hfc) emissions. Atmospheric Environment, 123:200- 209, 2015. [47] Rachel M. Hoesly, Steven J. Smith, Leyang Feng, Zbigniew Klimont, Greet Janssens- Maenhout, Tyler Pitkanen, Jonathan J. Seibert, Linh Vu, Robert J. Andres, Ryan M. Bolt, Tami C. Bond, Laura Dawidowski, Nazar Kholod, June- ichi Kurokawa, Meng Li, Liang Liu, Zifeng Lu, Maria Cecilia P. Moura, Patrick R. O'Rourke, and Qiang Zhang. Historical (1750- 2014) anthropogenic emissions of reactive gases and aerosols from the community emissions data system (CEDS). Geoscientific Model Development, 11(1):369- 408, jan 2018. doi: 10.5194/gmd- 11- 369- 2018. [48] Margreet J. E. van Marle, Silvia Kloster, Brian I. Magi, Jennifer R. Marlon, Anne- Laure Daniau, Robert D. Field, Almut Arneth, Matthew Forrest, Stijn Hanston, Natalie M. Kehrwald, Wolfgang Knorr, Gitta Lasslop, Fang Li, Stéphane Mangeon, Chao Yue, Johannes W. Kaiser, and Guido R. van der Werf. Historic global biomass burning emissions for CMIP6 (BB4cmip) based on merging satellite observations with proxies and fire models (1750- 2015). Geoscientific Model Development, 10(9):3329- 3357, sep 2017. doi: 10.5194/gmd- 10- 3329- 2017. [49] Corinne Le Quéré, Robbie M Andrew, Josep G Canadell, Stephen Sitch, Jan Ivar Korsbakken, Glen P Peters, Andrew C Manning, Thomas A Boden, Pieter P Tans, Richard A Houghton, et al. Global carbon budget 2016. Earth System Science Data, 8(2):605- 649, 2016. [50] WMO. Wmo: Scientific assessment of ozone depletion. World Meteorological Organization, Geneva, Switzerland, page 416 pp., 2014.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 90, 886, 905]]<|/det|>
+[51] WMO. Wmo: Scientific assessment of ozone depletion. World Meteorological Organization, Geneva, Switzerland, page 572 pp., 2006. [52] Malte Meinshausen, Zebedee RJ Nicholls, Jared Lewis, Matthew J Gidden, Elisabeth Vogel, Mandy Freund, Urs Beyerle, Claudia Gessner, Alexander Nauels, Nico Bauer, et al. The shared socio- economic pathway (ssp) greenhouse gas concentrations and their extensions to 2500. Geoscientific Model Development, 13(8):3571- 3605, 2020. [53] S. Schongart, L. Gudmundsson, M. Hauser, P. Pfleiderer, Q. Lejeune, S. Nath, S. I. Seneviratne, and C.- F. Schleußner. Introducing the mesmer- m- tpv0.1.0 module: Spatially explicit earth system model emulation for monthly precipitation and temperature. EGUsphere, 2024:1- 51, 2024. doi: 10.5194/egusphere- 2024- 278. URL https://egusphere.copernicus.org/preprints/2024/egusphere- 2024- 278/. [54] Sarah Schongart. Mesmer- m- tp version 0.1.0. Zenodo [code], 2024. URL https://zenodo.org/doi/10.5281/zenodo.11086167. [55] VP Masson- Delmotte, Pannao Zhai, SL Pirani, C Connors, S Pean, N Berger, Y Caud, L Chen, MI Goldfarb, and Pedro M Scheel Monteiro. Ipcc, 2021: Summary for policymakers. in: Climate change 2021: The physical science basis. contribution of working group i to the sixth assessment report of the intergovernmental panel on climate change. 2021. [56] Martin Dix, Daohua Bi, Peter Dobrohotoff, Russell Fiedler, Ian Harman, Rachel Law, Chloe Mackallah, Simon Marsland, Siobhan O'Farrell, Harun Rashid, Jhan Srbinovsky, Arnold Sullivan, Claire Trenham, Peter Vohralik, Ian Watterson, Gareth Williams, Matthew Woodhouse, Roger Bodman, Fabio Boeira Dias, Catia M. Domingues, Nicholas Hannah, Aidan Heerdegen, Abhishek Savita, Scott Wales, Chris Allen, Kelsey Drukne, Ben Evans, Clare Richards, Syazwan Mohamed Ridzwan, Dale Roberts, Jon Smillie, Kate Snow, Marshall Ward, and Rui Yang. CSIRO- ARCCSS ACCESS- CM2 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.2285. [57] Tilo Ziehn, Matthew Chamberlain, Andrew Lenton, Rachel Law, Roger Bodman, Martin Dix, Yingping Wang, Peter Dobrohotoff, Jhan Srbinovsky, Lauren Stevens, Peter Vohralik, Chloe Mackallah, Arnold Sullivan, Siobhan O'Farrell, and Kelsey Drukne. CSIRO ACCESS- ESM1.5 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.2291. [58] Tido Semmler, Sergey Danilov, Thomas Rackow, Dmitry Sidorenko, Dirk Barbi, Jan Hegewald, Himansu Kesari Pradhan, Dmitri Sein, Qiang Wang, and Thomas Jung. AWI AWI- CM1.1MR model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.376. [59] Gokhan Danabasoglu. NCAR CESM2- WACCM model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.10026. [60] Gokhan Danabasoglu. NCAR CESM2 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.2201. [61] Tomas Lovato and Daniele Peano. CMCC CMCC- CM2- SR5 model output prepared for CMIP6 scenarioMIP, 2020. URL https://doi.org/10.22033/ESGF/CMIP6.1365. [62] Aurore Volodire. CNRM- CERFACS CNRM- CM6- 1- HR model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.1388. [63] Aurore Volodire. CNRM- CERFACS CNRM- CM6- 1 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.1384. [64] Roland Seferian. CNRM- CERFACS CNRM- ESM2- 1 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.1395. [65] Neil Cameron Swart, Jason N.S. Cole, Viatcheslav V. Kharin, Mike Lazare, John F. Scinocca, Nathan P. Gillett, James Anstey, Vivek Arora, James R. Christian, Yanjun Jiao, Warren G. Lee, Fouad Majaess, Oleg A. Saenko, Christian Seiler, Clint Seinen, Andrew Shao, Larry Solheim, Knut von Salzen, Duo Yang, Barbara Winter, and Michael Sigmond. CCCma CanESM5 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.1317. [66] David C. Bader, Ruby Leung, Mark Taylor, and Renata B. McCoy. E3SM- project E3SM1.1 model output prepared for CMIP6 scenarioMIP, 2020. URL https://doi.org/10.22033/ESGF/CMIP6.15103. [67] Yongqiang YU. CAS FGOALS- f3- L model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.2046. [68] Lijuan Li. CAS FGOALS- g3 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.2056. [69] Zhenya Song, Fangli Qiao, Ying Bao, Qi Shu, Yajuan Song, and Xiaodan Yang. FIO- QLNM FIO- ESM2.0 model
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 90, 884, 904]]<|/det|>
+output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.9051. [70] Peter Good. MOHC HadGEM3- GC31- LL model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.10845. [71] Laura Jackson. MOHC HadGEM3- GC31- MM model output prepared for CMIP6 scenarioMIP, 2020. URL https://doi.org/10.22033/ESGF/CMIP6.10846. [72] Olivier Boucher, Sébastien Denvil, Guillaume Levavasseur, Anne Cozic, Arnaud Caubel, Marie- Alice Foujols, Yann Meurdesoif, Patricia Cadule, Marion Devilliers, Eliott Dupont, and Thibaut Lurton. IPSL IPSL- CM6A- LR model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.1532. [73] Martin Schupfner, Karl- Hermann Wieners, Fabian Wachsmann, Christian Steger, Matthias Bittner, Johann Jungclaus, Barbara Früh, Klaus Pankatz, Marco Giorgetta, Christian Reick, Stephanie Legutke, Monika Esch, Veronika Gayler, Helmuth Haak, Philipp de Vrese, Thomas Raddatz, Thorsten Mauritsen, Jin- Song von Storch, Jörg Behrens, Victor Brovkin, Martin Claussen, Traute Crueger, Irina Fast, Stephanie Fiedler, Stefan Hagemann, Cathy Hohenegger, Thomas Jahns, Silvia Kloster, Stefan Kinne, Gitta Lasslop, Luis Kornblueh, Jochem Marotzke, Daniela Matei, Katharina Meraner, Uwe Mikolajewicz, Kameswarrao Modali, Wolfgang Müller, Julia Nabel, Dirk Notz, Karsten Peters- von Gehlen, Robert Pincus, Holger Pohlmann, Julia Pongratz, Sebastian Rast, Hauke Schmidt, Reiner Schnur, Uwe Schulzweida, Katharina Six, Bjorn Stevens, Aiko Voigt, and Erich Roeckner. DKRZ MPI- ESM1.2- HR model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.2450. [74] Martin Schupfner, Karl- Hermann Wieners, Fabian Wachsmann, Sebastian Milinski, Christian Steger, Matthias Bittner, Johann Jungclaus, Barbara Früh, Klaus Pankatz, Marco Giorgetta, Christian Reick, Stephanie Legutke, Monika Esch, Veronika Gayler, Helmuth Haak, Philipp de Vrese, Thomas Raddatz, Thorsten Mauritsen, Jin- Song von Storch, Jörg Behrens, Victor Brovkin, Martin Claussen, Traute Crueger, Irina Fast, Stephanie Fiedler, Stefan Hagemann, Cathy Hohenegger, Thomas Jahns, Silvia Kloster, Stefan Kinne, Gitta Lasslop, Luis Kornblueh, Jochem Marotzke, Daniela Matei, Katharina Meraner, Uwe Mikolajewicz, Kameswarrao Modali, Wolfgang Müller, Julia Nabel, Dirk Notz, Karsten Peters- von Gehlen, Robert Pincus, Holger Pohlmann, Julia Pongratz, Sebastian Rast, Hauke Schmidt, Reiner Schnur, Uwe Schulzweida, Katharina Six, Bjorn Stevens, Aiko Voigt, and Erich Roeckner. DKRZ MPI- ESM1.2- LR model output prepared for CMIP6 scenarioMIP, 2021. URL https://doi.org/10.22033/ESGF/CMIP6.15349. [75] Seiji Yukimoto, Tsuyoshi Koshiro, Hideaki Kawai, Naga Oshima, Kohei Yoshida, Shogo Urakawa, Hiroyuki Tsujino, Makoto Deushi, Taichu Tanaka, Masahiro Hosaka, Hiromasa Yoshimura, Eiki Shindo, Ryo Mizuta, Masayoshi Ishii, Atsushi Obata, and Yukimasa Adachi. MRI MRI- ESM2.0 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.638. [76] Jian Cao. NUIST NESMv3 model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.2027. [77] Oyvind Seland, Mats Bentsen, Dirk Jan Leo Olivie, Thomas Toniazzo, Ada Gjermundsen, Lise Seland Graff, Jens Boldingh Debernard, Alok Kumar Gupta, Yanchun He, Alf Kirkevåg, Jörg Schwinger, Jerry Tjiputra, Kjetil Schanke Aas, Ingo Bethke, Yuanchao Fan, Jan Griesfeller, Alf Grini, Chuncheng Guo, Mehmet Ilicak, Inger Helene Hafshal Karset, Oskar Andreas Landgren, Johan Liakka, Kine Onsum Moseid, Aleksi Nummelin, Clemens Spensberger, Hui Tang, Zhongshi Zhang, Christoph Heinze, Trond Iversen, and Michael Schulz. NCC NorESM2- LM model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.604. [78] Mats Bentsen, Dirk Jan Leo Olivie, Oyvind Seland, Thomas Toniazzo, Ada Gjermundsen, Lise Seland Graff, Jens Boldingh Debernard, Alok Kumar Gupta, Yanchun He, Alf Kirkevåg, Jörg Schwinger, Jerry Tjiputra, Kjetil Schanke Aas, Ingo Bethke, Yuanchao Fan, Jan Griesfeller, Alf Grini, Chuncheng Guo, Mehmet Ilicak, Inger Helene Hafshal Karset, Oskar Andreas Landgren, Johan Liakka, Kine Onsum Moseid, Aleksi Nummelin, Clemens Spensberger, Hui Tang, Zhongshi Zhang, Christoph Heinze, Trond Iversen, and Michael Schulz. NCC NorESM2- MM model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.608. [79] Peter Good, Alistair Sellar, Yongming Tang, Steve Rumbold, Rich Ellis, Douglas Kelley, Till Kuhlbrodt, and Jeremy Walton. MOHC UKESM1.0- LL model output prepared for CMIP6 scenarioMIP, 2019. URL https://doi.org/10.22033/ESGF/CMIP6.1567. [80] Shabtai Cohen and Gerald Stanhill. Chapter 29 - widespread surface solar radiation changes and their effects: Dimming and brightening. In Trevor M. Letcher, editor, Climate Change (Second Edition), pages 491- 511. Elsevier, Boston, second edition edition, 2016. ISBN 978- 0- 444- 63524- 2. doi: https://doi.org/10.1016/ B978- 0- 444- 63524- 2.00029- 4. URL https://www.sciencedirect.com/science/article/pii/
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[83, 91, 343, 104]]<|/det|>
+B9780444635242000294.
+
+<|ref|>text<|/ref|><|det|>[[85, 106, 884, 180]]<|/det|>
+[81] Aolin Jia, Shunlin Liang, Dongdong Wang, Bo Jiang, and Xiaotong Zhang. Air pollution slows down surface warming over the tibetan plateau. Atmospheric Chemistry and Physics, 20(2):881- 899, 2020. [82] Zhili Wang, Lei Lin, Yangyang Xu, Huizheng Che, Xiaoye Zhang, Hua Zhang, Wenjie Dong, Chense Wang, Ke Gui, and Bing Xie. Incorrect asian aerosols affecting the attribution and projection of regional climate change in cmip6 models. npj Climate and Atmospheric Science, 4(1):2, 2021.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 43, 312, 71]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[43, 93, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[59, 131, 378, 230]]<|/det|>
+- supplement.pdf- AttributedGMT.csv- processedextremesfrequency.csv- processedextremesintensity.csv
+
+<--- Page Split --->
diff --git a/preprint/preprint__03cad287deb044c05daa550c40716d2819e5af19adf18b7b6e72878c97733fe6/images_list.json b/preprint/preprint__03cad287deb044c05daa550c40716d2819e5af19adf18b7b6e72878c97733fe6/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..cf1c5ceb6742ab73c87991a32dce8556b81af798
--- /dev/null
+++ b/preprint/preprint__03cad287deb044c05daa550c40716d2819e5af19adf18b7b6e72878c97733fe6/images_list.json
@@ -0,0 +1,100 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1 Map of the 1980-2019 mean WHI values for 400 sites across the USA and Canada. Circle size corresponds to the two consecutive days with low flows beginning with the Saturday/Sunday (SS, largest symbols) combination and ending with the Friday/Saturday (FS, smallest symbols).",
+ "footnote": [],
+ "bbox": [
+ [
+ 115,
+ 170,
+ 880,
+ 632
+ ]
+ ],
+ "page_idx": 36
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2 Histogram of the 1980-2019 frequency distribution of low flow days and corresponding WHI values. Black bars denote the two consecutive days with low flows while red bars represent the WHI values for 400 sites across the USA and Canada, 1980-2019. Fractions of the two consecutive days with low flows are partitioned according to positive (solid) and negative (hatched) WHI values. The days of the week begin with the Saturday/Sunday (SS) combination and end with the Friday/Saturday (FS) combination. The horizontal black line denotes the expected value if the two-day low flows were distributed randomly while the horizontal red line marks the mean WHI across the 400 sites.",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 214,
+ 875,
+ 664
+ ]
+ ],
+ "page_idx": 37
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4 Map of the 1980-2019 monotonic trends in WHI at 380 sites across the USA and Canada. Red upward (blue downward) pointing triangles indicate positive (negative) trends. Trend magnitudes are proportional to the triangle sizes and green circles (pink outlines) indicate locally (globally) statistically-significant trends \\((p < 0.05)\\) . Results are shown only when \\(n_{y} \\geq 30\\) years.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 38
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 42,
+ 90,
+ 955,
+ 644
+ ]
+ ],
+ "page_idx": 39
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 50,
+ 50,
+ 944,
+ 586
+ ]
+ ],
+ "page_idx": 41
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 44,
+ 40,
+ 950,
+ 500
+ ]
+ ],
+ "page_idx": 43
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 42,
+ 42,
+ 959,
+ 597
+ ]
+ ],
+ "page_idx": 44
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5.mmd b/preprint/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..6e97a5e03bdf49f32cac139e27efcc489155deb7
--- /dev/null
+++ b/preprint/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5.mmd
@@ -0,0 +1,289 @@
+
+# Mn-inlaid antiphase boundaries in perovskite structure
+
+Lingyan Wang 1.y.wang@mail.xjtu.edu.cn
+
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University
+
+Chao Li Xi'an Jiaotong University
+
+Liqiang Xu
+
+Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University
+
+Xuerong Ren
+
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University
+
+Fangzhou Yao
+
+Wuzhen Laboratory/Center of Advanced Ceramic Materials and Devices, Yangtze Delta Region Institute of Tsinghua University
+
+Jiangbo Lu School of Physics and Information Technology, Shaanxi Normal University
+
+Dong Wang Xi'an Jiaotong University
+
+zhongshuai Liang Xi'an Jiaotong University
+
+Ping Huang Xi'an Jiaotong University https://orcid.org/0000- 0002- 5295- 8216
+
+Shengqiang Wu
+
+School of Materials Science and Engineering, Peking University
+
+Hongmei Jing
+
+School of Physics and Information Technology, Shaanxi Normal University
+
+Yijun Zhang
+
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University
+
+Guohua Dong
+
+Xi'an Jiaotong University https://orcid.org/0000- 0002- 5484- 5442
+
+<--- Page Split --->
+
+Haixia Liu Xi'an Jiaotong University
+
+Chuansheng Ma Instrumental Analysis Center, Xi'an Jiaotong University
+
+Yinong Lyu Nanjing Tech University
+
+Xiaoyong Wei
+
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi'an Jiao Tong University
+
+Wei Ren
+
+Xi'an Jiaotong University School of Electronic and Information Engineering
+
+Ke Wang
+
+State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, P. R. China https://orcid.org/0000- 0001- 9840- 2427
+
+Zuo-Guang Ye
+
+Simon Fraser University https://orcid.org/0000- 0003- 2378- 7304
+
+Feng Chen
+
+High Magnetic Field Laboratory, Chinese Academy of Sciences
+
+## Article
+
+Keywords:
+
+Posted Date: February 5th, 2024
+
+DOI: https://doi.org/10.21203/rs.3.rs- 3884985/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on August 7th, 2024. See the published version at https://doi.org/10.1038/s41467- 024- 51024- 2.
+
+<--- Page Split --->
+
+## Mn-inlaid antiphase boundaries in perovskite structure
+
+High- performance perovskite ferroelectrics are central to various electro- mechanical functional devices \(^{1,2}\) . However, the use of toxic Pb- based ferroelectrics in high- end applications is being limited due to environmental concerns and the related legislations \(^{3}\) . As an eco- friendly alternative, lead- free perovskite potassium sodium niobate (K \(_4\) Na \(_1\) - \(_3\) NbO \(_3\) , KNN)- based perovskite ferroelectrics materials have been intensively studied since the discovery of a large piezoelectric coefficient \(d_{33}\) value of 416 pC/N for KNN- based ceramics by Saito et al. \(^{4 - 6}\) . With advancements in the ferroelectric performances of the KNN- based ceramics and single crystals \(^{7 - 10}\) , a great deal of efforts have also been made to prepare the KNN- based thin films by various deposition techniques \(^{11 - 14}\) . However, the volatilization of the alkali ions has been identified as a major issue in obtaining high- quality KNN- based thin films. The inevitable loss of potassium and sodium elements during the vapor or chemical solution- based depositions changes the stoichiometry, resulting in the formation of undesired alkali- deficient secondary phases and defects. Consequently, KNN- based films exhibit high electrical conduction and poor ferroelectric response \(^{15}\) . Previous strategies focused on chemical composition adjustment to compensate for the elemental volatilization, and construction of morphotropic or polytropic phase boundaries to enhance the dielectric and ferroelectric properties of KNN- based thin films \(^{16 - 19}\) . Recently, some other methods, such as interface effects, flexible substrates, and defects engineering have been explored to modulate lattice strain, displacement polarization and electronic structure \(^{11,12,20 - 23}\) . All those efforts have led to a gradual improvement in the overall ferroelectric performances, which, however, still remain significantly inferior to Pb- based thin films and thereby are far from being suitable for practical applications in new micro electro- mechanical devices, ferroelectric field- effect transistors, nonvolatile memories, electro- optic devices, etc. \(^{1,24,25}\) .
+
+Material properties are strongly influenced by the microstructure. In terms of crystal structure, the above- mentioned attempts primarily focused on distorting or tilting the lattices within the basic perovskite framework, which has given rise to limited effects in improving the ferroelectric properties. It has been observed that the physical constraints of underlying substrate and the large unit cell of oxide perovskite structure can lead to the generation and propagation of out- of- phase boundary defects through the entire thickness of the film, especially with special deposition processes \(^{12,26}\) . These charged out- of- phase boundaries, originated from the alkali- deficiency, have been identified and found to play an important role in the piezoelectric performances of NaNbO \(_3\) and KNN thin films \(^{12}\) . In this work, we also harnessed these inherent characteristics (alkali deficiency and out- of- phase boundaries) to create a unique nanocolumnar structure, and then incorporated another element at the boundaries between the KNN nanocolumns to form a new perovskite derivative structure. Specifically, the nanocolumnar KNN- based thin film consists of perovskite KNN nanocolumns that are interspersed with Mn- inlaid antiphase boundaries. Atomic resolution images revealed that the thickness of perovskite KNN slabs varied from a few to tens of nanometers, while the coherent antiphase boundaries consisted of one or two atomic layers enriched with Mn. This strategic incorporation of Mn not only helped to balance the charges originated from alkali ions deficiency, leading to a reduced leakage current, but also induced a noticeable out- of- plane tensile strain in the KNN nanocolumns. This strain promoted a high degree of tetragonality, resulting in a remarkable improvement in ferroelectric polarization, with a high twice remanent polarization value of \(114 \mu \mathrm{C} / \mathrm{cm}^2\) .
+
+A ceramic target of \(\mathrm{K}_{0.5}\mathrm{Na}_{0.5}\mathrm{NbO}_{3}\) with \(2 \mathrm{wt\% MnO}_2\) addition (KNN- M) was used for deposition of the KNN- M films on \(\mathrm{La}_{0.07}\mathrm{Sr}_{0.93}\mathrm{SnO}_3\) (LSSO)- coated STO (001) substrates by
+
+<--- Page Split --->
+
+pulsed laser deposition (PLD) method. High- resolution X- ray diffraction (HRXRD) techniques were employed to assess the crystalline quality of the KNN- M films. Fig. 1a shows the X- ray diffraction (XRD) \(\theta - 2\theta\) pattern of a representative KNN- M film. Only the (00l) \((l = 1, 2, 3)\) reflection peaks of KNN- M, LSSO and STO are observed, indicating that the film is epitaxially grown along the \(c\) - axis direction with a single phase. The rocking curves shown in Fig. 1b exhibit a full- width- at- half- maximum of approximately \(0.182^{\circ}\) for KNN- M (002) and \(0.093^{\circ}\) for LSSO (002), demonstrating a high crystallinity of the films. To examine the epitaxial relationship and the strain state of the samples, X- ray reciprocal space mappings (RSMs) around the symmetric (002) and asymmetric \((\overline{1} 03)\) reflections of the film are shown in Figs. 1c and d respectively. The discrete and clear spots in Figs. 1c and d confirm the orientation relationship between the (001) films and the (001) STO substrate. As displayed in Fig. 1d, the \(Q_{x}\) value of the KNN- M \((\overline{1} 03)\) RSM spot obviously deviates from that of STO and LSSO, suggesting a relaxation of the lattice mismatch strain between the film and substrate. Based on the RSM results, the out- of- plane lattice parameter " \(c\) " and in- plane lattice parameters " \(a\) " or " \(b\) " of the KNN- M films were calculated to be \(4.02 \mathring{\mathrm{A}}\) and \(3.95 \mathring{\mathrm{A}}\) , respectively.
+
+Fig. 1e displays a high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) image of the KNN- M thin film, recorded along the [010] direction. It is evident that the KNN- M thin film consists of vertically aligned nanocolumns in the out- of- plane direction, rather than a homogeneous and smooth cross section (Fig.1e). X- ray energy dispersive spectroscopy (EDS) analysis confirms the presence of Mn enrichment at the column boundaries along the out- of- plane direction, as seen in Supplementary Fig. 1. Additionally, the selected area electron diffraction (SAED) pattern of the KNN- M thin films along the [010] zone axis, as shown in Fig 1f, reveals classic single crystal diffraction spots in the out- of- plane direction, while the streaks along the in- plane direction are attributed to the "shape effect". This effect arises from the principle that a small thickness in real space corresponds to a large length in reciprocal space, and vice versa. Thus, the reciprocal diffraction pattern further supports the presence of nanocolumns in the specimens, which is consistent with the HAADF image in real space. Atomic resolution HAADF images reveal a series of nanocolumn grains exhibiting the classic single crystal phase perovskite structure, as shown in Fig. 1g. However, it is observed that the lattices of neighboring perovskite KNN nanocolumns undergo a relative shift by half a unit cell length at the phase boundaries along the out- of- plane direction, indicated by the red triangle in Fig.1g.
+
+Due to the overlap of the nanocolumnar structure in the cross- sectional observation direction, indicated by the brace in Fig. 1g and Supplementary Fig. 2, we studied the microstructure using a plan- view sample without substrate. We found that the KNN- M films present the 'Tetris- like' microstructure consisting of dense nanocolumns with sizes ranging from a few to tens of nanometers. Through annular bright field (ABF) imaging, we observed that the nanocolumns predominantly exhibit atomic- scale linear dark contrast along both the [001] and [010] directions, as shown in Fig. 1h and Supplementary Fig. 3. The corresponding EDS composition analysis reveals that the nanocolumn areas are composed of K, Na, Mn, Nb and O elements, with apparent Mn enrichment observed in some linear dark contrast areas, as shown in Fig. 1i and Supplementary Fig. 4. Electron energy loss spectroscopy (EELS) analysis indicates that the Mn ions mainly exhibit bivalence (Mn \(^{2 + }\) ) (Supplementary Fig. 5). In addition, atomic resolution HAADF imaging reveal that the lattices of adjacent perovskite KNN nanocolumns are coherent, but undergo a half- unit cell shift relative to each other across the atomic- scale antiphase boundaries with Mn enrichment, as marked within the yellow rectangle in Fig. 1j. At the ends of these antiphase boundaries, the lattice misregistry of 1/2 unit cell is gradually reduced to zero
+
+<--- Page Split --->
+
+with continuous atom deficiency along the boundaries and no more Mn element could be detected with EDS analysis, as shown in the red rectangles in Fig. 1j and Supplementary Fig. 6.
+
+
+
+Fig. 1 | Crystalline structure and microstructure of the KNN-M thin film grown on a LSSO-buffered STO (001) substrate. a, XRD \(\theta -2\theta\) pattern. b, Rocking curves around STO (002), LSSO (002) and KNN-M (002). c, d, Reciprocal space maps around the STO (002) and (f03) reflections. e, Cross-sectional low magnification HAADF image. f, SEAD pattern of the KNN-M thin film in the out-of-plane direction. g, Atomic resolution HAADF image of the KNN-M thin film. h, Planar-view low-magnification ABF image. i, Corresponding EDS mapping of Mn element for the KNN-M thin film. j, Plan-view atomic resolution HAADF image of the KNN-M thin film. The scale bars in (g) and (j) are 2 nm.
+
+<--- Page Split --->
+
+Furthermore, we have identified two different atomic configurations for the Mn- inlaid antiphase boundaries, as illustrated in Fig. 2. Fig. 2a displays an atomic resolution HAADF image of one type of antiphase boundary structure (referred to as Type- I). In this image, a coherent antiphase feature is observed, where the A- site lattice of one KNN nanocolumn runs into the B- site lattice of the neighboring nanocolumn across a single atomic column. This single atomic column exhibits a brighter contrast than the A- site K/Na atomic columns, but a darker contrast compared to the B- site Nb/O atom columns. Line- scans of image intensity were performed along the single atomic column layer. The line profile of intensity reveals similar atomic column intensities, as shown in Fig. 2b. Based on the uniform image contrasts and corresponding line profiles, it can be inferred that the atomic columns in the Type- I antiphase boundaries have similar chemical compositions. The intensity of the atomic column in HAADF image is approximately proportional to the square of the atomic number \((Z^{2})^{27}\) , making the HAADF images suitable for composition analysis. However, due to the much smaller scattering cross- section of oxygen, the light element oxygen cannot be observed in the HAADF image. Therefore, we also obtained atomic resolution integrated differential phase contrast (iDPC) images to visualize the distribution of all atoms, as shown in Fig. 2c. The iDPC image reveals only one atomic column at the antiphase boundary plane, and no separate oxygen atom columns are observed in the plan- view direction. In addition, we observed that the single atomic layer at the antiphase boundaries can gradually translate to a "Ruddlesden- Popper" like double atomic layer with in- situ beam irradiation in STEM mode, and vice versa (Fig. 2d, Supplementary Fig. 7 and Supplementary Fig. 8).
+
+We performed the EDS mapping to study the atomic resolution composition distribution in Type- I antiphase boundary regions, as shown in Fig. 2e. The color- coded elemental maps of K, Na, O, Mn and Nb are presented in Figs. 2f- j, respectively. It is evident that all the elements are generally distributed uniformly in the KNN- based nanocolumns. However, the atomic columns at the antiphase boundary layer are primarily composed of the Mn and O elements, with a trace amount of K/Na. The composite map of Nb and Mn, as shown in Fig. 2k, illustrates the relative positions of the Nb and Mn atoms. Based on the elemental distribution maps, we find that Mn occupies the A- site of the perovskite lattice. Due to the structural changes at the boundaries during in- situ beam irradiation, as shown in Fig. 2d and Supplementary Fig. 7, Mn enrichments is observed along the boundary, but the location of Mn signals at the antiphase boundaries does not precisely correspond to the atomic- scale image from the EDS analysis. By analyzing the atomic resolution images in both the planar- view and cross- sectional directions (Supplementary Fig. 2) and conducting composition analysis, we have depicted the schematic structure of Type- I antiphase boundaries in Fig. 2l. This structure consists of nanocolumn perovskite KNN sheets alternating with a single Mn/O sheet running along the \(c\) axis direction and the neighboring perovskite slabs relatively shifting by half a unit cell length in both the in- plane and out- of- plane directions. At Type- I antiphase boundaries, the lattice site corresponds to the A- site of one KNN nanocolumn and the O- site of another KNN nanocolumn. Therefore, both the Mn and O atoms can randomly occupy the atom site at the boundaries theoretically.
+
+The other antiphase boundary (Type- II) is illustrated in Fig. 2m, where the two adjacent KNN phases coherently transit across a double atom layer, and the distance between the neighboring Nb atomic columns at the boundaries is approximately 3/2- unit cells. Notably, we observed distinct contrast variation for the atom columns at the transition layers, which differ from the uniform contrast of the atom columns at Type- I antiphase boundaries. The line profile of intensity also exhibits noticeable difference for the atomic column along one row of transition atomic columns in Fig. 2m, as shown in Fig. 2n. The observed variations in image contrast or line profiles can be attributed to composition differences in each atomic column at Type- II
+
+<--- Page Split --->
+
+antiphase boundaries. Through atomic resolution composition analysis, we determined that the atom columns with bright contrast primarily consist of Nb atoms, while the dark atom columns are composed of K/Na/Mn (Supplementary Fig. 9). Additionally, we also observed the presence of Mn enrichment at the boundaries. However, the signals are noticeably weaker compared to the distinct single Mn- rich layer observed at Type- I antiphase boundaries (Supplementary Fig. 10). We also acquired the iDPC images for Type- II antiphase boundaries (Fig. 2o), which reveal separated O atom columns that can bond with neighboring Nb atoms to form oxygen octahedra at the boundaries. Furthermore, we found that Type- II antiphase boundaries remained stable under beam irradiation. Based on the aforementioned experimental results, we constructed the schematic structural model of Type- II antiphase boundaries, as depicted in Fig. 2p.
+
+For comparison, we also prepared the undoped KNN thin films with a similar deposition process. From cross- sectional view, serials of nanocolumns can also be observed (Supplementary Fig. 11a). Atomic resolution HAADF images revealed no noticeable lattice shifts between two adjacent nanocolumns in the out- of- plane direction (Supplementary Fig. 11b). However, the plan- view image displayed a high density of stacking faults due to the K/Na deficiency (Supplementary Fig. 11c). This deficiency resulted in a high leakage current and prevented the display of ferroelectricity at room temperature \(^{12,14}\) .
+
+<--- Page Split --->
+
+
+Fig.2 | In-plane atomic structure of Mn-inlaid antiphase boundaries in the KNN-M thin films. a, In-plane atomic resolution HAADF image of Type-I antiphase boundaries. b, Line-profile of the single antiphase atomic columns along the direction of the antiphase boundary in (A). c, iDPC image of Type-I antiphase boundaries. d, HAADF image of Type-I antiphase boundaries with in-situ electron irradiations. e, In-plane HAADF image of the KNN-M thin film containing Type-I antiphase boundaries. f-j, Corresponding color-coded atomic resolution EDS mapping of the K, Na, O, Mn and Nb elements, respectively. K, Composite elemental map with Nb (in red) and Mn (in green). I, Schematic structural models of Type-I Mn-inlaid antiphase boundaries, where the red, purple, green, and cyanine colors represent the O, K/Na, Mn and Nb elements, respectively. m, In-plane atomic resolution HAADF image of Type-II antiphase boundaries. n, Line-profile of the single antiphase atomic columns along the direction of the transition boundary in (m). o, iDPC image of Type-II antiphase boundaries. p, Schematic structural model of Type-II antiphase boundaries, where the red, purple, green, and cyanine colors represent the O, K/Na, Mn and Nb elements, respectively. The scale bar is 1nm.
+
+<--- Page Split --->
+
+We examined the ferroelectric polarization of this film and found that the out-of-plane phase image of the as-grown film without dc bias exhibits a remarkable homogeneity across the layer with a weak contrast, as shown in Fig. 3a, indicating an ordered out-of-plane polarization component. This result is also attested to the excellent epitaxial quality of the films. The out-of-plane piezoelectric force microscope (PFM) phase can switch to the opposite direction under a voltage of - 8 V. When a positive dc bias of \(+8\mathrm{V}\) was applied, the PFM phase switched to the same direction as the as-grown film, which confirms that the out-of-plane polarization of film is directed uniformly toward the bottom of the film. Additionally, well-saturated ferroelectric polarization-electric field \((P - E)\) hysteresis loops of the KNN- M film were displayed at room temperature (Fig. 3b). The film demonstrated a remarkable enhancement in remanent polarization \((P_{r})\) with the \(2P_{r}\) value reaching \(114\mu \mathrm {C}/\mathrm {cm}^{2}\) when subjected to an applied electric field of \(606\mathrm {kV/cm}\) . Furthermore, at the temperature of \(80\mathrm {K}\) , no significant variation in \(P_{r}\) was observed, but the breakdown field strength increased to \(2700\mathrm {kV/cm}\) , as shown in Fig. 3c. Notably, the \(2P_{r}\) value of the KNN- M thin film is larger than the values so far reported for most KNN- based films \((7.1-64.9\mu \mathrm {C}/\mathrm {cm}^{2})\) , as shown in Fig. 3d. Moreover, the \(P_{r}\) value is comparable to that of typical PZT ferroelectric thin films \({}^{24}\) .
+
+
+
+Fig. 3 | Ferroelectric properties of the KNN-M thin films. a, Out-of-plane polarization switching of the KNN-M film captured using PFM imaging technique, under a dc bias of \(\pm 8\mathrm {V}\) . b, Room-temperature polarization–electric field \((P - E)\) hysteresis loops displayed under different electric fields. c, \(P - E\) hysteresis loops under different electric field for the KNN-M thin films at a low-temperature of \(80\mathrm {K}\) . d, Comparison of the polarization \((2P_{r})\) of the present KNN-M films with previously reported values of the KNN-based films.
+
+<--- Page Split --->
+
+Based on the microstructure analysis and the ferroelectric properties, we delve into the mechanisms behind the formation of nanocolumnar structure with Mn- inlaid antiphase boundaries and enhancement of ferroelectric polarization. In the case of pure KNN thin films without Mn doping, the unique deposition process led to the formation of vertical nanocolumnar structures aligned along the out- of- plane direction. Through atomic resolution investigation of microstructure, it was observed that the KNN nanocolumns maintained the normal perovskite structure. Significant K/Na deficiencies primarily occurred at the boundaries, resulting in lattice rearrangement and formation of charged out- of- phase boundaries. These crystallographic out- of- phase boundaries, commonly found in epitaxial perovskite films, tend to propagate throughout the entire thickness of the film. Consequently, nanocolumnar KNN thin films exhibited large leakage currents, as depicted in Supplementary Fig. 12 and Ref. 12. However, consistent with previous studies \(^{11,16,19}\) , our experimental results showed the addition of a small concentration of Mn into KNN film was very effective in reducing the leakage current density. Due to the smaller radius of Mn ion than those of the A- site \(\mathrm{K^{+} / Na^{+}}\) ions, the solid solubility of Mn is low in KNN lattice. When doping Mn into the KNN films, the Mn ions are believed to occupy a small number of A- site vacancies, which were formed due to the volatilization of the \(\mathrm{K^{+} / Na^{+}}\) ions in the KNN nanocolumns, according to the atomic structural imaging and composition analysis. Considering its primary valence, \(\mathrm{Mn^{2 + }}\) can act as a donor- dopant on the A- site of the perovskite lattice. However, in order to balance the charge, the occupancy of \(\mathrm{Mn^{2 + }}\) on the A- site vacancies was only partial, with every other A- site occupied. As a result, partial A- site deficiency still existed in the KNN nanocolumns \(^{18}\) . On the contrary, the high density of Mn accumulated at the phase boundaries to form atomic- scale Mn- rich layer, which could compensate the serious K/Na deficiencies at the boundaries. In the case of Type- I antiphase boundaries, both cation \(\mathrm{Mn^{2 + }}\) and anion \(\mathrm{O^{2 - }}\) can occupy the atomic site at the single antiphase boundary layer. By adjusting the ratio of Mn/O, we can achieve charge balance in optimum experimental conditions (Supplementary Fig. 13). For Type- II antiphase boundaries, which resemble the Ruddlesden- Popper structure, separate atomic columns of cations and anion \(\mathrm{O^{2 - }}\) were observed. The cation atomic sites at these boundaries can be occupied by the \(\mathrm{Nb^{5 + }}\) , \(\mathrm{Mn^{2 + }}\) , \(\mathrm{K^{+}}\) and \(\mathrm{Na^{+}}\) ions. The ratios among these four cations could also be adjusted experimentally to maintain charge balance (Supplementary Fig. 14). Consequently, the leakage currents can be significantly reduced, which is crucial for the ferroelectric functionality of the thin film. In our study, we investigated a series of Mn- doped samples with the Mn concentration ranging from 1 to \(5\mathrm{wt}\%\) . It was observed that the sample with a low Mn doping content, such as \(1\mathrm{wt}\%\) , exhibited a vertical nanocolumns structure, but the K/Na deficiencies were not fully compensated (Supplementary Fig. 15). As the doping level increased to \(5\%\) , the nanoscale Mn enriched phases were observed, which disrupted the epitaxial growth of the thin films, as shown in Supplementary Fig. 16.
+
+More importantly, the specific atomic configurations at the Mn- inlaid antiphase boundaries induce noticeable change in the lattice structure compared to the KNN nanocolumns. The high- density boundaries are organized in an ordered manner on a nanoscale and extend vertically in the film, resulting in the generation of apparent lattice strains. These strains also impact the neighboring KNN nanocolumns, as evidenced by the ADF images (Supplementary Fig. 17, Supplementary Fig. 18), where the brighter image contrast indicates the presence of apparent lattice strains near the Mn- inlaid antiphase boundaries. It is well- known that lattice strain can significantly influence the ferroelectric polarization of thin films. We examined the relative lattice strain and the evolution of lattice parameters using the geometry phase analysis method. Fig. 4a displays an ADF image of the KNN- M thin film, revealing the presence of two types of boundaries. The corresponding relative lattice strain are plotted in Fig. 4b \((\epsilon_{xx})\) , Fig. 4c \((\epsilon_{yy})\) and
+
+<--- Page Split --->
+
+Fig. 4d \((\epsilon_{xy})\) , respectively. It can be seen that the boundaries exhibit apparent relative lattice strains, mainly perpendicular to their orientation with no observable relative strains parallel to the boundaries (Supplementary Fig. 19). The increased atomic spacing at the boundaries, indicative of tensile strain, is accompanied by the compressive strain in the KNN nanocolumns. It is worth noting that a strain in one direction typically induces an opposite strain component in the other direction to achieve overall relaxation \(^{28}\) . Consequently, the in-plane compressive strain induces an out-of-plane tensile strain, as confirmed by the XRD results with a larger \(c\) than \(a\) and \(b\) in the KNN lattice, which is advantageous for achieving high ferroelectric polarization \(^{7}\) .
+
+The displacement of the center polar B- site cations relative to the corner A- site cations \((\delta_{\mathrm{B - A}})\) was used as a measure of the local polarization. Fig. 4e displays a colored arrow map of \(\delta_{\mathrm{B - A}}\) , representing the orientation and magnitude of the polarization. The film exhibited apparent displacement polarization, with the largest polarization observed near the boundaries. The different strains present at each type of boundary resulted in the formation of multidomain structures with a mixture of various orientations of polarizations. To investigate the impact of boundary strain on ferroelectric polarization, we conducted phase field simulations. The phenomenological model and relative lattice strain distributions used in these simulations were obtained from Fig. 4a- d, as shown in Supplementary Fig. 20. Specifically, we examined the different lattice strains, namely \(\epsilon_{\mathrm{local}}(0, 0.1, \text{and} 0.2)\) , induced by the Mn accumulated boundary, to elucidate their effects. Our simulations employed the orthorhombic phase with the [110]- oriented polarization of KNN at room temperature \(^{16}\) , as illustrated in Supplementary Fig. 21, which showcases the detailed microstructural evolution. As the applied external electric field increased, the polarizations transitioned from the orthorhombic phase (represented by different colors in Fig. 4f) to the tetragonal phase (indicated by light blue color in Fig. 4g). Importantly, the lattice strains around the boundaries induced larger polarization in both in- plane and out- of- plane directions, as shown in Fig. 4f and Supplementary Fig. 22. The simulated ferroelectric loop demonstrated an increase in both the coercive electric field strength \((E_{\mathrm{c}})\) and ferroelectric polarization in the out- of- plane directions with the increase in lattice strain (see Fig. 4h and Supplementary Fig. 21a). Thus, the Mn- inlaid antiphase boundaries offer a new structural framework for enhancing the ferroelectric polarization of lead- free ferroelectric thin films.
+
+In summary, we prepared and observed the new Mn- inlaid antiphase boundaries structure in perovskites. The high- density vertical Mn- inlaid antiphase boundaries show the positivity effect on charge balance, coherent transition to the neighboring KNN nanocolumns and the induction of large strain for the nanocolumnar KNN lattice in the entire KNN- M thin films. Therefore, the ever higher ferroelectric polarizations have been observed for the KNN- based thin films. The Mn- inlaid antiphase boundaries also give a new possible structure frame to modulate the various properties of perovskites.
+
+<--- Page Split --->
+
+
+Fig. 4 | Strains and atom displacement polarizations in the KNN-M thin film. a, Planar-view atomic-resolution HAADF image of the KNN-M thin film. b-d, Maps depicting the relative lattice strains: (b) \(\epsilon_{xx}\) (in-plane strain), (c) \(\epsilon_{yy}\) (out-of-plane strain) and (d) \(\epsilon_{xy}\) (shear strain). e, Colored arrows map of polarizations \((\partial_{Nb-KNa})\) , indicating the polarization orientation of the KNN nanocolumns in (a). f, Polarization of KNN-M obtained from phase-field simulation. g, Mapping of the piezoelectric response of the KNN-M film under an applied electric field obtained from phase-field simulation. h, Calculated P-E curves with different local strains.
+
+## References
+
+1 Martin, L. W. & Rappe, A. M. Thin- film ferroelectric materials and their applications. Nature Reviews Materials 2, 16087, doi:10.1038/natrevmats.2016.87 (2016). 2 Yang, Q. et al. Ferroelectricity in layered bismuth oxide down to 1 nanometer. Science 379, 1218- 1224, doi:10.1126/science.abm5134 (2023). 3 Zhang, S., Malič, B., Li, J.- F. & Rödel, J. Lead- free ferroelectric materials: Prospective applications. J. Mater. Res. 36, 985- 995, doi:10.1557/s43578- 021- 00180- y (2021). 4 Saito, Y. et al. Lead- free piezoceramics. Nature 432, 84- 87, doi:10.1038/nature03028 (2004). 5 Wu, J., Xiao, D. & Zhu, J. Potassium- Sodium Niobate Lead- Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries. Chem. Rev. 115, 2559- 2595, doi:10.1021/cr5006809 (2015). 6 Zhang, N., Zheng, T. & Wu, J. Lead- Free (K,Na)NbO3- Based Materials: Preparation Techniques and Piezoelectricity. ACS Omega 5, 3099- 3107, doi:10.1021/acsomega.9b03658 (2020). 7 Gao, X. et al. The mechanism for the enhanced piezoelectricity in multi- elements doped (K,Na)NbO3 ceramics. Nature Communications 12, 881, doi:10.1038/s41467- 021- 21202- 7 (2021). 8 Xu, K. et al. Superior Piezoelectric Properties in Potassium- Sodium Niobate Lead- Free Ceramics. Adv. Mater. 28, 8519- 8523, doi:10.1002/adma.201601859 (2016).
+
+<--- Page Split --->
+
+9 Zhu, B. et al. New Potassium Sodium Niobate Single Crystal with Thickness-independent High-performance for Photoacoustic Angiography of Atherosclerotic Lesion. Sci. Rep. 6, 39679, doi:10.1038/srep39679 (2016). 10 Yin, F. et al. Transparent Lead-Free Ferroelectric (K,Na)NbO Single Crystal with Giant Second Harmonic Generation and Wide Mid- Infrared Transparency Window. Advanced Optical Materials 10, 2201721, doi:10.1002/adom.202201721 (2022). 11 Xu, L. et al. Robust Ferroelectric Properties in (K,Na)NbO3- Based Lead- Free Films via a Self- Assembled Nanocomposite Approach. ACS Appl. Mat. Interfaces 12, 4616- 4624, doi:10.1021/acsami.9b20311 (2020). 10 12 Waqar, M. et al. Origin of giant electric- field- induced strain in faulted alkali niobate films. Nature Communications 13, 3922, doi:10.1038/s41467- 022- 31630- 8 (2022). 13 Li, C. et al. A Novel Multiple Interface Structure with the Segregation of Dopants in Lead- Free Ferroelectric (K0.5Na0.5)NbO3 Thin Films. Advanced Materials Interfaces 5, 1700972, doi:10.1002/admi.201700972 (2018). 15 Liu, H. et al. Giant piezoelectricity in oxide thin films with nanopillar structure. Science 369, 292- 297, doi:10.1126/science.abb3209 (2020). 15 Cho, C.- R. & Grishin, A. Background Oxygen Effects on Pulsed Laser Deposited Na0.5K0.5NbO Films: From Superparaelectric State to Ferroelectricity. J. Appl. Phys. 87, 4439- 4448, doi:10.1063/1.373089 (2000). 20 Seog, H. J. et al. Recent Progress in Potassium Sodium Niobate Lead- free Thin Films. Journal of the Korean Physical Society 72, 1467- 1483, doi:10.3938/jkps.72.1467 (2018). 17 Chen, W., Zhao, J., Wang, L., Ren, W. & Liu, M. Lead- free piezoelectric KNN- BZ- BNT films with a vertical morphotropic phase boundary. AIP Advances 5, 077190, doi:10.1063/1.4928095 (2015). 25 Rubio- Marcos, F. et al. Effect of MnO doping on the structure, microstructure and electrical properties of the (K,Na,Li)(Nb,Ta,Sb)O3 lead- free piezoceramics. J. Alloys Compd. 509, 8804- 8811, doi:https://doi.org/10.1016/j.jallcom.2011.06.080 (2011). 19 Won, S. S. et al. Lead- free Mn- doped (K0.5,Na0.5)NbO3 piezoelectric thin films for MEMS- based vibrational energy harvester applications. Appl. Phys. Lett. 108, 30 doi:10.1063/1.4953623 (2016). 20 Li, C. et al. Atomic Resolution Interfacial Structure of Lead- free Ferroelectric K0.5Na0.5NbO3 Thin films Deposited on SrTiO3. Sci. Rep. 6, 37788, doi:10.1038/srep37788 (2016). 21 Luo, J. et al. Monoclinic (K,Na)NbO3 Ferroelectric Phase in Epitaxial Films. Advanced Electronic Materials 3, 1700226, doi:10.1002/aelm.201700226 (2017). 22 Cheng, Y.- Y.- S. et al. All- Inorganic Flexible (K, Na)NbO3- Based Lead- Free Piezoelectric Thin Films Spin- Coated on Metallic Foils. ACS Appl. Mat. Interfaces 13, 39633- 39640, doi:10.1021/acsami.1c11418 (2021). 23 Shiraishi, T. et al. Ferroelectric and piezoelectric properties of KNbO3 films deposited on flexible organic substrate by hydrothermal method. Jpn. J. Appl. Phys. 53, 09PA10, doi:10.7567/JJAP.53.09PA10 (2014). 24 Nishino, R., Fujita, T. C., Kagawa, F. & Kawasaki, M. Evolution of ferroelectricity in ultrathin PbTiO3 films as revealed by electric double layer gating. Sci. Rep. 10, 10864, doi:10.1038/s41598- 020- 67580- 8 (2020). 45 Dahl, O., Grepstad, J. K. & Tybell, T. Polarization direction and stability in ferroelectric lead titanate thin films. J. Appl. Phys. 106, 084104, doi:10.1063/1.3240331 (2009). 26 Zurbuchen, M. A. et al. Morphology, structure, and nucleation of out- of- phase boundaries (OPBs) in epitaxial films of layered oxides. J. Mater. Res. 22, 1439- 1471,
+
+<--- Page Split --->
+
+doi:10.1557/JMR.2007.0198 (2007).
+
+27 Pennycook, S. J. Z- contrast stem for materials science. Ultramicroscopy 30, 58- 69, doi:10.1016/0304- 3991(89)90173- 3 (1989).
+
+28 Zhao, J. et al. Strained hybrid perovskite thin films and their impact on the intrinsic stability of perovskite solar cells. Science Advances 3, eaa05616, doi:10.1126/sciadv.aa05616 (2017).
+
+1. L. W. Martin, A. M. Rappe, Thin-film ferroelectric materials and their applications. Nature Reviews Materials 2, 16087 (2016). doi: 10.1038/natrevmat.2016.87.
+
+2. Q. Yang, J. Hu, Y.-W. Fang, Y. Jia, R. Yang, S. Deng, Y. Lu, O. Dieguez, L. Fan, D. Zheng, X. Zhang, Y. Dong, Z. Luo, Z. Wang, H. Wang, M. Sui, X. Xing, J. Chen, J. Tian, L. Zhang, Ferroelectricity in layered bismuth oxide down to 1 nanometer. Science 379, 1218-1224 (2023). doi: doi:10.1126/science.abm5134.
+
+3. S. Zhang, B. Malič, J.-F. Li, J. Rödel, Lead-free ferroelectric materials: Prospective applications. J. Mater. Res. 36, 985-995 (2021). doi: 10.1557/s43578-021-00180-y.
+
+4. Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, M. Nakamura, Lead-free piezoceramics. Nature 432, 84-87 (2004). doi: 10.1038/nature03028.
+
+5. J. Wu, D. Xiao, J. Zhu, Potassium-Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries. Chem. Rev. 115, 2559-2595 (2015). doi: 10.1021/cr5006809.
+
+6. N. Zhang, T. Zheng, J. Wu, Lead-Free (K,Na)NbO₃-Based Materials: Preparation Techniques and Piezoelectricity. ACS Omega 5, 3099-3107 (2020). doi: 10.1021/acsomega.9b03658.
+
+7. X. Gao, Z. Cheng, Z. Chen, Y. Liu, X. Meng, X. Zhang, J. Wang, Q. Guo, B. Li, H. Sun, Q. Gu, H. Hao, Q. Shen, J. Wu, X. Liao, S. P. Ringer, H. Liu, L. Zhang, W. Chen, F. Li, S. Zhang, The mechanism for the enhanced piezoelectricity in multi-elements doped (K,Na)NbO₃ ceramics. Nature Communications 12, 881 (2021). doi: 10.1038/s41467-021-21202-7.
+
+8. K. Xu, J. Li, X. Lv, J. Wu, X. Zhang, D. Xiao, J. Zhu, Superior Piezoelectric Properties in Potassium-Sodium Niobate Lead-Free Ceramics. Adv. Mater. 28, 8519-8523 (2016). doi: 10.1002/adma.201601859.
+
+9. B. Zhu, Y. Zhu, J. Yang, J. Ou-Yang, X. Yang, Y. Li, W. Wei, New Potassium Sodium Niobate Single Crystal with Thickness-independent High-performance for Photoacoustic Angiography of Atherosclerotic Lesion. Sci. Rep. 6, 39679 (2016). doi: 10.1038/srep39679.
+
+10. F. Yin, L. Liu, M. Zhu, J. Lv, X. Guan, J. Zhang, N. Lin, X. Fu, Z. Jia, X. Tao, Transparent Lead-Free Ferroelectric (K,Na)NbO₃ Single Crystal with Giant Second Harmonic Generation and Wide Mid-Infrared Transparency Window. Advanced Optical Materials 10, 2201721 (2022). doi: 10.1002/adom.202201721.
+
+11. L. Xu, F. Chen, F. Jin, H. Huang, L. Qu, K. Zhang, Z. Zhang, G. Gao, Y. Lu, F. Zhang, K. Wang, C. Ma, W. Wu, Robust Ferroelectric Properties in (K,Na)NbO₃-Based Lead-Free Films via a Self-Assembled Nanocomposite Approach. ACS Appl. Mat. Interfaces 12, 4616-4624 (2020). doi: 10.1021/acsami.9b20311.
+
+12. M. Waqar, H. Wu, K. P. Ong, H. Liu, C. Li, P. Yang, W. Zang, W. H. Liew, C. Diao, S. Xi, D. J. Singh, Q. He, K. Yao, S. J. Pennycook, J. Wang, Origin of giant electric-field-induced strain in faulted alkali niobate films. Nature Communications 13, 3922 (2022). doi: 10.1038/s41467-022-31630-8.
+
+13. C. Li, L. Wang, W. Chen, L. Lu, H. Nan, D. Wang, Y. Zhang, Y. Yang, C.-L. Jia, A Novel
+
+<--- Page Split --->
+
+Multiple Interface Structure with the Segregation of Dopants in Lead- Free Ferroelectric \(\mathrm{(K_{0.5}Na_{0.5})NbO_{3}}\) Thin Films. Advanced Materials Interfaces 5, 1700972 (2018). doi: 10.1002/admi.201700972. 14. H. Liu, H. Wu, K. P. Ong, T. Yang, P. Yang, P. K. Das, X. Chi, Y. Zhang, C. Diao, W. K. A. Wong, E. P. Chew, Y. F. Chen, C. K. I. Tan, A. Rusydi, M. B. H. Breese, D. J. Singh, L.- Q. Chen, S. J. Pennycook, K. Yao, Giant piezoelectricity in oxide thin films with nanopillar structure. Science 369, 292- 297 (2020). doi: 10.1126/science.abb3209. 15. C.- R. Cho, A. Grishin, Background Oxygen Effects on Pulsed Laser Deposited \(\mathrm{Na_{0.5}K_{0.5}NbO_{3}}\) Films: From Superparaelectric State to Ferroelectricity. J. Appl. Phys. 87, 4439- 4448 (2000). doi: 10.1063/1.373089. 16. H. J. Seog, A. Ullah, C. W. Ahn, I. W. Kim, S. Y. Lee, J. Park, H. J. Lee, S. S. Won, S.- H. Kim, Recent Progress in Potassium Sodium Niobate Lead- free Thin Films. Journal of the Korean Physical Society 72, 1467- 1483 (2018). doi: 10.3938/jkps.72.1467. 17. W. Chen, J. Zhao, L. Wang, W. Ren, M. Liu, Lead- free piezoelectric KNN- BZ- BNT films with a vertical morphotropic phase boundary. AIP Advances 5, 077190 (2015). doi: 10.1063/1.4928095. 18. F. Rubio- Marcos, P. Marchet, X. Vendrell, J. J. Romero, F. Remondiere, L. Mestres, J. F. Fernandez, Effect of MnO doping on the structure, microstructure and electrical properties of the \(\mathrm{(K,Na,Li)(Nb,Ta,Sb)O_{3}}\) lead- free piezoceramics. J. Alloys Compd. 509, 8804- 8811 (2011). doi: https://doi.org/10.1016/j.jallcom.2011.06.080. 19. S. S. Won, J. Lee, V. Venugopal, D.- J. Kim, J. Lee, I. W. Kim, A. I. Kingon, S.- H. Kim, Lead- free Mn- doped \(\mathrm{(K_{0.5}Na_{0.5})NbO_{3}}\) piezoelectric thin films for MEMS- based vibrational energy harvester applications. Appl. Phys. Lett. 108, (2016). doi: 10.1063/1.4953623. 25. C. Li, L. Wang, Z. Wang, Y. Yang, W. Ren, G. Yang, Atomic Resolution Interfacial Structure of Lead- free Ferroelectric \(\mathrm{K_{0.5}Na_{0.5}NbO_{3}}\) Thin films Deposited on SrTiO3. Sci. Rep. 6, 37788 (2016). doi: 10.1038/srep37788. 21. J. Luo, W. Sun, Z. Zhou, H.- Y. Lee, K. Wang, F. Zhu, Y. Bai, Z. J. Wang, J.- F. Li, Monoclinic \(\mathrm{(K,Na)NbO_{3}}\) Ferroelectric Phase in Epitaxial Films. Advanced Electronic Materials 3, 1700226 (2017). doi: 10.1002/aelm.201700226. 22. Y.- Y.- S. Cheng, L. Liu, Y. Huang, L. Shu, Y.- X. Liu, L. Wei, J.- F. Li, All- Inorganic Flexible (K, Na)NbO3- Based Lead- Free Piezoelectric Thin Films Spin- Coated on Metallic Foils. ACS Appl. Mat. Interfaces 13, 39633- 39640 (2021). doi: 10.1021/acsami.1c11418. 23. T. Shiraishi, N. Kaneko, M. Kurosawa, H. Uchida, T. Hirayama, H. Funakubo, Ferroelectric and piezoelectric properties of KNbO3 films deposited on flexible organic substrate by hydrothermal method. Jpn. J. Appl. Phys. 53, 09PA10 (2014). doi: 10.7567/JJAP.53.09PA10. 24. R. Nishino, T. C. Fujita, F. Kagawa, M. Kawasaki, Evolution of ferroelectricity in ultrathin PbTiO3 films as revealed by electric double layer gating. Sci. Rep. 10, 10864 (2020). doi: 10.1038/s41598- 020- 67580- 8. 25. O. Dahl, J. K. Grepstad, T. Tybell, Polarization direction and stability in ferroelectric lead titanate thin films. J. Appl. Phys. 106, 084104 (2009). doi: 10.1063/1.3240331. 26. M. A. Zurbuchen, W. Tian, X. Q. Pan, D. Fong, S. K. Streiffer, M. E. Hawley, J. Lettieri, Y. Jia, G. Asayama, S. J. Fulk, D. J. Comstock, S. Knapp, A. H. Carim, D. G. Schlom, Morphology, structure, and nucleation of out- of- phase boundaries (OPBs) in epitaxial films of layered oxides. J. Mater. Res. 22, 1439- 1471 (2007). doi: 10.1557/JMR.2007.0198.
+
+<--- Page Split --->
+
+27. S. J. Pennycook, Z-contrast stem for materials science. Ultramicroscopy 30, 58-69 (1989). doi: 10.1016/0304-3991(89)90173-3.
+28. J. Zhao, Y. Deng, H. Wei, X. Zheng, Z. Yu, Y. Shao, J. E. Shield, J. Huang, Strained hybrid perovskite thin films and their impact on the intrinsic stability of perovskite solar cells. Science Advances 3, eaao5616 (2017). doi: 10.1126/sciadv.aao5616.
+
+## Methods
+
+## The ceramic targets synthesis
+
+The ceramic targets synthesisThe ceramic targets of \((\mathrm{K,Na}) \mathrm{NbO}_3 - 0 / 1 / 2 / 5 \mathrm{wt\% Mn}\) (KNN-M) were fabricated using the conventional solid-state reaction method. High-purity materials, including \(\mathrm{K}_2\mathrm{CO}_3(99.0\%)\) , \(\mathrm{Na}_2\mathrm{CO}_3(99.8\%)\) , \(\mathrm{Nb}_2\mathrm{O}_5(99.9\%)\) and \(\mathrm{MnO}_2(98.8\%)\) , were obtained from Sinopharm Chemical Reagent Beijing Co. Ltd. Initially, the raw materials were accurately weighed according to the stoichiometric ratio of \((\mathrm{K}_0.5\mathrm{Na}_0.5)\mathrm{NbO}_3\) and then homogenized in a planetary mill for 24h using ethyl alcohol as the medium. After calcination at \(750^{\circ}\mathrm{C}\) for 4h, the resulting powder mixtures were milled, dried, and sieved. Subsequently, additional \(\mathrm{MnO}_2\) was incorporated into the powders and homogenized for another 24 h in the planetary mill. The resulting powder mixtures were then dried and sieved. Next, the mixed KNN-Mn powders were compacted into disks by uniaxial pressing at a pressure of \(150\mathrm{MPa}\) for \(2\mathrm{min}\) . Finally, the KNN-Mn pellets, with a diameter of \(30\mathrm{mm}\) , were sintered at \(1120^{\circ}\mathrm{C}\) for \(4\mathrm{h}\) to prepare the target
+
+## Thin Films Growth
+
+Thin Films GrowthThe KNN-M films were deposited onto the (001) SrTiO\(_3\) (STO) substrate buffered with \(\mathrm{La}_{0.07}\mathrm{Sr}_{0.93}\mathrm{SnO}_3\) (LSSO) layer using the PLD technique with a \(248\mathrm{nm}\) KrF excimer laser. The deposition process involved maintaining the substrate temperature at \(735^{\circ}\mathrm{C}\) and the \(\mathrm{O}_2\) pressure at \(15\mathrm{Pa}\) for the LSSO layer, followed by deposition of the KNN-film rat \(700^{\circ}\mathrm{C}\) and \(30\mathrm{Pa}\) . The target-substrate distance was set at \(5\mathrm{cm}\) , and the laser energy were kept at \(2\mathrm{J / cm}^2\) . The thicknesses of the KNN-M and LSSO were approximately \(300\mathrm{nm}\) and \(30\mathrm{nm}\) , respectively. After deposition, each film underwent in-situ annealing for 15 minutes before being cooled down to room temperature.
+
+## X-ray diffraction
+
+X-ray diffractionThe crystalline phase of films was characterized by high-resolution X-ray diffraction (XRD) using Cu Kα1 radiation. The samples were mounted in the diffractometer (PANalytical, X'Pert), for linear scans, rocking curves, and reciprocal space mappings (RSM) at room temperature.
+
+## Transmission Electron Microscopy (TEM)
+
+Transmission Electron Microscopy (TEM)The specimens were prepared using both the Tripod method (ALLIED Multiprep) and focused ion beam (FIB, Thermofisher Helios UX5) for the cross-section and plan-view STEM observation. TEM characterizations, low magnification STEM imaging, and EDS composition analysis were performed using the Thermofisher Talos F200X. Atomic resolution HAADF and iDPC images were acquired using the Thermofisher Titan Themis Z. Atom resolution HAADF, ADF image and EDS mapping were obtained using the Thermofisher Titan cubed Themis G2 300. The acquisition of EELS data was carried out using Gatan electron energy loss spectroscopy (EELS) on both the FEI Titan G2 80- 300 and JEOL ARM300.
+
+<--- Page Split --->
+
+## Electrical Testing
+
+Electrical TestingPolarization versus electric field \((P - E)\) hysteresis loops were measured through the ferroelectric test system (TF Analyzer 2000E, Germany) at \(1\mathrm{kHz}\) in room temperature. The \(P - E\) loops at liquid nitrogen temperature of \(80\mathrm{K}\) were obtained with Cryogenic Probe Station supplied by Lake Shore Company. The ferroelectric domains and polarization reversal behaviors were characterized by piezoresponse force microscopy (PFM, Asylum Cypher).
+
+## The calculation of the displacements in ADF images
+
+A standard peak finding algorithm is employed for the ADF image, which is based on fitting two- dimensional Gaussian functions to the intensity maxima. This algorithm allows us to determine the position and brightness of each column. Using these data, we can calculate the offcenter ion displacements between the Nb column and the center of the unit cell. The center of the unit cell is determined by the average coordinate of the four K/Na atomic columns. We use the following formula to calculate the displacements: \(\mathbf{u}_{ij} = \mathbf{r}_{ij} - 1 / 4\) \((R_{ij} + (i + 1) + (j + 1) + (i + 1)(j + 1))\) . Here, \(\mathrm{i} / \mathrm{j}\) indicate the row/column number of each atom column, \(\mathbf{r}_{\mathrm{ij}}\) indicates the position of Nb atomic columns, and \(\mathrm{R_{ij}}\) indicates the position of K/Na atomic columns.
+
+## Phase-Field Simulations
+
+A single crystal considering Cubic \((C)\) to Orthorhombic (O) ferroelectric transition with Mninlaid antiphase boundaries has been carried out in phase- field simulations. The total free energy of the ferroelectric system can be described as (29- 32):
+
+\[F = \int_{\nu}(f_{\mathrm{bulk}} + f_{\mathrm{grad}} + f_{\mathrm{couple}})dV + \int_{\nu}(f_{\mathrm{elas}} + f_{\mathrm{elec}})dV \quad (1)\]
+
+where \(f_{\mathrm{bulk}}\) represents the bulk free energy density,
+
+\[f_{\mathrm{bulk}} = \alpha_{1}(P_{1}^{2} + P_{2}^{2} + P_{3}^{2}) - \alpha_{11}(P_{1}^{2} + P_{2}^{2} + P_{3}^{3})^{2} + \alpha_{12}(P_{1}^{2}P_{2}^{2} + P_{2}^{2}P_{3}^{2} + P_{1}^{2}P_{3}^{2})\] \[\qquad +\alpha_{112}(P_{1}^{4}P_{2}^{2} + P_{2}^{4}P_{3}^{2} + P_{1}^{4}P_{3}^{2} + P_{1}^{2}P_{2}^{4} + P_{2}^{2}P_{3}^{4} + P_{1}^{2}P_{3}^{4}) + \alpha_{113}(P_{1}^{2}P_{2}^{2}P_{3}^{2})\] \[\qquad +\alpha_{111}(P_{1}^{2} + P_{2}^{2} + P_{3}^{3})^{3}\]
+
+where \(\alpha_{ij}\) is the coefficient and depends on concentration \(c\) and temperature \(T\)
+
+\(f_{\mathrm{grad}}\) represents the gradient energy density,
+
+\[f_{\mathrm{grad}} = \frac{1}{2} G_{11}((P_{1,1})^{2} + (P_{1,2})^{2} + (P_{1,3})^{2} + (P_{2,1})^{2} + (P_{2,2})^{2} + (P_{2,3})^{2} + (P_{3,1})^{2} + (P_{3,2})^{2} + (P_{3,3})^{2}) \quad (3)\]
+
+where \(G_{11}\) is the gradient energy coefficient. \(f_{\mathrm{couple}}\) represents the couple effect caused by lattice strain \(\epsilon_{\mathrm{local}}(33)\)
+
+\[f_{\mathrm{couple}} = -(q_{11}\epsilon_{11} + q_{12}\epsilon_{22} + q_{12}\epsilon_{33})P_{1}^{2} - (q_{11}\epsilon_{22} + q_{12}\epsilon_{11} + q_{12}\epsilon_{33})P_{2}^{2}\] \[-(q_{11}\epsilon_{33} + q_{12}\epsilon_{11} + q_{12}\epsilon_{22})P_{3}^{2} - 2q_{44}(\epsilon_{12}P_{1}P_{2} + \epsilon_{23}P_{2}P_{3} + \epsilon_{13}P_{1}P_{3})~,\]
+
+where \(q_{11} = C_{11}Q_{11} + 2C_{12}Q_{12}\) , \(q_{12} = C_{11}Q_{12} + C_{12}(Q_{11} + Q_{12})\) , \(q_{44} = 2C_{44}Q_{44}\) , \(C_{11}\) , \(C_{12}\) , and \(C_{44}\) is the elastic constants in Voigt's notation and \(Q_{\mathrm{ij}}\) is the electrostrictive coefficients. \(f_{\mathrm{elas}}\) is the long- range elastic interaction energy densities and \(f_{\mathrm{elec}}\) is the electrostatic interaction energy densities.
+
+\(f_{\mathrm{elas}} = \frac{1}{2} c_{ijkl}e_{ij}e_{kl} = \frac{1}{2} c_{ijkl}(\epsilon_{ij} - \epsilon_{ij}^{0})(\epsilon_{kl} - \epsilon_{kl}^{0})\) , where \(c_{ijkl}\) is the elastic constant tensor, \(\epsilon_{ij}\) the total strain, \(\epsilon^{0}_{kl}\) the electrostrictive stress- free strain, i.e., \(\epsilon^{0}_{kl} = Q_{ijkl}P_{k}P_{l}\) . \(f_{\mathrm{elec}} = f_{\mathrm{dipole}} + f_{\mathrm{depola}} + f_{\mathrm{appl}}\) , where \(f_{\mathrm{dipole}}\) is the dipole- dipole interaction caused by polarization, \(f_{\mathrm{depola}}\) the depolarization energy density and \(f_{\mathrm{appl}}\) the energy density caused by applied electric field. The dimensionless parameters used in our simulations:
+
+\[\alpha_{1} = -0.1134, \alpha_{11} = -2.2896, \alpha_{12} = -7.5572, \alpha_{111} = 12.94, \alpha_{112} = 1.776, \alpha_{123} = 144.6.\]
+
+<--- Page Split --->
+
+\[C_{11} = 1780, C_{12} = 964, C_{44} = 1220, Q_{11} = 0.1, Q_{12} = -0.034, Q_{44} = 0.029.\]
+
+The temporal evolution of the spontaneous polarization field \((P)\) can be obtained by solving the time dependent Ginzburg Landau (TDGL) equation: \(\frac{dP_{i}(x,t)}{dt} = - M\frac{\delta F}{\delta P_{i}(X,t)}, i = 1,2,3\) , where \(M\) is the kinetic coefficient, \(F\) is the total free energy, and \(t\) is time.
+
+## Data availability
+
+The data that support the findings of this study are available from the corresponding authors upon request.
+
+29. D. Wang, X. Ke, Y. Wang, J. Gao, Y. Wang, L. Zhang, S. Yang, X. Ren, Phase diagram of polar states in doped ferroelectric systems. Phys. Rev. B 86, 054120 (2012). doi: 10.1103/PhysRevB.86.054120.
+30. S. Semenovskaya, A. G. Khachaturyan, Development of ferroelectric mixed states in a random field of static defects. J. Appl. Phys. 83, 5125-5136 (1998). doi: 10.1063/1.367330.
+31. Y. L. Li, L. E. Cross, L. Q. Chen, A phenomenological thermodynamic potential for BaTiO₃ single crystals. J. Appl. Phys. 98, (2005). doi: 10.1063/1.2042528.
+32. L. Zhang, H. Wang, D. Wang, M. Guo, X. Lou, D. Wang, A New Strategy for Large Dynamic Piezoelectric Responses in Lead-Free Ferroelectrics: The Relaxor/Morphotropic Phase Boundary Crossover. Adv. Funct. Mater. 30, 2004641 (2020). doi: 10.1002/adfm.202004641.
+33. Y. L. Li, S. Y. Hu, Z. K. Liu, L. Q. Chen, Effect of substrate constraint on the stability and evolution of ferroelectric domain structures in thin films. Acta Mater. 50, 395-411 (2002). doi: 10.1016/S1359-6454(01)00360-3.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+SupplementaryInformation2. pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5_det.mmd b/preprint/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..901f93696cc377f05672492721912efd23fdab7b
--- /dev/null
+++ b/preprint/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5/preprint__03d68cf8e193cb35c9be6144c0f8c2e40f012dc558e3da2c1ab952dea9dac6d5_det.mmd
@@ -0,0 +1,388 @@
+<|ref|>title<|/ref|><|det|>[[44, 106, 825, 175]]<|/det|>
+# Mn-inlaid antiphase boundaries in perovskite structure
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 333, 240]]<|/det|>
+Lingyan Wang 1.y.wang@mail.xjtu.edu.cn
+
+<|ref|>text<|/ref|><|det|>[[44, 267, 891, 311]]<|/det|>
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 316, 272, 357]]<|/det|>
+Chao Li Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 363, 141, 381]]<|/det|>
+Liqiang Xu
+
+<|ref|>text<|/ref|><|det|>[[44, 384, 896, 428]]<|/det|>
+Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University
+
+<|ref|>text<|/ref|><|det|>[[44, 432, 157, 450]]<|/det|>
+Xuerong Ren
+
+<|ref|>text<|/ref|><|det|>[[44, 453, 893, 497]]<|/det|>
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 501, 168, 519]]<|/det|>
+Fangzhou Yao
+
+<|ref|>text<|/ref|><|det|>[[44, 522, 950, 565]]<|/det|>
+Wuzhen Laboratory/Center of Advanced Ceramic Materials and Devices, Yangtze Delta Region Institute of Tsinghua University
+
+<|ref|>text<|/ref|><|det|>[[44, 570, 698, 612]]<|/det|>
+Jiangbo Lu School of Physics and Information Technology, Shaanxi Normal University
+
+<|ref|>text<|/ref|><|det|>[[44, 617, 272, 657]]<|/det|>
+Dong Wang Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 662, 272, 702]]<|/det|>
+zhongshuai Liang Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 708, 630, 750]]<|/det|>
+Ping Huang Xi'an Jiaotong University https://orcid.org/0000- 0002- 5295- 8216
+
+<|ref|>text<|/ref|><|det|>[[44, 755, 184, 774]]<|/det|>
+Shengqiang Wu
+
+<|ref|>text<|/ref|><|det|>[[44, 777, 603, 797]]<|/det|>
+School of Materials Science and Engineering, Peking University
+
+<|ref|>text<|/ref|><|det|>[[44, 802, 168, 820]]<|/det|>
+Hongmei Jing
+
+<|ref|>text<|/ref|><|det|>[[44, 823, 700, 842]]<|/det|>
+School of Physics and Information Technology, Shaanxi Normal University
+
+<|ref|>text<|/ref|><|det|>[[44, 847, 150, 866]]<|/det|>
+Yijun Zhang
+
+<|ref|>text<|/ref|><|det|>[[44, 869, 890, 911]]<|/det|>
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 916, 166, 934]]<|/det|>
+Guohua Dong
+
+<|ref|>text<|/ref|><|det|>[[50, 937, 630, 957]]<|/det|>
+Xi'an Jiaotong University https://orcid.org/0000- 0002- 5484- 5442
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[44, 42, 272, 84]]<|/det|>
+Haixia Liu Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 90, 530, 131]]<|/det|>
+Chuansheng Ma Instrumental Analysis Center, Xi'an Jiaotong University
+
+<|ref|>text<|/ref|><|det|>[[44, 137, 264, 177]]<|/det|>
+Yinong Lyu Nanjing Tech University
+
+<|ref|>text<|/ref|><|det|>[[44, 183, 164, 201]]<|/det|>
+Xiaoyong Wei
+
+<|ref|>text<|/ref|><|det|>[[44, 204, 950, 246]]<|/det|>
+Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi'an Jiao Tong University
+
+<|ref|>text<|/ref|><|det|>[[44, 251, 118, 268]]<|/det|>
+Wei Ren
+
+<|ref|>text<|/ref|><|det|>[[44, 272, 702, 293]]<|/det|>
+Xi'an Jiaotong University School of Electronic and Information Engineering
+
+<|ref|>text<|/ref|><|det|>[[44, 298, 125, 316]]<|/det|>
+Ke Wang
+
+<|ref|>text<|/ref|><|det|>[[44, 319, 925, 361]]<|/det|>
+State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, P. R. China https://orcid.org/0000- 0001- 9840- 2427
+
+<|ref|>text<|/ref|><|det|>[[44, 366, 168, 384]]<|/det|>
+Zuo-Guang Ye
+
+<|ref|>text<|/ref|><|det|>[[50, 387, 622, 407]]<|/det|>
+Simon Fraser University https://orcid.org/0000- 0003- 2378- 7304
+
+<|ref|>text<|/ref|><|det|>[[44, 412, 138, 430]]<|/det|>
+Feng Chen
+
+<|ref|>text<|/ref|><|det|>[[50, 434, 601, 454]]<|/det|>
+High Magnetic Field Laboratory, Chinese Academy of Sciences
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 495, 103, 512]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 533, 137, 551]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 570, 325, 590]]<|/det|>
+Posted Date: February 5th, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 608, 475, 628]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 3884985/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 645, 916, 689]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 707, 535, 727]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 762, 925, 806]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on August 7th, 2024. See the published version at https://doi.org/10.1038/s41467- 024- 51024- 2.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[226, 89, 769, 110]]<|/det|>
+## Mn-inlaid antiphase boundaries in perovskite structure
+
+<|ref|>text<|/ref|><|det|>[[112, 133, 883, 515]]<|/det|>
+High- performance perovskite ferroelectrics are central to various electro- mechanical functional devices \(^{1,2}\) . However, the use of toxic Pb- based ferroelectrics in high- end applications is being limited due to environmental concerns and the related legislations \(^{3}\) . As an eco- friendly alternative, lead- free perovskite potassium sodium niobate (K \(_4\) Na \(_1\) - \(_3\) NbO \(_3\) , KNN)- based perovskite ferroelectrics materials have been intensively studied since the discovery of a large piezoelectric coefficient \(d_{33}\) value of 416 pC/N for KNN- based ceramics by Saito et al. \(^{4 - 6}\) . With advancements in the ferroelectric performances of the KNN- based ceramics and single crystals \(^{7 - 10}\) , a great deal of efforts have also been made to prepare the KNN- based thin films by various deposition techniques \(^{11 - 14}\) . However, the volatilization of the alkali ions has been identified as a major issue in obtaining high- quality KNN- based thin films. The inevitable loss of potassium and sodium elements during the vapor or chemical solution- based depositions changes the stoichiometry, resulting in the formation of undesired alkali- deficient secondary phases and defects. Consequently, KNN- based films exhibit high electrical conduction and poor ferroelectric response \(^{15}\) . Previous strategies focused on chemical composition adjustment to compensate for the elemental volatilization, and construction of morphotropic or polytropic phase boundaries to enhance the dielectric and ferroelectric properties of KNN- based thin films \(^{16 - 19}\) . Recently, some other methods, such as interface effects, flexible substrates, and defects engineering have been explored to modulate lattice strain, displacement polarization and electronic structure \(^{11,12,20 - 23}\) . All those efforts have led to a gradual improvement in the overall ferroelectric performances, which, however, still remain significantly inferior to Pb- based thin films and thereby are far from being suitable for practical applications in new micro electro- mechanical devices, ferroelectric field- effect transistors, nonvolatile memories, electro- optic devices, etc. \(^{1,24,25}\) .
+
+<|ref|>text<|/ref|><|det|>[[112, 517, 883, 865]]<|/det|>
+Material properties are strongly influenced by the microstructure. In terms of crystal structure, the above- mentioned attempts primarily focused on distorting or tilting the lattices within the basic perovskite framework, which has given rise to limited effects in improving the ferroelectric properties. It has been observed that the physical constraints of underlying substrate and the large unit cell of oxide perovskite structure can lead to the generation and propagation of out- of- phase boundary defects through the entire thickness of the film, especially with special deposition processes \(^{12,26}\) . These charged out- of- phase boundaries, originated from the alkali- deficiency, have been identified and found to play an important role in the piezoelectric performances of NaNbO \(_3\) and KNN thin films \(^{12}\) . In this work, we also harnessed these inherent characteristics (alkali deficiency and out- of- phase boundaries) to create a unique nanocolumnar structure, and then incorporated another element at the boundaries between the KNN nanocolumns to form a new perovskite derivative structure. Specifically, the nanocolumnar KNN- based thin film consists of perovskite KNN nanocolumns that are interspersed with Mn- inlaid antiphase boundaries. Atomic resolution images revealed that the thickness of perovskite KNN slabs varied from a few to tens of nanometers, while the coherent antiphase boundaries consisted of one or two atomic layers enriched with Mn. This strategic incorporation of Mn not only helped to balance the charges originated from alkali ions deficiency, leading to a reduced leakage current, but also induced a noticeable out- of- plane tensile strain in the KNN nanocolumns. This strain promoted a high degree of tetragonality, resulting in a remarkable improvement in ferroelectric polarization, with a high twice remanent polarization value of \(114 \mu \mathrm{C} / \mathrm{cm}^2\) .
+
+<|ref|>text<|/ref|><|det|>[[112, 866, 883, 900]]<|/det|>
+A ceramic target of \(\mathrm{K}_{0.5}\mathrm{Na}_{0.5}\mathrm{NbO}_{3}\) with \(2 \mathrm{wt\% MnO}_2\) addition (KNN- M) was used for deposition of the KNN- M films on \(\mathrm{La}_{0.07}\mathrm{Sr}_{0.93}\mathrm{SnO}_3\) (LSSO)- coated STO (001) substrates by
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 80, 882, 343]]<|/det|>
+pulsed laser deposition (PLD) method. High- resolution X- ray diffraction (HRXRD) techniques were employed to assess the crystalline quality of the KNN- M films. Fig. 1a shows the X- ray diffraction (XRD) \(\theta - 2\theta\) pattern of a representative KNN- M film. Only the (00l) \((l = 1, 2, 3)\) reflection peaks of KNN- M, LSSO and STO are observed, indicating that the film is epitaxially grown along the \(c\) - axis direction with a single phase. The rocking curves shown in Fig. 1b exhibit a full- width- at- half- maximum of approximately \(0.182^{\circ}\) for KNN- M (002) and \(0.093^{\circ}\) for LSSO (002), demonstrating a high crystallinity of the films. To examine the epitaxial relationship and the strain state of the samples, X- ray reciprocal space mappings (RSMs) around the symmetric (002) and asymmetric \((\overline{1} 03)\) reflections of the film are shown in Figs. 1c and d respectively. The discrete and clear spots in Figs. 1c and d confirm the orientation relationship between the (001) films and the (001) STO substrate. As displayed in Fig. 1d, the \(Q_{x}\) value of the KNN- M \((\overline{1} 03)\) RSM spot obviously deviates from that of STO and LSSO, suggesting a relaxation of the lattice mismatch strain between the film and substrate. Based on the RSM results, the out- of- plane lattice parameter " \(c\) " and in- plane lattice parameters " \(a\) " or " \(b\) " of the KNN- M films were calculated to be \(4.02 \mathring{\mathrm{A}}\) and \(3.95 \mathring{\mathrm{A}}\) , respectively.
+
+<|ref|>text<|/ref|><|det|>[[113, 343, 882, 639]]<|/det|>
+Fig. 1e displays a high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) image of the KNN- M thin film, recorded along the [010] direction. It is evident that the KNN- M thin film consists of vertically aligned nanocolumns in the out- of- plane direction, rather than a homogeneous and smooth cross section (Fig.1e). X- ray energy dispersive spectroscopy (EDS) analysis confirms the presence of Mn enrichment at the column boundaries along the out- of- plane direction, as seen in Supplementary Fig. 1. Additionally, the selected area electron diffraction (SAED) pattern of the KNN- M thin films along the [010] zone axis, as shown in Fig 1f, reveals classic single crystal diffraction spots in the out- of- plane direction, while the streaks along the in- plane direction are attributed to the "shape effect". This effect arises from the principle that a small thickness in real space corresponds to a large length in reciprocal space, and vice versa. Thus, the reciprocal diffraction pattern further supports the presence of nanocolumns in the specimens, which is consistent with the HAADF image in real space. Atomic resolution HAADF images reveal a series of nanocolumn grains exhibiting the classic single crystal phase perovskite structure, as shown in Fig. 1g. However, it is observed that the lattices of neighboring perovskite KNN nanocolumns undergo a relative shift by half a unit cell length at the phase boundaries along the out- of- plane direction, indicated by the red triangle in Fig.1g.
+
+<|ref|>text<|/ref|><|det|>[[113, 639, 883, 899]]<|/det|>
+Due to the overlap of the nanocolumnar structure in the cross- sectional observation direction, indicated by the brace in Fig. 1g and Supplementary Fig. 2, we studied the microstructure using a plan- view sample without substrate. We found that the KNN- M films present the 'Tetris- like' microstructure consisting of dense nanocolumns with sizes ranging from a few to tens of nanometers. Through annular bright field (ABF) imaging, we observed that the nanocolumns predominantly exhibit atomic- scale linear dark contrast along both the [001] and [010] directions, as shown in Fig. 1h and Supplementary Fig. 3. The corresponding EDS composition analysis reveals that the nanocolumn areas are composed of K, Na, Mn, Nb and O elements, with apparent Mn enrichment observed in some linear dark contrast areas, as shown in Fig. 1i and Supplementary Fig. 4. Electron energy loss spectroscopy (EELS) analysis indicates that the Mn ions mainly exhibit bivalence (Mn \(^{2 + }\) ) (Supplementary Fig. 5). In addition, atomic resolution HAADF imaging reveal that the lattices of adjacent perovskite KNN nanocolumns are coherent, but undergo a half- unit cell shift relative to each other across the atomic- scale antiphase boundaries with Mn enrichment, as marked within the yellow rectangle in Fig. 1j. At the ends of these antiphase boundaries, the lattice misregistry of 1/2 unit cell is gradually reduced to zero
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 80, 883, 116]]<|/det|>
+with continuous atom deficiency along the boundaries and no more Mn element could be detected with EDS analysis, as shown in the red rectangles in Fig. 1j and Supplementary Fig. 6.
+
+<|ref|>image<|/ref|><|det|>[[130, 128, 863, 744]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 750, 883, 880]]<|/det|>
+Fig. 1 | Crystalline structure and microstructure of the KNN-M thin film grown on a LSSO-buffered STO (001) substrate. a, XRD \(\theta -2\theta\) pattern. b, Rocking curves around STO (002), LSSO (002) and KNN-M (002). c, d, Reciprocal space maps around the STO (002) and (f03) reflections. e, Cross-sectional low magnification HAADF image. f, SEAD pattern of the KNN-M thin film in the out-of-plane direction. g, Atomic resolution HAADF image of the KNN-M thin film. h, Planar-view low-magnification ABF image. i, Corresponding EDS mapping of Mn element for the KNN-M thin film. j, Plan-view atomic resolution HAADF image of the KNN-M thin film. The scale bars in (g) and (j) are 2 nm.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 80, 882, 448]]<|/det|>
+Furthermore, we have identified two different atomic configurations for the Mn- inlaid antiphase boundaries, as illustrated in Fig. 2. Fig. 2a displays an atomic resolution HAADF image of one type of antiphase boundary structure (referred to as Type- I). In this image, a coherent antiphase feature is observed, where the A- site lattice of one KNN nanocolumn runs into the B- site lattice of the neighboring nanocolumn across a single atomic column. This single atomic column exhibits a brighter contrast than the A- site K/Na atomic columns, but a darker contrast compared to the B- site Nb/O atom columns. Line- scans of image intensity were performed along the single atomic column layer. The line profile of intensity reveals similar atomic column intensities, as shown in Fig. 2b. Based on the uniform image contrasts and corresponding line profiles, it can be inferred that the atomic columns in the Type- I antiphase boundaries have similar chemical compositions. The intensity of the atomic column in HAADF image is approximately proportional to the square of the atomic number \((Z^{2})^{27}\) , making the HAADF images suitable for composition analysis. However, due to the much smaller scattering cross- section of oxygen, the light element oxygen cannot be observed in the HAADF image. Therefore, we also obtained atomic resolution integrated differential phase contrast (iDPC) images to visualize the distribution of all atoms, as shown in Fig. 2c. The iDPC image reveals only one atomic column at the antiphase boundary plane, and no separate oxygen atom columns are observed in the plan- view direction. In addition, we observed that the single atomic layer at the antiphase boundaries can gradually translate to a "Ruddlesden- Popper" like double atomic layer with in- situ beam irradiation in STEM mode, and vice versa (Fig. 2d, Supplementary Fig. 7 and Supplementary Fig. 8).
+
+<|ref|>text<|/ref|><|det|>[[113, 448, 882, 779]]<|/det|>
+We performed the EDS mapping to study the atomic resolution composition distribution in Type- I antiphase boundary regions, as shown in Fig. 2e. The color- coded elemental maps of K, Na, O, Mn and Nb are presented in Figs. 2f- j, respectively. It is evident that all the elements are generally distributed uniformly in the KNN- based nanocolumns. However, the atomic columns at the antiphase boundary layer are primarily composed of the Mn and O elements, with a trace amount of K/Na. The composite map of Nb and Mn, as shown in Fig. 2k, illustrates the relative positions of the Nb and Mn atoms. Based on the elemental distribution maps, we find that Mn occupies the A- site of the perovskite lattice. Due to the structural changes at the boundaries during in- situ beam irradiation, as shown in Fig. 2d and Supplementary Fig. 7, Mn enrichments is observed along the boundary, but the location of Mn signals at the antiphase boundaries does not precisely correspond to the atomic- scale image from the EDS analysis. By analyzing the atomic resolution images in both the planar- view and cross- sectional directions (Supplementary Fig. 2) and conducting composition analysis, we have depicted the schematic structure of Type- I antiphase boundaries in Fig. 2l. This structure consists of nanocolumn perovskite KNN sheets alternating with a single Mn/O sheet running along the \(c\) axis direction and the neighboring perovskite slabs relatively shifting by half a unit cell length in both the in- plane and out- of- plane directions. At Type- I antiphase boundaries, the lattice site corresponds to the A- site of one KNN nanocolumn and the O- site of another KNN nanocolumn. Therefore, both the Mn and O atoms can randomly occupy the atom site at the boundaries theoretically.
+
+<|ref|>text<|/ref|><|det|>[[114, 778, 882, 917]]<|/det|>
+The other antiphase boundary (Type- II) is illustrated in Fig. 2m, where the two adjacent KNN phases coherently transit across a double atom layer, and the distance between the neighboring Nb atomic columns at the boundaries is approximately 3/2- unit cells. Notably, we observed distinct contrast variation for the atom columns at the transition layers, which differ from the uniform contrast of the atom columns at Type- I antiphase boundaries. The line profile of intensity also exhibits noticeable difference for the atomic column along one row of transition atomic columns in Fig. 2m, as shown in Fig. 2n. The observed variations in image contrast or line profiles can be attributed to composition differences in each atomic column at Type- II
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 80, 882, 255]]<|/det|>
+antiphase boundaries. Through atomic resolution composition analysis, we determined that the atom columns with bright contrast primarily consist of Nb atoms, while the dark atom columns are composed of K/Na/Mn (Supplementary Fig. 9). Additionally, we also observed the presence of Mn enrichment at the boundaries. However, the signals are noticeably weaker compared to the distinct single Mn- rich layer observed at Type- I antiphase boundaries (Supplementary Fig. 10). We also acquired the iDPC images for Type- II antiphase boundaries (Fig. 2o), which reveal separated O atom columns that can bond with neighboring Nb atoms to form oxygen octahedra at the boundaries. Furthermore, we found that Type- II antiphase boundaries remained stable under beam irradiation. Based on the aforementioned experimental results, we constructed the schematic structural model of Type- II antiphase boundaries, as depicted in Fig. 2p.
+
+<|ref|>text<|/ref|><|det|>[[114, 255, 882, 378]]<|/det|>
+For comparison, we also prepared the undoped KNN thin films with a similar deposition process. From cross- sectional view, serials of nanocolumns can also be observed (Supplementary Fig. 11a). Atomic resolution HAADF images revealed no noticeable lattice shifts between two adjacent nanocolumns in the out- of- plane direction (Supplementary Fig. 11b). However, the plan- view image displayed a high density of stacking faults due to the K/Na deficiency (Supplementary Fig. 11c). This deficiency resulted in a high leakage current and prevented the display of ferroelectricity at room temperature \(^{12,14}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[132, 85, 867, 666]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 672, 883, 880]]<|/det|>
+Fig.2 | In-plane atomic structure of Mn-inlaid antiphase boundaries in the KNN-M thin films. a, In-plane atomic resolution HAADF image of Type-I antiphase boundaries. b, Line-profile of the single antiphase atomic columns along the direction of the antiphase boundary in (A). c, iDPC image of Type-I antiphase boundaries. d, HAADF image of Type-I antiphase boundaries with in-situ electron irradiations. e, In-plane HAADF image of the KNN-M thin film containing Type-I antiphase boundaries. f-j, Corresponding color-coded atomic resolution EDS mapping of the K, Na, O, Mn and Nb elements, respectively. K, Composite elemental map with Nb (in red) and Mn (in green). I, Schematic structural models of Type-I Mn-inlaid antiphase boundaries, where the red, purple, green, and cyanine colors represent the O, K/Na, Mn and Nb elements, respectively. m, In-plane atomic resolution HAADF image of Type-II antiphase boundaries. n, Line-profile of the single antiphase atomic columns along the direction of the transition boundary in (m). o, iDPC image of Type-II antiphase boundaries. p, Schematic structural model of Type-II antiphase boundaries, where the red, purple, green, and cyanine colors represent the O, K/Na, Mn and Nb elements, respectively. The scale bar is 1nm.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 80, 883, 360]]<|/det|>
+We examined the ferroelectric polarization of this film and found that the out-of-plane phase image of the as-grown film without dc bias exhibits a remarkable homogeneity across the layer with a weak contrast, as shown in Fig. 3a, indicating an ordered out-of-plane polarization component. This result is also attested to the excellent epitaxial quality of the films. The out-of-plane piezoelectric force microscope (PFM) phase can switch to the opposite direction under a voltage of - 8 V. When a positive dc bias of \(+8\mathrm{V}\) was applied, the PFM phase switched to the same direction as the as-grown film, which confirms that the out-of-plane polarization of film is directed uniformly toward the bottom of the film. Additionally, well-saturated ferroelectric polarization-electric field \((P - E)\) hysteresis loops of the KNN- M film were displayed at room temperature (Fig. 3b). The film demonstrated a remarkable enhancement in remanent polarization \((P_{r})\) with the \(2P_{r}\) value reaching \(114\mu \mathrm {C}/\mathrm {cm}^{2}\) when subjected to an applied electric field of \(606\mathrm {kV/cm}\) . Furthermore, at the temperature of \(80\mathrm {K}\) , no significant variation in \(P_{r}\) was observed, but the breakdown field strength increased to \(2700\mathrm {kV/cm}\) , as shown in Fig. 3c. Notably, the \(2P_{r}\) value of the KNN- M thin film is larger than the values so far reported for most KNN- based films \((7.1-64.9\mu \mathrm {C}/\mathrm {cm}^{2})\) , as shown in Fig. 3d. Moreover, the \(P_{r}\) value is comparable to that of typical PZT ferroelectric thin films \({}^{24}\) .
+
+<|ref|>image<|/ref|><|det|>[[140, 370, 857, 808]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 818, 883, 915]]<|/det|>
+Fig. 3 | Ferroelectric properties of the KNN-M thin films. a, Out-of-plane polarization switching of the KNN-M film captured using PFM imaging technique, under a dc bias of \(\pm 8\mathrm {V}\) . b, Room-temperature polarization–electric field \((P - E)\) hysteresis loops displayed under different electric fields. c, \(P - E\) hysteresis loops under different electric field for the KNN-M thin films at a low-temperature of \(80\mathrm {K}\) . d, Comparison of the polarization \((2P_{r})\) of the present KNN-M films with previously reported values of the KNN-based films.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 95, 883, 725]]<|/det|>
+Based on the microstructure analysis and the ferroelectric properties, we delve into the mechanisms behind the formation of nanocolumnar structure with Mn- inlaid antiphase boundaries and enhancement of ferroelectric polarization. In the case of pure KNN thin films without Mn doping, the unique deposition process led to the formation of vertical nanocolumnar structures aligned along the out- of- plane direction. Through atomic resolution investigation of microstructure, it was observed that the KNN nanocolumns maintained the normal perovskite structure. Significant K/Na deficiencies primarily occurred at the boundaries, resulting in lattice rearrangement and formation of charged out- of- phase boundaries. These crystallographic out- of- phase boundaries, commonly found in epitaxial perovskite films, tend to propagate throughout the entire thickness of the film. Consequently, nanocolumnar KNN thin films exhibited large leakage currents, as depicted in Supplementary Fig. 12 and Ref. 12. However, consistent with previous studies \(^{11,16,19}\) , our experimental results showed the addition of a small concentration of Mn into KNN film was very effective in reducing the leakage current density. Due to the smaller radius of Mn ion than those of the A- site \(\mathrm{K^{+} / Na^{+}}\) ions, the solid solubility of Mn is low in KNN lattice. When doping Mn into the KNN films, the Mn ions are believed to occupy a small number of A- site vacancies, which were formed due to the volatilization of the \(\mathrm{K^{+} / Na^{+}}\) ions in the KNN nanocolumns, according to the atomic structural imaging and composition analysis. Considering its primary valence, \(\mathrm{Mn^{2 + }}\) can act as a donor- dopant on the A- site of the perovskite lattice. However, in order to balance the charge, the occupancy of \(\mathrm{Mn^{2 + }}\) on the A- site vacancies was only partial, with every other A- site occupied. As a result, partial A- site deficiency still existed in the KNN nanocolumns \(^{18}\) . On the contrary, the high density of Mn accumulated at the phase boundaries to form atomic- scale Mn- rich layer, which could compensate the serious K/Na deficiencies at the boundaries. In the case of Type- I antiphase boundaries, both cation \(\mathrm{Mn^{2 + }}\) and anion \(\mathrm{O^{2 - }}\) can occupy the atomic site at the single antiphase boundary layer. By adjusting the ratio of Mn/O, we can achieve charge balance in optimum experimental conditions (Supplementary Fig. 13). For Type- II antiphase boundaries, which resemble the Ruddlesden- Popper structure, separate atomic columns of cations and anion \(\mathrm{O^{2 - }}\) were observed. The cation atomic sites at these boundaries can be occupied by the \(\mathrm{Nb^{5 + }}\) , \(\mathrm{Mn^{2 + }}\) , \(\mathrm{K^{+}}\) and \(\mathrm{Na^{+}}\) ions. The ratios among these four cations could also be adjusted experimentally to maintain charge balance (Supplementary Fig. 14). Consequently, the leakage currents can be significantly reduced, which is crucial for the ferroelectric functionality of the thin film. In our study, we investigated a series of Mn- doped samples with the Mn concentration ranging from 1 to \(5\mathrm{wt}\%\) . It was observed that the sample with a low Mn doping content, such as \(1\mathrm{wt}\%\) , exhibited a vertical nanocolumns structure, but the K/Na deficiencies were not fully compensated (Supplementary Fig. 15). As the doping level increased to \(5\%\) , the nanoscale Mn enriched phases were observed, which disrupted the epitaxial growth of the thin films, as shown in Supplementary Fig. 16.
+
+<|ref|>text<|/ref|><|det|>[[115, 723, 882, 916]]<|/det|>
+More importantly, the specific atomic configurations at the Mn- inlaid antiphase boundaries induce noticeable change in the lattice structure compared to the KNN nanocolumns. The high- density boundaries are organized in an ordered manner on a nanoscale and extend vertically in the film, resulting in the generation of apparent lattice strains. These strains also impact the neighboring KNN nanocolumns, as evidenced by the ADF images (Supplementary Fig. 17, Supplementary Fig. 18), where the brighter image contrast indicates the presence of apparent lattice strains near the Mn- inlaid antiphase boundaries. It is well- known that lattice strain can significantly influence the ferroelectric polarization of thin films. We examined the relative lattice strain and the evolution of lattice parameters using the geometry phase analysis method. Fig. 4a displays an ADF image of the KNN- M thin film, revealing the presence of two types of boundaries. The corresponding relative lattice strain are plotted in Fig. 4b \((\epsilon_{xx})\) , Fig. 4c \((\epsilon_{yy})\) and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 80, 882, 220]]<|/det|>
+Fig. 4d \((\epsilon_{xy})\) , respectively. It can be seen that the boundaries exhibit apparent relative lattice strains, mainly perpendicular to their orientation with no observable relative strains parallel to the boundaries (Supplementary Fig. 19). The increased atomic spacing at the boundaries, indicative of tensile strain, is accompanied by the compressive strain in the KNN nanocolumns. It is worth noting that a strain in one direction typically induces an opposite strain component in the other direction to achieve overall relaxation \(^{28}\) . Consequently, the in-plane compressive strain induces an out-of-plane tensile strain, as confirmed by the XRD results with a larger \(c\) than \(a\) and \(b\) in the KNN lattice, which is advantageous for achieving high ferroelectric polarization \(^{7}\) .
+
+<|ref|>text<|/ref|><|det|>[[113, 222, 882, 585]]<|/det|>
+The displacement of the center polar B- site cations relative to the corner A- site cations \((\delta_{\mathrm{B - A}})\) was used as a measure of the local polarization. Fig. 4e displays a colored arrow map of \(\delta_{\mathrm{B - A}}\) , representing the orientation and magnitude of the polarization. The film exhibited apparent displacement polarization, with the largest polarization observed near the boundaries. The different strains present at each type of boundary resulted in the formation of multidomain structures with a mixture of various orientations of polarizations. To investigate the impact of boundary strain on ferroelectric polarization, we conducted phase field simulations. The phenomenological model and relative lattice strain distributions used in these simulations were obtained from Fig. 4a- d, as shown in Supplementary Fig. 20. Specifically, we examined the different lattice strains, namely \(\epsilon_{\mathrm{local}}(0, 0.1, \text{and} 0.2)\) , induced by the Mn accumulated boundary, to elucidate their effects. Our simulations employed the orthorhombic phase with the [110]- oriented polarization of KNN at room temperature \(^{16}\) , as illustrated in Supplementary Fig. 21, which showcases the detailed microstructural evolution. As the applied external electric field increased, the polarizations transitioned from the orthorhombic phase (represented by different colors in Fig. 4f) to the tetragonal phase (indicated by light blue color in Fig. 4g). Importantly, the lattice strains around the boundaries induced larger polarization in both in- plane and out- of- plane directions, as shown in Fig. 4f and Supplementary Fig. 22. The simulated ferroelectric loop demonstrated an increase in both the coercive electric field strength \((E_{\mathrm{c}})\) and ferroelectric polarization in the out- of- plane directions with the increase in lattice strain (see Fig. 4h and Supplementary Fig. 21a). Thus, the Mn- inlaid antiphase boundaries offer a new structural framework for enhancing the ferroelectric polarization of lead- free ferroelectric thin films.
+
+<|ref|>text<|/ref|><|det|>[[115, 586, 882, 708]]<|/det|>
+In summary, we prepared and observed the new Mn- inlaid antiphase boundaries structure in perovskites. The high- density vertical Mn- inlaid antiphase boundaries show the positivity effect on charge balance, coherent transition to the neighboring KNN nanocolumns and the induction of large strain for the nanocolumnar KNN lattice in the entire KNN- M thin films. Therefore, the ever higher ferroelectric polarizations have been observed for the KNN- based thin films. The Mn- inlaid antiphase boundaries also give a new possible structure frame to modulate the various properties of perovskites.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[128, 85, 876, 430]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 437, 883, 550]]<|/det|>
+Fig. 4 | Strains and atom displacement polarizations in the KNN-M thin film. a, Planar-view atomic-resolution HAADF image of the KNN-M thin film. b-d, Maps depicting the relative lattice strains: (b) \(\epsilon_{xx}\) (in-plane strain), (c) \(\epsilon_{yy}\) (out-of-plane strain) and (d) \(\epsilon_{xy}\) (shear strain). e, Colored arrows map of polarizations \((\partial_{Nb-KNa})\) , indicating the polarization orientation of the KNN nanocolumns in (a). f, Polarization of KNN-M obtained from phase-field simulation. g, Mapping of the piezoelectric response of the KNN-M film under an applied electric field obtained from phase-field simulation. h, Calculated P-E curves with different local strains.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 558, 208, 574]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[111, 584, 884, 916]]<|/det|>
+1 Martin, L. W. & Rappe, A. M. Thin- film ferroelectric materials and their applications. Nature Reviews Materials 2, 16087, doi:10.1038/natrevmats.2016.87 (2016). 2 Yang, Q. et al. Ferroelectricity in layered bismuth oxide down to 1 nanometer. Science 379, 1218- 1224, doi:10.1126/science.abm5134 (2023). 3 Zhang, S., Malič, B., Li, J.- F. & Rödel, J. Lead- free ferroelectric materials: Prospective applications. J. Mater. Res. 36, 985- 995, doi:10.1557/s43578- 021- 00180- y (2021). 4 Saito, Y. et al. Lead- free piezoceramics. Nature 432, 84- 87, doi:10.1038/nature03028 (2004). 5 Wu, J., Xiao, D. & Zhu, J. Potassium- Sodium Niobate Lead- Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries. Chem. Rev. 115, 2559- 2595, doi:10.1021/cr5006809 (2015). 6 Zhang, N., Zheng, T. & Wu, J. Lead- Free (K,Na)NbO3- Based Materials: Preparation Techniques and Piezoelectricity. ACS Omega 5, 3099- 3107, doi:10.1021/acsomega.9b03658 (2020). 7 Gao, X. et al. The mechanism for the enhanced piezoelectricity in multi- elements doped (K,Na)NbO3 ceramics. Nature Communications 12, 881, doi:10.1038/s41467- 021- 21202- 7 (2021). 8 Xu, K. et al. Superior Piezoelectric Properties in Potassium- Sodium Niobate Lead- Free Ceramics. Adv. Mater. 28, 8519- 8523, doi:10.1002/adma.201601859 (2016).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[110, 80, 886, 920]]<|/det|>
+9 Zhu, B. et al. New Potassium Sodium Niobate Single Crystal with Thickness-independent High-performance for Photoacoustic Angiography of Atherosclerotic Lesion. Sci. Rep. 6, 39679, doi:10.1038/srep39679 (2016). 10 Yin, F. et al. Transparent Lead-Free Ferroelectric (K,Na)NbO Single Crystal with Giant Second Harmonic Generation and Wide Mid- Infrared Transparency Window. Advanced Optical Materials 10, 2201721, doi:10.1002/adom.202201721 (2022). 11 Xu, L. et al. Robust Ferroelectric Properties in (K,Na)NbO3- Based Lead- Free Films via a Self- Assembled Nanocomposite Approach. ACS Appl. Mat. Interfaces 12, 4616- 4624, doi:10.1021/acsami.9b20311 (2020). 10 12 Waqar, M. et al. Origin of giant electric- field- induced strain in faulted alkali niobate films. Nature Communications 13, 3922, doi:10.1038/s41467- 022- 31630- 8 (2022). 13 Li, C. et al. A Novel Multiple Interface Structure with the Segregation of Dopants in Lead- Free Ferroelectric (K0.5Na0.5)NbO3 Thin Films. Advanced Materials Interfaces 5, 1700972, doi:10.1002/admi.201700972 (2018). 15 Liu, H. et al. Giant piezoelectricity in oxide thin films with nanopillar structure. Science 369, 292- 297, doi:10.1126/science.abb3209 (2020). 15 Cho, C.- R. & Grishin, A. Background Oxygen Effects on Pulsed Laser Deposited Na0.5K0.5NbO Films: From Superparaelectric State to Ferroelectricity. J. Appl. Phys. 87, 4439- 4448, doi:10.1063/1.373089 (2000). 20 Seog, H. J. et al. Recent Progress in Potassium Sodium Niobate Lead- free Thin Films. Journal of the Korean Physical Society 72, 1467- 1483, doi:10.3938/jkps.72.1467 (2018). 17 Chen, W., Zhao, J., Wang, L., Ren, W. & Liu, M. Lead- free piezoelectric KNN- BZ- BNT films with a vertical morphotropic phase boundary. AIP Advances 5, 077190, doi:10.1063/1.4928095 (2015). 25 Rubio- Marcos, F. et al. Effect of MnO doping on the structure, microstructure and electrical properties of the (K,Na,Li)(Nb,Ta,Sb)O3 lead- free piezoceramics. J. Alloys Compd. 509, 8804- 8811, doi:https://doi.org/10.1016/j.jallcom.2011.06.080 (2011). 19 Won, S. S. et al. Lead- free Mn- doped (K0.5,Na0.5)NbO3 piezoelectric thin films for MEMS- based vibrational energy harvester applications. Appl. Phys. Lett. 108, 30 doi:10.1063/1.4953623 (2016). 20 Li, C. et al. Atomic Resolution Interfacial Structure of Lead- free Ferroelectric K0.5Na0.5NbO3 Thin films Deposited on SrTiO3. Sci. Rep. 6, 37788, doi:10.1038/srep37788 (2016). 21 Luo, J. et al. Monoclinic (K,Na)NbO3 Ferroelectric Phase in Epitaxial Films. Advanced Electronic Materials 3, 1700226, doi:10.1002/aelm.201700226 (2017). 22 Cheng, Y.- Y.- S. et al. All- Inorganic Flexible (K, Na)NbO3- Based Lead- Free Piezoelectric Thin Films Spin- Coated on Metallic Foils. ACS Appl. Mat. Interfaces 13, 39633- 39640, doi:10.1021/acsami.1c11418 (2021). 23 Shiraishi, T. et al. Ferroelectric and piezoelectric properties of KNbO3 films deposited on flexible organic substrate by hydrothermal method. Jpn. J. Appl. Phys. 53, 09PA10, doi:10.7567/JJAP.53.09PA10 (2014). 24 Nishino, R., Fujita, T. C., Kagawa, F. & Kawasaki, M. Evolution of ferroelectricity in ultrathin PbTiO3 films as revealed by electric double layer gating. Sci. Rep. 10, 10864, doi:10.1038/s41598- 020- 67580- 8 (2020). 45 Dahl, O., Grepstad, J. K. & Tybell, T. Polarization direction and stability in ferroelectric lead titanate thin films. J. Appl. Phys. 106, 084104, doi:10.1063/1.3240331 (2009). 26 Zurbuchen, M. A. et al. Morphology, structure, and nucleation of out- of- phase boundaries (OPBs) in epitaxial films of layered oxides. J. Mater. Res. 22, 1439- 1471,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[170, 80, 464, 98]]<|/det|>
+doi:10.1557/JMR.2007.0198 (2007).
+
+<|ref|>text<|/ref|><|det|>[[115, 99, 883, 135]]<|/det|>
+27 Pennycook, S. J. Z- contrast stem for materials science. Ultramicroscopy 30, 58- 69, doi:10.1016/0304- 3991(89)90173- 3 (1989).
+
+<|ref|>text<|/ref|><|det|>[[115, 135, 882, 188]]<|/det|>
+28 Zhao, J. et al. Strained hybrid perovskite thin films and their impact on the intrinsic stability of perovskite solar cells. Science Advances 3, eaa05616, doi:10.1126/sciadv.aa05616 (2017).
+
+<|ref|>text<|/ref|><|det|>[[115, 188, 882, 223]]<|/det|>
+1. L. W. Martin, A. M. Rappe, Thin-film ferroelectric materials and their applications. Nature Reviews Materials 2, 16087 (2016). doi: 10.1038/natrevmat.2016.87.
+
+<|ref|>text<|/ref|><|det|>[[115, 223, 882, 293]]<|/det|>
+2. Q. Yang, J. Hu, Y.-W. Fang, Y. Jia, R. Yang, S. Deng, Y. Lu, O. Dieguez, L. Fan, D. Zheng, X. Zhang, Y. Dong, Z. Luo, Z. Wang, H. Wang, M. Sui, X. Xing, J. Chen, J. Tian, L. Zhang, Ferroelectricity in layered bismuth oxide down to 1 nanometer. Science 379, 1218-1224 (2023). doi: doi:10.1126/science.abm5134.
+
+<|ref|>text<|/ref|><|det|>[[115, 292, 882, 328]]<|/det|>
+3. S. Zhang, B. Malič, J.-F. Li, J. Rödel, Lead-free ferroelectric materials: Prospective applications. J. Mater. Res. 36, 985-995 (2021). doi: 10.1557/s43578-021-00180-y.
+
+<|ref|>text<|/ref|><|det|>[[115, 328, 882, 380]]<|/det|>
+4. Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, M. Nakamura, Lead-free piezoceramics. Nature 432, 84-87 (2004). doi: 10.1038/nature03028.
+
+<|ref|>text<|/ref|><|det|>[[115, 380, 882, 433]]<|/det|>
+5. J. Wu, D. Xiao, J. Zhu, Potassium-Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries. Chem. Rev. 115, 2559-2595 (2015). doi: 10.1021/cr5006809.
+
+<|ref|>text<|/ref|><|det|>[[115, 432, 882, 485]]<|/det|>
+6. N. Zhang, T. Zheng, J. Wu, Lead-Free (K,Na)NbO₃-Based Materials: Preparation Techniques and Piezoelectricity. ACS Omega 5, 3099-3107 (2020). doi: 10.1021/acsomega.9b03658.
+
+<|ref|>text<|/ref|><|det|>[[115, 485, 882, 572]]<|/det|>
+7. X. Gao, Z. Cheng, Z. Chen, Y. Liu, X. Meng, X. Zhang, J. Wang, Q. Guo, B. Li, H. Sun, Q. Gu, H. Hao, Q. Shen, J. Wu, X. Liao, S. P. Ringer, H. Liu, L. Zhang, W. Chen, F. Li, S. Zhang, The mechanism for the enhanced piezoelectricity in multi-elements doped (K,Na)NbO₃ ceramics. Nature Communications 12, 881 (2021). doi: 10.1038/s41467-021-21202-7.
+
+<|ref|>text<|/ref|><|det|>[[115, 572, 882, 625]]<|/det|>
+8. K. Xu, J. Li, X. Lv, J. Wu, X. Zhang, D. Xiao, J. Zhu, Superior Piezoelectric Properties in Potassium-Sodium Niobate Lead-Free Ceramics. Adv. Mater. 28, 8519-8523 (2016). doi: 10.1002/adma.201601859.
+
+<|ref|>text<|/ref|><|det|>[[115, 625, 882, 696]]<|/det|>
+9. B. Zhu, Y. Zhu, J. Yang, J. Ou-Yang, X. Yang, Y. Li, W. Wei, New Potassium Sodium Niobate Single Crystal with Thickness-independent High-performance for Photoacoustic Angiography of Atherosclerotic Lesion. Sci. Rep. 6, 39679 (2016). doi: 10.1038/srep39679.
+
+<|ref|>text<|/ref|><|det|>[[115, 696, 882, 766]]<|/det|>
+10. F. Yin, L. Liu, M. Zhu, J. Lv, X. Guan, J. Zhang, N. Lin, X. Fu, Z. Jia, X. Tao, Transparent Lead-Free Ferroelectric (K,Na)NbO₃ Single Crystal with Giant Second Harmonic Generation and Wide Mid-Infrared Transparency Window. Advanced Optical Materials 10, 2201721 (2022). doi: 10.1002/adom.202201721.
+
+<|ref|>text<|/ref|><|det|>[[115, 766, 882, 835]]<|/det|>
+11. L. Xu, F. Chen, F. Jin, H. Huang, L. Qu, K. Zhang, Z. Zhang, G. Gao, Y. Lu, F. Zhang, K. Wang, C. Ma, W. Wu, Robust Ferroelectric Properties in (K,Na)NbO₃-Based Lead-Free Films via a Self-Assembled Nanocomposite Approach. ACS Appl. Mat. Interfaces 12, 4616-4624 (2020). doi: 10.1021/acsami.9b20311.
+
+<|ref|>text<|/ref|><|det|>[[115, 835, 882, 904]]<|/det|>
+12. M. Waqar, H. Wu, K. P. Ong, H. Liu, C. Li, P. Yang, W. Zang, W. H. Liew, C. Diao, S. Xi, D. J. Singh, Q. He, K. Yao, S. J. Pennycook, J. Wang, Origin of giant electric-field-induced strain in faulted alkali niobate films. Nature Communications 13, 3922 (2022). doi: 10.1038/s41467-022-31630-8.
+
+<|ref|>text<|/ref|><|det|>[[115, 904, 882, 922]]<|/det|>
+13. C. Li, L. Wang, W. Chen, L. Lu, H. Nan, D. Wang, Y. Zhang, Y. Yang, C.-L. Jia, A Novel
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[56, 70, 886, 920]]<|/det|>
+Multiple Interface Structure with the Segregation of Dopants in Lead- Free Ferroelectric \(\mathrm{(K_{0.5}Na_{0.5})NbO_{3}}\) Thin Films. Advanced Materials Interfaces 5, 1700972 (2018). doi: 10.1002/admi.201700972. 14. H. Liu, H. Wu, K. P. Ong, T. Yang, P. Yang, P. K. Das, X. Chi, Y. Zhang, C. Diao, W. K. A. Wong, E. P. Chew, Y. F. Chen, C. K. I. Tan, A. Rusydi, M. B. H. Breese, D. J. Singh, L.- Q. Chen, S. J. Pennycook, K. Yao, Giant piezoelectricity in oxide thin films with nanopillar structure. Science 369, 292- 297 (2020). doi: 10.1126/science.abb3209. 15. C.- R. Cho, A. Grishin, Background Oxygen Effects on Pulsed Laser Deposited \(\mathrm{Na_{0.5}K_{0.5}NbO_{3}}\) Films: From Superparaelectric State to Ferroelectricity. J. Appl. Phys. 87, 4439- 4448 (2000). doi: 10.1063/1.373089. 16. H. J. Seog, A. Ullah, C. W. Ahn, I. W. Kim, S. Y. Lee, J. Park, H. J. Lee, S. S. Won, S.- H. Kim, Recent Progress in Potassium Sodium Niobate Lead- free Thin Films. Journal of the Korean Physical Society 72, 1467- 1483 (2018). doi: 10.3938/jkps.72.1467. 17. W. Chen, J. Zhao, L. Wang, W. Ren, M. Liu, Lead- free piezoelectric KNN- BZ- BNT films with a vertical morphotropic phase boundary. AIP Advances 5, 077190 (2015). doi: 10.1063/1.4928095. 18. F. Rubio- Marcos, P. Marchet, X. Vendrell, J. J. Romero, F. Remondiere, L. Mestres, J. F. Fernandez, Effect of MnO doping on the structure, microstructure and electrical properties of the \(\mathrm{(K,Na,Li)(Nb,Ta,Sb)O_{3}}\) lead- free piezoceramics. J. Alloys Compd. 509, 8804- 8811 (2011). doi: https://doi.org/10.1016/j.jallcom.2011.06.080. 19. S. S. Won, J. Lee, V. Venugopal, D.- J. Kim, J. Lee, I. W. Kim, A. I. Kingon, S.- H. Kim, Lead- free Mn- doped \(\mathrm{(K_{0.5}Na_{0.5})NbO_{3}}\) piezoelectric thin films for MEMS- based vibrational energy harvester applications. Appl. Phys. Lett. 108, (2016). doi: 10.1063/1.4953623. 25. C. Li, L. Wang, Z. Wang, Y. Yang, W. Ren, G. Yang, Atomic Resolution Interfacial Structure of Lead- free Ferroelectric \(\mathrm{K_{0.5}Na_{0.5}NbO_{3}}\) Thin films Deposited on SrTiO3. Sci. Rep. 6, 37788 (2016). doi: 10.1038/srep37788. 21. J. Luo, W. Sun, Z. Zhou, H.- Y. Lee, K. Wang, F. Zhu, Y. Bai, Z. J. Wang, J.- F. Li, Monoclinic \(\mathrm{(K,Na)NbO_{3}}\) Ferroelectric Phase in Epitaxial Films. Advanced Electronic Materials 3, 1700226 (2017). doi: 10.1002/aelm.201700226. 22. Y.- Y.- S. Cheng, L. Liu, Y. Huang, L. Shu, Y.- X. Liu, L. Wei, J.- F. Li, All- Inorganic Flexible (K, Na)NbO3- Based Lead- Free Piezoelectric Thin Films Spin- Coated on Metallic Foils. ACS Appl. Mat. Interfaces 13, 39633- 39640 (2021). doi: 10.1021/acsami.1c11418. 23. T. Shiraishi, N. Kaneko, M. Kurosawa, H. Uchida, T. Hirayama, H. Funakubo, Ferroelectric and piezoelectric properties of KNbO3 films deposited on flexible organic substrate by hydrothermal method. Jpn. J. Appl. Phys. 53, 09PA10 (2014). doi: 10.7567/JJAP.53.09PA10. 24. R. Nishino, T. C. Fujita, F. Kagawa, M. Kawasaki, Evolution of ferroelectricity in ultrathin PbTiO3 films as revealed by electric double layer gating. Sci. Rep. 10, 10864 (2020). doi: 10.1038/s41598- 020- 67580- 8. 25. O. Dahl, J. K. Grepstad, T. Tybell, Polarization direction and stability in ferroelectric lead titanate thin films. J. Appl. Phys. 106, 084104 (2009). doi: 10.1063/1.3240331. 26. M. A. Zurbuchen, W. Tian, X. Q. Pan, D. Fong, S. K. Streiffer, M. E. Hawley, J. Lettieri, Y. Jia, G. Asayama, S. J. Fulk, D. J. Comstock, S. Knapp, A. H. Carim, D. G. Schlom, Morphology, structure, and nucleation of out- of- phase boundaries (OPBs) in epitaxial films of layered oxides. J. Mater. Res. 22, 1439- 1471 (2007). doi: 10.1557/JMR.2007.0198.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 80, 883, 170]]<|/det|>
+27. S. J. Pennycook, Z-contrast stem for materials science. Ultramicroscopy 30, 58-69 (1989). doi: 10.1016/0304-3991(89)90173-3.
+28. J. Zhao, Y. Deng, H. Wei, X. Zheng, Z. Yu, Y. Shao, J. E. Shield, J. Huang, Strained hybrid perovskite thin films and their impact on the intrinsic stability of perovskite solar cells. Science Advances 3, eaao5616 (2017). doi: 10.1126/sciadv.aao5616.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 201, 190, 217]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 244, 364, 260]]<|/det|>
+## The ceramic targets synthesis
+
+<|ref|>text<|/ref|><|det|>[[115, 260, 882, 452]]<|/det|>
+The ceramic targets synthesisThe ceramic targets of \((\mathrm{K,Na}) \mathrm{NbO}_3 - 0 / 1 / 2 / 5 \mathrm{wt\% Mn}\) (KNN-M) were fabricated using the conventional solid-state reaction method. High-purity materials, including \(\mathrm{K}_2\mathrm{CO}_3(99.0\%)\) , \(\mathrm{Na}_2\mathrm{CO}_3(99.8\%)\) , \(\mathrm{Nb}_2\mathrm{O}_5(99.9\%)\) and \(\mathrm{MnO}_2(98.8\%)\) , were obtained from Sinopharm Chemical Reagent Beijing Co. Ltd. Initially, the raw materials were accurately weighed according to the stoichiometric ratio of \((\mathrm{K}_0.5\mathrm{Na}_0.5)\mathrm{NbO}_3\) and then homogenized in a planetary mill for 24h using ethyl alcohol as the medium. After calcination at \(750^{\circ}\mathrm{C}\) for 4h, the resulting powder mixtures were milled, dried, and sieved. Subsequently, additional \(\mathrm{MnO}_2\) was incorporated into the powders and homogenized for another 24 h in the planetary mill. The resulting powder mixtures were then dried and sieved. Next, the mixed KNN-Mn powders were compacted into disks by uniaxial pressing at a pressure of \(150\mathrm{MPa}\) for \(2\mathrm{min}\) . Finally, the KNN-Mn pellets, with a diameter of \(30\mathrm{mm}\) , were sintered at \(1120^{\circ}\mathrm{C}\) for \(4\mathrm{h}\) to prepare the target
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 470, 280, 486]]<|/det|>
+## Thin Films Growth
+
+<|ref|>text<|/ref|><|det|>[[115, 486, 882, 626]]<|/det|>
+Thin Films GrowthThe KNN-M films were deposited onto the (001) SrTiO\(_3\) (STO) substrate buffered with \(\mathrm{La}_{0.07}\mathrm{Sr}_{0.93}\mathrm{SnO}_3\) (LSSO) layer using the PLD technique with a \(248\mathrm{nm}\) KrF excimer laser. The deposition process involved maintaining the substrate temperature at \(735^{\circ}\mathrm{C}\) and the \(\mathrm{O}_2\) pressure at \(15\mathrm{Pa}\) for the LSSO layer, followed by deposition of the KNN-film rat \(700^{\circ}\mathrm{C}\) and \(30\mathrm{Pa}\) . The target-substrate distance was set at \(5\mathrm{cm}\) , and the laser energy were kept at \(2\mathrm{J / cm}^2\) . The thicknesses of the KNN-M and LSSO were approximately \(300\mathrm{nm}\) and \(30\mathrm{nm}\) , respectively. After deposition, each film underwent in-situ annealing for 15 minutes before being cooled down to room temperature.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 644, 260, 660]]<|/det|>
+## X-ray diffraction
+
+<|ref|>text<|/ref|><|det|>[[115, 661, 882, 713]]<|/det|>
+X-ray diffractionThe crystalline phase of films was characterized by high-resolution X-ray diffraction (XRD) using Cu Kα1 radiation. The samples were mounted in the diffractometer (PANalytical, X'Pert), for linear scans, rocking curves, and reciprocal space mappings (RSM) at room temperature.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 731, 472, 748]]<|/det|>
+## Transmission Electron Microscopy (TEM)
+
+<|ref|>text<|/ref|><|det|>[[115, 748, 882, 888]]<|/det|>
+Transmission Electron Microscopy (TEM)The specimens were prepared using both the Tripod method (ALLIED Multiprep) and focused ion beam (FIB, Thermofisher Helios UX5) for the cross-section and plan-view STEM observation. TEM characterizations, low magnification STEM imaging, and EDS composition analysis were performed using the Thermofisher Talos F200X. Atomic resolution HAADF and iDPC images were acquired using the Thermofisher Titan Themis Z. Atom resolution HAADF, ADF image and EDS mapping were obtained using the Thermofisher Titan cubed Themis G2 300. The acquisition of EELS data was carried out using Gatan electron energy loss spectroscopy (EELS) on both the FEI Titan G2 80- 300 and JEOL ARM300.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 81, 265, 98]]<|/det|>
+## Electrical Testing
+
+<|ref|>text<|/ref|><|det|>[[115, 99, 882, 187]]<|/det|>
+Electrical TestingPolarization versus electric field \((P - E)\) hysteresis loops were measured through the ferroelectric test system (TF Analyzer 2000E, Germany) at \(1\mathrm{kHz}\) in room temperature. The \(P - E\) loops at liquid nitrogen temperature of \(80\mathrm{K}\) were obtained with Cryogenic Probe Station supplied by Lake Shore Company. The ferroelectric domains and polarization reversal behaviors were characterized by piezoresponse force microscopy (PFM, Asylum Cypher).
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 203, 550, 220]]<|/det|>
+## The calculation of the displacements in ADF images
+
+<|ref|>text<|/ref|><|det|>[[115, 220, 882, 360]]<|/det|>
+A standard peak finding algorithm is employed for the ADF image, which is based on fitting two- dimensional Gaussian functions to the intensity maxima. This algorithm allows us to determine the position and brightness of each column. Using these data, we can calculate the offcenter ion displacements between the Nb column and the center of the unit cell. The center of the unit cell is determined by the average coordinate of the four K/Na atomic columns. We use the following formula to calculate the displacements: \(\mathbf{u}_{ij} = \mathbf{r}_{ij} - 1 / 4\) \((R_{ij} + (i + 1) + (j + 1) + (i + 1)(j + 1))\) . Here, \(\mathrm{i} / \mathrm{j}\) indicate the row/column number of each atom column, \(\mathbf{r}_{\mathrm{ij}}\) indicates the position of Nb atomic columns, and \(\mathrm{R_{ij}}\) indicates the position of K/Na atomic columns.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 367, 320, 384]]<|/det|>
+## Phase-Field Simulations
+
+<|ref|>text<|/ref|><|det|>[[115, 391, 882, 444]]<|/det|>
+A single crystal considering Cubic \((C)\) to Orthorhombic (O) ferroelectric transition with Mninlaid antiphase boundaries has been carried out in phase- field simulations. The total free energy of the ferroelectric system can be described as (29- 32):
+
+<|ref|>equation<|/ref|><|det|>[[115, 443, 610, 470]]<|/det|>
+\[F = \int_{\nu}(f_{\mathrm{bulk}} + f_{\mathrm{grad}} + f_{\mathrm{couple}})dV + \int_{\nu}(f_{\mathrm{elas}} + f_{\mathrm{elec}})dV \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 472, 518, 490]]<|/det|>
+where \(f_{\mathrm{bulk}}\) represents the bulk free energy density,
+
+<|ref|>equation<|/ref|><|det|>[[115, 490, 725, 560]]<|/det|>
+\[f_{\mathrm{bulk}} = \alpha_{1}(P_{1}^{2} + P_{2}^{2} + P_{3}^{2}) - \alpha_{11}(P_{1}^{2} + P_{2}^{2} + P_{3}^{3})^{2} + \alpha_{12}(P_{1}^{2}P_{2}^{2} + P_{2}^{2}P_{3}^{2} + P_{1}^{2}P_{3}^{2})\] \[\qquad +\alpha_{112}(P_{1}^{4}P_{2}^{2} + P_{2}^{4}P_{3}^{2} + P_{1}^{4}P_{3}^{2} + P_{1}^{2}P_{2}^{4} + P_{2}^{2}P_{3}^{4} + P_{1}^{2}P_{3}^{4}) + \alpha_{113}(P_{1}^{2}P_{2}^{2}P_{3}^{2})\] \[\qquad +\alpha_{111}(P_{1}^{2} + P_{2}^{2} + P_{3}^{3})^{3}\]
+
+<|ref|>text<|/ref|><|det|>[[115, 561, 728, 578]]<|/det|>
+where \(\alpha_{ij}\) is the coefficient and depends on concentration \(c\) and temperature \(T\)
+
+<|ref|>text<|/ref|><|det|>[[115, 582, 470, 599]]<|/det|>
+\(f_{\mathrm{grad}}\) represents the gradient energy density,
+
+<|ref|>equation<|/ref|><|det|>[[115, 600, 765, 635]]<|/det|>
+\[f_{\mathrm{grad}} = \frac{1}{2} G_{11}((P_{1,1})^{2} + (P_{1,2})^{2} + (P_{1,3})^{2} + (P_{2,1})^{2} + (P_{2,2})^{2} + (P_{2,3})^{2} + (P_{3,1})^{2} + (P_{3,2})^{2} + (P_{3,3})^{2}) \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[115, 636, 881, 671]]<|/det|>
+where \(G_{11}\) is the gradient energy coefficient. \(f_{\mathrm{couple}}\) represents the couple effect caused by lattice strain \(\epsilon_{\mathrm{local}}(33)\)
+
+<|ref|>equation<|/ref|><|det|>[[115, 672, 593, 718]]<|/det|>
+\[f_{\mathrm{couple}} = -(q_{11}\epsilon_{11} + q_{12}\epsilon_{22} + q_{12}\epsilon_{33})P_{1}^{2} - (q_{11}\epsilon_{22} + q_{12}\epsilon_{11} + q_{12}\epsilon_{33})P_{2}^{2}\] \[-(q_{11}\epsilon_{33} + q_{12}\epsilon_{11} + q_{12}\epsilon_{22})P_{3}^{2} - 2q_{44}(\epsilon_{12}P_{1}P_{2} + \epsilon_{23}P_{2}P_{3} + \epsilon_{13}P_{1}P_{3})~,\]
+
+<|ref|>text<|/ref|><|det|>[[115, 720, 882, 777]]<|/det|>
+where \(q_{11} = C_{11}Q_{11} + 2C_{12}Q_{12}\) , \(q_{12} = C_{11}Q_{12} + C_{12}(Q_{11} + Q_{12})\) , \(q_{44} = 2C_{44}Q_{44}\) , \(C_{11}\) , \(C_{12}\) , and \(C_{44}\) is the elastic constants in Voigt's notation and \(Q_{\mathrm{ij}}\) is the electrostrictive coefficients. \(f_{\mathrm{elas}}\) is the long- range elastic interaction energy densities and \(f_{\mathrm{elec}}\) is the electrostatic interaction energy densities.
+
+<|ref|>text<|/ref|><|det|>[[115, 781, 882, 881]]<|/det|>
+\(f_{\mathrm{elas}} = \frac{1}{2} c_{ijkl}e_{ij}e_{kl} = \frac{1}{2} c_{ijkl}(\epsilon_{ij} - \epsilon_{ij}^{0})(\epsilon_{kl} - \epsilon_{kl}^{0})\) , where \(c_{ijkl}\) is the elastic constant tensor, \(\epsilon_{ij}\) the total strain, \(\epsilon^{0}_{kl}\) the electrostrictive stress- free strain, i.e., \(\epsilon^{0}_{kl} = Q_{ijkl}P_{k}P_{l}\) . \(f_{\mathrm{elec}} = f_{\mathrm{dipole}} + f_{\mathrm{depola}} + f_{\mathrm{appl}}\) , where \(f_{\mathrm{dipole}}\) is the dipole- dipole interaction caused by polarization, \(f_{\mathrm{depola}}\) the depolarization energy density and \(f_{\mathrm{appl}}\) the energy density caused by applied electric field. The dimensionless parameters used in our simulations:
+
+<|ref|>equation<|/ref|><|det|>[[135, 881, 685, 900]]<|/det|>
+\[\alpha_{1} = -0.1134, \alpha_{11} = -2.2896, \alpha_{12} = -7.5572, \alpha_{111} = 12.94, \alpha_{112} = 1.776, \alpha_{123} = 144.6.\]
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[135, 80, 644, 99]]<|/det|>
+\[C_{11} = 1780, C_{12} = 964, C_{44} = 1220, Q_{11} = 0.1, Q_{12} = -0.034, Q_{44} = 0.029.\]
+
+<|ref|>text<|/ref|><|det|>[[114, 105, 883, 185]]<|/det|>
+The temporal evolution of the spontaneous polarization field \((P)\) can be obtained by solving the time dependent Ginzburg Landau (TDGL) equation: \(\frac{dP_{i}(x,t)}{dt} = - M\frac{\delta F}{\delta P_{i}(X,t)}, i = 1,2,3\) , where \(M\) is the kinetic coefficient, \(F\) is the total free energy, and \(t\) is time.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 216, 256, 234]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[115, 241, 883, 277]]<|/det|>
+The data that support the findings of this study are available from the corresponding authors upon request.
+
+<|ref|>text<|/ref|><|det|>[[112, 300, 884, 565]]<|/det|>
+29. D. Wang, X. Ke, Y. Wang, J. Gao, Y. Wang, L. Zhang, S. Yang, X. Ren, Phase diagram of polar states in doped ferroelectric systems. Phys. Rev. B 86, 054120 (2012). doi: 10.1103/PhysRevB.86.054120.
+30. S. Semenovskaya, A. G. Khachaturyan, Development of ferroelectric mixed states in a random field of static defects. J. Appl. Phys. 83, 5125-5136 (1998). doi: 10.1063/1.367330.
+31. Y. L. Li, L. E. Cross, L. Q. Chen, A phenomenological thermodynamic potential for BaTiO₃ single crystals. J. Appl. Phys. 98, (2005). doi: 10.1063/1.2042528.
+32. L. Zhang, H. Wang, D. Wang, M. Guo, X. Lou, D. Wang, A New Strategy for Large Dynamic Piezoelectric Responses in Lead-Free Ferroelectrics: The Relaxor/Morphotropic Phase Boundary Crossover. Adv. Funct. Mater. 30, 2004641 (2020). doi: 10.1002/adfm.202004641.
+33. Y. L. Li, S. Y. Hu, Z. K. Liu, L. Q. Chen, Effect of substrate constraint on the stability and evolution of ferroelectric domain structures in thin films. Acta Mater. 50, 395-411 (2002). doi: 10.1016/S1359-6454(01)00360-3.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[43, 92, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 365, 150]]<|/det|>
+SupplementaryInformation2. pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__03e6375d91ba2acc0d93fa9c97f15a5154400d7aed2f4249391cfd96e1971e8e/images_list.json b/preprint/preprint__03e6375d91ba2acc0d93fa9c97f15a5154400d7aed2f4249391cfd96e1971e8e/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..14fb0e567f6c2c0283846bf16b52bf381067c7ed
--- /dev/null
+++ b/preprint/preprint__03e6375d91ba2acc0d93fa9c97f15a5154400d7aed2f4249391cfd96e1971e8e/images_list.json
@@ -0,0 +1,77 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 61,
+ 100,
+ 940,
+ 360
+ ]
+ ],
+ "page_idx": 11
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 68,
+ 75,
+ 925,
+ 685
+ ]
+ ],
+ "page_idx": 12
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 78,
+ 65,
+ 900,
+ 580
+ ]
+ ],
+ "page_idx": 13
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 72,
+ 66,
+ 911,
+ 440
+ ]
+ ],
+ "page_idx": 14
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5",
+ "footnote": [],
+ "bbox": [
+ [
+ 68,
+ 61,
+ 925,
+ 519
+ ]
+ ],
+ "page_idx": 15
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a/images_list.json b/preprint/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..877d054b4e4507a255cfb1b238f183e2774156db
--- /dev/null
+++ b/preprint/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a/images_list.json
@@ -0,0 +1,122 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "FIG. 1. Three different structural states of 2D vortices/rotors - hyperuniformity for Euler point vortices (A) and QG rotors/surface rotors (B), (C) phase enrichment induced by circulation differences where green (black) represents vortices of high (low) circulation, and (D) crystallization arising from hydrosteric interactions. The insets of (A), (B) and (C) show the structure factor, \\(S(q)\\) . In (A) and (B) \\(S(q)\\) decays to zero at small \\(q\\) , indicating that the distribution is hyperuniform. In (C) the structure factor shows the six distinct peaks of a hexagonal lattice.",
+ "footnote": [],
+ "bbox": [
+ [
+ 168,
+ 68,
+ 836,
+ 205
+ ]
+ ],
+ "page_idx": 2
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "FIG. 2. (A) A representation of a membrane rotor — a disk rotating due to a torque \\(\\tau\\) in the plane of the membrane. (B) The velocity field due to a membrane rotor (solid line) which scales as a point vortex \\(v \\sim 1 / r\\) at small distances (dotted), \\(r / \\lambda \\ll 1\\) , transitioning to a QG behavior at large distances \\(v \\sim 1 / r^2\\) (dashed). (C) Contour dynamics of an ellipse with radii ratios \\(r_l / r_s \\leq 3\\) , where \\(r_l\\) ( \\(r_s\\) ) is the major (minor) axis. Starting from the same contour, the dynamics differ according to the radius relative to the SD length. Blue is in the limit \\(r_l \\ll \\lambda\\) . In this limit the ellipse is rotating as a rigid body, as predicted by Kelvin (38) for an elliptic patch in an Euler fluid. Black is in the limit \\(r_l \\gg \\lambda\\) , no longer conserving its shape since the large distance flow is in the quasigeostrophic regime. (D) 200 point membrane rotors, blue is the initial random configuration, black is the final configuration. Solid line shows typical trajectory of an individual vortex. Note that the area did not change considerably since the system of vortices is self-bounding. (E) the relative error in \\(\\mathcal{H}\\) and \\(M\\) over a few cycle times, \\(t_c\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 66,
+ 896,
+ 188
+ ]
+ ],
+ "page_idx": 3
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "FIG. 3. Hyperuniformity in ensembles of point vortices and rotors. (A) Snapshots of 10,000 point vortices initially (left) and at steady-state (right). Insets show the structure factor, \\(S(\\mathbf{q})\\) showing a distinct cavity at steady-state. (B) Angular average of the structure factor shown in A, in a log-log scale with solid line showing a \\(q^{1.3}\\) scaling. Error bars are standard deviation over 10 well separated timesteps. Inset shows the structure factor of the rotors shown in (C) with increasing hue corresponding to increased concentration \\(\\phi = (0.14, 0.24, 0.37, 0.54)\\) . Solid line is the same \\(\\alpha \\sim 1.3\\) scaling. (C) Steady state configurations of 2,000 membrane rotors with the corresponding structure factors, showing a transition from disordered hyperuniformity to a hexagonal lattice. (D) A plot of the returnity measuring the deviation of particle \\(i\\) at position \\(r_i\\) from its position at the previous cycle, \\(returnity = \\Delta r_i(t_{\\mathrm{cyc}}) / R\\) , where \\(R\\) is the initial radius of the ensemble. The cycle time, \\(t_{\\mathrm{cyc}}\\) , is defined at steady state as the distance between two adjacent minima of the function \\(f = \\sum_i^N \\Delta r_i(\\Delta t)\\) , where \\(\\Delta t\\) is the time difference. Color scheme is from blue to yellow with increasing deviation.",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 70,
+ 876,
+ 494
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "FIG. 4. Two populations of vortices with different circulations showing phase enrichment, \\(\\Gamma_{l} = 2\\pi\\) in black and \\(\\Gamma_{h} = 256\\pi\\) in green. (A) Steady-state configuration for ten thousand point vortices of a circulation ratio \\(\\gamma = \\Gamma_{h} / \\Gamma_{l} = 128\\) . Each inset shows a close-up view of one of the populations within the same physical region. (B) Density of the configuration in (A), \\(\\rho (r)\\) , averaged over angle as a function of distance from the center. Note how density fluctuations are suppressed for the high circulation vortices, as is more clearly observed by the averaged structure factor, \\(S(q)\\) , in (C), where the solid green line shows a \\(\\sim q^{1.3}\\) power law. (D) The second moment for \\(N = 10,000\\) vortices. Plotted separately for the high (in green) and low (in black) vortices at steady state as a function of \\(\\gamma\\) (i.e. increasing \\(\\Gamma_{h}\\) ). (E) LOSSLESS compression for the two populations showing an increase (decrease) in file size (an estimate of entropy) for the low (high) circulation vortices over a couple of cycles. In blue is the file size for the total system. Solid line is a moving average, time is normalized by an average cycle time \\(t_{c}\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 123,
+ 75,
+ 874,
+ 325
+ ]
+ ],
+ "page_idx": 5
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 55,
+ 100,
+ 940,
+ 285
+ ]
+ ],
+ "page_idx": 8
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 58,
+ 510,
+ 947,
+ 650
+ ]
+ ],
+ "page_idx": 8
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 55,
+ 102,
+ 940,
+ 608
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 55,
+ 50,
+ 940,
+ 352
+ ]
+ ],
+ "page_idx": 10
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a_det.mmd b/preprint/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..d38a5067f3071be764d6e0d73f82943301dd519b
--- /dev/null
+++ b/preprint/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a/preprint__0417a97ecc0d13717181d9623733f3148d5ba9e7ac583590ea0cf0862739b60a_det.mmd
@@ -0,0 +1,238 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 888, 175]]<|/det|>
+# Hyperuniformity and phase enrichment in vortex and rotor assemblies
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 574, 238]]<|/det|>
+Naomi Oppenheimer ( naomiop@gmail.com ) Tel Aviv University https://orcid.org/0000- 0002- 8212- 3404
+
+<|ref|>text<|/ref|><|det|>[[44, 243, 588, 383]]<|/det|>
+David Stein Flatiron Institute Matan Yah Ben Zion New York University https://orcid.org/0000- 0002- 9876- 787X Michael Shelley Flatiron Institute https://orcid.org/0000- 0002- 4835- 0339
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 418, 102, 436]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 455, 877, 499]]<|/det|>
+Keywords: Particle Ensembles, Two- dimensional Fluid, Spontaneous Self- assembly, Hamiltonian Structure, Topological Defects
+
+<|ref|>text<|/ref|><|det|>[[44, 515, 296, 536]]<|/det|>
+Posted Date: April 26th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 553, 463, 574]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 385285/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 591, 910, 635]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 669, 945, 713]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on February 10th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 28375- 9.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[160, 63, 841, 81]]<|/det|>
+# Hyperuniformity and phase enrichment in vortex and rotor assemblies
+
+<|ref|>text<|/ref|><|det|>[[87, 93, 920, 181]]<|/det|>
+Naomi Oppenheimer, \(^{1,*}\) David B. Stein, \(^{2}\) Matan Yah Ben Zion, \(^{3}\) and Michael J. Shelley \(^{2,4,}\) \(^{1}\) School of Physics, and the Center for Physics and Chemistry of Living Systems, Tel Aviv University, Tel Aviv 6997801, Israel \(^{2}\) Center for Computational Biology, Flatiron Institute, New York, NY 10010, USA \(^{3}\) Laboratoire Gulliver, UMR CNRS 7083, ESPCI Paris, PSL Research University, 75005 Paris, France \(^{4}\) Courant Institute, New York University, New York, NY 10012, USA(Dated: April 13, 2021)
+
+<|ref|>text<|/ref|><|det|>[[174, 188, 830, 360]]<|/det|>
+Ensembles of particles rotating in a two- dimensional fluid can exhibit chaotic dynamics yet develop signatures of hidden order. Such "rotors" are found in the natural world spanning vastly disparate length scales — from the rotor proteins in cellular membranes to models of atmospheric dynamics. Here we show that an initially random distribution of either ideal vortices in an inviscid fluid, or driven rotors in a viscous membrane, spontaneously self assembles. Despite arising from drastically different physics, these systems share a Hamiltonian structure that sets geometrical conservation laws resulting in distinct structural states. We find that the rotationally invariant interactions isotropically suppress long wavelength fluctuations — a hallmark of a disordered hyperuniform material. With increasing area fraction, the system orders into a hexagonal lattice. In mixtures of two co- rotating populations, the stronger population will gain order from the other and both will become phase enriched. Finally, we show that classical 2D point vortex systems arise as exact limits of the experimentally accessible microscopic membrane rotors, yielding a new system through which to study topological defects.
+
+<|ref|>text<|/ref|><|det|>[[86, 384, 487, 558]]<|/det|>
+Two- dimensional (or nearly so) fluid flows show rich and complex vortical dynamics. These can arise from flow interactions with boundaries (1, 2), the inverse cascades of 2D turbulence (3- 5), from Coriolis force dominated atmospheric flows (6), and from quantization effects in super fluid He- II (7, 8). Point vortices have long been staples for the modeling of such inertially dominated inviscid flows. Kirchoff (9) was the first to describe point vortices using a Hamiltonian framework and his work was extended by many others [e.g. (10- 13)], notably, Onsager (14) in his statistical mechanics treatment of 2D turbulence as clouds of point vortices.
+
+<|ref|>text<|/ref|><|det|>[[86, 559, 487, 775]]<|/det|>
+Remarkably, structurally identical Hamiltonian and moment constraints can arise in the microscopic viscously- dominated realm from a strict balance of dissipation with drive on immersed rotating objects. These objects include models of interacting transmembrane ATP- synthase "rotor- proteins" (15- 17), and the planar interactions of rotors — microscopic particles driven to rotate by an external torque (18, 19). We refer to such systems as BDD systems, as in balanced drive and dissipation. In modeling rotational BDD systems other physical effects may also come into play, such as steric interactions, that can yield interesting complexities (17). Interacting assemblies of driven- to- rotate particles has become an area of intensifying interest in the active matter community (18- 26)
+
+<|ref|>text<|/ref|><|det|>[[86, 776, 487, 848]]<|/det|>
+Here we study both point vortices and a BDD rotor system of rotationally- driven microscopic particles — membrane rotors — immersed in a flat membrane. We show that in both systems, their Hamiltonian conservation laws lead to distinct structural states — hyperuniformity, phase enrichment and crystallization (see Fig. 1), not yet observed for either system. We use the Hamiltonian to derive a bound for spatial correlations requiring hyperuniformity. We demonstrate numerically that rotational dynamics robustly self- assembles particles into a disordered hyperuniform 2D material; This self- assembly is insensitive to the details of the hydrodynamic interactions, steric repulsion, or the presence of impurities in the form of different rotation rates. At steady state, the long wavelength configuration is characterized by an isotropically vanishing structure factor, \(S(\mathbf{q} \to 0) \to 0\) (where \(\mathbf{q}\) is the wavevector), leading to an isotropic band- gap (27- 29).
+
+<|ref|>text<|/ref|><|det|>[[516, 384, 916, 573]]<|/det|>
+mity, phase enrichment and crystallization (see Fig. 1), not yet observed for either system. We use the Hamiltonian to derive a bound for spatial correlations requiring hyperuniformity. We demonstrate numerically that rotational dynamics robustly self- assembles particles into a disordered hyperuniform 2D material; This self- assembly is insensitive to the details of the hydrodynamic interactions, steric repulsion, or the presence of impurities in the form of different rotation rates. At steady state, the long wavelength configuration is characterized by an isotropically vanishing structure factor, \(S(\mathbf{q} \to 0) \to 0\) (where \(\mathbf{q}\) is the wavevector), leading to an isotropic band- gap (27- 29).
+
+<|ref|>text<|/ref|><|det|>[[516, 574, 916, 730]]<|/det|>
+In classical mechanics, symmetries of the Hamiltonian \(\mathcal{H}\) restrict the phase- space of the conjugate variables, position and momentum. However, in 2D point vortex or BDD point rotor systems, the conjugate variables are the actual spatial coordinates of the ensemble \(\{x_{i}\}\) and \(\{y_{i}\}\) . The conservation laws are therefore geometrical in nature, bounding the proximity and distribution of the particles. For both point vortices and membrane rotors, as well as for a myriad of other 2D rotating systems (18- 21, 24, 30), the dynamics are dictated by Hamilton's equations,
+
+<|ref|>equation<|/ref|><|det|>[[668, 737, 914, 755]]<|/det|>
+\[\Gamma_{i}\mathbf{v}_{1} = \partial_{i}^{\perp}\mathcal{H}, \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[516, 763, 916, 836]]<|/det|>
+where \(\partial_{i}^{\perp} = (\partial y_{i}, - \partial x_{i})\) , \(\mathbf{v}_{1}\) is the velocity of rotor \(i\) , and \(\Gamma_{i}\) is the circulation (proportional to the magnitude of the torque for rotors). Our finding, as we will show, is that the spatial arrangements of point vortices, as measured by \(S(\mathbf{q})\) , are dictated by the Hamiltonian,
+
+<|ref|>equation<|/ref|><|det|>[[617, 842, 914, 877]]<|/det|>
+\[\mathcal{H}[\rho (\mathbf{r})] = \frac{N\Gamma^{2}}{4\pi}\int \mathrm{d}\mathbf{q}\frac{S(\mathbf{q})}{q^{2}}. \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[516, 883, 916, 911]]<|/det|>
+To derive Eq. 2 and to find the Hamiltonian of \(N\) particles, we first describe the flow due to a single vortex in
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[168, 68, 836, 205]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 225, 919, 293]]<|/det|>
+FIG. 1. Three different structural states of 2D vortices/rotors - hyperuniformity for Euler point vortices (A) and QG rotors/surface rotors (B), (C) phase enrichment induced by circulation differences where green (black) represents vortices of high (low) circulation, and (D) crystallization arising from hydrosteric interactions. The insets of (A), (B) and (C) show the structure factor, \(S(q)\) . In (A) and (B) \(S(q)\) decays to zero at small \(q\) , indicating that the distribution is hyperuniform. In (C) the structure factor shows the six distinct peaks of a hexagonal lattice.
+
+<|ref|>text<|/ref|><|det|>[[86, 320, 487, 450]]<|/det|>
+an ideal Euler fluid and show its equivalence to a point rotor in a viscous membrane. We then use the linearity of the equations to extend the result to the many- body case. An ideal point vortex is given by a singular vorticity, \(\omega = \nabla \times \mathbf{v} = \delta (\mathbf{r})\) . A 2D incompressible fluid can be described using a stream function \(\Psi\) such that the velocity, \(\mathbf{v}\) , is given by \(\mathbf{v} = \partial^{\perp}\Psi\) . This equation, combined with the equation above gives, \(\Psi = - \frac{1}{2\pi}\log r\) (12). The flow, \(\mathbf{v}(r)\) , therefore, scales as \(1 / r\) , where \(r = |\mathbf{r}|\) .
+
+<|ref|>text<|/ref|><|det|>[[86, 450, 487, 552]]<|/det|>
+We switch now to a point rotor in a viscous membrane, driven by an external torque \(\tau\) . Following Saffman and Delbruck's seminal work (31), and many others that followed (32- 34), we assume that the membrane is incompressible \((\nabla \cdot \mathbf{v} = 0)\) , and that inertia is negligible. Under these assumptions, the Stokes momentum conservation equation for the membrane reads,
+
+<|ref|>equation<|/ref|><|det|>[[140, 559, 485, 597]]<|/det|>
+\[0 = \eta_{2D}\nabla^{2}\mathbf{v} + \eta_{3D}\frac{\partial\mathbf{u}^{\pm}}{\partial z}\bigg|_{z = 0^{\pm}} + \tau \partial^{\perp}\delta (\mathbf{r}), \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[86, 607, 487, 760]]<|/det|>
+where \(\mathbf{v}\) is the 2D velocity in the plane of the membrane, \(\mathbf{u}^{\pm}\) is the 3D flow in the outer fluids, \(\eta_{2D}\) is the 2D viscosity, and \(\eta_{3D}\) is the viscosity of the outer fluids. The second term on the right hand side is the surface shear stress of the outer fluids, and the third term is the force due to a rotating point object. There is no pressure contribution when the motion is purely rotational. This equation is coupled to the equations of the outer fluids. It is easy to solve the above equations using a 2D Fourier Transform \((\tilde{F} (\mathbf{q}) = \int_{-\infty}^{\infty}\int_{-\infty}^{\infty}F(\mathbf{r})e^{-i\mathbf{q}\cdot \mathbf{r}}d^{2}r)\) , giving:
+
+<|ref|>equation<|/ref|><|det|>[[156, 768, 485, 802]]<|/det|>
+\[\tilde{\mathbf{v}} (\mathbf{q}) = \Gamma \partial^{\perp}\tilde{\Psi} \quad ; \quad \tilde{\Psi} = \frac{1}{q(q + \lambda^{-1})}, \quad (4)\]
+
+<|ref|>text<|/ref|><|det|>[[86, 812, 487, 912]]<|/det|>
+where \(\Gamma = \tau /\eta_{2D}\) , and \(\lambda = \eta_{2D} / 2\eta_{3D}\) is the Saffman Delbruck length. At small distances ( \(r \ll \lambda\) ) momentum travels in the plane of the membrane. At large distances ( \(r \gg \lambda\) ) momentum travels through the outer fluid as well (35, 36). In real space \(\Psi (\mathbf{r}) = 1 / 4(H_{0}(r / \lambda) - Y_{0}(r / \lambda))\) , where \(H_{0}\) and \(Y_{0}\) are zeroth order Struve function and Bessel function of the second kind respectively.
+
+<|ref|>text<|/ref|><|det|>[[513, 320, 916, 596]]<|/det|>
+In the limit of small distances, \(r \ll \lambda\) , the stream function is, \(\Psi \approx - \frac{1}{2\pi}\log r\) , i.e. exactly the same as for an ideal point vortex. In the opposite limit, \(r \gg \lambda\) , the stream function becomes \(\Psi = \frac{1}{2\pi r}\) as in quasigeostrophic (QG) flows — atmospheric or oceanic flows coming from gradients in pressure coupled to the Coriolis force (37), or driven rotors on the surface of a fluid (22). A membrane rotor, therefore, transitions from a point vortex for Euler at small distances to that of QG flow at large distances. The velocity is given by derivatives of \(\Psi\) and is thus proportional to \(1 / r\) ( \(1 / r^{2}\) ) in the limit of small (large) distances (see Fig. 2B). For simplicity, we work primarily in the limit of small distances, \(r \ll \lambda\) , since in this limit the dynamics in a membrane converge with those of point vortices (many results still apply to the more general case as shown in the SI). In what follows, we will use "point vortices" when there are only hydrodynamic interactions and "rotors" when the particles have steric interactions in addition to hydrodynamic ones.
+
+<|ref|>text<|/ref|><|det|>[[513, 607, 916, 912]]<|/det|>
+The dynamics of \(N\) point vortices follows from the Hamiltonian \(\mathcal{H} = \frac{1}{2}\sum_{i \neq j}\Gamma_{i}\Gamma_{j}\Psi (|\mathbf{r}_{i} - \mathbf{r}_{j}|)\) , where \(\Gamma_{i}\) is the circulation of vortex \(i\) (in a membrane \(\Gamma_{i} = \tau_{i} / \eta_{2D}\) ). The Hamiltonian depends on the conjugate variables \(\mathbf{r}_{i} = (x_{i}, y_{i})\) , [normalized by the circulation \(\sqrt{|\Gamma_{i}|} \operatorname{sgn}(\Gamma_{i})\) ], i.e. the positions of the vortices (12). The symmetries of the Hamiltonian correspond to conservation laws (39). In this case, we have symmetries with respect to translation in time, space, and rotation, corresponding to conservation of the Hamiltonian itself, and of the first and second moments of the distribution, \(\mathbf{L} = \sum_{i}\Gamma_{i}\mathbf{r}_{i} (= \mathbf{0}\) wlog), and \(M = \sum_{i,j}\Gamma_{i}r_{i}^{2}\) . Thus, the initial area cannot change dramatically, particles cannot drift to infinity since the second moment is fixed, nor can they collapse to a point since the Hamiltonian is conserved. These properties are readily observed in simulations. Figure 2D shows typical trajectories of 200 membrane rotors. The initial distribution is random in a predefined finite area, and the dynamics are chaotic (40). The final configuration occupies nearly the same region of space as the initial configuration does, and the conservation laws hold
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 66, 896, 188]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[84, 201, 919, 323]]<|/det|>
+FIG. 2. (A) A representation of a membrane rotor — a disk rotating due to a torque \(\tau\) in the plane of the membrane. (B) The velocity field due to a membrane rotor (solid line) which scales as a point vortex \(v \sim 1 / r\) at small distances (dotted), \(r / \lambda \ll 1\) , transitioning to a QG behavior at large distances \(v \sim 1 / r^2\) (dashed). (C) Contour dynamics of an ellipse with radii ratios \(r_l / r_s \leq 3\) , where \(r_l\) ( \(r_s\) ) is the major (minor) axis. Starting from the same contour, the dynamics differ according to the radius relative to the SD length. Blue is in the limit \(r_l \ll \lambda\) . In this limit the ellipse is rotating as a rigid body, as predicted by Kelvin (38) for an elliptic patch in an Euler fluid. Black is in the limit \(r_l \gg \lambda\) , no longer conserving its shape since the large distance flow is in the quasigeostrophic regime. (D) 200 point membrane rotors, blue is the initial random configuration, black is the final configuration. Solid line shows typical trajectory of an individual vortex. Note that the area did not change considerably since the system of vortices is self-bounding. (E) the relative error in \(\mathcal{H}\) and \(M\) over a few cycle times, \(t_c\) .
+
+<|ref|>text<|/ref|><|det|>[[85, 350, 487, 394]]<|/det|>
+to high precision in our simulations, as shown in Fig. 2E. This self confining property of vortex dynamics has further consequences, as we now show.
+
+<|ref|>text<|/ref|><|det|>[[86, 394, 488, 669]]<|/det|>
+Hyperuniformity. Hyperuniformity is the suppression of density- density fluctuations at small wavenumbers (or correspondingly, at large distances) (41- 43). Disordered hyperuniformity can emerge due to short ranged interactions such as those that arise in sheared suspensions (30, 44, 45), jammed materials (46), and for spinning particles (47). Here we will show hyperuniformity emerging from long ranged interactions, similar to its emergence in sedimentation of irregular objects (48). A good way to characterize hyperuniformity is the structure factor, defined as \(S(\mathbf{q}) = N^{- 1}|\tilde{\rho} (\mathbf{q})|^2\) , where \(\rho (\mathbf{r}) = \sum_i \delta (\mathbf{r} - \mathbf{r}_i)\) is the coarse grained density. In a hyperuniform material, \(S(q)\) goes to zero as a power law at small wavenumbers. We argue that point vortices must be hyperuniform due to the conservation of the Hamiltonian. For a density of rotors, the Hamiltonian is given by \(\mathcal{H}[\rho (\mathbf{r})] \sim \frac{\Gamma^2}{2} \int \mathrm{d}\mathbf{r} \int \mathrm{d}\mathbf{r}' \rho (\mathbf{r}) \rho (\mathbf{r}') \psi (|\mathbf{r} - \mathbf{r}'|)\) . Using the convolution theorem, we find a general relation between the Hamiltonian and the structure factor
+
+<|ref|>equation<|/ref|><|det|>[[172, 675, 487, 710]]<|/det|>
+\[\mathcal{H}[\rho (\mathbf{r})] = \frac{N\Gamma^2}{4\pi} \int \mathrm{d}\mathbf{q} S(\mathbf{q}) \tilde{\Psi} (\mathbf{q}). \quad (5)\]
+
+<|ref|>text<|/ref|><|det|>[[86, 721, 488, 840]]<|/det|>
+In the case of point vortices, \(\tilde{\Psi} (\mathbf{q}) = 1 / q^2\) , which gives Eq. 2. For the integral of Eq. 2 to converge in 2D, \(S(\mathbf{q}) \sim q^\alpha\) near the origin, and we must have \(\alpha > 0\) . In other words, an ensemble of point vortices is hyperuniform (a similar calculation in the QG limit, where \(\tilde{\Psi} = \lambda /q\) , yields \(\alpha > - 1\) ). Figures 3B and 4C, show an apparent \(\alpha \sim 1.3\) scaling for point vortices, consistent with the above argument.
+
+<|ref|>text<|/ref|><|det|>[[86, 841, 488, 912]]<|/det|>
+Using simulations we show that a set of \(N\) vortices, uniformly distributed within a radius \(R\) , evolves to a disordered steady- state with a hidden order visible to the naked eye (compare Figures 3A left and right). We quantitatively characterize the system in steady- state in three
+
+<|ref|>text<|/ref|><|det|>[[515, 350, 917, 740]]<|/det|>
+ways: (1) The structure factor. At steady- state \(S(\mathbf{q})\) shows a distinct cavity, at \(q \approx 0\) , \(S(\mathbf{q}) \to 0\) , for both points vortices (Fig. 3A) and rotors (Fig. 3C). All simulations produce a hyperuniform arrangement. (2) Perturbations. We demonstrate that hyperuniformity is robust under different perturbations, be it in the form of numerical errors, repulsive interactions, or impurities (in the next section). For point vortices, the steady state appears later and later as the timestep is decreased, suggesting that perturbations are necessary for convergence, here very small but persistent timestepping errors (49). Adding steric interactions, hyperuniformity appears on a timescale that is independent of the timestep. Moreover, with steric interactions, as the area fraction \(\phi\) of the particles is increased, the system transitions from disordered hyperuniform, to an ordered hyperuniform hexagonal lattice at \(\phi \sim 0.5\) , as can be seen in Fig. 3C. The inset of Fig. 3B shows the averaged structure factor where at intermediate area fractions we see Percus- Yevick type features for the structure factor of disks (50). (3) The returnity. We observe that at late times the ensemble of point vortices rotates almost as a rigid body and each particle goes back to its position at the previous cycle. We measure particle deviations by what we term the "returnity" (see Fig. 3D for details). The system may seem to have reached an absorbing state, but the motion of vortices over many cycles is still chaotic.
+
+<|ref|>text<|/ref|><|det|>[[515, 768, 917, 912]]<|/det|>
+Rotation induced phase enrichment. We now show that for mixed populations of fast and slow rotating particles, there is phase enrichment of both populations and hyperuniformity of the fast ones. Consider a mixture of two equally numbered populations ( \(\rho_l = \rho_h\) at \(t = 0\) ) initially placed within the same radius \(R\) . \(\rho_l\) rotates slowly with \(\Gamma_l \ll \Gamma_h\) , where \(\Gamma_h\) is the circulation of the second population. Figure 4A shows long- time simulation results for 10,000 point vortices. The two populations behave very differently. The fast vortices remain in
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 70, 876, 494]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[84, 504, 919, 641]]<|/det|>
+FIG. 3. Hyperuniformity in ensembles of point vortices and rotors. (A) Snapshots of 10,000 point vortices initially (left) and at steady-state (right). Insets show the structure factor, \(S(\mathbf{q})\) showing a distinct cavity at steady-state. (B) Angular average of the structure factor shown in A, in a log-log scale with solid line showing a \(q^{1.3}\) scaling. Error bars are standard deviation over 10 well separated timesteps. Inset shows the structure factor of the rotors shown in (C) with increasing hue corresponding to increased concentration \(\phi = (0.14, 0.24, 0.37, 0.54)\) . Solid line is the same \(\alpha \sim 1.3\) scaling. (C) Steady state configurations of 2,000 membrane rotors with the corresponding structure factors, showing a transition from disordered hyperuniformity to a hexagonal lattice. (D) A plot of the returnity measuring the deviation of particle \(i\) at position \(r_i\) from its position at the previous cycle, \(returnity = \Delta r_i(t_{\mathrm{cyc}}) / R\) , where \(R\) is the initial radius of the ensemble. The cycle time, \(t_{\mathrm{cyc}}\) , is defined at steady state as the distance between two adjacent minima of the function \(f = \sum_i^N \Delta r_i(\Delta t)\) , where \(\Delta t\) is the time difference. Color scheme is from blue to yellow with increasing deviation.
+
+<|ref|>text<|/ref|><|det|>[[86, 680, 487, 827]]<|/det|>
+a disk of only slightly smaller size than their initial area (Fig. 4B). The slow particle distribution shows a significant expansion. In addition, there is a striking difference when comparing the independently computed structure factors of these two populations, the fast vortices are hyperuniform with the same scaling as before, \(S(q) \sim q^{1.3}\) , whereas the slow ones show no signs of hyperuniformity (Fig. 4C). This difference is dramatic enough to be visible in a cursory examination of the separate distributions; see Fig. 4A.
+
+<|ref|>text<|/ref|><|det|>[[86, 840, 487, 911]]<|/det|>
+Using a heuristic model, we show that the conservation laws allow two solutions at steady- state. In one solution, the two populations remain confined to a circle of the same radius. In the second solution, the radius of the slower population expands, while the radius of the faster
+
+<|ref|>text<|/ref|><|det|>[[515, 682, 917, 899]]<|/det|>
+population contracts. We then show that the segregated solution is the one that maximizes the number of states in the system. For simplicity, we assume that the final steady states are uniform (not true for the slow vortices as is clear from Fig. 4B). There are two possible solutions where \(\mathcal{H}\) and \(M\) are conserved — in the first, the initial radius, \(R\) , does not change; in the second, the radius of the fast vortices slightly decreases to \(R_h\) , allowing the slow vortices to expand to a larger radius \(R_l\) given by \(R_l^2 = (\gamma + 1)R^2 - R_h^2 \gamma\) , where \(\gamma = \Gamma_h / \Gamma_l\) (see Fig. 4D). Linearly expanding in \(1 / \gamma\) , we find that \(R_h \simeq R(1 - \beta / \gamma)\) for the high circulation vortices, where \(\beta\) is a positive prefactor of order 1. The slow vortices asymptote to \(R_l \simeq R\sqrt{1 + 2\beta} + O(1 / \gamma)\) . The simulation results indicate that the outer radius indeed asymptotes to a larger valued
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[123, 75, 874, 325]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 338, 919, 460]]<|/det|>
+FIG. 4. Two populations of vortices with different circulations showing phase enrichment, \(\Gamma_{l} = 2\pi\) in black and \(\Gamma_{h} = 256\pi\) in green. (A) Steady-state configuration for ten thousand point vortices of a circulation ratio \(\gamma = \Gamma_{h} / \Gamma_{l} = 128\) . Each inset shows a close-up view of one of the populations within the same physical region. (B) Density of the configuration in (A), \(\rho (r)\) , averaged over angle as a function of distance from the center. Note how density fluctuations are suppressed for the high circulation vortices, as is more clearly observed by the averaged structure factor, \(S(q)\) , in (C), where the solid green line shows a \(\sim q^{1.3}\) power law. (D) The second moment for \(N = 10,000\) vortices. Plotted separately for the high (in green) and low (in black) vortices at steady state as a function of \(\gamma\) (i.e. increasing \(\Gamma_{h}\) ). (E) LOSSLESS compression for the two populations showing an increase (decrease) in file size (an estimate of entropy) for the low (high) circulation vortices over a couple of cycles. In blue is the file size for the total system. Solid line is a moving average, time is normalized by an average cycle time \(t_{c}\) .
+
+<|ref|>text<|/ref|><|det|>[[86, 487, 488, 516]]<|/det|>
+constant as \(\gamma\) increases and does not increase indefinitely (see Fig. 4D and SI).
+
+<|ref|>text<|/ref|><|det|>[[86, 517, 488, 737]]<|/det|>
+A solution with two different radii is therefore possible and is indeed observed at large circulation ratios. Such a solution is favored entropically since it maximizes the available states. Asymptotically at large \(\gamma\) , the main entropical contribution is volumetric, \(\Delta S_{\mathrm{volume}} = 2N \log (R_{\mathrm{final}} / R_{\mathrm{initial}})\) . Since the high circulation vortices hardly change radius, \(R_{h} \xrightarrow{\gamma \to \infty} R\) , the change in entropy is coming mainly from the expansion of the low circulation vortices and is given by \(\Delta S_{\mathrm{total}} \sim N \log (1 + 2\beta) > 0\) . Coupling the two populations allows one population to expand where before it was bounded (51). The situation is analogous to depletion interactions, where the net entropy of a system increases by condensing the large particles allowing for the small particles to explore a larger volume (52).
+
+<|ref|>text<|/ref|><|det|>[[86, 738, 488, 825]]<|/det|>
+A simple way to estimate the entropy in a system is by using LOSSLESS compression, as suggested by Refs. (53, 54). Compressing plots of particle positions in a system of 10,000 point vortices with circulation ratio \(\Gamma_{h} / \Gamma_{l} = 128\) shows an increase in file size for \(\rho_{l}\) and a decrease for \(\rho_{h}\) , while the combined system is increasing, see Fig. 4E.
+
+<|ref|>text<|/ref|><|det|>[[86, 827, 488, 911]]<|/det|>
+Discussion. We have shown that driven particles in a membrane or a soap film, as well as point vortices in an ideal 2D fluid, have geometrical conservation laws which limit their distribution. These conservation laws dictate different possible structural states — namely hyperuniformity and phase enrichment. We have shown that hy
+
+<|ref|>text<|/ref|><|det|>[[515, 486, 917, 631]]<|/det|>
+peruniformity is robust to several forms of perturbations whether arising due to numerical errors, steric interactions, or impurities in the form of low circulation vortices. For rotors with steric interactions, the unbounded ensemble crystallizes into a hexagonal lattice when the area fraction \(\phi \gtrsim 0.5\) (see also (17)). We have limited the discussion to membrane rotors and vortices, but the results hold for other settings in which mass is conserved in the 2D plane, e.g. particles at the surface of a fluid (see SI).
+
+<|ref|>text<|/ref|><|det|>[[515, 634, 917, 836]]<|/det|>
+What is especially interesting about our particular BDD system is its potential for experimental realizability, its moment and Hamiltonian structure, and that its near- field interactions (i.e. below the Saffman- Delbruck length) are identical to those of Euler point vortices. Further, the far- field interactions of membrane rotors are identical to those of point vortices of the semiquasigeostrophic equations (37, 55, 56) used to model atmospheric flows. Thus, to observe the interesting dynamical features we describe, one does not need to go to the atmospheric scale, or cool a fluid to near- zero temperature. In principle, one can simply observe microscopic particles on a soap film, in smectic films, a membrane, or even at the surface of a fluid (19, 22, 57, 58).
+
+<|ref|>text<|/ref|><|det|>[[515, 839, 917, 911]]<|/det|>
+Methods. Simulations. Simulations were performed in Python. Random initial configurations within the unit disk were found by rejection sampling (points in the unit rectangle were sampled uniformly, transformed to the rectangle \([- 1,1]^{2}\) , and those with \(r > 1\) were discarded). The initial Hamiltonian \(H_{0}\) is computed at \(t = 0\) , and the relative error \(\epsilon (t) = |H_{t} - H_{0}| / H_{0}\) is
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[86, 67, 488, 237]]<|/det|>
+monitored as a measure of fidelity. For simulations of rotors (i.e. with steric repulsion), a 5th order explicit Runge- Kutta method based on the Dormand- Prince scheme (59) with a fixed timestep size of \(\delta t = 10^{- 7}\) was used. Long integration times were required for simulations of point vortices, and for these simulations an explicit eighth- order adaptive method based on the Dormand- Prince scheme (60, 61) was used, with both relative and absolute tolerances set to \(10^{- 6}\) . The specific implementation of the scheme used was the \(DOP853\) method of scipy.integrate (62). For simulations of 10,000 point vortices with \(\Gamma = 2\pi\) , \(\epsilon (t) < 1.6 \times 10^{- 3}\) up to \(t \approx 16,000\) cycles, while for simulations with 5,000 vortices with \(\Gamma = 2\pi\) and 5,000 vortices with \(\Gamma = 256\pi\) , \(\epsilon (t) < 5 \cdot 10^{- 3}\) up to \(t \approx 10\) cycles. Time is normalized by the average cycle time, \(t_c \approx 4\pi^2 R^2 / \sum_i \Gamma_i\) , where \(R\) is the initial radius.
+
+<|ref|>text<|/ref|><|det|>[[86, 237, 488, 320]]<|/det|>
+Steric interactions were taken as the repulsive part of a harmonic potential, i.e. for two particles whose centers are distance \(r_i\) apart, \(F = - kr_{ij}\) if \(r_{ij} < 2a\) and zero otherwise. The use of a harmonic potential, rather than a sharp step function for hard core particles, provided improved numerical stability and convergence. A large \(k\) value was chosen to ensure no overlap between particles, \(k = 1 \cdot 10^6\) , for particles of size \(a = 0.01\) .
+
+<|ref|>text<|/ref|><|det|>[[86, 320, 488, 369]]<|/det|>
+Structure factor. To accurately compute the structure factor \(S(\mathbf{q})\) we use a type- 1 non- uniform fast- Fourier transform (63). Explicitly, points are restricted to a windowing region which is confined entirely within the unit disk. The frequencies \(\tilde{\rho} (\mathbf{q})\) are com
+
+<|ref|>text<|/ref|><|det|>[[515, 67, 917, 163]]<|/det|>
+puted for the first 512 modes in each direction, and the average value (i.e. \(\tilde{\rho} (0)\) ) is set to 0. This results in structure factors in the plane, such as those shown in Fig. 3. Except in those cases where crystallization occurs, these structure factors are azimuthally isotropic. To summarize this information, the angular average over the structure factor was calculated by slicing the result to 1000 equal bins between \(q_{\mathrm{min}}\) and \(q_{\mathrm{max}}\) and taking the mean of the results that fell within each slice.
+
+<|ref|>text<|/ref|><|det|>[[515, 163, 917, 237]]<|/det|>
+Compression. A plot of the positions of the point vortices was compressed using PNG with AGG backend. Each vortex was plotted by a single pixel. The total size of the plots was kept fixed in time. The figure size was chosen to minimize overlap between neighboring vortices but maintaining a computationally accessible file size.
+
+<|ref|>text<|/ref|><|det|>[[515, 237, 917, 366]]<|/det|>
+Acknowledgment We thank Haim Diamant for insightful discussions regarding the emergence of hyperuniformity from the conservation laws, to Martin Lenz for suggesting a simple heuristic model of the phase enrichment, and to Enkeleida Lushi. N.O. acknowledges supported by the Israel Science Foundation (grant No. 1752/20). M.J.S. acknowledges support by the National Science Foundation under Awards Nos. DMR- 1420073 (NYU MRSEC), DMS- 1620331, and DMR- 2004469.
+
+<|ref|>text<|/ref|><|det|>[[85, 420, 488, 912]]<|/det|>
+[1] R. King, Ocean Engineering 4, 141 (1977). [2] M. J. Shelley and J. Zhang, Annual Review of Fluid Mechanics 43, 449 (2011). [3] R. Fjortoft, Tellus 5, 225 (1953). [4] R. H. Kraichnan, Physics of Fluids 10, 1417 (1967). [5] D. Bernard, G. Boffetta, A. Celani, and G. Falkovich, Nature Physics 2, 124 (2006). [6] R. P. Behringer, S. D. Meyers, and H. L. Swinney, Physics of Fluids A: Fluid Dynamics 3, 1243 (1991). [7] A. Abrikosov, Sov. Phys. - JETP (Engl. Transl.); (United States) (1957). [8] M. R. Matthews, B. P. Anderson, P. C. Haljan, D. S. Hall, C. E. Wieman, and E. A. Cornell, Physical Review Letters 83, 2498 (1999), arXiv:9908209 [cond- mat]. [9] G. Kirchhoff, Vorlesungen über mathematische physik: mechanik, Vol. 1 (BG Teubner, 1876). [10] H. Aref, Annual Review of Fluid Mechanics 15, 345 (1983). [11] C. C. Lin, Proceedings of the National Academy of Sciences 27, 570 (1941). [12] P. K. Newton, The N- Vortex Problem, Applied Mathematical Sciences, Vol. 145 (Springer New York, New York, NY, 2001). [13] A. Bogatskiy and P. Wiegmann, Physical Review Letters 122, 214505 (2019), arXiv:1812.00763. [14] L. Onsager, Il Nuovo Cimento 6, 279 (1949). [15] P. Lenz, J.- F. Joanny, F. Julicher, and J. Prost, Physical Review Letters 91, 108104 (2003). [16] P. Lenz, J.- F. Joanny, F. Julicher, and J. Prost, The European Physical Journal E 13, 379 (2004). [17] N. Oppenheimer, D. B. Stein, and M. J. Shelley, Phys. Rev. Lett. 123, 148101 (2019), arXiv:1903.00940. [18] B. a. Grzybowski, H. a. Stone, and G. M. Whitesides, Nature 405, 1033 (2000). [19] V. Soni, E. S. Bililign, S. Magkiriadou, S. Sacanna, D. Bartolo, M. J. Shelley, and W. T. M. Irvine, Nature Physics (2019).
+
+<|ref|>text<|/ref|><|det|>[[514, 420, 919, 912]]<|/det|>
+[20] N. H. P. Nguyen, D. Klotsa, M. Engel, and S. C. Glotzer, Physical Review Letters 112, 075701 (2014). [21] E. Lushi, H. Wioland, and R. E. Goldstein, Proceedings of the National Academy of Sciences 111, 9733 (2014), arXiv:1407.3633. [22] K. Yeo, E. Lushi, and P. M. Vlahovska, Physical Review Letters 114, 188301 (2015). [23] E. Lushi and P. M. Vlahovska, Journal of Nonlinear Science 25, 1111 (2015). [24] Y. Goto and H. Tanaka, Nature Communications 6, 5994 (2015). [25] Z. Shen and J. S. Lintuvuori, Physical Review Letters 125, 228002 (2020), arXiv:2007.16142. [26] E. S. Bililign, F. B. Usabiaga, Y. A. Ganan, V. Soni, S. Magkiriadou, M. J. Shelley, D. Bartolo, and W. T. M. Irvine, 1 (2021), arXiv:2102.03263. [27] S. John, Phys. Rev. Lett. 58, 2486 (1987). [28] E. Yablonovitch, Phys. Rev. Lett. 58, 2059 (1987). [29] W. Man, M. Florescu, E. P. Williamson, Y. He, S. R. Hashemizad, B. Y. C. Leung, D. R. Liner, S. Torquato, P. M. Chaikin, and P. J. Steinhardt, Proceedings of the National Academy of Sciences 110, 15886 (2013). [30] J. H. Weijs, R. Jeanneret, R. Dreyfus, and D. Bartolo, Phys. Rev. Lett. 115, 1 (2015). [31] P. G. Saffman and M. Delbruck, Proceedings of the National Academy of Sciences 72, 3111 (1975). [32] A. J. Levine, T. B. Liverpool, and F. C. MacKintosh, Physical Review E 69, 021503 (2004). [33] K. Seki, S. Mogre, and S. Komura, Physical Review E 89, 022713 (2014). [34] B. A. Camley and F. L. H. Brown, Physical Review Letters 105, 148102 (2010), arXiv:1105.4898. [35] N. Oppenheimer and H. Diamant, Biophysical Journal 96, 3041 (2009), arXiv:0809.4163. [36] N. Oppenheimer and H. A. Stone, Biophysical Journal 113, 440 (2017). [37] I. M. Held, R. T. Pierrehubert, S. T. Garner, and K. L.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 68, 490, 512]]<|/det|>
+Swanson, J. Fluid Mech. 282, 1 (1995). [38] W. Thomson, The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 10, 155 (1880). [39] E. Noether, Nachr D Konig Gesellschaft D Wiss Zu Gottingen Mathphys Klasse (1918). [40] H. Aref and N. Pomphrey, Proc. Natl. Acad. Sci. 380, 359 (1982). [41] S. Torquato, Physical Review E 94, 022122 (2016). [42] D. Hexner and D. Levine, Physical Review Letters 114, 110602 (2015). [43] G. Ariel and H. Diamant, Physical Review E 102, 022110 (2020), arXiv:2004.10588. [44] S. Wilken, R. E. Guerra, D. J. Pine, and P. M. Chaikin, arXiv, 0 (2020), arXiv:2002.04499. [45] J. Wang, J. M. Schwarz, and J. D. Paulsen, Nature Communications 9, 2836 (2018), arXiv:1711.06731. [46] S. Torquato, Physics Reports 745, 1 (2018). [47] Q.- L. Lei and R. Ni, Proceedings of the National Academy of Sciences 116, 22983 (2019), arXiv:1904.07514. [48] T. Goldfriend, H. Diamant, and T. A. Witten, Physical Review Letters 118, 158005 (2017), arXiv:1612.08632. [49] W. Dai and M. J. Shelley, Physics of Fluids A: Fluid Dynamics 5, 2131 (1993). [50] J. K. Percus and G. J. Yevick, Physical Review 110, 1 (1958). [51] On a side note, as Onsager first suggested [Onsager1949], in a bound system, configurational entropy must have a maximum. Entropy therefore decreases beyond a critical energy, and the system has a negative temperature. Negative temperature manifests itself as an increase in order with an increase in the energy. When coupling two vortical systems of negative temperature, there is a tendency
+
+<|ref|>text<|/ref|><|det|>[[515, 69, 919, 530]]<|/det|>
+to segregate. [52] M. Kardar, Statistical Physics of Particles (Cambridge University Press, Cambridge, 2007). [53] S. Martiniani, P. M. Chaikin, and D. Levine, Physical Review X 9, 011031 (2019), arXiv:1708.04993. [54] R. Avinery, M. Kornreich, and R. Beck, Physical Review Letters 123, 178102 (2019), arXiv:1709.10164. [55] G. Falkovich, Journal of Physics A: Mathematical and Theoretical 42, 123001 (2009). [56] D. Córdoba, C. Fefferman, and J. L. Rodrigo, Proc. Natal. Acad. Sci. 101, 2687 (2004). [57] Z. H. Nguyen, M. Atkinson, C. S. Park, J. Maclennan, M. Glaser, and N. Clark, Physical Review Letters 105, 268304 (2010). [58] G. Lumay, N. Obara, F. Weyer, and N. Vandewalle, Soft Matter 9, 2420 (2013). [59] J. R. Dormand and P. J. Prince, Journal of computational and applied mathematics 6, 19 (1980). [60] P. J. Prince and J. R. Dormand, Journal of computational and applied mathematics 7, 67 (1981). [61] E. Hairer, S. P. Norsett, and G. Wanner, Solving Ordinary Differential Equations I (2nd Revised. Ed.): Nons- tiff Problems (Springer- Verlag, Berlin, Heidelberg, 1993). [62] P. Virtanen, R. Gommers, T. E. Oliphant, M. Haberland, T. Reddy, D. Cournapeau, E. Burovski, P. Peterson, W. Weckesser, J. Bright, S. J. van der Walt, M. Brett, J. Wilson, K. J. Millman, N. Mayorov, A. R. J. Nelson, E. Jones, R. Kern, E. Larson, C. J. Carey, I. Polat, Y. Feng, E. W. Moore, J. VanderPlas, D. Laxalde, J. Perktold, R. Cimrman, I. Henriksen, E. A. Quintero, C. R. Harris, A. M. Archibald, A. H. Ribeiro, F. Pedregosa, P. van Mulbregt, and SciPy 1.0 Contributors, Nature Methods 17, 261 (2020). [63] A. H. Barnett, J. Magland, and L. af Klinteberg, SIAM Journal on Scientific Computing 41, C479 (2019).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 44, 143, 70]]<|/det|>
+## Figures
+
+<|ref|>image<|/ref|><|det|>[[55, 100, 940, 285]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 323, 116, 343]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[41, 364, 951, 499]]<|/det|>
+Three different structural states of 2D vortices/rotors - hyperuniformity for Euler point vortices (A) and QG ro- tors/surface rotors (B), (C) phase enrichment induced by circulation differences where green (black) represents vortices of high (low) circulation, and (D) crystallization arising from hydrosteric interactions. The insets of (A), (B) and (C) show the structure factor, S(q). In (A) and (B) S(q) decays to zero at small q, indicating that the distribution is hyperuniform. In (C) the structure factor shows the six distinct peaks of a hexagonal lattice.
+
+<|ref|>image<|/ref|><|det|>[[58, 510, 947, 650]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 679, 117, 699]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[40, 720, 955, 923]]<|/det|>
+(A) A representation of a membrane rotor - a disk rotating due to a torque \(\tau\) in the plane of the membrane. (B) The velocity field due to a membrane rotor (solid line) which scales as a point vortex \(\nu \mathbb{Q} /1 / r\) at small distances (dotted), \(r / \lambda \ll 1\) , transitioning to a QG behavior at large distances \(\nu \mathbb{Q} /1 / r2\) (dashed). (C) Contour dynamics of an ellipse with radii ratios \(\mathrm{rl} / \mathrm{rs} \leq 3\) , where \(\mathrm{rl}\) (rs) is the major (minor) axis. Starting from the same contour, the dynamics differ according to the radius relative to the SD length. Blue is in the limit \(\mathrm{rl} \ll \lambda\) . In this limit the ellipse is rotating as a rigid body, as predicted by Kelvin (38) for an elliptic patch in an Euler fluid. Black is in the limit \(\mathrm{rl} \gg \lambda\) , no longer conserving its shape since the large distance flow is in the quasigeostrophic regime. (D) 200 point membrane rotors, blue is the initial random configuration, black is the final configuration. Solid line shows typical trajectory of an individual vortex.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 45, 907, 88]]<|/det|>
+Note that the area did not change considerably since the system of vortices is self- bounding. (E) the relative error in H and M over a few cycle times, tc.
+
+<|ref|>image<|/ref|><|det|>[[55, 102, 940, 608]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 633, 115, 653]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[42, 676, 905, 718]]<|/det|>
+Hyperuniformity in ensembles of point vortices and rotors. Please see manuscript .pdf for full figure caption
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[55, 50, 940, 352]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 382, 117, 401]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[40, 424, 958, 673]]<|/det|>
+Two populations of vortices with different circulations showing phase enrichment, \(\Gamma 1 = 2\pi\) in black and \(\Gamma h = 256\pi\) in green. (A) Steady- state configuration for ten thousand point vortices of a circulation ratio \(\gamma = \Gamma h / \Gamma 1 = 128\) . Each inset shows a close- up view of one of the populations within the same physical region. (B) Density of the configuration in (A), \(\rho (r)\) , averaged over angle as a function of distance from the center. Note how density fluctuations are suppressed for the high circulation vortices, as is more clearly observed by the averaged structure factor, S(q), in (C), where the solid green line shows a \(\mathbb{Q}1.3\) power law. (D) The second moment for \(\mathrm{N} = 10,000\) vortices. Plotted separately for the high (in green) and low (in black) vortices at steady state as a function of \(\gamma\) (i.e. increasing \(\Gamma h\) ). (E) LOSSLESS compression for the two populations showing an increase (decrease) in file size (an estimate of entropy) for the low (high) circulation vortices over a couple of cycles. In blue is the file size for the total system. Solid line is a moving average, time is normalized by an average cycle time tc.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 695, 311, 722]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 746, 764, 767]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 785, 137, 803]]<|/det|>
+- SI.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397/images_list.json b/preprint/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..ccae126ada8889b3bb866babbfc03c09593d0e71
--- /dev/null
+++ b/preprint/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397/images_list.json
@@ -0,0 +1,40 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_0.jpg",
+ "caption": "524",
+ "footnote": [],
+ "bbox": [
+ [
+ 115,
+ 144,
+ 850,
+ 432
+ ]
+ ],
+ "page_idx": 28
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2 Tumor response dynamics were recapitulated by modeling. a. Schematic plot of tumor growth model. b. Box plots of model parameters \\(Kd\\) , \\(F\\) and \\(Kg\\) across organs. Significance was calculated using Kruskal-Wallis tests. The box extends from the 25th to 75th percentiles and the line in the middle is plotted as the median. The whiskers are drawn down to the 10th percentile and up to the 90th percentile. Points below and above the whiskers represent individual lesions. c. The correlations between model parameters. d. The correlations between model parameters and tumor baseline volume. The size of the dots represents lesion number (reported in panel b). The dashed lines with gray area are the linear",
+ "footnote": [],
+ "bbox": [
+ [
+ 128,
+ 115,
+ 845,
+ 680
+ ]
+ ],
+ "page_idx": 29
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4 Patient relapse sequence association with patient survival. a. Patients were clustered into five",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 31
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397.mmd b/preprint/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..af13ab28a20a5ebc20ee8065655a4dc8f58d4190
--- /dev/null
+++ b/preprint/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397/preprint__042a95bb963a3fded623677d176d398a6df7372697fadd494fd320558dfef397.mmd
@@ -0,0 +1,407 @@
+
+# Mapping Intrapatient Response Heterogeneity and Lesion-specific Relapse Dynamics in Metastatic Colorectal Cancer
+
+Jiawei Zhou University of North Carolina at Chapel Hill Amber Cipriani University of North Carolina at Chapel Hill https://orcid.org/0000- 0003- 3596- 0581 Yutong Liu University of North Carolina at Chapel Hill Gang Fang University of North Carolina at Chapel Hill Quefeng Li University of North Carolina at Chapel Hill Yanguang Cao ( yanguang@unc.edu ) University of North Carolina at Chapel Hill https://orcid.org/0000- 0002- 3974- 9073
+
+Article
+
+Keywords:
+
+Posted Date: March 28th, 2022
+
+DOI: https://doi.org/10.21203/rs.3.rs- 1447896/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+
+# Mapping Intrapatient Response Heterogeneity and Lesion-specific Relapse Dynamics in Metastatic
+
+# Colorectal Cancer
+
+Jiawei Zhou \(^{1}\) , Amber Cipriani \(^{1,2}\) , Yutong Liu \(^{3}\) , Gang Fang \(^{4}\) , Quefeng Li \(^{3}\) , Yanguang Cao \(^{1,5*}\) \(^{1}\) Division of Pharmacotherapy and Experimental Therapeutics, School of Pharmacy, University of North Carolina at Chapel Hill, NC 27599, USA; \(^{2}\) UNC Health Medical Center, Department of Pharmacy, Chapel Hill, NC 27514; \(^{3}\) School of Public Health, University of North Carolina at Chapel Hill, NC 27599, USA; \(^{4}\) Division of Pharmaceutical Outcomes and Policy, School of Pharmacy, University of North Carolina at Chapel Hill, NC 27599, USA; \(^{5}\) Lineberger Comprehensive Cancer Center, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
+
+# Corresponding author:
+
+Yanguang Cao, Ph.D. Division of Pharmacotherapy and Experimental Therapeutics, UNC School of Pharmacy 2318 Kerr Hall, UNC Eshelman School of Pharmacy Chapel Hill, NC 27599- 7569 E- mail: yanguang@unc.edu Phone: +1- 919- 966- 4040.
+
+<--- Page Split --->
+
+## 17 Abstract
+
+Achieving systemic tumor control across metastases is vital for long- term patient survival but remains intractable in many patients. High intrapatient heterogeneity persists, conferring many dissociated responses across metastatic lesions. Most studies of metastatic disease focus on tumor molecular and cellular features, which are crucial to elucidating the mechanisms underlying intrapatient heterogeneity. However, our understanding of intrapatient heterogeneity on the macroscopic level, such as lesion dynamics in growth, response, and relapse during treatment, remains rudimentary. This study investigated intrapatient heterogeneity through analyzing 116,542 observations of 40,612 lesions in 4,308 metastatic colorectal cancer (mCRC) patients. Despite significant differences in their response and relapse dynamics, metastatic lesions converged on four phenotypes that varied with anatomical site. Importantly, we found that organ- level relapse sequence was closely associated with patient survival, and that patients with the first relapses in the liver often had worse survival. In conclusion, our study provides insights into intrapatient response heterogeneity in mCRC and creates impetus for metastasis- specific therapeutics.
+
+<--- Page Split --->
+
+Metastasis is the leading cause of cancer mortality1. Unfortunately, antitumor therapies are still designed mostly based on the biology of primary tumors, with little consideration of metastases2,3. Achieving systemic tumor control across metastases is critical for long- term survival but remains intractable in many patients. Some metastases respond highly to treatment while others do not at all, resulting in many dissociated and heterogeneous responses within patients4-7. Lesion- level response and relapse heterogeneity are common in many cancer types, but our understanding of such intrapatient heterogeneity and its relevance to prognosis remains rudimentary.
+
+Most investigations of intrapatient lesion heterogeneity focus on tumor genetic mutations, clonal compositions, or transcriptomics8-10. These molecular and cellular characterizations are critical to elucidating the underlying mechanisms of intrapatient response heterogeneity11,12. However, it is equivalently critical to study intrapatient heterogeneity on the macroscopic level, such as distinct lesion dynamics in growth, response, and relapse during treatment, as well as their potential phenotypic convergence anatomically. These phenotypes would complement molecular and cellular analyses for a holistic view of intrapatient heterogeneity. This study sought to investigate intrapatient response heterogeneity through mapping lesion- specific response and relapse dynamics in metastatic CRC (mCRC).
+
+Colorectal cancer (CRC) is the third leading cause of cancer- related death13. About \(20\%\) of CRC patients have distant metastases at diagnosis; the five- year relative survival rate is only \(14\%\) for these patients14,15. Intrapatient response heterogeneity is common in CRC patients treated with either standard chemotherapy alone or in combination with targeted therapy16. We, along with others, have found that high intrapatient response heterogeneity is associated with worse survival16-19. Importantly, we also found favorable responses in liver metastases predicted longer patient survival, compared to lesions in the lungs and lymph nodes (LN)16. Characterizing intrapatient response heterogeneity in mCRC is valuable for prognosis and therapies.
+
+<--- Page Split --->
+
+The local microenvironment selects tumor phenotypes in response to treatment, leading to heterogeneity across anatomically distinct lesions in terms of response and relapse dynamics20,21. Characterizing their phenotypic differences (divergence) or similarities (convergence) could yield insights into tumor ecological features and systemic resistance. To map the lesion- level response and relapse patterns in mCRC, we first applied a mathematical model to capture tumor growth dynamics in 4,308 mCRC patients. Next, individual lesion- specific response and relapse probabilities were mapped to predict their phenotypic divergence and convergence across anatomical sites. Last, we applied a machine learning approach to analyze the relapse sequence across lesions and its relevance to long- term patient survival. Our study provides insights into intrapatient phenotypic heterogeneity in mCRC and yields substantial implications for designing metastasis- specific therapeutics.
+
+<--- Page Split --->
+
+## Results
+
+## Data Sources and Structure
+
+To evaluate lesion- level response and relapse dynamics in mCRC, we collected longitudinal radiographic measurements of metastatic lesions in colorectal cancer (CRC) patients from Project Data Sphere. In total, 4,308 patients with 40,612 lesions from eight Phase III trials were included. The inclusion and exclusion criteria are presented in Fig. 1a. The distribution of lesion number across organs is shown in Fig. 1b. The total target lesions were 19,180 with 94,174 radiographic measurements, and there were 18,594 nontarget lesions and 2,838 new lesions with response status over time. Additional information including patients' demographic and clinical characteristics (e.g., age, gender, race, body mass index [BMI], tumor type, treatment history, RECIST response, and KRAS status), progression- free survival (PFS) and overall survival (OS) are reported in Table 1. We also included the tumor longitudinal measurements in a head and neck squamous cell carcinomas (mHNSCC) trial for external validation. The data was also from Project Data Sphere with similar criteria as CRC data (Supplementary Fig. 3a).
+
+## Model recapitulated tumor growth dynamics of individual lesions
+
+The tumor growth dynamics of 19,180 target lesions with 94,174 radiographical measurements were recapitulated with a widely adopted growth model22. The three dynamic parameters in the model are the regression rate \(Kd\) , the fraction of non- responding cells \(F\) , and the progression rate \(Kg\) (Fig. 2a). The model was optimized using a nonlinear mixed effect (NLME) modeling approach, which allows the estimation of three dynamic parameters at the individual level and their inter- lesion variance in the population. Overall, the model adequately recapitulated the longitudinal profiles of tumor radiographic measurements for each lesion. The goodness- of- fit and model visual predictive check plots, as well as representative individual fittings, show good model predictive performance (Supplementary Fig. 1).
+
+<--- Page Split --->
+
+Population estimates and inter- lesion variances in tumor dynamic parameters are summarized in Supplementary Table 1. The parameters for individual lesions significantly differed across organs ( \(\mathrm{p}<\) 0.0001, Fig. 2b). Among all metastases, lesions in the bone exhibited the lowest response depth (1- \(F\) ), while lesions in the genitourinary and reproductive (GR) system had the fastest progression rates ( \(Kg\) ), and kidney lesions showed the lowest regression rates ( \(Kd\) ). Among three most abundant metastatic sites (liver, lung, and LN), lesions in the liver showed the highest response depth but the fastest progression rates, suggesting the unique growth feature of liver lesions.
+
+Higher treatment- resistant cell fraction \(F\) is associated with slower rates of regression ( \(Kd\) , \(\mathrm{r} = - 0.69\) , \(\mathrm{p}< 0.005\) ) and faster rates of progression ( \(Kg\) , \(\mathrm{r} = 0.53\) , \(\mathrm{p}< 0.05\) , Fig. 2c). Progression rates seemed to be independent of regression rates (Fig. 2c). Remarkably, no significant correlations were observed between baseline tumor burden and all tumor dynamic parameters (Fig. 2d). Large tumor burden, on the individual lesion level, did not necessarily confer slow regression rates, high treatment- resistant fractions, or slow progression rates, implying that tumor burden at baseline is not a robust prognostic factor in mCRC \(^{23 - 25}\) . Notably, metastatic lesions under antibody targeted therapy (bevacizumab and/or panitumumab) plus chemotherapy (FOLFOX or FOLFIRI), compared to standard chemotherapy alone, showed significantly deeper response (effect size = 0.43) and lower progression rates (effect size = 0.26), but had a moderate effect on tumor regression rates (effect size = 0.06, Supplementary Fig. 2).
+
+## Response and relapse dynamics suggest phenotypic convergence on organ level
+
+The tumor growth model predicted the longitudinal profiles of response and relapse for each target lesion. Response and relapse times were then derived as the duration from the start of treatment to the time of response or relapse per RECIST \(\mathrm{v}1.1^{26}\) , respectively. We integrated the response time for both target and non- target lesions and the relapse time for all lesions, including the new ones, into random effect Cox proportional models \(^{27}\) . The Cox model predicted the relative probabilities of lesion response or relapse at the organ level. Of note, treatment effects from either chemotherapy or combination therapy were included as a confounding factor in the Cox regression model. With that, we could focus on the organ
+
+<--- Page Split --->
+
+intrinsic response and relapse characteristics. The hazard ratios for the response and relapse across organs are shown in Fig. 3a and Fig. 3b.
+
+With abdominal lesions as the reference, metastatic lesions in the liver were most likely to respond to treatments, whereas lesions in the brain/central nervous system (CNS) were least likely (Fig. 3a). Lesions in the gastrointestinal (GI) system, skin, and bone were significantly less likely to respond than abdominal lesions. Lesions in the spleen, lung, and peritoneum showed comparable responses. The probability of relapse also differed greatly across anatomical sites (Fig. 3b). The metastatic lesions with the highest likelihood of relapse were those in the brain/CNS, GR system, and liver, while lesions in the GI system, and regional and distal LNs were least likely.
+
+We then integrated organ- specific response and relapse probabilities to investigate their potential phenotypic convergence across anatomical sites. As in Fig. 3c, an anatomical chart of organ- specific response and relapse probabilities was created based on their relative hazards in the Cox model. Four types of phenotypic features emerge in CRC- metastatic organs defined by their associated lesions' likelihood of response and relapse. Notably, bone and brain lesions had low response and high relapse probabilities (low- high phenotype), while liver lesions had high probabilities of both response and relapse (high- high phenotype). Patients with these metastases, particularly those with low- high phenotype, had much worse survival outcomes (OS median 378 days vs. 561 days, p<0.0001, Supplementary Fig. 3a). On the other side, metastatic lesions in the lung and LN showed high response and low relapse probabilities (high- low phenotypes). Patients who have metastases in high- low phenotype organs only tend to have a better prognosis than patients with other phenotypic metastases do (OS median 770 days vs. 524 days, p<0.0001, Supplementary Fig. 3b).
+
+Interestingly, most metastatic lesions with high relapse probabilities tend to occur in organs known to have immunosuppressive microenvironments, such as the liver, bone, and brain/CNS28- 31. To discern the influence of local tissue environment on tumor response phenotype, we performed the same analyses in head and neck squamous cell carcinomas (mHNSCC) to see whether a similar anatomical chart exists
+
+<--- Page Split --->
+
+(Fig. 3d). A total of 393 patients with 1,892 lesions were analyzed, including eleven metastatic organs (Supplementary Fig. 4a and 4b). Patients' demographics are reported in Supplementary Table 2. The organ-specific hazard ratios for relapse and response were ranked, as we did in mCRC (Supplementary Fig. 4c and 4d). In mHNSCC, metastases in the liver, bone, and brain also showed high relapse potential, in line with what we observed in mCRC. Metastatic lesions in the LNs exhibit a high-low phenotype, consistent with mCRC. Similar anatomical charts across cancer types suggest that organ-intrinsic microenvironmental factors, such as the local physical and immunological components, could be key modulators to the mechanisms underlying the probabilities of tumor response and relapse.
+
+Treatment effects on organ- specific responses were also investigated. For simplicity, treatments were divided into two groups, chemotherapy alone and in combination with antibody targeted therapy. The combined antibody targeted therapies are either panitumumab or bevacizumab, or both. Surprisingly, combination with the antibody targeted therapies did not significantly influence organ- specific response probabilities (Fig. 3e), suggesting low direct cytotoxic effects of antibody- based therapies. Notably, the primary therapeutic benefit of antibody targeted therapies was to decrease relapse potential (Fig. 3f). Relapse hazards significantly decreased in most metastatic organs except for the skin, brain/CNS, spleen, and kidney. Taken together, antibody targeted therapies had the primary effect of decreasing lesion relapse probability but had limited influence on the lesion response probability. Interestingly, high- relapse organs in Fig. 3c also had high relapse probability during cytotoxic chemotherapies in Fig. 3f, suggesting a critical role for local tissue environments in long- term tumor control.
+
+## Relapse sequence across organs predicts patient survival
+
+We built a k- means unsupervised clustering model to cluster patients based on their organ- level lesion relapse sequence to investigate their relevance to patient survival. Elbow sum of square \(^{32}\)
+
+(Supplementary Fig. 5a) and Silhouette score \(^{33}\) (Supplementary Fig. 5b) were calculated to determine the optimal \(\mathrm{k} (= 5)\) in the final classification. Five groups of patients were identified with distinct patterns of organ- specific relapse sequences and were stratified by relapsing organ number and first- relapsing
+
+<--- Page Split --->
+
+organ: Mono- Organ (n=1,425), Hetero- Organ (n=801), Lung- First (n=577), Liver- First (n=1,194), and the Other- First (n=888) groups. The clinical demographics and baseline information of each group are summarized in Supplementary Table 3.
+
+Organ- level relapse sequence is significantly correlated with long- term patient survival (p < 0.0001, Fig. 4b). As expected, patients with multiple organ relapses had worse survival than patients with only one organ relapse (OS median Hetero- Organ 385 days vs. Mono- Organ 653 days). Remarkably, despite comparable number of baseline metastases, patients whose first relapses were in the liver had a much worse prognosis than those whose first relapses were in lungs or other sites (OS median Liver- First 450 days vs. Lung- First 679 days vs. Other- First 581 days, Fig. 4b). This is consistent with earlier
+
+observations (Fig. 3c) that lesions in the lung had high- low phenotype that is often associated with good patient prognosis. Patients with relapse first in the liver had faster subsequent relapses than patients whose relapses occurred in lungs or other sites, suggesting that relapsing lesions in the liver have high systemic consequences (p<0.0001, Fig. 4c). It also aligns with our previous finding that the response of liver lesions to treatments strongly predicted patient survival16.
+
+Next, we performed k- means unsupervised clustering in the Hetero- Organ group to further investigate relapse patterns in patients with extensive metastases and relapses. Four groups of patients were optimally clustered (Supplementary Fig. 5c and 5d), and one distinctive feature among these clusters was the relapse order of liver lesions (Supplementary Fig. 6a). Despite similar metastases, patients with first or second relapse occurring in the liver had worse survival than those with early relapses occurring in other organs (Supplementary Fig. 6b and 6c). This observation further underlines the importance of liver lesions to systemic response and resistance.
+
+## Targeted antibody therapies minimally influence lesion relapse sequence
+
+We compared the relapse sequence in patients under different treatments (chemotherapy alone vs. combination with antibody targeted therapy). In patients with Liver- First, Lung- First or Other- First
+
+<--- Page Split --->
+
+relapse patterns, antibody targeted therapies significantly improved patient overall survival (p < 0.0001, Fig. 5a). However, neither the proportion of patients with each relapsing pattern (Fig. 5b) nor the sequence of relapse across metastatic organs were significantly different (Fig. 5c- 5e). Relapses in the GR and pancreas occurred slightly earlier in antibody targeted therapy, which did not seem to translate meaningful difference in patient survival. Despite the similar sequence, patients under antibody targeted therapies had significantly slower first and second relapses, but had non- significant difference in the third or later relapses (Fig. 5f- 5g). The average relapse times were much longer in combination therapy compared to chemotherapy alone.
+
+In patients with the Hetero- Organ pattern, antibody targeted therapies did not meaningfully improve overall survival (Supplementary Fig. 7a) compared to chemotherapy alone, and the proportions of patients in each subcluster were similar between the two treatment groups (Supplementary Fig. 7b). Patients' relapse patterns and lesion relapse time were largely comparable, especially for those who had early liver lesion relapse (Supplementary Fig. 7c- h). Similarly, antibody targeted therapies did not influence lesion relapse sequence. Overall, the primary therapeutic benefit of antibody targeted therapies was to delay relapse in patients with few (< 4) metastatic organs, but not in those with broad metastases.
+
+## Machine learning model predicts lesion relapse sequence.
+
+In order to predict patient relapse sequence at the time of diagnosis, we built a gradient boosting model using patient baseline characteristics and metastases profiles34. The model parameters are in Supplementary Table 4. The area under the receiver operating characteristic (ROC) curve of the testing data was 0.91, which indicated fair performance (Supplementary Fig. 8a). The model could predict Mono- Organ and Hetero- Organ groups better than Lung- First, Liver- First, and Other- First groups with higher area under the ROC curve. This indicates that more follow- up information is imperative to accurately predict the relapse sequences of the latter three groups (Supplementary Fig. 8b).
+
+<--- Page Split --->
+
+## Discussion
+
+Metastasis is responsible for the majority of cancer- related mortality. Unfortunately, systemic tumor control across metastases remains intractable in many patients. This study investigated inter- lesion heterogeneity by analyzing response dynamics of 40,612 lesions in 4,308 mCRC patients. Unlike most molecular characterizations of metastases, we focused on the phenotypic features associated with lesion response and relapse dynamics as well as the anatomical divergence and convergence of these features. Our analyses yielded several intriguing findings. First, metastases differed considerably in their response to treatment, with depth of response positively correlating with regression rate and negatively correlating with progression rate. Second, metastatic lesions within the same organ exhibited congruent response and relapse dynamics, converging upon four organ- level phenotypes. Metastatic lesions in the liver exhibited high response and high relapse probabilities (high- high phenotype), while lesions in the bone and brain/CNS had low response and high relapse probabilities (low- high phenotype). These phenotypes appear to be consistent across cancers. Third, we found that organ- level relapse sequence was closely associated with patient survival, and patients with the first relapse in the liver had worse survival outcomes compared to patients with first relapse in other sites.
+
+This study quantified the degree of inter- lesion heterogeneity by modeling tumor regression and progression dynamics. By assuming first- order regression of drug- sensitive cancer cells (log- kill hypothesis), the empirical model adequately recapitulated the longitudinal size measurements on the lesion level. The first- order regression implies that drug- sensitive cancer cells may have only one rate- limiting step on the path to cell death35. Baseline tumor burden did not correlate with regression rates in our analyses, restating the first- order regression. Large tumors are often expected to have tumor regression potentially deviating from strict first- order kinetics because of their non- uniform drug distributions inside the tumor or only the surface tumor cells being actively proliferating and sensitive to treatment36- 38. Our analyses did not find evidence to support these speculations. In contrast, despite large
+
+<--- Page Split --->
+
+sizes, metastatic lesions in the liver had relatively high regression rates compared to lesions at other organ sites.
+
+The progression rates of drug- resistant tumor cells varied more between lesions than their associated regression rates and accounted the majority of intrapatient heterogeneity. Lesion relapse time was more closely associated with the progression rates than with the regression rates, in line with Stein et al., who reported that progression rates were a stronger predictor of patient survival39. If validated prospectively, the progression rates would offer more appropriate efficacy endpoints in clinical trials than the current ones that focus on the early response and regression, such as response rate and best of response.
+
+Antibody therapies significantly increased response depths and decreased progression rates, but did not considerably affect regression rates. These observations indicate that the primary therapeutic benefit of combined antibody therapies is from growth suppression rather than direct cytotoxicity. In renal cell carcinomas, bevacizumab significantly reduced the growth rate constants, and the effect could become more apparent after relapse, in line with our observations in mCRC40. Interestingly, despite the broad evidence of its antibody- dependent cellular cytotoxicity (ADCC)41 or complement- dependent cytotoxicity in vitro systems42, the other antibody panitumumab in our analyses did not significantly affect tumor regression rates either, suggesting its low direct cytotoxicity in patients. In fact, the magnitude of the ADCC elicited by EGFR- targeting antibodies in patient remains hard to define, especially considering the restricted and highly varying infiltrations of effector cells in tumor beds43,44. Panitumumab (IgG2), compared to another EGFR- targeting antibody cetuximab (IgG1) showed reduced ADCC- dependent therapeutic effect, probably related to the reduced avidity of IgG2 for CD16, as compared to IgG145,46. Unfortunately, our analyses did not include patients under cetuximab treatment, precluding direct comparison.
+
+Metastatic lesions with lower fractions of resistant cells also had slower progression rates, suggesting consistent fitness of resistant cells before treatment and after relapse. However, metastatic lesions in the liver appear to behave differently; they had higher probability to respond, but also faster progression rates
+
+<--- Page Split --->
+
+than lesions in the LN and lungs, suggesting unique ecological properties of liver lesions. Our analyses highlight the importance of tissue microenvironments to metastatic phenotypes. Metastatic lesions with higher responses were typically found in the liver, spleen, LN, and lungs. These organs have discontinuous or fenestrated endothelial membranes, which may lead to higher drug exposure, potentially conferring high treatment responses47,48. In contrast, the organs bearing poorly- responding lesions are usually those with continuous endothelial membranes and thus more limited drug distribution, such as the muscle and brain/CNS49- 52. Some organs that bear poorly- responding metastatic lesions, such as kidney and muscle, have relatively dense tissue matrices. This could limit the growth rate of metastatic lesions within these organs53,54 and render them less responsive to cytotoxic chemotherapy55,56.
+
+On the other hand, organ- specific relapse probabilities seem to closely relate to the local immune microenvironments. Metastatic lesions with higher relapse potentials were found in the liver, bone, and brain/CNS, which either are immune- privileged or tolerogenic organs20,21,28- 31. Interestingly, high relapses in these organs also occurred during cytotoxic chemotherapies that primarily work through DNA damage- induced cell death (Fig. 3f). Higher containment of tumor relapses in immunocompetent organs highlights the critical role anticancer immunity plays in long- term tumor control. Patients with highly relapsing lesions, such as lesions in the liver and bones, had much worse survival outcomes and likely require more effective and targeted therapeutics.
+
+Tumor relapse is a serious impediment to cancer treatment, but organ- level relapse patterns remain poorly characterized. We found that early relapses in the liver, compared to early relapses in other sites, predicts worse patient survival and more rapid subsequent relapses. The liver's anatomical location, as a trafficking hub for CRC cells to spread to other organs, possibly underlies this finding57. By modeling large autopsy data sets in mCRC, Newton et al. highlighted that liver metastases could serve as tumor "spreaders"58, and that there are multidirectional paths of tumor spread during progression58,59. Although we did not estimate transit probabilities from site to site, we speculate it is likely that early relapses in liver metastases could lead to more resistant cells spreading throughout the body and cause more frequent
+
+<--- Page Split --->
+
+subsequent relapses. Our population- level analysis supports this speculation and shows that liver metastases were often associated with a more pronounced tumor spread in the body.
+
+The primary therapeutic benefit of antibody targeted therapies was to delay tumor progression and systemic relapses, without strong preferential effect on any organ- specific metastases. As such, antibody therapies did not affect relapse sequences, and the fraction of patients with the first relapse in the liver were largely comparable to chemotherapy alone. Unfortunately, in patients with multiple relapsed metastases ( \(>4\) relapsed organs), the therapeutic benefit of antibody therapies is minimal, and more effective treatments remain sorely needed to treat patients with broad metastases.
+
+In conclusion, we quantified intrapatient heterogeneity by modeling the longitudinal size measurement of metastatic lesions. This study provided a broad characterization of the phenotypic heterogeneity across metastatic lesions in mCRC, which could complement conventional molecular and cellular analyses to promote a more comprehensive view of intrapatient heterogeneity and yield substantial implications for metastasis- targeting therapies.
+
+<--- Page Split --->
+
+## Methods
+
+## Data
+
+Multiple mCRC and mHNSCC studies with longitudinal measurements of individual metastatic tumor information were included for the analyses. All datasets are accessible in Project Data Sphere (https://www.projectdatasphere.org/). Patients under one of the following conditions were excluded: (1) no target lesion longitudinal measurements; (2) baseline tumor size measured more than 12 weeks before the treatment. Patients' demographics and survival information were collected if applicable. The size and anatomical site about target/non- target lesion and occurring time and anatomical sites of new lesions were all recorded and analyzed if any.
+
+All study protocols were approved by institutional review boards at each participating center. All patients have been provided written informed consent before study- related procedures were performed. All data sharing plans have been approved by the data sponsors.
+
+## Lesion-specific tumor growth dynamics
+
+The longest diameter was converted to volume assuming the ellipsoidal shape of tumor (Equation 1) and the ratio of the tumor long versus short axis as \(1.31^{60}\) . An empirical tumor growth model (Equation 2) was used to recapitulate lesion- specific tumor growth dynamics.
+
+\[V = \frac{(\log a x i s)\times(\mathrm{short} a x i s)^{2}}{2} (E q u a t i o n I)\]
+
+\[V = V0\cdot [F\cdot e^{Kg\cdot t} + (1 - F)\cdot e^{-Kd\cdot t}](Equation 2)\]
+
+\(V\) is the tumor volume, \(V0\) is the tumor baseline volume, \(t\) is the time. The model has three parameters for estimation: \(F\) is the fraction of non- responding tumor cells, with \(1 - F\) as the response depth; \(Kg\) is the progression rate and \(Kd\) is the regression rate. We fitted the model for all target lesions simultaneously using the Non- Linear Mixed Effect (NLME) method in Monolix2020R1. Stochastic approximation expectation- maximization (SAEM) algorithm was applied to search global optimum in the estimation. M3
+
+<--- Page Split --->
+
+method \(^{61}\) was applied for quantifying size below the quantification of limit ( \(< 200 \mathrm{mm}^{3})^{62}\) . In the NLME method, the model parameters are described in Equation 3- 5.
+
+\[\ln \left(K g^{j}\right) = \ln \left(\theta_{K g}\right) + \eta_{K g j}\left(\text{Equation 3}\right)\]
+
+\[\ln \left(K d^{j}\right) = \ln \left(\theta_{K d}\right) + \eta_{K d j}\left(\text{Equation 4}\right)\]
+
+\[\mathrm{logit}\big(F^{j}\big) = \mathrm{logit}\big(\theta_{F}\big) + \eta_{F j}\left(\text{Equation 5}\right)\]
+
+where \(\theta\) is the population typical value, and \(\eta\) is the random effect with a log- normal distribution
+
+describing the difference between individuals and population average for each lesion \(j\) . Proportional error
+
+model was assumed. The initial values of \(K g\) , \(K d\) and \(F\) were 0.01 day \(^{- 1}\) , 0.01 day \(^{- 1}\) , and 0.1 (unitless).
+
+## Tumor response and relapse times
+
+Tumor growth dynamic parameters were further taken to predict the longitudinal profiles of response and relapses for each target lesions. The longitudinal response and relapse status for each target or non- target lesion were determined per RECIST V1.1 \(^{26}\) . Target lesion response time (when the lesion size decreases \(\geq 20\%\) from baseline) and relapse time (when the lesion size increases \(\geq 30\%\) from tumor nadir or at least \(200 \mathrm{mm}^{3}\) increase from nadir) were derived using tumor growth model with NLME- estimated parameters on the individual lesion level. Non- target lesions responded when “partial response” or “complete response” was firstly observed during the treatment and relapsed when “progressive disease” appeared in tumor evaluation. The relapse time for new lesions were defined as the detection time.
+
+## Cox proportional regression model
+
+Cox proportional models were built to estimate lesion response and relapse probabilities across organs and treatments in R- 4.1.0 and RStudio “coxme” package. Inter- patient variability was adjusted in the Cox models as random effect. Lesions without relapse or response during the treatment were labeled as censored by the last day of that patient in the trial. New lesions were considered only in the relapse hazard estimation.
+
+<--- Page Split --->
+
+## Relapse pattern classification and prediction
+
+We used the k- means machine learning algorithm to classify all the patients based on their organ relapse sequence in Spyder (Python 3.8) in Anaconda using the SCIKIT- LEARN 1.0.2 software package. Elbow method and Silhouette score were applied to find optimal k. The relapse patterns of patients clustered with different k were compared to help determine the choice of k in the final classification.
+
+Gradient Boosting algorithm was applied to build a relapse pattern predictive model in Spyder (Python 3.8) in Anaconda using the SCIKIT- LEARN 1.0.2 software package. The research samples were randomly divided into a training and testing groups at a ratio of 4:1. The initial value of the hyperparameters used in this model was determined by parameter grid search, using 5- fold cross- validation and F1- score as a metric (Supplementary Table 4). The model outcome is the patient relapse sequence classified in k- means algorithm. Model predictors included patient clinical and demographic characteristics, as well as the baseline metastatic profiles, including the metastatic organs, metastatic numbers, metastatic target lesion baseline volume. Continuous predictors were normalized and categorical predictors were transformed to dummy variables. Performance index accuracy, precision, recall rate and area ROC curves were used to evaluate model performance.
+
+## Statistical analysis
+
+Comparisons of continuous variables were performed using the two- tailed Mann- Whitney test or Kruskal- Wallis test. Multiple comparisons were adjusted by Dunn's test. PFS (defined as the start of therapies until RECIST- defined progression or death) and OS (defined as the start of therapies until patient death) among the groups were depicted using Kaplan- Meier curves and compared using log- rank tests. All the statistical tests were performed in GraphPad Prism 9.
+
+<--- Page Split --->
+
+364 References
+
+365 1. Welch, D. R. & Hurst, D. R. Defining the hallmarks of metastasis. Cancer Res. 79, 3011- 3027 (2019).
+
+367 2. Eccles, S. A. & Welch, D. R. Metastasis: recent discoveries and novel treatment strategies. Lancet 369, 1742- 1757 (2007).
+
+369 3. Anderson, R. L. et al. A framework for the development of effective anti-metastatic agents. Nat. Rev. Clin. Oncol. 16, 185- 204 (2019).
+
+371 4. Schmid, S. et al. Organ-specific response to nivolumab in patients with non-small cell lung cancer (NSCLC). Cancer Immunol. Immunother. 67, 1825- 1832 (2018).
+
+373 5. Osorio, J. C. et al. Lesion-Level Response Dynamics to Programmed Cell Death Protein (PD-1) Blockade. J. Clin. Oncol. JCO1900709 (2019) doi:10.1200/JCO.19.00709.
+
+375 6. Crusz, S. M. et al. Heterogeneous response and progression patterns reveal phenotypic heterogeneity of tyrosine kinase inhibitor response in metastatic renal cell carcinoma. BMC Med. 14, 1- 9 (2016).
+
+378 7. Pires da Silva, I. et al. Site-specific response patterns, pseudoprogression, and acquired resistance in patients with melanoma treated with ipilimumab combined with anti- PD- 1 therapy. Cancer 126, 86- 97 (2020).
+
+381 8. Merz, M. et al. Deciphering spatial genomic heterogeneity at a single cell resolution in multiple myeloma. Nat. Commun. 13, 1- 15 (2022).
+
+383 9. Wu, F. et al. Single-cell profiling of tumor heterogeneity and the microenvironment in advanced non- small cell lung cancer. Nat. Commun. 12, 1- 11 (2021).
+
+385 10. Russo, M. et al. Tumor heterogeneity and lesion-specific response to targeted therapy in colorectal
+
+<--- Page Split --->
+
+386 cancer. Cancer Discov. 6, 147–153 (2016).
+
+387 11. Kashyap, A. et al. Quantification of tumor heterogeneity: from data acquisition to metric generation. Trends Biotechnol. (2021).
+
+389 12. Huang, S. Reconciling non-genetic plasticity with somatic evolution in cancer. Trends in cancer 7, 309–322 (2021).
+
+391 13. Siegel, R. L. et al. Colorectal cancer statistics, 2020. CA. Cancer J. Clin. (2020).
+
+392 14. Viale, P. H. The American Cancer Society's facts & figures: 2020 edition. J. Adv. Pract. Oncol. 11, 135 (2020).
+
+395 325, 669–685 (2021).
+
+396 16. Zhou, J., Li, Q. & Cao, Y. Spatiotemporal heterogeneity across metastases and organ-specific response informs drug efficacy and patient survival in colorectal cancer. Cancer Res. 81, 2522–2533 (2021).
+
+399 17. Asleh, K. et al. Proteomic analysis of archival breast cancer clinical specimens identifies biological subtypes with distinct survival outcomes. Nat. Commun. 13, 1–19 (2022).
+
+401 18. McDonald, K. A. et al. Tumor Heterogeneity Correlates with Less Immune Response and Worse Survival in Breast Cancer Patients. Ann. Surg. Oncol. 26, 2191–2199 (2019).
+
+403 19. Sveen, A. et al. Intra-patient inter-metastatic genetic heterogeneity in colorectal cancer as a key determinant of survival after curative liver resection. PLoS Genet. 12, e1006225 (2016).
+
+405 20. Binnewies, M. et al. Understanding the tumor immune microenvironment (TIME) for effective therapy. Nat. Med. 24, 541–550 (2018).
+
+407 21. Pao, W. et al. Tissue-specific immunoregulation: a call for better understanding of the
+
+<--- Page Split --->
+
+408 "immunostat" in the context of cancer. Cancer Discov. 8, 395- 402 (2018). 409 22. Wilkerson, J. et al. Estimation of tumour regression and growth rates during treatment in patients 410 with advanced prostate cancer: a retrospective analysis. Lancet Oncol. 18, 143- 154 (2017). 411 23. Dai, W. et al. Does tumor size have its prognostic role in colorectal cancer? Re- evaluating its 412 value in colorectal adenocarcinoma with different macroscopic growth pattern. Int. J. Surg. 45, 413 105- 112 (2017). 414 24. Kornprat, P. et al. Value of tumor size as a prognostic variable in colorectal cancer: a critical 415 reappraisal. Am. J. Clin. Oncol. 34, 43- 49 (2011). 416 25. Santullo, F. et al. Tumor size as a prognostic factor in patients with stage IIa colon cancer. Am. J. 417 Surg. 215, 71- 77 (2018). 418 26. Eisenhauer, E. A. et al. New response evaluation criteria in solid tumours: revised RECIST 419 guideline (version 1.1). Eur. J. Cancer 45, 228- 247 (2009). 420 27. Murphy, S. A. Consistency in a proportional hazards model incorporating a random effect. Ann. 421 Stat. 22, 712- 731 (1994). 422 28. Ilkovitch, D. & Lopez, D. M. The liver is a site for tumor- induced myeloid- derived suppressor cell 423 accumulation and immunosuppression. Cancer Res. 69, 5514- 5521 (2009). 424 29. Mundy, G. R. Metastasis to bone: causes, consequences and therapeutic opportunities. Nat. Rev. 425 Cancer 2, 584- 593 (2002). 426 30. Zhao, E. et al. Bone marrow and the control of immunity. Cell. Mol. Immunol. 9, 11- 19 (2012). 427 31. Fabry, Z., Schreiber, H. A., Harris, M. G. & Sandor, M. Sensing the microenvironment of the 428 central nervous system: immune cells in the central nervous system and their pharmacological 429 manipulation. Curr. Opin. Pharmacol. 8, 496- 507 (2008).
+
+<--- Page Split --->
+
+32. Syakur, M. A., Khotimah, B. K., Rochman, E. M. S. & Satoto, B. D. Integration k-means clustering method and elbow method for identification of the best customer profile cluster. in IOP conference series: materials science and engineering vol. 336 12017 (IOP Publishing, 2018).
+
+34. Natekin, A. & Knoll, A. Gradient boosting machines, a tutorial. Front. Neurorobot. 7, 21 (2013).
+
+36. Norton, L. The norton-simon hypothesis revisited. Cancer Treat Rep 70, 163-169 (1986).
+
+37. Fu, F., Nowak, M. A. & Bonhoeffer, S. Spatial heterogeneity in drug concentrations can facilitate the emergence of resistance to cancer therapy. PLoS Comput. Biol. 11, e1004142 (2015).
+
+39. Stein, W. D. et al. Tumor regression and growth rates determined in five intramural NCI prostate cancer trials: the growth rate constant as an indicator of therapeutic efficacy. Clin. Cancer Res. 17, 907-917 (2011).
+
+40. Stein, W. D., Yang, J., Bates, S. E. & Fojo, T. Bevacizumab reduces the growth rate constants of renal carcinomas: a novel algorithm suggests early discontinuation of bevacizumab resulted in a lack of survival advantage. Oncologist 13, 1055-1062 (2008).
+
+41. Kurai, J. et al. Antibody-dependent cellular cytotoxicity mediated by cetuximab against lung cancer cell lines. Clin. Cancer Res. 13, 1552-1561 (2007).
+
+<--- Page Split --->
+
+Bleeker, W. K. et al. Dual mode of action of a human anti- epidermal growth factor receptor monoclonal antibody for cancer therapy. J. Immunol. 173, 4699–4707 (2004).
+
+Weiner, L. M. Building better magic bullets—improving unconjugated monoclonal antibody therapy for cancer. Nat. Rev. Cancer 7, 701–706 (2007).
+
+Wheeler, D. L., Dunn, E. F. & Harari, P. M. Understanding resistance to EGFR inhibitors—impact on future treatment strategies. Nat. Rev. Clin. Oncol. 7, 493–507 (2010).
+
+Lee, S. C., Srivastava, R. M., López-Albaitero, A., Ferrone, S. & Ferris, R. L. Natural killer (NK): dendritic cell (DC) cross talk induced by therapeutic monoclonal antibody triggers tumor antigen-specific T cell immunity. Immunol. Res. 50, 248–254 (2011).
+
+Monteverde, M. et al. The relevance of ADCC for EGFR targeting: a review of the literature and a clinically-applicable method of assessment in patients. Crit. Rev. Oncol. Hematol. 95, 179–190 (2015).
+
+Claesson-Welsh, L., Dejana, E. & McDonald, D. M. Permeability of the endothelial barrier: identifying and reconciling controversies. Trends Mol. Med. 27, 314–331 (2021).
+
+Gifre-Renom, L., Daems, M., Luttun, A. & Jones, E. A. V. Organ-Specific Endothelial Cell Differentiation and Impact of Microenvironmental Cues on Endothelial Heterogeneity. Int. J. Mol. Sci. 23, 1477 (2022).
+
+Sarin, H. Physiologic upper limits of pore size of different blood capillary types and another perspective on the dual pore theory of microvascular permeability. J. Angiogenes. Res. 2, 1–19 (2010).
+
+Parton, R. G., Schrotz, P., Bucci, C. & Gruenberg, J. Plasticity of early endosomes. J. Cell Sci. 103, 335–348 (1992).
+
+Augustin, H. G., Kozian, D. H. & Johnson, R. C. Differentiation of endothelial cells: analysis of
+
+<--- Page Split --->
+
+the constitutive and activated endothelial cell phenotypes. Bioessays 16, 901- 906 (1994).
+
+Cao, Y., Balthasar, J. P. & Jusko, W. J. Second- generation minimal physiologically- based pharmacokinetic model for monoclonal antibodies. J. Pharmacokinet. Pharmacodyn. 40, 597- 607 (2013).
+
+Kay, K., Dolcy, K., Bies, R. & Shah, D. K. Estimation of solid tumor doubling times from progression- free survival plots using a novel statistical approach. AAPS J. 21, 1- 12 (2019).
+
+Zharinov, G. M. et al. Prognostic value of tumor growth kinetic parameters in prostate cancer patients. Oncotarget 10, 5020 (2019).
+
+Lin, Z., Fan, Z., Zhang, X., Wan, J. & Liu, T. Cellular plasticity and drug resistance in sarcoma. Life Sci. 263, 118589 (2020).
+
+Amato, R. J. Chemotherapy for renal cell carcinoma. in Seminars in oncology vol. 27 177- 186 (2000).
+
+Clark, A. M., Ma, B., Taylor, D. L., Griffith, L. & Wells, A. Liver metastases: microenvironment and ex- vivo models. Exp. Biol. Med. 241, 1639- 1652 (2016).
+
+Newton, P. K. et al. Spreaders and sponges define metastasis in lung cancer: a Markov chain Monte Carlo mathematical model. Cancer Res. 73, 2760- 2769 (2013).
+
+Quinn, J. J. et al. Single- cell lineages reveal the rates, routes, and drivers of metastasis in cancer xenografts. Science (80-. ). 371, eabc1944 (2021).
+
+Zhou, J., Liu, Y., Zhang, Y., Li, Q. & Cao, Y. Modeling tumor evolutionary dynamics to predict clinical outcomes for patients with metastatic colorectal cancer: a retrospective analysis. Cancer Res. 80, 591- 601 (2020).
+
+Ahn, J. E., Karlsson, M. O., Dunne, A. & Ludden, T. M. Likelihood based approaches to handling
+
+<--- Page Split --->
+
+498 data below the quantification limit using NONMEM VI. J. Pharmacokinet. Pharmacodyn. 35, 499 401–421 (2008).
+
+500 62. Erdi, Y. E. Limits of tumor detectability in nuclear medicine and PET. Mol. Imaging Radionucl. 501 Ther. 21, 23 (2012).
+
+<--- Page Split --->
+
+## Data Availability
+
+The clinical data that support the findings of this study are available in the Project Data Sphere, https://data.projectdatasphere.org/projectdatasphere/html/access. The machine learning algorithms codes were deposited at https://github.com/zhoujw14/Mapping- Metastasis.git. All source data for our model development and plotting will be provided upon request.
+
+## Acknowledgements
+
+We thank Mr. Timothy Qi and Dr. Tyler Dunlap from University of North Carolina at Chapel Hill, Eshelman School of Pharmacy for providing valuable suggestions and edits for the manuscript. Funding Source: National Institute of Health, R35GM119661
+
+## Author Contributions
+
+Conceptualizations: J.Z., and Y.C.; methodology: J.Z., A.C., G.F., Q.L., and Y.C.; formal analysis: J.Z.; investigation: J.Z., Y.L., Q.L., and Y.C.; writing- original draft: J.Z., and Y.C.; writing- reviewing and editing: J.Z., A.C., G.F., Y.L., Q.L., and Y.C.; supervision: Y.C.
+
+## Competing Interests
+
+All the authors declare no competing interests.
+
+Correspondence and requests for materials should be addressed to Y.C.
+
+<--- Page Split --->
+
+# 519 Tables
+
+520 Table 1. Demographic information of colorectal cancer patients.
+
+| Variable | |
| Age, years (mean, sd) | 60.2 (10.8) |
| Gender (n, %) | |
| Male | 2538 (58.9) |
| Female | 1770 (41.1) |
| Race (n, %) | |
| White/Caucasian | 3883 (90.1) |
| Black/African American | 104 (2.4) |
| Asian | 142 (3.3) |
| Other | 179 (4.2) |
| Body Mass Index, \(\mathrm {kg}/\mathrm {m}^{2}\) (mean, sd) | 26.2 (5.1) |
| Tumor Type (n, %) | |
| Colon | 2581 (59.9) |
| Rectal | 1359 (31.5) |
| Unspecified | 368 (8.5) |
| Prior Surgery (n, %) | |
| Yes | 2993 (69.5) |
| No | 1315 (30.5) |
| Prior Radiation (n, %) | |
| Yes | 445 (10.3) |
| No | 3345 (77.6) |
| Unknown | 518 (12.1) |
+
+<--- Page Split --->
+
+| Treatment1 (n, %) | |
| Bevacizumab plus chemotherapy | 376 (8.7) |
| Bevacizumab plus FOLFOX | 640 (14.9) |
| FOLFIRI alone | 1303 (30.2) |
| FOLFOX alone | 762 (17.7) |
| Panitumumab plus Bevacizumab plus chemotherapy | 372 (8.6) |
| Panitumumab plus FOLFOX | 441 (10.2) |
| Panitumumab plus FOLFIRI | 424 (9.8) |
| Response (n, %) | |
| Complete Response | 118 (2.7) |
| Partial Response | 1473 (34.2) |
| Progressive Disease | 781 (18.1) |
| Stable Disease | 1806 (41.9) |
| Not Evaluable | 130 (3) |
| Metastatic organ number (n, %) | |
| 1 | 553 (12.8) |
| 2 | 1159 (26.9) |
| 3 | 1146 (26.6) |
| ≥4 | 1450 (33.7) |
| KRAS status (n, %) | |
| Wild-Type | 795 (18.4) |
| Mutant | 593 (13.8) |
| Unknown | 2920 (67.8) |
+
+521 'FOLFOX is the combination of folinic acid, fluorouracil and oxaliplatin. FOLFIRI is the combination of folinic acid, fluorouracil and irinotecan.
+
+<--- Page Split --->
+
+
+524
+
+525 Fig. 1 Data source. a. CONSORT diagram of metastatic colorectal cancer data inclusion and exclusion 526 criteria. b. The number of all lesions (target, non- target and new) and target lesions across organs. GR, 527 Genitourinary and Reproductive; CNS, central nervous system; GI, Gastrointestinal tract; LN, lymph 528 nodes.
+
+<--- Page Split --->
+
+
+Fig. 2 Tumor response dynamics were recapitulated by modeling. a. Schematic plot of tumor growth model. b. Box plots of model parameters \(Kd\) , \(F\) and \(Kg\) across organs. Significance was calculated using Kruskal-Wallis tests. The box extends from the 25th to 75th percentiles and the line in the middle is plotted as the median. The whiskers are drawn down to the 10th percentile and up to the 90th percentile. Points below and above the whiskers represent individual lesions. c. The correlations between model parameters. d. The correlations between model parameters and tumor baseline volume. The size of the dots represents lesion number (reported in panel b). The dashed lines with gray area are the linear
+
+<--- Page Split --->
+
+537 regression with \(95\%\) confidence interval. The correlation coefficients and significance were calculated using two- tailed Pearson correlation tests.
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+Fig. 3 Organ- level tumor response and relapse probabilities suggest phenotypic convergence. a and b rank the hazard ratio estimates with \(95\%\) confidence interval by organs on lesion response and relapse in colorectal cancer patients. c and d are the anatomical charts of organ- specific response and relapse hazard ratios in metastatic colorectal cancer (mCRC) and metastatic head and neck squamous cell carcinomas (mHNSCC). e and f are response and relapse hazard ratio with \(95\%\) confidence interval by organs stratified on treatments in mCRC. P- values were calculated by comparing the hazard ratios in antibody targeted therapies plus chemotherapy (TAR+Chemo) vs. chemotherapy alone (Chemo Alone) within each organ.
+
+<--- Page Split --->
+![PLACEHOLDER_33_0]
+
+Fig. 4 Patient relapse sequence association with patient survival. a. Patients were clustered into five
+
+groups based on their lesion relapse sequence. The column labels are the relapse sequence. Color of the heatmap represents the log10 scale of patient number (all plus one to avoid zero values). b. Kaplan- Meier curves of clustered patients overall survival. c. The mean and standard deviation of the first lesion relapse time (1st), time between first and second relapse (2nd- 1st), time between second and third relapse (3rd- 2nd), time between third and fourth relapse (4th- 3rd), and the average relapse time in Lung- First (n=577), Other- First (n=639), and Liver- First (n=930).
+
+<--- Page Split --->
+![PLACEHOLDER_34_0]
+
+
+<--- Page Split --->
+
+Fig. 5. Targeted therapy decreases average time to relapse but has minimal effect on relapse sequence. a. Lung- First, Other- First and Liver- First patients overall survival stratified by treatments. b. Lung- First, Other- First and Liver- First patient proportions by treatments. c, d, and e are patient relapse sequences stratified by treatments. f, g, and h are the mean and standard deviation of the first lesion relapse time (1st), time between first and second relapse (2nd- 1st), time between second and third relapse (3rd- 2nd), time between third and fourth relapse (4th- 3rd), and the average relapse time by treatments of the groups in c, d, and e. TAR+Chemo, antibody targeted therapies plus chemotherapy; Chemo Alone, chemotherapy alone.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+Supplementary3.13. pdf ClinicalTrialInformationNCOMMS2209853. xlsx
+
+<--- Page Split --->
diff --git a/preprint/preprint__04370ec5a4accd2d6e3e1f489050ff616fcd50df7e181fd6b1932f46cd42e1a5/preprint__04370ec5a4accd2d6e3e1f489050ff616fcd50df7e181fd6b1932f46cd42e1a5.mmd b/preprint/preprint__04370ec5a4accd2d6e3e1f489050ff616fcd50df7e181fd6b1932f46cd42e1a5/preprint__04370ec5a4accd2d6e3e1f489050ff616fcd50df7e181fd6b1932f46cd42e1a5.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..864853ab2b128efb8c512357cc5ed836315e4f7e
--- /dev/null
+++ b/preprint/preprint__04370ec5a4accd2d6e3e1f489050ff616fcd50df7e181fd6b1932f46cd42e1a5/preprint__04370ec5a4accd2d6e3e1f489050ff616fcd50df7e181fd6b1932f46cd42e1a5.mmd
@@ -0,0 +1,710 @@
+
+# Immune privilege of adipocyte mitochondria protects from obesity
+
+Anh Cuong Hoang Ulm University
+
+Haidong Yu Ulm University
+
+Ya- Tin Lin Chang Gung University https://orcid.org/0000- 0001- 7910- 1223
+
+Jin- Chung Chen Chang Gung University
+
+Chia- Chun Chen Chang Gung University
+
+Victoria Diedrich Ulm University
+
+Annika Herwig Ulm University
+
+Kathrin Landgraf
+
+University of Leipzig, Pediatric Research Centre, Department of Women's and Child Health https://orcid.org/0000- 0002- 6878- 6033
+
+Antje Körner
+
+Center for Pediatric Research Leipzig (CPL), University Hospital for Children & Adolescents, University of Leipzig, Leipzig https://orcid.org/0000- 0001- 6001- 0356
+
+Tamas Roszer (tamas.roeszer@uni- ulm.de) Ulm University
+
+## Article
+
+Keywords: innate immunity, obesity, interferons, IFI16, vitamin D
+
+Posted Date: November 4th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 988599/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+
+Version of Record: A version of this preprint was published at Nature Metabolism on November 28th, 2022. See the published version at https://doi.org/10.1038/s42255-022-00683-w.
+
+<--- Page Split --->
+
+# Immune privilege of adipocyte mitochondria protects from obesity
+
+Anh Cuong Hoang \(^{1}\) ; Haidong Yu \(^{1}\) , Ya- Tin Lin \(^{2}\) , Jin- Chung Chen \(^{2}\) , Chia- Chun Chen \(^{3}\) , Victoria Diedrich \(^{1}\) , Annika Herwig \(^{1}\) , Kathrin Landgraf \(^{4}\) , Antje Körner \(^{4}\) , Tamás Röszer \(^{1*}\)
+
+\(^{1}\) Institute of Neurobiology, Ulm University, Ulm, Germany \(^{2}\) Department of Physiology and Pharmacology, Graduate Institute of Biomedical Sciences, School of Medicine; Healthy Aging Research Center, Chang Gung University, Taiwan \(^{3}\) Molecular Medicine Research Center, Chang Gung Memorial Hospital at Linkou, Taiwan \(^{4}\) Center for Pediatric Research, University Hospital for Children and Adolescents, University of Leipzig, Germany
+
+\*Correspondence to: tamas.roeszer@uni- ulm.de, Fax: +49 (0) 731- 50- 22629
+
+Short title: Anti- mitochondrial immune response aggravates obesity
+
+Key words: innate immunity – obesity – interferons – IFI16 – vitamin D
+
+<--- Page Split --->
+
+## Abstract
+
+Infant nutrition is rich in lipids, and the adipose tissue has been adapted to properly break down neutral lipids and oxidize fatty acids in infancy. Accordingly, infant adipose tissue contains so- called beige adipocytes, which burn off lipids to heat, and impede fat storage and obesity. We show here that infant adipocytes are immune privileged sites for mitochondria due to a blockade in interferon regulatory factor 7 (IRF7)- signaling, which allows mitochondrial RNA to trigger beige adipocyte differentiation through mitochondria- to- nucleus signaling. These mechanisms serve to maintain an extensive mitochondrial network in beige adipocytes and protect against obesity. By contrast, fat storing white adipocytes lack these mechanisms and respond to their mitochondrial content with inflammation. We show that obesity subverts the immune privilege for mitochondria in adipocytes, which reduces mitochondrial mass and abrogates beige adipocyte development. In turn, suppressing IRF7 signaling and restoring the RNA- mediated mitochondria- to- nucleus signaling in adipocytes effectively reduces obesity.
+
+<--- Page Split --->
+
+
+
+## Graphical Abstract
+
+Infant adipocytes have a suppressed IRF7 expression and a mitochondria- to- nucleus signaling through mitochondrial RNA (mtRNA), which stimulates the transcription of beige adipocyte genes, and is key for mitobiogenesis and burning off fat as heat.
+
+## Video summary
+
+https://figshare.com/s/36e7ca6a4953471fba42
+
+<--- Page Split --->
+
+Childhood obesity is a serious public health crisis and is associated with an increased risk of obesity and diabetes in adulthood, which is projected to affect \(\sim 58\%\) of the world's adult population by 2030 (1- 3). Obesity is an excessive accumulation of white adipose tissue (WAT) mediated by a mismatch between energy supply and utilization. Infant nutrition is rich in lipids, and adipocytes in the infant WAT break down lipids to free fatty acids, and generate energy and heat from lipids in their extensive mitochondrial network (4- 6). These fat oxidizing and thermogenic fat cells are termed as beige adipocytes (7, 8). In adults however, adipocytes of the subcutaneous fat depots are scarce in mitochondria and accumulate fat (9, 10). WAT is necessary for metabolic and endocrine health in adulthood, however its excess expansion accounts for metabolic diseases (1- 3). Previous studies have suggested that the premature loss of fat oxidizing and thermogenic potential in infant WAT is accelerated in childhood obesity (2, 3, 10), and delaying or reverting the metabolic shift of WAT from fat catabolism to storage has therapeutic potential in the prevention of obesity (7, 8).
+
+Cell metabolism of fat into ATP and heat requires an extensive mitochondrial network and mitochondrial uncoupling (8), which increases the abundance of "misplaced" mitochondria- associated danger signals in the cytoplasm, such as prokaryote- type mitochondrial DNA (mtDNA) and virus- like double stranded RNA (dsRNA). These signals trigger inflammasome activation and interferon (IFN) response (11), which abrogate the expansion of the mitochondrial network and the capacity of fat oxidation, and cause metabolic inflammation (12). Obesity is a hyper- inflammatory disorder, and IFNs trigger obesity- associated metabolic diseases (13, 14), especially in children with insufficient breastfeeding (15), who are prone for premature WAT expansion (7).
+
+These observations prompted us to question whether infant adipocytes have a unique nucleic acid immunity that supports their mitochondrial network. We found that the infant
+
+<--- Page Split --->
+
+subcutaneous adipocytes were immune privileged towards mitochondria due to the suppression of cytosolic mtDNA recognition and interferon regulatory factor 7 (IRF7). Mitochondrial RNA (mtRNA) eventually activated a mitochondria- to- nucleus signaling which stimulated mitobiogenesis and beige adipocyte development without provoking an IFN- response against mitochondrial content. These mechanisms were lacking from the adult subcutaneous adipocytes, which responded with IFN- burst to mitochondrial content and were hostile for mitochondria. Obesity subverted mitochondrial immune privilege in adipocytes, and in turn, restoring mtRNA- mediated signaling effectively reduced obesity. Innate immune sensing of mitochondrial nucleic acids is hence a novel mechanism which controls early adipose tissue development and protects against obesity.
+
+## Results
+
+## Infant subcutaneous fat is immune privileged for mitochondria
+
+After birth, subcutaneous adipose tissue is a relevant fat depot in mouse and human (6), hence we surveyed the transcriptional landscape of mouse inguinal adipose tissue (iAT) at postnatal day 6 (P6) and P56 by next- generation sequencing (NGS) (Fig. S1A, Fig. S2A,B). P6 iAT was rich in beige adipocytes and mtDNA, and expressed beige adipocyte- associated transcripts together with Prdm16, encoding PR domain containing 16, a key transcriptional regulator of thermogenic fat development (Fig. S1B- E) (10, 16). By contrast, P56 iAT lacked beige adipocytes, contained significantly lower amounts of mtDNA, and expressed transcripts associated with white adipocytes (Fig. S1B- E). Thus, infant but not adult mouse fat is rich in thermogenic, fat- oxidizing adipocytes (6). Beige adipocytes have been reported in the subcutaneous adipose tissue of human infants and children (7, 10), and we found that the level of \(UCP1\) , encoding uncoupling protein 10, in human
+
+<--- Page Split --->
+
+infant iAT correlated positively with the level of beige adipocyte genes and negatively with white adipocyte markers (Fig. S1F).
+
+IFN- stimulated genes (ISGs) were suppressed in adipocytes at P6 (Fig. 1A- C), and the under- represented ISGs belonged to one network (Fig. S2B), and included the stimulator of interferon genes (STING) and IFN- inducible protein absent in melanoma 2 (AIM2) pathways (Fig. 1B). These pathways trigger DNA- inflammasome assembly, inflammasome activation and IFN- response to cytosolic DNA (17). Cytosolic B- DNA is recognized by DDX41 (DEAD- box helicase 41) and p204, also known as IFN- - inducible protein 204 (IFI204) in BALB/C mice, IFI205 in C57/BL6 mice, and IFI16 in human (17) (for details see Fig. S2C). Cytosolic Z- DNA, which is prevalent in transcriptionally active cells (18), is recognized by ZBP1 (Z- DNA- binding protein 1, also termed DAI (19)). Transcription of these cytosolic DNA sensors was low at P6, specifically in adipocytes (Fig. 1B,C, Fig. S2D- H).
+
+The STING and AIM2 pathways converge on interferon regulatory factor 3 and 7 (IRF3, IRF7), and the adipocyte level of Irf7 was significantly lower at P6 than at P56 (Fig. 1B,C). Accordingly, P6 adipocytes were protected from inflammasome activation by cytosolic DNA (Fig. 1B, Fig. S3A- D, S4A- C) or endosomal DNA (Fig. S5A- F), and genetic ablation of IRF7 protected adipocytes from IFN- response against mtDNA (Fig. S4E). IRF7 activation triggered the expression of the STING/AIM2 pathway in P56 adipocytes (Fig. S4F), and consistently, the STING/AIM2 pathway proteins were lacking in P6 adipocytes (Fig. 1D). In turn, AIM2, DDX41, p204 and ZBP1 were present in the perinuclear region and in the cytoplasm of P56 adipocytes, which distribution is consistent with their known tasks to monitor DNA fragments in specific subcellular compartments (Fig. 1D) (19, 20).
+
+<--- Page Split --->
+
+We next examined the expression of the STING/AIM2 pathways and IRF7 in the inguinal adipose tissue (iAT) of human infants and children (0.3–6.9 years of age, N=26). Overweight (BMI- SDS>1.28) and obesity (BMI- SDS>1.88) strongly increased the expression of IFI16, ZBP1, and IRF7, and moderately increased TMEM173 level (Fig. 1E, S6A- C), which was coherent with the loss of beige adipocytes in childhood obesity (3, 7, 21). IFI16 protein level positively correlated with adipocyte size (Fig. 1E). IRF7 and IFI16 expression was triggered by in vitro white adipogenesis (Fig. 1E, Fig. S6D), and TMEM173 expression positively correlated with IFI16 and IRF7 levels and was increased by premature loss of beige fat (Fig. 1E, Fig. S6D). We next extended the age group of our analysis (7.0–11.0 years, N=73; 11.1–20.5 years, N=155) and found that in lean subjects the STING/AIM2 pathways moderately increased with age, matching the time scale of the physiological WAT expansion (Fig. S6E).
+
+In summary, immune response to cytosolic mtDNA and mtRNA was lacking in P6 adipocytes and was dependent on IRF7 (Fig. 1F, Fig. S3D, Fig. S4C- E). Moreover, STING had opposing functions in P6 and P56 adipocytes: activation of STING with its natural activator 2'3'- cyclic- GMP- AMP (cGAMP), increased autophagosome number and mitophagy in P6 adipocytes (Fig. 1G,H,I, Fig. S7A- C), while STING inhibition compromised mitophagy, reduced mitochondrial mass and led to inflammation in P6 adipocytes (Fig S7D- G). On the contrary, cGAMP triggered IFN- response in P56 adipocytes (Fig. 1F, Fig. S3D).
+
+STING stimulates IFN- response against mtDNA (22), however it is known that the STING signaling may also induce autophagy (23, 24). Mitophagy is a form of autophagy and protects the cytosol from leaking mtDNA (25). Our data show that an autophagy- inducer effect of STING protects from cytosolic mtDNA accumulation in infant adipocytes (Fig. S7D- G), and infant adipocytes are also protected against the STING- induced IFN- response (Fig. 1I).
+
+<--- Page Split --->
+
+
+Fig 1. Infant adipocytes are immune privileged for mitochondria
+
+(A) NGS analysis of mouse iAT, DEGs: differentially expressed genes, ISGs: interferon stimulated genes. (B) Excerpt of the interactome-, and heat map of genes underrepresented in P6 iAT. Scheme of STING signaling, and inflammasome-associated caspase 1 (CASP1) activity in P6 and P56 iAT in response to 18h cGAMP treatment. Cyt-B-DNA: cytosolic B-DNA; Cyt-Z-DNA: cytosolic Z-DNA. (C) Transcription of the STING/AIM2 pathways in mouse iAT at P6 and P56. (D) Expression of DNA sensors in adipocytes. (E) Transcription of the STING/AIM2 pathway in iAT of human infants and children. Correlation of IFI16 level and adipocyte (AC) size in human. IRF7 level in human preadipocytes (Pre-ACs) and white ACs. Correlation of IFI16 and IRF7 with TMEM173 levels in human infant iAT. (F) Response of P6 and P56 adipocytes to 18h cGAMP treatment. (G) Mito-Tracker-Red (MTR) staining of P6 adipocytes after 2h cGAMP treatment. (H) Top: Labeling of autophagosomes (APh) in P6 adipocytes. nc: nucleus, Bottom: APh number in P6 adipocytes and in 3T3-L1 cells following vehicle or 2h cGAMP treatment. TEM image of a P6 adipocyte showing autophagosome formation. Php: phagophore, Phs: phagosome, Phl: phagolysosome, Mt: mitochondrion. Scale: 10 μm (D,G,H); 0.1 μm (TEM). \(*P< 0.05\) , \(**P< 0.01\) , \(***P< 0.001\) . Student's 2-tailed unpaired \(t\) -test or one-way ANOVA with Dunnett's post-hoc test. (I) Opposing effects of STING activation in P6 and P56 iAT.
+
+<--- Page Split --->
+
+## Infant adipocytes employ mtRNA as a paracrine signal for beige fat development
+
+We found that P6 adipocytes secreted mitochondrial contents in extracellular vesicles (EVs). Adipocyte EVs were generated in the endosomal pathway, by inverse budding of endosomes, leading to the formation of multivesicular bodies (MVBs) (Fig. 2A,B; S8A- G). In line with this, transcripts necessary for inverse budding of endosomes and the generation of MVBs were overrepresented in iAT at P6 (Fig. 2B). Inverse budding allows cytosolic nucleic acids to be delivered to MVBs, and this process is a form of micro- autophagy (26). Endosomal content can be further targeted for degradation in the lysosomes; however lysosomal genes were underrepresented in P6 iAT and by contrast, transcripts required for exocytosis were over- represented in P6 iAT (Fig. 2B). P6 EVs were packed with mtDNA molecules and mitochondrial mRNA and rRNA species (Fig. 2C- E). Some of the EV cargo mRNAs, including Nds, Col and Cytb, are known to generate non- coding mtRNA species (27, 28). The adipose tissue mesenchymal stem cell EV- specific microRNA miR29a- 5p was absent in P6 EVs (Fig. S8H). P6 EVs also contained minimal amounts of circular- RNA, piwi- RNAs and the adipocyte- specific microRNA miR34a, together with traces of Ucp1 mRNA (Fig. S8I). P6 adipocytes released more EVs than their P56 counterparts (Fig. S8J), and inhibitors of EV generation suppressed both DNA and RNA release from adipocytes (Fig. S8K).
+
+P6 EVs increased mitochondrial content, mitobiogenesis, uncoupling protein- 1 (UCP1) expression and thermogenesis in recipient adipocytes, without inducing unfavorable mitochondrial swelling (Fig. 2F,G; Fig. S9A). P6 EVs also triggered the transcription of beige adipocyte genes (Fig. 2H). Adipocyte EVs carried dsRNA (Fig. 2E, S9B), which may activate Toll- like receptor 3 (TLR3), or the retinoic acid- inducible gene- I (RIG- I) and RIG- I- like melanoma differentiation- associated protein 5 (MDA5) signaling (29, 30). Cytosolic single stranded RNA, or stimulation of
+
+<--- Page Split --->
+
+TLR3 did not mirror the effects of EVs (Fig. S10A- C), unlike the activation of RIG- I/MDA5 which induced strong beige adipocyte gene transcription (Fig. 2I, S10D- H).
+
+Beige- inducing effect of EVs was dependent on IL- 6/STAT3 and RIG- I/MDA5 signaling (Fig. 2J, Fig. S11A- E), and the lack of RIG- I or MDA5 led to the loss of beige adipocytes and compromised mitobiogenesis, and compromised the expression of the nucleus- encoded mitochondrial succinate dehydrogenase complex (Fig. 11F,G).
+
+Nucleic acids in EVs are protected from extracellular nucleases by the surrounding membrane and they may function as intercellular messengers (31). Accordingly, delivery of total mRNA into the cytosol induced beige adipocyte gene expression, mitobiogenesis and mitochondrial thermogenesis (Fig. 2I, Fig. S10G,H) in a RIG- I/MDA5- dependent manner (Fig. 2J,K, Fig. S11H). Cytosolic mtDNA stimulated mitophagy in infant adipocytes (Fig. S12A,B). In summary, EVs of infant adipocytes conveyed mtRNA and mtDNA to recipient adipocytes and triggered beige adipocyte differentiation and mitophagy, respectively.
+
+Breast milk is a known beige- inducing signal (7), and we found that human breast milk EVs were rich in mtRNA (Fig. S12C). Eventually, breast milk EVs – unlike formula milk EVs – induced beige adipocyte gene expression, mitobiogenesis and mitochondrial thermogenesis, and in turn reduced IRF7 abundance in human adipocytes (Fig. S12D,E).
+
+<--- Page Split --->
+
+
+Fig. 2. Infant adipocytes cast away mtRNA to induce beige adipose tissue development (A) Clathrin-coated pits, endosome budding [1-4] and multivesicular bodies (MVBs) [5] in P6 adipocyte. Pm: plasma membrane, En: endosome, Aly: autolysosome, Cav: caveolae, arrowhead: EVs in MVBs. Scale: \(1 \mu \mathrm{m}\) . (B) P6/P56 iAT comparison of transcripts associated with endosomes, MVBs, lysosomes and exocytosis. (C) TEM image of EVs released by P6 adipocytes. Scale: \(0.1 \mu \mathrm{m}\) . FACS analysis of nucleic acids in EVs of P6 adipocytes. N-St: non-stained; St: stained with SytoxGreen. Amount of EV-bound nucleic acids in cell culture media of P6 adipocytes. (D) Level of mtDNA in EVs of P6 adipocytes. \(l\) : light chain; \(h\) : heavy chain. (E) Labeling of dsRNA with J2 antibody in P6 adipocytes; scale: \(10 \mu \mathrm{m}\) . Quantification of RNA species released by EVs of P6 adipocytes. Effect of P6 EVs on mitochondrial content, mitobiogenesis (F), UCP1 level (G) and beige gene expression (H) in P56 adipocytes. -EVs: cells cultured in EV-free media, +EVs: cells treated with EVs. Scale: \(10 \mu \mathrm{m}\) (MTR); \(50 \mu \mathrm{m}\) (UCP1), MFI: mean fluorescence intensity. (I) Cytosolic delivery of mtDNA and mtRNA into 3T3-L1 cells, and their effect on beige gene transcription and mitobiogenesis. (J) Effect of P6 EVs on mitobiogenesis of adipocytes. \(Ddx58^{- / - }\) : RIG-I (DDX58)-deficient adipocytes, \(Mda5^{- / - }\) : MDA5-deficient adipocytes. \(*P< 0.05\) , \(**P< 0.01\) , \(***P< 0.001\) . Student's 2-tailed unpaired \(t\) -test or one-way ANOVA with Dunnett's post-hoc test. (K) Scheme of mtRNA-activated signal transduction in infant adipocytes.
+
+<--- Page Split --->
+
+## Suppressed IRF7 signaling permits beige adipogenesis by mtRNA
+
+P56 adipocytes expressed IRF7, unlike P6 adipocytes. Activation of the STING/AIM2 and RIG- I/MDA5 pathway was strong in P56 adipocytes with synthetic ligands, with mtRNA or with mtDNA, leading to Ifnb expression (Fig. S13A). Ultimately, IFNβ damaged adipocyte mitochondria (Fig. S13B,C). In turn, IRF7- deficient adipocytes were immune privileged for mitochondria (Fig. 3A, S4E), and mice lacking IRF7 retained their beige adipocytes to adulthood (Fig. 3B). This is coherent with the protection of IRF7- deficient mice from obesity (32). Moreover, P6 EVs reduced Irf7 mRNA and IRF7 protein levels in adipocytes (Fig. 3C) and did not induce IFN- response (Fig. S13D). On the contrary, P56 EVs induced IFN- response and triggered Irf7 expression, and reduced mitochondrial content in adipocytes (Fig. S13D,E).
+
+Vitamin D receptor (VDR)- controlled gene networks were highly expressed in P6 iAT (Fig. S2A). The known VDR- target Camp, encoding cathelicidin, an adipose tissue enriched antimicrobial peptide (33), was highly expressed at P6. In turn, the VDR- repressed gene Corola had a low transcript level at P6 (Fig. 3D). Corola encodes coronin A1, also known as tryptophan- aspartate containing coat protein (TACO), which inhibits autophagosome formation (34). Low levels of coronin A1 allow autophagy (34), which is in accordance with the prominent autophagy we found in P6 iAT (Fig. 1H). The transcription of vitamin D metabolizing enzymes favored the storage of vitamin D3 (Vit- D3) and the synthesis of the potent VDR- agonist calcitriol in P6 iAT (Fig. 3D). Moreover, miR434- 3p, a VDR- controlled miRNA which had complementarity to Irf7 mRNA (35) was also highly expressed in P6 iAT (Fig. 3E). IRF7 level and inflammasome activation was effectively reduced by miR434- 3p in adipocytes (Fig. 3E). Moreover, P6 EVs were rich in Vit- D3, and cytosolic mRNA increased the transcription of the calcitriol synthesis gene Cyp27b1 in adipocytes (Fig. 3F). VDR protein expression was higher in P6 than in P56 iAT, and
+
+<--- Page Split --->
+
+Vit- D3 effectively suppressed Irf7 transcription in a VDR- dependent manner in adipocytes (Fig. 3F). Diet- induced obesity diminished adipocyte Vdr expression, and concomitantly upregulated Irf7 in mice (Fig. 3G). Accordingly, inhibition of VDR signaling in young mice led to the loss of beige adipocytes in iAT, along with increased IRF7 level in adipocytes (Fig. 3H). In turn, suppression of IRF7 level with miR434- 3p protected from inflammasome activation in adipocytes of HFD- fed mice (Fig. 3I).
+
+IRF7 is a hub for the transcription of AIM2/STING pathway (Fig. 13F,G), and thus repression of IRF7 expression is a potential mechanism that protects infant adipocytes from an IFN- response to cytosolic mtDNA/mtRNA (Fig. 13H). We found that VDR signaling suppressed IRF7 expression and abolished immune response towards cytosolic mtDNA/mtRNA in mouse and human adipocytes (Fig. 3J- L), but did not affect Il6 transcription and IL- 6 release (Fig. 3K,L). VDR thus did not block the beige adipocyte- inducing IL- 6 production, however suppressed IRF7- dependent inflammatory signaling. This allowed cytosolic mtRNA to induce mitobiogenesis and beige gene expression, and mtDNA to trigger mitophagy, without unfavorable induction of an IFN- response (Fig. 3M).
+
+## Obesity in early postnatal life compromises immune privilege of adipocyte mitochondria
+
+We found that childhood obesity compromised VDR- controlled gene networks and decreased the expression of the calcitriol producing CYP27A1 (Fig. 4A), and increased IRF7 expression in the iAT (Fig. 1E). Similarly, diet induced obesity compromised Vdr and increased Irf7 expression in mouse, and inhibition of VDR signaling in infant mice led to the loss of beige fat cells (Fig. 3G,H). Next, we studied a mouse model of childhood obesity, using infant mice which were nursed by dams fed with HFD (Fig. 4B) (36). In the offspring of HFD- fed dams adipocytes had a
+
+<--- Page Split --->
+
+compromised Vdr, and a robust Irf7 expression (Fig. 4C), and beige adipocytes were lacking from the iAT (Fig. 4D). Eventually obesity developed and the adipocytes had a sustained inflammasome activation (Fig. 4E). Moreover, the mitochondrial network was compromised in adipocytes (Fig. 4F), and AIM2/STING pathway proteins were expressed in the cytosol and in the nuclei of adipocytes of mice nursed by HFD-fed dams (Fig. 4F). In turn, Vit-D3 reverted these adverse effects and protected the beige adipocyte content in infant mice (Fig. 4G), reduced obesity and adipocyte inflammation (Fig. 4H). In adult HFD-fed mice, cytosolic delivery of mtRNA into the iAT, combined with Vit-D3 treatment, reduced IRF7 level and increased beige adipocyte content in the iAT (Fig. 4I,J), reduced obesity and adipocyte inflammation, increased mitochondrial mass, thermogenesis and energy expenditure, inhibited inflammasome activation following STING activation, and induced adipocyte expression of calcitriol forming Cyp27b1 (Fig. 4K-N, Fig. S14A-C).
+
+Altogether, the immune privilege of mitochondrial content was dependent on the suppression of adipocyte IRF7 level by VDR. In human, childhood obesity compromised VDR signaling and increased IRF7 expression in the adipose tissue. Adipocyte maturation increased IRF7 level, and in turn, Vit-D3 reduced IRF7 expression and immune response to cytosolic mtRNA and mtDNA in human adipocytes. Similarly, diet induced obesity compromised Vdr and triggered Irf7 transcription in both adult and infant mice and triggered immune response against cytosolic mtDNA and mtRNA. These data show that beige adipocytes lack an immune response against mtDNA/mtRNA at least in part due to VDR signaling (Fig. 5A). When VDR sustains this immune privilege of mitochondria, cytosolic mtRNA stimulates the expression of nucleus- encoded mitochondrial genes and promotes beige adipocyte development (Fig. 5B). This mitochondria- to- nucleus signaling protects against obesity.
+
+<--- Page Split --->
+
+
+Fig. 3. VDR abrogates IRF7 expression in the infant adipocytes
+
+(A) Response of P56 adipocytes to cGAMP, CCCP (carbonyl cyanide m-chlorophenyl hydrazone)-induced mitochondrial damage, cytosolic mtDNA and mtRNA. Irf7-/-: IRF7-deficient adipocytes. (B) iAT of adult wt and Irf7-/- mice. Scale: \(25 \mu \mathrm{m}\) . H&E: hematoxylin-eosin (C) Effect or P6 EVs on Irf7 and IRF7 level in mouse adipocytes (D) Structure of miR434-3p, its level in P6 and P56 iAT, and its effect on IRF7 level and inflammasome activity in mouse adipocytes. (E) P6/P56 transcript level of Vdr, VDR-controlled genes and vitamin D metabolism genes in iAT. (F) Top: Level of Vit-D3 in P6 EVs, effect of cytosolic mtRNA on the expression of calcitriol synthesizing Cyp27b1, and the ratio of VitD3/VDR in P6 iAT. Bottom: Effect of 48h Vit-D3 treatment on Irf7 level in mouse adipocytes. PS121912: VDR inhibitor. (G) Level of Vdr and Irf7 in iAT of HFD-fed mice. (H) Left: Histology of iAT at P10 of mice treated with vehicle or PS12912. Scale: \(25 \mu \mathrm{m}\) . Right: Adipocyte IRF7 protein level of the same mice. (I) Effect of overexpression of miR434-3p on HFD-induced inflammasome activation in adipocytes. (J,K) Response of \(1 \mu \mathrm{M}\) Vit-D3 pretreated mouse adipocytes to cytosolic mtDNA, mtRNA, or cGAMP. (L) IRF7 level and cGAMP response of human adipocytes treated with vehicle or Vit-D3. \(*P< 0.05\) , \(**P< 0.01\) , \(***P< 0.001\) . Student's 2-tailed unpaired \(t\) -test or one-way ANOVA with Dunnett's post-hoc test. (M) Scheme of VDR function in infant adipocytes.
+
+<--- Page Split --->
+
+
+Fig. 4. Effect of cytosolic mRNA combined vit Vit-D3 treatment in diet-induced obesity (A) VDR-controlled gene expression in iAT of children. (B) Nursing mice received high-fat diet (HFD) or normal chow diet (NCD) between postnatal day 6 and 9 of the offspring. Mice nursed by NCD-fed or HFD-fed dams were analyzed on postnatal day 10 (P10). (C) \(Vdr\) and \(Irf7\) expression in iAT. (D) Histology of iAT. H&E: hematoxylin and eosin staining, UCP1: UCP1 immunostaining, Scale: \(50 \mu \mathrm{m}\) . Note the lack of multilocular adipocytes in mice nursed by HFD-fed dams. (E) Ratio of iAT and body weight, and inflammasome caspase 1 (CASP1) activity of the adipocytes. (F) Mitochondrial network and the expression of AIM2, DDX41, p204 and ZBP1 in adipocytes. MTR: MitoTracker Red. Scale \(50 \mu \mathrm{m}\) . (G) Mice were nursed by HFD-fed dams, and treated with vehicle or Vit-D3 from P6 to P9. Histology of iAT on P10. Scale: 100 \(\mu \mathrm{m}\) (H) Ratio of iAT and body weight, and CASP1 activity of the adipocytes on P10. (I) In adult HFD-fed mice the iAT was transfected with vehicle or mtRNA, and IRF7 protein level was measured in adipocytes. (J) Histology of iAT of vehicle- or mtRNA-transfected mice. (K) Adipose tissue weight/body weight ratio, and CASP1 activity of adipocytes. eAT: epididymal adipose tissue (L) Mitochondrial network of adipocytes isolated from vehicle- or mtRNA-transfected mice. Scale: \(10 \mu \mathrm{m}\) . Note the expansion of the mitochondrial network after mtRNA treatment. (M) Mitochondrial mass (relative MTR fluorescent intensity) and mitochondrial temperature change (Mito-ΔT) in adipocytes isolated from vehicle- or mtRNA-transfected mice. (L) CASP1 activity of adipocytes isolated from vehicle- or mtRNA-transfected mice, and treated with vehicle of cGAMP for 4h. \(**P< 0.01\) , \(***P< 0.001\) . Student’s 2-tailed unpaired \(t\) -test or one-way ANOVA with Dunnett’s post-hoc test.
+
+<--- Page Split --->
+
+## Discussion
+
+Adipose tissue inflammation is considered deleterious for metabolism (37). However, various lines of evidence show that differentiation of thermogenic adipose tissue requires JAK/STAT3 signaling (7, 38, 39), and an autocrine IL- 6/STAT3 signaling loop is sustained by breast milk- derived lipid signaling in the newborn adipose tissue (7). Some inflammatory signal mechanisms that cause obesity- associated metabolic impairment also sustain beige adipocytes (40, 41). Here we report the unexpected finding that beige adipocyte development is promoted by a potentially inflammation- evoking cytosolic RNA signal, released by the mitochondria of infant adipocytes.
+
+
+
+Fig. 5. Role of mtRNA signaling in beige adipocytes
+
+(A) Under physiological conditions infant adipocytes release cytosolic mtRNA and mtDNA in extracellular vesicles (EVs). Eventually, mtRNA serves as endogenous signal for beige adipogenesis in neighboring cells through the RIG-I/MDA5/IL-6/STAT3 pathway. In turn, mtDNA content of the EVs triggers mitophagy through STING signaling. (B) Albeit cytosolic mtRNA and mtRNA are noxious signals, they can act as metabolically beneficial mitochondria-to-nucleus signals when IRF7 expression is suppressed. VDR is an effective suppressor of IRF7 and abrogates IFN-response to cytosolic mtRNA and mtDNA in infant adipocytes. Infant adipocytes are hence immune privileged sites for mitochondria, allowing a retrograde mitochondria-to-nucleus signaling through mtRNA, which is key for mitobiogenesis and beige fat development.
+
+<--- Page Split --->
+
+The endosymbiotic origin of mitochondria has led to a metabolic co- dependence of the mitochondria and the host cell (42). This is driven by a retrograde, mitochondria- to- nucleus signaling pathway, as the majority of genes required for the maintenance of mitochondria are encoded in the nuclear genome. We show that, analogous to a parasite- host interaction, mitochondrial nucleic acids are released by EVs, and are taken up by surrounding adipocytes to activate cytosolic RNA sensors that stimulate an autocrine IL- 6/STAT3 signaling loop, ultimately triggering the nuclear expression of beige adipocyte genes (Fig. 2K, Fig. 5A). Non- coding RNA species of mitochondria are known to increase the transcription of mitochondrial genome- encoded genes (27). As an equivalent mechanism, we show that mtRNA species boost the transcription of nuclear genome- encoded genes for mitochondrial biogenesis and thermogenesis. This is key for mitobiogenesis since the majority of the mitochondrial genes are encoded in the nuclear genome (42). The release of EVs containing mitochondrial nucleic acids resembles the recently explored mechanism that allows nucleic acid delivery from bacteria to host cells in membrane microvesicles (43, 44).
+
+The primary sensors of cytoplasmic mtRNA are RIG- I and MDA5. RIG- I detects dsRNAs with or without a 5'- triphosphate end; MDA5 binds uncapped RNA; and RIG- I and MDA5 selectively recognize short and long dsRNAs, respectively (29, 30). Given the prokaryote origin of mitochondria, various mtRNA species such as mitochondrial ribosomal RNAs, uncapped mitochondrial mRNA, and non- coding mtRNAs, can potentially stimulate the cytoplasmic RNA sensor system (45, 46). Beige adipocyte gene transcription was achievable by indirect RIG- I activation using cytosolic p(dA:dT), and also by MDA5 activation using cytosolic high molecular weight p(I:C), but not with cytosolic ssRNA. Coherently, lack of RIG- I and MDA5 signaling
+
+<--- Page Split --->
+
+compromised the mtRNA- mediated beige adipocyte development, and abrogated nucleus- encoded SDH- A expression and mitobiogenesis, and promoted the loss of beige adipocytes in mice.
+
+Nevertheless, excessive release of mitochondrial content is a danger signal, and activates an IFN- response, which is detrimental for thermogenic fat development (16, 47, 48), triggers obesity, mitochondrial dysfunction and the mitochondrial pathway of adipocyte apoptosis (49, 50), and may aggravate obesity- associated metabolic diseases (51, 52). We show here that beige adipocytes lack cytosolic DNA sensors and show suppressed expression of IRF7. Consequently, cytosolic mtDNA and mtRNA do not stimulate an IFN- response in beige adipocytes. Instead, beige adipocytes respond by activating mitophagy to cytoplasmic mtDNA, allowing the removal of damaged mitochondria and curtailing inflammation. Moreover, cytosolic mtRNA stimulates mitobiogenesis. The key protective mechanism – i.e., compromised IRF7 signaling – is a trait of the infant adipocytes, and is lost in the course of adipocyte maturation. While the activation of STAT1 and NFκB signaling may account for the increasing IRF7 expression during adipocyte maturation (6), we show that VDR signaling contributes to the suppression of IRF7 level in infant adipocytes, and cytosolic mtRNA stimulates mitochondrial calcitriol synthesis – hence supplies a VDR ligand – in infant adipocytes. However, diet- induced obesity in mouse, and obesity in children were associated with robust expression of the cytosolic DNA sensor system and IRF7, leading to the loss of the immune privilege of mitochondria.
+
+VDR signaling is involved in the innate immune response in the adipose tissue (33), and VDR may also skew IFN- response and IRF7 expression (53, 54). Vit- D3 supplementation is today routine in postnatal care, however, Vit- D3 deficiency is prevalent among obese children and adolescents and is a risk factor for metabolic diseases (55- 57). Vit- D3/VDR is proposed to inhibit weight gain by activating UCP3 in the muscles (58), albeit VDR overexpression promotes weight
+
+<--- Page Split --->
+
+gain in mouse (59). Indeed, promotion of formula feeding originally served to increase Vit- D3 supply and induce weight gain (60). Formula milk lacks maternal lipid species that maintain beige fat and has obesogenic effects (7). We also show here that formula milk lacks beige- inducing mRNA signals. Moreover, VDR signaling was impaired in the adipose tissue of obese children, therefore despite its increased Vit- D3 level, formula milk is not sufficient to trigger beige adipogenesis. However, when Vit- D3 supplementation is combined with stimulation of cytosolic mRNA signaling, beige adipocytes develop and obesity is reduced.
+
+In summary, beige adipocyte development is dependent on a mtRNA- mediated signaling and the suppression of IFN- response. Restoring the mtRNA- mediated mitochondria- to- nucleus signaling may represent a novel and effective mechanism to increase beige fat and reduce obesity.
+
+<--- Page Split --->
+
+## Methods
+
+## Animals and cells
+
+We used wt male C57BL/6 (Charles River Laboratories, Wilmington, MA), Irf7- (RIKEN, Wako, Japan), Ddx58- and Mda5- (kindly provided by Gunther Hartmann, University of Bonn, Germany) mice. All mouse lines were housed under SPF conditions. Animal experiments were approved by the local ethics committees. Primary mouse adipocytes were isolated by collagenase digestion and separation of cell fractions and subsequently analyzed or cultured, as described (7).
+
+## Human samples
+
+Subcutaneous adipose tissue from human infants, adolescents and young adults were collected in the Leipzig Childhood Adipose Tissue cohort during elective surgery (3). For all children included in the study written informed consent was obtained from the parents. The study protocol was approved by the local ethics committee of the Medical Faculty, University of Leipzig (#265- 08- ff; NCT02208141). Adult adipocytes samples were collected in our previous study (7).
+
+## mRNA analysis and next-generation sequencing
+
+Extraction of total RNA was performed as described (6). qPCR assays were carried out on the Quantabio platform (Beverly, MA), using Bactin, Gapdh and Pgia as references. Primer sequences are provided in Supplemental Table 1. NGS analysis was carried out on the BGISEQ- 500 platform by BGI Genomics Inc. (Cambridge, MA), generating about 26.20M reads per sample (Fig. S15). EnrichR, Panther and Interferome- 2.0 were used for annotation of transcripts; clustered image maps (CIMs, heat- maps) were rendered by CIM- Miner and Heatmapper. Gene expression in human samples was quantified by ILLUMINA HT12v4 Gene Expression BeadChip arrays and data were background corrected and quantile normalized (6).
+
+<--- Page Split --->
+
+## Supplemental methods
+
+Cytosolic delivery of RNA/DNA, viral infections, ELISA assays, overexpression studies, autophagosome/lysosome labeling, EV collection, FACS, histology, image analysis, and TEM analysis are provided in the Supplemental Information.
+
+## Data representation and statistics
+
+Data are represented as mean \(\pm\) s.e.m, along with each individual data point. When data are represented as CIMs to visualize gene transcription differences between experimental conditions, we indicate fold changes or Z- scores of the relative abundance. Statistical significance is indicated as \(^{*}P< 0.01\) , \(^{**}P< 0.01\) ; \(^{***}P< 0.001\) , Student's 2- tailed unpaired \(t\) - test, or 1- way ANOVA with Dunnett's post hoc test.
+
+## Data and materials availability
+
+Materials and data are available for secondary use upon request. Flow Repository identifiers of FACS data are as follows: #FR- FCM- Z236, #FR- FCM- Z2R6, #FR- FCM- ZYPU, #FR- FCM- ZYUU. NGS data are deposited at GEO with the accession number #GSE185317. For secondary analysis, we used our previously published DNA Chip and NGS datasets, with accession numbers #GSE125405, #GSE90658, #GSE154925 and #GSE133500.
+
+## Acknowledgements
+
+We thank Dr. Kenneth McCreath for editing the manuscript.
+
+## Funding
+
+This study was supported by the German Research Fund (DFG, RO 4856- 1, to TR; DFG, CRC1052 C05, to AK), the European Foundation for the Study of Diabetes on New Targets for Type 2 Diabetes, Supported by MSD (No. 96403, to TR), by the Federal Ministry of Education and Research (BMBF), Germany (FKZ: 01EO1501 IFB Adiposity Diseases, to AK.
+
+<--- Page Split --->
+
+## Author contribution
+
+ACH, HY, YTL, CCC, VD carried out experiments, AK, AH, JC designed experiments, TR conceived the project, designed experiments and wrote the manuscript.
+
+## References
+
+1. Chobot A, Górowska-Kowolik K, Sokolowska M, and Jarosz-Chobot P. Obesity and diabetes—Not only a simple link between two epidemics. Diabetes/Metabolism Research and Reviews. 2018:e3042.
+2. Geserick M, Vogel M, Gausche R, Lipek T, Spielau U, Keller E, et al. Acceleration of BMI in early childhood and risk of sustained obesity. The New England journal of medicine. 2018;379(14):1303-12.
+3. Landgraf K, Rockstroh D, Wagner IV, Weise S, Tauscher R, Schwartze JT, et al. Evidence of early alterations in adipose tissue biology and function and its association with obesity-related inflammation and insulin resistance in children. Diabetes. 2015;64(4):1249-61.
+4. Herrera E, and Amusquivar E. Lipid metabolism in the fetus and the newborn. Diabetes Metab Res Rev. 2000;16(3):202-10.
+5. Stave U. Perinatal physiology. New York, London: Plenum Medical Company; 1970.
+6. Hoang AC, Yu H, and Röszer T. Transcriptional Landscaping Identifies a Beige Adipocyte Depot in the Newborn Mouse. Cells. 2021;10(9):2368.
+7. Yu H, Dilbaz S, Coßmann J, Hoang AC, Diedrich V, Herwig A, et al. Breast milk alkylglycerols sustain beige adipocytes through adipose tissue macrophages. The Journal of Clinical Investigation. 2019;129(6):2485-99.
+8. Ikeda K, Maretic H, and Kajimura S. The Common and Distinct Features of Brown and Beige Adipocytes. Trends in Endocrinology & Metabolism. 2018;29(3):191-200.
+9. Hahn P, and Novak M. Development of brown and white adipose tissue. Journal of lipid research. 1975;16(2):79-91.
+
+<--- Page Split --->
+
+10. Rockstroh D, Landgraf K, Wagner IV, Gesing J, Tauscher R, Lakowa N, et al. Direct evidence of brown adipocytes in different fat depots in children. PLOS ONE. 2015;10(2):e0117841.
+
+11. Zhong Z, Liang S, Sanchez-Lopez E, He F, Shalapour S, Lin XJ, et al. New mitochondrial DNA synthesis enables NLRP3 inflammasome activation. Nature. 2018;560(7717):198-203.
+
+12. Beyerlein A, Donnachie E, Jergens S, and Ziegler A-G. Infections in Early Life and Development of Type 1 Diabetes. JAMA. 2016;315(17):1899-901.
+
+13. Atkinson RL. Viruses as an etiology of obesity. Mayo Clinic proceedings. 2007;82(10):1192-8.
+
+14. Shoelson SE, Lee J, and Goldfine AB. Inflammation and insulin resistance. J Clin Invest. 2006;116(7):1793-801.
+
+15. Lempainen J, Tauriainen S, Vaarala O, Makela M, Honkanen H, Marttila J, et al. Interaction of enterovirus infection and cow's milk-based formula nutrition in type 1 diabetes-associated autoimmunity. Diabetes Metab Res Rev. 2012;28(2):177-85.
+
+16. Kissig M, Ishibashi J, Harms MJ, Lim H-W, Stine RR, Won K-J, et al. PRDM16 represses the type I interferon response in adipocytes to promote mitochondrial and thermogenic programing. The EMBO Journal. 2017;36(11):1528-42.
+
+17. Motwani M, Pesiridis S, and Fitzgerald KA. DNA sensing by the cGAS-STING pathway in health and disease. Nature Reviews Genetics. 2019;20(11):657-74.
+
+18. Shin S-I, Ham S, Park J, Seo SH, Lim CH, Jeon H, et al. Z-DNA-forming sites identified by ChIP-Seq are associated with actively transcribed regions in the human genome. DNA Res. 2016;23(5):477-86.
+
+19. Takaoka A, Wang Z, Choi M, Yanai H, Negishi H, Ban T, et al. DAI (DLM-1/ZBP1) is a cytosolic DNA sensor and an activator of innate immune response. Nature. 2007;448:501-5.
+
+20. Lugrin J, and Martinon F. The AIM2 inflammasome: Sensor of pathogens and cellular perturbations. Immunological Reviews. 2018;281(1):99-114.
+
+21. Geserick M, Vogel M, Gausche R, Lipek T, Spielau U, Keller E, et al. Acceleration of BMI in Early Childhood and Risk of Sustained Obesity. The New England journal of medicine. 2018;379(14):1303-12.
+
+<--- Page Split --->
+
+22. Bahat A, MacVicar T, and Langer T. Metabolism and Innate Immunity Meet at the Mitochondria. Frontiers in Cell and Developmental Biology. 2021;9(2019).
+
+23. Liu D, Wu H, Wang C, Li Y, Tian H, Siraj S, et al. STING directly activates autophagy to tune the innate immune response. Cell Death & Differentiation. 2019;26(9):1735-49.
+
+24. Devi TS, Yumnamcha T, Yao F, Somayajulu M, Kowluru RA, and Singh LP. TXNIP mediates high glucose-induced mitophagic flux and lysosome enlargement in human retinal pigment epithelial cells. Biology open. 2019;8(4):bio038521.
+
+25. Nakahira K, Haspel JA, Rathinam VAK, Lee S-J, Dolinay T, Lam HC, et al. Autophagy proteins regulate innate immune responses by inhibiting the release of mitochondrial DNA mediated by the NALP3 inflammasome. Nature immunology. 2011;12(3):222-30.
+
+26. Fujiwara Y, Wada K, and Kabuta T. Lysosomal degradation of intracellular nucleic acids—multiple autophagic pathways. The Journal of Biochemistry. 2016;161(2):145-54.
+
+27. Ro S, Ma H-Y, Park C, Ortogero N, Song R, Hennig GW, et al. The mitochondrial genome encodes abundant small noncoding RNAs. Cell Research. 2013;23(6):759-74.
+
+28. Rackham O, Shearwood A-MJ, Mercer TR, Davies SMK, Mattick JS, and Filipovska A. Long noncoding RNAs are generated from the mitochondrial genome and regulated by nuclear-encoded proteins. RNA. 2011;17(12):2085-93.
+
+29. Dias Junior AG, Sampaio NG, and Rehwinkel J. A Balancing Act: MDA5 in Antiviral Immunity and Autoinflammation. Trends in Microbiology. 2019;27(1):75-85.
+
+30. Kato H, Takeuchi O, Mikamo-Satoh E, Hirai R, Kawai T, Matsushita K, et al. Length-dependent recognition of double-stranded ribonucleic acids by retinoic acid-inducible gene-I and melanoma differentiation-associated gene 5. The Journal of experimental medicine. 2008;205(7):1601-10.
+
+31. Abels ER, and Breakefield XO. Introduction to Extracellular Vesicles: Biogenesis, RNA Cargo Selection, Content, Release, and Uptake. Cell Mol Neurobiol. 2016;36(3):301-12.
+
+32. Wang XA, Zhang R, Zhang S, Deng S, Jiang D, Zhong J, et al. Interferon regulatory factor 7 deficiency prevents diet-induced obesity and insulin resistance. American journal of physiology Endocrinology and metabolism. 2013;305(4):E485-95.
+
+33. Zhang LJ, Guerrero-Juarez CF, Hata T, Bapat SP, Ramos R, Plikus MV, et al. Innate immunity. Dermal adipocytes protect against invasive Staphylococcus aureus skin infection. Science. 2015;347(6217):67-71.
+
+<--- Page Split --->
+
+34. Seto S, Tsujimura K, and Koide Y. Coronin-1a inhibits autophagosome formation around Mycobacterium tuberculosis-containing phagosomes and assists mycobacterial survival in macrophages. Cellular Microbiology. 2012;14(5):710-27.
+
+35. Yu P, Song H, Gao J, Li B, Liu Y, and Wang Y. Vitamin D (1,25-(OH)2D3) regulates the gene expression through competing endogenous RNAs networks in high glucose-treated endothelial progenitor cells. The Journal of Steroid Biochemistry and Molecular Biology. 2019;193:105425.
+
+36. Masuyama H, and Hiramatsu Y. Additive Effects of Maternal High Fat Diet during Lactation on Mouse Offspring. PLOS ONE. 2014;9(3):e92805.
+
+37. Christ A, and Latz E. The Western lifestyle has lasting effects on metaflammation. Nature Reviews Immunology. 2019;19(5):267-8.
+
+38. Derecka M, Gornicka A, Koralov SB, Szczepanek K, Morgan M, Raje V, et al. Tyk2 and Stat3 regulate brown adipose tissue differentiation and obesity. Cell metabolism. 2012;16(6):814-24.
+
+39. Babaei R, Schuster M, Melin I, Lerch S, Ghandour RA, Pisani DF, et al. Jak-TGFβ cross-talk links transient adipose tissue inflammation to beige adipogenesis. Science Signaling. 2018;11(527).
+
+40. Alsaggar M, Mills M, and Liu D. Interferon beta overexpression attenuates adipose tissue inflammation and high-fat diet-induced obesity and maintains glucose homeostasis. Gene Ther. 2017;24(1):60-6.
+
+41. Cao W, Daniel KW, Robidoux J, Puigserver P, Medvedev AV, Bai X, et al. p38 Mitogen-Activated Protein Kinase Is the Central Regulator of Cyclic AMP-Dependent Transcription of the Brown Fat Uncoupling Protein 1 Gene. Molecular and Cellular Biology. 2004;24(7):3057-67.
+
+42. Youle RJ. Mitochondria—Striking a balance between host and endosymbiont. Science. 2019;365(6454):eaaw9855.
+
+43. Toyofuku M, Nomura N, and Eberl L. Types and origins of bacterial membrane vesicles. Nature Reviews Microbiology. 2019;17(1):13-24.
+
+44. Bitto NJ, Chapman R, Pidot S, Costin A, Lo C, Choi J, et al. Bacterial membrane vesicles transport their DNA cargo into host cells. Scientific reports. 2017;7(1):7072-.
+
+<--- Page Split --->
+
+45. Eberle F, Sirin M, Binder M, and Dalpke AH. Bacterial RNA is recognized by different sets of immunoreceptors. European Journal of Immunology. 2009;39(9):2537-47.
+
+46. Eigenbrod T, and Dalpke AH. Bacterial RNA: An Underestimated Stimulus for Innate Immune Responses. The Journal of Immunology. 2015;195(2):411-8.
+
+47. Kumari M, Wang X, Lantier L, Lyubetskaya A, Eguchi J, Kang S, et al. IRF3 promotes adipose inflammation and insulin resistance and represses browning. J Clin Invest. 2016;126(8):2839-54.
+
+48. Bai J, Cervantes C, He S, He J, Plasko GR, Wen J, et al. Mitochondrial stress-activated cGAS-STING pathway inhibits thermogenic program and contributes to overnutrition-induced obesity in mice. Communications Biology. 2020;3(1):257.
+
+49. Bai J, and Liu F. The cGAS-cGAMP-STING Pathway: A Molecular Link Between Immunity and Metabolism. Diabetes. 2019;68(6):1099-108.
+
+50. Gkirtzimanaki K, Kabrani E, Nikoleri D, Polyzos A, Blanas A, Sidiropoulos P, et al. IFNα Impairs Autophagic Degradation of mtDNA Promoting Autoreactivity of SLE Monocytes in a STING-Dependent Fashion. Cell reports. 2018;25(4):921-33.e5.
+
+51. Tian Y, Jennings J, Gong Y, and Sang Y. Viral Infections and Interferons in the Development of Obesity. Biomolecules. 2019;9(11).
+
+52. Birk RZ, and Rubinstein M. IFN-alpha induces apoptosis of adipose tissue cells. Biochem Biophys Res Commun. 2006;345(2):669-74.
+
+53. Cippitelli M, and Santoni A. Vitamin D3: a transcriptional modulator of the interferon-γ gene. European Journal of Immunology. 1998;28(10):3017-30.
+
+54. Stoppelenburg AJ, von Hegedus JH, Huis in't Veld R, Bont L, and Boes M. Defective control of vitamin D receptor-mediated epithelial STAT1 signalling predisposes to severe respiratory syncytial virus bronchiolitis. The Journal of Pathology. 2014;232(1):57-64.
+
+55. Roth CL, Elfers C, Kratz M, and Hoofnagle AN. Vitamin d deficiency in obese children and its relationship to insulin resistance and adipokines. J Obes. 2011;2011:495101-.
+
+56. de Oliveira LF, de Azevedo LG, da Mota Santana J, de Sales LPC, and Pereira-Santos M. Obesity and overweight decreases the effect of vitamin D supplementation in adults: systematic review and meta-analysis of randomized controlled trials. 2020;21(1):67-76.
+
+57. Pramono A, Jocken JWE, and Blaak EE. Vitamin D deficiency in the aetiology of obesity-related insulin resistance. 2019;35(5):e3146.
+
+<--- Page Split --->
+
+58. Fan Y, Futawaka K, Koyama R, Fukuda Y, Hayashi M, Imamoto M, et al. Vitamin D3/VDR resists diet-induced obesity by modulating UCP3 expression in muscles. J Biomed Sci. 2016;23(1):56-.
+59. Xu Y, Lou Y, and Kong J. VDR regulates energy metabolism by modulating remodeling in adipose tissue. European journal of pharmacology. 2019;865:172761.
+60. Biggs K, Hurrell K, Matthews E, Khaleva E, Munblit D, and Boyle R. Formula Milk Supplementation on the Postnatal Ward: A Cross-Sectional Analytical Study. Nutrients. 2018;10(5):608.
+
+<--- Page Split --->
+
+
+Supplemental Figure 1. Characterization of mouse inguinal adipose tissue at P6 and P56, and human inguinal adipose tissue in infancy
+
+(A) Scheme of NGS analysis. For RNA sequencing we obtained inguinal fat depots (iAT) of 3-3 mice at postnatal day 6 (P6) and P56 and compared their transcriptional profiles. The differentially expressed genes (DEGs) were analyzed further in this study. (B) Hematoxylin and eosin (H&E) staining, and immunostaining of UCP1 in mouse iAT at P6 and P56. Scale: 50 μm. (C) Abundance of mtDNA (16S and Ndl genes) relative to genomic DNA in mouse iAT at P6 and P56. (D) Gene network associated with PR/SET domain 16 (PRDM16), a key regulator of brown adipocyte development (1-3). Red symbols indicate DEGs overrepresented in P6 iAT. Beige/brown adipocyte-associated genes were overrepresented in P6 iAT. (E) Transcription of Prdm16 in mouse adipocytes at P6 and P56. Heat map summarizing the transcription level of beige/brown adipocyte marker genes and white adipocyte marker genes in P6 and P56 iAT. Ucp1 is necessary for thermogenesis; Ppargc1a for mitochondrial biogenesis; Cidea, Cox7a1, Dio2, Zic1 are associated with brown/beige adipocytes; Tmem26 and Tbx1 are beige adipocyte markers; Evala is a brown adipocyte marker (4-9); Myf5 is expressed by progenitors of brown adipocytes (10). Levels of Hoxc8 and Hoxc9 increase along white adipocyte development (4), although Hoxc9 may also be a marker of beige adipocytes (9). Lep, Fabp4, Plin2, Adipoq, Gpd1, Slc2a4 and Pparg are associated with white adipocyte maturation (11). See also (12). (F) Correlation of UCP1 levels with beige/brown adipocyte-associated transcripts (PPARGC1A, TMEM26, CIDEA, LHX8) and white adipocyte markers (HOXC8, HOXC9) in the iAT of human male infants (4, 13). P values were determined with linear regression analysis. Age 0.2-3.5 years. Further details regarding beige adipocyte content in mouse and human fat depots are provided in (4, 12-14), and reviewed in the introduction section of (3).
+
+<--- Page Split --->
+
+
+Supplemental Figure 2. Expression of the STING/AIM2 pathways in P6 and P56 iAT
+
+(A) Gene ontology and STRING protein-protein association network of DEGs overrepresented in P6 iAT. Further analysis is available in (12). Vdr and its gene network were overrepresented at P6. (B) Gene ontology and protein-protein association network of underrepresented DEGs at P6 (15). (C) Structure of the DNA-sensor p204. The three DNA-binding domains are labeled A, B and C. p204 is encoded by Ifi204 in BALB/C mice. In C57/BL6, however, Ifi204 has a frameshift mutation and its function is taken over by Ifi205 (16-18). In 3T3-L1 cells, which have a BALB/C origin, we measured Ifi204, whereas we measured Ifi205 in adipocytes from C57/BL6 mice. Level of Ifi204 in P6 and P56-derived adipocytes mirrored that of Ifi205, shown in Figure 1. (D) Expression of Tmem173 and Mb21d in metabolic organs at P56. Note their prominent expression in iAT and in the epididymal adipose tissue (eAT). (E) Level of Tmem173 and Mb21d in iAT of mice fed normal chow diet (NCD) or high-fat diet (HFD). Amount of STING-expressing ATMs in iAT following NCD or HFD. STING expression was not influenced by HFD. (F) FACS plot of adipose tissue macrophages (ATMs) and adipocytes (ACs) from iAT. ATMs were defined as F4/80+, CD11b+. (G) Single cell sequencing data retrieved from the TabulaMuris consortium (19), showing that the STING pathway is expressed in both ATMs and in adipocytes. There is a marked expression of Ifi205 in adipocytes. (H) FACS analysis of the STING pathway in ATMs at P6 and P56.
+
+<--- Page Split --->
+
+
+Supplemental Figure 3. Cytosolic DNA sensing in adipocytes
+
+(A) Left: Possible routes of DNA and RNA release into the cytosol: membrane fusion with EVs [1]; release of mtDNA and mtRNA into the cytosol [2]. Both mechanisms can activate RIG-I/MDA5 or STING signaling. Middle: Scheme of RIG-I/MDA5 signaling. RNA Pol III: RNA polymerase III, which can generate dsRNA from DNA templates, ultimately activating the RIG-I/MDA5 pathway. Right: Expression of RNA Pol III and RIG-I/MDA5 pathway genes in P6 iAT. As a comparison, genes of the STING signaling pathway are also shown. See also the heatmap in Figure 1. (B) Left: Scheme of LyoVec-encapsulated dsDNA. The LyoVec lipid carrier fuses with the cell membrane and dsDNA is released into the cytosol of the recipient cell. Right: Responsiveness of P6 and P56 adipocytes to the synthetic dsDNA poly dA:dT (pdA:dT) packed in LyoVec (5 μg/ml, 2 h). (C) Left: Scheme of LyoVec encapsulated VACV-70 (Vaccinia virus DNA sequence), a ligand for IFI16 in human and p204/p205 in mouse. Responsiveness of P6 and P56 adipocytes to 1 μg/ml VACV-70 (18 h). (D) Left: Structure of cGAMP and scheme of its entry into the cytosol mediated by the solute carrier SLC19a (20). Transcript level of Slc19a1 was equivalent in P6 and P56 iAT. Right: IFN-response of P6 and P56 iAT after cGAMP treatment (10 μg/ml, 18 h). *P<0.05, **P<0.01, ***P<0.001. Student's 2-tailed unpaired t-test or one-way ANOVA with Dunnett's post-hoc test.
+
+<--- Page Split --->
+
+
+
+## Supplemental Figure 4. Cytosolic mtDNA/mtRNA sensing in adipocytes
+
+(A) Scheme of lipofectamine-encapsulated total mtDNA and its delivery into the cytosol of adipocytes. Cytosolic mtDNA is recognized by p204 (IFI16 in humans) and AIM2, and ultimately activates inflammasome and STING signaling. (B) Scheme of lipofectamine-encapsulated total mtRNA and its delivery into the cytosol of adipocytes. Cytosolic mtRNA activates RIG-I and MDA5 signaling. (C) Inflammasome activation of P56 and P6 adipocytes after 4-h challenge with cytoplasmic mtDNA or mtRNA. CASP1: caspase-1 of the inflammasome (D) IFN-response of P56 and P6 adipocytes following transfection with mtDNA or mtRNA (2 µg/ml, 18 h). (E) Ifnb transcription of wild-type (wt) and Irf7-/- adipocytes following transfection with vehicle, mtDNA or mtRNA (2 µg/ml, 4 h). (F) Transcription of the STING/AIM2 pathway, Ddx58 and Irf7 following 18-h activation of IRF7 signaling with LyoVec-encapsulated p(I:C). *P<0.05, **P<0.01, ***P<0.001. Student's 2-tailed unpaired t-test or one-way ANOVA with Dunnett's post-hoc test.
+
+<--- Page Split --->
+
+
+Supplemental Figure 5. Endosomal DNA/RNA sensing in adipocytes
+
+(A) Scheme of DNA sensing pathways activated by endosomal uptake of DNA. (B) Rhodamine-conjugated naked DNA molecules (p(dA:dT) and CpG) were readily taken up by P6 adipocytes. Scale: \(10 \mu \mathrm{m}\) . (C) Effect of naked CpG on inflammatory gene expression in P6 and P56 adipocytes. (D) TEM image of two adjacent adipocytes in vitro. The cell membranes form numerous endosomes allowing the interchange of EV cargos. en: endosomes; mt: mitochondria; scale: \(1 \mu \mathrm{m}\) . (E) Transcript level of TLRs in P6 and P56 iAT. Respective ligands (dsRNA, ssRNA, DNA and rRNA) of the receptors are indicated. Mitochondrial RNA stimulates human TLR8 (21) and triggers inflammation in mouse macrophages mediated by TLR9 (22). (F) J2 antibody labeling of dsRNA at the lamellipodia of adipocytes, in an active region of endocytosis (23). nc: nucleus, scale: \(10 \mu \mathrm{m}\) .
+
+<--- Page Split --->
+
+
+Supplemental Figure 6. STING/AIM2 pathways in human adipose tissue
+
+(A) Anatomical sites of human inguinal adipose tissue (iAT) samples used in this study. Left: in infants, and Right: in children and adults. For proper comparison we used equivalent fat depots in all age groups, from the region bordered by the inguinal ligament, the fundiform ligament of the penis, and the linea alba. (B) Scheme of human STING/AIM2 pathways and the relative abundance of their gene products in the iAT collected from human infants (0.2–1.0 years of age, N=24), toddlers (1.1–2.0 years, N=29), children (3.0–11.0 years, N=99), adolescents and young adults (11.1–20.5 years, N=155). (C) Top: transcript level of adipose tissue AIM2, DDX41, MB21D (encoding cGAS) and IRF3 in lean (BMI-SDS<1.28) and overweight or obese (BMI-SDS>1.28) infants and children; Illumina HT12v4 assay. Bottom: Correlation of age in years (y) and the transcript level of adipose tissue STING/AIM2 pathway genes in human infants. (D) Top: Immunostaining of IFI16 in a human preadipocyte (Pre-AC) and white adipocyte (AC). Samples from studies (14) and (24). Scale: 50 μm. Bottom: Level of adipose tissue TMEM173 in breastfed and formula-fed infants. Formula-fed infants show premature loss of beige adipocytes in the subcutaneous fat depot (14). (E) Transcript level of the human adipose tissue STING/AIM2 pathway genes at various age groups. Correlation between TMEM173 expression and the level of various DNA sensors. Age group: 0.1–20.5 years. Gender, gestational age, maternal age, maternal diabetes were not correlated with the above parameters. Linear regression analyses with Pearson’s correlation.
+
+<--- Page Split --->
+
+
+Supplemental Figure 7. STING-mediated mitophagy in P6 adipocytes
+
+(A) Autophagosome (APh) number and size in P6 adipocytes and in 3T3-L1 adipocytes treated with vehicle or \(5\mu \mathrm{g / ml}\) cGAMP for 6h. (B) Top: Western blotting of LC3 in P6 adipocytes and 3T3-L1 cells treated with vehicle or cGAMP (5 \(\mu \mathrm{g / ml}\) , 6 h). Bottom: GFP-labeled mitochondrial remnants accumulate in autophagosomes after cGAMP treatment. Scale: \(10\mu \mathrm{m}\) . (C) Autophagosomes and lysosomes (labeled with Lyso-View) in 3T3-L1 cells cultured in \(10\%\) fetal calf serum (FCS) or in \(1\%\) FCS-containing medium for \(18\mathrm{h}\) . (D) Effect of STING inhibition with \(0.5\mu \mathrm{M}\) H151 on mitochondrial content and morphology in P6 adipocytes. MTR: MitoTracker Red labeling, GFP: GFP labeling of newly synthesized mitochondria with the BacMan 0.2 labeling system, nc: nucleus; scale: \(10\mu \mathrm{m}\) . (E) FACS analysis of MTR labeling of P6 adipocytes, and transcription of inflammatory genes and DNA sensors after \(18\mathrm{h}\) H151 treatment. H151 covalently binds to STING (25). Ddx58 encodes RIG-I. (F) Autophagosomes (arrows) containing GFP-labeled mitochondrial remnants in P6 adipocytes. Scale: \(10\mu \mathrm{m}\) . (G) TEM image of an autophagosome containing mitochondria. mt: mitochondria, MVB: multivesicular body, arrow indicates autophagosome with mitochondrial remnants. Scale: \(500\mathrm{nm}\) . (H) Western blotting of LC3 in P6 adipocytes following 6-h serum deprivation. Cells were treated with vehicle or H151 during serum deprivation. (I) GFP-labeled mitochondrial remnants in autophagosomes of P6 adipocytes following 6-h serum deprivation. Cells were treated with vehicle or H151 during serum deprivation. Scale: \(10\mu \mathrm{m}\) . \(*P< 0.05\) , \(**P< 0.01\) , \(***P< 0.001\) . Student's 2-tailed unpaired \(t\) - test.
+
+<--- Page Split --->
+
+
+Supplemental Figure 8. Biogenesis of EVs by P6 adipocytes
+
+(A) TEM image of EVs released by P6 adipocytes in vitro. Scale: 1 μm. Three distinct EV morphologies were recognized: electron-lucent or clear (Cl), electron-dense (Ds) and complex (Cp) EVs. Electron-lucent appearance is typical for EVs (26). Electron-dense EVs may be frequent in EVs within multivesicular bodies (MVBs) (27). Complex EVs contain remnants of intracellular membranes. Size distribution of P6 EVs; inset showing negative TEM staining of EVs. Scale: 100 nm. EVs were classified in small and large categories according to a recent study (28). (B) FACS analysis of EVs secreted by P6 adipocytes. Free beads: remainder of capture beads used to enrich EVs. (C) TEM image of an MVB; scale: 1 μm. (D) Endosomal pathway of EV generation was tested by incubating P6 adipocytes with FITC-conjugated dextran, a marker of fluid-phase endocytosis (pinocytosis). Dextran is taken up by endosomes and may later accumulate in MVBs or in lysosomes. (E) Left: FACS analysis of P6 adipocytes cultured without FITC-conjugated dextran (-Dextran) or after incubation with dextran (+Dextran). Right: P6 adipocytes readily endocytosed FITC-dextran, as confirmed with fluorescence microscopy. nc: nucleus; scale: 10 μm. EVs secreted by the dextran-incubated adipocytes were collected and analyzed further with FACS. Dextran was present in the EVs, showing that the endosomal pathway contributed to EV generation. (F) Adipocytes were incubated without EVs (-EVs) or with FITC dextran-labeled EVs (+EVs) for 4h. Mean fluorescence intensity (MFI) of the adipocytes was measured by FACS, confirming the uptake of EV cargo by adipocytes. (G) Phagocytosis activity of P6 adipocytes was tested with using 50-nm large latex beads. Adipocytes failed to phagocytose these particles, showing that EVs were not taken up by phagocytosis. (H) Level of an adipose tissue mesenchymal stem cell-specific microRNA (miR-29a-5p) in P6 and P56 EVs (29). Effect of miR-29a-5p overexpression of the mitochondrial content (MTR fluorescence intensity). (I) Ucp1 and small non-coding RNA species in the EV cargo of P6 adipocytes. As a comparison, the level of the mitochondrionally-encoded 12S ribosomal RNA (Rn12s) is shown. (J) FACS plots of EVs secreted by P6 and P56 adipocytes. (K) Inhibitors of EV generation reduced the DNA and RNA content in the culture medium of P6 adipocytes. Isoproterenol (1 μM) inhibits EV release (30), and fumonisin B1 (30 μM) inhibits ceramide synthase, a key enzyme of negative budding of MVBs (31).
+
+<--- Page Split --->
+
+
+Supplemental Figure 9. Effect of adipocyte EV cargo on mitochondrial morphology, and predicted secondary structure of mtRNA species found in adipocyte EVs (A) Mitochondrial morphometry of 3T3-L1 cells without extracellular vesicles (-EVs) or with P6 EVs (+EVs). \*\*\*P<0.001. Student's 2-tailed unpaired \(t\) -test. (B) Predicted minimum free energy (MFE) secondary structures of mtRNA species found in P6 EVs. Results were computed using ViennaRNA Package 2.0 and RNAfold 2.2.18, as described (32, 33).
+
+<--- Page Split --->
+
+
+
+## Supplemental Figure 10. Cytosolic and endosomal RNA effects on mitobiogenesis
+
+(A) Secondary and schematic structures of the synthetic ligands used to activate cytosolic RNA sensors. ssRNA41: single-stranded RNA, 3p-hp-RNA: 5' triphosphate hairpin RNA, is an RIG-I ligand (34), 5'ppp-dsRNA: 5' triphosphate dsRNA, a ligand for RIG-I, cytosolic p(I:C) activates MDA5 and RIG-I (35), and cytosolic p(dA:dT) is transcribed into RNA and ultimately activates RIG-I (36). (B) Adipocytes were transfected with 2 µg/ml ssRNA41 using the LyoVec transfection system for cytosol delivery. Levels of beige marker genes was measured 18 h after transfection. (C) 3T3-L1 cells were treated with 5 µg/ml naked pI:pC to stimulate TLR3 and beige adipocyte gene transcription was then measured 18h after treatment. (D,E,F) Adipocytes were transfected with RIG-I/MDA5 ligands: 5'ppp-dsRNA, 3p-hairpin-RNA, p(dA:dT) and p(I:C) in LyoVec. Levels of beige marker genes was measured 18 h after transfection. (G) Transcript level of beige adipocyte genes in P56 adipocytes transfected with mtRNA for 18h. (H) Mitochondrial temperature change (Mito-ΔT) measured with the heat-sensitive probe Mitothermoy-Yellow (MTY) in mouse and human primary adipocytes. Adipocytes were transfected with vehicle, mtDNA or mtRNA for 18 h. *P<0.05, **P<0.01, ***P<0.001. Student's 2-tailed unpaired t-test.
+
+<--- Page Split --->
+
+
+Supplemental Figure 11. IL-6/STAT3 and RIG-I/MDA5 signaling and mitoagonesis (A) Mitobigenesis was assessed by measuring SDH-A (succinate dehydrogenase complex, subunit A) and COX-1 (cyclooxygenase 1) by FACS. SDH-A is encoded by genomic DNA (gDNA), COX-I by mtDNA. Representative FACS histograms of COX-I and SDH-A in 3T3-L1 cells after P6 EV treatment. Histochemical staining of SDH-A activity of 3T3-L1 cells cultured without EVs (-EVs), with P6 EVs (+EVs) or with 0.2 ng/ml IL-6 for 18 h. Scale: 10 μm. (B) Effect of 200 pg/ml IL-6 on the net mitochondrial mass labeled with MitoTracker Red (MTR), and on the amount of newly synthesized (GFP-expressing) mitochondria. Scale: 50 μm. (C) FACS analysis of IL-6 content of P6 EVs. Iso: isotype control; IgG: labeling with anti-IL-6 IgG. Effect of P6 EVs on adipocyte Il6 expression and IL-6 release. Effect of P6 EVs on Cox7a1 expression (D) Effect of 200 pg/ml IL-6 on the Mitothermo-Yellow (MTY) signal in 3T3-L1 cells. Correlation of Il6 and Ucp1 relative expression in adipocytes. Heat map showing expression levels of beige adipocyte genes in 3T3-L1 cells treated with P6 EVs for 18 h. (E) MTR signal in 3T3-L1 cells treated with P6 EVs for 18 h. RXL: cells were simultaneously treated with the JAK2/STAT3 inhibitor ruxolitinib; BAY11-7082: cells were treated with an NFkB inhibitor to abrogate the effect of IL-6. (F) Histology of iAT from wild-type (wt), RIG-I-deficient (Ddx58-/-) and MDA5-deficient (Mda5-/-) mice. Note the absence of beige (multicolour) adipocytes in Ddx58-/- and Mda5-/- mice. Scale 50 μm. (G) Mitobigenesis (relative COX-I and SDH-A levels) in wt, Ddx58-/- and Mda5-/- adipocytes. (H) Heat map showing expression levels of beige adipocyte genes in wt or Ddx58-/- adipocytes treated with vehicle or mtRNA for 18 h. *P<0.05, **P<0.01, ***P<0.001. Student’s 2-tailed unpaired t-test.
+
+<--- Page Split --->
+
+
+Supplemental Figure 12. Cytosolic DNA/RNA effects on mitobiogenesis
+
+(A) Autophagosomes (APh) in P6 adipocytes treated with vehicle or transfected with \(2\mu \mathrm{g / ml}\) total mtDNA for \(18\mathrm{h}\) . Scale: \(10\mu \mathrm{m}\) . (B) Scheme of LyoVec-encapsulated pCMV6 plasmid – an activator of the c-GAS/STING pathway – and its effect on beige adipocyte gene expression in P6 adipocytes. (C) Relative abundance of mtRNA species in human breast milk EVs and commercially available formula milk EVs. (D) Effect of breast milk EVs on beige adipocyte gene expression in P56 adipocytes. As a comparison, adipocytes were treated with formula milk-derived EVs (FM). (E) Effect of breast milk EVs on the mitobiogenesis of human subcutaneous adipocytes, Irf7 mRNA levels in mouse adipocytes, and IRF7 protein levels of human adipocytes. Adipocytes were treated with breast milk-derived EVs for \(18\mathrm{h}\) . COX-I: cytochrome oxidase, SDH-A: succinate dehydrogenase, \(*P< 0.05\) , \(**P< 0.01\) , \(***P< 0.001\) . Student’s 2-tailed unpaired \(t\)-test.
+
+<--- Page Split --->
+![PLACEHOLDER_42_0]
+
+Supplemental Figure 13. IFN-response to EV cargo in adipocytes
+
+(A) Effect of cytosolic DNA/RNA on Ifnb expression in P56 adipocytes. pCMV6: transfection with pCMV6 plasmid (circular cytosolic DNA), pCMV6 EVs: treatment with extracellular vesicles released by pCMV6 plasmid-transfected adipocytes) (B) Effect of IFNβ on the mitochondrial network in P56 adipocytes. Scale: \(20 \mu \mathrm{m}\) . (C) Effect of IFNβ and IFNα on mitochondrial mass measured by MitoTracker Red (MTR) staining intensity. Cells were treated with vehicle, \(1 \mathrm{pg / ml}\) IFNβ or \(1 \mathrm{pg / ml}\) IFNα for \(18 \mathrm{h}\) . (D) EVs of P6 adipocytes were collected and added to cultures of P56 adipocytes. Similarly, EVs of P56 adipocytes were collected and added to P56 or P6 adipocytes. Levels of Ifnb and Tnfa were then measured. P6 EVs did not induce IFN-response, whereas P56 EVs triggered a robust IFN-response. (E) Transcript level of Irf7, and MTR staining intensity in P6 adipocytes treated with P56 EVs. Unlike P6 EVs, which suppressed Irf7, P56 EVs stimulated robust Irf7 expression (see Figure 3C) and reduced mitochondrial content. (F) Relative position and percentage of transcription factor binding sites in the promoters of the AIM2/STING pathway and Irf7. (G) Effect of LPS on the transcription of AIM2/STING pathway and Irf7 in adipocytes. (H) Scheme of the VDR-suppressed signal path which control the expression of Irf7, AIM2/STING pathway and IFN-response to cytosolic DNA/RNA (37-40).
+
+<--- Page Split --->
+![PLACEHOLDER_43_0]
+
+Supplemental Figure 14. Metabolic role of mtRNA-mediated signaling
+
+(A) Indirect calorimetry assay of HFD-fed adult male C57BL/6 mice. The inguinal fat depot was transfected with vehicle or with \(0.6 \mu \mathrm{g / g}\) body weight (BW) per day mtRNA for 14 days. The mtRNA was delivered into the adipocyte cytoplasm using magnetofection. Both groups received \(4 \mathrm{ng / g}\) BW Vit-D3 daily. MR: metabolic rate, EE: energy expenditure, RER: respiratory exchange rate (B) BW, daily food intake normalized to BW, and liver weight normalized to BW. Plasma level of TNFα and IL-6 (% of vehicle) from vehicle- or mtRNA-transfected mice, and the level of Irf7 in quadriceps muscle and liver. (C) Left: Transcription of Cyp27b1 (encoding a Vit-D3/calcitriol converting mitochondrial enzyme) in adipocytes treated with vehicle or transfected with mtRNA for 18h. Middle: Rate of Vit-D3/calcitriol conversion in the same cells. Right: Effect of calcitriol on the transcription of Vdr in adipocytes. \(*P< 0.05\) , \(**P< 0.01\) , \(***P< 0.001\) . Student's 2-tailed unpaired \(t\) -test.
+
+<--- Page Split --->
+![PLACEHOLDER_44_0]
+
+Supplemental Figure 15. Technical information on next-generation sequencing and image analysis
+
+(A) Work flow of the next-generation sequencing analysis. (B) Steps of image analysis in histomorphometry. (C) Negative control specimens. Left: Adipocytes in vitro, stained with secondary antibodies only; nuclei are labeled with DAPI. Scale: \(10 \mu \mathrm{m}\) . Middle: Brown adipose tissue section labeled with secondary antibody only. Scale: \(20 \mu \mathrm{m}\) . Right: human adipose tissue labeled with secondary antibody only. Scale: \(20 \mu \mathrm{m}\) .
+
+![PLACEHOLDER_44_1]
+
+
+<--- Page Split --->
+
+
+Supplemental Table 1. Mouse qPCR primer sequences used in the study
+
+| Bactin | fw | GCACCAGGGTGTGATGGTG |
| rev | CCAGATCTTCTCCATGTCGTCC |
| Ppia | fw | ATTTCTTTTGACTTGCGGGC |
| rev | AGACTTGAAGGGGAATG |
| Gapdh | fw | TGACGTGCCGCCTGGAGAAA |
| rev | AGTGTAGCCCAAGATGCCCTTCAG |
| Aim2 | fw | GATTCAAAGTGCAGGTGCGG |
| rev | TCTGAGGGTTAGCTTGAGGAC |
| Ddx41 | fw | ACAGGAGAAGCGGTTGCCTTTC |
| rev | GACGGCAGTAATACTCCAGGATG |
| Ifi204 | fw | CAGGGAAAATGGGAAGTGGTG |
| rev | CAGAGAGGTTCTCCCGACTG |
| Zbp1 | fw | AACCCTCAATCAAGTCCTTTACCGC |
| rev | TCTTCCACGTCTGTCGTCATAGCT |
| Mb21d | fw | AGGAAGCCCTGCTGTAACACTTCT |
| rev | AGCCAGCCTTGAATAGGTAGGTAGTCCT |
| Tmem173 | fw | GGGCCCTGTCACTTTGGTC |
| rev | GAGTATGGCATCAGCAGCCAC |
| Irf3 | fw | GGCTTGTGATGGTCAAGGTT |
| rev | CATGTCCTCCACCAAGTCCT |
| Irf7 | fw | CGACTTCAGCACTTTCTTCGGAGA |
| rev | AGATGGTGTAGTGCTGGTGCACCTT |
| If6 | fw | GCTACCAAACTGGATATAATCAGGA |
| rev | CCAGGTAGCTATGGTACTCCAGAA |
| Tnfa | fw | TGCCTATGTCTCAGCCTCTTC |
| rev | GAGGCCATTTGGGAACTTCT |
| Ifnb | fw | CCAGCTCCAAGAAAGGACGA |
| rev | CGCCCTGTAGGTGAGGTTGAT |
| Ifna | fw | TGAAGGACAGGAAGGACTTTG |
| rev | GAATGAGTCTAGGAGGGTTGT |
| 28S | fw | CAGGGGAATCCGACTGTTTA |
| rev | ATGACGAGGCATTTGGCTAC |
| 18S | fw | CGCGGTTCTATTTTGTTGGT |
| rev | AGTCGGCATCGTTTATGGTC |
| 16S | fw | ACACCGGAATGCCCTAAAGGA |
| rev | ATACCGCGGCGTTAAACTT |
| 12S | fw | ACACCTTGCCATAGCCACACC |
| rev | GTGGCTGGCACGAAATTTACCA |
| Nd1 | fw | GCTTTACGAGCCGTAGCCCA |
| rev | GGGTCAGGCCTGGCAGAAGTAA |
| Cytb | fw | TCCTTCATGTCGGACGAGGC |
| rev | AATGCTGTGGCTATGACTGCG |
| Nd5 | fw | GCCCTACACCAGTTTCAGC |
| rev | AGGGCTCCGAGGCAAGATAT |
| Co1 | fw | TCAACATGAAACCCCCAGCCA |
| rev | GCGGCTAGCACTGGTAGTGA |
+
+<--- Page Split --->
+
+| Ucp1 | fw | CCTGCTCTCTCGGAACAA |
| rev | CTGTAGGCTGCCCAATGAAC |
| Ppargc1 | fw | GACTCAGTGTcACCACCGAAA |
| rev | TGAACGAGAGCGCATCCTT |
| Cox7a1 | fw | ATGAGGCCCTACGGGTCTC |
| rev | CATTGTCGGCCTGGAAAGAG |
| Cidea | fw | TACTACCCGGTGTCCATTTCT |
| rev | ATCACAACTGGCCTGGTTACG |
| Dio2 | fw | GTCCGCAAATGACCCCTTT |
| rev | CCCACCCACTCTCTGACTTTC |
| Ifi205 | fw | CAAGCAGGCCACTTCTGTG |
| rev | TCAAACGGGTCTGTGTCAGT |
| Ddx58 | fw | CAAACCGGGCAACAGGAATG |
| rev | ATCTCCGCTGGCTCTGAATG |
| Ifi202b | fw | AAGTTCCCGGTGTCAGAAC |
| rev | TCCAGGAGAGGCTTGAGGTT |
| Mndal | fw | GACAGCACACTAGAAACCCC |
| rev | CTTGTCTCCTACTCAGTCCG |
| miR34a | fw | TCTTTGGCAGTGTCTTAGCTGG |
| rev | ACAATGTGCAGCACTTCTAGGG |
| circRNA | fw | CTGCTCCTCCAGCTCTT |
| rev | AGTGATCTTGAACCCCAAAG |
| piRNA 6464.1 | fw | GGCAAGCTTAGGAGGTGTCC |
| rev | CGTGGGTCCACTGTATCACC |
| piRNA 6463.1 | fw | TAAAGCCCTAAAGCCCACGG |
| rev | AGGTGTAATGCCAGCCAGTC |
| Pnp1 | fw | CTTGGACATGGTGCTCTTGC |
| rev | GCCAAACTTCCACCACATGC |
| Adrb3 | fw | GTCGTCTTCTGTGTAGCTACGGT |
| rev | CATAGCCATCAAACCTGTTGAG |
| Lipe (Hsl) | fw | AGCCTCATGGACCCTCTTCT |
| rev | AGCGAAATGTCTCTCTGCAC |
| Atg (Pnpla2) | fw | ACTGAACCAACCCAACCCTT |
| rev | CGCACTGGTAGCATGTTGGA |
| Cyp27b1 | fw | AGCTCCTGCGACAAGAAAGT |
| rev | ATTCTTCACCATCCGCCGTTA |
| Vdr | fw | ACTTTGACCGGAATGTGCCT |
| rev | CATGCTCCGCCTGAAGAAAC |
+
+<--- Page Split --->
+
+
+Supplemental Table 1. (cont.) qPCR primers for measuring mouse mtDNA
+
+| Nd1 | fw | GCTTTACGAGCCGTAGCCCA |
| rev | GGGTCAGGCTGGCAGAAGTAA |
| 16S | fw | ACACCGGAATGCTCAAAGGA |
| rev | ATACCGCGGCCGTTAACTT |
| 12S | fw | ACACCTTGCCTAGCCACACC |
| rev | GTGGCTGGCACGAAATTTACCA |
| D-loop | fw | AATCTACCATCCTCCGTGAAACC |
| rev | TCAGTTTAGCTACCCCAAGTTTAA |
| Cytb | fw | TCCTTCATGTCGGACGAGGC |
| rev | AATGCTGTGGCTATGACTGCG |
| Atp6 | fw | AGCTCACTTGCCCACTTCCT |
| rev | AAGCCGGACTGCTAATGCCA |
| Nd5 | fw | GGCCCTACACCAGTTTCAGC |
| rev | AGGGCTCCGAGGCAAGATAT |
| Co1 | fw | TCAACATGAAACCCCCAGCCA |
| rev | GCGGCTAGCACTGGTAGTGA |
| HK2 | fw | GCCAGCCTCTCCTGATTTTAGTGT |
| rev | GGGAACACAAAAGACCTCTTCTGG |
+
+Supplemental Table 1. (cont.) qPCR primers for measuring bovine/human mtRNA
+
+| 16S | fw | GACTTCACCAGTCAAGACGA |
| rev | ACATCGAGGTCGTAAACCCT |
| 12S | fw | ACTGCTCGCCAGAACACTAC |
| rev | GGTGAGGTTGATCGGGGTTT |
| ND1 | fw | GCAGCCGCTATTAAAGGTTCG |
| rev | TATCATTTACGGGGGAAGGCG |
| ND5 | fw | TATGTGCTCCGGGTCCTCA |
| rev | CTGCTAATGCTAGGCTGCCA |
| CO1 | fw | TCAGGCTACACCCTAGACCA |
| rev | CCGGATAGGCCGAGAAAGTG |
| CYTB | fw | AACTTCGGCTCACTCCTTG |
| rev | CTCAGAGTGATGTGGGCGATT |
+
+Supplemental Table 1. (cont.) qPCR primers for measuring bovine/human mtDNA
+
+| 16S | fw | GACTTCACCAGTCAAGACGA |
| rev | ACATCGAGGTCGTAAACCCT |
| 12S | fw | ACTGCTCGCCAGAACACTAC |
| rev | GGTGAGGTTGATCGGGGTTT |
| ND1 | fw | GCAGCCGCTATTAAAGGTTCG |
| rev | TATCATTTACGGGGGAAGGCG |
| ND5 | fw | TATGTGCTCCGGGTCCTCA |
| rev | CTGCTAATGCTAGGCTGCCA |
| CO1 | fw | TCAGGCTACACCCTAGACCA |
| rev | CCGGATAGGCCGAGAAAGTG |
| CYTB | fw | AACTTCGGCTCACTCCTTG |
| rev | CTCAGAGTGATGTGGGCGATT |
+
+<--- Page Split --->
+
+
+Supplemental Table 2. Antibodies used in the study (h, human; m, mouse)
+
+| Target | Cat. No. | IgG type, source |
| h/m STING | NBP2-24683 | Rabbit polyclonal Novus Biologicals, Denver, CO |
| h/m AIM2 | 201708-T10 | Rabbit polyclonal Sino Biological, Eschborn, Germany |
| h/m DDX41 | 102459-T32 | Rabbit polyclonal Sino Biological, Eschborn, Germany |
| h/m p204 (IFI16) | NBP2-27153 | Rabbit Polyclonal Novus Biologicals, Denver, CO |
| h/m ZBP1 | 207744-T08 | Rabbit polyclonal Sino Biological, Eschborn, Germany |
| h/m LC3 | L8918 | Rabbit polyclonal, Merck Sigma-Aldrich, St. Louis, MO, Darmstadt, Germany |
| h/m UCP1 | PA1-24894 | Rabbit polyclonal ThermoFisher Scientific, Rockford, IL |
| m NPFF | ab10352 | Rabbit polyclonal Abcam, Cambridge, UK |
| β-actin | NB600-532SS | Rabbit polyclonal Novus Biologicals, Denver, CO |
| h/m DDX41 | 102459-T32 | Rabbit polyclonal Invitrogen, Carlsbad, CA |
| h/m Tmem150b | PA5-71527 | Rabbit polyclonal Invitrogen, Carlsbad, CA |
| J2 (dsRNA) | Anti-dsRNA [J2] | Mouse monoclonal Absolute Antibody, Wilton, UK |
| m IRF7 | 12-5829-82 | PE-conjugated monoclonal IgG, and matching isotype IgG, ThermoFisher, Waltham, MA |
| m F4/80 antigen | sc-377009 | F4/80 APC, CD45 PerCy5.5, CD11b APC or PE or AF700 (FACS analysis), eBioscience, ThermoFisher, Waltham, MA, Santa Cruz Biotech (for IHC) |
| m CD11b | E-AB-F1081E | H+L, cross-Adsorbed, FITC, polyclonal, secondary antibody, Invitrogen, Carlsbad, CA |
| Rabbit anti-goat IgG | F-2765 | Goat anti-Rabbit IgG (H+L), HRP-conjugated Invitrogen, Carlsbad, CA |
| Goat anti-rabbit IgG | A16096 | |
+
+<--- Page Split --->
+
+## Supplemental Methods
+
+## Activation and inhibition of cytosolic DNA/RNA sensors
+
+Activation and inhibition of cytosolic DNA/RNA sensorsTo activate STING, we treated adipocytes or 3T3- L1 cells with cGAMP (InvivoGene, Toulouse, France) for 6- 18 h, or overexpressed the pCMV6 plasmid (OriGene Technologies, Rockville, MD). In the latter case, \(1 \mu \mathrm{g}\) of DNA was transfected into 300,000 cells using TurboFect Transfection Reagent (Fisher Scientific, Hampton, NH). Control cells received transfection reagent only. Analyses were performed 18- h after transfection. To stimulate RIG- IMDA5, we transfected 3T3- L1 cells at \(80\%\) confluency with high molecular weight polyinosine- polycytidylic acid (p(I:C)) or poly(deoxaydenylic- deoxythymidylic) acid (p(dA:dT)) using the LyoVec cationic lipid- based transfection reagent (InvivoGene, Toulouse, France). Control cells were treated with LyoVec transfection reagent only. We used \(2.5 - 5 \mu \mathrm{g / ml}\) p(dA:dT) or p(I:C), and cells were analyzed 2- 24 h after transfection. IFI16/p204 was activated with \(1 \mu \mathrm{g / ml}\) VACV- 70 conjugated to LyoVec transfection reagent (InvivoGene; 18 h) (41). Treatments are summarized in the table below.
+
+| Activation of cytosolic nucleic acid sensors with various ligands |
| Receptor | Ligand | EC50 | Applied concentration |
| STING | 2'3 cGAMP | 20 nM | 10 μg/ml |
| poly(dA:dT) 2h | 40-200 ng/ml | 2.5-5 μg/ml |
| human/mouse mtDNA | - | 2 μg/ml |
| cGAS | pCMV6 circular DNA | - | 1 μg/well |
| 3p-hpRNA | 5 ng/ml | 0.5 μg/ml |
| 5'ppp-dsRNA | 1.2 nM | 1 μg/ml |
| RIG-I | poly(I:C) HMW | 70±10 ng/ml | 0.5 μg/ml |
| poly(dA:dT) 18-24h | 40-200 ng/ml | 2.5-5 μg/ml |
| low molecular weight poly(I:C) | 82±8 ng/ml | 1 μg/ml |
| human/mouse mtRNA | - | 2 μg/well |
| AIM2 | poly(dA:dT) 2h | 40-200 ng/ml | 2.5-5 μg/ml |
| DDX41 | poly(dA:dT) 2h | 40-200 ng/ml | 2.5-5 μg/ml |
| dsDNA (VACV-70) | - | 1 μg/ml |
| IFI16 (p204 or Ifi204) | poly(dA:dT) 2h | 40-200 ng/ml | 2.5-5 μg/ml |
| dsDNA (VACV-70) | - | 1 μg/ml |
| ZBP1 | poly(dA:dT) 2h | 40-200 ng/ml | 2.5-5 μg/ml |
+
+TLR3 was stimulated with naked p(I:C) (Sigma- Aldrich, \(10 \mathrm{ng / ml}\) , \(18 \mathrm{h}\) ) and TLR8/9 with naked p(dA:dT) or CpG ( \(1 \mu \mathrm{g / ml}\) synthetic oligonucleotides that contain unmethylated CpG dinucleotides; InvivoGene) for \(8 \mathrm{h}\) . STING was inhibited with the irreversible STING inhibitor H- 151 (0.5 \(\mu \mathrm{M}\) , InvivoGene) (25). As a negative control we used ssRNA (InvivoGene). NFκB was inhibited with \(5 \mu \mathrm{M}\) BAY 11- 7082 and JAK2/STAT3 with \(280 \mathrm{nM}\) ruxolitinib (Cayman Chemical Company, Ann Arbor, MI). Mitochondrial damage was induced with \(10 \mathrm{ng / ml}\) LPS or with CCCP (carbonyl cyanide m- chlorophenyl hydrazone, \(1 \mu \mathrm{M}\) , \(15 \mathrm{min}\) treatment).
+
+Vit- D3 and calcitriol were purchased from Sigma- Aldrich; IL- 6, IFNα and IFNβ from ImmunoTools (Friesoythe, Germany), NPVF, human and mouse NPFF from Tocris Bioscience (Bristol, UK). Isoproterenol and fumonisin B1 were purchased from Sigma
+
+<--- Page Split --->
+
+Aldrich and from Cayman Chemical Company, respectively. To test the inhibitory effect of Vit- D3 on IRF7 signaling, 3T3- L1 cells were treated with \(1\mu \mathrm{M}\) Vit- D3 for \(48\mathrm{h}\) , and treated further with vehicle or \(5\mu \mathrm{g / ml}\) cGAMP for \(6\mathrm{h}\) , or were transfected with mtRNA for \(18\mathrm{h}\) . VDR was inhibited with PS121912, as described (42). Cellular uptake of cGAMP is dependent on the transporter Slc19a1 (20), whose level was similar in P6 and P56 adipocytes (GEO submission #GSE154925).
+
+Isolation of extracellular vesicles from cell culture media, breast milk and formula milk Extracellular vesicles (EVs) were collected from adipocyte culture media, human breast milk, or from commercially available cattle milk- based infant formula. Human breast milk was collected from healthy volunteers. For cell culture, to avoid contamination with bovine EVs, we used EV- depleted fetal calf serum throughout the study (Gibco). EVs were precipitated with the EPStep exosome precipitation solution (Immunostep, Centro de Investigación del Cáncer, Campus Miguel de Unamuno, Salamanca, Spain) and concentrated by centrifugation. EVs were analyzed with FACS using capture beads and labeling for CD63 (Immunostep). EV pellets were used for treating recipient cells, to extract DNA/RNA, or were processed for FACS. Fractions of EV pellets and adipocytes were also fixed in paraformaldehyde/glutaraldehyde, and processed for transmission electron microscopy (TEM) analysis, as described (43). Morphology of EVs was analyzed with conventional TEM, and with negative staining for TEM (44). EV diameter and area was measured with ImageJ (NIH) with manual annotation, and EVs were classified according to their morphology and electron density, as described (26, 27).
+
+## Phagocytosis and endocytosis assays
+
+Uptake of naked nucleic acids was assessed microscopically by incubating adipocytes with rhodamine- conjugated p(dA:dT) or FITC- conjugated ODN 1668 CpG (both from InvivoGene) for \(1\mathrm{h}\) . Endocytosis by means of pinocytosis was assessed by incubating adipocytes with FITC- conjugated dextran, followed by FACS analysis or fluorescence microscopy. Uptake of solid particles was assessed with the use of fluorescent latex beads (Sigma- Aldrich) and FACS analysis (BD LSR II).
+
+## ELISA assays
+
+Tissue samples were weighed and homogenized in RIPA buffer using a Roche bead mill homogenizer at \(6,500\mathrm{rpm}\) for \(1\mathrm{min}\) . Cell culture supernatants and plasma samples were centrifuged at \(0.8\mathrm{g}\) for \(10\mathrm{min}\) to remove cell debris, and supernatants were used for analysis. We used commercial ELISA kits to measure the levels of IL- 6, TNF \(\alpha\) (Fisher Scientific), Vit- D3, calcitriol and VDR (MBS268259- 48, MBS2701844- 24, MyBioSource). All samples were stored at \(- 80^{\circ}\mathrm{C}\) until analysis.
+
+## mtRNA isolation and in vitro transfection
+
+Adipocyte mitochondria were isolated with a commercial mitochondrial isolation kit (Thermo Fisher Scientific, Waltham, MA). Mitochondrial RNA (mtRNA) was isolated by lysing the mitochondrial pellet with TRI Reagent (Sigma- Aldrich), as described (1). 3T3L1 cells were transfected with \(2\mu \mathrm{g}\) of mtRNA in 6- or 24- well plates with cells at \(80–90\%\) confluency. As
+
+<--- Page Split --->
+
+a transfection reagent we used Lipofectamine 3000 (Invitrogen) at a 1:3 ratio. Control cells received transfection reagent only. Cells were analyzed 18 h after transfection.
+
+## mtDNA isolation and transfection
+
+Mitochondrial DNA (mtDNA) was isolated from mitochondria pellets using TRI Reagent (Merck Sigma- Aldrich) and reconstituted in TE buffer (10 mM Tris- HCL, 1 mM EDTA, pH 8.0). 3T3L1 cells were transfected for 18 h with \(1 \mu \mathrm{g / ml}\) mtDNA using the TurboFect Transfection Reagent. Control cells received transfection reagent only. Agarose gel electrophoresis was used to examine mtDNA integrity.
+
+## Cytosolic mtRNA isolation
+
+Cytosolic mtRNA isolationCytosol fractions of 3T3- L1 preadipocytes were collected by subcellular fractionation of the cytoplasm and the cell organelles using digitonin, as described (45). Digitonin buffer contained \(150 \mathrm{mM NaCl}\) , \(50 \mathrm{mM HEPES}\) (pH 7.4) and \(25 \mu \mathrm{g / ml}\) digitonin (D141, Merck Sigma- Aldrich). Treated cells were processed until the step in which cytoplasm was obtained as described (1). 3T3- L1 cytoplasm ( \(250 \mu \mathrm{l}\) ) was added to \(750 \mu \mathrm{l}\) TRI Reagent (T3934, Merck Sigma- Aldrich) and total RNA extraction was performed as described (24).
+
+## Histology and image analysis
+
+Histology and image analysisTissues were fixed with \(4\%\) paraformaldehyde and embedded in paraffin, as described (1). Sections were stained with hematoxylin and eosin (Carl Roth, Karlsruhe, Germany). Antibodies are listed in Supplemental Table 2. UCP1, IF116, AIM2 and NPFFR1 immunohistochemistry was performed on paraffin- embedded tissue sections. For histomorphometry of fat cells we used Image J, with an image- processing algorithm that incorporated the Euclidean distance- based Watershed transformation to segment the images. Briefly, binarized images were generated using Otsu's method for thresholding; enhanced images were generated using contrast limited adaptive histogram equalization (CLAHE), and finally segmented images were generated using the Watershed transformation (Supplemental Figure 20). Negative control specimens of our fluorescent imaging and immunostaining are shown in Supplemental Figure 15. Mitochondrial content and morphology was analyzed with ImageJ, as described (14). Beige adipose area was measured with our custom- developed image analysis software (BeAR©, (14)).
+
+## Oil Red-O staining and quantification of UCP1 staining
+
+The triglyceride content of cultured adipocytes was examined by Oil Red- O using a commercial kit from BioOptica (Milan, Italy), as described (24). In vitro UCP1 immunostaining was performed in 6- well culture plates, and samples were imaged and the optical density was measured using digital image analysis. Original images are available upon request through Figshare. Mitochondria were also labeled using an SDH- A histochemistry assay (BioOptica).
+
+## Adipocyte differentiation
+
+Mouse preadipocytes of the stromal vascular fraction (SVF) were isolated and maintained as described (24, 43, 46). To ensure the depletion of adipose tissue macrophages (ATMs) from the harvested preadipocytes, we used magnetic bead cell purification of the SVF with an antibody against the F4/80 antigen (Miltenyi Biotec, Bergisch Gladbach, Germany) (47).
+
+<--- Page Split --->
+
+Human subcutaneous adipose tissue preadipocytes were harvested as described (24, 43). Preadipocytes were maintained in cell culture medium supplemented with \(20 \mu \mathrm{g / mL}\) insulin. To induce white differentiation of preadipocytes of the SVF, we treated the cells with \(50 \mu \mathrm{M}\) IBMX, \(1 \mu \mathrm{M}\) dexamethasone, \(1 \mu \mathrm{M}\) rosiglitazone and \(20 \mu \mathrm{g / ml}\) insulin (all from Merck Sigma- Aldrich), as described (14).
+
+## Flow cytometry analysis of DNA sensors, mitochondrial biogenesis, mitochondrial content and mitochondrial uncoupling
+
+Mitochondrial content was analyzed with MitoTracker dyes (Thermo Fisher Scientific). Mitochondrial biogenesis was detected with the MitoBiogenesis™ Flow Cytometry Kit (Abcam, Cambridge, UK). MitoThermo Yellow (MTY), a temperature- sensitive fluorescent probe (48) was used to assess mitochondrial thermogenesis and uncoupling, as described (49, 50). Temperature difference between the control and the test groups was expressed as Mito- \(\Delta \mathrm{T}\) , and shown in the respective figures. MTY was developed and provided by Dr. Y- T. Chang (Center for Self- Assembly and Complexity, Institute for Basic Science & Department of Chemistry, Pohang University of Science and Technology, Pohang 37673, Republic of Korea). We used MTY for FACS analysis at \(0.1 \mathrm{ng / ml}\) to label \(10^{6} / \mathrm{ml}\) cells. Cells were maintained at \(37^{\circ} \mathrm{C}\) throughout the assay. DNA sensors (STING, p204, AIM2, DDX41) were detected with unconjugated antibodies (listed in Supplemental Table 2) and labeled with an FITC- conjugated secondary antibody for FACS analysis. Nucleic acids were labeled with Sytox Green (Thermo Fisher). Flow Repository identifiers of raw FACS data are as follows: #FR- FCM- Z236, #FR- FCM- Z2R6, #FR- FCM- ZYPU, #FR- FCM- ZYUU.
+
+## Imaging of mitochondrial content, autophagy and lysosomes
+
+For fluorescent microscopy of mitochondrial content and morphology preadipocytes or 3T3- L1 cells were grown on optical transparent glass- bottom plates (Greiner Bio- One GmbH, Frickenhausen, Germany) or glass coverslips. Functional mitochondria were labeled with MitoTracker Red. Mitochondria were also labeled with GFP using the BacMan 2.0 transfection system (Fisher Scientific). Oxygen consumption was assayed with the Extracellular \(\mathrm{O}_2\) Consumption Reagent (Abcam) for 30–120 min. Mitochondrial respiration was evaluated with the WST- 81 assay (Carl Roth), as described (51). Autophagosomes and lysosomes were labeled with Cell Meter Autophagy Fluorescence Imaging kit (AAT Bioquest, Sunnyvale, CA), Lyso Brite Orange (Bertin Bioreagent, Montigny le Bretonneux, France) and Lyso View 405 (Biotium, Inc. Fremont, C). Inflammasome activity was measured with the Caspase- Glo 1 Inflammasome Assay (Promega Co., Madison, WI).
+
+## High fat diet feeding and indirect calorimetry
+
+Respiratory exchange rate (RER), oxygen consumption \((\mathrm{VO}_2)\) and energy expenditure (EE) were measured in each individual mouse for \(24 \mathrm{~h}\) using a small animal indirect calorimetry system (CaloBox, Phenosys, Germany). Mean RER, \(\mathrm{VO}_2\) and EE values were determined over \(7 \mathrm{~h}\) in the middle of both the day and the night phases. Basal glucose levels and glucose tolerance were measured as described (24). For HFD feeding of mice (dams with litters P6 to P9, or mice at P28 for 12 weeks) we used a rodent HFD from SSNIFF Spezialdiäten (Soest,
+
+<--- Page Split --->
+
+Germany) (24). Vit- D3 was supplemented in diet, mtRNA was transfected with magnetofection for 14 days.
+
+## miRNA detection
+
+Total RNA was extracted by TRIzol reagent (Invitrogen, Carlsbad, CA, USA) according to the manufacturer's instructions and was quantified using the NanoDrop™ 8000 Fluorospectrometer (Thermo Fisher Scientific). In total, 50 ng of purified RNA was subjected to reverse transcription using a TaqMan miRNA Reverse Transcription Kit and TaqMan® MicroRNA Assays (Applied Biosystems, Foster City, CA) according to the manufacturer's instructions (Assay ID: mmu- miR- 434- 3p, 002604; mmu- miR- 29a- 5p, 002447; RUN6B, 001973). Quantification of individual miRNAs was using a QuantStudio™ 12K flex real- time PCR system (Applied Biosystems) and the relative expression values were calculated by using the 2- ΔΔCt method and normalized to RUN6B. miRNA 434- 3p was overexpressed using a custom- synthesized RNA (Sigma- Aldrich) and transfected with Turbofect transfection reagent (Fisher Scientific). To identify potential Irf7- interacting miRNA species, we searched the TargetScan database for miRNAs with complementarity to Irf7 mRNA. In the next step, we used miRNA to identify precursor-, and mature sequences of the candidate miRNA species (52).
+
+## Cell viability assay
+
+We used the Presto Blue Cell Viability Assay (Thermo Fisher Scientific) and the Rotitest Vital (Carl Roth) assays according to the manufacturers' instructions.
+
+## Western blotting
+
+Cells were lysed in ice- cold RIPA buffer supplemented with Pierce™ protease and phosphatase inhibitor mini tablets (Thermo Scientific). Protein concentration was measured by the Pierce™ Rapid Gold BCA Protein Assay Kit and 30- 40 μg protein samples were run on \(16\%\) SDS gels for protein separation, followed by blotting the gels on \(0.2 - \mu \mathrm{m}\) nitrocellulose blotting membrane (Amersham, Freiberg, Germany) at \(300\mathrm{mA}\) for \(1\mathrm{h}\) in a cold room. After blotting, membranes were blocked with \(5\%\) skimmed milk for \(1\mathrm{h}\) . Providers of the \(\beta\) - actin and LC3 antibodies are listed in Supplement Table 2. Antibody concentrations used were as follows: \(\beta\) - actin, 1:10,000, LC3, \(0.2\mu \mathrm{g / ml}\) .
+
+## Quantification of nucleic acids in extracellular vesicles
+
+We collected EV pellets from cells, from formula milk or infant formula in a clean Eppendorf tube, which was centrifuged at \(0.8\mathrm{g}\) to remove cell debris. To isolate the EV- associated DNA from the pellets or from the cell culture media, we used the Zymo Quick DNA Microprep Kit (Zymo Research, Irvine, CA). After determination of the DNA concentration, we used \(5\mathrm{ng}\) for qPCR assays. EV- depleted cell culture media was used as a reference. For comparison between groups, we used the \(\Delta \Delta \mathrm{Ct}\) method to determine relative changes in mtDNA levels. For extraction of mtRNA and other EV- associated RNA species from cell EV pellets and culture media, we used Trizol Reagent. After determination of the RNA concentration, we used \(50\mathrm{ng}\) of RNA to generate cDNA.
+
+<--- Page Split --->
+
+## mtDNA copy number in the inguinal adipose tissue
+
+We used Trizol Reagent DNA isolation from iAT at P6 and P56. DNA was reconstituted in TE buffer and adjusted to \(10\mathrm{ng / \mu l}\) . We performed qPCR using \(HK2\) as a reference nuclear genome- encoded gene, and measured the DNA copy number of mtDNA- encoded 16S and Nd1. We calculated the copy number according to the formula:
+
+\[\Delta \mathrm{Ct} = \mathrm{Ct}_{\mathrm{Target~gene}} - \mathrm{Ct}_{\mathrm{Reference~gene}} \quad (1)\]
+
+## Magnetofection of mtRNA
+
+In vivo delivery of mtRNA into the cytosol of adipocytes was achieved with magnetofection, using mtRNA- magnetic nanoparticle complexes (DogtorMag, OzBiosciences, San Diego, CA). Briefly, mtRNA- nanoparticle complexes were injected into the inguinal adipose tissue of mice, and enrichment of the magnetic nanoparticles was ensured by magnetic exposure of the fat depot, as described (53). MicroRNA was transfected using Lipofectamine 3000 (Thermo Fisher).
+
+## Institutional Review Board Statement
+
+Research involving animals was approved by the regional governmental ethics and animal welfare committee in Tübingen, Germany (#1511; #1557; #1492; #1546; #0.232- 1,2,4,5).
+
+## Acknowledgements for the supplemental information
+
+The VDR inhibitor was provided by Prof. Dr. Leggy A. Arnold, University of Wisconsin, USA. MTY was developed and provided by Dr. Y- T. Chang (Center for Self- assembly and Complexity, Institute for Basic Science & Department of Chemistry, Pohang University of Science and Technology, Republic of Korea. The authors thank Prof. Hartmut Geiger (Ulm University) for providing access to the FACS equipment. The assistance of Katharina Schormair and Burak Yildiz in image analysis is much appreciated. The contribution of Vincent Pflüger, Yun Chen, Antonia Stubenvoll, Angelika Bauer are acknowledged. Elements of the 3D artwork used in the graphical abstract was provided by Dreamstime Stock Photography.
+
+## References
+
+1. Seale P, Bjork B, Yang W, Kajimura S, Chin S, Kuang S, et al. PRDM16 controls a brown fat/skeletal muscle switch. Nature. 2008;454(7207):961-7.
+2. Kissig M, Ishibashi J, Harms MJ, Lim H-W, Stine RR, Won K-J, et al. PRDM16 represses the type I interferon response in adipocytes to promote mitochondrial and thermogenic programing. The EMBO Journal. 2017;36(11):1528-42.
+3. Seale P, Kajimura S, Yang W, Chin S, Rohas LM, Uldry M, et al. Transcriptional control of brown fat determination by PRDM16. Cell metabolism. 2007;6(1):38-54.
+4. Jespersen NZ, Larsen TJ, Peijs L, Daugaard S, Homøe P, Loft A, et al. A classical brown adipose tissue mRNA signature partly overlaps with brite in the supraclavicular region of adult humans. Cell Metab. 2013;17(5):798-805.
+
+<--- Page Split --->
+
+5. Kozak LP. The genetics of brown adipocyte induction in white fat depots. Front Endocrinol (Lausanne). 2011;2:64.
+6. Nascimento EBM, Sparks LM, Divoux A, van Gisbergen MW, Broeders EPM, Jörgensen JA, et al. Genetic Markers of Brown Adipose Tissue Identity and In Vitro Brown Adipose Tissue Activity in Humans. Obesity. 2018;26(1):135-40.
+7. Perugini J, Bordoni L, Venema W, Acciarini S, Cinti S, Gabbianelli R, et al. Zic1 mRNA is transiently upregulated in subcutaneous fat of acutely cold-exposed mice. 2019;234(3):2031-6.
+8. Pilkington A-C, Paz HA, and Wankhade UD. Beige Adipose Tissue Identification and Marker Specificity—Overview. Front Endocrinol (Lausanne). 2021;12(8).
+9. Carobbio S, Rosen B, and Vidal-Puig A. Adipogenesis: new insights into brown adipose tissue differentiation. Journal of molecular endocrinology. 2013;51(3):T75-T85.
+10. Sanchez-Gurmaches J, and Guertin DA. Adipocyte lineages: tracing back the origins of fat. Biochim Biophys Acta. 2014;1842(3):340-51.
+11. Lee K-H, and Kim NH. Differential Expression of Adipocyte-Related Molecules in the Distal Epididymal Fat of Mouse during Postnatal Period. Development & Reproduction. 2019;23(3):213-21.
+12. Hoang AC, Yu H, and Röszer T. Transcriptional Landscaping Identifies a Beige Adipocyte Depot in the Newborn Mouse. Cells. 2021;10(9):2368.
+13. Rockstroh D, Landgraf K, Wagner IV, Gesing J, Tauscher R, Lakowa N, et al. Direct evidence of brown adipocytes in different fat depots in children. PLOS ONE. 2015;10(2):e0117841.
+14. Yu H, Dilbaz S, Coßmann J, Hoang AC, Diedrich V, Herwig A, et al. Breast milk alkylglycerols sustain beige adipocytes through adipose tissue macrophages. The Journal of Clinical Investigation. 2019;129(6):2485-99.
+15. Szklarczyk D, Gable AL, Lyon D, Junge A, Wyder S, Huerta-Cepas J, et al. STRING v11: protein-protein association networks with increased coverage, supporting functional discovery in genome-wide experimental datasets. Nucleic acids research. 2019;47(D1):D607-d13.
+16. Luan Y, Lengyel P, and Liu C-J. p204, a p200 family protein, as a multifunctional regulator of cell proliferation and differentiation. Cytokine Growth Factor Rev. 2008;19(0):357-69.
+17. Bourette RP, and Mouchiroud G. The biological role of interferon-inducible P204 protein in the development of the mononuclear phagocyte system. Front Biosci. 2008;13:879-86.
+18. Choubey D, and Panchanathan R. Interferon-inducible Ifi200-family genes in systemic lupus erythematosus. Immunol Lett. 2008;119(1-2):32-41.
+19. Tabula Muris C, Overall c, Logistical c, Organ c, processing, Library p, et al. Single-cell transcriptomics of 20 mouse organs creates a Tabula Muris. Nature. 2018;562(7727):367-72.
+20. Ritchie C, Cordova AF, Hess GT, Bassik MC, and Li L. SLC19A1 Is an Importer of the Immunotransmitter cGAMP. Molecular Cell. 2019;75(2):372-81.e5.
+21. Karikó K, Buckstein M, Ni H, and Weissman D. Suppression of RNA Recognition by Toll-like Receptors: The Impact of Nucleoside Modification and the Evolutionary Origin of RNA. Immunity. 2005;23(2):165-75.
+22. Bakker P, Scantlebery A, Butter L, Claessen N, Teske G, Poll T, et al. TLR9 Mediates Remote Liver Injury following Severe Renal Ischemia Reperfusion. PloS one. 2015;10:e0137511.
+
+<--- Page Split --->
+
+23. Hines JH, Henle SJ, Carlstrom LP, Abu-Rub M, and Henley JR. Single vesicle imaging indicates distinct modes of rapid membrane retrieval during nerve growth. BMC Biology. 2012;10(1):4.
+
+24. Waqas SFH, Hoang A, Lin Y, Ampem G, et al, and Röszer T. Neuropeptide FF increases M2 activation and self-renewal of adipose tissue macrophages. The Journal of Clinical Investigation 2017;127(7):2842-54.
+
+25. Haag SM, Gulen MF, Reymond L, Gibelin A, Abrami L, Decout A, et al. Targeting STING with covalent small-molecule inhibitors. Nature. 2018;559(7713):269-73.
+
+26. Waldenström A, Gennebäck N, Hellman U, and Ronquist G. Cardiomyocyte Microvesicles Contain DNA/RNA and Convey Biological Messages to Target Cells. PloS one. 2012;7:e34653.
+
+27. Zabeo D, Cvjetkovic A, Lässer C, Schorb M, Lötvall J, and Höög JL. Exosomes purified from a single cell type have diverse morphology. Journal of extracellular vesicles. 2017;6(1):1329476-.
+
+28. Durcin M, Fleury A, Taillebois E, Hilairet G, Krupova Z, Henry C, et al. Characterisation of adipocyte-derived extracellular vesicle subtypes identifies distinct protein and lipid signatures for large and small extracellular vesicles. Journal of extracellular vesicles. 2017;6(1):1305677.
+
+29. Ragni E, Perucca Orfei C, De Luca P, Viganò M, Colombini A, Lugano G, et al. miR-22-5p and miR-29a-5p Are Reliable Reference Genes for Analyzing Extracellular Vesicle-Associated miRNAs in Adipose-Derived Mesenchymal Stem Cells and Are Stable under Inflammatory Priming Mimicking Osteoarthritis Condition. Stem Cell Reviews and Reports. 2019;15(5):743-54.
+
+30. Datta A, Kim H, McGee L, Johnson AE, Talwar S, Marugan J, et al. High-throughput screening identified selective inhibitors of exosome biogenesis and secretion: A drug repurposing strategy for advanced cancer. Scientific Reports. 2018;8(1):8161.
+
+31. Zitomer NC, Mitchell T, Voss KA, Bondy GS, Pruett ST, Garnier-Ambard EC, et al. Ceramide synthase inhibition by fumonisin B1 causes accumulation of 1-deoxyosphinganine: a novel category of bioactive 1-deoxyosphingoid bases and 1-deoxydihydroceramides biosynthesized by mammalian cell lines and animals. The Journal of biological chemistry. 2009;284(8):4786-95.
+
+32. Narvaez CJ, Matthews D, Broun E, Chan M, and Welsh J. Lean phenotype and resistance to diet-induced obesity in vitamin D receptor knockout mice correlates with induction of uncoupling protein-1 in white adipose tissue. Endocrinology. 2009;150(2):651-61.
+
+33. Lorenz R, Bernhart SH, Hörner Zu Siederdissen C, Tafer H, Flamm C, Stadler PF, et al. ViennaRNA Package 2.0. Algorithms for molecular biology : AMB. 2011;6:26.
+
+34. Hornung V, Ellegast J, Kim S, Brzózka K, Jung A, Kato H, et al. 5'-Triphosphate RNA Is the Ligand for RIG-I. science. 2006;314(5801):994-7.
+
+35. Kato H, Takeuchi O, Mikamo-Satoh E, Hirai R, Kawai T, Matsushita K, et al. Length-dependent recognition of double-stranded ribonucleic acids by retinoic acid-inducible gene-I and melanoma differentiation-associated gene 5. The Journal of experimental medicine. 2008;205(7):1601-10.
+
+36. Ablasser A, Bauernfeind F, Hartmann G, Latz E, Fitzgerald KA, and Hornung V. RIG-I-dependent sensing of poly(dA:dT) through the induction of an RNA polymerase III–transcribed RNA intermediate. Nature Immunology. 2009;10(10):1065-72.
+
+37. Stoppelenburg AJ, von Hegedus JH, Huis in't Veld R, Bont L, and Boes M. Defective control of vitamin D receptor-mediated epithelial STAT1 signalling predisposes to severe respiratory syncytial virus bronchiolitis. The Journal of Pathology. 2014;232(1):57-64.
+
+<--- Page Split --->
+
+38. Cippitelli M, and Santoni A. Vitamin D3: a transcriptional modulator of the interferon-γ gene. European Journal of Immunology. 1998;28(10):3017-30.
+39. Helming L, Böse J, Ehrchen J, Schiebe S, Frahm T, Geffers R, et al. 1α,25-dihydroxyvitamin D3 is a potent suppressor of interferon γ–mediated macrophage activation. Blood. 2005;106(13):4351-8.
+40. Das M, Tomar N, Sreenivas V, Gupta N, and Goswami R. Effect of vitamin D supplementation on cathelicidin, IFN-γ, IL-4 and Th1/Th2 transcription factors in young healthy females. European Journal of Clinical Nutrition. 2014;68(3):338-43.
+41. Unterholzner L, Keating SE, Baran M, Horan KA, Jensen SB, Sharma S, et al. IF116 is an innate immune sensor for intracellular DNA. Nature immunology. 2010;11(11):997-1004.
+42. Sidhu PS, Teske K, Feleke B, Yuan NY, Guthrie ML, Fernstrum GB, et al. Anticancer activity of VDR-coregulator inhibitor PS121912. Cancer Chemother Pharmacol. 2014;74(4):787-98.
+43. Waqas SFH, Noble A, Hoang A, Ampem G, Popp M, Strauß S, et al. Adipose tissue macrophages develop from bone marrow-independent progenitors in Xenopus laevis and mouse. Journal of Leukocyte Biology. 2017;102(3):845-55.
+44. De Carlo S, and Harris JR. Negative staining and cryo-negative staining of macromolecules and viruses for TEM. Micron. 2011;42(2):117-31.
+45. Holden P, and Horton WA. Crude subcellular fractionation of cultured mammalian cell lines. BMC research notes. 2009;2:243.
+46. Hausman DB, Park HJ, and Hausman GJ. Isolation and culture of preadipocytes from rodent white adipose tissue. Methods in molecular biology. 2008;456:201-19.
+47. Ampem G, and Röszer T. In: Badr MZ ed. Nuclear Receptors: Methods and Experimental Protocols. New York, NY: Springer New York; 2019:225-36.
+48. Arai S, Suzuki M, Park SJ, Yoo JS, Wang L, Kang NY, et al. Mitochondria-targeted fluorescent thermometer monitors intracellular temperature gradient. Chemical communications. 2015;51(38):8044-7.
+49. Lane N. Hot mitochondria? PLoS biology. 2018;16(1):e2005113.
+50. Chrétien D, Bénit P, Ha H-H, Keipert S, El-Khoury R, Chang Y-T, et al. Mitochondria are physiologically maintained at close to 50 °C. PLoS biology. 2018;16(1):e2003992.
+51. Karabatsiakis A, Böck C, Salinas-Manrique J, Kolassa S, Calzia E, Dietrich DE, et al. Mitochondrial respiration in peripheral blood mononuclear cells correlates with depressive subsymptoms and severity of major depression. Translational Psychiatry. 2014;4(6):e397-e.
+52. Agarwal V, Bell GW, Nam J-W, and Bartel DP. Predicting effective microRNA target sites in mammalian mRNAs. eLife. 2015;4:e05005.
+53. Plank C, and Rosenecker J. Magnetofection: The Use of Magnetic Nanoparticles for Nucleic Acid Delivery. Cold Spring Harbor Protocols. 2009;2009(6):pdb.prot5230.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+HoangSupplementaryInformation.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/images_list.json b/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..2622d410579849c9dc40b090749352663ef72c87
--- /dev/null
+++ b/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/images_list.json
@@ -0,0 +1,122 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. Relationships between tropical Pacific and North Atlantic climate variability. Regression of a boreal spring (March-May) SST anomalies (shading; \\(^\\circ \\mathrm{C}\\) ) upon the preceding winter (November-January) Niño3.4 (black box; \\(5^{\\circ}\\mathrm{S} - 5^{\\circ}\\mathrm{N}\\) , \\(120^{\\circ} - 170^{\\circ}\\mathrm{W}\\) ) index and \\(\\mathbf{b}\\) boreal winter SST anomalies (shading; \\(^\\circ \\mathrm{C}\\) ) upon the preceding spring NTA (blue box; \\(0^{\\circ} - 15^{\\circ}\\mathrm{N}\\) , \\(90^{\\circ} - 0^{\\circ}\\mathrm{W}\\) ) SST anomaly. Dots in (a-b) indicate regression coefficients that are statistically significant at the \\(95\\%\\) confidence level. c 15-yr running lead-lagged correlation of the boreal winter Niño3.4 index with the NTA SST anomaly. Solid, dashed, and dotted lines mark the region with values exceeding the \\(80\\%\\) , \\(90\\%\\) and \\(95\\%\\) confidence levels, respectively. d Lead-lagged correlation of the boreal winter Niño3.4 index with the observed (solid) and reconstructed (dashed) NTA SST anomaly for bandpass filtering of 2-3-yr (blue) and 3-5-yr (red) periods by using a Fast Fourier Transform filter. For the y-axis of (c-d), negative and positive values indicate NTA-lead and NTA-lag at monthly scale, respectively. e Lead-lagged correlation of the boreal winter Niño3.4 index with NTA SST anomaly in the idealized pacemaker experiments with different Pacific SST forcing (see Methods). Gray dashed lines in (d-e) indicate the \\(95\\%\\) confidence levels.",
+ "footnote": [],
+ "bbox": [
+ [
+ 214,
+ 99,
+ 777,
+ 505
+ ]
+ ],
+ "page_idx": 15
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Phase relationship of NTA SST anomalies with ENSO in pi-control",
+ "footnote": [],
+ "bbox": [
+ [
+ 225,
+ 95,
+ 820,
+ 500
+ ]
+ ],
+ "page_idx": 16
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Phase relationship of NTA SST anomalies with ENSO in future warming simulations. Scatterplot of ENSO period and lead-time at which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Niño3.4 index for the SSP2-4.5 (red) and SSP5-8.5 (purple) scenarios. The linear fits (solid black) are displayed together with respective correlation coefficient R and slope.",
+ "footnote": [],
+ "bbox": [
+ [
+ 198,
+ 95,
+ 832,
+ 500
+ ]
+ ],
+ "page_idx": 17
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4. Schematic trans-basin relationships between tropical Pacific and North Atlantic oceans regulated by the ENSO periodicity. In the quasi-biennial ENSO cycle (red loop), an El Niño condition in boreal winter (left panel) leads to positive NTA warming during subsequent spring (upper panel) at a \\(\\sim 4\\) -month lead time, which in turn can see a La Niña formation (right panel) typically following El Niño in the subsequent winter, showing a statistical \\(\\sim 8\\) -month lead time of the NTA. Likewise, a La Niña condition in boreal winter (right panel) gives rise to the following spring NTA SST cooling (lower panel) with a lag of \\(\\sim 4\\) months, which is often followed by an El Niño formation (left panel), corresponding to a statistical \\(\\sim 8\\) -month lead time of the NTA. The same applies for the quasi-quadrennial ENSO cycle (blue loop) except for the negative correlation of NTA SST variability with the following ENSO event by \\(\\sim 20\\) months.",
+ "footnote": [],
+ "bbox": [
+ [
+ 155,
+ 116,
+ 824,
+ 460
+ ]
+ ],
+ "page_idx": 18
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 70,
+ 108,
+ 881,
+ 732
+ ]
+ ],
+ "page_idx": 19
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 75,
+ 210,
+ 886,
+ 830
+ ]
+ ],
+ "page_idx": 20
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 78,
+ 70,
+ 915,
+ 660
+ ]
+ ],
+ "page_idx": 22
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 72,
+ 60,
+ 900,
+ 525
+ ]
+ ],
+ "page_idx": 23
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f.mmd b/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..f5f17d0da74e155fa446f2f001cda4b764591702
--- /dev/null
+++ b/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f.mmd
@@ -0,0 +1,296 @@
+
+# Spurious North Tropical Atlantic pre-cursors to ENSO
+
+Wenjun Zhang ( \(\boxed{\infty}\) zhangwj@nuist.edu.cn)
+
+Nanjing University of Information Science and Technology https://orcid.org/0000- 0002- 6375- 8826
+
+Feng Jiang Nanjing University of Information Science and Technology
+
+Malte Stuecker University of Hawai'i at Manoa
+
+Fei- Fei Jin University of Hawaii at Manoa
+
+Axel Timmermann Pusan National University
+
+## Article
+
+Keywords: El Niño- Southern Oscillation (ENSO), North Tropical Atlantic (NTA), sea surface temperature (SST)
+
+Posted Date: February 26th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 85237/v1
+
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on May 25th, 2021. See the published version at https://doi.org/10.1038/s41467- 021- 23411- 6.
+
+<--- Page Split --->
+
+# Spurious North Tropical Atlantic pre-cursors to ENSO
+
+Wenjun Zhang \(^{1}\) , Feng Jiang \(^{1}\) , Malte F. Stuecker \(^{2}\) , Fei- Fei Jin \(^{3}\) , Axel Timmermann \(^{4,5}\)
+
+\(^{1}\) Key Laboratory of Meteorological Disaster of Ministry of Education (KLME), Nanjing University of Information Science and Technology, Nanjing, China \(^{2}\) Department of Oceanography & International Pacific Research Center (IPRC), SOEST, University of Hawai'i at Manoa, Honolulu, HI, USA \(^{3}\) Department of Atmospheric Sciences, SOEST, University of Hawai'i at Manoa, Honolulu, HI, USA \(^{4}\) Institute for Basic Science, Center for Climate Physics, Busan, South Korea \(^{5}\) Pusan National University, Busan, South Korea
+
+Abstract: The El Niño- Southern Oscillation (ENSO), the primary driver of year- to- year global climate variability, is known to influence the North Tropical Atlantic (NTA) sea surface temperature (SST), especially during boreal spring season. Focusing on statistical lead- lag relationships, previous studies have proposed that interannual NTA SST variability can also feed back on ENSO in a predictable manner. However, these studies do not properly account for ENSO's autocorrelation and the fact that the SST in the Atlantic and Pacific, as well as their atmospheric interaction are seasonally modulated. This can lead to misinterpretations of causality and the spurious identification of Atlantic precursors for ENSO. Revisiting this issue under consideration of seasonality, time- varying ENSO frequency, and greenhouse warming, we demonstrate that the cross- correlation characteristics between NTA SST and ENSO, are fully consistent with a one- way Pacific to Atlantic forcing, even though the interpretation of lead- lag relationships may suggest otherwise.
+
+The El Niño- Southern Oscillation (ENSO) phenomenon is characterized by interannual fluctuations between warm (El Niño) and cold (La Niña) sea surface temperature (SST) conditions in the equatorial Pacific. Its dynamics and associated coupled changes in the atmosphere and ocean have been studied extensively \(^{1,2}\) . Conceptual frameworks for ENSO have been proposed to explain the statistical and physical characteristics in terms of a Pacific eigenscillation that originates from positive air- sea interactions and delayed oceanic negative feedbacks \(^{3- 6}\) . ENSO is further
+
+<--- Page Split --->
+
+energized by stochastic atmospheric forcing7 and modulated by the seasonal cycle8- 9. Counterintuitively, despite significant advances in both ENSO theory and ENSO representation in climate models, the predictability of central- to- eastern tropical Pacific SST anomalies has decreased in the past two decades to only one season10- 12. Research over the past years has further revealed that SST anomalies in other ocean basins may also play an important role shaping the evolution of El Niño events and its predictability13- 24. In particular, the North Tropical Atlantic (NTA) SST has been highlighted as a potential precursor candidate18,22- 24.
+
+The NTA ocean, home to a variety of societally relevant climate phenomena has received widespread attention25- 29. Typically, NTA SST warming lags the El Niño mature winter phase, peaking in the following spring (Fig. 1a) and persisting into early summer30. It is caused by El Niño- induced atmospheric forcing that both modulates the Walker Circulation and excites the Pacific- North America teleconnection pattern31- 35. In turn, this NTA warming is argued to stimulate a westward- propagating off- equatorial Rossby wave train, conducive to an ensuing La Niña formation18,24. However, this reverse connection, which is characterized by a negative ENSO/NTA cross- correlation with the NTA SST leading by about 8 months (Fig. 1b), is highly variable and especially absent before the 1990s22 (Fig. 1c). Despite some presumptions involved22,36, the mechanisms responsible for the puzzling connection are less appreciated and a comprehensive understanding of the two- way interaction between NTA variability and ENSO is required. In this study, we use both observations and climate model simulations to investigate the underlying mechanisms for the time- varying relationship. We demonstrate that changes in the NTA/ENSO relationship can be explained in terms of changes in ENSO frequency. The proposed mechanism is fully consistent with ENSO forcing NTA, rather than the opposite.
+
+## ENSO-NTA SST relationship in observations
+
+ENSO generally commences its development in boreal summer and peaks in winter, stimulating atmospheric forcing over the NTA through two distinct pathways involving tropical and extra- tropical teleconnections30,34,35. Analyzing observed SST anomalies
+
+<--- Page Split --->
+
+(see Methods), we see that the El Nino remote forcing is felt in the NTA SST a few months later around the spring season (Fig. 1a), possibly due to the local SST adjustment timescale37 and the seasonality of the atmospheric teleconnection to the Atlantic30,35. This robust ENSO/NTA connection can be detected during the entire study period notwithstanding a slight reduction of the correlation coefficient in the recent two decades (red shading in Fig. 1c; see also ref. 38). In turn, the spring NTA warming appears to contribute to the following La Niña development in the Pacific Ocean (and similarly a spring NTA cooling contributing to a following El Niño) (Fig. 1b) with a relatively weak correlation at about 8-month lag. However, we must also emphasize here that an NTA warming in spring following an El Niño will automatically be correlated with La Niña conditions 8 months later, because El Niño conditions are usually followed by La Niña in the following year, without even involving a physical NTA-to- ENSO relationship. Therefore, one needs to be careful in interpreting seasonally modulated teleconnections of ENSO (see for instance discussion in ref. 21). The 8-month leading relationship of NTA over ENSO is observed after the early 1990s while it is absent in the preceding period (blue shading in Fig. 1c; see also ref. 22). Prior to the 1990s we find a much longer characteristic lead of \(\sim 20\) - month (blue shading in Fig. 1c). Interestingly, this decadal change of the NTA- lead- time corresponds well to a shift in ENSO frequency from quasi- quadrennial to quasi- biennial (Supplementary Fig. 1; see also ref. 39). This regime change is also accompanied by more frequent occurrences of Central Pacific (CP) ENSO events (characterized by quasi- biennial timescale) and a reduction of the canonical Eastern Pacific (EP) ENSO events (characterized by quasi- quadrennial timescale) 2,12.
+
+Here we hypothesize that the changing ENSO- NTA SST phase- lag relationships can be explained in the context of different ENSO regimes manifested by quasi- biennial and quasi- quadrennial periodicities. An El Niño is typically followed by a La Niña event during the subsequent winter in a quasi- biennial ENSO cycle, whereby the NTA warming in the decaying El Niño spring accompanies a La Niña formation about 8- month later. For a quasi- quadrennial ENSO cycle, it takes around two years for the phase transition on average and correspondingly an El Niño induced NTA warming
+
+<--- Page Split --->
+
+statistically leads the next La Niña mature phase by about 20 months. Observed ENSO cycles are not perfect oscillations with a distinct periodicity, in the case of the quasi- quadrennial cycle in which a strong El Niño event is prone to be followed by consecutive La Niña events. However, the complicated ENSO cycle features do not affect the relationship of NTA SST with following ENSO from a statistical standpoint.
+
+To further illustrate the abovementioned physical linkage between lead time and ENSO frequency, we conduct 2- 3- and 3- 5- yr bandpass filtering of the observed ENSO and NTA indices to differentiate two- way ENSO- NTA SST connections associated with quasi- biennial and quasi- quadrennial periodicities, respectively. ENSO impacts on boreal spring NTA SST anomalies are clearly displayed in both ENSO frequency bands (Fig. 1d), consistent with the robust relationship derived from the raw data (red shading in Fig. 1c), substantiating ENSO's physical regulation of the following spring NTA SST. To understand the distinct statistical relationships of the NTA SST with quasi- biennial and quasi- quadrennial ENSO (negative lags in Fig. 1c), we need to consider first that for these timescales El Niño and La Niña are anticorrelated at a lag of \(\sim 12\) months and \(\sim 24\) months, respectively. With El Niño causing robust spring NTA warming, the spring NTA warming will then be automatically anticorrelated with Niño3.4 SST anomalies at lag 8 (=12- 4) and lag 20 (=24- 4) months, for the quasi- biennial and quasi- quadrennial modes, respectively (Fig. 1d). The decadal shifts in the NTA- ENSO relationship are thus fully consistent with a robust one- way ENSO to NTA forcing relationship combined with a shift of ENSO's dominant frequency (Supplementary Fig. 1b). The notion of NTA serving as precursor for ENSO is therefore equivalent to simply saying that the El Niño is precursor to the next La Niña.
+
+Next, to understand the role of ENSO forcing in fostering NTA variability when considering its time- varying periodicity change, we use an extension of the original stochastic climate model40 for NTA SST anomalies that includes both remote observed ENSO forcing and a damping rate modulated by the annual cycle (see Methods and ref. 21 for the original application of the model). The observed monthly time- varying NTA SST anomaly can be well captured by the ENSO- forced model (R=0.55, statistically significant at the 95% confidence level; Supplementary Fig. 2). Importantly, the
+
+<--- Page Split --->
+
+residual variability has no preferred interannual spectral peak (Supplementary Fig. 3). The reconstructed NTA SST exhibits a very similar lead- lag relationship with ENSO compared to that of the observations (Fig. 1d), further collaborating our hypothesis of a one- way relationship between the tropical Pacific and North Atlantic climate variability.
+
+## ENSO-NTA SST relationship in idealized pacemaker experiments
+
+Observed ENSO variability has a broad spectrum in the range of 2- 7 years, characterized by quasi- biennial and quasi- quadrennial spectral peaks, which cannot be completely isolated using current linear methods2. To demonstrate trans- basin relationships that would result from different purely periodic ENSO oscillations, a set of idealized pacemaker experiments is conducted by imposing ENSO SST anomaly forcing with idealized 2- and 4- yr cycles in the tropical Pacific (see Methods). In this modeling set- up only ENSO can force NTA, but not vice versa. Given that there is a shift in the ENSO's zonal location around the 1990s, we also consider different SST forcing patterns associated with the EP and CP El Niño types in the pacemaker experiments (Supplementary Fig. 4; see Methods), to investigate possible influences of the zonal SST anomaly structure in addition to ENSO timescale changes. The observed robust ENSO effect on the subsequent spring NTA SST can be well reproduced in all ENSO- forced experiments (Fig. 1e). In the experiments with 2- yr ENSO forcing, the NTA SST variability is significantly correlated with subsequent ENSO conditions of opposite sign, having the maximum correlation at an 8- month lead- time of NTA over ENSO regardless of the ENSO SST anomaly patterns. This statistical ENSO/NTA relationship corresponds to what we see in the observations before the 1990s (Fig. 1c). Our results clearly show that the 8- month lead of NTA over ENSO can be obtained, even though the set- up of our model experiments does not allow for NTA to influence ENSO. In the 4- yr ENSO forced experiments, the spring NTA SST anomaly as a response to the preceding ENSO is followed by the subsequent ENSO formation at about 20- month lead time for both EP and CP associated SST forcing. These pacemaker experiments indicate that the statistical ENSO and NTA relationship is largely
+
+<--- Page Split --->
+
+controlled by ENSO periodicity rather than its spatial pattern and that the ENSO autocorrelation itself causes this peculiar phase- relationship.
+
+## ENSO-NTA SST relationship in the CMIP6 simulations
+
+Considering the limited sample size of the short observational record though supported by our idealized pacemaker experiments, we further examine the trans- basin relationship between ENSO and NTA SST in 46 coupled models in pre- industrial control (pi- control) simulations participating in Phase 6 of the Coupled Model Intercomparison Project (CMIP6) (Supplementary Table 1). Almost all coupled models are capable of capturing the robust ENSO forcing on the NTA SST (Supplementary Fig. 5). However, the models exhibit a large diversity in the statistical relationship between boreal spring NTA SST variability and subsequent winter ENSO at \(\sim 8\) - month lead- time, whereas a statistically significant relationship can only be simulated in about a quarter of the CMIP6 models (Fig. 2a). To determine the underlying mechanisms responsible for this, we rank the models based on their correlation between spring NTA SST anomaly and subsequent winter ENSO conditions, and then select the 10 models closest to the observations with the highest negative correlation (left side in Fig. 2a) and the 10 models most different from the observations that show a weakly positive correlation (right side in Fig. 2a).
+
+Although both model groups show a very similar ENSO SST anomaly pattern (Fig. 2b), these two groups exhibit distinct ENSO spectral characteristics (Fig. 2c). The models that have a statistically significant 8- month ENSO/NTA lagged relationship exhibit a relatively shorter ENSO periodicity, analogous to the observations after the 1990s (Fig. 2c). In contrast, the models without a significant relationship at 8- month NTA- lead- time have longer ENSO periodicities resembling the observations before the 1990s (Fig. 2c). In addition, there is a high inter- model linear correlation (R=0.75, statistically significant at the 95% confidence level) between simulated dominant ENSO periodicity and the lead- time of the most pronounced negative correlation of NTA SST leading ENSO (Fig. 2d). This again supports our hypothesis that the statistical
+
+<--- Page Split --->
+
+lead- time of NTA SST anomalies over the subsequent ENSO conditions is tightly controlled by the ENSO periodicity.
+
+There exists considerable uncertainty in the projections of trans- basin interactions and the pan- tropical climate patterns that will emerge in a warming world23. Thus, we next investigate the ENSO/NTA trans- basin interaction in CMIP6 future greenhouse- gas emission scenarios (see Methods). We find that almost all of these models in the SSP2- 4.5 (25 of 25) and SSP5- 8.5 (26 of 28) simulations are able to simulate the robust ENSO effect on the subsequent spring NTA SST (Supplementary Fig. 6). The in- turn linear relationship between NTA- lead- time over ENSO and ENSO periodicity continues to hold in the global warming scenarios (Figure 3). High correlations can be detected in both warming scenarios (R=0.79 for the SSP2- 4.5 scenario and R=0.81 for the SSP5- 8.5 scenario, exceeding 95% confidence level). It further supports that the trans- basin ENSO/NTA relationships are predominately determined by ENSO and its internal pacing.
+
+## Discussion
+
+In summary, ENSO plays a leading role in generating NTA SST variability in boreal spring following its peak phase via seasonally modulated atmospheric forcing and further influenced by the local SST adjustment timescale in the Atlantic (upper- left quadrant in Fig. 4). In turn, the observed time- varying relationship between these ENSO- induced NTA SST anomalies and the following ENSO conditions (Fig. 1c) can be explained by the ENSO regime shifting from dominantly quasi- quadrennial to dominantly quasi- biennial around the 1990s (upper- right quadrant in Figure 4). We emphasize that the observed ENSO cycles are not perfect oscillations with single frequencies. In nature, stochastic noise and nonlinearities can play important roles in shaping ENSO characteristics41.
+
+Here we demonstrated using observational data, a simple seasonally modulated ENSO- forced model, idealized pacemaker experiments, and CMIP6 simulations that the character of the observed cross correlation between ENSO and NTA is fully consistent with an ENSO forced system. We conclude that previous suggestions about
+
+<--- Page Split --->
+
+possible NTA pre- cursors on ENSO predictability and capacitor arguments remain spurious. We further show that our main results are robust even in a warming world.
+
+## Methods
+
+Observation and statistics. The utilized SST datasets are the global sea ice and SST analyses (1960- 2019) from the Hadley Centre (HadISST) provided by the Met Office Hadley Centre with the horizonal resolution of \(1^{\circ}\) longitude \(\times 1^{\circ}\) latitude \(^{42}\) . Anomalies were derived relative to the monthly mean climatology over the entire study period (1960- 2019). A linear trend was removed to avoid possible influences associated with global warming. The Multi- Taper method (MTM), which uses a median smoother to distinguish signals from background noises, is used for spectral estimates \(^{43}\) with 3 (Supplementary Fig. 1b) or 5 tapers (Figs. 2, 3 and Supplementary Fig. 3) in consideration of different sample sizes. We test the spectra against the null hypothesis of an autoregressive model of order one (AR(1)) and calculate the respective \(95\%\) confidence levels. A nine- point smoothing is applied in Figs. 1c- e to avoid possible noise disturbance. All statistical significance tests were performed using the two- tailed Student's \(t\) test. El Niño events were identified according to the definition of the Climate Prediction Center based on a threshold of \(\pm 0.5^{\circ}\mathrm{C}\) of the Niño3.4 index (averaged SST anomaly in the domain of \(5^{\circ}\mathrm{S} - 5^{\circ}\mathrm{N}\) , \(120^{\circ} - 170^{\circ}\mathrm{W}\) ) for five consecutive months. EP and CP indices (EPI and CPI) are calculated using a mathematic rotation of the Niño3 (averaged SST anomaly in the domain of \(5^{\circ}\mathrm{S}\) to \(5^{\circ}\mathrm{N}\) , \(90^{\circ}\) to \(150^{\circ}\mathrm{W}\) ) and Niño4 (averaged SST anomaly in the domain of \(5^{\circ}\mathrm{S}\) to \(5^{\circ}\mathrm{N}\) , \(160^{\circ}\mathrm{E}\) to \(150^{\circ}\mathrm{W}\) ) indices \(^{44}\) . El Niño events with EPI greater than CPI were classified as EP events while those with CPI greater than EPI are defined as CP events. Following this criterium, we identified seven EP El Niño events (1965, 1972, 1976, 1982, 1991, 1997, 2015) and twelve CP El Niño events (1963, 1968, 1969, 1977, 1979, 1986, 1994, 2002, 2004, 2006, 2009, 2019).
+
+Simple physical model. We proposed a physically motivated model for the NTA SST anomaly as an extension \(^{21}\) of the stochastic climate model \(^{40}\) :
+
+<--- Page Split --->
+
+\[\frac{dT(t)}{dt} = (-\lambda_0 + \lambda_a\cos (\omega_a + \phi))T(t) + \beta ENSO(t) + \xi (t),\]
+
+where \(\mathrm{T(t)}\) is the monthly NTA SST anomaly, ENSO(t) the monthly Niño 3.4 index, \((-\lambda_0 + \lambda_a\cos (\omega_a + \phi))\) the seasonally modulated damping rate, in which \(\lambda_0\) and \(\lambda_{\mathrm{a}}\) denote the mean and annul cycle of the damping coefficient, \(\omega_{\mathrm{a}}\) the frequency of the annual cycle, \(\phi\) the phase shift, and \(\beta\) a scaling coefficient. The model parameters are estimated by multivariate linear regression using the observed NTA SST anomaly time series and Niño 3.4 index (following ref. 45). The ENSO- independent stochastic forcing term \((\xi (t))\) is neglected in the model for simplicity.
+
+CMIP6 simulations. Monthly SST outputs from the CMIP6 pi- control and future (the Shared Socioeconomic Pathways (SSP) 2- 4.5 and SSP5- 8.5) simulations are utilized. The external forcing (e.g., greenhouse gases and aerosols) is kept constant in the pi- control simulations while the SSP2- 4.5 with radiative forcing reaching \(4.5\mathrm{Wm}^{- 2}\) and SSP5- 8.5 reaching \(8.5\mathrm{Wm}^{- 2}\) during 2015- 210046,47. For the pi- control simulations, the last 100 years of 46 available model simulations are used for the analysis, among which 25 models are obtained for the SSP2- 4.5 scenario and 28 models for the SSP5- 8.5 scenario, respectively (see Table S1). Only one ensemble member for each model is used, mostly r1i1p1f1 with select models using ensemble member f2.
+
+Idealized pacemaker experiments. Numerical experiments are conducted by using the Geophysical Fluid Dynamics Laboratory coupled model, version 2.1 (GFDL- CM2.1), with a horizontal resolution of \(2.5^{\circ}\) longitude \(\times 2^{\circ}\) latitude and 24 vertical levels48. Four sensitivity experiments are performed by using an idealized sinusoidal EP and CP ENSO forcing with 2- and 4- yr periodicities, respectively. Composed EP El Niño SST anomalies over the tropical Pacific (25°S- 25°N, 150°E- 90°W) are used to derive the SST anomalies forcing patterns for the EXP_2yr_EP experiment with repeated sinusoidal 2- yr periodicity and the EXP_4yr_EP experiment with repeated 4- yr periodicity. The other two experiments (EXP_2yr_CP and EXP_4yr_CP) are the same, except that the SST anomalies are the composites for the observed CP El Niño
+
+<--- Page Split --->
+
+events. SST anomalies outside the forcing area are set to zero and only the positive loading in the forcing region is used. The SSTs are allowed to evolve freely outside of the prescribed regions. ENSO peak phases will occur aligned with the boreal winter season for these idealized 2- and 4- yr periodicities. The simulations are integrated for 100 years and the output from the last 80 years is used for the analyses. Anomalies in GFDL- CM2.1 are relative to a 100- year control simulation (EXP_CTRL) in which the model is forced with seasonal varying climatological SSTs.
+
+## Data availability
+
+The data used to reproduce the results of this paper are available online or by contacting the corresponding author. Hadley SST data is publicly available at: https://www.metoffice.gov.uk/hadobs/hadisst/data/download.html. The CMIP6 datasets are available at https://esgf- node.llnl.gov/projects/cmip6/.
+
+## References
+
+1. McPhaden, M. J., Zebiak, S. E., & Glantz, M. H. ENSO as an integrating concept in Earth science. Science 314(5806), 1740-1745 (2006).
+2. Timmermann, A. et al. El Niño-Southern Oscillation complexity. Nature 26, 535-545 (2018).
+3. Cane, M. A. & Zebiak S. E. A theory for El Niño and the Southern Oscillation. Science 228, 1085-1087 (1985).
+4. Battisti D. S. & Hirst A. C. Interannual variability in a tropical atmosphere-ocean model: influence of the basic state, ocean geometry and nonlinearity. J. Atmos. Sci. 46:1687-1712 (1989).
+5. Jin, F.-F. An equatorial recharge paradigm for ENSO. Part I: Conceptual model. J. Atmos. Sci. 54, 811-829 (1997).
+6. Neelin, J. D. et al. ENSO theory. J. Geophys. Res. 103, 14 261-14 290 (1998).
+7. Kessler W. S., McPhaden, M. J. & Weickmann K. M. Forcing of intraseasonal Kelvin waves in the equatorial Pacific. J. Geophys. Res. 100:10613-10632 (1995).
+
+<--- Page Split --->
+
+8. McGregor, S., Timmermann, A., Schneider, N., Stuecker, M. F. & England, M. H. The effect of the South Pacific convergence zone on the termination of El Niño events and the meridional asymmetry of ENSO. J. Clim. 25, 5566–5586 (2012).
+
+9. Stuecker, M. F., Timmermann, A., Jin, F.-F., McGregor, S. & Ren, H.-L. A combination mode of the annual cycle and the El Niño/Southern Oscillation. Nat. Geosci. 6, 540–544 (2013).
+
+10. Hendon, H. H., Lim, E., Wang, G., Alves, O. & Hudson, D. Prospects for predicting two flavors of El Niño. Geophys. Res. Lett. 36, L19713 (2009).
+
+11. Wang, W., Chen, M. & Kumar, A. An assessment of the CFS real time seasonal forecasts. Weather and Forecasting 25(3), 950-969 (2010).
+
+12. Zhang, W. et al. ENSO regime changes responsible for decadal phase relationship variations between ENSO sea surface temperature and warm water volume. Geophys. Res. Lett. 46, 7546–7553 (2019).
+
+13. Kug J.-S. & Kang I.-S. Interactive feedback between ENSO and the Indian Ocean. J. Clim. 19, 1784–1801 (2006).
+
+14. Jansen MF, Dommenget D, Keenlyside N. Tropical atmosphere–ocean interactions in a conceptual framework. J Clim 22:550–567 (2009).
+
+15. Rodríguez-Fonseca B. et al. Are Atlantic Niños enhancing Pacific ENSO events in recent decades? Geophys. Res. Lett. 36, L20705 (2009).
+
+16. Izumo T. et al. Influence of the state of the Indian Ocean Dipole on the following year’s El Niño. Nature Geosci. 3, 168–172 (2010).
+
+17. Santoso A., England M. H. & Cai W. Impact of Indo-Pacific feedback interactions on ENSO dynamics diagnosed using ensemble climate simulations. J. Clim. 25, 7743–7763 (2012).
+
+18. Ham Y.-G., Kug J.-S., Park J.-Y. & Jin F.-F. Sea surface temperature in the north tropical Atlantic as a trigger for El Niño/Southern Oscillation events. Nature Geosci. 6, 112–116 (2013).
+
+19. Keenlyside N. S., Ding H. & Latif M. Potential of equatorial Atlantic variability to enhance El Niño prediction. Geophys. Res. Lett. 40(10): 2278-2283 (2013).
+
+<--- Page Split --->
+
+20. Dommenget D. & Yu Y. The effects of remote SST forcings on ENSO dynamics, variability and diversity. Clim. Dyn. 49, 2605-2624 (2017).
+
+21. Stuecker, M. F. et al. Revisiting ENSO/Indian Ocean dipole phase relationships. Geophys. Res. Lett. 44(5), 2481-2492 (2017).
+
+22. Wang L., Yu J.-Y. & Paek H. Enhanced biennial variability in the Pacific due to Atlantic capacitor effect. Nature Commun. 8, 14887 (2017).
+
+23. Cai W. et al. Science 363, eaav4236 (2019). DOI: 10.1126/science.aav4236
+
+24. Ham Y.-G., Kug J.-S. & Park J.-Y. Two distinct roles of Atlantic SSTs in ENSO variability: North tropical Atlantic SST and Atlantic Niño. Geophys. Res. Lett. 40, 4012-4017 (2013).
+
+25. Enfield, D. B. Relationships of inter-American rainfall to tropical Atlantic and Pacific SST variability. Geophys. Res. Lett. 23, 33053308 (1996).
+
+26. Chang, P., Saravanan, R., Ji, L. & Hegerl, G. C. The effect of local sea surface temperatures on atmospheric circulation over the tropical Atlantic sector. J. Clim. 13, 21952216 (2000).
+
+27. Wang, C., Enfield, D. B., Lee, S-K. & Landsea, C. W. Influences of the Atlantic warm pool on Western Hemisphere Summer Rainfall and Atlantic Hurricanes. J. Clim. 19, 30113028 (2006).
+
+28. Watanabe, M. & Kimoto, M. Tropical-extratropical connection in the Atlantic atmosphere-ocean variability. Geophys. Res. Lett. 26, 22472250 (1999).
+
+29. Smith, D. M. et al. Skillful multi-year predictions of Atlantic hurricane frequency. Nature Geosci. 3, 846849 (2009).
+
+30. Enfield D. B. & Mayer D. A. Tropical Atlantic sea surface temperature variability and its relation to El Niño-Southern Oscillation. J. Geophys. Res. 102, 929-945 (1997).
+
+31. Wallace J. M. & Gutzler D. S. Teleconnections in the geopotential height field during the northern hemisphere winter. Mon. Weather Rev. 109, 784-812 (1981).
+
+32. Klein S. A., Soden B. J. & Lau N.-C. Remote sea surface temperature variations during ENSO: Evidence for a tropical atmospheric bridge. J. Clim. 12, 917-932 (1999).
+
+<--- Page Split --->
+
+33. Alexander, M. A. et al. The atmospheric bridge: The influence of ENSO teleconnections on air-sea interaction over the global oceans. J. Clim. 15(16), 2205-2231 (2002).
+
+34. Chang P. et al. Climate fluctuations of tropical coupled systems-The role of ocean dynamics. J. Clim. 19, 5122-5174 (2006).
+
+35. García-Serrano J. et al. Revisiting the ENSO teleconnection to the tropical North Atlantic. J. Clim. 30, 6945-6957 (2017).
+
+36. Jia F., Wu L., Gan B. & Cai W. Global warming attenuates the tropical Atlantic-Pacific teleconnection. Sci. Rep. 6, 20078 (2016).
+
+37. Chiang, J. C. H. & Sobel, A. H. Tropical tropospheric temperature variations caused by ENSO and their influence on the remote tropical climate. J. Clim. 15, 2616-2631 (2002).
+
+38. Park, J. H. & Li, T. Interdecadal modulation of El Niño-tropical North Atlantic teleconnection by the Atlantic multi-decadal oscillation. Clim. Dyn. 52(9-10), 5345-5360 (2019).
+
+39. Ren H.-L. & Jin F.-F. Recharge oscillator mechanisms in two types of ENSO. J. Clim. 26, 6506-6523 (2013)
+
+40. Hasselmann, K. Stochastic climate models Part I. Theory. Tellus. 28, 473-485 (1976).
+
+41. Jin, F.-F. et al. Simple ENSO Models. In El Niño Southern Oscillation in a Changing Climate. (eds Santoso A., Cai W., & McPhaden, M. J.) (AGU in press, 2020).
+
+42. Rayner, N. A. et al. A. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. 108, 4407 (2003).
+
+43. Thomson, D. J. Spectrum estimation and harmonic analysis. Proceedings of the IEEE 70, 1055-1096 (1982)
+
+44. Ren, H.-L. & Jin, F.-F. Niño indices for two types of ENSO. Geophys. Res. Lett. 38, L04704 (2011).
+
+<--- Page Split --->
+
+45. Zhao, S., Jin, F.-F. & Stuecker, M. F. Improved predictability of the Indian Ocean Dipole using seasonally modulated ENSO forcing forecasts. Geophys. Res. Lett. 46 (2019).
+
+46. O'Neill, B. C. et al. The scenario model intercomparison project (ScenarioMIP) for CMIP6. Geosci. Model Dev. 9, 3461-3482 (2016).
+
+47. Eyring, V. et al. Overview of the coupled model intercomparison project phase 6 (CMIP6) experimental design and organization. Geosci. Model Dev. 9, 1937-1958 (2016).
+
+48. Delworth, T. L. et al. GFDL's CM2 global coupled climate models. Part I: formulation and simulation characteristics. J. Clim. 19, 643-674 (2006).
+
+Acknowledgements: This work was supported by the National Key Research and Development Program (2018YFC1506002) and the National Nature Science Foundation of China (41675073). This is IPRC publication number X and SOEST contribution number Y.
+
+Author contributions: WZ, FJ, MFS, and FFJ conceived the idea. WZ and FJ conducted the data analyses and prepared the figures. All authors discussed the results and wrote the paper.
+
+Correspondence: Correspondence and requests for materials should be addressed to W. Zhang (email: zhangwj@nuist.edu.cn) and F.-F. Jin (email: jff@hawaii.edu).
+
+Competing financial interests: The authors declare no competing financial interests.
+
+<--- Page Split --->
+
+
+Figure 1. Relationships between tropical Pacific and North Atlantic climate variability. Regression of a boreal spring (March-May) SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding winter (November-January) Niño3.4 (black box; \(5^{\circ}\mathrm{S} - 5^{\circ}\mathrm{N}\) , \(120^{\circ} - 170^{\circ}\mathrm{W}\) ) index and \(\mathbf{b}\) boreal winter SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding spring NTA (blue box; \(0^{\circ} - 15^{\circ}\mathrm{N}\) , \(90^{\circ} - 0^{\circ}\mathrm{W}\) ) SST anomaly. Dots in (a-b) indicate regression coefficients that are statistically significant at the \(95\%\) confidence level. c 15-yr running lead-lagged correlation of the boreal winter Niño3.4 index with the NTA SST anomaly. Solid, dashed, and dotted lines mark the region with values exceeding the \(80\%\) , \(90\%\) and \(95\%\) confidence levels, respectively. d Lead-lagged correlation of the boreal winter Niño3.4 index with the observed (solid) and reconstructed (dashed) NTA SST anomaly for bandpass filtering of 2-3-yr (blue) and 3-5-yr (red) periods by using a Fast Fourier Transform filter. For the y-axis of (c-d), negative and positive values indicate NTA-lead and NTA-lag at monthly scale, respectively. e Lead-lagged correlation of the boreal winter Niño3.4 index with NTA SST anomaly in the idealized pacemaker experiments with different Pacific SST forcing (see Methods). Gray dashed lines in (d-e) indicate the \(95\%\) confidence levels.
+
+<--- Page Split --->
+
+
+Figure 2. Phase relationship of NTA SST anomalies with ENSO in pi-control
+
+climate simulations. a Lead correlation of boreal spring NTA SST anomaly with the subsequent winter Nino3.4 index for 46 CMIP6 models and observations as a reference. The models are ranked by the NTA/ENSO correlation coefficients in an ascending order. The error bar for the multi- model ensemble (MME) mean corresponds to one standard deviation. The dashed purple lines represent the \(80\%\) , \(90\%\) and \(95\%\) confidence levels. b Regression of SST anomalies ( \(^\circ \mathrm{C}\) ) upon the Nino3.4 index averaged for the left 10 models with most negative correlation (contours with interval: \(0.4^\circ \mathrm{C}\) ; models indicated by striped blue bars in panel a) and the right 10 models with most positive correlation (shading; models indicated by striped red bars in panel a). c Multi- Taper- Method (MTM) power spectra averaged for the left 10 models with most negative correlation (solid thick blue) and the right 10 models with most positive correlation (solid thick red), superimposed by one standard deviation (blue and red shading). The observed spectral peaks of pre- and post-1990 periods (grey shading) are shown for comparison. The averaged AR(1) null hypothesis is displayed by a dashed thin line and the \(95\%\) confidence level is indicated by a solid thin line. d Scatterplot of ENSO period and lead- time for which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Nino3.4 index. The linear fit (solid black) is displayed together with the correlation coefficient R and slope.
+
+<--- Page Split --->
+
+
+Figure 3. Phase relationship of NTA SST anomalies with ENSO in future warming simulations. Scatterplot of ENSO period and lead-time at which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Niño3.4 index for the SSP2-4.5 (red) and SSP5-8.5 (purple) scenarios. The linear fits (solid black) are displayed together with respective correlation coefficient R and slope.
+
+<--- Page Split --->
+
+
+Figure 4. Schematic trans-basin relationships between tropical Pacific and North Atlantic oceans regulated by the ENSO periodicity. In the quasi-biennial ENSO cycle (red loop), an El Niño condition in boreal winter (left panel) leads to positive NTA warming during subsequent spring (upper panel) at a \(\sim 4\) -month lead time, which in turn can see a La Niña formation (right panel) typically following El Niño in the subsequent winter, showing a statistical \(\sim 8\) -month lead time of the NTA. Likewise, a La Niña condition in boreal winter (right panel) gives rise to the following spring NTA SST cooling (lower panel) with a lag of \(\sim 4\) months, which is often followed by an El Niño formation (left panel), corresponding to a statistical \(\sim 8\) -month lead time of the NTA. The same applies for the quasi-quadrennial ENSO cycle (blue loop) except for the negative correlation of NTA SST variability with the following ENSO event by \(\sim 20\) months.
+
+<--- Page Split --->
+
+## Figures
+
+
+
+Figure 1
+
+Relationships between tropical Pacific and North Atlantic climate variability. Regression of a boreal spring (March- May) SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding winter (November- January) Nino3.4 (black box; \(5^{\circ}\mathrm{S} - 5^{\circ}\mathrm{N}\) , \(120^{\circ} - 170^{\circ}\mathrm{W}\) ) index and b boreal winter SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding spring NTA (blue box; \(0^{\circ} - 15^{\circ}\mathrm{N}\) , \(90^{\circ} - 0^{\circ}\mathrm{W}\) ) SST anomaly. Dots in (a- b) indicate regression coefficients that are statistically significant at the \(95\%\) confidence level. c 15- yr running lead- lagged correlation of the boreal winter Nino3.4 index with the NTA SST anomaly. Solid, dashed, and dotted lines mark the region with values exceeding the \(80\%\) , \(90\%\) and \(95\%\) confidence levels, respectively. d Lead- lagged correlation of
+
+<--- Page Split --->
+
+the boreal winter Niño3.4 index with the observed (solid) and reconstructed (dashed) NTA SST anomaly for bandpass filtering of 2- 3- yr (blue) and 3- 5- yr (red) periods by using a Fast Fourier Transform filter. For the y- axis of (c- d), negative and positive values indicate NTA- lead and NTA- lag at monthly scale, respectively. e Lead- lagged correlation of the boreal winter Niño3.4 index with NTA SST anomaly in the idealized pacemaker experiments with different Pacific SST forcing (see Methods). Gray dashed lines in (d- e) indicate the 95% confidence levels.
+
+
+
+Figure 2
+
+Phase relationship of NTA SST anomalies with ENSO in pi- control climate simulations. a Lead correlation of boreal spring NTA SST anomaly with the subsequent winter Niño3.4 index for 46 CMIP6 models and
+
+<--- Page Split --->
+
+observations as a reference. The models are ranked by the NTA/ENSO correlation coefficients in an ascending order. The error bar for the multi- model ensemble (MME) mean corresponds to one standard deviation. The dashed purple lines represent the \(80\%\) , \(90\%\) and \(95\%\) confidence levels. b Regression of SST anomalies (°C) upon the Niño3.4 index averaged for the left 10 models with most negative correlation (contours with interval: \(0.4^{\circ}C\) ; models indicated by striped blue bars in panel a) and the right 10 models with most positive correlation (shading; models indicated by striped red bars in panel a). c Multi- Taper- Method (MTM) power spectra averaged for the left 10 models with most negative correlation (solid thick blue) and the right 10 models with most positive correlation (solid thick red), superimposed by one standard deviation (blue and red shading). The observed spectral peaks of pre- and post-1990 periods (grey shading) are shown for comparison. The averaged AR(1) null hypothesis is displayed by a dashed thin line and the \(95\%\) confidence level is indicated by a solid thin line. d Scatterplot of ENSO period and lead- time for which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Niño3.4 index. The linear fit (solid black) is displayed together with the correlation coefficient R and slope.
+
+<--- Page Split --->
+
+
+Figure 3
+
+Phase relationship of NTA SST anomalies with ENSO in future warming simulations. Scatterplot of ENSO period and lead- time at which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Niño3.4 index for the SSP2- 4.5 (red) and SSP5- 8.5 (purple) scenarios. The linear fits (solid black) are displayed together with respective correlation coefficient R and slope.
+
+<--- Page Split --->
+
+
+Figure 4
+
+Schematic trans- basin relationships between tropical Pacific and North Atlantic oceans regulated by the ENSO periodicity. In the quasi- biennial ENSO cycle (red loop), an El Niño condition in boreal winter (left panel) leads to positive NTA warming during subsequent spring (upper panel) at a \(\sim 4\) - month lead time, which in turn can see a La Niña formation (right panel) typically following El Niño in the subsequent winter, showing a statistical \(\sim 8\) - month lead time of the NTA. Likewise, a La Niña condition in boreal winter (right panel) gives rise to the following spring NTA SST cooling (lower panel) with a lag of \(\sim 4\) months, which is often followed by an El Niño formation (left panel), corresponding to a statistical \(\sim 8\) - month lead time of the NTA. The same applies for the quasi- quadrennial ENSO cycle (blue loop) except for the negative correlation of NTA SST variability with the following ENSO event by \(\sim 20\) months.
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- SupplementalNTA20200918final.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f_det.mmd b/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..97511d8ac624de70724837a1f9800ef237967df4
--- /dev/null
+++ b/preprint/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f/preprint__044192f1c210d2b128ea12550aed987a7bd494d2d9c59299caf93d282ac1c77f_det.mmd
@@ -0,0 +1,386 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 861, 174]]<|/det|>
+# Spurious North Tropical Atlantic pre-cursors to ENSO
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 427, 216]]<|/det|>
+Wenjun Zhang ( \(\boxed{\infty}\) zhangwj@nuist.edu.cn)
+
+<|ref|>text<|/ref|><|det|>[[44, 217, 920, 238]]<|/det|>
+Nanjing University of Information Science and Technology https://orcid.org/0000- 0002- 6375- 8826
+
+<|ref|>text<|/ref|><|det|>[[44, 243, 561, 285]]<|/det|>
+Feng Jiang Nanjing University of Information Science and Technology
+
+<|ref|>text<|/ref|><|det|>[[44, 290, 323, 331]]<|/det|>
+Malte Stuecker University of Hawai'i at Manoa
+
+<|ref|>text<|/ref|><|det|>[[44, 336, 320, 377]]<|/det|>
+Fei- Fei Jin University of Hawaii at Manoa
+
+<|ref|>text<|/ref|><|det|>[[44, 382, 283, 423]]<|/det|>
+Axel Timmermann Pusan National University
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 463, 102, 481]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 500, 928, 545]]<|/det|>
+Keywords: El Niño- Southern Oscillation (ENSO), North Tropical Atlantic (NTA), sea surface temperature (SST)
+
+<|ref|>text<|/ref|><|det|>[[44, 561, 333, 581]]<|/det|>
+Posted Date: February 26th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 599, 452, 619]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 85237/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 636, 910, 680]]<|/det|>
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 716, 910, 760]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on May 25th, 2021. See the published version at https://doi.org/10.1038/s41467- 021- 23411- 6.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[243, 93, 800, 114]]<|/det|>
+# Spurious North Tropical Atlantic pre-cursors to ENSO
+
+<|ref|>text<|/ref|><|det|>[[245, 125, 792, 170]]<|/det|>
+Wenjun Zhang \(^{1}\) , Feng Jiang \(^{1}\) , Malte F. Stuecker \(^{2}\) , Fei- Fei Jin \(^{3}\) , Axel Timmermann \(^{4,5}\)
+
+<|ref|>text<|/ref|><|det|>[[145, 177, 845, 306]]<|/det|>
+\(^{1}\) Key Laboratory of Meteorological Disaster of Ministry of Education (KLME), Nanjing University of Information Science and Technology, Nanjing, China \(^{2}\) Department of Oceanography & International Pacific Research Center (IPRC), SOEST, University of Hawai'i at Manoa, Honolulu, HI, USA \(^{3}\) Department of Atmospheric Sciences, SOEST, University of Hawai'i at Manoa, Honolulu, HI, USA \(^{4}\) Institute for Basic Science, Center for Climate Physics, Busan, South Korea \(^{5}\) Pusan National University, Busan, South Korea
+
+<|ref|>text<|/ref|><|det|>[[145, 340, 852, 691]]<|/det|>
+Abstract: The El Niño- Southern Oscillation (ENSO), the primary driver of year- to- year global climate variability, is known to influence the North Tropical Atlantic (NTA) sea surface temperature (SST), especially during boreal spring season. Focusing on statistical lead- lag relationships, previous studies have proposed that interannual NTA SST variability can also feed back on ENSO in a predictable manner. However, these studies do not properly account for ENSO's autocorrelation and the fact that the SST in the Atlantic and Pacific, as well as their atmospheric interaction are seasonally modulated. This can lead to misinterpretations of causality and the spurious identification of Atlantic precursors for ENSO. Revisiting this issue under consideration of seasonality, time- varying ENSO frequency, and greenhouse warming, we demonstrate that the cross- correlation characteristics between NTA SST and ENSO, are fully consistent with a one- way Pacific to Atlantic forcing, even though the interpretation of lead- lag relationships may suggest otherwise.
+
+<|ref|>text<|/ref|><|det|>[[145, 728, 852, 914]]<|/det|>
+The El Niño- Southern Oscillation (ENSO) phenomenon is characterized by interannual fluctuations between warm (El Niño) and cold (La Niña) sea surface temperature (SST) conditions in the equatorial Pacific. Its dynamics and associated coupled changes in the atmosphere and ocean have been studied extensively \(^{1,2}\) . Conceptual frameworks for ENSO have been proposed to explain the statistical and physical characteristics in terms of a Pacific eigenscillation that originates from positive air- sea interactions and delayed oceanic negative feedbacks \(^{3- 6}\) . ENSO is further
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 88, 852, 303]]<|/det|>
+energized by stochastic atmospheric forcing7 and modulated by the seasonal cycle8- 9. Counterintuitively, despite significant advances in both ENSO theory and ENSO representation in climate models, the predictability of central- to- eastern tropical Pacific SST anomalies has decreased in the past two decades to only one season10- 12. Research over the past years has further revealed that SST anomalies in other ocean basins may also play an important role shaping the evolution of El Niño events and its predictability13- 24. In particular, the North Tropical Atlantic (NTA) SST has been highlighted as a potential precursor candidate18,22- 24.
+
+<|ref|>text<|/ref|><|det|>[[144, 312, 852, 777]]<|/det|>
+The NTA ocean, home to a variety of societally relevant climate phenomena has received widespread attention25- 29. Typically, NTA SST warming lags the El Niño mature winter phase, peaking in the following spring (Fig. 1a) and persisting into early summer30. It is caused by El Niño- induced atmospheric forcing that both modulates the Walker Circulation and excites the Pacific- North America teleconnection pattern31- 35. In turn, this NTA warming is argued to stimulate a westward- propagating off- equatorial Rossby wave train, conducive to an ensuing La Niña formation18,24. However, this reverse connection, which is characterized by a negative ENSO/NTA cross- correlation with the NTA SST leading by about 8 months (Fig. 1b), is highly variable and especially absent before the 1990s22 (Fig. 1c). Despite some presumptions involved22,36, the mechanisms responsible for the puzzling connection are less appreciated and a comprehensive understanding of the two- way interaction between NTA variability and ENSO is required. In this study, we use both observations and climate model simulations to investigate the underlying mechanisms for the time- varying relationship. We demonstrate that changes in the NTA/ENSO relationship can be explained in terms of changes in ENSO frequency. The proposed mechanism is fully consistent with ENSO forcing NTA, rather than the opposite.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 813, 537, 831]]<|/det|>
+## ENSO-NTA SST relationship in observations
+
+<|ref|>text<|/ref|><|det|>[[147, 840, 851, 915]]<|/det|>
+ENSO generally commences its development in boreal summer and peaks in winter, stimulating atmospheric forcing over the NTA through two distinct pathways involving tropical and extra- tropical teleconnections30,34,35. Analyzing observed SST anomalies
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 87, 852, 722]]<|/det|>
+(see Methods), we see that the El Nino remote forcing is felt in the NTA SST a few months later around the spring season (Fig. 1a), possibly due to the local SST adjustment timescale37 and the seasonality of the atmospheric teleconnection to the Atlantic30,35. This robust ENSO/NTA connection can be detected during the entire study period notwithstanding a slight reduction of the correlation coefficient in the recent two decades (red shading in Fig. 1c; see also ref. 38). In turn, the spring NTA warming appears to contribute to the following La Niña development in the Pacific Ocean (and similarly a spring NTA cooling contributing to a following El Niño) (Fig. 1b) with a relatively weak correlation at about 8-month lag. However, we must also emphasize here that an NTA warming in spring following an El Niño will automatically be correlated with La Niña conditions 8 months later, because El Niño conditions are usually followed by La Niña in the following year, without even involving a physical NTA-to- ENSO relationship. Therefore, one needs to be careful in interpreting seasonally modulated teleconnections of ENSO (see for instance discussion in ref. 21). The 8-month leading relationship of NTA over ENSO is observed after the early 1990s while it is absent in the preceding period (blue shading in Fig. 1c; see also ref. 22). Prior to the 1990s we find a much longer characteristic lead of \(\sim 20\) - month (blue shading in Fig. 1c). Interestingly, this decadal change of the NTA- lead- time corresponds well to a shift in ENSO frequency from quasi- quadrennial to quasi- biennial (Supplementary Fig. 1; see also ref. 39). This regime change is also accompanied by more frequent occurrences of Central Pacific (CP) ENSO events (characterized by quasi- biennial timescale) and a reduction of the canonical Eastern Pacific (EP) ENSO events (characterized by quasi- quadrennial timescale) 2,12.
+
+<|ref|>text<|/ref|><|det|>[[147, 728, 852, 914]]<|/det|>
+Here we hypothesize that the changing ENSO- NTA SST phase- lag relationships can be explained in the context of different ENSO regimes manifested by quasi- biennial and quasi- quadrennial periodicities. An El Niño is typically followed by a La Niña event during the subsequent winter in a quasi- biennial ENSO cycle, whereby the NTA warming in the decaying El Niño spring accompanies a La Niña formation about 8- month later. For a quasi- quadrennial ENSO cycle, it takes around two years for the phase transition on average and correspondingly an El Niño induced NTA warming
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 88, 852, 220]]<|/det|>
+statistically leads the next La Niña mature phase by about 20 months. Observed ENSO cycles are not perfect oscillations with a distinct periodicity, in the case of the quasi- quadrennial cycle in which a strong El Niño event is prone to be followed by consecutive La Niña events. However, the complicated ENSO cycle features do not affect the relationship of NTA SST with following ENSO from a statistical standpoint.
+
+<|ref|>text<|/ref|><|det|>[[144, 226, 853, 720]]<|/det|>
+To further illustrate the abovementioned physical linkage between lead time and ENSO frequency, we conduct 2- 3- and 3- 5- yr bandpass filtering of the observed ENSO and NTA indices to differentiate two- way ENSO- NTA SST connections associated with quasi- biennial and quasi- quadrennial periodicities, respectively. ENSO impacts on boreal spring NTA SST anomalies are clearly displayed in both ENSO frequency bands (Fig. 1d), consistent with the robust relationship derived from the raw data (red shading in Fig. 1c), substantiating ENSO's physical regulation of the following spring NTA SST. To understand the distinct statistical relationships of the NTA SST with quasi- biennial and quasi- quadrennial ENSO (negative lags in Fig. 1c), we need to consider first that for these timescales El Niño and La Niña are anticorrelated at a lag of \(\sim 12\) months and \(\sim 24\) months, respectively. With El Niño causing robust spring NTA warming, the spring NTA warming will then be automatically anticorrelated with Niño3.4 SST anomalies at lag 8 (=12- 4) and lag 20 (=24- 4) months, for the quasi- biennial and quasi- quadrennial modes, respectively (Fig. 1d). The decadal shifts in the NTA- ENSO relationship are thus fully consistent with a robust one- way ENSO to NTA forcing relationship combined with a shift of ENSO's dominant frequency (Supplementary Fig. 1b). The notion of NTA serving as precursor for ENSO is therefore equivalent to simply saying that the El Niño is precursor to the next La Niña.
+
+<|ref|>text<|/ref|><|det|>[[145, 727, 852, 914]]<|/det|>
+Next, to understand the role of ENSO forcing in fostering NTA variability when considering its time- varying periodicity change, we use an extension of the original stochastic climate model40 for NTA SST anomalies that includes both remote observed ENSO forcing and a damping rate modulated by the annual cycle (see Methods and ref. 21 for the original application of the model). The observed monthly time- varying NTA SST anomaly can be well captured by the ENSO- forced model (R=0.55, statistically significant at the 95% confidence level; Supplementary Fig. 2). Importantly, the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 88, 852, 220]]<|/det|>
+residual variability has no preferred interannual spectral peak (Supplementary Fig. 3). The reconstructed NTA SST exhibits a very similar lead- lag relationship with ENSO compared to that of the observations (Fig. 1d), further collaborating our hypothesis of a one- way relationship between the tropical Pacific and North Atlantic climate variability.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 256, 715, 275]]<|/det|>
+## ENSO-NTA SST relationship in idealized pacemaker experiments
+
+<|ref|>text<|/ref|><|det|>[[145, 280, 852, 917]]<|/det|>
+Observed ENSO variability has a broad spectrum in the range of 2- 7 years, characterized by quasi- biennial and quasi- quadrennial spectral peaks, which cannot be completely isolated using current linear methods2. To demonstrate trans- basin relationships that would result from different purely periodic ENSO oscillations, a set of idealized pacemaker experiments is conducted by imposing ENSO SST anomaly forcing with idealized 2- and 4- yr cycles in the tropical Pacific (see Methods). In this modeling set- up only ENSO can force NTA, but not vice versa. Given that there is a shift in the ENSO's zonal location around the 1990s, we also consider different SST forcing patterns associated with the EP and CP El Niño types in the pacemaker experiments (Supplementary Fig. 4; see Methods), to investigate possible influences of the zonal SST anomaly structure in addition to ENSO timescale changes. The observed robust ENSO effect on the subsequent spring NTA SST can be well reproduced in all ENSO- forced experiments (Fig. 1e). In the experiments with 2- yr ENSO forcing, the NTA SST variability is significantly correlated with subsequent ENSO conditions of opposite sign, having the maximum correlation at an 8- month lead- time of NTA over ENSO regardless of the ENSO SST anomaly patterns. This statistical ENSO/NTA relationship corresponds to what we see in the observations before the 1990s (Fig. 1c). Our results clearly show that the 8- month lead of NTA over ENSO can be obtained, even though the set- up of our model experiments does not allow for NTA to influence ENSO. In the 4- yr ENSO forced experiments, the spring NTA SST anomaly as a response to the preceding ENSO is followed by the subsequent ENSO formation at about 20- month lead time for both EP and CP associated SST forcing. These pacemaker experiments indicate that the statistical ENSO and NTA relationship is largely
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 89, 849, 137]]<|/det|>
+controlled by ENSO periodicity rather than its spatial pattern and that the ENSO autocorrelation itself causes this peculiar phase- relationship.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 173, 628, 192]]<|/det|>
+## ENSO-NTA SST relationship in the CMIP6 simulations
+
+<|ref|>text<|/ref|><|det|>[[147, 201, 852, 609]]<|/det|>
+Considering the limited sample size of the short observational record though supported by our idealized pacemaker experiments, we further examine the trans- basin relationship between ENSO and NTA SST in 46 coupled models in pre- industrial control (pi- control) simulations participating in Phase 6 of the Coupled Model Intercomparison Project (CMIP6) (Supplementary Table 1). Almost all coupled models are capable of capturing the robust ENSO forcing on the NTA SST (Supplementary Fig. 5). However, the models exhibit a large diversity in the statistical relationship between boreal spring NTA SST variability and subsequent winter ENSO at \(\sim 8\) - month lead- time, whereas a statistically significant relationship can only be simulated in about a quarter of the CMIP6 models (Fig. 2a). To determine the underlying mechanisms responsible for this, we rank the models based on their correlation between spring NTA SST anomaly and subsequent winter ENSO conditions, and then select the 10 models closest to the observations with the highest negative correlation (left side in Fig. 2a) and the 10 models most different from the observations that show a weakly positive correlation (right side in Fig. 2a).
+
+<|ref|>text<|/ref|><|det|>[[147, 617, 853, 888]]<|/det|>
+Although both model groups show a very similar ENSO SST anomaly pattern (Fig. 2b), these two groups exhibit distinct ENSO spectral characteristics (Fig. 2c). The models that have a statistically significant 8- month ENSO/NTA lagged relationship exhibit a relatively shorter ENSO periodicity, analogous to the observations after the 1990s (Fig. 2c). In contrast, the models without a significant relationship at 8- month NTA- lead- time have longer ENSO periodicities resembling the observations before the 1990s (Fig. 2c). In addition, there is a high inter- model linear correlation (R=0.75, statistically significant at the 95% confidence level) between simulated dominant ENSO periodicity and the lead- time of the most pronounced negative correlation of NTA SST leading ENSO (Fig. 2d). This again supports our hypothesis that the statistical
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 89, 850, 136]]<|/det|>
+lead- time of NTA SST anomalies over the subsequent ENSO conditions is tightly controlled by the ENSO periodicity.
+
+<|ref|>text<|/ref|><|det|>[[147, 145, 852, 470]]<|/det|>
+There exists considerable uncertainty in the projections of trans- basin interactions and the pan- tropical climate patterns that will emerge in a warming world23. Thus, we next investigate the ENSO/NTA trans- basin interaction in CMIP6 future greenhouse- gas emission scenarios (see Methods). We find that almost all of these models in the SSP2- 4.5 (25 of 25) and SSP5- 8.5 (26 of 28) simulations are able to simulate the robust ENSO effect on the subsequent spring NTA SST (Supplementary Fig. 6). The in- turn linear relationship between NTA- lead- time over ENSO and ENSO periodicity continues to hold in the global warming scenarios (Figure 3). High correlations can be detected in both warming scenarios (R=0.79 for the SSP2- 4.5 scenario and R=0.81 for the SSP5- 8.5 scenario, exceeding 95% confidence level). It further supports that the trans- basin ENSO/NTA relationships are predominately determined by ENSO and its internal pacing.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 507, 243, 523]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[147, 533, 852, 802]]<|/det|>
+In summary, ENSO plays a leading role in generating NTA SST variability in boreal spring following its peak phase via seasonally modulated atmospheric forcing and further influenced by the local SST adjustment timescale in the Atlantic (upper- left quadrant in Fig. 4). In turn, the observed time- varying relationship between these ENSO- induced NTA SST anomalies and the following ENSO conditions (Fig. 1c) can be explained by the ENSO regime shifting from dominantly quasi- quadrennial to dominantly quasi- biennial around the 1990s (upper- right quadrant in Figure 4). We emphasize that the observed ENSO cycles are not perfect oscillations with single frequencies. In nature, stochastic noise and nonlinearities can play important roles in shaping ENSO characteristics41.
+
+<|ref|>text<|/ref|><|det|>[[147, 811, 852, 913]]<|/det|>
+Here we demonstrated using observational data, a simple seasonally modulated ENSO- forced model, idealized pacemaker experiments, and CMIP6 simulations that the character of the observed cross correlation between ENSO and NTA is fully consistent with an ENSO forced system. We conclude that previous suggestions about
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 89, 850, 137]]<|/det|>
+possible NTA pre- cursors on ENSO predictability and capacitor arguments remain spurious. We further show that our main results are robust even in a warming world.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 174, 227, 190]]<|/det|>
+## Methods
+
+<|ref|>text<|/ref|><|det|>[[144, 199, 852, 833]]<|/det|>
+Observation and statistics. The utilized SST datasets are the global sea ice and SST analyses (1960- 2019) from the Hadley Centre (HadISST) provided by the Met Office Hadley Centre with the horizonal resolution of \(1^{\circ}\) longitude \(\times 1^{\circ}\) latitude \(^{42}\) . Anomalies were derived relative to the monthly mean climatology over the entire study period (1960- 2019). A linear trend was removed to avoid possible influences associated with global warming. The Multi- Taper method (MTM), which uses a median smoother to distinguish signals from background noises, is used for spectral estimates \(^{43}\) with 3 (Supplementary Fig. 1b) or 5 tapers (Figs. 2, 3 and Supplementary Fig. 3) in consideration of different sample sizes. We test the spectra against the null hypothesis of an autoregressive model of order one (AR(1)) and calculate the respective \(95\%\) confidence levels. A nine- point smoothing is applied in Figs. 1c- e to avoid possible noise disturbance. All statistical significance tests were performed using the two- tailed Student's \(t\) test. El Niño events were identified according to the definition of the Climate Prediction Center based on a threshold of \(\pm 0.5^{\circ}\mathrm{C}\) of the Niño3.4 index (averaged SST anomaly in the domain of \(5^{\circ}\mathrm{S} - 5^{\circ}\mathrm{N}\) , \(120^{\circ} - 170^{\circ}\mathrm{W}\) ) for five consecutive months. EP and CP indices (EPI and CPI) are calculated using a mathematic rotation of the Niño3 (averaged SST anomaly in the domain of \(5^{\circ}\mathrm{S}\) to \(5^{\circ}\mathrm{N}\) , \(90^{\circ}\) to \(150^{\circ}\mathrm{W}\) ) and Niño4 (averaged SST anomaly in the domain of \(5^{\circ}\mathrm{S}\) to \(5^{\circ}\mathrm{N}\) , \(160^{\circ}\mathrm{E}\) to \(150^{\circ}\mathrm{W}\) ) indices \(^{44}\) . El Niño events with EPI greater than CPI were classified as EP events while those with CPI greater than EPI are defined as CP events. Following this criterium, we identified seven EP El Niño events (1965, 1972, 1976, 1982, 1991, 1997, 2015) and twelve CP El Niño events (1963, 1968, 1969, 1977, 1979, 1986, 1994, 2002, 2004, 2006, 2009, 2019).
+
+<|ref|>text<|/ref|><|det|>[[147, 868, 848, 914]]<|/det|>
+Simple physical model. We proposed a physically motivated model for the NTA SST anomaly as an extension \(^{21}\) of the stochastic climate model \(^{40}\) :
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[270, 88, 763, 118]]<|/det|>
+\[\frac{dT(t)}{dt} = (-\lambda_0 + \lambda_a\cos (\omega_a + \phi))T(t) + \beta ENSO(t) + \xi (t),\]
+
+<|ref|>text<|/ref|><|det|>[[145, 125, 852, 312]]<|/det|>
+where \(\mathrm{T(t)}\) is the monthly NTA SST anomaly, ENSO(t) the monthly Niño 3.4 index, \((-\lambda_0 + \lambda_a\cos (\omega_a + \phi))\) the seasonally modulated damping rate, in which \(\lambda_0\) and \(\lambda_{\mathrm{a}}\) denote the mean and annul cycle of the damping coefficient, \(\omega_{\mathrm{a}}\) the frequency of the annual cycle, \(\phi\) the phase shift, and \(\beta\) a scaling coefficient. The model parameters are estimated by multivariate linear regression using the observed NTA SST anomaly time series and Niño 3.4 index (following ref. 45). The ENSO- independent stochastic forcing term \((\xi (t))\) is neglected in the model for simplicity.
+
+<|ref|>text<|/ref|><|det|>[[145, 347, 852, 590]]<|/det|>
+CMIP6 simulations. Monthly SST outputs from the CMIP6 pi- control and future (the Shared Socioeconomic Pathways (SSP) 2- 4.5 and SSP5- 8.5) simulations are utilized. The external forcing (e.g., greenhouse gases and aerosols) is kept constant in the pi- control simulations while the SSP2- 4.5 with radiative forcing reaching \(4.5\mathrm{Wm}^{- 2}\) and SSP5- 8.5 reaching \(8.5\mathrm{Wm}^{- 2}\) during 2015- 210046,47. For the pi- control simulations, the last 100 years of 46 available model simulations are used for the analysis, among which 25 models are obtained for the SSP2- 4.5 scenario and 28 models for the SSP5- 8.5 scenario, respectively (see Table S1). Only one ensemble member for each model is used, mostly r1i1p1f1 with select models using ensemble member f2.
+
+<|ref|>text<|/ref|><|det|>[[145, 625, 852, 896]]<|/det|>
+Idealized pacemaker experiments. Numerical experiments are conducted by using the Geophysical Fluid Dynamics Laboratory coupled model, version 2.1 (GFDL- CM2.1), with a horizontal resolution of \(2.5^{\circ}\) longitude \(\times 2^{\circ}\) latitude and 24 vertical levels48. Four sensitivity experiments are performed by using an idealized sinusoidal EP and CP ENSO forcing with 2- and 4- yr periodicities, respectively. Composed EP El Niño SST anomalies over the tropical Pacific (25°S- 25°N, 150°E- 90°W) are used to derive the SST anomalies forcing patterns for the EXP_2yr_EP experiment with repeated sinusoidal 2- yr periodicity and the EXP_4yr_EP experiment with repeated 4- yr periodicity. The other two experiments (EXP_2yr_CP and EXP_4yr_CP) are the same, except that the SST anomalies are the composites for the observed CP El Niño
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 89, 852, 275]]<|/det|>
+events. SST anomalies outside the forcing area are set to zero and only the positive loading in the forcing region is used. The SSTs are allowed to evolve freely outside of the prescribed regions. ENSO peak phases will occur aligned with the boreal winter season for these idealized 2- and 4- yr periodicities. The simulations are integrated for 100 years and the output from the last 80 years is used for the analyses. Anomalies in GFDL- CM2.1 are relative to a 100- year control simulation (EXP_CTRL) in which the model is forced with seasonal varying climatological SSTs.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 312, 293, 329]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[147, 338, 852, 443]]<|/det|>
+The data used to reproduce the results of this paper are available online or by contacting the corresponding author. Hadley SST data is publicly available at: https://www.metoffice.gov.uk/hadobs/hadisst/data/download.html. The CMIP6 datasets are available at https://esgf- node.llnl.gov/projects/cmip6/.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 480, 245, 496]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[144, 506, 852, 884]]<|/det|>
+1. McPhaden, M. J., Zebiak, S. E., & Glantz, M. H. ENSO as an integrating concept in Earth science. Science 314(5806), 1740-1745 (2006).
+2. Timmermann, A. et al. El Niño-Southern Oscillation complexity. Nature 26, 535-545 (2018).
+3. Cane, M. A. & Zebiak S. E. A theory for El Niño and the Southern Oscillation. Science 228, 1085-1087 (1985).
+4. Battisti D. S. & Hirst A. C. Interannual variability in a tropical atmosphere-ocean model: influence of the basic state, ocean geometry and nonlinearity. J. Atmos. Sci. 46:1687-1712 (1989).
+5. Jin, F.-F. An equatorial recharge paradigm for ENSO. Part I: Conceptual model. J. Atmos. Sci. 54, 811-829 (1997).
+6. Neelin, J. D. et al. ENSO theory. J. Geophys. Res. 103, 14 261-14 290 (1998).
+7. Kessler W. S., McPhaden, M. J. & Weickmann K. M. Forcing of intraseasonal Kelvin waves in the equatorial Pacific. J. Geophys. Res. 100:10613-10632 (1995).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 89, 852, 170]]<|/det|>
+8. McGregor, S., Timmermann, A., Schneider, N., Stuecker, M. F. & England, M. H. The effect of the South Pacific convergence zone on the termination of El Niño events and the meridional asymmetry of ENSO. J. Clim. 25, 5566–5586 (2012).
+
+<|ref|>text<|/ref|><|det|>[[144, 175, 852, 248]]<|/det|>
+9. Stuecker, M. F., Timmermann, A., Jin, F.-F., McGregor, S. & Ren, H.-L. A combination mode of the annual cycle and the El Niño/Southern Oscillation. Nat. Geosci. 6, 540–544 (2013).
+
+<|ref|>text<|/ref|><|det|>[[144, 257, 852, 303]]<|/det|>
+10. Hendon, H. H., Lim, E., Wang, G., Alves, O. & Hudson, D. Prospects for predicting two flavors of El Niño. Geophys. Res. Lett. 36, L19713 (2009).
+
+<|ref|>text<|/ref|><|det|>[[144, 312, 852, 358]]<|/det|>
+11. Wang, W., Chen, M. & Kumar, A. An assessment of the CFS real time seasonal forecasts. Weather and Forecasting 25(3), 950-969 (2010).
+
+<|ref|>text<|/ref|><|det|>[[144, 367, 852, 441]]<|/det|>
+12. Zhang, W. et al. ENSO regime changes responsible for decadal phase relationship variations between ENSO sea surface temperature and warm water volume. Geophys. Res. Lett. 46, 7546–7553 (2019).
+
+<|ref|>text<|/ref|><|det|>[[144, 450, 850, 496]]<|/det|>
+13. Kug J.-S. & Kang I.-S. Interactive feedback between ENSO and the Indian Ocean. J. Clim. 19, 1784–1801 (2006).
+
+<|ref|>text<|/ref|><|det|>[[144, 505, 852, 552]]<|/det|>
+14. Jansen MF, Dommenget D, Keenlyside N. Tropical atmosphere–ocean interactions in a conceptual framework. J Clim 22:550–567 (2009).
+
+<|ref|>text<|/ref|><|det|>[[144, 561, 852, 607]]<|/det|>
+15. Rodríguez-Fonseca B. et al. Are Atlantic Niños enhancing Pacific ENSO events in recent decades? Geophys. Res. Lett. 36, L20705 (2009).
+
+<|ref|>text<|/ref|><|det|>[[144, 616, 852, 662]]<|/det|>
+16. Izumo T. et al. Influence of the state of the Indian Ocean Dipole on the following year’s El Niño. Nature Geosci. 3, 168–172 (2010).
+
+<|ref|>text<|/ref|><|det|>[[144, 671, 852, 745]]<|/det|>
+17. Santoso A., England M. H. & Cai W. Impact of Indo-Pacific feedback interactions on ENSO dynamics diagnosed using ensemble climate simulations. J. Clim. 25, 7743–7763 (2012).
+
+<|ref|>text<|/ref|><|det|>[[144, 755, 852, 830]]<|/det|>
+18. Ham Y.-G., Kug J.-S., Park J.-Y. & Jin F.-F. Sea surface temperature in the north tropical Atlantic as a trigger for El Niño/Southern Oscillation events. Nature Geosci. 6, 112–116 (2013).
+
+<|ref|>text<|/ref|><|det|>[[144, 840, 852, 886]]<|/det|>
+19. Keenlyside N. S., Ding H. & Latif M. Potential of equatorial Atlantic variability to enhance El Niño prediction. Geophys. Res. Lett. 40(10): 2278-2283 (2013).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[140, 89, 852, 137]]<|/det|>
+20. Dommenget D. & Yu Y. The effects of remote SST forcings on ENSO dynamics, variability and diversity. Clim. Dyn. 49, 2605-2624 (2017).
+
+<|ref|>text<|/ref|><|det|>[[140, 144, 848, 191]]<|/det|>
+21. Stuecker, M. F. et al. Revisiting ENSO/Indian Ocean dipole phase relationships. Geophys. Res. Lett. 44(5), 2481-2492 (2017).
+
+<|ref|>text<|/ref|><|det|>[[140, 199, 850, 247]]<|/det|>
+22. Wang L., Yu J.-Y. & Paek H. Enhanced biennial variability in the Pacific due to Atlantic capacitor effect. Nature Commun. 8, 14887 (2017).
+
+<|ref|>text<|/ref|><|det|>[[140, 255, 794, 275]]<|/det|>
+23. Cai W. et al. Science 363, eaav4236 (2019). DOI: 10.1126/science.aav4236
+
+<|ref|>text<|/ref|><|det|>[[140, 283, 850, 359]]<|/det|>
+24. Ham Y.-G., Kug J.-S. & Park J.-Y. Two distinct roles of Atlantic SSTs in ENSO variability: North tropical Atlantic SST and Atlantic Niño. Geophys. Res. Lett. 40, 4012-4017 (2013).
+
+<|ref|>text<|/ref|><|det|>[[140, 367, 850, 414]]<|/det|>
+25. Enfield, D. B. Relationships of inter-American rainfall to tropical Atlantic and Pacific SST variability. Geophys. Res. Lett. 23, 33053308 (1996).
+
+<|ref|>text<|/ref|><|det|>[[140, 421, 850, 496]]<|/det|>
+26. Chang, P., Saravanan, R., Ji, L. & Hegerl, G. C. The effect of local sea surface temperatures on atmospheric circulation over the tropical Atlantic sector. J. Clim. 13, 21952216 (2000).
+
+<|ref|>text<|/ref|><|det|>[[140, 505, 850, 580]]<|/det|>
+27. Wang, C., Enfield, D. B., Lee, S-K. & Landsea, C. W. Influences of the Atlantic warm pool on Western Hemisphere Summer Rainfall and Atlantic Hurricanes. J. Clim. 19, 30113028 (2006).
+
+<|ref|>text<|/ref|><|det|>[[140, 588, 850, 635]]<|/det|>
+28. Watanabe, M. & Kimoto, M. Tropical-extratropical connection in the Atlantic atmosphere-ocean variability. Geophys. Res. Lett. 26, 22472250 (1999).
+
+<|ref|>text<|/ref|><|det|>[[140, 643, 848, 690]]<|/det|>
+29. Smith, D. M. et al. Skillful multi-year predictions of Atlantic hurricane frequency. Nature Geosci. 3, 846849 (2009).
+
+<|ref|>text<|/ref|><|det|>[[140, 698, 850, 774]]<|/det|>
+30. Enfield D. B. & Mayer D. A. Tropical Atlantic sea surface temperature variability and its relation to El Niño-Southern Oscillation. J. Geophys. Res. 102, 929-945 (1997).
+
+<|ref|>text<|/ref|><|det|>[[140, 782, 850, 829]]<|/det|>
+31. Wallace J. M. & Gutzler D. S. Teleconnections in the geopotential height field during the northern hemisphere winter. Mon. Weather Rev. 109, 784-812 (1981).
+
+<|ref|>text<|/ref|><|det|>[[140, 837, 850, 912]]<|/det|>
+32. Klein S. A., Soden B. J. & Lau N.-C. Remote sea surface temperature variations during ENSO: Evidence for a tropical atmospheric bridge. J. Clim. 12, 917-932 (1999).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 89, 851, 163]]<|/det|>
+33. Alexander, M. A. et al. The atmospheric bridge: The influence of ENSO teleconnections on air-sea interaction over the global oceans. J. Clim. 15(16), 2205-2231 (2002).
+
+<|ref|>text<|/ref|><|det|>[[144, 171, 850, 219]]<|/det|>
+34. Chang P. et al. Climate fluctuations of tropical coupled systems-The role of ocean dynamics. J. Clim. 19, 5122-5174 (2006).
+
+<|ref|>text<|/ref|><|det|>[[144, 227, 850, 275]]<|/det|>
+35. García-Serrano J. et al. Revisiting the ENSO teleconnection to the tropical North Atlantic. J. Clim. 30, 6945-6957 (2017).
+
+<|ref|>text<|/ref|><|det|>[[144, 282, 850, 331]]<|/det|>
+36. Jia F., Wu L., Gan B. & Cai W. Global warming attenuates the tropical Atlantic-Pacific teleconnection. Sci. Rep. 6, 20078 (2016).
+
+<|ref|>text<|/ref|><|det|>[[144, 338, 850, 415]]<|/det|>
+37. Chiang, J. C. H. & Sobel, A. H. Tropical tropospheric temperature variations caused by ENSO and their influence on the remote tropical climate. J. Clim. 15, 2616-2631 (2002).
+
+<|ref|>text<|/ref|><|det|>[[144, 422, 850, 497]]<|/det|>
+38. Park, J. H. & Li, T. Interdecadal modulation of El Niño-tropical North Atlantic teleconnection by the Atlantic multi-decadal oscillation. Clim. Dyn. 52(9-10), 5345-5360 (2019).
+
+<|ref|>text<|/ref|><|det|>[[144, 505, 850, 553]]<|/det|>
+39. Ren H.-L. & Jin F.-F. Recharge oscillator mechanisms in two types of ENSO. J. Clim. 26, 6506-6523 (2013)
+
+<|ref|>text<|/ref|><|det|>[[144, 560, 850, 608]]<|/det|>
+40. Hasselmann, K. Stochastic climate models Part I. Theory. Tellus. 28, 473-485 (1976).
+
+<|ref|>text<|/ref|><|det|>[[144, 615, 850, 690]]<|/det|>
+41. Jin, F.-F. et al. Simple ENSO Models. In El Niño Southern Oscillation in a Changing Climate. (eds Santoso A., Cai W., & McPhaden, M. J.) (AGU in press, 2020).
+
+<|ref|>text<|/ref|><|det|>[[144, 699, 850, 775]]<|/det|>
+42. Rayner, N. A. et al. A. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. 108, 4407 (2003).
+
+<|ref|>text<|/ref|><|det|>[[144, 783, 850, 830]]<|/det|>
+43. Thomson, D. J. Spectrum estimation and harmonic analysis. Proceedings of the IEEE 70, 1055-1096 (1982)
+
+<|ref|>text<|/ref|><|det|>[[144, 838, 850, 886]]<|/det|>
+44. Ren, H.-L. & Jin, F.-F. Niño indices for two types of ENSO. Geophys. Res. Lett. 38, L04704 (2011).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 88, 852, 163]]<|/det|>
+45. Zhao, S., Jin, F.-F. & Stuecker, M. F. Improved predictability of the Indian Ocean Dipole using seasonally modulated ENSO forcing forecasts. Geophys. Res. Lett. 46 (2019).
+
+<|ref|>text<|/ref|><|det|>[[144, 172, 850, 219]]<|/det|>
+46. O'Neill, B. C. et al. The scenario model intercomparison project (ScenarioMIP) for CMIP6. Geosci. Model Dev. 9, 3461-3482 (2016).
+
+<|ref|>text<|/ref|><|det|>[[144, 228, 850, 303]]<|/det|>
+47. Eyring, V. et al. Overview of the coupled model intercomparison project phase 6 (CMIP6) experimental design and organization. Geosci. Model Dev. 9, 1937-1958 (2016).
+
+<|ref|>text<|/ref|><|det|>[[144, 312, 850, 359]]<|/det|>
+48. Delworth, T. L. et al. GFDL's CM2 global coupled climate models. Part I: formulation and simulation characteristics. J. Clim. 19, 643-674 (2006).
+
+<|ref|>text<|/ref|><|det|>[[144, 395, 850, 497]]<|/det|>
+Acknowledgements: This work was supported by the National Key Research and Development Program (2018YFC1506002) and the National Nature Science Foundation of China (41675073). This is IPRC publication number X and SOEST contribution number Y.
+
+<|ref|>text<|/ref|><|det|>[[144, 533, 850, 608]]<|/det|>
+Author contributions: WZ, FJ, MFS, and FFJ conceived the idea. WZ and FJ conducted the data analyses and prepared the figures. All authors discussed the results and wrote the paper.
+
+<|ref|>text<|/ref|><|det|>[[144, 644, 850, 691]]<|/det|>
+Correspondence: Correspondence and requests for materials should be addressed to W. Zhang (email: zhangwj@nuist.edu.cn) and F.-F. Jin (email: jff@hawaii.edu).
+
+<|ref|>text<|/ref|><|det|>[[144, 728, 844, 747]]<|/det|>
+Competing financial interests: The authors declare no competing financial interests.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[214, 99, 777, 505]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 512, 851, 808]]<|/det|>
+Figure 1. Relationships between tropical Pacific and North Atlantic climate variability. Regression of a boreal spring (March-May) SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding winter (November-January) Niño3.4 (black box; \(5^{\circ}\mathrm{S} - 5^{\circ}\mathrm{N}\) , \(120^{\circ} - 170^{\circ}\mathrm{W}\) ) index and \(\mathbf{b}\) boreal winter SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding spring NTA (blue box; \(0^{\circ} - 15^{\circ}\mathrm{N}\) , \(90^{\circ} - 0^{\circ}\mathrm{W}\) ) SST anomaly. Dots in (a-b) indicate regression coefficients that are statistically significant at the \(95\%\) confidence level. c 15-yr running lead-lagged correlation of the boreal winter Niño3.4 index with the NTA SST anomaly. Solid, dashed, and dotted lines mark the region with values exceeding the \(80\%\) , \(90\%\) and \(95\%\) confidence levels, respectively. d Lead-lagged correlation of the boreal winter Niño3.4 index with the observed (solid) and reconstructed (dashed) NTA SST anomaly for bandpass filtering of 2-3-yr (blue) and 3-5-yr (red) periods by using a Fast Fourier Transform filter. For the y-axis of (c-d), negative and positive values indicate NTA-lead and NTA-lag at monthly scale, respectively. e Lead-lagged correlation of the boreal winter Niño3.4 index with NTA SST anomaly in the idealized pacemaker experiments with different Pacific SST forcing (see Methods). Gray dashed lines in (d-e) indicate the \(95\%\) confidence levels.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[225, 95, 820, 500]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 511, 853, 533]]<|/det|>
+Figure 2. Phase relationship of NTA SST anomalies with ENSO in pi-control
+
+<|ref|>text<|/ref|><|det|>[[147, 533, 855, 863]]<|/det|>
+climate simulations. a Lead correlation of boreal spring NTA SST anomaly with the subsequent winter Nino3.4 index for 46 CMIP6 models and observations as a reference. The models are ranked by the NTA/ENSO correlation coefficients in an ascending order. The error bar for the multi- model ensemble (MME) mean corresponds to one standard deviation. The dashed purple lines represent the \(80\%\) , \(90\%\) and \(95\%\) confidence levels. b Regression of SST anomalies ( \(^\circ \mathrm{C}\) ) upon the Nino3.4 index averaged for the left 10 models with most negative correlation (contours with interval: \(0.4^\circ \mathrm{C}\) ; models indicated by striped blue bars in panel a) and the right 10 models with most positive correlation (shading; models indicated by striped red bars in panel a). c Multi- Taper- Method (MTM) power spectra averaged for the left 10 models with most negative correlation (solid thick blue) and the right 10 models with most positive correlation (solid thick red), superimposed by one standard deviation (blue and red shading). The observed spectral peaks of pre- and post-1990 periods (grey shading) are shown for comparison. The averaged AR(1) null hypothesis is displayed by a dashed thin line and the \(95\%\) confidence level is indicated by a solid thin line. d Scatterplot of ENSO period and lead- time for which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Nino3.4 index. The linear fit (solid black) is displayed together with the correlation coefficient R and slope.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[198, 95, 832, 500]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 512, 852, 610]]<|/det|>
+Figure 3. Phase relationship of NTA SST anomalies with ENSO in future warming simulations. Scatterplot of ENSO period and lead-time at which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Niño3.4 index for the SSP2-4.5 (red) and SSP5-8.5 (purple) scenarios. The linear fits (solid black) are displayed together with respective correlation coefficient R and slope.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[155, 116, 824, 460]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[147, 475, 851, 696]]<|/det|>
+Figure 4. Schematic trans-basin relationships between tropical Pacific and North Atlantic oceans regulated by the ENSO periodicity. In the quasi-biennial ENSO cycle (red loop), an El Niño condition in boreal winter (left panel) leads to positive NTA warming during subsequent spring (upper panel) at a \(\sim 4\) -month lead time, which in turn can see a La Niña formation (right panel) typically following El Niño in the subsequent winter, showing a statistical \(\sim 8\) -month lead time of the NTA. Likewise, a La Niña condition in boreal winter (right panel) gives rise to the following spring NTA SST cooling (lower panel) with a lag of \(\sim 4\) months, which is often followed by an El Niño formation (left panel), corresponding to a statistical \(\sim 8\) -month lead time of the NTA. The same applies for the quasi-quadrennial ENSO cycle (blue loop) except for the negative correlation of NTA SST variability with the following ENSO event by \(\sim 20\) months.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 43, 143, 69]]<|/det|>
+## Figures
+
+<|ref|>image<|/ref|><|det|>[[70, 108, 881, 732]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 753, 115, 772]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[42, 794, 955, 953]]<|/det|>
+Relationships between tropical Pacific and North Atlantic climate variability. Regression of a boreal spring (March- May) SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding winter (November- January) Nino3.4 (black box; \(5^{\circ}\mathrm{S} - 5^{\circ}\mathrm{N}\) , \(120^{\circ} - 170^{\circ}\mathrm{W}\) ) index and b boreal winter SST anomalies (shading; \(^\circ \mathrm{C}\) ) upon the preceding spring NTA (blue box; \(0^{\circ} - 15^{\circ}\mathrm{N}\) , \(90^{\circ} - 0^{\circ}\mathrm{W}\) ) SST anomaly. Dots in (a- b) indicate regression coefficients that are statistically significant at the \(95\%\) confidence level. c 15- yr running lead- lagged correlation of the boreal winter Nino3.4 index with the NTA SST anomaly. Solid, dashed, and dotted lines mark the region with values exceeding the \(80\%\) , \(90\%\) and \(95\%\) confidence levels, respectively. d Lead- lagged correlation of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[40, 45, 945, 180]]<|/det|>
+the boreal winter Niño3.4 index with the observed (solid) and reconstructed (dashed) NTA SST anomaly for bandpass filtering of 2- 3- yr (blue) and 3- 5- yr (red) periods by using a Fast Fourier Transform filter. For the y- axis of (c- d), negative and positive values indicate NTA- lead and NTA- lag at monthly scale, respectively. e Lead- lagged correlation of the boreal winter Niño3.4 index with NTA SST anomaly in the idealized pacemaker experiments with different Pacific SST forcing (see Methods). Gray dashed lines in (d- e) indicate the 95% confidence levels.
+
+<|ref|>image<|/ref|><|det|>[[75, 210, 886, 830]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 856, 117, 875]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[42, 897, 953, 940]]<|/det|>
+Phase relationship of NTA SST anomalies with ENSO in pi- control climate simulations. a Lead correlation of boreal spring NTA SST anomaly with the subsequent winter Niño3.4 index for 46 CMIP6 models and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[40, 45, 955, 361]]<|/det|>
+observations as a reference. The models are ranked by the NTA/ENSO correlation coefficients in an ascending order. The error bar for the multi- model ensemble (MME) mean corresponds to one standard deviation. The dashed purple lines represent the \(80\%\) , \(90\%\) and \(95\%\) confidence levels. b Regression of SST anomalies (°C) upon the Niño3.4 index averaged for the left 10 models with most negative correlation (contours with interval: \(0.4^{\circ}C\) ; models indicated by striped blue bars in panel a) and the right 10 models with most positive correlation (shading; models indicated by striped red bars in panel a). c Multi- Taper- Method (MTM) power spectra averaged for the left 10 models with most negative correlation (solid thick blue) and the right 10 models with most positive correlation (solid thick red), superimposed by one standard deviation (blue and red shading). The observed spectral peaks of pre- and post-1990 periods (grey shading) are shown for comparison. The averaged AR(1) null hypothesis is displayed by a dashed thin line and the \(95\%\) confidence level is indicated by a solid thin line. d Scatterplot of ENSO period and lead- time for which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Niño3.4 index. The linear fit (solid black) is displayed together with the correlation coefficient R and slope.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[78, 70, 915, 660]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 690, 117, 710]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[40, 732, 953, 824]]<|/det|>
+Phase relationship of NTA SST anomalies with ENSO in future warming simulations. Scatterplot of ENSO period and lead- time at which negative correlation coefficients are maximized for boreal spring NTA SST anomaly with the subsequent Niño3.4 index for the SSP2- 4.5 (red) and SSP5- 8.5 (purple) scenarios. The linear fits (solid black) are displayed together with respective correlation coefficient R and slope.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[72, 60, 900, 525]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 555, 117, 574]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[40, 595, 940, 799]]<|/det|>
+Schematic trans- basin relationships between tropical Pacific and North Atlantic oceans regulated by the ENSO periodicity. In the quasi- biennial ENSO cycle (red loop), an El Niño condition in boreal winter (left panel) leads to positive NTA warming during subsequent spring (upper panel) at a \(\sim 4\) - month lead time, which in turn can see a La Niña formation (right panel) typically following El Niño in the subsequent winter, showing a statistical \(\sim 8\) - month lead time of the NTA. Likewise, a La Niña condition in boreal winter (right panel) gives rise to the following spring NTA SST cooling (lower panel) with a lag of \(\sim 4\) months, which is often followed by an El Niño formation (left panel), corresponding to a statistical \(\sim 8\) - month lead time of the NTA. The same applies for the quasi- quadrennial ENSO cycle (blue loop) except for the negative correlation of NTA SST variability with the following ENSO event by \(\sim 20\) months.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 821, 311, 850]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 871, 763, 892]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 908, 404, 928]]<|/det|>
+- SupplementalNTA20200918final.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/images_list.json b/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..4e7832d84dc2bb0e5a5046830e17d13a8c957332
--- /dev/null
+++ b/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/images_list.json
@@ -0,0 +1,122 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1 | UNAGI overview: resolving cellular dynamics of complex disease & potential therapeutics through single-cell embeddings. a, Phase 1: UNAGI employs a VAE-GAN paired with a graph convolution layer. This setup harnesses the complexities of single-cell data, producing a 'Z' latent space that bridges encoding and decoding with minimal error. b, Phase 2: Derived from the 'Z' embeddings, a temporal dynamics graph emerges. Here, the Leiden clustering method discerns cell populations, subsequently connecting them across stages based on their inherent similarity. c, Phase 3: The iDREM tool comes into play, spotlighting key gene regulators and genes that influence disease progression. These insights are channeled into an iterative model training, honing in on specific gene markers of the disease. d, With the model in place, UNAGI initiates in-silico perturbations, either directly tweaking drug target gene expressions (i) or manipulating gene expressions via established gene interaction networks (ii) to simulate drug treatment impact. e, UNAGI's encoder processes the perturbed cell population alongside its peers. The perturbation scores, derived from the 'Z' space embeddings generated by the UNAGI encoder, assist in identifying potential drug candidates. These candidates are evaluated based on their ability to transition diseased cells towards healthier states, such as those resembling healthy control cells, thereby contributing to the treatment of the disease.",
+ "footnote": [],
+ "bbox": [
+ [
+ 95,
+ 78,
+ 904,
+ 670
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2 | UNAGI identifies progressive heterogenous cell populations across IPF stages. a, UMAP visualization: Mesenchymal cells across various IPF stages are depicted. Each point corresponds to a cell; the first column categorizes them by cell type (e.g., SMC = smooth muscle cell, VE = vascular endothelial), and the second by Leiden cluster IDs. This panel underscores UNAGI's ability to learn a potent cell embedding, ensuring premium cell clustering. b, Gene dot plots: Dot plots illustrating the key biomarkers for each identified cell type across four stages of IPF. In these plots, the size of each circle indicates the proportion of cells expressing the gene, and the circle's color reflects the level of normalized gene expression. c, Cell composition chart: A visualization of the shifts in cell type composition along with IPF disease progression. Colors indicate the specific cell type. Notably, there's a discernible expansion of fibroblast cells as the disease progresses.",
+ "footnote": [],
+ "bbox": [
+ [
+ 92,
+ 111,
+ 900,
+ 608
+ ]
+ ],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "**Fig. 3 | UNAGI reconstructs the temporal dynamics and the underlying gene regulatory networks of cellular dynamics during IPF progression. a,** Dynamics graph of IPF progression within the mesenchymal cell lineage, comprising four IPF stages. Each node symbolizes a cell population, colored according to cell type, and the edges between two nodes depict the progression trajectory across disease stages. Trajectories, spanning from Control to Stage 3, are termed progression tracks. Each track is named with the specific cell type and the corresponding Control cluster-ID. **b,** Gene regulatory networks for the FibAlv-4 track, were reconstructed using the iDREM tool. Individual nodes signify a set of genes, and edges connecting two nodes represent gene regulators regulating expression changes. Paths encompassing nodes from Control to Stage 3 depict a consistent set of genes displaying the same expression changes throughout IPF progression. The enriched pathways associated with gene paths were also provided. **c,** the temporal regulatory networks for the FibAdv-17 track. **d,** Line chart of expression of the top dynamic gene candidates on the FibAlv-4 and FibAdv-17 tracks, the top 10 most increasing and the top 10 most decreasing candidate marker genes through the IPF progression.",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 110,
+ 900,
+ 688
+ ]
+ ],
+ "page_idx": 7
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4 I UNAGI comprehensively captures novel dynamical and hierarchical static markers across various IPF stages. a, Heatmaps presenting the most pronounced increasing (left) and decreasing (right) temporal dynamic markers' expressions, each z-score normalized, across tracks. b, The left panel showcases heatmaps of dynamic gene markers from the FibAlv-4 cluster. Importantly, the right panel provides experimental verification of these markers through corresponding protein expressions derived from proteomics data. Line plots accompanying these highlight gene expression shifts of these dynamic markers over the course of IPF progression. c, Dendrogram visualizing control cell populations. Each node signifies a cell type-specific population. The Fibroblast Adventitial cluster is accentuated. Using UNAGI, various hierarchical biomarkers are discernible at different levels, either contrasting with other cell types or juxtaposing subpopulations within the same cell type. d, Heatmap detailing the top 25 hierarchical static markers' expressions, all z-score normalized, for the Fibroblast Adventitial cluster at level 0. This highlights UNAGI's proficiency in pinpointing general cell type markers. e, Heatmap delineating the top 25 hierarchical marker gene expressions, z-score normalized, for the Fibroblast Adventitial cluster at level 4, set against two Fibroblast Alveolar clusters, emphasizing UNAGI's capability in cell subtype marker identification.",
+ "footnote": [],
+ "bbox": [
+ [
+ 95,
+ 81,
+ 904,
+ 675
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Fig. 5 I UNAGI identifies potential therapeutic pathways and potent drugs for IPF treatments. a, Bar chart of the track FibAlv-4 pathway perturbation results. The highlighted pathways are also identified in the reconstructed gene regulatory network of the track. b, Split-violin plot of the gene expression differences for the top 20 most changing genes of in-silico extracellular matrix (ECM) organization pathway perturbation in Stage 1 of the FibAlv-4 track. c, PCA plots of latent space Z of in-silico ECM organization pathway perturbation effects and dots represent cells from distinct stages. Lines connected to two nodes are the PAGA connectivity score between two clusters, where the width of a line is proportional to the strength of the score, and the length of the line can represent the distance between the UNAGI embeddings of the two connected clusters. (e.g., Line connecting Control and Perturbed Stage 1 \\((L_{CP_1})\\) ). d, Bar chart of the top overall drug perturbation results. e, Split-violin plot of gene expressions for the top 10 changing targets of Nintedanib in the gene interactions network both before and after perturbation in Stage 1 of the FibAlv-4 track. f, PCA plots of Nintedanib perturbation effectiveness.",
+ "footnote": [],
+ "bbox": [
+ [
+ 90,
+ 70,
+ 901,
+ 640
+ ]
+ ],
+ "page_idx": 11
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Fig. 6 I UNAGI outperforms alternative approaches in learning the cell embeddings and can effectively identify efficacious drugs in in-silico perturbations. a, Adjusted Rand Index (ARI) and b, Normalized Mutual Information (NMI) illustrate the effectiveness of the learned cell embeddings for downstream clustering tasks. c, Label score, indicating that cells within neighborhoods primarily have the same cell type. d, Silhouette score. e, Davis-Bouldin index (DBI); a lower DBI signifies better clustering. These scores (c, d, e) are unsupervised metrics employed to demonstrate the clustering quality derived from the learned cell embeddings. f, Box plot presenting the silhouette scores of UNAGI across various training iterations, emphasizing that the iterative strategy progressively enhances cell embeddings and clustering quality with each iteration. g, PCA representation highlighting the impact of sanitary perturbation, which involves reversing the gene expression at Stage 1 back to the patterns observed in the control stage. This process essentially seeks to \"normalize\" or \"sanitize\" the aberrant gene expressions, bringing them in line with a control or reference state. h, Distribution patterns for various drug/compound perturbations. The x-axis represents the perturbation score, while the y-axis portrays the density of the fitted Gaussian distribution for each specific setting. i, AUROC and AUPRC metrics in relation to perturbation verification. As a reference, a random drug effectiveness predictor is used as a baseline, with an AUC (Area Under the Curve) score of 0.5, indicating no predictive discrimination, and an average precision (AP) score of 0.5, representing a baseline precision level.",
+ "footnote": [],
+ "bbox": [
+ [
+ 95,
+ 80,
+ 901,
+ 518
+ ]
+ ],
+ "page_idx": 13
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_7.jpg",
+ "caption": "Fig. 7 I The predictions of UNAGI align with human precision-cut lung slices (PCLS) drug validations. a, UMAP visualization of the PCLS data with each dot representing an individual cell. b, UMAP representation emphasizing the similarity between the real-world treatments of Nifedipine and Nintedanib. Furthermore, cells under in-silico drug treatments (Nifedipine and Nintedanib) closely mirror those under actual treatments. c, Violin plots showcasing that Nintedanib and Nifedipine treatments markedly shift fibrotic cells, bringing them closer in resemblance to healthy control cells. (e.g., \\(D_{e}\\) (Fibrosis, Nifedipine) is the distance between fibrosis cells and fibrosis cells after Nifedipine treatment). d, Violin plots highlighting the strong alignment between in-silico drug treatments and their real-world counterparts. e, The RRHO (Ranked Rank Hypergeometric Overlap) plots for both Nifedipine and Nintedanib. These plots juxtapose in-silico perturbations post-VAE reconstruction against actual treatments, emphasizing the high degree of similarity between in-silico and real treatments. Specifically, the genes up-regulated and down-regulated in in-silico treatments show strong correlations with those affected in real treatments. f, Box plots and \\(R^2\\) plots compare the expression of the top differential genes of real treatments (Nintedanib or Nifedipine vs. fibrosis) to in-silico perturbation results. The box plot visualizes the top 25 differential genes (ranked based on log fold changes) for each treatment. The gene expression of the top 100 differential genes in real and in-silico drug treatments are used to calculate the adjusted \\(R^2\\) metric and generate \\(R^2\\) plots. This representation is intended to underline the remarkable similarity observed between in-silico drug perturbations and the corresponding actual drug treatments for both Nifedipine and Nintedanib. g, Box plots and \\(R^2\\) plots of ECM organization target gene expressions from real treatments and in-silico perturbations. The box plots visualize the top 15 genes of ECM based on log fold changes between real treatments and fibrosis cells. The gene expressions of all ECM organization target genes in real and in-silico drug treatments are used to calculate the adjusted \\(R^2\\) metric and generate \\(R^2\\) plots.",
+ "footnote": [],
+ "bbox": [
+ [
+ 95,
+ 68,
+ 905,
+ 576
+ ]
+ ],
+ "page_idx": 14
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_8.jpg",
+ "caption": "Fig. 8 | UNAGI in-silico analysis unveils COVID-19 cellular dynamics and therapeutic opportunities. a, UMAP display of stage 2 COVID-19 data with each dot symbolizing an individual cell. Cells are color-coded based on their respective cell types. b, Dot plot illustrating the expression levels of canonical cell type markers present within the stage 2 COVID-19 data set. c, Dynamic graphs representing the cellular dynamics underlying the COVID-19 progression. Within these graphs, each node corresponds to a cell cluster, and the connecting edges signify the relationships between these nodes (shift of the cell population along with COVID-19 progression). d, Depiction of the reconstructed gene regulatory network for the track 12-CD16. Prominent gene regulators, genes, and pathways discerned from the enrichment analysis are enumerated. e, Bar chart detailing the principal pathway perturbation outcomes. Pathways highlighted have literature support, indicating their potential as therapeutic targets against COVID-19. f, Bar chart outlining the top 10 drug perturbation results. Drugs that are emphasized have been highlighted based on literature support, suggesting their candidacy for treating COVID-19.",
+ "footnote": [],
+ "bbox": [
+ [
+ 95,
+ 222,
+ 902,
+ 640
+ ]
+ ],
+ "page_idx": 16
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec.mmd b/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..1c155a8ba248066efecf1eddd0acc43130bff024
--- /dev/null
+++ b/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec.mmd
@@ -0,0 +1,585 @@
+
+# Unagi: Deep Generative Model for Deciphering Cellular Dynamics and In-Silico Drug Discovery in Complex Diseases
+
+Yumin Zheng McGill University Jonas Schupp Yale University https://orcid.org/0000- 0002- 7714- 8076 Taylor Adams Yale University https://orcid.org/0000- 0003- 4280- 9070 Geremy Clair Pacific Northwestern National Laboratory Aurelien Justet Yale University Farida Ahangari Yale University Xiting Yan Yale University Paul Hansen McGill University Marianne Carlon KU Leuven https://orcid.org/0000- 0002- 8263- 0350 Emanuela Cortesi KU Leuven Marie Vermant KU Leuven Robin Vos KU Leuven Laurens De Sadeleer KU Leuven Ivan Rosas Baylor College of Medicine Ricardo Pineda University of Pittsburgh John Sembrat
+
+<--- Page Split --->
+
+University of Pittsburgh
+
+Melanie Königshoff University of Pittsburgh
+
+John Mcdonough Yale University
+
+Bart Vanaudenaerde KU Leuven
+
+Wim Wuyts KU Leuven
+
+Naftali Kaminski Yale University https://orcid.org/0000- 0001- 5917- 4601
+
+Jun Ding
+
+jun.ding@mcgill.ca
+
+McGill University
+
+## Article
+
+# Keywords:
+
+Posted Date: December 18th, 2023
+
+DOI: https://doi.org/10.21203/rs.3.rs- 3676579/v1
+
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: Yes there is potential Competing Interest. NK is a scientific founder at Thyron, served as a consultant to Boehringer Ingelheim, Pilant, Astra Zeneca, RohBar, Veracyte, Augmanity, CSL Behring, Splisense, Galapagos, Fibrogen, GSK, Merck and Thyron over the last 3 years, reports Equity in Pilant and Thyron, and grants from Veracyte, Boehringer Ingelheim, BMS and non- financial support from Astra Zeneca.
+
+Version of Record: A version of this preprint was published at Nature Biomedical Engineering on June 20th, 2025. See the published version at https://doi.org/10.1038/s41551- 025- 01423- 7.
+
+<--- Page Split --->
+
+# Unagi: Deep Generative Model for Deciphering Cellular Dynamics and In-Silico Drug Discovery in Complex Diseases
+
+Yumin Zheng \(^{1,2\dagger}\) , Jonas C. Schupp \(^{3\dagger}\) , Taylor Adams \(^{3}\) , Geremy Clair \(^{4}\) , Aurelien Justet \(^{3}\) , Farida Ahangari \(^{3}\) , Xiting Yan \(^{3}\) , Paul Hansen \(^{2}\) , Marianne Carlon \(^{5}\) , Emanuela Cortesi \(^{5}\) , Marie Vermant \(^{5}\) , Robin Vos \(^{5}\) , Laurens J. De Sadleer \(^{5}\) , Ivan O Rosas \(^{6}\) , Ricardo Pineda \(^{7}\) , John Sembrat \(^{7}\) , Melanie Königshoff \(^{7}\) , John E. McDonough \(^{3}\) , Bart M. Vanaudenaerde \(^{5}\) , Wim A. Wuyts \(^{5}\) , Naftali Kaminski \(^{3\dagger}\) , Jun Ding \(^{1,2,8\ast}\)
+
+1 Quantitative Life Sciences, Faculty of Medicine & Health Sciences, McGill University, Montreal, QC, Canada. 2 Meakins- Christie Laboratories, Translational Research in Respiratory Diseases Program, Research Institute of the McGill University Health Centre, Montreal, QC, Canada. 3 Pulmonary, Critical Care and Sleep Medicine, Yale University, School of Medicine, New Haven, CT, United States. 4 Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, United States. 5 Laboratory of Respiratory Diseases and Thoracic Surgery (BREATHE), Department of Chronic Diseases and Metabolism, KU Leuven, Belgium. 6 Division of Pulmonary, Critical Care and Sleep Medicine, Baylor College of Medicine, Houston, TX, USA. 7 Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA. 8 Mila - Quebec AI Institute, Montreal, QC, Canada
+
+\(^{\dagger}\) These authors contributed equally \(^{\ast}\) Corresponding authors, NK (naftali.kaminski@yale.edu); JD (jun.ding@mcgill.ca)
+
+## Abstract
+
+Human diseases are characterized by intricate cellular dynamics. Single- cell sequencing provides critical insights, yet a persistent gap remains in computational tools for detailed disease progression analysis and targeted in- silico drug interventions. Here, we introduce UNAGI, a deep generative neural network tailored to analyze time- series single- cell transcriptomic data. This tool captures the complex cellular dynamics underlying disease progression, enhancing drug perturbation modeling and discovery. When applied to a dataset from patients with Idiopathic Pulmonary Fibrosis (IPF), UNAGI learns disease- informed cell embeddings that sharpen our understanding of disease progression, leading to the identification of potential therapeutic drug candidates. Validation via proteomics reveals the accuracy of UNAGI's cellular dynamics analyses, and the use of the Fibrotic Cocktail treated human Precision- cut Lung Slices confirms UNAGI's predictions that Nifedipine, an antihypertensive drug, may have antifibrotic effects on human tissues. UNAGI's versatility extends to other diseases, including a COVID dataset, demonstrating adaptability and confirming its broader applicability in decoding complex cellular dynamics beyond IPF, amplifying its utility in the quest for therapeutic solutions across diverse pathological landscapes.
+
+## Main
+
+Complex diseases emerge through the interaction of genetic and environmental factors over time. The complexity of the interactions between these heterogeneous factors among individuals and populations challenges the understanding of disease progression \(^{1 - 3}\) . Treating multifactorial diseases requires therapies that address multiple interacting processes, which complicates and prolongs the drug development process \(^{4,5}\) . The lack of understanding of disease cellular dynamics poses challenges to the effectiveness of therapeutic targets and developed drugs, as most of them are developed in animal or cell culture models that ignore the complexity and dynamics of the human disease.
+
+Single- cell RNA sequencing (scRNA- seq) stands at the frontier of potential solutions, offering an unprecedented opportunity to analyze cell populations at single- cell resolution \(^{6,7}\) , and profile the complex and heterogeneous systems \(^{8,9}\) , thereby uncovering rare cell populations and aberrant cell states that are pivotal to diseases \(^{10}\) . Computation methods including Seurat \(^{11}\) , Scanpy \(^{12}\) , Monocle \(^{13}\) , Cellar \(^{14}\) and scVI \(^{15}\) could analyze the noisy, high- dimensional, and large- scale scRNA- seq data and sketch cellular dynamics. However, scRNA- seq data is often a snapshot of the cellular states at a specific time point and cannot account for the continuous biological process, such as differentiation or immune responses, during the progression of a disease. Time- series scRNA- seq data can enhance our grasp on the regulatory mechanisms underpinning disease progression based on distinct samples from multiple time points \(^{16}\) . Nevertheless, cell asynchrony presents new computational challenges to uncover the temporal cellular dynamics \(^{8,16,17}\) . When applying snapshot- based scRNA- seq analysis tools to time- series data, they tend to perceive the data as discrete snapshots, overlooking
+
+<--- Page Split --->
+
+the continuity and temporal progression inherent to time- series data. The omission of nuanced temporal information, like disease stage transitions, is not accurately modeled.
+
+Computational methods have been developed to address the challenges raised by time- series single- cell transcriptome data, however both conventional methods such as scdiff18 and CSHMMs19,20, and deep learning- based methods such as RVAgene21 and TDL22 are engineered for generic single- cell data processing, inadvertently bypassing the specialized necessities tied to complex diseases. Rigorous preprocessing and normalization, often needed by noisy single- cell data for complex diseases, can shift the data into unconventional distributions, making them ill- suited for the direct application of many existing models on single- cell applications15,23,24. These techniques were often not originally designed to handle data that deviates from conventional distributions, leading to suboptimal or even inaccurate results. When it comes to the critical step of cell embedding learning, these methods typically employ a one- size- fits- all approach. Their dimensionality reductions and cell embedding strategies are largely generic, devoid of the flexibility to integrate disease- specific signatures or intricacies, rendering them less effective in capturing nuanced biological variances associated with complex diseases. Another salient gap in current single- cell methodologies is the absence of unsupervised in- silico exploration capabilities. Although GEARS25 and scGen23 are able to perform in- silico perturbations, they weren't designed to process time- series data and require the in- vitro screening of perturbation response of disease and drug treatments as the supervision. Thus, there is a pressing need for methods that can virtually examine thousands of potential drugs and compounds on single- cell disease data without ground truth training data. The surge in large- scale public drug treatment databases, like the Connectivity Map (CMAP) database26,27, may provide the missing link to the unsupervised single- cell in- silico drug perturbations. Coupled with this, given the vast pool of drug candidates and the intricate cellular dynamics of diseases, an interactive visualization tool is indispensable for efficiently probing potential drugs and priming them for further experimental validation.
+
+Addressing these pressing gaps, we present UNAGI, a comprehensive unsupervised in- silico cellular dynamics and drug discovery framework. UNAGI deciphers cellular dynamics from human disease time- series single- cell data and facilitates in- silico drug perturbations to earmark therapeutic targets and drugs potentially active against complex human diseases. All outputs, from cellular dynamics to drug perturbations, are rendered in an interactive visual format within the UNAGI framework. Nestled within a deep learning architecture Variational Autoencoder- Generative adversarial network (VAE- GAN), UNAGI is tailored to manage diverse data distributions frequently arising post- normalization. It also employs disease- informed cell embeddings, harnessing crucial gene markers derived from the disease dataset. On achieving cell embeddings, UNAGI fabricates a graph that chronologically links cell clusters across disease stages, subsequently deducing the gene regulatory network orchestrating these connections. UNAGI is primed to leverage time- series data, enabling a precise portrayal of cellular dynamics and capture of disease markers and gene regulators. Lastly, the deep generative prowess of the UNAGI framework powers an in- silico drug perturbation module, simulating drug impacts by manipulating the latent space informed by real drug perturbation data from the CMAP database. This allows for an empirical assessment of drug efficacy based on cellular shifts towards healthier states following drug treatment. The in- silico perturbation module can similarly be utilized to investigate therapeutic pathways, employing an approach akin to the one used in drug perturbation analysis.
+
+We demonstrate UNAGI on a comprehensive single- nuclei RNA- seq (snRNA- seq) IPF dataset. IPF is a complex lethal lung disease characterized by irreversible lung scarring, leading to progressive decline in lung function and death28- 30. Present therapeutic options for IPF are markedly narrow; only two FDA- approved medications, Pirfenidone31 and Nintedanib32, exist, and their main effect is slowing lung function decline, not reversing fibrosis, or making the patient feel better33. Despite their approval, their specific impact on disease mechanisms remains unclear32- 34. Recent studies10,35 highlighted the molecular and cellular diversity of the IPF lung, but this information has not been yet incorporated in the development of therapies for IPF, although some studies suggested that computational analyses may identify potential drugs for human pulmonary fibrosis36. The push towards developing potent IPF therapeutics is hampered further by the incomplete understanding of the dynamic changes of diverse cellular populations throughout IPF progression. We apply UNAGI to a unique dataset that contains samples from differentially affected lung regions, allowing analysis of disease progression, and highlighting UNAGI's ability to generate compact low- dimensional representations for subsequent tasks, outclassing existing methods. Further, we apply proteomics analysis and Precision- cut Lung Slices (PCLS) analysis37,38 to experimentally confirm the results and predictions of UNAGI. Taken together, our findings corroborate UNAGI's capability not just in decoding cellular dynamics and underpinning regulatory networks but also in potentially accelerating drug development by spotlighting potential therapeutic targets and drug candidates.
+
+<--- Page Split --->
+
+
+Fig. 1 | UNAGI overview: resolving cellular dynamics of complex disease & potential therapeutics through single-cell embeddings. a, Phase 1: UNAGI employs a VAE-GAN paired with a graph convolution layer. This setup harnesses the complexities of single-cell data, producing a 'Z' latent space that bridges encoding and decoding with minimal error. b, Phase 2: Derived from the 'Z' embeddings, a temporal dynamics graph emerges. Here, the Leiden clustering method discerns cell populations, subsequently connecting them across stages based on their inherent similarity. c, Phase 3: The iDREM tool comes into play, spotlighting key gene regulators and genes that influence disease progression. These insights are channeled into an iterative model training, honing in on specific gene markers of the disease. d, With the model in place, UNAGI initiates in-silico perturbations, either directly tweaking drug target gene expressions (i) or manipulating gene expressions via established gene interaction networks (ii) to simulate drug treatment impact. e, UNAGI's encoder processes the perturbed cell population alongside its peers. The perturbation scores, derived from the 'Z' space embeddings generated by the UNAGI encoder, assist in identifying potential drug candidates. These candidates are evaluated based on their ability to transition diseased cells towards healthier states, such as those resembling healthy control cells, thereby contributing to the treatment of the disease.
+
+ResultsOverview of UNAGI conceptual framework
+
+<--- Page Split --->
+
+UNAGI, unified in- silico cellular dynamics and drug discovery framework, is a computational framework that integrates time- series single- cell sequencing data with sophisticated deep- learning techniques to unravel intricate cellular dynamics and identify potent therapeutic interventions against multifaceted diseases. This is achieved using the following three components: (1) UNAGI applies a VAE- GAN to capture cellular information in a reduced latent space (Fig. 1a). It processes single- cell data as continuous, zero- inflated log- normal (ZILN) distributions (or other distributions that well fit the data in other application scenarios) because this often better matches the distribution of single- cell data post rigorous preprocessing and normalization (e.g., in the IPF data employed in this study). With a cell- by- gene normalized counts matrix as input, a cell graph convolution (GCN) layer is introduced to manage the sparse and noisy nature of the data. Particularly, the GCN layer leverages the structured relationships between cells to mitigate the dropout noise common in single- cell data, enhancing the accuracy of cellular representations. This data, further refined by a VAE, results in lower- dimensional embeddings, with an adversarial discriminator ensuring the synthetic quality of these representations. (2) After embedding, cell populations are identified using the Leiden clustering approach and visualized with UMAP. A temporal dynamics graph is then constructed by evaluating cell population similarities during the disease progression, linking them based on their likeness (Fig. 1b). Each trajectory within the graph then forms the basis for deriving gene regulatory networks using the iDREM tool (Fig. 1c). (3) An iterative refinement process toggles between the embedding and temporal dynamics stages. Critical gene regulators, including transcription factors, cofactors, and epigenetic modulators, identified from the temporal cellular dynamics reconstruction stage are emphasized during the subsequent embedding phase, ensuring that the cell representation learning places heightened focus on these pivotal elements related to disease progression in each iteration. (4) Upon reaching predefined stopping criteria, UNAGI then employs in- silico perturbations to quantify the effectiveness of therapeutic interventions (Fig. 1d). Using the trained VAE- GAN generative model, UNAGI simulates cells under various drug treatments or pathway perturbations. Each perturbation's impact is scored and ranked based on its ability to shift the diseased cells closer to a healthier state (Fig. 1e).
+
+## Staging samples based on tissue involvement as measured by the surface density allows assessments of mesenchymal cellular population dynamics during disease progression
+
+A true longitudinal profiling of the lung cells from the same patient across different IPF stages is impossible because patients are rarely if ever biopsied more than once. Thus, to investigate the cellular dynamics along the progression of human IPF tissues, we analyze samples from differentially affected regions of the IPF lung using a strategy previously described. To build the surrogate "longitudinal" single- cell data, here we employed a Gaussian density estimator to classify all samples (and thus all cells) into different IPF stages. The model will learn the best number of IPF stages and the associated Gaussian parameters (mean and standard deviation) for each IPF tissue involvement stage based on the profiled alveolar surface density (Supplementary Fig. 1a,b) as previously described. All the samples were categorized based on their alveolar surface density into 4 IPF stages: Healthy (Control, or stage 0), Normal looking IPF (stage 1), moderately involved IPF (stage 2), and Severe (stage 3). This 4- stage classification matches the existing understanding of the disease and has been previously validated.39- 41. After the density estimation analysis, we got the samples and cells assigned to these 4 IPF stages (Supplementary Fig. 1c). Specifically, 30 samples were categorized as healthy (135,536 cells). Seven samples were classified as the IPF stage 1 (41, 957 cells). The stage 2 data is composed of 7 samples (21, 531 cells) while the stage 3 data comprises 10 samples (22, 520 cells) (Supplementary Fig. 1d). As shown in Supplementary Fig. 1e, there's a discernible increase in mesenchymal cells starting from IPF stage 1, hinting at a possible rise in fibroblast cells from this stage onward.
+
+## UNAGI effectively identifies varying cell populations across IPF stages
+
+After applying UNAGI on the four stages IPF snRNA- seq dataset and performing clustering and visualization on the latent space, we have observed a continuous trajectory of healthy fibroblasts towards corresponding, fibrotic IPF archetypes, prompting us to focus on and explore stromal cells using UNAGI. UNAGI showed its effectiveness in cell embeddings by achieving a 0.74 average ARI of all stages. UNAGI identified 11 distinct cell types in Controls, with more emerging in subsequent IPF stages (Fig. 2a), which we annotated based on the expression of canonical cell markers (Fig. 2b and independent manual cell- type annotations in supplementary Fig. 2). UNAGI can capture cell subpopulations, like fibrotic fibroblasts and airway fibroblast cells, suggesting extended fibrosis through the progression. Furthermore, UNAGI revealed differences in cellular heterogeneity: Smooth muscle cells (SMC; marked by ZNF385D and PRUNE2), and alveolar pericyte cells (characterized by ADARB2 and LRRTM4) were predominantly homogenous. In contrast, fibroblast cell populations displayed greater heterogeneity, within both alveolar (denoted by ROBO2 and SLIT2) and adventitial fibroblasts. Fibroblast proportions substantially increase in IPF compared to controls — from less than 15% to more than 40%—validating that fibroblast accumulation is a hallmark of IPF progression. (Fig. 2c). The alveolar fibroblast cell population exhibited the most substantial increase, while the fibrotic fibroblast archetype appeared only in subsequent IPF stages. The proportions of vascular endothelial cells consistently
+
+<--- Page Split --->
+
+decreased as IPF progressed. The cell embeddings from IPF data reveal a progressive cell population across IPF stages, serving as a foundation for constructing a temporal dynamic graph depicting IPF progression.
+
+
+
+Fig. 2 | UNAGI identifies progressive heterogenous cell populations across IPF stages. a, UMAP visualization: Mesenchymal cells across various IPF stages are depicted. Each point corresponds to a cell; the first column categorizes them by cell type (e.g., SMC = smooth muscle cell, VE = vascular endothelial), and the second by Leiden cluster IDs. This panel underscores UNAGI's ability to learn a potent cell embedding, ensuring premium cell clustering. b, Gene dot plots: Dot plots illustrating the key biomarkers for each identified cell type across four stages of IPF. In these plots, the size of each circle indicates the proportion of cells expressing the gene, and the circle's color reflects the level of normalized gene expression. c, Cell composition chart: A visualization of the shifts in cell type composition along with IPF disease progression. Colors indicate the specific cell type. Notably, there's a discernible expansion of fibroblast cells as the disease progresses.
+
+## UNAGI reconstructs the temporal dynamics graph and the underlying gene regulatory networks during disease progression
+
+UNAGI can effectively reconstruct the cellular dynamics associated with time series or disease progression data based on the cell embeddings learned by the model. Within our analytical framework, a "track" delineates a distinct trajectory within the reconstructed dynamics graph, marking the sequential cellular state transitions corresponding to specific cell clusters or populations. These tracks not only identify pathways but also chronicle the journey of cellular progression and evolution. Within mesenchymal cells, we have discerned 10 distinct progression tracks (Fig. 3a), transitioning from the IPF stage 0 (healthy controls) to IPF stage 3 (severe fibrosis). Two of these tracks are composed of fibroblast cells, FibAlv- 4 traces the cellular state shifts of alveolar fibroblast cells during IPF progression while FibAdv- 17 illustrates the cellular dynamics of remaining adventitial,
+
+<--- Page Split --->
+
+airway, and fibrotic fibroblasts. Of note, the fibroblast tracks in the dynamics graph contain multiple branches, potentially reflecting the multifaceted roles of fibroblast cells in the fibrosis process44.
+
+
+
+
+
+**Fig. 3 | UNAGI reconstructs the temporal dynamics and the underlying gene regulatory networks of cellular dynamics during IPF progression. a,** Dynamics graph of IPF progression within the mesenchymal cell lineage, comprising four IPF stages. Each node symbolizes a cell population, colored according to cell type, and the edges between two nodes depict the progression trajectory across disease stages. Trajectories, spanning from Control to Stage 3, are termed progression tracks. Each track is named with the specific cell type and the corresponding Control cluster-ID. **b,** Gene regulatory networks for the FibAlv-4 track, were reconstructed using the iDREM tool. Individual nodes signify a set of genes, and edges connecting two nodes represent gene regulators regulating expression changes. Paths encompassing nodes from Control to Stage 3 depict a consistent set of genes displaying the same expression changes throughout IPF progression. The enriched pathways associated with gene paths were also provided. **c,** the temporal regulatory networks for the FibAdv-17 track. **d,** Line chart of expression of the top dynamic gene candidates on the FibAlv-4 and FibAdv-17 tracks, the top 10 most increasing and the top 10 most decreasing candidate marker genes through the IPF progression.
+
+The gene regulatory network of FibAlv-4, as reconstructed by UNAGI, highlights the central role of gene regulators CTCF, RAD21, SMC3, and especially fibrosis-promoting EP30045,46. This is further supported by
+
+<--- Page Split --->
+
+the genes in Path A of the FibAlv- 4 track, which include recognized fibrosis biomarkers like LTBP1 and LTBP247,48 (Fig. 3b). Pathways enriched in track FibAlv- 4 include: in Path A, Collagen and Extracellular Matrix (ECM) pathways49; in Path B, the PI3K- Akt- mTOR signaling pathway and the focal adhesion pathway, both hallmarks of IPF fibroblasts 50- 52 (Fig. 3b); and in Path C, SLIT2, a known marker of IPF42. The FibAdv- 17 track highlights the contribution of adventitial fibroblasts to matrix remodeling. The discovery of recognized collagen genes like COL3A1 and COL1A253,54, are pivotal markers for IPF. Enriched pathways encompass general ECM- related pathways including ones of collagen formation, organization, trimerization, and degradation, with some variation between paths A to C (Fig. 3c). The MET- activated PTK2 signaling pathway55, a substantial player in pulmonary fibrosis progression, is also highlighted. The genes in Path B, including KCNMA156, NPAS257, ITGA858, and DIO259, all closely associated with IPF.
+
+The depth and precision of the reconstructed gene regulatory network are underscored by its ability to pinpoint not only pivotal gene regulators and pathways but also the target genes they regulate. These target genes, especially those that exhibit differential expression across disease stages, provide invaluable insights into the temporal dynamics of IPF progression. In the context of the FibAlv- 4 track, the method identifies genes like COL3A1 and SERPINE1, which are induced by the TGF- Beta pathway60, a key player in IPF. Furthermore, the inclusion of top dynamic marker candidates such as DCLK162, TENM3, TENM2, ADRA1A, and GRIA1, all of which have established associations with IPF61- 64, attests to the method's robustness in capturing disease- relevant genes (Fig. 3d).
+
+Taken, together, UNAGI's comprehensive mapping of gene regulators, pathways, and their target genes in the reconstructed gene regulatory network underscores the method's unparalleled capability in unraveling the intricate molecular interplay underlying IPF.
+
+## UNAGI comprehensively captures novel dynamical and hierarchical static markers across various disease stages
+
+Conventional single- cell analysis primarily identifies differentially expressed markers between healthy and diseased cells. In contrast, we developed UNAGI to identify dynamic marker genes that offer a longitudinal profile of cellular state changes throughout IPF progression. It discerns dynamic markers for individual cell populations, tracing gene expression shifts across disease stages. All identified candidate biomarker genes from the above cell dynamics gene regulatory network for each track will be subjected to a permutation test to assess their statistical significance. This test involves random shuffling of cells from the track across various stages. Subsequently, we calculate the sum of fold changes in gene expression between these stages to establish a background distribution for comparative analysis. Candidate genes that are deemed statistically significant through this test will be considered as dynamic markers, closely associated with the track in the analysis (as detailed in the "Dynamic markers discovery" section of the Methods).
+
+Fig. 4a showcases heatmaps of the top 5 dynamic markers for each track, both those that increase and decrease during disease progression (a comprehensive list is available in Supplementary Table 1). For instance, in the FibAdv- 17 track, markers like LUZP2, ITGBL1, and AOX1, previously reported as differentially expressed in IPF65, are highlighted. Notably, NLGN1, GFRA1, and AOX1 are markers for adventitial fibroblasts66 and emerge as a top- decreasing temporal dynamic marker in this track, suggestive of a loss of respective cell identity. The FibAlv- 4 track, on the other hand, features markers like DCLK1, TENM3, ADRA1A, GRIA1, and EPHA3, all of which have strong ties to lung fibrosis61- 64,67. It is important to mention that while our discussion here primarily focused on monotonically increasing and decreasing biomarkers, which are of main interest in our study, the model we developed is also able to identify biomarker genes with other patterns. An example of this is genes that initially increase and then decrease, as observed in path B of the FibAdv- 17 track.
+
+To experimentally verify the dynamic markers identified by UNAGI, we performed proteomics of matched tissue blocks, 3 samples each from 10 IPF patients across different stages (based on the same surface density criteria) and one each from 10 control donors (Supplementary Table 2). We identified 1070 dynamic proteins from the proteomics data and 606 dynamic gene markers in the snRNA- seq dataset. Further analysis revealed that 151 dynamic proteins have corresponding protein- coding genes in the snRNA- seq data. Interestingly, 40 out of 151 dynamic markers overlapped with dynamic proteins(Supplementary Fig. 3a). Hypergeometric testing on individual tracks revealed statistical significance \((P - value < 0.05\) is set as the default cut- off) for protein- coding genes of dynamic proteins in four specific tracks: FibAlv- 4 \((P - value = 0.003)\) , VEven- 2 \((P - value = 0.015)\) , LymEnd- 19 \((P - value = 0.033)\) , and VEcap- 1 \((P - value = 0.048)\) , as well as in the overall result (Supplementary Fig. 3b). Notably, the FibAlv- 4 track contained 137 dynamic protein- encoding genes, and 14 of these genes produce dynamic proteins (Fig 4b).
+
+<--- Page Split --->
+
+
+Fig. 4 I UNAGI comprehensively captures novel dynamical and hierarchical static markers across various IPF stages. a, Heatmaps presenting the most pronounced increasing (left) and decreasing (right) temporal dynamic markers' expressions, each z-score normalized, across tracks. b, The left panel showcases heatmaps of dynamic gene markers from the FibAlv-4 cluster. Importantly, the right panel provides experimental verification of these markers through corresponding protein expressions derived from proteomics data. Line plots accompanying these highlight gene expression shifts of these dynamic markers over the course of IPF progression. c, Dendrogram visualizing control cell populations. Each node signifies a cell type-specific population. The Fibroblast Adventitial cluster is accentuated. Using UNAGI, various hierarchical biomarkers are discernible at different levels, either contrasting with other cell types or juxtaposing subpopulations within the same cell type. d, Heatmap detailing the top 25 hierarchical static markers' expressions, all z-score normalized, for the Fibroblast Adventitial cluster at level 0. This highlights UNAGI's proficiency in pinpointing general cell type markers. e, Heatmap delineating the top 25 hierarchical marker gene expressions, z-score normalized, for the Fibroblast Adventitial cluster at level 4, set against two Fibroblast Alveolar clusters, emphasizing UNAGI's capability in cell subtype marker identification.
+
+A notable observation from our snRNA-seq and proteomics data is that five of these overlapping dynamic markers are collagens (COL1A1, COL1A2, COL3A1, COL3A1, COL14A1), confirming that progressive matrix
+
+<--- Page Split --->
+
+remodeling is intrinsically intertwined with the development of fibrosis68. Moreover, a majority of the overlapped dynamic markers have been previously associated with pulmonary fibrosis54,69- 71, including CCN5, CDH13, MYH10, PAPSS2, and LMCD. This proteomics data serves as a validation, confirming that the discovered dynamical genes play a crucial role in the progression of IPF.
+
+UNAGI can identify both dynamic and static markers. While dynamic markers offer insights into cellular state changes throughout disease progression, static markers are crucial for distinguishing between different cell types and subpopulations within a given stage. Existing static biomarker discovery pipelines11,12 usually employ a "one vs. the rest" strategy and may fail to distinguish the difference between different subtypes.
+
+UNAGI explores the hierarchies of marker genes that not only distinguish different cell populations but also capture the finer heterogeneity among cell subpopulations. For instance, focusing on the FibAdv- 17 cluster of controls, cell subpopulations are primarily divided into three main groups: fibroblasts, vascular endothelial cells, and lymphatic endothelial cells (Fig. 4c, and dendrograms of all four stages are in Supplementary Fig. 4). The fibroblast adventitial population spans 5 levels in the dendrogram. Fig. 4d showcases the top twenty- five positive hierarchical static markers for fibroblast adventitial cells at dendrogram level 0. These markers distinguish the fibroblast adventitial cluster from all other clusters. UNAGI's results are consistent with the dendrogram structure, highlighting the close relationship between fibroblast adventitial and fibroblast alveolar clusters. Notably, UNAGI identified key markers like IGF1 and collagen genes such as COL24A1 and COL7A1, emphasizing the role of elevated interstitial collagen levels in IPF72. Other markers like ANGPTL4 and WT1 further underscore the method's precision in identifying relevant genes73 (top 25 level 0 positive and negative markers are detailed in Supplementary Fig. 5).
+
+Fig. 4e presents the top 25 positive hierarchical static markers for the fibroblast adventitial cluster at level 4 (sub- type level). While there's an overlap with level 0 markers, level 4 introduces unique markers potentially for subtypes like NLGN1, a cell type marker for adventitial fibroblasts66, and MFAP5, previous research indicates that MFAP5+ fibroblast cells are localized to vascular adventitial74 (top 25 level 4 positive and negative markers are detailed in Supplementary Fig. 6). UNAGI's ability to identify both temporal dynamic markers and hierarchical static markers offers a comprehensive lens to study IPF. This dual approach allows for detailed profiling of the disease from both intra- stage and longitudinal (inter- stage) perspectives, enhancing our understanding of its complexities.
+
+## UNAGI identifies potential therapeutic pathways for IPF treatments
+
+In the preceding sections, we delved into how UNAGI enhances our comprehension of biomarkers and cellular dynamics in the progression of IPF. Building upon this foundational understanding, we now shift our focus to the therapeutic frontiers opened by UNAGI. This involves leveraging its in- silico perturbation capabilities, which are rooted in IPF- specific cell embeddings and the temporal dynamic graph of IPF. This approach paves the way for pinpointing potential therapeutic targets and pathways, a development that promises to be a substantial stride in IPF treatment. Detailed results of these pathway perturbations are systematically presented in Supplementary Table 3.
+
+Many of the top pathways predicted by UNAGI are in alignment with known IPF- centric pathways. Impressively, of the top 10 therapeutic pathways identified, at least seven have been previously associated with IPF progression and potential treatments. For instance, the discovery of the ROBO pathway: Signaling by ROBO receptors (Score=0.5890, \(\mathrm{FDR} = 1.1028 \times 10^{- 14}\) ) which has been strongly linked to IPF progression42,75. Additionally, the Netrin 1 signaling pathway (Score=0.6548, \(\mathrm{FDR} = 3.4698 \times 10^{- 19}\) ) has been correlated with various forms of pulmonary fibrosis, including bleomycin- induced pulmonary fibrosis62,76. Moreover, UNAGI's ability to identify target genes within these pathways offers a deeper understanding of disease progression. For example, the Calcium signaling pathway in fibroblast is highly related to fibrosis77, genes within the pathway such as EGFR, which is linked to fibroblast proliferation77,78, have been highlighted. Beyond known pathways, UNAGI also uncovered novel pathways. While some of these pathways might not have a direct association with IPF, their target genes often play critical roles in the disease's progression. This is evident in the discovery of genes like GRIA61,79 and ERBB48,63, both of which have substantial associations with IPF progression.
+
+The results from pathway perturbations, as showcased in Fig. 5a,b, further demonstrate UNAGI's capability. The perturbations reveal the potential of certain pathways to revert cells to a healthier state, suggesting their therapeutic potential. For instance, the perturbation of the ECM organization pathway in various IPF stages suggests its potential to guide cells to a less severe IPF cellular state.
+
+<--- Page Split --->
+
+
+Fig. 5 I UNAGI identifies potential therapeutic pathways and potent drugs for IPF treatments. a, Bar chart of the track FibAlv-4 pathway perturbation results. The highlighted pathways are also identified in the reconstructed gene regulatory network of the track. b, Split-violin plot of the gene expression differences for the top 20 most changing genes of in-silico extracellular matrix (ECM) organization pathway perturbation in Stage 1 of the FibAlv-4 track. c, PCA plots of latent space Z of in-silico ECM organization pathway perturbation effects and dots represent cells from distinct stages. Lines connected to two nodes are the PAGA connectivity score between two clusters, where the width of a line is proportional to the strength of the score, and the length of the line can represent the distance between the UNAGI embeddings of the two connected clusters. (e.g., Line connecting Control and Perturbed Stage 1 \((L_{CP_1})\) ). d, Bar chart of the top overall drug perturbation results. e, Split-violin plot of gene expressions for the top 10 changing targets of Nintedanib in the gene interactions network both before and after perturbation in Stage 1 of the FibAlv-4 track. f, PCA plots of Nintedanib perturbation effectiveness.
+
+A central takeaway from Fig. 5c is its demonstration that in- silico pathway perturbations effectively shift the cellular states towards healthier conditions. The perturbation's impact on gene expression, especially within the ECM organization pathway, is evident in the reduction of regulated gene expressions. By introducing these perturbed cells into the VAE- GAN model, cell embeddings are produced. To visualize these embeddings, Principal Components Analysis (PCA) was employed. Fig. 5c provides a visual representation of the effects of repressing the ECM organization pathway across IPF stages 1, 2, and 3. In the Stage 1 perturbation, the
+
+<--- Page Split --->
+
+perturbed cell population, denoted as \(P_{1}\) , is observed to be closer to the Control stage C than to the stage 1 cells, \(S_{1}\) , and is notably distant from stage 3 cells, \(S_{3}\) . The distance in the PCA plot serves as a metric of similarity, indicating that \(P_{1}\) more closely resembles the Control stage C than \(S_{1}\) , suggesting a potential regression of the cellular state towards a healthier condition. This similarity is further emphasized by the thickness of connection lines between cell clusters, which represents the strength of the PAGA connectivity score. Specifically, the line \(L_{CP_{1}}\) is thicker than \(L_{CS_{1}}\) , indicating a higher similarity between the Control stage C and \(P_{1}\) in the latent space. In the Stage 2 perturbation, the perturbed cell population, \(P_{2}\) , gravitates towards \(S_{1}\) . Both PCA distance and PAGA connectivity scores suggest that a perturbation in Stage 2 could potentially guide cells towards a milder IPF cellular state. A similar trend is observed in Stage 3, where the perturbed cell population, \(P_{3}\) , shifts towards a relatively healthier cellular state.
+
+## UNAGI discovers novel drug candidates for IPF treatments
+
+UNAGI's in- silico drug perturbation approach, akin to its pathway perturbation, leverages and integrates the CMAP dataset. Hereby, UNAGI has pinpointed several drug candidates that could substantially impact the progression of IPF (Fig. 5d). Comprehensive results of all drug perturbations are detailed in Supplementary Table 4.
+
+Apicidin, with a score of 0.5021 and an FDR=4.551 \(\times 10^{- 105}\) , is a histone deacetylase inhibitor. Previous studies have highlighted its potential as an antifibrotic drug in pulmonary fibrosis80,81. Nifedipine, scoring 0.3834 with an \(\mathrm{FDR} = 1.152\times 10^{- 57}\) , has been shown to reduce bleomycin- induced pulmonary fibrosis by disrupting calcium signaling in fibroblasts78. Cilomilast, a phosphodiesterase 4 (PDE4) inhibitor, has a score of 0.3082 and an \(\mathrm{FDR} = 4.407\times 10^{- 35}\) . It has demonstrated potential in attenuating pulmonary fibrosis in mice82. Niguledipine, scoring 0.3842 and an \(\mathrm{FDR} = 6.160\times 10^{- 58}\) , is a calcium channel blocker and an \(\alpha 1\) adrenergic receptor antagonist, showing anti- fibrotic effects in the lung78. The compound 8- bromo- cGMP, which impacts PRKG1, has a score of 0.3099 and an \(\mathrm{FDR} = 1.562\times 10^{- 35}\) , and is associated with the TGF- beta pathways in the fibrosis process83.
+
+Moreover, drugs like Ibudilast (Score=0.3053, \(\mathrm{FDR} = 2.465\times 10^{- 34}\) ) and Topiramate (Score=0.3203, \(\mathrm{FDR} = 2.411\times 10^{- 38}\) ) have been identified, with the former potentially having anti- fibrotic effects similar to other PDE4 inhibitors84, and the latter regulating GRIA1, which is associated with lung fibrotic diseases61,79. Myricitrin (Score=0.2045, \(\mathrm{FDR} = 2.590\times 10^{- 13}\) ) has been shown to exhibit anti- fibrotic activity in certain conditions85, while Regorafenib (Score=0.1407, \(\mathrm{FDR} = 2.653\times 10^{- 5}\) ) attenuates fibrosis by inhibiting the TGF- beta pathway86. Notably, UNAGI also identified Nintedanib (Score=0.1102, \(\mathrm{FDR} = 0.0111\) ), an FDA- approved drug for IPF treatment.
+
+The target gene intervention of Nintedanib is shown in Fig. 5e. The corresponding perturbation results, visualized in Fig. 5f across IPF stages 1, 2, and 3, emphasize the potential of these drugs to shift cell populations towards healthier states. The consistently higher PAGA connectivity scores between perturbed cell populations and healthier cellular stages indicate that the perturbed cell populations are more akin to healthier cells.
+
+## Benchmarking and computational verifications
+
+To underscore the effectiveness of UNAGI in cell representation learning, we juxtaposed its capabilities against established methods like scVI15 and SCANPY12. scVI, a deep generative model rooted in VAE, employs the zero- inflated negative binomial (ZINB) distribution to capture the raw count distribution of single- cell data. On the other hand, SCANPY, a standard single- cell analysis pipeline, relies on PCA to encapsulate the high- dimensional single- cell data. Moreover, we performed ablation experiments to verify the effectiveness of individual computational module components of UNAGI. The UNAGI framework's VAE model is designed with the flexibility to select from various data distributions, such as Gaussian, NB (Negative Binomial), ZINB, and ZILN depending on the observed gene expression distribution in a given dataset. For the IPF snRNA- seq data analyzed in this study, the gene expression distribution aligns with a ZILN pattern. To showcase the benefits of adopting a proper data distribution to the cell embedding learning, the VAE model employing ZILN distribution served as the baseline model (BL), GAN and GCN were added to the BL model in our UNAGI framework. Contrasting with the ablation baseline, the full- fledged UNAGI framework integrates all the key components — the ZILN, GAN, and GCN — for the effective learning of cell embeddings. To ensure a balanced evaluation, we employed the Leiden clustering method on the embeddings generated by all seven techniques, adjusting parameters to produce a comparable number of clusters for each stage (UMAPs of all benchmarking methods are detailed in Supplementary Fig. 7). Five metrics were evaluated (Fig. 6a- e): For label metrics including Adjust Rand Index (ARI)87 and Nearest Mutual Information (NMI)88, UNAGI steadily outperforms SCANPY and scVI. For non- label metrics, the label score89 of UNAGI is at least 4% better than other methods,
+
+<--- Page Split --->
+
+
+Fig. 6 I UNAGI outperforms alternative approaches in learning the cell embeddings and can effectively identify efficacious drugs in in-silico perturbations. a, Adjusted Rand Index (ARI) and b, Normalized Mutual Information (NMI) illustrate the effectiveness of the learned cell embeddings for downstream clustering tasks. c, Label score, indicating that cells within neighborhoods primarily have the same cell type. d, Silhouette score. e, Davis-Bouldin index (DBI); a lower DBI signifies better clustering. These scores (c, d, e) are unsupervised metrics employed to demonstrate the clustering quality derived from the learned cell embeddings. f, Box plot presenting the silhouette scores of UNAGI across various training iterations, emphasizing that the iterative strategy progressively enhances cell embeddings and clustering quality with each iteration. g, PCA representation highlighting the impact of sanitary perturbation, which involves reversing the gene expression at Stage 1 back to the patterns observed in the control stage. This process essentially seeks to "normalize" or "sanitize" the aberrant gene expressions, bringing them in line with a control or reference state. h, Distribution patterns for various drug/compound perturbations. The x-axis represents the perturbation score, while the y-axis portrays the density of the fitted Gaussian distribution for each specific setting. i, AUROC and AUPRC metrics in relation to perturbation verification. As a reference, a random drug effectiveness predictor is used as a baseline, with an AUC (Area Under the Curve) score of 0.5, indicating no predictive discrimination, and an average precision (AP) score of 0.5, representing a baseline precision level.
+
+also suggesting a high homogeneity inside cell neighborhoods. With an average silhouette score nearing 0.205, UNAGI's clusters are more cohesive and distinct. The Davies- Bouldin Index (DBI), averaging at a lower 1.6, further attests to UNAGI's ability to produce clusters that are not only distinct but also internally homogeneous. Diving deeper, we explored the potential of the ZILN distribution to better model normalized single- cell data compared to the ZINB in this study. When scVI was adapted to this distribution, its performance surpassed its original ZINB- based counterpart in this dataset. This underscores the ZILN model's proficiency in capturing the nuanced continuous information inherent in normalized single- cell data, as opposed to the more discrete ZINB. The silhouette score presented in Fig. 6f effectively illustrates the benefits of iterative
+
+<--- Page Split --->
+
+
+Fig. 7 I The predictions of UNAGI align with human precision-cut lung slices (PCLS) drug validations. a, UMAP visualization of the PCLS data with each dot representing an individual cell. b, UMAP representation emphasizing the similarity between the real-world treatments of Nifedipine and Nintedanib. Furthermore, cells under in-silico drug treatments (Nifedipine and Nintedanib) closely mirror those under actual treatments. c, Violin plots showcasing that Nintedanib and Nifedipine treatments markedly shift fibrotic cells, bringing them closer in resemblance to healthy control cells. (e.g., \(D_{e}\) (Fibrosis, Nifedipine) is the distance between fibrosis cells and fibrosis cells after Nifedipine treatment). d, Violin plots highlighting the strong alignment between in-silico drug treatments and their real-world counterparts. e, The RRHO (Ranked Rank Hypergeometric Overlap) plots for both Nifedipine and Nintedanib. These plots juxtapose in-silico perturbations post-VAE reconstruction against actual treatments, emphasizing the high degree of similarity between in-silico and real treatments. Specifically, the genes up-regulated and down-regulated in in-silico treatments show strong correlations with those affected in real treatments. f, Box plots and \(R^2\) plots compare the expression of the top differential genes of real treatments (Nintedanib or Nifedipine vs. fibrosis) to in-silico perturbation results. The box plot visualizes the top 25 differential genes (ranked based on log fold changes) for each treatment. The gene expression of the top 100 differential genes in real and in-silico drug treatments are used to calculate the adjusted \(R^2\) metric and generate \(R^2\) plots. This representation is intended to underline the remarkable similarity observed between in-silico drug perturbations and the corresponding actual drug treatments for both Nifedipine and Nintedanib. g, Box plots and \(R^2\) plots of ECM organization target gene expressions from real treatments and in-silico perturbations. The box plots visualize the top 15 genes of ECM based on log fold changes between real treatments and fibrosis cells. The gene expressions of all ECM organization target genes in real and in-silico drug treatments are used to calculate the adjusted \(R^2\) metric and generate \(R^2\) plots.
+
+optimization (additional metrics refer to Supplementary Fig. 8). This result underscores the importance of the iterative training approach, which fosters a synergistic relationship between cell- embedding learning and the
+
+<--- Page Split --->
+
+inference of cellular dynamics. Such an approach not only markedly enhances the method's performance over successive iterations but also demonstrates that disease- sensitive cell representation learning is instrumental in achieving improved cell clustering and potentially enhancing other downstream tasks.
+
+To rigorously evaluate the proficiency of UNAGI's in- silico perturbations, we embarked on a Stage 1 sanity perturbation, wherein the perturbations were aimed at redirecting them back to control levels (refer to methods for an in- depth explanation). Cells subjected to sanity perturbation overwhelmingly align with the control stage as opposed to their native Stage 1 state (Fig. 6g). Reinforcing this trend, the PAGA connectivity scores indicate that these perturbed cells bear a high resemblance to Control cells, and they substantially deviate from Stage 3 cells. These observations strongly vouch for UNAGI's unmatched precision and efficacy in handling in- silico perturbations. In addition, we delved deeper into assessing UNAGI's aptitude for identifying potent drug candidates using in- silico methodologies. The insights, presented in Fig. 6h, underscore the salience of this tool: in- silico drug perturbations, particularly those with significant FDR values, consistently surpassed the therapeutic scores of random perturbations as expected. Impressively, these results were congruent with the outcomes from sanity drug perturbations, during which we intentionally tweaked target gene expressions to reflect that of an adjacent, healthier stage. This robust alignment unequivocally attests to UNAGI's exceptional ability to single out drugs with a high potential to combat IPF.
+
+To further stress- test UNAGI's capabilities, especially its prowess in drug repurposing, we set forth a meticulously planned simulation. This simulation was designed to test UNAGI's ability to accurately identify and replicate the effects of known drugs, referred to as 'ground- truth' drugs in our in- silico drug discovery simulation (as detailed in the Methods section). Our approach involved a strategic implantation of drugs within the simulation. We did this by altering the target gene expressions of these drugs at specific magnitudes across various disease stages, thereby establishing a set of ground truths. These modified gene expression levels were intended to mimic the real- world effects of the drugs at different stages of disease progression. Next, we applied the UNAGI to the simulated dataset (with ground truth) to predict the drugs that act against the simulated gene expression changes and examine whether the model can recapture the implanted drugs in the simulation data. The performance of UNAGI in this simulation was rigorously evaluated using two established metrics: the Area Under the Receiver Operating Characteristic Curve (AUROC) and the Area Under the Precision- Recall Curve (AUPRC). UNAGI achieves scores of 0.89 and 0.93, respectively (Fig. 6i). These high scores indicate that UNAGI is highly effective at identifying drugs that target genes with dynamic regulation during disease progression.
+
+## Experimental validation of in-silico drug perturbations via precision-cut lung slices.
+
+To experimentally validate UNAGI predictions, we utilized the fibrotic cocktail model of PCLS90. We chose to test the model predictions for Nifedipine, an antihypertensive drug not known to have a role in fibrosis treatment, and Nintedanib, an FDA- approved drug for IPF. We stimulated PCLS with DMSO as the Control for 5 days. In the treatment group, PCLS were treated for 3 days with the fibrotic cocktail to induce fibrosis, and treatment, Nifedipine or Nintedanib, started from day 3 until day 5. As read- out, we performed snRNA sequencing (Fig. 7). Latent embeddings of fibroblasts derived from this PCLS experiment reveal intriguing patterns (Fig. 7a). When assessed based on experimental conditions, cells under both Nifedipine and Nintedanib treatments exhibit similar clustering behaviors on the UMAP. This suggests their parallel roles in inhibiting fibroblast activation.
+
+Utilizing UNAGI's perturbation module, Nintedanib and Nifedipine in- silico perturbed cells gravitate towards the Nintedanib treated population, demonstrating potential therapeutic effects (Fig. 7b). Pairwise Euclidean distances between latent embeddings indicate that both treatments effectively steer the cellular state of fibrosis cells toward a healthier baseline (Fig. 7c) and the in- silico treatments behave like real treatments (Fig. 7d). This observation is solidified by the Mann- Whitney U test confirming the analogous anti- fibrotic properties of both treatments. The Ranked Rank Hypergeometric Overlap (RRHO) confirms that the markers identified in- silico align closely with the biomarkers observed in the PCLS experiments (Fig. 7e). The adjusted \(R^2\) scores for Nintedanib in- silico (0.906) and Nifedipine in- silico (0.932) with respect to the top 100 differentially expressed genes (DEGs) in actual treatment versus fibrosis, as well as the top 25 markers in side- by- side comparisons (Fig. 7f, top 100 DEGs comparisons are detailed in Supplementary Fig. 9), demonstrate the consistency of gene expression patterns between in- silico and real treatments markers. Known IPF markers like IL3391, ADAM1292, and CXCL893 exhibit similar changes in gene expression in both real treatment experiments and in- silico predictions. (Fig. 7g, all ECM organization pathway genes comparisons are listed in Supplementary Fig. 10). The \(R^2\) scores and side- by- side comparisons of real treatments and in- silico gene expression of the ECM organization pathway further validate the capability of the UNAGI model to accurately
+
+<--- Page Split --->
+
+simulate in-silico perturbations on IPF-related targets. The alignment between in-silico drug perturbations and actual drug treatments on the PCLS stands as a testament to the reliability of UNAGI's predictions.
+
+## UNAGI in-silico analysis unveils COVID-19 cellular dynamics and therapeutic opportunities
+
+To demonstrate the expansive applicability of UNAGI to various complex diseases, we studied the intricate dynamics of COVID- 19. We used a subset of a COVID- 19 dataset94 consisting of 246,948 peripheral blood mononuclear cells from 130 samples with various severities of COVID- 19. We categorized them into four COVID- 19 stages based on the disease severity of patients: Healthy (Control, or stage 0), Asymptomatic or Mild (stage 1), Moderate (stage 2), and Severe or Critical (stage 3). The UNAGI pipeline is applied to the COVID- 19 dataset to reveal the temporal dynamics and discover potential therapeutic targets.
+
+
+
+Fig. 8 | UNAGI in-silico analysis unveils COVID-19 cellular dynamics and therapeutic opportunities. a, UMAP display of stage 2 COVID-19 data with each dot symbolizing an individual cell. Cells are color-coded based on their respective cell types. b, Dot plot illustrating the expression levels of canonical cell type markers present within the stage 2 COVID-19 data set. c, Dynamic graphs representing the cellular dynamics underlying the COVID-19 progression. Within these graphs, each node corresponds to a cell cluster, and the connecting edges signify the relationships between these nodes (shift of the cell population along with COVID-19 progression). d, Depiction of the reconstructed gene regulatory network for the track 12-CD16. Prominent gene regulators, genes, and pathways discerned from the enrichment analysis are enumerated. e, Bar chart detailing the principal pathway perturbation outcomes. Pathways highlighted have literature support, indicating their potential as therapeutic targets against COVID-19. f, Bar chart outlining the top 10 drug perturbation results. Drugs that are emphasized have been highlighted based on literature support, suggesting their candidacy for treating COVID-19.
+
+After learning the latent cell representations (Supplementary Fig. 11), UNAGI identified 14 unique cell populations at stage 2 (Fig. 8a), spotlighting nuanced interactions such as between platelet and T- cells, a finding resonating with the previous research94. Here, UNAGI can elucidate unique markers for cell populations, such as MS4A1 and CD79A in B cells, and underscore differential expressions, notably CD8A and CD8B, in CD8 T cells—findings that harmonize with manual annotations (Fig. 8b).
+
+<--- Page Split --->
+
+Focusing on the cellular dynamics across the trajectory of COVID- 19, UNAGI identified 7 distinctive tracks reflecting the evolving cellular interplay across the disease stages (Fig. 8c). Fig. 8d deepens the narrative, spotlighting pivotal genes central to the COVID- 19's progression of CD16+ Monocytes, like BHLHE40 which finds an up- regulation in moderate patients95, and EGR1, recognized for influencing SARS- CoV- 2 replication and antiviral responses96. Notably, genes like GRN97 and PLAC898 emerge as notably up- regulated in COVID- 19. Gene enrichment analyses further discern crucial pathways tied to the disease such as interferon signaling and immune system pathways99- 101. Transitioning to predictive capabilities, UNAGI identified potential therapeutic pathways such as the RHO GTPases Activate NADPH Oxidases pathway aligns with modern findings emphasizing its substantial role in COVID- 19102,103 (Fig. 8e). A deep dive into pathways related to Toll- Like Receptors and interferon responses104 further broadens the therapeutic landscape.
+
+In culmination, Figure 8f accentuates UNAGI's expertise in drug recommendation. Aloxistatin stands out, achieving the highest drug perturbation scores and drawing attention due to its potential against SARS- CoV- 2 proteases105. Additionally, Didanosine, notable for its efficacy against COVID- 19 Polymerase and Exonuclease106, and Ponatinib, are recognized as potent COVID- 19 drugs by other machine learning methods107. This detailed alignment with ongoing research105- 109 not only emphasizes UNAGI's precision but heralds its indispensable role in crafting therapeutic strategies for multifaceted diseases.
+
+## Discussion
+
+In this manuscript, we describe UNAGI, a computational tool designed to model the temporal cellular dynamics inherent in complex disease progression. Rooted in its design is the use of a Gaussian Mixture Model- based density estimator, which classifies samples into specific disease stages. Harnessing the power of the graph VAE- GAN model, UNAGI handles high- dimensional single- cell data to extract latent embeddings. These embeddings play a crucial role in formulating progression tracks for distinct cell populations, subsequently facilitating the detailed reconstruction of temporal gene regulatory networks. The implementation of UNAGI to differentially affected tissues in IPF allows high- resolution modeling of the cellular trajectories, pivotal gene regulators, and genes that drive or associate with progressive tissue fibrosis in the human lung. Through iterative training, UNAGI sharpens the focus on IPF- specific features, priming itself for simulating and evaluating perturbations on potential target genes and drugs. The fruits of this methodical approach are manifold: UNAGI not only delivers an in- depth understanding of cellular dynamics and the foundational cell- specific gene regulatory networks during the progression of fibrosis but also pinpoints potential therapeutic pathways and drugs against IPF, marking the potential of UNAGI in modeling disease and developing novel therapeutics.
+
+UNAGI offers a suite of characteristics that distinguish it in the domain of disease comprehension and therapeutic discovery. First and foremost, UNAGI distinguishes itself by its proficiency in creating precise cell embeddings and synthesizing cells via a deep generative neural network. This precision in embeddings enables enhanced cell clustering and identification, surpassing existing methods primarily focused on general cell representation learning. Different from other existing methods, UNAGI's approach involves learning and incorporating key genes, including dynamic markers and gene regulators, that are integral to the specific disease progression. This results in disease- oriented cell embeddings that are finely tuned for diverse downstream tasks related to the disease. Additionally, UNAGI's capability to artificially generate cells from the learned latent space is leveraged to conduct in- silico perturbations. This feature adds a dynamic aspect to disease modeling, allowing for more comprehensive and nuanced exploration of disease mechanisms and potential treatments. Third, UNAGI excels in unraveling the intricate cellular dynamics associated with the progression of a disease. Utilizing the cell embeddings it generates, UNAGI employs a graphical methodology to construct a 'cellular dynamics tree'. This tree effectively maps out the transitions of various cell states and populations as the disease advances. Crucially, UNAGI goes a step further by identifying the underlying gene regulatory network that governs these cellular dynamics, thereby highlighting potential biomarkers and therapeutic targets. In addition, UNAGI's sophisticated analysis enables the comprehensive identification of dynamic markers that track the evolution of the disease, as well as hierarchical static markers that differentiate between distinct cell populations. This dual approach provides a detailed understanding of the cellular heterogeneity at different stages of the disease and its transformation throughout its progression, offering valuable insights into the disease's biology and potential intervention points. Fourth, a standout feature of UNAGI, setting it apart from existing methods, is its ability to perform unsupervised in- silico analysis of pathways and drug perturbations. This aspect of UNAGI allows for the exploration and identification of promising therapeutic pathways and potential drug candidates without the need for pre- existing drug perturbation training datasets, which are often challenging to acquire. This capability provides users with a powerful tool to investigate, evaluate, and prioritize therapeutic options associated with different pathway
+
+<--- Page Split --->
+
+alterations or drug interventions. As a result, UNAGI uncovers a wealth of potential therapeutic strategies and promising drug candidates. Its unsupervised nature substantially enhances the method's applicability and practicality across a variety of complex diseases, offering an advantage over many current drug perturbation approaches that rely on supervised learning and extensive training sets. Lastly, to democratize access to its innovations, we've launched the UNAGI web server, an interactive framework that brings cellular dynamics to life and facilitates in- silico perturbation functions, streamlining the exploration of disease dynamics and potential therapeutic interventions.
+
+As described UNAGI has led to many biological observations, first by allowing us to uncover in an unbiased manner the trajectories that mesenchymal cells undergo during the progression of fibrosis. One notable observation is the marked proliferation of fibroblast cells, which correlates with the extensive accumulation of fibrosis, a defining characteristic of IPF progression. This proliferation underscores the fibroblasts' central role in the disease's pathology. Moreover, we noted that adventitial and alveolar cells exhibit dynamic and active involvement in IPF development. Conversely, the proportion of vascular endothelial cells consistently decreased as IPF progressed. Second, it allows identifying the cell- specific gene regulators that drive the phenotypic changes during disease progressions such as gene regulators like CTCF, EP300, and SMC3 and their target genes, identified dynamic markers such as COL1A1, COL1A2, COL1A3, and COL14A1, which were validated by proteomics analysis, and suggested hierarchical static markers for sub- cell types, including NLGN1 and MFAP5 for fibroblast adventitial cells. These discoveries enrich our understanding of IPF and could lead to the identification of novel biomarkers and more precise therapies. Finally, UNAGI also illuminates potential IPF pathways that could be targeted for therapeutic interventions like Netrin- 1 signaling and Signaling by ROBO receptors, as well as drugs that may reverse these pathways. Impressively, we were able to validate our model's predictions regarding drugs like nifedipine, previously not considered an antibiotic, and potentially identify marker genes that could be used in the future as biomarkers for target engagement and efficacy. Moreover, UNAGI extends its utility to other complex diseases, such as COVID- 19, with several of its top drug predictions corroborated as repurposed medications for COVID- 19, including Aloxistatin and Didanosine, highlighting its broad potential in biomedical research.
+
+Despite its array of abilities, it's imperative to recognize UNAGI's limitations, especially its dependency on the CMAP database for in- silico drug perturbation. The CMAP database, though invaluable, has its set of challenges. It doesn't encompass all potential drugs and compounds, thereby narrowing UNAGI's drug discovery horizon. Additionally, the impact of numerous drug perturbations on a variety of cell types within CMAP remains either inadequately explored or ambiguous. Furthermore, the database may not consistently offer drug perturbation profiles tailored to the lung or other pertinent cell types, a critical aspect for diseases like IPF. Incorporating a more detailed and expansive drug perturbation or drug target database could amplify UNAGI's prowess in in- silico drug perturbation.
+
+In summary, UNAGI is an AI- based computational tool that can be used to uncover distinct cellular trajectories during human disease progression, using distinct disease stages or severities or real- time course data, address regulatory and perturbation shifts that drive their phenotypes, and allow computational predictions of drugs that will reverse these shifts. We demonstrate its performance in a unique dataset of differentially affected tissues from patients with IPF, providing detailed observation, proteomic and experimental validations as well as relevance to another disease - COVID- 19. We believe that the wide availability of UNAGI will enhance our understanding of complex diseases and accelerate the development of novel therapeutic strategies through the repositioning of known compounds, as well as the modeling of the effects of novel compounds.
+
+## Methods
+
+## Dataset description and preprocessing
+
+The snRNA- seq IPF datasets were collected from a total of 19 individuals, comprising 10 healthy donors and 9 IPF patients. Recognizing that different regions of the lung may be at varying stages of disease progression, we utilized cells isolated from these distinct regions within the IPF lung to model the temporal progression of IPF. Altogether, the dataset consists of 30 samples from control subjects and 24 samples from IPF patients. After sequencing, raw fastq files were trimmed with cutadapt110 (version 1.17) to remove read2 contamination of 5- prime template switch oligo and 3- prime polyadenylated tails; read pairs were discarded if read2 was trimmed below 30 bases. Trimmed reads were mapped to GRCh38 annotated with GENCODE111 (release 37) with the STARsolo112 implementation of STAR (v2.7.6a); the barcode whitelist file and barcode length parameters were based on the manufacturer's (10X Genomics) guidelines for 3- prime v3.1 scRNAseq assays. Transcript count information was taken from STAR's unfiltered 'GeneFull' output, all barcodes with at least 300
+
+<--- Page Split --->
+
+transcripts were imported into R (v 4.0.5) alongside statistics for each barcode's percent of transcripts spliced, unspliced, or ambiguous from STAR's 'velocyt' output. Cell barcode cleaning and cell type annotation were performed with tools from the R package Seurat (v4.1.1). To conduct an independent and manual cell type annotation, each sample of data was subjected to an iterative and recursive process of dimension reduction, graph embedding, and cluster analysis. After each iteration, the cell type labelling is refined, spurious nuclei are removed, and a subset of relatively similar cell types is isolated for the next iteration. This process was repeated recursively until all spurious nuclei were removed and new cell subpopulations could no longer be resolved. After each sample was cleaned and annotated, all samples were combined. Seurat's reciprocal PCA integration method was used to adjust for batch effects at the cDNA library level. The gene expression results generated from integration were used for a final iteration of UMAP embedding and clustering. Final cell type assignments (the 'Ground Truth' column in Supplementary Fig 2) were determined by evaluating the true (not integrated) gene expression marker signatures of a cluster and confirming that the pattern was consistent across each sample. Following the preprocessing, we adopted the mesenchymal cell line which encompassed 231,544 cells to validate the UNAGI method. Please note that all subsequent analyses using the deep generative model solely utilize the normalized cell-by-gene matrix obtained from this preprocessing step. These analyses are augmented with manual cell type annotations performed independently via the Seurat pipeline, as detailed in this subsection. Crucially, all cell embeddings and clustering results presented in this manuscript were produced using our deep generative neural network framework, not the Seurat pipeline. The role of the Seurat framework was strictly confined to data preprocessing.
+
+## Gaussian mixture density estimator
+
+The Gaussian Mixture Model (GMM) clustering method \(^{113}\) leverages multivariate Gaussian components to characterize various stages of IPF samples. This approach aims to categorize samples into discrete stages of the disease, optimizing the probability or density representation of these stages. In this study, the GMM clustering approach is founded on the concept of surface density, serving as a measure of the extent of fibrosis. We assume that the surface density of all samples is independently and identically distributed, represented as \(S_{density} = \{s_1, s_2, \ldots , s_n\}\) , where \(n\) is the total number of samples. The GMM is fitted to the data to identify optimal components that maximize the log- likelihood: \(P(S_{density}|\mu_{1,\ldots ,c}, \sigma_{1,\ldots ,c}) = \sum_{i} \log N(S_{density}|\mu_{i}, \sigma_{i})\) . Here, \(N\) represents the Gaussian density function of the GMM for each sample, and \(c\) is the total number of Gaussian components, each characterized by a mean \(\mu_{i}\) and standard deviation \(\sigma_{i}\) . After identifying the optimal components, the samples \(S\) and their corresponding cells are softly classified into different stages, constructing the dataset \(X = X_{1}, \ldots , X_{T}\) where each \(X \in R^{m_{T} \times n}\) . Here, \(T\) refers to the number of IPF stages, and each stage has \(m_{T}\) cells with \(n\) genes.
+
+## Graph Variational Autoencoder-Generative Adversarial Networks (Graph VAE-GAN)
+
+Our UNAGI method introduces a Graph VAE- GAN model. To leverage cellular neighbors to diminish the effects of dropouts and noise \(^{114}\) , we stacked a cell graph convolution (GCN) layer on top of VAE. A graph convolution layer is a specialized type of neural network that is can capture the topological structure of data, particularly by identifying features within local neighborhoods. GCN aggregates cell- cell relationships to construct a graph \((V, E)\) , where \(V\) denotes the vertices (cells) and \(E\) represents the edges (connections between cells). To establish this graph, the K- nearest neighbors (KNN) algorithm is employed to build the connectivity matrix \(A\) which defines the similarity between cells. The graph convolution is defined as \(f_{GCN}(X, A) = \alpha (AXW^{GCN})\) , where \(W^{GCN}\) refers to the trainable weights of the GCN layer, and \(\alpha\) is the activation function. Importantly, cells from different disease stages are not connected in the connectivity graph \(A\) , maintaining a stage- specific cell graph convolution.
+
+UNAGI employs a VAE- based deep learning model \(^{24}\) to model the cellular dynamics behind complex disease progression and simulate the drug perturbations. The VAE's encoder- decoder structure can model the probability distribution of high- dimensional data in a lower- dimensional space and generating new samples from this reduced- dimensional distribution. As a variational method, it facilitates the in- silico perturbation of cells by modulating their gene expressions. To refine the generative ability of VAE, we follow the previous method \(^{116}\) to use GAN to guide the generation of VAE with the min- max training strategy \(^{115}\) . The encoder of the Graph VAE- GAN, \(E_{\theta}: R^{n} \to R^{l}\) consists of a GCN layer and several multi- layer perceptrons (MLPs). It can transform a cell \(x_{i} \in R^{m}\) to its corresponding \(l\) - dimensional latent vector \(z_{i}\) . The GCN layer takes the normalized cell- by- gene count matrix \(X\) and connectivity matrix \(A\) , generating a graph representation \(f_{GCN}(X, A) = \alpha (AXW^{GCN})\) where \(W^{GCN}\) is weights of the GCN layer. Acknowledging that the latent distribution of single- cell data follows a multivariate normal distribution, two MLPs are employed to determine the means vectors \(\mu_{z} = f_{\mu_{\theta}}(\mu_{z}|f_{GCN}(X, A))\) and standard deviation vectors \(\sigma_{z} = f_{\sigma_{\theta}}(\sigma_{z}|f_{GCN}(X, A))\) of the latent representation. The latent representation for a cell is represented as \(z \sim \mathcal{N}(\mu_{z}, \sigma_{z}^{2})\) and the approximated posterior distribution is represented as \(q_{\theta}(Z|X, A)\) .
+
+<--- Page Split --->
+
+The decoder \(p_{\phi}:R^{l}\to R^{3n}\) takes \(Z\) as input to reconstruct the cell-by-gene count matrix. We employ the ZILN distribution to model the gene expression. The ZILN model is a composite distribution that integrates two distinct distributions: the first part is a Bernoulli distribution, Bernoulli \((\rho)\) , which accounts for the dropout events commonly observed in single-cell sequencing. The second component of the ZILN model captures the actual gene expression levels following a log transformation, represented by \(\log \mathcal{N}(\mu ,\sigma^{2})\) . The likelihood function of a reconstructed cell \(x\in X\) can be written as:
+
+\[p_{\phi}(x|z) = \prod_{j\in g e n e s}Z I L N(x_{j}|\rho_{j},\mu_{j},\sigma_{j}^{2}) = \rho_{j}\delta_{0}(x_{j}) + (1 - \rho_{j})L N(x_{j}|\mu_{j},\sigma_{j}^{2}) \quad (1)\]
+
+\[L N(x_{j}|\mu_{j},\sigma_{j}^{2}) = \left\{ \begin{array}{l l}{\frac{1}{x_{j}\sigma_{j}\sqrt{2\pi}} e^{-\frac{-\left(\ln x_{j} - \mu_{j}\right)^{2}}{2\sigma_{j}^{2}}},} & {i f x_{j} > 0}\\ {0,} & {i f x_{j} = 0} \end{array} \right. \quad (2)\]
+
+\[\delta_{0}(x_{j}) = \left\{ \begin{array}{l l}{1,i f x_{j} = 0}\\ {0,i f x_{j}\neq 0} \end{array} \right. \quad (3)\]
+
+To reconstruct the cell- by- gene matrix \(X\) , the decoder \(p_{\phi}\) will learn parameters of the ZILN distribution including the zero- inflation probability \(\rho = f_{\rho_{\phi}}(\rho |Z)\) , scale of the log- normal distribution \(\sigma\) for each gene (a vector of learnable parameters), and mean \(\mu\) of the log- normal distribution, denoted as \(\mu = f_{\mu_{\phi}}(\mu |Z,\sigma)\) . The prior distribution \(p(Z)\) is a multivariate standard normal distribution. Within our framework, we designate the entire Graph VAE model as the generator \(G\) . The loss function of the generator \(L_{G}\) can be formulated as:
+
+\[L_{G} = L(\theta ,\phi ,X,A) = KL(q_{\theta}(Z|X,A)||p(Z)) - E_{q_{\theta}(Z|X,A)}[\log p_{\phi}(X|Z)] \quad (4)\]
+
+The first term of \(L_{G}\) is the Kullback- Leibler divergences (KL), which quantifies the difference between the latent representation \(q_{\theta}(Z|X,A)\) learned by the encoder and the predefined prior distribution \(p(Z)\) . The second term is the expected log- likelihood of the input data given the reconstruction generated by the decoder, acting as a reconstruction loss. Together, \(L_{G}\) promotes the model's generative performance with the probabilistic constraints of the latent space.
+
+To further refine the generative capabilities of the Graph VAE, an adversarial discriminator is incorporated into the model's architecture. This discriminator is a classifier based on MLPs to distinguish between original cells \(X\) and the reconstructed cells \(G(X,A)\) generated by the Graph VAE. A min- max adversarial training strategy is then applied, aimed at optimizing the loss function \(L_{GAN}\) .
+
+\[L_{GAN} = L(X,A) = \min_{G}\max_{D}\mathbb{E}_{X}[\log (D(X))] + \mathbb{E}_{X}\left[1 - \log \left(D(G(X,A))\right)\right] \quad (5)\]
+
+Here, \(D\) is the adversarial discriminator, \(G\) is the generator (Graph VAE). During the training phase, cells are labelled as real or fake (produced by the generator for the purpose of adversarial training). The discriminator, \(D\) , is optimized to effectively distinguish between real and fake cell labels, aiming to maximize the probability of correctly identifying real and generated cells. Simultaneously, the second term of \(L_{GAN}\) incentivizes the generation of cell reconstructions that are highly similar to the original data that \(D\) cannot distinguish them from real cells. The overall loss function of UNAGI denoted as \(L\) , is a composite of the Graph VAE loss and the GAN, written as \(L = L_{G} + L_{GAN}\) . By integrating these components, UNAGI harnesses the strengths of various architectures, the GCN can leverage the cell- cell relationship information, the VAE can model the complex single- cell data, and the GAN can refine the quality of cell generation.
+
+## Dynamics graph and underlying gene regulatory networks inference
+
+UNAGI builds a dynamic graph to illustrate the progression of each cell population (cell type or subtypes) throughout disease progression. We apply Leiden clustering117 on the latent embeddings, generated by Graph VAE- GAN, to identify distinct cell populations at each disease stage. To measure distances between cell populations in adjacent stages, we use the KL divergence rather than Euclidean distance, which can be problematic in high- dimensional data contexts118,119. For each cell population (e.g., cell type), we approximate its distribution using a Monte Carlo Sampling strategy120 involving the sampling of each dimension of the latent embeddings a thousand times to form a multivariate normal distribution. The KL divergence is calculated to measure the distance between these populations' multivariate normal distributions.
+
+Additionally, we identify the top 100 differentially expressed genes (DEGs) in each cell population. We then calculate DEG distances among cell populations across stages. The DEG distance is defined as \(T_{d}(DEG_{c1},DEG_{c2}) * \Sigma_{j\in DEG_{c1}}|R_{j}^{c1} - R_{j}^{c2}|\) , where the first term is the Jaccard Distance between \(DEG_{c1}\) and \(DEG_{c2}\) , DEGs of two cell populations. The second term considers the ranking difference between two DEG lists. Here, \(R_{j}^{c1}\) and \(R_{j}^{c2}\) represent the ranking of gene \(j\) in \(DEG_{c1}\) and \(DEG_{c2}\) , respectively. To render the KL
+
+<--- Page Split --->
+
+divergence and the distances of differentially expressed genes (DEGs) comparable, we implemented min- max normalization for each metric across all potential connections within a specific cluster. After normalization, we represented the distances between each cluster pair as the sum of the normalized KL divergence and the normalized DEGs distances. We then compiled these normalized distances for all possible connections across various disease stages to create a background distance distribution. This distribution is essential for assessing the statistical significance of connections between clusters throughout the different stages of the disease. In scenarios where a cluster is connected to more than one cluster in an adjacent stage, the most statistically significant one will be used. These significant connections form tracks that trace from the control stage to the final stage of the disease, defining the disease progression. Consequently, the dynamic graph \(G_{dynamic}\) produced includes these progression tracks, each representing comprehensive cellular state transition associated with a specific cell population during disease progression.
+
+Moreover, we employ iDREM (Interactive Dynamic Regulatory Events Miner)121, a machine learning model based on an Input- Output Hidden Markov Model, to reconstruct the temporal gene regulatory network underlying each track (i.e., associated with each cell population) in the reconstructed cellular dynamics graph \(G_{dynamic}\) . This gene regulatory network consists of co- expressed genes and gene regulators that regulate the temporal progression of the disease within each cell population. For each track in \(G_{dynamic}\) , iDREM identifies the genes that undergo similar expression change patterns throughout the disease progression, which was termed as gene paths, some with increasing expression patterns while others with decreasing patterns. For each of the identified co- expressed gene paths, iDREM also provides its enriched GO terms and pathways. Beyond the identification of co- expressed gene paths, iDREM also captures the gene regulators that modulate those gene paths during disease progression. The dynamic genes and gene regulators identified through this process are considered dynamic marker candidates and hold potential as therapeutic targets for the disease.
+
+## Iterative training strategy of UNAGI
+
+The training strategy for UNAGI is structured as an iterative process, consisting of two primary phases that are cyclically repeated: (1) learning cell embeddings using the VAE- GAN framework, (2) constructing a cellular dynamics graph, and identifying substantial genes and gene regulators. Initially, with the cell embeddings learned with equal importance of all genes, we will employ the dynamics graph module to reconstruct the cellular dynamics and identify critical genes that influence disease progression, employing the iDREM algorithm. Based on this identification, UNAGI establishes and updates a gene- weights table for each cell. This table quantifies the importance of each gene and gene regulator, reflecting their roles in disease progression. As the training progresses through each iteration, dynamic marker genes and gene regulators that are deemed important in the reconstructed gene regulatory network are assigned increased weights. In contrast, genes not identified as critical or as gene regulators undergo a systematic decay in importance—specifically, a \(30\%\) decrement in weight with each iteration. This approach guarantees that genes consistently identified as critical in disease progression across various iterations receive progressively higher weights. Conversely, genes that are only occasionally deemed important will gradually lose prominence and be systematically deprioritized. Next, in the cell embedding learning of the subsequent iteration, the VAE model undergoes fine- tuning with a modified loss function that accentuates the high- weight genes. This enhancement is accomplished by integrating the gene weights in all cells into the reconstruction loss function, thereby shifting the model's focus from generic genes to those disease- associated genes identified through gene regulatory network inference. During each iteration, after the cell embeddings are updated, the cellular dynamics module steps in to rebuild the cellular dynamics graph and the associated gene regulatory networks. This stage plays a crucial role in refining and updating the disease- associated genes. These enhancements feed back into and improve the cell embedding learning in the next iteration. On the other hand, the revised cell embeddings generate an updated cellular dynamics graph and its gene regulatory network, offering a deeper understanding of disease progression and potentially advancing the identification of disease- specific genes, which will in return improve the cell embedding learning in the next iteration.
+
+Upon model convergence, the highest- weighted genes are associated with the disease and thus indicating that UNAGI model can indeed 'comprehend' the disease and recognize important disease- relevant genes during the iterative training. For instance, enrichment analysis shows that the top 100 weighted genes in fibrotic fibroblast cells are closely associated with IPF (Supplementary Fig. 12). At each training iteration \(t\) , the gene weights are transformed into a ranking matrix, \(R^t\) . The objective functions of UNAGI during its iterative training can be then refined as follows to integrate the distilled disease knowledge in the gene- weights table for each cell:
+
+\[L_{G}^{t} = L(\theta^{t},\phi^{t},X,A) = KL\left(q_{\theta^{t}}(Z|X,A)||p(Z)\right) - \mathbb{E}_{q_{\theta^{t}}(Z|X,A)}\left[\log p_{\phi^{t}}(X|Z)\cdot \frac{1}{(R^{t})^{\tau}}\right] \quad (6)\]
+
+<--- Page Split --->
+
+\[L_{GAN}^{t} = L(X,A) = \min_{G^{t}}\max_{D^{t}}\mathbb{E}_{X}\left[\log (D^{t}(X))\right] + \mathbb{E}_{X}\left[1 - \log \left(D^{t}(G^{t}(X,A))\right)\right] \quad (7)\]
+
+Here, \(G^{t}\) represents the generator at the \(t\) - th iteration, and \(D^{t}\) is the discriminator at the same iteration. \(L_{G}^{t}\) denotes the loss of generator, and \(L_{GAN}^{t}\) denotes the loss of GAN at the \(t\) - th iteration and \(\tau\) is a hyperparameter which is responsible for controlling the influence of gene weights on the reconstruction loss (empirically set \(\tau\) as 0.5). Through this iterative training, UNAGI progressively hones its ability to generate disease- specific cell embeddings. This approach allows for the identification of disease- specific markers and supports disease- specific in- silico perturbations.
+
+## Dynamic markers discovery
+
+To characterize the temporal progression of the disease for each cell population, we identify dynamic markers. They are genes that change considerably throughout the disease's progression. For each track in the cellular dynamics graph, iDREM identifies the gene paths with co- expression patterns during disease progression as discussed above. Next, we computed the sum of fold changes for each gene in each of the gene paths across all disease stages associated with each cell dynamic track (i.e., a cell type or subtype). Genes in those identified gene paths were considered as candidate dynamic biomarkers for further statistical examinations. To calculate the statistical significance of the candidate markers, we randomly shuffle cells within each stage of the track to generate the background simulation tracks. We then calculate the accumulated foldchanges among all neighboring stages of these candidate markers across all simulation tracks. This simulation process was repeated \(N\) times \((N > 1000)\) to establish a random background foldchange distribution. We then evaluated the P- values for each candidate marker based on its accumulated sum fold change against this background distribution. To ensure a high level of confidence in our selection of dynamic markers, we imposed a more stringent FDR cut- off \((\mathrm{FDR}< 0.01)\) than the default (FDR \(< 0.05\) ). These selected dynamic markers are pivotal in delineating the progression tracks and provide a nuanced understanding of the longitudinal evolution of the disease within each distinct cell population.
+
+## Hierarchical static markers discovery
+
+The hierarchical static marker discovery approach supports the identification of intra- stage static markers through hierarchical clustering. UNAGI conducts hierarchical clustering based on the embeddings of cell populations at each disease stage, thereby generating dendrograms to depict the relationships among these populations. Initially, we identify distinct cell populations using their latent embeddings \(Z\) . Hierarchical clustering is then applied to these embeddings to construct a dendrogram for the cell populations within the same disease stage. This dendrogram serves as a tool to explore the hierarchical structure of cell populations. In this dendrogram, when focusing on a particular cluster, we analyze it at various levels to identify hierarchical static markers. At lower levels of the dendrogram, the selected cluster compares with a broader range of sibling clusters. Here, the hierarchical static markers identified tend to represent general features of the cell population, as the siblings encompass a wider scope. For instance, at level 0, the selected cluster is compared against all other clusters within that stage. Conversely, at higher dendrogram levels, the siblings are more closely related to the selected cluster. This closeness allows for the identification of markers that highlight the subtle heterogeneities among cell subpopulations within the same cell type. By examining these nuanced differences, we can gain a deeper understanding of the cell subpopulation's characteristics.
+
+## In-silico perturbation strategies
+
+In- silico perturbation can be executed through two strategies: (1) Direct gene expression regulation. This approach involves the direct up- regulation or down- regulation of specific genes of interest. For a cluster of cells, we define an expression regulation vector \(\Delta = [\Delta_{g1}, \Delta_{g2}, \dots , \Delta_{gn}]\) , where each \(\Delta_{gn}\) represents the expression change of gene \(gn\) (e.g. \(\Delta_{g1} = 0.5\) would indicate an increase in the expression of gene \(g1\) by 0.5). The gene expression for a perturbed cell population \(X'_{c}\) can be defined as:
+
+\[X^{\prime}_{c} = \max \left(X_{c} + \mathbf{1}_{M_{c}}\Delta ,0\right) \quad (9)\]
+
+Here, \(X_{c}\) represents the original cell- by- gene matrix of a cell population \(c\) , and \(M_{c}\) represents the number of cells within the cell population. (2) Gene Interaction (GI) Network- based regulation. In this strategy, we regulate the genes of interest and their interacting partners based on the gene interaction network curated from public domains. From the HIPPIE database \(^{122}\) and STRINGDB \(^{123}\) , we obtain the strength of gene interactions \(\gamma\) of different gene pairs. For a certain cell population \(c\) , we transformed the cell- by- gene matrix \(X_{c}\) into a gene- by- cell matrix \(Y_{c}\) and employed PCA to generate low- dimensional embeddings \(P_{gene}\) for each gene across the cell population. The influence factor \(I(Q, R) \in (- 1, 1)\) quantifies the extent to which the perturbation of a given gene \(Q\) impacts on another gene \(R\) . \(I(Q, R)\) is defined as:
+
+<--- Page Split --->
+
+\[\begin{array}{r}I(Q,R) = \left\{ \begin{array}{ll}0, & \mathrm{if~}Q\mathrm{~and~}R\mathrm{~are~not~connected}\\ \displaystyle sgn(cor(\mathbf{y}_Q,\mathbf{y}_R))\exp (-\mathbf{w}\frac{\|P_Q - P_R\|_2}{\prod_{k\in (Q,R)}\gamma_k}), & \mathrm{otherwise} \end{array} \right. \end{array} \quad (10)\]
+
+Here, \(\mathbf{y}_Q\) and \(\mathbf{y}_R\) are gene expression vectors of genes \(Q\) and \(R\) , respectively, in the \(Y_{c}\) . The term \((Q,R)\) denotes a sequence of hops from \(Q\) to \(R\) in the GI network, \(\gamma_k\) denotes the strength of gene interactions of a hop in \((Q,R)\) , \(w\) is the steepness weight \((w > 0\) and empirically set to 0.2 by default) to control the influence factor, \(cor(\mathbf{y}_Q,\mathbf{y}_R)\) quantifies the correlation between two genes and \(sgn(x)\) indicates the direction of their interactions. The gene of interest will tend to impose higher impacts on genes that it directly interacts with. Conversely, genes that are further away in the GI network are less influenced. When regulating a specific gene \(\eta\) by changing a certain magnitude \(\Delta_{\eta}\) (e.g., \(\Delta_{\eta} = - 0.5\) can decrease the expression of gene \(\eta\) by 0.5). The expression regulation vector for this scenario is formulated as \(\Delta = [\Delta_{\eta}I(\eta ,g_1),\Delta_{\eta}I(\eta ,g_2),\dots,\Delta_{\eta}I(\eta ,g_n)]\) . If multiple genes \(G_{P}\) are perturbed with individual magnitudes, the expression regulation vector is:
+
+\[\Delta = [\Sigma_{i\in G_P}\Delta_iI(i,g_1),\Sigma_{i\in G_P}\Delta_iI(i,g_2),\dots,\Sigma_{i\in G_P}\Delta_iI(i,g_n)] \quad (12)\]
+
+The gene expression for a perturbed cell population \(X^{\prime}\) is then calculated as defined in equation (9).
+
+## In-silico perturbation scoring
+
+We perform perturbations on every stage of individual tracks using the perturbed cell- by- gene expression matrix \(X^{\prime}\) . This matrix \(X^{\prime}\) is fed into the encoder of the Graph VAE- GAN, yielding the perturbed latent cell representation \(Z^{\prime} = E_{\theta}(X^{\prime},A)\) . The efficacy of these perturbations is assessed by examining the changes in the distances between cell populations within the latent cell embedding space. Specifically, the distance between two cell populations in the latent space \(Z\) can be quantified as \(\delta_{i,j} = \| Z_i' - Z_j\| _2\) , where \(i'\) is the perturbed cell population and \(j\) is another cell population within the same track. The perturbation score of a track \(S_{track}\in [- 1,1]\) at a perturbed stage \(i\) is defined as:
+
+\[S_{track}(i) = \frac{1}{\tau}\Sigma_{j = 0,j\neq i}^{T}\left(1 - \frac{2}{1 + exp(w(\delta_{i,j} - \delta_{i,j})sgn(j - i))}\right) \quad (13)\]
+
+Here, \(T\) represents the total number of stages, \(i\) is the perturbed stage, \(w\) is a hyper- parameter to control the scaling ( \(w\) is set as 100 in our case), \(\delta_{i,j}\) is the distance between stage \(j\) and \(i\) (unperturbed) and \(\delta_{i,j}\) is the distance between stage \(j\) and \(i\) (perturbed). The function \(sgn(x)\) (as defined in equation (11)) is a perturbation indicator function to ensure the perturbed cell population that comes closer to the control stage will always have a positive and higher score while moving away leads to a negative and lower score. In addition to track- level perturbation scoring, an overall score \(S\) assesses perturbation effects across all tracks. This overall score is normalized based on the proportion of cells in each perturbed track within the dataset. It also incorporates the gene- regulating directions of compounds, as indicated in the relevant database, including their reversed directions. The overall score \(S\) for all stages is defined as follows,
+
+\[S = \sum_{h\in tracks}\frac{N_h}{N}\sum_{i\in stage}\frac{|S_h^d(i) - S_h^B(i)|}{2} \quad (14)\]
+
+where \(\mathcal{A}\) represents the perturbation direction that aligns with the reported direction of the drug target expression change, while \(B\) denotes the opposite drug target expression change direction as reported in the CMAP database. The overall score \(S\) is calculated by considering in- silico perturbations in both directions, enhancing robustness. This approach is based on the premise that perturbing the targets of an effective drug in opposite directions should lead to a higher \(S_h^d(i)\) and lower \(S_h^B(i)\) , resulting in an increased score \(S\) . \(N\) here is the total number of cells and \(N_h\) is the number of cells in the perturbed track.
+
+## Therapeutic pathways discovery
+
+We use pathway data from REACTOME \(^{124}\) , MatrisomeDB \(^{125}\) , and KEGG \(^{126}\) databases, providing lists of genes associated with various biological pathways. The set of genes present in individual single- cell transcriptomics datasets might vary, especially after data preprocessing. Therefore, we used expressed genes after preprocessing, and are listed as pathways' targets for in- silico pathway perturbations. We applied the scoring and ranking strategies as discussed in the 'In- silico perturbation strategies' and 'In- silico perturbation scoring' sections above to identify potential therapeutic pathways. Pathways that do not share any genes with our processed single- cell data are excluded from this analysis, as they cannot be effectively evaluated. To assess the significance of our in- silico pathways perturbations, we establish a random background dataset by randomly sampling \(n\) genes 1000 times where \(n\) is set to the median number of genes across all pathways. The perturbation strength \(\Delta\) used for random background perturbations was matched to that employed for the
+
+<--- Page Split --->
+
+actual pathway in- silico perturbations. We executed in- silico perturbations using the random dataset described above to generate a random background therapeutic score distribution. By contrasting the perturbation scores with this background distribution, we could ascertain the statistical significance of the in- silico pathway perturbations. This approach aids in identifying potential therapeutic pathways with a false discovery rate (FDR) of less than 0.05.
+
+## Candidate drugs and compounds discovery
+
+We use the compound and their target genes from the Connectivity Map (CMAP) database \(^{26,27}\) which contains 34, 396 compound or drug profiles. Similar to the pathway perturbation, we used expressed genes after preprocessing, and are listed as drugs' targets for in- silico drug perturbations. We applied the scoring and ranking strategies as discussed in the 'In- silico perturbation strategies' and 'In- silico perturbation scoring' sections above to identify potential drug candidates. The method for calculating the statistical significance of in- silico drug perturbations was akin to that used for therapeutic pathway perturbations, as mentioned previously. The primary distinction lies in the number of genes selected for creating the random background dataset and the perturbation strength \(\Delta\) , which was aligned with that of the actual drug perturbations.
+
+## Clustering parameters optimization
+
+To maintain consistency in cluster numbers and sizes, as well as the distances between cell neighbors, across various stages, we introduce a Clustering Parameter Optimization (CPO) method. Connectivity graph- based community detection clustering methods, like Leiden clustering \(^{117}\) , can automatically identify the number of clusters. However, the improper number of neighbors in the neighborhood graph or the improper resolution setting can lead to over- clustering or under- clustering, introducing complications in the analysis process. The consistency in the number and size of clusters is important for tracing the lineage of cell populations through various stages of development or disease progression. The proposed CPO method encompasses two primary steps. (1) Searching for the optimal number of neighbors to construct graphs with consistent cell- neighbor distances across different stages. We start by selecting an anchor stage, which is the stage with a cell count closest to the median count of all stages, denoted as \(N_{anchor}\) . We then calculate the average distance between cells and their neighbors in this anchor stage, establishing the anchor neighbor distance. The goal for other stages is to find a number of neighbors that yields a neighbor distance similar to that of the anchor stage. (2) The second step involves determining the optimal clustering resolution. We aim to find a set of resolutions within the predefined range \([R_{min} = 0.8, R_{max} = 1.5]\) for different stages that result in a similar median number of cells per cluster across these stages. For different application scenarios, users have the option to select a resolution range larger than the default setting. This flexibility enables adaptation to various analytical needs and preferences. By employing the CPO method, we ensure that the neighborhood graphs for different stages maintain similar cell- neighbor distances. Additionally, this approach ensures a consistent number and size of clusters across different stages, thereby enhancing the coherence and robustness of our analytical framework.
+
+## Benchmarking
+
+To evaluate UNAGI's performance in learning latent embeddings from single- cell data, it is benchmarked against scVI \(^{15}\) and SCANPY \(^{12}\) . SCANPY applies Principal Component Analysis (PCA) for dimensionality reduction, whereas scVI uses a VAE model to capture the latent structures of single- cell data. We employ non- label metrics including the Silhouette score \(^{127}\) , which assesses cluster cohesion and separation, Davies- Bouldin index \(^{128}\) , which gauges average similarity ratios between clusters, and Label score \(^{89}\) , which evaluates the cell type consistency in the cell neighborhoods. For labeled metrics, the independent manual cell- type annotation served as a reference for calculating ARI \(^{87}\) and NMI \(^{88}\) . In the benchmarking and ablation experiments, we compare UANGI with scVI, SCANPY, the baseline VAE model (BL) using ZILN distribution, and the baseline model with GCN (BL_GCN) and GAN (BL_GAN), respectively. To ensure a fair comparison, we run each method for 15 rounds, each with different random seeds, and utilize Leiden clustering to generate the clustering results. Furthermore, the effectiveness of the ZILN distribution in modeling rigorously normalized single- cell data was evaluated by comparing scVI- ZILN with standard scVI. To assess UNAGI's iterative training strategy, it was executed five times with different seeds, and the results from the initial five iterations were benchmarked.
+
+## In-silico drug discovery simulation
+
+We developed a simulation dataset to assess the ability of UNAGI to identify potential therapeutic targets. We selected drugs and compounds that are least likely (set FDR>0.95 as the default cut- off) to be effective in disease medication. For the generation of positive simulation data, we manipulated the target gene expression levels across various disease stages. Specifically, for compounds known to down- regulate their targets, we set their target expression levels as a progressive series \([B, 2B, \ldots , T * B]\) , where \(B > 0\) at each disease stage (in total, we have \(T\) disease stages). Conversely, for compounds that up- regulate their targets, the expression
+
+<--- Page Split --->
+
+levels were set in a decremental series \([T * B,(T - 1) * B,\ldots ,B]\) . In the context of negative data, we maintained consistent gene expression levels without any alteration. In the in- silico drug perturbation, the drug will increase the expression to \(\epsilon\) times or decrease to its \(1 / \epsilon\) . We conducted experiments in four separate simulation rounds, each utilizing different \(B\) values (0.5, 1.0, 1.5, 2.0). Within each round, we explored the effects of four distinct \(\epsilon\) values (1.5,2.5,3.5,4.5). We established a random background score distribution by randomly sampling \(n\) genes 1000 times, where \(n\) is set to the median number of genes across all perturbed drugs. The drug candidates with a significant FDR cut- off (FDR<0.01) than the default 0.05 were considered as successfully predicted. The model's performance in drug discovery was assessed using the Area Under the Receiver Operating Characteristic Curve (AUROC) and the Area Under the Precision- Recall Curve (AUPRC) metrics, as implemented in scikit- learn129.
+
+## Sanity perturbation approach
+
+To evaluate the effectiveness of our proposed in- silico perturbation strategy, we also employed a sanity perturbation approach. This involved randomly selecting a specific track from the temporal dynamics graph and calculating the average gene expression at each stage along this track to determine the centroid for each stage. For all stages other than the control, we adjusted the gene expression of all cells within each stage to match that of the preceding stage. This was achieved by subtracting the centroid differences between these stages on each of the cells from the stage. Subsequently, the perturbed cells were input into the UNAGI model, and following the 'In- silico perturbation strategies' and 'In- silico perturbation scoring' sections above to obtain the perturbed cell embeddings. We then calculated the perturbation scores, which served as a metric to evaluate the effectiveness of our perturbation strategy. Sanity perturbations should result in positive and far larger therapeutic scores compared to random perturbations.
+
+## Verify UNAGI biomarkers by proteomics data
+
+Proteins were extracted from pulmonary tissues using the MPLEx protocol as previously described130- 133. Thirty tissue blocks from IPF donors and 10 from control donors were employed. Briefly, the tissue samples were then homogenized using a Qiagen TissueLyser II with a \(2 \times 24\) adapter (chilled to \(- 20^{\circ} \mathrm{C}\) ) following vendor's instruction133. The aqueous polar metabolites and proteins were extracted from each homogenate using the MPLEx protocol. Keeping each sample on ice, a volume of chilled chloroform and water were added to a final ratio of 3:8:4 water- chloroform- methanol, mixing gently after each addition. The samples were chilled on ice for 5 min before mixing well and separating the layers by centrifugation (10,000 g, 10 min, \(4^{\circ} \mathrm{C}\) ). Proteins were isolated and concentrated to dryness in a vacuum concentrator and stored at \(- 70^{\circ} \mathrm{C}\) until ready for further processing. For each sample proteins were denatured, alkylated, digested with trypsin, and desalted on a C18 solid- phase extraction (SPE) cartridge using previously detailed methods132. For the analyses, 5 μL of resulting peptides at the concentration of \(0.1 \mu \mathrm{g} / \mu \mathrm{L}\) were analyzed by reverse phase liquid chromatography coupled with an Orbitrap Lumos instrument (Thermo Scientific) in data- dependent mode (DDA). Briefly, samples were loaded on an SPE column via a 5 μL sample loop separated by the C18 column using a 120 min gradient. The effluents from the LC column were ionized by electrospray ionization and introduced into the mass spectrometer via a heated capillary maintained at \(250^{\circ} \mathrm{C}\) for ion desalvation. The resulting ions were mass analyzed by the Orbitrap at a resolution of 60,000 covering the mass range from 300 to 1,800 Da. The top 12 most intense ions were then targeted for fragmentation per cycle time. Tandem mass MS2, ions were isolated by quadrupole mass filter in monoisotopic peak selection mode using an isolation window of 0.7 Da, maximum injection time of 50 ms with AGC setting at 1E5 ions and fragmented by high- energy collision dissociation (HCD) with nitrogen at \(32\%\) normalized collision energy. Fragment ions were mass analyzed by the Orbitrap at a resolution of 7,500, and spectra were recorded in the centroid mode. Ions once selected for MS2 were dynamically excluded for the next 45s. The instrument raw files are publicly available on MassIVE (Server: massive.ucsd.edu, User: MSV000093129, Password: Lung5172). The raw files were analyzed using MaxQuant v1.6.0.16 LFQ quantification. Downstream data processing and statistics were performed using RomicsProcessor134. The resulting LFQ intensities were log2 transformed and median- centered. ANOVA and Student's T- test were performed, and FDR p- value corrections were applied. The data processing code is available on GitHub (https://github.com/GeremyClair/IPF_DDA_proteomics/).
+
+After preprocessing, we adopted a more stringent FDR cut- off (FDR<0.01) than the default (FDR<0.05) to identify highly confident dynamic proteins. To verify the temporal dynamic markers determined for each progression track, we applied hypergeometric testing. This test assessed the overlapping ratio between dynamic proteins and dynamic markers. The overlapping between these two marker lists associated with a track is considered statistically significant if the FDR from the hypergeometric test is less than 0.05. We then use heatmaps to visualize the LFQ intensities and gene expression from proteomics data and snRNA- seq data, respectively.
+
+<--- Page Split --->
+
+## Precision-cut lung slice (PCLS) experiments
+
+Precision- cut lung slice (PCLS) experimentsFresh lung tissue of explanted donor lungs was used for human PCLS according to previously published protocols37,90,135. Donor lung samples were sourced from 6 males and 4 females and were obtained from the Center for Organ Recovery and Education (CORE) at the University of Pittsburgh. Donor lung samples originated from lungs deemed unsuitable for organ transplantation. For the fibrosis induction in hPCLS, PCLS were treated for 5 days with a control cocktail (CC) including all vehicles or a pro- fibrotic cocktail (FC) consisting of TGF- \(\beta\) (5 ng/ml, Bio- Techne), PDGF- AB (10 ng/ml, Thermo Fisher), TNF- \(\alpha\) (10 ng/ml, Bio- Techne), and LPA (5 \(\mu \mathrm{M}\) , Cayman chemical) as described before90,136. For drug treatments, PCLS were treated with FC allowing for the induction of fibrosis, and drug treatment started at day 3 until day 5. At the end of the experiment, PCLS were snap- frozen individually in liquid nitrogen for single nuclei analysis, as described above. The study was approved by the University of Pittsburgh (IRB PRO14010265). Written informed consent was obtained for all study participants. Nuclei were extracted using the Nuclei Isolation kit (CG000505, 10X Genomics).20 000 nuclei were loaded on a Chip G with Chromium Single Cell 3' v3.1 gel beads and reagents (3' GEX v3.1, 10x Genomics). Final libraries were analyzed on an Agilent Bioanalyzer High Sensitivity DNA chip for qualitative control purposes. cDNA libraries were sequenced on a HiSeq 4000 Illumina platform aiming for 150 million reads per library and a sequencing configuration of 26 base pair (bp) on read1 and 98 bp on read2.
+
+Basceals were converted to reads with the software Cell Ranger's137 (v4.0.0) implementation mkfastq. Multiple fastq files from the same library and strand were catenated to single files. Read2 files were subject to two passes of contaminant trimming with Cutadapt110 (4.1) for the template switch oligo sequence anchored on the 5' end and for poly(A) sequences on the 3' end. Following trimming, read pairs were removed if the read2 was trimmed below 30 bp.
+
+Paired reads were filtered if either the cell barcode or unique molecular identifier (UMI) sequence had more than 1 bp with a phred of \(< 20\) . Reads were aligned with STAR112 (v2.7.9a) to the human genome reference GRCh38111 release 99. After preprocessing, analysis of the ex vivo human PCLS snRNA- seq data was conducted using the Seurat11 package (version 1.8.2). Cells with less than 750 transcripts profiled were then removed.
+
+To minimize the possible effect of potential batch correction methods, we first processed and annotated each library separately, before integrating them together and annotating them jointly. To integrate the multiple snRNA- seq datasets, we employed Robust Principal Component Analysis (RPCA)138. Based on the cellular diversity, we chose to use PCLS treated with DMSO as the reference for the integration. Following the RPCA decomposition, we utilized the low- rank component as the integrated representation of the snRNA- seq datasets. This component captured shared biological signals across conditions while mitigating dataset- specific variations. Subsequent analyses, such as clustering and differential expression analysis, were performed on the non- integrated but normalized gene expression values. To validate the effectiveness of the integrated representation, we performed various analyses, including cell- type clustering, and identification of marker genes. We also compared the results of these analyses to those obtained from individual datasets to evaluate the improvement gained through the integration process. Marker genes were computed using a Wilcoxon rank- sum test, and genes were considered marker genes if the FDR- corrected p- value was below 0.05 and the log2 fold change was above 0.5.
+
+We then applied the Graph VAE- GAN to learn the latent embeddings of the PCLS data. To quantify the effects after treating the fibrosis cells with the drugs, we calculate the pairwise Euclidean distance from control cells to real treatment cells and fibrosis cells in the reduced latent space. We used the difference between the centroid of fibrosis cells and centroids of real treatments as the perturbation strength vector \(\Delta\) . We conducted in- silico drug perturbations on fibrosis cells using a consistent perturbation strength \(\Delta\) . The efficacy of these in- silico perturbations was evaluated through UMAP visualizations and by measuring the pairwise Euclidean distances between cell embeddings in latent space. Our primary objective was to ascertain if in- silico drug perturbations could replicate the cell embeddings in latent space as observed with actual drug treatments, thereby validating the accuracy of UNAGI- driven in- silico drug perturbations. Additionally, to compare the similarity of the differential genes associated with the in- silico drug perturbations (in- silico drug perturbation vs. fibrosis) and those of real drug treatment (drug vs. fibrosis), we employed Ranked- Ranked Hypergeometric Overlap (RRHO) plots. Moreover, box plots and the \(R^2\) score were used as analytical tools to quantify gene expression similarities between cells under actual drug treatments and cells produced from our in- silico perturbations for both Nintedanib and Nifedipine.
+
+## Reporting Summary
+
+<--- Page Split --->
+
+Further information on research design is available in the Nature Research Reporting Summary linked to this article.
+
+## Data availability
+
+Data availabilityIPF snRNA-seq and PCLS data will be made publicly accessible upon the publication of this work. The COVID- 19 dataset (COVID- 19 PBMC Ncl- Cambridge- UCL) is currently available from the COVID- 19 Cell Atlas at https://covid19cellatlas.org/. The proteomics data are publicly available on MassIVE (Server: massive.ucsd.edu, User: MSV000093129, Password: Lung5172).
+
+## Code availability
+
+Code availabilityThe UNAGI software package and source code are available at our GitHub repository (https://github.com/mcgilldinglab/UNAGI). The results and downstream analysis are available on our web server (http://dinglab.rimuhc.ca/unagi). All preprocessed .h5ad files used in this study are also available in the same GitHub repository.
+
+## References
+
+References1. Mitchell, K. J. What is complex about complex disorders? Genome Biol. 13, 237 (2012).2. Schork, N. J. Genetics of Complex Disease: Approaches, Problems, and Solutions. Am. J. Respir. Crit. Care Med. 156, S103–S109 (1997).3. Ramsay, R. R., Popovic-Nikolic, M. R., Nikolic, K., Uliassi, E. & Bolognesi, M. L. A perspective on multi-target drug discovery and design for complex diseases. Clin. Transl. Med. 7, (2018).4. Iyengar, R. Complex diseases require complex therapies. EMBO Rep. 14, 1039–1042 (2013).5. Dickson, M. & Gagnon, J. P. Key factors in the rising cost of new drug discovery and development. Nat. Rev. Drug Discov. 3, 417–429 (2004).6. Wang, Y. et al. Dynamic Observation of Autophagy and Transcriptome Profiles in a Mouse Model of Bleomycin-Induced Pulmonary Fibrosis. Front. Mol. Biosci. 8, 664913 (2021).7. McDonough, J. E. et al. Transcriptional regulatory model of fibrosis progression in the human lung. JCI Insight 4, e131597 (2019).8. Angerer, P. et al. Single cells make big data: New challenges and opportunities in transcriptomics. Curr. Opin. Syst. Biol. 4, 85–91 (2017).9. Stubbington, M. J. T., Rozenblatt-Rosen, O., Regev, A. & Teichmann, S. A. Single-cell transcriptomics to explore the immune system in health and disease. Science 358, 58–63 (2017).10. Habermann, A. C. et al. Single-cell RNA sequencing reveals profibrotic roles of distinct epithelial and mesenchymal lineages in pulmonary fibrosis. Sci. Adv. 6, eaba1972 (2020).11. Hao, Y. et al. Integrated analysis of multimodal single-cell data. Cell 184, 3573-3587. e29 (2021).12. Wolf, F. A., Angerer, P. & Theis, F. J. SCANPY: large-scale single-cell gene expression data analysis. Genome Biol. 19, 15 (2018).
+
+<--- Page Split --->
+
+13. Cao, J. et al. The single-cell transcriptional landscape of mammalian organogenesis. Nature 566, 496–502 (2019).
+14. Hasanaj, E., Wang, J., Sarathi, A., Ding, J. & Bar-Joseph, Z. Interactive single-cell data analysis using Cellar. Nat. Commun. 13, 1998 (2022).
+15. Lopez, R., Regier, J., Cole, M. B., Jordan, M. I. & Yosef, N. Deep generative modeling for single-cell transcriptomics. Nat. Methods 15, 1053–1058 (2018).
+16. Shao, L. et al. Identify differential genes and cell subclusters from time-series scRNA-seq data using scTITANS. Comput. Struct. Biotechnol. J. 19, 4132–4141 (2021).
+17. Wang, Z. et al. DTWscore: differential expression and cell clustering analysis for time-series single-cell RNA-seq data. BMC Bioinformatics 18, 270 (2017).
+18. Ding, J. et al. Reconstructing differentiation networks and their regulation from time series single-cell expression data. Genome Res. 28, 383–395 (2018).
+19. Lin, C. & Bar-Joseph, Z. Continuous-state HMMs for modeling time-series single-cell RNA-Seq data. Bioinforma. Oxf. Engl. 35, 4707–4715 (2019).
+20. Hurley, K. et al. Reconstructed Single-Cell Fate Trajectories Define Lineage Plasticity Windows during Differentiation of Human PSC-Derived Distal Lung Progenitors. Cell Stem Cell 26, 593-608.e8 (2020).
+21. Mitra, R. & MacLean, A. L. RVAgene: generative modeling of gene expression time series data. Bioinformatics 37, 3252–3262 (2021).
+22. Yuan, Y. & Bar-Joseph, Z. Deep learning of gene relationships from single cell time-course expression data. Brief. Bioinform. 22, bbab142 (2021).
+23. Lotfollahi, M., Wolf, F. A. & Theis, F. J. scGen predicts single-cell perturbation responses. Nat. Methods 16, 715–721 (2019).
+24. Gronbech, C. H. et al. scVAE: variational auto-encoders for single-cell gene expression data. Bioinformatics 36, 4415–4422 (2020).
+25. Roohani, Y., Huang, K. & Leskovec, J. Predicting transcriptional outcomes of novel multigene perturbations with GEARS. Nat. Biotechnol. (2023) doi:10.1038/s41587-023-01905-6.
+26. Lamb, J. et al. The Connectivity Map: Using Gene-Expression Signatures to Connect Small Molecules, Genes, and Disease. Science 313, 1929–1935 (2006).
+
+<--- Page Split --->
+
+27. Subramanian, A. et al. A Next Generation Connectivity Map: L1000 Platform and the First 1,000,000 Profiles. Cell 171, 1437-1452. e17 (2017).
+
+28. Thannickal, V. J., Toews, G. B., White, E. S., Lynch lii, J. P. & Martinez, F. J. Mechanisms of Pulmonary Fibrosis. Annu. Rev. Med. 55, 395-417 (2004).
+29. Ballester, B., Milara, J. & Cortijo, J. Idiopathic Pulmonary Fibrosis and Lung Cancer: Mechanisms and Molecular Targets. Int. J. Mol. Sci. 20, 593 (2019).
+30. Schwartz, D. A. IDIOPATHIC PULMONARY FIBROSIS IS A COMPLEX GENETIC DISORDER. Trans. Am. Clin. Climatol. Assoc. 127, 34-45 (2016).
+31. Lee, B.-S., Margolin, S. B. & Nowak, R. A. Pirfenidone: A Novel Pharmacological Agent That Inhibits Leiomyoma Cell Proliferation and Collagen Production. J. Clin. Endocrinol. Metab. 83, 219-223 (1998).
+32. Wollin, L. et al. Mode of action of nintedanib in the treatment of idiopathic pulmonary fibrosis. Eur. Respir. J. 45, 1434-1445 (2015).
+33. Karimi-Shah, B. A. & Chowdhury, B. A. Forced Vital Capacity in Idiopathic Pulmonary Fibrosis - FDA Review of Pirfenidone and Nintedanib. N. Engl. J. Med. 372, 1189-1191 (2015).
+34. Azuma, A. et al. Double-blind, Placebo-controlled Trial of Pirfenidone in Patients with Idiopathic Pulmonary Fibrosis. Am. J. Respir. Crit. Care Med. 171, 1040-1047 (2005).
+35. Adams, T. S. et al. Single-cell RNA-seq reveals ectopic and aberrant lung-resident cell populations in idiopathic pulmonary fibrosis. Sci. Adv. 6, eaba1983 (2020).
+36. Ahangari, F. et al. Saracatinib, a Selective Src Kinase Inhibitor, Blocks Fibrotic Responses in Preclinical Models of Pulmonary Fibrosis. Am. J. Respir. Crit. Care Med. 206, 1463-1479 (2022).
+37. Liu, G. et al. Use of precision cut lung slices as a translational model for the study of lung biology. Respir. Res. 20, 162 (2019).
+38. Viana, F., O'Kane, C. M. & Schroeder, G. N. Precision-cut lung slices: A powerful ex vivo model to investigate respiratory infectious diseases. Mol. Microbiol. 117, 578-588 (2022).
+39. De Saddeer, L. J. et al. Lung Microenvironments and Disease Progression in Fibrotic Hypersensitivity Pneumonitis. Am. J. Respir. Crit. Care Med. 205, 60-74 (2022).
+40. Tanabe, N. et al. Pathology of Idiopathic Pulmonary Fibrosis Assessed by a Combination of Microcomputed Tomography, Histology, and Immunohistochemistry. Am. J. Pathol. 190, 2427-2435 (2020).
+
+<--- Page Split --->
+
+41. Xu, F. et al. The transition from normal lung anatomy to minimal and established fibrosis in idiopathic pulmonary fibrosis (IPF). EBioMedicine 66, 103325 (2021).
+42. Pilling, D., Zheng, Z., Vakil, V. & Gomer, R. H. Fibroblasts secrete Slit2 to inhibit fibrocyte differentiation and fibrosis. Proc. Natl. Acad. Sci. 111, 18291–18296 (2014).
+43. Ramos, C. et al. Fibroblasts from Idiopathic Pulmonary Fibrosis and Normal Lungs Differ in Growth Rate, Apoptosis, and Tissue Inhibitor of Metalloproteinases Expression. Am. J. Respir. Cell Mol. Biol. 24, 591–598 (2001).
+44. Kendall, R. T. & Feghali-Bostwick, C. A. Fibroblasts in fibrosis: novel roles and mediators. Front. Pharmacol. 5, (2014).
+45. Saito, S. et al. HDAC8 inhibition ameliorates pulmonary fibrosis. Am. J. Physiol.-Lung Cell. Mol. Physiol. 316, L175–L186 (2019).
+46. Rubio, K. et al. Inactivation of nuclear histone deacetylases by EP300 disrupts the MiCEE complex in idiopathic pulmonary fibrosis. Nat. Commun. 10, 2229 (2019).
+47. Zou, M. et al. Latent Transforming Growth Factor-β Binding Protein-2 Regulates Lung Fibroblast-to-Myofibroblast Differentiation in Pulmonary Fibrosis via NF-κB Signaling. Front. Pharmacol. 12, 788714 (2021).
+48. Enomoto, Y. et al. LTBP2 is secreted from lung myofibroblasts and is a potential biomarker for idiopathic pulmonary fibrosis. Clin. Sci. 132, 1565–1580 (2018).
+49. Herrera, J., Henke, C. A. & Bitterman, P. B. Extracellular matrix as a driver of progressive fibrosis. J. Clin. Invest. 128, 45–53 (2018).
+50. Hu, X. et al. PI3K-Akt-mTOR/PFKFB3 pathway mediated lung fibroblast aerobic glycolysis and collagen synthesis in lipopolysaccharide-induced pulmonary fibrosis. Lab. Invest. 100, 801–811 (2020).
+51. Wang, J. et al. Targeting PI3K/AKT signaling for treatment of idiopathic pulmonary fibrosis. Acta Pharm. Sin. B 12, 18–32 (2022).
+52. Lagares, D. et al. Inhibition of focal adhesion kinase prevents experimental lung fibrosis and myofibroblast formation. Arthritis Rheum. 64, 1653–1664 (2012).
+53. Tsukui, T. et al. Collagen-producing lung cell atlas identifies multiple subsets with distinct localization and relevance to fibrosis. Nat. Commun. 11, 1920 (2020).
+54. Wan, H. et al. Identification of Hub Genes and Pathways Associated With Idiopathic Pulmonary Fibrosis via Bioinformatics Analysis. Front. Mol. Biosci. 8, 711239 (2021).
+
+<--- Page Split --->
+
+55. Kinoshita, K. et al. Antibiotic effects of focal adhesion kinase inhibitor in bleomycin-induced pulmonary fibrosis in mice. Am. J. Respir. Cell Mol. Biol. 49, 536–543 (2013).56. Gangwar, I. et al. Detecting the Molecular System Signatures of Idiopathic Pulmonary Fibrosis through Integrated Genomic Analysis. Sci. Rep. 7, 1554 (2017).57. Chen, Y., He, Z., Zhao, B. & Zheng, R. Downregulation of a potential therapeutic target NPAS2, regulated by p53, alleviates pulmonary fibrosis by inhibiting epithelial-mesenchymal transition via suppressing HES1. Cell. Signal. 109, 110795 (2023).58. Hung, C. F., Wilson, C. L., Chow, Y.-H. & Schnapp, L. M. Role of integrin alpha8 in murine model of lung fibrosis. PLOS ONE 13, e0197937 (2018).59. Morris, A. Thyroid hormone therapy resolves pulmonary fibrosis in mice. Nat. Rev. Endocrinol. 14, 64–64 (2018).60. Wei, P. et al. Transforming growth factor (TGF)- \(\beta 1\) -induced miR-133a inhibits myofibroblast differentiation and pulmonary fibrosis. Cell Death Dis. 10, 670 (2019).61. Li, Z. et al. Artificial neural network identified the significant genes to distinguish Idiopathic pulmonary fibrosis. Sci. Rep. 13, 1225 (2023).62. Gao, R. et al. Macrophage-derived netrin-1 drives adrenergic nerve-associated lung fibrosis. J. Clin. Invest. 131, e136542, 136542 (2021).63. Higo, H. et al. Identification of targetable kinases in idiopathic pulmonary fibrosis. Respir. Res. 23, 20 (2022).64. Hannandlu, A. et al. Transcriptomic and Epigenetic Profiling of Fibroblasts in Idiopathic Pulmonary Fibrosis. Am. J. Respir. Cell Mol. Biol. 66, 53–63 (2022).65. DePianto, D. J. et al. Heterogeneous gene expression signatures correspond to distinct lung pathologies and biomarkers of disease severity in idiopathic pulmonary fibrosis. Thorax 70, 48–56 (2015).66. Schupp, J. C. et al. Integrated Single-Cell Atlas of Endothelial Cells of the Human Lung. Circulation 144, 286–302 (2021).67. Hohmann, M. S. et al. Antibody-mediated depletion of CCR10+ EphA3+ cells ameliorates fibrosis in IPF. JCI Insight (2021) doi:10.1172/jci.insight.141061.68. McKleroy, W., Lee, T.- H. & Atabai, K. Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis. Am. J. Physiol. Lung Cell. Mol. Physiol. 304, L709- 721 (2013).
+
+<--- Page Split --->
+
+69. Bogatkevich, G. S., Atanlishvili, I., Bogatkevich, A. M. & Silver, R. M. Critical Role of LMCD1 in Promoting Profibrotic Characteristics of Lung Myofibroblasts in Experimental and Scleroderma-Associated Lung Fibrosis. Arthritis Rheumatol. 75, 438–448 (2023).
+70. Zhang, L., Li, Y., Liang, C. & Yang, W. CCN5 overexpression inhibits profibrotic phenotypes via the PI3K/Akt signaling pathway in lung fibroblasts isolated from patients with idiopathic pulmonary fibrosis and in an in vivo model of lung fibrosis. Int. J. Mol. Med. 33, 478–486 (2014).
+71. Kim, H.-T. et al. Myh10 deficiency leads to defective extracellular matrix remodeling and pulmonary disease. Nat. Commun. 9, 4600 (2018).
+72. Jessen, H. et al. Turnover of type I and III collagen predicts progression of idiopathic pulmonary fibrosis. Respir. Res. 22, 205 (2021).
+73. Sontake, V. et al. Wilms' tumor 1 drives fibroproliferation and myofibroblast transformation in severe fibrotic lung disease. JCI Insight 3, e121252 (2018).
+74. Kadefors, M. et al. CD105+CD90+CD13+ identifies a clonogenic subset of adventitial lung fibroblasts. Sci. Rep. 11, 24417 (2021).
+75. Herrera, J. A. et al. Morphologically intact airways in lung fibrosis have an abnormal proteome. Respir. Res. 24, 99 (2023).
+76. Sun, H. et al. Netrin-1 regulates fibrocyte accumulation in the decellularized fibrotic scleroderma lung microenvironment and in bleomycin induced pulmonary fibrosis: Netrin-1 and Collagen production by PBMCs in Scleroderma. Arthritis Rheumatol. n/a-n/a (2016) doi:10.1002/art.39575.
+77. Roach, K. M. & Bradding, P. Ca \(^{2+}\) signalling in fibroblasts and the therapeutic potential of K \(_{Ca}\) 3.1 channel blockers in fibrotic diseases. Br. J. Pharmacol. 177, 1003–1024 (2020).
+78. Mukherjee, S. et al. Disruption of Calcium Signaling in Fibroblasts and Attenuation of Bleomycin-Induced Fibrosis by Nifedipine. Am. J. Respir. Cell Mol. Biol. 53, 450–458 (2015).
+79. Ghandikota, S., Sharma, M., Ediga, H. H., Madala, S. K. & Jegga, A. G. Consensus Gene Co-Expression Network Analysis Identifies Novel Genes Associated with Severity of Fibrotic Lung Disease. Int. J. Mol. Sci. 23, 5447 (2022).
+80. Sanders, Y. Y. et al. Histone deacetylase inhibition promotes fibroblast apoptosis and ameliorates pulmonary fibrosis in mice. Eur. Respir. J. 43, 1448–1458 (2014).
+81. Korfai, M., Mahavadi, P. & Guenther, A. Targeting Histone Deacetylases in Idiopathic Pulmonary Fibrosis: A Future Therapeutic Option. Cells 11, 1626 (2022).
+
+<--- Page Split --->
+
+82. Udalov, S. et al. Effects of phosphodiesterase 4 inhibition on bleomycin-induced pulmonary fibrosis in mice. BMC Pulm. Med. 10, 26 (2010).
+83. Martin, P. et al. Relevant role of PKG in the progression of fibrosis induced by TNF-like weak inducer of apoptosis. Am. J. Physiol.-Ren. Physiol. 307, F75–F85 (2014).
+84. Yang, D., Yang, Y. & Zhao, Y. Ibudilast, a Phosphodiesterase-4 Inhibitor, Ameliorates Acute Respiratory Distress Syndrome in Neonatal Mice by Alleviating Inflammation and Apoptosis. Med. Sci. Monit. 26, (2020).
+85. Domitrovic, R. et al. Myricitrin exhibits antioxidant, anti-inflammatory and antifibrotic activity in carbon tetrachloride-intoxicated mice. Chem. Biol. Interact. 230, 21–29 (2015).
+86. Li, X. et al. Regorafenib-Attenuated, Bleomycin-Induced Pulmonary Fibrosis by Inhibiting the TGF-β1 Signaling Pathway. Int. J. Mol. Sci. 22, 1985 (2021).
+87. Hubert, L. & Arabie, P. Comparing partitions. J. Classif. 2, 193–218 (1985).
+88. Vinh, N. X., Epps, J. & Bailey, J. Information Theoretic Measures for Clusterings Comparison: Variants, Properties, Normalization and Correction for Chance. J. Mach. Learn. Res. 11, 2837–2854 (2010).
+89. Yuan, H. & Kelley, D. R. scBasset: sequence-based modeling of single-cell ATAC-seq using convolutional neural networks. Nat. Methods 19, 1088–1096 (2022).
+90. Alsafadi, H. N. et al. An ex vivo model to induce early fibrosis-like changes in human precision-cut lung slices. Am. J. Physiol.-Lung Cell. Mol. Physiol. 312, L896–L902 (2017).
+91. Li, D. et al. IL-33 promotes ST2-dependent lung fibrosis by the induction of alternatively activated macrophages and innate lymphoid cells in mice. J. Allergy Clin. Immunol. 134, 1422–1432.e11 (2014).
+92. Sobecki, M. et al. Vaccination-based immunotherapy to target profibrotic cells in liver and lung. Cell Stem Cell 29, 1459–1474.e9 (2022).
+93. Mukaida, N. Pathophysiological roles of interleukin-8/CXCL8 in pulmonary diseases. Am. J. Physiol.-Lung Cell. Mol. Physiol. 284, L566–L577 (2003).
+94. Cambridge Institute of Therapeutic Immunology and Infectious Disease-National Institute of Health Research (CITIID-NIHR) COVID-19 BioResource Collaboration et al. Single-cell multi-omics analysis of the immune response in COVID-19. Nat. Med. 27, 904–916 (2021).
+95. Vázquez-Jiménez, A. et al. On Deep Landscape Exploration of COVID-19 Patients Cells and Severity Markers. Front. Immunol. 12, 705646 (2021).
+
+<--- Page Split --->
+
+96. Zou, K. & Zeng, Z. Role of early growth response 1 in inflammation-associated lung diseases. Am. J. Physiol.-Lung Cell. Mol. Physiol. 325, L143–L154 (2023).
+
+97. Brandes, F. et al. Progranulin signaling in sepsis, community-acquired bacterial pneumonia and COVID-19: a comparative, observational study. Intensive Care Med. Exp. 9, 43 (2021).
+
+98. Ugalde, A. P. et al. Autophagy-linked plasma and lysosomal membrane protein PLAC8 is a key host factor for SARS-CoV-2 entry into human cells. EMBO J. 41, e110727 (2022).
+
+99. Galbraith, M. D. et al. Specialized interferon action in COVID-19. Proc. Natl. Acad. Sci. 119, e2116730119 (2022).
+
+100. Rieder, M. et al. Serum Protein Profiling Reveals a Specific Upregulation of the Immunomodulatory Protein Progranulin in Coronavirus Disease 2019. J. Infect. Dis. 223, 775–784 (2021).
+
+101. Schulte-Schrepping, J. et al. Severe COVID-19 Is Marked by a Dysregulated Myeloid Cell Compartment. Cell 182, 1419-1440.e23 (2020).
+
+102. De Oliveira, A. A. & Nunes, K. P. Crosstalk of TLR4, vascular NADPH oxidase, and COVID-19 in diabetes: What are the potential implications? Vascul. Pharmacol. 139, 106879 (2021).
+
+103. Hou, W. et al. Small GTPase—A Key Role in Host Cell for Coronavirus Infection and a Potential Target for Coronavirus Vaccine Adjuvant Discovery. Viruses 14, 2044 (2022).
+
+104. Liu, Z.-M., Yang, M.-H., Yu, K., Lian, Z.-X. & Deng, S.-L. Toll-like receptor (TLRs) agonists and antagonists for COVID-19 treatments. Front. Pharmacol. 13, 989664 (2022).
+
+105. Yousefi, H., Mashouri, L., Okpechi, S. C., Alahari, N. & Alahari, S. K. Repurposing existing drugs for the treatment of COVID-19/SARS-CoV-2 infection: A review describing drug mechanisms of action.
+
+106. Rabie, A. M. Efficacious Preclinical Repurposing of the Nucleoside Analogue Didanosine against COVID-19 Polymerase and Exonuclease. ACS Omega 7, 21385–21396 (2022).
+
+107. Chan, M. et al. Machine learning identifies molecular regulators and therapeutics for targeting SARS-CoV2-induced cytokine release. Mol. Syst. Biol. 17, e10426 (2021).
+
+108. Garcia, G. et al. Antiviral drug screen identifies DNA-damage response inhibitor as potent blocker of SARS-CoV-2 replication. Cell Rep. 35, 108940 (2021).
+
+109. Delre, P., Caporuscio, F., Saviano, M. & Mangiatordi, G. F. Repurposing Known Drugs as Covalent and Non-covalent Inhibitors of the SARS-CoV-2 Papain-Like Protease. Front. Chem. 8, 594009 (2020).
+
+<--- Page Split --->
+
+110. Martin, M. Cutadapt removes adapter sequences from high-throughput sequencing reads. EMBNet journal 17, 10 (2011).111. Frankish, A. et al. GENCODE reference annotation for the human and mouse genomes. Nucleic Acids Res. 47, D766–D773 (2019).112. Dobin, A. et al. STAR: ultrafast universal RNA-seq aligner. Bioinformatics 29, 15–21 (2013).113. Yang, M.-S., Lai, C.-Y. & Lin, C.-Y. A robust EM clustering algorithm for Gaussian mixture models. Pattern Recognit. 45, 3950–3961 (2012).114. Wang, J. et al. scGNN is a novel graph neural network framework for single-cell RNA-Seq analyses. Nat. Commun. 12, 1882 (2021).115. Larsen, A. B. L., Sonderby, S. K., Larochelle, H. & Winther, O. Autoencoding beyond pixels using a learned similarity metric. Preprint at http://arxiv.org/abs/1512.09300 (2016).116. Ganin, Y. et al. Domain-Adversarial Training of Neural Networks. (2015) doi:10.48550/ARXIV.1505.07818.117. Traag, V. A., Waltman, L. & Van Eck, N. J. From Louvain to Leiden: guaranteeing well-connected communities. Sci. Rep. 9, 5233 (2019).118. Aggarwal, C. C., Hinneburg, A. & Keim, D. A. On the Surprising Behavior of Distance Metrics in High Dimensional Space. in Database Theory — ICDT 2001 (eds. Van Den Bussche, J. & Vianu, V.) vol. 1973 420–434 (Springer Berlin Heidelberg, 2001).119. Koh, W. & Hoon, S. MapCell: Learning a Comparative Cell Type Distance Metric With Siamese Neural Nets With Applications Toward Cell-Type Identification Across Experimental Datasets. Front. Cell Dev. Biol. 9, 767897 (2021).120. Shapiro, A. Monte Carlo Sampling Methods. in Handbooks in Operations Research and Management Science vol. 10 353–425 (Elsevier, 2003).121. Ding, J., Hagoed, J. S., Ambalavanan, N., Kaminski, N. & Bar-Joseph, Z. iDREM: Interactive visualization of dynamic regulatory networks. PLOS Comput. Biol. 14, e1006019 (2018).122. Alanis-Lobato, G., Andrade-Navarro, M. A. & Schaefer, M. H. HIPPIE v2.0: enhancing meaningfulness and reliability of protein–protein interaction networks. Nucleic Acids Res. 45, D408–D414 (2017).123. Szklarczyk, D. et al. The STRING database in 2017: quality-controlled protein–protein association networks, made broadly accessible. Nucleic Acids Res. 45, D362–D368 (2017).
+
+<--- Page Split --->
+
+124. Jassal, B. et al. The reactome pathway knowledgebase. Nucleic Acids Res. gkz1031 (2019) doi:10.1093/nar/gkz1031.
+125. Shao, X., Taha, I. N., Clauser, K. R., Gao, Y. (Tom) & Naba, A. MatrisomeDB: the ECM-protein knowledge database. Nucleic Acids Res. 48, D1136–D1144 (2020).
+126. Kanehisa, M. The KEGG Database. in Novartis Foundation Symposia (eds. Bock, G. & Goode, J. A.) vol. 247 91–103 (John Wiley & Sons, Ltd, 2002).
+127. Rousseeuw, P. J. Silhouettes: A graphical aid to the interpretation and validation of cluster analysis. J. Comput. Appl. Math. 20, 53–65 (1987).
+128. Davies, D. L. & Bouldin, D. W. A Cluster Separation Measure. IEEE Trans. Pattern Anal. Mach. Intell. PAMI-1, 224–227 (1979).
+129. Pedregosa, F. et al. Scikit-learn: Machine Learning in Python. (2012) doi:10.48550/ARXIV.1201.0490.
+130. Nakayasu, E. S. et al. MPLEx: a Robust and Universal Protocol for Single-Sample Integrative Proteomic, Metabolomic, and Lipidomic Analyses. mSystems 1, e00043-16 (2016).
+131. Clair, G. et al. Proteomic Analysis of Human Lung Development. Am. J. Respir. Crit. Care Med. 205, 208–218 (2022).
+132. Dylag, A. M. et al. New insights into the natural history of bronchopulmonary dysplasia from proteomics and multiplexed immunohistochemistry. Am. J. Physiol. Lung Cell. Mol. Physiol. 325, L419–L433 (2023).
+133. Moghieb, A. et al. Time-resolved proteome profiling of normal lung development. Am. J. Physiol. Lung Cell. Mol. Physiol. 315, L11–L24 (2018).
+134. Woo, J. et al. Three-dimensional feature matching improves coverage for single-cell proteomics based on ion mobility filtering. Cell Syst. 13, 426-434.e4 (2022).
+135. Gerckens, M. et al. Generation of Human 3D Lung Tissue Cultures (3D-LTCs) for Disease Modeling. J. Vis. Exp. 58437 (2019) doi:10.3791/58437.
+136. Lehmann, M. et al. Differential effects of Nintedanib and Pirfenidone on lung alveolar epithelial cell function in ex vivo murine and human lung tissue cultures of pulmonary fibrosis. Respir. Res. 19, 175 (2018).
+137. Zheng, G. X. Y. et al. Massively parallel digital transcriptional profiling of single cells. Nat. Commun. 8, 14049 (2017).
+
+<--- Page Split --->
+
+1498 138. Candès, E. J., Li, X., Ma, Y. & Wright, J. Robust principal component analysis? J. ACM 58, 1- 37 (2011).
+
+1500
+
+## Acknowledgements
+
+This work is supported by Three Lakes Foundation [JD, NK, MK]. Partial supports also come from the Canadian Institutes of Health Research (CIHR) [PJT- 180505 to J.D]; the Fonds de recherche du Québec - Santé (FRQS) [295298 to J.D., 295299 to J.D.]; the Meakins- Christie Chair in Respiratory Research [to J.D.]; R01HL127349; R01HL141852; U01HL145567; R21HL161723; P01HL11450, U01HL148860; the U.S. Department of Defense [Discovery Award W81XWH- 19- 1- 0131 to J.C.S]; the Else Kröner- Fresenius Foundation [EKFS 2021_EKEA.16 and 2020_EKSP.78 to J.C.S.]; CORE100Pilot (Advanced) Clinician Scientist Program of Hannover Medical School funded by EKFS and the Niedersächsisches Ministerium für Wissenschaft und Kultur to J.C.S., and the German Research Foundation [SCHU 3147/4- 1 to J.C.S.]. Fond de dotation du Souffle [Fds 2019- Ostinelli to AJ]. This work is also part of HCA publication bundle (HCA- 9).
+
+## Author contributions
+
+N.K. and J.D. conceived and designed the experiments, performed the experiments, analyzed the data, contributed materials/analysis tools, and wrote the paper. Y.Z. designed the algorithmic framework, analyzed data, ran experiments, and wrote the paper. J.C.S., T.A., G.C., and A.J. performed the experiments, analyzed the data, and wrote the paper. F.A., I.O.R, R.P., J.S., and J.E.M performed experiments. X.Y., and P.H. analyzed the data. M.K. performed the experiments and wrote the paper. M.C., E.C., M.V., R.V., L.J.D., B.M.V, and W.A.W. contributed materials.
+
+## Competing interests
+
+NK is a scientific founder at Thyron, served as a consultant to Boehringer Ingelheim, Pliant, Astra Zeneca, RohBar, Veracyte, Augmanity, CSL Behring, Splisense, Galapagos, Fibrogen, GSK, Merck and Thyron over the last 3 years, reports Equity in Pliant and Thyron, and grants from Veracyte, Boehringer Ingelheim, BMS and non- financial support from Astra Zeneca.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+UNAIGsupplementaryfigs.pdf supplementarytable1. xlsx supplementarytable2. xlsx supplementarytable3. xlsx supplementarytable4. xlsx
+
+<--- Page Split --->
diff --git a/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec_det.mmd b/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..57b751e406bc858d3d4a4b3a5a7a189f5b3cabf2
--- /dev/null
+++ b/preprint/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec/preprint__0445794c05f9fc748fee03c0280ad85c984085049205d04438e49cdf6c4bd4ec_det.mmd
@@ -0,0 +1,752 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 896, 208]]<|/det|>
+# Unagi: Deep Generative Model for Deciphering Cellular Dynamics and In-Silico Drug Discovery in Complex Diseases
+
+<|ref|>text<|/ref|><|det|>[[42, 227, 545, 950]]<|/det|>
+Yumin Zheng McGill University Jonas Schupp Yale University https://orcid.org/0000- 0002- 7714- 8076 Taylor Adams Yale University https://orcid.org/0000- 0003- 4280- 9070 Geremy Clair Pacific Northwestern National Laboratory Aurelien Justet Yale University Farida Ahangari Yale University Xiting Yan Yale University Paul Hansen McGill University Marianne Carlon KU Leuven https://orcid.org/0000- 0002- 8263- 0350 Emanuela Cortesi KU Leuven Marie Vermant KU Leuven Robin Vos KU Leuven Laurens De Sadeleer KU Leuven Ivan Rosas Baylor College of Medicine Ricardo Pineda University of Pittsburgh John Sembrat
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[50, 45, 262, 64]]<|/det|>
+University of Pittsburgh
+
+<|ref|>text<|/ref|><|det|>[[44, 70, 262, 110]]<|/det|>
+Melanie Königshoff University of Pittsburgh
+
+<|ref|>text<|/ref|><|det|>[[44, 115, 201, 155]]<|/det|>
+John Mcdonough Yale University
+
+<|ref|>text<|/ref|><|det|>[[44, 161, 225, 201]]<|/det|>
+Bart Vanaudenaerde KU Leuven
+
+<|ref|>text<|/ref|><|det|>[[44, 208, 150, 247]]<|/det|>
+Wim Wuyts KU Leuven
+
+<|ref|>text<|/ref|><|det|>[[44, 254, 196, 293]]<|/det|>
+Naftali Kaminski Yale University https://orcid.org/0000- 0001- 5917- 4601
+
+<|ref|>text<|/ref|><|det|>[[44, 300, 125, 319]]<|/det|>
+Jun Ding
+
+<|ref|>text<|/ref|><|det|>[[55, 327, 258, 346]]<|/det|>
+jun.ding@mcgill.ca
+
+<|ref|>text<|/ref|><|det|>[[55, 374, 204, 394]]<|/det|>
+McGill University
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 434, 103, 453]]<|/det|>
+## Article
+
+<|ref|>title<|/ref|><|det|>[[44, 472, 135, 491]]<|/det|>
+# Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 509, 350, 530]]<|/det|>
+Posted Date: December 18th, 2023
+
+<|ref|>text<|/ref|><|det|>[[42, 548, 475, 569]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 3676579/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 585, 915, 629]]<|/det|>
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 645, 944, 757]]<|/det|>
+Additional Declarations: Yes there is potential Competing Interest. NK is a scientific founder at Thyron, served as a consultant to Boehringer Ingelheim, Pilant, Astra Zeneca, RohBar, Veracyte, Augmanity, CSL Behring, Splisense, Galapagos, Fibrogen, GSK, Merck and Thyron over the last 3 years, reports Equity in Pilant and Thyron, and grants from Veracyte, Boehringer Ingelheim, BMS and non- financial support from Astra Zeneca.
+
+<|ref|>text<|/ref|><|det|>[[42, 793, 925, 837]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Biomedical Engineering on June 20th, 2025. See the published version at https://doi.org/10.1038/s41551- 025- 01423- 7.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[108, 66, 888, 95]]<|/det|>
+# Unagi: Deep Generative Model for Deciphering Cellular Dynamics and In-Silico Drug Discovery in Complex Diseases
+
+<|ref|>text<|/ref|><|det|>[[100, 95, 900, 153]]<|/det|>
+Yumin Zheng \(^{1,2\dagger}\) , Jonas C. Schupp \(^{3\dagger}\) , Taylor Adams \(^{3}\) , Geremy Clair \(^{4}\) , Aurelien Justet \(^{3}\) , Farida Ahangari \(^{3}\) , Xiting Yan \(^{3}\) , Paul Hansen \(^{2}\) , Marianne Carlon \(^{5}\) , Emanuela Cortesi \(^{5}\) , Marie Vermant \(^{5}\) , Robin Vos \(^{5}\) , Laurens J. De Sadleer \(^{5}\) , Ivan O Rosas \(^{6}\) , Ricardo Pineda \(^{7}\) , John Sembrat \(^{7}\) , Melanie Königshoff \(^{7}\) , John E. McDonough \(^{3}\) , Bart M. Vanaudenaerde \(^{5}\) , Wim A. Wuyts \(^{5}\) , Naftali Kaminski \(^{3\dagger}\) , Jun Ding \(^{1,2,8\ast}\)
+
+<|ref|>text<|/ref|><|det|>[[90, 164, 905, 339]]<|/det|>
+1 Quantitative Life Sciences, Faculty of Medicine & Health Sciences, McGill University, Montreal, QC, Canada. 2 Meakins- Christie Laboratories, Translational Research in Respiratory Diseases Program, Research Institute of the McGill University Health Centre, Montreal, QC, Canada. 3 Pulmonary, Critical Care and Sleep Medicine, Yale University, School of Medicine, New Haven, CT, United States. 4 Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, United States. 5 Laboratory of Respiratory Diseases and Thoracic Surgery (BREATHE), Department of Chronic Diseases and Metabolism, KU Leuven, Belgium. 6 Division of Pulmonary, Critical Care and Sleep Medicine, Baylor College of Medicine, Houston, TX, USA. 7 Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA. 8 Mila - Quebec AI Institute, Montreal, QC, Canada
+
+<|ref|>text<|/ref|><|det|>[[92, 352, 709, 382]]<|/det|>
+\(^{\dagger}\) These authors contributed equally \(^{\ast}\) Corresponding authors, NK (naftali.kaminski@yale.edu); JD (jun.ding@mcgill.ca)
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 395, 164, 408]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[92, 408, 905, 595]]<|/det|>
+Human diseases are characterized by intricate cellular dynamics. Single- cell sequencing provides critical insights, yet a persistent gap remains in computational tools for detailed disease progression analysis and targeted in- silico drug interventions. Here, we introduce UNAGI, a deep generative neural network tailored to analyze time- series single- cell transcriptomic data. This tool captures the complex cellular dynamics underlying disease progression, enhancing drug perturbation modeling and discovery. When applied to a dataset from patients with Idiopathic Pulmonary Fibrosis (IPF), UNAGI learns disease- informed cell embeddings that sharpen our understanding of disease progression, leading to the identification of potential therapeutic drug candidates. Validation via proteomics reveals the accuracy of UNAGI's cellular dynamics analyses, and the use of the Fibrotic Cocktail treated human Precision- cut Lung Slices confirms UNAGI's predictions that Nifedipine, an antihypertensive drug, may have antifibrotic effects on human tissues. UNAGI's versatility extends to other diseases, including a COVID dataset, demonstrating adaptability and confirming its broader applicability in decoding complex cellular dynamics beyond IPF, amplifying its utility in the quest for therapeutic solutions across diverse pathological landscapes.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 624, 133, 636]]<|/det|>
+## Main
+
+<|ref|>text<|/ref|><|det|>[[92, 636, 905, 737]]<|/det|>
+Complex diseases emerge through the interaction of genetic and environmental factors over time. The complexity of the interactions between these heterogeneous factors among individuals and populations challenges the understanding of disease progression \(^{1 - 3}\) . Treating multifactorial diseases requires therapies that address multiple interacting processes, which complicates and prolongs the drug development process \(^{4,5}\) . The lack of understanding of disease cellular dynamics poses challenges to the effectiveness of therapeutic targets and developed drugs, as most of them are developed in animal or cell culture models that ignore the complexity and dynamics of the human disease.
+
+<|ref|>text<|/ref|><|det|>[[92, 750, 905, 907]]<|/det|>
+Single- cell RNA sequencing (scRNA- seq) stands at the frontier of potential solutions, offering an unprecedented opportunity to analyze cell populations at single- cell resolution \(^{6,7}\) , and profile the complex and heterogeneous systems \(^{8,9}\) , thereby uncovering rare cell populations and aberrant cell states that are pivotal to diseases \(^{10}\) . Computation methods including Seurat \(^{11}\) , Scanpy \(^{12}\) , Monocle \(^{13}\) , Cellar \(^{14}\) and scVI \(^{15}\) could analyze the noisy, high- dimensional, and large- scale scRNA- seq data and sketch cellular dynamics. However, scRNA- seq data is often a snapshot of the cellular states at a specific time point and cannot account for the continuous biological process, such as differentiation or immune responses, during the progression of a disease. Time- series scRNA- seq data can enhance our grasp on the regulatory mechanisms underpinning disease progression based on distinct samples from multiple time points \(^{16}\) . Nevertheless, cell asynchrony presents new computational challenges to uncover the temporal cellular dynamics \(^{8,16,17}\) . When applying snapshot- based scRNA- seq analysis tools to time- series data, they tend to perceive the data as discrete snapshots, overlooking
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 65, 905, 95]]<|/det|>
+the continuity and temporal progression inherent to time- series data. The omission of nuanced temporal information, like disease stage transitions, is not accurately modeled.
+
+<|ref|>text<|/ref|><|det|>[[90, 108, 905, 410]]<|/det|>
+Computational methods have been developed to address the challenges raised by time- series single- cell transcriptome data, however both conventional methods such as scdiff18 and CSHMMs19,20, and deep learning- based methods such as RVAgene21 and TDL22 are engineered for generic single- cell data processing, inadvertently bypassing the specialized necessities tied to complex diseases. Rigorous preprocessing and normalization, often needed by noisy single- cell data for complex diseases, can shift the data into unconventional distributions, making them ill- suited for the direct application of many existing models on single- cell applications15,23,24. These techniques were often not originally designed to handle data that deviates from conventional distributions, leading to suboptimal or even inaccurate results. When it comes to the critical step of cell embedding learning, these methods typically employ a one- size- fits- all approach. Their dimensionality reductions and cell embedding strategies are largely generic, devoid of the flexibility to integrate disease- specific signatures or intricacies, rendering them less effective in capturing nuanced biological variances associated with complex diseases. Another salient gap in current single- cell methodologies is the absence of unsupervised in- silico exploration capabilities. Although GEARS25 and scGen23 are able to perform in- silico perturbations, they weren't designed to process time- series data and require the in- vitro screening of perturbation response of disease and drug treatments as the supervision. Thus, there is a pressing need for methods that can virtually examine thousands of potential drugs and compounds on single- cell disease data without ground truth training data. The surge in large- scale public drug treatment databases, like the Connectivity Map (CMAP) database26,27, may provide the missing link to the unsupervised single- cell in- silico drug perturbations. Coupled with this, given the vast pool of drug candidates and the intricate cellular dynamics of diseases, an interactive visualization tool is indispensable for efficiently probing potential drugs and priming them for further experimental validation.
+
+<|ref|>text<|/ref|><|det|>[[90, 421, 905, 666]]<|/det|>
+Addressing these pressing gaps, we present UNAGI, a comprehensive unsupervised in- silico cellular dynamics and drug discovery framework. UNAGI deciphers cellular dynamics from human disease time- series single- cell data and facilitates in- silico drug perturbations to earmark therapeutic targets and drugs potentially active against complex human diseases. All outputs, from cellular dynamics to drug perturbations, are rendered in an interactive visual format within the UNAGI framework. Nestled within a deep learning architecture Variational Autoencoder- Generative adversarial network (VAE- GAN), UNAGI is tailored to manage diverse data distributions frequently arising post- normalization. It also employs disease- informed cell embeddings, harnessing crucial gene markers derived from the disease dataset. On achieving cell embeddings, UNAGI fabricates a graph that chronologically links cell clusters across disease stages, subsequently deducing the gene regulatory network orchestrating these connections. UNAGI is primed to leverage time- series data, enabling a precise portrayal of cellular dynamics and capture of disease markers and gene regulators. Lastly, the deep generative prowess of the UNAGI framework powers an in- silico drug perturbation module, simulating drug impacts by manipulating the latent space informed by real drug perturbation data from the CMAP database. This allows for an empirical assessment of drug efficacy based on cellular shifts towards healthier states following drug treatment. The in- silico perturbation module can similarly be utilized to investigate therapeutic pathways, employing an approach akin to the one used in drug perturbation analysis.
+
+<|ref|>text<|/ref|><|det|>[[90, 677, 905, 922]]<|/det|>
+We demonstrate UNAGI on a comprehensive single- nuclei RNA- seq (snRNA- seq) IPF dataset. IPF is a complex lethal lung disease characterized by irreversible lung scarring, leading to progressive decline in lung function and death28- 30. Present therapeutic options for IPF are markedly narrow; only two FDA- approved medications, Pirfenidone31 and Nintedanib32, exist, and their main effect is slowing lung function decline, not reversing fibrosis, or making the patient feel better33. Despite their approval, their specific impact on disease mechanisms remains unclear32- 34. Recent studies10,35 highlighted the molecular and cellular diversity of the IPF lung, but this information has not been yet incorporated in the development of therapies for IPF, although some studies suggested that computational analyses may identify potential drugs for human pulmonary fibrosis36. The push towards developing potent IPF therapeutics is hampered further by the incomplete understanding of the dynamic changes of diverse cellular populations throughout IPF progression. We apply UNAGI to a unique dataset that contains samples from differentially affected lung regions, allowing analysis of disease progression, and highlighting UNAGI's ability to generate compact low- dimensional representations for subsequent tasks, outclassing existing methods. Further, we apply proteomics analysis and Precision- cut Lung Slices (PCLS) analysis37,38 to experimentally confirm the results and predictions of UNAGI. Taken together, our findings corroborate UNAGI's capability not just in decoding cellular dynamics and underpinning regulatory networks but also in potentially accelerating drug development by spotlighting potential therapeutic targets and drug candidates.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[95, 78, 904, 670]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[92, 681, 906, 881]]<|/det|>
+Fig. 1 | UNAGI overview: resolving cellular dynamics of complex disease & potential therapeutics through single-cell embeddings. a, Phase 1: UNAGI employs a VAE-GAN paired with a graph convolution layer. This setup harnesses the complexities of single-cell data, producing a 'Z' latent space that bridges encoding and decoding with minimal error. b, Phase 2: Derived from the 'Z' embeddings, a temporal dynamics graph emerges. Here, the Leiden clustering method discerns cell populations, subsequently connecting them across stages based on their inherent similarity. c, Phase 3: The iDREM tool comes into play, spotlighting key gene regulators and genes that influence disease progression. These insights are channeled into an iterative model training, honing in on specific gene markers of the disease. d, With the model in place, UNAGI initiates in-silico perturbations, either directly tweaking drug target gene expressions (i) or manipulating gene expressions via established gene interaction networks (ii) to simulate drug treatment impact. e, UNAGI's encoder processes the perturbed cell population alongside its peers. The perturbation scores, derived from the 'Z' space embeddings generated by the UNAGI encoder, assist in identifying potential drug candidates. These candidates are evaluated based on their ability to transition diseased cells towards healthier states, such as those resembling healthy control cells, thereby contributing to the treatment of the disease.
+
+<|ref|>text<|/ref|><|det|>[[92, 895, 432, 925]]<|/det|>
+ResultsOverview of UNAGI conceptual framework
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 65, 905, 410]]<|/det|>
+UNAGI, unified in- silico cellular dynamics and drug discovery framework, is a computational framework that integrates time- series single- cell sequencing data with sophisticated deep- learning techniques to unravel intricate cellular dynamics and identify potent therapeutic interventions against multifaceted diseases. This is achieved using the following three components: (1) UNAGI applies a VAE- GAN to capture cellular information in a reduced latent space (Fig. 1a). It processes single- cell data as continuous, zero- inflated log- normal (ZILN) distributions (or other distributions that well fit the data in other application scenarios) because this often better matches the distribution of single- cell data post rigorous preprocessing and normalization (e.g., in the IPF data employed in this study). With a cell- by- gene normalized counts matrix as input, a cell graph convolution (GCN) layer is introduced to manage the sparse and noisy nature of the data. Particularly, the GCN layer leverages the structured relationships between cells to mitigate the dropout noise common in single- cell data, enhancing the accuracy of cellular representations. This data, further refined by a VAE, results in lower- dimensional embeddings, with an adversarial discriminator ensuring the synthetic quality of these representations. (2) After embedding, cell populations are identified using the Leiden clustering approach and visualized with UMAP. A temporal dynamics graph is then constructed by evaluating cell population similarities during the disease progression, linking them based on their likeness (Fig. 1b). Each trajectory within the graph then forms the basis for deriving gene regulatory networks using the iDREM tool (Fig. 1c). (3) An iterative refinement process toggles between the embedding and temporal dynamics stages. Critical gene regulators, including transcription factors, cofactors, and epigenetic modulators, identified from the temporal cellular dynamics reconstruction stage are emphasized during the subsequent embedding phase, ensuring that the cell representation learning places heightened focus on these pivotal elements related to disease progression in each iteration. (4) Upon reaching predefined stopping criteria, UNAGI then employs in- silico perturbations to quantify the effectiveness of therapeutic interventions (Fig. 1d). Using the trained VAE- GAN generative model, UNAGI simulates cells under various drug treatments or pathway perturbations. Each perturbation's impact is scored and ranked based on its ability to shift the diseased cells closer to a healthier state (Fig. 1e).
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 422, 904, 451]]<|/det|>
+## Staging samples based on tissue involvement as measured by the surface density allows assessments of mesenchymal cellular population dynamics during disease progression
+
+<|ref|>text<|/ref|><|det|>[[92, 451, 905, 679]]<|/det|>
+A true longitudinal profiling of the lung cells from the same patient across different IPF stages is impossible because patients are rarely if ever biopsied more than once. Thus, to investigate the cellular dynamics along the progression of human IPF tissues, we analyze samples from differentially affected regions of the IPF lung using a strategy previously described. To build the surrogate "longitudinal" single- cell data, here we employed a Gaussian density estimator to classify all samples (and thus all cells) into different IPF stages. The model will learn the best number of IPF stages and the associated Gaussian parameters (mean and standard deviation) for each IPF tissue involvement stage based on the profiled alveolar surface density (Supplementary Fig. 1a,b) as previously described. All the samples were categorized based on their alveolar surface density into 4 IPF stages: Healthy (Control, or stage 0), Normal looking IPF (stage 1), moderately involved IPF (stage 2), and Severe (stage 3). This 4- stage classification matches the existing understanding of the disease and has been previously validated.39- 41. After the density estimation analysis, we got the samples and cells assigned to these 4 IPF stages (Supplementary Fig. 1c). Specifically, 30 samples were categorized as healthy (135,536 cells). Seven samples were classified as the IPF stage 1 (41, 957 cells). The stage 2 data is composed of 7 samples (21, 531 cells) while the stage 3 data comprises 10 samples (22, 520 cells) (Supplementary Fig. 1d). As shown in Supplementary Fig. 1e, there's a discernible increase in mesenchymal cells starting from IPF stage 1, hinting at a possible rise in fibroblast cells from this stage onward.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 692, 660, 707]]<|/det|>
+## UNAGI effectively identifies varying cell populations across IPF stages
+
+<|ref|>text<|/ref|><|det|>[[92, 707, 905, 922]]<|/det|>
+After applying UNAGI on the four stages IPF snRNA- seq dataset and performing clustering and visualization on the latent space, we have observed a continuous trajectory of healthy fibroblasts towards corresponding, fibrotic IPF archetypes, prompting us to focus on and explore stromal cells using UNAGI. UNAGI showed its effectiveness in cell embeddings by achieving a 0.74 average ARI of all stages. UNAGI identified 11 distinct cell types in Controls, with more emerging in subsequent IPF stages (Fig. 2a), which we annotated based on the expression of canonical cell markers (Fig. 2b and independent manual cell- type annotations in supplementary Fig. 2). UNAGI can capture cell subpopulations, like fibrotic fibroblasts and airway fibroblast cells, suggesting extended fibrosis through the progression. Furthermore, UNAGI revealed differences in cellular heterogeneity: Smooth muscle cells (SMC; marked by ZNF385D and PRUNE2), and alveolar pericyte cells (characterized by ADARB2 and LRRTM4) were predominantly homogenous. In contrast, fibroblast cell populations displayed greater heterogeneity, within both alveolar (denoted by ROBO2 and SLIT2) and adventitial fibroblasts. Fibroblast proportions substantially increase in IPF compared to controls — from less than 15% to more than 40%—validating that fibroblast accumulation is a hallmark of IPF progression. (Fig. 2c). The alveolar fibroblast cell population exhibited the most substantial increase, while the fibrotic fibroblast archetype appeared only in subsequent IPF stages. The proportions of vascular endothelial cells consistently
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 66, 905, 97]]<|/det|>
+decreased as IPF progressed. The cell embeddings from IPF data reveal a progressive cell population across IPF stages, serving as a foundation for constructing a temporal dynamic graph depicting IPF progression.
+
+<|ref|>image<|/ref|><|det|>[[92, 111, 900, 608]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[90, 616, 905, 746]]<|/det|>
+Fig. 2 | UNAGI identifies progressive heterogenous cell populations across IPF stages. a, UMAP visualization: Mesenchymal cells across various IPF stages are depicted. Each point corresponds to a cell; the first column categorizes them by cell type (e.g., SMC = smooth muscle cell, VE = vascular endothelial), and the second by Leiden cluster IDs. This panel underscores UNAGI's ability to learn a potent cell embedding, ensuring premium cell clustering. b, Gene dot plots: Dot plots illustrating the key biomarkers for each identified cell type across four stages of IPF. In these plots, the size of each circle indicates the proportion of cells expressing the gene, and the circle's color reflects the level of normalized gene expression. c, Cell composition chart: A visualization of the shifts in cell type composition along with IPF disease progression. Colors indicate the specific cell type. Notably, there's a discernible expansion of fibroblast cells as the disease progresses.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 760, 904, 789]]<|/det|>
+## UNAGI reconstructs the temporal dynamics graph and the underlying gene regulatory networks during disease progression
+
+<|ref|>text<|/ref|><|det|>[[92, 789, 905, 904]]<|/det|>
+UNAGI can effectively reconstruct the cellular dynamics associated with time series or disease progression data based on the cell embeddings learned by the model. Within our analytical framework, a "track" delineates a distinct trajectory within the reconstructed dynamics graph, marking the sequential cellular state transitions corresponding to specific cell clusters or populations. These tracks not only identify pathways but also chronicle the journey of cellular progression and evolution. Within mesenchymal cells, we have discerned 10 distinct progression tracks (Fig. 3a), transitioning from the IPF stage 0 (healthy controls) to IPF stage 3 (severe fibrosis). Two of these tracks are composed of fibroblast cells, FibAlv- 4 traces the cellular state shifts of alveolar fibroblast cells during IPF progression while FibAdv- 17 illustrates the cellular dynamics of remaining adventitial,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 65, 904, 95]]<|/det|>
+airway, and fibrotic fibroblasts. Of note, the fibroblast tracks in the dynamics graph contain multiple branches, potentially reflecting the multifaceted roles of fibroblast cells in the fibrosis process44.
+
+<|ref|>image<|/ref|><|det|>[[100, 110, 900, 688]]<|/det|>
+
+
+<|ref|>image_caption<|/ref|><|det|>[[92, 695, 906, 881]]<|/det|>
+**Fig. 3 | UNAGI reconstructs the temporal dynamics and the underlying gene regulatory networks of cellular dynamics during IPF progression. a,** Dynamics graph of IPF progression within the mesenchymal cell lineage, comprising four IPF stages. Each node symbolizes a cell population, colored according to cell type, and the edges between two nodes depict the progression trajectory across disease stages. Trajectories, spanning from Control to Stage 3, are termed progression tracks. Each track is named with the specific cell type and the corresponding Control cluster-ID. **b,** Gene regulatory networks for the FibAlv-4 track, were reconstructed using the iDREM tool. Individual nodes signify a set of genes, and edges connecting two nodes represent gene regulators regulating expression changes. Paths encompassing nodes from Control to Stage 3 depict a consistent set of genes displaying the same expression changes throughout IPF progression. The enriched pathways associated with gene paths were also provided. **c,** the temporal regulatory networks for the FibAdv-17 track. **d,** Line chart of expression of the top dynamic gene candidates on the FibAlv-4 and FibAdv-17 tracks, the top 10 most increasing and the top 10 most decreasing candidate marker genes through the IPF progression.
+
+<|ref|>text<|/ref|><|det|>[[92, 894, 904, 922]]<|/det|>
+The gene regulatory network of FibAlv-4, as reconstructed by UNAGI, highlights the central role of gene regulators CTCF, RAD21, SMC3, and especially fibrosis-promoting EP30045,46. This is further supported by
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 65, 905, 210]]<|/det|>
+the genes in Path A of the FibAlv- 4 track, which include recognized fibrosis biomarkers like LTBP1 and LTBP247,48 (Fig. 3b). Pathways enriched in track FibAlv- 4 include: in Path A, Collagen and Extracellular Matrix (ECM) pathways49; in Path B, the PI3K- Akt- mTOR signaling pathway and the focal adhesion pathway, both hallmarks of IPF fibroblasts 50- 52 (Fig. 3b); and in Path C, SLIT2, a known marker of IPF42. The FibAdv- 17 track highlights the contribution of adventitial fibroblasts to matrix remodeling. The discovery of recognized collagen genes like COL3A1 and COL1A253,54, are pivotal markers for IPF. Enriched pathways encompass general ECM- related pathways including ones of collagen formation, organization, trimerization, and degradation, with some variation between paths A to C (Fig. 3c). The MET- activated PTK2 signaling pathway55, a substantial player in pulmonary fibrosis progression, is also highlighted. The genes in Path B, including KCNMA156, NPAS257, ITGA858, and DIO259, all closely associated with IPF.
+
+<|ref|>text<|/ref|><|det|>[[92, 223, 905, 338]]<|/det|>
+The depth and precision of the reconstructed gene regulatory network are underscored by its ability to pinpoint not only pivotal gene regulators and pathways but also the target genes they regulate. These target genes, especially those that exhibit differential expression across disease stages, provide invaluable insights into the temporal dynamics of IPF progression. In the context of the FibAlv- 4 track, the method identifies genes like COL3A1 and SERPINE1, which are induced by the TGF- Beta pathway60, a key player in IPF. Furthermore, the inclusion of top dynamic marker candidates such as DCLK162, TENM3, TENM2, ADRA1A, and GRIA1, all of which have established associations with IPF61- 64, attests to the method's robustness in capturing disease- relevant genes (Fig. 3d).
+
+<|ref|>text<|/ref|><|det|>[[92, 351, 905, 394]]<|/det|>
+Taken, together, UNAGI's comprehensive mapping of gene regulators, pathways, and their target genes in the reconstructed gene regulatory network underscores the method's unparalleled capability in unraveling the intricate molecular interplay underlying IPF.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 407, 904, 436]]<|/det|>
+## UNAGI comprehensively captures novel dynamical and hierarchical static markers across various disease stages
+
+<|ref|>text<|/ref|><|det|>[[92, 436, 905, 579]]<|/det|>
+Conventional single- cell analysis primarily identifies differentially expressed markers between healthy and diseased cells. In contrast, we developed UNAGI to identify dynamic marker genes that offer a longitudinal profile of cellular state changes throughout IPF progression. It discerns dynamic markers for individual cell populations, tracing gene expression shifts across disease stages. All identified candidate biomarker genes from the above cell dynamics gene regulatory network for each track will be subjected to a permutation test to assess their statistical significance. This test involves random shuffling of cells from the track across various stages. Subsequently, we calculate the sum of fold changes in gene expression between these stages to establish a background distribution for comparative analysis. Candidate genes that are deemed statistically significant through this test will be considered as dynamic markers, closely associated with the track in the analysis (as detailed in the "Dynamic markers discovery" section of the Methods).
+
+<|ref|>text<|/ref|><|det|>[[92, 592, 905, 750]]<|/det|>
+Fig. 4a showcases heatmaps of the top 5 dynamic markers for each track, both those that increase and decrease during disease progression (a comprehensive list is available in Supplementary Table 1). For instance, in the FibAdv- 17 track, markers like LUZP2, ITGBL1, and AOX1, previously reported as differentially expressed in IPF65, are highlighted. Notably, NLGN1, GFRA1, and AOX1 are markers for adventitial fibroblasts66 and emerge as a top- decreasing temporal dynamic marker in this track, suggestive of a loss of respective cell identity. The FibAlv- 4 track, on the other hand, features markers like DCLK1, TENM3, ADRA1A, GRIA1, and EPHA3, all of which have strong ties to lung fibrosis61- 64,67. It is important to mention that while our discussion here primarily focused on monotonically increasing and decreasing biomarkers, which are of main interest in our study, the model we developed is also able to identify biomarker genes with other patterns. An example of this is genes that initially increase and then decrease, as observed in path B of the FibAdv- 17 track.
+
+<|ref|>text<|/ref|><|det|>[[92, 763, 905, 922]]<|/det|>
+To experimentally verify the dynamic markers identified by UNAGI, we performed proteomics of matched tissue blocks, 3 samples each from 10 IPF patients across different stages (based on the same surface density criteria) and one each from 10 control donors (Supplementary Table 2). We identified 1070 dynamic proteins from the proteomics data and 606 dynamic gene markers in the snRNA- seq dataset. Further analysis revealed that 151 dynamic proteins have corresponding protein- coding genes in the snRNA- seq data. Interestingly, 40 out of 151 dynamic markers overlapped with dynamic proteins(Supplementary Fig. 3a). Hypergeometric testing on individual tracks revealed statistical significance \((P - value < 0.05\) is set as the default cut- off) for protein- coding genes of dynamic proteins in four specific tracks: FibAlv- 4 \((P - value = 0.003)\) , VEven- 2 \((P - value = 0.015)\) , LymEnd- 19 \((P - value = 0.033)\) , and VEcap- 1 \((P - value = 0.048)\) , as well as in the overall result (Supplementary Fig. 3b). Notably, the FibAlv- 4 track contained 137 dynamic protein- encoding genes, and 14 of these genes produce dynamic proteins (Fig 4b).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[95, 81, 904, 675]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[92, 682, 905, 883]]<|/det|>
+Fig. 4 I UNAGI comprehensively captures novel dynamical and hierarchical static markers across various IPF stages. a, Heatmaps presenting the most pronounced increasing (left) and decreasing (right) temporal dynamic markers' expressions, each z-score normalized, across tracks. b, The left panel showcases heatmaps of dynamic gene markers from the FibAlv-4 cluster. Importantly, the right panel provides experimental verification of these markers through corresponding protein expressions derived from proteomics data. Line plots accompanying these highlight gene expression shifts of these dynamic markers over the course of IPF progression. c, Dendrogram visualizing control cell populations. Each node signifies a cell type-specific population. The Fibroblast Adventitial cluster is accentuated. Using UNAGI, various hierarchical biomarkers are discernible at different levels, either contrasting with other cell types or juxtaposing subpopulations within the same cell type. d, Heatmap detailing the top 25 hierarchical static markers' expressions, all z-score normalized, for the Fibroblast Adventitial cluster at level 0. This highlights UNAGI's proficiency in pinpointing general cell type markers. e, Heatmap delineating the top 25 hierarchical marker gene expressions, z-score normalized, for the Fibroblast Adventitial cluster at level 4, set against two Fibroblast Alveolar clusters, emphasizing UNAGI's capability in cell subtype marker identification.
+
+<|ref|>text<|/ref|><|det|>[[92, 895, 904, 925]]<|/det|>
+A notable observation from our snRNA-seq and proteomics data is that five of these overlapping dynamic markers are collagens (COL1A1, COL1A2, COL3A1, COL3A1, COL14A1), confirming that progressive matrix
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 66, 905, 124]]<|/det|>
+remodeling is intrinsically intertwined with the development of fibrosis68. Moreover, a majority of the overlapped dynamic markers have been previously associated with pulmonary fibrosis54,69- 71, including CCN5, CDH13, MYH10, PAPSS2, and LMCD. This proteomics data serves as a validation, confirming that the discovered dynamical genes play a crucial role in the progression of IPF.
+
+<|ref|>text<|/ref|><|det|>[[92, 137, 905, 194]]<|/det|>
+UNAGI can identify both dynamic and static markers. While dynamic markers offer insights into cellular state changes throughout disease progression, static markers are crucial for distinguishing between different cell types and subpopulations within a given stage. Existing static biomarker discovery pipelines11,12 usually employ a "one vs. the rest" strategy and may fail to distinguish the difference between different subtypes.
+
+<|ref|>text<|/ref|><|det|>[[92, 208, 905, 380]]<|/det|>
+UNAGI explores the hierarchies of marker genes that not only distinguish different cell populations but also capture the finer heterogeneity among cell subpopulations. For instance, focusing on the FibAdv- 17 cluster of controls, cell subpopulations are primarily divided into three main groups: fibroblasts, vascular endothelial cells, and lymphatic endothelial cells (Fig. 4c, and dendrograms of all four stages are in Supplementary Fig. 4). The fibroblast adventitial population spans 5 levels in the dendrogram. Fig. 4d showcases the top twenty- five positive hierarchical static markers for fibroblast adventitial cells at dendrogram level 0. These markers distinguish the fibroblast adventitial cluster from all other clusters. UNAGI's results are consistent with the dendrogram structure, highlighting the close relationship between fibroblast adventitial and fibroblast alveolar clusters. Notably, UNAGI identified key markers like IGF1 and collagen genes such as COL24A1 and COL7A1, emphasizing the role of elevated interstitial collagen levels in IPF72. Other markers like ANGPTL4 and WT1 further underscore the method's precision in identifying relevant genes73 (top 25 level 0 positive and negative markers are detailed in Supplementary Fig. 5).
+
+<|ref|>text<|/ref|><|det|>[[92, 393, 905, 508]]<|/det|>
+Fig. 4e presents the top 25 positive hierarchical static markers for the fibroblast adventitial cluster at level 4 (sub- type level). While there's an overlap with level 0 markers, level 4 introduces unique markers potentially for subtypes like NLGN1, a cell type marker for adventitial fibroblasts66, and MFAP5, previous research indicates that MFAP5+ fibroblast cells are localized to vascular adventitial74 (top 25 level 4 positive and negative markers are detailed in Supplementary Fig. 6). UNAGI's ability to identify both temporal dynamic markers and hierarchical static markers offers a comprehensive lens to study IPF. This dual approach allows for detailed profiling of the disease from both intra- stage and longitudinal (inter- stage) perspectives, enhancing our understanding of its complexities.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 522, 627, 536]]<|/det|>
+## UNAGI identifies potential therapeutic pathways for IPF treatments
+
+<|ref|>text<|/ref|><|det|>[[92, 536, 905, 635]]<|/det|>
+In the preceding sections, we delved into how UNAGI enhances our comprehension of biomarkers and cellular dynamics in the progression of IPF. Building upon this foundational understanding, we now shift our focus to the therapeutic frontiers opened by UNAGI. This involves leveraging its in- silico perturbation capabilities, which are rooted in IPF- specific cell embeddings and the temporal dynamic graph of IPF. This approach paves the way for pinpointing potential therapeutic targets and pathways, a development that promises to be a substantial stride in IPF treatment. Detailed results of these pathway perturbations are systematically presented in Supplementary Table 3.
+
+<|ref|>text<|/ref|><|det|>[[92, 650, 905, 836]]<|/det|>
+Many of the top pathways predicted by UNAGI are in alignment with known IPF- centric pathways. Impressively, of the top 10 therapeutic pathways identified, at least seven have been previously associated with IPF progression and potential treatments. For instance, the discovery of the ROBO pathway: Signaling by ROBO receptors (Score=0.5890, \(\mathrm{FDR} = 1.1028 \times 10^{- 14}\) ) which has been strongly linked to IPF progression42,75. Additionally, the Netrin 1 signaling pathway (Score=0.6548, \(\mathrm{FDR} = 3.4698 \times 10^{- 19}\) ) has been correlated with various forms of pulmonary fibrosis, including bleomycin- induced pulmonary fibrosis62,76. Moreover, UNAGI's ability to identify target genes within these pathways offers a deeper understanding of disease progression. For example, the Calcium signaling pathway in fibroblast is highly related to fibrosis77, genes within the pathway such as EGFR, which is linked to fibroblast proliferation77,78, have been highlighted. Beyond known pathways, UNAGI also uncovered novel pathways. While some of these pathways might not have a direct association with IPF, their target genes often play critical roles in the disease's progression. This is evident in the discovery of genes like GRIA61,79 and ERBB48,63, both of which have substantial associations with IPF progression.
+
+<|ref|>text<|/ref|><|det|>[[92, 850, 905, 906]]<|/det|>
+The results from pathway perturbations, as showcased in Fig. 5a,b, further demonstrate UNAGI's capability. The perturbations reveal the potential of certain pathways to revert cells to a healthier state, suggesting their therapeutic potential. For instance, the perturbation of the ECM organization pathway in various IPF stages suggests its potential to guide cells to a less severe IPF cellular state.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[90, 70, 901, 640]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[90, 644, 906, 818]]<|/det|>
+Fig. 5 I UNAGI identifies potential therapeutic pathways and potent drugs for IPF treatments. a, Bar chart of the track FibAlv-4 pathway perturbation results. The highlighted pathways are also identified in the reconstructed gene regulatory network of the track. b, Split-violin plot of the gene expression differences for the top 20 most changing genes of in-silico extracellular matrix (ECM) organization pathway perturbation in Stage 1 of the FibAlv-4 track. c, PCA plots of latent space Z of in-silico ECM organization pathway perturbation effects and dots represent cells from distinct stages. Lines connected to two nodes are the PAGA connectivity score between two clusters, where the width of a line is proportional to the strength of the score, and the length of the line can represent the distance between the UNAGI embeddings of the two connected clusters. (e.g., Line connecting Control and Perturbed Stage 1 \((L_{CP_1})\) ). d, Bar chart of the top overall drug perturbation results. e, Split-violin plot of gene expressions for the top 10 changing targets of Nintedanib in the gene interactions network both before and after perturbation in Stage 1 of the FibAlv-4 track. f, PCA plots of Nintedanib perturbation effectiveness.
+
+<|ref|>text<|/ref|><|det|>[[92, 831, 906, 918]]<|/det|>
+A central takeaway from Fig. 5c is its demonstration that in- silico pathway perturbations effectively shift the cellular states towards healthier conditions. The perturbation's impact on gene expression, especially within the ECM organization pathway, is evident in the reduction of regulated gene expressions. By introducing these perturbed cells into the VAE- GAN model, cell embeddings are produced. To visualize these embeddings, Principal Components Analysis (PCA) was employed. Fig. 5c provides a visual representation of the effects of repressing the ECM organization pathway across IPF stages 1, 2, and 3. In the Stage 1 perturbation, the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 66, 905, 212]]<|/det|>
+perturbed cell population, denoted as \(P_{1}\) , is observed to be closer to the Control stage C than to the stage 1 cells, \(S_{1}\) , and is notably distant from stage 3 cells, \(S_{3}\) . The distance in the PCA plot serves as a metric of similarity, indicating that \(P_{1}\) more closely resembles the Control stage C than \(S_{1}\) , suggesting a potential regression of the cellular state towards a healthier condition. This similarity is further emphasized by the thickness of connection lines between cell clusters, which represents the strength of the PAGA connectivity score. Specifically, the line \(L_{CP_{1}}\) is thicker than \(L_{CS_{1}}\) , indicating a higher similarity between the Control stage C and \(P_{1}\) in the latent space. In the Stage 2 perturbation, the perturbed cell population, \(P_{2}\) , gravitates towards \(S_{1}\) . Both PCA distance and PAGA connectivity scores suggest that a perturbation in Stage 2 could potentially guide cells towards a milder IPF cellular state. A similar trend is observed in Stage 3, where the perturbed cell population, \(P_{3}\) , shifts towards a relatively healthier cellular state.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 225, 564, 239]]<|/det|>
+## UNAGI discovers novel drug candidates for IPF treatments
+
+<|ref|>text<|/ref|><|det|>[[92, 239, 905, 296]]<|/det|>
+UNAGI's in- silico drug perturbation approach, akin to its pathway perturbation, leverages and integrates the CMAP dataset. Hereby, UNAGI has pinpointed several drug candidates that could substantially impact the progression of IPF (Fig. 5d). Comprehensive results of all drug perturbations are detailed in Supplementary Table 4.
+
+<|ref|>text<|/ref|><|det|>[[92, 308, 905, 440]]<|/det|>
+Apicidin, with a score of 0.5021 and an FDR=4.551 \(\times 10^{- 105}\) , is a histone deacetylase inhibitor. Previous studies have highlighted its potential as an antifibrotic drug in pulmonary fibrosis80,81. Nifedipine, scoring 0.3834 with an \(\mathrm{FDR} = 1.152\times 10^{- 57}\) , has been shown to reduce bleomycin- induced pulmonary fibrosis by disrupting calcium signaling in fibroblasts78. Cilomilast, a phosphodiesterase 4 (PDE4) inhibitor, has a score of 0.3082 and an \(\mathrm{FDR} = 4.407\times 10^{- 35}\) . It has demonstrated potential in attenuating pulmonary fibrosis in mice82. Niguledipine, scoring 0.3842 and an \(\mathrm{FDR} = 6.160\times 10^{- 58}\) , is a calcium channel blocker and an \(\alpha 1\) adrenergic receptor antagonist, showing anti- fibrotic effects in the lung78. The compound 8- bromo- cGMP, which impacts PRKG1, has a score of 0.3099 and an \(\mathrm{FDR} = 1.562\times 10^{- 35}\) , and is associated with the TGF- beta pathways in the fibrosis process83.
+
+<|ref|>text<|/ref|><|det|>[[92, 451, 905, 553]]<|/det|>
+Moreover, drugs like Ibudilast (Score=0.3053, \(\mathrm{FDR} = 2.465\times 10^{- 34}\) ) and Topiramate (Score=0.3203, \(\mathrm{FDR} = 2.411\times 10^{- 38}\) ) have been identified, with the former potentially having anti- fibrotic effects similar to other PDE4 inhibitors84, and the latter regulating GRIA1, which is associated with lung fibrotic diseases61,79. Myricitrin (Score=0.2045, \(\mathrm{FDR} = 2.590\times 10^{- 13}\) ) has been shown to exhibit anti- fibrotic activity in certain conditions85, while Regorafenib (Score=0.1407, \(\mathrm{FDR} = 2.653\times 10^{- 5}\) ) attenuates fibrosis by inhibiting the TGF- beta pathway86. Notably, UNAGI also identified Nintedanib (Score=0.1102, \(\mathrm{FDR} = 0.0111\) ), an FDA- approved drug for IPF treatment.
+
+<|ref|>text<|/ref|><|det|>[[92, 565, 905, 636]]<|/det|>
+The target gene intervention of Nintedanib is shown in Fig. 5e. The corresponding perturbation results, visualized in Fig. 5f across IPF stages 1, 2, and 3, emphasize the potential of these drugs to shift cell populations towards healthier states. The consistently higher PAGA connectivity scores between perturbed cell populations and healthier cellular stages indicate that the perturbed cell populations are more akin to healthier cells.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 650, 468, 664]]<|/det|>
+## Benchmarking and computational verifications
+
+<|ref|>text<|/ref|><|det|>[[92, 664, 905, 923]]<|/det|>
+To underscore the effectiveness of UNAGI in cell representation learning, we juxtaposed its capabilities against established methods like scVI15 and SCANPY12. scVI, a deep generative model rooted in VAE, employs the zero- inflated negative binomial (ZINB) distribution to capture the raw count distribution of single- cell data. On the other hand, SCANPY, a standard single- cell analysis pipeline, relies on PCA to encapsulate the high- dimensional single- cell data. Moreover, we performed ablation experiments to verify the effectiveness of individual computational module components of UNAGI. The UNAGI framework's VAE model is designed with the flexibility to select from various data distributions, such as Gaussian, NB (Negative Binomial), ZINB, and ZILN depending on the observed gene expression distribution in a given dataset. For the IPF snRNA- seq data analyzed in this study, the gene expression distribution aligns with a ZILN pattern. To showcase the benefits of adopting a proper data distribution to the cell embedding learning, the VAE model employing ZILN distribution served as the baseline model (BL), GAN and GCN were added to the BL model in our UNAGI framework. Contrasting with the ablation baseline, the full- fledged UNAGI framework integrates all the key components — the ZILN, GAN, and GCN — for the effective learning of cell embeddings. To ensure a balanced evaluation, we employed the Leiden clustering method on the embeddings generated by all seven techniques, adjusting parameters to produce a comparable number of clusters for each stage (UMAPs of all benchmarking methods are detailed in Supplementary Fig. 7). Five metrics were evaluated (Fig. 6a- e): For label metrics including Adjust Rand Index (ARI)87 and Nearest Mutual Information (NMI)88, UNAGI steadily outperforms SCANPY and scVI. For non- label metrics, the label score89 of UNAGI is at least 4% better than other methods,
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[95, 80, 901, 518]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[92, 528, 905, 757]]<|/det|>
+Fig. 6 I UNAGI outperforms alternative approaches in learning the cell embeddings and can effectively identify efficacious drugs in in-silico perturbations. a, Adjusted Rand Index (ARI) and b, Normalized Mutual Information (NMI) illustrate the effectiveness of the learned cell embeddings for downstream clustering tasks. c, Label score, indicating that cells within neighborhoods primarily have the same cell type. d, Silhouette score. e, Davis-Bouldin index (DBI); a lower DBI signifies better clustering. These scores (c, d, e) are unsupervised metrics employed to demonstrate the clustering quality derived from the learned cell embeddings. f, Box plot presenting the silhouette scores of UNAGI across various training iterations, emphasizing that the iterative strategy progressively enhances cell embeddings and clustering quality with each iteration. g, PCA representation highlighting the impact of sanitary perturbation, which involves reversing the gene expression at Stage 1 back to the patterns observed in the control stage. This process essentially seeks to "normalize" or "sanitize" the aberrant gene expressions, bringing them in line with a control or reference state. h, Distribution patterns for various drug/compound perturbations. The x-axis represents the perturbation score, while the y-axis portrays the density of the fitted Gaussian distribution for each specific setting. i, AUROC and AUPRC metrics in relation to perturbation verification. As a reference, a random drug effectiveness predictor is used as a baseline, with an AUC (Area Under the Curve) score of 0.5, indicating no predictive discrimination, and an average precision (AP) score of 0.5, representing a baseline precision level.
+
+<|ref|>text<|/ref|><|det|>[[92, 771, 905, 886]]<|/det|>
+also suggesting a high homogeneity inside cell neighborhoods. With an average silhouette score nearing 0.205, UNAGI's clusters are more cohesive and distinct. The Davies- Bouldin Index (DBI), averaging at a lower 1.6, further attests to UNAGI's ability to produce clusters that are not only distinct but also internally homogeneous. Diving deeper, we explored the potential of the ZILN distribution to better model normalized single- cell data compared to the ZINB in this study. When scVI was adapted to this distribution, its performance surpassed its original ZINB- based counterpart in this dataset. This underscores the ZILN model's proficiency in capturing the nuanced continuous information inherent in normalized single- cell data, as opposed to the more discrete ZINB. The silhouette score presented in Fig. 6f effectively illustrates the benefits of iterative
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[95, 68, 905, 576]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[90, 583, 905, 888]]<|/det|>
+Fig. 7 I The predictions of UNAGI align with human precision-cut lung slices (PCLS) drug validations. a, UMAP visualization of the PCLS data with each dot representing an individual cell. b, UMAP representation emphasizing the similarity between the real-world treatments of Nifedipine and Nintedanib. Furthermore, cells under in-silico drug treatments (Nifedipine and Nintedanib) closely mirror those under actual treatments. c, Violin plots showcasing that Nintedanib and Nifedipine treatments markedly shift fibrotic cells, bringing them closer in resemblance to healthy control cells. (e.g., \(D_{e}\) (Fibrosis, Nifedipine) is the distance between fibrosis cells and fibrosis cells after Nifedipine treatment). d, Violin plots highlighting the strong alignment between in-silico drug treatments and their real-world counterparts. e, The RRHO (Ranked Rank Hypergeometric Overlap) plots for both Nifedipine and Nintedanib. These plots juxtapose in-silico perturbations post-VAE reconstruction against actual treatments, emphasizing the high degree of similarity between in-silico and real treatments. Specifically, the genes up-regulated and down-regulated in in-silico treatments show strong correlations with those affected in real treatments. f, Box plots and \(R^2\) plots compare the expression of the top differential genes of real treatments (Nintedanib or Nifedipine vs. fibrosis) to in-silico perturbation results. The box plot visualizes the top 25 differential genes (ranked based on log fold changes) for each treatment. The gene expression of the top 100 differential genes in real and in-silico drug treatments are used to calculate the adjusted \(R^2\) metric and generate \(R^2\) plots. This representation is intended to underline the remarkable similarity observed between in-silico drug perturbations and the corresponding actual drug treatments for both Nifedipine and Nintedanib. g, Box plots and \(R^2\) plots of ECM organization target gene expressions from real treatments and in-silico perturbations. The box plots visualize the top 15 genes of ECM based on log fold changes between real treatments and fibrosis cells. The gene expressions of all ECM organization target genes in real and in-silico drug treatments are used to calculate the adjusted \(R^2\) metric and generate \(R^2\) plots.
+
+<|ref|>text<|/ref|><|det|>[[90, 897, 905, 926]]<|/det|>
+optimization (additional metrics refer to Supplementary Fig. 8). This result underscores the importance of the iterative training approach, which fosters a synergistic relationship between cell- embedding learning and the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 66, 905, 110]]<|/det|>
+inference of cellular dynamics. Such an approach not only markedly enhances the method's performance over successive iterations but also demonstrates that disease- sensitive cell representation learning is instrumental in achieving improved cell clustering and potentially enhancing other downstream tasks.
+
+<|ref|>text<|/ref|><|det|>[[92, 123, 905, 310]]<|/det|>
+To rigorously evaluate the proficiency of UNAGI's in- silico perturbations, we embarked on a Stage 1 sanity perturbation, wherein the perturbations were aimed at redirecting them back to control levels (refer to methods for an in- depth explanation). Cells subjected to sanity perturbation overwhelmingly align with the control stage as opposed to their native Stage 1 state (Fig. 6g). Reinforcing this trend, the PAGA connectivity scores indicate that these perturbed cells bear a high resemblance to Control cells, and they substantially deviate from Stage 3 cells. These observations strongly vouch for UNAGI's unmatched precision and efficacy in handling in- silico perturbations. In addition, we delved deeper into assessing UNAGI's aptitude for identifying potent drug candidates using in- silico methodologies. The insights, presented in Fig. 6h, underscore the salience of this tool: in- silico drug perturbations, particularly those with significant FDR values, consistently surpassed the therapeutic scores of random perturbations as expected. Impressively, these results were congruent with the outcomes from sanity drug perturbations, during which we intentionally tweaked target gene expressions to reflect that of an adjacent, healthier stage. This robust alignment unequivocally attests to UNAGI's exceptional ability to single out drugs with a high potential to combat IPF.
+
+<|ref|>text<|/ref|><|det|>[[92, 323, 905, 523]]<|/det|>
+To further stress- test UNAGI's capabilities, especially its prowess in drug repurposing, we set forth a meticulously planned simulation. This simulation was designed to test UNAGI's ability to accurately identify and replicate the effects of known drugs, referred to as 'ground- truth' drugs in our in- silico drug discovery simulation (as detailed in the Methods section). Our approach involved a strategic implantation of drugs within the simulation. We did this by altering the target gene expressions of these drugs at specific magnitudes across various disease stages, thereby establishing a set of ground truths. These modified gene expression levels were intended to mimic the real- world effects of the drugs at different stages of disease progression. Next, we applied the UNAGI to the simulated dataset (with ground truth) to predict the drugs that act against the simulated gene expression changes and examine whether the model can recapture the implanted drugs in the simulation data. The performance of UNAGI in this simulation was rigorously evaluated using two established metrics: the Area Under the Receiver Operating Characteristic Curve (AUROC) and the Area Under the Precision- Recall Curve (AUPRC). UNAGI achieves scores of 0.89 and 0.93, respectively (Fig. 6i). These high scores indicate that UNAGI is highly effective at identifying drugs that target genes with dynamic regulation during disease progression.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 536, 760, 551]]<|/det|>
+## Experimental validation of in-silico drug perturbations via precision-cut lung slices.
+
+<|ref|>text<|/ref|><|det|>[[92, 551, 905, 679]]<|/det|>
+To experimentally validate UNAGI predictions, we utilized the fibrotic cocktail model of PCLS90. We chose to test the model predictions for Nifedipine, an antihypertensive drug not known to have a role in fibrosis treatment, and Nintedanib, an FDA- approved drug for IPF. We stimulated PCLS with DMSO as the Control for 5 days. In the treatment group, PCLS were treated for 3 days with the fibrotic cocktail to induce fibrosis, and treatment, Nifedipine or Nintedanib, started from day 3 until day 5. As read- out, we performed snRNA sequencing (Fig. 7). Latent embeddings of fibroblasts derived from this PCLS experiment reveal intriguing patterns (Fig. 7a). When assessed based on experimental conditions, cells under both Nifedipine and Nintedanib treatments exhibit similar clustering behaviors on the UMAP. This suggests their parallel roles in inhibiting fibroblast activation.
+
+<|ref|>text<|/ref|><|det|>[[92, 692, 905, 907]]<|/det|>
+Utilizing UNAGI's perturbation module, Nintedanib and Nifedipine in- silico perturbed cells gravitate towards the Nintedanib treated population, demonstrating potential therapeutic effects (Fig. 7b). Pairwise Euclidean distances between latent embeddings indicate that both treatments effectively steer the cellular state of fibrosis cells toward a healthier baseline (Fig. 7c) and the in- silico treatments behave like real treatments (Fig. 7d). This observation is solidified by the Mann- Whitney U test confirming the analogous anti- fibrotic properties of both treatments. The Ranked Rank Hypergeometric Overlap (RRHO) confirms that the markers identified in- silico align closely with the biomarkers observed in the PCLS experiments (Fig. 7e). The adjusted \(R^2\) scores for Nintedanib in- silico (0.906) and Nifedipine in- silico (0.932) with respect to the top 100 differentially expressed genes (DEGs) in actual treatment versus fibrosis, as well as the top 25 markers in side- by- side comparisons (Fig. 7f, top 100 DEGs comparisons are detailed in Supplementary Fig. 9), demonstrate the consistency of gene expression patterns between in- silico and real treatments markers. Known IPF markers like IL3391, ADAM1292, and CXCL893 exhibit similar changes in gene expression in both real treatment experiments and in- silico predictions. (Fig. 7g, all ECM organization pathway genes comparisons are listed in Supplementary Fig. 10). The \(R^2\) scores and side- by- side comparisons of real treatments and in- silico gene expression of the ECM organization pathway further validate the capability of the UNAGI model to accurately
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 66, 905, 95]]<|/det|>
+simulate in-silico perturbations on IPF-related targets. The alignment between in-silico drug perturbations and actual drug treatments on the PCLS stands as a testament to the reliability of UNAGI's predictions.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 108, 821, 123]]<|/det|>
+## UNAGI in-silico analysis unveils COVID-19 cellular dynamics and therapeutic opportunities
+
+<|ref|>text<|/ref|><|det|>[[92, 123, 905, 210]]<|/det|>
+To demonstrate the expansive applicability of UNAGI to various complex diseases, we studied the intricate dynamics of COVID- 19. We used a subset of a COVID- 19 dataset94 consisting of 246,948 peripheral blood mononuclear cells from 130 samples with various severities of COVID- 19. We categorized them into four COVID- 19 stages based on the disease severity of patients: Healthy (Control, or stage 0), Asymptomatic or Mild (stage 1), Moderate (stage 2), and Severe or Critical (stage 3). The UNAGI pipeline is applied to the COVID- 19 dataset to reveal the temporal dynamics and discover potential therapeutic targets.
+
+<|ref|>image<|/ref|><|det|>[[95, 222, 902, 640]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[92, 652, 905, 824]]<|/det|>
+Fig. 8 | UNAGI in-silico analysis unveils COVID-19 cellular dynamics and therapeutic opportunities. a, UMAP display of stage 2 COVID-19 data with each dot symbolizing an individual cell. Cells are color-coded based on their respective cell types. b, Dot plot illustrating the expression levels of canonical cell type markers present within the stage 2 COVID-19 data set. c, Dynamic graphs representing the cellular dynamics underlying the COVID-19 progression. Within these graphs, each node corresponds to a cell cluster, and the connecting edges signify the relationships between these nodes (shift of the cell population along with COVID-19 progression). d, Depiction of the reconstructed gene regulatory network for the track 12-CD16. Prominent gene regulators, genes, and pathways discerned from the enrichment analysis are enumerated. e, Bar chart detailing the principal pathway perturbation outcomes. Pathways highlighted have literature support, indicating their potential as therapeutic targets against COVID-19. f, Bar chart outlining the top 10 drug perturbation results. Drugs that are emphasized have been highlighted based on literature support, suggesting their candidacy for treating COVID-19.
+
+<|ref|>text<|/ref|><|det|>[[92, 836, 905, 910]]<|/det|>
+After learning the latent cell representations (Supplementary Fig. 11), UNAGI identified 14 unique cell populations at stage 2 (Fig. 8a), spotlighting nuanced interactions such as between platelet and T- cells, a finding resonating with the previous research94. Here, UNAGI can elucidate unique markers for cell populations, such as MS4A1 and CD79A in B cells, and underscore differential expressions, notably CD8A and CD8B, in CD8 T cells—findings that harmonize with manual annotations (Fig. 8b).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 65, 905, 210]]<|/det|>
+Focusing on the cellular dynamics across the trajectory of COVID- 19, UNAGI identified 7 distinctive tracks reflecting the evolving cellular interplay across the disease stages (Fig. 8c). Fig. 8d deepens the narrative, spotlighting pivotal genes central to the COVID- 19's progression of CD16+ Monocytes, like BHLHE40 which finds an up- regulation in moderate patients95, and EGR1, recognized for influencing SARS- CoV- 2 replication and antiviral responses96. Notably, genes like GRN97 and PLAC898 emerge as notably up- regulated in COVID- 19. Gene enrichment analyses further discern crucial pathways tied to the disease such as interferon signaling and immune system pathways99- 101. Transitioning to predictive capabilities, UNAGI identified potential therapeutic pathways such as the RHO GTPases Activate NADPH Oxidases pathway aligns with modern findings emphasizing its substantial role in COVID- 19102,103 (Fig. 8e). A deep dive into pathways related to Toll- Like Receptors and interferon responses104 further broadens the therapeutic landscape.
+
+<|ref|>text<|/ref|><|det|>[[92, 223, 905, 310]]<|/det|>
+In culmination, Figure 8f accentuates UNAGI's expertise in drug recommendation. Aloxistatin stands out, achieving the highest drug perturbation scores and drawing attention due to its potential against SARS- CoV- 2 proteases105. Additionally, Didanosine, notable for its efficacy against COVID- 19 Polymerase and Exonuclease106, and Ponatinib, are recognized as potent COVID- 19 drugs by other machine learning methods107. This detailed alignment with ongoing research105- 109 not only emphasizes UNAGI's precision but heralds its indispensable role in crafting therapeutic strategies for multifaceted diseases.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 337, 185, 350]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[92, 351, 905, 552]]<|/det|>
+In this manuscript, we describe UNAGI, a computational tool designed to model the temporal cellular dynamics inherent in complex disease progression. Rooted in its design is the use of a Gaussian Mixture Model- based density estimator, which classifies samples into specific disease stages. Harnessing the power of the graph VAE- GAN model, UNAGI handles high- dimensional single- cell data to extract latent embeddings. These embeddings play a crucial role in formulating progression tracks for distinct cell populations, subsequently facilitating the detailed reconstruction of temporal gene regulatory networks. The implementation of UNAGI to differentially affected tissues in IPF allows high- resolution modeling of the cellular trajectories, pivotal gene regulators, and genes that drive or associate with progressive tissue fibrosis in the human lung. Through iterative training, UNAGI sharpens the focus on IPF- specific features, priming itself for simulating and evaluating perturbations on potential target genes and drugs. The fruits of this methodical approach are manifold: UNAGI not only delivers an in- depth understanding of cellular dynamics and the foundational cell- specific gene regulatory networks during the progression of fibrosis but also pinpoints potential therapeutic pathways and drugs against IPF, marking the potential of UNAGI in modeling disease and developing novel therapeutics.
+
+<|ref|>text<|/ref|><|det|>[[92, 564, 905, 922]]<|/det|>
+UNAGI offers a suite of characteristics that distinguish it in the domain of disease comprehension and therapeutic discovery. First and foremost, UNAGI distinguishes itself by its proficiency in creating precise cell embeddings and synthesizing cells via a deep generative neural network. This precision in embeddings enables enhanced cell clustering and identification, surpassing existing methods primarily focused on general cell representation learning. Different from other existing methods, UNAGI's approach involves learning and incorporating key genes, including dynamic markers and gene regulators, that are integral to the specific disease progression. This results in disease- oriented cell embeddings that are finely tuned for diverse downstream tasks related to the disease. Additionally, UNAGI's capability to artificially generate cells from the learned latent space is leveraged to conduct in- silico perturbations. This feature adds a dynamic aspect to disease modeling, allowing for more comprehensive and nuanced exploration of disease mechanisms and potential treatments. Third, UNAGI excels in unraveling the intricate cellular dynamics associated with the progression of a disease. Utilizing the cell embeddings it generates, UNAGI employs a graphical methodology to construct a 'cellular dynamics tree'. This tree effectively maps out the transitions of various cell states and populations as the disease advances. Crucially, UNAGI goes a step further by identifying the underlying gene regulatory network that governs these cellular dynamics, thereby highlighting potential biomarkers and therapeutic targets. In addition, UNAGI's sophisticated analysis enables the comprehensive identification of dynamic markers that track the evolution of the disease, as well as hierarchical static markers that differentiate between distinct cell populations. This dual approach provides a detailed understanding of the cellular heterogeneity at different stages of the disease and its transformation throughout its progression, offering valuable insights into the disease's biology and potential intervention points. Fourth, a standout feature of UNAGI, setting it apart from existing methods, is its ability to perform unsupervised in- silico analysis of pathways and drug perturbations. This aspect of UNAGI allows for the exploration and identification of promising therapeutic pathways and potential drug candidates without the need for pre- existing drug perturbation training datasets, which are often challenging to acquire. This capability provides users with a powerful tool to investigate, evaluate, and prioritize therapeutic options associated with different pathway
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 65, 905, 167]]<|/det|>
+alterations or drug interventions. As a result, UNAGI uncovers a wealth of potential therapeutic strategies and promising drug candidates. Its unsupervised nature substantially enhances the method's applicability and practicality across a variety of complex diseases, offering an advantage over many current drug perturbation approaches that rely on supervised learning and extensive training sets. Lastly, to democratize access to its innovations, we've launched the UNAGI web server, an interactive framework that brings cellular dynamics to life and facilitates in- silico perturbation functions, streamlining the exploration of disease dynamics and potential therapeutic interventions.
+
+<|ref|>text<|/ref|><|det|>[[92, 179, 905, 451]]<|/det|>
+As described UNAGI has led to many biological observations, first by allowing us to uncover in an unbiased manner the trajectories that mesenchymal cells undergo during the progression of fibrosis. One notable observation is the marked proliferation of fibroblast cells, which correlates with the extensive accumulation of fibrosis, a defining characteristic of IPF progression. This proliferation underscores the fibroblasts' central role in the disease's pathology. Moreover, we noted that adventitial and alveolar cells exhibit dynamic and active involvement in IPF development. Conversely, the proportion of vascular endothelial cells consistently decreased as IPF progressed. Second, it allows identifying the cell- specific gene regulators that drive the phenotypic changes during disease progressions such as gene regulators like CTCF, EP300, and SMC3 and their target genes, identified dynamic markers such as COL1A1, COL1A2, COL1A3, and COL14A1, which were validated by proteomics analysis, and suggested hierarchical static markers for sub- cell types, including NLGN1 and MFAP5 for fibroblast adventitial cells. These discoveries enrich our understanding of IPF and could lead to the identification of novel biomarkers and more precise therapies. Finally, UNAGI also illuminates potential IPF pathways that could be targeted for therapeutic interventions like Netrin- 1 signaling and Signaling by ROBO receptors, as well as drugs that may reverse these pathways. Impressively, we were able to validate our model's predictions regarding drugs like nifedipine, previously not considered an antibiotic, and potentially identify marker genes that could be used in the future as biomarkers for target engagement and efficacy. Moreover, UNAGI extends its utility to other complex diseases, such as COVID- 19, with several of its top drug predictions corroborated as repurposed medications for COVID- 19, including Aloxistatin and Didanosine, highlighting its broad potential in biomedical research.
+
+<|ref|>text<|/ref|><|det|>[[92, 464, 905, 580]]<|/det|>
+Despite its array of abilities, it's imperative to recognize UNAGI's limitations, especially its dependency on the CMAP database for in- silico drug perturbation. The CMAP database, though invaluable, has its set of challenges. It doesn't encompass all potential drugs and compounds, thereby narrowing UNAGI's drug discovery horizon. Additionally, the impact of numerous drug perturbations on a variety of cell types within CMAP remains either inadequately explored or ambiguous. Furthermore, the database may not consistently offer drug perturbation profiles tailored to the lung or other pertinent cell types, a critical aspect for diseases like IPF. Incorporating a more detailed and expansive drug perturbation or drug target database could amplify UNAGI's prowess in in- silico drug perturbation.
+
+<|ref|>text<|/ref|><|det|>[[92, 592, 905, 723]]<|/det|>
+In summary, UNAGI is an AI- based computational tool that can be used to uncover distinct cellular trajectories during human disease progression, using distinct disease stages or severities or real- time course data, address regulatory and perturbation shifts that drive their phenotypes, and allow computational predictions of drugs that will reverse these shifts. We demonstrate its performance in a unique dataset of differentially affected tissues from patients with IPF, providing detailed observation, proteomic and experimental validations as well as relevance to another disease - COVID- 19. We believe that the wide availability of UNAGI will enhance our understanding of complex diseases and accelerate the development of novel therapeutic strategies through the repositioning of known compounds, as well as the modeling of the effects of novel compounds.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 750, 163, 763]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 765, 405, 779]]<|/det|>
+## Dataset description and preprocessing
+
+<|ref|>text<|/ref|><|det|>[[92, 779, 905, 923]]<|/det|>
+The snRNA- seq IPF datasets were collected from a total of 19 individuals, comprising 10 healthy donors and 9 IPF patients. Recognizing that different regions of the lung may be at varying stages of disease progression, we utilized cells isolated from these distinct regions within the IPF lung to model the temporal progression of IPF. Altogether, the dataset consists of 30 samples from control subjects and 24 samples from IPF patients. After sequencing, raw fastq files were trimmed with cutadapt110 (version 1.17) to remove read2 contamination of 5- prime template switch oligo and 3- prime polyadenylated tails; read pairs were discarded if read2 was trimmed below 30 bases. Trimmed reads were mapped to GRCh38 annotated with GENCODE111 (release 37) with the STARsolo112 implementation of STAR (v2.7.6a); the barcode whitelist file and barcode length parameters were based on the manufacturer's (10X Genomics) guidelines for 3- prime v3.1 scRNAseq assays. Transcript count information was taken from STAR's unfiltered 'GeneFull' output, all barcodes with at least 300
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 65, 905, 338]]<|/det|>
+transcripts were imported into R (v 4.0.5) alongside statistics for each barcode's percent of transcripts spliced, unspliced, or ambiguous from STAR's 'velocyt' output. Cell barcode cleaning and cell type annotation were performed with tools from the R package Seurat (v4.1.1). To conduct an independent and manual cell type annotation, each sample of data was subjected to an iterative and recursive process of dimension reduction, graph embedding, and cluster analysis. After each iteration, the cell type labelling is refined, spurious nuclei are removed, and a subset of relatively similar cell types is isolated for the next iteration. This process was repeated recursively until all spurious nuclei were removed and new cell subpopulations could no longer be resolved. After each sample was cleaned and annotated, all samples were combined. Seurat's reciprocal PCA integration method was used to adjust for batch effects at the cDNA library level. The gene expression results generated from integration were used for a final iteration of UMAP embedding and clustering. Final cell type assignments (the 'Ground Truth' column in Supplementary Fig 2) were determined by evaluating the true (not integrated) gene expression marker signatures of a cluster and confirming that the pattern was consistent across each sample. Following the preprocessing, we adopted the mesenchymal cell line which encompassed 231,544 cells to validate the UNAGI method. Please note that all subsequent analyses using the deep generative model solely utilize the normalized cell-by-gene matrix obtained from this preprocessing step. These analyses are augmented with manual cell type annotations performed independently via the Seurat pipeline, as detailed in this subsection. Crucially, all cell embeddings and clustering results presented in this manuscript were produced using our deep generative neural network framework, not the Seurat pipeline. The role of the Seurat framework was strictly confined to data preprocessing.
+
+<|ref|>sub_title<|/ref|><|det|>[[94, 350, 386, 364]]<|/det|>
+## Gaussian mixture density estimator
+
+<|ref|>text<|/ref|><|det|>[[90, 364, 905, 542]]<|/det|>
+The Gaussian Mixture Model (GMM) clustering method \(^{113}\) leverages multivariate Gaussian components to characterize various stages of IPF samples. This approach aims to categorize samples into discrete stages of the disease, optimizing the probability or density representation of these stages. In this study, the GMM clustering approach is founded on the concept of surface density, serving as a measure of the extent of fibrosis. We assume that the surface density of all samples is independently and identically distributed, represented as \(S_{density} = \{s_1, s_2, \ldots , s_n\}\) , where \(n\) is the total number of samples. The GMM is fitted to the data to identify optimal components that maximize the log- likelihood: \(P(S_{density}|\mu_{1,\ldots ,c}, \sigma_{1,\ldots ,c}) = \sum_{i} \log N(S_{density}|\mu_{i}, \sigma_{i})\) . Here, \(N\) represents the Gaussian density function of the GMM for each sample, and \(c\) is the total number of Gaussian components, each characterized by a mean \(\mu_{i}\) and standard deviation \(\sigma_{i}\) . After identifying the optimal components, the samples \(S\) and their corresponding cells are softly classified into different stages, constructing the dataset \(X = X_{1}, \ldots , X_{T}\) where each \(X \in R^{m_{T} \times n}\) . Here, \(T\) refers to the number of IPF stages, and each stage has \(m_{T}\) cells with \(n\) genes.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 554, 760, 568]]<|/det|>
+## Graph Variational Autoencoder-Generative Adversarial Networks (Graph VAE-GAN)
+
+<|ref|>text<|/ref|><|det|>[[90, 568, 905, 710]]<|/det|>
+Our UNAGI method introduces a Graph VAE- GAN model. To leverage cellular neighbors to diminish the effects of dropouts and noise \(^{114}\) , we stacked a cell graph convolution (GCN) layer on top of VAE. A graph convolution layer is a specialized type of neural network that is can capture the topological structure of data, particularly by identifying features within local neighborhoods. GCN aggregates cell- cell relationships to construct a graph \((V, E)\) , where \(V\) denotes the vertices (cells) and \(E\) represents the edges (connections between cells). To establish this graph, the K- nearest neighbors (KNN) algorithm is employed to build the connectivity matrix \(A\) which defines the similarity between cells. The graph convolution is defined as \(f_{GCN}(X, A) = \alpha (AXW^{GCN})\) , where \(W^{GCN}\) refers to the trainable weights of the GCN layer, and \(\alpha\) is the activation function. Importantly, cells from different disease stages are not connected in the connectivity graph \(A\) , maintaining a stage- specific cell graph convolution.
+
+<|ref|>text<|/ref|><|det|>[[90, 723, 905, 928]]<|/det|>
+UNAGI employs a VAE- based deep learning model \(^{24}\) to model the cellular dynamics behind complex disease progression and simulate the drug perturbations. The VAE's encoder- decoder structure can model the probability distribution of high- dimensional data in a lower- dimensional space and generating new samples from this reduced- dimensional distribution. As a variational method, it facilitates the in- silico perturbation of cells by modulating their gene expressions. To refine the generative ability of VAE, we follow the previous method \(^{116}\) to use GAN to guide the generation of VAE with the min- max training strategy \(^{115}\) . The encoder of the Graph VAE- GAN, \(E_{\theta}: R^{n} \to R^{l}\) consists of a GCN layer and several multi- layer perceptrons (MLPs). It can transform a cell \(x_{i} \in R^{m}\) to its corresponding \(l\) - dimensional latent vector \(z_{i}\) . The GCN layer takes the normalized cell- by- gene count matrix \(X\) and connectivity matrix \(A\) , generating a graph representation \(f_{GCN}(X, A) = \alpha (AXW^{GCN})\) where \(W^{GCN}\) is weights of the GCN layer. Acknowledging that the latent distribution of single- cell data follows a multivariate normal distribution, two MLPs are employed to determine the means vectors \(\mu_{z} = f_{\mu_{\theta}}(\mu_{z}|f_{GCN}(X, A))\) and standard deviation vectors \(\sigma_{z} = f_{\sigma_{\theta}}(\sigma_{z}|f_{GCN}(X, A))\) of the latent representation. The latent representation for a cell is represented as \(z \sim \mathcal{N}(\mu_{z}, \sigma_{z}^{2})\) and the approximated posterior distribution is represented as \(q_{\theta}(Z|X, A)\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 78, 905, 167]]<|/det|>
+The decoder \(p_{\phi}:R^{l}\to R^{3n}\) takes \(Z\) as input to reconstruct the cell-by-gene count matrix. We employ the ZILN distribution to model the gene expression. The ZILN model is a composite distribution that integrates two distinct distributions: the first part is a Bernoulli distribution, Bernoulli \((\rho)\) , which accounts for the dropout events commonly observed in single-cell sequencing. The second component of the ZILN model captures the actual gene expression levels following a log transformation, represented by \(\log \mathcal{N}(\mu ,\sigma^{2})\) . The likelihood function of a reconstructed cell \(x\in X\) can be written as:
+
+<|ref|>equation<|/ref|><|det|>[[230, 164, 903, 201]]<|/det|>
+\[p_{\phi}(x|z) = \prod_{j\in g e n e s}Z I L N(x_{j}|\rho_{j},\mu_{j},\sigma_{j}^{2}) = \rho_{j}\delta_{0}(x_{j}) + (1 - \rho_{j})L N(x_{j}|\mu_{j},\sigma_{j}^{2}) \quad (1)\]
+
+<|ref|>equation<|/ref|><|det|>[[301, 201, 903, 270]]<|/det|>
+\[L N(x_{j}|\mu_{j},\sigma_{j}^{2}) = \left\{ \begin{array}{l l}{\frac{1}{x_{j}\sigma_{j}\sqrt{2\pi}} e^{-\frac{-\left(\ln x_{j} - \mu_{j}\right)^{2}}{2\sigma_{j}^{2}}},} & {i f x_{j} > 0}\\ {0,} & {i f x_{j} = 0} \end{array} \right. \quad (2)\]
+
+<|ref|>equation<|/ref|><|det|>[[414, 260, 903, 293]]<|/det|>
+\[\delta_{0}(x_{j}) = \left\{ \begin{array}{l l}{1,i f x_{j} = 0}\\ {0,i f x_{j}\neq 0} \end{array} \right. \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[92, 291, 905, 372]]<|/det|>
+To reconstruct the cell- by- gene matrix \(X\) , the decoder \(p_{\phi}\) will learn parameters of the ZILN distribution including the zero- inflation probability \(\rho = f_{\rho_{\phi}}(\rho |Z)\) , scale of the log- normal distribution \(\sigma\) for each gene (a vector of learnable parameters), and mean \(\mu\) of the log- normal distribution, denoted as \(\mu = f_{\mu_{\phi}}(\mu |Z,\sigma)\) . The prior distribution \(p(Z)\) is a multivariate standard normal distribution. Within our framework, we designate the entire Graph VAE model as the generator \(G\) . The loss function of the generator \(L_{G}\) can be formulated as:
+
+<|ref|>equation<|/ref|><|det|>[[235, 369, 903, 389]]<|/det|>
+\[L_{G} = L(\theta ,\phi ,X,A) = KL(q_{\theta}(Z|X,A)||p(Z)) - E_{q_{\theta}(Z|X,A)}[\log p_{\phi}(X|Z)] \quad (4)\]
+
+<|ref|>text<|/ref|><|det|>[[92, 388, 905, 464]]<|/det|>
+The first term of \(L_{G}\) is the Kullback- Leibler divergences (KL), which quantifies the difference between the latent representation \(q_{\theta}(Z|X,A)\) learned by the encoder and the predefined prior distribution \(p(Z)\) . The second term is the expected log- likelihood of the input data given the reconstruction generated by the decoder, acting as a reconstruction loss. Together, \(L_{G}\) promotes the model's generative performance with the probabilistic constraints of the latent space.
+
+<|ref|>text<|/ref|><|det|>[[92, 474, 905, 534]]<|/det|>
+To further refine the generative capabilities of the Graph VAE, an adversarial discriminator is incorporated into the model's architecture. This discriminator is a classifier based on MLPs to distinguish between original cells \(X\) and the reconstructed cells \(G(X,A)\) generated by the Graph VAE. A min- max adversarial training strategy is then applied, aimed at optimizing the loss function \(L_{GAN}\) .
+
+<|ref|>equation<|/ref|><|det|>[[235, 530, 903, 558]]<|/det|>
+\[L_{GAN} = L(X,A) = \min_{G}\max_{D}\mathbb{E}_{X}[\log (D(X))] + \mathbb{E}_{X}\left[1 - \log \left(D(G(X,A))\right)\right] \quad (5)\]
+
+<|ref|>text<|/ref|><|det|>[[92, 561, 905, 691]]<|/det|>
+Here, \(D\) is the adversarial discriminator, \(G\) is the generator (Graph VAE). During the training phase, cells are labelled as real or fake (produced by the generator for the purpose of adversarial training). The discriminator, \(D\) , is optimized to effectively distinguish between real and fake cell labels, aiming to maximize the probability of correctly identifying real and generated cells. Simultaneously, the second term of \(L_{GAN}\) incentivizes the generation of cell reconstructions that are highly similar to the original data that \(D\) cannot distinguish them from real cells. The overall loss function of UNAGI denoted as \(L\) , is a composite of the Graph VAE loss and the GAN, written as \(L = L_{G} + L_{GAN}\) . By integrating these components, UNAGI harnesses the strengths of various architectures, the GCN can leverage the cell- cell relationship information, the VAE can model the complex single- cell data, and the GAN can refine the quality of cell generation.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 703, 640, 718]]<|/det|>
+## Dynamics graph and underlying gene regulatory networks inference
+
+<|ref|>text<|/ref|><|det|>[[92, 717, 905, 833]]<|/det|>
+UNAGI builds a dynamic graph to illustrate the progression of each cell population (cell type or subtypes) throughout disease progression. We apply Leiden clustering117 on the latent embeddings, generated by Graph VAE- GAN, to identify distinct cell populations at each disease stage. To measure distances between cell populations in adjacent stages, we use the KL divergence rather than Euclidean distance, which can be problematic in high- dimensional data contexts118,119. For each cell population (e.g., cell type), we approximate its distribution using a Monte Carlo Sampling strategy120 involving the sampling of each dimension of the latent embeddings a thousand times to form a multivariate normal distribution. The KL divergence is calculated to measure the distance between these populations' multivariate normal distributions.
+
+<|ref|>text<|/ref|><|det|>[[92, 845, 905, 920]]<|/det|>
+Additionally, we identify the top 100 differentially expressed genes (DEGs) in each cell population. We then calculate DEG distances among cell populations across stages. The DEG distance is defined as \(T_{d}(DEG_{c1},DEG_{c2}) * \Sigma_{j\in DEG_{c1}}|R_{j}^{c1} - R_{j}^{c2}|\) , where the first term is the Jaccard Distance between \(DEG_{c1}\) and \(DEG_{c2}\) , DEGs of two cell populations. The second term considers the ranking difference between two DEG lists. Here, \(R_{j}^{c1}\) and \(R_{j}^{c2}\) represent the ranking of gene \(j\) in \(DEG_{c1}\) and \(DEG_{c2}\) , respectively. To render the KL
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 65, 905, 225]]<|/det|>
+divergence and the distances of differentially expressed genes (DEGs) comparable, we implemented min- max normalization for each metric across all potential connections within a specific cluster. After normalization, we represented the distances between each cluster pair as the sum of the normalized KL divergence and the normalized DEGs distances. We then compiled these normalized distances for all possible connections across various disease stages to create a background distance distribution. This distribution is essential for assessing the statistical significance of connections between clusters throughout the different stages of the disease. In scenarios where a cluster is connected to more than one cluster in an adjacent stage, the most statistically significant one will be used. These significant connections form tracks that trace from the control stage to the final stage of the disease, defining the disease progression. Consequently, the dynamic graph \(G_{dynamic}\) produced includes these progression tracks, each representing comprehensive cellular state transition associated with a specific cell population during disease progression.
+
+<|ref|>text<|/ref|><|det|>[[92, 237, 905, 412]]<|/det|>
+Moreover, we employ iDREM (Interactive Dynamic Regulatory Events Miner)121, a machine learning model based on an Input- Output Hidden Markov Model, to reconstruct the temporal gene regulatory network underlying each track (i.e., associated with each cell population) in the reconstructed cellular dynamics graph \(G_{dynamic}\) . This gene regulatory network consists of co- expressed genes and gene regulators that regulate the temporal progression of the disease within each cell population. For each track in \(G_{dynamic}\) , iDREM identifies the genes that undergo similar expression change patterns throughout the disease progression, which was termed as gene paths, some with increasing expression patterns while others with decreasing patterns. For each of the identified co- expressed gene paths, iDREM also provides its enriched GO terms and pathways. Beyond the identification of co- expressed gene paths, iDREM also captures the gene regulators that modulate those gene paths during disease progression. The dynamic genes and gene regulators identified through this process are considered dynamic marker candidates and hold potential as therapeutic targets for the disease.
+
+<|ref|>sub_title<|/ref|><|det|>[[94, 426, 375, 440]]<|/det|>
+## Iterative training strategy of UNAGI
+
+<|ref|>text<|/ref|><|det|>[[92, 440, 905, 784]]<|/det|>
+The training strategy for UNAGI is structured as an iterative process, consisting of two primary phases that are cyclically repeated: (1) learning cell embeddings using the VAE- GAN framework, (2) constructing a cellular dynamics graph, and identifying substantial genes and gene regulators. Initially, with the cell embeddings learned with equal importance of all genes, we will employ the dynamics graph module to reconstruct the cellular dynamics and identify critical genes that influence disease progression, employing the iDREM algorithm. Based on this identification, UNAGI establishes and updates a gene- weights table for each cell. This table quantifies the importance of each gene and gene regulator, reflecting their roles in disease progression. As the training progresses through each iteration, dynamic marker genes and gene regulators that are deemed important in the reconstructed gene regulatory network are assigned increased weights. In contrast, genes not identified as critical or as gene regulators undergo a systematic decay in importance—specifically, a \(30\%\) decrement in weight with each iteration. This approach guarantees that genes consistently identified as critical in disease progression across various iterations receive progressively higher weights. Conversely, genes that are only occasionally deemed important will gradually lose prominence and be systematically deprioritized. Next, in the cell embedding learning of the subsequent iteration, the VAE model undergoes fine- tuning with a modified loss function that accentuates the high- weight genes. This enhancement is accomplished by integrating the gene weights in all cells into the reconstruction loss function, thereby shifting the model's focus from generic genes to those disease- associated genes identified through gene regulatory network inference. During each iteration, after the cell embeddings are updated, the cellular dynamics module steps in to rebuild the cellular dynamics graph and the associated gene regulatory networks. This stage plays a crucial role in refining and updating the disease- associated genes. These enhancements feed back into and improve the cell embedding learning in the next iteration. On the other hand, the revised cell embeddings generate an updated cellular dynamics graph and its gene regulatory network, offering a deeper understanding of disease progression and potentially advancing the identification of disease- specific genes, which will in return improve the cell embedding learning in the next iteration.
+
+<|ref|>text<|/ref|><|det|>[[92, 797, 905, 896]]<|/det|>
+Upon model convergence, the highest- weighted genes are associated with the disease and thus indicating that UNAGI model can indeed 'comprehend' the disease and recognize important disease- relevant genes during the iterative training. For instance, enrichment analysis shows that the top 100 weighted genes in fibrotic fibroblast cells are closely associated with IPF (Supplementary Fig. 12). At each training iteration \(t\) , the gene weights are transformed into a ranking matrix, \(R^t\) . The objective functions of UNAGI during its iterative training can be then refined as follows to integrate the distilled disease knowledge in the gene- weights table for each cell:
+
+<|ref|>equation<|/ref|><|det|>[[201, 895, 903, 928]]<|/det|>
+\[L_{G}^{t} = L(\theta^{t},\phi^{t},X,A) = KL\left(q_{\theta^{t}}(Z|X,A)||p(Z)\right) - \mathbb{E}_{q_{\theta^{t}}(Z|X,A)}\left[\log p_{\phi^{t}}(X|Z)\cdot \frac{1}{(R^{t})^{\tau}}\right] \quad (6)\]
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[226, 66, 904, 100]]<|/det|>
+\[L_{GAN}^{t} = L(X,A) = \min_{G^{t}}\max_{D^{t}}\mathbb{E}_{X}\left[\log (D^{t}(X))\right] + \mathbb{E}_{X}\left[1 - \log \left(D^{t}(G^{t}(X,A))\right)\right] \quad (7)\]
+
+<|ref|>text<|/ref|><|det|>[[90, 100, 904, 188]]<|/det|>
+Here, \(G^{t}\) represents the generator at the \(t\) - th iteration, and \(D^{t}\) is the discriminator at the same iteration. \(L_{G}^{t}\) denotes the loss of generator, and \(L_{GAN}^{t}\) denotes the loss of GAN at the \(t\) - th iteration and \(\tau\) is a hyperparameter which is responsible for controlling the influence of gene weights on the reconstruction loss (empirically set \(\tau\) as 0.5). Through this iterative training, UNAGI progressively hones its ability to generate disease- specific cell embeddings. This approach allows for the identification of disease- specific markers and supports disease- specific in- silico perturbations.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 202, 318, 216]]<|/det|>
+## Dynamic markers discovery
+
+<|ref|>text<|/ref|><|det|>[[90, 216, 905, 431]]<|/det|>
+To characterize the temporal progression of the disease for each cell population, we identify dynamic markers. They are genes that change considerably throughout the disease's progression. For each track in the cellular dynamics graph, iDREM identifies the gene paths with co- expression patterns during disease progression as discussed above. Next, we computed the sum of fold changes for each gene in each of the gene paths across all disease stages associated with each cell dynamic track (i.e., a cell type or subtype). Genes in those identified gene paths were considered as candidate dynamic biomarkers for further statistical examinations. To calculate the statistical significance of the candidate markers, we randomly shuffle cells within each stage of the track to generate the background simulation tracks. We then calculate the accumulated foldchanges among all neighboring stages of these candidate markers across all simulation tracks. This simulation process was repeated \(N\) times \((N > 1000)\) to establish a random background foldchange distribution. We then evaluated the P- values for each candidate marker based on its accumulated sum fold change against this background distribution. To ensure a high level of confidence in our selection of dynamic markers, we imposed a more stringent FDR cut- off \((\mathrm{FDR}< 0.01)\) than the default (FDR \(< 0.05\) ). These selected dynamic markers are pivotal in delineating the progression tracks and provide a nuanced understanding of the longitudinal evolution of the disease within each distinct cell population.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 445, 393, 459]]<|/det|>
+## Hierarchical static markers discovery
+
+<|ref|>text<|/ref|><|det|>[[90, 459, 905, 660]]<|/det|>
+The hierarchical static marker discovery approach supports the identification of intra- stage static markers through hierarchical clustering. UNAGI conducts hierarchical clustering based on the embeddings of cell populations at each disease stage, thereby generating dendrograms to depict the relationships among these populations. Initially, we identify distinct cell populations using their latent embeddings \(Z\) . Hierarchical clustering is then applied to these embeddings to construct a dendrogram for the cell populations within the same disease stage. This dendrogram serves as a tool to explore the hierarchical structure of cell populations. In this dendrogram, when focusing on a particular cluster, we analyze it at various levels to identify hierarchical static markers. At lower levels of the dendrogram, the selected cluster compares with a broader range of sibling clusters. Here, the hierarchical static markers identified tend to represent general features of the cell population, as the siblings encompass a wider scope. For instance, at level 0, the selected cluster is compared against all other clusters within that stage. Conversely, at higher dendrogram levels, the siblings are more closely related to the selected cluster. This closeness allows for the identification of markers that highlight the subtle heterogeneities among cell subpopulations within the same cell type. By examining these nuanced differences, we can gain a deeper understanding of the cell subpopulation's characteristics.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 673, 347, 687]]<|/det|>
+## In-silico perturbation strategies
+
+<|ref|>text<|/ref|><|det|>[[90, 687, 905, 760]]<|/det|>
+In- silico perturbation can be executed through two strategies: (1) Direct gene expression regulation. This approach involves the direct up- regulation or down- regulation of specific genes of interest. For a cluster of cells, we define an expression regulation vector \(\Delta = [\Delta_{g1}, \Delta_{g2}, \dots , \Delta_{gn}]\) , where each \(\Delta_{gn}\) represents the expression change of gene \(gn\) (e.g. \(\Delta_{g1} = 0.5\) would indicate an increase in the expression of gene \(g1\) by 0.5). The gene expression for a perturbed cell population \(X'_{c}\) can be defined as:
+
+<|ref|>equation<|/ref|><|det|>[[404, 760, 904, 777]]<|/det|>
+\[X^{\prime}_{c} = \max \left(X_{c} + \mathbf{1}_{M_{c}}\Delta ,0\right) \quad (9)\]
+
+<|ref|>text<|/ref|><|det|>[[90, 778, 905, 895]]<|/det|>
+Here, \(X_{c}\) represents the original cell- by- gene matrix of a cell population \(c\) , and \(M_{c}\) represents the number of cells within the cell population. (2) Gene Interaction (GI) Network- based regulation. In this strategy, we regulate the genes of interest and their interacting partners based on the gene interaction network curated from public domains. From the HIPPIE database \(^{122}\) and STRINGDB \(^{123}\) , we obtain the strength of gene interactions \(\gamma\) of different gene pairs. For a certain cell population \(c\) , we transformed the cell- by- gene matrix \(X_{c}\) into a gene- by- cell matrix \(Y_{c}\) and employed PCA to generate low- dimensional embeddings \(P_{gene}\) for each gene across the cell population. The influence factor \(I(Q, R) \in (- 1, 1)\) quantifies the extent to which the perturbation of a given gene \(Q\) impacts on another gene \(R\) . \(I(Q, R)\) is defined as:
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[257, 63, 904, 155]]<|/det|>
+\[\begin{array}{r}I(Q,R) = \left\{ \begin{array}{ll}0, & \mathrm{if~}Q\mathrm{~and~}R\mathrm{~are~not~connected}\\ \displaystyle sgn(cor(\mathbf{y}_Q,\mathbf{y}_R))\exp (-\mathbf{w}\frac{\|P_Q - P_R\|_2}{\prod_{k\in (Q,R)}\gamma_k}), & \mathrm{otherwise} \end{array} \right. \end{array} \quad (10)\]
+
+<|ref|>text<|/ref|><|det|>[[92, 157, 905, 290]]<|/det|>
+Here, \(\mathbf{y}_Q\) and \(\mathbf{y}_R\) are gene expression vectors of genes \(Q\) and \(R\) , respectively, in the \(Y_{c}\) . The term \((Q,R)\) denotes a sequence of hops from \(Q\) to \(R\) in the GI network, \(\gamma_k\) denotes the strength of gene interactions of a hop in \((Q,R)\) , \(w\) is the steepness weight \((w > 0\) and empirically set to 0.2 by default) to control the influence factor, \(cor(\mathbf{y}_Q,\mathbf{y}_R)\) quantifies the correlation between two genes and \(sgn(x)\) indicates the direction of their interactions. The gene of interest will tend to impose higher impacts on genes that it directly interacts with. Conversely, genes that are further away in the GI network are less influenced. When regulating a specific gene \(\eta\) by changing a certain magnitude \(\Delta_{\eta}\) (e.g., \(\Delta_{\eta} = - 0.5\) can decrease the expression of gene \(\eta\) by 0.5). The expression regulation vector for this scenario is formulated as \(\Delta = [\Delta_{\eta}I(\eta ,g_1),\Delta_{\eta}I(\eta ,g_2),\dots,\Delta_{\eta}I(\eta ,g_n)]\) . If multiple genes \(G_{P}\) are perturbed with individual magnitudes, the expression regulation vector is:
+
+<|ref|>equation<|/ref|><|det|>[[290, 290, 904, 308]]<|/det|>
+\[\Delta = [\Sigma_{i\in G_P}\Delta_iI(i,g_1),\Sigma_{i\in G_P}\Delta_iI(i,g_2),\dots,\Sigma_{i\in G_P}\Delta_iI(i,g_n)] \quad (12)\]
+
+<|ref|>text<|/ref|><|det|>[[92, 308, 840, 323]]<|/det|>
+The gene expression for a perturbed cell population \(X^{\prime}\) is then calculated as defined in equation (9).
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 337, 328, 351]]<|/det|>
+## In-silico perturbation scoring
+
+<|ref|>text<|/ref|><|det|>[[92, 352, 905, 455]]<|/det|>
+We perform perturbations on every stage of individual tracks using the perturbed cell- by- gene expression matrix \(X^{\prime}\) . This matrix \(X^{\prime}\) is fed into the encoder of the Graph VAE- GAN, yielding the perturbed latent cell representation \(Z^{\prime} = E_{\theta}(X^{\prime},A)\) . The efficacy of these perturbations is assessed by examining the changes in the distances between cell populations within the latent cell embedding space. Specifically, the distance between two cell populations in the latent space \(Z\) can be quantified as \(\delta_{i,j} = \| Z_i' - Z_j\| _2\) , where \(i'\) is the perturbed cell population and \(j\) is another cell population within the same track. The perturbation score of a track \(S_{track}\in [- 1,1]\) at a perturbed stage \(i\) is defined as:
+
+<|ref|>equation<|/ref|><|det|>[[293, 453, 904, 490]]<|/det|>
+\[S_{track}(i) = \frac{1}{\tau}\Sigma_{j = 0,j\neq i}^{T}\left(1 - \frac{2}{1 + exp(w(\delta_{i,j} - \delta_{i,j})sgn(j - i))}\right) \quad (13)\]
+
+<|ref|>text<|/ref|><|det|>[[92, 492, 905, 622]]<|/det|>
+Here, \(T\) represents the total number of stages, \(i\) is the perturbed stage, \(w\) is a hyper- parameter to control the scaling ( \(w\) is set as 100 in our case), \(\delta_{i,j}\) is the distance between stage \(j\) and \(i\) (unperturbed) and \(\delta_{i,j}\) is the distance between stage \(j\) and \(i\) (perturbed). The function \(sgn(x)\) (as defined in equation (11)) is a perturbation indicator function to ensure the perturbed cell population that comes closer to the control stage will always have a positive and higher score while moving away leads to a negative and lower score. In addition to track- level perturbation scoring, an overall score \(S\) assesses perturbation effects across all tracks. This overall score is normalized based on the proportion of cells in each perturbed track within the dataset. It also incorporates the gene- regulating directions of compounds, as indicated in the relevant database, including their reversed directions. The overall score \(S\) for all stages is defined as follows,
+
+<|ref|>equation<|/ref|><|det|>[[357, 620, 904, 658]]<|/det|>
+\[S = \sum_{h\in tracks}\frac{N_h}{N}\sum_{i\in stage}\frac{|S_h^d(i) - S_h^B(i)|}{2} \quad (14)\]
+
+<|ref|>text<|/ref|><|det|>[[92, 660, 905, 747]]<|/det|>
+where \(\mathcal{A}\) represents the perturbation direction that aligns with the reported direction of the drug target expression change, while \(B\) denotes the opposite drug target expression change direction as reported in the CMAP database. The overall score \(S\) is calculated by considering in- silico perturbations in both directions, enhancing robustness. This approach is based on the premise that perturbing the targets of an effective drug in opposite directions should lead to a higher \(S_h^d(i)\) and lower \(S_h^B(i)\) , resulting in an increased score \(S\) . \(N\) here is the total number of cells and \(N_h\) is the number of cells in the perturbed track.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 761, 354, 775]]<|/det|>
+## Therapeutic pathways discovery
+
+<|ref|>text<|/ref|><|det|>[[92, 775, 905, 918]]<|/det|>
+We use pathway data from REACTOME \(^{124}\) , MatrisomeDB \(^{125}\) , and KEGG \(^{126}\) databases, providing lists of genes associated with various biological pathways. The set of genes present in individual single- cell transcriptomics datasets might vary, especially after data preprocessing. Therefore, we used expressed genes after preprocessing, and are listed as pathways' targets for in- silico pathway perturbations. We applied the scoring and ranking strategies as discussed in the 'In- silico perturbation strategies' and 'In- silico perturbation scoring' sections above to identify potential therapeutic pathways. Pathways that do not share any genes with our processed single- cell data are excluded from this analysis, as they cannot be effectively evaluated. To assess the significance of our in- silico pathways perturbations, we establish a random background dataset by randomly sampling \(n\) genes 1000 times where \(n\) is set to the median number of genes across all pathways. The perturbation strength \(\Delta\) used for random background perturbations was matched to that employed for the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 66, 905, 138]]<|/det|>
+actual pathway in- silico perturbations. We executed in- silico perturbations using the random dataset described above to generate a random background therapeutic score distribution. By contrasting the perturbation scores with this background distribution, we could ascertain the statistical significance of the in- silico pathway perturbations. This approach aids in identifying potential therapeutic pathways with a false discovery rate (FDR) of less than 0.05.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 151, 444, 165]]<|/det|>
+## Candidate drugs and compounds discovery
+
+<|ref|>text<|/ref|><|det|>[[92, 165, 905, 281]]<|/det|>
+We use the compound and their target genes from the Connectivity Map (CMAP) database \(^{26,27}\) which contains 34, 396 compound or drug profiles. Similar to the pathway perturbation, we used expressed genes after preprocessing, and are listed as drugs' targets for in- silico drug perturbations. We applied the scoring and ranking strategies as discussed in the 'In- silico perturbation strategies' and 'In- silico perturbation scoring' sections above to identify potential drug candidates. The method for calculating the statistical significance of in- silico drug perturbations was akin to that used for therapeutic pathway perturbations, as mentioned previously. The primary distinction lies in the number of genes selected for creating the random background dataset and the perturbation strength \(\Delta\) , which was aligned with that of the actual drug perturbations.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 294, 377, 307]]<|/det|>
+## Clustering parameters optimization
+
+<|ref|>text<|/ref|><|det|>[[92, 308, 905, 580]]<|/det|>
+To maintain consistency in cluster numbers and sizes, as well as the distances between cell neighbors, across various stages, we introduce a Clustering Parameter Optimization (CPO) method. Connectivity graph- based community detection clustering methods, like Leiden clustering \(^{117}\) , can automatically identify the number of clusters. However, the improper number of neighbors in the neighborhood graph or the improper resolution setting can lead to over- clustering or under- clustering, introducing complications in the analysis process. The consistency in the number and size of clusters is important for tracing the lineage of cell populations through various stages of development or disease progression. The proposed CPO method encompasses two primary steps. (1) Searching for the optimal number of neighbors to construct graphs with consistent cell- neighbor distances across different stages. We start by selecting an anchor stage, which is the stage with a cell count closest to the median count of all stages, denoted as \(N_{anchor}\) . We then calculate the average distance between cells and their neighbors in this anchor stage, establishing the anchor neighbor distance. The goal for other stages is to find a number of neighbors that yields a neighbor distance similar to that of the anchor stage. (2) The second step involves determining the optimal clustering resolution. We aim to find a set of resolutions within the predefined range \([R_{min} = 0.8, R_{max} = 1.5]\) for different stages that result in a similar median number of cells per cluster across these stages. For different application scenarios, users have the option to select a resolution range larger than the default setting. This flexibility enables adaptation to various analytical needs and preferences. By employing the CPO method, we ensure that the neighborhood graphs for different stages maintain similar cell- neighbor distances. Additionally, this approach ensures a consistent number and size of clusters across different stages, thereby enhancing the coherence and robustness of our analytical framework.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 593, 211, 606]]<|/det|>
+## Benchmarking
+
+<|ref|>text<|/ref|><|det|>[[92, 606, 905, 805]]<|/det|>
+To evaluate UNAGI's performance in learning latent embeddings from single- cell data, it is benchmarked against scVI \(^{15}\) and SCANPY \(^{12}\) . SCANPY applies Principal Component Analysis (PCA) for dimensionality reduction, whereas scVI uses a VAE model to capture the latent structures of single- cell data. We employ non- label metrics including the Silhouette score \(^{127}\) , which assesses cluster cohesion and separation, Davies- Bouldin index \(^{128}\) , which gauges average similarity ratios between clusters, and Label score \(^{89}\) , which evaluates the cell type consistency in the cell neighborhoods. For labeled metrics, the independent manual cell- type annotation served as a reference for calculating ARI \(^{87}\) and NMI \(^{88}\) . In the benchmarking and ablation experiments, we compare UANGI with scVI, SCANPY, the baseline VAE model (BL) using ZILN distribution, and the baseline model with GCN (BL_GCN) and GAN (BL_GAN), respectively. To ensure a fair comparison, we run each method for 15 rounds, each with different random seeds, and utilize Leiden clustering to generate the clustering results. Furthermore, the effectiveness of the ZILN distribution in modeling rigorously normalized single- cell data was evaluated by comparing scVI- ZILN with standard scVI. To assess UNAGI's iterative training strategy, it was executed five times with different seeds, and the results from the initial five iterations were benchmarked.
+
+<|ref|>sub_title<|/ref|><|det|>[[93, 820, 372, 834]]<|/det|>
+## In-silico drug discovery simulation
+
+<|ref|>text<|/ref|><|det|>[[92, 834, 905, 921]]<|/det|>
+We developed a simulation dataset to assess the ability of UNAGI to identify potential therapeutic targets. We selected drugs and compounds that are least likely (set FDR>0.95 as the default cut- off) to be effective in disease medication. For the generation of positive simulation data, we manipulated the target gene expression levels across various disease stages. Specifically, for compounds known to down- regulate their targets, we set their target expression levels as a progressive series \([B, 2B, \ldots , T * B]\) , where \(B > 0\) at each disease stage (in total, we have \(T\) disease stages). Conversely, for compounds that up- regulate their targets, the expression
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[92, 66, 905, 210]]<|/det|>
+levels were set in a decremental series \([T * B,(T - 1) * B,\ldots ,B]\) . In the context of negative data, we maintained consistent gene expression levels without any alteration. In the in- silico drug perturbation, the drug will increase the expression to \(\epsilon\) times or decrease to its \(1 / \epsilon\) . We conducted experiments in four separate simulation rounds, each utilizing different \(B\) values (0.5, 1.0, 1.5, 2.0). Within each round, we explored the effects of four distinct \(\epsilon\) values (1.5,2.5,3.5,4.5). We established a random background score distribution by randomly sampling \(n\) genes 1000 times, where \(n\) is set to the median number of genes across all perturbed drugs. The drug candidates with a significant FDR cut- off (FDR<0.01) than the default 0.05 were considered as successfully predicted. The model's performance in drug discovery was assessed using the Area Under the Receiver Operating Characteristic Curve (AUROC) and the Area Under the Precision- Recall Curve (AUPRC) metrics, as implemented in scikit- learn129.
+
+<|ref|>sub_title<|/ref|><|det|>[[94, 224, 330, 238]]<|/det|>
+## Sanity perturbation approach
+
+<|ref|>text<|/ref|><|det|>[[92, 238, 905, 380]]<|/det|>
+To evaluate the effectiveness of our proposed in- silico perturbation strategy, we also employed a sanity perturbation approach. This involved randomly selecting a specific track from the temporal dynamics graph and calculating the average gene expression at each stage along this track to determine the centroid for each stage. For all stages other than the control, we adjusted the gene expression of all cells within each stage to match that of the preceding stage. This was achieved by subtracting the centroid differences between these stages on each of the cells from the stage. Subsequently, the perturbed cells were input into the UNAGI model, and following the 'In- silico perturbation strategies' and 'In- silico perturbation scoring' sections above to obtain the perturbed cell embeddings. We then calculated the perturbation scores, which served as a metric to evaluate the effectiveness of our perturbation strategy. Sanity perturbations should result in positive and far larger therapeutic scores compared to random perturbations.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 394, 455, 408]]<|/det|>
+## Verify UNAGI biomarkers by proteomics data
+
+<|ref|>text<|/ref|><|det|>[[92, 409, 905, 797]]<|/det|>
+Proteins were extracted from pulmonary tissues using the MPLEx protocol as previously described130- 133. Thirty tissue blocks from IPF donors and 10 from control donors were employed. Briefly, the tissue samples were then homogenized using a Qiagen TissueLyser II with a \(2 \times 24\) adapter (chilled to \(- 20^{\circ} \mathrm{C}\) ) following vendor's instruction133. The aqueous polar metabolites and proteins were extracted from each homogenate using the MPLEx protocol. Keeping each sample on ice, a volume of chilled chloroform and water were added to a final ratio of 3:8:4 water- chloroform- methanol, mixing gently after each addition. The samples were chilled on ice for 5 min before mixing well and separating the layers by centrifugation (10,000 g, 10 min, \(4^{\circ} \mathrm{C}\) ). Proteins were isolated and concentrated to dryness in a vacuum concentrator and stored at \(- 70^{\circ} \mathrm{C}\) until ready for further processing. For each sample proteins were denatured, alkylated, digested with trypsin, and desalted on a C18 solid- phase extraction (SPE) cartridge using previously detailed methods132. For the analyses, 5 μL of resulting peptides at the concentration of \(0.1 \mu \mathrm{g} / \mu \mathrm{L}\) were analyzed by reverse phase liquid chromatography coupled with an Orbitrap Lumos instrument (Thermo Scientific) in data- dependent mode (DDA). Briefly, samples were loaded on an SPE column via a 5 μL sample loop separated by the C18 column using a 120 min gradient. The effluents from the LC column were ionized by electrospray ionization and introduced into the mass spectrometer via a heated capillary maintained at \(250^{\circ} \mathrm{C}\) for ion desalvation. The resulting ions were mass analyzed by the Orbitrap at a resolution of 60,000 covering the mass range from 300 to 1,800 Da. The top 12 most intense ions were then targeted for fragmentation per cycle time. Tandem mass MS2, ions were isolated by quadrupole mass filter in monoisotopic peak selection mode using an isolation window of 0.7 Da, maximum injection time of 50 ms with AGC setting at 1E5 ions and fragmented by high- energy collision dissociation (HCD) with nitrogen at \(32\%\) normalized collision energy. Fragment ions were mass analyzed by the Orbitrap at a resolution of 7,500, and spectra were recorded in the centroid mode. Ions once selected for MS2 were dynamically excluded for the next 45s. The instrument raw files are publicly available on MassIVE (Server: massive.ucsd.edu, User: MSV000093129, Password: Lung5172). The raw files were analyzed using MaxQuant v1.6.0.16 LFQ quantification. Downstream data processing and statistics were performed using RomicsProcessor134. The resulting LFQ intensities were log2 transformed and median- centered. ANOVA and Student's T- test were performed, and FDR p- value corrections were applied. The data processing code is available on GitHub (https://github.com/GeremyClair/IPF_DDA_proteomics/).
+
+<|ref|>text<|/ref|><|det|>[[92, 807, 905, 908]]<|/det|>
+After preprocessing, we adopted a more stringent FDR cut- off (FDR<0.01) than the default (FDR<0.05) to identify highly confident dynamic proteins. To verify the temporal dynamic markers determined for each progression track, we applied hypergeometric testing. This test assessed the overlapping ratio between dynamic proteins and dynamic markers. The overlapping between these two marker lists associated with a track is considered statistically significant if the FDR from the hypergeometric test is less than 0.05. We then use heatmaps to visualize the LFQ intensities and gene expression from proteomics data and snRNA- seq data, respectively.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[92, 65, 448, 80]]<|/det|>
+## Precision-cut lung slice (PCLS) experiments
+
+<|ref|>text<|/ref|><|det|>[[92, 80, 905, 309]]<|/det|>
+Precision- cut lung slice (PCLS) experimentsFresh lung tissue of explanted donor lungs was used for human PCLS according to previously published protocols37,90,135. Donor lung samples were sourced from 6 males and 4 females and were obtained from the Center for Organ Recovery and Education (CORE) at the University of Pittsburgh. Donor lung samples originated from lungs deemed unsuitable for organ transplantation. For the fibrosis induction in hPCLS, PCLS were treated for 5 days with a control cocktail (CC) including all vehicles or a pro- fibrotic cocktail (FC) consisting of TGF- \(\beta\) (5 ng/ml, Bio- Techne), PDGF- AB (10 ng/ml, Thermo Fisher), TNF- \(\alpha\) (10 ng/ml, Bio- Techne), and LPA (5 \(\mu \mathrm{M}\) , Cayman chemical) as described before90,136. For drug treatments, PCLS were treated with FC allowing for the induction of fibrosis, and drug treatment started at day 3 until day 5. At the end of the experiment, PCLS were snap- frozen individually in liquid nitrogen for single nuclei analysis, as described above. The study was approved by the University of Pittsburgh (IRB PRO14010265). Written informed consent was obtained for all study participants. Nuclei were extracted using the Nuclei Isolation kit (CG000505, 10X Genomics).20 000 nuclei were loaded on a Chip G with Chromium Single Cell 3' v3.1 gel beads and reagents (3' GEX v3.1, 10x Genomics). Final libraries were analyzed on an Agilent Bioanalyzer High Sensitivity DNA chip for qualitative control purposes. cDNA libraries were sequenced on a HiSeq 4000 Illumina platform aiming for 150 million reads per library and a sequencing configuration of 26 base pair (bp) on read1 and 98 bp on read2.
+
+<|ref|>text<|/ref|><|det|>[[92, 323, 905, 395]]<|/det|>
+Basceals were converted to reads with the software Cell Ranger's137 (v4.0.0) implementation mkfastq. Multiple fastq files from the same library and strand were catenated to single files. Read2 files were subject to two passes of contaminant trimming with Cutadapt110 (4.1) for the template switch oligo sequence anchored on the 5' end and for poly(A) sequences on the 3' end. Following trimming, read pairs were removed if the read2 was trimmed below 30 bp.
+
+<|ref|>text<|/ref|><|det|>[[92, 408, 905, 480]]<|/det|>
+Paired reads were filtered if either the cell barcode or unique molecular identifier (UMI) sequence had more than 1 bp with a phred of \(< 20\) . Reads were aligned with STAR112 (v2.7.9a) to the human genome reference GRCh38111 release 99. After preprocessing, analysis of the ex vivo human PCLS snRNA- seq data was conducted using the Seurat11 package (version 1.8.2). Cells with less than 750 transcripts profiled were then removed.
+
+<|ref|>text<|/ref|><|det|>[[92, 493, 905, 679]]<|/det|>
+To minimize the possible effect of potential batch correction methods, we first processed and annotated each library separately, before integrating them together and annotating them jointly. To integrate the multiple snRNA- seq datasets, we employed Robust Principal Component Analysis (RPCA)138. Based on the cellular diversity, we chose to use PCLS treated with DMSO as the reference for the integration. Following the RPCA decomposition, we utilized the low- rank component as the integrated representation of the snRNA- seq datasets. This component captured shared biological signals across conditions while mitigating dataset- specific variations. Subsequent analyses, such as clustering and differential expression analysis, were performed on the non- integrated but normalized gene expression values. To validate the effectiveness of the integrated representation, we performed various analyses, including cell- type clustering, and identification of marker genes. We also compared the results of these analyses to those obtained from individual datasets to evaluate the improvement gained through the integration process. Marker genes were computed using a Wilcoxon rank- sum test, and genes were considered marker genes if the FDR- corrected p- value was below 0.05 and the log2 fold change was above 0.5.
+
+<|ref|>text<|/ref|><|det|>[[92, 692, 905, 893]]<|/det|>
+We then applied the Graph VAE- GAN to learn the latent embeddings of the PCLS data. To quantify the effects after treating the fibrosis cells with the drugs, we calculate the pairwise Euclidean distance from control cells to real treatment cells and fibrosis cells in the reduced latent space. We used the difference between the centroid of fibrosis cells and centroids of real treatments as the perturbation strength vector \(\Delta\) . We conducted in- silico drug perturbations on fibrosis cells using a consistent perturbation strength \(\Delta\) . The efficacy of these in- silico perturbations was evaluated through UMAP visualizations and by measuring the pairwise Euclidean distances between cell embeddings in latent space. Our primary objective was to ascertain if in- silico drug perturbations could replicate the cell embeddings in latent space as observed with actual drug treatments, thereby validating the accuracy of UNAGI- driven in- silico drug perturbations. Additionally, to compare the similarity of the differential genes associated with the in- silico drug perturbations (in- silico drug perturbation vs. fibrosis) and those of real drug treatment (drug vs. fibrosis), we employed Ranked- Ranked Hypergeometric Overlap (RRHO) plots. Moreover, box plots and the \(R^2\) score were used as analytical tools to quantify gene expression similarities between cells under actual drug treatments and cells produced from our in- silico perturbations for both Nintedanib and Nifedipine.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 907, 255, 922]]<|/det|>
+## Reporting Summary
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 63, 905, 94]]<|/det|>
+Further information on research design is available in the Nature Research Reporting Summary linked to this article.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 123, 222, 137]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[92, 137, 905, 196]]<|/det|>
+Data availabilityIPF snRNA-seq and PCLS data will be made publicly accessible upon the publication of this work. The COVID- 19 dataset (COVID- 19 PBMC Ncl- Cambridge- UCL) is currently available from the COVID- 19 Cell Atlas at https://covid19cellatlas.org/. The proteomics data are publicly available on MassIVE (Server: massive.ucsd.edu, User: MSV000093129, Password: Lung5172).
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 224, 228, 238]]<|/det|>
+## Code availability
+
+<|ref|>text<|/ref|><|det|>[[92, 238, 905, 297]]<|/det|>
+Code availabilityThe UNAGI software package and source code are available at our GitHub repository (https://github.com/mcgilldinglab/UNAGI). The results and downstream analysis are available on our web server (http://dinglab.rimuhc.ca/unagi). All preprocessed .h5ad files used in this study are also available in the same GitHub repository.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 323, 186, 336]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[90, 337, 884, 925]]<|/det|>
+References1. Mitchell, K. J. What is complex about complex disorders? Genome Biol. 13, 237 (2012).2. Schork, N. J. Genetics of Complex Disease: Approaches, Problems, and Solutions. Am. J. Respir. Crit. Care Med. 156, S103–S109 (1997).3. Ramsay, R. R., Popovic-Nikolic, M. R., Nikolic, K., Uliassi, E. & Bolognesi, M. L. A perspective on multi-target drug discovery and design for complex diseases. Clin. Transl. Med. 7, (2018).4. Iyengar, R. Complex diseases require complex therapies. EMBO Rep. 14, 1039–1042 (2013).5. Dickson, M. & Gagnon, J. P. Key factors in the rising cost of new drug discovery and development. Nat. Rev. Drug Discov. 3, 417–429 (2004).6. Wang, Y. et al. Dynamic Observation of Autophagy and Transcriptome Profiles in a Mouse Model of Bleomycin-Induced Pulmonary Fibrosis. Front. Mol. Biosci. 8, 664913 (2021).7. McDonough, J. E. et al. Transcriptional regulatory model of fibrosis progression in the human lung. JCI Insight 4, e131597 (2019).8. Angerer, P. et al. Single cells make big data: New challenges and opportunities in transcriptomics. Curr. Opin. Syst. Biol. 4, 85–91 (2017).9. Stubbington, M. J. T., Rozenblatt-Rosen, O., Regev, A. & Teichmann, S. A. Single-cell transcriptomics to explore the immune system in health and disease. Science 358, 58–63 (2017).10. Habermann, A. C. et al. Single-cell RNA sequencing reveals profibrotic roles of distinct epithelial and mesenchymal lineages in pulmonary fibrosis. Sci. Adv. 6, eaba1972 (2020).11. Hao, Y. et al. Integrated analysis of multimodal single-cell data. Cell 184, 3573-3587. e29 (2021).12. Wolf, F. A., Angerer, P. & Theis, F. J. SCANPY: large-scale single-cell gene expression data analysis. Genome Biol. 19, 15 (2018).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[20, 60, 904, 884]]<|/det|>
+13. Cao, J. et al. The single-cell transcriptional landscape of mammalian organogenesis. Nature 566, 496–502 (2019).
+14. Hasanaj, E., Wang, J., Sarathi, A., Ding, J. & Bar-Joseph, Z. Interactive single-cell data analysis using Cellar. Nat. Commun. 13, 1998 (2022).
+15. Lopez, R., Regier, J., Cole, M. B., Jordan, M. I. & Yosef, N. Deep generative modeling for single-cell transcriptomics. Nat. Methods 15, 1053–1058 (2018).
+16. Shao, L. et al. Identify differential genes and cell subclusters from time-series scRNA-seq data using scTITANS. Comput. Struct. Biotechnol. J. 19, 4132–4141 (2021).
+17. Wang, Z. et al. DTWscore: differential expression and cell clustering analysis for time-series single-cell RNA-seq data. BMC Bioinformatics 18, 270 (2017).
+18. Ding, J. et al. Reconstructing differentiation networks and their regulation from time series single-cell expression data. Genome Res. 28, 383–395 (2018).
+19. Lin, C. & Bar-Joseph, Z. Continuous-state HMMs for modeling time-series single-cell RNA-Seq data. Bioinforma. Oxf. Engl. 35, 4707–4715 (2019).
+20. Hurley, K. et al. Reconstructed Single-Cell Fate Trajectories Define Lineage Plasticity Windows during Differentiation of Human PSC-Derived Distal Lung Progenitors. Cell Stem Cell 26, 593-608.e8 (2020).
+21. Mitra, R. & MacLean, A. L. RVAgene: generative modeling of gene expression time series data. Bioinformatics 37, 3252–3262 (2021).
+22. Yuan, Y. & Bar-Joseph, Z. Deep learning of gene relationships from single cell time-course expression data. Brief. Bioinform. 22, bbab142 (2021).
+23. Lotfollahi, M., Wolf, F. A. & Theis, F. J. scGen predicts single-cell perturbation responses. Nat. Methods 16, 715–721 (2019).
+24. Gronbech, C. H. et al. scVAE: variational auto-encoders for single-cell gene expression data. Bioinformatics 36, 4415–4422 (2020).
+25. Roohani, Y., Huang, K. & Leskovec, J. Predicting transcriptional outcomes of novel multigene perturbations with GEARS. Nat. Biotechnol. (2023) doi:10.1038/s41587-023-01905-6.
+26. Lamb, J. et al. The Connectivity Map: Using Gene-Expression Signatures to Connect Small Molecules, Genes, and Disease. Science 313, 1929–1935 (2006).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[20, 60, 895, 88]]<|/det|>
+27. Subramanian, A. et al. A Next Generation Connectivity Map: L1000 Platform and the First 1,000,000 Profiles. Cell 171, 1437-1452. e17 (2017).
+
+<|ref|>text<|/ref|><|det|>[[20, 95, 885, 911]]<|/det|>
+28. Thannickal, V. J., Toews, G. B., White, E. S., Lynch lii, J. P. & Martinez, F. J. Mechanisms of Pulmonary Fibrosis. Annu. Rev. Med. 55, 395-417 (2004).
+29. Ballester, B., Milara, J. & Cortijo, J. Idiopathic Pulmonary Fibrosis and Lung Cancer: Mechanisms and Molecular Targets. Int. J. Mol. Sci. 20, 593 (2019).
+30. Schwartz, D. A. IDIOPATHIC PULMONARY FIBROSIS IS A COMPLEX GENETIC DISORDER. Trans. Am. Clin. Climatol. Assoc. 127, 34-45 (2016).
+31. Lee, B.-S., Margolin, S. B. & Nowak, R. A. Pirfenidone: A Novel Pharmacological Agent That Inhibits Leiomyoma Cell Proliferation and Collagen Production. J. Clin. Endocrinol. Metab. 83, 219-223 (1998).
+32. Wollin, L. et al. Mode of action of nintedanib in the treatment of idiopathic pulmonary fibrosis. Eur. Respir. J. 45, 1434-1445 (2015).
+33. Karimi-Shah, B. A. & Chowdhury, B. A. Forced Vital Capacity in Idiopathic Pulmonary Fibrosis - FDA Review of Pirfenidone and Nintedanib. N. Engl. J. Med. 372, 1189-1191 (2015).
+34. Azuma, A. et al. Double-blind, Placebo-controlled Trial of Pirfenidone in Patients with Idiopathic Pulmonary Fibrosis. Am. J. Respir. Crit. Care Med. 171, 1040-1047 (2005).
+35. Adams, T. S. et al. Single-cell RNA-seq reveals ectopic and aberrant lung-resident cell populations in idiopathic pulmonary fibrosis. Sci. Adv. 6, eaba1983 (2020).
+36. Ahangari, F. et al. Saracatinib, a Selective Src Kinase Inhibitor, Blocks Fibrotic Responses in Preclinical Models of Pulmonary Fibrosis. Am. J. Respir. Crit. Care Med. 206, 1463-1479 (2022).
+37. Liu, G. et al. Use of precision cut lung slices as a translational model for the study of lung biology. Respir. Res. 20, 162 (2019).
+38. Viana, F., O'Kane, C. M. & Schroeder, G. N. Precision-cut lung slices: A powerful ex vivo model to investigate respiratory infectious diseases. Mol. Microbiol. 117, 578-588 (2022).
+39. De Saddeer, L. J. et al. Lung Microenvironments and Disease Progression in Fibrotic Hypersensitivity Pneumonitis. Am. J. Respir. Crit. Care Med. 205, 60-74 (2022).
+40. Tanabe, N. et al. Pathology of Idiopathic Pulmonary Fibrosis Assessed by a Combination of Microcomputed Tomography, Histology, and Immunohistochemistry. Am. J. Pathol. 190, 2427-2435 (2020).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[20, 60, 900, 912]]<|/det|>
+41. Xu, F. et al. The transition from normal lung anatomy to minimal and established fibrosis in idiopathic pulmonary fibrosis (IPF). EBioMedicine 66, 103325 (2021).
+42. Pilling, D., Zheng, Z., Vakil, V. & Gomer, R. H. Fibroblasts secrete Slit2 to inhibit fibrocyte differentiation and fibrosis. Proc. Natl. Acad. Sci. 111, 18291–18296 (2014).
+43. Ramos, C. et al. Fibroblasts from Idiopathic Pulmonary Fibrosis and Normal Lungs Differ in Growth Rate, Apoptosis, and Tissue Inhibitor of Metalloproteinases Expression. Am. J. Respir. Cell Mol. Biol. 24, 591–598 (2001).
+44. Kendall, R. T. & Feghali-Bostwick, C. A. Fibroblasts in fibrosis: novel roles and mediators. Front. Pharmacol. 5, (2014).
+45. Saito, S. et al. HDAC8 inhibition ameliorates pulmonary fibrosis. Am. J. Physiol.-Lung Cell. Mol. Physiol. 316, L175–L186 (2019).
+46. Rubio, K. et al. Inactivation of nuclear histone deacetylases by EP300 disrupts the MiCEE complex in idiopathic pulmonary fibrosis. Nat. Commun. 10, 2229 (2019).
+47. Zou, M. et al. Latent Transforming Growth Factor-β Binding Protein-2 Regulates Lung Fibroblast-to-Myofibroblast Differentiation in Pulmonary Fibrosis via NF-κB Signaling. Front. Pharmacol. 12, 788714 (2021).
+48. Enomoto, Y. et al. LTBP2 is secreted from lung myofibroblasts and is a potential biomarker for idiopathic pulmonary fibrosis. Clin. Sci. 132, 1565–1580 (2018).
+49. Herrera, J., Henke, C. A. & Bitterman, P. B. Extracellular matrix as a driver of progressive fibrosis. J. Clin. Invest. 128, 45–53 (2018).
+50. Hu, X. et al. PI3K-Akt-mTOR/PFKFB3 pathway mediated lung fibroblast aerobic glycolysis and collagen synthesis in lipopolysaccharide-induced pulmonary fibrosis. Lab. Invest. 100, 801–811 (2020).
+51. Wang, J. et al. Targeting PI3K/AKT signaling for treatment of idiopathic pulmonary fibrosis. Acta Pharm. Sin. B 12, 18–32 (2022).
+52. Lagares, D. et al. Inhibition of focal adhesion kinase prevents experimental lung fibrosis and myofibroblast formation. Arthritis Rheum. 64, 1653–1664 (2012).
+53. Tsukui, T. et al. Collagen-producing lung cell atlas identifies multiple subsets with distinct localization and relevance to fibrosis. Nat. Commun. 11, 1920 (2020).
+54. Wan, H. et al. Identification of Hub Genes and Pathways Associated With Idiopathic Pulmonary Fibrosis via Bioinformatics Analysis. Front. Mol. Biosci. 8, 711239 (2021).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[20, 60, 909, 884]]<|/det|>
+55. Kinoshita, K. et al. Antibiotic effects of focal adhesion kinase inhibitor in bleomycin-induced pulmonary fibrosis in mice. Am. J. Respir. Cell Mol. Biol. 49, 536–543 (2013).56. Gangwar, I. et al. Detecting the Molecular System Signatures of Idiopathic Pulmonary Fibrosis through Integrated Genomic Analysis. Sci. Rep. 7, 1554 (2017).57. Chen, Y., He, Z., Zhao, B. & Zheng, R. Downregulation of a potential therapeutic target NPAS2, regulated by p53, alleviates pulmonary fibrosis by inhibiting epithelial-mesenchymal transition via suppressing HES1. Cell. Signal. 109, 110795 (2023).58. Hung, C. F., Wilson, C. L., Chow, Y.-H. & Schnapp, L. M. Role of integrin alpha8 in murine model of lung fibrosis. PLOS ONE 13, e0197937 (2018).59. Morris, A. Thyroid hormone therapy resolves pulmonary fibrosis in mice. Nat. Rev. Endocrinol. 14, 64–64 (2018).60. Wei, P. et al. Transforming growth factor (TGF)- \(\beta 1\) -induced miR-133a inhibits myofibroblast differentiation and pulmonary fibrosis. Cell Death Dis. 10, 670 (2019).61. Li, Z. et al. Artificial neural network identified the significant genes to distinguish Idiopathic pulmonary fibrosis. Sci. Rep. 13, 1225 (2023).62. Gao, R. et al. Macrophage-derived netrin-1 drives adrenergic nerve-associated lung fibrosis. J. Clin. Invest. 131, e136542, 136542 (2021).63. Higo, H. et al. Identification of targetable kinases in idiopathic pulmonary fibrosis. Respir. Res. 23, 20 (2022).64. Hannandlu, A. et al. Transcriptomic and Epigenetic Profiling of Fibroblasts in Idiopathic Pulmonary Fibrosis. Am. J. Respir. Cell Mol. Biol. 66, 53–63 (2022).65. DePianto, D. J. et al. Heterogeneous gene expression signatures correspond to distinct lung pathologies and biomarkers of disease severity in idiopathic pulmonary fibrosis. Thorax 70, 48–56 (2015).66. Schupp, J. C. et al. Integrated Single-Cell Atlas of Endothelial Cells of the Human Lung. Circulation 144, 286–302 (2021).67. Hohmann, M. S. et al. Antibody-mediated depletion of CCR10+ EphA3+ cells ameliorates fibrosis in IPF. JCI Insight (2021) doi:10.1172/jci.insight.141061.68. McKleroy, W., Lee, T.- H. & Atabai, K. Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis. Am. J. Physiol. Lung Cell. Mol. Physiol. 304, L709- 721 (2013).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[20, 60, 910, 914]]<|/det|>
+69. Bogatkevich, G. S., Atanlishvili, I., Bogatkevich, A. M. & Silver, R. M. Critical Role of LMCD1 in Promoting Profibrotic Characteristics of Lung Myofibroblasts in Experimental and Scleroderma-Associated Lung Fibrosis. Arthritis Rheumatol. 75, 438–448 (2023).
+70. Zhang, L., Li, Y., Liang, C. & Yang, W. CCN5 overexpression inhibits profibrotic phenotypes via the PI3K/Akt signaling pathway in lung fibroblasts isolated from patients with idiopathic pulmonary fibrosis and in an in vivo model of lung fibrosis. Int. J. Mol. Med. 33, 478–486 (2014).
+71. Kim, H.-T. et al. Myh10 deficiency leads to defective extracellular matrix remodeling and pulmonary disease. Nat. Commun. 9, 4600 (2018).
+72. Jessen, H. et al. Turnover of type I and III collagen predicts progression of idiopathic pulmonary fibrosis. Respir. Res. 22, 205 (2021).
+73. Sontake, V. et al. Wilms' tumor 1 drives fibroproliferation and myofibroblast transformation in severe fibrotic lung disease. JCI Insight 3, e121252 (2018).
+74. Kadefors, M. et al. CD105+CD90+CD13+ identifies a clonogenic subset of adventitial lung fibroblasts. Sci. Rep. 11, 24417 (2021).
+75. Herrera, J. A. et al. Morphologically intact airways in lung fibrosis have an abnormal proteome. Respir. Res. 24, 99 (2023).
+76. Sun, H. et al. Netrin-1 regulates fibrocyte accumulation in the decellularized fibrotic scleroderma lung microenvironment and in bleomycin induced pulmonary fibrosis: Netrin-1 and Collagen production by PBMCs in Scleroderma. Arthritis Rheumatol. n/a-n/a (2016) doi:10.1002/art.39575.
+77. Roach, K. M. & Bradding, P. Ca \(^{2+}\) signalling in fibroblasts and the therapeutic potential of K \(_{Ca}\) 3.1 channel blockers in fibrotic diseases. Br. J. Pharmacol. 177, 1003–1024 (2020).
+78. Mukherjee, S. et al. Disruption of Calcium Signaling in Fibroblasts and Attenuation of Bleomycin-Induced Fibrosis by Nifedipine. Am. J. Respir. Cell Mol. Biol. 53, 450–458 (2015).
+79. Ghandikota, S., Sharma, M., Ediga, H. H., Madala, S. K. & Jegga, A. G. Consensus Gene Co-Expression Network Analysis Identifies Novel Genes Associated with Severity of Fibrotic Lung Disease. Int. J. Mol. Sci. 23, 5447 (2022).
+80. Sanders, Y. Y. et al. Histone deacetylase inhibition promotes fibroblast apoptosis and ameliorates pulmonary fibrosis in mice. Eur. Respir. J. 43, 1448–1458 (2014).
+81. Korfai, M., Mahavadi, P. & Guenther, A. Targeting Histone Deacetylases in Idiopathic Pulmonary Fibrosis: A Future Therapeutic Option. Cells 11, 1626 (2022).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[26, 60, 905, 916]]<|/det|>
+82. Udalov, S. et al. Effects of phosphodiesterase 4 inhibition on bleomycin-induced pulmonary fibrosis in mice. BMC Pulm. Med. 10, 26 (2010).
+83. Martin, P. et al. Relevant role of PKG in the progression of fibrosis induced by TNF-like weak inducer of apoptosis. Am. J. Physiol.-Ren. Physiol. 307, F75–F85 (2014).
+84. Yang, D., Yang, Y. & Zhao, Y. Ibudilast, a Phosphodiesterase-4 Inhibitor, Ameliorates Acute Respiratory Distress Syndrome in Neonatal Mice by Alleviating Inflammation and Apoptosis. Med. Sci. Monit. 26, (2020).
+85. Domitrovic, R. et al. Myricitrin exhibits antioxidant, anti-inflammatory and antifibrotic activity in carbon tetrachloride-intoxicated mice. Chem. Biol. Interact. 230, 21–29 (2015).
+86. Li, X. et al. Regorafenib-Attenuated, Bleomycin-Induced Pulmonary Fibrosis by Inhibiting the TGF-β1 Signaling Pathway. Int. J. Mol. Sci. 22, 1985 (2021).
+87. Hubert, L. & Arabie, P. Comparing partitions. J. Classif. 2, 193–218 (1985).
+88. Vinh, N. X., Epps, J. & Bailey, J. Information Theoretic Measures for Clusterings Comparison: Variants, Properties, Normalization and Correction for Chance. J. Mach. Learn. Res. 11, 2837–2854 (2010).
+89. Yuan, H. & Kelley, D. R. scBasset: sequence-based modeling of single-cell ATAC-seq using convolutional neural networks. Nat. Methods 19, 1088–1096 (2022).
+90. Alsafadi, H. N. et al. An ex vivo model to induce early fibrosis-like changes in human precision-cut lung slices. Am. J. Physiol.-Lung Cell. Mol. Physiol. 312, L896–L902 (2017).
+91. Li, D. et al. IL-33 promotes ST2-dependent lung fibrosis by the induction of alternatively activated macrophages and innate lymphoid cells in mice. J. Allergy Clin. Immunol. 134, 1422–1432.e11 (2014).
+92. Sobecki, M. et al. Vaccination-based immunotherapy to target profibrotic cells in liver and lung. Cell Stem Cell 29, 1459–1474.e9 (2022).
+93. Mukaida, N. Pathophysiological roles of interleukin-8/CXCL8 in pulmonary diseases. Am. J. Physiol.-Lung Cell. Mol. Physiol. 284, L566–L577 (2003).
+94. Cambridge Institute of Therapeutic Immunology and Infectious Disease-National Institute of Health Research (CITIID-NIHR) COVID-19 BioResource Collaboration et al. Single-cell multi-omics analysis of the immune response in COVID-19. Nat. Med. 27, 904–916 (2021).
+95. Vázquez-Jiménez, A. et al. On Deep Landscape Exploration of COVID-19 Patients Cells and Severity Markers. Front. Immunol. 12, 705646 (2021).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[20, 60, 905, 88]]<|/det|>
+96. Zou, K. & Zeng, Z. Role of early growth response 1 in inflammation-associated lung diseases. Am. J. Physiol.-Lung Cell. Mol. Physiol. 325, L143–L154 (2023).
+
+<|ref|>text<|/ref|><|det|>[[20, 98, 905, 168]]<|/det|>
+97. Brandes, F. et al. Progranulin signaling in sepsis, community-acquired bacterial pneumonia and COVID-19: a comparative, observational study. Intensive Care Med. Exp. 9, 43 (2021).
+
+<|ref|>text<|/ref|><|det|>[[20, 177, 904, 223]]<|/det|>
+98. Ugalde, A. P. et al. Autophagy-linked plasma and lysosomal membrane protein PLAC8 is a key host factor for SARS-CoV-2 entry into human cells. EMBO J. 41, e110727 (2022).
+
+<|ref|>text<|/ref|><|det|>[[20, 233, 840, 280]]<|/det|>
+99. Galbraith, M. D. et al. Specialized interferon action in COVID-19. Proc. Natl. Acad. Sci. 119, e2116730119 (2022).
+
+<|ref|>text<|/ref|><|det|>[[20, 290, 895, 337]]<|/det|>
+100. Rieder, M. et al. Serum Protein Profiling Reveals a Specific Upregulation of the Immunomodulatory Protein Progranulin in Coronavirus Disease 2019. J. Infect. Dis. 223, 775–784 (2021).
+
+<|ref|>text<|/ref|><|det|>[[20, 346, 825, 393]]<|/det|>
+101. Schulte-Schrepping, J. et al. Severe COVID-19 Is Marked by a Dysregulated Myeloid Cell Compartment. Cell 182, 1419-1440.e23 (2020).
+
+<|ref|>text<|/ref|><|det|>[[20, 403, 877, 450]]<|/det|>
+102. De Oliveira, A. A. & Nunes, K. P. Crosstalk of TLR4, vascular NADPH oxidase, and COVID-19 in diabetes: What are the potential implications? Vascul. Pharmacol. 139, 106879 (2021).
+
+<|ref|>text<|/ref|><|det|>[[20, 459, 870, 506]]<|/det|>
+103. Hou, W. et al. Small GTPase—A Key Role in Host Cell for Coronavirus Infection and a Potential Target for Coronavirus Vaccine Adjuvant Discovery. Viruses 14, 2044 (2022).
+
+<|ref|>text<|/ref|><|det|>[[20, 516, 864, 563]]<|/det|>
+104. Liu, Z.-M., Yang, M.-H., Yu, K., Lian, Z.-X. & Deng, S.-L. Toll-like receptor (TLRs) agonists and antagonists for COVID-19 treatments. Front. Pharmacol. 13, 989664 (2022).
+
+<|ref|>text<|/ref|><|det|>[[20, 573, 900, 620]]<|/det|>
+105. Yousefi, H., Mashouri, L., Okpechi, S. C., Alahari, N. & Alahari, S. K. Repurposing existing drugs for the treatment of COVID-19/SARS-CoV-2 infection: A review describing drug mechanisms of action.
+
+<|ref|>text<|/ref|><|det|>[[20, 630, 433, 647]]<|/det|>
+106. Rabie, A. M. Efficacious Preclinical Repurposing of the Nucleoside Analogue Didanosine against COVID-19 Polymerase and Exonuclease. ACS Omega 7, 21385–21396 (2022).
+
+<|ref|>text<|/ref|><|det|>[[20, 657, 875, 704]]<|/det|>
+107. Chan, M. et al. Machine learning identifies molecular regulators and therapeutics for targeting SARS-CoV2-induced cytokine release. Mol. Syst. Biol. 17, e10426 (2021).
+
+<|ref|>text<|/ref|><|det|>[[20, 714, 904, 760]]<|/det|>
+108. Garcia, G. et al. Antiviral drug screen identifies DNA-damage response inhibitor as potent blocker of SARS-CoV-2 replication. Cell Rep. 35, 108940 (2021).
+
+<|ref|>text<|/ref|><|det|>[[20, 770, 900, 816]]<|/det|>
+109. Delre, P., Caporuscio, F., Saviano, M. & Mangiatordi, G. F. Repurposing Known Drugs as Covalent and Non-covalent Inhibitors of the SARS-CoV-2 Papain-Like Protease. Front. Chem. 8, 594009 (2020).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[25, 63, 900, 911]]<|/det|>
+110. Martin, M. Cutadapt removes adapter sequences from high-throughput sequencing reads. EMBNet journal 17, 10 (2011).111. Frankish, A. et al. GENCODE reference annotation for the human and mouse genomes. Nucleic Acids Res. 47, D766–D773 (2019).112. Dobin, A. et al. STAR: ultrafast universal RNA-seq aligner. Bioinformatics 29, 15–21 (2013).113. Yang, M.-S., Lai, C.-Y. & Lin, C.-Y. A robust EM clustering algorithm for Gaussian mixture models. Pattern Recognit. 45, 3950–3961 (2012).114. Wang, J. et al. scGNN is a novel graph neural network framework for single-cell RNA-Seq analyses. Nat. Commun. 12, 1882 (2021).115. Larsen, A. B. L., Sonderby, S. K., Larochelle, H. & Winther, O. Autoencoding beyond pixels using a learned similarity metric. Preprint at http://arxiv.org/abs/1512.09300 (2016).116. Ganin, Y. et al. Domain-Adversarial Training of Neural Networks. (2015) doi:10.48550/ARXIV.1505.07818.117. Traag, V. A., Waltman, L. & Van Eck, N. J. From Louvain to Leiden: guaranteeing well-connected communities. Sci. Rep. 9, 5233 (2019).118. Aggarwal, C. C., Hinneburg, A. & Keim, D. A. On the Surprising Behavior of Distance Metrics in High Dimensional Space. in Database Theory — ICDT 2001 (eds. Van Den Bussche, J. & Vianu, V.) vol. 1973 420–434 (Springer Berlin Heidelberg, 2001).119. Koh, W. & Hoon, S. MapCell: Learning a Comparative Cell Type Distance Metric With Siamese Neural Nets With Applications Toward Cell-Type Identification Across Experimental Datasets. Front. Cell Dev. Biol. 9, 767897 (2021).120. Shapiro, A. Monte Carlo Sampling Methods. in Handbooks in Operations Research and Management Science vol. 10 353–425 (Elsevier, 2003).121. Ding, J., Hagoed, J. S., Ambalavanan, N., Kaminski, N. & Bar-Joseph, Z. iDREM: Interactive visualization of dynamic regulatory networks. PLOS Comput. Biol. 14, e1006019 (2018).122. Alanis-Lobato, G., Andrade-Navarro, M. A. & Schaefer, M. H. HIPPIE v2.0: enhancing meaningfulness and reliability of protein–protein interaction networks. Nucleic Acids Res. 45, D408–D414 (2017).123. Szklarczyk, D. et al. The STRING database in 2017: quality-controlled protein–protein association networks, made broadly accessible. Nucleic Acids Res. 45, D362–D368 (2017).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[25, 60, 900, 911]]<|/det|>
+124. Jassal, B. et al. The reactome pathway knowledgebase. Nucleic Acids Res. gkz1031 (2019) doi:10.1093/nar/gkz1031.
+125. Shao, X., Taha, I. N., Clauser, K. R., Gao, Y. (Tom) & Naba, A. MatrisomeDB: the ECM-protein knowledge database. Nucleic Acids Res. 48, D1136–D1144 (2020).
+126. Kanehisa, M. The KEGG Database. in Novartis Foundation Symposia (eds. Bock, G. & Goode, J. A.) vol. 247 91–103 (John Wiley & Sons, Ltd, 2002).
+127. Rousseeuw, P. J. Silhouettes: A graphical aid to the interpretation and validation of cluster analysis. J. Comput. Appl. Math. 20, 53–65 (1987).
+128. Davies, D. L. & Bouldin, D. W. A Cluster Separation Measure. IEEE Trans. Pattern Anal. Mach. Intell. PAMI-1, 224–227 (1979).
+129. Pedregosa, F. et al. Scikit-learn: Machine Learning in Python. (2012) doi:10.48550/ARXIV.1201.0490.
+130. Nakayasu, E. S. et al. MPLEx: a Robust and Universal Protocol for Single-Sample Integrative Proteomic, Metabolomic, and Lipidomic Analyses. mSystems 1, e00043-16 (2016).
+131. Clair, G. et al. Proteomic Analysis of Human Lung Development. Am. J. Respir. Crit. Care Med. 205, 208–218 (2022).
+132. Dylag, A. M. et al. New insights into the natural history of bronchopulmonary dysplasia from proteomics and multiplexed immunohistochemistry. Am. J. Physiol. Lung Cell. Mol. Physiol. 325, L419–L433 (2023).
+133. Moghieb, A. et al. Time-resolved proteome profiling of normal lung development. Am. J. Physiol. Lung Cell. Mol. Physiol. 315, L11–L24 (2018).
+134. Woo, J. et al. Three-dimensional feature matching improves coverage for single-cell proteomics based on ion mobility filtering. Cell Syst. 13, 426-434.e4 (2022).
+135. Gerckens, M. et al. Generation of Human 3D Lung Tissue Cultures (3D-LTCs) for Disease Modeling. J. Vis. Exp. 58437 (2019) doi:10.3791/58437.
+136. Lehmann, M. et al. Differential effects of Nintedanib and Pirfenidone on lung alveolar epithelial cell function in ex vivo murine and human lung tissue cultures of pulmonary fibrosis. Respir. Res. 19, 175 (2018).
+137. Zheng, G. X. Y. et al. Massively parallel digital transcriptional profiling of single cells. Nat. Commun. 8, 14049 (2017).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[26, 65, 874, 108]]<|/det|>
+1498 138. Candès, E. J., Li, X., Ma, Y. & Wright, J. Robust principal component analysis? J. ACM 58, 1- 37 (2011).
+
+<|ref|>text<|/ref|><|det|>[[26, 123, 67, 135]]<|/det|>
+1500
+
+<|ref|>sub_title<|/ref|><|det|>[[94, 139, 258, 152]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[92, 152, 905, 283]]<|/det|>
+This work is supported by Three Lakes Foundation [JD, NK, MK]. Partial supports also come from the Canadian Institutes of Health Research (CIHR) [PJT- 180505 to J.D]; the Fonds de recherche du Québec - Santé (FRQS) [295298 to J.D., 295299 to J.D.]; the Meakins- Christie Chair in Respiratory Research [to J.D.]; R01HL127349; R01HL141852; U01HL145567; R21HL161723; P01HL11450, U01HL148860; the U.S. Department of Defense [Discovery Award W81XWH- 19- 1- 0131 to J.C.S]; the Else Kröner- Fresenius Foundation [EKFS 2021_EKEA.16 and 2020_EKSP.78 to J.C.S.]; CORE100Pilot (Advanced) Clinician Scientist Program of Hannover Medical School funded by EKFS and the Niedersächsisches Ministerium für Wissenschaft und Kultur to J.C.S., and the German Research Foundation [SCHU 3147/4- 1 to J.C.S.]. Fond de dotation du Souffle [Fds 2019- Ostinelli to AJ]. This work is also part of HCA publication bundle (HCA- 9).
+
+<|ref|>sub_title<|/ref|><|det|>[[94, 310, 262, 323]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[92, 323, 905, 410]]<|/det|>
+N.K. and J.D. conceived and designed the experiments, performed the experiments, analyzed the data, contributed materials/analysis tools, and wrote the paper. Y.Z. designed the algorithmic framework, analyzed data, ran experiments, and wrote the paper. J.C.S., T.A., G.C., and A.J. performed the experiments, analyzed the data, and wrote the paper. F.A., I.O.R, R.P., J.S., and J.E.M performed experiments. X.Y., and P.H. analyzed the data. M.K. performed the experiments and wrote the paper. M.C., E.C., M.V., R.V., L.J.D., B.M.V, and W.A.W. contributed materials.
+
+<|ref|>sub_title<|/ref|><|det|>[[94, 435, 258, 449]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[92, 450, 905, 508]]<|/det|>
+NK is a scientific founder at Thyron, served as a consultant to Boehringer Ingelheim, Pliant, Astra Zeneca, RohBar, Veracyte, Augmanity, CSL Behring, Splisense, Galapagos, Fibrogen, GSK, Merck and Thyron over the last 3 years, reports Equity in Pliant and Thyron, and grants from Veracyte, Boehringer Ingelheim, BMS and non- financial support from Astra Zeneca.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[43, 93, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[59, 130, 340, 257]]<|/det|>
+UNAIGsupplementaryfigs.pdf supplementarytable1. xlsx supplementarytable2. xlsx supplementarytable3. xlsx supplementarytable4. xlsx
+
+<--- Page Split --->
diff --git a/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/images_list.json b/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..588f5515c662f50b4c9e64ce0ae008a1bd297a5d
--- /dev/null
+++ b/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/images_list.json
@@ -0,0 +1,130 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_0.jpg",
+ "caption": "Fig. S1. Plasma binding and neutralizing activities from donor 27.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 42
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_1.jpg",
+ "caption": "Fig. S2. 1D8 reduces viral replication and tissue damages in liver and kidney of mice.",
+ "footnote": [],
+ "bbox": [
+ [
+ 150,
+ 90,
+ 836,
+ 290
+ ]
+ ],
+ "page_idx": 43
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_2.jpg",
+ "caption": "Fig. S3. Binding of 1D8 to gH/gL mutants and its competition with other gH/gL antibodies.",
+ "footnote": [],
+ "bbox": [
+ [
+ 156,
+ 92,
+ 835,
+ 264
+ ]
+ ],
+ "page_idx": 44
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 65,
+ 103,
+ 933,
+ 545
+ ]
+ ],
+ "page_idx": 45
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 70,
+ 55,
+ 872,
+ 692
+ ]
+ ],
+ "page_idx": 46
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 70,
+ 54,
+ 921,
+ 584
+ ]
+ ],
+ "page_idx": 47
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 58,
+ 50,
+ 930,
+ 650
+ ]
+ ],
+ "page_idx": 48
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5",
+ "footnote": [],
+ "bbox": [
+ [
+ 60,
+ 49,
+ 930,
+ 725
+ ]
+ ],
+ "page_idx": 49
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6",
+ "footnote": [],
+ "bbox": [
+ [
+ 60,
+ 118,
+ 870,
+ 830
+ ]
+ ],
+ "page_idx": 50
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb.mmd b/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..ebbbb294183f0ca6353e23c475bbc58804735e11
--- /dev/null
+++ b/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb.mmd
@@ -0,0 +1,510 @@
+
+# A potent and protective human neutralizing antibody targeting a key vulnerable site of Epstein-Barr Virus
+
+Qian- Ying Zhu Sun Yat- sen University Sisi Shan Tsinghua University https://orcid.org/0000- 0002- 7184- 6818 Jinfang Yu Tsinghua University https://orcid.org/0000- 0002- 2294- 0752 Si- Ying Peng Beijing IDMO Company Limited Cong Sun Sun Yat- sen University Cancer Center Yanan Zuo School of Medicine, Tsinghua University Shu- Mei Yan Sun Yat- Sen University Cancer Center Xiao Zhang Sun Yat- sen University Cancer Center Ziqing Yang Tsinghua University Lan- Yi Zhong Sun Yat- sen University Xuangling Shi Tsinghua University Su- Mei Cao Sun Yat- sen University Cancer Center Xinquan Wang Tsinghua University https://orcid.org/0000- 0003- 3136- 8070 Mu- Sheng Zeng Sun Yat- sen University Cancer Center https://orcid.org/0000- 0003- 3509- 5591 Linqi Zhang (zhanglinqi@tsinghua.edu.cn) Tsinghua University https://orcid.org/0000- 0003- 4931- 509X
+
+<--- Page Split --->
+
+Keywords: EBV, human neutralizing antibody, humanized mouse model, epitope
+
+Posted Date: January 25th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 151895/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on November 16th, 2021. See the published version at https://doi.org/10.1038/s41467- 021- 26912- 6.
+
+<--- Page Split --->
+
+# A potent and protective human neutralizing antibody targeting a key vulnerable site of Epstein-Barr Virus
+
+Qian- Ying Zhu \(^{1,6}\) , Sisi Shan \(^{2,6}\) , Jinfang Yu \(^{3,6}\) , Si- Ying Peng \(^{5}\) , Cong Sun \(^{1}\) , Yanan Zuo \(^{2}\) , Shu- Mei Yan \(^{1}\) , Xiao Zhang \(^{1}\) , Ziqing Yang \(^{2}\) , Lan- Yi Zhong \(^{1}\) , Xuanling Shi \(^{2}\) , Su- Mei Cao \(^{4}\) , Xinquan Wang \(^{3,*}\) , Mu- Sheng Zeng \(^{1,*}\) , Linqi Zhang \(^{2,7,*}\)
+
+\(^{1}\) State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Sun Yat- sen University Cancer Center (SYSUCC), Guangzhou 510060, China. \(^{2}\) Comprehensive AIDS Research Center, and Beijing Advanced Innovation Center for Structural Biology, School of Medicine and Vanke School of Public Health, Tsinghua University, Beijing 100084, China. \(^{3}\) The Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Collaborative Innovation Center for Biotherapy, School of Life Sciences, Tsinghua University, 100084 Beijing, China. \(^{4}\) State Key Laboratory of Oncology in South China, Department of Cancer Prevention Research, Sun Yat- sen University Cancer Center (SYSUCC), Guangzhou 510060, China. \(^{5}\) Beijing IDMO Company Limited, Beijing, China. \(^{6}\) These authors contributed equally to this work. \(^{7}\) Lead Contact
+
+\(^{7}\) Lead Contact \(^{*}\) Correspondence: xinquanwang@mail.tsinghua.edu.cn; zengmsh@sysucc.org.cn; zhanglingi@mail.tsinghua.edu.cn
+
+<--- Page Split --->
+
+## ABSTRACT
+
+Epstein- Barr virus (EBV) is associated with a range of epithelial and B cell malignancies as well as autoimmune disorders, for which there are still no specific treatments or effective vaccines. Here, we isolated EBV gH/gL- specific antibodies from an EBV- infected individual. One antibody, 1D8, efficiently neutralized EBV infection of two major target cell types, B cells and epithelial cells. In humanized mice, 1D8 provided strong protection against a high- dose EBV challenge by substantially reducing viral loads and associated tumor burden. Crystal structure analysis revealed that 1D8 binds to a key vulnerable interface between the D- I/D- II domains of the viral gH/gL protein, especially the D- II of the gH, thereby interfering with the gH/gL- mediated membrane fusion and binding to target cells. Overall, we identified a potent neutralizing antibody as a promising candidate for prophylactic and therapeutic interventions against EBV infection. The key vulnerable site also provides insights into the EBV vaccines design.
+
+KEY WORDS: EBV, human neutralizing antibody, humanized mouse model,
+
+epitope
+
+<--- Page Split --->
+
+## INTRODUCTION
+
+Epstein- Barr virus (EBV) is the causative agent of a wide range of diseases in humans such as infectious mononucleosis and lymphoproliferative disorders, as well as epithelial and B cell malignancies including nasopharyngeal carcinoma and Burkitt's lymphoma(1- 4). Despite decades of research, a safe and effectively vaccine against EBV still remains elusive, largely due to a lack of knowledge regarding the specificity and magnitude of immune responses required for protection(5- 8). EBV- infected individuals produce broad and potent neutralizing antibodies that can inhibit infection of both epithelial cells and B cells in vitro(9- 13). However, their specificity to viral antigens and potential mechanism of neutralization are not clear.
+
+Recent studies on monoclonal antibodies (mAbs) revealed some of the intricate interactions between antibodies and viral surface antigens, providing critical insights into the potential targets for antibody neutralization and vaccine development(14- 18). The reported mAbs recognize exclusively viral surface glycoproteins that work in concert in determining viral tropism and mediating viral fusion with the target cells, such as gp350, gH/gL, gB and gp42(19- 22). Recently, gH/gL and gB, which together constitute the fusion machinery of EBV, have drawn increasing attention as newer generations of antibodies targeting this machinery demonstrate broad and potent inhibitory activity against EBV infection of both B cells and epithelial cells(23), as well as cross- neutralizing reactivity to related herpesviruses of non- human primate(9, 24, 25).
+
+<--- Page Split --->
+
+As components of the fusion machinery, gH/gL and gB demonstrate unique structural and functional features that are critical for viral entry, but they also inadvertently expose some vulnerable sites during the process, and became susceptible to antibody binding and neutralization(26- 28). Structurally, gH/gL consists of four distinct domains named domain- I (D- I) to domain- IV (D- IV), forming an elongated structure(29). D- I is formed by gL and the N- terminus of gH, while D- II to D- IV are formed by the rest of gH. D- I and D- II are connected through a linker helix and form a structurally distinct groove. For viral fusion to occur, gH/gL must interact with gB, which triggers a cascade of events involving dramatic structural changes of gB from the pre- to the post- fusion conformation(27, 28). Mutations in the D- I and D- I/D- II interfaces of gH/gL were shown to affect the membrane fusion process, suggesting that these regions of gH/gL are important for the interaction and activation of gB(30, 31). Apart from the fusion machinery, EBV infection requires additional surface glycoproteins to complete the entry process, but the involved accessory molecules are rather different between B cells and epithelial cells(32). For instance, EBV utilizes gp350, one of the most abundant glycoproteins on the viral envelope, to attach to the cell surface through high- affinity interaction with CD21 or CD35(33- 35). Such attachment promotes the bridging effect of another surface glycoprotein, gp42, which inserts itself between gH/gL and human leukocyte antigen (HLA) class II, which triggers the downstream fusion machinery(36, 37). Interestingly, gp42 has an inhibitory effect on epithelial cell
+
+<--- Page Split --->
+
+infection, suggesting a different entry mechanism in B cells and epithelial cells(38). For infection of epithelial cells, gH/gL first binds to integrin and NMHC- IIA on the cell surface. The fusion machinery then interacts with neuropilin 1 (NRP1) and ephrin receptor A2 (EphA2)(39- 41), which leads to a conformational transition of gB, facilitating viral fusion(27, 42).
+
+Most of the current anti- gH/gL antibodies are of murine origin(36, 43). E1D1, CL59 and CL40 can block epithelial cell infection but fail to efficiently neutralize B cell infection(22). Only one human neutralizing antibody targeting gH/gL, AMMO1, was recently isolated from an EBV- infected individual(22). AMMO1 can potently block infection of both B cells and epithelial cells in vitro. AMMO1 can also protect humanized mice from EBV challenge and provide sterilizing immunity in macaques against oral challenge with rhesus lymphocytovirus, the EBV relative that infects rhesus macaques. These findings indicate that a vaccine capable of inducing AMMO1- like neutralizing antibodies may protect human from EBV infection. Cryo- electron microscopy (cryoEM) analysis of the AMMO1- gH/gL- gp42 complex revealed that AMMO1 binds to an epitope between D- I and D- II of gH/gL(22), which serves as a more precise and clear target for future vaccine design and development.
+
+Here, we sought to isolate more neutralizing antibodies from EBV- infected individuals targeting the EBV gH/gL. After screening a large number of infected individuals, we successfully isolated the anti- gH/gL antibody 1D8, which is capable of efficiently neutralizing EBV infection of epithelial cells and B cells in
+
+<--- Page Split --->
+
+vitro. 1D8 also provided potent protection against EBV challenge in humanized mice by significantly reducing the viral loads and associated tumor burden. Using X- ray crystallography, we determined the structure of the 1D8- gH/gL complex and showed that 1D8 recognizes a key epitope located at the top of the groove between D- I and D- II of gH/gL, especially the D- II of gH. Notably, this epitope is located on the opposite side of that recognized by AMMO1 and CL40. In addition, 1D8 also significantly inhibited viral membrane fusion and gH/gL binding to epithelial cell receptor EphA2. We believe that this new vulnerable site, together with that recognized by AMMO1 and CL40, suggests that D- I and D- II represent an attractive target for the rational design of vaccines aiming to elicit antibody responses similar to these mAbs. Finally, 1D8 could also be used alone or in combination with other mAbs in prophylactic and therapeutic interventions against EBV infection either in organ transplant recipients or immunocompromised patients.
+
+## RESULTS
+
+## Isolation of human monoclonal antibodies targeting the EBV gH/gL
+
+We first screened plasma samples from a cohort of high- risk individuals and nasopharyngeal carcinoma patients(44, 45) for those with the highest levels of binding and neutralizing activity. Of the 48 plasma samples screened, donor 27 from the high- risk group had antibodies with the highest affinity for gH/gL measured by ELISA, with the half- maximal effective concentration (EC50)
+
+<--- Page Split --->
+
+corresponding to a 6874- fold dilution (fig. S1A). The same plasma sample also displayed the most potent neutralizing activity against EBV infection of HNE1 epithelial cells and Raji B cells, with respective half- maximal inhibitory concentrations (IC50) corresponding to a 273- fold and 1250- fold dilution (fig. S1B). To isolate monoclonal antibodies, we used phycoerythrin (PE) conjugated gH/gL as baits to stain and sort the antigen- specific memory B cells from the peripheral blood mononuclear cells (PBMCs) of donor 27 using flow cytometry (Fig. 1A). Out of a total 54 sorted single B cells, we were able to clone and express 10 full- length human immunoglobulin G1 (IgG1) genes in transfected 293T cells. Two antibodies, 1D8 and 2A6, were found to have strong binding to gH/gL. As shown in Fig. 1B, 1D8 showed \(\sim 7\) - fold stronger binding to gH/gL than 2A6, with an EC50 of \(0.008\mu \mathrm{g / ml}\) and \(0.057\mu \mathrm{g / ml}\) , respectively. 1D8 also demonstrated higher neutralizing activity than 2A6 against EBV infection of HNE1 epithelial cells and Raji B cells (Fig. 1C,D and table S1). The IC50 of 1D8 was about 6 times lower than that of 2A6 for both cell types. Notably, 1D8 displayed comparable binding and neutralizing activities to AMMO1, a potent gH/gL- specific neutralizing antibody previously isolated from an EBV- infected individual(22). The equilibrium dissociation constant (KD) measured by SPR was \(0.59\mathrm{nM}\) for 1D8 and \(0.14\mathrm{nM}\) for AMMO1 (fig. S1C,D and table S2). When tested for neutralizing activity against EBV infection, 1D8 and AMMO1 showed IC50 values of 0.238 and \(0.318\mu \mathrm{g / ml}\) in Raji B cells, as well as 0.123 and \(0.127\mu \mathrm{g / ml}\) in HNE1 epithelial cells,
+
+<--- Page Split --->
+
+respectively (Fig. 1C,D and table S1).
+
+## 1D8 protects against lethal EBV challenge in humanized mice
+
+To test the protective potential of 1D8 in vivo, we used a humanized mouse model reconstituted with human cord blood- derived CD34+ stem cells that became susceptible to EBV infection and disease after approximately 8 weeks of development and maturation(46- 48). The entire experimental protocol and assays conducted to evaluate protection are outlined in Fig. 2A. Briefly, we administrated \(400\mu g\) of 1D8, AMMO1 as positive control, or 2G4 and PBS as negative controls to groups of seven to eight humanized mice via the intraperitoneal (i.p.) route. On the following day, the animals were challenged with 1,000 50% transforming dose (TD50) Akata EBV via the intravenous (i.v.) route. In the ensuing up to 6- week period, all animals received the testing antibodies or PBS weekly via the i.p. route and were monitored for body weight, survival, as well as various virological and immunological parameters.
+
+EBV DNA in the peripheral blood measured by quantitative PCR reflected the distinctions in clinical manifestation between these animals (Fig. 2B). In the animals treated with 1D8 and AMMO1, EBV DNA became detectable on week 3 after challenge and slowly increased in the following two weeks, but no animals had EBV DNA copy numbers greater than 10 copies/μl blood at week 5 post challenge. By contrast, in the animals treated with 2G4 and PBS, EBV DNA rapidly increased from week 3 onwards after the challenge and reached
+
+<--- Page Split --->
+
+about 100- fold higher copy numbers than in the groups treated with 1D8 and AMMO1 at week 5 post- challenge (Fig. 2B). All animals in the 1D8 and AMMO1 treated groups survived the challenge and demonstrated relatively stable body weight without obvious pathology (Fig. 2C,D). By contrast, negative control animals (2G4 and PBS groups) began significantly losing weight starting on day 28 (4 weeks), succumbed to disease and had to be euthanized by day 38 after the challenge.
+
+By the time they were ready for the protection experiments, the reconstituted animals had about \(20\%\) human CD45+ lymphocytes in the peripheral blood, nearly \(90\%\) of which were human CD20+ B cells and \(< 1\%\) were human CD3+ T cells (Fig. 2E- G). In addition, the dynamic change of human CD20+ B cells and CD3+ T cells in the peripheral blood was correlated with distinct pattern of disease progression between these animals. Animals in the 1D8 and AMMO1 treated groups showed a relatively slower decrease in the number of CD20+ B cells compared with the 2G4 and PBS treated groups. At the same time, the increase in the number of CD3+ T cells was slower in animals treated with 1D8 and AMMO1 compared to those treated by 2G4 and PBS (Fig. 2F,G).
+
+Furthermore, EBV DNA copy numbers measured in the spleen, liver and kidney collected at necropsy shared a similar trend with those measured in the peripheral blood (Fig. 2H,J). The copy numbers of EBV DNA were significantly lower in the 1D8 and AMMO1 treated groups than in the 2G4 and PBS treated groups, although the copy numbers were generally higher in the spleen than in
+
+<--- Page Split --->
+
+the liver and kidney (Fig. 2H,J). Taken together, these results demonstrated that 1D8 as well as the positive control AMMO1 can significantly reduce viral replication and provide complete protection from a lethal EBV challenge.
+
+## Marked reduction in viral replication and tissue damages in the protected animals
+
+To study the impact of protection at the tissue levels, we collected the spleen, liver and kidney of the animals at the necropsy. The most profound and visible changes were observed in the spleens. Morphologically, the spleens from the 2G4 and PBS groups were clearly enlarged with a few irregular and pale tumors across the entire surface. By contrast, the spleens in the 1D8 and AMMO1 groups were normal in size and color, without visible tumors (Fig. 3). We went on to perform histopathology analysis on the spleen sections using hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) for hCD3 and hCD20, as well as in situ hybridization for Epstein- Barr virus- encoded RNAs (EBERs) (Fig. 3). All mice treated with 2G4 or PBS presented with typically large B- cell lymphomas in the white pulp regions, which consisted of large and atypical lymphoid cells that were positive for hCD20 and EBER. They were abundant and widely distributed across the tissue sections. Morphologically their proliferations destroyed the underlying architecture of the tissue with some infiltration by hCD3+ T cells. Additionally, areas of coagulative necrosis were often present in the spleens of mice from the 2G4
+
+<--- Page Split --->
+
+and PBS groups. By contrast, in the 1D8 and AMMO1 groups, the overall tissue architecture remained largely intact, even if some atypical large transformed cells could also be seen. Among the large number of hCD20+ B cells in the white pulp areas, \(\text{EBER + }\) cells were relatively scarce. A few hCD3+ T cells were also found scattered within. Similarly, in the hepatic and renal sections from 2G4 and PBS groups, a large number of hCD20+ and \(\text{EBER + }\) B cells were identified, while they were rare in the 1D8 and AMMO1 groups (fig. S2). The infected cells were frequently found near the blood vessels in both the liver and kidney, likely the results of migration and seeding from the blood circulation. Collectively, these results show that 1D8 and AMMO1 can significantly reduce viral replication and tissue damage relative to 2G4 and PBS, offering an explanation for their impressive in vivo protection against a lethal EBV challenge.
+
+## 1D8 binds to a key epitope on \(\mathbf{gH / gL}\)
+
+To understand the neutralizing mechanism of 1D8, we sought to determine the structure of the 1D8- gH/gL complex by X- ray crystallography. After screening nearly 100 crystals with relatively weak diffraction, we obtained a dataset with 4.2 Å resolution and solved the structure by molecular replacement (table S3). The structure showed that 1D8 bound to the interface at the top of the groove formed by D- I and D- II of gH/gL, especially the D- II of gH (Fig. 4A). 1D8 bound to the unique epitope spanning of gH/gL, which comprised residues of both gH
+
+<--- Page Split --->
+
+and gL, burying a surface area of \(969 \text{Å}^2\) . CDRL1, CDRL3 and CDRH2 of 1D8 made practically no contribution to the binding of gH/gL. CDRL2 mainly bound to \(2\alpha - 2\) and \(2\beta - 2\) . The loop between \(2\alpha - 9\) and \(2\beta - 11\) was bound by CDRH1 and CDRH3. CDRH3 also bound to the loop between \(2\alpha - 1\) and \(2\beta - 1\) . The heavy chain of 1D8 bound to the loop between \(L\alpha - 1\) and \(L\alpha - 2\) (Fig. 4B). To identify the key residue for antibody binding, we generated a series of single alanine substitutions for the contacting residues on gH/gL. Except for two (L122A and C312A), the remaining 15 mutants were successfully expressed and purified from the supernatant of transfected 293F cells. We then performed ELISA to assess the impact of these mutants on 1D8 binding. One mutant, N310A, locate in the loop between \(2\alpha - 9\) and \(2\beta - 11\) , was identified to specifically reduce the binding of 1D8 but not AMMO1 (Fig. 4B and fig. S3A,B). When measured by SPR, the binding affinity of 1D8 for this particular mutant dropped to 31.6nM, representing more than 53-fold decrease compared to the wild type gH/gL. However, no significant change of binding was found for AMMO1 compared to the wild type gH/gL (fig. S3C,D and table S2). The unique binding of 1D8 is further supported by superimposing the antibodies with known structural information onto the same gH/gL molecule. As shown in Fig. 4C,D, 1D8 bound to gH/gL at the top of the groove formed between D-I and D-II, especially the D-II of gH, while AMMO1 binds the opposite side of the molecule through a discontinuous epitope formed at the D-I/D-II interface. The mouse-derived antibody CL40 partially overlaps with the epitope of AMMO1 by
+
+<--- Page Split --->
+
+binding to an epitope on \(\mathsf{gH}\) at the interface between D- II and D- III(22). Another mouse antibody E1D1, however, only recognizes \(\mathsf{gL}(36,43)\) (Fig. 4C,D). We also used bio- layer interferometry (BLI) to confirm that 1D8 does not compete with any of these antibodies in binding to \(\mathsf{gH} / \mathsf{gL}\) (fig. S3E). These results indicate that 1D8 recognizes a key vulnerable site on \(\mathsf{gH} / \mathsf{gL}\) and provide a good rational basis for combined use with other antibodies in suppressing EBV infection.
+
+## 1D8 inhibits \(\mathsf{gH} / \mathsf{gL}\) -mediated membrane fusion and binding to B and epithelial cells
+
+We next studied the ability of 1D8 to inhibit \(\mathsf{gH} / \mathsf{gL}\) mediated membrane fusion by monitoring the fusion efficiency between the effector and target cells. Specifically, effector CHO- K1 cells expressing the \(\mathsf{gH} / \mathsf{gL}\) and \(\mathsf{gB}\) fusion machinery were incubated with a saturated concentration of 1D8 or relevant controls at \(37^{\circ}\mathrm{C}\) for 1h before mixing at a 1:1 ratio with the target HEK293 cells. The inhibitory activity was measured 24h afterwards via the luciferase activity in the cell lysates, which only became detectable when fusion occurred. As shown in Fig. 5A- C, the effector CHO- K1 cells expressed good levels of \(\mathsf{gH} / \mathsf{gL}\) as measured by flow cytometry. In the presence of 1D8 or AMMO1, the fusion activity was barely measurable and similar to the background where only the effector cells were present (Fig. 5D). By contrast, incubation with the negative controls 2G4 or PBS resulted in high levels of luciferase activity
+
+<--- Page Split --->
+
+beyond one million relative light unit (RLU). In addition, we tested the ability of 1D8 to interfere with the binding of fluorescently labelled \(\mathsf{gH / gL}\) to Raji B cells and HK1 epithelial cells, both of which are susceptible to EBV infection in vitro(49, 50). Gp42 was included in the assessment of the binding to B cells but not for the epithelial cells, since the \(\mathsf{gH / gL - gp42}\) complex is specifically required for B cell activation and fusion(36). 1D8 and relevant controls were incubated with fluorescent- labeled \(\mathsf{gH / gL}\) at \(37^{\circ}\mathrm{C}\) for 1h before mixing with B cells or epithelia cells and further incubation on ice for 1h. The levels of inhibition of \(\mathsf{gH / gL}\) - mediated binding to both cell types were measured by flow cytometry. As shown in Fig. 5E, pre- incubation with 1D8 and AMMO1 significantly reduced but did not completely abrogate \(\mathsf{gH / gL - gp42}\) binding to B cells. While no difference was found between the negative controls 2G4 and PBS, AMMO1 appeared to be more potent than 1D8 in interfering with the binding of \(\mathsf{gH / gL}\) to B cells. Conversely, 1D8 seems to be more powerful than AMMO1 in inhibiting the binding of \(\mathsf{gH / gL}\) to the epithelia cells, whereas the negative controls showed negligible effect (Fig. 5F). Lastly, we studied the ability of 1D8 to inhibit the interaction between \(\mathsf{gH / gL}\) and EphA2, a recently identified receptor for EBV infection of epithelial cells that depends on an interaction with \(\mathsf{gH / gL}(39, 40)\) . Consistent with an earlier report(22), the interaction between EphA2- Fc and \(\mathsf{gH / gL}\) was indeed rather weak as measured by BLI. Nevertheless, pre- incubation of \(\mathsf{gH / gL}\) with 1D8 did result in a small and clear reduction in the interaction between \(\mathsf{gH / gL}\) and EphA2 (Fig.
+
+<--- Page Split --->
+
+5G). Conversely, such an effect was not noticed for AMMO1 or 2G4 (Fig. 5H,I). This may explain why 1D8 was more effective than AMMO1 in inhibiting EBV infection of epithelial cells (see above), although the underlying mechanism warrants further investigation. Taken together, these findings indicate that 1D8 as well as the positive control AMMO1 can significantly inhibit gH/gL-mediated membrane fusion and binding to B and epithelial cells, either through direct blocking of binding or by sterically interfering with the downstream interactions required for EBV infection.
+
+## DISCUSSION
+
+Neutralizing antibodies are the major component of protective immunity against viral infection in humans(51- 53). They exert their function by targeting crucial epitopes on the viral envelope glycoproteins. Identifying the neutralizing mAbs and their recognized epitopes is therefore the first crucial step for understanding the protective antibody response, which can inform the rational development of antibody- based therapy and vaccines(17, 18). In some EBV- infected individuals, high levels of serum neutralizing antibodies have been identified capable of blocking infection of both B cells and epithelia cells(9). This finding indicates that the human immune system is able to generate potent neutralizing antibodies to clear the infection and/or attenuate disease progression. However, the antigen and epitope specificity, as well as the potential mechanism of neutralization of these antibodies are not entirely
+
+<--- Page Split --->
+
+clear.
+
+We report here the isolation and characterization of the human neutralizing antibody 1D8, which protects EBV infection in both B cells and epithelial cells. Passive delivery of 1D8 significantly reduced the viral loads and tumor burden of EBV- induced lymphoma in humanized mice. Structural analysis of the 1D8- gH/gL complex identified a key epitope at the top groove of gH/gL between D- I and D- II, especially the D- II of gH, which is distinct from any of the reported antibodies. In addition, 1D8 was found to inhibit viral membrane fusion and reduce the binding of gH/gL to the epithelial cell receptor EphA2(39, 40). We believe that the new vulnerable site recognized by 1D8 represents another attractive target for the rational design of vaccines capable of eliciting 1D8- like neutralizing antibodies. 1D8 could also serve as a promising candidate for antibody- based therapy and prevention of EBV infection.
+
+A couple of points need to be highlighted here. First, as both B cells and epithelia cells are major targets for EBV infection(54), it is highly desirable to isolate neutralizing antibodies capable of blocking the virus and protecting both cell types from infection. 1D8, together with recently reported AMMO1(22), are the only two representatives of this class of antibodies with dual tropism. However, we are uncertain how much this type of antibodies contributes to the overall neutralizing activities in the infected individuals. Given the low frequency in identifying 1D8 and AMMO1 antibodies among the isolated memory B cells(22), it is reasonable to assume they are quite rare and might
+
+<--- Page Split --->
+
+only be induced among a small proportion of naturally infected patients. Perhaps, this is due to the elusive nature of their epitopes, which are only transiently exposed during viral entry. It could also be due to their highly dynamic nature involving multiple conformational changes during infection. The rapid movement across the D- I and D- II groove required for binding and triggering of gB glycoprotein supports this notion(30, 31, 55, 56). Furthermore, compared to gp350, gH/gL is much less abundant and therefore has a quantitative disadvantage in immune recognition and stimulation(19). However, identification of 1D8 and AMMO1 and their epitopes around D- I and D- II offer an unprecedented opportunity to expose this vulnerable site in much more precise and persistent manner so that more focused and stronger immune response like 1D8 and AMMO1 could be generated. This could be done either by including gH/gL in the vaccine regimen(9, 23) or singling out D- I and D- II domain as epitope- focused immunogens. Both approaches would require careful design and validation to ensure proper structure and exposure of vulnerable sites recognized by 1D8 and AMMO1. In support of this notion, nanoparticles displaying gH/gL elicited a strong neutralizing antibody response against EBV infection of both target cell types(9), even if this exciting report requires further confirmation. Lastly, given the relatively conserved nature of this region among herpesviruses(24, 27), carefully designed D- I and D- II immunogens may be able to induce an even broader and stronger cross- neutralizing antibody response against a wide variety of viral strains.
+
+<--- Page Split --->
+
+Second, despite structural and functional insights, we are still not certain of the exact mechanism through which 1D8 neutralizes EBV infection of both target cell types. Structurally, 1D8 recognized a key epitope within the groove between D- I and D- II, especially the D- II of gH, whereas AMMO1 was found to bind a discontinuous epitope spanning D- I and D- II on the opposite ridge of the groove(22). Such convergence on D- I and D- II domains suggests a common mechanism of neutralization, either by affecting coordination within and across D- I and D- II or their interaction with other viral glycoproteins such as gB or gp42 required for downstream viral entry (Fig. 6A,B). AMMO1 was postulated to lock D- I, D- II and the linker helix, preventing proper movement required for interaction and activation of gB(56). As residues with the D- I and D- II groove also mediate membrane fusion and several of these critical residues are near the epitope of 1D8(30, 31, 55, 56), it stands to reason that 1D8 could also exert its neutralization activity by inhibiting the fusion process. Instead of acting like a molecular clamp as AMMO1, 1D8 may act more like a molecular wedge forcing into the space within the groove. Certainly, as 1D8 and AMMO1 bind distinct epitopes, there must be some differences in the exact mechanisms underlying their inhibitory effects. For example, AMMO1 appears to be more potent than 1D8 in interfering with the binding of gH/gL to B cells (Fig. 5E), perhaps due to its ability to displace the c- terminal domain of gp42 through the gp42 N173 glycan(22). Conversely, 1D8 seems to be more powerful than AMMO1 in inhibiting binding of gH/gL to epithelia cells, likely by affecting the
+
+<--- Page Split --->
+
+interaction between EphA2- Fc and gH/gL (Fig. 5F,G and 6A). In any case, the 1D8 antibody identified in this study represents another potent human neutralizing antibody that can be used alone or in combination with other antibodies such as AMMO1 for antibody- based interventions against EBV infection. The epitope defined here will also assist the rational design of vaccines focusing more on the vulnerable sites to elicit powerful neutralizing antibodies similar to 1D8 and AMMO1.
+
+## MATERIALS AND METHODS
+
+## Human subjects
+
+We collected plasma samples from 48 participants including 23 histologically diagnosed NPC cases and 25 non- NPC high- risk healthy controls in a screening program in Sihui County in Guangdong Province of China from 2007 and 2018. Peripheral blood mononuclear cell (PBMC) sample of donors 27 were collected in 2018. The screening program has been introduced in detail in other manuscript. This study was reviewed and approved by the Ethics Committee of the Sun Yat- Sen University Cancer Center (SYSUCC; Guangzhou, Guangdong, China) and was conducted in accordance with the Declaration of Helsinki.
+
+## Cell lines
+
+All cell lines were cultured at \(37^{\circ}C\) in a humidified atmosphere comprising \(5\%\)
+
+<--- Page Split --->
+
+CO2. 293T cells (ATCC) were grown in DMEM (GIBCO) +10% FBS (GIBCO). CHO K- 1 cells (ATCC) were maintained in Ham's F- 12 (GIBCO) +10% FBS. Raji cells (ATCC), HNE1 cells(57) and HK1 cells(58) were maintained in RMPI1640+10% FBS. Akata B cells(59) harboring a modified EBV, in which the thymidine kinase gene has been replaced with a neomycin and green fluorescence protein (GFP) cassette (Akata- GFP), were grown in RMPI 1640 (GIBCO) +5% FBS. 293F cells (ThermoFisher) were maintained in Freestyle 293 medium (Union) with gentle shaking. All cells were grown with 100U/ml penicillin and 100μg/ml streptomycin.
+
+## Humanized mice
+
+The construction of the humanized mice was based on NOD.Cg- Prkdcem1IDMOII2rgem2IDMO mice (NOD- Prkdcnull IL2RYnull, NPI@)(60), which were kept in a specific pathogen free (SPF) facility and obtained from BEIJING IDMO Co., Ltd. To generate the humanized immune system, mice were i.p. injected with a single dose of Busulfan at 20mg/kg body weight. After 48h post- injection, the mice received an intravenous tail injection of human CD34+ cells, which were isolated from umbilical cord blood (Beijing Novay biotech) with a purity of over 90%. Human CD45+ cells in peripheral blood of each humanized mouse were detected at 4 and 8 weeks post engraftment by flow cytometry.
+
+<--- Page Split --->
+
+## Plasmids
+
+The gH/gL [residues 19 to 679 of gH and residues 24 to 137 of gL were linked by (G4S)3] and gp42 (residue 34 to 223) fragments were amplified from the bacterial artificial chromosome (BAC) of EBV- M81 by PCR and cloned into the pcDNA3.1 plasmid with an N- terminal CD5 leader peptide and a C- terminal HIS Tag. Targeted mutations were introduced into pcDNA3.1- CD5- gH/gL using the ClonExpress MultiS One Step Cloning Kit (Vazyme) and were confirmed by Sanger sequencing. The pCAGGS expression plasmids for gH, gL, gB, and pT7EMCLuc (which carries a luciferase- containing reporter plasmid under the control of the T7 promoter) were kindly provided by Dr. R. Longnecker. The ectodomain of EphA2 was cloned in an Fc construct as described previously(61).
+
+## Recombinant antibody cloning
+
+The VH and VK/Vλ genes of reference antibodies CL40, E1D1 and AMMO1 were obtained from PDB and codon optimized genes were synthesized by Tsingke Biological Technology Company. Antibody heavy chain and light chain variable gene fragments were obtained using separate primer pairs(62) with restriction enzyme cutting sites, including VH primers with 5'Agel and 3'Sall, VK primers with 5'Agel and 3'BsiWI, and Vλ primers with 5'Agel and 3'Xhol. Then PCR products were cloned into antibody expression vectors containing the constant regions of human IgG1. The sequences of the recombinant
+
+<--- Page Split --->
+
+plasmids were verified by Sanger sequencing.
+
+## Recombinant protein expression
+
+The 293F cells were transfected with plasmids encoding EBV glycoproteins, EphA2- Fc and recombinant antibodies at a density of \(1.5 \times 10^{6}\) cells/ml in Freestyle 293 medium using PEI (Polysciences) transfection reagent according to the manufacturer's instructions. After five days, the culture supernatant containing EBV glycoprotein was collected and passed through Ni- NTA resin (GE Healthcare), followed by washing (PBS with 20mM imidazole, pH7.4) and elution (PBS with 250mM imidazole, pH7.4). The proteins were further purified by size exclusion chromatography (SEC) and dialyzed into PBS. Clarified cell supernatant containing recombinant antibodies or EphA2- Fc was passed over Protein A agarose (GenScript), followed by extensive washing with PBS, and then eluted with 10 mL of 0.3M glycine, pH 2.0 into 1 mL of 1M Tris HCl, pH 8.0. Purified proteins were then dialyzed into PBS.
+
+## Recombinant protein biotinylation
+
+gH/gL were biotinylated at a theoretical 1.5:1 biotin/protein ratio using the EZ- Link Sulfo- NHS- Biotin (ThermoFisher) at room temperature for 30min. Free biotin was removed by 3 successive rounds of dilution with PBS.
+
+## Preparation of the antigen binding fragment
+
+<--- Page Split --->
+
+1D8 Fab was obtained by digesting 1D8 IgG with Endoproteinase Lys- C (Sigma) at \(37^{\circ}C\) (1 mg IgG: 250 ng Lys C) for 12h. Fab fragments were isolated with Fc fragments using protein A agarose, then further purified by SEC.
+
+## Biolayer Interferometry (BLI)
+
+Antibody competition binding assays (Octet Red 96, ForteBio, Pall LLC): 250nM gH/gL was captured onto HIS1K sensors (ForteBio, Pall LLC) for 120s. The baseline interference was then read for 60 s in KB buffer (PBS, 0.1% BSA, 0.02%Tween). Then the sensor was loaded with 1D8 (10μg/ml) or KB (blank) for 60s and balanced in KB for 60s, followed by association with 10μg/ml competitive antibodies (1D8, AMMO1, CL40, E1D1) for 120s and association with KB for 120s. One gH/gL- 1D8 loaded sensor was immersed in buffer as a reference during the association and dissociation steps and used to subtract the background signal.
+
+Antibody/EphA2 competition binding assays: 2μg/ml gH/gL- biotin was immobilized on streptavidin biosensors (ForteBio, Pall LLC), and then immersed into KB for 60s. Then the sensor was loaded with 1D8 (50nM), AMMO1 (50nM), 2G4 (50nM) or KB (blank) for 60s and balanced in KB for 60s, followed by associated with 1000nM EphA2- Fc for 100s and association with KB for 120s. One gH/gL- antibody loaded sensor was immersed in buffer as a reference during the association and dissociation steps and used to subtract the background signal.
+
+<--- Page Split --->
+
+## Surface Plasmon Resonance (SPR)
+
+The binding kinetics and affinity of antibodies for \(\mathsf{gH} / \mathsf{gL}\) or their mutants were analyzed by SPR (Biacore 8K, GE Healthcare). Anti- human IgG (Fc) antibody was covalently immobilized onto a CM5 sensor chip (GE Healthcare) via amine groups in \(10~\mathsf{mM}\) sodium acetate buffer (pH 5.0) for a final RU of around 5000. Specifically, antibodies 1D8 or AMMO1 (2μg/ml) were captured by anti- human IgG antibody for 10s. Diluted \(\mathsf{gH} / \mathsf{gL}\) or their mutants were run at a flow rate of \(30~\mu \mathrm{l} / \mathrm{min}\) in HBS- EP (aqueous buffer containing 0.01M HEPES pH7.4, 0.15M NaCl, 3mM EDTA and \(0.05\% (\mathsf{v} / \mathsf{v})\) Tween 20, filtered through a \(0.2\mu \mathrm{m}\) filter). The sensograms were fit to a 1:1 binding model using the Biacore Insight Evaluation Software (GE Healthcare).
+
+## Enzyme-Linked Immunosorbent Assay (ELISA)
+
+For ELISA, 100ng/well of EBV glycoprotein was coated in 96- well enzyme- linked immunosorbent assay plates overnight at \(4^{\circ}\mathrm{C}\) . Then, the plates were blocked with \(5\%\) bovine serum albumin (BSA) in PBS and \(0.1\%\) Tween- 20 (blocking buffer) at \(37^{\circ}\mathrm{C}\) for \(1\mathrm{~h}\) . After blocking, the plates were washed three times with \(0.1\%\) Tween- 20 in PBS (washing buffer). Plasma samples or recombinant antibodies were diluted serially in blocking buffer and incubated at \(37^{\circ}\mathrm{C}\) for \(1\mathrm{~h}\) . Following three times of washing, a 1:4000 goat anti- human IgG- HRP (Promega) in blocking buffer was added to each well and incubated
+
+<--- Page Split --->
+
+at \(37^{\circ}C\) for 45 minutes. Plates were washed five times and incubated with \(3,3',5,5'\) - tetramethylbenzidine substrate (TMB) (TIANGEN) for 5 minutes at room temperature. Then 1M hydrochloric acid (HCl) was added and the \(\mathrm{OD}_{450}\) was read on a microplate reader (Epoch2). For the binding analysis of \(\mathrm{gH / gL}\) mutants, \(500\mathrm{ng / well}\) of antibody was coated in plates overnight at \(4^{\circ}C\) . The plates were then blocked and washed. The \(\mathrm{gH / gL}\) mutants were diluted serially in blocking buffer and incubated at \(37^{\circ}C\) for 1h. Following three times of washing, 1:3000 diluted mouse anti- his antibody (TRANSGEN BIOTECH) in blocking buffer was added to each well and incubated at \(37^{\circ}C\) for 1h. After three times of washing, a 1:5000 diluted goat anti- mouse- HRP antibody (Invitrogen) was added and incubated at \(37^{\circ}C\) for 1h. The final steps were the same as above.
+
+## B cells sorting
+
+Cryopreserved 10 million PBMC were thawed into 1 ml preheated RPMI1640, centrifuged at \(300\times \mathrm{g}\) for 5 min, re- suspended in \(500\mu \mathrm{l}\) FACS buffer (PBS+2% FBS), and incubated with 200nM his- tagged antigen (gH/gL) for 45 min at \(4^{\circ}C\) . The PBMC were then washed two times with 1ml FACS buffer and resuspended in 100μl FACS buffer. The PBMC were stained with the following antibodies: CD3- PE- Cy5 (BD Biosciences) at a 1:25 dilution, CD14- PE- Cy5 (eBioscience) at a 1:50 dilution, CD16- PE- Cy5 (BD Biosciences) at a 1:25 dilution, CD235a- PE- Cy5 (BD Biosciences) at a 1:100 dilution,
+
+<--- Page Split --->
+
+CD19- APC- Cy7 (BD Biosciences) at a 1:100 dilution, CD20- PE- Cy7 (BD Biosciences) at a 1:200 dilution, IgG- FITC (BD Biosciences) at a 1:25 dilution, and anti- his- PE (BioLegend) at a 1:20 dilution for 30 min at 4°C. The PBMC were washed three times with 1ml FACS buffer and resuspended in 500μl FACS buffer, then subjected to FACS on a BD FACS Aria II (BD Biosciences). Antigen- positive B cells (CD3-, CD14-, CD16-, CD235a-, CD19+, CD20+, IgG+, PE+) were sorted individually into 96- well PCR vital- plates containing 20μl first strand buffer (5μl first strand buffer, 0.5μl of RNase inhibitor (Invitrogen), 1.25μl of 100μM DTT, 0.06μl of IGEPAL (Sigma).
+
+## VH/VL recovery from sorted cells
+
+Wells containing sorted cells were mixed with 6μl of reverse transcription (RT) buffer containing 1.5μl mixed primers specific for human IgG, IgM, IgD, IgA1, IgA2, K and \(\lambda\) constant gene regions, 1.5μl of 25 mM dNTP mix (Invitrogen), and 0.25μl of superscript III reverse transcriptase (Invitrogen). The RT temperature program included 42°C for 10 min, 25°C for 10 min, 60°C for 50 min, and 94°C for 5 min, followed by a hold at 4°C. The VH, VK and Vλ genes were amplified from 5μl of cDNA separately using nested PCR (HotStarTaq DNA Polymerase, QIAGEN). The PCR products were purified and subjected to Sanger sequencing. Then, the VH, VK and Vλ variable genes were assembled into functional linear Ig gene expression cassettes by overlap- extension PCR. The function of the expressed antibodies was determined using ELISA
+
+<--- Page Split --->
+
+screening.
+
+## Virus production
+
+Akata cells carrying EBV, in which the thymidine kinase gene was interrupted with a double cassette expressing GFP and a neomycin resistance gene, were resuspended in FBS- free RPMI 1640 medium at a concentration of \(2 - 3 \times 10^{6}\) cells per ml, followed by induction with \(0.75\%\) (v/v) of goat anti- human immunoglobulin G serum (Shuangliu Zhenglong Biochem Lab) for 6h at \(37^{\circ}\mathrm{C}\) . After culture in fresh RPMI1640 medium supplemented with \(5\%\) FBS for 3 days, virus from the supernatant was collected under sterile conditions, passed through two Millipore filters (0.8 and \(0.45\mu \mathrm{m}\) ), concentrated 100- fold by high- speed centrifugation at 50,000g, and then resuspended in fresh FBS- free RPMI1640. The virus was stored at \(80^{\circ}\mathrm{C}\) and thawed immediately before infection. To assess the virus titer, 10- fold dilutions of EBV were used to inoculate \(2 \times 10^{5}\) PBMC per well in 24- well plates with \(2\mu \mathrm{g / ml}\) cyclosporin A (CsA) (Sigma). The cultures were fed weekly by replacing half of the medium with fresh medium containing CsA. After 6 weeks, the \(\mathrm{TD}_{50}\) was determined based on the number of proliferating lymphocytes in the wells (63).
+
+## Neutralization assay
+
+Plasma samples from study individuals or recombinant antibodies were incubated with GFP- expressing EBV at serial dilutions for 3h at \(4^{\circ}\mathrm{C}\) . Then the
+
+<--- Page Split --->
+
+mixtures were added to Raji B cells or HNE1 epithelial cells and incubated for 3h at \(37^{\circ}C\) . Then the unbound virus was removed by washing with PBS twice. Infected cells were cultured in fresh medium for 48h, followed by detection and analysis of GFP- positive cells using a flow cytometer and FlowJo 10 software (FlowJo, USA). The neutralization rate of each sample was defined as: \((\% \mathrm{GFP + }\) cells in the positive control well containing virus alone - \(\% \mathrm{GFP + }\) cells in the plasma or antibody containing well)/ \(\% \mathrm{GFP + }\) cells in the positive control well \(\times 100\) .
+
+## EBV infection in humanized mice
+
+At 8 weeks post CD34+ stem cells transfer, 0.4 mg of experimental or control antibodies were i.p. injected per humanized mouse. After 24 h, the mice received a dose of Akata EBV equivalent to 1,000 \(\mathrm{TD}_{50}\) via i.v. injection. In the following period, the mice received a dose of 0.4mg antibody weekly. The blood collection and recording of body weight and health status were also done every week. The mice were euthanized 6 weeks post EBV infection or earlier if they became clinically ill (e.g. body weight loss of approximately \(20\%\) ).
+
+## Detection of EBV DNA in blood and tissues
+
+DNA was extracted from the peripheral blood (100μl) or tissues of the mice using commercial DNA extraction kits (Omega). The EBV genome copy
+
+<--- Page Split --->
+
+number was determined by real- time PCR (Roche Light Cycler 480) using the TaqMan BamHI probes (40) as described previously. The copy numbers of EBV were quantified using a standard EBV genome (BDS biotech) as control.
+
+## H&E staining, IHC, and in situ hybridization
+
+Tissues were fixed in \(10\%\) formalin and embedded in paraffin. Consecutive sections were used for staining with H&E. Immunostaining of human T cells and B cells was performed using hCD3 antibody (VENTANA) and hCD20 antibody (VENTANA) at 1:200 dilution. EBERs were stained by in situ hybridization using the EBER detection kit (ZSGB- BIO), according to the manufacturer's instructions. Histological staining was evaluated by experienced pathologists.
+
+## Detection of human immune cells in the blood of humanized mice
+
+Peripheral blood of mice was treated with 1ml red blood cell lysis buffer (BioLegend) at room temperature for 10min. Then the cells were centrifuged at \(300 \times g\) , washed twice with PBS, re- suspended in PBS, and stained with antibodies including anti- human CD45- PE (BD Biosciences), CD3- PerCP- Cy5.5 (BD Biosciences) and CD20- FITC (BD Biosciences) at 1:100 dilution for 30 min at \(4^{\circ}C\) . After washing with PBS, the percentage of CD3+ or CD20+ cells among the CD45+ cells was quantified using a flow cytometer.
+
+<--- Page Split --->
+
+## Cell surface binding assays
+
+For the cell- surface binding assay, 1mg of gH/gL- biotin conjugated with SA- PE (gH/gL- PE) was diluted in 10ml of PBS into individual wells of a 96 well plate. An equimolar amount of gp42 was added to select wells containing gH/gL- PE. 5mg/ml of monoclonal antibodies, including 1D8, AMMO1, or 2G4, were added to select wells containing gH/gL with or without gp42 and incubated for 1h at \(37^{\circ}C\) . At the same time, adherent HK1 cells were trypsinized (NCM Biotech), washed with RMPI 1640 and then allowed to recover at \(37^{\circ}C\) in a humidified atmosphere comprising \(5\% \mathrm{CO}_2\) for 1h with gentle agitation twice during the period. Recovered HK1 and Raji cells were pelleted by centrifugation at \(300\times\) g for 5min and then resuspended at a density of \(2\times 10^{6}\) cells/ml in ice- cold \(0.5\%\) bovine serum albumin (BSA) in PBS. Then, \(100\mu \mathrm{l}\) of the HK1 or Raji cells suspension were added to wells containing SA- PE, gH/gL- PE with or without gp42 and antibodies, and incubated on ice for 1h. The cells were pelleted by centrifugation at \(300\times \mathrm{g}\) for 5min, washed with 1 ml of ice cold \(0.5\%\) BSA in PBS, pelleted again and resuspended in \(10\%\) phosphate buffered formalin. The amount of PE staining was quantified using a flow cytometer.
+
+## Virus-free fusion assay
+
+Effector CHO- K1 cells were transiently transfected with expression plasmid (pCAGGS- gH, pCAGGS- gL, pCAGGS- gB and pT7EMCLuc, which carries a
+
+<--- Page Split --->
+
+luciferase- containing reporter plasmid under the control of the T7 promoter). Target cells (HEK- 293T) were transfected with expression plasmid pCAGT7 (expressing T7 DNA polymerase). After 24h, the effector cells were trypsinized and re- suspended at a density of \(1 \times 10^{6}\) cells/ml. Aliquots comprising 250μl/well of effector cell suspension was pre- incubated with 2μg 1D8, AMMO1 or 2G4 antibody at \(37^{\circ}C\) for 1h. Then the target cells were also trypsinized and re- suspended at a density of \(1 \times 10^{6}\) cells/ml. An aliquot comprising 250μl of the effector cell suspension was added to the effector cells with or without antibody. After 24h, the medium was aspirated and the cells were lysed in 100μl of luciferase agent (Dual- Glo Luciferase Assay System). Then, 75μl of cell lysate was transferred to a white- bottom assay plate and luciferase activity was read on a GloMax- 96 Microplate Luminometer (Promega).
+
+## Cell surface staining
+
+Following 24h after expression plasmid transfection, the effector CHO- K1 cells were trypsinized and re- suspended at a density of \(1 \times 10^{6}\) cells/ml. The expression level of gH/gL was detected using the indicated antibody. AMMO1 and 1D8 were used for gH/gL staining and 2G4 as a control. Then, 10μg/ml of antibody was added to the cell suspension and incubated at \(4^{\circ}C\) for 1h. The cells were washed twice with PBS and stained with human IgG- PerCP- Cy5.5 (PC5.5) (BioLegend) at a 1:100 dilution. After washing with PBS, the
+
+<--- Page Split --->
+
+percentage of PC5.5+ cells was quantified using a flow cytometer (CytoFLEX, BECKMAN).
+
+## Crystallization of the 1D8 Fab and data collection
+
+To purify the gH/gL- 1D8 Fab complex, 1D8 Fab was incubated with gH/gL for 1 h on ice in HBS buffer, and the mixture was then subjected to gel filtration chromatography. Fractions containing the complex were pooled and concentrated to 10 mg/ml. Crystals were successfully grown at \(18^{\circ}C\) in sitting drops, over wells containing 200 mM sodium citrate, 100 mM HEPES sodium salt, pH 7.5, 15% w/v MPD. The drops were made by mixing 200 nl gH/gL- 1D8 Fab complex in HBS buffer with 200 nl well solution. Crystals were harvested, soaked briefly in 200 mM sodium citrate, 100 mM HEPES sodium salt, pH 7.5, 15% w/v MPD, 20% glycerol, and flash- frozen in liquid nitrogen. Diffraction data were collected at the BL17U beam line of the Shanghai Synchrotron Research Facility (SSRF). Diffraction data were processed with HKL2000 and the crystal diffracted to \(4.2\mathrm{\AA}\) . The data processing statistics are listed in Supplementary Table 3.
+
+## Structure solution and refinement
+
+The structure was determined via the molecular replacement method using PHASER in CCP4 suite. The search models were gH/gL (PDB code 5T1D) and the antibody with the highest sequence identity with 1D8. Density map
+
+<--- Page Split --->
+
+improvement by atoms update and refinement was performed with ARP/wARP29. Subsequent model building and refinement were performed using COOT and PHENIX, respectively. Final Ramachandran statistics indicated that \(91.48\%\) residues were in favored conformations, \(7.06\%\) allowed and \(1.46\%\) outliers for the final structure. The structural refinement statistics are listed in Supplementary Table 3. All structural figures were generated with PyMol (DeLano, 2002).
+
+## Statistical analysis
+
+Unless noted otherwise, a two- tailed, unpaired \(t\) - test was used to assess statistical significance. Statistical calculations were performed in GraphPad Prism 8. The number of replicates and a description of the statistical method are provided in the corresponding figure legends. Differences with P values of less than 0.05 were considered to be statistically significant. \(*P < 0.05\) , \(**P < 0.01\) , \(***P < 0.001\) , ns=not significant.
+
+## REFERENCES AND NOTES
+
+1. G. de-The et al., Sero-epidemiology of the Epstein-Barr virus: preliminary analysis of an international study - a review. IARC Sci Publ, 3-16 (1975).
+2. L. S. Young, L. F. Yap, P. G. Murray, Epstein-Barr virus: more than 50 years old and still providing surprises. Nat Rev Cancer 16, 789-802 (2016).
+3. J. I. Cohen, A. S. Fauci, H. Varmus, G. J. Nabel, Epstein-Barr virus: an important vaccine target for cancer prevention. Sci Transl Med 3, 107fs107 (2011).
+4. L. S. Young, C. W. Dawson, Epstein-Barr virus and nasopharyngeal carcinoma. Chin J Cancer 33, 581-590 (2014).
+5. S. E. Henrickson, To EBV or not to EBV: Rational vaccine design for a common infection. Sci Immunol 3, (2018).
+6. D. G. van Zyl, J. Mautner, H. J. Delecluse, Progress in EBV Vaccines. Front Oncol 9, 104 (2019).
+
+<--- Page Split --->
+
+737 7. J. I. Cohen, Epstein- barr virus vaccines. Clin Transl Immunology 4, e32 (2015).738 8. J. I. Cohen, E. S. Mocarski, N. Raab- Traub, L. Corey, G. J. Nabel, The need and challenges for development of an Epstein- Barr virus vaccine. Vaccine 31 Suppl 2, B194- 196 (2013).739 9. W. Bu et al., Immunization with Components of the Viral Fusion Apparatus Elicits Antibodies That Neutralize Epstein- Barr Virus in B Cells and Epithelial Cells. Immunity 50, 1305- 1316 e1306 (2019).743 10. A. E. Coghill et al., High Levels of Antibody that Neutralize B- cell Infection of Epstein- Barr Virus and that Bind EBV gp350 Are Associated with a Lower Risk of Nasopharyngeal Carcinoma. Clin Cancer Res 22, 3451- 3457 (2016).744 11. A. E. Coghill et al., Evaluation of Total and IgA- Specific Antibody Targeting Epstein- Barr Virus Glycoprotein 350 and Nasopharyngeal Carcinoma Risk. J Infect Dis 218, 886- 891 (2018).745 12. W. Bu et al., Kinetics of Epstein- Barr Virus (EBV) Neutralizing and Virus- Specific Antibodies after Primary Infection with EBV. Clin Vaccine Immunol 23, 363- 369 (2016).746 13. J. Sashihara, P. D. Burbelo, B. Savoldo, T. C. Pierson, J. I. Cohen, Human antibody titers to Epstein- Barr Virus (EBV) gp350 correlate with neutralization of infectivity better than antibody titers to EBV gp42 using a rapid flow cytometry- based EBV neutralization assay. Virology 391, 249- 256 (2009).747 14. D. Sok, D. R. Burton, Recent progress in broadly neutralizing antibodies to HIV. Nat Immunol 19, 1179- 1188 (2018).748 15. E. O. Saphire, S. L. Schendel, B. M. Gunn, J. C. Milligan, G. Alter, Antibody- mediated protection against Ebola virus. Nat Immunol 19, 1169- 1178 (2018).749 16. F. Yu et al., Receptor- binding domain- specific human neutralizing monoclonal antibodies against SARS- CoV and SARS- CoV- 2. Signal Transduct Target Ther 5, 212 (2020).750 17. L. M. Walker, D. R. Burton, Passive immunotherapy of viral infections: 'super- antibodies' enter the fray. Nat Rev Immunol 18, 297- 308 (2018).751 18. A. Lanzavecchia, A. Fruhwirth, L. Perez, D. Corti, Antibody- guided vaccine design: identification of protective epitopes. Curr Opin Immunol 41, 62- 67 (2016).752 19. L. M. Hutt- Fletcher, EBV glycoproteins: where are we now? Future Virol 10, 1155- 1162 (2015).753 20. B. S. Mohl, J. Chen, R. Longnecker, Gammaherpesvirus entry and fusion: A tale how two human pathogenic viruses enter their host cells. Adv Virus Res 104, 313- 343 (2019).754 21. T. Haque et al., A mouse monoclonal antibody against Epstein- Barr virus envelope glycoprotein 350 prevents infection both in vitro and in vivo. J Infect Dis 194, 584- 587 (2006).755 22. J. Snijder et al., An Antibody Targeting the Fusion Machinery Neutralizes Dual- Tropic Infection and Defines a Site of Vulnerability on Epstein- Barr Virus. Immunity 48, 799- 811 e799 (2018).756 23. X. Cui et al., Rabbits immunized with Epstein- Barr virus gH/gl or gB recombinant proteins elicit higher serum virus neutralizing activity than gp350. Vaccine 34, 4050- 4055 (2016).757 24. S. A. Connolly, J. O. Jackson, T. S. Jardetzky, R. Longnecker, Fusing structure and function: a structural view of the herpesvirus entry machinery. Nat Rev Microbiol 9, 369- 381 (2011).758 25. S. Singh et al., Neutralizing Antibodies Protect against Oral Transmission of Lymphocryptovirus. Cell Rep Med 1, (2020).759 26. B. S. Mohl, J. Chen, K. Sathiyamoorthy, T. S. Jardetzky, R. Longnecker, Structural and Mechanistic Insights into the Tropism of Epstein- Barr Virus. Mol Cells 39, 286- 291 (2016).760 27. S. A. Connolly, T. S. Jardetzky, R. Longnecker, The structural basis of herpesvirus entry. Nat Rev Microbiol, (2020).
+
+<--- Page Split --->
+
+781 28. L. S. Chesnokova, L. M. Hutt-Fletcher, Epstein-Barr virus infection mechanisms. Chin J Cancer 782 33, 545-548 (2014). 783 29. H. Matsuura, A. N. Kirschner, R. Longnecker, T. S. Jardetzky, Crystal structure of the Epstein-Barr virus (EBV) glycoprotein H/glycoprotein L (gH/gL) complex. Proc Natl Acad Sci U S 785 A 107, 22641-22646 (2010). 786 30. B. S. Mohl, K. Sathiyamoorthy, T. S. Jardetzky, R. Longnecker, The conserved disulfide bond within domain II of Epstein-Barr virus gH has divergent roles in membrane fusion with epithelial cells and B cells. J Virol 88, 13570-13579 (2014). 787 31. J. Chen, T. S. Jardetzky, R. Longnecker, The large groove found in the gH/gL structure is an important functional domain for Epstein-Barr virus fusion. J Virol 87, 3620-3627 (2013). 788 32. K. Sathiyamoorthy et al., Assembly and architecture of the EBV B cell entry triggering complex. PLoS Pathog 10, e1004309 (2014). 789 33. M. Kanekiyo et al., Rational Design of an Epstein-Barr Virus Vaccine Targeting the Receptor-Binding Site. Cell 162, 1090-1100 (2015). 790 34. K. A. Young, A. P. Herbert, P. N. Barlow, V. M. Holers, J. P. Hannan, Molecular basis of the interaction between complement receptor type 2 (CR2/CD21) and Epstein-Barr virus glycoprotein gp350. J Virol 82, 11217-11227 (2008). 791 35. G. Szakonyi et al., Structure of the Epstein-Barr virus major envelope glycoprotein. Nat Struct Mol Biol 13, 996-1001 (2006). 792 36. K. Sathiyamoorthy et al., Structural basis for Epstein-Barr virus host cell tropism mediated by gp42 and gHgL entry glycoproteins. Nat Commun 7, 13557 (2016). 793 37. M. M. Mullen, K. M. Haan, R. Longnecker, T. S. Jardetzky, Structure of the Epstein-Barr virus gp42 protein bound to the MHC class II receptor HLA-DR1. Mol Cell 9, 375-385 (2002). 794 38. A. N. Kirschner, J. Omerovic, B. Popov, R. Longnecker, T. S. Jardetzky, Soluble Epstein-Barr virus glycoproteins gH, gL, and gp42 form a 1:1:1 stable complex that acts like soluble gp42 in B-cell fusion but not in epithelial cell fusion. J Virol 80, 9444-9454 (2006). 795 39. J. Chen et al., Ephrin receptor A2 is a functional entry receptor for Epstein-Barr virus. Nat Microbiol 3, 172-180 (2018). 796 40. H. Zhang et al., Ephrin receptor A2 is an epithelial cell receptor for Epstein-Barr virus entry. Nat Microbiol 3, 1-8 (2018). 797 41. H. B. Wang et al., Neuropilin 1 is an entry factor that promotes EBV infection of nasopharyngeal epithelial cells. Nat Commun 6, 6240 (2015). 798 42. J. Chen, R. Longnecker, Epithelial cell infection by Epstein-Barr virus. FEMS Microbiol Rev 43, 674-683 (2019). 799 43. K. Sathiyamoorthy et al., Inhibition of EBV-mediated membrane fusion by anti-gHgL antibodies. Proc Natl Acad Sci U S A 114, E8703-E8710 (2017). 800 44. Z. Liu et al., Two Epstein-Barr virus-related serologic antibody tests in nasopharyngeal carcinoma screening: results from the initial phase of a cluster randomized controlled trial in Southern China. Am J Epidemiol 177, 242-250 (2013). 801 45. Y. Liu et al., Establishment of VCA and EBNA1 IgA-based combination by enzyme-linked immunosorbent assay as preferred screening method for nasopharyngeal carcinoma: a two-stage design with a preliminary performance study and a mass screening in southern China. Int J Cancer 131, 406-416 (2012). 802 46. S. Fujiwara, K. Imadome, M. Takei, Modeling EBV infection and pathogenesis in
+
+<--- Page Split --->
+
+new- generation humanized mice. Exp Mol Med 47, e135 (2015).E. K. Lee et al., Effects of lymphocyte profile on development of EBV- induced lymphoma subtypes in humanized mice. Proc Natl Acad Sci U S A 112, 13081- 13086 (2015).C. Munz, Humanized mouse models for Epstein Barr virus infection. Curr Opin Virol 25, 113- 118 (2017).E. A. Caves et al., Air- Liquid Interface Method To Study Epstein- Barr Virus Pathogenesis in Nasopharyngeal Epithelial Cells. mSphere 3, (2018).R. Lin et al., Development of a robust, higher throughput green fluorescent protein (GFP)- based Epstein- Barr Virus (EBV) micro- neutralization assay. J Virol Methods 247, 15- 21 (2017).D. R. Burton, L. Hangartner, Broadly Neutralizing Antibodies to HIV and Their Role in Vaccine Design. Annu Rev Immunol 34, 635- 659 (2016).L. L. Lu, T. J. Suscovich, S. M. Fortune, G. Alter, Beyond binding: antibody effector functions in infectious diseases. Nat Rev Immunol 18, 46- 61 (2018).G. Zhou, Q. Zhao, Perspectives on therapeutic neutralizing antibodies against the Novel Coronavirus SARS- CoV- 2. Int J Biol Sci 16, 1718- 1723 (2020).O. A. Odumade, K. A. Hogquist, H. H. Balfour, Jr., Progress and problems in understanding and managing primary Epstein- Barr virus infections. Clin Microbiol Rev 24, 193- 209 (2011).B. S. Mohl, J. Chen, S. J. Park, T. S. Jardetzky, R. Longnecker, Epstein- Barr Virus Fusion with Epithelial Cells Triggered by gB Is Restricted by a gL Glycosylation Site. J Virol 91, (2017).J. Omerovic, L. Lev, R. Longnecker, The amino terminus of Epstein- Barr virus glycoprotein gH is important for fusion with epithelial and B cells. J Virol 79, 12408- 12415 (2005).F. Zhan et al., [Primary study of differentially expressed cDNA sequences in cell line HNE1 of human nasopharyngeal carcinoma by cDNA representational difference analysis]. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 15, 341- 344 (1998).D. P. Huang et al., Establishment of a cell line (NPC/HK1) from a differentiated squamous carcinoma of the nasopharynx. Int J Cancer 26, 127- 132 (1980).S. J. Molesworth, C. M. Lake, C. M. Borza, S. M. Turk, L. M. Hutt- Fletcher, Epstein- Barr virus gH is essential for penetration of B cells but also plays a role in attachment of virus to epithelial cells. J Virol 74, 6324- 6332 (2000).S. Guo et al., Oncological and genetic factors impacting PDX model construction with NSG mice in pancreatic cancer. FASEB J 33, 873- 884 (2019).J. Chen, S. Schaller, T. S. Jardetzky, R. Longnecker, EBV gH/gL and KSHV gH/gL bind to different sites on EphA2 to trigger fusion. J Virol, (2020).H. X. Liao et al., High- throughput isolation of immunoglobulin genes from single human B cells and expression as monoclonal antibodies. J Virol Methods 158, 171- 179 (2009).M. Yajima et al., A new humanized mouse model of Epstein- Barr virus infection that reproduces persistent infection, lymphoproliferative disorder, and cell- mediated and humoral immune responses. J Infect Dis 198, 673- 682 (2008).
+
+Acknowledgements: We thank Chang Song and Cui Qiao from Beijing IDMOCompany for help with the animal experiment. The plasmids pCAGGS- T7,
+
+<--- Page Split --->
+
+pCAGGS- gH, pCAGGS- gL, pCAGGS- gB and pT7EMCLuc were kindly provided by Professor Richard Longnecker. Funding: This work was supported by the following grant supports: the National Key Research and Development Program of China (2017YFA0505600, 2016YFA0502100, 2018ZX10731101- 002, 2017ZX10201101), the National Natural Science Foundation of China (81530065, 81520108022, 81830090 and 81621004), Guangdong Province key research and development program (2019B020226002) and Beijing Municipal Science & Technology Commission (Z181100001918043, 171100000517). Author contributions: L.Z., M.Z., and X.W. conceptualized the study. Q.Z., S.S., J.Y., Y.Z., and C.S. performed experiments and analyzed data. Q.Z., S.S., J.Y., L.Z., M.Z., and X.W. wrote the manuscript, and all authors contributed to editing and figure preparation. Funding was secured by L.Z., M.Z., and X.W. Competing interests: The authors declare no potential conflicts of interest. Data availability: The atomic model of 1D8- gH/gL (PDB ID: 7D5Z) has been deposited in the Protein Data Bank.
+
+<--- Page Split --->
+
+## MAIN FIGURE LEGENDS
+
+Fig. 1. Isolation of gH/gL- specific monoclonal antibodies using single B cell sorting and cloning. (A) FACS- based sorting strategy for gH/gL- specific B cells. (B) Binding activities of 1D8 and 2A6, the positive control AMMO1, and the negative control 2G4 to EBV gH/gL measured by ELISA. The data are presented as means \(\pm\) SEM. (C) Neutralizing activities of 1D8 and 2A6, the positive control AMMO1, and the negative control 2G4 against EBV infection of Raji B cell lines and (D) HNE1 epithelia cell line. The data shown is means \(\pm\) SEM. SSC- A, side- scatter area; FSC- A, forward- scatter area.
+
+Fig. 2. Protective efficacy of 1D8 against lethal EBV challenge in humanized mice. (A) Timeline for engrafting CD34+ human hematopoietic stem cells (HSC), antibody administration, viral challenge, and monitoring for various biological and clinical outcomes. Four hundred micrograms of 1D8, positive control AMMO1, negative control 2G4, or PBS negative control were administered to the humanized mice via intraperitoneal injection either 24h prior to or weekly for 5 weeks after intravenous challenge with Akata EBV. (B) EBV DNA in the peripheral blood, (C) body weight, and (D) survival were monitored weekly. The percent changes in (E) hCD45+, (F) hCD20+, or (G) hCD3+ cells over the experiment period. On week 6 post infection, (H) virus titers in spleen, (I) liver, (J) kidney were analyzed. All data are presented as mean \(\pm\) SEM. \(^{*}p < 0.05\) ; \(^{**}p < 0.01\) ; \(^{***}p < 0.001\) ; ns, no significant.
+
+<--- Page Split --->
+
+Fig. 3. 1D8 reduces viral replication and tissue damages in humanized mice. Representative of macroscopic spleens and splenic sections stained for hematoxylin and eosin (H&E), EBV encoded RNA (EBER), human CD20 (hCD20), and human CD3 (hCD3) at necropsy. The scale bars are indicated.
+
+Fig. 4. 1D8 targets an unique epitope on \(\mathsf{gH / gL}\) . (A) Structure overview in a cartoon representation with gL in cyan, gH D- I in blue, D- II in wheat, D- III in green, D- IV in yellow, and 1D8 Fab in purple. The map is contoured at 1.2 RMS to show the density. (B) Zoomed- in view of the interaction between 1D8 and D- I and D- II. The key binding residue N310 of gH was indicated by a red star. (C) Cartoon representation of Fab 1D8 and other previously published Fabs AMMO1, CL40, and E1D1 bound to a single gH/gL molecule. The color scheme for gH/gL is as in (A) whereas 1D8 Fab in purple, AMMO1 Fab in light blue, CL40 Fab in pink, and E1D1 Fab in dark green. (D) Surface mapping of the four Fab epitopes on gH/gL with the same color in (C). Areas in black indicate the region where structural change was found upon binding to AMMO1 or CL40.
+
+Fig. 5. 1D8 interferes with cell fusion and binding. Quality control of gH/gL expression on the surface of CHO- K1 cells by staining with 1D8 (A), positive control AMMO1 (B), and negative control 2G4 (C) before proceeded to the
+
+<--- Page Split --->
+
+fusion experiment shown in (D). (D) Marked reduction in cell- cell fusion in the presence of 1D8, the positive control AMMMO1, but not the negative control 2G4. Marked reduction in gH/gL binding to Raji B cell (E) and HK1 epithelial cell (F) in the presence of 1D8, the positive control AMMO1, but not the negative control 2G4. Binding of EphA1- Fc to gH/gL was reduced by 1D8 (G), but not by AMMO1 (H) or 2G4 (I) measured by Bio- layer interferometry (BLI). All data are presented as mean ± SEM. \(^{*}p < 0.05\) ; \(^{**}p < 0.01\) ; \(^{***}p < 0.001\) ; ns, no significant. SSC- A, side- scatter area; PC5.5, PerCP- Cy5.5; RLU, relative light unit; SA- PE, streptavidin- phycoerythrin; MFI, mean fluorescence intensity.
+
+Fig. 6. Possible mechanisms of 1D8- mediated neutralization. (A) For epithelia cells, 1D8 could interfere the interaction between gH/gL and EphA2 either by directly restricting access to the interface or by indirectly posing allosteric hindrance. It could also restrict the movement across the D- I/D- II groove of gH/gL that is required for gB interaction and triggering. (B) For B cells, 1D8 could also restrict the movement across the D- I/D- II groove of gH/gL that is required for downstream viral entry. 1D8 does not appear influence interaction between gp42 and its receptor HLA class II.
+
+<--- Page Split --->
+
+Fig. 1
+
+
+
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+
+Fig. S1. Plasma binding and neutralizing activities from donor 27.
+
+(A) Plasma binding activities to gH/gL measured by ELISA. (B) Plasma neutralizing activities against EBV infection of Raji B cells and HNE1 epithelial cells. Binding activity of 1D8 (C) or AMMO1 (D) to gH/gL measured by surface plasmon resonance (SPR). All experiments were performed in duplicate, and the data shown are means with SEM.
+
+<--- Page Split --->
+
+
+Fig. S2. 1D8 reduces viral replication and tissue damages in liver and kidney of mice.
+
+Hepatic and renal sections stained for hematoxylin and eosin (H&E), human CD20 (hCD20), human CD3 (hCD3), and EBV encoded RNA (EBER) at necropsy. Scale bar of \(100\mu \mathrm{m}\) is shown.
+
+<--- Page Split --->
+
+
+Fig. S3. Binding of 1D8 to gH/gL mutants and its competition with other gH/gL antibodies.
+
+(A) 1D8 and (B) AMMO1 binding to various gH/gL mutants measured by ELISA. ELISA was performed in duplicate wells, and the data shown are means with SEM. Binding activity of 1D8 (C) and AMMO1 (D) to gH-N310A/gL mutant measured by surface plasmon resonance (SPR). (E) Competitive binding of 1D8 with AMMO1, CL40 or E1D1 to gH/gL measured by bio-layer interferometry (BLI).
+
+<--- Page Split --->
+
+Table S1. Neutralization potency of monoclonal antibodies.
+
+| Mab | Epithelial cells (μg/ml) | B cells (μg/ml) |
| \(IC_{50}\) | \(IC_{90}\) | \(IC_{50}\) | \(IC_{90}\) |
| 1D8 | 0.123 | 0.187 | 0.238 | 0.442 |
| 2A6 | 0.745 | 2.270 | 1.320 | \(>50\) |
| AMMO1 | 0.127 | 0.305 | 0.318 | 1.148 |
| 2G4 | NA | NA | NA | NA |
+
+1077
+
+1078
+
+1079
+
+1080
+
+1081
+
+1082
+
+1083
+
+1084
+
+1085
+
+1086
+
+1087
+
+1088
+
+1089
+
+1090
+
+1091
+
+1092
+
+1093
+
+1094
+
+<--- Page Split --->
+
+Table S2. Kinetic Analysis of Antibodies Binding to gH/gL Measured by
+
+| Ligand | Anylate | kon (1/Ms) ×105 | koff (1/s) ×10-4 | KD (nM) |
| 1D8 | gH/gL S97A | 1.33 | 1.36 | 1.02 |
| 1D8 | gH/gL L100A | 1.07 | 1.55 | 1.44 |
| 1D8 | gH V95A/gL | 1.30 | 2.31 | 1.77 |
| 1D8 | gH M100A/gL | 1.51 | 1.96 | 1.30 |
| 1D8 | gH Q101A/gL | 0.95 | 1.95 | 2.03 |
| 1D8 | gH D103A/gL | 0.72 | 0.69 | 0.95 |
| 1D8 | gH S105A/gL | 0.90 | 0.97 | 1.08 |
| 1D8 | gH K106A/gL | 1.26 | 1.09 | 0.86 |
| 1D8 | gH G110A/gL | 2.66 | 0.26 | 0.10 |
| 1D8 | gH V111A/gL | 1.11 | 1.48 | 1.34 |
| 1D8 | gH P125A/gL | 0.71 | 2.00 | 2.79 |
| 1D8 | gH T308A/gL | 1.04 | 1.01 | 0.97 |
| 1D8 | gH G309A/gL | 0.95 | 0.95 | 1.00 |
| 1D8 | gH N310A/gL | 1.75 | 55.20 | 31.60 |
| 1D8 | gH G311A/gL | 0.78 | 2.05 | 2.62 |
| 1D8 | gH/gL WT | 2.45 | 1.46 | 0.59 |
| AMMO1 | gH N310A/gL | 4.97 | 0.96 | 0.19 |
| AMMO1 | gH/gL WT | 5.77 | 0.85 | 0.14 |
+
+<--- Page Split --->
+
+
+Table S3. Data collection and refinement statistics.
+
+ | EBV gH/gL-1D8 |
| Data collection | |
| Space group | P4,2,2 |
| Cell dimensions | |
| a, b, c (Å) | 212.865, 212.865, 598.128 |
| α, β, γ, (°) | 90, 90, 90 |
| Resolution (Å) | 50.03-4.201(4.351-4.201) * |
| Rsym or Rmerge | 0.131 (1.261) |
| I / sI | 8 (1.4) |
| Completeness (%) | 99.34 (98.99) |
| Redundancy | 8.1 (8.2) |
| Refinement | |
| Resolution (Å) | 50.03-4.201 |
| No. reflections | 100331 |
| Rwork / Rfree | 23.31/26.77 |
| No. atoms | |
| Protein | 36304 |
| B-factors | |
| Protein | 161.73 |
| R.m.s. deviations | |
| Bond lengths (Å) | 0.009 |
| Bond angles (°) | 1.98 |
| Ramachandran plot (%) | |
| Favored | 91.48% |
| Allowed | 7.06% |
| outlier | 1.46% |
+
+One crystal was used. \\*Values in parentheses are for highest-resolution shell.
+
+<--- Page Split --->
+
+## Figures
+
+![PLACEHOLDER_54_0]
+
+Figure 1
+
+Isolation of gH/gL specific monoclonal antibodies using single B cell sorting and cloning A FACS based sorting strategy for gH/gL specific B cells. B Binding activities of 1D8 and 2A6, the positive control AMMO1, and the negative control 2G4 to EBV gH/gL measured by ELISA. The data are presented as means \(\pm\) SEM. C Neutralizing activities of 1 D8 and 2A6, the positive control AMMO1, and the negative control 2G4 against EBV infection of Raji B cell lines and D HNE1 epithelia cell line. The data shown is means \(\pm\) SEM. SSC A, side scatter area; FSC A, forward scatter area.
+
+<--- Page Split --->
+![PLACEHOLDER_55_0]
+
+Figure 2
+
+Protective effi cacy of 1D8 against lethal EBV challenge in humanized mice A Timeline for engrafting CD34+ human hematopoietic stem cells (HSC), antibody administration, viral challenge, and monitoring for various biological and clinical outcomes. Four hundred micrograms of 1D8, positive control AMMO1, negative control 2G4, or PBS negative control were administered to the humanized mice via intraperitoneal injection either 24h prior to or weekly for 5 weeks after intravenous challenge with Akata EBV. (B) EBV DNA in the peripheral blood, (C) body weight, and D) survival were monito red weekly. The percent changes in (E) hCD45+, F) hCD20+, or G) hCD3+ cells over the experiment period. On week 6 post infection, (H) virus titers in spleen, (I) liver, J) kidney were analyzed. All data are presented as mean \(\pm\) SEM. \(^{*}p< 0.05\) ; \(^{**}p< 0.01\) ; \(^{***}p< 0.001\) ; ns, no significant.
+
+<--- Page Split --->
+![PLACEHOLDER_56_0]
+
+Figure 3
+
+1D8 reduces viral replication and tissue damages in humanized mice Representative of macroscopic spleens and splenic sections stained for hematoxylin and eosin (H&E), EBV encoded RNA (EBER), human CD20 (and human CD3 (hCD3) at necropsy. The scale bars are indicated.
+
+<--- Page Split --->
+![PLACEHOLDER_57_0]
+
+Figure 4
+
+1D8 targets an unique epitope on gH/gL A Structure overview in a cartoon representation with gL in cyan, gH D I in blue, D II in wheat, D III in green, D IV in yellow, and 1D8 Fa b in purple. The map is contoured at 1.2 RMS to show the density. B Zoomed in view of the interaction between 1D8 and D I and D II. The key binding residue N310 of gH was indicated by a red star. C Cartoon representation of Fab 1D8 and other previously published Fabs AMMO1, CL40, and E1D1 bound to a single gH/gL molecule. The color scheme for gH/gL is as in (A) whereas 1D8 Fab in purple, AMMO1 Fab in light blue, CL40 Fab in pink, and E1D1 Fab in dark k green. D Surface mapping of the four Fab epitopes on gH/gL with the same color in C)). Areas in black indicate the region where structural change was found upon binding to AMMO1 or CL40.
+
+<--- Page Split --->
+![PLACEHOLDER_58_0]
+
+Figure 5
+
+1D8 interferes with cell fusion and binding Quality control of gH/gL expression on the surface of CHO K1 cells by staining with 1D8 (A), positive control AMMO1 (B), and negative control 2G4 (C) before proceeded to the fusion experiment shown in (D). (D) Marked reduction in cell cell-cell fusion in the presence of 1D8, the positive control AMMO1, but not the negative control 2G4. Marked reduction in gH/gL binding to Raji B cell (E) and HK1 epithelial cell (F) in the presence of 1D8, the positive control AM MO1, but not the negative control 2G4. Binding of EphA1 EphA1-Fc to gH/gL was reduced by 1D8 (G), but not by AMMO1 (H) or 2G4 (I) measured by Bio Bio-layer interferometry (BLI). All data are presented as
+
+<--- Page Split --->
+
+mean ± SEM. \*p < 0.05; **p < 0.01; ***p < 0.001; ns, no significant. SSC SSC-A, side side-scatter area; PC5.5, PerCP PerCP-Cy5.5; RLU, relative light unit; SA SA-PE, streptavidin streptavidin-phycoerythrin; MFI, mean fluorescence intensity.
+
+![PLACEHOLDER_59_0]
+
+
+
+Figure 6
+
+Possible mechanisms of 1D8 1D8-mediated neutralization neutralization. (A) For epithelia cells, 1D8 could interfere the interaction between gH/gL and EphA2 either by directly restricting access to the
+
+<--- Page Split --->
+
+interface or by indirectly posing allosteric hindrance. It could also restrict the movement across the D D- I/D - II groove of gH/gL t hat is required for gB interaction and triggering. (B) For B cells, 1D8 could also restrict the movement across the D D- I/D - II groove of gH/gL that is required for downstream viral entry. 1D8 does not appear influence interaction between gp42 and its receptor r HLA class II.
+
+<--- Page Split --->
diff --git a/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb_det.mmd b/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..d9bdf89280c709339a728c89e3a975815de9c673
--- /dev/null
+++ b/preprint/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb/preprint__0449714976f6fe4303823453c8f58d92d5c0b799e6a3133e0f0220cd7881e3cb_det.mmd
@@ -0,0 +1,624 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 955, 177]]<|/det|>
+# A potent and protective human neutralizing antibody targeting a key vulnerable site of Epstein-Barr Virus
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 588, 900]]<|/det|>
+Qian- Ying Zhu Sun Yat- sen University Sisi Shan Tsinghua University https://orcid.org/0000- 0002- 7184- 6818 Jinfang Yu Tsinghua University https://orcid.org/0000- 0002- 2294- 0752 Si- Ying Peng Beijing IDMO Company Limited Cong Sun Sun Yat- sen University Cancer Center Yanan Zuo School of Medicine, Tsinghua University Shu- Mei Yan Sun Yat- Sen University Cancer Center Xiao Zhang Sun Yat- sen University Cancer Center Ziqing Yang Tsinghua University Lan- Yi Zhong Sun Yat- sen University Xuangling Shi Tsinghua University Su- Mei Cao Sun Yat- sen University Cancer Center Xinquan Wang Tsinghua University https://orcid.org/0000- 0003- 3136- 8070 Mu- Sheng Zeng Sun Yat- sen University Cancer Center https://orcid.org/0000- 0003- 3509- 5591 Linqi Zhang (zhanglinqi@tsinghua.edu.cn) Tsinghua University https://orcid.org/0000- 0003- 4931- 509X
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[44, 45, 731, 65]]<|/det|>
+Keywords: EBV, human neutralizing antibody, humanized mouse model, epitope
+
+<|ref|>text<|/ref|><|det|>[[44, 83, 328, 102]]<|/det|>
+Posted Date: January 25th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 121, 463, 141]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 151895/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 159, 910, 202]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 237, 956, 280]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on November 16th, 2021. See the published version at https://doi.org/10.1038/s41467- 021- 26912- 6.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[170, 88, 828, 137]]<|/det|>
+# A potent and protective human neutralizing antibody targeting a key vulnerable site of Epstein-Barr Virus
+
+<|ref|>text<|/ref|><|det|>[[144, 170, 851, 250]]<|/det|>
+Qian- Ying Zhu \(^{1,6}\) , Sisi Shan \(^{2,6}\) , Jinfang Yu \(^{3,6}\) , Si- Ying Peng \(^{5}\) , Cong Sun \(^{1}\) , Yanan Zuo \(^{2}\) , Shu- Mei Yan \(^{1}\) , Xiao Zhang \(^{1}\) , Ziqing Yang \(^{2}\) , Lan- Yi Zhong \(^{1}\) , Xuanling Shi \(^{2}\) , Su- Mei Cao \(^{4}\) , Xinquan Wang \(^{3,*}\) , Mu- Sheng Zeng \(^{1,*}\) , Linqi Zhang \(^{2,7,*}\)
+
+<|ref|>text<|/ref|><|det|>[[144, 281, 852, 712]]<|/det|>
+\(^{1}\) State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Sun Yat- sen University Cancer Center (SYSUCC), Guangzhou 510060, China. \(^{2}\) Comprehensive AIDS Research Center, and Beijing Advanced Innovation Center for Structural Biology, School of Medicine and Vanke School of Public Health, Tsinghua University, Beijing 100084, China. \(^{3}\) The Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Collaborative Innovation Center for Biotherapy, School of Life Sciences, Tsinghua University, 100084 Beijing, China. \(^{4}\) State Key Laboratory of Oncology in South China, Department of Cancer Prevention Research, Sun Yat- sen University Cancer Center (SYSUCC), Guangzhou 510060, China. \(^{5}\) Beijing IDMO Company Limited, Beijing, China. \(^{6}\) These authors contributed equally to this work. \(^{7}\) Lead Contact
+
+<|ref|>text<|/ref|><|det|>[[144, 720, 576, 860]]<|/det|>
+\(^{7}\) Lead Contact \(^{*}\) Correspondence: xinquanwang@mail.tsinghua.edu.cn; zengmsh@sysucc.org.cn; zhanglingi@mail.tsinghua.edu.cn
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 94, 262, 112]]<|/det|>
+## ABSTRACT
+
+<|ref|>text<|/ref|><|det|>[[144, 125, 853, 636]]<|/det|>
+Epstein- Barr virus (EBV) is associated with a range of epithelial and B cell malignancies as well as autoimmune disorders, for which there are still no specific treatments or effective vaccines. Here, we isolated EBV gH/gL- specific antibodies from an EBV- infected individual. One antibody, 1D8, efficiently neutralized EBV infection of two major target cell types, B cells and epithelial cells. In humanized mice, 1D8 provided strong protection against a high- dose EBV challenge by substantially reducing viral loads and associated tumor burden. Crystal structure analysis revealed that 1D8 binds to a key vulnerable interface between the D- I/D- II domains of the viral gH/gL protein, especially the D- II of the gH, thereby interfering with the gH/gL- mediated membrane fusion and binding to target cells. Overall, we identified a potent neutralizing antibody as a promising candidate for prophylactic and therapeutic interventions against EBV infection. The key vulnerable site also provides insights into the EBV vaccines design.
+
+<|ref|>text<|/ref|><|det|>[[147, 688, 830, 710]]<|/det|>
+KEY WORDS: EBV, human neutralizing antibody, humanized mouse model,
+
+<|ref|>text<|/ref|><|det|>[[147, 727, 217, 743]]<|/det|>
+epitope
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 94, 306, 112]]<|/det|>
+## INTRODUCTION
+
+<|ref|>text<|/ref|><|det|>[[144, 130, 854, 483]]<|/det|>
+Epstein- Barr virus (EBV) is the causative agent of a wide range of diseases in humans such as infectious mononucleosis and lymphoproliferative disorders, as well as epithelial and B cell malignancies including nasopharyngeal carcinoma and Burkitt's lymphoma(1- 4). Despite decades of research, a safe and effectively vaccine against EBV still remains elusive, largely due to a lack of knowledge regarding the specificity and magnitude of immune responses required for protection(5- 8). EBV- infected individuals produce broad and potent neutralizing antibodies that can inhibit infection of both epithelial cells and B cells in vitro(9- 13). However, their specificity to viral antigens and potential mechanism of neutralization are not clear.
+
+<|ref|>text<|/ref|><|det|>[[144, 500, 853, 891]]<|/det|>
+Recent studies on monoclonal antibodies (mAbs) revealed some of the intricate interactions between antibodies and viral surface antigens, providing critical insights into the potential targets for antibody neutralization and vaccine development(14- 18). The reported mAbs recognize exclusively viral surface glycoproteins that work in concert in determining viral tropism and mediating viral fusion with the target cells, such as gp350, gH/gL, gB and gp42(19- 22). Recently, gH/gL and gB, which together constitute the fusion machinery of EBV, have drawn increasing attention as newer generations of antibodies targeting this machinery demonstrate broad and potent inhibitory activity against EBV infection of both B cells and epithelial cells(23), as well as cross- neutralizing reactivity to related herpesviruses of non- human primate(9, 24, 25).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 896]]<|/det|>
+As components of the fusion machinery, gH/gL and gB demonstrate unique structural and functional features that are critical for viral entry, but they also inadvertently expose some vulnerable sites during the process, and became susceptible to antibody binding and neutralization(26- 28). Structurally, gH/gL consists of four distinct domains named domain- I (D- I) to domain- IV (D- IV), forming an elongated structure(29). D- I is formed by gL and the N- terminus of gH, while D- II to D- IV are formed by the rest of gH. D- I and D- II are connected through a linker helix and form a structurally distinct groove. For viral fusion to occur, gH/gL must interact with gB, which triggers a cascade of events involving dramatic structural changes of gB from the pre- to the post- fusion conformation(27, 28). Mutations in the D- I and D- I/D- II interfaces of gH/gL were shown to affect the membrane fusion process, suggesting that these regions of gH/gL are important for the interaction and activation of gB(30, 31). Apart from the fusion machinery, EBV infection requires additional surface glycoproteins to complete the entry process, but the involved accessory molecules are rather different between B cells and epithelial cells(32). For instance, EBV utilizes gp350, one of the most abundant glycoproteins on the viral envelope, to attach to the cell surface through high- affinity interaction with CD21 or CD35(33- 35). Such attachment promotes the bridging effect of another surface glycoprotein, gp42, which inserts itself between gH/gL and human leukocyte antigen (HLA) class II, which triggers the downstream fusion machinery(36, 37). Interestingly, gp42 has an inhibitory effect on epithelial cell
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 263]]<|/det|>
+infection, suggesting a different entry mechanism in B cells and epithelial cells(38). For infection of epithelial cells, gH/gL first binds to integrin and NMHC- IIA on the cell surface. The fusion machinery then interacts with neuropilin 1 (NRP1) and ephrin receptor A2 (EphA2)(39- 41), which leads to a conformational transition of gB, facilitating viral fusion(27, 42).
+
+<|ref|>text<|/ref|><|det|>[[144, 277, 852, 745]]<|/det|>
+Most of the current anti- gH/gL antibodies are of murine origin(36, 43). E1D1, CL59 and CL40 can block epithelial cell infection but fail to efficiently neutralize B cell infection(22). Only one human neutralizing antibody targeting gH/gL, AMMO1, was recently isolated from an EBV- infected individual(22). AMMO1 can potently block infection of both B cells and epithelial cells in vitro. AMMO1 can also protect humanized mice from EBV challenge and provide sterilizing immunity in macaques against oral challenge with rhesus lymphocytovirus, the EBV relative that infects rhesus macaques. These findings indicate that a vaccine capable of inducing AMMO1- like neutralizing antibodies may protect human from EBV infection. Cryo- electron microscopy (cryoEM) analysis of the AMMO1- gH/gL- gp42 complex revealed that AMMO1 binds to an epitope between D- I and D- II of gH/gL(22), which serves as a more precise and clear target for future vaccine design and development.
+
+<|ref|>text<|/ref|><|det|>[[144, 760, 852, 892]]<|/det|>
+Here, we sought to isolate more neutralizing antibodies from EBV- infected individuals targeting the EBV gH/gL. After screening a large number of infected individuals, we successfully isolated the anti- gH/gL antibody 1D8, which is capable of efficiently neutralizing EBV infection of epithelial cells and B cells in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 596]]<|/det|>
+vitro. 1D8 also provided potent protection against EBV challenge in humanized mice by significantly reducing the viral loads and associated tumor burden. Using X- ray crystallography, we determined the structure of the 1D8- gH/gL complex and showed that 1D8 recognizes a key epitope located at the top of the groove between D- I and D- II of gH/gL, especially the D- II of gH. Notably, this epitope is located on the opposite side of that recognized by AMMO1 and CL40. In addition, 1D8 also significantly inhibited viral membrane fusion and gH/gL binding to epithelial cell receptor EphA2. We believe that this new vulnerable site, together with that recognized by AMMO1 and CL40, suggests that D- I and D- II represent an attractive target for the rational design of vaccines aiming to elicit antibody responses similar to these mAbs. Finally, 1D8 could also be used alone or in combination with other mAbs in prophylactic and therapeutic interventions against EBV infection either in organ transplant recipients or immunocompromised patients.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 648, 245, 666]]<|/det|>
+## RESULTS
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 686, 794, 706]]<|/det|>
+## Isolation of human monoclonal antibodies targeting the EBV gH/gL
+
+<|ref|>text<|/ref|><|det|>[[146, 722, 852, 891]]<|/det|>
+We first screened plasma samples from a cohort of high- risk individuals and nasopharyngeal carcinoma patients(44, 45) for those with the highest levels of binding and neutralizing activity. Of the 48 plasma samples screened, donor 27 from the high- risk group had antibodies with the highest affinity for gH/gL measured by ELISA, with the half- maximal effective concentration (EC50)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 90, 852, 896]]<|/det|>
+corresponding to a 6874- fold dilution (fig. S1A). The same plasma sample also displayed the most potent neutralizing activity against EBV infection of HNE1 epithelial cells and Raji B cells, with respective half- maximal inhibitory concentrations (IC50) corresponding to a 273- fold and 1250- fold dilution (fig. S1B). To isolate monoclonal antibodies, we used phycoerythrin (PE) conjugated gH/gL as baits to stain and sort the antigen- specific memory B cells from the peripheral blood mononuclear cells (PBMCs) of donor 27 using flow cytometry (Fig. 1A). Out of a total 54 sorted single B cells, we were able to clone and express 10 full- length human immunoglobulin G1 (IgG1) genes in transfected 293T cells. Two antibodies, 1D8 and 2A6, were found to have strong binding to gH/gL. As shown in Fig. 1B, 1D8 showed \(\sim 7\) - fold stronger binding to gH/gL than 2A6, with an EC50 of \(0.008\mu \mathrm{g / ml}\) and \(0.057\mu \mathrm{g / ml}\) , respectively. 1D8 also demonstrated higher neutralizing activity than 2A6 against EBV infection of HNE1 epithelial cells and Raji B cells (Fig. 1C,D and table S1). The IC50 of 1D8 was about 6 times lower than that of 2A6 for both cell types. Notably, 1D8 displayed comparable binding and neutralizing activities to AMMO1, a potent gH/gL- specific neutralizing antibody previously isolated from an EBV- infected individual(22). The equilibrium dissociation constant (KD) measured by SPR was \(0.59\mathrm{nM}\) for 1D8 and \(0.14\mathrm{nM}\) for AMMO1 (fig. S1C,D and table S2). When tested for neutralizing activity against EBV infection, 1D8 and AMMO1 showed IC50 values of 0.238 and \(0.318\mu \mathrm{g / ml}\) in Raji B cells, as well as 0.123 and \(0.127\mu \mathrm{g / ml}\) in HNE1 epithelial cells,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 94, 487, 113]]<|/det|>
+respectively (Fig. 1C,D and table S1).
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 168, 740, 188]]<|/det|>
+## 1D8 protects against lethal EBV challenge in humanized mice
+
+<|ref|>text<|/ref|><|det|>[[145, 202, 854, 633]]<|/det|>
+To test the protective potential of 1D8 in vivo, we used a humanized mouse model reconstituted with human cord blood- derived CD34+ stem cells that became susceptible to EBV infection and disease after approximately 8 weeks of development and maturation(46- 48). The entire experimental protocol and assays conducted to evaluate protection are outlined in Fig. 2A. Briefly, we administrated \(400\mu g\) of 1D8, AMMO1 as positive control, or 2G4 and PBS as negative controls to groups of seven to eight humanized mice via the intraperitoneal (i.p.) route. On the following day, the animals were challenged with 1,000 50% transforming dose (TD50) Akata EBV via the intravenous (i.v.) route. In the ensuing up to 6- week period, all animals received the testing antibodies or PBS weekly via the i.p. route and were monitored for body weight, survival, as well as various virological and immunological parameters.
+
+<|ref|>text<|/ref|><|det|>[[145, 648, 852, 891]]<|/det|>
+EBV DNA in the peripheral blood measured by quantitative PCR reflected the distinctions in clinical manifestation between these animals (Fig. 2B). In the animals treated with 1D8 and AMMO1, EBV DNA became detectable on week 3 after challenge and slowly increased in the following two weeks, but no animals had EBV DNA copy numbers greater than 10 copies/μl blood at week 5 post challenge. By contrast, in the animals treated with 2G4 and PBS, EBV DNA rapidly increased from week 3 onwards after the challenge and reached
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 336]]<|/det|>
+about 100- fold higher copy numbers than in the groups treated with 1D8 and AMMO1 at week 5 post- challenge (Fig. 2B). All animals in the 1D8 and AMMO1 treated groups survived the challenge and demonstrated relatively stable body weight without obvious pathology (Fig. 2C,D). By contrast, negative control animals (2G4 and PBS groups) began significantly losing weight starting on day 28 (4 weeks), succumbed to disease and had to be euthanized by day 38 after the challenge.
+
+<|ref|>text<|/ref|><|det|>[[144, 352, 852, 707]]<|/det|>
+By the time they were ready for the protection experiments, the reconstituted animals had about \(20\%\) human CD45+ lymphocytes in the peripheral blood, nearly \(90\%\) of which were human CD20+ B cells and \(< 1\%\) were human CD3+ T cells (Fig. 2E- G). In addition, the dynamic change of human CD20+ B cells and CD3+ T cells in the peripheral blood was correlated with distinct pattern of disease progression between these animals. Animals in the 1D8 and AMMO1 treated groups showed a relatively slower decrease in the number of CD20+ B cells compared with the 2G4 and PBS treated groups. At the same time, the increase in the number of CD3+ T cells was slower in animals treated with 1D8 and AMMO1 compared to those treated by 2G4 and PBS (Fig. 2F,G).
+
+<|ref|>text<|/ref|><|det|>[[144, 722, 852, 893]]<|/det|>
+Furthermore, EBV DNA copy numbers measured in the spleen, liver and kidney collected at necropsy shared a similar trend with those measured in the peripheral blood (Fig. 2H,J). The copy numbers of EBV DNA were significantly lower in the 1D8 and AMMO1 treated groups than in the 2G4 and PBS treated groups, although the copy numbers were generally higher in the spleen than in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 188]]<|/det|>
+the liver and kidney (Fig. 2H,J). Taken together, these results demonstrated that 1D8 as well as the positive control AMMO1 can significantly reduce viral replication and provide complete protection from a lethal EBV challenge.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 242, 850, 297]]<|/det|>
+## Marked reduction in viral replication and tissue damages in the protected animals
+
+<|ref|>text<|/ref|><|det|>[[144, 310, 852, 897]]<|/det|>
+To study the impact of protection at the tissue levels, we collected the spleen, liver and kidney of the animals at the necropsy. The most profound and visible changes were observed in the spleens. Morphologically, the spleens from the 2G4 and PBS groups were clearly enlarged with a few irregular and pale tumors across the entire surface. By contrast, the spleens in the 1D8 and AMMO1 groups were normal in size and color, without visible tumors (Fig. 3). We went on to perform histopathology analysis on the spleen sections using hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) for hCD3 and hCD20, as well as in situ hybridization for Epstein- Barr virus- encoded RNAs (EBERs) (Fig. 3). All mice treated with 2G4 or PBS presented with typically large B- cell lymphomas in the white pulp regions, which consisted of large and atypical lymphoid cells that were positive for hCD20 and EBER. They were abundant and widely distributed across the tissue sections. Morphologically their proliferations destroyed the underlying architecture of the tissue with some infiltration by hCD3+ T cells. Additionally, areas of coagulative necrosis were often present in the spleens of mice from the 2G4
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 560]]<|/det|>
+and PBS groups. By contrast, in the 1D8 and AMMO1 groups, the overall tissue architecture remained largely intact, even if some atypical large transformed cells could also be seen. Among the large number of hCD20+ B cells in the white pulp areas, \(\text{EBER + }\) cells were relatively scarce. A few hCD3+ T cells were also found scattered within. Similarly, in the hepatic and renal sections from 2G4 and PBS groups, a large number of hCD20+ and \(\text{EBER + }\) B cells were identified, while they were rare in the 1D8 and AMMO1 groups (fig. S2). The infected cells were frequently found near the blood vessels in both the liver and kidney, likely the results of migration and seeding from the blood circulation. Collectively, these results show that 1D8 and AMMO1 can significantly reduce viral replication and tissue damage relative to 2G4 and PBS, offering an explanation for their impressive in vivo protection against a lethal EBV challenge.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 611, 500, 632]]<|/det|>
+## 1D8 binds to a key epitope on \(\mathbf{gH / gL}\)
+
+<|ref|>text<|/ref|><|det|>[[144, 647, 852, 892]]<|/det|>
+To understand the neutralizing mechanism of 1D8, we sought to determine the structure of the 1D8- gH/gL complex by X- ray crystallography. After screening nearly 100 crystals with relatively weak diffraction, we obtained a dataset with 4.2 Å resolution and solved the structure by molecular replacement (table S3). The structure showed that 1D8 bound to the interface at the top of the groove formed by D- I and D- II of gH/gL, especially the D- II of gH (Fig. 4A). 1D8 bound to the unique epitope spanning of gH/gL, which comprised residues of both gH
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 90, 852, 895]]<|/det|>
+and gL, burying a surface area of \(969 \text{Å}^2\) . CDRL1, CDRL3 and CDRH2 of 1D8 made practically no contribution to the binding of gH/gL. CDRL2 mainly bound to \(2\alpha - 2\) and \(2\beta - 2\) . The loop between \(2\alpha - 9\) and \(2\beta - 11\) was bound by CDRH1 and CDRH3. CDRH3 also bound to the loop between \(2\alpha - 1\) and \(2\beta - 1\) . The heavy chain of 1D8 bound to the loop between \(L\alpha - 1\) and \(L\alpha - 2\) (Fig. 4B). To identify the key residue for antibody binding, we generated a series of single alanine substitutions for the contacting residues on gH/gL. Except for two (L122A and C312A), the remaining 15 mutants were successfully expressed and purified from the supernatant of transfected 293F cells. We then performed ELISA to assess the impact of these mutants on 1D8 binding. One mutant, N310A, locate in the loop between \(2\alpha - 9\) and \(2\beta - 11\) , was identified to specifically reduce the binding of 1D8 but not AMMO1 (Fig. 4B and fig. S3A,B). When measured by SPR, the binding affinity of 1D8 for this particular mutant dropped to 31.6nM, representing more than 53-fold decrease compared to the wild type gH/gL. However, no significant change of binding was found for AMMO1 compared to the wild type gH/gL (fig. S3C,D and table S2). The unique binding of 1D8 is further supported by superimposing the antibodies with known structural information onto the same gH/gL molecule. As shown in Fig. 4C,D, 1D8 bound to gH/gL at the top of the groove formed between D-I and D-II, especially the D-II of gH, while AMMO1 binds the opposite side of the molecule through a discontinuous epitope formed at the D-I/D-II interface. The mouse-derived antibody CL40 partially overlaps with the epitope of AMMO1 by
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 336]]<|/det|>
+binding to an epitope on \(\mathsf{gH}\) at the interface between D- II and D- III(22). Another mouse antibody E1D1, however, only recognizes \(\mathsf{gL}(36,43)\) (Fig. 4C,D). We also used bio- layer interferometry (BLI) to confirm that 1D8 does not compete with any of these antibodies in binding to \(\mathsf{gH} / \mathsf{gL}\) (fig. S3E). These results indicate that 1D8 recognizes a key vulnerable site on \(\mathsf{gH} / \mathsf{gL}\) and provide a good rational basis for combined use with other antibodies in suppressing EBV infection.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 390, 850, 444]]<|/det|>
+## 1D8 inhibits \(\mathsf{gH} / \mathsf{gL}\) -mediated membrane fusion and binding to B and epithelial cells
+
+<|ref|>text<|/ref|><|det|>[[144, 461, 852, 894]]<|/det|>
+We next studied the ability of 1D8 to inhibit \(\mathsf{gH} / \mathsf{gL}\) mediated membrane fusion by monitoring the fusion efficiency between the effector and target cells. Specifically, effector CHO- K1 cells expressing the \(\mathsf{gH} / \mathsf{gL}\) and \(\mathsf{gB}\) fusion machinery were incubated with a saturated concentration of 1D8 or relevant controls at \(37^{\circ}\mathrm{C}\) for 1h before mixing at a 1:1 ratio with the target HEK293 cells. The inhibitory activity was measured 24h afterwards via the luciferase activity in the cell lysates, which only became detectable when fusion occurred. As shown in Fig. 5A- C, the effector CHO- K1 cells expressed good levels of \(\mathsf{gH} / \mathsf{gL}\) as measured by flow cytometry. In the presence of 1D8 or AMMO1, the fusion activity was barely measurable and similar to the background where only the effector cells were present (Fig. 5D). By contrast, incubation with the negative controls 2G4 or PBS resulted in high levels of luciferase activity
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 90, 852, 896]]<|/det|>
+beyond one million relative light unit (RLU). In addition, we tested the ability of 1D8 to interfere with the binding of fluorescently labelled \(\mathsf{gH / gL}\) to Raji B cells and HK1 epithelial cells, both of which are susceptible to EBV infection in vitro(49, 50). Gp42 was included in the assessment of the binding to B cells but not for the epithelial cells, since the \(\mathsf{gH / gL - gp42}\) complex is specifically required for B cell activation and fusion(36). 1D8 and relevant controls were incubated with fluorescent- labeled \(\mathsf{gH / gL}\) at \(37^{\circ}\mathrm{C}\) for 1h before mixing with B cells or epithelia cells and further incubation on ice for 1h. The levels of inhibition of \(\mathsf{gH / gL}\) - mediated binding to both cell types were measured by flow cytometry. As shown in Fig. 5E, pre- incubation with 1D8 and AMMO1 significantly reduced but did not completely abrogate \(\mathsf{gH / gL - gp42}\) binding to B cells. While no difference was found between the negative controls 2G4 and PBS, AMMO1 appeared to be more potent than 1D8 in interfering with the binding of \(\mathsf{gH / gL}\) to B cells. Conversely, 1D8 seems to be more powerful than AMMO1 in inhibiting the binding of \(\mathsf{gH / gL}\) to the epithelia cells, whereas the negative controls showed negligible effect (Fig. 5F). Lastly, we studied the ability of 1D8 to inhibit the interaction between \(\mathsf{gH / gL}\) and EphA2, a recently identified receptor for EBV infection of epithelial cells that depends on an interaction with \(\mathsf{gH / gL}(39, 40)\) . Consistent with an earlier report(22), the interaction between EphA2- Fc and \(\mathsf{gH / gL}\) was indeed rather weak as measured by BLI. Nevertheless, pre- incubation of \(\mathsf{gH / gL}\) with 1D8 did result in a small and clear reduction in the interaction between \(\mathsf{gH / gL}\) and EphA2 (Fig.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 373]]<|/det|>
+5G). Conversely, such an effect was not noticed for AMMO1 or 2G4 (Fig. 5H,I). This may explain why 1D8 was more effective than AMMO1 in inhibiting EBV infection of epithelial cells (see above), although the underlying mechanism warrants further investigation. Taken together, these findings indicate that 1D8 as well as the positive control AMMO1 can significantly inhibit gH/gL-mediated membrane fusion and binding to B and epithelial cells, either through direct blocking of binding or by sterically interfering with the downstream interactions required for EBV infection.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 427, 277, 446]]<|/det|>
+## DISCUSSION
+
+<|ref|>text<|/ref|><|det|>[[144, 462, 852, 893]]<|/det|>
+Neutralizing antibodies are the major component of protective immunity against viral infection in humans(51- 53). They exert their function by targeting crucial epitopes on the viral envelope glycoproteins. Identifying the neutralizing mAbs and their recognized epitopes is therefore the first crucial step for understanding the protective antibody response, which can inform the rational development of antibody- based therapy and vaccines(17, 18). In some EBV- infected individuals, high levels of serum neutralizing antibodies have been identified capable of blocking infection of both B cells and epithelia cells(9). This finding indicates that the human immune system is able to generate potent neutralizing antibodies to clear the infection and/or attenuate disease progression. However, the antigen and epitope specificity, as well as the potential mechanism of neutralization of these antibodies are not entirely
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 95, 200, 110]]<|/det|>
+clear.
+
+<|ref|>text<|/ref|><|det|>[[144, 128, 852, 560]]<|/det|>
+We report here the isolation and characterization of the human neutralizing antibody 1D8, which protects EBV infection in both B cells and epithelial cells. Passive delivery of 1D8 significantly reduced the viral loads and tumor burden of EBV- induced lymphoma in humanized mice. Structural analysis of the 1D8- gH/gL complex identified a key epitope at the top groove of gH/gL between D- I and D- II, especially the D- II of gH, which is distinct from any of the reported antibodies. In addition, 1D8 was found to inhibit viral membrane fusion and reduce the binding of gH/gL to the epithelial cell receptor EphA2(39, 40). We believe that the new vulnerable site recognized by 1D8 represents another attractive target for the rational design of vaccines capable of eliciting 1D8- like neutralizing antibodies. 1D8 could also serve as a promising candidate for antibody- based therapy and prevention of EBV infection.
+
+<|ref|>text<|/ref|><|det|>[[144, 575, 852, 892]]<|/det|>
+A couple of points need to be highlighted here. First, as both B cells and epithelia cells are major targets for EBV infection(54), it is highly desirable to isolate neutralizing antibodies capable of blocking the virus and protecting both cell types from infection. 1D8, together with recently reported AMMO1(22), are the only two representatives of this class of antibodies with dual tropism. However, we are uncertain how much this type of antibodies contributes to the overall neutralizing activities in the infected individuals. Given the low frequency in identifying 1D8 and AMMO1 antibodies among the isolated memory B cells(22), it is reasonable to assume they are quite rare and might
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 90, 853, 895]]<|/det|>
+only be induced among a small proportion of naturally infected patients. Perhaps, this is due to the elusive nature of their epitopes, which are only transiently exposed during viral entry. It could also be due to their highly dynamic nature involving multiple conformational changes during infection. The rapid movement across the D- I and D- II groove required for binding and triggering of gB glycoprotein supports this notion(30, 31, 55, 56). Furthermore, compared to gp350, gH/gL is much less abundant and therefore has a quantitative disadvantage in immune recognition and stimulation(19). However, identification of 1D8 and AMMO1 and their epitopes around D- I and D- II offer an unprecedented opportunity to expose this vulnerable site in much more precise and persistent manner so that more focused and stronger immune response like 1D8 and AMMO1 could be generated. This could be done either by including gH/gL in the vaccine regimen(9, 23) or singling out D- I and D- II domain as epitope- focused immunogens. Both approaches would require careful design and validation to ensure proper structure and exposure of vulnerable sites recognized by 1D8 and AMMO1. In support of this notion, nanoparticles displaying gH/gL elicited a strong neutralizing antibody response against EBV infection of both target cell types(9), even if this exciting report requires further confirmation. Lastly, given the relatively conserved nature of this region among herpesviruses(24, 27), carefully designed D- I and D- II immunogens may be able to induce an even broader and stronger cross- neutralizing antibody response against a wide variety of viral strains.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 90, 854, 895]]<|/det|>
+Second, despite structural and functional insights, we are still not certain of the exact mechanism through which 1D8 neutralizes EBV infection of both target cell types. Structurally, 1D8 recognized a key epitope within the groove between D- I and D- II, especially the D- II of gH, whereas AMMO1 was found to bind a discontinuous epitope spanning D- I and D- II on the opposite ridge of the groove(22). Such convergence on D- I and D- II domains suggests a common mechanism of neutralization, either by affecting coordination within and across D- I and D- II or their interaction with other viral glycoproteins such as gB or gp42 required for downstream viral entry (Fig. 6A,B). AMMO1 was postulated to lock D- I, D- II and the linker helix, preventing proper movement required for interaction and activation of gB(56). As residues with the D- I and D- II groove also mediate membrane fusion and several of these critical residues are near the epitope of 1D8(30, 31, 55, 56), it stands to reason that 1D8 could also exert its neutralization activity by inhibiting the fusion process. Instead of acting like a molecular clamp as AMMO1, 1D8 may act more like a molecular wedge forcing into the space within the groove. Certainly, as 1D8 and AMMO1 bind distinct epitopes, there must be some differences in the exact mechanisms underlying their inhibitory effects. For example, AMMO1 appears to be more potent than 1D8 in interfering with the binding of gH/gL to B cells (Fig. 5E), perhaps due to its ability to displace the c- terminal domain of gp42 through the gp42 N173 glycan(22). Conversely, 1D8 seems to be more powerful than AMMO1 in inhibiting binding of gH/gL to epithelia cells, likely by affecting the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 336]]<|/det|>
+interaction between EphA2- Fc and gH/gL (Fig. 5F,G and 6A). In any case, the 1D8 antibody identified in this study represents another potent human neutralizing antibody that can be used alone or in combination with other antibodies such as AMMO1 for antibody- based interventions against EBV infection. The epitope defined here will also assist the rational design of vaccines focusing more on the vulnerable sites to elicit powerful neutralizing antibodies similar to 1D8 and AMMO1.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 390, 422, 409]]<|/det|>
+## MATERIALS AND METHODS
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 428, 307, 447]]<|/det|>
+## Human subjects
+
+<|ref|>text<|/ref|><|det|>[[144, 462, 852, 780]]<|/det|>
+We collected plasma samples from 48 participants including 23 histologically diagnosed NPC cases and 25 non- NPC high- risk healthy controls in a screening program in Sihui County in Guangdong Province of China from 2007 and 2018. Peripheral blood mononuclear cell (PBMC) sample of donors 27 were collected in 2018. The screening program has been introduced in detail in other manuscript. This study was reviewed and approved by the Ethics Committee of the Sun Yat- Sen University Cancer Center (SYSUCC; Guangzhou, Guangdong, China) and was conducted in accordance with the Declaration of Helsinki.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 835, 240, 853]]<|/det|>
+## Cell lines
+
+<|ref|>text<|/ref|><|det|>[[144, 871, 850, 891]]<|/det|>
+All cell lines were cultured at \(37^{\circ}C\) in a humidified atmosphere comprising \(5\%\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 411]]<|/det|>
+CO2. 293T cells (ATCC) were grown in DMEM (GIBCO) +10% FBS (GIBCO). CHO K- 1 cells (ATCC) were maintained in Ham's F- 12 (GIBCO) +10% FBS. Raji cells (ATCC), HNE1 cells(57) and HK1 cells(58) were maintained in RMPI1640+10% FBS. Akata B cells(59) harboring a modified EBV, in which the thymidine kinase gene has been replaced with a neomycin and green fluorescence protein (GFP) cassette (Akata- GFP), were grown in RMPI 1640 (GIBCO) +5% FBS. 293F cells (ThermoFisher) were maintained in Freestyle 293 medium (Union) with gentle shaking. All cells were grown with 100U/ml penicillin and 100μg/ml streptomycin.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 464, 310, 482]]<|/det|>
+## Humanized mice
+
+<|ref|>text<|/ref|><|det|>[[144, 500, 852, 856]]<|/det|>
+The construction of the humanized mice was based on NOD.Cg- Prkdcem1IDMOII2rgem2IDMO mice (NOD- Prkdcnull IL2RYnull, NPI@)(60), which were kept in a specific pathogen free (SPF) facility and obtained from BEIJING IDMO Co., Ltd. To generate the humanized immune system, mice were i.p. injected with a single dose of Busulfan at 20mg/kg body weight. After 48h post- injection, the mice received an intravenous tail injection of human CD34+ cells, which were isolated from umbilical cord blood (Beijing Novay biotech) with a purity of over 90%. Human CD45+ cells in peripheral blood of each humanized mouse were detected at 4 and 8 weeks post engraftment by flow cytometry.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 94, 240, 111]]<|/det|>
+## Plasmids
+
+<|ref|>text<|/ref|><|det|>[[144, 130, 852, 520]]<|/det|>
+The gH/gL [residues 19 to 679 of gH and residues 24 to 137 of gL were linked by (G4S)3] and gp42 (residue 34 to 223) fragments were amplified from the bacterial artificial chromosome (BAC) of EBV- M81 by PCR and cloned into the pcDNA3.1 plasmid with an N- terminal CD5 leader peptide and a C- terminal HIS Tag. Targeted mutations were introduced into pcDNA3.1- CD5- gH/gL using the ClonExpress MultiS One Step Cloning Kit (Vazyme) and were confirmed by Sanger sequencing. The pCAGGS expression plasmids for gH, gL, gB, and pT7EMCLuc (which carries a luciferase- containing reporter plasmid under the control of the T7 promoter) were kindly provided by Dr. R. Longnecker. The ectodomain of EphA2 was cloned in an Fc construct as described previously(61).
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 576, 446, 594]]<|/det|>
+## Recombinant antibody cloning
+
+<|ref|>text<|/ref|><|det|>[[144, 610, 852, 891]]<|/det|>
+The VH and VK/Vλ genes of reference antibodies CL40, E1D1 and AMMO1 were obtained from PDB and codon optimized genes were synthesized by Tsingke Biological Technology Company. Antibody heavy chain and light chain variable gene fragments were obtained using separate primer pairs(62) with restriction enzyme cutting sites, including VH primers with 5'Agel and 3'Sall, VK primers with 5'Agel and 3'BsiWI, and Vλ primers with 5'Agel and 3'Xhol. Then PCR products were cloned into antibody expression vectors containing the constant regions of human IgG1. The sequences of the recombinant
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 94, 562, 113]]<|/det|>
+plasmids were verified by Sanger sequencing.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 168, 465, 187]]<|/det|>
+## Recombinant protein expression
+
+<|ref|>text<|/ref|><|det|>[[144, 202, 855, 636]]<|/det|>
+The 293F cells were transfected with plasmids encoding EBV glycoproteins, EphA2- Fc and recombinant antibodies at a density of \(1.5 \times 10^{6}\) cells/ml in Freestyle 293 medium using PEI (Polysciences) transfection reagent according to the manufacturer's instructions. After five days, the culture supernatant containing EBV glycoprotein was collected and passed through Ni- NTA resin (GE Healthcare), followed by washing (PBS with 20mM imidazole, pH7.4) and elution (PBS with 250mM imidazole, pH7.4). The proteins were further purified by size exclusion chromatography (SEC) and dialyzed into PBS. Clarified cell supernatant containing recombinant antibodies or EphA2- Fc was passed over Protein A agarose (GenScript), followed by extensive washing with PBS, and then eluted with 10 mL of 0.3M glycine, pH 2.0 into 1 mL of 1M Tris HCl, pH 8.0. Purified proteins were then dialyzed into PBS.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 686, 479, 706]]<|/det|>
+## Recombinant protein biotinylation
+
+<|ref|>text<|/ref|><|det|>[[145, 722, 852, 817]]<|/det|>
+gH/gL were biotinylated at a theoretical 1.5:1 biotin/protein ratio using the EZ- Link Sulfo- NHS- Biotin (ThermoFisher) at room temperature for 30min. Free biotin was removed by 3 successive rounds of dilution with PBS.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 872, 571, 891]]<|/det|>
+## Preparation of the antigen binding fragment
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 93, 852, 188]]<|/det|>
+1D8 Fab was obtained by digesting 1D8 IgG with Endoproteinase Lys- C (Sigma) at \(37^{\circ}C\) (1 mg IgG: 250 ng Lys C) for 12h. Fab fragments were isolated with Fc fragments using protein A agarose, then further purified by SEC.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 242, 425, 261]]<|/det|>
+## Biolayer Interferometry (BLI)
+
+<|ref|>text<|/ref|><|det|>[[144, 275, 853, 593]]<|/det|>
+Antibody competition binding assays (Octet Red 96, ForteBio, Pall LLC): 250nM gH/gL was captured onto HIS1K sensors (ForteBio, Pall LLC) for 120s. The baseline interference was then read for 60 s in KB buffer (PBS, 0.1% BSA, 0.02%Tween). Then the sensor was loaded with 1D8 (10μg/ml) or KB (blank) for 60s and balanced in KB for 60s, followed by association with 10μg/ml competitive antibodies (1D8, AMMO1, CL40, E1D1) for 120s and association with KB for 120s. One gH/gL- 1D8 loaded sensor was immersed in buffer as a reference during the association and dissociation steps and used to subtract the background signal.
+
+<|ref|>text<|/ref|><|det|>[[144, 611, 855, 891]]<|/det|>
+Antibody/EphA2 competition binding assays: 2μg/ml gH/gL- biotin was immobilized on streptavidin biosensors (ForteBio, Pall LLC), and then immersed into KB for 60s. Then the sensor was loaded with 1D8 (50nM), AMMO1 (50nM), 2G4 (50nM) or KB (blank) for 60s and balanced in KB for 60s, followed by associated with 1000nM EphA2- Fc for 100s and association with KB for 120s. One gH/gL- antibody loaded sensor was immersed in buffer as a reference during the association and dissociation steps and used to subtract the background signal.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 130, 489, 149]]<|/det|>
+## Surface Plasmon Resonance (SPR)
+
+<|ref|>text<|/ref|><|det|>[[144, 166, 853, 521]]<|/det|>
+The binding kinetics and affinity of antibodies for \(\mathsf{gH} / \mathsf{gL}\) or their mutants were analyzed by SPR (Biacore 8K, GE Healthcare). Anti- human IgG (Fc) antibody was covalently immobilized onto a CM5 sensor chip (GE Healthcare) via amine groups in \(10~\mathsf{mM}\) sodium acetate buffer (pH 5.0) for a final RU of around 5000. Specifically, antibodies 1D8 or AMMO1 (2μg/ml) were captured by anti- human IgG antibody for 10s. Diluted \(\mathsf{gH} / \mathsf{gL}\) or their mutants were run at a flow rate of \(30~\mu \mathrm{l} / \mathrm{min}\) in HBS- EP (aqueous buffer containing 0.01M HEPES pH7.4, 0.15M NaCl, 3mM EDTA and \(0.05\% (\mathsf{v} / \mathsf{v})\) Tween 20, filtered through a \(0.2\mu \mathrm{m}\) filter). The sensograms were fit to a 1:1 binding model using the Biacore Insight Evaluation Software (GE Healthcare).
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 576, 600, 595]]<|/det|>
+## Enzyme-Linked Immunosorbent Assay (ELISA)
+
+<|ref|>text<|/ref|><|det|>[[144, 610, 853, 892]]<|/det|>
+For ELISA, 100ng/well of EBV glycoprotein was coated in 96- well enzyme- linked immunosorbent assay plates overnight at \(4^{\circ}\mathrm{C}\) . Then, the plates were blocked with \(5\%\) bovine serum albumin (BSA) in PBS and \(0.1\%\) Tween- 20 (blocking buffer) at \(37^{\circ}\mathrm{C}\) for \(1\mathrm{~h}\) . After blocking, the plates were washed three times with \(0.1\%\) Tween- 20 in PBS (washing buffer). Plasma samples or recombinant antibodies were diluted serially in blocking buffer and incubated at \(37^{\circ}\mathrm{C}\) for \(1\mathrm{~h}\) . Following three times of washing, a 1:4000 goat anti- human IgG- HRP (Promega) in blocking buffer was added to each well and incubated
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 520]]<|/det|>
+at \(37^{\circ}C\) for 45 minutes. Plates were washed five times and incubated with \(3,3',5,5'\) - tetramethylbenzidine substrate (TMB) (TIANGEN) for 5 minutes at room temperature. Then 1M hydrochloric acid (HCl) was added and the \(\mathrm{OD}_{450}\) was read on a microplate reader (Epoch2). For the binding analysis of \(\mathrm{gH / gL}\) mutants, \(500\mathrm{ng / well}\) of antibody was coated in plates overnight at \(4^{\circ}C\) . The plates were then blocked and washed. The \(\mathrm{gH / gL}\) mutants were diluted serially in blocking buffer and incubated at \(37^{\circ}C\) for 1h. Following three times of washing, 1:3000 diluted mouse anti- his antibody (TRANSGEN BIOTECH) in blocking buffer was added to each well and incubated at \(37^{\circ}C\) for 1h. After three times of washing, a 1:5000 diluted goat anti- mouse- HRP antibody (Invitrogen) was added and incubated at \(37^{\circ}C\) for 1h. The final steps were the same as above.
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 575, 290, 593]]<|/det|>
+## B cells sorting
+
+<|ref|>text<|/ref|><|det|>[[144, 609, 852, 891]]<|/det|>
+Cryopreserved 10 million PBMC were thawed into 1 ml preheated RPMI1640, centrifuged at \(300\times \mathrm{g}\) for 5 min, re- suspended in \(500\mu \mathrm{l}\) FACS buffer (PBS+2% FBS), and incubated with 200nM his- tagged antigen (gH/gL) for 45 min at \(4^{\circ}C\) . The PBMC were then washed two times with 1ml FACS buffer and resuspended in 100μl FACS buffer. The PBMC were stained with the following antibodies: CD3- PE- Cy5 (BD Biosciences) at a 1:25 dilution, CD14- PE- Cy5 (eBioscience) at a 1:50 dilution, CD16- PE- Cy5 (BD Biosciences) at a 1:25 dilution, CD235a- PE- Cy5 (BD Biosciences) at a 1:100 dilution,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 93, 852, 411]]<|/det|>
+CD19- APC- Cy7 (BD Biosciences) at a 1:100 dilution, CD20- PE- Cy7 (BD Biosciences) at a 1:200 dilution, IgG- FITC (BD Biosciences) at a 1:25 dilution, and anti- his- PE (BioLegend) at a 1:20 dilution for 30 min at 4°C. The PBMC were washed three times with 1ml FACS buffer and resuspended in 500μl FACS buffer, then subjected to FACS on a BD FACS Aria II (BD Biosciences). Antigen- positive B cells (CD3-, CD14-, CD16-, CD235a-, CD19+, CD20+, IgG+, PE+) were sorted individually into 96- well PCR vital- plates containing 20μl first strand buffer (5μl first strand buffer, 0.5μl of RNase inhibitor (Invitrogen), 1.25μl of 100μM DTT, 0.06μl of IGEPAL (Sigma).
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 464, 468, 483]]<|/det|>
+## VH/VL recovery from sorted cells
+
+<|ref|>text<|/ref|><|det|>[[144, 499, 852, 892]]<|/det|>
+Wells containing sorted cells were mixed with 6μl of reverse transcription (RT) buffer containing 1.5μl mixed primers specific for human IgG, IgM, IgD, IgA1, IgA2, K and \(\lambda\) constant gene regions, 1.5μl of 25 mM dNTP mix (Invitrogen), and 0.25μl of superscript III reverse transcriptase (Invitrogen). The RT temperature program included 42°C for 10 min, 25°C for 10 min, 60°C for 50 min, and 94°C for 5 min, followed by a hold at 4°C. The VH, VK and Vλ genes were amplified from 5μl of cDNA separately using nested PCR (HotStarTaq DNA Polymerase, QIAGEN). The PCR products were purified and subjected to Sanger sequencing. Then, the VH, VK and Vλ variable genes were assembled into functional linear Ig gene expression cassettes by overlap- extension PCR. The function of the expressed antibodies was determined using ELISA
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[147, 95, 245, 111]]<|/det|>
+screening.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 168, 312, 186]]<|/det|>
+## Virus production
+
+<|ref|>text<|/ref|><|det|>[[145, 201, 852, 746]]<|/det|>
+Akata cells carrying EBV, in which the thymidine kinase gene was interrupted with a double cassette expressing GFP and a neomycin resistance gene, were resuspended in FBS- free RPMI 1640 medium at a concentration of \(2 - 3 \times 10^{6}\) cells per ml, followed by induction with \(0.75\%\) (v/v) of goat anti- human immunoglobulin G serum (Shuangliu Zhenglong Biochem Lab) for 6h at \(37^{\circ}\mathrm{C}\) . After culture in fresh RPMI1640 medium supplemented with \(5\%\) FBS for 3 days, virus from the supernatant was collected under sterile conditions, passed through two Millipore filters (0.8 and \(0.45\mu \mathrm{m}\) ), concentrated 100- fold by high- speed centrifugation at 50,000g, and then resuspended in fresh FBS- free RPMI1640. The virus was stored at \(80^{\circ}\mathrm{C}\) and thawed immediately before infection. To assess the virus titer, 10- fold dilutions of EBV were used to inoculate \(2 \times 10^{5}\) PBMC per well in 24- well plates with \(2\mu \mathrm{g / ml}\) cyclosporin A (CsA) (Sigma). The cultures were fed weekly by replacing half of the medium with fresh medium containing CsA. After 6 weeks, the \(\mathrm{TD}_{50}\) was determined based on the number of proliferating lymphocytes in the wells (63).
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 799, 347, 817]]<|/det|>
+## Neutralization assay
+
+<|ref|>text<|/ref|><|det|>[[145, 833, 850, 890]]<|/det|>
+Plasma samples from study individuals or recombinant antibodies were incubated with GFP- expressing EBV at serial dilutions for 3h at \(4^{\circ}\mathrm{C}\) . Then the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 93, 852, 372]]<|/det|>
+mixtures were added to Raji B cells or HNE1 epithelial cells and incubated for 3h at \(37^{\circ}C\) . Then the unbound virus was removed by washing with PBS twice. Infected cells were cultured in fresh medium for 48h, followed by detection and analysis of GFP- positive cells using a flow cytometer and FlowJo 10 software (FlowJo, USA). The neutralization rate of each sample was defined as: \((\% \mathrm{GFP + }\) cells in the positive control well containing virus alone - \(\% \mathrm{GFP + }\) cells in the plasma or antibody containing well)/ \(\% \mathrm{GFP + }\) cells in the positive control well \(\times 100\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 427, 468, 446]]<|/det|>
+## EBV infection in humanized mice
+
+<|ref|>text<|/ref|><|det|>[[144, 462, 852, 742]]<|/det|>
+At 8 weeks post CD34+ stem cells transfer, 0.4 mg of experimental or control antibodies were i.p. injected per humanized mouse. After 24 h, the mice received a dose of Akata EBV equivalent to 1,000 \(\mathrm{TD}_{50}\) via i.v. injection. In the following period, the mice received a dose of 0.4mg antibody weekly. The blood collection and recording of body weight and health status were also done every week. The mice were euthanized 6 weeks post EBV infection or earlier if they became clinically ill (e.g. body weight loss of approximately \(20\%\) ).
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 797, 565, 817]]<|/det|>
+## Detection of EBV DNA in blood and tissues
+
+<|ref|>text<|/ref|><|det|>[[144, 833, 850, 890]]<|/det|>
+DNA was extracted from the peripheral blood (100μl) or tissues of the mice using commercial DNA extraction kits (Omega). The EBV genome copy
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 93, 852, 188]]<|/det|>
+number was determined by real- time PCR (Roche Light Cycler 480) using the TaqMan BamHI probes (40) as described previously. The copy numbers of EBV were quantified using a standard EBV genome (BDS biotech) as control.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 242, 566, 262]]<|/det|>
+## H&E staining, IHC, and in situ hybridization
+
+<|ref|>text<|/ref|><|det|>[[144, 278, 852, 521]]<|/det|>
+Tissues were fixed in \(10\%\) formalin and embedded in paraffin. Consecutive sections were used for staining with H&E. Immunostaining of human T cells and B cells was performed using hCD3 antibody (VENTANA) and hCD20 antibody (VENTANA) at 1:200 dilution. EBERs were stained by in situ hybridization using the EBER detection kit (ZSGB- BIO), according to the manufacturer's instructions. Histological staining was evaluated by experienced pathologists.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 576, 780, 595]]<|/det|>
+## Detection of human immune cells in the blood of humanized mice
+
+<|ref|>text<|/ref|><|det|>[[144, 610, 852, 891]]<|/det|>
+Peripheral blood of mice was treated with 1ml red blood cell lysis buffer (BioLegend) at room temperature for 10min. Then the cells were centrifuged at \(300 \times g\) , washed twice with PBS, re- suspended in PBS, and stained with antibodies including anti- human CD45- PE (BD Biosciences), CD3- PerCP- Cy5.5 (BD Biosciences) and CD20- FITC (BD Biosciences) at 1:100 dilution for 30 min at \(4^{\circ}C\) . After washing with PBS, the percentage of CD3+ or CD20+ cells among the CD45+ cells was quantified using a flow cytometer.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[148, 130, 418, 149]]<|/det|>
+## Cell surface binding assays
+
+<|ref|>text<|/ref|><|det|>[[144, 163, 853, 750]]<|/det|>
+For the cell- surface binding assay, 1mg of gH/gL- biotin conjugated with SA- PE (gH/gL- PE) was diluted in 10ml of PBS into individual wells of a 96 well plate. An equimolar amount of gp42 was added to select wells containing gH/gL- PE. 5mg/ml of monoclonal antibodies, including 1D8, AMMO1, or 2G4, were added to select wells containing gH/gL with or without gp42 and incubated for 1h at \(37^{\circ}C\) . At the same time, adherent HK1 cells were trypsinized (NCM Biotech), washed with RMPI 1640 and then allowed to recover at \(37^{\circ}C\) in a humidified atmosphere comprising \(5\% \mathrm{CO}_2\) for 1h with gentle agitation twice during the period. Recovered HK1 and Raji cells were pelleted by centrifugation at \(300\times\) g for 5min and then resuspended at a density of \(2\times 10^{6}\) cells/ml in ice- cold \(0.5\%\) bovine serum albumin (BSA) in PBS. Then, \(100\mu \mathrm{l}\) of the HK1 or Raji cells suspension were added to wells containing SA- PE, gH/gL- PE with or without gp42 and antibodies, and incubated on ice for 1h. The cells were pelleted by centrifugation at \(300\times \mathrm{g}\) for 5min, washed with 1 ml of ice cold \(0.5\%\) BSA in PBS, pelleted again and resuspended in \(10\%\) phosphate buffered formalin. The amount of PE staining was quantified using a flow cytometer.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 799, 373, 817]]<|/det|>
+## Virus-free fusion assay
+
+<|ref|>text<|/ref|><|det|>[[147, 833, 850, 890]]<|/det|>
+Effector CHO- K1 cells were transiently transfected with expression plasmid (pCAGGS- gH, pCAGGS- gL, pCAGGS- gB and pT7EMCLuc, which carries a
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 560]]<|/det|>
+luciferase- containing reporter plasmid under the control of the T7 promoter). Target cells (HEK- 293T) were transfected with expression plasmid pCAGT7 (expressing T7 DNA polymerase). After 24h, the effector cells were trypsinized and re- suspended at a density of \(1 \times 10^{6}\) cells/ml. Aliquots comprising 250μl/well of effector cell suspension was pre- incubated with 2μg 1D8, AMMO1 or 2G4 antibody at \(37^{\circ}C\) for 1h. Then the target cells were also trypsinized and re- suspended at a density of \(1 \times 10^{6}\) cells/ml. An aliquot comprising 250μl of the effector cell suspension was added to the effector cells with or without antibody. After 24h, the medium was aspirated and the cells were lysed in 100μl of luciferase agent (Dual- Glo Luciferase Assay System). Then, 75μl of cell lysate was transferred to a white- bottom assay plate and luciferase activity was read on a GloMax- 96 Microplate Luminometer (Promega).
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 612, 349, 631]]<|/det|>
+## Cell surface staining
+
+<|ref|>text<|/ref|><|det|>[[144, 647, 853, 891]]<|/det|>
+Following 24h after expression plasmid transfection, the effector CHO- K1 cells were trypsinized and re- suspended at a density of \(1 \times 10^{6}\) cells/ml. The expression level of gH/gL was detected using the indicated antibody. AMMO1 and 1D8 were used for gH/gL staining and 2G4 as a control. Then, 10μg/ml of antibody was added to the cell suspension and incubated at \(4^{\circ}C\) for 1h. The cells were washed twice with PBS and stained with human IgG- PerCP- Cy5.5 (PC5.5) (BioLegend) at a 1:100 dilution. After washing with PBS, the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 93, 850, 150]]<|/det|>
+percentage of PC5.5+ cells was quantified using a flow cytometer (CytoFLEX, BECKMAN).
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 205, 622, 224]]<|/det|>
+## Crystallization of the 1D8 Fab and data collection
+
+<|ref|>text<|/ref|><|det|>[[144, 240, 852, 707]]<|/det|>
+To purify the gH/gL- 1D8 Fab complex, 1D8 Fab was incubated with gH/gL for 1 h on ice in HBS buffer, and the mixture was then subjected to gel filtration chromatography. Fractions containing the complex were pooled and concentrated to 10 mg/ml. Crystals were successfully grown at \(18^{\circ}C\) in sitting drops, over wells containing 200 mM sodium citrate, 100 mM HEPES sodium salt, pH 7.5, 15% w/v MPD. The drops were made by mixing 200 nl gH/gL- 1D8 Fab complex in HBS buffer with 200 nl well solution. Crystals were harvested, soaked briefly in 200 mM sodium citrate, 100 mM HEPES sodium salt, pH 7.5, 15% w/v MPD, 20% glycerol, and flash- frozen in liquid nitrogen. Diffraction data were collected at the BL17U beam line of the Shanghai Synchrotron Research Facility (SSRF). Diffraction data were processed with HKL2000 and the crystal diffracted to \(4.2\mathrm{\AA}\) . The data processing statistics are listed in Supplementary Table 3.
+
+<|ref|>sub_title<|/ref|><|det|>[[147, 761, 475, 780]]<|/det|>
+## Structure solution and refinement
+
+<|ref|>text<|/ref|><|det|>[[147, 797, 850, 891]]<|/det|>
+The structure was determined via the molecular replacement method using PHASER in CCP4 suite. The search models were gH/gL (PDB code 5T1D) and the antibody with the highest sequence identity with 1D8. Density map
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 93, 852, 335]]<|/det|>
+improvement by atoms update and refinement was performed with ARP/wARP29. Subsequent model building and refinement were performed using COOT and PHENIX, respectively. Final Ramachandran statistics indicated that \(91.48\%\) residues were in favored conformations, \(7.06\%\) allowed and \(1.46\%\) outliers for the final structure. The structural refinement statistics are listed in Supplementary Table 3. All structural figures were generated with PyMol (DeLano, 2002).
+
+<|ref|>sub_title<|/ref|><|det|>[[148, 391, 333, 409]]<|/det|>
+## Statistical analysis
+
+<|ref|>text<|/ref|><|det|>[[144, 427, 852, 632]]<|/det|>
+Unless noted otherwise, a two- tailed, unpaired \(t\) - test was used to assess statistical significance. Statistical calculations were performed in GraphPad Prism 8. The number of replicates and a description of the statistical method are provided in the corresponding figure legends. Differences with P values of less than 0.05 were considered to be statistically significant. \(*P < 0.05\) , \(**P < 0.01\) , \(***P < 0.001\) , ns=not significant.
+
+<|ref|>sub_title<|/ref|><|det|>[[149, 678, 412, 695]]<|/det|>
+## REFERENCES AND NOTES
+
+<|ref|>text<|/ref|><|det|>[[144, 698, 852, 899]]<|/det|>
+1. G. de-The et al., Sero-epidemiology of the Epstein-Barr virus: preliminary analysis of an international study - a review. IARC Sci Publ, 3-16 (1975).
+2. L. S. Young, L. F. Yap, P. G. Murray, Epstein-Barr virus: more than 50 years old and still providing surprises. Nat Rev Cancer 16, 789-802 (2016).
+3. J. I. Cohen, A. S. Fauci, H. Varmus, G. J. Nabel, Epstein-Barr virus: an important vaccine target for cancer prevention. Sci Transl Med 3, 107fs107 (2011).
+4. L. S. Young, C. W. Dawson, Epstein-Barr virus and nasopharyngeal carcinoma. Chin J Cancer 33, 581-590 (2014).
+5. S. E. Henrickson, To EBV or not to EBV: Rational vaccine design for a common infection. Sci Immunol 3, (2018).
+6. D. G. van Zyl, J. Mautner, H. J. Delecluse, Progress in EBV Vaccines. Front Oncol 9, 104 (2019).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 90, 854, 900]]<|/det|>
+737 7. J. I. Cohen, Epstein- barr virus vaccines. Clin Transl Immunology 4, e32 (2015).738 8. J. I. Cohen, E. S. Mocarski, N. Raab- Traub, L. Corey, G. J. Nabel, The need and challenges for development of an Epstein- Barr virus vaccine. Vaccine 31 Suppl 2, B194- 196 (2013).739 9. W. Bu et al., Immunization with Components of the Viral Fusion Apparatus Elicits Antibodies That Neutralize Epstein- Barr Virus in B Cells and Epithelial Cells. Immunity 50, 1305- 1316 e1306 (2019).743 10. A. E. Coghill et al., High Levels of Antibody that Neutralize B- cell Infection of Epstein- Barr Virus and that Bind EBV gp350 Are Associated with a Lower Risk of Nasopharyngeal Carcinoma. Clin Cancer Res 22, 3451- 3457 (2016).744 11. A. E. Coghill et al., Evaluation of Total and IgA- Specific Antibody Targeting Epstein- Barr Virus Glycoprotein 350 and Nasopharyngeal Carcinoma Risk. J Infect Dis 218, 886- 891 (2018).745 12. W. Bu et al., Kinetics of Epstein- Barr Virus (EBV) Neutralizing and Virus- Specific Antibodies after Primary Infection with EBV. Clin Vaccine Immunol 23, 363- 369 (2016).746 13. J. Sashihara, P. D. Burbelo, B. Savoldo, T. C. Pierson, J. I. Cohen, Human antibody titers to Epstein- Barr Virus (EBV) gp350 correlate with neutralization of infectivity better than antibody titers to EBV gp42 using a rapid flow cytometry- based EBV neutralization assay. Virology 391, 249- 256 (2009).747 14. D. Sok, D. R. Burton, Recent progress in broadly neutralizing antibodies to HIV. Nat Immunol 19, 1179- 1188 (2018).748 15. E. O. Saphire, S. L. Schendel, B. M. Gunn, J. C. Milligan, G. Alter, Antibody- mediated protection against Ebola virus. Nat Immunol 19, 1169- 1178 (2018).749 16. F. Yu et al., Receptor- binding domain- specific human neutralizing monoclonal antibodies against SARS- CoV and SARS- CoV- 2. Signal Transduct Target Ther 5, 212 (2020).750 17. L. M. Walker, D. R. Burton, Passive immunotherapy of viral infections: 'super- antibodies' enter the fray. Nat Rev Immunol 18, 297- 308 (2018).751 18. A. Lanzavecchia, A. Fruhwirth, L. Perez, D. Corti, Antibody- guided vaccine design: identification of protective epitopes. Curr Opin Immunol 41, 62- 67 (2016).752 19. L. M. Hutt- Fletcher, EBV glycoproteins: where are we now? Future Virol 10, 1155- 1162 (2015).753 20. B. S. Mohl, J. Chen, R. Longnecker, Gammaherpesvirus entry and fusion: A tale how two human pathogenic viruses enter their host cells. Adv Virus Res 104, 313- 343 (2019).754 21. T. Haque et al., A mouse monoclonal antibody against Epstein- Barr virus envelope glycoprotein 350 prevents infection both in vitro and in vivo. J Infect Dis 194, 584- 587 (2006).755 22. J. Snijder et al., An Antibody Targeting the Fusion Machinery Neutralizes Dual- Tropic Infection and Defines a Site of Vulnerability on Epstein- Barr Virus. Immunity 48, 799- 811 e799 (2018).756 23. X. Cui et al., Rabbits immunized with Epstein- Barr virus gH/gl or gB recombinant proteins elicit higher serum virus neutralizing activity than gp350. Vaccine 34, 4050- 4055 (2016).757 24. S. A. Connolly, J. O. Jackson, T. S. Jardetzky, R. Longnecker, Fusing structure and function: a structural view of the herpesvirus entry machinery. Nat Rev Microbiol 9, 369- 381 (2011).758 25. S. Singh et al., Neutralizing Antibodies Protect against Oral Transmission of Lymphocryptovirus. Cell Rep Med 1, (2020).759 26. B. S. Mohl, J. Chen, K. Sathiyamoorthy, T. S. Jardetzky, R. Longnecker, Structural and Mechanistic Insights into the Tropism of Epstein- Barr Virus. Mol Cells 39, 286- 291 (2016).760 27. S. A. Connolly, T. S. Jardetzky, R. Longnecker, The structural basis of herpesvirus entry. Nat Rev Microbiol, (2020).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[90, 87, 855, 900]]<|/det|>
+781 28. L. S. Chesnokova, L. M. Hutt-Fletcher, Epstein-Barr virus infection mechanisms. Chin J Cancer 782 33, 545-548 (2014). 783 29. H. Matsuura, A. N. Kirschner, R. Longnecker, T. S. Jardetzky, Crystal structure of the Epstein-Barr virus (EBV) glycoprotein H/glycoprotein L (gH/gL) complex. Proc Natl Acad Sci U S 785 A 107, 22641-22646 (2010). 786 30. B. S. Mohl, K. Sathiyamoorthy, T. S. Jardetzky, R. Longnecker, The conserved disulfide bond within domain II of Epstein-Barr virus gH has divergent roles in membrane fusion with epithelial cells and B cells. J Virol 88, 13570-13579 (2014). 787 31. J. Chen, T. S. Jardetzky, R. Longnecker, The large groove found in the gH/gL structure is an important functional domain for Epstein-Barr virus fusion. J Virol 87, 3620-3627 (2013). 788 32. K. Sathiyamoorthy et al., Assembly and architecture of the EBV B cell entry triggering complex. PLoS Pathog 10, e1004309 (2014). 789 33. M. Kanekiyo et al., Rational Design of an Epstein-Barr Virus Vaccine Targeting the Receptor-Binding Site. Cell 162, 1090-1100 (2015). 790 34. K. A. Young, A. P. Herbert, P. N. Barlow, V. M. Holers, J. P. Hannan, Molecular basis of the interaction between complement receptor type 2 (CR2/CD21) and Epstein-Barr virus glycoprotein gp350. J Virol 82, 11217-11227 (2008). 791 35. G. Szakonyi et al., Structure of the Epstein-Barr virus major envelope glycoprotein. Nat Struct Mol Biol 13, 996-1001 (2006). 792 36. K. Sathiyamoorthy et al., Structural basis for Epstein-Barr virus host cell tropism mediated by gp42 and gHgL entry glycoproteins. Nat Commun 7, 13557 (2016). 793 37. M. M. Mullen, K. M. Haan, R. Longnecker, T. S. Jardetzky, Structure of the Epstein-Barr virus gp42 protein bound to the MHC class II receptor HLA-DR1. Mol Cell 9, 375-385 (2002). 794 38. A. N. Kirschner, J. Omerovic, B. Popov, R. Longnecker, T. S. Jardetzky, Soluble Epstein-Barr virus glycoproteins gH, gL, and gp42 form a 1:1:1 stable complex that acts like soluble gp42 in B-cell fusion but not in epithelial cell fusion. J Virol 80, 9444-9454 (2006). 795 39. J. Chen et al., Ephrin receptor A2 is a functional entry receptor for Epstein-Barr virus. Nat Microbiol 3, 172-180 (2018). 796 40. H. Zhang et al., Ephrin receptor A2 is an epithelial cell receptor for Epstein-Barr virus entry. Nat Microbiol 3, 1-8 (2018). 797 41. H. B. Wang et al., Neuropilin 1 is an entry factor that promotes EBV infection of nasopharyngeal epithelial cells. Nat Commun 6, 6240 (2015). 798 42. J. Chen, R. Longnecker, Epithelial cell infection by Epstein-Barr virus. FEMS Microbiol Rev 43, 674-683 (2019). 799 43. K. Sathiyamoorthy et al., Inhibition of EBV-mediated membrane fusion by anti-gHgL antibodies. Proc Natl Acad Sci U S A 114, E8703-E8710 (2017). 800 44. Z. Liu et al., Two Epstein-Barr virus-related serologic antibody tests in nasopharyngeal carcinoma screening: results from the initial phase of a cluster randomized controlled trial in Southern China. Am J Epidemiol 177, 242-250 (2013). 801 45. Y. Liu et al., Establishment of VCA and EBNA1 IgA-based combination by enzyme-linked immunosorbent assay as preferred screening method for nasopharyngeal carcinoma: a two-stage design with a preliminary performance study and a mass screening in southern China. Int J Cancer 131, 406-416 (2012). 802 46. S. Fujiwara, K. Imadome, M. Takei, Modeling EBV infection and pathogenesis in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[100, 88, 854, 810]]<|/det|>
+new- generation humanized mice. Exp Mol Med 47, e135 (2015).E. K. Lee et al., Effects of lymphocyte profile on development of EBV- induced lymphoma subtypes in humanized mice. Proc Natl Acad Sci U S A 112, 13081- 13086 (2015).C. Munz, Humanized mouse models for Epstein Barr virus infection. Curr Opin Virol 25, 113- 118 (2017).E. A. Caves et al., Air- Liquid Interface Method To Study Epstein- Barr Virus Pathogenesis in Nasopharyngeal Epithelial Cells. mSphere 3, (2018).R. Lin et al., Development of a robust, higher throughput green fluorescent protein (GFP)- based Epstein- Barr Virus (EBV) micro- neutralization assay. J Virol Methods 247, 15- 21 (2017).D. R. Burton, L. Hangartner, Broadly Neutralizing Antibodies to HIV and Their Role in Vaccine Design. Annu Rev Immunol 34, 635- 659 (2016).L. L. Lu, T. J. Suscovich, S. M. Fortune, G. Alter, Beyond binding: antibody effector functions in infectious diseases. Nat Rev Immunol 18, 46- 61 (2018).G. Zhou, Q. Zhao, Perspectives on therapeutic neutralizing antibodies against the Novel Coronavirus SARS- CoV- 2. Int J Biol Sci 16, 1718- 1723 (2020).O. A. Odumade, K. A. Hogquist, H. H. Balfour, Jr., Progress and problems in understanding and managing primary Epstein- Barr virus infections. Clin Microbiol Rev 24, 193- 209 (2011).B. S. Mohl, J. Chen, S. J. Park, T. S. Jardetzky, R. Longnecker, Epstein- Barr Virus Fusion with Epithelial Cells Triggered by gB Is Restricted by a gL Glycosylation Site. J Virol 91, (2017).J. Omerovic, L. Lev, R. Longnecker, The amino terminus of Epstein- Barr virus glycoprotein gH is important for fusion with epithelial and B cells. J Virol 79, 12408- 12415 (2005).F. Zhan et al., [Primary study of differentially expressed cDNA sequences in cell line HNE1 of human nasopharyngeal carcinoma by cDNA representational difference analysis]. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 15, 341- 344 (1998).D. P. Huang et al., Establishment of a cell line (NPC/HK1) from a differentiated squamous carcinoma of the nasopharynx. Int J Cancer 26, 127- 132 (1980).S. J. Molesworth, C. M. Lake, C. M. Borza, S. M. Turk, L. M. Hutt- Fletcher, Epstein- Barr virus gH is essential for penetration of B cells but also plays a role in attachment of virus to epithelial cells. J Virol 74, 6324- 6332 (2000).S. Guo et al., Oncological and genetic factors impacting PDX model construction with NSG mice in pancreatic cancer. FASEB J 33, 873- 884 (2019).J. Chen, S. Schaller, T. S. Jardetzky, R. Longnecker, EBV gH/gL and KSHV gH/gL bind to different sites on EphA2 to trigger fusion. J Virol, (2020).H. X. Liao et al., High- throughput isolation of immunoglobulin genes from single human B cells and expression as monoclonal antibodies. J Virol Methods 158, 171- 179 (2009).M. Yajima et al., A new humanized mouse model of Epstein- Barr virus infection that reproduces persistent infection, lymphoproliferative disorder, and cell- mediated and humoral immune responses. J Infect Dis 198, 673- 682 (2008).
+
+<|ref|>text<|/ref|><|det|>[[92, 852, 850, 911]]<|/det|>
+Acknowledgements: We thank Chang Song and Cui Qiao from Beijing IDMOCompany for help with the animal experiment. The plasmids pCAGGS- T7,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 670]]<|/det|>
+pCAGGS- gH, pCAGGS- gL, pCAGGS- gB and pT7EMCLuc were kindly provided by Professor Richard Longnecker. Funding: This work was supported by the following grant supports: the National Key Research and Development Program of China (2017YFA0505600, 2016YFA0502100, 2018ZX10731101- 002, 2017ZX10201101), the National Natural Science Foundation of China (81530065, 81520108022, 81830090 and 81621004), Guangdong Province key research and development program (2019B020226002) and Beijing Municipal Science & Technology Commission (Z181100001918043, 171100000517). Author contributions: L.Z., M.Z., and X.W. conceptualized the study. Q.Z., S.S., J.Y., Y.Z., and C.S. performed experiments and analyzed data. Q.Z., S.S., J.Y., L.Z., M.Z., and X.W. wrote the manuscript, and all authors contributed to editing and figure preparation. Funding was secured by L.Z., M.Z., and X.W. Competing interests: The authors declare no potential conflicts of interest. Data availability: The atomic model of 1D8- gH/gL (PDB ID: 7D5Z) has been deposited in the Protein Data Bank.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[147, 93, 388, 112]]<|/det|>
+## MAIN FIGURE LEGENDS
+
+<|ref|>text<|/ref|><|det|>[[145, 130, 852, 410]]<|/det|>
+Fig. 1. Isolation of gH/gL- specific monoclonal antibodies using single B cell sorting and cloning. (A) FACS- based sorting strategy for gH/gL- specific B cells. (B) Binding activities of 1D8 and 2A6, the positive control AMMO1, and the negative control 2G4 to EBV gH/gL measured by ELISA. The data are presented as means \(\pm\) SEM. (C) Neutralizing activities of 1D8 and 2A6, the positive control AMMO1, and the negative control 2G4 against EBV infection of Raji B cell lines and (D) HNE1 epithelia cell line. The data shown is means \(\pm\) SEM. SSC- A, side- scatter area; FSC- A, forward- scatter area.
+
+<|ref|>text<|/ref|><|det|>[[145, 463, 852, 892]]<|/det|>
+Fig. 2. Protective efficacy of 1D8 against lethal EBV challenge in humanized mice. (A) Timeline for engrafting CD34+ human hematopoietic stem cells (HSC), antibody administration, viral challenge, and monitoring for various biological and clinical outcomes. Four hundred micrograms of 1D8, positive control AMMO1, negative control 2G4, or PBS negative control were administered to the humanized mice via intraperitoneal injection either 24h prior to or weekly for 5 weeks after intravenous challenge with Akata EBV. (B) EBV DNA in the peripheral blood, (C) body weight, and (D) survival were monitored weekly. The percent changes in (E) hCD45+, (F) hCD20+, or (G) hCD3+ cells over the experiment period. On week 6 post infection, (H) virus titers in spleen, (I) liver, (J) kidney were analyzed. All data are presented as mean \(\pm\) SEM. \(^{*}p < 0.05\) ; \(^{**}p < 0.01\) ; \(^{***}p < 0.001\) ; ns, no significant.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 130, 851, 263]]<|/det|>
+Fig. 3. 1D8 reduces viral replication and tissue damages in humanized mice. Representative of macroscopic spleens and splenic sections stained for hematoxylin and eosin (H&E), EBV encoded RNA (EBER), human CD20 (hCD20), and human CD3 (hCD3) at necropsy. The scale bars are indicated.
+
+<|ref|>text<|/ref|><|det|>[[144, 315, 852, 744]]<|/det|>
+Fig. 4. 1D8 targets an unique epitope on \(\mathsf{gH / gL}\) . (A) Structure overview in a cartoon representation with gL in cyan, gH D- I in blue, D- II in wheat, D- III in green, D- IV in yellow, and 1D8 Fab in purple. The map is contoured at 1.2 RMS to show the density. (B) Zoomed- in view of the interaction between 1D8 and D- I and D- II. The key binding residue N310 of gH was indicated by a red star. (C) Cartoon representation of Fab 1D8 and other previously published Fabs AMMO1, CL40, and E1D1 bound to a single gH/gL molecule. The color scheme for gH/gL is as in (A) whereas 1D8 Fab in purple, AMMO1 Fab in light blue, CL40 Fab in pink, and E1D1 Fab in dark green. (D) Surface mapping of the four Fab epitopes on gH/gL with the same color in (C). Areas in black indicate the region where structural change was found upon binding to AMMO1 or CL40.
+
+<|ref|>text<|/ref|><|det|>[[145, 797, 851, 891]]<|/det|>
+Fig. 5. 1D8 interferes with cell fusion and binding. Quality control of gH/gL expression on the surface of CHO- K1 cells by staining with 1D8 (A), positive control AMMO1 (B), and negative control 2G4 (C) before proceeded to the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 92, 852, 410]]<|/det|>
+fusion experiment shown in (D). (D) Marked reduction in cell- cell fusion in the presence of 1D8, the positive control AMMMO1, but not the negative control 2G4. Marked reduction in gH/gL binding to Raji B cell (E) and HK1 epithelial cell (F) in the presence of 1D8, the positive control AMMO1, but not the negative control 2G4. Binding of EphA1- Fc to gH/gL was reduced by 1D8 (G), but not by AMMO1 (H) or 2G4 (I) measured by Bio- layer interferometry (BLI). All data are presented as mean ± SEM. \(^{*}p < 0.05\) ; \(^{**}p < 0.01\) ; \(^{***}p < 0.001\) ; ns, no significant. SSC- A, side- scatter area; PC5.5, PerCP- Cy5.5; RLU, relative light unit; SA- PE, streptavidin- phycoerythrin; MFI, mean fluorescence intensity.
+
+<|ref|>text<|/ref|><|det|>[[144, 463, 852, 744]]<|/det|>
+Fig. 6. Possible mechanisms of 1D8- mediated neutralization. (A) For epithelia cells, 1D8 could interfere the interaction between gH/gL and EphA2 either by directly restricting access to the interface or by indirectly posing allosteric hindrance. It could also restrict the movement across the D- I/D- II groove of gH/gL that is required for gB interaction and triggering. (B) For B cells, 1D8 could also restrict the movement across the D- I/D- II groove of gH/gL that is required for downstream viral entry. 1D8 does not appear influence interaction between gp42 and its receptor HLA class II.
+
+<--- Page Split --->
+<|ref|>image_caption<|/ref|><|det|>[[147, 96, 207, 113]]<|/det|>
+Fig. 1
+
+<|ref|>image<|/ref|><|det|>[[157, 125, 792, 435]]<|/det|>
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[155, 137, 795, 602]]<|/det|>
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[160, 135, 828, 515]]<|/det|>
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[163, 131, 825, 515]]<|/det|>
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[155, 130, 833, 920]]<|/det|>
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[156, 140, 828, 680]]<|/det|>
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[175, 167, 800, 468]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[144, 483, 777, 502]]<|/det|>
+Fig. S1. Plasma binding and neutralizing activities from donor 27.
+
+<|ref|>text<|/ref|><|det|>[[144, 519, 852, 688]]<|/det|>
+(A) Plasma binding activities to gH/gL measured by ELISA. (B) Plasma neutralizing activities against EBV infection of Raji B cells and HNE1 epithelial cells. Binding activity of 1D8 (C) or AMMO1 (D) to gH/gL measured by surface plasmon resonance (SPR). All experiments were performed in duplicate, and the data shown are means with SEM.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[150, 90, 836, 290]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[145, 315, 848, 370]]<|/det|>
+Fig. S2. 1D8 reduces viral replication and tissue damages in liver and kidney of mice.
+
+<|ref|>text<|/ref|><|det|>[[145, 389, 850, 483]]<|/det|>
+Hepatic and renal sections stained for hematoxylin and eosin (H&E), human CD20 (hCD20), human CD3 (hCD3), and EBV encoded RNA (EBER) at necropsy. Scale bar of \(100\mu \mathrm{m}\) is shown.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[156, 92, 835, 264]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[145, 279, 850, 335]]<|/det|>
+Fig. S3. Binding of 1D8 to gH/gL mutants and its competition with other gH/gL antibodies.
+
+<|ref|>text<|/ref|><|det|>[[144, 352, 852, 560]]<|/det|>
+(A) 1D8 and (B) AMMO1 binding to various gH/gL mutants measured by ELISA. ELISA was performed in duplicate wells, and the data shown are means with SEM. Binding activity of 1D8 (C) and AMMO1 (D) to gH-N310A/gL mutant measured by surface plasmon resonance (SPR). (E) Competitive binding of 1D8 with AMMO1, CL40 or E1D1 to gH/gL measured by bio-layer interferometry (BLI).
+
+<--- Page Split --->
+<|ref|>table_caption<|/ref|><|det|>[[140, 87, 716, 101]]<|/det|>
+Table S1. Neutralization potency of monoclonal antibodies.
+
+<|ref|>table<|/ref|><|det|>[[135, 103, 858, 247]]<|/det|>
+
+| Mab | Epithelial cells (μg/ml) | B cells (μg/ml) |
| \(IC_{50}\) | \(IC_{90}\) | \(IC_{50}\) | \(IC_{90}\) |
| 1D8 | 0.123 | 0.187 | 0.238 | 0.442 |
| 2A6 | 0.745 | 2.270 | 1.320 | \(>50\) |
| AMMO1 | 0.127 | 0.305 | 0.318 | 1.148 |
| 2G4 | NA | NA | NA | NA |
+
+<|ref|>text<|/ref|><|det|>[[83, 260, 123, 270]]<|/det|>
+1077
+
+<|ref|>text<|/ref|><|det|>[[83, 297, 123, 307]]<|/det|>
+1078
+
+<|ref|>text<|/ref|><|det|>[[83, 334, 123, 344]]<|/det|>
+1079
+
+<|ref|>text<|/ref|><|det|>[[83, 371, 123, 381]]<|/det|>
+1080
+
+<|ref|>text<|/ref|><|det|>[[83, 408, 123, 418]]<|/det|>
+1081
+
+<|ref|>text<|/ref|><|det|>[[83, 445, 123, 455]]<|/det|>
+1082
+
+<|ref|>text<|/ref|><|det|>[[83, 483, 123, 493]]<|/det|>
+1083
+
+<|ref|>text<|/ref|><|det|>[[83, 520, 123, 530]]<|/det|>
+1084
+
+<|ref|>text<|/ref|><|det|>[[83, 557, 123, 567]]<|/det|>
+1085
+
+<|ref|>text<|/ref|><|det|>[[83, 594, 123, 604]]<|/det|>
+1086
+
+<|ref|>text<|/ref|><|det|>[[83, 631, 123, 641]]<|/det|>
+1087
+
+<|ref|>text<|/ref|><|det|>[[83, 668, 123, 678]]<|/det|>
+1088
+
+<|ref|>text<|/ref|><|det|>[[83, 705, 123, 715]]<|/det|>
+1089
+
+<|ref|>text<|/ref|><|det|>[[83, 742, 123, 752]]<|/det|>
+1090
+
+<|ref|>text<|/ref|><|det|>[[83, 779, 123, 789]]<|/det|>
+1091
+
+<|ref|>text<|/ref|><|det|>[[83, 816, 123, 826]]<|/det|>
+1092
+
+<|ref|>text<|/ref|><|det|>[[83, 853, 123, 863]]<|/det|>
+1093
+
+<|ref|>text<|/ref|><|det|>[[83, 890, 123, 900]]<|/det|>
+1094
+
+<--- Page Split --->
+<|ref|>table_caption<|/ref|><|det|>[[135, 95, 830, 112]]<|/det|>
+Table S2. Kinetic Analysis of Antibodies Binding to gH/gL Measured by
+
+<|ref|>table<|/ref|><|det|>[[135, 155, 858, 609]]<|/det|>
+| Ligand | Anylate | kon (1/Ms) ×105 | koff (1/s) ×10-4 | KD (nM) |
| 1D8 | gH/gL S97A | 1.33 | 1.36 | 1.02 |
| 1D8 | gH/gL L100A | 1.07 | 1.55 | 1.44 |
| 1D8 | gH V95A/gL | 1.30 | 2.31 | 1.77 |
| 1D8 | gH M100A/gL | 1.51 | 1.96 | 1.30 |
| 1D8 | gH Q101A/gL | 0.95 | 1.95 | 2.03 |
| 1D8 | gH D103A/gL | 0.72 | 0.69 | 0.95 |
| 1D8 | gH S105A/gL | 0.90 | 0.97 | 1.08 |
| 1D8 | gH K106A/gL | 1.26 | 1.09 | 0.86 |
| 1D8 | gH G110A/gL | 2.66 | 0.26 | 0.10 |
| 1D8 | gH V111A/gL | 1.11 | 1.48 | 1.34 |
| 1D8 | gH P125A/gL | 0.71 | 2.00 | 2.79 |
| 1D8 | gH T308A/gL | 1.04 | 1.01 | 0.97 |
| 1D8 | gH G309A/gL | 0.95 | 0.95 | 1.00 |
| 1D8 | gH N310A/gL | 1.75 | 55.20 | 31.60 |
| 1D8 | gH G311A/gL | 0.78 | 2.05 | 2.62 |
| 1D8 | gH/gL WT | 2.45 | 1.46 | 0.59 |
| AMMO1 | gH N310A/gL | 4.97 | 0.96 | 0.19 |
| AMMO1 | gH/gL WT | 5.77 | 0.85 | 0.14 |
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[140, 115, 860, 760]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[144, 87, 635, 103]]<|/det|>
+Table S3. Data collection and refinement statistics.
+
+ | EBV gH/gL-1D8 |
| Data collection | |
| Space group | P4,2,2 |
| Cell dimensions | |
| a, b, c (Å) | 212.865, 212.865, 598.128 |
| α, β, γ, (°) | 90, 90, 90 |
| Resolution (Å) | 50.03-4.201(4.351-4.201) * |
| Rsym or Rmerge | 0.131 (1.261) |
| I / sI | 8 (1.4) |
| Completeness (%) | 99.34 (98.99) |
| Redundancy | 8.1 (8.2) |
| Refinement | |
| Resolution (Å) | 50.03-4.201 |
| No. reflections | 100331 |
| Rwork / Rfree | 23.31/26.77 |
| No. atoms | |
| Protein | 36304 |
| B-factors | |
| Protein | 161.73 |
| R.m.s. deviations | |
| Bond lengths (Å) | 0.009 |
| Bond angles (°) | 1.98 |
| Ramachandran plot (%) | |
| Favored | 91.48% |
| Allowed | 7.06% |
| outlier | 1.46% |
+
+<|ref|>table_footnote<|/ref|><|det|>[[144, 757, 639, 794]]<|/det|>
+One crystal was used. \\*Values in parentheses are for highest-resolution shell.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 44, 144, 70]]<|/det|>
+## Figures
+
+<|ref|>image<|/ref|><|det|>[[65, 103, 933, 545]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 588, 115, 607]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[40, 629, 936, 764]]<|/det|>
+Isolation of gH/gL specific monoclonal antibodies using single B cell sorting and cloning A FACS based sorting strategy for gH/gL specific B cells. B Binding activities of 1D8 and 2A6, the positive control AMMO1, and the negative control 2G4 to EBV gH/gL measured by ELISA. The data are presented as means \(\pm\) SEM. C Neutralizing activities of 1 D8 and 2A6, the positive control AMMO1, and the negative control 2G4 against EBV infection of Raji B cell lines and D HNE1 epithelia cell line. The data shown is means \(\pm\) SEM. SSC A, side scatter area; FSC A, forward scatter area.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[70, 55, 872, 692]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 712, 118, 732]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[39, 752, 955, 959]]<|/det|>
+Protective effi cacy of 1D8 against lethal EBV challenge in humanized mice A Timeline for engrafting CD34+ human hematopoietic stem cells (HSC), antibody administration, viral challenge, and monitoring for various biological and clinical outcomes. Four hundred micrograms of 1D8, positive control AMMO1, negative control 2G4, or PBS negative control were administered to the humanized mice via intraperitoneal injection either 24h prior to or weekly for 5 weeks after intravenous challenge with Akata EBV. (B) EBV DNA in the peripheral blood, (C) body weight, and D) survival were monito red weekly. The percent changes in (E) hCD45+, F) hCD20+, or G) hCD3+ cells over the experiment period. On week 6 post infection, (H) virus titers in spleen, (I) liver, J) kidney were analyzed. All data are presented as mean \(\pm\) SEM. \(^{*}p< 0.05\) ; \(^{**}p< 0.01\) ; \(^{***}p< 0.001\) ; ns, no significant.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[70, 54, 921, 584]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 630, 118, 650]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[42, 671, 949, 738]]<|/det|>
+1D8 reduces viral replication and tissue damages in humanized mice Representative of macroscopic spleens and splenic sections stained for hematoxylin and eosin (H&E), EBV encoded RNA (EBER), human CD20 (and human CD3 (hCD3) at necropsy. The scale bars are indicated.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[58, 50, 930, 650]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 683, 117, 702]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[40, 723, 958, 905]]<|/det|>
+1D8 targets an unique epitope on gH/gL A Structure overview in a cartoon representation with gL in cyan, gH D I in blue, D II in wheat, D III in green, D IV in yellow, and 1D8 Fa b in purple. The map is contoured at 1.2 RMS to show the density. B Zoomed in view of the interaction between 1D8 and D I and D II. The key binding residue N310 of gH was indicated by a red star. C Cartoon representation of Fab 1D8 and other previously published Fabs AMMO1, CL40, and E1D1 bound to a single gH/gL molecule. The color scheme for gH/gL is as in (A) whereas 1D8 Fab in purple, AMMO1 Fab in light blue, CL40 Fab in pink, and E1D1 Fab in dark k green. D Surface mapping of the four Fab epitopes on gH/gL with the same color in C)). Areas in black indicate the region where structural change was found upon binding to AMMO1 or CL40.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[60, 49, 930, 725]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 755, 118, 773]]<|/det|>
+Figure 5
+
+<|ref|>text<|/ref|><|det|>[[42, 794, 951, 952]]<|/det|>
+1D8 interferes with cell fusion and binding Quality control of gH/gL expression on the surface of CHO K1 cells by staining with 1D8 (A), positive control AMMO1 (B), and negative control 2G4 (C) before proceeded to the fusion experiment shown in (D). (D) Marked reduction in cell cell-cell fusion in the presence of 1D8, the positive control AMMO1, but not the negative control 2G4. Marked reduction in gH/gL binding to Raji B cell (E) and HK1 epithelial cell (F) in the presence of 1D8, the positive control AM MO1, but not the negative control 2G4. Binding of EphA1 EphA1-Fc to gH/gL was reduced by 1D8 (G), but not by AMMO1 (H) or 2G4 (I) measured by Bio Bio-layer interferometry (BLI). All data are presented as
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[40, 45, 944, 110]]<|/det|>
+mean ± SEM. \*p < 0.05; **p < 0.01; ***p < 0.001; ns, no significant. SSC SSC-A, side side-scatter area; PC5.5, PerCP PerCP-Cy5.5; RLU, relative light unit; SA SA-PE, streptavidin streptavidin-phycoerythrin; MFI, mean fluorescence intensity.
+
+<|ref|>image<|/ref|><|det|>[[60, 118, 870, 830]]<|/det|>
+
+
+<|ref|>image_caption<|/ref|><|det|>[[42, 871, 120, 890]]<|/det|>
+Figure 6
+
+<|ref|>text<|/ref|><|det|>[[42, 914, 911, 956]]<|/det|>
+Possible mechanisms of 1D8 1D8-mediated neutralization neutralization. (A) For epithelia cells, 1D8 could interfere the interaction between gH/gL and EphA2 either by directly restricting access to the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[41, 44, 936, 134]]<|/det|>
+interface or by indirectly posing allosteric hindrance. It could also restrict the movement across the D D- I/D - II groove of gH/gL t hat is required for gB interaction and triggering. (B) For B cells, 1D8 could also restrict the movement across the D D- I/D - II groove of gH/gL that is required for downstream viral entry. 1D8 does not appear influence interaction between gp42 and its receptor r HLA class II.
+
+<--- Page Split --->
diff --git a/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/images_list.json b/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..5f6b2da4b6f113051a348098b19f3e47774dc3cf
--- /dev/null
+++ b/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/images_list.json
@@ -0,0 +1,70 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1. A proposed biosynthetic pathway of furochromones and genomic statistics in S. divaricata. a, The proposed biosynthetic pathway and catalytic enzymes. PT, prenyltransferase; PCS, pentaketide chromone synthase; CYP450, cytochrome P450 enzyme; OMT, O-methyltransferase; UGT, uridine diphosphate-dependent glycosyltransferase. 1, malonyl-CoA; 2, noreugentin; 3, puecinin; 4, visamminol; 5, 5-O-methylvisamminol; 6, 5-O-methylvisamminoside;",
+ "footnote": [],
+ "bbox": [
+ [
+ 95,
+ 336,
+ 904,
+ 777
+ ]
+ ],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2. Biosynthesis of the furochromone skeleton, demonstrating the functional characterization of SdPCS (a), SdPT (b), and SdPC (c). Shown are HPLC/UV chromatograms of enzyme catalysis reactions ( \\(\\lambda = 280 \\mathrm{nm}\\) ), together with (+)-ESI-MS and MS/MS spectra of the products. Control, reaction mixtures incubated with boiled enzymes or microsomes.",
+ "footnote": [],
+ "bbox": [
+ [
+ 85,
+ 95,
+ 910,
+ 578
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4. The dissected biosynthetic pathway of furochromes and their de novo biosynthesis in tobacco leaves. a, Genomic location of biosynthetic genes in S. divaricata. b–c, Catalytic functions of biosynthetic genes responsible for the formation (b) and modification (c) of furochrome skeleton. Extracted ion chromatograms (EICs) of biosynthetic products in LC/MS analysis are shown. STD, reference standards. EV, agrobacterium-mediated transient expression using vector without any biosynthetic genes.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 11
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Fig. 5. High expression of SdPCS2 promotes the accumulation of furochromones in the root of S. divaricata. a,",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 88,
+ 888,
+ 900
+ ]
+ ],
+ "page_idx": 13
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Fig. 6 The absence of functional \\(PC\\) leads to low furochrome content in most Apiaceae plants. a, Syntenic regions containing \\(SdPC\\) . The syntenic gene pairs are connected by grey lines. b, Phylogenetic relationship and gene structure of Apiaceae PCs. As05G02748 (AsDC) is the same as AS05g00644 in the initial annotation version. c, HPLC/UV chromatograms showing the in vitro enzymatic activity of potential Apiaceae PCs \\((\\lambda = 280 \\mathrm{nm})\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 103,
+ 88,
+ 900,
+ 679
+ ]
+ ],
+ "page_idx": 16
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf.mmd b/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..2add70963147f2a26db7defba37cfdaa48228b9f
--- /dev/null
+++ b/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf.mmd
@@ -0,0 +1,428 @@
+
+# Complete biosynthetic pathway of furochromones and its evolutionary mechanism in Apiaceae plants
+
+Min Ye
+
+yemin@bjmu.edu.cn
+
+Peking University https://orcid.org/0000- 0002- 9952- 2380
+
+Jianlin Zou
+
+Peking University https://orcid.org/0009- 0008- 4125- 429X
+
+Hongye Li
+
+Peking University
+
+Bao Nie
+
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+Zi- Long Wang
+
+Peking University https://orcid.org/0000- 0002- 7875- 0704
+
+Chunxue Zhao
+
+Peking University
+
+Yungang Tian
+
+Peking University
+
+Liqun Lin
+
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+Weizhe Xu
+
+Civil Aviation Medicine Center, Civil Aviation Administration of China
+
+Zhuangwei Hou
+
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+Wenkai Sun
+
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+Xiaoxu Han
+
+Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences
+
+Meng Zhang
+
+Peking University
+
+Hao- Tian Wang
+
+<--- Page Split --->
+
+Peking University
+
+Qingyan Li Civil Aviation Medicine Center, Civil Aviation Administration of China
+
+Li Wang Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences
+
+## Article
+
+Keywords:
+
+Posted Date: July 31st, 2024
+
+DOI: https://doi.org/10.21203/rs.3.rs- 4779533/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on April 1st, 2025. See the published version at https://doi.org/10.1038/s41467- 025- 58498- 8.
+
+<--- Page Split --->
+
+# Complete biosynthetic pathway of furochromones and its evolutionary mechanism in Apiaceae plants
+
+3
+
+Jian- lin Zou \(^{1, \#}\) , Hong- ye Li \(^{1, \#}\) , Bao Nie \(^{2, \#}\) , Zi- long Wang \(^{1}\) , Chun- xue Zhao \(^{1}\) , Yun- gang Tian \(^{1}\) , Li- qun Lin \(^{2}\) , Wei- zhe Xu \(^{3}\) , Zhuang- wei Hou \(^{2}\) , Wen- kai Sun \(^{2}\) , Xiao- xu Han \(^{2}\) , Meng Zhang \(^{1}\) , Hao- tian Wang \(^{1}\) , Qing- yan Li \(^{3}\) , Li Wang \(^{2, *}\) , Min Ye \(^{1, *}\)
+
+\(^{1}\) State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, 38 Xueyuan Road, Beijing 100191, China
+
+\(^{2}\) Shenzhen Branch, Guangdong Laboratory of Lingnan Modern Agriculture, Key Laboratory of Synthetic Biology, Ministry of Agriculture and Rural Affairs, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518120, China
+
+\(^{3}\) Civil Aviation Medicine Center, Civil Aviation Administration of China, A- 1 Gaojing, Beijing 100123, China
+
+14
+
+\(*\) Corresponding authors.
+
+Email address: wangli03@caas.cn (Li Wang); yemin@bjmu.edu.cn (Min Ye).
+
+<--- Page Split --->
+
+## Abstract
+
+Furochromones are bioactive and specific secondary metabolites of many Apiaceae plants. Their biosynthesis remains largely unexplored. In this work, we dissected the complete biosynthetic pathway of major furochromones in the medicinal plant Saposhnikovia divaricata by characterizing novel prenyltransferase, peucenin cyclase, methyltransferase, hydroxylase, and glycosyltransferases. De novo biosynthesis of prim- O- glucosylcimifugin and 5- O- methylvisamminoside was then realized in tobacco leaves. Through comparative genomic and transcriptomic analyses, we further found that proximal duplication and high expression of a pentaketide chromone synthase gene SdPCS, together with the presence of a lineage- specific peucenin cyclase gene SdPC, led to the predominant accumulation of furochromones in the roots of S. divaricata among surveyed Apiaceae plants. This study paves the way for metabolic engineering production of furochromones, and sheds light into evolutionary mechanism of furochromone biosynthesis among Apiaceae plants.
+
+<--- Page Split --->
+
+Furochromones are an important class of bioactive natural products. They demonstrate antiinflammatory1,2, hepatoprotective3, antinociceptive4, antiviral4,5, and anti- aging6 activities. While chromones are widely present in plants, furochromones have only been reported in a few families including Apiaceae, Ranunculaceae, and Leguminosae7. In Apiaceae, furochromones are the major bioactive compounds of Saposhnikovia divaricata8, Ammi visnaga9, and Cnidium monnieri10. Particularly, S. divaricata contains abundant prim- O- glucosylcimifugin (POG) and 5- O- methylvisamminoside (5- O- MVG), and their total contents could be above 0.24% of dry weight11. S. divaricata is a medicinal plant widely used in traditional medicines for the treatment of influenza and rheumatic arthritis.
+
+The structures of POG and 5- O- MVG feature in the substitution of an isoprenyl group at C- 6, which forms a fused dihydrofuran ring12,13 (Supplementary Fig. 1). The biosynthesis of simple chromones has been extensively studied. The chromone skeleton is generated by polyketide synthases, such as PECPS from Aquilaria sinensis and AaPCS from Aloe arborescens14,15. However, little is known about the biosynthesis of furochromones. In the early 1970s, researchers fed sodium [1- 14C] acetate to shoots of Ammi visnaga, and revealed that pucenin and visamminol were biosynthetic intermediates of furochromones16. For the biosynthesis of POG or 5- O- MVG, a prenyltransferase (PT) is expected to introduce an isoprenyl group to C- 6 of the chromone skeleton17. Very few enzymes have been reported to catalyze cyclization of an isoprenyl group to form a dihydrofuran ring. While CYP76F112 from Ficus carica, PpDC and PpOC from Peucedanum praeruptorum, NiDC and NiOC from Notopterigium incisum, as well as AsDC and AsOC from Angelica sinensis have been reported to catalyze similar reactions to produce furocoumarins18- 21, no enzymes have been testified to generate furochromones. On the other hand, glycosyl substitutions at hydroxyl groups linking to the quaternary C- 3' or the secondary C- 11 are rare for natural products, and these reactions are hypothesized to be catalyzed by uridine diphosphate-dependent glycosyltransferases (UGTs)22. Moreover, both POG and 5- O- MVG contain a methoxyl group at C- 5, and the methylation reaction was proposed to be catalyzed by an O- methyltransferase (OMT)23. Although a big family of OMTs have been reported from plants, few OMTs could catalyze methylation at the less active 5- OH. Limited examples include the isoflavone 5- O- methyltransferase from Lupinus luteus24 and CdFOMT5 from Citrus depressa25. For POG, the extra primary hydroxyl group is likely to be introduced by a cytochrome P450 (CYP450) enzyme26.
+
+<--- Page Split --->
+
+Based on the above analysis, we tentatively hypothesized the biosynthetic pathway of 5- O- MVG (6) and POG (9) (Fig. 1a). While the enzyme categories catalyzing each step seem obvious, the specific enzymes with expected functions are illusive.
+
+In this work, we dissected the biosynthetic pathway of POG and 5- O- MVG in S. divaricata. The functions of seven novel enzymes were characterized, including SdPCS, SdPT, SdPC, SdCH, SdOMT, SdUGT1, and SdUGT2. The complete biosynthesis of POG and 5- O- MVG was realized in tobacco leaves. Moreover, we unravelled the genetic mechanisms for high abundance of POG and 5- O- MVG in S. divaricata among Apiaceae plants.
+
+## Results and Discussion
+
+Proposed biosynthetic pathway of furochromones in Saposhnikovia divaricata and gene mining.
+
+First, we analyzed the chemical constituents of three organs of S. divaricata (leaf, petiole, and root, Fig. 1b–c) by liquid chromatography coupled with mass spectrometry (LC/MS). At least five furochromones (5–9) could be detected, which to some extent supported the validity of our proposed biosynthetic pathway. Subsequently, the contents of major compounds 5, 6, 8 and 9 in five tissue samples (roots at three developmental stages, petiole, and leaf) were quantitatively determined (Supplementary Figs. 2–6). The results indicated the roots contained more abundant furochromones, particularly the glycosides 6 and 9, than the petiole and leaf samples (Fig. 1d).
+
+In order to obtain a complete list of candidate genes involved in the biosynthesis of POG and 5- O- MVG, we sequenced, assembled, and annotated a chromosome- level genome of S. divaricata. Based on 28.65 Gb PacBio CCS long reads, we assembled the genome to 1.95 Gb (Supplementary Table 1), which was consistent with the estimate by flow cytometry (1.74 ± 0.07 Gb) (Supplementary Fig. 7) and the published assembly27. The assembly contig N50 was 2.22 Mb and the Benchmarking Universal Single- Copy Ortholog (BUSCO) score was 96.1%, indicating good genome continuity and completeness (Supplementary Tables 2–3). By Hi- C technology, 94.27% contigs were anchored onto eight chromosomes (Fig. 1e, Supplementary Fig. 8 and Table 4). Multiple- tissue RNA- Seq data (Supplementary Table 5), ab initio prediction, and homolog protein evidence were combined for
+
+<--- Page Split --->
+
+genome annotation, which allowed the identification of 38,704 high- confidence protein- coding genes and 65,734 transcripts. Finally, a total of 1,751,401 repetitive elements were annotated, accounting for \(76.78\%\) of the genome (Supplementary Table 6). With this high- quality genome and multiple- tissue RNA- Seq data, we quantified the gene expression abundance (fragments per kilobase of exon model per million mapped fragments, FPKM) of the five tissue samples mentioned above. Subsequently, we screened candidate genes according to genome annotation or local blastn search, and selected genes whose expression levels were correlated with the contents of downstream secondary metabolites in different organs for functional characterization.
+
+
+
+Fig. 1. A proposed biosynthetic pathway of furochromones and genomic statistics in S. divaricata. a, The proposed biosynthetic pathway and catalytic enzymes. PT, prenyltransferase; PCS, pentaketide chromone synthase; CYP450, cytochrome P450 enzyme; OMT, O-methyltransferase; UGT, uridine diphosphate-dependent glycosyltransferase. 1, malonyl-CoA; 2, noreugentin; 3, puecinin; 4, visamminol; 5, 5-O-methylvisamminol; 6, 5-O-methylvisamminoside;
+
+<--- Page Split --->
+
+7, norcimifugin; 8, cimifugin; 9, prim- O- glucosylcimifugin. b, Image of the sampled S. divaricata. c, Total ion currents (TICs) and extracted ion chromatograms (EICs) of the root, petiole, and leave of S. divaricata by LC/MS analysis. EIC mass range: \(m / z\) 291.11- 291.12 + 293.09- 293.10. d, Contents of 5, 6, 8 and 9 in different organs, calculated on the basis of dry weight. e, Genomic statistics of S. divaricata, showing eight chromosomes (Chr1- Chr8). i, pseudochromosomes; ii, gene density; iii, Gypsy LTR density; iv, Copia LRT density; v, Helitron density; vi, GC content.
+
+## Biosynthesis of the furochromone skeleton.
+
+The first step of the biosynthetic pathway is from malonyl- CoA (1) to noreugenin (2). The pentaketide chromone synthase AaPCS from Aloe arborescens is the only reported enzyme to catalyze this type of reaction15. Thus, we conducted a local blastn search using AaPCS as a query, and ten candidate genes with \(e\) values \(< 10^{- 21}\) were discovered. The expression levels (FPKMs) of one gene, SdPCS, was highly correlated with the furochromones contents with Pearson correlation coefficient (PCC) \(> 0.95\) (Supplementary Table 7). It was sub- cloned into the pET28a (+) vector for protein expression in E. coli BL21 (DE3) cells. The function was characterized by enzyme catalysis reactions with 1 as substrate. According to high- performance liquid chromatography (HPLC) and LC/MS analyses, SdPCS generated a new peak, which was identified as 2 by comparing with a reference standard. From the genome of S. divaricata, we further discovered SdPCS2 with the same function (Fig. 2a). The sequence similarity between SdPCS and SdPCS2 was 91.33% (Supplementary Fig. 9).
+
+To discover prenyltransferase (PT) converting 2 to peucenin (3), we obtained one candidate gene SdPT (PCC \(> 0.95\) , Supplementary Table 8) among the 20 annotated PT genes. SdPT was sub- cloned to pESC- Leu vector and expressed in yeast WAT11 cells28. When the yeast microsomes were incubated with 2, DMAPP and \(\mathrm{MgCl}_2\) , HPLC analysis showed a new product, which exhibited an \([\mathrm{M} + \mathrm{H}]^+\) ion at \(m / z\) 261.11 in LC/MS analysis. The MS/MS spectrum showed an abundant \([\mathrm{M} - 56 + \mathrm{H}]^+\) fragment at \(m / z\) 205.05, indicating a prenyl substitution at C- 6 or C- 829 (Fig. 2b). Then we purified 0.8 mg of the product from scaled- up enzymatic reactions. The \(^1\mathrm{H}\) - NMR spectrum showed two methylene signals at \(\delta_{\mathrm{H}}3.17\) (m, H- 1'), one olefinic signal at \(\delta_{\mathrm{H}}5.16\) (t, \(J = 6.0\mathrm{Hz}\) , H- 2'), and two methyl signals at \(\delta_{\mathrm{H}}1.61\) (H- 4') and 1.71 (H- 5'), indicating the presence of an isoprenyl group. The HMBC cross peaks from H- 1' to C- 5 ( \(\delta_{\mathrm{C}}158.1\) ), C- 6 ( \(\delta_{\mathrm{C}}111.1\) ) and C- 7 ( \(\delta_{\mathrm{C}}164.8\) ) indicated the isoprenyl group was located at C- 6
+
+<--- Page Split --->
+
+(Supplementary Figs. 10–13). Thus, the product was identified as peucenin (3) (Supplementary Table 9). SdPT represented the first prenyltransferase utilizing chromones as substrate. We also obtained SdPT2 which showed the same function with gene sequence similarity of \(85.79\%\) (Supplementary Fig. 14).
+
+Few enzymes are known to catalyze the oxidative cyclization of isoprenyl groups, except for several CYP450 enzymes involved in the biosynthesis of furocoumarins19- 21. Since these enzymes belong to the CYP736 family, we screened candidates from the same family in S. divaricata, and chose four potential genes whose expression levels were highly correlated with the furochromones contents (PCC >0.90, Supplementary Table 10). When SdPC was expressed in yeast WAT11 cells28, incubation of the yeast microsomes with 3 and NADPH yielded a new product. LC/MS analysis showed an [M+H]+ ion at m/z 277, which could fragment into m/z 259 and m/z 205. Its structure was proposed to be visamminol (4). As no reference standard was available, we prepared 4 through hydrolysis of visamminol 3'-O-glucoside catalyzed by β-glucosidase (Supplementary Fig. 15), and confirmed its structure by NMR analysis. The 1H-NMR spectrum showed two methyl signals at δH 1.13 (s, H-4') and δH 1.14 (s, H-5'), a tertiary proton signal at δH 4.71 (t, J = 8.6 Hz, H-2'), and a methylene signal at δH 3.02 (d, J = 8.6 Hz, H-1'), indicating the presence of a furan ring. The HMBC cross peaks from H-2' (δH 4.71) to C-1' (δC 26.6), C-7 (δC 166.4), and C-6 (δH 109.5) indicated the furan ring was conjugated with the benzene ring (Supplementary Figs. 16-19, Supplementary Table 9). HPLC and LC/MS analyses indicated the product had the same retention time and mass spectra with 4 (Fig. 2c). As the oxidative cyclization of isoprenyl phenolic compounds by chemical synthesis requires strong oxidizers like m-chloroperbenzoic acid30, SdPC represents an efficient enzyme catalyst for this reaction.
+
+<--- Page Split --->
+
+
+Fig. 2. Biosynthesis of the furochromone skeleton, demonstrating the functional characterization of SdPCS (a), SdPT (b), and SdPC (c). Shown are HPLC/UV chromatograms of enzyme catalysis reactions ( \(\lambda = 280 \mathrm{nm}\) ), together with (+)-ESI-MS and MS/MS spectra of the products. Control, reaction mixtures incubated with boiled enzymes or microsomes.
+
+## Post-modification steps for the biosynthesis of furochromones.
+
+C- 11 of compounds 7- 9 is hydroxylated, indicating the presence of a CYP450 enzyme. However, very few enzymes have been reported to catalyze a similar reaction, and no suitable templates are available for gene blast search. By analyzing the transcriptome data, we selected 12 candidate CYP genes, whose expression levels were highly correlated with the total contents of 8 and 9 ( \(\mathrm{PCC} > 0.95\) , Supplementary Table 11). These genes were expressed in yeast WAT11 cells, and the microsomes were incubated with NADPH (Tris- HCl buffer, 50 mM) for functional characterization. LC/MS analysis
+
+<--- Page Split --->
+
+indicated that SdCH could convert **4** and **5** (5- O- methylvisamminol) into **7** (norcimifugin) and **8** (cimifugin), respectively (Fig. 3a, Supplementary Fig. 20).
+
+Likewise, we discovered the 5- O- methyltransferase SdOMT which converted **4** and **7** into **5** and **8**, respectively (PCC > 0.90, Supplementary Table 12). Its function was characterized by enzymatic reaction and LC/MS analysis (Fig. 3b, Supplementary Fig. 21).
+
+Glycosylation is the final step in the biosynthetic pathway. A total of 8 UGT genes with FPKM>10 in the roots were chosen as candidate genes, and were cloned and expressed in _E. coli_ BL21(DE3) (Supplementary Table 13). The functions were characterized by enzymatic catalysis with UDP- Glc (UDPG) as sugar donor, and **5** or **8** as sugar acceptor. SdUGT1 could catalyze the glucosylation of 3'- OH of **5** (tertiary alcohol) and 11- OH of **8** (primary alcohol) to produce **6** (5- O- methylvisamminoside, 5- O- MVG) and **9** (prim- O- glucosylcimifugin, POG), respectively. The products could lose 162 Da in the MS/MS spectra, and their structures were identified by comparing with reference standards (Fig. 3c- d). Moreover, we discovered SdUGT2, which exhibited a high sequence similarity (54.93%) with SdUGT1 and showed the same enzymatic activities (Supplementary Fig. 22). We noticed that SdUGT1 and SdUGT2 only catalyzed 11- O-, but not 3'- O- glycosylation of **8**. Consistently, these two UGTs showed 2.8 or 31- fold higher catalytic efficiency (\(k_{\text{cat}}/K_{\text{m}}\) value) with **8** than with **5** as substrate (Fig. 3e, Supplementary Figs. 23- 24).
+
+To elucidate mechanisms for the preference towards 11- OH, we solved the crystal structure of SdUGT2 in complex with UDP through X- ray diffraction (PDB ID: 8ZNK, 1.88 Å) (Fig. 3f, Supplementary Fig. 25, Supplementary Table 14). The structure of SdUGT2 showed a typical GT- B fold with two Rossmann- like \(\beta /\alpha /\beta\) domains. The N- terminal domain (NTD, residues 1- 261 and 454- 480) and the C- terminal domain (CTD, residues 262- 453) are primarily responsible for sugar acceptor and sugar donor binding, respectively. Subsequently, we simulated the SdUGT2/UDPG model based on the structure of GgCGT/UDPG31. Two potential binding modes of **8** were obtained through molecular docking32. In both modes, His32 is close to the glycosylation sites (11- OH or 3'- OH) with a distance below 3.1 Å. Thus, the hydroxyl groups could be easily deprotonated to initiate the glycosylation reaction. Notably, the sugar moiety of sugar donor and hydroxy group of sugar acceptor
+
+<--- Page Split --->
+
+should form an obtuse angle for inverting GTs33. The docking results showed that the angle for 11- O-glycosylation was over \(90^{\circ}\), whereas the angle for 3'- O-glycosylation was less than \(90^{\circ}\). This result interpreted why SdUGT2 showed high preference towards 11- OH.
+
+
+
+
+<--- Page Split --->
+
+Fig. 3. Post-modification reactions for the biosynthesis of furochromones, demonstrating the functional characterization of SdCH (a), SdOMT (b), and SdUGT1/2 (c, d). Shown are HPLC/UV chromatograms of the enzyme catalysis reactions ( \(\lambda = 280 \mathrm{nm}\) ), together with (+)-ESI-MS and MS/MS spectra of the products. e, Kinetic parameters of SdUGT1 and SdUGT2. f, Crystal structure of SdUGT2. STD, reference standard. Control, reaction mixtures incubated with boiled enzymes or microsomes.
+
+Thus, by combining chemical analysis and genomic and transcriptomic data mining, we identified seven enzymes from S. divaricata catalyzing biosynthesis of the two major furochromones 6 and 9. These genes are located at different chromosomes. Specifically, SdCH and SdUGT1 are located at Chr1, SdPCS and SdPC at Chr2, SdPT at Chr3, SdOMT at Chr6, and SdUGT2 at Chr8 (Fig. 4a). The absence of a biosynthetic gene cluster suggests expressions of these genes are not co- regulated. To our knowledge, this is the first work to unravel the complete biosynthetic pathway of furochromones. The expression levels of identified genes, except for SdUGT1 and SdUGT2, are highly correlated with the distribution of major furochromones among different organs of S. divaricata. Both SdUGT1 and SdUGT2 showed strong preference for 11- OH, which is consistent with the lack of furochromone \(3^{\prime},11\) - di- \(O\) - glucosides in S. divaricata8.
+
+## De novo biosynthesis of Saposhnikovia furochromones in tobacco leaves.
+
+POG and 5- O- MVG are important bioactive compounds in S. divaricata, and their extraction and purification are time and labor- consuming. It is imperative to engineer the biosynthetic pathway in chassis organisms. In this work, we realized the de novo biosynthesis of furochromones in tobacco leaves. Transient expression of the seven genes in tobacco leaves revealed that all genes showed the expected catalytic activities, and the corresponding products were detected (Fig. 4b–c). When all the seven genes were infiltrated into tobacco leaves, 6 and 9 could be produced at a yield of \(11.54 \mu \mathrm{g / g}\) and \(4.21 \mu \mathrm{g / g}\) (dry weight), respectively.
+
+<--- Page Split --->
+
+
+Fig. 4. The dissected biosynthetic pathway of furochromes and their de novo biosynthesis in tobacco leaves. a, Genomic location of biosynthetic genes in S. divaricata. b–c, Catalytic functions of biosynthetic genes responsible for the formation (b) and modification (c) of furochrome skeleton. Extracted ion chromatograms (EICs) of biosynthetic products in LC/MS analysis are shown. STD, reference standards. EV, agrobacterium-mediated transient expression using vector without any biosynthetic genes.
+
+## The distribution of furochromones and their biosynthetic genes in Apiaceae plants.
+
+To gain a deep insight into the evolution of biosynthetic pathway of furochromones in Apiaceae,
+
+<--- Page Split --->
+
+we incorporated another seven Apiaceae species (Coriandrum sativum, Apium graveolens, Angelica sinensis, Ligusticum chuanxiong, Daucus carota, Bupleurum chinense, Centella asiatica) into metabolic, comparative genomic and transcriptomic analyses (Supplementary Tables 15- 18). These species represented different evolutionary lineages, including the subfamilies Mackinlayoideae and Apiodeae (including the tribe Bupleureae, Apieae, Sinodielsia Clade, Selineae). We first determined and compared the contents of four typical furochromones (5, 6, 8, and 9) among the eight species (Supplementary Figs. 26- 46). Unexpectedly, the furochromones did not show a stepwise accumulation along the phylogeny backbone but exhibited a drastic enrichment in S. divaricata. The contents of furochromones in the other species were generally low (Fig. 5a, Supplementary Table 19). This result implied substantial differences in furochromone biosynthesis between S. divaricata and the other Apiaceae plants.
+
+To investigate the evolutionary shift in furochromone biosynthesis from early diverged Apiaceae lineage to S. divaricata, we constructed a maximum likelihood (ML) phylogeny of Apiaceae based on 398 strict single- copy orthologous genes (Fig. 5a). It revealed that S. divaricata belonged to the latest diverged clade including C. sativum. Then, the conserved syntenic gene blocks containing each furochromone- biosynthetic gene was identified in each Apiaceae species (Supplementary Figs. 47- 57). The syntenic and homologous genes of most downstream tailoring genes, including OMT, CH and UGTs, were detected in all the Apiaceae species (Supplementary Figs. 47- 53). However, the syntenic genes of two skeleton- forming genes, SdPCS and SdPC were not detected in any other Apiaceae species (Fig. 5 and Fig. 6a). This clue motivated us to speculate that most Apiaceae species except S. divaricata may not contain any functional PCS and PC, thus leading to low furochromone content. To test this hypothesis, we focused on potential Apiaceae PCSs and PCs.
+
+## Proximal duplication of SdPCS promotes furochromone accumulation in S. divaricata.
+
+We retrieved all potential PKS III genes in S. divaricata and the other seven Apiaceae species and constructed an ML tree, on which a strongly supported (bootstrap support value (BS) = 100) clade containing SdPCS and 19 potential Apiaceae PCSs was identified (Fig. 5b). Most genes in this clade were in the same syntenic region, implying they shared the same ancestor (Supplementary Fig. 56). No PCS was detected in C. asiatica, one of the most basal species in Apiaceae, indicating that PCS may first emerge in the Apiodeae subfamily. Then we expressed and characterized all the 19 genes, and compared their functions by enzymatic assays (Fig. 2a, Supplementary Figs. 58- 63). Most of these enzymes showed similar catalytic abilities by converting 1 to 2 (Fig. 5b). However, the expression level of SdPCS in the root of S. divaricata was remarkably higher than the other Apiaceae homologous
+
+<--- Page Split --->
+
+We are aware that direct inter-species comparison of FPKM might lead to misinterpretation since the utilization of FPKM value is usually limited to intra-species level. Instead, we compared the FPKM ratio between SdPCS and other potential Apiaceous PCSs against 9,470- 27,214 pairs of orthologous genes as genomic background. It showed the \(\log_{2}\) (FPKM ratio) value of \(>95\%\) genome- wide ortholog pairs between S. divaricata and other Apiaceous species in root/rhizome is \(< 5.00\) , with a mean near zero (- 0.005). This result indicates that FPKM values of the investigated species are basically comparable. It is noteworthy that the \(\log_{2}\) (FPKM ratio) between SdPCS and other Apiaceous PCSs in root/rhizome, ranging from 6.12 to 20.63 (mean \(= 14.15\) ), was higher than \(95\%\) of genome- wide orthologous gene pairs (Fig. 5c). Thus, we deduced the expression abundance of SdPCS was significantly higher than other Apiaceous PCSs. As the initial step is usually the rate- limiting step in biosynthetic pathway34, the exceptionally high expression of SdPCS may contribute to the furochromone accumulation in S. divaricata.
+
+Moreover, we traced the origin of SdPCS (SaDchr02G001054), and found it might originate from proximal duplication of the nearby SdPCS2 (SaDchr02G001052) (Fig. 5d). The PCS ML tree revealed that the two PCS copies in S. divaricata clustered in the same clade, indicating SaDchr02G001054 was originated from S. divaricata specific duplication event rather than from ancestor species. The syntenic analysis further confirmed this deduction. Although syntenic genes of SdPCS were not detected in other Apiaceous species, those of the ancestral SdPCS2 were identified in most species (Fig. 5d). Remarkably, we found that SdPCS2 was nearly not expressed in any tissue (Fig. 5e), and its syntenic genes in other Apiaceous species were almost not expressed, either (Supplementary Table 20). Thus, the proximal duplication and high expression of SdPCS profoundly contributed to the biosynthesis of furochromones in the root of S. divaricata.
+
+<--- Page Split --->
+
+
+Fig. 5. High expression of SdPCS2 promotes the accumulation of furochromones in the root of S. divaricata. a,
+
+<--- Page Split --->
+
+Contents of typical furochromones in various organs of Apiaceae plants, and syntenic gene analysis. b, Phylogenetic relationships, enzymatic activities, and expression abundance of Apiaceae \(PCSs\) . The PCS enzyme activity was quantified by HPLC/UV peak area of generated noreugenin (2) \((\lambda = 280 \mathrm{nm})\) . c, Comparison of the FPKM between \(SdPCS\) and other potential Apiaceae \(PCSs\) in the genome- wide context. Each red line represents a \(\log_2\) (FPKM ratio) between \(SdPCS\) and a potential Apiaceae \(PCS\) . Each grey density plot indicates the \(\log_2\) (FPKM ratio) distribution of genome- wide orthologous genes of one Apiaceae species. d, Syntenic regions containing Apiaceae \(PCSs\) . e, Expression levels of three \(PCS\) copies in \(S\) . divaricata.
+
+## The absence of functional \(PC\) gene leads to low furochromone content in most Apiaceae plants.
+
+Likewise, we did not detect syntenic genes of \(SdPC\) in other Apiaceae plants (Fig. 6a). We retrieved all Apiaceae \(CYP736s\) and constructed an ML tree. The reported \(PpDC\) was also included19. A robust clade (BS = 100) containing \(SdPC\) and 18 other potential \(PCs\) was identified (Fig. 6b, Supplementary Fig. 57). Although DCAR_313045 and As05G002751 were not included in this clade, they were syntenic with several genes, e.g., SaDchr05G002066 and LCX7BG003145 (Supplementary Fig. 64). The 11 potential \(PCs\) from \(A\) . sinensis lost one exon and was likely to lose the cyclization activity, thus they were not included in further assays. Finally, we cloned and characterized the other 10 potential \(PCs\) . Strikingly, none of them except for \(SdPC\) was effective in producing visamminol (4) (Fig. 6c). This observation confirmed our hypothesis that the absence of \(PC\) genes may lead to the low contents of furochromones in most Apiaceae species. However, we cannot exclude the possibility that these or other potential \(PCs\) might weakly catalyze the reactions in vivo, as trace furochromones were detected in all Apiaceae plants.
+
+Since PpDC participated in the generation of furocoumarins19, we tested the catalytic activities of homologous PCs using demethylisuberosin as substrate. SdPC4, AsDC, LcPC2 and DcPC showed cyclization activities (Supplementary Fig. 65). However, SdPC could not catalyze this reaction despite its high sequence similarity with SdPC4 (Supplementary Fig. 66). Interestingly, these four genes were located at the same syntenic block, which did not include \(SdPC\) (Supplementary Fig. 64). Thus, SdPC is a homologous enzyme with novel function, and its evolutionary origin warrants to be investigated in the future.
+
+<--- Page Split --->
+![PLACEHOLDER_18_0]
+
+Fig. 6 The absence of functional \(PC\) leads to low furochrome content in most Apiaceae plants. a, Syntenic regions containing \(SdPC\) . The syntenic gene pairs are connected by grey lines. b, Phylogenetic relationship and gene structure of Apiaceae PCs. As05G02748 (AsDC) is the same as AS05g00644 in the initial annotation version. c, HPLC/UV chromatograms showing the in vitro enzymatic activity of potential Apiaceae PCs \((\lambda = 280 \mathrm{nm})\) .
+
+Furochromones emerge as an important class of bioactive nature products in medicinal plants. However, little is known on their biosynthesis14,15. Particularly, the formation of furan ring and post modifications leading to structural diversities of furochromones remain largely unexplored. This work dissected the complete biosynthetic pathway of prim- \(O\) - glucosylcimifugin and 5- \(O\)
+
+<--- Page Split --->
+
+methylvisamminoside, two bioactive furochromone glucosides abundant in S. divaricata. Nine biosynthetic enzymes in the biosynthetic pathways were characterized. Among them, proximal duplication and high expression of a pentaketide chromone synthase gene SdPCS, as well as the presence of a lineage- specific peucenin cyclase gene SdPC, contribute to the accumulation of furochromones in the roots of S. divaricata. The results provide new insights into the biosynthesis of furochromones and serve as a platform for their metabolic engineering production.
+
+In recent years, the biosynthetic evolution of natural products in plant kingdom has attracted increasing interest. For example, Berman et al illustrated the parallel evolution of cannabinoid biosynthesis35, and Jiao et al studied the independent loss of biosynthetic pathway for two tropane alkaloids in the Solanaceae family36. In the present work, SdPCS is likely to originate from SdPCS2 through proximal duplication. However, the origin of SdPC still remains unknown. Moreover, some homologous enzymes of SdPC in S. divaricata and other species catalyze the generation of furocoumarins but not furochromones. Catalytic mechanisms and structural evidences for substrate selectivity of these enzymes also warrants further investigation.
+
+## Methods
+
+## Materials and Reagents
+
+The sources of fresh plants of Saposhnikovia divaricata, Centella asiatica, Bupleurum chinense, Daucus carota, Angelica sinensis, Apium graveolens, and Coriandrum sativum are given in Supplementary Table 15. To extract RNA, the roots, leaves, and petioles were used.
+
+The chemical reference standards and sugar donors used in this study were purchased from YuanYe Biotechnology Co., Ltd. (Shanghai, China). Methanol and acetonitrile (Thermo Fisher Scientific, USA) were of HPLC grade. The conversion rates were determined by HPLC/UV analysis on an Agilent HPLC 1260 instrument. Samples were separated on a Zorbax SB- C18 column (4.6×250 mm, 5 μm, Agilent, USA). The column temperature was 30°C. To calculate the conversion rates, peak areas of both substrate and product were integrated by Chromeleon® at a certain wavelength. LC/MS analysis was performed on a Q- Exactive quadrupole Orbitrap mass spectrometer (Thermo Fisher Scientific, USA).
+
+<--- Page Split --->
+
+## Genome sequencing, assembly, and annotation
+
+For the PacBio library construction, \(15\mu \mathrm{g}\) genomic DNA from the leaves of S. divaricata was fragmented into approximately \(15\mathrm{kb}\) using g- TUBEs (Covaris, USA). After removing short fragments and single- strand overhangs, the retained fragments were converted into the proprietary SMRTbell library with the PacBio DNA Template Preparation Kit (Pacific Biosciences, CA, USA). Single Molecule Real Time (SMRT) sequencing was performed on a PacBio Sequel II sequencing platform. For Hi- C library construction, chromatin was first fixed in place with formaldehyde in the nucleus and then extracted. The extracted chromatin was digested with DpnII. The \(5^{\prime}\) overhangs of resulting fragments were then filled in with biotinylated nucleotides, and free blunt ends were ligated. After ligation, the DNA was purified from protein and treated following the Illumina Next Generation manufacturer's instructions. The libraries were subsequently sequenced on Illumina Hiseq X, producing 190.37 Gb \(2\times 150\) bp paired- end reads. The raw data of PacBio subreads was filtered to HiFi reads by PBccs (v6.4.0) (https://github.com/PacificBiosciences/ccs), and subsequently assembled with Hifiasm (v0.16.0) \(^{37}\) . The initial assembled contigs were anchored to chromosomes by 3D- DNA pipeline (v201008) \(^{38}\) and further manually adjusted to produce a chromosome- level genome. BUSCO (v5.4.3) \(^{39}\) was used for benchmarking the genome with the "embryophyte_odb10" database.
+
+EDTA (v2.0.0) \(^{40}\) was used to de novo identify, annotate, and classify the repetitive elements in the genome of S. divaricata. Prior to protein- coding gene annotation, the annotated repetitive elements in the genome were soft masked with bedtools (v2.28.0) \(^{41}\) . RNA- Seq raw reads of S. divaricata were filtered with fastx- toolkits (v0.0.14) (http://hannonlab.cshl.edu/fastx_toolkit/index.html) and then assembled through Hisat2 (v2.2.1) \(^{42}\) and Stringtic (v2.2.0) \(^{43}\) . The raw assembly of transcripts was further validated by PASA (v2.5.1) \(^{44}\) , which were then incorporated into the MAKER (v3.01.03) \(^{45}\) pipeline to automatically identify protein- coding genes. Finally, the gene models identified by MAKER were updated by PASA (v2.5.1) \(^{44}\) . Function annotations of the protein- coding genes were carried out by BLASTP searches against entries in both NCBI non- redundant protein (NR) (https://www.ncbi.nlm.nih.gov/) and Swiss- Prot (https://www.uniprot.org/) databases. The prediction of conserved domains for the genes was performed by InterProScan (v5.11- 51.0) \(^{46}\) . The annotations of the GO terms (http://geneontology.org/) and KEGG pathways (https://www.genome.jp/kegg/) for the
+
+<--- Page Split --->
+
+genes were annotated with eggNOG- mapper (v2.1.10- 0)47.
+
+## Total RNA isolation, RNA-Seq, and gene expression quantification
+
+The total RNA was extracted with the TranZol™ kit (Transgen Biotech, China) following the manufacturer's instructions, and was used to synthesize the first- stranded complementary DNA (cDNA) with TransScript one- step genomic DNA (gDNA) removal and cDNA synthesis SuperMix (Transgen Biotech, China). The transcriptome data of different tissues of S. divaricata were sequenced at Novogene Co., Ltd. (Beijing, China).
+
+The raw RNA- seq reads were filtered in fastp48 with default parameters and then mapped to the reference genome of S. divaricata by Hisat2 (v2.2.1)42. The counts of reads mapping to exons of each gene were calculated by featureCounts49. The FPKM value of each gene was calculated in R.
+
+## Genome-wide mining for furochromone biosynthesis genes
+
+HMMER3 (v3.3.2)50 was used to identify 47PKSs, PTs, CYPs, OMTs and UGTs with an e- value of 1e- 6. The HMMER profiles PF02797 and PF00195 were used for PKS III search. PF01040 and PF00067 was utilized to identify CYPs and PTs. PF00891 and PF08100 were employed to search OMTs, PF00201 was applied for UGT identification. The possible pseudogenes (length of predicted CDS \(< 200\) amino acids) were discarded. Gene structures of all candidate genes were manually adjusted with IGV- GSAman (https://gitee.com/CJchen/IGV- sRNA).
+
+Pearson correlation coefficients and the \(P\) values between contents of furochromones and the FPKM of genes among different tissues of S. divaricata were calculated with the corr.test function in R package psych (https://rdocumentation.org/packages/psych/versions/2.3.3). Those unexpressed genes were not incorporated in correlation analysis.
+
+## Phylogenetic and microsynteny analyses
+
+ML phylogeny was constructed based on 398 strict single- copy orthologous genes identified by OrthoFinder (v2.5.4)51 to clarify the phylogenetic relationship among the eight Apiaceae species. The protein sequences were aligned by MUSCLE (v5.1.1. linux64)52 and subsequently concatenated by
+
+<--- Page Split --->
+
+Phylosuite (v1.2.2) \(^{53}\) . ModelTest- NG (v0.1.7) \(^{54}\) was used to detect the best- fit amino acid substitution model, based on which RAxML- NG (v1.1.0) \(^{55}\) was employed to construct the ML phylogeny with 1,000 bootstrap analyses. The construction of phylogeny of biosynthetic genes follows the same method above.
+
+The microsyntenic analyses generally followed the methods of Griesmann et al. (2018) and Yang et al. (2023). All vs. all blastp (E- value \(= 1\mathrm{e}^{- 5}\) ) was conducted for the protein sequences among eight Apiaceae genomes with BLAST (v2.13.0+) \(^{56}\) . The output protein identity matrix was loaded in JCVI (v1.2.7) to produce collinear gene blocks. Subsequently, we identified the syntenic region containing the furochromone biosynthetic genes \((\pm 100\mathrm{kb})\) in each species using the genome of S. divaricata as the reference. Because the syntenic retention varied between different species pairs, we compared the syntenic gene pairs for all species pairs and retained those gene pairs demonstrating consistent syntenic relationships. To eliminate the bias induced by mistaken annotation, we manually checked the corrected gene structure in syntenic region and re- organized the microsyntenic gene pairs.
+
+## Molecular cloning
+
+The full- length candidate genes were amplified from cDNA with TransStart FastPfu DNA Polymerase (Transgen, China). Candidate genes for PCS, OMT and UGT were recombined in the pET- 28a (+) vector (Invitrogen, USA) at BamH I site. Candidate genes for PT, PC and CH were cloned into pESC- Leu vector at BamH I (Invitrogen, USA). Sequences of the primers used in this study are listed in Supplementary Table 21.
+
+## Expression of candidate biosynthetic genes
+
+The recombinant plasmids for PCS, OMTs and OGTs were introduced into E. coli BL21 (DE3) (Transgen Biotech, China) for heterologous expression. The E. coli cells were grown in \(500\mathrm{mL}\) Luria- Bertani medium containing kanamycin (50 \(\mu \mathrm{g / mL}\) ) at \(37^{\circ}\mathrm{C}\) . After \(\mathrm{OD}_{600}\) reached 0.4–0.6, the cells were induced with \(0.1\mathrm{mM}\) IPTG at \(18^{\circ}\mathrm{C}\) . After 18–24 h, the cell pellets were harvested by centrifugation (7,500 rpm, 3 min at \(4^{\circ}\mathrm{C}\) ), and then resuspended in \(15\mathrm{mL}\) lysis buffer ( \(50\mathrm{mMNaH_2PO_4}\) pH 8.0, \(300\mathrm{mMNaCl}\) , \(30\mathrm{mM}\) imidazole, pH 8.0). Then cells were disrupted by sonication on ice, and
+
+<--- Page Split --->
+
+the cell debris was removed by centrifugation at 7,500 rpm for 50 min at \(4^{\circ}\mathrm{C}\) . The supernatant was collected and loaded onto a pre-equilibrated column (His Trap™ HP, 5 mL, GE Healthcare), and eluted with different concentrations of elution buffer (50 mM \(\mathrm{NaH_2PO_4}\) , pH 8.0, 300 mM NaCl, 30/300 mM imidazole) \(^{57}\) . The purified protein solution was added with approximately 0.5 mL glycerol (25%) and stored at \(- 80^{\circ}\mathrm{C}\) .
+
+The recombinant plasmids for PT, PC and CH were introduced into yeast strain Saccharomyces cerevisiae WAT11 for heterologous expression. The yeast cells were grown in synthetic dropin medium without leucine (SD- Leu). Liquid cultures of the recombinant strains were set up by picking a single colony and growing in \(50~\mathrm{mL}\) of SD- Leu medium containing \(20~\mathrm{g / L}\) glucose at \(28^{\circ}\mathrm{C}\) overnight. The cells were collected by centrifugation (1,000 g, 2 min) and resuspended in \(25~\mathrm{mL}\) of SD- Leu medium containing \(20~\mathrm{g / L}\) galactose to induce target protein expression for 24- 48 hours at \(28^{\circ}\mathrm{C}\) . The microsomes of yeast cells were prepared as reported \(^{28}\) .
+
+## Enzyme activity assay
+
+The purified proteins and prepared microsomes were used for functional characterization by in vitro enzymatic reactions. The reactions were conducted in \(100~\mu \mathrm{L}\) Tris- HCl buffer (50 mM, pH 8.0) containing \(50~\mu \mathrm{g}\) purified enzymes or \(20~\mu \mathrm{L}\) microsomes. The incubation mixtures include substrates (0.1 mM, malonyl- CoA for PCSs, noreguenin for PTs, peucenin for PCs, visamminol for OMTs and CHs, 5- O- methylvisamminol for CHs and SdUGT1/2, norcimifugin for OMTs, and cimifugin for SdUGT1/2), and donors/cofactors (0.5 mM, dimethylallyl pyrophosphate (DMAPP) for PTs, nicotinamide adenine dinucleotide phosphate (NADPH) for PCs and CHs, S- adenosylmethionine (SAM) and dithiothreitol (DTT) for OMTs, and uridine diphosphate glucose (UDPG) for SdUGT1/2). The reactions continued in a shaking incubator for 2 hours ( \(37^{\circ}\mathrm{C}\) for OMTs and UGTs, \(30^{\circ}\mathrm{C}\) for PCSs, PTs, PCs and CHs). For PCSs, reactions were terminated by adding \(10~\mu \mathrm{L}\) \(20\%\) HCl followed by extraction with \(300~\mu \mathrm{L}\) ethyl acetate and redissolution in \(100~\mu \mathrm{L}\) MeOH. The other reactions were terminated by adding \(100~\mu \mathrm{L}\) ice- cold MeOH. The mixtures were then centrifuged at 15,000 rpm for 20 min. The supernatants were analyzed by HPLC and LC/MS.
+
+<--- Page Split --->
+
+The conversion rates in percentage were calculated from peak areas of products and substrates in HPLC/UV chromatograms (Agilent 1260, USA). Samples were separated on a Zorbax SB- C18 column (4.6×250 mm, 5 μm, Agilent, USA). The HPLC methods are shown in Supplementary Table 22. LC/MS analysis was performed on a Q- Exactive hybrid quadrupole- Orbitrap mass spectrometer equipped with a heated ESI source (Thermo Fisher Scientific, USA). The MS parameters were as follows: sheath gas pressure 45 arb, aux gas pressure 10 arb, discharge voltage 4.5 kV, capillary temperature \(350^{\circ}\mathrm{C}\) . MS \(^1\) resolution was set as 70,000 FWHM, AGC target \(1^{*}\mathrm{E}^{6}\) , maximum injection time 50 ms, and scan range \(m / z\) 100–1,000. MS \(^2\) resolution was set as 17,500 FWHM, AGC target \(1^{*}\mathrm{E}5\) , maximum injection time 100 ms, NCE 35.
+
+## Biochemical properties of SdUGT1 and SdUGT2
+
+To optimize the pH value, different reaction buffers with pH from 4.0–6.0 (citric acid- sodium citrate buffer), 6.0- 8.0 (Na \(_2\) HPO \(_4\) - NaH \(_2\) PO \(_4\) buffer), 7.0- 9.0 (Tris- HCl buffer), and 9.0- 11.0 (Na \(_2\) CO \(_3\) - NaHCO \(_3\) buffer) were tested. To optimize the reaction temperature, the reactions were incubated at 4, 18, 30, 37, 45, or 60 °C. All enzymatic reactions (100 μL reaction mixtures including 0.1 mM 5 or 8, 0.5 mM UDPG, and 10 μg of purified enzyme) were conducted in three parallel experiments ( \(n = 3\) ). The reactions were terminated with pre- cooled methanol and centrifuged at 15,000 rpm for 20 min for HPLC analysis as described above.
+
+## Determination of kinetic parameters of SdUGT1 and SdUGT2
+
+Reactions were conducted in a final volume of 50 μL with 50 mM reaction buffer, suitable concentration of protein, 1 mol/L of saturated UDPG, and different concentrations of substrate (5 or 8) (Supplementary Table 23). The reactions were quenched with 70 μL pre- cooled methanol after incubating at the optimal temperature for 15 min, and then centrifuged at 15,000 rpm for 20 min. The supernatants were used for HPLC analysis. All experiments were performed in triplicate. The conversion rates were calculated as described above. The kinetic parameters were calculated with Michaelis- Menten plot fitted by Graphapad Prism 8.0 \(^{58}\) .
+
+## Scaled-up enzymatic reactions
+
+<--- Page Split --->
+
+To prepare the prenylated product, the reaction mixtures contained \(100~\mu \mathrm{L}\) buffer (50 mM Tris- HCl, \(\mathrm{pH}8.0\) ), \(0.2\mathrm{mM}\) noreugenin, \(1.0\mathrm{mM}\) DMAPP, \(2.0\mathrm{mM}\) \(\mathrm{MgCl}_2\) , and \(20~\mu \mathrm{L}\) microsome. A total of 1,200 parallel tube reactions were conducted. The reactions were performed at \(30^{\circ}\mathrm{C}\) overnight and terminated by extraction with 4- fold volume of ethyl acetate. The organic solvent was removed under reduced pressure. The residue was dissolved in \(1.5\mathrm{mL}\) of methanol. The products were then purified by reversed- phase semi- preparative HPLC. The structures were characterized by HRMS and extensive 1D and 2D NMR analyses.
+
+To prepare the hydrolyzed product of visamminol- \(3^{1}\) - O- glucoside, the reaction mixture contained \(20\mathrm{mL}\) buffer ( \(50\mathrm{mM}\mathrm{NaH}_2\mathrm{PO}_4\mathrm{- Na}_2\mathrm{HPO}_4\) , \(\mathrm{pH}6.0\) ), \(0.5\mathrm{mM}\) visamminol- \(3^{1}\) - O- glucoside, and \(200\mathrm{mg}\) \(\beta\) - glucosidase (Solarbio, Beijing, China). A total of 5 parallel tubes were used. The reactions were performed at \(45^{\circ}\mathrm{C}\) for 4 hours and terminated by extraction with 4- fold volume of ethyl acetate. The extract was treated as described above.
+
+## Crystallization and structural determination
+
+The full- length cDNA of SdUGT2 was cloned into pET- 28a (+) vector. The S- tag of pET28a was removed. A TrxA- tag and \(6\times\) His- tag followed by thrombin site were added before the N- terminus of the target protein to facilitate purification. The TrxA- His- thrombin- SdUGT2 protein was expressed in E. coli (DE3) strain and purified by Ni- affinity chromatography (GE Healthcare). After purification, the recombinant protein was digested by thrombin to remove tag ( \(4^{\circ}\mathrm{C}\) , \(8\mathrm{h}\) ). The sample was mixed with Ni- NTA affinity beads for the second time to purify the protein. The flow- through was concentrated and then applied to size- exclusion chromatography on a Superdex™ 200 increase \(10 / 300\) GL prepacked column (GE Healthcare) for further purification. The elution buffer was \(20\mathrm{mM}\) Tris- HCl (pH 7.5) and \(50\mathrm{mM}\) NaCl. Fractions containing SdUGT2 were collected and concentrated to 20 mg/mL, flash- frozen on liquid nitrogen, and then stored in a \(- 80^{\circ}\mathrm{C}\) freezer. The purified protein was incubated with \(6\mathrm{mM}\) UDP for \(2\mathrm{h}\) . The crystals of SdUGT2 were obtained after 5 days at \(16^{\circ}\mathrm{C}\) in hanging drops containing \(1\mu \mathrm{L}\) of protein solution and \(1\mu \mathrm{L}\) of reservoir solution ( \(0.2\mathrm{M}\) lithium sulfate monohydrate, \(0.1\mathrm{M}\) Bis- Tris pH 5.25, \(28\%\) \(w / v\) polyethylene glycol 3,350) (Supplementary Fig. 25). The crystals were flash- frozen in the reservoir solution supplemented with \(25\%\) \((v / v)\) glycerol.
+
+<--- Page Split --->
+
+The diffraction data of SdUGT2 crystal were collected at beamlines BL19U1 and BL02U1 Shanghai Synchrotron Radiation Facility (SSRF). The data were processed with XDS. The structures were solved by molecular replacement with Phaser. Crystallographic refinement was performed repeatedly with Phenix and COOT. The refined structures were validated by Phenix and the PDB validation server (https://validate-rcsb-1.wwpdb.org/). The final refined structures were deposited in the Protein Data Bank. The diffraction data and structure refinement statistics are shown in Supplementary Table 14.
+
+## Molecular docking
+
+Since all the reported UGT structures are highly conserved for the UDP- sugar binding domain, we simulated the SdUGT2/UDPG sugar complex structures by superimposing the UDP parts of UDPG to reported structures. Compound 8 was docked into the complex by Autodock. A total of 50 docking conformations were generated. The conformations with the lowest binding energy were selected for further study.
+
+## De novo biosynthesis of furochromones in tobacco
+
+The full- length DNA sequences of SdPCS, SdPT, SdPC, SdOMT, SdCH and SdUGT1/2 were amplified with primers given in Supplementary Table 21. The PCR products were sub- cloned into pDonr207 vectors with the Gateway BP Clonase II Enzyme Mix and then cloned into pEAQ- HT- DEST1 vector with the Gateway LR Clonase II Enzyme Mix according to the manufacturer's instructions. The recombinant pEAQ- HT- DEST1- target gene vectors were transformed into Agrobacterium tumefaciens strain GV3101 by chemical conversion method. Single colonies were inoculated at \(28^{\circ}\mathrm{C}\) and subsequently shaked in LB culture medium (50 \(\mu \mathrm{g / mL}\) kanamycin and 50 \(\mu \mathrm{g / mL}\) rifampicin) until \(\mathrm{OD}_{600} = 0.6\) . After centrifugation, bacteria were re- suspended in MMA buffer to \(\mathrm{OD}_{600} = 0.2\) for each strain. Different strains were mixed for transformation. The infection solution was infiltrated into leaves of 5- 6 weeks- old tobacco. After 7 days, the samples were harvested and freeze- dried. The secondary metabolites were extracted by methanol and analyzed by LC/MS. The contents of compounds 5, 6, 8 and 9 were quantified by regression equations. Reference standards 5, 6, 8 and 9 were respectively dissolved in DMSO to make solutions of 1 \(\mathrm{mg / mL}\) , which were 1:1 mixed to obtain the mixed stock solution. The stock solution was serially diluted with methanol containing 4
+
+<--- Page Split --->
+
+\(\mu \mathrm{g / mL}\) bergenin as internal standard to obtain calibration standard solutions (diluted by 2, 4, 8, 16, 32, 64, 128, 256, 512, 1,024, 2,048, 4,096, 8,192, 16,384, 32,768, 65,536 and 131,072 folds, respectively). The regression equations of 5, 6, 8 and 9 were listed in Supplementary Figs. 67–70. The LC/MS method parameters are listed in Supplementary Table 22.
+
+## Metabolite quantification
+
+The secondary metabolites of different Apiaceae plants were extracted by methanol and analyzed by LC/MS following the methods mentioned above.
+
+## Acknowledgements
+
+This work was supported by the National Key Research and Development Program of China (No. 2023YFA0914100 to M. Y., and No. 2023YFA0915800 to L. W.), Beijing Natural Science Foundation (No. QY23076 to J.L. Z., and 83001Y0439 to C.X.Z.), and National Natural Science Foundation of China (No. 81725023 to M. Y.). We thank Dr. Rong-shen Wang and Xi-ran Zhang of Ye Lab and Xun- meng Feng and Jiao- jiao Ji of Wang Lab for their technical assistance. We also thank the staff at BL19U1/BL02U1 beamlines at SSRF of the National Facility for Protein Science in Shanghai (NFPS), Shanghai Advanced Research Institute, Chinese Academy of Sciences, for providing technical support in X- ray diffraction data collection and analysis.
+
+## Data availability
+
+Data supporting the findings of this study are available in the article, supplementary materials, or public database. The gene sequence data generated in this study have been deposited in the NCBI database under the accession numbers listed in Supplementary Table 24. The crystal structure in this study has been deposited in the RCSB PDB database under the accession number: SdUGT2 (8ZNK). The assembled genome and annotation files of S. divaricata are available at figshare (https://figshare.com/projects/Saposhnikovia_divaricata_genome/206434). The raw data of transcriptome sequencing of S. divaricata have been deposited to the Genome Sequence Archive at the National Genomics Data Center (NGDC) under BioProject no. PRJCA026506. The sources of genome data and RNA-seq data of other Apiaceae plants are listed in Supplementary Tables 16–17.
+
+<--- Page Split --->
+
+1. Sun, Y. et al. New chromones from the roots of Saposhnikovia divaricata (Turcz.) Schischk with anti-inflammatory activity. Bioorg. Chem. 134, 106447 (2023).
+2. Abu-Hashem, A. A. & Youssef, M. M. Synthesis of new visnagen and khellin furochromone pyrimidine derivatives and their anti-inflammatory and analgesic activity. Molecules 16, 1956-1972 (2011).
+3. Zhang, T. et al. Multi-omics reveals that 5-O-methylvisammioside prevention acute liver injury in mice by regulating the TNF/MAPK/NF-κB/arachidonic acid pathway. Phytomedicine 128, 155550 (2024).
+4. Wu, L. Q. et al. Antinociceptive effects of prim-O-glucosylcimifugin in inflammatory nociception via reducing spinal COX-2. Biomol. Ther. 24, 418-425 (2016).
+5. Abdelhafez, O. M., Abedelatif, N. A. & Badria, F. A. DNA binding, antiviral activities and cytotoxicity of new furochromone and benzofuran derivatives. Arch. Pharm. Res. 34, 1623-1632 (2011).
+6. Wang, Y. et al. Prim-O-glucosylcimifugin ameliorates aging-impaired endogenous tendon regeneration by rejuvenating senescent tendon stem/progenitor cells. Bone Res. 11, 784-802 (2023).
+7. Amen, Y., Elsbae, M., Othman, A., Sallam, M. & Shimizu, K. Naturally occurring chromone glycosides: sources, bioactivities, and spectroscopic features. Molecules 26, 7646 (2021).
+8. Kreiner, J., Pang, E., Lenon, G. B. & Yang, A. W. H. Saposhnikoviae divaricata: a phytochemical, pharmacological, and pharmacokinetic review. Chin. J. Nat. Med. 15, 255-264 (2017).
+9. Khalil, N., Bishr, M., Desouky, S. & Salama, O. Ammi visnaga L., a potential medicinal plant: a review. Molecules 25 (2020).
+10. Sun, Y., Yang, A. W. H. & Lenon, G. B. Phytochemistry, ethnopharmacology, pharmacokinetics and toxicology of Cnidium monnieri (L.) Cusson. Int. J. Mol. Sci. 21 (2020).
+11. Commission, C. P. Pharmacopoeia of the People's Republic of China. Vol. 1, p156 (China Medical Science and Technology Press, 2020).
+12. Erst, A. S., Petrova, N. V., Kaidash, O. A., Wang, W. & Kostikova, V. A. The genus Eranthis: prospects of research on its phytochemistry, pharmacology, and biotechnology. Plants (Basel) 12, 3795 (2023).
+13. Urbagarova, B. M. et al. Chromones and coumarins from Saposhnikovia divaricata (Turcz.) Schischk. growing in Buryatia and Mongolia and their cytotoxicity. J. Ethnopharmacol. 261, 112517 (2020).
+14. Wang, X. H. et al. Identification of a diarylpentanoid-producing polyketide synthase revealing an unusual biosynthetic pathway of 2-(2-phenylethyl) chromones in agarwood. Nat. Commun. 13, 348 (2022).
+15. Abe, I. et al. Structure-based engineering of a plant type III polyketide synthase: formation of an unnatural nonketide naphthopyrone. J. Am. Chem. Soc. 129, 5976-5980 (2007).
+16. Harrison, P. G., Bailey, B. K. & Steck, W. Biosynthesis of furanochromones. Can. J. Biochem. 49, 964-970 (1971).
+17. de Bruijn, W. J. C., Levisson, M., Beekwilder, J., van Berkel, W. J. H. & Vincken, J. P. Plant aromatic prenyltransferases: tools for microbial cell factories. Trends Biotechnol. 38, 917-934 (2020).
+18. Villard, C. et al. A new P450 involved in the furanocoumarin pathway underlies a recent case of convergent evolution. New Phytol. 231, 1923-1939 (2021).
+19. Zhao, Y. et al. Two types of coumarins-specific enzymes complete the last missing steps in pyran- and furanocoumarins biosynthesis. Acta Pharm. Sin. B 14, 869-880 (2024).
+20. Li, Q. et al. The chromosome-scale assembly of the Notopterygium incisum genome provides insight into the structural diversity of coumarins. Acta Pharmaceutica. Sin. B https://doi.org/10.1016/j.apsb.2024.04.005 (2024).
+21. Wang, K. et al. Three types of enzymes complete the furanocoumarins core skeleton biosynthesis in Angelica sinensis. Phytochemistry 222, 114102 (2024).
+22. Tiwari, P., Sangwan, R. S. & Sangwan, N. S. Plant secondary metabolism linked glycosyltransferases: an update on expanding knowledge and scopes. Biotechnol. Adv. 34, 714-739 (2016).
+
+<--- Page Split --->
+
+23. Liu, Y., Fernie, A. R. & Tohge, T. Diversification of chemical structures of methoxylated flavonoids and genes encoding flavonoid-O-methyltransferases. Plants (Basel) 11, 564 (2022).
+24. Khouri, H. E., Tahara, S. & Ibrahim, R. K. Partial-purification, characterization, and kinetic-analysis of isoflavone 5-O-methyltransferase from yellow lupin roots. Arch. Biochem. Biophys. 262, 592-598 (1988).
+25. Itoh, N., Iwata, C. & Toda, H. Molecular cloning and characterization of a flavonoid-O-methyltransferase with broad substrate specificity and regioselectivity from Citrus depressa. BMC Plant Biol. 16, 180 (2016).
+26. Isin, E. M. & Guengerich, F. P. Complex reactions catalyzed by cytochrome P450 enzymes. Biochim. Biophys. Acta 1770, 314-329 (2007).
+27. Wang, Z. H. et al. Genomic, transcriptomic, and metabolomic analyses provide insights into the evolution and development of a medicinal plant Saposhnikovia divaricata (Apiaceae). Hortic. Res. https://doi.org/10.1093/hr/uhae105 (2024).
+28. Alagoz, Y., Mi, J., Balakrishna, A., Almarwae, L. & Al-Babili, S. Characterizing cytochrome P450 enzymes involved in plant apocarotenoid metabolism by using an engineered yeast system. Method Enzymol. 671, 527-552 (2022).
+29. Shang, Z. et al. Characterization of prenylated phenolics in Glycyrrhiza uralensis by offline two-dimensional liquid chromatography/mass spectrometry coupled with mass defect filter. J. Pharm. Biomed. Anal. 220, 115009 (2022).
+30. Marumoto, S. & Miyazawa, M. Structure-activity relationships for naturally occurring coumarins as β-secretase inhibitor. Bioorg. Med. Chem. 20, 784-788 (2012).
+31. Zhang, M. et al. Functional Characterization and Structural Basis of an Efficient Di-C-glycosyltransferase from Glycyrrhiza glabra. J. Am. Chem. Soc. 142, 3506-3512 (2020).
+32. Eberhardt, J., Santos-Martins, D., Tillack, A. F. & Forli, S. AutoDock Vina 1.2.0: new docking methods, expanded force field, and python bindings. J. Chem. Inf. Model. 61, 3891-3898 (2021).
+33. Wang, H. T. et al. Insights into the missing apiosylation step in flavonoid apiosides biosynthesis of Leguminosae plants. Nat. Commun. 14, 6658 (2023).
+34. Zhou, X. et al. Phytoene synthase: the key rate-limiting enzyme of carotenoid biosynthesis in plants. Front. Plant Sci. 13, 884720 (2022).
+35. Berman, P. et al. Parallel evolution of cannabinoid biosynthesis. Nat. Plants 9, 817-831 (2023).
+36. Yang, J. et al. Multiple independent losses of the biosynthetic pathway for two tropane alkaloids in the Solanaceae family. Nat Commun. 14, 8457 (2023).
+37. Cheng, H. et al. Haplotype-resolved assembly of diploid genomes without parental data. Nat. Biotechnol. 40, 1332-1335 (2022).
+38. Dudchenko, O. et al. De novo assembly of the Aedes aegypti genome using Hi-C yields chromosome-length scaffolds. Science 356, 92-95 (2017).
+39. Evgeny, Z. BUSCO update: novel and streamlined workflows along with broader and deeper phylogenetic coverage for scoring of eukaryotic, prokaryotic, and viral genomes. Mol. Biol. Evol. 10, 4647-4654 (2021).
+40. Ou, S. et al. Benchmarking transposable element annotation methods for creation of a streamlined, comprehensive pipeline. Genome Biol. 20, 275 (2019).
+41. Quinlan, A. R. & Hall, I. M. BEDTools: a flexible suite of utilities for comparing genomic features. Bioinformatics 26, 841-842 (2010).
+42. Kim, D., Paggi, J. M., Park, C., Bennett, C. & Salzberg, S. L. Graph-based genome alignment and genotyping with HISAT2 and HISAT-genotype. Nat. Biotechnol. 37, 907-915 (2019).
+43. Pertea, M. et al. StringTie enables improved reconstruction of a transcriptome from RNA-seq reads. Nat. Biotechnol. 33, 290-295 (2015).
+
+<--- Page Split --->
+
+44. Haas, B. J. et al. Improving the Arabidopsis genome annotation using maximal transcript alignment assemblies. Nucleic Acids Res. 31, 5654-5666 (2003).
+45. Campbell, M. S., Holt, C., Moore, B. & Yandell, M. Genome annotation and curation using MAKER and MAKER-P. Curr. Protoc. bioinform. 48, 4.11.11-4.11.39 (2014).
+46. Jones, P. et al. InterProScan 5: genome-scale protein function classification. Bioinformatics 30, 1236-1240 (2014).
+47. Huerta-Cepas, J. et al. Fast genome-wide functional annotation through orthology assignment by eggNOG-Mapper. Mol. Biol. Evol. 34, 2115-2122 (2017).
+48. Chen, S. Ultrafast one-pass FASTQ data preprocessing, quality control, and deduplication using fastp. Imeta 2, e107 (2023).
+49. Liao, Y., Smyth, G. K. & Shi, W. featureCounts: an efficient general purpose program for assigning sequence reads to genomic features. Bioinformatics 30, 923-930 (2014).
+50. Mistry, J., Finn, R. D., Eddy, S. R., Bateman, A. & Punta, M. Challenges in homology search: HMMER3 and convergent evolution of coiled-coil regions. Nucleic Acids Res. 41, e121 (2013).
+51. Emms, D. M. & Kelly, S. OrthoFinder: phylogenetic orthology inference for comparative genomics. Genome Biol. 20, 238 (2019).
+52. Edgar, R. C. MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Res. 32, 1792-1797 (2004).
+53. Zhang, D. et al. PhyloSuite: an integrated and scalable desktop platform for streamlined molecular sequence data management and evolutionary phylogenetics studies. Mol. Ecol. Resour. 20, 348-355 (2020).
+54. Darriba, D. et al. ModelTest-NG: a new and scalable tool for the selection of DNA and protein evolutionary models. Mol. Biol. Evol. 37, 291-294 (2020).
+55. Stamatakis, A. RAxML version 8: a tool for phylogenetic analysis and post-analysis of large phylogenies. Bioinformatics 30, 1312-1313 (2014).
+56. Camacho, C. et al. BLAST+: architecture and applications. BMC Bioinformatics 10, 421 (2009).
+57. Labrou, N. E. Protein purification: an overview. Methods Mol. Biol. (Clifton, N.J.) 1129, 3-10 (2014).
+58. Hoare, S. R. J. Receptor binding kinetics equations: Derivation using the Laplace transform method. J. Pharmacol. Toxicol. Methods 89, 26-38 (2018).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+SupplementaryTables.xlsx - SuppplementaryFigures.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf_det.mmd b/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..e87b1e301633beb8c1f042f672173e615b4d3bd0
--- /dev/null
+++ b/preprint/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf/preprint__0481817a811ef5943e02c6f71c38db6c4ebc3f3451bbc8d278f2dbfe56469ccf_det.mmd
@@ -0,0 +1,544 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 930, 175]]<|/det|>
+# Complete biosynthetic pathway of furochromones and its evolutionary mechanism in Apiaceae plants
+
+<|ref|>text<|/ref|><|det|>[[44, 196, 99, 213]]<|/det|>
+Min Ye
+
+<|ref|>text<|/ref|><|det|>[[52, 223, 245, 240]]<|/det|>
+yemin@bjmu.edu.cn
+
+<|ref|>text<|/ref|><|det|>[[50, 268, 567, 288]]<|/det|>
+Peking University https://orcid.org/0000- 0002- 9952- 2380
+
+<|ref|>text<|/ref|><|det|>[[44, 293, 144, 310]]<|/det|>
+Jianlin Zou
+
+<|ref|>text<|/ref|><|det|>[[50, 315, 567, 334]]<|/det|>
+Peking University https://orcid.org/0009- 0008- 4125- 429X
+
+<|ref|>text<|/ref|><|det|>[[44, 340, 135, 358]]<|/det|>
+Hongye Li
+
+<|ref|>text<|/ref|><|det|>[[52, 363, 208, 380]]<|/det|>
+Peking University
+
+<|ref|>text<|/ref|><|det|>[[44, 386, 115, 403]]<|/det|>
+Bao Nie
+
+<|ref|>text<|/ref|><|det|>[[44, 408, 945, 450]]<|/det|>
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+<|ref|>text<|/ref|><|det|>[[44, 455, 166, 473]]<|/det|>
+Zi- Long Wang
+
+<|ref|>text<|/ref|><|det|>[[50, 478, 567, 496]]<|/det|>
+Peking University https://orcid.org/0000- 0002- 7875- 0704
+
+<|ref|>text<|/ref|><|det|>[[44, 502, 170, 519]]<|/det|>
+Chunxue Zhao
+
+<|ref|>text<|/ref|><|det|>[[52, 525, 208, 542]]<|/det|>
+Peking University
+
+<|ref|>text<|/ref|><|det|>[[44, 548, 166, 566]]<|/det|>
+Yungang Tian
+
+<|ref|>text<|/ref|><|det|>[[52, 571, 208, 589]]<|/det|>
+Peking University
+
+<|ref|>text<|/ref|><|det|>[[44, 595, 125, 612]]<|/det|>
+Liqun Lin
+
+<|ref|>text<|/ref|><|det|>[[44, 617, 945, 658]]<|/det|>
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+<|ref|>text<|/ref|><|det|>[[44, 663, 137, 681]]<|/det|>
+Weizhe Xu
+
+<|ref|>text<|/ref|><|det|>[[50, 685, 646, 704]]<|/det|>
+Civil Aviation Medicine Center, Civil Aviation Administration of China
+
+<|ref|>text<|/ref|><|det|>[[44, 710, 183, 727]]<|/det|>
+Zhuangwei Hou
+
+<|ref|>text<|/ref|><|det|>[[44, 732, 945, 773]]<|/det|>
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+<|ref|>text<|/ref|><|det|>[[44, 779, 149, 796]]<|/det|>
+Wenkai Sun
+
+<|ref|>text<|/ref|><|det|>[[44, 801, 945, 842]]<|/det|>
+Guangdong Laboratory for Lingnan Modern Agriculture/Genome Analysis Laboratory of the Ministry of Agriculture/Agricultural Genomics Institute at Shenzhen,Chinese Academy of Agriculture
+
+<|ref|>text<|/ref|><|det|>[[44, 847, 147, 864]]<|/det|>
+Xiaoxu Han
+
+<|ref|>text<|/ref|><|det|>[[44, 870, 816, 888]]<|/det|>
+Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences
+
+<|ref|>text<|/ref|><|det|>[[44, 894, 155, 912]]<|/det|>
+Meng Zhang
+
+<|ref|>text<|/ref|><|det|>[[52, 916, 208, 934]]<|/det|>
+Peking University
+
+<|ref|>text<|/ref|><|det|>[[44, 940, 179, 958]]<|/det|>
+Hao- Tian Wang
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[55, 46, 207, 64]]<|/det|>
+Peking University
+
+<|ref|>text<|/ref|><|det|>[[44, 70, 648, 110]]<|/det|>
+Qingyan Li Civil Aviation Medicine Center, Civil Aviation Administration of China
+
+<|ref|>text<|/ref|><|det|>[[44, 116, 816, 158]]<|/det|>
+Li Wang Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 199, 103, 216]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 236, 137, 255]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 274, 295, 294]]<|/det|>
+Posted Date: July 31st, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 312, 475, 332]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 4779533/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 350, 914, 393]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 410, 535, 430]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 465, 904, 508]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on April 1st, 2025. See the published version at https://doi.org/10.1038/s41467- 025- 58498- 8.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[42, 92, 911, 150]]<|/det|>
+# Complete biosynthetic pathway of furochromones and its evolutionary mechanism in Apiaceae plants
+
+<|ref|>text<|/ref|><|det|>[[42, 170, 60, 184]]<|/det|>
+3
+
+<|ref|>text<|/ref|><|det|>[[42, 200, 911, 275]]<|/det|>
+Jian- lin Zou \(^{1, \#}\) , Hong- ye Li \(^{1, \#}\) , Bao Nie \(^{2, \#}\) , Zi- long Wang \(^{1}\) , Chun- xue Zhao \(^{1}\) , Yun- gang Tian \(^{1}\) , Li- qun Lin \(^{2}\) , Wei- zhe Xu \(^{3}\) , Zhuang- wei Hou \(^{2}\) , Wen- kai Sun \(^{2}\) , Xiao- xu Han \(^{2}\) , Meng Zhang \(^{1}\) , Hao- tian Wang \(^{1}\) , Qing- yan Li \(^{3}\) , Li Wang \(^{2, *}\) , Min Ye \(^{1, *}\)
+
+<|ref|>text<|/ref|><|det|>[[42, 293, 911, 339]]<|/det|>
+\(^{1}\) State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, 38 Xueyuan Road, Beijing 100191, China
+
+<|ref|>text<|/ref|><|det|>[[42, 357, 911, 432]]<|/det|>
+\(^{2}\) Shenzhen Branch, Guangdong Laboratory of Lingnan Modern Agriculture, Key Laboratory of Synthetic Biology, Ministry of Agriculture and Rural Affairs, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518120, China
+
+<|ref|>text<|/ref|><|det|>[[42, 450, 911, 496]]<|/det|>
+\(^{3}\) Civil Aviation Medicine Center, Civil Aviation Administration of China, A- 1 Gaojing, Beijing 100123, China
+
+<|ref|>text<|/ref|><|det|>[[42, 515, 60, 529]]<|/det|>
+14
+
+<|ref|>text<|/ref|><|det|>[[42, 545, 291, 562]]<|/det|>
+\(*\) Corresponding authors.
+
+<|ref|>text<|/ref|><|det|>[[42, 572, 715, 591]]<|/det|>
+Email address: wangli03@caas.cn (Li Wang); yemin@bjmu.edu.cn (Min Ye).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[88, 91, 166, 106]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[85, 116, 913, 415]]<|/det|>
+Furochromones are bioactive and specific secondary metabolites of many Apiaceae plants. Their biosynthesis remains largely unexplored. In this work, we dissected the complete biosynthetic pathway of major furochromones in the medicinal plant Saposhnikovia divaricata by characterizing novel prenyltransferase, peucenin cyclase, methyltransferase, hydroxylase, and glycosyltransferases. De novo biosynthesis of prim- O- glucosylcimifugin and 5- O- methylvisamminoside was then realized in tobacco leaves. Through comparative genomic and transcriptomic analyses, we further found that proximal duplication and high expression of a pentaketide chromone synthase gene SdPCS, together with the presence of a lineage- specific peucenin cyclase gene SdPC, led to the predominant accumulation of furochromones in the roots of S. divaricata among surveyed Apiaceae plants. This study paves the way for metabolic engineering production of furochromones, and sheds light into evolutionary mechanism of furochromone biosynthesis among Apiaceae plants.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 912, 330]]<|/det|>
+Furochromones are an important class of bioactive natural products. They demonstrate antiinflammatory1,2, hepatoprotective3, antinociceptive4, antiviral4,5, and anti- aging6 activities. While chromones are widely present in plants, furochromones have only been reported in a few families including Apiaceae, Ranunculaceae, and Leguminosae7. In Apiaceae, furochromones are the major bioactive compounds of Saposhnikovia divaricata8, Ammi visnaga9, and Cnidium monnieri10. Particularly, S. divaricata contains abundant prim- O- glucosylcimifugin (POG) and 5- O- methylvisamminoside (5- O- MVG), and their total contents could be above 0.24% of dry weight11. S. divaricata is a medicinal plant widely used in traditional medicines for the treatment of influenza and rheumatic arthritis.
+
+<|ref|>text<|/ref|><|det|>[[85, 366, 912, 916]]<|/det|>
+The structures of POG and 5- O- MVG feature in the substitution of an isoprenyl group at C- 6, which forms a fused dihydrofuran ring12,13 (Supplementary Fig. 1). The biosynthesis of simple chromones has been extensively studied. The chromone skeleton is generated by polyketide synthases, such as PECPS from Aquilaria sinensis and AaPCS from Aloe arborescens14,15. However, little is known about the biosynthesis of furochromones. In the early 1970s, researchers fed sodium [1- 14C] acetate to shoots of Ammi visnaga, and revealed that pucenin and visamminol were biosynthetic intermediates of furochromones16. For the biosynthesis of POG or 5- O- MVG, a prenyltransferase (PT) is expected to introduce an isoprenyl group to C- 6 of the chromone skeleton17. Very few enzymes have been reported to catalyze cyclization of an isoprenyl group to form a dihydrofuran ring. While CYP76F112 from Ficus carica, PpDC and PpOC from Peucedanum praeruptorum, NiDC and NiOC from Notopterigium incisum, as well as AsDC and AsOC from Angelica sinensis have been reported to catalyze similar reactions to produce furocoumarins18- 21, no enzymes have been testified to generate furochromones. On the other hand, glycosyl substitutions at hydroxyl groups linking to the quaternary C- 3' or the secondary C- 11 are rare for natural products, and these reactions are hypothesized to be catalyzed by uridine diphosphate-dependent glycosyltransferases (UGTs)22. Moreover, both POG and 5- O- MVG contain a methoxyl group at C- 5, and the methylation reaction was proposed to be catalyzed by an O- methyltransferase (OMT)23. Although a big family of OMTs have been reported from plants, few OMTs could catalyze methylation at the less active 5- OH. Limited examples include the isoflavone 5- O- methyltransferase from Lupinus luteus24 and CdFOMT5 from Citrus depressa25. For POG, the extra primary hydroxyl group is likely to be introduced by a cytochrome P450 (CYP450) enzyme26.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 911, 163]]<|/det|>
+Based on the above analysis, we tentatively hypothesized the biosynthetic pathway of 5- O- MVG (6) and POG (9) (Fig. 1a). While the enzyme categories catalyzing each step seem obvious, the specific enzymes with expected functions are illusive.
+
+<|ref|>text<|/ref|><|det|>[[85, 200, 912, 330]]<|/det|>
+In this work, we dissected the biosynthetic pathway of POG and 5- O- MVG in S. divaricata. The functions of seven novel enzymes were characterized, including SdPCS, SdPT, SdPC, SdCH, SdOMT, SdUGT1, and SdUGT2. The complete biosynthesis of POG and 5- O- MVG was realized in tobacco leaves. Moreover, we unravelled the genetic mechanisms for high abundance of POG and 5- O- MVG in S. divaricata among Apiaceae plants.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 368, 287, 385]]<|/det|>
+## Results and Discussion
+
+<|ref|>text<|/ref|><|det|>[[88, 394, 910, 415]]<|/det|>
+Proposed biosynthetic pathway of furochromones in Saposhnikovia divaricata and gene mining.
+
+<|ref|>text<|/ref|><|det|>[[85, 421, 912, 617]]<|/det|>
+First, we analyzed the chemical constituents of three organs of S. divaricata (leaf, petiole, and root, Fig. 1b–c) by liquid chromatography coupled with mass spectrometry (LC/MS). At least five furochromones (5–9) could be detected, which to some extent supported the validity of our proposed biosynthetic pathway. Subsequently, the contents of major compounds 5, 6, 8 and 9 in five tissue samples (roots at three developmental stages, petiole, and leaf) were quantitatively determined (Supplementary Figs. 2–6). The results indicated the roots contained more abundant furochromones, particularly the glycosides 6 and 9, than the petiole and leaf samples (Fig. 1d).
+
+<|ref|>text<|/ref|><|det|>[[85, 654, 912, 895]]<|/det|>
+In order to obtain a complete list of candidate genes involved in the biosynthesis of POG and 5- O- MVG, we sequenced, assembled, and annotated a chromosome- level genome of S. divaricata. Based on 28.65 Gb PacBio CCS long reads, we assembled the genome to 1.95 Gb (Supplementary Table 1), which was consistent with the estimate by flow cytometry (1.74 ± 0.07 Gb) (Supplementary Fig. 7) and the published assembly27. The assembly contig N50 was 2.22 Mb and the Benchmarking Universal Single- Copy Ortholog (BUSCO) score was 96.1%, indicating good genome continuity and completeness (Supplementary Tables 2–3). By Hi- C technology, 94.27% contigs were anchored onto eight chromosomes (Fig. 1e, Supplementary Fig. 8 and Table 4). Multiple- tissue RNA- Seq data (Supplementary Table 5), ab initio prediction, and homolog protein evidence were combined for
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 914, 303]]<|/det|>
+genome annotation, which allowed the identification of 38,704 high- confidence protein- coding genes and 65,734 transcripts. Finally, a total of 1,751,401 repetitive elements were annotated, accounting for \(76.78\%\) of the genome (Supplementary Table 6). With this high- quality genome and multiple- tissue RNA- Seq data, we quantified the gene expression abundance (fragments per kilobase of exon model per million mapped fragments, FPKM) of the five tissue samples mentioned above. Subsequently, we screened candidate genes according to genome annotation or local blastn search, and selected genes whose expression levels were correlated with the contents of downstream secondary metabolites in different organs for functional characterization.
+
+<|ref|>image<|/ref|><|det|>[[95, 336, 904, 777]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 803, 911, 905]]<|/det|>
+Fig. 1. A proposed biosynthetic pathway of furochromones and genomic statistics in S. divaricata. a, The proposed biosynthetic pathway and catalytic enzymes. PT, prenyltransferase; PCS, pentaketide chromone synthase; CYP450, cytochrome P450 enzyme; OMT, O-methyltransferase; UGT, uridine diphosphate-dependent glycosyltransferase. 1, malonyl-CoA; 2, noreugentin; 3, puecinin; 4, visamminol; 5, 5-O-methylvisamminol; 6, 5-O-methylvisamminoside;
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 90, 912, 247]]<|/det|>
+7, norcimifugin; 8, cimifugin; 9, prim- O- glucosylcimifugin. b, Image of the sampled S. divaricata. c, Total ion currents (TICs) and extracted ion chromatograms (EICs) of the root, petiole, and leave of S. divaricata by LC/MS analysis. EIC mass range: \(m / z\) 291.11- 291.12 + 293.09- 293.10. d, Contents of 5, 6, 8 and 9 in different organs, calculated on the basis of dry weight. e, Genomic statistics of S. divaricata, showing eight chromosomes (Chr1- Chr8). i, pseudochromosomes; ii, gene density; iii, Gypsy LTR density; iv, Copia LRT density; v, Helitron density; vi, GC content.
+
+<|ref|>sub_title<|/ref|><|det|>[[85, 284, 459, 302]]<|/det|>
+## Biosynthesis of the furochromone skeleton.
+
+<|ref|>text<|/ref|><|det|>[[85, 311, 912, 610]]<|/det|>
+The first step of the biosynthetic pathway is from malonyl- CoA (1) to noreugenin (2). The pentaketide chromone synthase AaPCS from Aloe arborescens is the only reported enzyme to catalyze this type of reaction15. Thus, we conducted a local blastn search using AaPCS as a query, and ten candidate genes with \(e\) values \(< 10^{- 21}\) were discovered. The expression levels (FPKMs) of one gene, SdPCS, was highly correlated with the furochromones contents with Pearson correlation coefficient (PCC) \(> 0.95\) (Supplementary Table 7). It was sub- cloned into the pET28a (+) vector for protein expression in E. coli BL21 (DE3) cells. The function was characterized by enzyme catalysis reactions with 1 as substrate. According to high- performance liquid chromatography (HPLC) and LC/MS analyses, SdPCS generated a new peak, which was identified as 2 by comparing with a reference standard. From the genome of S. divaricata, we further discovered SdPCS2 with the same function (Fig. 2a). The sequence similarity between SdPCS and SdPCS2 was 91.33% (Supplementary Fig. 9).
+
+<|ref|>text<|/ref|><|det|>[[85, 644, 912, 916]]<|/det|>
+To discover prenyltransferase (PT) converting 2 to peucenin (3), we obtained one candidate gene SdPT (PCC \(> 0.95\) , Supplementary Table 8) among the 20 annotated PT genes. SdPT was sub- cloned to pESC- Leu vector and expressed in yeast WAT11 cells28. When the yeast microsomes were incubated with 2, DMAPP and \(\mathrm{MgCl}_2\) , HPLC analysis showed a new product, which exhibited an \([\mathrm{M} + \mathrm{H}]^+\) ion at \(m / z\) 261.11 in LC/MS analysis. The MS/MS spectrum showed an abundant \([\mathrm{M} - 56 + \mathrm{H}]^+\) fragment at \(m / z\) 205.05, indicating a prenyl substitution at C- 6 or C- 829 (Fig. 2b). Then we purified 0.8 mg of the product from scaled- up enzymatic reactions. The \(^1\mathrm{H}\) - NMR spectrum showed two methylene signals at \(\delta_{\mathrm{H}}3.17\) (m, H- 1'), one olefinic signal at \(\delta_{\mathrm{H}}5.16\) (t, \(J = 6.0\mathrm{Hz}\) , H- 2'), and two methyl signals at \(\delta_{\mathrm{H}}1.61\) (H- 4') and 1.71 (H- 5'), indicating the presence of an isoprenyl group. The HMBC cross peaks from H- 1' to C- 5 ( \(\delta_{\mathrm{C}}158.1\) ), C- 6 ( \(\delta_{\mathrm{C}}111.1\) ) and C- 7 ( \(\delta_{\mathrm{C}}164.8\) ) indicated the isoprenyl group was located at C- 6
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 911, 193]]<|/det|>
+(Supplementary Figs. 10–13). Thus, the product was identified as peucenin (3) (Supplementary Table 9). SdPT represented the first prenyltransferase utilizing chromones as substrate. We also obtained SdPT2 which showed the same function with gene sequence similarity of \(85.79\%\) (Supplementary Fig. 14).
+
+<|ref|>text<|/ref|><|det|>[[85, 227, 912, 693]]<|/det|>
+Few enzymes are known to catalyze the oxidative cyclization of isoprenyl groups, except for several CYP450 enzymes involved in the biosynthesis of furocoumarins19- 21. Since these enzymes belong to the CYP736 family, we screened candidates from the same family in S. divaricata, and chose four potential genes whose expression levels were highly correlated with the furochromones contents (PCC >0.90, Supplementary Table 10). When SdPC was expressed in yeast WAT11 cells28, incubation of the yeast microsomes with 3 and NADPH yielded a new product. LC/MS analysis showed an [M+H]+ ion at m/z 277, which could fragment into m/z 259 and m/z 205. Its structure was proposed to be visamminol (4). As no reference standard was available, we prepared 4 through hydrolysis of visamminol 3'-O-glucoside catalyzed by β-glucosidase (Supplementary Fig. 15), and confirmed its structure by NMR analysis. The 1H-NMR spectrum showed two methyl signals at δH 1.13 (s, H-4') and δH 1.14 (s, H-5'), a tertiary proton signal at δH 4.71 (t, J = 8.6 Hz, H-2'), and a methylene signal at δH 3.02 (d, J = 8.6 Hz, H-1'), indicating the presence of a furan ring. The HMBC cross peaks from H-2' (δH 4.71) to C-1' (δC 26.6), C-7 (δC 166.4), and C-6 (δH 109.5) indicated the furan ring was conjugated with the benzene ring (Supplementary Figs. 16-19, Supplementary Table 9). HPLC and LC/MS analyses indicated the product had the same retention time and mass spectra with 4 (Fig. 2c). As the oxidative cyclization of isoprenyl phenolic compounds by chemical synthesis requires strong oxidizers like m-chloroperbenzoic acid30, SdPC represents an efficient enzyme catalyst for this reaction.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[85, 95, 910, 578]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 591, 911, 689]]<|/det|>
+Fig. 2. Biosynthesis of the furochromone skeleton, demonstrating the functional characterization of SdPCS (a), SdPT (b), and SdPC (c). Shown are HPLC/UV chromatograms of enzyme catalysis reactions ( \(\lambda = 280 \mathrm{nm}\) ), together with (+)-ESI-MS and MS/MS spectra of the products. Control, reaction mixtures incubated with boiled enzymes or microsomes.
+
+<|ref|>sub_title<|/ref|><|det|>[[85, 729, 624, 747]]<|/det|>
+## Post-modification steps for the biosynthesis of furochromones.
+
+<|ref|>text<|/ref|><|det|>[[85, 756, 912, 915]]<|/det|>
+C- 11 of compounds 7- 9 is hydroxylated, indicating the presence of a CYP450 enzyme. However, very few enzymes have been reported to catalyze a similar reaction, and no suitable templates are available for gene blast search. By analyzing the transcriptome data, we selected 12 candidate CYP genes, whose expression levels were highly correlated with the total contents of 8 and 9 ( \(\mathrm{PCC} > 0.95\) , Supplementary Table 11). These genes were expressed in yeast WAT11 cells, and the microsomes were incubated with NADPH (Tris- HCl buffer, 50 mM) for functional characterization. LC/MS analysis
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[86, 88, 911, 137]]<|/det|>
+indicated that SdCH could convert **4** and **5** (5- O- methylvisamminol) into **7** (norcimifugin) and **8** (cimifugin), respectively (Fig. 3a, Supplementary Fig. 20).
+
+<|ref|>text<|/ref|><|det|>[[86, 172, 911, 248]]<|/det|>
+Likewise, we discovered the 5- O- methyltransferase SdOMT which converted **4** and **7** into **5** and **8**, respectively (PCC > 0.90, Supplementary Table 12). Its function was characterized by enzymatic reaction and LC/MS analysis (Fig. 3b, Supplementary Fig. 21).
+
+<|ref|>text<|/ref|><|det|>[[85, 283, 912, 608]]<|/det|>
+Glycosylation is the final step in the biosynthetic pathway. A total of 8 UGT genes with FPKM>10 in the roots were chosen as candidate genes, and were cloned and expressed in _E. coli_ BL21(DE3) (Supplementary Table 13). The functions were characterized by enzymatic catalysis with UDP- Glc (UDPG) as sugar donor, and **5** or **8** as sugar acceptor. SdUGT1 could catalyze the glucosylation of 3'- OH of **5** (tertiary alcohol) and 11- OH of **8** (primary alcohol) to produce **6** (5- O- methylvisamminoside, 5- O- MVG) and **9** (prim- O- glucosylcimifugin, POG), respectively. The products could lose 162 Da in the MS/MS spectra, and their structures were identified by comparing with reference standards (Fig. 3c- d). Moreover, we discovered SdUGT2, which exhibited a high sequence similarity (54.93%) with SdUGT1 and showed the same enzymatic activities (Supplementary Fig. 22). We noticed that SdUGT1 and SdUGT2 only catalyzed 11- O-, but not 3'- O- glycosylation of **8**. Consistently, these two UGTs showed 2.8 or 31- fold higher catalytic efficiency (\(k_{\text{cat}}/K_{\text{m}}\) value) with **8** than with **5** as substrate (Fig. 3e, Supplementary Figs. 23- 24).
+
+<|ref|>text<|/ref|><|det|>[[85, 644, 912, 916]]<|/det|>
+To elucidate mechanisms for the preference towards 11- OH, we solved the crystal structure of SdUGT2 in complex with UDP through X- ray diffraction (PDB ID: 8ZNK, 1.88 Å) (Fig. 3f, Supplementary Fig. 25, Supplementary Table 14). The structure of SdUGT2 showed a typical GT- B fold with two Rossmann- like \(\beta /\alpha /\beta\) domains. The N- terminal domain (NTD, residues 1- 261 and 454- 480) and the C- terminal domain (CTD, residues 262- 453) are primarily responsible for sugar acceptor and sugar donor binding, respectively. Subsequently, we simulated the SdUGT2/UDPG model based on the structure of GgCGT/UDPG31. Two potential binding modes of **8** were obtained through molecular docking32. In both modes, His32 is close to the glycosylation sites (11- OH or 3'- OH) with a distance below 3.1 Å. Thus, the hydroxyl groups could be easily deprotonated to initiate the glycosylation reaction. Notably, the sugar moiety of sugar donor and hydroxy group of sugar acceptor
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[80, 90, 911, 163]]<|/det|>
+should form an obtuse angle for inverting GTs33. The docking results showed that the angle for 11- O-glycosylation was over \(90^{\circ}\), whereas the angle for 3'- O-glycosylation was less than \(90^{\circ}\). This result interpreted why SdUGT2 showed high preference towards 11- OH.
+
+<|ref|>image<|/ref|><|det|>[[90, 200, 888, 900]]<|/det|>
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 91, 912, 220]]<|/det|>
+Fig. 3. Post-modification reactions for the biosynthesis of furochromones, demonstrating the functional characterization of SdCH (a), SdOMT (b), and SdUGT1/2 (c, d). Shown are HPLC/UV chromatograms of the enzyme catalysis reactions ( \(\lambda = 280 \mathrm{nm}\) ), together with (+)-ESI-MS and MS/MS spectra of the products. e, Kinetic parameters of SdUGT1 and SdUGT2. f, Crystal structure of SdUGT2. STD, reference standard. Control, reaction mixtures incubated with boiled enzymes or microsomes.
+
+<|ref|>text<|/ref|><|det|>[[85, 255, 914, 527]]<|/det|>
+Thus, by combining chemical analysis and genomic and transcriptomic data mining, we identified seven enzymes from S. divaricata catalyzing biosynthesis of the two major furochromones 6 and 9. These genes are located at different chromosomes. Specifically, SdCH and SdUGT1 are located at Chr1, SdPCS and SdPC at Chr2, SdPT at Chr3, SdOMT at Chr6, and SdUGT2 at Chr8 (Fig. 4a). The absence of a biosynthetic gene cluster suggests expressions of these genes are not co- regulated. To our knowledge, this is the first work to unravel the complete biosynthetic pathway of furochromones. The expression levels of identified genes, except for SdUGT1 and SdUGT2, are highly correlated with the distribution of major furochromones among different organs of S. divaricata. Both SdUGT1 and SdUGT2 showed strong preference for 11- OH, which is consistent with the lack of furochromone \(3^{\prime},11\) - di- \(O\) - glucosides in S. divaricata8.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 562, 707, 580]]<|/det|>
+## De novo biosynthesis of Saposhnikovia furochromones in tobacco leaves.
+
+<|ref|>text<|/ref|><|det|>[[85, 589, 914, 785]]<|/det|>
+POG and 5- O- MVG are important bioactive compounds in S. divaricata, and their extraction and purification are time and labor- consuming. It is imperative to engineer the biosynthetic pathway in chassis organisms. In this work, we realized the de novo biosynthesis of furochromones in tobacco leaves. Transient expression of the seven genes in tobacco leaves revealed that all genes showed the expected catalytic activities, and the corresponding products were detected (Fig. 4b–c). When all the seven genes were infiltrated into tobacco leaves, 6 and 9 could be produced at a yield of \(11.54 \mu \mathrm{g / g}\) and \(4.21 \mu \mathrm{g / g}\) (dry weight), respectively.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[95, 90, 900, 680]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 703, 912, 830]]<|/det|>
+Fig. 4. The dissected biosynthetic pathway of furochromes and their de novo biosynthesis in tobacco leaves. a, Genomic location of biosynthetic genes in S. divaricata. b–c, Catalytic functions of biosynthetic genes responsible for the formation (b) and modification (c) of furochrome skeleton. Extracted ion chromatograms (EICs) of biosynthetic products in LC/MS analysis are shown. STD, reference standards. EV, agrobacterium-mediated transient expression using vector without any biosynthetic genes.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 858, 799, 876]]<|/det|>
+## The distribution of furochromones and their biosynthetic genes in Apiaceae plants.
+
+<|ref|>text<|/ref|><|det|>[[120, 883, 909, 902]]<|/det|>
+To gain a deep insight into the evolution of biosynthetic pathway of furochromones in Apiaceae,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 82, 914, 348]]<|/det|>
+we incorporated another seven Apiaceae species (Coriandrum sativum, Apium graveolens, Angelica sinensis, Ligusticum chuanxiong, Daucus carota, Bupleurum chinense, Centella asiatica) into metabolic, comparative genomic and transcriptomic analyses (Supplementary Tables 15- 18). These species represented different evolutionary lineages, including the subfamilies Mackinlayoideae and Apiodeae (including the tribe Bupleureae, Apieae, Sinodielsia Clade, Selineae). We first determined and compared the contents of four typical furochromones (5, 6, 8, and 9) among the eight species (Supplementary Figs. 26- 46). Unexpectedly, the furochromones did not show a stepwise accumulation along the phylogeny backbone but exhibited a drastic enrichment in S. divaricata. The contents of furochromones in the other species were generally low (Fig. 5a, Supplementary Table 19). This result implied substantial differences in furochromone biosynthesis between S. divaricata and the other Apiaceae plants.
+
+<|ref|>text<|/ref|><|det|>[[85, 377, 914, 643]]<|/det|>
+To investigate the evolutionary shift in furochromone biosynthesis from early diverged Apiaceae lineage to S. divaricata, we constructed a maximum likelihood (ML) phylogeny of Apiaceae based on 398 strict single- copy orthologous genes (Fig. 5a). It revealed that S. divaricata belonged to the latest diverged clade including C. sativum. Then, the conserved syntenic gene blocks containing each furochromone- biosynthetic gene was identified in each Apiaceae species (Supplementary Figs. 47- 57). The syntenic and homologous genes of most downstream tailoring genes, including OMT, CH and UGTs, were detected in all the Apiaceae species (Supplementary Figs. 47- 53). However, the syntenic genes of two skeleton- forming genes, SdPCS and SdPC were not detected in any other Apiaceae species (Fig. 5 and Fig. 6a). This clue motivated us to speculate that most Apiaceae species except S. divaricata may not contain any functional PCS and PC, thus leading to low furochromone content. To test this hypothesis, we focused on potential Apiaceae PCSs and PCs.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 672, 827, 691]]<|/det|>
+## Proximal duplication of SdPCS promotes furochromone accumulation in S. divaricata.
+
+<|ref|>text<|/ref|><|det|>[[85, 697, 914, 914]]<|/det|>
+We retrieved all potential PKS III genes in S. divaricata and the other seven Apiaceae species and constructed an ML tree, on which a strongly supported (bootstrap support value (BS) = 100) clade containing SdPCS and 19 potential Apiaceae PCSs was identified (Fig. 5b). Most genes in this clade were in the same syntenic region, implying they shared the same ancestor (Supplementary Fig. 56). No PCS was detected in C. asiatica, one of the most basal species in Apiaceae, indicating that PCS may first emerge in the Apiodeae subfamily. Then we expressed and characterized all the 19 genes, and compared their functions by enzymatic assays (Fig. 2a, Supplementary Figs. 58- 63). Most of these enzymes showed similar catalytic abilities by converting 1 to 2 (Fig. 5b). However, the expression level of SdPCS in the root of S. divaricata was remarkably higher than the other Apiaceae homologous
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 134, 912, 422]]<|/det|>
+We are aware that direct inter-species comparison of FPKM might lead to misinterpretation since the utilization of FPKM value is usually limited to intra-species level. Instead, we compared the FPKM ratio between SdPCS and other potential Apiaceous PCSs against 9,470- 27,214 pairs of orthologous genes as genomic background. It showed the \(\log_{2}\) (FPKM ratio) value of \(>95\%\) genome- wide ortholog pairs between S. divaricata and other Apiaceous species in root/rhizome is \(< 5.00\) , with a mean near zero (- 0.005). This result indicates that FPKM values of the investigated species are basically comparable. It is noteworthy that the \(\log_{2}\) (FPKM ratio) between SdPCS and other Apiaceous PCSs in root/rhizome, ranging from 6.12 to 20.63 (mean \(= 14.15\) ), was higher than \(95\%\) of genome- wide orthologous gene pairs (Fig. 5c). Thus, we deduced the expression abundance of SdPCS was significantly higher than other Apiaceous PCSs. As the initial step is usually the rate- limiting step in biosynthetic pathway34, the exceptionally high expression of SdPCS may contribute to the furochromone accumulation in S. divaricata.
+
+<|ref|>text<|/ref|><|det|>[[85, 450, 913, 691]]<|/det|>
+Moreover, we traced the origin of SdPCS (SaDchr02G001054), and found it might originate from proximal duplication of the nearby SdPCS2 (SaDchr02G001052) (Fig. 5d). The PCS ML tree revealed that the two PCS copies in S. divaricata clustered in the same clade, indicating SaDchr02G001054 was originated from S. divaricata specific duplication event rather than from ancestor species. The syntenic analysis further confirmed this deduction. Although syntenic genes of SdPCS were not detected in other Apiaceous species, those of the ancestral SdPCS2 were identified in most species (Fig. 5d). Remarkably, we found that SdPCS2 was nearly not expressed in any tissue (Fig. 5e), and its syntenic genes in other Apiaceous species were almost not expressed, either (Supplementary Table 20). Thus, the proximal duplication and high expression of SdPCS profoundly contributed to the biosynthesis of furochromones in the root of S. divaricata.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[100, 88, 888, 900]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[90, 882, 911, 900]]<|/det|>
+Fig. 5. High expression of SdPCS2 promotes the accumulation of furochromones in the root of S. divaricata. a,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 83, 912, 230]]<|/det|>
+Contents of typical furochromones in various organs of Apiaceae plants, and syntenic gene analysis. b, Phylogenetic relationships, enzymatic activities, and expression abundance of Apiaceae \(PCSs\) . The PCS enzyme activity was quantified by HPLC/UV peak area of generated noreugenin (2) \((\lambda = 280 \mathrm{nm})\) . c, Comparison of the FPKM between \(SdPCS\) and other potential Apiaceae \(PCSs\) in the genome- wide context. Each red line represents a \(\log_2\) (FPKM ratio) between \(SdPCS\) and a potential Apiaceae \(PCS\) . Each grey density plot indicates the \(\log_2\) (FPKM ratio) distribution of genome- wide orthologous genes of one Apiaceae species. d, Syntenic regions containing Apiaceae \(PCSs\) . e, Expression levels of three \(PCS\) copies in \(S\) . divaricata.
+
+<|ref|>sub_title<|/ref|><|det|>[[85, 259, 849, 302]]<|/det|>
+## The absence of functional \(PC\) gene leads to low furochromone content in most Apiaceae plants.
+
+<|ref|>text<|/ref|><|det|>[[85, 308, 912, 598]]<|/det|>
+Likewise, we did not detect syntenic genes of \(SdPC\) in other Apiaceae plants (Fig. 6a). We retrieved all Apiaceae \(CYP736s\) and constructed an ML tree. The reported \(PpDC\) was also included19. A robust clade (BS = 100) containing \(SdPC\) and 18 other potential \(PCs\) was identified (Fig. 6b, Supplementary Fig. 57). Although DCAR_313045 and As05G002751 were not included in this clade, they were syntenic with several genes, e.g., SaDchr05G002066 and LCX7BG003145 (Supplementary Fig. 64). The 11 potential \(PCs\) from \(A\) . sinensis lost one exon and was likely to lose the cyclization activity, thus they were not included in further assays. Finally, we cloned and characterized the other 10 potential \(PCs\) . Strikingly, none of them except for \(SdPC\) was effective in producing visamminol (4) (Fig. 6c). This observation confirmed our hypothesis that the absence of \(PC\) genes may lead to the low contents of furochromones in most Apiaceae species. However, we cannot exclude the possibility that these or other potential \(PCs\) might weakly catalyze the reactions in vivo, as trace furochromones were detected in all Apiaceae plants.
+
+<|ref|>text<|/ref|><|det|>[[85, 626, 912, 793]]<|/det|>
+Since PpDC participated in the generation of furocoumarins19, we tested the catalytic activities of homologous PCs using demethylisuberosin as substrate. SdPC4, AsDC, LcPC2 and DcPC showed cyclization activities (Supplementary Fig. 65). However, SdPC could not catalyze this reaction despite its high sequence similarity with SdPC4 (Supplementary Fig. 66). Interestingly, these four genes were located at the same syntenic block, which did not include \(SdPC\) (Supplementary Fig. 64). Thus, SdPC is a homologous enzyme with novel function, and its evolutionary origin warrants to be investigated in the future.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[103, 88, 900, 679]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 688, 912, 770]]<|/det|>
+Fig. 6 The absence of functional \(PC\) leads to low furochrome content in most Apiaceae plants. a, Syntenic regions containing \(SdPC\) . The syntenic gene pairs are connected by grey lines. b, Phylogenetic relationship and gene structure of Apiaceae PCs. As05G02748 (AsDC) is the same as AS05g00644 in the initial annotation version. c, HPLC/UV chromatograms showing the in vitro enzymatic activity of potential Apiaceae PCs \((\lambda = 280 \mathrm{nm})\) .
+
+<|ref|>text<|/ref|><|det|>[[85, 806, 912, 909]]<|/det|>
+Furochromones emerge as an important class of bioactive nature products in medicinal plants. However, little is known on their biosynthesis14,15. Particularly, the formation of furan ring and post modifications leading to structural diversities of furochromones remain largely unexplored. This work dissected the complete biosynthetic pathway of prim- \(O\) - glucosylcimifugin and 5- \(O\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 90, 913, 248]]<|/det|>
+methylvisamminoside, two bioactive furochromone glucosides abundant in S. divaricata. Nine biosynthetic enzymes in the biosynthetic pathways were characterized. Among them, proximal duplication and high expression of a pentaketide chromone synthase gene SdPCS, as well as the presence of a lineage- specific peucenin cyclase gene SdPC, contribute to the accumulation of furochromones in the roots of S. divaricata. The results provide new insights into the biosynthesis of furochromones and serve as a platform for their metabolic engineering production.
+
+<|ref|>text<|/ref|><|det|>[[85, 283, 913, 498]]<|/det|>
+In recent years, the biosynthetic evolution of natural products in plant kingdom has attracted increasing interest. For example, Berman et al illustrated the parallel evolution of cannabinoid biosynthesis35, and Jiao et al studied the independent loss of biosynthetic pathway for two tropane alkaloids in the Solanaceae family36. In the present work, SdPCS is likely to originate from SdPCS2 through proximal duplication. However, the origin of SdPC still remains unknown. Moreover, some homologous enzymes of SdPC in S. divaricata and other species catalyze the generation of furocoumarins but not furochromones. Catalytic mechanisms and structural evidences for substrate selectivity of these enzymes also warrants further investigation.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 535, 166, 551]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 562, 295, 580]]<|/det|>
+## Materials and Reagents
+
+<|ref|>text<|/ref|><|det|>[[86, 589, 912, 664]]<|/det|>
+The sources of fresh plants of Saposhnikovia divaricata, Centella asiatica, Bupleurum chinense, Daucus carota, Angelica sinensis, Apium graveolens, and Coriandrum sativum are given in Supplementary Table 15. To extract RNA, the roots, leaves, and petioles were used.
+
+<|ref|>text<|/ref|><|det|>[[85, 700, 916, 915]]<|/det|>
+The chemical reference standards and sugar donors used in this study were purchased from YuanYe Biotechnology Co., Ltd. (Shanghai, China). Methanol and acetonitrile (Thermo Fisher Scientific, USA) were of HPLC grade. The conversion rates were determined by HPLC/UV analysis on an Agilent HPLC 1260 instrument. Samples were separated on a Zorbax SB- C18 column (4.6×250 mm, 5 μm, Agilent, USA). The column temperature was 30°C. To calculate the conversion rates, peak areas of both substrate and product were integrated by Chromeleon® at a certain wavelength. LC/MS analysis was performed on a Q- Exactive quadrupole Orbitrap mass spectrometer (Thermo Fisher Scientific, USA).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[88, 119, 490, 137]]<|/det|>
+## Genome sequencing, assembly, and annotation
+
+<|ref|>text<|/ref|><|det|>[[85, 145, 913, 555]]<|/det|>
+For the PacBio library construction, \(15\mu \mathrm{g}\) genomic DNA from the leaves of S. divaricata was fragmented into approximately \(15\mathrm{kb}\) using g- TUBEs (Covaris, USA). After removing short fragments and single- strand overhangs, the retained fragments were converted into the proprietary SMRTbell library with the PacBio DNA Template Preparation Kit (Pacific Biosciences, CA, USA). Single Molecule Real Time (SMRT) sequencing was performed on a PacBio Sequel II sequencing platform. For Hi- C library construction, chromatin was first fixed in place with formaldehyde in the nucleus and then extracted. The extracted chromatin was digested with DpnII. The \(5^{\prime}\) overhangs of resulting fragments were then filled in with biotinylated nucleotides, and free blunt ends were ligated. After ligation, the DNA was purified from protein and treated following the Illumina Next Generation manufacturer's instructions. The libraries were subsequently sequenced on Illumina Hiseq X, producing 190.37 Gb \(2\times 150\) bp paired- end reads. The raw data of PacBio subreads was filtered to HiFi reads by PBccs (v6.4.0) (https://github.com/PacificBiosciences/ccs), and subsequently assembled with Hifiasm (v0.16.0) \(^{37}\) . The initial assembled contigs were anchored to chromosomes by 3D- DNA pipeline (v201008) \(^{38}\) and further manually adjusted to produce a chromosome- level genome. BUSCO (v5.4.3) \(^{39}\) was used for benchmarking the genome with the "embryophyte_odb10" database.
+
+<|ref|>text<|/ref|><|det|>[[85, 588, 913, 916]]<|/det|>
+EDTA (v2.0.0) \(^{40}\) was used to de novo identify, annotate, and classify the repetitive elements in the genome of S. divaricata. Prior to protein- coding gene annotation, the annotated repetitive elements in the genome were soft masked with bedtools (v2.28.0) \(^{41}\) . RNA- Seq raw reads of S. divaricata were filtered with fastx- toolkits (v0.0.14) (http://hannonlab.cshl.edu/fastx_toolkit/index.html) and then assembled through Hisat2 (v2.2.1) \(^{42}\) and Stringtic (v2.2.0) \(^{43}\) . The raw assembly of transcripts was further validated by PASA (v2.5.1) \(^{44}\) , which were then incorporated into the MAKER (v3.01.03) \(^{45}\) pipeline to automatically identify protein- coding genes. Finally, the gene models identified by MAKER were updated by PASA (v2.5.1) \(^{44}\) . Function annotations of the protein- coding genes were carried out by BLASTP searches against entries in both NCBI non- redundant protein (NR) (https://www.ncbi.nlm.nih.gov/) and Swiss- Prot (https://www.uniprot.org/) databases. The prediction of conserved domains for the genes was performed by InterProScan (v5.11- 51.0) \(^{46}\) . The annotations of the GO terms (http://geneontology.org/) and KEGG pathways (https://www.genome.jp/kegg/) for the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[87, 90, 564, 110]]<|/det|>
+genes were annotated with eggNOG- mapper (v2.1.10- 0)47.
+
+<|ref|>sub_title<|/ref|><|det|>[[87, 145, 660, 164]]<|/det|>
+## Total RNA isolation, RNA-Seq, and gene expression quantification
+
+<|ref|>text<|/ref|><|det|>[[87, 172, 917, 304]]<|/det|>
+The total RNA was extracted with the TranZol™ kit (Transgen Biotech, China) following the manufacturer's instructions, and was used to synthesize the first- stranded complementary DNA (cDNA) with TransScript one- step genomic DNA (gDNA) removal and cDNA synthesis SuperMix (Transgen Biotech, China). The transcriptome data of different tissues of S. divaricata were sequenced at Novogene Co., Ltd. (Beijing, China).
+
+<|ref|>text<|/ref|><|det|>[[87, 338, 912, 414]]<|/det|>
+The raw RNA- seq reads were filtered in fastp48 with default parameters and then mapped to the reference genome of S. divaricata by Hisat2 (v2.2.1)42. The counts of reads mapping to exons of each gene were calculated by featureCounts49. The FPKM value of each gene was calculated in R.
+
+<|ref|>sub_title<|/ref|><|det|>[[87, 450, 595, 469]]<|/det|>
+## Genome-wide mining for furochromone biosynthesis genes
+
+<|ref|>text<|/ref|><|det|>[[87, 477, 912, 637]]<|/det|>
+HMMER3 (v3.3.2)50 was used to identify 47PKSs, PTs, CYPs, OMTs and UGTs with an e- value of 1e- 6. The HMMER profiles PF02797 and PF00195 were used for PKS III search. PF01040 and PF00067 was utilized to identify CYPs and PTs. PF00891 and PF08100 were employed to search OMTs, PF00201 was applied for UGT identification. The possible pseudogenes (length of predicted CDS \(< 200\) amino acids) were discarded. Gene structures of all candidate genes were manually adjusted with IGV- GSAman (https://gitee.com/CJchen/IGV- sRNA).
+
+<|ref|>text<|/ref|><|det|>[[87, 672, 912, 775]]<|/det|>
+Pearson correlation coefficients and the \(P\) values between contents of furochromones and the FPKM of genes among different tissues of S. divaricata were calculated with the corr.test function in R package psych (https://rdocumentation.org/packages/psych/versions/2.3.3). Those unexpressed genes were not incorporated in correlation analysis.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 812, 436, 830]]<|/det|>
+## Phylogenetic and microsynteny analyses
+
+<|ref|>text<|/ref|><|det|>[[87, 839, 912, 914]]<|/det|>
+ML phylogeny was constructed based on 398 strict single- copy orthologous genes identified by OrthoFinder (v2.5.4)51 to clarify the phylogenetic relationship among the eight Apiaceae species. The protein sequences were aligned by MUSCLE (v5.1.1. linux64)52 and subsequently concatenated by
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 912, 192]]<|/det|>
+Phylosuite (v1.2.2) \(^{53}\) . ModelTest- NG (v0.1.7) \(^{54}\) was used to detect the best- fit amino acid substitution model, based on which RAxML- NG (v1.1.0) \(^{55}\) was employed to construct the ML phylogeny with 1,000 bootstrap analyses. The construction of phylogeny of biosynthetic genes follows the same method above.
+
+<|ref|>text<|/ref|><|det|>[[85, 226, 913, 479]]<|/det|>
+The microsyntenic analyses generally followed the methods of Griesmann et al. (2018) and Yang et al. (2023). All vs. all blastp (E- value \(= 1\mathrm{e}^{- 5}\) ) was conducted for the protein sequences among eight Apiaceae genomes with BLAST (v2.13.0+) \(^{56}\) . The output protein identity matrix was loaded in JCVI (v1.2.7) to produce collinear gene blocks. Subsequently, we identified the syntenic region containing the furochromone biosynthetic genes \((\pm 100\mathrm{kb})\) in each species using the genome of S. divaricata as the reference. Because the syntenic retention varied between different species pairs, we compared the syntenic gene pairs for all species pairs and retained those gene pairs demonstrating consistent syntenic relationships. To eliminate the bias induced by mistaken annotation, we manually checked the corrected gene structure in syntenic region and re- organized the microsyntenic gene pairs.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 516, 248, 533]]<|/det|>
+## Molecular cloning
+
+<|ref|>text<|/ref|><|det|>[[86, 542, 913, 672]]<|/det|>
+The full- length candidate genes were amplified from cDNA with TransStart FastPfu DNA Polymerase (Transgen, China). Candidate genes for PCS, OMT and UGT were recombined in the pET- 28a (+) vector (Invitrogen, USA) at BamH I site. Candidate genes for PT, PC and CH were cloned into pESC- Leu vector at BamH I (Invitrogen, USA). Sequences of the primers used in this study are listed in Supplementary Table 21.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 710, 459, 728]]<|/det|>
+## Expression of candidate biosynthetic genes
+
+<|ref|>text<|/ref|><|det|>[[85, 737, 913, 896]]<|/det|>
+The recombinant plasmids for PCS, OMTs and OGTs were introduced into E. coli BL21 (DE3) (Transgen Biotech, China) for heterologous expression. The E. coli cells were grown in \(500\mathrm{mL}\) Luria- Bertani medium containing kanamycin (50 \(\mu \mathrm{g / mL}\) ) at \(37^{\circ}\mathrm{C}\) . After \(\mathrm{OD}_{600}\) reached 0.4–0.6, the cells were induced with \(0.1\mathrm{mM}\) IPTG at \(18^{\circ}\mathrm{C}\) . After 18–24 h, the cell pellets were harvested by centrifugation (7,500 rpm, 3 min at \(4^{\circ}\mathrm{C}\) ), and then resuspended in \(15\mathrm{mL}\) lysis buffer ( \(50\mathrm{mMNaH_2PO_4}\) pH 8.0, \(300\mathrm{mMNaCl}\) , \(30\mathrm{mM}\) imidazole, pH 8.0). Then cells were disrupted by sonication on ice, and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 90, 912, 220]]<|/det|>
+the cell debris was removed by centrifugation at 7,500 rpm for 50 min at \(4^{\circ}\mathrm{C}\) . The supernatant was collected and loaded onto a pre-equilibrated column (His Trap™ HP, 5 mL, GE Healthcare), and eluted with different concentrations of elution buffer (50 mM \(\mathrm{NaH_2PO_4}\) , pH 8.0, 300 mM NaCl, 30/300 mM imidazole) \(^{57}\) . The purified protein solution was added with approximately 0.5 mL glycerol (25%) and stored at \(- 80^{\circ}\mathrm{C}\) .
+
+<|ref|>text<|/ref|><|det|>[[85, 256, 912, 444]]<|/det|>
+The recombinant plasmids for PT, PC and CH were introduced into yeast strain Saccharomyces cerevisiae WAT11 for heterologous expression. The yeast cells were grown in synthetic dropin medium without leucine (SD- Leu). Liquid cultures of the recombinant strains were set up by picking a single colony and growing in \(50~\mathrm{mL}\) of SD- Leu medium containing \(20~\mathrm{g / L}\) glucose at \(28^{\circ}\mathrm{C}\) overnight. The cells were collected by centrifugation (1,000 g, 2 min) and resuspended in \(25~\mathrm{mL}\) of SD- Leu medium containing \(20~\mathrm{g / L}\) galactose to induce target protein expression for 24- 48 hours at \(28^{\circ}\mathrm{C}\) . The microsomes of yeast cells were prepared as reported \(^{28}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 480, 280, 497]]<|/det|>
+## Enzyme activity assay
+
+<|ref|>text<|/ref|><|det|>[[85, 506, 912, 860]]<|/det|>
+The purified proteins and prepared microsomes were used for functional characterization by in vitro enzymatic reactions. The reactions were conducted in \(100~\mu \mathrm{L}\) Tris- HCl buffer (50 mM, pH 8.0) containing \(50~\mu \mathrm{g}\) purified enzymes or \(20~\mu \mathrm{L}\) microsomes. The incubation mixtures include substrates (0.1 mM, malonyl- CoA for PCSs, noreguenin for PTs, peucenin for PCs, visamminol for OMTs and CHs, 5- O- methylvisamminol for CHs and SdUGT1/2, norcimifugin for OMTs, and cimifugin for SdUGT1/2), and donors/cofactors (0.5 mM, dimethylallyl pyrophosphate (DMAPP) for PTs, nicotinamide adenine dinucleotide phosphate (NADPH) for PCs and CHs, S- adenosylmethionine (SAM) and dithiothreitol (DTT) for OMTs, and uridine diphosphate glucose (UDPG) for SdUGT1/2). The reactions continued in a shaking incubator for 2 hours ( \(37^{\circ}\mathrm{C}\) for OMTs and UGTs, \(30^{\circ}\mathrm{C}\) for PCSs, PTs, PCs and CHs). For PCSs, reactions were terminated by adding \(10~\mu \mathrm{L}\) \(20\%\) HCl followed by extraction with \(300~\mu \mathrm{L}\) ethyl acetate and redissolution in \(100~\mu \mathrm{L}\) MeOH. The other reactions were terminated by adding \(100~\mu \mathrm{L}\) ice- cold MeOH. The mixtures were then centrifuged at 15,000 rpm for 20 min. The supernatants were analyzed by HPLC and LC/MS.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 912, 340]]<|/det|>
+The conversion rates in percentage were calculated from peak areas of products and substrates in HPLC/UV chromatograms (Agilent 1260, USA). Samples were separated on a Zorbax SB- C18 column (4.6×250 mm, 5 μm, Agilent, USA). The HPLC methods are shown in Supplementary Table 22. LC/MS analysis was performed on a Q- Exactive hybrid quadrupole- Orbitrap mass spectrometer equipped with a heated ESI source (Thermo Fisher Scientific, USA). The MS parameters were as follows: sheath gas pressure 45 arb, aux gas pressure 10 arb, discharge voltage 4.5 kV, capillary temperature \(350^{\circ}\mathrm{C}\) . MS \(^1\) resolution was set as 70,000 FWHM, AGC target \(1^{*}\mathrm{E}^{6}\) , maximum injection time 50 ms, and scan range \(m / z\) 100–1,000. MS \(^2\) resolution was set as 17,500 FWHM, AGC target \(1^{*}\mathrm{E}5\) , maximum injection time 100 ms, NCE 35.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 376, 511, 395]]<|/det|>
+## Biochemical properties of SdUGT1 and SdUGT2
+
+<|ref|>text<|/ref|><|det|>[[85, 403, 912, 590]]<|/det|>
+To optimize the pH value, different reaction buffers with pH from 4.0–6.0 (citric acid- sodium citrate buffer), 6.0- 8.0 (Na \(_2\) HPO \(_4\) - NaH \(_2\) PO \(_4\) buffer), 7.0- 9.0 (Tris- HCl buffer), and 9.0- 11.0 (Na \(_2\) CO \(_3\) - NaHCO \(_3\) buffer) were tested. To optimize the reaction temperature, the reactions were incubated at 4, 18, 30, 37, 45, or 60 °C. All enzymatic reactions (100 μL reaction mixtures including 0.1 mM 5 or 8, 0.5 mM UDPG, and 10 μg of purified enzyme) were conducted in three parallel experiments ( \(n = 3\) ). The reactions were terminated with pre- cooled methanol and centrifuged at 15,000 rpm for 20 min for HPLC analysis as described above.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 627, 627, 645]]<|/det|>
+## Determination of kinetic parameters of SdUGT1 and SdUGT2
+
+<|ref|>text<|/ref|><|det|>[[85, 654, 912, 840]]<|/det|>
+Reactions were conducted in a final volume of 50 μL with 50 mM reaction buffer, suitable concentration of protein, 1 mol/L of saturated UDPG, and different concentrations of substrate (5 or 8) (Supplementary Table 23). The reactions were quenched with 70 μL pre- cooled methanol after incubating at the optimal temperature for 15 min, and then centrifuged at 15,000 rpm for 20 min. The supernatants were used for HPLC analysis. All experiments were performed in triplicate. The conversion rates were calculated as described above. The kinetic parameters were calculated with Michaelis- Menten plot fitted by Graphapad Prism 8.0 \(^{58}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 877, 351, 894]]<|/det|>
+## Scaled-up enzymatic reactions
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 914, 276]]<|/det|>
+To prepare the prenylated product, the reaction mixtures contained \(100~\mu \mathrm{L}\) buffer (50 mM Tris- HCl, \(\mathrm{pH}8.0\) ), \(0.2\mathrm{mM}\) noreugenin, \(1.0\mathrm{mM}\) DMAPP, \(2.0\mathrm{mM}\) \(\mathrm{MgCl}_2\) , and \(20~\mu \mathrm{L}\) microsome. A total of 1,200 parallel tube reactions were conducted. The reactions were performed at \(30^{\circ}\mathrm{C}\) overnight and terminated by extraction with 4- fold volume of ethyl acetate. The organic solvent was removed under reduced pressure. The residue was dissolved in \(1.5\mathrm{mL}\) of methanol. The products were then purified by reversed- phase semi- preparative HPLC. The structures were characterized by HRMS and extensive 1D and 2D NMR analyses.
+
+<|ref|>text<|/ref|><|det|>[[85, 312, 913, 441]]<|/det|>
+To prepare the hydrolyzed product of visamminol- \(3^{1}\) - O- glucoside, the reaction mixture contained \(20\mathrm{mL}\) buffer ( \(50\mathrm{mM}\mathrm{NaH}_2\mathrm{PO}_4\mathrm{- Na}_2\mathrm{HPO}_4\) , \(\mathrm{pH}6.0\) ), \(0.5\mathrm{mM}\) visamminol- \(3^{1}\) - O- glucoside, and \(200\mathrm{mg}\) \(\beta\) - glucosidase (Solarbio, Beijing, China). A total of 5 parallel tubes were used. The reactions were performed at \(45^{\circ}\mathrm{C}\) for 4 hours and terminated by extraction with 4- fold volume of ethyl acetate. The extract was treated as described above.
+
+<|ref|>sub_title<|/ref|><|det|>[[85, 479, 474, 497]]<|/det|>
+## Crystallization and structural determination
+
+<|ref|>text<|/ref|><|det|>[[83, 505, 914, 887]]<|/det|>
+The full- length cDNA of SdUGT2 was cloned into pET- 28a (+) vector. The S- tag of pET28a was removed. A TrxA- tag and \(6\times\) His- tag followed by thrombin site were added before the N- terminus of the target protein to facilitate purification. The TrxA- His- thrombin- SdUGT2 protein was expressed in E. coli (DE3) strain and purified by Ni- affinity chromatography (GE Healthcare). After purification, the recombinant protein was digested by thrombin to remove tag ( \(4^{\circ}\mathrm{C}\) , \(8\mathrm{h}\) ). The sample was mixed with Ni- NTA affinity beads for the second time to purify the protein. The flow- through was concentrated and then applied to size- exclusion chromatography on a Superdex™ 200 increase \(10 / 300\) GL prepacked column (GE Healthcare) for further purification. The elution buffer was \(20\mathrm{mM}\) Tris- HCl (pH 7.5) and \(50\mathrm{mM}\) NaCl. Fractions containing SdUGT2 were collected and concentrated to 20 mg/mL, flash- frozen on liquid nitrogen, and then stored in a \(- 80^{\circ}\mathrm{C}\) freezer. The purified protein was incubated with \(6\mathrm{mM}\) UDP for \(2\mathrm{h}\) . The crystals of SdUGT2 were obtained after 5 days at \(16^{\circ}\mathrm{C}\) in hanging drops containing \(1\mu \mathrm{L}\) of protein solution and \(1\mu \mathrm{L}\) of reservoir solution ( \(0.2\mathrm{M}\) lithium sulfate monohydrate, \(0.1\mathrm{M}\) Bis- Tris pH 5.25, \(28\%\) \(w / v\) polyethylene glycol 3,350) (Supplementary Fig. 25). The crystals were flash- frozen in the reservoir solution supplemented with \(25\%\) \((v / v)\) glycerol.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 89, 912, 273]]<|/det|>
+The diffraction data of SdUGT2 crystal were collected at beamlines BL19U1 and BL02U1 Shanghai Synchrotron Radiation Facility (SSRF). The data were processed with XDS. The structures were solved by molecular replacement with Phaser. Crystallographic refinement was performed repeatedly with Phenix and COOT. The refined structures were validated by Phenix and the PDB validation server (https://validate-rcsb-1.wwpdb.org/). The final refined structures were deposited in the Protein Data Bank. The diffraction data and structure refinement statistics are shown in Supplementary Table 14.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 312, 253, 329]]<|/det|>
+## Molecular docking
+
+<|ref|>text<|/ref|><|det|>[[85, 339, 912, 470]]<|/det|>
+Since all the reported UGT structures are highly conserved for the UDP- sugar binding domain, we simulated the SdUGT2/UDPG sugar complex structures by superimposing the UDP parts of UDPG to reported structures. Compound 8 was docked into the complex by Autodock. A total of 50 docking conformations were generated. The conformations with the lowest binding energy were selected for further study.
+
+<|ref|>sub_title<|/ref|><|det|>[[86, 507, 519, 525]]<|/det|>
+## De novo biosynthesis of furochromones in tobacco
+
+<|ref|>text<|/ref|><|det|>[[85, 533, 912, 916]]<|/det|>
+The full- length DNA sequences of SdPCS, SdPT, SdPC, SdOMT, SdCH and SdUGT1/2 were amplified with primers given in Supplementary Table 21. The PCR products were sub- cloned into pDonr207 vectors with the Gateway BP Clonase II Enzyme Mix and then cloned into pEAQ- HT- DEST1 vector with the Gateway LR Clonase II Enzyme Mix according to the manufacturer's instructions. The recombinant pEAQ- HT- DEST1- target gene vectors were transformed into Agrobacterium tumefaciens strain GV3101 by chemical conversion method. Single colonies were inoculated at \(28^{\circ}\mathrm{C}\) and subsequently shaked in LB culture medium (50 \(\mu \mathrm{g / mL}\) kanamycin and 50 \(\mu \mathrm{g / mL}\) rifampicin) until \(\mathrm{OD}_{600} = 0.6\) . After centrifugation, bacteria were re- suspended in MMA buffer to \(\mathrm{OD}_{600} = 0.2\) for each strain. Different strains were mixed for transformation. The infection solution was infiltrated into leaves of 5- 6 weeks- old tobacco. After 7 days, the samples were harvested and freeze- dried. The secondary metabolites were extracted by methanol and analyzed by LC/MS. The contents of compounds 5, 6, 8 and 9 were quantified by regression equations. Reference standards 5, 6, 8 and 9 were respectively dissolved in DMSO to make solutions of 1 \(\mathrm{mg / mL}\) , which were 1:1 mixed to obtain the mixed stock solution. The stock solution was serially diluted with methanol containing 4
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 88, 912, 193]]<|/det|>
+\(\mu \mathrm{g / mL}\) bergenin as internal standard to obtain calibration standard solutions (diluted by 2, 4, 8, 16, 32, 64, 128, 256, 512, 1,024, 2,048, 4,096, 8,192, 16,384, 32,768, 65,536 and 131,072 folds, respectively). The regression equations of 5, 6, 8 and 9 were listed in Supplementary Figs. 67–70. The LC/MS method parameters are listed in Supplementary Table 22.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 229, 310, 247]]<|/det|>
+## Metabolite quantification
+
+<|ref|>text<|/ref|><|det|>[[88, 256, 911, 304]]<|/det|>
+The secondary metabolites of different Apiaceae plants were extracted by methanol and analyzed by LC/MS following the methods mentioned above.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 340, 258, 357]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[85, 366, 914, 581]]<|/det|>
+This work was supported by the National Key Research and Development Program of China (No. 2023YFA0914100 to M. Y., and No. 2023YFA0915800 to L. W.), Beijing Natural Science Foundation (No. QY23076 to J.L. Z., and 83001Y0439 to C.X.Z.), and National Natural Science Foundation of China (No. 81725023 to M. Y.). We thank Dr. Rong-shen Wang and Xi-ran Zhang of Ye Lab and Xun- meng Feng and Jiao- jiao Ji of Wang Lab for their technical assistance. We also thank the staff at BL19U1/BL02U1 beamlines at SSRF of the National Facility for Protein Science in Shanghai (NFPS), Shanghai Advanced Research Institute, Chinese Academy of Sciences, for providing technical support in X- ray diffraction data collection and analysis.
+
+<|ref|>sub_title<|/ref|><|det|>[[88, 618, 234, 635]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[85, 643, 914, 888]]<|/det|>
+Data supporting the findings of this study are available in the article, supplementary materials, or public database. The gene sequence data generated in this study have been deposited in the NCBI database under the accession numbers listed in Supplementary Table 24. The crystal structure in this study has been deposited in the RCSB PDB database under the accession number: SdUGT2 (8ZNK). The assembled genome and annotation files of S. divaricata are available at figshare (https://figshare.com/projects/Saposhnikovia_divaricata_genome/206434). The raw data of transcriptome sequencing of S. divaricata have been deposited to the Genome Sequence Archive at the National Genomics Data Center (NGDC) under BioProject no. PRJCA026506. The sources of genome data and RNA-seq data of other Apiaceae plants are listed in Supplementary Tables 16–17.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[30, 100, 912, 910]]<|/det|>
+1. Sun, Y. et al. New chromones from the roots of Saposhnikovia divaricata (Turcz.) Schischk with anti-inflammatory activity. Bioorg. Chem. 134, 106447 (2023).
+2. Abu-Hashem, A. A. & Youssef, M. M. Synthesis of new visnagen and khellin furochromone pyrimidine derivatives and their anti-inflammatory and analgesic activity. Molecules 16, 1956-1972 (2011).
+3. Zhang, T. et al. Multi-omics reveals that 5-O-methylvisammioside prevention acute liver injury in mice by regulating the TNF/MAPK/NF-κB/arachidonic acid pathway. Phytomedicine 128, 155550 (2024).
+4. Wu, L. Q. et al. Antinociceptive effects of prim-O-glucosylcimifugin in inflammatory nociception via reducing spinal COX-2. Biomol. Ther. 24, 418-425 (2016).
+5. Abdelhafez, O. M., Abedelatif, N. A. & Badria, F. A. DNA binding, antiviral activities and cytotoxicity of new furochromone and benzofuran derivatives. Arch. Pharm. Res. 34, 1623-1632 (2011).
+6. Wang, Y. et al. Prim-O-glucosylcimifugin ameliorates aging-impaired endogenous tendon regeneration by rejuvenating senescent tendon stem/progenitor cells. Bone Res. 11, 784-802 (2023).
+7. Amen, Y., Elsbae, M., Othman, A., Sallam, M. & Shimizu, K. Naturally occurring chromone glycosides: sources, bioactivities, and spectroscopic features. Molecules 26, 7646 (2021).
+8. Kreiner, J., Pang, E., Lenon, G. B. & Yang, A. W. H. Saposhnikoviae divaricata: a phytochemical, pharmacological, and pharmacokinetic review. Chin. J. Nat. Med. 15, 255-264 (2017).
+9. Khalil, N., Bishr, M., Desouky, S. & Salama, O. Ammi visnaga L., a potential medicinal plant: a review. Molecules 25 (2020).
+10. Sun, Y., Yang, A. W. H. & Lenon, G. B. Phytochemistry, ethnopharmacology, pharmacokinetics and toxicology of Cnidium monnieri (L.) Cusson. Int. J. Mol. Sci. 21 (2020).
+11. Commission, C. P. Pharmacopoeia of the People's Republic of China. Vol. 1, p156 (China Medical Science and Technology Press, 2020).
+12. Erst, A. S., Petrova, N. V., Kaidash, O. A., Wang, W. & Kostikova, V. A. The genus Eranthis: prospects of research on its phytochemistry, pharmacology, and biotechnology. Plants (Basel) 12, 3795 (2023).
+13. Urbagarova, B. M. et al. Chromones and coumarins from Saposhnikovia divaricata (Turcz.) Schischk. growing in Buryatia and Mongolia and their cytotoxicity. J. Ethnopharmacol. 261, 112517 (2020).
+14. Wang, X. H. et al. Identification of a diarylpentanoid-producing polyketide synthase revealing an unusual biosynthetic pathway of 2-(2-phenylethyl) chromones in agarwood. Nat. Commun. 13, 348 (2022).
+15. Abe, I. et al. Structure-based engineering of a plant type III polyketide synthase: formation of an unnatural nonketide naphthopyrone. J. Am. Chem. Soc. 129, 5976-5980 (2007).
+16. Harrison, P. G., Bailey, B. K. & Steck, W. Biosynthesis of furanochromones. Can. J. Biochem. 49, 964-970 (1971).
+17. de Bruijn, W. J. C., Levisson, M., Beekwilder, J., van Berkel, W. J. H. & Vincken, J. P. Plant aromatic prenyltransferases: tools for microbial cell factories. Trends Biotechnol. 38, 917-934 (2020).
+18. Villard, C. et al. A new P450 involved in the furanocoumarin pathway underlies a recent case of convergent evolution. New Phytol. 231, 1923-1939 (2021).
+19. Zhao, Y. et al. Two types of coumarins-specific enzymes complete the last missing steps in pyran- and furanocoumarins biosynthesis. Acta Pharm. Sin. B 14, 869-880 (2024).
+20. Li, Q. et al. The chromosome-scale assembly of the Notopterygium incisum genome provides insight into the structural diversity of coumarins. Acta Pharmaceutica. Sin. B https://doi.org/10.1016/j.apsb.2024.04.005 (2024).
+21. Wang, K. et al. Three types of enzymes complete the furanocoumarins core skeleton biosynthesis in Angelica sinensis. Phytochemistry 222, 114102 (2024).
+22. Tiwari, P., Sangwan, R. S. & Sangwan, N. S. Plant secondary metabolism linked glycosyltransferases: an update on expanding knowledge and scopes. Biotechnol. Adv. 34, 714-739 (2016).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[31, 87, 912, 900]]<|/det|>
+23. Liu, Y., Fernie, A. R. & Tohge, T. Diversification of chemical structures of methoxylated flavonoids and genes encoding flavonoid-O-methyltransferases. Plants (Basel) 11, 564 (2022).
+24. Khouri, H. E., Tahara, S. & Ibrahim, R. K. Partial-purification, characterization, and kinetic-analysis of isoflavone 5-O-methyltransferase from yellow lupin roots. Arch. Biochem. Biophys. 262, 592-598 (1988).
+25. Itoh, N., Iwata, C. & Toda, H. Molecular cloning and characterization of a flavonoid-O-methyltransferase with broad substrate specificity and regioselectivity from Citrus depressa. BMC Plant Biol. 16, 180 (2016).
+26. Isin, E. M. & Guengerich, F. P. Complex reactions catalyzed by cytochrome P450 enzymes. Biochim. Biophys. Acta 1770, 314-329 (2007).
+27. Wang, Z. H. et al. Genomic, transcriptomic, and metabolomic analyses provide insights into the evolution and development of a medicinal plant Saposhnikovia divaricata (Apiaceae). Hortic. Res. https://doi.org/10.1093/hr/uhae105 (2024).
+28. Alagoz, Y., Mi, J., Balakrishna, A., Almarwae, L. & Al-Babili, S. Characterizing cytochrome P450 enzymes involved in plant apocarotenoid metabolism by using an engineered yeast system. Method Enzymol. 671, 527-552 (2022).
+29. Shang, Z. et al. Characterization of prenylated phenolics in Glycyrrhiza uralensis by offline two-dimensional liquid chromatography/mass spectrometry coupled with mass defect filter. J. Pharm. Biomed. Anal. 220, 115009 (2022).
+30. Marumoto, S. & Miyazawa, M. Structure-activity relationships for naturally occurring coumarins as β-secretase inhibitor. Bioorg. Med. Chem. 20, 784-788 (2012).
+31. Zhang, M. et al. Functional Characterization and Structural Basis of an Efficient Di-C-glycosyltransferase from Glycyrrhiza glabra. J. Am. Chem. Soc. 142, 3506-3512 (2020).
+32. Eberhardt, J., Santos-Martins, D., Tillack, A. F. & Forli, S. AutoDock Vina 1.2.0: new docking methods, expanded force field, and python bindings. J. Chem. Inf. Model. 61, 3891-3898 (2021).
+33. Wang, H. T. et al. Insights into the missing apiosylation step in flavonoid apiosides biosynthesis of Leguminosae plants. Nat. Commun. 14, 6658 (2023).
+34. Zhou, X. et al. Phytoene synthase: the key rate-limiting enzyme of carotenoid biosynthesis in plants. Front. Plant Sci. 13, 884720 (2022).
+35. Berman, P. et al. Parallel evolution of cannabinoid biosynthesis. Nat. Plants 9, 817-831 (2023).
+36. Yang, J. et al. Multiple independent losses of the biosynthetic pathway for two tropane alkaloids in the Solanaceae family. Nat Commun. 14, 8457 (2023).
+37. Cheng, H. et al. Haplotype-resolved assembly of diploid genomes without parental data. Nat. Biotechnol. 40, 1332-1335 (2022).
+38. Dudchenko, O. et al. De novo assembly of the Aedes aegypti genome using Hi-C yields chromosome-length scaffolds. Science 356, 92-95 (2017).
+39. Evgeny, Z. BUSCO update: novel and streamlined workflows along with broader and deeper phylogenetic coverage for scoring of eukaryotic, prokaryotic, and viral genomes. Mol. Biol. Evol. 10, 4647-4654 (2021).
+40. Ou, S. et al. Benchmarking transposable element annotation methods for creation of a streamlined, comprehensive pipeline. Genome Biol. 20, 275 (2019).
+41. Quinlan, A. R. & Hall, I. M. BEDTools: a flexible suite of utilities for comparing genomic features. Bioinformatics 26, 841-842 (2010).
+42. Kim, D., Paggi, J. M., Park, C., Bennett, C. & Salzberg, S. L. Graph-based genome alignment and genotyping with HISAT2 and HISAT-genotype. Nat. Biotechnol. 37, 907-915 (2019).
+43. Pertea, M. et al. StringTie enables improved reconstruction of a transcriptome from RNA-seq reads. Nat. Biotechnol. 33, 290-295 (2015).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[30, 85, 914, 586]]<|/det|>
+44. Haas, B. J. et al. Improving the Arabidopsis genome annotation using maximal transcript alignment assemblies. Nucleic Acids Res. 31, 5654-5666 (2003).
+45. Campbell, M. S., Holt, C., Moore, B. & Yandell, M. Genome annotation and curation using MAKER and MAKER-P. Curr. Protoc. bioinform. 48, 4.11.11-4.11.39 (2014).
+46. Jones, P. et al. InterProScan 5: genome-scale protein function classification. Bioinformatics 30, 1236-1240 (2014).
+47. Huerta-Cepas, J. et al. Fast genome-wide functional annotation through orthology assignment by eggNOG-Mapper. Mol. Biol. Evol. 34, 2115-2122 (2017).
+48. Chen, S. Ultrafast one-pass FASTQ data preprocessing, quality control, and deduplication using fastp. Imeta 2, e107 (2023).
+49. Liao, Y., Smyth, G. K. & Shi, W. featureCounts: an efficient general purpose program for assigning sequence reads to genomic features. Bioinformatics 30, 923-930 (2014).
+50. Mistry, J., Finn, R. D., Eddy, S. R., Bateman, A. & Punta, M. Challenges in homology search: HMMER3 and convergent evolution of coiled-coil regions. Nucleic Acids Res. 41, e121 (2013).
+51. Emms, D. M. & Kelly, S. OrthoFinder: phylogenetic orthology inference for comparative genomics. Genome Biol. 20, 238 (2019).
+52. Edgar, R. C. MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Res. 32, 1792-1797 (2004).
+53. Zhang, D. et al. PhyloSuite: an integrated and scalable desktop platform for streamlined molecular sequence data management and evolutionary phylogenetics studies. Mol. Ecol. Resour. 20, 348-355 (2020).
+54. Darriba, D. et al. ModelTest-NG: a new and scalable tool for the selection of DNA and protein evolutionary models. Mol. Biol. Evol. 37, 291-294 (2020).
+55. Stamatakis, A. RAxML version 8: a tool for phylogenetic analysis and post-analysis of large phylogenies. Bioinformatics 30, 1312-1313 (2014).
+56. Camacho, C. et al. BLAST+: architecture and applications. BMC Bioinformatics 10, 421 (2009).
+57. Labrou, N. E. Protein purification: an overview. Methods Mol. Biol. (Clifton, N.J.) 1129, 3-10 (2014).
+58. Hoare, S. R. J. Receptor binding kinetics equations: Derivation using the Laplace transform method. J. Pharmacol. Toxicol. Methods 89, 26-38 (2018).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[43, 93, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 131, 327, 178]]<|/det|>
+SupplementaryTables.xlsx - SuppplementaryFigures.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/images_list.json b/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..82ba72ef48b82bb2a534b2aefbcebb631b89cbea
--- /dev/null
+++ b/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/images_list.json
@@ -0,0 +1,77 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. Standard characterization of the cobalt catalysts and photosystem. A) Cobalt complex in dimethylformamide titration with water followed by in-situ UV-Vis, with insert showing the effect of acid in the spectrum, it represents with and without acid in water; B) proposed structure of the catalyst in water, which was used to anchor the catalyst to Au NPs; C) UV-Vis spectra of Au NPs region before and after addition of the cobalt complex on thin film, on insert the amino region followed by infrared spectroscopy: i) catalyst before anchoring; ii) catalyst after anchoring it to the Au NPs; D) photosystem structure used for the photo-electrocatalytic \\(\\mathrm{H}_2\\) evolution.",
+ "footnote": [],
+ "bbox": [
+ [
+ 128,
+ 90,
+ 880,
+ 460
+ ]
+ ],
+ "page_idx": 5
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Electrochemical and photo-electrocatalytic studies. A) Bulk electrolysis of cobalt catalysts in water and the presence of 3 mM acetic acid, using glassy carbon as the working electrode, Pt wire as the counter electrode, Ag/AgCl as reference electrode, 0.1 M LiCl as supporting electrolyte (pH = 5.2) and scan rate 50mV/s; B) Cyclic voltammetry of the NiO/Au and NiO/Au/Co-catalyst in water using Pt wire as a counter electrode, Ag/AgCl as reference electrode and 0.1 M LiCl as supporting electrolyte (pH = 5.2) (scan rate 50 mV/s); C) Effect of light in the chronoamperometry of the complete photosystem applying -0.65 V potential with the insert showing the catalytic wave when the experiments are performed with 3 mM acetic",
+ "footnote": [],
+ "bbox": [
+ [
+ 123,
+ 275,
+ 833,
+ 672
+ ]
+ ],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Transient spectroscopy data after LSPR excitation at \\(550 \\mathrm{nm}\\) . A) Kinetic traces of Au, NiO/Au, NiO/Au/Co-catalyst, extracted at \\(490 \\mathrm{nm}\\) from the TAS measurements; B) TIRAS map of the NiO/Au/Co-catalyst; C) TIRAS kinetic trace extracted at \\(4705 \\mathrm{nm}\\) for NiO/Au and NiO/Au/Co-catalyst; D) TIRAS kinetic trace extracted at \\(4705 \\mathrm{nm}\\) for Au/ligand and Au/Co-catalyst.",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 275,
+ 840,
+ 661
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4. In situ NAP-XPS of NiO/Au/Co-catalyst under variable potential in the presence of acid with an X-ray photon energy of 5000 eV. The potentials are vs Ag/AgCl reference electrode. A) O \\(Is\\) signals (the inset shows a magnification of the prominent peaks, highlighting the binding energy shift due to the potential applied); B) Co \\(2p\\) signals.",
+ "footnote": [],
+ "bbox": [
+ [
+ 140,
+ 395,
+ 820,
+ 694
+ ]
+ ],
+ "page_idx": 10
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5. Schematic representation of the catalytic cycle leading to \\(\\mathrm{H}_{2}\\) evolution. The NiO was omitted to improve figure legibility.",
+ "footnote": [],
+ "bbox": [
+ [
+ 124,
+ 480,
+ 880,
+ 808
+ ]
+ ],
+ "page_idx": 12
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d.mmd b/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..6ec085433f55862bab9b04e7eab2218cffe7e7a1
--- /dev/null
+++ b/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d.mmd
@@ -0,0 +1,280 @@
+
+# Plasmon-ligand-mediated hydrogen evolution with visible light
+
+Jacinto Sa ( \(\boxed{\bullet}\) jacinto.sa@kemi.uu.se) Uppsala University https://orcid.org/0000- 0003- 2124- 9510
+
+Ananta Dey Uppsala University
+
+Amal Mendalz Uppsala University
+
+Anna Wach Paul Scherrer Institut https://orcid.org/0000- 0003- 3112- 2759
+
+Robert Vadell Uppsala University
+
+Vitor R. Silveira Uppsala University
+
+Paul Maurice Leidinger Paul Scherrer Institut
+
+Thomas Huthwelker Paul Scherrer Institute
+
+Vitalii Shtender Uppsala University
+
+Zbynek Novotny Paul Scherrer Institut
+
+Luca Artiglia Paul Scherrer Institute https://orcid.org/0000- 0003- 4683- 6447
+
+Article
+
+Keywords:
+
+Posted Date: May 2nd, 2023
+
+DOI: https://doi.org/10.21203/rs.3.rs- 2751820/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+
+Version of Record: A version of this preprint was published at Nature Communications on January 10th, 2024. See the published version at https://doi.org/10.1038/s41467-024-44752-y.
+
+<--- Page Split --->
+
+# Plasmon-ligand-mediated hydrogen evolution with visible light
+
+Ananta Dey \(^{1}\) , Amal Mendalz, \(^{1}\) Anna Wach \(^{2}\) , Robert Bericat Vadell \(^{1}\) , Vitor R. Silveira \(^{1}\) , Paul Maurice Leidinger \(^{2}\) , Thomas Huthwelker \(^{2}\) , Vitalii Shtender \(^{3}\) , Zbynek Novotny \(^{2}\) , Luca Artiglia \(^{2}\) , Jacinto Sá \(^{1,4*}\)
+
+\(^{1}\) Department of Chemistry- Ångström, Physical Chemistry division, Uppsala University, Box 532, 751 20 Uppsala, Sweden. \(^{2}\) Paul Scherrer Institut, CH- 5232 Villigen PSI, Switzerland. \(^{3}\) Department of Materials Science and Engineering, division of Applied Materials Science, Uppsala University, 75103 Uppsala, Sweden. \(^{4}\) Institute of Physical Chemistry, Polish Academy of Sciences, Marcina Kasprzaka 44/52, 01- 224 Warsaw, Poland.
+
+\*Corresponding author. Email: jacinto.sa@kemi.uu.se
+
+Abstract: Plasmonic systems convert light into electrical charges and heat that mediate catalytic transformations. However, the debate about the involvement of hot carriers in the catalytic process remains shredded in controversy. Here, we demonstrate the direct use of plasmon hot electrons in the hydrogen evolution with visible light. A plasmonic nanohybrid system consisting of \(\mathrm{NiO / Au / [Co^{II}(phen - NH_2)_2(H_2O)_2]}\) (phen- \(\mathrm{NH_2} = 1,10\) - Phenanthroline- 5- amine) that is unstable at water thermolysis temperatures was consciously assembled, ensuring that the plasmon contribution to the catalytic process is solely from hot carriers. With the combination of photoelectrocatalysis and advanced in situ spectroscopies, one could establish the reaction mechanism, which consisted of electron injection into the phenanthroline- ligands followed by two quick, concerted proton- coupled electron transfer steps resulting in the evolution of hydrogen. Light- driven hydrogen evolution with plasmons provides a sustainable route for producing green hydrogen, which modern society strives to achieve.
+
+<--- Page Split --->
+
+Plasmonic photocatalysis uses electrical charges formed during the plasmon resonance decay triggered by light absorption. A plasmon is a quantized oscillation of the electron density, and its decay can generate hot carriers. Hot carriers in plasmonics refer to the generation of high- energy electrons (and holes) in metal due to the interaction between plasmons and incident light, causing them to become 'hot' or have high kinetic energy.\(^{1}\) These hot carriers can then be used to generate electrical current or to drive chemical reactions. However, hot electrons involvement in catalysis remains disputed, despite reports of their participation in processes such as such as solar to chemical energy reactions,\(^{2- 5}\) epoxidations,\(^{6,7}\) dehydrogenations,\(^{8}\) ammonia electrosynthesis,\(^{9}\) etc.\(^{10- 13}\) The skepticism surrounding their involvement relates to the hot carriers' ultrafast relaxation (ca. 100 fs),\(^{14}\) and that several examples rationalize their participation as enhancer of the photothermal process. Therefore, the catalytic output is prone to errors since the surface temperature of plasmonic materials is notoriously tricky to measure accurately, thus underestimating the thermal contribution to the catalysis.\(^{15,16}\) Despite the significant progress, it remains challenging to disentangle charge carrier catalysis from photothermal effects.\(^{17- 20}\)
+
+The hot electron energy distribution is broad, with a significant fraction of the carriers having energies above the Fermi level of the metal caused by the non- Fermi- Dirac distribution.\(^{21}\) More research is needed to fully understand plasmonics' hot carrier energy distribution dynamic behaviour,\(^{22,23}\) but the ultrafast relaxation can be partially mitigated via ultrafast charge transfer to suitable acceptors consecutively,\(^{24,25}\) or simultaneously,\(^{26}\) forming this contribution scientific basis to demonstrate the direct involvement of hot carriers in the catalytic process. Moreover, the hot electrons were used to reduce protons to hydrogen. Water can be converted into hydrogen through thermolysis. The exact temperature required for thermal water splitting depends on the specific conditions. Still, typically temperatures in the range of 500- 2000°C are required for efficient thermal water splitting,\(^{27}\) a temperature at which the catalytic system presented herein is unstable.
+
+Herein, a plasmonic nanohybrid system consisting of \(\mathrm{NiO / Au / [Co^{II}(phen - NH_2)_2(H_2O)_2]}\) (phen- \(\mathrm{NH_2 = 1,10}\) - Phenanthrolin- 5- amine) was assembled and tested in hydrogen evolution reaction (HER). NiO acted as a hole acceptor,\(^{28- 31}\) and the cobalt complex, a mimic of the HER catalyst reported by Luo et al.\(^{32}\) and the hydrolytic DNA cleavage agent by Sharma et al.,\(^{33}\) as an electron acceptor. The reaction mechanism was monitored by a combination of photoelectrocatalysis, ultrafast spectroscopies, and in situ electrochemistry, followed by near- ambient pressure X- ray photoelectron spectroscopy (NAP- XPS) studies (Figure S1). The results suggest a reaction mediated by the phenanthroline- ligands that accept the electrons from the plasmon and transfer
+
+<--- Page Split --->
+
+them to the cobalt centre in two concerted proton- coupled electron transfers (CEPT) that significantly lowers the energy threshold of the steps as it avoids the formation of higher energy intermediates. \(^{34}\) During the preparation of this work, a study was published with a similar concept, namely a cobalt porphyrin supported on plasmonic that, on illumination, produced \(\mathrm{H}_2\) . \(^{35}\) Still, there is a clear distinction. In the present contribution, only the Au nanoparticles (Au NPs) are photoactive, contrasting with the published study where the catalyst and Au NPs are photoactive. Thus, their observation might be related to photonic enhancement instead of a plasmonic hot carrier. This contribution also offers more resounding experimental support for the mechanism underpinning the reaction involving the plasmon hot carrier and complex catalyst ligands that are markedly different from what has been published on cobalt systems for HER, including the recent study. The findings distinctly support the involvement of hot electrons in the catalytic process, while the combined spectroscopically approach offers a robust methodology to measure the reaction mechanism on real electrodes.
+
+The as- prepared catalyst has the cobalt centre coordinated into two 1,10- Phenanthroline- 5- amine ligands and a bidentate nitrate group. A second out- sphere nitrate ensures complex neutrality (Figure 1B), consistent with previously reported crystal structures. \(^{33}\) Details on the catalyst, sample preparation, and characterization can be found in supporting information (SI). The optical spectrum of the as- prepared catalyst in dimethylformamide is shown in Figure S2. It displays a strong absorption peak centered at \(290 \mathrm{nm}\) with a shoulder at \(360 \mathrm{nm}\) , characteristic of phenanthroline complexes. \(^{36}\) Cobalt nitrate complexes are known to have their nitrate exchanged with water, \(^{37}\) which is the solvent used to attach the complex to the Au NPs. Therefore, the complex dissolved in dimethylformamide was titrated with water to evaluate if this occurred. Figure 1A shows the increase of the UV- Vis shoulder located at \(360 \mathrm{nm}\) , with an increase in water content, saturating at around \(20\%\) water. The exchange was also confirmed by the X- ray photoelectron spectroscopy (XPS) analysis. The N \(1s\) region in Figure S7, acquired in the vacuum after introducing the electrode in the analysis chamber, displays a sharp peak centered at \(398.6 \mathrm{eV}\) . Such a binding energy value can be assigned to pyridinic nitrogen of the phenanthroline ligand. \(^{38}\) Nitrate ligands are typically found at a binding energy of \(408 \mathrm{eV}\) , where the collected spectrum shows no features. \(^{39}\) Notably, adding acid to the aqua complex did not change its optical absorption, suggesting that it forms a stable di- aqua complex from the exchange of the bidentate nitrate ligand by water molecules (Figure 1B and 1D).
+
+<--- Page Split --->
+
+
+Figure 1. Standard characterization of the cobalt catalysts and photosystem. A) Cobalt complex in dimethylformamide titration with water followed by in-situ UV-Vis, with insert showing the effect of acid in the spectrum, it represents with and without acid in water; B) proposed structure of the catalyst in water, which was used to anchor the catalyst to Au NPs; C) UV-Vis spectra of Au NPs region before and after addition of the cobalt complex on thin film, on insert the amino region followed by infrared spectroscopy: i) catalyst before anchoring; ii) catalyst after anchoring it to the Au NPs; D) photosystem structure used for the photo-electrocatalytic \(\mathrm{H}_2\) evolution.
+
+The attachment of the complex was followed by UV- Vis and infrared spectroscopies (Figure 1C). The UV- Vis of the Au NPs supported on glass shows the characteristic localized surface plasmon resonant (LSPR) peak at \(535 \mathrm{nm}\) , consistent with an average particle size of \(8 \pm 2 \mathrm{nm}\) (determined by dynamic light scattering, Figure S3)). The Au LSPR peak shifts to lower energy when the cobalt catalyst is added (Figure 1C), confirming the anchoring and good electronic coupling between both structures. Additionally, it is possible to see the complex absorption shoulder located at \(370 \mathrm{nm}\) , corroborating the attachment between catalyst and Au NPs. Unfortunately, the glass support (FTO or cover glass) covers the rest of the complex UV- Vis band precluding their measurement. The anchoring was also confirmed by the
+
+<--- Page Split --->
+
+disappearance of the amino bands in the infrared (Figure 1C insert). Before anchoring the complex has two small peaks located between 3300- 3450 cm- 1 associated with N- H bending modes of primary amino groups, which disappear after coordination to the gold surface. The complete disappearance suggests that the catalyst coordinates to the Au NPs via both 1,10- Phenanthroline- 5- amine ligands, as shown schematically in Figure 1D. Note that this was not observed when Au NPs were absent, confirming the selective anchoring of the catalyst to the Au NPs via the amino groups.42
+
+
+
+Figure 2. Electrochemical and photo-electrocatalytic studies. A) Bulk electrolysis of cobalt catalysts in water and the presence of 3 mM acetic acid, using glassy carbon as the working electrode, Pt wire as the counter electrode, Ag/AgCl as reference electrode, 0.1 M LiCl as supporting electrolyte (pH = 5.2) and scan rate 50mV/s; B) Cyclic voltammetry of the NiO/Au and NiO/Au/Co-catalyst in water using Pt wire as a counter electrode, Ag/AgCl as reference electrode and 0.1 M LiCl as supporting electrolyte (pH = 5.2) (scan rate 50 mV/s); C) Effect of light in the chronoamperometry of the complete photosystem applying -0.65 V potential with the insert showing the catalytic wave when the experiments are performed with 3 mM acetic
+
+<--- Page Split --->
+
+acid \(\mathrm{(pH = 3.5)}\) ; D) Effect of light in the chronoamperometry of the NiO/Au and NiO/Au/ligand applying - 0.65 V potential in \(3\mathrm{mM}\) acetic acid and \(0.1\mathrm{M}\) LiCl \(\mathrm{(pH = 3.5)}\) .
+
+Bulk electrolysis of the cobalt catalyst in water using \(0.1\mathrm{M}\) LiCl as a supporting electrolyte without acid (Figure 2A) shows no distinguishable reduction peaks before the onset of the catalytic wave, contrasting with what has been proposed elsewhere. \(^{32}\) Addition of acid led to a peak at - 1.2V vs \(\mathrm{Ag / Ag / Cl}\) , suggesting that in the presence of a significant excess of protons, the catalyst follows a stepwise reduction process. \(^{43}\) In contrast, in the absence of protons, it is a concerted single- step two electrons and two protons additions. Unsurprisingly the presence of protons increases the amplitude of the catalytic wave, showing that proton availability is a determining factor when accessing catalytic performance in this system. Therefore, all the catalytic data is acquired in the presence of \(3\mathrm{mM}\) acetic acid.
+
+Figure 2B shows the cyclic voltammetry of the NiO/Au and NiO/Au/Co- catalyst thin films in water. The NiO/Au shows a reduction peak centred at around - \(0.49\mathrm{V}\) vs \(\mathrm{Ag / AgCl}\) related to the reduction of gold surface oxygen and weak catalytic wave staring at - \(0.90\mathrm{V}\) vs \(\mathrm{Ag / Ag / Cl}\) . Adding the cobalt catalyst drastically reduced the peak at - \(0.49\mathrm{V}\) vs \(\mathrm{Ag / Ag / Cl}\) , suggesting that surface functionalization by the catalyst decreases the amount of adsorbed oxygen on Au NPs. The cobalt loading in the complete system was determined to be \(11.4\mu \mathrm{g} / \mathrm{cm}^2\) by inductively coupled plasma - optical emission spectrometry (ICP- OES), equating to \(0.29\mathrm{wt.\%}\) of Co. The low loading creates issues regarding spectroscopy signal- to- noise but ensures that the activity is primarily due to the catalyst and enables the detection of catalyst degradation evidence.
+
+Chronoamperometry data at - \(0.65\mathrm{V}\) vs \(\mathrm{Ag / Ag / Cl}\) in the absence and presence of light (CW laser \(532\mathrm{nm}\) , selectively exciting only the Au plasmon) is presented in Figure 2C. The photosystem is responsive to the light, increasing the photocurrent by ca. - \(15\mu \mathrm{A}\) (- \(19\mu \mathrm{A} / \mathrm{cm}^2\) ). The increase in photocurrent was shown to be due to the evolution of \(\mathrm{H}_2\) , as confirmed by online quadrupole mass spectrometry (QMS) analysis (Figure S4). The response was found to be constant during the cycling of light on and off for the duration of the experiment (ca. \(360\mathrm{min}\) ). The findings indicate that the photosystem is relatively stable, and the process is catalytic. The significant increase in evolved \(\mathrm{H}_2\) relates to the presence of cobalt catalyst since neither the NiO/Au nor NiO/Au/ligand systems produce significant photocurrent (Figure 2D) and had no detectable hydrogen evolution by online QMS analysis. The observed differences are related to heating effects from the illumination and plasmonic decay.
+
+Having established that the photosystem is responsive to light, it is essential to determine if the enhancement is related to plasmon hot electrons. Transient absorption spectroscopy (TAS) was
+
+<--- Page Split --->
+
+performed to evaluate charge transfer in the photosystem. Excitation of the Au NPs LSPR results in a bleach signal and two small winglets on each side of the bleach to broadening of the LSPR peak44 (see the representative spectrum in SI Figure S5). Figure 3A shows the kinetic traces extracted at \(490~\mathrm{nm}\) (edge of the positive winglet) after excitation at \(550~\mathrm{nm}\) of the Au NPs, NiO/Au and NiO/Au/Co- catalyst systems. The kinetic traces were fitted with a rising edge and a double exponential decay. The rising edge is assigned to the electron- electron (e- e) scattering lifetime, the shorter exponential decay to electron- phonon (e- ph) scattering lifetime and the longer decay to photo- phonon (ph- ph) scattering lifetime.25,26,45 Recently, we demonstrated that charge transfer can be established from changes in the e- ph lifetime. Both electron and hole transfer reduce the e- ph lifetime compared to the plasmon nanoparticles without charge transfer. Hot electrons reduce the e- ph by taking energy from the resonance. Hot holes decrease the e- ph by injecting cold electrons into the resonance, reducing the average electron temperature.25,26
+
+The Au NPs on glass have e- e lifetime estimated to be \(167 \pm 49\) fs and an e- ph of \(5.1 \pm 0.4\) ps, which is within what has been published previously.23 When attached to NiO (hole acceptor), the Au NPs e- e increased slightly to \(198 \pm 85\) fs with a noticeable decrease in e- ph lifetime to \(3.4 \pm 1.0\) ps, consistent with what is anticipated if holes are transferred from Au NPs to NiO. The system composed of Au/Co- catalyst has an e- e of \(148 \pm 30\) fs and a significantly shorter e- ph lifetime \((4.2 \pm 0.3\) ps) compared with Au NPs alone. Since the catalyst is expected to be the electron acceptor, the reduction in e- ph lifetime suggests that electrons are transferred from Au NPs to the catalyst. The complete photosystem had an e- e of \(198 \pm 116\) fs and the biggest reduction in the e- ph from \(5.1 \pm 0.4\) ps (Au NPs) to \(2.6 \pm 1.0\) ps, suggesting the hot holes and electrons are transferred to the respective acceptors. In sum, the presence of electron and hole acceptors reduced the e- ph, consistent with charge transfer from Au NPs to the acceptors, with the largest e- ph lifetime reduction observed when both electron and hole acceptors are present. To corroborate the TAS's findings, transient infrared absorption spectroscopy (TIRAS) spectroscopy studies were performed. Free carriers absorb strongly in the infrared domain due to the formation of a quasi- metallic state.46 The signal is characterized by broad and featureless infrared absorption, often depicted as a background shift in the infrared spectrum.47 A representative TIRAS data map after LSPR excitation at \(550~\mathrm{nm}\) is shown in Figure 3B. Kinetic traces extracted between \(4645 - 4700\mathrm{nm}\) \((2150 - 2130\mathrm{cm}^{- 1})\) were fitted with a rising edge and two exponential decay, ascribed to injection and recombination processes lifetime, respectively. NiO/Au shows a rising edge with a \(196\pm 104\) fs time component, suggesting fast injection of
+
+<--- Page Split --->
+
+the hole. Most of the injected charge recombines within \(417 \pm 117\) fs (ca. \(91\%\) ). The complete system displayed a similar injection time ( \(100 \pm 23\) fs) and increased recombination time (6.6 \(\pm 4.2\) ps, \(85\%\) of the signal). However, an increase in signal amplitude is noticeable, suggesting that more charge is transferred when both acceptors are present. Consequently, the complete system has more charge for the catalysis. In both cases, \(5 - 10\%\) of the charge survives past 1 ns, making it useful for catalytic transformations. The TIRAS confirmed that charge is indeed transferred and that one has electrons surviving long enough to perform \(\mathrm{H}_2\) evolution.
+
+
+
+Figure 3. Transient spectroscopy data after LSPR excitation at \(550 \mathrm{nm}\) . A) Kinetic traces of Au, NiO/Au, NiO/Au/Co-catalyst, extracted at \(490 \mathrm{nm}\) from the TAS measurements; B) TIRAS map of the NiO/Au/Co-catalyst; C) TIRAS kinetic trace extracted at \(4705 \mathrm{nm}\) for NiO/Au and NiO/Au/Co-catalyst; D) TIRAS kinetic trace extracted at \(4705 \mathrm{nm}\) for Au/ligand and Au/Co-catalyst.
+
+Noteworthy is that TIRAS measurements without the NiO, namely with Au/Co- catalyst and Au/ligand, also show a broad featureless infrared absorption (Figure S6), characteristic of free carrier absorption not localized charge. The kinetic traces in Figure 3D are noisy due to low signal and thus challenging to fit. However, the signal qualitatively shows a concise rising
+
+<--- Page Split --->
+
+component (faster than the instrument response function (ca. 100 fs), suggesting a very fast electron injection. In the case of the Au/ligand, the decay is very fast, but when Co is present, the decay is comparatively slow, with the charge surviving past 1 ns. The shape of the TIRAS signal indicates that electrons are injected into the ligands due to the strong coupling between ligand and Au NPs; the charge is delocalised through the aromatic rings and acts as a free carrier. The presence of Co improves hot electrons' lifetime due to some charge stabilization. Still, the metal is not reduced since this would lead to the disappearance of the 'free carrier' infrared absorption behavior, which does not happen for at least 1 ns. The TIRAS observation is also consistent with the absence of Co reduction peaks in the electrochemistry. This is a peculiar observation because from the speculated mechanism of the analogous \(^{32}\) and relatable cobalt complexes, \(^{48,49}\) the metal center plays a central role, undergoing two sequential reductions. At the same time, the ligands are often spectators of the catalytic process.
+
+
+
+Figure 4. In situ NAP-XPS of NiO/Au/Co-catalyst under variable potential in the presence of acid with an X-ray photon energy of 5000 eV. The potentials are vs Ag/AgCl reference electrode. A) O \(Is\) signals (the inset shows a magnification of the prominent peaks, highlighting the binding energy shift due to the potential applied); B) Co \(2p\) signals.
+
+To corroborate the peculiar finding, electrochemical experiments combined with in situ near ambient pressure (NAP)- XPS measurements were performed using the dip- and- pull approach \(^{50}\) in the absence (Figure S8) and presence (Figure 4) of acetic acid. The measurements were
+
+<--- Page Split --->
+
+performed with the mesoporous films used for photocatalytic data. This significantly reduces the signal intensity and requires adaptation of the dip- and- pull method to reduce the amount of electrolyte trapped in the porous film.
+
+Briefly, only the lowest segment of the sample was dipped into the electrolyte solution, while the rest formed a liquid film via capillary forces. After some equilibration time (ca. 30 min), the liquid film settled to a point where the photoemission signals of the electrode (O \(1s\) , Co \(2p\) and N \(1s\) ) were detectable together with the signal of liquid and gas phase water (O \(1s\) ). Figures 4A and S8A show the O \(1s\) spectra acquired in situ at different applied potentials. Three prominent peaks, centered at approximately \(530.5 \mathrm{eV}\) , \(532.5 \mathrm{eV}\) and \(534.5 \mathrm{eV}\) , are assigned to lattice oxygen (electrode), liquid water (thin electrolyte film on top of the electrode) and gas phase water, respectively. \(^{51,52}\) Potential control and the availability of a continuous liquid film up to the position monitored by XPS were surveyed by the shifting of the O \(1s\) signal according to the applied potential. Figures 4A and S8A show a shift in the central peak of O \(1s\) , centered at \(532.5 \mathrm{eV}\) and assigned to liquid water (thin electrolyte layer), as the potential was applied (detected as a positive binding energy shift, proportional to the potential applied to the working electrode), confirming experiment validity and thus access to Co oxidation state at different potentials.
+
+Confident that NAP- XPS experiments reflected the Co oxidation state at different potentials, one can proceed with the analysis of Co \(2p\) region (Figure 4B). Despite the low signal- to- noise, the main features of Co \(2p\) peaks can be detected. The Co \(2p_{3 / 2}\) prominent peak is centered at around \(780 \mathrm{eV}\) , ascribed to \(\mathrm{Co}^{2 + }\) as expected. \(^{53,54}\) The peak position does not shift with the applied potential, as the working electrode is set to ground potential during the experiment. Nevertheless, also a peak shift due to the formation of a different cobalt species is not observed either in the presence or in the absence of acetic acid (Figure S8B). Indeed, the reduction of cobalt from \(2+\) to the metallic state leads to a shift of the binding energy of the \(2p_{3 / 2}\) peak by about \(2 \mathrm{eV}\) , from \(780\) to \(778 \mathrm{eV}\) . \(^{55,56}\) Figure 4B also shows that at \(- 0.65 \mathrm{V}\) vs Ag/AgCl the cobalt signal decreases in intensity. Such a potential is sufficient for the evolution of \(\mathrm{H}_{2}\) since bubbles were detected at the electrode and marked the onset of the catalytic wave (Figure S9). Thus, the decrease in signal- to- noise ratio relates to experimental conditions since the signal statistics are affected by the \(\mathrm{H}_{2}\) bubbles formation at the highest potential. Therefore, only \(\mathrm{Co}^{2 + }\) is present until \(\mathrm{H}_{2}\) formation; thus, the reduction peak at lower voltages relates to the reduction of the phenanthroline ligands (Figure S9). Since cobalt reduction is required to evolve hydrogen, not seeing its reduction suggests that the cobalt centre reduction and protonation steps are fast and
+
+<--- Page Split --->
+
+just before the hydrogen evolution, i.e., changes at the cobalt not rate limiting and cannot be detected due to the NAP- XPS temporal resolution. \(^{57}\)
+
+The observation Similar results occur in the absence of acid but the onset potential of \(\mathrm{H}_{2}\) evolution was shifted to \(0.8 \mathrm{~V}\) vs \(\mathrm{Ag / AgCl}\) , i.e., about \(0.15 - 0.2 \mathrm{~V}\) , as observed in the catalysis (Figure S9). Furthermore, the \(\mathrm{Co} 2p\) signal intensity detected was lower. The following hypotheses can be postulated, to explain such a behavior: i) the liquid electrolyte film was thicker in this case, attenuating more the signal of the substrate; ii) the surface of the electrode is slightly different in the absence of the acid, suggested by the more prominent electrode- related shoulder (centered at ca. \(530.5 \mathrm{eV}\) ) in the \(\mathrm{O} 1s\) spectra (Figure S8).
+
+Figure 5 shows a schematic representation of the hypothetic catalytic cycle. Excitation of Au plasmon results in the formation of hot electrons and holes as part of its resonance decoherence via Landau damping. The hot holes are transferred to the NiO and react at the counter electrode leading to \(\mathrm{O}_{2}\) production. The electrons are transferred to the phenanthroline ligands. Once both ligands are charged, two very fast concerted proton- coupled electron transfer (CPET) steps take place, resulting in the reduction and protonation of the cobalt catalyst and, subsequently, \(\mathrm{H}_{2}\) evolution.
+
+
+
+Figure 5. Schematic representation of the catalytic cycle leading to \(\mathrm{H}_{2}\) evolution. The NiO was omitted to improve figure legibility.
+
+<--- Page Split --->
+
+In conclusion, the photosystem proposed herein confirmed the involvement of hot electrons in the \(\mathrm{H}_2\) evolution process, settling the hot debate on their participation in photocatalysis. The proposed photosystem is not stable at water thermolysis conditions, thus precluding temperature (heat) from being the culprit for the observed \(\mathrm{H}_2\) evolution. Ultrafast spectroscopic measurements confirmed the charge to transfer to the respective acceptors. Moreover, and in conjunction with NAP- XPS under variable potential, a reaction mechanism was postulated in which the cobalt catalyst ligands have a significant role. They accept the electrons coming from Au plasmon and, in two quick CEPT steps, reduce and protonate the metal centre resulting in the evolution of the product.
+
+Acknowledgements: the authors would like to thank the Paul Scherrer Institute for providing access to the Phoenix beamline at the Swiss Light Source.
+
+## Funding:
+
+Olle Engkvists stiftelse (OES) (grant no. 210- 0007) Knut & Alice Wallenberg Foundation (Grant No. 2019- 0071) Swedish Research Council (grant no. 2019- 03597)
+
+Competing interests: Authors declare that they have no competing interests.
+
+## Supplementary Materials
+
+Materials and Methods Figs. S1 to S8
+
+## References:
+
+<--- Page Split --->
+
+3. Aslam, U., Rao, V. G., Chavez, S., Linic, S. Catalytic conversion of solar to chemical energy on plasmonic metal nanostructures. Nat. Catal. 1, 656-665 (2018).
+
+4. Li, R., Cheng, W.-H., Richter, M. H., DuChene, J. S., Tian, W., Li, C., Atwater, H. A. Unassisted Highly Selective Gas-Phase \(\mathrm{CO_2}\) Reduction with a Plasmonic Au/p-GaN Photocatalyst Using \(\mathrm{H_2O}\) as an Electron Donor. ACS Energy Lett. 6, 1849-1856 (2021).
+
+5. Kumari, G., Zhang, X., Devasia, D., Heo, J., Jain, P. K. Watching visible light-drive \(\mathrm{CO_2}\) reduction on a plasmonic nanoparticle catalyst. ACS Nano 12, 8330-8340 (2018).
+
+6. Marimuthu, A., Zhang, J., Linic, S. Tuning selectivity in propylene epoxidation by plasmon mediated photo-switching of Cu oxidation state. Science 339, 1590-1593 (2013).
+
+7. Linic, S., Aslam, U., Boerigter, C., Morabito, M. Photochemical transformations on plasmonic metal nanoparticles. Nat. Mater. 14, 567-576 (2015).
+
+8. Vadai, M., Angell, D. K., Hayee, F., Sytwu, K., Dionne, J. A. In-situ observation of plasmon-controlled photocatalytic dehydrogenation of individual palladium nanoparticles. Nat. Commun. 9, 4658 (2018).
+
+9. Contreras, E., Nixon, R., Litts, C., Zhang, W., Alcorn, F. M., Jain, P. K. Plasmon-assisted ammonia synthesis. J. Am. Chem. Soc. 144, 10743-10751 (2022).
+
+10. Chen, K., Wang, H. Plasmon-driven photocatalytic molecular transformations on metallic nanostructure surfaces: mechanistic insights gained from plasmon-enhanced Raman spectroscopy. Mol. Syst. Des. Eng. 6, 250-280 (2021).
+
+11. Frontiera, R, Guenke, N. L., van Duyne, R. Fano-line resonaces arising from long-lived molecule-plasmon interactions in colloidal nanoantennas. Nano Lett. 12, 5989-5994 (2012.)
+
+12. Wilson, A. J., Mohan, V., Jain, P. K.. Mechanistic understanding of plasmon-enhanced electrochemistry. J. Phys. Chem. C 123, 29360-29369 (2019).
+
+13. Chen, K., Wang, H. Plasmon-driven photocatalytic molecular transformations on metallic nanostructure surfaces: mechanistic insights gained from plasmon-enhanced Raman spectroscopy. Mol. Syst. Des. Eng. 6, 250-280 (2021).
+
+14. Brongersma, M. L., Halas, N. J., Nordlander, P. Plasmon-induced hot carrier science and technology. Nat. Nanotechnol. 10, 25-34 (2015).
+
+15. Sivan, Y., Un, I. W., Dubi, Y. Assistance of metal nanoparticles in photocatalysis - nothing more than a classical heat source. Faraday Discuss. 214, 215-233 (2019).
+
+16. Baffou, G., Bordacchini, I., Baldi, A., Quidant, R. Simple experimental procedures to distinguish photothermal from hot-carrier processes in plasmonics. Light Sci. Appl. 9, 108 (2020).
+
+<--- Page Split --->
+
+17. Zhan, C., Liu, B.-W., Huang, Y.-F., Hu, S., Ren, B., Moskovits, M., Tian, Z.-Q. Disentangling charge carrier from photothermal effects in plasmonic metal nanostructures. Nat. Commun. 10, 2671 (2019).
+
+18. Zhang, X., Li, X., Reish, M. E., Zhang, D., Su, N. Q., Gutiérrez, Y., Moreno, F., Yang, W., Everitt, H. O., Liu, J. Plasmon-Enhanced Catalysis: Distinguishing Thermal and Nonthermal Effects. Nano Lett. 18, 1714-1723 (2018).
+
+19. Jain, P. K. Taking the heat off of plasmonics chemistry. J. Phys. Chem. C 123, 24347-24351 (2019).
+
+20. Kamarudheen, R., Aalbers, G. J. W., Hamans, R. F., Kamp, L. P. J., Baldi, A. Distinguishing amongs all possible activation mechanisms of a plasmon-driven chemical reaction. ACS Energy Lett. 5, 2605-2613 (2020).
+
+21. Rossi, T. P., Erhart, P., Kuisma, M. Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure. ACS Nano 14, 9963-9971 (2020).
+
+22. Fann, W. S., Strotz, R., Tom, H. W. K., Bokor, J. Electron thermalization in gold. Phys. Rev. B 46, 13592 (1992).
+
+23. Link, S., El-Sayed, M. A. Spectral Properties and Relaxation Dynamics of Surface Plasmon Electronic Oscillations in Gold and Silver Nanodots and Nanorods. J. Phys. Chem. B 103, 8410-8426 (1999).
+
+24. Furube, A., Du, L., Hara, K., Katoh, R., Tachiya, M. Ultrafast Plasmon-Induced Electron Transfer from Gold Nanodots into \(\mathrm{TiO_2}\) Nanoparticles. J. Am. Chem. Soc. 129, 14852-14853 (2007).
+
+25. Tagliabue, G., DuChene, J. S., Abdellah, M., Habib, A., Gosztola, D. J., Hattori, Y., Cheng, W.-H., Zheng, K., Canton, S. E., Sundararaman, R., Sa, J., Atwater, H. A. Ultrafast Hot-Hole Injection Modifies Hot-Electron Dynamics in Au/p-GaN Heterostructures. Nat. Mater. 19, 1312-1318 (2020).
+
+26. Hattori, Y., Abdellah, M., Meng, J., Zheng, K., Sa, J. Simultaneous hot electron and hole injection upon excitation of gold surface plasmon. J. Phys. Chem. Lett. 10, 3140-3146 (2019).
+
+27. https://www.energy.gov/eere/fuelcells/hydrogen-production-thermochemical-water-splitting (Accessed on 2023-02-20)
+
+28. Odobel, F., Pellegrin, Y. Recent Advances in the Sensitization of Wide-Band-Gap Nanostructured P-Type Semiconductors. Photovoltaic and Photocatalytic Applications. J. Phys. Chem. Lett. 4, 2551-2564 (2013).
+
+<--- Page Split --->
+
+29. Gardner, J. M., Beyler, M., Karnahl, M., Tschierlei, S., Ott, S., Hammarström, L. Light-Driven Electron Transfer between a Photosensitizer and a Proton-Reducing Catalyst Co-Adsorbed to NiO. J. Am. Chem. Soc. 134, 19322-19325 (2012).
+
+30. Tong, L., Iwase, A., Nattestad, A., Bach, U., Weidelener, M., Gotz, G., Mishra, A., Bäuerle, P., Amal, R., Wallace, G. G., Mozer, A. J. Sustained Solar Hydrogen Generation Using a Dye-Sensitized NiO Photocathode/BiVO4 Tandem Photo-Electrochemical Device. Energy Environ. Sci. 5, 9472-9475 (2012).
+
+31. Nakamura, K., Oshikiri, T., Ueno, K., Wang, Y., Kamata, Y., Kotake, Y., Misawa, H. Properties of Plasmon-Induced Photoelectric Conversion on a TiO2/NiO p-n Junction with Au Nanoparticles. J. Phys. Chem. Lett. 7, 1004-1009 (2016).
+
+32. Luo, S.-P., Tang, L.-Z., Zhan, S.-Z. A cobalt(II) complex of 2,2-bipyridine, a catalyst for electro- and photo-catalytic hydrogen production in purely aqueous media. Inorg. Chem. Commun. 86, 276-280 (2017).
+
+33. Sharma, S., Toupet, L., Arjmand, F. De novo design of a hydrolytic DNA cleavage agent, mono nitratobis(phen)cobalt(II) aqua nitrate complex. New J. Chem. 41, 2883-2886 (2017).
+
+34. Saveant, J. M. Electrochemical approach to proton-coupled electron transfers: recent advances. Energy Environ. Sci. 5, 7718-7731 (2012).
+
+35. Sheng, H., Wang, J., Huang, J., Li, Z., Ren, G., Zhang, L., Yu, L., Zho, M., Li, X., Li, G., Wang, N., Shen, C., Lu, G. Strong synergy between gold nanoparticles and cobalt porphyrin induces highly efficient photocatalytic hydrogen evolution. Nat. Commun. 14, 1528 (2023).
+
+36. Al-Omair, M. A. Biochemical activities and electronic spectra of different cobalt phenanthroline complexes. Arabian J. Chem. 12, 1061-1069 (2019).
+
+37. Katzin, L. I., Gebert, E. Spectrophotometric Investigation of Cobaltous Nitrate in Organic Solvents. J. Am. Chem. Soc. 72, 5455-5463 (1950).
+
+38. Lazar, P., Mach, R., Otyepka, M. Spectrophotometric Investigation of Cobaltous Nitrate in Organic Solvents. J. Am. Chem. Soc. 72, 5455-5463 (1950).
+
+39. Beard, B. C. cellulose nitrate as a binding energy reference in N(1s) XPS studies of nitrogen-containing organic molecules. Appl. Surf. Scie. 45, 221-227 (1990).
+
+40. Silveira, V. R., Bericat-Vadell, R., Sá, J. Photoelectrocatalytic Conversion of Nitrates to Ammonia with Plasmon Hot Electrons. J. Phys. Chem. C 127, 5425-5431 (2023)-
+
+41. Rossi, T. P., Shegai, T., Erhart, P., Antosiewicz, T. J. Strong plasmon-molecule coupling at the nanoscale revealed by first-principles modeling. Nat. Commun. 10, 3336 (2019).
+
+<--- Page Split --->
+
+42. Pavliuk, M. V., Fernandes, A. B., Abdellah, M., Fernandes, D. L. A., Machado, C. O., Rocha, I., Hattori, Y., Paun, C., Bastos, E. L., Sá, J. Nano-hybrid plasmonic photocatalyst for hydrogen production at 20% efficiency. \*Scie. Rep.\* 7, 8670 (2017).
+
+43. Li, C.-B., Bagnall, A. J., Sun, D., Rendon, J., Koepf, M., Gambarelli, S., Mouesca, J.-M., Chavarot-Kerlidou, M., Artero, V. Electrocatalytic reduction of protons to dihydrogen by the cobalt tetraazamacrocyclic complex [Co(N4H)Cl2]+: mechanism and benchmarking of performances. \*Sustain. Energy Fuels\* 6, 143-149 (2022).
+
+44. van Turnhout, L., Hattori, H., Meng, J., Zheng, K., Sá, J. Direct Observation of a Plasmon-Induced Hot Electron Flow in a Multimetallic Nanostructure. \*Nano Lett.\* 20, 8220-8228 (2020).
+
+45. Groeneveld, R. H. M., Sprik, R., Lagendijk, A. Femtosecond spectroscopy of electron-electron and electron-phonon relaxation in Ag and Au. \*Phys. Rev. B\* 51, 11433 (1995).
+
+46. Antila, L. J., Santomauro, F. G., Hammaström, L., Fernandes, D. L. A., Sá, J. Hunting for the elusive shallow traps in TiO₂. \*Chem. Commun.\* 51, 10914-10916 (2015).
+
+47. Berger, T., Sterrer, M.; Diwald, O., Knözinger, E., Panayotov, D., Thompson, T. L., Yates Jr, J. T. Light-Induced Charge Separation in Anatase TiO₂ Particles. \*J. Phys. Chem. B\* 109, 6061-6068 (2005).
+
+48. Queyriaux, N., Sun, D., Fize, J., Pécaut, J., Field, M. J., Chavarot-Kerlidou, M., Artero, V. Electrocatalytic Hydrogen Evolution with a Cobalt Complex Bearing Pendant Proton Relays: Acid Strength and Applied Potential Govern Mechanism and Stability. \*J. Am. Chem. Soc.\* 142, 274-282 (2020).
+
+49. Eckenhoff, W. T, McNamara, W. R., Du, P., Eisenberg, R. Cobalt complexes as artificial hydrogenases for reductive side of water splitting. \*Biochim. Biophys. Acta: Bioenergetics\* 1827, 958-973 (2013).
+
+50. Novotny, Z., Aegerter, D., Comini, N., Tobler, B., Artiglia, L., Maier, U., Moehl, T., Fabbri, E., Huthwelker, T., Schmidt, T., Ammann, M., van Bokhoven, J. A., Raabe, J., Osterwalder, J. Probing the solid–liquid interface with tender x rays: A new ambient-pressure x-ray photoelectron spectroscopy endstation at the Swiss Light Source. \*Rev. Sci. Instrum.\* 91, 023103 (2020).
+
+51. Axnanda, S., Crumlin, E. J., Mao, B., Rani, S., Chang, R., Karlsson, P. G., Edwards, M. O. M., Lundvist, M., Moberg, R., Ross, P., Hussain, Z., Liu, Z. Using “Tender” X-ray Ambient Pressure X-Ray Photoelectron Spectroscopy as A Direct Probe of Solid-Liquid Interface. \*Scie. Rep.\* 5, 9788 (2015).
+
+<--- Page Split --->
+
+52. Favaro, M., Jeong, B., Ross, P. N., Yano, J., Hussain, Z., Liu, Z., Crumlin, E. J. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface Nat. Commun. 7, 12695 (2016).
+53. Lázaro-Martínez, J. M., Lupano, L. V. L., Piehl, L. L., Rodríguez-castellón, E., Dall’Orto, V. C. New Insights about the Selectivity in the Activation of Hydrogen Peroxide by Cobalt or Copper Hydrogel Heterogeneous Catalysts in the Generation of Reactive Oxygen Species. J. Phys. Chem. C 120, 29332-29347 (2016).
+54. Khalil, T. E., Soliman, S. M., Khalil, N. A., El-Faham, A., Foro, S., El-Dissouky, A. Synthesis, structure, X-ray photoelectron spectroscopy (XPS), and antimicrobial, anticancer, and antioxidant activities of Co (III) complexes based on the antihypertensive hydralazine. Appl. Org. Chem. 36, e6565 (2022).
+55. Bridge, M. E., Lambert, R. M. Oxygen chemisorption, surface oxidation, and the oxidation of carbon monoxide on cobalt (0001). Surf. Scie. 82, 413-424 (1979).
+56. Hyman, M. P., Vohs, J. M. Reaction of ethanol on oxidized and metallic cobalt surfaces. Surf. Scie. 605, 383-389 (2011).
+57. Moonshiran, D., Gimbert-Suriñach, C., Guda, A., Picon, A., Lehmann, C. S., Zhang, X., Doumy, G., March, A. M., Benet-Buchholz, J., Soldatov, A., Llobet, A., Southworth, S. H. Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water. J. Am. Chem. Soc. 138, 10586-10596 (2016).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- H2evolutionSI.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d_det.mmd b/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..e54be9fbf0c053f3086b73a7f76d0fb3e97cab79
--- /dev/null
+++ b/preprint/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d/preprint__04b173197c545f10945642520e847eff78301d76d085be0937577c7b3426ca9d_det.mmd
@@ -0,0 +1,369 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 920, 175]]<|/det|>
+# Plasmon-ligand-mediated hydrogen evolution with visible light
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 576, 236]]<|/det|>
+Jacinto Sa ( \(\boxed{\bullet}\) jacinto.sa@kemi.uu.se) Uppsala University https://orcid.org/0000- 0003- 2124- 9510
+
+<|ref|>text<|/ref|><|det|>[[44, 243, 220, 281]]<|/det|>
+Ananta Dey Uppsala University
+
+<|ref|>text<|/ref|><|det|>[[44, 289, 220, 328]]<|/det|>
+Amal Mendalz Uppsala University
+
+<|ref|>text<|/ref|><|det|>[[44, 335, 595, 375]]<|/det|>
+Anna Wach Paul Scherrer Institut https://orcid.org/0000- 0003- 3112- 2759
+
+<|ref|>text<|/ref|><|det|>[[44, 381, 220, 420]]<|/det|>
+Robert Vadell Uppsala University
+
+<|ref|>text<|/ref|><|det|>[[44, 427, 220, 465]]<|/det|>
+Vitor R. Silveira Uppsala University
+
+<|ref|>text<|/ref|><|det|>[[44, 472, 245, 511]]<|/det|>
+Paul Maurice Leidinger Paul Scherrer Institut
+
+<|ref|>text<|/ref|><|det|>[[44, 519, 248, 557]]<|/det|>
+Thomas Huthwelker Paul Scherrer Institute
+
+<|ref|>text<|/ref|><|det|>[[44, 565, 220, 603]]<|/det|>
+Vitalii Shtender Uppsala University
+
+<|ref|>text<|/ref|><|det|>[[44, 610, 240, 649]]<|/det|>
+Zbynek Novotny Paul Scherrer Institut
+
+<|ref|>text<|/ref|><|det|>[[44, 656, 608, 697]]<|/det|>
+Luca Artiglia Paul Scherrer Institute https://orcid.org/0000- 0003- 4683- 6447
+
+<|ref|>text<|/ref|><|det|>[[44, 743, 101, 760]]<|/det|>
+Article
+
+<|ref|>text<|/ref|><|det|>[[44, 780, 136, 798]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 818, 290, 837]]<|/det|>
+Posted Date: May 2nd, 2023
+
+<|ref|>text<|/ref|><|det|>[[44, 856, 474, 875]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 2751820/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 894, 909, 936]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 100, 940, 142]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on January 10th, 2024. See the published version at https://doi.org/10.1038/s41467-024-44752-y.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[180, 90, 815, 111]]<|/det|>
+# Plasmon-ligand-mediated hydrogen evolution with visible light
+
+<|ref|>text<|/ref|><|det|>[[128, 162, 872, 231]]<|/det|>
+Ananta Dey \(^{1}\) , Amal Mendalz, \(^{1}\) Anna Wach \(^{2}\) , Robert Bericat Vadell \(^{1}\) , Vitor R. Silveira \(^{1}\) , Paul Maurice Leidinger \(^{2}\) , Thomas Huthwelker \(^{2}\) , Vitalii Shtender \(^{3}\) , Zbynek Novotny \(^{2}\) , Luca Artiglia \(^{2}\) , Jacinto Sá \(^{1,4*}\)
+
+<|ref|>text<|/ref|><|det|>[[115, 261, 875, 430]]<|/det|>
+\(^{1}\) Department of Chemistry- Ångström, Physical Chemistry division, Uppsala University, Box 532, 751 20 Uppsala, Sweden. \(^{2}\) Paul Scherrer Institut, CH- 5232 Villigen PSI, Switzerland. \(^{3}\) Department of Materials Science and Engineering, division of Applied Materials Science, Uppsala University, 75103 Uppsala, Sweden. \(^{4}\) Institute of Physical Chemistry, Polish Academy of Sciences, Marcina Kasprzaka 44/52, 01- 224 Warsaw, Poland.
+
+<|ref|>text<|/ref|><|det|>[[116, 459, 557, 477]]<|/det|>
+\*Corresponding author. Email: jacinto.sa@kemi.uu.se
+
+<|ref|>text<|/ref|><|det|>[[114, 515, 884, 806]]<|/det|>
+Abstract: Plasmonic systems convert light into electrical charges and heat that mediate catalytic transformations. However, the debate about the involvement of hot carriers in the catalytic process remains shredded in controversy. Here, we demonstrate the direct use of plasmon hot electrons in the hydrogen evolution with visible light. A plasmonic nanohybrid system consisting of \(\mathrm{NiO / Au / [Co^{II}(phen - NH_2)_2(H_2O)_2]}\) (phen- \(\mathrm{NH_2} = 1,10\) - Phenanthroline- 5- amine) that is unstable at water thermolysis temperatures was consciously assembled, ensuring that the plasmon contribution to the catalytic process is solely from hot carriers. With the combination of photoelectrocatalysis and advanced in situ spectroscopies, one could establish the reaction mechanism, which consisted of electron injection into the phenanthroline- ligands followed by two quick, concerted proton- coupled electron transfer steps resulting in the evolution of hydrogen. Light- driven hydrogen evolution with plasmons provides a sustainable route for producing green hydrogen, which modern society strives to achieve.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 81, 884, 446]]<|/det|>
+Plasmonic photocatalysis uses electrical charges formed during the plasmon resonance decay triggered by light absorption. A plasmon is a quantized oscillation of the electron density, and its decay can generate hot carriers. Hot carriers in plasmonics refer to the generation of high- energy electrons (and holes) in metal due to the interaction between plasmons and incident light, causing them to become 'hot' or have high kinetic energy.\(^{1}\) These hot carriers can then be used to generate electrical current or to drive chemical reactions. However, hot electrons involvement in catalysis remains disputed, despite reports of their participation in processes such as such as solar to chemical energy reactions,\(^{2- 5}\) epoxidations,\(^{6,7}\) dehydrogenations,\(^{8}\) ammonia electrosynthesis,\(^{9}\) etc.\(^{10- 13}\) The skepticism surrounding their involvement relates to the hot carriers' ultrafast relaxation (ca. 100 fs),\(^{14}\) and that several examples rationalize their participation as enhancer of the photothermal process. Therefore, the catalytic output is prone to errors since the surface temperature of plasmonic materials is notoriously tricky to measure accurately, thus underestimating the thermal contribution to the catalysis.\(^{15,16}\) Despite the significant progress, it remains challenging to disentangle charge carrier catalysis from photothermal effects.\(^{17- 20}\)
+
+<|ref|>text<|/ref|><|det|>[[114, 450, 884, 715]]<|/det|>
+The hot electron energy distribution is broad, with a significant fraction of the carriers having energies above the Fermi level of the metal caused by the non- Fermi- Dirac distribution.\(^{21}\) More research is needed to fully understand plasmonics' hot carrier energy distribution dynamic behaviour,\(^{22,23}\) but the ultrafast relaxation can be partially mitigated via ultrafast charge transfer to suitable acceptors consecutively,\(^{24,25}\) or simultaneously,\(^{26}\) forming this contribution scientific basis to demonstrate the direct involvement of hot carriers in the catalytic process. Moreover, the hot electrons were used to reduce protons to hydrogen. Water can be converted into hydrogen through thermolysis. The exact temperature required for thermal water splitting depends on the specific conditions. Still, typically temperatures in the range of 500- 2000°C are required for efficient thermal water splitting,\(^{27}\) a temperature at which the catalytic system presented herein is unstable.
+
+<|ref|>text<|/ref|><|det|>[[114, 720, 884, 911]]<|/det|>
+Herein, a plasmonic nanohybrid system consisting of \(\mathrm{NiO / Au / [Co^{II}(phen - NH_2)_2(H_2O)_2]}\) (phen- \(\mathrm{NH_2 = 1,10}\) - Phenanthrolin- 5- amine) was assembled and tested in hydrogen evolution reaction (HER). NiO acted as a hole acceptor,\(^{28- 31}\) and the cobalt complex, a mimic of the HER catalyst reported by Luo et al.\(^{32}\) and the hydrolytic DNA cleavage agent by Sharma et al.,\(^{33}\) as an electron acceptor. The reaction mechanism was monitored by a combination of photoelectrocatalysis, ultrafast spectroscopies, and in situ electrochemistry, followed by near- ambient pressure X- ray photoelectron spectroscopy (NAP- XPS) studies (Figure S1). The results suggest a reaction mediated by the phenanthroline- ligands that accept the electrons from the plasmon and transfer
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 81, 884, 397]]<|/det|>
+them to the cobalt centre in two concerted proton- coupled electron transfers (CEPT) that significantly lowers the energy threshold of the steps as it avoids the formation of higher energy intermediates. \(^{34}\) During the preparation of this work, a study was published with a similar concept, namely a cobalt porphyrin supported on plasmonic that, on illumination, produced \(\mathrm{H}_2\) . \(^{35}\) Still, there is a clear distinction. In the present contribution, only the Au nanoparticles (Au NPs) are photoactive, contrasting with the published study where the catalyst and Au NPs are photoactive. Thus, their observation might be related to photonic enhancement instead of a plasmonic hot carrier. This contribution also offers more resounding experimental support for the mechanism underpinning the reaction involving the plasmon hot carrier and complex catalyst ligands that are markedly different from what has been published on cobalt systems for HER, including the recent study. The findings distinctly support the involvement of hot electrons in the catalytic process, while the combined spectroscopically approach offers a robust methodology to measure the reaction mechanism on real electrodes.
+
+<|ref|>text<|/ref|><|det|>[[114, 425, 884, 863]]<|/det|>
+The as- prepared catalyst has the cobalt centre coordinated into two 1,10- Phenanthroline- 5- amine ligands and a bidentate nitrate group. A second out- sphere nitrate ensures complex neutrality (Figure 1B), consistent with previously reported crystal structures. \(^{33}\) Details on the catalyst, sample preparation, and characterization can be found in supporting information (SI). The optical spectrum of the as- prepared catalyst in dimethylformamide is shown in Figure S2. It displays a strong absorption peak centered at \(290 \mathrm{nm}\) with a shoulder at \(360 \mathrm{nm}\) , characteristic of phenanthroline complexes. \(^{36}\) Cobalt nitrate complexes are known to have their nitrate exchanged with water, \(^{37}\) which is the solvent used to attach the complex to the Au NPs. Therefore, the complex dissolved in dimethylformamide was titrated with water to evaluate if this occurred. Figure 1A shows the increase of the UV- Vis shoulder located at \(360 \mathrm{nm}\) , with an increase in water content, saturating at around \(20\%\) water. The exchange was also confirmed by the X- ray photoelectron spectroscopy (XPS) analysis. The N \(1s\) region in Figure S7, acquired in the vacuum after introducing the electrode in the analysis chamber, displays a sharp peak centered at \(398.6 \mathrm{eV}\) . Such a binding energy value can be assigned to pyridinic nitrogen of the phenanthroline ligand. \(^{38}\) Nitrate ligands are typically found at a binding energy of \(408 \mathrm{eV}\) , where the collected spectrum shows no features. \(^{39}\) Notably, adding acid to the aqua complex did not change its optical absorption, suggesting that it forms a stable di- aqua complex from the exchange of the bidentate nitrate ligand by water molecules (Figure 1B and 1D).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[128, 90, 880, 460]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 462, 884, 655]]<|/det|>
+Figure 1. Standard characterization of the cobalt catalysts and photosystem. A) Cobalt complex in dimethylformamide titration with water followed by in-situ UV-Vis, with insert showing the effect of acid in the spectrum, it represents with and without acid in water; B) proposed structure of the catalyst in water, which was used to anchor the catalyst to Au NPs; C) UV-Vis spectra of Au NPs region before and after addition of the cobalt complex on thin film, on insert the amino region followed by infrared spectroscopy: i) catalyst before anchoring; ii) catalyst after anchoring it to the Au NPs; D) photosystem structure used for the photo-electrocatalytic \(\mathrm{H}_2\) evolution.
+
+<|ref|>text<|/ref|><|det|>[[114, 682, 884, 900]]<|/det|>
+The attachment of the complex was followed by UV- Vis and infrared spectroscopies (Figure 1C). The UV- Vis of the Au NPs supported on glass shows the characteristic localized surface plasmon resonant (LSPR) peak at \(535 \mathrm{nm}\) , consistent with an average particle size of \(8 \pm 2 \mathrm{nm}\) (determined by dynamic light scattering, Figure S3)). The Au LSPR peak shifts to lower energy when the cobalt catalyst is added (Figure 1C), confirming the anchoring and good electronic coupling between both structures. Additionally, it is possible to see the complex absorption shoulder located at \(370 \mathrm{nm}\) , corroborating the attachment between catalyst and Au NPs. Unfortunately, the glass support (FTO or cover glass) covers the rest of the complex UV- Vis band precluding their measurement. The anchoring was also confirmed by the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 81, 884, 248]]<|/det|>
+disappearance of the amino bands in the infrared (Figure 1C insert). Before anchoring the complex has two small peaks located between 3300- 3450 cm- 1 associated with N- H bending modes of primary amino groups, which disappear after coordination to the gold surface. The complete disappearance suggests that the catalyst coordinates to the Au NPs via both 1,10- Phenanthroline- 5- amine ligands, as shown schematically in Figure 1D. Note that this was not observed when Au NPs were absent, confirming the selective anchoring of the catalyst to the Au NPs via the amino groups.42
+
+<|ref|>image<|/ref|><|det|>[[123, 275, 833, 672]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 678, 884, 870]]<|/det|>
+Figure 2. Electrochemical and photo-electrocatalytic studies. A) Bulk electrolysis of cobalt catalysts in water and the presence of 3 mM acetic acid, using glassy carbon as the working electrode, Pt wire as the counter electrode, Ag/AgCl as reference electrode, 0.1 M LiCl as supporting electrolyte (pH = 5.2) and scan rate 50mV/s; B) Cyclic voltammetry of the NiO/Au and NiO/Au/Co-catalyst in water using Pt wire as a counter electrode, Ag/AgCl as reference electrode and 0.1 M LiCl as supporting electrolyte (pH = 5.2) (scan rate 50 mV/s); C) Effect of light in the chronoamperometry of the complete photosystem applying -0.65 V potential with the insert showing the catalytic wave when the experiments are performed with 3 mM acetic
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 881, 125]]<|/det|>
+acid \(\mathrm{(pH = 3.5)}\) ; D) Effect of light in the chronoamperometry of the NiO/Au and NiO/Au/ligand applying - 0.65 V potential in \(3\mathrm{mM}\) acetic acid and \(0.1\mathrm{M}\) LiCl \(\mathrm{(pH = 3.5)}\) .
+
+<|ref|>text<|/ref|><|det|>[[114, 155, 884, 371]]<|/det|>
+Bulk electrolysis of the cobalt catalyst in water using \(0.1\mathrm{M}\) LiCl as a supporting electrolyte without acid (Figure 2A) shows no distinguishable reduction peaks before the onset of the catalytic wave, contrasting with what has been proposed elsewhere. \(^{32}\) Addition of acid led to a peak at - 1.2V vs \(\mathrm{Ag / Ag / Cl}\) , suggesting that in the presence of a significant excess of protons, the catalyst follows a stepwise reduction process. \(^{43}\) In contrast, in the absence of protons, it is a concerted single- step two electrons and two protons additions. Unsurprisingly the presence of protons increases the amplitude of the catalytic wave, showing that proton availability is a determining factor when accessing catalytic performance in this system. Therefore, all the catalytic data is acquired in the presence of \(3\mathrm{mM}\) acetic acid.
+
+<|ref|>text<|/ref|><|det|>[[113, 376, 884, 590]]<|/det|>
+Figure 2B shows the cyclic voltammetry of the NiO/Au and NiO/Au/Co- catalyst thin films in water. The NiO/Au shows a reduction peak centred at around - \(0.49\mathrm{V}\) vs \(\mathrm{Ag / AgCl}\) related to the reduction of gold surface oxygen and weak catalytic wave staring at - \(0.90\mathrm{V}\) vs \(\mathrm{Ag / Ag / Cl}\) . Adding the cobalt catalyst drastically reduced the peak at - \(0.49\mathrm{V}\) vs \(\mathrm{Ag / Ag / Cl}\) , suggesting that surface functionalization by the catalyst decreases the amount of adsorbed oxygen on Au NPs. The cobalt loading in the complete system was determined to be \(11.4\mu \mathrm{g} / \mathrm{cm}^2\) by inductively coupled plasma - optical emission spectrometry (ICP- OES), equating to \(0.29\mathrm{wt.\%}\) of Co. The low loading creates issues regarding spectroscopy signal- to- noise but ensures that the activity is primarily due to the catalyst and enables the detection of catalyst degradation evidence.
+
+<|ref|>text<|/ref|><|det|>[[114, 596, 884, 866]]<|/det|>
+Chronoamperometry data at - \(0.65\mathrm{V}\) vs \(\mathrm{Ag / Ag / Cl}\) in the absence and presence of light (CW laser \(532\mathrm{nm}\) , selectively exciting only the Au plasmon) is presented in Figure 2C. The photosystem is responsive to the light, increasing the photocurrent by ca. - \(15\mu \mathrm{A}\) (- \(19\mu \mathrm{A} / \mathrm{cm}^2\) ). The increase in photocurrent was shown to be due to the evolution of \(\mathrm{H}_2\) , as confirmed by online quadrupole mass spectrometry (QMS) analysis (Figure S4). The response was found to be constant during the cycling of light on and off for the duration of the experiment (ca. \(360\mathrm{min}\) ). The findings indicate that the photosystem is relatively stable, and the process is catalytic. The significant increase in evolved \(\mathrm{H}_2\) relates to the presence of cobalt catalyst since neither the NiO/Au nor NiO/Au/ligand systems produce significant photocurrent (Figure 2D) and had no detectable hydrogen evolution by online QMS analysis. The observed differences are related to heating effects from the illumination and plasmonic decay.
+
+<|ref|>text<|/ref|><|det|>[[115, 871, 881, 915]]<|/det|>
+Having established that the photosystem is responsive to light, it is essential to determine if the enhancement is related to plasmon hot electrons. Transient absorption spectroscopy (TAS) was
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 81, 884, 395]]<|/det|>
+performed to evaluate charge transfer in the photosystem. Excitation of the Au NPs LSPR results in a bleach signal and two small winglets on each side of the bleach to broadening of the LSPR peak44 (see the representative spectrum in SI Figure S5). Figure 3A shows the kinetic traces extracted at \(490~\mathrm{nm}\) (edge of the positive winglet) after excitation at \(550~\mathrm{nm}\) of the Au NPs, NiO/Au and NiO/Au/Co- catalyst systems. The kinetic traces were fitted with a rising edge and a double exponential decay. The rising edge is assigned to the electron- electron (e- e) scattering lifetime, the shorter exponential decay to electron- phonon (e- ph) scattering lifetime and the longer decay to photo- phonon (ph- ph) scattering lifetime.25,26,45 Recently, we demonstrated that charge transfer can be established from changes in the e- ph lifetime. Both electron and hole transfer reduce the e- ph lifetime compared to the plasmon nanoparticles without charge transfer. Hot electrons reduce the e- ph by taking energy from the resonance. Hot holes decrease the e- ph by injecting cold electrons into the resonance, reducing the average electron temperature.25,26
+
+<|ref|>text<|/ref|><|det|>[[113, 400, 884, 900]]<|/det|>
+The Au NPs on glass have e- e lifetime estimated to be \(167 \pm 49\) fs and an e- ph of \(5.1 \pm 0.4\) ps, which is within what has been published previously.23 When attached to NiO (hole acceptor), the Au NPs e- e increased slightly to \(198 \pm 85\) fs with a noticeable decrease in e- ph lifetime to \(3.4 \pm 1.0\) ps, consistent with what is anticipated if holes are transferred from Au NPs to NiO. The system composed of Au/Co- catalyst has an e- e of \(148 \pm 30\) fs and a significantly shorter e- ph lifetime \((4.2 \pm 0.3\) ps) compared with Au NPs alone. Since the catalyst is expected to be the electron acceptor, the reduction in e- ph lifetime suggests that electrons are transferred from Au NPs to the catalyst. The complete photosystem had an e- e of \(198 \pm 116\) fs and the biggest reduction in the e- ph from \(5.1 \pm 0.4\) ps (Au NPs) to \(2.6 \pm 1.0\) ps, suggesting the hot holes and electrons are transferred to the respective acceptors. In sum, the presence of electron and hole acceptors reduced the e- ph, consistent with charge transfer from Au NPs to the acceptors, with the largest e- ph lifetime reduction observed when both electron and hole acceptors are present. To corroborate the TAS's findings, transient infrared absorption spectroscopy (TIRAS) spectroscopy studies were performed. Free carriers absorb strongly in the infrared domain due to the formation of a quasi- metallic state.46 The signal is characterized by broad and featureless infrared absorption, often depicted as a background shift in the infrared spectrum.47 A representative TIRAS data map after LSPR excitation at \(550~\mathrm{nm}\) is shown in Figure 3B. Kinetic traces extracted between \(4645 - 4700\mathrm{nm}\) \((2150 - 2130\mathrm{cm}^{- 1})\) were fitted with a rising edge and two exponential decay, ascribed to injection and recombination processes lifetime, respectively. NiO/Au shows a rising edge with a \(196\pm 104\) fs time component, suggesting fast injection of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 82, 884, 253]]<|/det|>
+the hole. Most of the injected charge recombines within \(417 \pm 117\) fs (ca. \(91\%\) ). The complete system displayed a similar injection time ( \(100 \pm 23\) fs) and increased recombination time (6.6 \(\pm 4.2\) ps, \(85\%\) of the signal). However, an increase in signal amplitude is noticeable, suggesting that more charge is transferred when both acceptors are present. Consequently, the complete system has more charge for the catalysis. In both cases, \(5 - 10\%\) of the charge survives past 1 ns, making it useful for catalytic transformations. The TIRAS confirmed that charge is indeed transferred and that one has electrons surviving long enough to perform \(\mathrm{H}_2\) evolution.
+
+<|ref|>image<|/ref|><|det|>[[125, 275, 840, 661]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[114, 666, 884, 782]]<|/det|>
+Figure 3. Transient spectroscopy data after LSPR excitation at \(550 \mathrm{nm}\) . A) Kinetic traces of Au, NiO/Au, NiO/Au/Co-catalyst, extracted at \(490 \mathrm{nm}\) from the TAS measurements; B) TIRAS map of the NiO/Au/Co-catalyst; C) TIRAS kinetic trace extracted at \(4705 \mathrm{nm}\) for NiO/Au and NiO/Au/Co-catalyst; D) TIRAS kinetic trace extracted at \(4705 \mathrm{nm}\) for Au/ligand and Au/Co-catalyst.
+
+<|ref|>text<|/ref|><|det|>[[114, 812, 884, 906]]<|/det|>
+Noteworthy is that TIRAS measurements without the NiO, namely with Au/Co- catalyst and Au/ligand, also show a broad featureless infrared absorption (Figure S6), characteristic of free carrier absorption not localized charge. The kinetic traces in Figure 3D are noisy due to low signal and thus challenging to fit. However, the signal qualitatively shows a concise rising
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 81, 884, 371]]<|/det|>
+component (faster than the instrument response function (ca. 100 fs), suggesting a very fast electron injection. In the case of the Au/ligand, the decay is very fast, but when Co is present, the decay is comparatively slow, with the charge surviving past 1 ns. The shape of the TIRAS signal indicates that electrons are injected into the ligands due to the strong coupling between ligand and Au NPs; the charge is delocalised through the aromatic rings and acts as a free carrier. The presence of Co improves hot electrons' lifetime due to some charge stabilization. Still, the metal is not reduced since this would lead to the disappearance of the 'free carrier' infrared absorption behavior, which does not happen for at least 1 ns. The TIRAS observation is also consistent with the absence of Co reduction peaks in the electrochemistry. This is a peculiar observation because from the speculated mechanism of the analogous \(^{32}\) and relatable cobalt complexes, \(^{48,49}\) the metal center plays a central role, undergoing two sequential reductions. At the same time, the ligands are often spectators of the catalytic process.
+
+<|ref|>image<|/ref|><|det|>[[140, 395, 820, 694]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 722, 884, 816]]<|/det|>
+Figure 4. In situ NAP-XPS of NiO/Au/Co-catalyst under variable potential in the presence of acid with an X-ray photon energy of 5000 eV. The potentials are vs Ag/AgCl reference electrode. A) O \(Is\) signals (the inset shows a magnification of the prominent peaks, highlighting the binding energy shift due to the potential applied); B) Co \(2p\) signals.
+
+<|ref|>text<|/ref|><|det|>[[115, 845, 884, 912]]<|/det|>
+To corroborate the peculiar finding, electrochemical experiments combined with in situ near ambient pressure (NAP)- XPS measurements were performed using the dip- and- pull approach \(^{50}\) in the absence (Figure S8) and presence (Figure 4) of acetic acid. The measurements were
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 883, 150]]<|/det|>
+performed with the mesoporous films used for photocatalytic data. This significantly reduces the signal intensity and requires adaptation of the dip- and- pull method to reduce the amount of electrolyte trapped in the porous film.
+
+<|ref|>text<|/ref|><|det|>[[114, 156, 884, 494]]<|/det|>
+Briefly, only the lowest segment of the sample was dipped into the electrolyte solution, while the rest formed a liquid film via capillary forces. After some equilibration time (ca. 30 min), the liquid film settled to a point where the photoemission signals of the electrode (O \(1s\) , Co \(2p\) and N \(1s\) ) were detectable together with the signal of liquid and gas phase water (O \(1s\) ). Figures 4A and S8A show the O \(1s\) spectra acquired in situ at different applied potentials. Three prominent peaks, centered at approximately \(530.5 \mathrm{eV}\) , \(532.5 \mathrm{eV}\) and \(534.5 \mathrm{eV}\) , are assigned to lattice oxygen (electrode), liquid water (thin electrolyte film on top of the electrode) and gas phase water, respectively. \(^{51,52}\) Potential control and the availability of a continuous liquid film up to the position monitored by XPS were surveyed by the shifting of the O \(1s\) signal according to the applied potential. Figures 4A and S8A show a shift in the central peak of O \(1s\) , centered at \(532.5 \mathrm{eV}\) and assigned to liquid water (thin electrolyte layer), as the potential was applied (detected as a positive binding energy shift, proportional to the potential applied to the working electrode), confirming experiment validity and thus access to Co oxidation state at different potentials.
+
+<|ref|>text<|/ref|><|det|>[[114, 500, 884, 888]]<|/det|>
+Confident that NAP- XPS experiments reflected the Co oxidation state at different potentials, one can proceed with the analysis of Co \(2p\) region (Figure 4B). Despite the low signal- to- noise, the main features of Co \(2p\) peaks can be detected. The Co \(2p_{3 / 2}\) prominent peak is centered at around \(780 \mathrm{eV}\) , ascribed to \(\mathrm{Co}^{2 + }\) as expected. \(^{53,54}\) The peak position does not shift with the applied potential, as the working electrode is set to ground potential during the experiment. Nevertheless, also a peak shift due to the formation of a different cobalt species is not observed either in the presence or in the absence of acetic acid (Figure S8B). Indeed, the reduction of cobalt from \(2+\) to the metallic state leads to a shift of the binding energy of the \(2p_{3 / 2}\) peak by about \(2 \mathrm{eV}\) , from \(780\) to \(778 \mathrm{eV}\) . \(^{55,56}\) Figure 4B also shows that at \(- 0.65 \mathrm{V}\) vs Ag/AgCl the cobalt signal decreases in intensity. Such a potential is sufficient for the evolution of \(\mathrm{H}_{2}\) since bubbles were detected at the electrode and marked the onset of the catalytic wave (Figure S9). Thus, the decrease in signal- to- noise ratio relates to experimental conditions since the signal statistics are affected by the \(\mathrm{H}_{2}\) bubbles formation at the highest potential. Therefore, only \(\mathrm{Co}^{2 + }\) is present until \(\mathrm{H}_{2}\) formation; thus, the reduction peak at lower voltages relates to the reduction of the phenanthroline ligands (Figure S9). Since cobalt reduction is required to evolve hydrogen, not seeing its reduction suggests that the cobalt centre reduction and protonation steps are fast and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 881, 125]]<|/det|>
+just before the hydrogen evolution, i.e., changes at the cobalt not rate limiting and cannot be detected due to the NAP- XPS temporal resolution. \(^{57}\)
+
+<|ref|>text<|/ref|><|det|>[[114, 131, 884, 298]]<|/det|>
+The observation Similar results occur in the absence of acid but the onset potential of \(\mathrm{H}_{2}\) evolution was shifted to \(0.8 \mathrm{~V}\) vs \(\mathrm{Ag / AgCl}\) , i.e., about \(0.15 - 0.2 \mathrm{~V}\) , as observed in the catalysis (Figure S9). Furthermore, the \(\mathrm{Co} 2p\) signal intensity detected was lower. The following hypotheses can be postulated, to explain such a behavior: i) the liquid electrolyte film was thicker in this case, attenuating more the signal of the substrate; ii) the surface of the electrode is slightly different in the absence of the acid, suggested by the more prominent electrode- related shoulder (centered at ca. \(530.5 \mathrm{eV}\) ) in the \(\mathrm{O} 1s\) spectra (Figure S8).
+
+<|ref|>text<|/ref|><|det|>[[114, 303, 884, 468]]<|/det|>
+Figure 5 shows a schematic representation of the hypothetic catalytic cycle. Excitation of Au plasmon results in the formation of hot electrons and holes as part of its resonance decoherence via Landau damping. The hot holes are transferred to the NiO and react at the counter electrode leading to \(\mathrm{O}_{2}\) production. The electrons are transferred to the phenanthroline ligands. Once both ligands are charged, two very fast concerted proton- coupled electron transfer (CPET) steps take place, resulting in the reduction and protonation of the cobalt catalyst and, subsequently, \(\mathrm{H}_{2}\) evolution.
+
+<|ref|>image<|/ref|><|det|>[[124, 480, 880, 808]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 811, 881, 855]]<|/det|>
+Figure 5. Schematic representation of the catalytic cycle leading to \(\mathrm{H}_{2}\) evolution. The NiO was omitted to improve figure legibility.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 82, 884, 297]]<|/det|>
+In conclusion, the photosystem proposed herein confirmed the involvement of hot electrons in the \(\mathrm{H}_2\) evolution process, settling the hot debate on their participation in photocatalysis. The proposed photosystem is not stable at water thermolysis conditions, thus precluding temperature (heat) from being the culprit for the observed \(\mathrm{H}_2\) evolution. Ultrafast spectroscopic measurements confirmed the charge to transfer to the respective acceptors. Moreover, and in conjunction with NAP- XPS under variable potential, a reaction mechanism was postulated in which the cobalt catalyst ligands have a significant role. They accept the electrons coming from Au plasmon and, in two quick CEPT steps, reduce and protonate the metal centre resulting in the evolution of the product.
+
+<|ref|>text<|/ref|><|det|>[[115, 353, 881, 396]]<|/det|>
+Acknowledgements: the authors would like to thank the Paul Scherrer Institute for providing access to the Phoenix beamline at the Swiss Light Source.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 426, 198, 444]]<|/det|>
+## Funding:
+
+<|ref|>text<|/ref|><|det|>[[115, 457, 618, 523]]<|/det|>
+Olle Engkvists stiftelse (OES) (grant no. 210- 0007) Knut & Alice Wallenberg Foundation (Grant No. 2019- 0071) Swedish Research Council (grant no. 2019- 03597)
+
+<|ref|>text<|/ref|><|det|>[[115, 552, 743, 570]]<|/det|>
+Competing interests: Authors declare that they have no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 599, 339, 617]]<|/det|>
+## Supplementary Materials
+
+<|ref|>text<|/ref|><|det|>[[115, 623, 305, 664]]<|/det|>
+Materials and Methods Figs. S1 to S8
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 700, 218, 717]]<|/det|>
+## References:
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 100, 875, 140]]<|/det|>
+3. Aslam, U., Rao, V. G., Chavez, S., Linic, S. Catalytic conversion of solar to chemical energy on plasmonic metal nanostructures. Nat. Catal. 1, 656-665 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 146, 872, 215]]<|/det|>
+4. Li, R., Cheng, W.-H., Richter, M. H., DuChene, J. S., Tian, W., Li, C., Atwater, H. A. Unassisted Highly Selective Gas-Phase \(\mathrm{CO_2}\) Reduction with a Plasmonic Au/p-GaN Photocatalyst Using \(\mathrm{H_2O}\) as an Electron Donor. ACS Energy Lett. 6, 1849-1856 (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 221, 872, 264]]<|/det|>
+5. Kumari, G., Zhang, X., Devasia, D., Heo, J., Jain, P. K. Watching visible light-drive \(\mathrm{CO_2}\) reduction on a plasmonic nanoparticle catalyst. ACS Nano 12, 8330-8340 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 270, 880, 313]]<|/det|>
+6. Marimuthu, A., Zhang, J., Linic, S. Tuning selectivity in propylene epoxidation by plasmon mediated photo-switching of Cu oxidation state. Science 339, 1590-1593 (2013).
+
+<|ref|>text<|/ref|><|det|>[[113, 319, 820, 362]]<|/det|>
+7. Linic, S., Aslam, U., Boerigter, C., Morabito, M. Photochemical transformations on plasmonic metal nanoparticles. Nat. Mater. 14, 567-576 (2015).
+
+<|ref|>text<|/ref|><|det|>[[113, 368, 872, 435]]<|/det|>
+8. Vadai, M., Angell, D. K., Hayee, F., Sytwu, K., Dionne, J. A. In-situ observation of plasmon-controlled photocatalytic dehydrogenation of individual palladium nanoparticles. Nat. Commun. 9, 4658 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 441, 872, 485]]<|/det|>
+9. Contreras, E., Nixon, R., Litts, C., Zhang, W., Alcorn, F. M., Jain, P. K. Plasmon-assisted ammonia synthesis. J. Am. Chem. Soc. 144, 10743-10751 (2022).
+
+<|ref|>text<|/ref|><|det|>[[115, 490, 878, 559]]<|/det|>
+10. Chen, K., Wang, H. Plasmon-driven photocatalytic molecular transformations on metallic nanostructure surfaces: mechanistic insights gained from plasmon-enhanced Raman spectroscopy. Mol. Syst. Des. Eng. 6, 250-280 (2021).
+
+<|ref|>text<|/ref|><|det|>[[115, 565, 864, 632]]<|/det|>
+11. Frontiera, R, Guenke, N. L., van Duyne, R. Fano-line resonaces arising from long-lived molecule-plasmon interactions in colloidal nanoantennas. Nano Lett. 12, 5989-5994 (2012.)
+
+<|ref|>text<|/ref|><|det|>[[115, 638, 848, 681]]<|/det|>
+12. Wilson, A. J., Mohan, V., Jain, P. K.. Mechanistic understanding of plasmon-enhanced electrochemistry. J. Phys. Chem. C 123, 29360-29369 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 687, 878, 755]]<|/det|>
+13. Chen, K., Wang, H. Plasmon-driven photocatalytic molecular transformations on metallic nanostructure surfaces: mechanistic insights gained from plasmon-enhanced Raman spectroscopy. Mol. Syst. Des. Eng. 6, 250-280 (2021).
+
+<|ref|>text<|/ref|><|det|>[[115, 761, 870, 804]]<|/det|>
+14. Brongersma, M. L., Halas, N. J., Nordlander, P. Plasmon-induced hot carrier science and technology. Nat. Nanotechnol. 10, 25-34 (2015).
+
+<|ref|>text<|/ref|><|det|>[[115, 810, 825, 853]]<|/det|>
+15. Sivan, Y., Un, I. W., Dubi, Y. Assistance of metal nanoparticles in photocatalysis - nothing more than a classical heat source. Faraday Discuss. 214, 215-233 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 859, 878, 926]]<|/det|>
+16. Baffou, G., Bordacchini, I., Baldi, A., Quidant, R. Simple experimental procedures to distinguish photothermal from hot-carrier processes in plasmonics. Light Sci. Appl. 9, 108 (2020).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 100, 875, 167]]<|/det|>
+17. Zhan, C., Liu, B.-W., Huang, Y.-F., Hu, S., Ren, B., Moskovits, M., Tian, Z.-Q. Disentangling charge carrier from photothermal effects in plasmonic metal nanostructures. Nat. Commun. 10, 2671 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 172, 856, 240]]<|/det|>
+18. Zhang, X., Li, X., Reish, M. E., Zhang, D., Su, N. Q., Gutiérrez, Y., Moreno, F., Yang, W., Everitt, H. O., Liu, J. Plasmon-Enhanced Catalysis: Distinguishing Thermal and Nonthermal Effects. Nano Lett. 18, 1714-1723 (2018).
+
+<|ref|>text<|/ref|><|det|>[[115, 245, 852, 288]]<|/det|>
+19. Jain, P. K. Taking the heat off of plasmonics chemistry. J. Phys. Chem. C 123, 24347-24351 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 294, 870, 362]]<|/det|>
+20. Kamarudheen, R., Aalbers, G. J. W., Hamans, R. F., Kamp, L. P. J., Baldi, A. Distinguishing amongs all possible activation mechanisms of a plasmon-driven chemical reaction. ACS Energy Lett. 5, 2605-2613 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 368, 866, 411]]<|/det|>
+21. Rossi, T. P., Erhart, P., Kuisma, M. Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure. ACS Nano 14, 9963-9971 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 416, 868, 459]]<|/det|>
+22. Fann, W. S., Strotz, R., Tom, H. W. K., Bokor, J. Electron thermalization in gold. Phys. Rev. B 46, 13592 (1992).
+
+<|ref|>text<|/ref|><|det|>[[115, 465, 870, 533]]<|/det|>
+23. Link, S., El-Sayed, M. A. Spectral Properties and Relaxation Dynamics of Surface Plasmon Electronic Oscillations in Gold and Silver Nanodots and Nanorods. J. Phys. Chem. B 103, 8410-8426 (1999).
+
+<|ref|>text<|/ref|><|det|>[[115, 539, 871, 606]]<|/det|>
+24. Furube, A., Du, L., Hara, K., Katoh, R., Tachiya, M. Ultrafast Plasmon-Induced Electron Transfer from Gold Nanodots into \(\mathrm{TiO_2}\) Nanoparticles. J. Am. Chem. Soc. 129, 14852-14853 (2007).
+
+<|ref|>text<|/ref|><|det|>[[115, 612, 871, 705]]<|/det|>
+25. Tagliabue, G., DuChene, J. S., Abdellah, M., Habib, A., Gosztola, D. J., Hattori, Y., Cheng, W.-H., Zheng, K., Canton, S. E., Sundararaman, R., Sa, J., Atwater, H. A. Ultrafast Hot-Hole Injection Modifies Hot-Electron Dynamics in Au/p-GaN Heterostructures. Nat. Mater. 19, 1312-1318 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 711, 871, 779]]<|/det|>
+26. Hattori, Y., Abdellah, M., Meng, J., Zheng, K., Sa, J. Simultaneous hot electron and hole injection upon excitation of gold surface plasmon. J. Phys. Chem. Lett. 10, 3140-3146 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 785, 830, 836]]<|/det|>
+27. https://www.energy.gov/eere/fuelcells/hydrogen-production-thermochemical-water-splitting (Accessed on 2023-02-20)
+
+<|ref|>text<|/ref|><|det|>[[115, 851, 866, 919]]<|/det|>
+28. Odobel, F., Pellegrin, Y. Recent Advances in the Sensitization of Wide-Band-Gap Nanostructured P-Type Semiconductors. Photovoltaic and Photocatalytic Applications. J. Phys. Chem. Lett. 4, 2551-2564 (2013).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 100, 870, 170]]<|/det|>
+29. Gardner, J. M., Beyler, M., Karnahl, M., Tschierlei, S., Ott, S., Hammarström, L. Light-Driven Electron Transfer between a Photosensitizer and a Proton-Reducing Catalyst Co-Adsorbed to NiO. J. Am. Chem. Soc. 134, 19322-19325 (2012).
+
+<|ref|>text<|/ref|><|det|>[[115, 175, 870, 266]]<|/det|>
+30. Tong, L., Iwase, A., Nattestad, A., Bach, U., Weidelener, M., Gotz, G., Mishra, A., Bäuerle, P., Amal, R., Wallace, G. G., Mozer, A. J. Sustained Solar Hydrogen Generation Using a Dye-Sensitized NiO Photocathode/BiVO4 Tandem Photo-Electrochemical Device. Energy Environ. Sci. 5, 9472-9475 (2012).
+
+<|ref|>text<|/ref|><|det|>[[115, 272, 868, 339]]<|/det|>
+31. Nakamura, K., Oshikiri, T., Ueno, K., Wang, Y., Kamata, Y., Kotake, Y., Misawa, H. Properties of Plasmon-Induced Photoelectric Conversion on a TiO2/NiO p-n Junction with Au Nanoparticles. J. Phys. Chem. Lett. 7, 1004-1009 (2016).
+
+<|ref|>text<|/ref|><|det|>[[115, 344, 870, 411]]<|/det|>
+32. Luo, S.-P., Tang, L.-Z., Zhan, S.-Z. A cobalt(II) complex of 2,2-bipyridine, a catalyst for electro- and photo-catalytic hydrogen production in purely aqueous media. Inorg. Chem. Commun. 86, 276-280 (2017).
+
+<|ref|>text<|/ref|><|det|>[[115, 417, 873, 486]]<|/det|>
+33. Sharma, S., Toupet, L., Arjmand, F. De novo design of a hydrolytic DNA cleavage agent, mono nitratobis(phen)cobalt(II) aqua nitrate complex. New J. Chem. 41, 2883-2886 (2017).
+
+<|ref|>text<|/ref|><|det|>[[115, 492, 835, 535]]<|/det|>
+34. Saveant, J. M. Electrochemical approach to proton-coupled electron transfers: recent advances. Energy Environ. Sci. 5, 7718-7731 (2012).
+
+<|ref|>text<|/ref|><|det|>[[115, 540, 873, 632]]<|/det|>
+35. Sheng, H., Wang, J., Huang, J., Li, Z., Ren, G., Zhang, L., Yu, L., Zho, M., Li, X., Li, G., Wang, N., Shen, C., Lu, G. Strong synergy between gold nanoparticles and cobalt porphyrin induces highly efficient photocatalytic hydrogen evolution. Nat. Commun. 14, 1528 (2023).
+
+<|ref|>text<|/ref|><|det|>[[115, 638, 805, 681]]<|/det|>
+36. Al-Omair, M. A. Biochemical activities and electronic spectra of different cobalt phenanthroline complexes. Arabian J. Chem. 12, 1061-1069 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 687, 874, 730]]<|/det|>
+37. Katzin, L. I., Gebert, E. Spectrophotometric Investigation of Cobaltous Nitrate in Organic Solvents. J. Am. Chem. Soc. 72, 5455-5463 (1950).
+
+<|ref|>text<|/ref|><|det|>[[115, 736, 866, 779]]<|/det|>
+38. Lazar, P., Mach, R., Otyepka, M. Spectrophotometric Investigation of Cobaltous Nitrate in Organic Solvents. J. Am. Chem. Soc. 72, 5455-5463 (1950).
+
+<|ref|>text<|/ref|><|det|>[[115, 785, 825, 828]]<|/det|>
+39. Beard, B. C. cellulose nitrate as a binding energy reference in N(1s) XPS studies of nitrogen-containing organic molecules. Appl. Surf. Scie. 45, 221-227 (1990).
+
+<|ref|>text<|/ref|><|det|>[[115, 834, 835, 877]]<|/det|>
+40. Silveira, V. R., Bericat-Vadell, R., Sá, J. Photoelectrocatalytic Conversion of Nitrates to Ammonia with Plasmon Hot Electrons. J. Phys. Chem. C 127, 5425-5431 (2023)-
+
+<|ref|>text<|/ref|><|det|>[[115, 884, 868, 927]]<|/det|>
+41. Rossi, T. P., Shegai, T., Erhart, P., Antosiewicz, T. J. Strong plasmon-molecule coupling at the nanoscale revealed by first-principles modeling. Nat. Commun. 10, 3336 (2019).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 99, 876, 170]]<|/det|>
+42. Pavliuk, M. V., Fernandes, A. B., Abdellah, M., Fernandes, D. L. A., Machado, C. O., Rocha, I., Hattori, Y., Paun, C., Bastos, E. L., Sá, J. Nano-hybrid plasmonic photocatalyst for hydrogen production at 20% efficiency. \*Scie. Rep.\* 7, 8670 (2017).
+
+<|ref|>text<|/ref|><|det|>[[115, 174, 873, 266]]<|/det|>
+43. Li, C.-B., Bagnall, A. J., Sun, D., Rendon, J., Koepf, M., Gambarelli, S., Mouesca, J.-M., Chavarot-Kerlidou, M., Artero, V. Electrocatalytic reduction of protons to dihydrogen by the cobalt tetraazamacrocyclic complex [Co(N4H)Cl2]+: mechanism and benchmarking of performances. \*Sustain. Energy Fuels\* 6, 143-149 (2022).
+
+<|ref|>text<|/ref|><|det|>[[115, 271, 835, 337]]<|/det|>
+44. van Turnhout, L., Hattori, H., Meng, J., Zheng, K., Sá, J. Direct Observation of a Plasmon-Induced Hot Electron Flow in a Multimetallic Nanostructure. \*Nano Lett.\* 20, 8220-8228 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 344, 852, 387]]<|/det|>
+45. Groeneveld, R. H. M., Sprik, R., Lagendijk, A. Femtosecond spectroscopy of electron-electron and electron-phonon relaxation in Ag and Au. \*Phys. Rev. B\* 51, 11433 (1995).
+
+<|ref|>text<|/ref|><|det|>[[115, 392, 874, 436]]<|/det|>
+46. Antila, L. J., Santomauro, F. G., Hammaström, L., Fernandes, D. L. A., Sá, J. Hunting for the elusive shallow traps in TiO₂. \*Chem. Commun.\* 51, 10914-10916 (2015).
+
+<|ref|>text<|/ref|><|det|>[[115, 441, 870, 509]]<|/det|>
+47. Berger, T., Sterrer, M.; Diwald, O., Knözinger, E., Panayotov, D., Thompson, T. L., Yates Jr, J. T. Light-Induced Charge Separation in Anatase TiO₂ Particles. \*J. Phys. Chem. B\* 109, 6061-6068 (2005).
+
+<|ref|>text<|/ref|><|det|>[[115, 515, 880, 606]]<|/det|>
+48. Queyriaux, N., Sun, D., Fize, J., Pécaut, J., Field, M. J., Chavarot-Kerlidou, M., Artero, V. Electrocatalytic Hydrogen Evolution with a Cobalt Complex Bearing Pendant Proton Relays: Acid Strength and Applied Potential Govern Mechanism and Stability. \*J. Am. Chem. Soc.\* 142, 274-282 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 612, 872, 681]]<|/det|>
+49. Eckenhoff, W. T, McNamara, W. R., Du, P., Eisenberg, R. Cobalt complexes as artificial hydrogenases for reductive side of water splitting. \*Biochim. Biophys. Acta: Bioenergetics\* 1827, 958-973 (2013).
+
+<|ref|>text<|/ref|><|det|>[[115, 687, 870, 803]]<|/det|>
+50. Novotny, Z., Aegerter, D., Comini, N., Tobler, B., Artiglia, L., Maier, U., Moehl, T., Fabbri, E., Huthwelker, T., Schmidt, T., Ammann, M., van Bokhoven, J. A., Raabe, J., Osterwalder, J. Probing the solid–liquid interface with tender x rays: A new ambient-pressure x-ray photoelectron spectroscopy endstation at the Swiss Light Source. \*Rev. Sci. Instrum.\* 91, 023103 (2020).
+
+<|ref|>text<|/ref|><|det|>[[115, 809, 860, 903]]<|/det|>
+51. Axnanda, S., Crumlin, E. J., Mao, B., Rani, S., Chang, R., Karlsson, P. G., Edwards, M. O. M., Lundvist, M., Moberg, R., Ross, P., Hussain, Z., Liu, Z. Using “Tender” X-ray Ambient Pressure X-Ray Photoelectron Spectroscopy as A Direct Probe of Solid-Liquid Interface. \*Scie. Rep.\* 5, 9788 (2015).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 98, 880, 562]]<|/det|>
+52. Favaro, M., Jeong, B., Ross, P. N., Yano, J., Hussain, Z., Liu, Z., Crumlin, E. J. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface Nat. Commun. 7, 12695 (2016).
+53. Lázaro-Martínez, J. M., Lupano, L. V. L., Piehl, L. L., Rodríguez-castellón, E., Dall’Orto, V. C. New Insights about the Selectivity in the Activation of Hydrogen Peroxide by Cobalt or Copper Hydrogel Heterogeneous Catalysts in the Generation of Reactive Oxygen Species. J. Phys. Chem. C 120, 29332-29347 (2016).
+54. Khalil, T. E., Soliman, S. M., Khalil, N. A., El-Faham, A., Foro, S., El-Dissouky, A. Synthesis, structure, X-ray photoelectron spectroscopy (XPS), and antimicrobial, anticancer, and antioxidant activities of Co (III) complexes based on the antihypertensive hydralazine. Appl. Org. Chem. 36, e6565 (2022).
+55. Bridge, M. E., Lambert, R. M. Oxygen chemisorption, surface oxidation, and the oxidation of carbon monoxide on cobalt (0001). Surf. Scie. 82, 413-424 (1979).
+56. Hyman, M. P., Vohs, J. M. Reaction of ethanol on oxidized and metallic cobalt surfaces. Surf. Scie. 605, 383-389 (2011).
+57. Moonshiran, D., Gimbert-Suriñach, C., Guda, A., Picon, A., Lehmann, C. S., Zhang, X., Doumy, G., March, A. M., Benet-Buchholz, J., Soldatov, A., Llobet, A., Southworth, S. H. Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water. J. Am. Chem. Soc. 138, 10586-10596 (2016).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 43, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 131, 253, 149]]<|/det|>
+- H2evolutionSI.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/images_list.json b/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..212adbeae092458ac3b6e6aa6a3aceced3676eed
--- /dev/null
+++ b/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/images_list.json
@@ -0,0 +1,62 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1. A type II MCA depletion model affects seed physiology and vacuolar morphology.",
+ "footnote": [],
+ "bbox": [
+ [
+ 117,
+ 415,
+ 907,
+ 828
+ ]
+ ],
+ "page_idx": 15
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2. MCA-IIs associate with and affect the ER.",
+ "footnote": [],
+ "bbox": [
+ [
+ 118,
+ 73,
+ 860,
+ 445
+ ]
+ ],
+ "page_idx": 17
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig. 3. MCA-Ils associate with CDC48 and PUX10 in the LDAD pathway.",
+ "footnote": [],
+ "bbox": [
+ [
+ 122,
+ 123,
+ 905,
+ 696
+ ]
+ ],
+ "page_idx": 18
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig. 4. MCA-lls modulate ERAD by regulating CDC48 localization.",
+ "footnote": [],
+ "bbox": [
+ [
+ 118,
+ 74,
+ 850,
+ 551
+ ]
+ ],
+ "page_idx": 20
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf.mmd b/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..1e36d99647513d6c37f6a7c1fc2f5dc3dd263557
--- /dev/null
+++ b/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf.mmd
@@ -0,0 +1,364 @@
+
+# Seed Longevity is Controlled by Metacaspases
+
+Panagiotis Moschou panagiotis.moschou@lsu.se
+
+Uppsala BioCenter https://orcid.org/0000- 0001- 7212- 0595
+
+Chen Liu Swedish University of Agricultural Sciences and Linnean Center for Plant Biology https://orcid.org/0000- 0002- 1604- 0694
+
+Ioannis Chatzianestis University Of Crete
+
+Thorsten Pfirrmann HMU Potsdam
+
+Reza Salim Uppsala University
+
+Elena Minina SLU https://orcid.org/0000- 0002- 2619- 1859
+
+Ali Moazzami Department of Molecular Sciences, Uppsala BioCenter, Swedish University of Agricultural Sciences
+
+Simon Stael Swedish University of Agricultural Sciences
+
+Emilio Gutierrez- Beltran Universidad de Sevilla, Spain
+
+Eugenia Pitsili Centre for Research in Agricultural Genomics
+
+Peter Dörmann University of Bonn https://orcid.org/0000- 0002- 5845- 9370
+
+Sabine D'Andrea INRA Institut Jean- Pierre Bourgin
+
+Kris Gevaert Francisco Romero- Campero University of Sevilla https://orcid.org/0000- 0001- 9834- 030X
+
+Pingtao Ding Leiden University
+
+Moritz Nowack Universität Köln
+
+<--- Page Split --->
+
+Frank van Breusegem VIB
+
+Jonathan Jones
+
+The Sainsbury Laboratory, University of East Anglia https://orcid.org/0000- 0002- 4953- 261X
+
+Peter Bozhkov SLU
+
+Article
+
+Keywords:
+
+Posted Date: May 2nd, 2023
+
+DOI: https://doi.org/10.21203/rs.3.rs- 2836590/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on August 8th, 2024. See the published version at https://doi.org/10.1038/s41467- 024- 50848- 2.
+
+<--- Page Split --->
+
+# Seed Longevity is Controlled by Metacaspases
+
+Chen Liu \(^{1,2}\) , Ioannis H. Hatzianestis \(^{1,3}\) , Thorsten Pfirrmann \(^{4}\) , Salim H. Reza \(^{5}\) , Elena A. Minina \(^{6}\) , Ali Moazzami \(^{6}\) , Simon Stael \(^{6,7,8}\) , Emilio Gutierrez- Beltran \(^{9,10}\) , Evgenia Pitsili \(^{7,8}\) , Peter Dörmann \(^{11}\) , Sabine D' Andrea \(^{12}\) , Kris Gevaert \(^{7,8}\) , Francisco Romero- Campero \(^{7,8}\) , Pingtao Ding \(^{13}\) , Moritz K. Nowack \(^{7,8}\) , Frank Van Breusegem \(^{7,8}\) , Jonathan D. G. Jones \(^{14}\) , Peter V Bozhkov \(^{6}\) , Panagiotis N. Moschou \(^{1,2,3*}\)
+
+\(^{1}\) Department of Biology, University of Crete, Heraklion, Greece \(^{2}\) Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden \(^{3}\) Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology – Hellas, Heraklion, Greece \(^{4}\) Department of Medicine, Health and Medical University, Potsdam, Germany \(^{5}\) Plant Ecology and Evolution, Department of Ecology and Genetics, Evolutionary Biology Centre and the Linnean Centre for Plant Biology in Uppsala, Uppsala University, Uppsala, Sweden \(^{6}\) Department of Molecular Sciences, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden \(^{7}\) VIB- Ugent Center for Plant Systems Biology, Technologiepark 71, 9052 Ghent, Belgium \(^{8}\) Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 71, 9052 Ghent, Belgium \(^{9}\) Instituto de Bioquimica Vegetal y Fotosintesis, Consejo Superior de Investigaciones Cientificas (CSIC)- Universidad de Sevilla, Sevilla, Spain \(^{10}\) Departamento de Bioquimica Vegetal y Biologia Molecular, Facultad de Biologia, Universidad de Sevilla, Sevilla, Spain \(^{11}\) University of Bonn, Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), Karlrobert- Kreiten- Straße 13, 53115 Bonn, Germany \(^{12}\) Institut Jean- Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris- Saclay, 78000 Versailles, France \(^{13}\) Institute of Biology Leiden, Leiden University, Leiden 2333 BE, The Netherlands \(^{14}\) The Sainsbury Laboratory, University of East Anglia, NR4 7UH Norwich, United Kingdom
+
+\*Corresponding author: Panagiotis N. Moschou. Email: Panagiotis.moschou@uoc.gr
+
+<--- Page Split --->
+
+## Abstract
+
+To survive extreme desiccation, seeds enter a period of dormancy that can last millennia. Seed dormancy involves the accumulation of protective storage proteins through unknown adjustments in proteasomal degradation. Mutating all six type II metacaspase (MCA- II) proteases in Arabidopsis thaliana revealed their essential roles in modulating proteasomal degradation. MCA- II mutant seeds fail to target the AAA ATPase CELL DIVISION CYCLE 48 (CDC48) at the endoplasmic reticulum to discard misfolded proteins, compromising their storability. Moreover, we show that MCA- IIs cleave a PUX (ubiquitination regulatory X domain- containing) adaptor, which is responsible for the localization of CDC48 to lipid droplets. This cleavage enables the shuttling of CDC48 between lipid droplets and the endoplasmic reticulum, constituting an important step in the regulation of spatiotemporal proteolysis. In summary, we uncovered a proteolytic pathway conferring seed longevity.
+
+<--- Page Split --->
+
+## Introduction
+
+The desiccation- associated phytohormone abscisic acid (ABA) modulates seed dormancy by repurposing pre- existing stress- related networks into a seed dormancy program. This rewiring allows large amounts of proteins to be stored in the seed to protect and nourish the embryo 1. These proteins are highly structurally disordered 2, which could be expected to activate the unfolded protein response (UPR) 3. The UPR is a proteolytic mechanism involving the proteasome that slows translation to help remove misfolded or even disordered proteins that cause endoplasmic reticulum (ER) stress. A constitutive UPR slows translation by decreasing the rate of protein biosynthesis, which is achieved by inducing the INOSITOL- REQUIRING 1- 1 (IRE1)- dependent RNA degradation (RIDD) pathway that degrades RNAs, especially for secretory proteins bound to ribosomes 4. Notably, seeds can maintain high protein contents without activating protein homeostasis pathways, suggesting they have the ability to control proteolytic mechanisms (e.g., the UPR).
+
+The cysteine proteases metacaspases (MCAs) are present in bacteria and all eukaryotes except animals 5. In contrast to animal- specific caspases, MCAs cleave proteins after arginine (R) or lysine (K) residues, but not aspartate (D) 5. While some organisms contain a single MCA gene (e.g., budding yeast [Saccharomyces cerevisiae]), land plants contain multiple MCA family members. For example, the model plant Arabidopsis (Arabidopsis thaliana) has nine MCAs, which are classified as type I or II (with three [MCA- I] and six [MCA- II] members; Fig. 1A) based on their structure. MCA- Is modulate pathogen- induced programmed cell death (PCD), vascular development, and the clearing of protein aggregates 6- 8, while plant- specific MCA- IIs are involved in abiotic stress responses, wound- induced damage- associated molecular pattern signaling, and developmental PCD 9- 12.
+
+Despite their importance, the exact molecular functions of MCA- IIs remain elusive. Indeed, four of the six MCA- II genes are located in tandem on Arabidopsis chromosome 1, making it challenging to obtain double or high- order transfer (T)- DNA- based mutants (Fig. 1A, note the nomenclature used for MCA- IIs as in 5).
+
+## Results
+
+## Type II metacaspases have redundant functions
+
+To overcome the potential redundancies among MCA- IIs, we used clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR- associated nuclease 9 (Cas9)- mediated genome editing to obtain homozygous plants harboring single or higher- order mutations in MCA- II genes in various combinations, as well as two independent transgene- free lines lacking function of all six MCA- IIs. The sextuple MCA- II mutants are referred to hereafter as mca- II- KOc (c for "clean line" without CRISPR transgenes; fig. S1A- E). Both mca- II- KOc lines are likely loss- of- function mutants, as they displayed 1) no MCA- II- a protein using a specific antibody in immunoblots (this antibody does not cross- react with other MCA- IIs), accompanied by lower transcript levels of MCA- II genes, suggesting that the mutations introduced by gene editing led to nonsense- mediated decay, a process known to affect transcripts with frameshifts that induce premature stop codons 13; 2) diminished cleavage of the known MCA- II substrate TUDOR STAPHYLOCOCCAL NUCLEASE 14; and 3) lower in vitro activity on a fluorogenic substrate that is also cleaved by MCA- IIs (9; Fig. 1B,C and fig. S1F).
+
+Remarkably, the mca- II- KOc plants displayed only mild developmental defects, with reduced leaf serration (i.e., the formation of teeth at leaf margins), earlier flowering, and earlier leaf
+
+<--- Page Split --->
+
+senescence compared to the wild type (WT) (fig. S2A). However, these plants did not show signs of compromised developmental PCD, e.g., in the root cap, but showed compromised PCD when challenged with virulent strains of the pathogens Botrytis cinerea and Pseudomonas syringae (fig. S2B- D). In agreement with our results, a quadruple mutant in MCA- II genes showed a similarly compromised response to Botrytis infection 15. Furthermore, effectortriggered immunity (ETI)- associated PCD (i.e., hypersensitive response) was abolished in mca- II- KOc lines challenged with the effector AvrRps4 (fig. S2C, left panel), which is recognized by TIR (Toll- like, Interleukin- 1 receptor, Resistance protein) intracellular NLR (nucleotide- binding, leucine- rich repeat) immune receptors 16. By contrast, we observed no obvious differences in AvrRpt2- induced ETI- associated PCD (fig. S2C, right panel), which is mediated by coiled- coil (CC) NLR receptors. Although AvrRpt2- induced ion leakage (serving as a proxy for the hypersensitive response) was reported to be slightly reduced at early time points 17, we detected no obvious difference after one day of treatment in mca- II- a single mutants compared to the WT (fig. S2C). We thus postulate that MCA- IIs play both redundant and specific roles in TIR- NLR- mediated PCD, but likely not in CC- NLR- mediated PCD, at least with the effectors tested here. On the contrary, MCA- IIs might not be involved in the execution of generic cell death programs during development, at least in Arabidopsis, suggesting other modes of action.
+
+During our studies, we noticed that freshly collected mca- II- KOc seeds germinated more quickly than WT seeds, suggesting reduced seed dormancy. When the same batch of seeds was stored for 3 months or longer at \(4^{\circ}\mathrm{C}\) (as low temperatures increase the lifespan of Arabidopsis seeds), the germination rate of the mutant seeds rapidly declined relative to the WT (Fig. 1D- F). Germination failure was accompanied by the presence of fragmented and irregularly shaped vacuoles that accumulated aggregates. This vacuolar fragmentation was associated with unknown large structures that appeared to mechanically compress and deform the vacuolar membrane (Fig. 1G). We discuss the nature of these structures below. The seed germination phenotype was mostly specific to mca- II- KOc lines and was seldom observed in the corresponding lower- order mutants. Even the presence of a single active MCA- II was sufficient to suppress this phenotype (fig. S3A, B; note the expression of MCA- IIs in seeds). These results suggest that MCA- IIs redundantly control aspects of seed physiology.
+
+## Metacaspases participate in the ER stress response
+
+As we observed vacuoles resembling those rich in protein aggregates (storage vacuoles) reported in 18, we speculated that MCA- IIs regulate aspects of protein homeostasis in seeds via their proteolytic activity. To identify proteolytic targets of MCA- IIs, we conducted a proteomic analysis of mca- II- KOc and WT dry seeds (stored at \(4^{\circ}\mathrm{C}\) for 3 months, before mca- II- KOc seeds lose substantial viability). We used a log2fold- change (FC)>1 between mca- II- KOc and WT peptides as the criterion for protein enrichment (Data S1). Gene ontology (GO) analysis of the enriched proteins showed that mca- II- KOc seeds accumulate proteins residing at the ER or associated structures (i.e., lipid droplets) and proteins related to the UPR, e.g., the major ER stress- associated chaperones BiP (binding immunoglobulin protein) and disulfide isomerases (PDIs) (Fig 2A and Data S1; 19,20). To determine the localizations of MCA- II- a and MCA- II- d, we generated transgenic plants carrying a translational fusion construct encoding MCA- II- a or MCA- II- d fused to green fluorescent protein (GFP) under the control of their respective native promoters. We detected GFP fluorescence associated with the ER in embryonic root cells; we validated this observation by cell fractionation on sucrose density gradients, with GFP- MCA- II- a co- fractionating with the ER marker protein BiP2 (Fig. 2B, C). These findings suggest that MCA- IIs cleave proteins at the ER to regulate their abundance.
+
+<--- Page Split --->
+
+To test whether MCA- IIs directly cleave the identified proteins that accumulated at the ER in vivo, we performed N- terminome analysis of the seed proteome via combined fractional diagonal chromatography (COFRADIC) 21. This approach enables the identification of cleavage sites introduced by proteases and the resulting novel N termini (neo- N termini) formed in vivo upon proteolysis (fig. S3C, D). However, we failed to detect any of the enriched ER proteins identified in the mca- II- KOc mutants as direct targets of MCA- IIs by COFRADIC analysis of the proteome from WT seeds (fig. S3E and Data S2). Hence, we examined the alternative possibility that mca- II- KOc seeds indirectly accumulate the identified ER proteins by mounting an ER stress response, leading to the activation of the UPR associated with the accumulation of BiP and PDIs 4. However, transcriptome deep sequencing (RNA- seq) experiments did not identify the known transcriptional signatures associated with the UPR in mca- II- KOc seeds (fig. S4A- C and Data S3; 2). Taken together, these results suggest that although mca- II- KOc seeds show ER stress, they do not activate a constitutive UPR.
+
+Based on these results, we hypothesized that MCAs function independently of a constitutive UPR. We thus tested whether MCA- IIs regulate the proteasome using MCA- II- a and MCA- II- b and their inactive Proteolytically- Dead (MCA- II- a/bPD, with catalytic Cys replaced with Ala) variants as baits for affinity purification followed by liquid chromatography- tandem mass spectrometry (fig. S5A and Data S4). These assays showed that MCA- IIs interact weakly with two chaperones involved in proteasome assembly (fig. S5B; 2 out of 32 proteins in the proteasome assembly; REGULATORY PARTICLE TRIPLE- A ATPASE 5A- RPT5a and AT5G45620- SS regulatory sub 13a, 7 and 1 peptides for MCA- II- b, respectively). Mutating the catalytic Cys (MCA- II- a/bPD) facilitated these interactions, likely because these proteins remained bound to their substrates, as they do not catalyze their cleavage (Data S4). The mutant MCA- II- aPD bait, but not its WT version, associated with (poly- )ubiquitin (Ub)- conjugated proteins, which are normally recognized by the proteasome. As only the mutant bait associated with Ub- conjugated proteins, this suggests that MCA- IIs preferentially target Ub- conjugated/associated proteins forming with these transient complexes (fig. S5C, D). In support of this idea, Ub- conjugated proteins were more abundant in mca- II- KOc relative to WT (Fig. 2D; \(\sim 3\) - fold). Moreover, regulatory subunits of the proteasome accumulated to higher levels in mca- II- KOc compared to WT, as revealed by total proteomic analysis of mca- II- KOc seeds (Data S1). In particular, we observed accumulation of the 26S proteasome, a phenotype reminiscent of proteasomal receptor mutants, e.g., mutants of the REGULATORY PARTICLE NON- ATPASE 10 (rpn10) subunit of the proteasome (22; fig. S5E- G). Furthermore, mca- II- KOc mutants were insensitive to treatment with the proteasome inhibitor MG132 (a peptide aldehyde that reversibly inhibits the proteasome), but not with other proteolytic inhibitors, as was reported for several proteasomal mutants (fig. S5H and 23). Notably, MCA- II- a did not cleave K48 tetra- Ub isopeptide linkages, which represent the most abundant and canonical degradation signals (fig. S6 and 24). This finding argues against the possibility that MCA- IIs remove Ub from proteins (i.e., they are not deubiquitinases). Taken together, these results suggest that MCA- IIs modulate proteasome activity.
+
+## Type II metacaspases regulate the lipid droplet-associated degradation pathway in seeds via interaction with CDC48
+
+As the UPR was not induced while proteasomal activity was compromised in mca- II- KOc mutants, we hypothesized that Arabidopsis seeds rely on alternative pathways for protein homeostasis. We focused on ER- associated degradation (ERAD), as this process would still promote the retrotranslocation of Ub- proteins from the ER to the cytosol for degradation by the proteasome, much like the UPR 25. Furthermore, ERAD would fit well in the context of
+
+<--- Page Split --->
+
+seed proteostasis by allowing the excess accumulation of secreted seed storage proteins (e.g., 2S albumins, late embryogenesis abundant proteins, and 12S globulins) that nurture and protect the embryo, unlike the UPR pathway, which would compromise the production of secreted proteins by eliciting translational suppression through RIDD \(^{25,26}\) . In plants, ERAD promotes the formation of an impermeable cuticle, a waxy layer that attenuates desiccation stress by retaining water in the plant body \(^{27}\) . The enzymes for cuticle biosynthesis are localized to the ER. The cuticle also renders young seedlings (e.g., 3- day- old) less responsive to ABA and is required for proper apical hook formation \(^{28}\) , which is indispensable for protecting the delicate shoot apical meristem. Seeds of the core proteasomal mutant rpn10 display compromised longevity, compromised hypocotyl elongation due to the accumulation of the transcription factor ELONGATED HYPOCOTYL 5 (HY5), and hypersensitivity to ABA and ER stress \(^{29}\) . Accordingly and in line with a possible link between MCA- II and ERAD (and proteasome), we observed cuticle abnormalities in 3- day- old etiolated mca- II- KOc seedlings, as revealed by toluidine blue permeability assays (Fig. 3A, \(^{28}\) ). This phenotype was absent from mca- II- KOc plants harboring a complementation construct expressing MCA- II- a driven by the meristem- specific RIBOSOMAL PROTEIN S5a (RPS5a, from locus AT3G11940) promoter (Fig. 3A, "Com"). We corroborated these results by staining cuticles with the suberin- specific dye FluoroI Yellow 088 (FY088) in embryonic roots and observing defects typically linked to cuticle loss, such as sensitivity to ABA and the absence of an apical hook, in mca- II- KOc (fig. S7A- C; \(^{30}\) ). Hence, mca- II- KOc may show compromised ERAD.
+
+In budding yeast, the sole type I MCA (Mca1p) interacts with the AAA ATPase CELL DIVISION CYCLE 48 (CDC48; valosin- containing protein [VCP] in vertebrates) to regulate protein homeostasis \(^{31}\) . CDC48 is a major ERAD component that exports proteins from the ER for proteasomal delivery and regulates proteasome activity, functioning as an "unfoldase/segregase" \(^{26}\) . We identified CDC48 as a direct interactor of MCA- II- a and confirmed their colocalization and direct interaction via a quantitative in vivo proximity ligation assay (PLA) and in embryonic roots harboring the transgenes RPS5apro:mNeon- MCA- II and 35Spro:mCherry- CDC48 \(^{32,33}\) ; furthermore, MCA- II- a localized on lipid droplets together with CDC48 (Fig. 3B- E and fig. S8C). From these assays, we conclude that in seeds, MCA- II- a and CDC48 colocalize to lipid droplets at a higher concentration than in the surrounding cytoplasm (Fig. 3B, C, arrowheads).
+
+Since CDC48 interacted with MCA- II- a, and its homologs (e.g., CDC48E) were 4.1- times more abundant in the mca- II- KOc proteome dataset compared to WT (Data S1), we asked whether MCA- IIs regulate CDC48 activity. We focused on the specialized type of ERAD pathway named lipid droplets- associated degradation (LDAD), which removes Ub- oleosins from lipid droplets in seeds, facilitating their breakdown and remobilization during seed germination \(^{34}\) . Lipid droplets fuse with one another to form larger droplets in loss- of- function oleosin mutants \(^{35}\) . In agreement with this finding, we observed reduced abundance of oleosin in mca- II- KOc (by \(>30\) - fold), which was associated with an increased size of lipid droplets and the localization of MCA- II- a on lipid droplets (Fig. 3F, G; note the partial complementation of this phenotype in the "Com" line). Notably, the mutations in mca- II- KOc plants did not significantly affect fatty acid levels or composition (fig. S7D), suggesting that LDAD does not substantially contribute to lipid pools in seeds.
+
+During LDAD, the CDC48 adaptor PUX10 (ubiquitination regulatory X [UBX] domain- containing 10), one of the 16 PUX adaptors in Arabidopsis defined by a ubiquitin- like UBX domain, specifically recognizes Ub- oleosin for degradation; accordingly, oleosin accumulates in pux10 mutants \(^{34}\) . PUX10 harbors a ubiquitin- associated (UBA) domain at its N terminus \(^{36}\) . The UBA domain increases protein stability by reducing the incorporation of proteins into the proteasome; conversely, removing the UBA domain from proteins results in their degradation
+
+<--- Page Split --->
+
+37. We confirmed that MCA-II-α and PUX10 colocalize and interact in Fösters resonance energy transfer-sensitized emission (FRET-SE) and PLA by examining embryonic roots harboring the transgenes RPS5apro:MCA-II-a-tagRFP and PUX10pro:PUX10-GFP (Fig. 3C, E, upper panel and fig. S8A-C). Notably, MCA-II-a colocalized with PUX10 only when the levels of PUX10 were low, suggesting an inverse correlation between the signals of the two proteins (R²=-0.45; see below for an explanation). From these assays, we conclude that in seeds, MCA-II-a and PUX10 colocalize, but MCA-II-a appears to reduce PUX10 levels. These results suggest that MCA-IIs regulate LDAD by associating with CDC48 and PUX10.
+
+## The antagonism between lipid droplet- and ER-associated protein degradation pathways determines seed longevity
+
+In our colocalization assays, we observed that PUX10- GFP levels in cells were inversely correlated with the levels of MCA-II- a- tagRFP (Fig. 4A, Pearson's correlation coefficient \(\mathrm{R} =\) - 0.36). However, in a transgenic line that accumulated GFP- PUX10 (i.e., tagged N- terminally with GFP this time), the presence of MCA- II- a- tagRFP had no effect on GFP fluorescence levels, suggesting that the N- terminal fragment of PUX10 remained stable. To resolve this conundrum, we used Nicotiana benthamiana leaves as a heterologous transient expression system. We detected the specific cleavage of PUX10 by MCA- II- a, leading to the accumulation of an N- terminal fragment of PUX10 that interacted with MCA- II- a in co- immunoprecipitation assay (Fig S8D- F). Accordingly, in our COFRADIC data, the N terminus of a PUX homolog (PUX5) was highly enriched in WT but not in mca- II- KOc samples (fig. S3F and Data S2). Hence, although PUX10 is cleaved and its C- terminal region that interacts with CDC48 is degraded (i.e., the UBX part), the N- terminal fragment containing the stabilizing UBA domain remains associated with MCA- IIs, likely through Ub.
+
+The lack of PUX10 cleavage in mca- II- KOc would be expected to lead to increased retention of CDC48 attached to lipid droplets. This hypothesis was validated by the observation that, in contrast to WT, in mca- II- KOc, mCherry- CDC48 decorated large intracellular structures reminiscent of lipid droplets, whereas its ER signal decreased (Fig. 4B). We reasoned that the depletion of CDC48 from the ER in mca- II- KOc would lead to aggravated ER stress and cell death in seeds. To test this idea, we first compared the effects of external inhibition of CDC48 activity in WT and mca- II- KOc using CB- 5083, a specific inhibitor of CDC48 \(^{36}\) . Indeed, loss of function of MCA- II enhanced the response of seedlings to CB- 5083 (Fig. 4C, note the root swelling). Next, we measured seed viability using tetrazolium staining and found increased PCD in mca- II- KOc (Fig. 4D). Together, these results suggest that efficient ERAD requires an MCA- II- dependent pathway that involves PUX10 cleavage to enable the attenuation of LDAD and the ER targeting of CDC48 to promote seed longevity (Fig. 4E, model).
+
+## Discussion
+
+We uncovered a mechanism for the regulation of spatial proteasomal activity that involves the specific cleavage of a PUX adaptor to modulate the intracellular location of CDC48 in the specialized ERAD pathway. Interestingly, the deletion of the PUX10 homolog Alveolar soft part locus (ASPL) or Ubiquitin regulatory X4 (UBX4) impaired ERAD and led to toxicity in mammalian cells and budding yeast, respectively \(^{38,39}\) . In the seed context, however, balancing LDAD is an important step in the regulation of ERAD, which likely involves other PUX proteins. Further research is required to uncover additional links between PUXs and MCAs. In line with our results, the localization of UBXD8 (Ubiquitin regulatory X domain- containing protein 8), a mammalian CDC48 adaptor, is regulated by a rhomboid pseudoprotease, which is responsible for shuttling CDC48 between the ER and lipid droplets, thereby regulating energy squandering \(^{25,40}\) . In non- plant models, suppressing protein anabolism can lead to enhanced longevity; likewise, reduced protein translation via UPR waves may be functionally equivalent
+
+<--- Page Split --->
+
+but likely would not suit the seed context in which high protein accumulation is required. The pathway linking MCA- II- dependent PUX cleavage and CDC48 activity appears to have evolved as an elegant solution to this problem by enabling sustained protein production while maintaining protein homeostasis.
+
+## Methods
+
+## Plant material
+
+All the plant lines used in this study were in the Arabidopsis Columbia- 0 (Col- 0) ecotype. The following mutants were used smb41, mca- II- d (SALK_127688) and mca- II- f (GABI_540H06). The two mca mutants were used as a background for CRISPR. Primers used for genotyping of mutant lines can be found in Table S1. The following transgenic lines used in this study were described previously: PUX10pro:PUX10- GFP42 and MCA- II- fpro:MCA- II- f- GFP43. Seedlings were grown on half- strength Murashige and Skoog (MS) plant agar media under long- day conditions (16h- light/8h- dark, or as indicated) and were harvested, treated, or examined as indicated in the context of each experiment. In all experiments, seedlings, or plants from T1/F1 (co- localization experiments), T2/F2, or T3/4/5 (for physiological experiments) generations were used. Arabidopsis seeds were sterilized and germinated on half- strength MS agar medium under long- day conditions (16 h light/8 h dark). Arabidopsis plants for crosses, phenotyping of the above- ground part, and seed collection were grown on soil in a plant Aralab chamber at \(22^{\circ}C / 19^{\circ}\) and a light intensity of \(150\mu \mathrm{mol}\mathrm{m}^{- 2}\mathrm{s}^{- 1}\) with \(60\%\) relative humidity stabilized by an infrared sensor. The seeds harvested at the same time under the same condition were used for experiments unless otherwise indicated in the text or figure legends. Nicotiana benthamiana plants were grown in Aralab or Percival cabinets at \(22^{\circ}C\) , 16- h- light/8- h- dark cycles, and a light intensity of \(150\mu \mathrm{mol}\mathrm{m}^{- 2}\mathrm{s}^{- 1}\) .
+
+## Metacaspase phylogeny
+
+Alignments of MCAs sequences were performed in MUSCLE. Unrooted trees were constructed using the neighbour- joining method44 using the yeast homologue as an outgroup. A phyldendrogram was constructed using MEGA11 and PAUP software (http://paup.csit.fsu.edu). The bootstrap analysis was performed with 1,000 repeats, and branches with bootstrap values over \(70\%\) were retained. The sequences used can be found in Data S5.
+
+## Drugs and stainings
+
+The stock solutions of \(2\mathrm{mM}\) FM4- 64, \(10\mathrm{mM}\) CB- 5083 (1- (4- (benzylamino)- 7,8- dihydro- 5H- pyrano- (4,3- d)- pyrimidin- 2- yl)- 2- methyl- 1H- indole- 4- carboxamide), \(1\mathrm{mM}\) BCECF (2',7'- Bis- (2- Carboxyethyl)- 5- (and- 6)- Carboxyfluorescein, Acetoxymethyl Ester), LipidTox (1:1000 dilution, Thermo, H34477), ER tracker (1:1000 dilution, Thermo, E34251), Lysotracker (1:1000 dilution, Thermo, L7528), \(50\mathrm{mM}\) MG132, \(2\mathrm{mM}\) Concanamycin A (Con A), \(33\mathrm{mM}\) wortmannin (Wm) and \(10\mathrm{mM}\) E64d were dissolved in dimethyl sulfoxide (DMSO), while \(1\mathrm{M}\) dithiothreitol (DTT) was dissolved in water. Propidium iodide (PI) was dissolved in water. These inhibitors, drugs and stains were diluted in a half- strength MS medium with corresponding concentration and duration, and the final DMSO concentration was \(\leq 0.1\%\) (v/v) in all experiments. Vertically grown 4- to 5- day- old Arabidopsis seedlings were incubated in a half- strength liquid MS medium containing the corresponding drugs for each specific time course treatment as indicated. For confocal microscopy of reporters and mutants, fluorescence images were captured on Leica SP8 or Zeiss780 microscopes and were processed with ImageJ (National Institutes of Health). Cell contours were visualized with propidium iodide (PI) (Molecular Probes) or FM4- 64. For the FDA- PI viability staining, seedlings were mounted on a glass slide in FDA solution (1 \(\mu \mathrm{L}\) dissolved FDA stock solution [2 mg in 1 ml acetone] in 1 ml of 1/2 MS) supplemented with \(10\mu \mathrm{g / ml}\) PI. For the seed viability test, tetrazolium red assays were done as described previously45. In short, dry seeds from different genotypes were incubated in the dark in an aqueous solution of \(1\%\) (w/v) 2,3,5- triphenyl tetrazolium (TZ) at \(28^{\circ}C\) for \(24\mathrm{to}48\mathrm{h}\) with or without indicated treatment. Seeds were rinsed in water before imaging. For the cuticle
+
+<--- Page Split --->
+
+integrity assay, the experiment was done as described previously \(^{46}\) . In short, 48h- post germinated seedlings were incubated in Fluorol Yellow (FY)- 088 (0.01% [w/v] in lactic acid) for \(70^{\circ}C\) , 20min incubation, and the seedlings were rinsed in water and checked under Zeiss 780 microscopes with GFP channel setting (Ex: 488- 490 nm, Em: 530- 550 nm). For studying the permeability with toluidine blue \(^{47}\) , 4 to 5- day- old etiolated seedlings grown on \(1 / 2\) MS plate were collected and then incubated in an aqueous solution of \(0.05\%\) [w/v] toluidine blue/0.1% [w/w] Tween 20 for 120 sec followed by a quick washing step in \(\mathrm{ddH_2O}\) . Seedlings were observed with Leica DM6000. For lipid droplet staining, lipidTox (Thermo Fisher Scientific; 500- fold dilution) was used as previously described \(^{42}\) .
+
+## Plant infection assay
+
+The Botrytis cinerea strain B05.10 was used in the infection experiments and stored as conidia suspension at \(- 80^{\circ}C\) in \(40\%\) (v/v) glycerol. For conidia production culture was grown in Hydroxyapatite (HA) medium (1% (w/v) Malt extract/ \(0.4\%\) (w/v) Glucose / \(0.4\%\) (w/v) Yeast extract / \(1.5\%\) (w/v) Agar, pH 5.5) and incubated at \(25^{\circ}C\) for 7 days. 3- 4 weeks plants with fully expanded leaves were used for inoculations. Spore suspensions were prepared in Gamborg Minimal medium (3 g Gamborg B5 basal salt mixtures, \(1.36 \mathrm{g} \mathrm{KH}_2 \mathrm{PO}_4\) , and \(9.9 \mathrm{g}\) glucose per liter), collected by scraping the mycelial colony and adjusted to a concentration of \(2 \times 10^{5}\) spores \(\mathrm{ml}^{- 1}\) . A droplet of conidia suspension (10 \(\mu \mathrm{l}\) ) was placed at one different point of the adaxial surface of each leaf. Control plants were sprayed or drenched with sterile tap water.
+
+## Hypersensitive cell death response phenotyping in Arabidopsis
+
+The desired avirulent effectors AvrRps4 or AvrRpt2 were delivered to the Arabidopsis plants via a Pseudomonas fluorescens effector- to- host analyzer strain (EtHAn), with a P. syringae pv. Syringae 61 hrp/hrcc cluster (Type III secretion system machinery) stably integrated into the chromosome in Pf0- 1 (Thomas et al., 2009). EtHAn:AvrRps4 and EtHAn:AvrRpt2 were grown on selective KB plates for \(24 \mathrm{h}\) at \(28^{\circ}C\) \(^{48}\) . Bacteria were harvested from the plates, resuspended in infiltration buffer ( \(10 \mathrm{mM} \mathrm{MgCl}_2\) ), and the concentration was adjusted to \(\mathrm{OD}_{600} = 0.2\) (108 CFU \(\mathrm{ml}^{- 1}\) ). The abaxial surfaces of 5- week- old Arabidopsis leaves were hand infiltrated with a 1 ml needleless syringe. Cell death was monitored \(24 \mathrm{h}\) after infiltration.
+
+## Protease activity assay
+
+Protease activities were measured by fluorogenic peptide- based substrate (EGR- AMC: H- GluGly- Arg- 7- amino- 4- methylcoumarin) as described in \(^{49}\) . Plant (0.01g seeds or equal amount of 7- day- old seedlings) extract from WT and different mutants using reaction buffer: \(50 \mathrm{mM}\) HEPES, pH 7.4, \(0.1\%\) (w/v) 3- [(3- cholamido- propyl) dimethylammonio]- 1- propanesulfonate (CHAPS), \(50 \mathrm{mM} \mathrm{CaCl}_2\) , \(5 \mathrm{mM}\) dithiothreitol (DTT); EGR- AMC were added at \(50 \mu \mathrm{M}\) final. The release of AMC was measured every \(2 \mathrm{min}\) at \(30^{\circ}C\) with a Microtiter Plate Fluorometer (Microplate reader Fluostar Omega) using an excitation wavelength of \(360 \mathrm{nm}\) and an emission wavelength of \(460 \mathrm{nm}\) . Data time points were analyzed by the Omega Fluostar software, and activities were expressed in fluorescence units/min/mg or \(\mu \mathrm{g}\) of total protein. Protein concentration was determined using the Bradford reagent (Bio- Rad).
+
+## DNA manipulation and production of transgenic lines
+
+Electrocompetent Agrobacterium (Agrobacterium tumefaciens) strain C58C1 Rif \(^{R}\) (pMP90) or GV3101 Rif \(^{R}\) (i.e., a cured nopaline strain commonly used for infiltration) was used for electroporation, N. benthamiana infiltration and floral dip transformation in Arabidopsis \(^{50}\) . The following constructs used in the study were described previously: 35Spro:mCherry- PUX10, 35Spro:mCherry- CDC48a \(^{42}\) . Transcriptional and translational reporters and overexpression constructs used in this study were produced through either Gateway (Invitrogen) cloning using pENTR/D and pENTR5' lines or through GOLDENGATE (Addgene) in the following backbones: (i) pGWB505 and pGWB560 \(^{51}\) (ii) pMDC32 \(^{52}\) (iii) (iv) pLCSL86900 and pLCSL86922 (Addgene). The cDNA of MCA- II- a was PCR amplified with Phusion \(^{TM}\) High- Fidelity DNA Polymerase & dNTP Mix (Thermo Fisher Scientific, F530N) using cDNA from 7- day- old seedlings. MCA- II- a- PD was generated with site- directed mutagenesis with pENTR of
+
+<--- Page Split --->
+
+MCA- IIa. Constructs of MCA- IIa or MCA- IIa- PD were generated by Gateway cloning with pENTR into different destination vectors which have different tags in N- or C- termini. The coding sequence of CDC48a, PUX10 were PCR amplified with Phusion™ High- Fidelity DNA Polymerase & dNTP Mix (Thermo Fisher Scientific, F530N) using the cDNA from 7- day- old seedling with pENTR™/D- TOPO™ Cloning Kit (Thermo Fisher Scientific, K240020). Primer sequences used for the amplification of promoters and genes are listed in Table S1.
+
+## Construction of MCA-II mutants
+
+The pICSL binary vector series was utilized to generate CRISPR lines in this study. Primer sequences used for the amplification of promoters and genes are listed in Table S3. To generate the Cas9 expression cassettes, the RPS5a and Cas9z coding sequences and the E9 terminator were amplified using primers flanked with BpII restriction sites associated with Golden Gate compatible overhangs (Table S1). Combinations of three Level 0 vectors containing respectively a promoter, a Cas9z coding sequence and a terminator were assembled in Level 1 vector pICH47811 (Position 2, reverse) by the same 'Golden Gate' protocol but using 0.5 μl of BpII enzyme (10U/μl, ThermoFisher) instead of 0.5 μl of BsaI- HF. To create the MCA- II/s deletion mutant, a previously described multiplexed editing approach was used \(^{53}\) . The sgRNAs were designed using the CRISPR- P 2.0 (http://crispr.hzau.edu.cn/CRISPR2) \(^{54}\) and CHOP- CHOP (https://chopchop.cbu.uib.no/) \(^{55}\) . To generate the sgRNA expression cassettes, DNA fragments containing the classic or the 'EF' backbone with 7, 67 or 192 bp of the U6- 26 terminator were amplified using primers flanked with BsaI restriction sites associated with Golden Gate compatible overhangs (Table S4). The amplicons were assembled with the U6- 26 promoter (pICSL90002) in Level 1 vector pICH7751 (gRNA- MCA- II- e, Position 3), pICH7761 (gRNA- MCA- II- b, Position 4), pICH7772 (gRNA- MCA- II- a, Position 5) and pICH7781 (gRNA- MCA- II- c, Position 6) by the 'Golden Gate' protocol using the BsaI- HF enzyme. Combinations of three Level 1 vectors containing a red seed coat maker (FAST- Red, pICSL11015, Position2, OLE1pro:OLE1- RFP), a Cas9 expression cassette, and four sgRNA expression cassettes were assembled in Level 2 pAGM4723 (without an overdrive) or pICSL4723 (with an overdrive) by the 'Golden Gate' protocol using the BpII enzyme. All the plasmids were prepared using a ThermoScientific kit on Escherichia coli DH10B electrocompetent cells selected with appropriate antibiotics and X- gal. All the plasmid identification numbers refer to the 'addgene database' (www.addgene.org/). We selected red fluorescing seeds and screened the resulting seedlings for mutation and CRISPR clean lines were selected based on the crossing to WT and to get the segregation lines for further screening of non- red seed coat and resequencing.
+
+## RNA extraction, RNA-seq and quantitative RT-PCR analysis
+
+Total RNA from the seedlings was extracted using RNeasy Plant Mini Kit with DNaseI digestion (QIAGEN). Reverse transcription was carried out with 500 ng of total RNA using the iScript cDNA synthesis kit (Bio- Rad) according to the manufacturer's protocol. Quantitative PCR with gene- specific primers was performed with the SsoAdvanced SYBR Green Supermix (Bio- Rad) on a CFX96 Real- Time PCR detection system (BioRad). Signals were normalized to the reference genes ACTIN7 using the DCT method and the relative expression of a target gene was calculated from the ratio of test samples to WT. Primer sequences used for the amplification of promoters and genes are listed in Table S1. For each genotype, two biological replicates were assayed in three qPCR replicates. qRT- PCR primers were designed using QuantPrime \(^{56}\) . For RNA- seq the concentration of RNA was determined by Qubit® RNA HS Assay Kit (New England BioNordika BioLab, Q32852). All the RNA samples were treated with DNase I (ThermoFisher Scientific, EN0521) and further enriched with NEBNext® Poly(A) mRNA Magnetic Isolation Module (ThermoFisher Scientific, E7490S). The RNA was measured with Qubit® RNA HS Assay Kits again and libraries were prepared with NEBNext® Ultra™ II RNA Library Prep with Sample Purification Beads (Invitrogen Life Technologies (Ambion Applied Biosystem, E7775S) and NEBNext® Multiplex Oligos for Illumina® (Dual Index Primers Set 1) (New England BioNordika BioLab, E7600S). cDNA library quality was monitored with Agilent DNA 7500 Kit (Agilent Technologies Sweden AB, 5067- 1506). cDNA
+
+<--- Page Split --->
+
+libraries were sequenced with a paired- end sequencing strategy to produce \(2 \times 150\) - bp reads using Novogen sequencers and 20 million reads per sample (Novogene, England).
+
+## Cell fractionation
+
+Cell fractionation was done using MCA- II- apro:MCA- II- a- GFP lines based on sucrose gradient density ultracentrifugation \(^{57}\) . More specifically, leaves (5g) of the above line were ground followed by protein extraction buffer (50 mM Tris HCl pH 8.2, 2 mM EDTA pH 8.0, 1 mM DTT and protease inhibitors cocktail from Sigma- Aldrich at a 1:100 dilution plus 1 mM phenylmethylsulfonyl fluoride [PMSF]). The extract was filtered through miracloth and centrifuged at 5000 x g for 5 min for the removal of organelles and tissue debris, followed by ultracentrifuge at 100,000 x g for 45 min. Samples were ultracentrifuged overnight at 100,000 g. Subcellular fractions were collected in 2 ml Eppendorf and processed for immunoblot with the following antibodies: \(\alpha\) - GFP (Santa Cruz Biotechnology), \(\alpha\) - BIP2 (Agrisera), and \(\alpha\) - APX1 (Agrisera).
+
+## Fatty acid analysis
+
+The total fatty acid content and composition of mature seeds were determined by direct transmethylation followed by gas chromatography with a flame ionization detection \(^{58}\) .
+
+## Immunocytochemistry, PLA, and imaging
+
+Immunocytochemistry, PLA, and imagingImmunocytochemistry was done as described previously \(^{59}\) . The primary antibodies used were goat anti- CDC48a (VCP1) (diluted 1:500, Abcam. 206320) \(^{60}\) . In brief, samples were incubated with primary antibody at \(4^{\circ}C\) overnight and washed three times with PBS- T, and then incubated for 90 min with Alexa Fluor® 488 AffiniPure Donkey \(\alpha\) - Goat IgG (H+L) secondary antibody (Jackson ImmunoResearch, 705- 545- 147) diluted 1:200- 250, After washing in PBS- T and incubating with DAPI (1 \(\mu \mathrm{g / mL}\) ), specimens were mounted in Vectashield (Vector Laboratories) medium and observed within 48 h. PLA immunologicalization was done as described previously \(^{32}\) . Primary antibody combinations diluted 1:200 for \(\alpha\) - GFP mouse (Sigma- Aldrich, SAB2702197), 1:200 for \(\alpha\) - FLAG mouse (Sigma- Aldrich, F1804), 1:200 for \(\alpha\) - RFP mouse (Agrisera, AS15 3028) and 1:200 for \(\alpha\) - GFP rabbit (Millipore, AB10145) were used for overnight incubation at \(4^{\circ}C\) . Roots were then washed with MT- stabilizing buffer (MTSB: 50 mM PIPES, 5 mM EGTA, 2 mM MgSO4, 0.1% [v/v] Triton X- 100) and incubated at \(37^{\circ}C\) for 3 h either with \(\alpha\) - mouse plus and \(\alpha\) - rabbit minus for PLA assay (681 Duolink, Sigma- Aldrich). PLA samples were then washed with MTSB and incubated for 3 h at \(37^{\circ}C\) with ligase solution as described (Pasternak et al, 2018). Roots were then washed 2x with buffer A (Sigma- Aldrich, Duolink) and treated for 4 h at \(37^{\circ}C\) in a polymerase solution containing fluorescent nucleotides as described (Sigma- Aldrich, Duolink). Samples were then washed 2x with buffer B (Sigma- Aldrich, Duolink), with 1% (v/v) buffer B for another 5 min, and then the specimens were mounted in Vectashield (Vector Laboratories) medium.
+
+## Quantification of fluorescent intensity
+
+To create the most comparable lines to measure the fluorescence intensity of reporters in multiple mutant backgrounds, we crossed homozygous mutant bearing the marker with either a WT plant (outcross to yield progeny heterozygous for the recessive mutant alleles and the reporter) or crossed to a mutant only plant (backcross to yield progeny homozygous for the recessive mutant alleles and heterozygous for the reporter). Fluorescence was measured as the mean grey value with subtraction of the background. GFP and chloroplast autofluorescence was excited with the 488- nm line of an argon laser, mCherry and RFP with a 561- nm diode laser, YFP with the 514- nm line of an argon laser, and LipidTOX Deep Red with a 633- nm helium/neon laser. Fluorescence emission was detected between 495 and 510 nm for GFP, 522 to 550 nm for YFP, 600 to 625 nm for mCherry and RFP, and 637 to 650 nm for LipidTOX Deep Red. Chloroplast autofluorescence was imaged between 670 and 700 nm. For multilabeling studies, detection was performed in a sequential line- scanning mode. The apparent diameter of LDs observed by CLSM was estimated using Fiji software (https://fiji.sc/) by manually drawing the diameter using the "line" tool and measuring it with the "measure" function of the software. For BiFC excitation wavelengths and emission, filters were 514
+
+<--- Page Split --->
+
+nm/band-pass 530–550 nm for YFP, 561 nm/band-pass 600–630 nm for RFP and 488 nm/band-pass 650–710 nm for chloroplast auto- fluorescence. The objective used was an HC PL APO 40x/1,30 oil CS2 with NA=1.3 (Leica SP8 confocal system).
+
+## Ubiquitin cleavage assay
+
+Ubiquitin cleavage assayRecombinant proteins of GST- PROPEP1, MCA- II- a, MCA- II- a- PD, MCA- II- f, MCA- II- f and Usp2- cc were purified as previously described \(^{11}\) with the protocols described \(^{61}\) . The deubiquitylating activity of Usp2- cc, MCA- II- a and MCA- II- f was assayed against recombinant human K48- linked tetra- ubiquitin (BostonBiochem, #UC- 210B) by incubating the purified proteases with 2 µg substrate at 37°C for 30 min in either MC- II- f reaction buffer (50 mM MES, pH 5.5, 150 mM NaCl, 10% sucrose, 0.1% CHAPS, 10 mM DTT) or MCA- II- a reaction buffer (50 mM Hepes, pH 7.5, 150 mM NaCl, 10% glycerol, 50 mM CaCl₂, 10 mM DTT). Reactions were terminated by adding Sodium dodecyl- sulfate polyacrylamide gel electrophoresis (SDS- PAGE) sample buffer with an additional 50 mM EGTA for MCA- II- a reaction buffer, subjected to SDS- PAGE (12% polyacrylamide) and subsequent silver staining (Invitrogen, #LC6070).
+
+## Immunoblotting
+
+ImmunoblottingIn general, samples were flash- frozen in liquid \(\mathbb{N}_2\) and kept at \(- 80^{\circ}C\) until further processing. The samples were crushed using a liquid \(\mathbb{N}_2\) - cooled mortar and pestle, and the crushed material was transferred to a 1.5- mL or 15- mL tube. Extraction buffer (EB; 50 mM Tris- HCl pH 7.5, 150 mM NaCl, 10% [v/v] glycerol, 2 mM ethylenediamine tetraacetic acid [EDTA], 5 mM dithiothreitol [DTT], 1 mM phenylmethylsulfonyl fluoride [PMSF], Protease Inhibitor Cocktail [Sigma- Aldrich, P9599] and 0.5 % [v/v] IGEPAL CA- 630 [Sigma- Aldrich]) was added according to the plant material used. The lysates were pre- cleared by centrifugation at 16,000 g at 4°C for 15 min, and the supernatant was transferred to a 1.5- mL tube. This step was repeated two times and the protein concentration was determined by the RC DC Protein Assay Kit II (Bio- Rad, 5000122). 2X Laemmli buffer was added, and proteins were separated by SDS- PAGE (1.0 mm thick 4 to 12% [w/v] gradient polyacrylamide Criterion Bio- Rad) in 3- (N- Morpholino) propane sulfonic acid (MOPS) buffer (Bio- Rad) at 150 V or native polyacrylamide gel (Bio- Rad, Any kD TGX gels). Subsequently, proteins were transferred onto polyvinylidene fluoride (PVDF; Bio- Rad) membrane with 0.22- μm pore size. The membrane was blocked with 3% (w/v) BSA fraction V (Thermo Fisher Scientific) in phosphate buffered saline- Tween 20 (PBS- T) for 1 h at room temperature (RT), followed by incubation with horseradish peroxidase (HRP)- conjugated primary antibody at RT for 2 h (or primary antibody at RT for 2 h and corresponding secondary antibody at RT for 2 h). The following antibodies were used: rabbit α- OLE1 (anti- rS3) \(^{34}\) , rat α- tubulin (Santa Cruz Biotechnology, 1:1000), rabbit α- GFP (Millipore, AB10145, 1:10,000), mouse α- RFP (Agrisera, AS15 3028, 1:5,000), rabbit α- 12S \(^{62}\) , rabbit α- APX1 (Agrisera, 1:2000), rabbit α- BIP2 (Agrisera, 1:2000), rabbit α- UBQ11 (Agrisera, 1:2000), goat α- CDC48a (VCP1) (diluted 1:2000, Abcam. 206320), rabbit α- PBA1 (Agrisera, 1:2000), rabbit α- PAG1 (Agrisera, 1:2000), rabbit α- BIP (Agrisera, 1:2000), rabbit α- ACTIN (Agrisera, 1:2000), α- mouse (Amersham ECL Mouse IgG, HRP- linked whole Ab [from sheep], NA931, 1:10,000), α- rabbit (Amersham ECL Rabbit IgG, HRP- linked whole Ab [from donkey], NA934, 1:10,000), α- rat (IRDye \(^{\text{®}}\) 800 CW Goat anti- Rat IgG [H + L], LI- COR, 925- 32219, 1:10,000) and α- rabbit (IRDye \(^{\text{®}}\) 800 CW Goat anti- Rabbit IgG, LI- COR, 926- 3221, 1:10,000). Chemiluminescence was detected with the ECL Prime Western Blotting Detection Reagent (Cytiva, GERPΝ2232) and SuperSignal™ West Femto Maximum Sensitivity Substrate (Thermo Fisher Scientific, 34094). The bands were visualized using an Odyssey infrared imaging system (LI- COR).
+
+## Total proteome analysis, COFRADIC and TAP
+
+Total proteome analysis, COFRADIC and TAPAn equal number of seeds of WT and mca- II- KO were used for the analysis of the total proteome using LC- MS/MS. For COFRADIC, a shortened protocol was used as previously described with the following modifications \(^{43}\) . To achieve a total protein content of 1 mg, 0.2 g frozen ground tissue was re- suspended in 1 mL of buffer containing 1% (w/v) 3- [(3- cholamidopropyl)- dimethylammonio]- 1- propane sulfonate (CHAPS), 0.5% (w/v) deoxycholate, 5 mM ethylenediaminetetraacetic acid, and 10% glycerol in 50 mM HEPES
+
+<--- Page Split --->
+
+buffer, pH 7.5, further containing the suggested amount of protease inhibitors (one tablet/10 mL buffer) according to the manufacturer's instructions (Roche Applied Science). The sample was centrifuged at 16,000g for 10 min at \(4^{\circ}C\) , and guanidinium hydrochloride was added to the cleared supernatant to reach a final concentration of 4 M. Protein concentrations were measured with the DC protein assay (Bio- Rad), and protein extracts were further modified for N- terminal COFRADIC analysis as described previously \(^{63}\) . Col- 0 (WT) primary amines were labelled with the N- hydroxysuccinimide (NHS) ester of \(^{12}\mathrm{C}_4\) - butyrate and mutants with NHS- \(^{13}\mathrm{C}_4\) - butyrate, resulting in a mass difference of approximately 4 Da between light ( \(^{12}\mathrm{C}_4\) ) and heavy ( \(^{13}\mathrm{C}_4\) ) labelled peptides. After equal amounts of the labelled proteomes had been mixed, tryptic digestion generated internal, non- N- terminal peptides that were removed by strong cation exchange at a low pH \(^{63}\) . Due to the low amount of input material, the COFRADIC protocol was cut short after the first reversed phase- high performance liquid chromatography (RP- HPLC) step and the resulting 15 fractions were subjected immediately for identification by LC- MS/MS. For TAP experiments, four- to five weeks- old Arabidopsis transgenic plants expressing MCA- II- a- TAPa, MCA- II- a- PD- TAPa, MCA- II- b- TAPa, MCA- II- b- PD- TAPa and sGFP- TAPa were harvested (2- 4 g, fresh weight) and ground in liquid N2 in 2 volumes of extraction buffer (50 mM Tris- HCl pH 7.5, 150 mM NaCl, 10% glycerol, 0.1% Nonidet P- 40 and \(1\times\) protease inhibitor cocktail; Sigma- Aldrich, 1:100 dilution). The analyses and further processing were done as described in \(^{64}\) .
+
+## Visualization of networks and analyses
+
+Cytoscape 3.5.1 was used. Tab- delimited files containing the input data were uploaded. Unless otherwise indicated, the default layout was an edge- weighted spring- embedded layout, with NormSpec used as edge weight. Nodes were manually re- arranged from this layout to increase visibility and highlight specific proximity interactions. The layout was exported as a PDF and eventually converted to a .TIFF file with Lempel- Ziv- Welch (common name LZW) compression.
+
+## Quantifications and statistics
+
+The numerical data used in this publication are provided as raw .csv files with the corresponding headings. Graphs were generated by GraphPad Prism v. 9 or R- 4.2.3 (https://www.r- project.org). Pearson correlation coefficient on images was calculated via Fiji, coloc2 tool. All statistical data show the mean \(\pm s.d\) . (box plots) or the distribution of values (violin plots, kernal density) of at least three biologically independent experiments or samples, or as otherwise stated. Individual data points are on the plots. For violin plots, datasets were smoothed using heavy smoothing which gives a better idea of the overall distribution. In captions, \(N\) denotes biological replicates, and "n" technical replicates or population size (or as indicated). Each data set was tested whether it followed normal distribution when \(N \geq 3\) by using the Shapiro normality test integrated into the GraphPad Prism v. 9. The significance threshold was set at \(P< 0.05\) , and the calculated \(P\) - values are shown in the graphs. Details of the statistical tests applied, including the choice of the statistical method, are indicated in the corresponding figure caption. In boxplots or violin plots, upper and lower box boundaries, or lines in the violin plots when visible, represent the first and third quantiles, respectively, horizontal lines mark the median and whiskers mark the highest and lowest values.
+
+## Acknowledgments
+
+We acknowledge Ikuko Hara- Nishimura (Kyoto University) and Hannele Tuominen (Umea University) for sharing materials. This work was supported by the EPIC- XS, Horizon 2020 programme of the European Union project number 823839 (KG, PNM); European Research Council (ERC) Starting Grant 'R- ELEVATION' grant 101039824 (PD); Future Leader Fellowship from the Biotechnology and Biological Sciences Research Council (BBSRC) BB/R012172/1 (PD); European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship, and Innovation, T2EΔK- 00597 under the call RESEARCH- CREATE- INNOVATE ("BIOME"; PNM); European Union Horizon 2020 Marie Curie- RISE PANTHEON grant 872969 (PNM); Hellenic Foundation of Research and
+
+<--- Page Split --->
+
+Innovation grant 1426 NESTOR- Theodoros Papazoglou- Always Strive for Excellence (PNM); Hellenic Foundation of Research and Innovation fellowship 5947 (IHH); The Swedish Research Council (VR) 2019- 04250 (PVB, PNM); Carl Trygger Foundation (CTS) 22:2025 (PVB); Knut and Alice Wallenberg Foundation 2018.0026 (PVB, PNM); European Union Marie Sklodowska- Curie Action IF project 656011 (PNM); DESTINY (BOF- UGent) (SS, FVB).
+
+## Author contributions
+
+Conceptualization: PNM, PVB, JDGJ, CL; Methodology: CL, IHH, TP, SHR, EAM, AM, SS; EGB, PD, SDA, KG, FRC, PD, MN, FVB; Investigation: CL, IHH, PNM; Visualization: CL, IHH, PNM; Funding acquisition: PVB, PNM; Project administration: PNM; Supervision: PNM; Writing - original draft: PNM, CL, IHH, PVB; Writing - review & editing: all authors.
+
+## Competing interests
+
+The authors declare that they have no competing interests.
+
+## Materials and Correspondence
+
+All data, code, and materials used in the analysis are available and were deposited in public repositories. The data are available from the corresponding author with detailed explanations upon reasonable request.
+
+
+
+Fig. 1. A type II MCA depletion model affects seed physiology and vacuolar morphology.
+
+(A) Schematic diagram of MCAs (top left) and phylogeny of type I and II MCAs (top right) in Arabidopsis and the nomenclature used. Bottom, chromosomal locations of all nine MCA genes in Arabidopsis; note the tandem arrangement of four MCA-II genes (MCA-II-a/-b/-c/-d)
+
+<--- Page Split --->
+
+on chromosome 1. Pro, prodomain; p20 and p10, large and small subunits; H, C, catalytic histidine-cysteine dyad.
+
+(B) Representative immunoblot with \(\alpha\) -MCA-II-a showing the absence of MCA-II-a in seedlings of the single mca-II-a mutant and the sextuple mca-II-KOc lines (individual lines #93 and #30) at 7 days post germination (DPG). \(\alpha\) -ACTIN was used as a loading control; the red arrowhead indicates MCA-II-a. The experiment was performed three times with similar results (biological replicates \(N = 3\) , technical replicates \(n = 20\) pooled seedlings per lane).
+
+(C) Representative immunoblot of Tudor Staphylococcus Nuclease (TSN) levels in total protein extracts from 7-DPG WT, mca-II-df double mutant (background used to generate the CRISPR mutants), and mca-II-KOc mutant seedlings. \(\alpha\) -TUBULIN was used as a loading control. The experiment was performed three times with similar results ( \(N = 3\) , \(n = 20\) pooled seedlings per lane). Right: relative quantification of TSN abundance (red arrowhead, full length). The data are from three experiments, and the indicated \(P\) -values were calculated by one-way ANOVA ( \(N = 3\) , \(n = 3\) ).
+
+(D) Representative images showing the growth of seedlings germinated from freshly collected WT and mca-II-KOc seeds at 3 and 7 DPG. The experiment was performed three times with similar results ( \(N = 3\) , \(n \geq 40\) ).
+
+(E) Representative images showing the growth of seedlings germinated from WT and mca-II-KOc (3, 6, and 9-month-old) seeds at 3 and 7 DPG. The experiment was performed three times with similar results ( \(N = 3\) , \(n \geq 40\) ).
+
+(F) Germination rate (%) of WT and mca-II-KOc seeds (from D and E). The data are from three experiments, and the indicated \(P\) -values were calculated by one-way ANOVA ( \(N = 3\) , \(n \geq 278\) ). The first \(P\) -value corresponds to the 1 to \(3^{\text{rd}}\) point interval, while the second \(P\) -value corresponds to the \(4^{\text{th}}\) point; the magenta and light-green areas around the individual points represent \(\pm 5\) .
+
+(G) Visualization of vacuoles in embryonic roots from WT and mca-II-KOc plants after a 2-day stratification (hydration) counter-stained with the pH-sensitive lumen dye BCECF. The styryl dye FM-64 was used to visualize the plasma membrane (cell contours, magenta). Yellow arrowheads point to vacuole-free regions in the cytoplasm that compress the vacuolar membrane in the mca-II-KOc lines (corresponding to lipid droplets). Scale bars, \(10 \mu \text{m}\) .
+
+<--- Page Split --->
+
+
+Fig. 2. MCA-IIs associate with and affect the ER.
+
+(A) Gene ontology (GO) enrichment analysis of biological processes for proteins more abundant in mca-II-KOc than in WT (log2FC ≥ 1) 3-month-old seeds. The black box highlight relevant and overrepresented and overlapping GO terms. The GO term "fatty acid metabolic process" (GO:0006631) was confirmed by the greatly diminished levels of oleosin and enlarged lipid droplets in the mutant (Fig. 3). Furthermore, the GO terms "protein folding" (GO:0006457) and "ER body organization" (GO:00080119), were enriched and included proteins such as HEAT SHOCK 70 kDa proteins (HSP70s) and protein disulfide-isomerases (PDI5, PDI6: 3,11- and 5.0-fold, respectively) BINDING PROTEIN 1 and 2 (BiP 3.4- and 2.6-fold, respectively). In the GO term "protein folding", the FKBP15-2 (FK506- AND RAPAMYCINBINDING PROTEIN 15 KD-2, immunophilin protein), was not found in WT, is involved in ER stress sensing, and accelerates protein folding. Furthermore, in the same GO term, the proteasomal subunits (GO, protein folding) such as PAG1 (20S proteasome alpha subunit G- 1: 1.3-fold) and PBA1 (20S proteasome subunit beta 1: not found in WT), were verified using α-PAG1 and α-PBA1 antibodies in Fig S5G, confirming the corresponding increases in abundance. In the term "ER body organization", PYK10 (BGLU23), BGLU18, and BGLU25 (highlighted) are β-glucosidases enriched ≥ 100-fold in mca-II-KOc. The GO term "gluconeogenesis" (GO:0006094) confirms the relevance of this analysis, as MCA-IIs were previously linked to this process 43. FDR, false discovery rate.
+
+(B) Representative immunoblot analysis of cell extracts of seed fractions from lines expressing MCA-II-apro:MCA-II-a-GFP separated by sucrose gradient density ultracentrifugation. BiP2 (ER) and ascorbate peroxidase (APX1, cytoplasm) were used to assess fraction quality.
+
+(C) Representative high-resolution confocal micrograph (120 nm axial) of epidermal cells from the meristematic regions of embryonic roots 2 days after seed hydration, from lines expressing MCA-II-apro:MCA-II-a-GFP. Scale bar, 10 μm.
+
+(D) Representative immunoblot analysis of seed protein extracts (50 seeds/genotype) probed with α-UBIQUITIN11 (UBQ11) antibody. The numbers indicate relative levels of ubiquitinated proteins compared to Ponceau S staining at the bottom (loading control). Left, WT (9-month-old seeds) and mca-II-KOc seeds harvested at different time points (3, 6, and 9-month-old).
+
+<--- Page Split --->
+
+Right, WT, the T-DNA double mutant mca- II- df, and mca- II- KOc (3- month- old). The experiment was repeated more than 10 times.
+
+
+
+Fig. 3. MCA-Ils associate with CDC48 and PUX10 in the LDAD pathway.
+
+(A) Representative images from permeability tests of etiolated seedlings 4-days post germination (DPG) of WT (9-month-old seeds), mca-II-KOc (fresh seeds, 3-, or 9-month-old), and a complementation line (Com., rescued with RPS5apro:MCA-II-a-mNeon; 9-month-old seeds) stained with toluidine blue (0.05% [w/v]). Scale bar, 0.5 cm.
+
+(B) Representative micrographs of lipid droplets stained with LipidTox in the hypocotyl regions of 2-DPG radicles from WT, mca-II-KOc, and the Com line. The two yellow arrowheads in the three insets from GFP, LipidTox, and Merge indicate lipid droplets (LDs). Scale bars, 10 μm (5 μm for inset).
+
+(C) Representative confocal micrographs of embryonic roots coexpressing RPS5apro:tagRFP-MCA-IIa and PUX10pro:PUX10-GFP or RPS5apro:MCA-II-a-mNeon and 35Spro:mCherry-CDC48. Pearson's correlation coefficients (R) were used to estimate colocalization and are shown on the merged micrographs. The yellow arrowheads denote sites of colocalization between PUX10 and MCA-II-a, while the red arrowhead denotes high
+
+<--- Page Split --->
+
+levels of PUX10 and the lack of MCA- II- a. The experiment was repeated more than five times. V, vacuole (autofluorescence). Scale bars, \(5\mu \mathrm{m}\) .
+
+(D) Representative confocal micrographs of embryo hypocotyl cells showing the colocalization of PUX10 or CDC48 with MCA-II-a from lines co-expressing RPS5apro:MCA-II-a-tagRFP and PUX10pro:PUX10-GFP or RPS5apro:MCA-II-a-mNeon and 35spro:mCherry-CDC48a (radicles produced similar results). The arrowheads denote colocalization between fluorescent signals. Scale bar, \(5\mu \mathrm{m}\) . The experiment was performed three times with similar results \((N = 3, n = 1)\) . V, vacuole (autofluorescence).
+
+(E) "Sensitized emission" FRET (FRET-SE) approach, where the emission spectrum of the donor (1) overlaps with the excitation spectrum of the acceptor (2), and if the distance ("r") between the two molecules is sufficiently short (i.e., connoting association), energy is transferred (3). Middle: Micrograph showing FRET-SE between PUX10-GFP and MCA-II-a-tagRFP from embryonic root epidermal cells. Scale bar, \(5\mu \mathrm{m}\) . Bottom graph: FRET-SE between PUX10-GFP and MCA-II-a-tagRFP in the absence (mock) or presence of MG132 and in the nucleus (Nuc) where PUX10-GFP and MCA-II-a-tagRFP also localized. GFP represents the negative control (free GFP; lines coexpressing GFP with MCA-II-a-tagRFP). Note that in the presence of MG132, FRET-SE increased, likely due to inhibition of the proteasome, which allowed the increased persistence of PUX10, an MCA-II-a transient complex. The data are from two experiments, and the indicated \(P\) -values were calculated by ordinary one-way ANOVA \((N = 2, n \geq 7)\) .
+
+(F) Representative immunoblots of total seed proteins from WT, mca-II-KOc (KOc), and the Com line probed with an \(\alpha\) -Oleosin antibody (3-month-old seeds). The numbers indicate relative levels compared to Ponceau S staining at the bottom (loading control). The experiment was performed three times with similar results \((N = 3, n = 1\) with 50 seeds/lane).
+
+(G) Representative confocal micrographs from lines harboring MCA-II-apro:MCA-II-a-GFP counterstained with LipidTox in the hypocotyl regions of 2-DPG seedlings. Insets (denoted 1 to 3) show details of lipid droplets. Scale bars, \(5\mu \mathrm{m}\) (1 \(\mu \mathrm{m}\) for insets). The experiment was repeated more than 10 times. Right, measurement of lipid droplet size. The data are from three experiments, and the indicated \(P\) -values were calculated by ordinary one-way ANOVA \((N = 3, n \geq 15)\) .
+
+<--- Page Split --->
+
+
+Fig. 4. MCA-lls modulate ERAD by regulating CDC48 localization.
+
+(A) Top: Representative confocal micrograph of embryonic root cells co-expressing RPS5apro:MCA-II-a-tagRFP and PUX10:PUX10-GFP. The inset in a merged micrograph shows the colocalization between PUX10 and MCA-II-a. "High" corresponds to high levels of either MCA-II-a or PUX10, while "Low" refers to reduced or non-detectable levels of the corresponding proteins. Note the inverse correlation between MCA-II-a and PUX10 levels. Bottom: Representative confocal micrograph of embryonic root cells co-expressing RPS5apro:MCA-II-a-mNeon and 35Spro:mCherry-CDC48. The yellow arrowheads denote structures reminiscent of lipid droplets and the highly correlated levels of CDC48 and MCA-II-a in puncta. R values denote Pearson correlation coefficients of signal intensities between tagRFP/GFP and mCherry/mNeon. Scale bars, 10 μm.
+
+(B) Representative confocal micrographs of embryonic root cells, 2 days post-hydration, from WT and mca-II-KOc harboring 35Spro:mCherry-CDC48a. Scale bars, 10 μm. The yellow arrowheads denote structures reminiscent of lipid droplets, while the red arrowheads denote the nucleus. The two insets show details of CDC48 localization in WT and mca-II-KOc ("1" and "2", respectively). Right: quantification of the intensity ratio between the mCherry-CDC48 signal at the lipid droplets (LDs) and cytoplasm. The data are from three experiments, and the indicated P-values were calculated by one-way ANOVA (N = 3, n = 8 cells/sample).
+
+(C) Representative images of 7-day-old seedlings of the indicated genotypes mock-treated (DMSO), treated with a CDC48 inhibitor (CB-5083, 2 μM), and following a 2-day recovery (9-day-old seedlings) from CB-5083 treatment on DMSO-containing plates. Note the swelling root tip phenotype observed in mca-II-KOc (two lines), which is indicative of hypersensitivity
+
+<--- Page Split --->
+
+to CB- 5083 (insets). The experiment was performed three times with similar results \((N = 3, n = 8 - 10\) seedlings/genotype).
+
+(D) Representative images showing seed viability tests with tetrazolium staining in WT and mca-Il-KOc. Seeds treated at \(100^{\circ}C\) represent a positive control for dead seeds. Viable seeds (stained red) are highlighted in the insets (red arrowheads). Right: quantification of viable seeds. The data are from three experiments, and the indicated \(P\) -values were calculated by one-way ANOVA \((N = 3, n \geq 176)\) .
+
+(E) A model for the role of MCA-lls in regulating CDC48 localization to the ER and lipid droplets. In the absence of MCA-lls, PUX10 is not cleaved and CDC48 is retained on lipid droplets; when MCA-lls are present, PUX10 is cleaved, releasing CDC48 to localize at the ER. This release is an important step in the spatiotemporal regulation of CDC48 activity and confers seed longevity.
+
+<--- Page Split --->
+
+765 1 de Vries, J. & Ischebeck, T. Ties between Stress and Lipid Droplets Pre-date Seeds. Trends in Plant Science 25, 1203- 1214 (2020). https://doi.org:10.1016/j.tplants.2020.07.017 2 Vitale, A. & Pedrazzini, E. StresSeed: The Unfolded Protein Response During Seed Development. Front Plant Sci 13, 869008 (2022). https://doi.org:10.3389/fpls.2022.869008 3 Lee, J. E., Cathey, P. I., Wu, H., Parker, R. & Voeltz, G. K. Endoplasmic reticulum contact sites regulate the dynamics of membraneless organelles. Science 367, eaay7108 (2020). https://doi.org:10.1126/science.aay7108 4 Srivastava, R. et al. Response to Persistent ER Stress in Plants: A Multiphasic Process That Transitions Cells from Prosurvival Activities to Cell Death. The Plant Cell 30, 1220- 1242 (2018). https://doi.org:10.1105/tpc.18.00153 5 Minina, E. A. et al. Classification and Nomenclature of Metacaspases and Paracaspases: No More Confusion with Caspases. Mol Cell 77, 927- 929 (2020). https://doi.org:10.1016/j.molcel.2019.12.020 780 6 Coll, N. S. et al. Arabidopsis type I metacaspases control cell death. Science 330, 1393- 1397 (2010). https://doi.org:10.1126/science.1194980 7 Coll, N. S. et al. The plant metacaspase AtMC1 in pathogen- triggered programmed cell death and aging: functional linkage with autophagy. Cell Death & Differentiation 21, 1399- 1408 (2014). https://doi.org:10.1038/cdd.2014.50 785 8 Pitsili, E. et al. A phloem- localized Arabidopsis metacaspase (AtMC3) improves drought tolerance. bioRxiv, 2022.2011.2009.515759 (2022). https://doi.org:10.1101/2022.11.09.515759 9 Tsiatsiani, L. et al. Metacaspases. Cell Death Differ 18, 1279- 1288 (2011). https://doi.org:10.1038/cdd.2011.66 790 10 Minina, E. A., Coll, N. S., Tuominen, H. & Bozhkov, P. V. Metacaspases versus caspases in development and cell fate regulation. Cell Death Differ 24, 1314- 1325 (2017). https://doi.org:10.1038/cdd.2017.18 11 Hander, T. et al. Damage on plants activates Ca(2+)- dependent metacaspases for release of immunomodulatory peptides. Science 363 (2019). https://doi.org:10.1126/science.aar7486 12 Bollhoner, B. et al. Post mortem function of AtMC9 in xylem vessel elements. New Phytol 200, 498- 510 (2013). https://doi.org:10.1111/nph.12387 13 Tuladhar, R. et al. CRISPR- Cas9- based mutagenesis frequently provokes on- target mRNA misregulation. Nat Commun 10, 4056 (2019). https://doi.org:10.1038/s41467- 019- 12028- 5 14 Sundstrom, J. F. et al. Tudor staphylococcal nuclease is an evolutionarily conserved component of the programmed cell death degradome. Nat Cell Biol 11, 1347- 1354 (2009). https://doi.org:10.1038/ncb1979 15 Shen, W., Liu, J. & Li, J. F. Type- II Metacaspases Mediate the Processing of Plant Elicitor Peptides in Arabidopsis. Mol Plant 12, 1524- 1533 (2019). https://doi.org:10.1016/j.molp.2019.08.003 16 Duxbury, Z. et al. Induced proximity of a TIR signaling domain on a plant- mammalian NLR chimera activates defense in plants. Proc Natl Acad Sci U S A (2020). https://doi.org:10.1073/pnas.2001185117 810 17 Watanabe, N. & Lam, E. Arabidopsis metacaspase 2d is a positive mediator of cell death induced during biotic and abiotic stresses. Plant J 66, 969- 982 (2011). https://doi.org:10.1111/j.1365- 313X.2011.04554.x 18 Oria, M. P., Hamaker, B. R., Axtell, J. D. & Huang, C.- P. A highly digestible sorghum mutant cultivar exhibits a unique folded structure of endosperm protein
+
+<--- Page Split --->
+
+bodies. Proceedings of the National Academy of Sciences 97, 5065- 5070 (2000). https://doi.org:10.1073/pnas.080076297 19 Vitale, M. et al. Inadequate BiP availability defines endoplasmic reticulum stress. eLife 8, e41168 (2019). https://doi.org:10.7554/eLife.41168 20 Oslowski, C. M. & Urano, F. Measuring ER stress and the unfolded protein response using mammalian tissue culture system. Methods Enzymol 490, 71- 92 (2011). https://doi.org:10.1016/b978- 0- 12- 385114- 7.00004- 0 21 Gevaert, K. et al. Exploring proteomes and analyzing protein processing by mass spectrometric identification of sorted N- terminal peptides. Nat Biotechnol 21, 566- 569 (2003). https://doi.org:10.1038/nbt810 22 Grimmer, J. et al. Mild proteasomal stress improves photosynthetic performance in Arabidopsis chloroplasts. Nat Commun 11, 1662 (2020). https://doi.org:10.1038/s41467- 020- 15539- 8 23 Kurepa, J., Toh- e, A. & Smalle, J. A. 26S proteasome regulatory particle mutants have increased oxidative stress tolerance. The Plant Journal 53, 102- 114 (2008). https://doi.org:https://doi.org/10.1111/j.1365- 313X.2007.03322. x 24 Finley, D. Recognition and processing of ubiquitin- protein conjugates by the proteasome. Annu Rev Biochem 78, 477- 513 (2009). https://doi.org:10.1146/annurev.biochem.78.081507.101607 25 Olzmann, J. A., Richter, C. M. & Kopito, R. R. Spatial regulation of UBXD8 and p97/VCP controls ATGL- mediated lipid droplet turnover. Proc Natl Acad Sci U S A 110, 1345- 1350 (2013). https://doi.org:10.1073/pnas.1213738110 26 Hwang, J. & Qi, L. Quality Control in the Endoplasmic Reticulum: Crosstalk between ERAD and UPR pathways. Trends Biochem Sci 43, 593- 605 (2018). https://doi.org:10.1016/j.tibs.2018.06.005 27 Liu, J. X., Srivastava, R., Che, P. & Howell, S. H. An endoplasmic reticulum stress response in Arabidopsis is mediated by proteolytic processing and nuclear relocation of a membrane- associated transcription factor, bZIP28. Plant Cell 19, 4111- 4119 (2007). https://doi.org:10.1105/tpc.106.050021 28 De Giorgi, J. et al. The Arabidopsis mature endosperm promotes seedling cuticle formation via release of sulfated peptides. Developmental Cell 56, 3066- 3081. e3065 (2021). https://doi.org:https://doi.org/10.1016/j.devcel.2021.10.005 29 Al- Hammad, A. S., Sreelakshmi, Y., Negi, S., Siddiqi, I. & Sharma, R. The polycytelson mutant of tomato shows enhanced polar auxin transport. Plant Physiol 133, 113- 125 (2003). 30 Stevenson, J., Huang, E. Y. & Olzmann, J. A. Endoplasmic Reticulum- Associated Degradation and Lipid Homeostasis. Annu Rev Nutr 36, 511- 542 (2016). https://doi.org:10.1146/annurev- nutr- 071715- 051030 31 Lee, R. E., Brunette, S., Puente, L. G. & Megeney, L. A. Metacaspase Yca1 is required for clearance of insoluble protein aggregates. Proc Natl Acad Sci U S A 107, 13348- 13353 (2010). https://doi.org:10.1073/pnas.1006610107 32 Liu, C. et al. Phase Separation of a Nodulin Sec14- like protein Maintains Auxin Efflux Carrier Polarity at Arabidopsis Plasma Membranes. bioRxiv (Plos Biol, under textual revision), 2022.2003.2026.485938 (2023). https://doi.org:10.1101/2022.03.26.485938 33 Teale, W. D. et al. Flavonol- mediated stabilization of PIN efflux complexes regulates polar auxin transport. Embo J 40, e104416 (2021). https://doi.org:10.15252/embj.2020104416 34 Deruyffelaere, C. et al. PUX10 Is a CDC48A Adaptor Protein That Regulates the Extraction of Ubiquitinated Oleosins from Seed Lipid Droplets in Arabidopsis. The Plant Cell 30, 2116- 2136 (2018). https://doi.org:10.1105/tpc.18.00275
+
+<--- Page Split --->
+
+35 Siloto, R. M. et al. The accumulation of oleosins determines the size of seed oilbodies in Arabidopsis. Plant Cell 18, 1961- 1974 (2006). https://doi.org:10.1105/tpc.106.041269
+
+36 Marshall, R. S., Hua, Z., Mali, S., McLoughlin, F. & Viertra, R. D. ATG8- Binding UIM Proteins Define a New Class of Autophagy Adaptors and Receptors. Cell 177, 766- 781. e724 (2019). https://doi.org:10.1016/j.cell.2019.02.009
+
+37 Heinen, C., Ács, K., Hoogstraten, D. & Dantuma, N. P. C- terminal UBA domains protect ubiquitin receptors by preventing initiation of protein degradation. Nat Commun 2, 191 (2011). https://doi.org:10.1038/ncomms1179 875 38 Alberts, S. M., Sonntag, C., Schäfer, A. & Wolf, D. H. Ubx4 Modulates Cdc48 Activity and Influences Degradation of Misfolded Proteins of the Endoplasmic Reticulum\*. Journal of Biological Chemistry 284, 16082- 16089 (2009). https://doi.org:https://doi.org/10.1074/jbc.M809282200 39 Arumughan, A. et al. Quantitative interaction mapping reveals an extended UBX domain in ASPL that disrupts functional p97 hexamers. Nat Commun 7, 13047 (2016). https://doi.org:10.1038/ncomms13047 40 Wang, C.- W. & Lee, S.- C. The ubiquitin- like (UBX)- domain- containing protein Ubx2/Ubx8 regulates lipid droplet homeostasis. J Cell Sci 125, 2930- 2939 (2012). https://doi.org:10.1242/jcs.100230 851 41 Garzon, M. et al. PRT6/At5g02310 encodes an Arabidopsis ubiquitin ligase of the N- end rule pathway with arginine specificity and is not the CER3 locus. Febs Lett 581, 3189- 3196 (2007). https://doi.org:10.1016/j.febslet.2007.06.005 42 Deruyffelaere, C. et al. PUX10 Is a CDC48A Adaptor Protein That Regulates the Extraction of Ubiquitinated Oleosins from Seed Lipid Droplets in Arabidopsis. Plant Cell 30, 2116- 2136 (2018). https://doi.org:10.1105/tpc.18.00275 43 Tsiatisani, L. et al. The Arabidopsis metacaspase9 degradome. Plant Cell 25, 2831- 2847 (2013). https://doi.org:10.1105/tpc.113.115287 44 Saitou, N. & Nei, M. The neighbor- joining method: a new method for reconstructing phylogenetic trees. Mol Biol Evol 4, 406- 425 (1987). https://doi.org:10.1093/oxfordjournals.molbev.a040454 45 Debeaujon, I., Leon- Kloosterziel, K. M. & Koornneef, M. Influence of the testa on seed dormancy, germination, and longevity in Arabidopsis. Plant Physiol 122, 403- 414 (2000). https://doi.org:10.1104/pp.122.2.403 46 Sexauer, M., Shen, D., Schon, M., Andersen, T. G. & Markmann, K. Visualizing polymeric components that define distinct root barriers across plant lineages. Development 148 (2021). https://doi.org:10.1242/dev.199820 47 Doll, N. M. et al. A two- way molecular dialogue between embryo and endosperm is required for seed development. Science 367, 431- 435 (2020). https://doi.org:10.1126/science.aaz4131 905 48 Sohn, K. H. et al. The Nuclear Immune Receptor RPS4 Is Required for RRS1SLH1- Dependent Constitutive Defense Activation in Arabidopsis thaliana. PLOS Genetics 10, e1004655 (2014). https://doi.org:10.1371/journal.pgen.1004655 49 Minina, E. A., Stael, S., Van Breusegem, F. & Bozhkov, P. V. Plant metacaspase activation and activity. Methods Mol Biol 1133, 237- 253 (2014). https://doi.org:10.1007/978- 1- 4939- 0357- 3_15 50 Clough, S. J. & Bent, A. F. Floral dip: a simplified method for Agrobacterium- mediated transformation of Arabidopsis thaliana. Plant J 16, 735- 743 (1998). https://doi.org:10.1046/j.1365- 313x.1998.00343. x 51 Nakagawa, T. et al. Improved Gateway binary vectors: high- performance vectors for creation of fusion constructs in transgenic analysis of plants. Biosci Biotechnol Biochem 71, 2095- 2100 (2007). https://doi.org:10.1271/bbb.70216
+
+<--- Page Split --->
+
+52 Curtis, M. D. & Grossniklaus, U. A gateway cloning vector set for high-throughput functional analysis of genes in planta. Plant Physiol 133, 462- 469 (2003). https://doi.org:10.1104/pp.103.027979920 53 Ursache, R., Fujita, S., Dénervaud Tendon, V. & Geldner, N. Combined fluorescent seed selection and multiplex CRISPR/Cas9 assembly for fast generation of multiple Arabidopsis mutants. Plant Methods 17, 111 (2021). https://doi.org:10.1186/s13007- 021- 00811- 954 Liu, H. et al. CRISPR- P 2.0: An Improved CRISPR- Cas9 Tool for a0;Genome Editing in Plants. Molecular Plant 10, 530- 532 (2017). https://doi.org:10.1016/j.molp.2017.01.00355 Labun, K. et al. CHOPCHOP v3: expanding the CRISPR web toolbox beyond genome editing. Nucleic Acids Res 47, W171- W174 (2019). https://doi.org:10.1093/nar/gkz36596 56 Arvidsson, S., Kwasniewski, M., Riano- Pachon, D. M. & Mueller- Roeber, B. QuantPrime- a flexible tool for reliable high- throughput primer design for quantitative PCR. BMC Bioinformatics 9, 465 (2008). https://doi.org:10.1186/1471- 2105- 9- 46557 Schaller, G. E. Isolation of Endoplasmic Reticulum and Its Membrane. Methods Mol Biol 1511, 119- 129 (2017). https://doi.org:10.1007/978- 1- 4939- 6533- 51058 Deruyffelaere, C. et al. Ubiquitin- Mediated Proteasomal Degradation of Oleosins is Involved in Oil Body Mobilization During Post- Germinative Seedling Growth in Arabidopsis. Plant Cell Physiol 56, 1374- 1387 (2015). https://doi.org:10.1093/pcp/pcv05659 Moschou, P. N., Gutierrez- Beltran, E., Bozhkov, P. V. & Smertenko, A. Separate Promotes Microtubule Polymerization by Activating CENP- E- Related Kinesin Kin7. Dev Cell 37, 350- 361 (2016). https://doi.org:10.1016/j.devcel.2016.04.01560 Roux, M. E. et al. The mRNA decay factor PAT1 functions in a pathway including MAP kinase 4 and immune receptor SUMM2. Embo J 34, 593- 608 (2015). https://doi.org:10.15252/embj.20148864561 Catanzariti, A. M., Soboleva, T. A., Jans, D. A., Board, P. G. & Baker, R. T. An efficient system for high- level expression and easy purification of authentic recombinant proteins. Protein Sci 13, 1331- 1339 (2004). https://doi.org:10.1110/ps.046189042 62 Li, L. et al. MAIGO2 Is Involved in Exit of Seed Storage Proteins from the Endoplasmic Reticulum in Arabidopsis thaliana. The Plant Cell 18, 3535- 3547 (2006). https://doi.org:10.1105/tpc.106.04615163 Staes, A. et al. Selecting protein N- terminal peptides by combined fractional diagonal chromatography. Nature Protocols 6, 1130- 1141 (2011). https://doi.org:10.1038/nprot.2011.35564 Gutierrez- Beltran, E. et al. Tudor staphylococcal nuclease is a docking platform for stress granule components and is essential for SnRK1 activation in Arabidopsis. Embo J 40, e105043 (2021). https://doi.org:10.15252/embj.2020105043
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+Supplementary Figures.pdf TableS1. Resourcesusedinthispaper.xlsx DataS1. ProteomicsanalysesofWTandmcallKOc3montholdseeds.xlsx DataS2. NTerminomicsCOFRADICAllreports.xlsx DataS3. RNAseqanalysisandUPRgeneexpressioninWTorinmcallKOc.xlsx DataS4. TAPinteractionsofMCtypell.xlsb
+
+<--- Page Split --->
diff --git a/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf_det.mmd b/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..d63dbe9274a11f43483df1ea560f7a10562f0566
--- /dev/null
+++ b/preprint/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf/preprint__04c1110170f51d637e585e71a9c6c8bbd8a399a8ced2f8b34e9af21273e25fdf_det.mmd
@@ -0,0 +1,487 @@
+<|ref|>title<|/ref|><|det|>[[44, 106, 857, 144]]<|/det|>
+# Seed Longevity is Controlled by Metacaspases
+
+<|ref|>text<|/ref|><|det|>[[44, 162, 333, 208]]<|/det|>
+Panagiotis Moschou panagiotis.moschou@lsu.se
+
+<|ref|>text<|/ref|><|det|>[[52, 234, 580, 255]]<|/det|>
+Uppsala BioCenter https://orcid.org/0000- 0001- 7212- 0595
+
+<|ref|>text<|/ref|><|det|>[[44, 260, 757, 323]]<|/det|>
+Chen Liu Swedish University of Agricultural Sciences and Linnean Center for Plant Biology https://orcid.org/0000- 0002- 1604- 0694
+
+<|ref|>text<|/ref|><|det|>[[44, 328, 234, 370]]<|/det|>
+Ioannis Chatzianestis University Of Crete
+
+<|ref|>text<|/ref|><|det|>[[44, 375, 216, 415]]<|/det|>
+Thorsten Pfirrmann HMU Potsdam
+
+<|ref|>text<|/ref|><|det|>[[44, 421, 220, 463]]<|/det|>
+Reza Salim Uppsala University
+
+<|ref|>text<|/ref|><|det|>[[44, 468, 451, 508]]<|/det|>
+Elena Minina SLU https://orcid.org/0000- 0002- 2619- 1859
+
+<|ref|>text<|/ref|><|det|>[[44, 514, 912, 556]]<|/det|>
+Ali Moazzami Department of Molecular Sciences, Uppsala BioCenter, Swedish University of Agricultural Sciences
+
+<|ref|>text<|/ref|><|det|>[[44, 560, 434, 602]]<|/det|>
+Simon Stael Swedish University of Agricultural Sciences
+
+<|ref|>text<|/ref|><|det|>[[44, 607, 306, 648]]<|/det|>
+Emilio Gutierrez- Beltran Universidad de Sevilla, Spain
+
+<|ref|>text<|/ref|><|det|>[[44, 653, 450, 694]]<|/det|>
+Eugenia Pitsili Centre for Research in Agricultural Genomics
+
+<|ref|>text<|/ref|><|det|>[[44, 699, 576, 741]]<|/det|>
+Peter Dörmann University of Bonn https://orcid.org/0000- 0002- 5845- 9370
+
+<|ref|>text<|/ref|><|det|>[[44, 745, 345, 787]]<|/det|>
+Sabine D'Andrea INRA Institut Jean- Pierre Bourgin
+
+<|ref|>text<|/ref|><|det|>[[44, 792, 588, 855]]<|/det|>
+Kris Gevaert Francisco Romero- Campero University of Sevilla https://orcid.org/0000- 0001- 9834- 030X
+
+<|ref|>text<|/ref|><|det|>[[44, 860, 207, 901]]<|/det|>
+Pingtao Ding Leiden University
+
+<|ref|>text<|/ref|><|det|>[[44, 906, 196, 947]]<|/det|>
+Moritz Nowack Universität Köln
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 42, 234, 82]]<|/det|>
+Frank van Breusegem VIB
+
+<|ref|>text<|/ref|><|det|>[[42, 90, 193, 108]]<|/det|>
+Jonathan Jones
+
+<|ref|>text<|/ref|><|det|>[[42, 111, 860, 131]]<|/det|>
+The Sainsbury Laboratory, University of East Anglia https://orcid.org/0000- 0002- 4953- 261X
+
+<|ref|>text<|/ref|><|det|>[[42, 136, 172, 176]]<|/det|>
+Peter Bozhkov SLU
+
+<|ref|>text<|/ref|><|det|>[[42, 217, 103, 235]]<|/det|>
+Article
+
+<|ref|>text<|/ref|><|det|>[[42, 255, 137, 274]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[42, 293, 290, 312]]<|/det|>
+Posted Date: May 2nd, 2023
+
+<|ref|>text<|/ref|><|det|>[[42, 331, 475, 351]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 2836590/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 368, 914, 410]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 428, 535, 448]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 484, 924, 527]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on August 8th, 2024. See the published version at https://doi.org/10.1038/s41467- 024- 50848- 2.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[270, 76, 728, 96]]<|/det|>
+# Seed Longevity is Controlled by Metacaspases
+
+<|ref|>text<|/ref|><|det|>[[117, 108, 881, 194]]<|/det|>
+Chen Liu \(^{1,2}\) , Ioannis H. Hatzianestis \(^{1,3}\) , Thorsten Pfirrmann \(^{4}\) , Salim H. Reza \(^{5}\) , Elena A. Minina \(^{6}\) , Ali Moazzami \(^{6}\) , Simon Stael \(^{6,7,8}\) , Emilio Gutierrez- Beltran \(^{9,10}\) , Evgenia Pitsili \(^{7,8}\) , Peter Dörmann \(^{11}\) , Sabine D' Andrea \(^{12}\) , Kris Gevaert \(^{7,8}\) , Francisco Romero- Campero \(^{7,8}\) , Pingtao Ding \(^{13}\) , Moritz K. Nowack \(^{7,8}\) , Frank Van Breusegem \(^{7,8}\) , Jonathan D. G. Jones \(^{14}\) , Peter V Bozhkov \(^{6}\) , Panagiotis N. Moschou \(^{1,2,3*}\)
+
+<|ref|>text<|/ref|><|det|>[[117, 214, 881, 576]]<|/det|>
+\(^{1}\) Department of Biology, University of Crete, Heraklion, Greece \(^{2}\) Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden \(^{3}\) Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology – Hellas, Heraklion, Greece \(^{4}\) Department of Medicine, Health and Medical University, Potsdam, Germany \(^{5}\) Plant Ecology and Evolution, Department of Ecology and Genetics, Evolutionary Biology Centre and the Linnean Centre for Plant Biology in Uppsala, Uppsala University, Uppsala, Sweden \(^{6}\) Department of Molecular Sciences, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden \(^{7}\) VIB- Ugent Center for Plant Systems Biology, Technologiepark 71, 9052 Ghent, Belgium \(^{8}\) Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 71, 9052 Ghent, Belgium \(^{9}\) Instituto de Bioquimica Vegetal y Fotosintesis, Consejo Superior de Investigaciones Cientificas (CSIC)- Universidad de Sevilla, Sevilla, Spain \(^{10}\) Departamento de Bioquimica Vegetal y Biologia Molecular, Facultad de Biologia, Universidad de Sevilla, Sevilla, Spain \(^{11}\) University of Bonn, Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), Karlrobert- Kreiten- Straße 13, 53115 Bonn, Germany \(^{12}\) Institut Jean- Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris- Saclay, 78000 Versailles, France \(^{13}\) Institute of Biology Leiden, Leiden University, Leiden 2333 BE, The Netherlands \(^{14}\) The Sainsbury Laboratory, University of East Anglia, NR4 7UH Norwich, United Kingdom
+
+<|ref|>text<|/ref|><|det|>[[120, 588, 750, 605]]<|/det|>
+\*Corresponding author: Panagiotis N. Moschou. Email: Panagiotis.moschou@uoc.gr
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[119, 77, 200, 92]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[118, 100, 880, 281]]<|/det|>
+To survive extreme desiccation, seeds enter a period of dormancy that can last millennia. Seed dormancy involves the accumulation of protective storage proteins through unknown adjustments in proteasomal degradation. Mutating all six type II metacaspase (MCA- II) proteases in Arabidopsis thaliana revealed their essential roles in modulating proteasomal degradation. MCA- II mutant seeds fail to target the AAA ATPase CELL DIVISION CYCLE 48 (CDC48) at the endoplasmic reticulum to discard misfolded proteins, compromising their storability. Moreover, we show that MCA- IIs cleave a PUX (ubiquitination regulatory X domain- containing) adaptor, which is responsible for the localization of CDC48 to lipid droplets. This cleavage enables the shuttling of CDC48 between lipid droplets and the endoplasmic reticulum, constituting an important step in the regulation of spatiotemporal proteolysis. In summary, we uncovered a proteolytic pathway conferring seed longevity.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[120, 78, 240, 94]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[120, 107, 881, 305]]<|/det|>
+The desiccation- associated phytohormone abscisic acid (ABA) modulates seed dormancy by repurposing pre- existing stress- related networks into a seed dormancy program. This rewiring allows large amounts of proteins to be stored in the seed to protect and nourish the embryo 1. These proteins are highly structurally disordered 2, which could be expected to activate the unfolded protein response (UPR) 3. The UPR is a proteolytic mechanism involving the proteasome that slows translation to help remove misfolded or even disordered proteins that cause endoplasmic reticulum (ER) stress. A constitutive UPR slows translation by decreasing the rate of protein biosynthesis, which is achieved by inducing the INOSITOL- REQUIRING 1- 1 (IRE1)- dependent RNA degradation (RIDD) pathway that degrades RNAs, especially for secretory proteins bound to ribosomes 4. Notably, seeds can maintain high protein contents without activating protein homeostasis pathways, suggesting they have the ability to control proteolytic mechanisms (e.g., the UPR).
+
+<|ref|>text<|/ref|><|det|>[[119, 318, 881, 483]]<|/det|>
+The cysteine proteases metacaspases (MCAs) are present in bacteria and all eukaryotes except animals 5. In contrast to animal- specific caspases, MCAs cleave proteins after arginine (R) or lysine (K) residues, but not aspartate (D) 5. While some organisms contain a single MCA gene (e.g., budding yeast [Saccharomyces cerevisiae]), land plants contain multiple MCA family members. For example, the model plant Arabidopsis (Arabidopsis thaliana) has nine MCAs, which are classified as type I or II (with three [MCA- I] and six [MCA- II] members; Fig. 1A) based on their structure. MCA- Is modulate pathogen- induced programmed cell death (PCD), vascular development, and the clearing of protein aggregates 6- 8, while plant- specific MCA- IIs are involved in abiotic stress responses, wound- induced damage- associated molecular pattern signaling, and developmental PCD 9- 12.
+
+<|ref|>text<|/ref|><|det|>[[120, 496, 880, 563]]<|/det|>
+Despite their importance, the exact molecular functions of MCA- IIs remain elusive. Indeed, four of the six MCA- II genes are located in tandem on Arabidopsis chromosome 1, making it challenging to obtain double or high- order transfer (T)- DNA- based mutants (Fig. 1A, note the nomenclature used for MCA- IIs as in 5).
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 577, 190, 593]]<|/det|>
+## Results
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 607, 561, 625]]<|/det|>
+## Type II metacaspases have redundant functions
+
+<|ref|>text<|/ref|><|det|>[[119, 637, 881, 867]]<|/det|>
+To overcome the potential redundancies among MCA- IIs, we used clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR- associated nuclease 9 (Cas9)- mediated genome editing to obtain homozygous plants harboring single or higher- order mutations in MCA- II genes in various combinations, as well as two independent transgene- free lines lacking function of all six MCA- IIs. The sextuple MCA- II mutants are referred to hereafter as mca- II- KOc (c for "clean line" without CRISPR transgenes; fig. S1A- E). Both mca- II- KOc lines are likely loss- of- function mutants, as they displayed 1) no MCA- II- a protein using a specific antibody in immunoblots (this antibody does not cross- react with other MCA- IIs), accompanied by lower transcript levels of MCA- II genes, suggesting that the mutations introduced by gene editing led to nonsense- mediated decay, a process known to affect transcripts with frameshifts that induce premature stop codons 13; 2) diminished cleavage of the known MCA- II substrate TUDOR STAPHYLOCOCCAL NUCLEASE 14; and 3) lower in vitro activity on a fluorogenic substrate that is also cleaved by MCA- IIs (9; Fig. 1B,C and fig. S1F).
+
+<|ref|>text<|/ref|><|det|>[[119, 881, 881, 915]]<|/det|>
+Remarkably, the mca- II- KOc plants displayed only mild developmental defects, with reduced leaf serration (i.e., the formation of teeth at leaf margins), earlier flowering, and earlier leaf
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 77, 880, 371]]<|/det|>
+senescence compared to the wild type (WT) (fig. S2A). However, these plants did not show signs of compromised developmental PCD, e.g., in the root cap, but showed compromised PCD when challenged with virulent strains of the pathogens Botrytis cinerea and Pseudomonas syringae (fig. S2B- D). In agreement with our results, a quadruple mutant in MCA- II genes showed a similarly compromised response to Botrytis infection 15. Furthermore, effectortriggered immunity (ETI)- associated PCD (i.e., hypersensitive response) was abolished in mca- II- KOc lines challenged with the effector AvrRps4 (fig. S2C, left panel), which is recognized by TIR (Toll- like, Interleukin- 1 receptor, Resistance protein) intracellular NLR (nucleotide- binding, leucine- rich repeat) immune receptors 16. By contrast, we observed no obvious differences in AvrRpt2- induced ETI- associated PCD (fig. S2C, right panel), which is mediated by coiled- coil (CC) NLR receptors. Although AvrRpt2- induced ion leakage (serving as a proxy for the hypersensitive response) was reported to be slightly reduced at early time points 17, we detected no obvious difference after one day of treatment in mca- II- a single mutants compared to the WT (fig. S2C). We thus postulate that MCA- IIs play both redundant and specific roles in TIR- NLR- mediated PCD, but likely not in CC- NLR- mediated PCD, at least with the effectors tested here. On the contrary, MCA- IIs might not be involved in the execution of generic cell death programs during development, at least in Arabidopsis, suggesting other modes of action.
+
+<|ref|>text<|/ref|><|det|>[[118, 386, 880, 582]]<|/det|>
+During our studies, we noticed that freshly collected mca- II- KOc seeds germinated more quickly than WT seeds, suggesting reduced seed dormancy. When the same batch of seeds was stored for 3 months or longer at \(4^{\circ}\mathrm{C}\) (as low temperatures increase the lifespan of Arabidopsis seeds), the germination rate of the mutant seeds rapidly declined relative to the WT (Fig. 1D- F). Germination failure was accompanied by the presence of fragmented and irregularly shaped vacuoles that accumulated aggregates. This vacuolar fragmentation was associated with unknown large structures that appeared to mechanically compress and deform the vacuolar membrane (Fig. 1G). We discuss the nature of these structures below. The seed germination phenotype was mostly specific to mca- II- KOc lines and was seldom observed in the corresponding lower- order mutants. Even the presence of a single active MCA- II was sufficient to suppress this phenotype (fig. S3A, B; note the expression of MCA- IIs in seeds). These results suggest that MCA- IIs redundantly control aspects of seed physiology.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 596, 591, 614]]<|/det|>
+## Metacaspases participate in the ER stress response
+
+<|ref|>text<|/ref|><|det|>[[118, 627, 880, 909]]<|/det|>
+As we observed vacuoles resembling those rich in protein aggregates (storage vacuoles) reported in 18, we speculated that MCA- IIs regulate aspects of protein homeostasis in seeds via their proteolytic activity. To identify proteolytic targets of MCA- IIs, we conducted a proteomic analysis of mca- II- KOc and WT dry seeds (stored at \(4^{\circ}\mathrm{C}\) for 3 months, before mca- II- KOc seeds lose substantial viability). We used a log2fold- change (FC)>1 between mca- II- KOc and WT peptides as the criterion for protein enrichment (Data S1). Gene ontology (GO) analysis of the enriched proteins showed that mca- II- KOc seeds accumulate proteins residing at the ER or associated structures (i.e., lipid droplets) and proteins related to the UPR, e.g., the major ER stress- associated chaperones BiP (binding immunoglobulin protein) and disulfide isomerases (PDIs) (Fig 2A and Data S1; 19,20). To determine the localizations of MCA- II- a and MCA- II- d, we generated transgenic plants carrying a translational fusion construct encoding MCA- II- a or MCA- II- d fused to green fluorescent protein (GFP) under the control of their respective native promoters. We detected GFP fluorescence associated with the ER in embryonic root cells; we validated this observation by cell fractionation on sucrose density gradients, with GFP- MCA- II- a co- fractionating with the ER marker protein BiP2 (Fig. 2B, C). These findings suggest that MCA- IIs cleave proteins at the ER to regulate their abundance.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 75, 881, 306]]<|/det|>
+To test whether MCA- IIs directly cleave the identified proteins that accumulated at the ER in vivo, we performed N- terminome analysis of the seed proteome via combined fractional diagonal chromatography (COFRADIC) 21. This approach enables the identification of cleavage sites introduced by proteases and the resulting novel N termini (neo- N termini) formed in vivo upon proteolysis (fig. S3C, D). However, we failed to detect any of the enriched ER proteins identified in the mca- II- KOc mutants as direct targets of MCA- IIs by COFRADIC analysis of the proteome from WT seeds (fig. S3E and Data S2). Hence, we examined the alternative possibility that mca- II- KOc seeds indirectly accumulate the identified ER proteins by mounting an ER stress response, leading to the activation of the UPR associated with the accumulation of BiP and PDIs 4. However, transcriptome deep sequencing (RNA- seq) experiments did not identify the known transcriptional signatures associated with the UPR in mca- II- KOc seeds (fig. S4A- C and Data S3; 2). Taken together, these results suggest that although mca- II- KOc seeds show ER stress, they do not activate a constitutive UPR.
+
+<|ref|>text<|/ref|><|det|>[[118, 320, 880, 763]]<|/det|>
+Based on these results, we hypothesized that MCAs function independently of a constitutive UPR. We thus tested whether MCA- IIs regulate the proteasome using MCA- II- a and MCA- II- b and their inactive Proteolytically- Dead (MCA- II- a/bPD, with catalytic Cys replaced with Ala) variants as baits for affinity purification followed by liquid chromatography- tandem mass spectrometry (fig. S5A and Data S4). These assays showed that MCA- IIs interact weakly with two chaperones involved in proteasome assembly (fig. S5B; 2 out of 32 proteins in the proteasome assembly; REGULATORY PARTICLE TRIPLE- A ATPASE 5A- RPT5a and AT5G45620- SS regulatory sub 13a, 7 and 1 peptides for MCA- II- b, respectively). Mutating the catalytic Cys (MCA- II- a/bPD) facilitated these interactions, likely because these proteins remained bound to their substrates, as they do not catalyze their cleavage (Data S4). The mutant MCA- II- aPD bait, but not its WT version, associated with (poly- )ubiquitin (Ub)- conjugated proteins, which are normally recognized by the proteasome. As only the mutant bait associated with Ub- conjugated proteins, this suggests that MCA- IIs preferentially target Ub- conjugated/associated proteins forming with these transient complexes (fig. S5C, D). In support of this idea, Ub- conjugated proteins were more abundant in mca- II- KOc relative to WT (Fig. 2D; \(\sim 3\) - fold). Moreover, regulatory subunits of the proteasome accumulated to higher levels in mca- II- KOc compared to WT, as revealed by total proteomic analysis of mca- II- KOc seeds (Data S1). In particular, we observed accumulation of the 26S proteasome, a phenotype reminiscent of proteasomal receptor mutants, e.g., mutants of the REGULATORY PARTICLE NON- ATPASE 10 (rpn10) subunit of the proteasome (22; fig. S5E- G). Furthermore, mca- II- KOc mutants were insensitive to treatment with the proteasome inhibitor MG132 (a peptide aldehyde that reversibly inhibits the proteasome), but not with other proteolytic inhibitors, as was reported for several proteasomal mutants (fig. S5H and 23). Notably, MCA- II- a did not cleave K48 tetra- Ub isopeptide linkages, which represent the most abundant and canonical degradation signals (fig. S6 and 24). This finding argues against the possibility that MCA- IIs remove Ub from proteins (i.e., they are not deubiquitinases). Taken together, these results suggest that MCA- IIs modulate proteasome activity.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 777, 863, 810]]<|/det|>
+## Type II metacaspases regulate the lipid droplet-associated degradation pathway in seeds via interaction with CDC48
+
+<|ref|>text<|/ref|><|det|>[[118, 824, 880, 907]]<|/det|>
+As the UPR was not induced while proteasomal activity was compromised in mca- II- KOc mutants, we hypothesized that Arabidopsis seeds rely on alternative pathways for protein homeostasis. We focused on ER- associated degradation (ERAD), as this process would still promote the retrotranslocation of Ub- proteins from the ER to the cytosol for degradation by the proteasome, much like the UPR 25. Furthermore, ERAD would fit well in the context of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 77, 880, 405]]<|/det|>
+seed proteostasis by allowing the excess accumulation of secreted seed storage proteins (e.g., 2S albumins, late embryogenesis abundant proteins, and 12S globulins) that nurture and protect the embryo, unlike the UPR pathway, which would compromise the production of secreted proteins by eliciting translational suppression through RIDD \(^{25,26}\) . In plants, ERAD promotes the formation of an impermeable cuticle, a waxy layer that attenuates desiccation stress by retaining water in the plant body \(^{27}\) . The enzymes for cuticle biosynthesis are localized to the ER. The cuticle also renders young seedlings (e.g., 3- day- old) less responsive to ABA and is required for proper apical hook formation \(^{28}\) , which is indispensable for protecting the delicate shoot apical meristem. Seeds of the core proteasomal mutant rpn10 display compromised longevity, compromised hypocotyl elongation due to the accumulation of the transcription factor ELONGATED HYPOCOTYL 5 (HY5), and hypersensitivity to ABA and ER stress \(^{29}\) . Accordingly and in line with a possible link between MCA- II and ERAD (and proteasome), we observed cuticle abnormalities in 3- day- old etiolated mca- II- KOc seedlings, as revealed by toluidine blue permeability assays (Fig. 3A, \(^{28}\) ). This phenotype was absent from mca- II- KOc plants harboring a complementation construct expressing MCA- II- a driven by the meristem- specific RIBOSOMAL PROTEIN S5a (RPS5a, from locus AT3G11940) promoter (Fig. 3A, "Com"). We corroborated these results by staining cuticles with the suberin- specific dye FluoroI Yellow 088 (FY088) in embryonic roots and observing defects typically linked to cuticle loss, such as sensitivity to ABA and the absence of an apical hook, in mca- II- KOc (fig. S7A- C; \(^{30}\) ). Hence, mca- II- KOc may show compromised ERAD.
+
+<|ref|>text<|/ref|><|det|>[[118, 411, 880, 592]]<|/det|>
+In budding yeast, the sole type I MCA (Mca1p) interacts with the AAA ATPase CELL DIVISION CYCLE 48 (CDC48; valosin- containing protein [VCP] in vertebrates) to regulate protein homeostasis \(^{31}\) . CDC48 is a major ERAD component that exports proteins from the ER for proteasomal delivery and regulates proteasome activity, functioning as an "unfoldase/segregase" \(^{26}\) . We identified CDC48 as a direct interactor of MCA- II- a and confirmed their colocalization and direct interaction via a quantitative in vivo proximity ligation assay (PLA) and in embryonic roots harboring the transgenes RPS5apro:mNeon- MCA- II and 35Spro:mCherry- CDC48 \(^{32,33}\) ; furthermore, MCA- II- a localized on lipid droplets together with CDC48 (Fig. 3B- E and fig. S8C). From these assays, we conclude that in seeds, MCA- II- a and CDC48 colocalize to lipid droplets at a higher concentration than in the surrounding cytoplasm (Fig. 3B, C, arrowheads).
+
+<|ref|>text<|/ref|><|det|>[[118, 598, 880, 797]]<|/det|>
+Since CDC48 interacted with MCA- II- a, and its homologs (e.g., CDC48E) were 4.1- times more abundant in the mca- II- KOc proteome dataset compared to WT (Data S1), we asked whether MCA- IIs regulate CDC48 activity. We focused on the specialized type of ERAD pathway named lipid droplets- associated degradation (LDAD), which removes Ub- oleosins from lipid droplets in seeds, facilitating their breakdown and remobilization during seed germination \(^{34}\) . Lipid droplets fuse with one another to form larger droplets in loss- of- function oleosin mutants \(^{35}\) . In agreement with this finding, we observed reduced abundance of oleosin in mca- II- KOc (by \(>30\) - fold), which was associated with an increased size of lipid droplets and the localization of MCA- II- a on lipid droplets (Fig. 3F, G; note the partial complementation of this phenotype in the "Com" line). Notably, the mutations in mca- II- KOc plants did not significantly affect fatty acid levels or composition (fig. S7D), suggesting that LDAD does not substantially contribute to lipid pools in seeds.
+
+<|ref|>text<|/ref|><|det|>[[118, 810, 880, 909]]<|/det|>
+During LDAD, the CDC48 adaptor PUX10 (ubiquitination regulatory X [UBX] domain- containing 10), one of the 16 PUX adaptors in Arabidopsis defined by a ubiquitin- like UBX domain, specifically recognizes Ub- oleosin for degradation; accordingly, oleosin accumulates in pux10 mutants \(^{34}\) . PUX10 harbors a ubiquitin- associated (UBA) domain at its N terminus \(^{36}\) . The UBA domain increases protein stability by reducing the incorporation of proteins into the proteasome; conversely, removing the UBA domain from proteins results in their degradation
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 75, 880, 208]]<|/det|>
+37. We confirmed that MCA-II-α and PUX10 colocalize and interact in Fösters resonance energy transfer-sensitized emission (FRET-SE) and PLA by examining embryonic roots harboring the transgenes RPS5apro:MCA-II-a-tagRFP and PUX10pro:PUX10-GFP (Fig. 3C, E, upper panel and fig. S8A-C). Notably, MCA-II-a colocalized with PUX10 only when the levels of PUX10 were low, suggesting an inverse correlation between the signals of the two proteins (R²=-0.45; see below for an explanation). From these assays, we conclude that in seeds, MCA-II-a and PUX10 colocalize, but MCA-II-a appears to reduce PUX10 levels. These results suggest that MCA-IIs regulate LDAD by associating with CDC48 and PUX10.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 222, 847, 255]]<|/det|>
+## The antagonism between lipid droplet- and ER-associated protein degradation pathways determines seed longevity
+
+<|ref|>text<|/ref|><|det|>[[118, 261, 880, 475]]<|/det|>
+In our colocalization assays, we observed that PUX10- GFP levels in cells were inversely correlated with the levels of MCA-II- a- tagRFP (Fig. 4A, Pearson's correlation coefficient \(\mathrm{R} =\) - 0.36). However, in a transgenic line that accumulated GFP- PUX10 (i.e., tagged N- terminally with GFP this time), the presence of MCA- II- a- tagRFP had no effect on GFP fluorescence levels, suggesting that the N- terminal fragment of PUX10 remained stable. To resolve this conundrum, we used Nicotiana benthamiana leaves as a heterologous transient expression system. We detected the specific cleavage of PUX10 by MCA- II- a, leading to the accumulation of an N- terminal fragment of PUX10 that interacted with MCA- II- a in co- immunoprecipitation assay (Fig S8D- F). Accordingly, in our COFRADIC data, the N terminus of a PUX homolog (PUX5) was highly enriched in WT but not in mca- II- KOc samples (fig. S3F and Data S2). Hence, although PUX10 is cleaved and its C- terminal region that interacts with CDC48 is degraded (i.e., the UBX part), the N- terminal fragment containing the stabilizing UBA domain remains associated with MCA- IIs, likely through Ub.
+
+<|ref|>text<|/ref|><|det|>[[118, 482, 880, 679]]<|/det|>
+The lack of PUX10 cleavage in mca- II- KOc would be expected to lead to increased retention of CDC48 attached to lipid droplets. This hypothesis was validated by the observation that, in contrast to WT, in mca- II- KOc, mCherry- CDC48 decorated large intracellular structures reminiscent of lipid droplets, whereas its ER signal decreased (Fig. 4B). We reasoned that the depletion of CDC48 from the ER in mca- II- KOc would lead to aggravated ER stress and cell death in seeds. To test this idea, we first compared the effects of external inhibition of CDC48 activity in WT and mca- II- KOc using CB- 5083, a specific inhibitor of CDC48 \(^{36}\) . Indeed, loss of function of MCA- II enhanced the response of seedlings to CB- 5083 (Fig. 4C, note the root swelling). Next, we measured seed viability using tetrazolium staining and found increased PCD in mca- II- KOc (Fig. 4D). Together, these results suggest that efficient ERAD requires an MCA- II- dependent pathway that involves PUX10 cleavage to enable the attenuation of LDAD and the ER targeting of CDC48 to promote seed longevity (Fig. 4E, model).
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 694, 220, 710]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[118, 725, 880, 920]]<|/det|>
+We uncovered a mechanism for the regulation of spatial proteasomal activity that involves the specific cleavage of a PUX adaptor to modulate the intracellular location of CDC48 in the specialized ERAD pathway. Interestingly, the deletion of the PUX10 homolog Alveolar soft part locus (ASPL) or Ubiquitin regulatory X4 (UBX4) impaired ERAD and led to toxicity in mammalian cells and budding yeast, respectively \(^{38,39}\) . In the seed context, however, balancing LDAD is an important step in the regulation of ERAD, which likely involves other PUX proteins. Further research is required to uncover additional links between PUXs and MCAs. In line with our results, the localization of UBXD8 (Ubiquitin regulatory X domain- containing protein 8), a mammalian CDC48 adaptor, is regulated by a rhomboid pseudoprotease, which is responsible for shuttling CDC48 between the ER and lipid droplets, thereby regulating energy squandering \(^{25,40}\) . In non- plant models, suppressing protein anabolism can lead to enhanced longevity; likewise, reduced protein translation via UPR waves may be functionally equivalent
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[119, 75, 880, 142]]<|/det|>
+but likely would not suit the seed context in which high protein accumulation is required. The pathway linking MCA- II- dependent PUX cleavage and CDC48 activity appears to have evolved as an elegant solution to this problem by enabling sustained protein production while maintaining protein homeostasis.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 157, 202, 172]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 193, 243, 207]]<|/det|>
+## Plant material
+
+<|ref|>text<|/ref|><|det|>[[118, 208, 880, 466]]<|/det|>
+All the plant lines used in this study were in the Arabidopsis Columbia- 0 (Col- 0) ecotype. The following mutants were used smb41, mca- II- d (SALK_127688) and mca- II- f (GABI_540H06). The two mca mutants were used as a background for CRISPR. Primers used for genotyping of mutant lines can be found in Table S1. The following transgenic lines used in this study were described previously: PUX10pro:PUX10- GFP42 and MCA- II- fpro:MCA- II- f- GFP43. Seedlings were grown on half- strength Murashige and Skoog (MS) plant agar media under long- day conditions (16h- light/8h- dark, or as indicated) and were harvested, treated, or examined as indicated in the context of each experiment. In all experiments, seedlings, or plants from T1/F1 (co- localization experiments), T2/F2, or T3/4/5 (for physiological experiments) generations were used. Arabidopsis seeds were sterilized and germinated on half- strength MS agar medium under long- day conditions (16 h light/8 h dark). Arabidopsis plants for crosses, phenotyping of the above- ground part, and seed collection were grown on soil in a plant Aralab chamber at \(22^{\circ}C / 19^{\circ}\) and a light intensity of \(150\mu \mathrm{mol}\mathrm{m}^{- 2}\mathrm{s}^{- 1}\) with \(60\%\) relative humidity stabilized by an infrared sensor. The seeds harvested at the same time under the same condition were used for experiments unless otherwise indicated in the text or figure legends. Nicotiana benthamiana plants were grown in Aralab or Percival cabinets at \(22^{\circ}C\) , 16- h- light/8- h- dark cycles, and a light intensity of \(150\mu \mathrm{mol}\mathrm{m}^{- 2}\mathrm{s}^{- 1}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 482, 334, 497]]<|/det|>
+## Metacaspase phylogeny
+
+<|ref|>text<|/ref|><|det|>[[119, 497, 880, 587]]<|/det|>
+Alignments of MCAs sequences were performed in MUSCLE. Unrooted trees were constructed using the neighbour- joining method44 using the yeast homologue as an outgroup. A phyldendrogram was constructed using MEGA11 and PAUP software (http://paup.csit.fsu.edu). The bootstrap analysis was performed with 1,000 repeats, and branches with bootstrap values over \(70\%\) were retained. The sequences used can be found in Data S5.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 605, 300, 620]]<|/det|>
+## Drugs and stainings
+
+<|ref|>text<|/ref|><|det|>[[118, 620, 880, 920]]<|/det|>
+The stock solutions of \(2\mathrm{mM}\) FM4- 64, \(10\mathrm{mM}\) CB- 5083 (1- (4- (benzylamino)- 7,8- dihydro- 5H- pyrano- (4,3- d)- pyrimidin- 2- yl)- 2- methyl- 1H- indole- 4- carboxamide), \(1\mathrm{mM}\) BCECF (2',7'- Bis- (2- Carboxyethyl)- 5- (and- 6)- Carboxyfluorescein, Acetoxymethyl Ester), LipidTox (1:1000 dilution, Thermo, H34477), ER tracker (1:1000 dilution, Thermo, E34251), Lysotracker (1:1000 dilution, Thermo, L7528), \(50\mathrm{mM}\) MG132, \(2\mathrm{mM}\) Concanamycin A (Con A), \(33\mathrm{mM}\) wortmannin (Wm) and \(10\mathrm{mM}\) E64d were dissolved in dimethyl sulfoxide (DMSO), while \(1\mathrm{M}\) dithiothreitol (DTT) was dissolved in water. Propidium iodide (PI) was dissolved in water. These inhibitors, drugs and stains were diluted in a half- strength MS medium with corresponding concentration and duration, and the final DMSO concentration was \(\leq 0.1\%\) (v/v) in all experiments. Vertically grown 4- to 5- day- old Arabidopsis seedlings were incubated in a half- strength liquid MS medium containing the corresponding drugs for each specific time course treatment as indicated. For confocal microscopy of reporters and mutants, fluorescence images were captured on Leica SP8 or Zeiss780 microscopes and were processed with ImageJ (National Institutes of Health). Cell contours were visualized with propidium iodide (PI) (Molecular Probes) or FM4- 64. For the FDA- PI viability staining, seedlings were mounted on a glass slide in FDA solution (1 \(\mu \mathrm{L}\) dissolved FDA stock solution [2 mg in 1 ml acetone] in 1 ml of 1/2 MS) supplemented with \(10\mu \mathrm{g / ml}\) PI. For the seed viability test, tetrazolium red assays were done as described previously45. In short, dry seeds from different genotypes were incubated in the dark in an aqueous solution of \(1\%\) (w/v) 2,3,5- triphenyl tetrazolium (TZ) at \(28^{\circ}C\) for \(24\mathrm{to}48\mathrm{h}\) with or without indicated treatment. Seeds were rinsed in water before imaging. For the cuticle
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 75, 880, 211]]<|/det|>
+integrity assay, the experiment was done as described previously \(^{46}\) . In short, 48h- post germinated seedlings were incubated in Fluorol Yellow (FY)- 088 (0.01% [w/v] in lactic acid) for \(70^{\circ}C\) , 20min incubation, and the seedlings were rinsed in water and checked under Zeiss 780 microscopes with GFP channel setting (Ex: 488- 490 nm, Em: 530- 550 nm). For studying the permeability with toluidine blue \(^{47}\) , 4 to 5- day- old etiolated seedlings grown on \(1 / 2\) MS plate were collected and then incubated in an aqueous solution of \(0.05\%\) [w/v] toluidine blue/0.1% [w/w] Tween 20 for 120 sec followed by a quick washing step in \(\mathrm{ddH_2O}\) . Seedlings were observed with Leica DM6000. For lipid droplet staining, lipidTox (Thermo Fisher Scientific; 500- fold dilution) was used as previously described \(^{42}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 225, 305, 240]]<|/det|>
+## Plant infection assay
+
+<|ref|>text<|/ref|><|det|>[[118, 240, 880, 391]]<|/det|>
+The Botrytis cinerea strain B05.10 was used in the infection experiments and stored as conidia suspension at \(- 80^{\circ}C\) in \(40\%\) (v/v) glycerol. For conidia production culture was grown in Hydroxyapatite (HA) medium (1% (w/v) Malt extract/ \(0.4\%\) (w/v) Glucose / \(0.4\%\) (w/v) Yeast extract / \(1.5\%\) (w/v) Agar, pH 5.5) and incubated at \(25^{\circ}C\) for 7 days. 3- 4 weeks plants with fully expanded leaves were used for inoculations. Spore suspensions were prepared in Gamborg Minimal medium (3 g Gamborg B5 basal salt mixtures, \(1.36 \mathrm{g} \mathrm{KH}_2 \mathrm{PO}_4\) , and \(9.9 \mathrm{g}\) glucose per liter), collected by scraping the mycelial colony and adjusted to a concentration of \(2 \times 10^{5}\) spores \(\mathrm{ml}^{- 1}\) . A droplet of conidia suspension (10 \(\mu \mathrm{l}\) ) was placed at one different point of the adaxial surface of each leaf. Control plants were sprayed or drenched with sterile tap water.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 404, 680, 420]]<|/det|>
+## Hypersensitive cell death response phenotyping in Arabidopsis
+
+<|ref|>text<|/ref|><|det|>[[118, 420, 880, 540]]<|/det|>
+The desired avirulent effectors AvrRps4 or AvrRpt2 were delivered to the Arabidopsis plants via a Pseudomonas fluorescens effector- to- host analyzer strain (EtHAn), with a P. syringae pv. Syringae 61 hrp/hrcc cluster (Type III secretion system machinery) stably integrated into the chromosome in Pf0- 1 (Thomas et al., 2009). EtHAn:AvrRps4 and EtHAn:AvrRpt2 were grown on selective KB plates for \(24 \mathrm{h}\) at \(28^{\circ}C\) \(^{48}\) . Bacteria were harvested from the plates, resuspended in infiltration buffer ( \(10 \mathrm{mM} \mathrm{MgCl}_2\) ), and the concentration was adjusted to \(\mathrm{OD}_{600} = 0.2\) (108 CFU \(\mathrm{ml}^{- 1}\) ). The abaxial surfaces of 5- week- old Arabidopsis leaves were hand infiltrated with a 1 ml needleless syringe. Cell death was monitored \(24 \mathrm{h}\) after infiltration.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 555, 325, 570]]<|/det|>
+## Protease activity assay
+
+<|ref|>text<|/ref|><|det|>[[118, 570, 880, 720]]<|/det|>
+Protease activities were measured by fluorogenic peptide- based substrate (EGR- AMC: H- GluGly- Arg- 7- amino- 4- methylcoumarin) as described in \(^{49}\) . Plant (0.01g seeds or equal amount of 7- day- old seedlings) extract from WT and different mutants using reaction buffer: \(50 \mathrm{mM}\) HEPES, pH 7.4, \(0.1\%\) (w/v) 3- [(3- cholamido- propyl) dimethylammonio]- 1- propanesulfonate (CHAPS), \(50 \mathrm{mM} \mathrm{CaCl}_2\) , \(5 \mathrm{mM}\) dithiothreitol (DTT); EGR- AMC were added at \(50 \mu \mathrm{M}\) final. The release of AMC was measured every \(2 \mathrm{min}\) at \(30^{\circ}C\) with a Microtiter Plate Fluorometer (Microplate reader Fluostar Omega) using an excitation wavelength of \(360 \mathrm{nm}\) and an emission wavelength of \(460 \mathrm{nm}\) . Data time points were analyzed by the Omega Fluostar software, and activities were expressed in fluorescence units/min/mg or \(\mu \mathrm{g}\) of total protein. Protein concentration was determined using the Bradford reagent (Bio- Rad).
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 734, 590, 750]]<|/det|>
+## DNA manipulation and production of transgenic lines
+
+<|ref|>text<|/ref|><|det|>[[118, 750, 880, 916]]<|/det|>
+Electrocompetent Agrobacterium (Agrobacterium tumefaciens) strain C58C1 Rif \(^{R}\) (pMP90) or GV3101 Rif \(^{R}\) (i.e., a cured nopaline strain commonly used for infiltration) was used for electroporation, N. benthamiana infiltration and floral dip transformation in Arabidopsis \(^{50}\) . The following constructs used in the study were described previously: 35Spro:mCherry- PUX10, 35Spro:mCherry- CDC48a \(^{42}\) . Transcriptional and translational reporters and overexpression constructs used in this study were produced through either Gateway (Invitrogen) cloning using pENTR/D and pENTR5' lines or through GOLDENGATE (Addgene) in the following backbones: (i) pGWB505 and pGWB560 \(^{51}\) (ii) pMDC32 \(^{52}\) (iii) (iv) pLCSL86900 and pLCSL86922 (Addgene). The cDNA of MCA- II- a was PCR amplified with Phusion \(^{TM}\) High- Fidelity DNA Polymerase & dNTP Mix (Thermo Fisher Scientific, F530N) using cDNA from 7- day- old seedlings. MCA- II- a- PD was generated with site- directed mutagenesis with pENTR of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 75, 880, 166]]<|/det|>
+MCA- IIa. Constructs of MCA- IIa or MCA- IIa- PD were generated by Gateway cloning with pENTR into different destination vectors which have different tags in N- or C- termini. The coding sequence of CDC48a, PUX10 were PCR amplified with Phusion™ High- Fidelity DNA Polymerase & dNTP Mix (Thermo Fisher Scientific, F530N) using the cDNA from 7- day- old seedling with pENTR™/D- TOPO™ Cloning Kit (Thermo Fisher Scientific, K240020). Primer sequences used for the amplification of promoters and genes are listed in Table S1.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 180, 400, 195]]<|/det|>
+## Construction of MCA-II mutants
+
+<|ref|>text<|/ref|><|det|>[[118, 196, 880, 600]]<|/det|>
+The pICSL binary vector series was utilized to generate CRISPR lines in this study. Primer sequences used for the amplification of promoters and genes are listed in Table S3. To generate the Cas9 expression cassettes, the RPS5a and Cas9z coding sequences and the E9 terminator were amplified using primers flanked with BpII restriction sites associated with Golden Gate compatible overhangs (Table S1). Combinations of three Level 0 vectors containing respectively a promoter, a Cas9z coding sequence and a terminator were assembled in Level 1 vector pICH47811 (Position 2, reverse) by the same 'Golden Gate' protocol but using 0.5 μl of BpII enzyme (10U/μl, ThermoFisher) instead of 0.5 μl of BsaI- HF. To create the MCA- II/s deletion mutant, a previously described multiplexed editing approach was used \(^{53}\) . The sgRNAs were designed using the CRISPR- P 2.0 (http://crispr.hzau.edu.cn/CRISPR2) \(^{54}\) and CHOP- CHOP (https://chopchop.cbu.uib.no/) \(^{55}\) . To generate the sgRNA expression cassettes, DNA fragments containing the classic or the 'EF' backbone with 7, 67 or 192 bp of the U6- 26 terminator were amplified using primers flanked with BsaI restriction sites associated with Golden Gate compatible overhangs (Table S4). The amplicons were assembled with the U6- 26 promoter (pICSL90002) in Level 1 vector pICH7751 (gRNA- MCA- II- e, Position 3), pICH7761 (gRNA- MCA- II- b, Position 4), pICH7772 (gRNA- MCA- II- a, Position 5) and pICH7781 (gRNA- MCA- II- c, Position 6) by the 'Golden Gate' protocol using the BsaI- HF enzyme. Combinations of three Level 1 vectors containing a red seed coat maker (FAST- Red, pICSL11015, Position2, OLE1pro:OLE1- RFP), a Cas9 expression cassette, and four sgRNA expression cassettes were assembled in Level 2 pAGM4723 (without an overdrive) or pICSL4723 (with an overdrive) by the 'Golden Gate' protocol using the BpII enzyme. All the plasmids were prepared using a ThermoScientific kit on Escherichia coli DH10B electrocompetent cells selected with appropriate antibiotics and X- gal. All the plasmid identification numbers refer to the 'addgene database' (www.addgene.org/). We selected red fluorescing seeds and screened the resulting seedlings for mutation and CRISPR clean lines were selected based on the crossing to WT and to get the segregation lines for further screening of non- red seed coat and resequencing.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 614, 643, 630]]<|/det|>
+## RNA extraction, RNA-seq and quantitative RT-PCR analysis
+
+<|ref|>text<|/ref|><|det|>[[118, 630, 880, 900]]<|/det|>
+Total RNA from the seedlings was extracted using RNeasy Plant Mini Kit with DNaseI digestion (QIAGEN). Reverse transcription was carried out with 500 ng of total RNA using the iScript cDNA synthesis kit (Bio- Rad) according to the manufacturer's protocol. Quantitative PCR with gene- specific primers was performed with the SsoAdvanced SYBR Green Supermix (Bio- Rad) on a CFX96 Real- Time PCR detection system (BioRad). Signals were normalized to the reference genes ACTIN7 using the DCT method and the relative expression of a target gene was calculated from the ratio of test samples to WT. Primer sequences used for the amplification of promoters and genes are listed in Table S1. For each genotype, two biological replicates were assayed in three qPCR replicates. qRT- PCR primers were designed using QuantPrime \(^{56}\) . For RNA- seq the concentration of RNA was determined by Qubit® RNA HS Assay Kit (New England BioNordika BioLab, Q32852). All the RNA samples were treated with DNase I (ThermoFisher Scientific, EN0521) and further enriched with NEBNext® Poly(A) mRNA Magnetic Isolation Module (ThermoFisher Scientific, E7490S). The RNA was measured with Qubit® RNA HS Assay Kits again and libraries were prepared with NEBNext® Ultra™ II RNA Library Prep with Sample Purification Beads (Invitrogen Life Technologies (Ambion Applied Biosystem, E7775S) and NEBNext® Multiplex Oligos for Illumina® (Dual Index Primers Set 1) (New England BioNordika BioLab, E7600S). cDNA library quality was monitored with Agilent DNA 7500 Kit (Agilent Technologies Sweden AB, 5067- 1506). cDNA
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 77, 879, 108]]<|/det|>
+libraries were sequenced with a paired- end sequencing strategy to produce \(2 \times 150\) - bp reads using Novogen sequencers and 20 million reads per sample (Novogene, England).
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 122, 272, 136]]<|/det|>
+## Cell fractionation
+
+<|ref|>text<|/ref|><|det|>[[118, 136, 880, 287]]<|/det|>
+Cell fractionation was done using MCA- II- apro:MCA- II- a- GFP lines based on sucrose gradient density ultracentrifugation \(^{57}\) . More specifically, leaves (5g) of the above line were ground followed by protein extraction buffer (50 mM Tris HCl pH 8.2, 2 mM EDTA pH 8.0, 1 mM DTT and protease inhibitors cocktail from Sigma- Aldrich at a 1:100 dilution plus 1 mM phenylmethylsulfonyl fluoride [PMSF]). The extract was filtered through miracloth and centrifuged at 5000 x g for 5 min for the removal of organelles and tissue debris, followed by ultracentrifuge at 100,000 x g for 45 min. Samples were ultracentrifuged overnight at 100,000 g. Subcellular fractions were collected in 2 ml Eppendorf and processed for immunoblot with the following antibodies: \(\alpha\) - GFP (Santa Cruz Biotechnology), \(\alpha\) - BIP2 (Agrisera), and \(\alpha\) - APX1 (Agrisera).
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 300, 285, 315]]<|/det|>
+## Fatty acid analysis
+
+<|ref|>text<|/ref|><|det|>[[120, 316, 880, 345]]<|/det|>
+The total fatty acid content and composition of mature seeds were determined by direct transmethylation followed by gas chromatography with a flame ionization detection \(^{58}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 359, 485, 375]]<|/det|>
+## Immunocytochemistry, PLA, and imaging
+
+<|ref|>text<|/ref|><|det|>[[118, 375, 880, 660]]<|/det|>
+Immunocytochemistry, PLA, and imagingImmunocytochemistry was done as described previously \(^{59}\) . The primary antibodies used were goat anti- CDC48a (VCP1) (diluted 1:500, Abcam. 206320) \(^{60}\) . In brief, samples were incubated with primary antibody at \(4^{\circ}C\) overnight and washed three times with PBS- T, and then incubated for 90 min with Alexa Fluor® 488 AffiniPure Donkey \(\alpha\) - Goat IgG (H+L) secondary antibody (Jackson ImmunoResearch, 705- 545- 147) diluted 1:200- 250, After washing in PBS- T and incubating with DAPI (1 \(\mu \mathrm{g / mL}\) ), specimens were mounted in Vectashield (Vector Laboratories) medium and observed within 48 h. PLA immunologicalization was done as described previously \(^{32}\) . Primary antibody combinations diluted 1:200 for \(\alpha\) - GFP mouse (Sigma- Aldrich, SAB2702197), 1:200 for \(\alpha\) - FLAG mouse (Sigma- Aldrich, F1804), 1:200 for \(\alpha\) - RFP mouse (Agrisera, AS15 3028) and 1:200 for \(\alpha\) - GFP rabbit (Millipore, AB10145) were used for overnight incubation at \(4^{\circ}C\) . Roots were then washed with MT- stabilizing buffer (MTSB: 50 mM PIPES, 5 mM EGTA, 2 mM MgSO4, 0.1% [v/v] Triton X- 100) and incubated at \(37^{\circ}C\) for 3 h either with \(\alpha\) - mouse plus and \(\alpha\) - rabbit minus for PLA assay (681 Duolink, Sigma- Aldrich). PLA samples were then washed with MTSB and incubated for 3 h at \(37^{\circ}C\) with ligase solution as described (Pasternak et al, 2018). Roots were then washed 2x with buffer A (Sigma- Aldrich, Duolink) and treated for 4 h at \(37^{\circ}C\) in a polymerase solution containing fluorescent nucleotides as described (Sigma- Aldrich, Duolink). Samples were then washed 2x with buffer B (Sigma- Aldrich, Duolink), with 1% (v/v) buffer B for another 5 min, and then the specimens were mounted in Vectashield (Vector Laboratories) medium.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 674, 454, 689]]<|/det|>
+## Quantification of fluorescent intensity
+
+<|ref|>text<|/ref|><|det|>[[118, 689, 880, 914]]<|/det|>
+To create the most comparable lines to measure the fluorescence intensity of reporters in multiple mutant backgrounds, we crossed homozygous mutant bearing the marker with either a WT plant (outcross to yield progeny heterozygous for the recessive mutant alleles and the reporter) or crossed to a mutant only plant (backcross to yield progeny homozygous for the recessive mutant alleles and heterozygous for the reporter). Fluorescence was measured as the mean grey value with subtraction of the background. GFP and chloroplast autofluorescence was excited with the 488- nm line of an argon laser, mCherry and RFP with a 561- nm diode laser, YFP with the 514- nm line of an argon laser, and LipidTOX Deep Red with a 633- nm helium/neon laser. Fluorescence emission was detected between 495 and 510 nm for GFP, 522 to 550 nm for YFP, 600 to 625 nm for mCherry and RFP, and 637 to 650 nm for LipidTOX Deep Red. Chloroplast autofluorescence was imaged between 670 and 700 nm. For multilabeling studies, detection was performed in a sequential line- scanning mode. The apparent diameter of LDs observed by CLSM was estimated using Fiji software (https://fiji.sc/) by manually drawing the diameter using the "line" tool and measuring it with the "measure" function of the software. For BiFC excitation wavelengths and emission, filters were 514
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 75, 880, 122]]<|/det|>
+nm/band-pass 530–550 nm for YFP, 561 nm/band-pass 600–630 nm for RFP and 488 nm/band-pass 650–710 nm for chloroplast auto- fluorescence. The objective used was an HC PL APO 40x/1,30 oil CS2 with NA=1.3 (Leica SP8 confocal system).
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 135, 342, 150]]<|/det|>
+## Ubiquitin cleavage assay
+
+<|ref|>text<|/ref|><|det|>[[118, 150, 880, 300]]<|/det|>
+Ubiquitin cleavage assayRecombinant proteins of GST- PROPEP1, MCA- II- a, MCA- II- a- PD, MCA- II- f, MCA- II- f and Usp2- cc were purified as previously described \(^{11}\) with the protocols described \(^{61}\) . The deubiquitylating activity of Usp2- cc, MCA- II- a and MCA- II- f was assayed against recombinant human K48- linked tetra- ubiquitin (BostonBiochem, #UC- 210B) by incubating the purified proteases with 2 µg substrate at 37°C for 30 min in either MC- II- f reaction buffer (50 mM MES, pH 5.5, 150 mM NaCl, 10% sucrose, 0.1% CHAPS, 10 mM DTT) or MCA- II- a reaction buffer (50 mM Hepes, pH 7.5, 150 mM NaCl, 10% glycerol, 50 mM CaCl₂, 10 mM DTT). Reactions were terminated by adding Sodium dodecyl- sulfate polyacrylamide gel electrophoresis (SDS- PAGE) sample buffer with an additional 50 mM EGTA for MCA- II- a reaction buffer, subjected to SDS- PAGE (12% polyacrylamide) and subsequent silver staining (Invitrogen, #LC6070).
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 315, 261, 330]]<|/det|>
+## Immunoblotting
+
+<|ref|>text<|/ref|><|det|>[[118, 330, 880, 798]]<|/det|>
+ImmunoblottingIn general, samples were flash- frozen in liquid \(\mathbb{N}_2\) and kept at \(- 80^{\circ}C\) until further processing. The samples were crushed using a liquid \(\mathbb{N}_2\) - cooled mortar and pestle, and the crushed material was transferred to a 1.5- mL or 15- mL tube. Extraction buffer (EB; 50 mM Tris- HCl pH 7.5, 150 mM NaCl, 10% [v/v] glycerol, 2 mM ethylenediamine tetraacetic acid [EDTA], 5 mM dithiothreitol [DTT], 1 mM phenylmethylsulfonyl fluoride [PMSF], Protease Inhibitor Cocktail [Sigma- Aldrich, P9599] and 0.5 % [v/v] IGEPAL CA- 630 [Sigma- Aldrich]) was added according to the plant material used. The lysates were pre- cleared by centrifugation at 16,000 g at 4°C for 15 min, and the supernatant was transferred to a 1.5- mL tube. This step was repeated two times and the protein concentration was determined by the RC DC Protein Assay Kit II (Bio- Rad, 5000122). 2X Laemmli buffer was added, and proteins were separated by SDS- PAGE (1.0 mm thick 4 to 12% [w/v] gradient polyacrylamide Criterion Bio- Rad) in 3- (N- Morpholino) propane sulfonic acid (MOPS) buffer (Bio- Rad) at 150 V or native polyacrylamide gel (Bio- Rad, Any kD TGX gels). Subsequently, proteins were transferred onto polyvinylidene fluoride (PVDF; Bio- Rad) membrane with 0.22- μm pore size. The membrane was blocked with 3% (w/v) BSA fraction V (Thermo Fisher Scientific) in phosphate buffered saline- Tween 20 (PBS- T) for 1 h at room temperature (RT), followed by incubation with horseradish peroxidase (HRP)- conjugated primary antibody at RT for 2 h (or primary antibody at RT for 2 h and corresponding secondary antibody at RT for 2 h). The following antibodies were used: rabbit α- OLE1 (anti- rS3) \(^{34}\) , rat α- tubulin (Santa Cruz Biotechnology, 1:1000), rabbit α- GFP (Millipore, AB10145, 1:10,000), mouse α- RFP (Agrisera, AS15 3028, 1:5,000), rabbit α- 12S \(^{62}\) , rabbit α- APX1 (Agrisera, 1:2000), rabbit α- BIP2 (Agrisera, 1:2000), rabbit α- UBQ11 (Agrisera, 1:2000), goat α- CDC48a (VCP1) (diluted 1:2000, Abcam. 206320), rabbit α- PBA1 (Agrisera, 1:2000), rabbit α- PAG1 (Agrisera, 1:2000), rabbit α- BIP (Agrisera, 1:2000), rabbit α- ACTIN (Agrisera, 1:2000), α- mouse (Amersham ECL Mouse IgG, HRP- linked whole Ab [from sheep], NA931, 1:10,000), α- rabbit (Amersham ECL Rabbit IgG, HRP- linked whole Ab [from donkey], NA934, 1:10,000), α- rat (IRDye \(^{\text{®}}\) 800 CW Goat anti- Rat IgG [H + L], LI- COR, 925- 32219, 1:10,000) and α- rabbit (IRDye \(^{\text{®}}\) 800 CW Goat anti- Rabbit IgG, LI- COR, 926- 3221, 1:10,000). Chemiluminescence was detected with the ECL Prime Western Blotting Detection Reagent (Cytiva, GERPΝ2232) and SuperSignal™ West Femto Maximum Sensitivity Substrate (Thermo Fisher Scientific, 34094). The bands were visualized using an Odyssey infrared imaging system (LI- COR).
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 810, 500, 825]]<|/det|>
+## Total proteome analysis, COFRADIC and TAP
+
+<|ref|>text<|/ref|><|det|>[[120, 825, 880, 914]]<|/det|>
+Total proteome analysis, COFRADIC and TAPAn equal number of seeds of WT and mca- II- KO were used for the analysis of the total proteome using LC- MS/MS. For COFRADIC, a shortened protocol was used as previously described with the following modifications \(^{43}\) . To achieve a total protein content of 1 mg, 0.2 g frozen ground tissue was re- suspended in 1 mL of buffer containing 1% (w/v) 3- [(3- cholamidopropyl)- dimethylammonio]- 1- propane sulfonate (CHAPS), 0.5% (w/v) deoxycholate, 5 mM ethylenediaminetetraacetic acid, and 10% glycerol in 50 mM HEPES
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 75, 880, 363]]<|/det|>
+buffer, pH 7.5, further containing the suggested amount of protease inhibitors (one tablet/10 mL buffer) according to the manufacturer's instructions (Roche Applied Science). The sample was centrifuged at 16,000g for 10 min at \(4^{\circ}C\) , and guanidinium hydrochloride was added to the cleared supernatant to reach a final concentration of 4 M. Protein concentrations were measured with the DC protein assay (Bio- Rad), and protein extracts were further modified for N- terminal COFRADIC analysis as described previously \(^{63}\) . Col- 0 (WT) primary amines were labelled with the N- hydroxysuccinimide (NHS) ester of \(^{12}\mathrm{C}_4\) - butyrate and mutants with NHS- \(^{13}\mathrm{C}_4\) - butyrate, resulting in a mass difference of approximately 4 Da between light ( \(^{12}\mathrm{C}_4\) ) and heavy ( \(^{13}\mathrm{C}_4\) ) labelled peptides. After equal amounts of the labelled proteomes had been mixed, tryptic digestion generated internal, non- N- terminal peptides that were removed by strong cation exchange at a low pH \(^{63}\) . Due to the low amount of input material, the COFRADIC protocol was cut short after the first reversed phase- high performance liquid chromatography (RP- HPLC) step and the resulting 15 fractions were subjected immediately for identification by LC- MS/MS. For TAP experiments, four- to five weeks- old Arabidopsis transgenic plants expressing MCA- II- a- TAPa, MCA- II- a- PD- TAPa, MCA- II- b- TAPa, MCA- II- b- PD- TAPa and sGFP- TAPa were harvested (2- 4 g, fresh weight) and ground in liquid N2 in 2 volumes of extraction buffer (50 mM Tris- HCl pH 7.5, 150 mM NaCl, 10% glycerol, 0.1% Nonidet P- 40 and \(1\times\) protease inhibitor cocktail; Sigma- Aldrich, 1:100 dilution). The analyses and further processing were done as described in \(^{64}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 376, 464, 392]]<|/det|>
+## Visualization of networks and analyses
+
+<|ref|>text<|/ref|><|det|>[[120, 391, 880, 483]]<|/det|>
+Cytoscape 3.5.1 was used. Tab- delimited files containing the input data were uploaded. Unless otherwise indicated, the default layout was an edge- weighted spring- embedded layout, with NormSpec used as edge weight. Nodes were manually re- arranged from this layout to increase visibility and highlight specific proximity interactions. The layout was exported as a PDF and eventually converted to a .TIFF file with Lempel- Ziv- Welch (common name LZW) compression.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 496, 379, 511]]<|/det|>
+## Quantifications and statistics
+
+<|ref|>text<|/ref|><|det|>[[119, 510, 880, 737]]<|/det|>
+The numerical data used in this publication are provided as raw .csv files with the corresponding headings. Graphs were generated by GraphPad Prism v. 9 or R- 4.2.3 (https://www.r- project.org). Pearson correlation coefficient on images was calculated via Fiji, coloc2 tool. All statistical data show the mean \(\pm s.d\) . (box plots) or the distribution of values (violin plots, kernal density) of at least three biologically independent experiments or samples, or as otherwise stated. Individual data points are on the plots. For violin plots, datasets were smoothed using heavy smoothing which gives a better idea of the overall distribution. In captions, \(N\) denotes biological replicates, and "n" technical replicates or population size (or as indicated). Each data set was tested whether it followed normal distribution when \(N \geq 3\) by using the Shapiro normality test integrated into the GraphPad Prism v. 9. The significance threshold was set at \(P< 0.05\) , and the calculated \(P\) - values are shown in the graphs. Details of the statistical tests applied, including the choice of the statistical method, are indicated in the corresponding figure caption. In boxplots or violin plots, upper and lower box boundaries, or lines in the violin plots when visible, represent the first and third quantiles, respectively, horizontal lines mark the median and whiskers mark the highest and lowest values.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 743, 293, 760]]<|/det|>
+## Acknowledgments
+
+<|ref|>text<|/ref|><|det|>[[119, 766, 880, 914]]<|/det|>
+We acknowledge Ikuko Hara- Nishimura (Kyoto University) and Hannele Tuominen (Umea University) for sharing materials. This work was supported by the EPIC- XS, Horizon 2020 programme of the European Union project number 823839 (KG, PNM); European Research Council (ERC) Starting Grant 'R- ELEVATION' grant 101039824 (PD); Future Leader Fellowship from the Biotechnology and Biological Sciences Research Council (BBSRC) BB/R012172/1 (PD); European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship, and Innovation, T2EΔK- 00597 under the call RESEARCH- CREATE- INNOVATE ("BIOME"; PNM); European Union Horizon 2020 Marie Curie- RISE PANTHEON grant 872969 (PNM); Hellenic Foundation of Research and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 76, 880, 175]]<|/det|>
+Innovation grant 1426 NESTOR- Theodoros Papazoglou- Always Strive for Excellence (PNM); Hellenic Foundation of Research and Innovation fellowship 5947 (IHH); The Swedish Research Council (VR) 2019- 04250 (PVB, PNM); Carl Trygger Foundation (CTS) 22:2025 (PVB); Knut and Alice Wallenberg Foundation 2018.0026 (PVB, PNM); European Union Marie Sklodowska- Curie Action IF project 656011 (PNM); DESTINY (BOF- UGent) (SS, FVB).
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 183, 318, 199]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[118, 199, 880, 266]]<|/det|>
+Conceptualization: PNM, PVB, JDGJ, CL; Methodology: CL, IHH, TP, SHR, EAM, AM, SS; EGB, PD, SDA, KG, FRC, PD, MN, FVB; Investigation: CL, IHH, PNM; Visualization: CL, IHH, PNM; Funding acquisition: PVB, PNM; Project administration: PNM; Supervision: PNM; Writing - original draft: PNM, CL, IHH, PVB; Writing - review & editing: all authors.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 273, 295, 289]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[120, 296, 590, 312]]<|/det|>
+The authors declare that they have no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 319, 388, 335]]<|/det|>
+## Materials and Correspondence
+
+<|ref|>text<|/ref|><|det|>[[118, 342, 880, 392]]<|/det|>
+All data, code, and materials used in the analysis are available and were deposited in public repositories. The data are available from the corresponding author with detailed explanations upon reasonable request.
+
+<|ref|>image<|/ref|><|det|>[[117, 415, 907, 828]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 830, 780, 862]]<|/det|>
+Fig. 1. A type II MCA depletion model affects seed physiology and vacuolar morphology.
+
+<|ref|>text<|/ref|><|det|>[[118, 867, 880, 915]]<|/det|>
+(A) Schematic diagram of MCAs (top left) and phylogeny of type I and II MCAs (top right) in Arabidopsis and the nomenclature used. Bottom, chromosomal locations of all nine MCA genes in Arabidopsis; note the tandem arrangement of four MCA-II genes (MCA-II-a/-b/-c/-d)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 75, 880, 106]]<|/det|>
+on chromosome 1. Pro, prodomain; p20 and p10, large and small subunits; H, C, catalytic histidine-cysteine dyad.
+
+<|ref|>text<|/ref|><|det|>[[115, 106, 880, 183]]<|/det|>
+(B) Representative immunoblot with \(\alpha\) -MCA-II-a showing the absence of MCA-II-a in seedlings of the single mca-II-a mutant and the sextuple mca-II-KOc lines (individual lines #93 and #30) at 7 days post germination (DPG). \(\alpha\) -ACTIN was used as a loading control; the red arrowhead indicates MCA-II-a. The experiment was performed three times with similar results (biological replicates \(N = 3\) , technical replicates \(n = 20\) pooled seedlings per lane).
+
+<|ref|>text<|/ref|><|det|>[[115, 183, 880, 288]]<|/det|>
+(C) Representative immunoblot of Tudor Staphylococcus Nuclease (TSN) levels in total protein extracts from 7-DPG WT, mca-II-df double mutant (background used to generate the CRISPR mutants), and mca-II-KOc mutant seedlings. \(\alpha\) -TUBULIN was used as a loading control. The experiment was performed three times with similar results ( \(N = 3\) , \(n = 20\) pooled seedlings per lane). Right: relative quantification of TSN abundance (red arrowhead, full length). The data are from three experiments, and the indicated \(P\) -values were calculated by one-way ANOVA ( \(N = 3\) , \(n = 3\) ).
+
+<|ref|>text<|/ref|><|det|>[[115, 288, 880, 334]]<|/det|>
+(D) Representative images showing the growth of seedlings germinated from freshly collected WT and mca-II-KOc seeds at 3 and 7 DPG. The experiment was performed three times with similar results ( \(N = 3\) , \(n \geq 40\) ).
+
+<|ref|>text<|/ref|><|det|>[[115, 333, 880, 379]]<|/det|>
+(E) Representative images showing the growth of seedlings germinated from WT and mca-II-KOc (3, 6, and 9-month-old) seeds at 3 and 7 DPG. The experiment was performed three times with similar results ( \(N = 3\) , \(n \geq 40\) ).
+
+<|ref|>text<|/ref|><|det|>[[115, 378, 880, 453]]<|/det|>
+(F) Germination rate (%) of WT and mca-II-KOc seeds (from D and E). The data are from three experiments, and the indicated \(P\) -values were calculated by one-way ANOVA ( \(N = 3\) , \(n \geq 278\) ). The first \(P\) -value corresponds to the 1 to \(3^{\text{rd}}\) point interval, while the second \(P\) -value corresponds to the \(4^{\text{th}}\) point; the magenta and light-green areas around the individual points represent \(\pm 5\) .
+
+<|ref|>text<|/ref|><|det|>[[115, 452, 880, 528]]<|/det|>
+(G) Visualization of vacuoles in embryonic roots from WT and mca-II-KOc plants after a 2-day stratification (hydration) counter-stained with the pH-sensitive lumen dye BCECF. The styryl dye FM-64 was used to visualize the plasma membrane (cell contours, magenta). Yellow arrowheads point to vacuole-free regions in the cytoplasm that compress the vacuolar membrane in the mca-II-KOc lines (corresponding to lipid droplets). Scale bars, \(10 \mu \text{m}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[118, 73, 860, 445]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[118, 459, 541, 474]]<|/det|>
+Fig. 2. MCA-IIs associate with and affect the ER.
+
+<|ref|>text<|/ref|><|det|>[[118, 474, 881, 745]]<|/det|>
+(A) Gene ontology (GO) enrichment analysis of biological processes for proteins more abundant in mca-II-KOc than in WT (log2FC ≥ 1) 3-month-old seeds. The black box highlight relevant and overrepresented and overlapping GO terms. The GO term "fatty acid metabolic process" (GO:0006631) was confirmed by the greatly diminished levels of oleosin and enlarged lipid droplets in the mutant (Fig. 3). Furthermore, the GO terms "protein folding" (GO:0006457) and "ER body organization" (GO:00080119), were enriched and included proteins such as HEAT SHOCK 70 kDa proteins (HSP70s) and protein disulfide-isomerases (PDI5, PDI6: 3,11- and 5.0-fold, respectively) BINDING PROTEIN 1 and 2 (BiP 3.4- and 2.6-fold, respectively). In the GO term "protein folding", the FKBP15-2 (FK506- AND RAPAMYCINBINDING PROTEIN 15 KD-2, immunophilin protein), was not found in WT, is involved in ER stress sensing, and accelerates protein folding. Furthermore, in the same GO term, the proteasomal subunits (GO, protein folding) such as PAG1 (20S proteasome alpha subunit G- 1: 1.3-fold) and PBA1 (20S proteasome subunit beta 1: not found in WT), were verified using α-PAG1 and α-PBA1 antibodies in Fig S5G, confirming the corresponding increases in abundance. In the term "ER body organization", PYK10 (BGLU23), BGLU18, and BGLU25 (highlighted) are β-glucosidases enriched ≥ 100-fold in mca-II-KOc. The GO term "gluconeogenesis" (GO:0006094) confirms the relevance of this analysis, as MCA-IIs were previously linked to this process 43. FDR, false discovery rate.
+
+<|ref|>text<|/ref|><|det|>[[118, 744, 880, 789]]<|/det|>
+(B) Representative immunoblot analysis of cell extracts of seed fractions from lines expressing MCA-II-apro:MCA-II-a-GFP separated by sucrose gradient density ultracentrifugation. BiP2 (ER) and ascorbate peroxidase (APX1, cytoplasm) were used to assess fraction quality.
+
+<|ref|>text<|/ref|><|det|>[[118, 789, 880, 834]]<|/det|>
+(C) Representative high-resolution confocal micrograph (120 nm axial) of epidermal cells from the meristematic regions of embryonic roots 2 days after seed hydration, from lines expressing MCA-II-apro:MCA-II-a-GFP. Scale bar, 10 μm.
+
+<|ref|>text<|/ref|><|det|>[[118, 835, 880, 895]]<|/det|>
+(D) Representative immunoblot analysis of seed protein extracts (50 seeds/genotype) probed with α-UBIQUITIN11 (UBQ11) antibody. The numbers indicate relative levels of ubiquitinated proteins compared to Ponceau S staining at the bottom (loading control). Left, WT (9-month-old seeds) and mca-II-KOc seeds harvested at different time points (3, 6, and 9-month-old).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 75, 880, 108]]<|/det|>
+Right, WT, the T-DNA double mutant mca- II- df, and mca- II- KOc (3- month- old). The experiment was repeated more than 10 times.
+
+<|ref|>image<|/ref|><|det|>[[122, 123, 905, 696]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[118, 704, 742, 721]]<|/det|>
+Fig. 3. MCA-Ils associate with CDC48 and PUX10 in the LDAD pathway.
+
+<|ref|>text<|/ref|><|det|>[[118, 726, 881, 789]]<|/det|>
+(A) Representative images from permeability tests of etiolated seedlings 4-days post germination (DPG) of WT (9-month-old seeds), mca-II-KOc (fresh seeds, 3-, or 9-month-old), and a complementation line (Com., rescued with RPS5apro:MCA-II-a-mNeon; 9-month-old seeds) stained with toluidine blue (0.05% [w/v]). Scale bar, 0.5 cm.
+
+<|ref|>text<|/ref|><|det|>[[118, 788, 880, 848]]<|/det|>
+(B) Representative micrographs of lipid droplets stained with LipidTox in the hypocotyl regions of 2-DPG radicles from WT, mca-II-KOc, and the Com line. The two yellow arrowheads in the three insets from GFP, LipidTox, and Merge indicate lipid droplets (LDs). Scale bars, 10 μm (5 μm for inset).
+
+<|ref|>text<|/ref|><|det|>[[118, 847, 880, 923]]<|/det|>
+(C) Representative confocal micrographs of embryonic roots coexpressing RPS5apro:tagRFP-MCA-IIa and PUX10pro:PUX10-GFP or RPS5apro:MCA-II-a-mNeon and 35Spro:mCherry-CDC48. Pearson's correlation coefficients (R) were used to estimate colocalization and are shown on the merged micrographs. The yellow arrowheads denote sites of colocalization between PUX10 and MCA-II-a, while the red arrowhead denotes high
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 75, 878, 106]]<|/det|>
+levels of PUX10 and the lack of MCA- II- a. The experiment was repeated more than five times. V, vacuole (autofluorescence). Scale bars, \(5\mu \mathrm{m}\) .
+
+<|ref|>text<|/ref|><|det|>[[117, 106, 880, 198]]<|/det|>
+(D) Representative confocal micrographs of embryo hypocotyl cells showing the colocalization of PUX10 or CDC48 with MCA-II-a from lines co-expressing RPS5apro:MCA-II-a-tagRFP and PUX10pro:PUX10-GFP or RPS5apro:MCA-II-a-mNeon and 35spro:mCherry-CDC48a (radicles produced similar results). The arrowheads denote colocalization between fluorescent signals. Scale bar, \(5\mu \mathrm{m}\) . The experiment was performed three times with similar results \((N = 3, n = 1)\) . V, vacuole (autofluorescence).
+
+<|ref|>text<|/ref|><|det|>[[117, 197, 880, 377]]<|/det|>
+(E) "Sensitized emission" FRET (FRET-SE) approach, where the emission spectrum of the donor (1) overlaps with the excitation spectrum of the acceptor (2), and if the distance ("r") between the two molecules is sufficiently short (i.e., connoting association), energy is transferred (3). Middle: Micrograph showing FRET-SE between PUX10-GFP and MCA-II-a-tagRFP from embryonic root epidermal cells. Scale bar, \(5\mu \mathrm{m}\) . Bottom graph: FRET-SE between PUX10-GFP and MCA-II-a-tagRFP in the absence (mock) or presence of MG132 and in the nucleus (Nuc) where PUX10-GFP and MCA-II-a-tagRFP also localized. GFP represents the negative control (free GFP; lines coexpressing GFP with MCA-II-a-tagRFP). Note that in the presence of MG132, FRET-SE increased, likely due to inhibition of the proteasome, which allowed the increased persistence of PUX10, an MCA-II-a transient complex. The data are from two experiments, and the indicated \(P\) -values were calculated by ordinary one-way ANOVA \((N = 2, n \geq 7)\) .
+
+<|ref|>text<|/ref|><|det|>[[117, 377, 880, 437]]<|/det|>
+(F) Representative immunoblots of total seed proteins from WT, mca-II-KOc (KOc), and the Com line probed with an \(\alpha\) -Oleosin antibody (3-month-old seeds). The numbers indicate relative levels compared to Ponceau S staining at the bottom (loading control). The experiment was performed three times with similar results \((N = 3, n = 1\) with 50 seeds/lane).
+
+<|ref|>text<|/ref|><|det|>[[117, 437, 880, 528]]<|/det|>
+(G) Representative confocal micrographs from lines harboring MCA-II-apro:MCA-II-a-GFP counterstained with LipidTox in the hypocotyl regions of 2-DPG seedlings. Insets (denoted 1 to 3) show details of lipid droplets. Scale bars, \(5\mu \mathrm{m}\) (1 \(\mu \mathrm{m}\) for insets). The experiment was repeated more than 10 times. Right, measurement of lipid droplet size. The data are from three experiments, and the indicated \(P\) -values were calculated by ordinary one-way ANOVA \((N = 3, n \geq 15)\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[118, 74, 850, 551]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[118, 563, 690, 579]]<|/det|>
+Fig. 4. MCA-lls modulate ERAD by regulating CDC48 localization.
+
+<|ref|>text<|/ref|><|det|>[[118, 579, 880, 728]]<|/det|>
+(A) Top: Representative confocal micrograph of embryonic root cells co-expressing RPS5apro:MCA-II-a-tagRFP and PUX10:PUX10-GFP. The inset in a merged micrograph shows the colocalization between PUX10 and MCA-II-a. "High" corresponds to high levels of either MCA-II-a or PUX10, while "Low" refers to reduced or non-detectable levels of the corresponding proteins. Note the inverse correlation between MCA-II-a and PUX10 levels. Bottom: Representative confocal micrograph of embryonic root cells co-expressing RPS5apro:MCA-II-a-mNeon and 35Spro:mCherry-CDC48. The yellow arrowheads denote structures reminiscent of lipid droplets and the highly correlated levels of CDC48 and MCA-II-a in puncta. R values denote Pearson correlation coefficients of signal intensities between tagRFP/GFP and mCherry/mNeon. Scale bars, 10 μm.
+
+<|ref|>text<|/ref|><|det|>[[118, 728, 880, 835]]<|/det|>
+(B) Representative confocal micrographs of embryonic root cells, 2 days post-hydration, from WT and mca-II-KOc harboring 35Spro:mCherry-CDC48a. Scale bars, 10 μm. The yellow arrowheads denote structures reminiscent of lipid droplets, while the red arrowheads denote the nucleus. The two insets show details of CDC48 localization in WT and mca-II-KOc ("1" and "2", respectively). Right: quantification of the intensity ratio between the mCherry-CDC48 signal at the lipid droplets (LDs) and cytoplasm. The data are from three experiments, and the indicated P-values were calculated by one-way ANOVA (N = 3, n = 8 cells/sample).
+
+<|ref|>text<|/ref|><|det|>[[118, 835, 880, 897]]<|/det|>
+(C) Representative images of 7-day-old seedlings of the indicated genotypes mock-treated (DMSO), treated with a CDC48 inhibitor (CB-5083, 2 μM), and following a 2-day recovery (9-day-old seedlings) from CB-5083 treatment on DMSO-containing plates. Note the swelling root tip phenotype observed in mca-II-KOc (two lines), which is indicative of hypersensitivity
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 75, 880, 107]]<|/det|>
+to CB- 5083 (insets). The experiment was performed three times with similar results \((N = 3, n = 8 - 10\) seedlings/genotype).
+
+<|ref|>text<|/ref|><|det|>[[117, 107, 880, 183]]<|/det|>
+(D) Representative images showing seed viability tests with tetrazolium staining in WT and mca-Il-KOc. Seeds treated at \(100^{\circ}C\) represent a positive control for dead seeds. Viable seeds (stained red) are highlighted in the insets (red arrowheads). Right: quantification of viable seeds. The data are from three experiments, and the indicated \(P\) -values were calculated by one-way ANOVA \((N = 3, n \geq 176)\) .
+
+<|ref|>text<|/ref|><|det|>[[117, 182, 880, 259]]<|/det|>
+(E) A model for the role of MCA-lls in regulating CDC48 localization to the ER and lipid droplets. In the absence of MCA-lls, PUX10 is not cleaved and CDC48 is retained on lipid droplets; when MCA-lls are present, PUX10 is cleaved, releasing CDC48 to localize at the ER. This release is an important step in the spatiotemporal regulation of CDC48 activity and confers seed longevity.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 88, 875, 914]]<|/det|>
+765 1 de Vries, J. & Ischebeck, T. Ties between Stress and Lipid Droplets Pre-date Seeds. Trends in Plant Science 25, 1203- 1214 (2020). https://doi.org:10.1016/j.tplants.2020.07.017 2 Vitale, A. & Pedrazzini, E. StresSeed: The Unfolded Protein Response During Seed Development. Front Plant Sci 13, 869008 (2022). https://doi.org:10.3389/fpls.2022.869008 3 Lee, J. E., Cathey, P. I., Wu, H., Parker, R. & Voeltz, G. K. Endoplasmic reticulum contact sites regulate the dynamics of membraneless organelles. Science 367, eaay7108 (2020). https://doi.org:10.1126/science.aay7108 4 Srivastava, R. et al. Response to Persistent ER Stress in Plants: A Multiphasic Process That Transitions Cells from Prosurvival Activities to Cell Death. The Plant Cell 30, 1220- 1242 (2018). https://doi.org:10.1105/tpc.18.00153 5 Minina, E. A. et al. Classification and Nomenclature of Metacaspases and Paracaspases: No More Confusion with Caspases. Mol Cell 77, 927- 929 (2020). https://doi.org:10.1016/j.molcel.2019.12.020 780 6 Coll, N. S. et al. Arabidopsis type I metacaspases control cell death. Science 330, 1393- 1397 (2010). https://doi.org:10.1126/science.1194980 7 Coll, N. S. et al. The plant metacaspase AtMC1 in pathogen- triggered programmed cell death and aging: functional linkage with autophagy. Cell Death & Differentiation 21, 1399- 1408 (2014). https://doi.org:10.1038/cdd.2014.50 785 8 Pitsili, E. et al. A phloem- localized Arabidopsis metacaspase (AtMC3) improves drought tolerance. bioRxiv, 2022.2011.2009.515759 (2022). https://doi.org:10.1101/2022.11.09.515759 9 Tsiatsiani, L. et al. Metacaspases. Cell Death Differ 18, 1279- 1288 (2011). https://doi.org:10.1038/cdd.2011.66 790 10 Minina, E. A., Coll, N. S., Tuominen, H. & Bozhkov, P. V. Metacaspases versus caspases in development and cell fate regulation. Cell Death Differ 24, 1314- 1325 (2017). https://doi.org:10.1038/cdd.2017.18 11 Hander, T. et al. Damage on plants activates Ca(2+)- dependent metacaspases for release of immunomodulatory peptides. Science 363 (2019). https://doi.org:10.1126/science.aar7486 12 Bollhoner, B. et al. Post mortem function of AtMC9 in xylem vessel elements. New Phytol 200, 498- 510 (2013). https://doi.org:10.1111/nph.12387 13 Tuladhar, R. et al. CRISPR- Cas9- based mutagenesis frequently provokes on- target mRNA misregulation. Nat Commun 10, 4056 (2019). https://doi.org:10.1038/s41467- 019- 12028- 5 14 Sundstrom, J. F. et al. Tudor staphylococcal nuclease is an evolutionarily conserved component of the programmed cell death degradome. Nat Cell Biol 11, 1347- 1354 (2009). https://doi.org:10.1038/ncb1979 15 Shen, W., Liu, J. & Li, J. F. Type- II Metacaspases Mediate the Processing of Plant Elicitor Peptides in Arabidopsis. Mol Plant 12, 1524- 1533 (2019). https://doi.org:10.1016/j.molp.2019.08.003 16 Duxbury, Z. et al. Induced proximity of a TIR signaling domain on a plant- mammalian NLR chimera activates defense in plants. Proc Natl Acad Sci U S A (2020). https://doi.org:10.1073/pnas.2001185117 810 17 Watanabe, N. & Lam, E. Arabidopsis metacaspase 2d is a positive mediator of cell death induced during biotic and abiotic stresses. Plant J 66, 969- 982 (2011). https://doi.org:10.1111/j.1365- 313X.2011.04554.x 18 Oria, M. P., Hamaker, B. R., Axtell, J. D. & Huang, C.- P. A highly digestible sorghum mutant cultivar exhibits a unique folded structure of endosperm protein
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 75, 878, 920]]<|/det|>
+bodies. Proceedings of the National Academy of Sciences 97, 5065- 5070 (2000). https://doi.org:10.1073/pnas.080076297 19 Vitale, M. et al. Inadequate BiP availability defines endoplasmic reticulum stress. eLife 8, e41168 (2019). https://doi.org:10.7554/eLife.41168 20 Oslowski, C. M. & Urano, F. Measuring ER stress and the unfolded protein response using mammalian tissue culture system. Methods Enzymol 490, 71- 92 (2011). https://doi.org:10.1016/b978- 0- 12- 385114- 7.00004- 0 21 Gevaert, K. et al. Exploring proteomes and analyzing protein processing by mass spectrometric identification of sorted N- terminal peptides. Nat Biotechnol 21, 566- 569 (2003). https://doi.org:10.1038/nbt810 22 Grimmer, J. et al. Mild proteasomal stress improves photosynthetic performance in Arabidopsis chloroplasts. Nat Commun 11, 1662 (2020). https://doi.org:10.1038/s41467- 020- 15539- 8 23 Kurepa, J., Toh- e, A. & Smalle, J. A. 26S proteasome regulatory particle mutants have increased oxidative stress tolerance. The Plant Journal 53, 102- 114 (2008). https://doi.org:https://doi.org/10.1111/j.1365- 313X.2007.03322. x 24 Finley, D. Recognition and processing of ubiquitin- protein conjugates by the proteasome. Annu Rev Biochem 78, 477- 513 (2009). https://doi.org:10.1146/annurev.biochem.78.081507.101607 25 Olzmann, J. A., Richter, C. M. & Kopito, R. R. Spatial regulation of UBXD8 and p97/VCP controls ATGL- mediated lipid droplet turnover. Proc Natl Acad Sci U S A 110, 1345- 1350 (2013). https://doi.org:10.1073/pnas.1213738110 26 Hwang, J. & Qi, L. Quality Control in the Endoplasmic Reticulum: Crosstalk between ERAD and UPR pathways. Trends Biochem Sci 43, 593- 605 (2018). https://doi.org:10.1016/j.tibs.2018.06.005 27 Liu, J. X., Srivastava, R., Che, P. & Howell, S. H. An endoplasmic reticulum stress response in Arabidopsis is mediated by proteolytic processing and nuclear relocation of a membrane- associated transcription factor, bZIP28. Plant Cell 19, 4111- 4119 (2007). https://doi.org:10.1105/tpc.106.050021 28 De Giorgi, J. et al. The Arabidopsis mature endosperm promotes seedling cuticle formation via release of sulfated peptides. Developmental Cell 56, 3066- 3081. e3065 (2021). https://doi.org:https://doi.org/10.1016/j.devcel.2021.10.005 29 Al- Hammad, A. S., Sreelakshmi, Y., Negi, S., Siddiqi, I. & Sharma, R. The polycytelson mutant of tomato shows enhanced polar auxin transport. Plant Physiol 133, 113- 125 (2003). 30 Stevenson, J., Huang, E. Y. & Olzmann, J. A. Endoplasmic Reticulum- Associated Degradation and Lipid Homeostasis. Annu Rev Nutr 36, 511- 542 (2016). https://doi.org:10.1146/annurev- nutr- 071715- 051030 31 Lee, R. E., Brunette, S., Puente, L. G. & Megeney, L. A. Metacaspase Yca1 is required for clearance of insoluble protein aggregates. Proc Natl Acad Sci U S A 107, 13348- 13353 (2010). https://doi.org:10.1073/pnas.1006610107 32 Liu, C. et al. Phase Separation of a Nodulin Sec14- like protein Maintains Auxin Efflux Carrier Polarity at Arabidopsis Plasma Membranes. bioRxiv (Plos Biol, under textual revision), 2022.2003.2026.485938 (2023). https://doi.org:10.1101/2022.03.26.485938 33 Teale, W. D. et al. Flavonol- mediated stabilization of PIN efflux complexes regulates polar auxin transport. Embo J 40, e104416 (2021). https://doi.org:10.15252/embj.2020104416 34 Deruyffelaere, C. et al. PUX10 Is a CDC48A Adaptor Protein That Regulates the Extraction of Ubiquitinated Oleosins from Seed Lipid Droplets in Arabidopsis. The Plant Cell 30, 2116- 2136 (2018). https://doi.org:10.1105/tpc.18.00275
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 78, 875, 115]]<|/det|>
+35 Siloto, R. M. et al. The accumulation of oleosins determines the size of seed oilbodies in Arabidopsis. Plant Cell 18, 1961- 1974 (2006). https://doi.org:10.1105/tpc.106.041269
+
+<|ref|>text<|/ref|><|det|>[[113, 115, 870, 187]]<|/det|>
+36 Marshall, R. S., Hua, Z., Mali, S., McLoughlin, F. & Viertra, R. D. ATG8- Binding UIM Proteins Define a New Class of Autophagy Adaptors and Receptors. Cell 177, 766- 781. e724 (2019). https://doi.org:10.1016/j.cell.2019.02.009
+
+<|ref|>text<|/ref|><|det|>[[113, 177, 870, 930]]<|/det|>
+37 Heinen, C., Ács, K., Hoogstraten, D. & Dantuma, N. P. C- terminal UBA domains protect ubiquitin receptors by preventing initiation of protein degradation. Nat Commun 2, 191 (2011). https://doi.org:10.1038/ncomms1179 875 38 Alberts, S. M., Sonntag, C., Schäfer, A. & Wolf, D. H. Ubx4 Modulates Cdc48 Activity and Influences Degradation of Misfolded Proteins of the Endoplasmic Reticulum\*. Journal of Biological Chemistry 284, 16082- 16089 (2009). https://doi.org:https://doi.org/10.1074/jbc.M809282200 39 Arumughan, A. et al. Quantitative interaction mapping reveals an extended UBX domain in ASPL that disrupts functional p97 hexamers. Nat Commun 7, 13047 (2016). https://doi.org:10.1038/ncomms13047 40 Wang, C.- W. & Lee, S.- C. The ubiquitin- like (UBX)- domain- containing protein Ubx2/Ubx8 regulates lipid droplet homeostasis. J Cell Sci 125, 2930- 2939 (2012). https://doi.org:10.1242/jcs.100230 851 41 Garzon, M. et al. PRT6/At5g02310 encodes an Arabidopsis ubiquitin ligase of the N- end rule pathway with arginine specificity and is not the CER3 locus. Febs Lett 581, 3189- 3196 (2007). https://doi.org:10.1016/j.febslet.2007.06.005 42 Deruyffelaere, C. et al. PUX10 Is a CDC48A Adaptor Protein That Regulates the Extraction of Ubiquitinated Oleosins from Seed Lipid Droplets in Arabidopsis. Plant Cell 30, 2116- 2136 (2018). https://doi.org:10.1105/tpc.18.00275 43 Tsiatisani, L. et al. The Arabidopsis metacaspase9 degradome. Plant Cell 25, 2831- 2847 (2013). https://doi.org:10.1105/tpc.113.115287 44 Saitou, N. & Nei, M. The neighbor- joining method: a new method for reconstructing phylogenetic trees. Mol Biol Evol 4, 406- 425 (1987). https://doi.org:10.1093/oxfordjournals.molbev.a040454 45 Debeaujon, I., Leon- Kloosterziel, K. M. & Koornneef, M. Influence of the testa on seed dormancy, germination, and longevity in Arabidopsis. Plant Physiol 122, 403- 414 (2000). https://doi.org:10.1104/pp.122.2.403 46 Sexauer, M., Shen, D., Schon, M., Andersen, T. G. & Markmann, K. Visualizing polymeric components that define distinct root barriers across plant lineages. Development 148 (2021). https://doi.org:10.1242/dev.199820 47 Doll, N. M. et al. A two- way molecular dialogue between embryo and endosperm is required for seed development. Science 367, 431- 435 (2020). https://doi.org:10.1126/science.aaz4131 905 48 Sohn, K. H. et al. The Nuclear Immune Receptor RPS4 Is Required for RRS1SLH1- Dependent Constitutive Defense Activation in Arabidopsis thaliana. PLOS Genetics 10, e1004655 (2014). https://doi.org:10.1371/journal.pgen.1004655 49 Minina, E. A., Stael, S., Van Breusegem, F. & Bozhkov, P. V. Plant metacaspase activation and activity. Methods Mol Biol 1133, 237- 253 (2014). https://doi.org:10.1007/978- 1- 4939- 0357- 3_15 50 Clough, S. J. & Bent, A. F. Floral dip: a simplified method for Agrobacterium- mediated transformation of Arabidopsis thaliana. Plant J 16, 735- 743 (1998). https://doi.org:10.1046/j.1365- 313x.1998.00343. x 51 Nakagawa, T. et al. Improved Gateway binary vectors: high- performance vectors for creation of fusion constructs in transgenic analysis of plants. Biosci Biotechnol Biochem 71, 2095- 2100 (2007). https://doi.org:10.1271/bbb.70216
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 75, 870, 770]]<|/det|>
+52 Curtis, M. D. & Grossniklaus, U. A gateway cloning vector set for high-throughput functional analysis of genes in planta. Plant Physiol 133, 462- 469 (2003). https://doi.org:10.1104/pp.103.027979920 53 Ursache, R., Fujita, S., Dénervaud Tendon, V. & Geldner, N. Combined fluorescent seed selection and multiplex CRISPR/Cas9 assembly for fast generation of multiple Arabidopsis mutants. Plant Methods 17, 111 (2021). https://doi.org:10.1186/s13007- 021- 00811- 954 Liu, H. et al. CRISPR- P 2.0: An Improved CRISPR- Cas9 Tool for a0;Genome Editing in Plants. Molecular Plant 10, 530- 532 (2017). https://doi.org:10.1016/j.molp.2017.01.00355 Labun, K. et al. CHOPCHOP v3: expanding the CRISPR web toolbox beyond genome editing. Nucleic Acids Res 47, W171- W174 (2019). https://doi.org:10.1093/nar/gkz36596 56 Arvidsson, S., Kwasniewski, M., Riano- Pachon, D. M. & Mueller- Roeber, B. QuantPrime- a flexible tool for reliable high- throughput primer design for quantitative PCR. BMC Bioinformatics 9, 465 (2008). https://doi.org:10.1186/1471- 2105- 9- 46557 Schaller, G. E. Isolation of Endoplasmic Reticulum and Its Membrane. Methods Mol Biol 1511, 119- 129 (2017). https://doi.org:10.1007/978- 1- 4939- 6533- 51058 Deruyffelaere, C. et al. Ubiquitin- Mediated Proteasomal Degradation of Oleosins is Involved in Oil Body Mobilization During Post- Germinative Seedling Growth in Arabidopsis. Plant Cell Physiol 56, 1374- 1387 (2015). https://doi.org:10.1093/pcp/pcv05659 Moschou, P. N., Gutierrez- Beltran, E., Bozhkov, P. V. & Smertenko, A. Separate Promotes Microtubule Polymerization by Activating CENP- E- Related Kinesin Kin7. Dev Cell 37, 350- 361 (2016). https://doi.org:10.1016/j.devcel.2016.04.01560 Roux, M. E. et al. The mRNA decay factor PAT1 functions in a pathway including MAP kinase 4 and immune receptor SUMM2. Embo J 34, 593- 608 (2015). https://doi.org:10.15252/embj.20148864561 Catanzariti, A. M., Soboleva, T. A., Jans, D. A., Board, P. G. & Baker, R. T. An efficient system for high- level expression and easy purification of authentic recombinant proteins. Protein Sci 13, 1331- 1339 (2004). https://doi.org:10.1110/ps.046189042 62 Li, L. et al. MAIGO2 Is Involved in Exit of Seed Storage Proteins from the Endoplasmic Reticulum in Arabidopsis thaliana. The Plant Cell 18, 3535- 3547 (2006). https://doi.org:10.1105/tpc.106.04615163 Staes, A. et al. Selecting protein N- terminal peptides by combined fractional diagonal chromatography. Nature Protocols 6, 1130- 1141 (2011). https://doi.org:10.1038/nprot.2011.35564 Gutierrez- Beltran, E. et al. Tudor staphylococcal nuclease is a docking platform for stress granule components and is essential for SnRK1 activation in Arabidopsis. Embo J 40, e105043 (2021). https://doi.org:10.15252/embj.2020105043
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 43, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[42, 93, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[59, 130, 707, 284]]<|/det|>
+Supplementary Figures.pdf TableS1. Resourcesusedinthispaper.xlsx DataS1. ProteomicsanalysesofWTandmcallKOc3montholdseeds.xlsx DataS2. NTerminomicsCOFRADICAllreports.xlsx DataS3. RNAseqanalysisandUPRgeneexpressioninWTorinmcallKOc.xlsx DataS4. TAPinteractionsofMCtypell.xlsb
+
+<--- Page Split --->
diff --git a/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/images_list.json b/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..3b4d3ef828166d7bede4096a138d6a7bf0e7647d
--- /dev/null
+++ b/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/images_list.json
@@ -0,0 +1,213 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. Estimated age-specific hospital admissions. The black lines represent the estimated medians. The dark gray lines correspond to \\(95\\%\\) credible intervals obtained from 2000 parameter samples from the posterior distribution, and the shaded regions show \\(95\\%\\) Bayesian prediction intervals. The dots are daily hospitalization admission data (all data points are included). Day 1 corresponds to 22 February 2020 which is 5 days prior to the first officially notified case in the Netherlands (27 February 2020). Panels a-h refer to different age groups.",
+ "footnote": [],
+ "bbox": [
+ [
+ 87,
+ 165,
+ 912,
+ 456
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Estimated age-specific probability of hospitalization. The violin shapes represent the marginal posterior distribution for 2000 samples of the probability of hospitalization in the model.",
+ "footnote": [],
+ "bbox": [
+ [
+ 290,
+ 604,
+ 700,
+ 875
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Estimated age-specific seroprevalence. The data (dots) are shown as the percentage of seropositive persons based on a seroprevalence survey that was conducted in April/May 2020. The number of positive and total samples defining this percentage for each age category is supplied in seroprevalence data file accompanying this study (see Data availability). The error bars represent the 95% confidence (Jeffreys) interval of the percentage. The violin shapes represent the marginal posterior distribution for 2000 samples of the percentage of seropositive persons in the model.",
+ "footnote": [],
+ "bbox": [
+ [
+ 288,
+ 85,
+ 700,
+ 368
+ ]
+ ],
+ "page_idx": 5
+ },
+ {
+ "type": "image",
+ "img_path": "images/Supplementary_Figure_4.jpg",
+ "caption": "Figure 4. Schematic timeline of the pandemic in the Netherlands during 2020. Outlined are times of the introduction and relaxation of control measures, and the estimated effective reproduction numbers for a - start of the pandemic (February 2020), b - full lockdown (April 2020), c - schools opening (August 2020), d - partial lockdown (November 2020). See Supplementary Figure 4 for the distributions of the reproduction numbers.",
+ "footnote": [],
+ "bbox": [
+ [
+ 80,
+ 163,
+ 910,
+ 504
+ ]
+ ],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5. Impact of reduction of two types of contacts on the effective reproduction number in August 2020. Percentage reduction in a other (non-school-related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \\(0\\%\\) reduction describes the situation in August 2020, when schools just opened in the Netherlands. The scenario with \\(100\\%\\) reduction represents a scenario with either a maximum reduction in other (non-school-related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \\(95\\%\\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \\(R_{e}\\) (situation August 2020), the green line is the value of \\(R_{e}\\) achieved for \\(100\\%\\) reduction in contacts. The blue line indicates \\(R_{e}\\) of 1. To control the pandemic, \\(R_{e}< 1\\) is necessary.",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 467,
+ 884,
+ 696
+ ]
+ ],
+ "page_idx": 7
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6. Impact of reduction of two types of contacts on the effective reproduction number in November 2020. Percentage reduction in a other (non-school-related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \\(0\\%\\) reduction describes the situation in November 2020. The scenario with \\(100\\%\\) reduction represents a scenario with either a maximum reduction in other (non-school-related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \\(95\\%\\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \\(R_{e}\\) (situation November 2020), the green line is the value of \\(R_{e}\\) achieved for \\(100\\%\\) reduction in contacts. To control the pandemic, \\(R_{e}< 1\\) is necessary.",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 265,
+ 884,
+ 491
+ ]
+ ],
+ "page_idx": 8
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_7.jpg",
+ "caption": "Figure 7. Impact of reduction of school contacts in different age groups on the effective reproduction number in November 2020. Percentage reduction in school contacts among a \\([0,5)\\) years old, b [5, 10) years old and c [10, 20) years old. In each panel, we varied the number of school contacts in one age group while keeping the number of school contacts in the other two age groups constant. The scenario with \\(0\\%\\) reduction describes the situation in November 2020 with \\(R_{e}\\) of about 1 (partial lockdown intended to prevent the second wave), where all schools are open without substantial additional measures. The reduction of \\(100\\%\\) in school contacts represents a scenario with the structure of non-school contacts in society in general as in November 2020 and schools for students in a given age group closed. The solid black line describes the median, the shaded region represents the \\(95\\%\\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \\(R_{e} = 1\\) (situation November 2020). The green line indicates the value of \\(R_{e}\\) achieved when schools for a given age group close.",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 85,
+ 890,
+ 250
+ ]
+ ],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_8.jpg",
+ "caption": "Figure 8. Transmission model. a Model schematic. Black arrows show epidemiological transitions. Red arrows indicate the compartments contributing to the force of infection. Susceptible persons in age group \\(k\\) \\((S_{k})\\) , where \\(k = 1,\\ldots ,n\\) , become latently infected \\((E_{k})\\) via contact with infectious persons in \\(m\\) infectious stages \\((I_{k,p}\\) \\(p = 1,\\ldots ,m)\\) at a rate \\(\\beta_{k}\\lambda_{k}\\) , where \\(\\lambda_{k}\\) is the force of infection, and \\(\\beta_{k}\\) is the reduction in susceptibility to infection of persons in age group \\(k\\) compared to persons in age group \\(n\\) . Exposed persons \\((E_{k})\\) become infectious \\((I_{k,1})\\) at rate \\(\\alpha\\) . Infectious persons progress through \\((m - 1)\\) infectious stages at rate \\(\\gamma m\\) , after which they recover \\((R_{k})\\) . From each stage, infectious persons are hospitalized at rate \\(\\nu_{k}\\) . Table 1 gives the summary of the model parameters. b-d Contact rates. b and c show contact rates in all locations before the pandemic and after the first lockdown (April 2020), respectively; d shows contact rates at schools before the pandemic. The color represents the average number of contacts per day a person in a given age group had with persons in another age group.",
+ "footnote": [],
+ "bbox": [
+ [
+ 190,
+ 124,
+ 808,
+ 718
+ ]
+ ],
+ "page_idx": 14
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 88,
+ 960,
+ 411
+ ]
+ ],
+ "page_idx": 26
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 42,
+ 40,
+ 729,
+ 491
+ ]
+ ],
+ "page_idx": 27
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 42,
+ 728,
+ 518
+ ]
+ ],
+ "page_idx": 28
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 42,
+ 950,
+ 420
+ ]
+ ],
+ "page_idx": 29
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 584,
+ 480,
+ 848
+ ]
+ ],
+ "page_idx": 29
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 29
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_8.jpg",
+ "caption": "Figure 8",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 30
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea.mmd b/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..9fbf5c559b8a2332f899d78d6b132a33b8b6c6c7
--- /dev/null
+++ b/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea.mmd
@@ -0,0 +1,477 @@
+
+# Model-based evaluation of school- and non-school-related measures to control the COVID-19 pandemic
+
+Ganna Rozhnova ( g.rozhnova@umcutrecht.nl ) University Medical Center Utrecht https://orcid.org/0000- 0002- 6725- 7359
+
+Christiaan van Dorp Los Alamos National Laboratory
+
+Patricia Bruijning- Verhagen UMC Utrecht https://orcid.org/0000- 0003- 4105- 9669
+
+Martin Bootsma University Medical Center Utrecht https://orcid.org/0000- 0003- 3005- 0255
+
+Janneke van de Wijgert University Medical Center Utrecht https://orcid.org/0000- 0003- 2728- 4560
+
+Marc J. M. Bonten University Medical Center Utrecht (UMCU)
+
+Mirjam Kretzschmar UMC Utrecht https://orcid.org/0000- 0002- 4394- 7697
+
+## Article
+
+Keywords: SARS- CoV- 2, epidemiology, school- based contacts, age- structured transmission model, age- specific seroprevalence, hospital admission data
+
+Posted Date: March 29th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 130264/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on March 12th, 2021. See the published version at https://doi.org/10.1038/s41467- 021- 21899- 6.
+
+<--- Page Split --->
+
+# Model-based evaluation of school- and non-school-related measures to control the COVID-19 pandemic
+
+Ganna Rozhnova, \(\mathrm{PhD}^{*1,2}\) , Christiaan H. van Dorp, \(\mathrm{PhD}^3\) , Patricia Bruijning- Verhagen, MD \(\mathrm{PhD}^1\) , Martin C.J. Bootsma, \(\mathrm{PhD}^{1,4}\) , Prof Janneke H.H.M. van de Wijgert, MD \(\mathrm{PhD}\) MPH \(^{1,5}\) , Prof Marc J.M. Bonten, MD \(\mathrm{PhD}^{1,6}\) , and Prof Mirjam E. Kretzschmar, \(\mathrm{PhD}^1\)
+
+1 Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands 2 BioISI—Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal 3 Theoretical Biology and Biophysics (T- 6), Los Alamos National Laboratory, Los Alamos, New Mexico, USA 4 Mathematical Institute, Utrecht University, Utrecht, The Netherlands 5 The Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK 6 Department of Medical Microbiology, University Medical Center Utrecht, Utrecht University, The Netherlands
+
+February 19, 2021
+
+<--- Page Split --->
+
+## Abstract
+
+The role of school- based contacts in the epidemiology of SARS- CoV- 2 is incompletely understood. We use an age- structured transmission model fitted to age- specific seroprevalence and hospital admission data to assess the effects of school- based measures at different time points during the COVID- 19 pandemic in the Netherlands. Our analyses suggest that the impact of measures reducing school- based contacts depends on the remaining opportunities to reduce non- school- based contacts. If opportunities to reduce the effective reproduction number \((R_{e})\) with non- school- based measures are exhausted or undesired and \(R_{e}\) is still close to 1, the additional benefit of school- based measures may be considerable, particularly among older school children. As two examples, we demonstrate that keeping schools closed after the summer holidays in 2020, in the absence of other measures, would not have prevented the second pandemic wave in autumn 2020 but closing schools in November 2020 could have reduced \(R_{e}\) below 1, with unchanged non- school- based contacts.
+
+## Introduction
+
+In autumn 2020, many countries, including the Netherlands, are experiencing a second wave of the COVID- 19 pandemic [1]. During the first wave in spring 2020, general population- based control measures were introduced in the Netherlands, which involved physical distancing (including refraining from hand- shaking), frequent hand- washing and other hygiene measures, and self- quarantine when symptomatic. In addition, many public places and schools were closed. These contact reduction measures were relaxed starting from May, and the incidence of COVID- 19 started to increase again at the end of July [1]. From the end of August onwards, contact reduction measures were intensified in a step- wise manner. Schools closed during July and August for summer break, reopened at the end of August, and have remained open until 16 December, with the exception of a one- week autumn break. Some measures were implemented in schools after the summer break to reduce transmission. Students and teachers in secondary schools have to wear masks when not seated at their desks, and students have to keep distance from teachers. A student with cold- or flu- like symptoms has to stay at home. The step- wise increase in control measures after the summer started with earlier closing times of bars and restaurants, reinforcement of working at home (in September), followed by closure of all bars and restaurants, theaters, cinemas and other cultural meeting places in November and obligatory mask wearing in all public places since December 1. According to the National Institute for Public Health and the Environment (RIVM), estimated effective reproduction numbers \((R_{e})\) for the Netherlands were about 1.3 in the period 27 August- 6 September and about 1.0 in the period 7- 13 November [1]. The aim of measures implemented by the government in autumn 2020 was to reduce \(R_{e}\) to 0.8. The failure to achieve this might be due to reduced societal acceptance of control measures, and/or due to the lack of school closure. The role of children and their contacts during school hours in the spread of SARS- CoV- 2 is in fact not well understood [2,3]. In this study, we explored this role with a mathematical model fitted to COVID- 19 data from the Netherlands.
+
+<--- Page Split --->
+
+Closure of schools is considered an effective strategy to contain an influenza pandemic [4], based on both model calculations and observational studies of the influence of school holidays on the spread of influenza [5, 6]. The reasons for this are the high contact rates in young age groups [7] and the susceptibility of children and young people to the influenza virus. In contrast to influenza, children seem to be less susceptible to SARS- CoV- 2 than adults and, based on sparse data, the susceptibility to SARS- CoV- 2 increases with age [8, 9].
+
+In the absence of empirical SARS- CoV- 2 data, mathematical modeling can help to quantify the role of different age groups in the distribution of SARS- CoV- 2 in the population [10, 11], and to evaluate the impact of interventions on transmission [12- 17]. Such models can help to estimate the reduction in the effective reproduction number for different contact- reduction scenarios within or outside school environments. Model predictions about the relative epidemic impacts of school- and non- school- based measures can assist policymakers in selecting combinations of measures during different stages of the pandemic that optimally balance potential harms and benefits. Predictions generated by models that include differences in susceptibility and contact rates in different age groups can also aid in deciding which school age groups should be the primary target of school- based interventions.
+
+We used an age- structured transmission model fitted in a Bayesian framework to age- specific hospital admission data (27 February—30 April 2020) and cross- sectional age- specific seroprevalence data (April/May 2020) [18] to evaluate the effects of control measures aimed at reducing school and other (non- school- related) contacts in society in general at different time points during the COVID- 19 pandemic in the Netherlands. The model makes use of age- specific contacts rates before and after the first lockdown [19] and contact rates in schools [7, 20], and accounts for different susceptibility to SARS- CoV- 2 among younger, middle- aged, and older persons. Using the model equipped with parameter estimates, we provide a comparative study of the impact of school- and non- school- related measures on the effective reproduction number in August 2020, before the most recent set of measures was implemented, and in November 2020, when the most recent measures were still in place. In particular, we assess whether keeping schools closed after the summer holidays in 2020 would have prevented the second pandemic wave in the autumn and whether closing schools in November 2020 could have helped to achieve the control of the pandemic. We quantify reductions in \(R_{e}\) due to closing schools for different ages and make recommendations on which school ages should be targeted to design effective school- based interventions.
+
+## 60 Results
+
+## 61 Epidemic dynamics
+
+The model shows a very good agreement between the estimated age- specific hospitalizations and the data (Figure 1). The number of hospitalizations increases with age, with the highest peaks in hospitalizations observed in persons above 60 years old. The estimated probability of hospitalization increases nearly exponentially with age (as shown by an approximately linear relationship on the logarithmic scale, Figure 2), except for persons under 30 years old,
+
+<--- Page Split --->
+
+in whom the number of hospitalizations was low. The estimated probability of hospitalization increased from \(0.09\%\) (95%CrI 0.05—0.15%) in persons under 20 years old to \(4.37\%\) (95%CrI 2.80—8.82%) in persons older than 80 years (Supplementary Figure 2).
+
+
+
+Figure 1. Estimated age-specific hospital admissions. The black lines represent the estimated medians. The dark gray lines correspond to \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution, and the shaded regions show \(95\%\) Bayesian prediction intervals. The dots are daily hospitalization admission data (all data points are included). Day 1 corresponds to 22 February 2020 which is 5 days prior to the first officially notified case in the Netherlands (27 February 2020). Panels a-h refer to different age groups.
+
+
+
+Figure 2. Estimated age-specific probability of hospitalization. The violin shapes represent the marginal posterior distribution for 2000 samples of the probability of hospitalization in the model.
+
+<--- Page Split --->
+
+
+Figure 3. Estimated age-specific seroprevalence. The data (dots) are shown as the percentage of seropositive persons based on a seroprevalence survey that was conducted in April/May 2020. The number of positive and total samples defining this percentage for each age category is supplied in seroprevalence data file accompanying this study (see Data availability). The error bars represent the 95% confidence (Jeffreys) interval of the percentage. The violin shapes represent the marginal posterior distribution for 2000 samples of the percentage of seropositive persons in the model.
+
+The model accurately reproduces the percentage of seropositive persons distributed across the age groups (Figure 3). The median seroprevalence in the population was \(2.7\%\) , with the maximum seroprevalence observed in persons between 20 and 40 years old (about \(3.5\%\) ). The lowest seroprevalence was among children in the 0 to 10 years age group ( \(0.9\%\) ). Note that if our model did not include age- dependence of susceptibility to SARS- CoV- 2, the seroprevalence peak would be expected among children because they have the largest numbers of contacts in the population.
+
+The estimated probability of transmission per contact was 0.07 ( \(95\%\) CrI 0.05—0.12) before the first lockdown and it decreased by \(48.84\%\) ( \(95\%\) CrI 23.81—87.44%) after the first lockdown. The reduction in susceptibility relative to susceptibility in persons above 60 years old was \(23\%\) ( \(95\%\) CrI 20—28%) in persons under 20 years old and \(61\%\) ( \(95\%\) CrI 50—72%) for persons between 20 and 60 years old (Supplementary Figure 3). The estimated basic reproduction number was 2.71 ( \(95\%\) CrI 2.15—5.18) in the absence of control measures (February 2020) (Supplementary Figure 4 a), and dropped to 0.62 ( \(95\%\) CrI 0.29—0.74) after the full lockdown (April 2020) (Supplementary Figure 4 b). Supplementary Figures 1,2, 3, and 4 show an overview of all parameter estimates.
+
+The joint posterior density of the estimated parameters reveals strong positive and negative correlations between some of the parameters (Supplementary Figure 5). For instance, the initial fraction of infected individuals is negatively correlated with the probability of transmission per contact and the hospitalization rate, as a small initial density can be compensated by a faster growth rate or a larger hospitalization rate. For that reason, the age- specific
+
+<--- Page Split --->
+
+hospitalization rates are all positively correlated. These correlations highlight the necessity of complementing the hospitalization time series data with seroprevalence data, even if the sample size of the latter is small. Without the seroprevalence data many parameters would be difficult to identify.
+
+
+
+Figure 4. Schematic timeline of the pandemic in the Netherlands during 2020. Outlined are times of the introduction and relaxation of control measures, and the estimated effective reproduction numbers for a - start of the pandemic (February 2020), b - full lockdown (April 2020), c - schools opening (August 2020), d - partial lockdown (November 2020). See Supplementary Figure 4 for the distributions of the reproduction numbers.
+
+## School and non-school-based measures
+
+The sequence of measures implemented and lifted during the pandemic in the Netherlands and the respective estimated values of the effective reproduction numbers are shown schematically in Figure 4. We used the fitted model to separately determine the effect on the effective reproduction number of decreasing contacts in schools and of decreasing other (non- school- related) contacts in society in general in August 2020 (Figure 5) and in November 2020 (Figure 6). In doing so, we varied one type of contact and kept the other type constant. For each scenario, the reduction in contact rate was varied between \(0\%\) and \(100\%\) . The aim of reducing the number of contacts of each type is to decrease the effective reproduction number below 1.
+
+We first considered the situation in August 2020 (Figure 5), when schools had just opened after the summer holidays and when control measures in the population were less stringent than in April (full lockdown). Between August and December 2020, the only infection prevention measure in primary schools was the advice to teachers and pupils to
+
+<--- Page Split --->
+
+stay at home in case of symptoms or a household member diagnosed with SARS- CoV- 2 infection; physical distancing between teachers and pupils (but not between pupils) only applied to secondary schools. We therefore assumed that the effective number of contacts in schools was the same as before the pandemic. For other (non- school- related) contacts in society in general we assumed that 1) the number of contacts increased after April 2020 (full lockdown) but was lower than before the pandemic, and that 2) reduction in probability of transmission per contact due to mask- wearing and hygiene measures was lower in August as compared to April (due to decreased adherence to measures). The starting point of our analyses is an effective reproduction number of 1.31 (95%CrI 1.15—2.07) in accordance with the state of the Dutch pandemic in August 2020 (Supplementary Figure 4 c).
+
+Figure 5 a demonstrates that in August 2020 other contacts in society in general would have to be reduced by at about \(60\%\) to bring the effective reproduction number to 1 (if school- related contacts do not change). A \(100\%\) reduction would resemble the number of contacts in April (full lockdown) and would bring the effective reproduction number to 0.83 (95%CrI 0.75—1.10). Figure 5 b demonstrates that reductions of school contacts would have a limited impact on the effective reproduction number (if non- school contacts do not change). A \(100\%\) reduction (complete closure of schools) would have reduced the effective reproduction number by only \(10\%\) (from 1.31 to 1.18 (95%CrI 1.04—1.83)).
+
+
+
+Figure 5. Impact of reduction of two types of contacts on the effective reproduction number in August 2020. Percentage reduction in a other (non-school-related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in August 2020, when schools just opened in the Netherlands. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non-school-related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(R_{e}\) (situation August 2020), the green line is the value of \(R_{e}\) achieved for \(100\%\) reduction in contacts. The blue line indicates \(R_{e}\) of 1. To control the pandemic, \(R_{e}< 1\) is necessary.
+
+Subsequently, we considered the Dutch pandemic situation in November 2020 (Figure 6), when the measures implemented since the end of August (partial lockdown intended to prevent the second wave) had led to an effective
+
+<--- Page Split --->
+
+reproduction number of 1.00 (95%CrI 0.94—1.33) (Supplementary Figure 4 d), and, as described above, only limited control measures were taken in schools. Now, the impact of interventions targeted at reducing school contacts (Figure 6 b) would reduce the effective reproduction number similarly as reducing non- school contacts in the rest of the population (Figure 6 a). Specifically, closing schools would reduce the effective reproduction number by 16% (from 1.0 to 0.84 (95%CrI 0.81—0.90)) (Figure 6 b). Almost the same \(R_{e} = 0.83\) (95%CrI 0.75—1.10), would have been achieved by reducing non- school- related contacts to the level of April 2020 while the schools remain open (Figure 6 a).
+
+
+
+Figure 6. Impact of reduction of two types of contacts on the effective reproduction number in November 2020. Percentage reduction in a other (non-school-related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in November 2020. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non-school-related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(R_{e}\) (situation November 2020), the green line is the value of \(R_{e}\) achieved for \(100\%\) reduction in contacts. To control the pandemic, \(R_{e}< 1\) is necessary.
+
+## Interventions for different school ages
+
+Next we investigated the impact of targeting interventions at different age groups, starting from the situation in November 2020 with the effective reproduction number being 1 (Supplementary Figure 4 d). Figure 7 a, b, and c show \(R_{e}\) as a function of the reduction of school contacts in age groups of [0,5), [5,10) and [10,20) y.o., respectively. In each panel, we varied the number of school contacts in one age group while keeping the number of school contacts in the other two age groups constant. \(0\%\) reduction corresponds to the situation in November 2020, and \(100\%\) reduction represents a scenario with schools for students in a given age group closed. The model predicts a maximum impact on \(R_{e}\) from reducing contacts of 10 to 20 year old children (Figure 7 c). Closing schools for this age group only could decrease \(R_{e}\) by about \(8\%\) (compare Figure 7 c and Figure 6 b where we expect the reduction
+
+<--- Page Split --->
+
+
+Figure 7. Impact of reduction of school contacts in different age groups on the effective reproduction number in November 2020. Percentage reduction in school contacts among a \([0,5)\) years old, b [5, 10) years old and c [10, 20) years old. In each panel, we varied the number of school contacts in one age group while keeping the number of school contacts in the other two age groups constant. The scenario with \(0\%\) reduction describes the situation in November 2020 with \(R_{e}\) of about 1 (partial lockdown intended to prevent the second wave), where all schools are open without substantial additional measures. The reduction of \(100\%\) in school contacts represents a scenario with the structure of non-school contacts in society in general as in November 2020 and schools for students in a given age group closed. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(R_{e} = 1\) (situation November 2020). The green line indicates the value of \(R_{e}\) achieved when schools for a given age group close.
+
+of \(16\%\) after closing schools for all ages). School closure for children aged 5 to 10 years would reduce \(R_{e}\) by about \(5\%\) (Figure 7 b). Contact reductions among 0 to 5 year old children would have a negligible impact on \(R_{e}\) as shown in Figure 7 a.
+
+in Figure 7 a.
+
+## Discussion
+
+We used an age- structured model for SARS- CoV- 2 fitted to hospital admission and seroprevalence data during spring 2020 to estimate the impact of school contacts on transmission of SARS- CoV- 2 and to assess the effects of school- based measures, including school closure, to mitigate the second wave in the autumn of 2020. We demonstrate how the relative impact of school- based measures aimed at reduction of contacts at schools on the effective reproduction number increases when the effects of non- school- based measures appear to be insufficient. These findings underscore the dilemma for policymakers of choosing between stronger enforcement of population- wide measures to reduce contacts in society in general or measures that reduce school- based contacts, including complete closure of schools. For the latter choice, our model predicts highest impact from measures implemented for the oldest school ages. We used the Netherlands as a case example but our model code is freely available and can be readily adapted to other countries given the availability of hospitalization and seroprevalence data. The findings in our manuscript can be relevant for guiding policy decisions in the Netherlands, but also in countries where the contact structure in the population is similar to that of the Netherlands [7].
+
+Our model integrates prior knowledge of epidemiological parameters and the quantitative assessment of the model
+
+<--- Page Split --->
+
+uncertainties in a Bayesian framework. To our knowledge, our modeling study is the first that uses this method to address the role of school- based contacts in the transmission of SARS- CoV- 2. Previous studies (e.g. [21- 25]) used individual- based or network models, that were not fit to epidemiological data using formal statistical procedures. Due to uncertainties in key model parameters, predictions of these models vary widely. Our model has been carefully validated to achieve an excellent fit to data of daily hospitalizations due to COVID- 19 and seroprevalence by age. Furthermore, reproduction numbers at different time points of the pandemic correlated well with estimates obtained from independent sources [1]. In addition, the Netherlands is one of few countries in the world for which the contact rate after the first lockdown is available (see [26] for the UK). We could, therefore, model the contact structure during the course of the pandemic as continuously changing between the contact structure before the pandemic and the contact structure when the measures were the most strict (first lockdown) without making additional assumptions about the impact of specific interventions on contacts in different age groups. Crucially, many prior models evaluating the impact of school- based contacts assumed age- independent susceptibility to infection with SARS- CoV- 2 (e.g. [13,23]). Here, we estimated susceptibility to infection with SARS- CoV- 2 to increase with age, which corroborates published findings from cohort studies [8,9]. Compared to adults older than 60 years, the estimated susceptibility was about 20% for children aged 0 to 20 years and about 60% for the age group of 20 to 60 years. However, even with extensive validation, we need to be careful when interpreting the predictions of our model as these depend on the sensitivity of serology to identify individuals with prior infection. Recent studies suggest that in persons who experience mild or asymptomatic infections, SARS- CoV- 2 antibodies may not always be detectable post- infection [27,28]. Therefore, more children may have had an infection than indicated by the seroprevalence survey because the proportion of asymptomatic in children is believed to be high. As a consequence, our study potentially underestimates the role of children in transmission.
+
+Naturally, our findings result from age- related differences in disease susceptibility and contact structure. Despite high numbers of contacts for children of all ages, and in particular in the age group of 10 to 20 years old, closing schools appeared to have much less impact on the effective reproduction number than contact reduction measures outside the school environment. In fact, measures effectively reducing non- school contacts, similar to those measures implemented in response to the first pandemic wave in spring 2020, could have prevented a second wave in autumn without school closures. With an estimated effective reproduction number of 1.3 in August 2020, continuation of school closures would have had much lower effects than measures aiming to reduce non- school- related contacts, which mainly occur in the adult population. Yet, that situation changes if the proposed measures fail. In November 2020, the measures implemented since August had reduced the effective reproduction number to around 1, instead of achieving the target value of about 0.8. In that situation, as our findings demonstrate, additional physical distancing measures in schools could assist in reducing the effective reproduction number further, in particular when implemented in secondary schools. Our analyses suggest that physical distancing measures in the youngest children will have no impact on the control of SARS- CoV- 2 infection. Of note, better adherence to non- school- based
+
+<--- Page Split --->
+
+measures would still have similar effects as reducing school- based contacts.
+
+Although there are several options for reducing the number of contacts between children at school, such as staggered start and end times and breaks, different forms of physical distancing for pupils and division of classes, the effects of such measures on transmission among children have not been quantified. Importantly, we have assumed that reductions in school- based contacts are not replaced by non- school- based contacts (among children and between children and adults) with similar transmission risk.
+
+Our modelling approach has several limitations. For estimating disease susceptibility we could only model children as a group of 0 to 20 years old. As disease susceptibility increases with age, it seems obvious that effects of reduced school contacts are most prominent in older children. Assuming equal susceptibility across these ages may have underestimated to some extent the effect of reducing school contacts for children between 10 and 20 years. At the same time, we assumed that school contact patterns in August- November 2020 reflect the pre- pandemic situation. Yet, general control measures in the Netherlands such as stay at home orders for symptomatic persons probably lower infectious contacts in school settings too, meaning that some reduction compared to pre- pandemic levels of contacts could already be present in schools. Effects of these measures in school settings should be smaller than in the general population and are hard to estimate due to a large number of asymptomatic cases among children, and therefore were not taken into account. In this respect, the results reported here describe the maximum possible reduction in the effective reproduction number due to school interventions. Furthermore, the contact matrices available did not allow differentiation between various types of contacts outside schools (like work, leisure, transport etc.), as these were not available for periods during the pandemic. Therefore, we could not model the impact of reducing work- related or leisure- related contacts separately. We also could not include hospitalization data from the second wave of the pandemic due to lack of data availability.
+
+The potential effects of opening or closing schools in different phases of the pandemic have been reported in other studies [13,21- 24,29,30]. Also based on a mathematical model, Panovska- Griffiths et al. [21] predicted that without very high levels of testing and contact tracing reopening schools after summer with a simultaneous relaxation of measures will lead to a second wave in the United Kingdom, peaking in December 2020. Their model predicted that this peak could be postponed for two months (to February 2021) by a rotating timetable in schools. Very early in the pandemic, in March 2020, the Scientific Advisory Group for Emergencies in the United Kingdom concluded that it would not be possible to reduce the effective reproduction number below 1 without closing schools [29]. In a modelling study on the impact of non- pharmaceutical interventions for COVID- 19 in the United Kingdom, Davies et al. found that the impact of school closures was low [13]. In another modeling study Rice et al. [24] found that school closures during the first wave of the pandemic could increase overall mortality, due to death being postponed to a second and subsequent waves. And based on an analysis of the impact of non- pharmaceutical measures in 41 countries between January and May 2020, Brauner et al. [30] concluded that closure of schools and universities had contributed the most to lowering the effective reproduction number. Yet, a major difficulty in estimating the effect
+
+<--- Page Split --->
+
+of school closure using observational data from the first wave is that other non- pharmaceutical interventions were implemented at or around the same time as school closures [31]. Similarly, lifting such measures often coincided with school re- openings. Observational data from the period after the first wave show conflicting results on within school transmission [32- 35] and the effect of school reopening and interpretation is further hampered by the variety in control measures implemented in schools across countries. Finally, Munday et al. showed that reopening secondary schools is likely to have a greater impact on community transmission than reopening primary schools in England [22]. While the modelling approach of [22] is different from ours, our findings are similar in the sense that secondary schools are predicted to make a larger contribution to transmission than primary schools, and are therefore more important for controlling COVID- 19.
+
+In conclusion, we have demonstrated that the potential effects of school- based measures to reduce contacts between children, including school closures, markedly depends on the reduction in the effective reproduction number achieved by other measures. With remaining opportunities to reduce the effective reproduction number with non- school- based measures, the additional benefit of school- based measures is low. Yet, if opportunities to reduce the effective reproduction number with non- school- based measures are considered to be exhausted or undesired for economic reasons and \(R_{e}\) is still close to 1, the additional benefit of school- based measures may be considerable. In such situations, the biggest impact on transmission is achieved by reducing contacts in secondary schools.
+
+## Methods
+
+## Overview
+
+Estimates of epidemiological parameters were obtained by fitting a transmission model to age- stratified COVID- 19 hospital admission data in the period from 27 February till 30 April 2020 ( \(n = 10,961\) ) and cross- sectional age- stratified SARS- CoV- 2 seroprevalence data assessed in April/May 2020 ( \(n = 3,207\) ) [18]. The model equipped with parameter estimates was subsequently used to investigate the impact of school- and non- school- based measures on controlling the pandemic.
+
+## Data
+
+The hospital data included \(n = 10,961\) COVID- 19 hospitalizations by date of admission and stratified by age during the period of 64 days following the first official case in the Netherlands (27 February 2020). The criteria for hospital admission have not changed during the pandemic, and from the early stages all hospitalized patients with a clinical suspicion of COVID- 19 were tested by RT- PCR. In all stages of the pandemic, patients requiring hospital admission were hospitalized and the practice of not referring patients for hospital admission (e.g. due to self- expressed treatment restrictions or moribund condition) did not change.
+
+<--- Page Split --->
+
+The SARS- CoV- 2 seroprevalence data was taken from a cross- sectional population- based serological study carried out in April/May 2020 (PIENTER Corona study) [18]. Participants for the serosurvey were enrolled from a previously established nationwide serosurveillance study, provided a self- collected fingerstick blood sample and completed a questionnaire. A total of 40 municipalities were randomly selected, with probabilities proportional to their population size. From these municipalities, an age- stratified sample was drawn from the population register, and 6, 102 persons were invited to participate. Serum samples and questionnaires were obtained from 3, 207 participants and included in the analyses. The majority of blood samples were drawn in the first week of April. IgG antibodies targeted against the spike S1- protein of SARS- CoV- 2 were quantified using a validated multiplex- immunoassay. Seroprevalence was estimated controlling for survey design, individual pre- pandemic concentration, and test performance.
+
+Our analyses made use of the demographic composition of the Dutch population in July 2020 from Statistics Netherlands [36] and age- stratified contact data for the Netherlands [19,20]. The contact rates before the pandemic were based on a cross- sectional survey carried out in 2016/2017, where participants reported the number and age of their contacts during the previous day [19]. The contact rates after the first lockdown were based on the same survey which was repeated in a sub- sample of the participants in April 2020 (PIENTER Corona study) [19]. School- specific contact rates for the Dutch population before the pandemic were taken from the POLYMOD study [7,20].
+
+## Transmission model
+
+We used a deterministic compartmental model describing SARS- CoV- 2 transmission in the population of the Netherlands stratified by infection status and age (Figure 8 a). Some modeling studies on the impact of interventions against COVID- 19 account for spatial variations of the disease [16,17,37]. Since the available data is aggregated on the country level and for the sake of the model's tractability, we disregarded regional stratification of the population. The dynamics of the model follows the Susceptible- Exposed- Infectious- Recovered structure. Persons in age group \(k\) , where \(k = 1,\ldots ,n\) , are classified as susceptible \((S_{k})\) , infected but not yet infectious (exposed, \(E_{k}\) ), infectious in \(m\) stages \((I_{k,p}\) , where \(p = 1,\ldots ,m\) ), hospitalized \((H_{k})\) and recovered without hospitalization \((R_{k})\) . Susceptible persons \((S_{k})\) can acquire infection via contact with infectious persons \((I_{k,p}\) , \(k = 1,\ldots ,n\) , \(p = 1,\ldots ,m\) ) and become latently infected \((E_{k})\) at a rate \(\beta_{k}\lambda_{k}\) , where \(\lambda_{k}\) is the force of infection, and \(\beta_{k}\) is the reduction in susceptibility to infection of persons in age group \(k\) compared to persons in age group \(n\) . Persons in the classes \((I_{k,p}\) , \(k = 1,\ldots ,n\) , \(p = 1,\ldots ,m\) ) are assumed to be equally infectious. After the latent period (duration \(1 / \alpha\) days), exposed persons become infectious \((I_{k,1})\) . Infectious persons progress through \((m - 1)\) stages of infection \((I_{k,p}\) , where \(p = 2,\ldots ,m\) ) at rate \(\gamma m\) , after which they recover \((R_{k})\) . Inclusion of \(m\) identical infectious stages allows for the tuning of the distribution of the infectious period (the time spent in the infectious compartments, \(I_{k,p}\) , \(p = 1,\ldots ,m\) ) [38,39], interpolating between an exponentially distributed infectious period \((m = 1)\) and a fixed infectious period \((m\rightarrow \infty)\) . Intermediate values of \(m\) correspond to an Erlang- distributed infectious period with mean \(1 / \gamma\) and standard de
+
+<--- Page Split --->
+
+
+Figure 8. Transmission model. a Model schematic. Black arrows show epidemiological transitions. Red arrows indicate the compartments contributing to the force of infection. Susceptible persons in age group \(k\) \((S_{k})\) , where \(k = 1,\ldots ,n\) , become latently infected \((E_{k})\) via contact with infectious persons in \(m\) infectious stages \((I_{k,p}\) \(p = 1,\ldots ,m)\) at a rate \(\beta_{k}\lambda_{k}\) , where \(\lambda_{k}\) is the force of infection, and \(\beta_{k}\) is the reduction in susceptibility to infection of persons in age group \(k\) compared to persons in age group \(n\) . Exposed persons \((E_{k})\) become infectious \((I_{k,1})\) at rate \(\alpha\) . Infectious persons progress through \((m - 1)\) infectious stages at rate \(\gamma m\) , after which they recover \((R_{k})\) . From each stage, infectious persons are hospitalized at rate \(\nu_{k}\) . Table 1 gives the summary of the model parameters. b-d Contact rates. b and c show contact rates in all locations before the pandemic and after the first lockdown (April 2020), respectively; d shows contact rates at schools before the pandemic. The color represents the average number of contacts per day a person in a given age group had with persons in another age group.
+
+<--- Page Split --->
+
+rates we used from the literature are additive [19,20], thus the contact rate before the lockdown \((b_{kl})\) can be written as a sum of the school contact rate at the pre-lockdown level \((s_{kl}\) , see Figure 8 d) and the contact rate for all locations but schools \((b_{kl} - s_{kl})\) . The contact rate after the lockdown \((a_{kl})\) by definition did not include any school contacts because all schools were closed. The contact rate incorporating the relaxation of control measures after the first lockdown is therefore modeled as follows
+
+\[c_{kl}(t) = \zeta_{1}g(t)a_{kl} + [1 - g(t)]\zeta_{2}(b_{kl} - s_{kl}) + \omega s_{kl}, \quad (3)\]
+
+where \(g(t) = 1 / \left[1 + e^{K_{2}(t - t_{2})}\right]\) with the mid- point value \(t_{2} > t_{1}\) and the logistic growth \(K_{2}\) . In Eq. 3, the first two terms describe the increase of non- school contacts from the level after the first lockdown \((a_{kl})\) to their pre- lockdown level \((b_{kl} - s_{kl})\) . The parameter \(\zeta_{2} \geq \zeta_{1}\) , \(0 \leq \zeta_{2} \leq 1\) implies that the probability of transmission increased due to reduced adherence to control measures. The last term describes opening of schools which we assume to happen instantaneously, where \(\omega\) , \(0 \leq \omega \leq 1\) , is the proportion of retained school contacts. Schools functioning without any measures correspond to \(\omega = 1\) . School closure is achieved by setting \(\omega = 0\) . A summary of the model parameters is given in Table 1.
+
+Table 1. Summary of the model parameters.
+
+| Description (unit) | Notation | Reference |
| Constant parameters | | |
| Number of age groups | n | 10 |
| Number of infectious stages | m | 3 |
| Basic reproduction number | R0 | Computed using the method in [40] |
| Effective reproduction number | Re | Computed using the method in [40] |
| Probability of transmission per contact | ε | Estimated |
| Reduction in post-lockdown probability of transmission per contact | (1-ζ1) | Estimated |
| Latent period (days) | 1/α | Estimated |
| Infectious period (1/day) | 1/γ | Estimated |
| Contribution of the contact rate after the lockdown | f(t)=1/[1+e-K1(t-t1)] | Eq. 2 |
| Mid-point value of the logistic function (days) | t1 | Estimated |
| Logistic growth (1/day) | K1 | Estimated |
| Over-dispersion parameter for the NegBinom distribution for hospitalizations | r | Estimated |
| Proportion of school contacts | ω | [0,1], calibrated |
| Reduction in probability of transmission per contact during relaxation | (1-ζ2) | [0,1], ζ2 ≥ ζ1, calibrated |
| Initial fraction of infected persons | θ | Estimated |
| Logistic function for relaxation | g(t)=1/[1+e-K2(t-t2)] | 0 ≤ g(t) ≤ 1, calibrated |
| Age-specific parameters* | | |
| Force of infection (1/day) | λk | Eq. 5 |
| Hospitalization rate (1/day) | νk | Estimated |
| Susceptibility of age group k relative to age group n† | βk | Estimated |
| General contact rate (1/day) | ckl | Eqs. 1 and 3 |
| Contact rate before the pandemic (1/day) | bkl | [19] |
| Contact rate after the first lockdown (1/day) | akl | [19] |
| School contact rate before the pandemic (1/day) | skl | [7,20] |
| Population size of age group k | Nk | [36] |
+
+\\*Indices \(k\) and \(l\) denote the age groups \(k,l = 1,\ldots ,n\) \(\ddagger\) In the estimation procedure the reference age group \(n\) is \(60+\) , and \(\beta_{60 + } = 1\) is fixed at 1.
+
+<--- Page Split --->
+
+The model was implemented in Mathematica 10.0.2.0 using a system of ordinary differential equations as follows
+
+\[\begin{array}{rcl}{\frac{\mathrm{d}S_k(t)}{\mathrm{d}t}} & = & {-\beta_k\lambda_k(t)S_k(t),}\\ {\frac{\mathrm{d}E_k(t)}{\mathrm{d}t}} & = & {\beta_k\lambda_k(t)S_k(t) - \alpha E_k(t),}\\ {\frac{\mathrm{d}I_{k,1}(t)}{\mathrm{d}t}} & = & {\alpha E_k(t) - (\gamma m + \nu_k)I_{k,1}(t),}\\ {\frac{\mathrm{d}I_{k,p}(t)}{\mathrm{d}t}} & = & {\gamma mI_{k,p - 1}(t) - (\gamma m + \nu_k)I_{k,p}(t),} & {p = 2,\ldots ,m,}\\ {\frac{\mathrm{d}R_k(t)}{\mathrm{d}t}} & = & {\gamma mI_{k,m}(t),}\\ {\frac{\mathrm{d}H_k(t)}{\mathrm{d}t}} & = & {\nu_k\sum_{p = 1}^{m}I_{k,p}(t),} \end{array} \quad (4)\]
+
+where \(S_{k}\) , \(E_{k}\) , \(R_{k}\) and \(H_{k}\) are the numbers of persons in age group \(k\) , \(k = 1, \ldots , n\) , who are susceptible, exposed, recovered and hospitalized, respectively. The number of infectious persons in age group \(k\) and stage \(p = 1, \ldots , m\) is denoted \(I_{k,p}\) . The force of infection is given by
+
+\[\lambda_{k}(t) = \epsilon \sum_{l = 1}^{n}\sum_{p = 1}^{m}c_{kl}(t)\frac{I_{l,p}(t)}{N_{l}}, \quad (5)\]
+
+where \(N_{l}\) is the number of individuals in age group \(l\) , \(N_{l} = S_{l}(t) + E_{l}(t) + \sum_{p = 1}^{m}I_{l,p}(t) + H_{l}(t) + R_{l}(t)\) . Note that the denominator in the force of infection \((N_{l})\) includes hospitalized persons, \(H_{l}(t)\) , where \(H_{l}(t)\) describes the cumulative number of hospital admissions at time \(t\) . The current number of hospitalized persons (not the cumulative) is not subtracted from \(N_{l}\) because we assume that hospitalized persons will be involved in contacts with medical personnel and visitors. Since we assume that contacts of the currently hospitalized persons (who may still be infectious) will not be infected due to the use of personal protective measures by medical personnel and hospital visitors, the current number of hospitalized persons does not contribute to the force of infection. As patients who are discharged and recovered (or deceased) also do not contribute to the force of infection, the cumulative number of hospitalized persons \((H_{l}(t))\) does not contribute to the force of infection either. In Eq. 5 we assumed a frequency- dependent transmission where the per capita rate at which a susceptible person becomes infected increases with the fraction of the population that is infectious. This choice is justified for the Netherlands as one of the most densely populated countries in Europe. Moreover, as the population size does not change during the time horizon of our analyses, there is no difference in the outcome between a frequency- dependent and a density dependent model once the parameters are fitted to obtain the observed reproduction number.
+
+We took 22 February 2020 as starting date \((t_{0})\) for the pandemic in the Netherlands, which is 5 days prior to the first officially notified case (27 February 2020). We assumed that there were no hospitalizations during this 5 day period.
+
+<--- Page Split --->
+
+353 To account for importation of new cases into the Netherlands at the beginning of the pandemic, we estimated a fraction \(\theta\) of each age group infected at time \(t_0\) . For simplicity, we assumed this fraction to be equally distributed between the exposed and infectious persons, i.e., \(E_k(t_0) = \frac{1}{2}\theta N_k\) , \(I_{k,p}(t_0) = \frac{1}{2m}\theta N_k\) and \(S_k(t_0) = (1 - \theta)N_k\) . In later stages of the pandemic, importations do not play such an important role because of existing pool of infected individuals within the country and ongoing control measures. For this reason, importations after \(t_0\) were not included in the model.
+
+## 359 Observation model and parameter estimation
+
+Given predictions of the model, we calculated the likelihood of the data as follows. In the model, infectious individuals are hospitalized at a continuous rate \(\nu_k\sum_{p = 1}^{m}I_{k,p}\) . However, the hospitalization data consists of a discrete number of hospital admissions \(h_{k,i}\) on day \(T_i\) for each age class \(k\) . As the probability of hospitalization is relatively small, we made the simplifying assumption that the daily incidence of hospitalizations is proportional to the prevalence of infectious individuals at that time point. To accommodate errors in reporting and within age class variability of the hospitalization rate, we allowed for over- dispersion in the number of hospitalizations using a Negative- Binomial distribution, i.e.,
+
+\[h_{k,i}\sim \mathrm{NegBinom}\left(\nu_k\sum_{p = 1}^{m}I_{k,p}(T_i),r\right), \quad (6)\]
+
+where we parameterize the \(\mathrm{NegBinom}(\mu ,r)\) distribution with the mean \(\mu\) and over- dispersion parameter \(r\) , such that the variance is equal to \(\mu +\mu^2 /r\) .
+
+We calculated the likelihood of the seroprevalence data using the model prediction of the fraction of non- susceptible individuals in each age class \(1 - S_k(T) / N_k\) . Here \(T\) denotes the median sampling time minus the expected duration from infection to seroconversion. We assumed that the probability of finding a seropositive individual in a random sample from the population is equal to the fraction of non- susceptible individuals, leading to a Binomial distribution for the number of positive samples \(\ell_k\) among all samples \(L_k\) from age group \(k\)
+
+\[\ell_k\sim \mathrm{Binom}(L_k,1 - S_k(T) / N_k). \quad (7)\]
+
+Parameters were estimated in a Bayesian framework based on the methods from [41,42]. The model given by Eq. 4 was fit to the data using the Hamiltonian Monte Carlo method as implemented in Stan (https://www.mc- stan.org) [43] with R and R Studio interfaces. We used 4 parallel chains of length 1500 with a warm- up phase of length 1000, resulting in 2000 parameter samples from the posterior distribution.
+
+We used age- specific contact rates with ten age groups (ages [0,5), [5,10), [10,20), [20,30), [30,40), [40,50), [50,60), [60,70), [70,80) and \(80+\) ). Due to the low number of hospitalizations in young persons, we assumed that hospitalization rates in the first three age groups (ages [0,5), [5,10), [10,20)) were equal, therefore only 8 hospitalization
+
+<--- Page Split --->
+
+rates were estimated. As the age-specific hospitalization rates are positively correlated (Supplementary Figure 5), we parameterized the model as \(\nu_{k} = \hat{\nu}_{k}\bar{\nu}\) , where \(\hat{\nu}_{k}\) is a simplex and \(\bar{\nu}\) a scalar. We kept the same age categories for the relative susceptibility as in the retrospective cohort study by Jing et al [8], from where we took the priors, i.e., the relative susceptibility was estimated for ages [0,20), [20,60), and \(60+\) age category was used as the reference corresponding to susceptibility equal to 1. As the age groups for which the seroprevalence was reported [18] are different from the age groups used in our model, we used demographic data from the Netherlands [36] and the smoothed age-specific seroprevalence curve estimated by Vos et al. [18] to correct for this discrepancy. The Bayesian prior distributions for the 10 estimated parameters (18 numbers in total as hospitalization rate and susceptibility are age-dependent) (see Table 1) are listed in Table 2. In the main text, we presented results for three infectious classes corresponding to an Erlang-distributed infectious period with shape parameter \(m = 3\) .
+
+Table 2. Prior distributions for the Bayesian statistical model.
+
+| Parameter | Prior* | Explanation |
| ε | Uniform(0,1) | flat prior |
| α | InvGamma(32.25,9.75) | 99% of the prior density of 1/α between 2 and 5 days |
| γ | InvGamma(22.6,2.44) | 99% of the prior density of 1/γ between 5 and 15 days |
| V(0,20), V(20,30) | | |
| V(30,40), V(40,50) | folded-Λ(0,5) | vague prior |
| V(50,60), V(60,70) | | |
| V(70,80), V(80+) | | |
| β(0,20) | LogNormal(-1.47,0.1) | Log-odds -1.47 = log(0.23) based on prior estimates [8] |
| β(20,60) | LogNormal(-0.45,0.1) | Log-odds -0.45 = log(0.64) based on prior estimates [8] |
| r | LogNormal(5,2) | vague prior |
| ζ1 | folded-Λ(1,0.1) | a priori, we expect the reduction in contacts after the first lockdown to account for most of the decrease in the transmission rate |
| t1 | Λ(23,7) | the mean of t1 is given by the day of initiation of most drastic social distancing measures (March 15); most measures were taken within two weeks from this date |
| K1 | Exp(1) | with K1 = 1 the uptake of measures takes approximately 6 days |
| θ | Uniform(10-7,5·10-4) | vague prior allowing for approximately 10-10⁵ infections at time t0 |
+
+\*The scale parameter of the normal and log-normal distributions is equal to the standard deviation. \(\ddagger \beta_{60 + } = 1\) for the reference group of \(60+\) .
+
+## Model outcomes
+
+We considered control measures aimed at reducing contact rate at schools or in all other locations. We evaluated the impact of a control measure by computing \(R_{e}\) using the next generation matrix (NGM) method [40,44,45,48], and percentage of contacts that need to be reduced to achieve control of the pandemic as quantified by \(R_{e} = 1\) . Previously, we applied this method for HIV and CMV transmission models [42,49]. The method for calculating the basic reproduction number \(R_{0}\) and \(R_{e}\) (Supplementary Figure 4) is described in detail in Supplementary Information. In short, Supplementary Figures 4 a and b were obtained using the next generation matrix (NGM) method and posterior distributions of the parameters (Supplementary Figure 3) that were estimated from fitting the model to
+
+<--- Page Split --->
+
+the data of the first 69 days of the pandemic (22 February till 30 April 2020). As hospitalization data during relaxation is not available, we calibrated the model to values of \(R_{e}\) as published on the dashboard of the National Institute for Public Health and the Environment (RIVM) [1]. These time- dependent \(R_{e}\) values are estimated from hospitalization data and later from case numbers using methods described in [46]. Specifically, we chose \(\omega\) , \(g\) and \(\zeta_{2}\) such that the median reproduction numbers in the model would equal the specific values estimated by the RIVM (about 1.3 in the period 27 August- 6 September and about 1 in the period 7- 13 November) [1]. The distributions shown in Supplementary Figures 4 c and d are therefore obtained using the NGM method with fixed \(\omega\) , \(g\) and \(\zeta_{2}\) and other parameters drawn from the posterior distributions as shown in Supplementary Figure 3. Note that the calibration of the model in the relaxation period is possible because the parameters describing epidemiology of SARS- CoV- 2 are assumed to be constant throughout the time horizon of the analyses which spans both pre- lockdown, post- lockdown and relaxation periods, and only contact structure varies with time (see Supplementary Information). In analyses, the parameters \(\omega\) and \(g\) were then used as control parameters to reduce the number of school- and non- school- related contacts (Figures 5, 6 and 7). In doing so, we varied one type of contact and kept the other type constant.
+
+## Reporting summary
+
+Further information on research design is available in the Nature Research Reporting Summary linked to this article.
+
+## Data availability
+
+All datasets analysed and generated during this study are available in the GitHub repository, https://github.
+
+com/lynxgav/COVID19- schools [47].
+
+## Code availability
+
+Mathematica, Stan, R and R Studio codes reproducing the results of this study are available in the GitHub
+
+repository, https://github.com/lynxgav/COVID19- schools [47].
+
+## References
+
+[1] Coronavirus dashboard; 2020. Available from: https://coronadashboard.government.nl/.
+
+[2] Thompson RN, Hollingsworth TD, Isham V, Arribas- Bel D, Ashby B, Britton T, et al. Key questions for modelling COVID- 19 exit strategies. Proceedings of the Royal Society B. 2020;287(1932):20201405.
+
+<--- Page Split --->
+
+[3] Flasche S, Edmunds WJ. The role of schools and school- aged children in SARS- CoV- 2 transmission. The Lancet Infectious Diseases. XXXX;doi:10.1016/S1473- 3099(20)30927- 0.
+
+[4] Ferguson NM, Cummings DA, Fraser C, Cajka JC, Cooley PC, Burke DS. Strategies for mitigating an influenza pandemic. Nature. 2006;442(7101):448- 452.
+
+[5] Cauchemez S, Ferguson NM, Wachtel C, Tegnell A, Saour G, Duncan B, et al. Closure of schools during an influenza pandemic. The Lancet Infectious Diseases. 2009;9:473- 481.
+
+[6] te Beest DE, Birrell PJ, Wallinga J, De Angelis D, van Boven M. Joint modelling of serological and hospitalization data reveals that high levels of pre- existing immunity and school holidays shaped the influenza A pandemic of 2009 in The Netherlands. Journal of The Royal Society Interface. 2015;12(103):20141244. doi:10.1098/rsif.2014.1244.
+
+[7] Mossong J, Hens N, Jit M, Beutels P, Auranen K, Mikolajczyk R, et al. Social contacts and mixing patterns relevant to the spread of infectious diseases. PLOS Medicine. 2008;5(3):1- 1. doi:10.1371/journal.pmed.0050074.
+
+[8] Jing Q, Liu M, Zhang Z, Fang L, Yuan J, Zhang A, et al. Household secondary attack rate of COVID- 19 and associated determinants in Guangzhou, China: a retrospective cohort study. Lancet Infect Dis. 2020;20(10):1141- 1150. doi:10.1016/S1473- 3099(20)30471- 0.
+
+[9] Goldstein E, Lipsitch M, Cevik M. On the effect of age on the transmission of SARS- CoV- 2 in households, schools and the community. The Journal of Infectious Diseases. 2020;doi:10.1093/infdis/jiaa691.
+
+[10] Prem K, Liu Y, Russell T, Kucharski A, Eggo R, Davies N, et al. The effect of control strategies to reduce social mixing on outcomes of the COVID- 19 epidemic in Wuhan, China: a modelling study. Lancet Public Health. 2020;5(5):e261- e270. doi:10.1016/S2468- 2667(20)30073- 6.
+
+[11] Davies NG, Klepac P, Liu Y, Prem K, Jit M, Pearson CAB, et al. Age- dependent effects in the transmission and control of COVID- 19 epidemics. Nature Medicine. 2020;26(8):1205- 1211. doi:10.1038/s41591- 020- 0962- 9.
+
+[12] Teslya A, Pham TM, Godijk NG, Kretzschmar ME, Bootsma MCJ, Rozhnova G. Impact of self- imposed prevention measures and short- term government- imposed social distancing on mitigating and delaying a COVID- 19 epidemic: A modelling study. PLOS Medicine. 2020;17(7):1- 21. doi:10.1371/journal.pmed.1003166.
+
+[13] Davies NG, Kucharski AJ, Eggo RM, Gimma A, Edmunds WJ, Jombart T, et al. Effects of non- pharmaceutical interventions on COVID- 19 cases, deaths, and demand for hospital services in the UK: a modelling study. The Lancet Public Health. 2020;
+
+[14] Dehning J, Zierenberg J, Spitzner FP, Wibral M, Neto JP, Wilczek M, et al. Inferring change points in the spread of COVID- 19 reveals the effectiveness of interventions. Science. 2020;369(6500). doi:10.1126/science.abb9789.
+
+<--- Page Split --->
+
+[15] Giordano G, Blanchini F, Bruno R, Colaneri P, Di Filippo A, Di Matteo A, et al. Modelling the COVID- 19 epidemic and implementation of population- wide interventions in Italy. Nature Med. 2020;26:855- 860. doi:10.1038/s41591- 020- 0883- 7.
+
+[16] Gatto M, Bertuzzo E, Mari L, Miccoli S, Carraro L, Casagrandi R, et al. Spread and dynamics of the COVID- 19 epidemic in Italy: Effects of emergency containment measures. Proceedings of the National Academy of Sciences. 2020;117(19):10484- 10491. doi:10.1073/pnas.2004978117.
+
+[17] Bertuzzo E, Mari L, Pasetto D, Miccoli S, Casagrandi R, Gatto M, et al. The geography of COVID- 19 spread in Italy and implications for the relaxation of confinement measures. Nature Communications. 2020;11(1):4264. doi:10.1038/s41467- 020- 18050- 2.
+
+[18] Vos ERA, den Hartog G, Schepp RM, Kaaijk P, van Vliet J, Helm K, et al. Nationwide seroprevalence of SARS- CoV- 2 and identification of risk factors in the general population of the Netherlands during the first epidemic wave. Journal of Epidemiology & Community Health. 2020;doi:10.1136/jech- 2020- 215678.
+
+[19] Backer JA, Mollema L, Vos RAE, Klinkenberg D, van der Klis FRM, de Melker HE, et al. The impact of physical distancing measures against COVID- 19 transmission on contacts and mixing patterns in the Netherlands: repeated cross- sectional surveys in 2016/2017, April 2020 and June 2020. medRxiv; Accepted for publication in Eurosurveillance. 2020;doi:10.1101/2020.05.18.20101501.
+
+[20] Prem K, Cook AR, Jit M. Projecting social contact matrices in 152 countries using contact surveys and demographic data. PLOS Computational Biology. 2017;13(9):1- 21. doi:10.1371/journal.pcbi.1005697.
+
+[21] Panovska- Griffiths J, Kerr C, Stuart R, Mistry D, Klein D, Viner R, et al. Determining the optimal strategy for reopening schools, the impact of test and trace interventions, and the risk of occurrence of a second COVID- 19 epidemic wave in the UK: a modelling study. Lancet Child Adolesc Health. 2020;4(11):817- 827. doi:10.1016/S2352- 4642(20)30250- 9.
+
+[22] Munday JD, Sherratt K, Meakin S, Endo A, Pearson CAB, Hellewell J, et al. Implications of the school- household network structure on SARS- CoV- 2 transmission under different school reopening strategies in England. medRxiv. 2020;doi:10.1101/2020.08.21.20167965.
+
+[23] Keskinocak P, Asplund J, Serban N, Oruc Aglar BE. Evaluating Scenarios for School Reopening under COVID19. medRxiv. 2020;doi:10.1101/2020.07.22.20160036.
+
+[24] Rice K, Wynne B, Martin V, Ackland GJ. Effect of school closures on mortality from coronavirus disease 2019: old and new predictions. BMJ. 2020;371. doi:10.1136/bmj.m3588.
+
+[25] Chang S, Harding N, Zachreson C, Cliff OM, Prokopenko M. Modelling transmission and control of the COVID- 19 pandemic in Australia. Nat Commun. 2020;11:5710. doi:https://doi.org/10.1038/s41467- 020- 19393- 6.
+
+<--- Page Split --->
+
+[26] Jarvis CI, Van Zandvoort K, Gimma A, Prem K, Auzenbergs M, O'Reilly K, et al. Quantifying the impact of physical distance measures on the transmission of COVID- 19 in the UK. BMC Medicine. 2020;18(1):124. doi:10.1186/s12916- 020- 01597- 8.
+
+[27] Sekine T, Perez- Potti A, Rivera- Ballesteros O, Strlin K, Gorin JB, Olsson A, et al. Robust T Cell Immunity in Convalescent Individuals with Asymptomatic or Mild COVID- 19. Cell. 2020;183(1):158 - 168. e14. doi:https://doi.org/10.1016/j.cell.2020.08.017.
+
+[28] Burgess S, Ponsford MJ, Gill D. Are we underestimating seroprevalence of SARS- CoV- 2? BMJ. 2020;370. doi:10.1136/bmj.m3364.
+
+[29] Scientific Advisory Group for Emergencies. Timing of the introduction of school closure for COVID- 19 epidemic suppression, 18 March 2020; 2020. Available from: https://www.gov.uk/government/publications/timing- of- the- introduction- of- school- closure- for- covid- 19- epidemic- suppression- 18- march- 2020.
+
+[30] Brauner JM, Mindermann S, Sharma M, Johnston D, Salvatier J, Gavenciak T, et al. The effectiveness of eight nonpharmaceutical interventions against COVID- 19 in 41 countries. medRxiv. 2020;doi:10.1101/2020.05.28.20116129.
+
+[31] Li Y, Campbell H, Kulkarni D, Harpur A, Nundy M, Wang X, et al. The temporal association of introducing and lifting non- pharmaceutical interventions with the time- varying reproduction number (R) of SARS- CoV- 2: a modelling study across 131 countries. The Lancet Infectious Diseases. 2020;doi:https://doi.org/10.1016/S1473- 3099(20)30785- 4.
+
+[32] Heavey L, Casey G, Kelly C, Kelly D, McDarby G. No evidence of secondary transmission of COVID- 19 from children attending school in Ireland, 2020. Eurosurveillance. 2020;25(21). doi:https://doi.org/10.2807/1560- 7917.ES.2020.25.21.2000903.
+
+[33] Yung CF, Kam Kq, Nadua KD, Chong CY, Tan NWH, Li J, et al. Novel Coronavirus 2019 Transmission Risk in Educational Settings. Clinical Infectious Diseases. 2020;doi:10.1093/cid/ciaa794.
+
+[34] Macartney K, Quinn H, Pillsbury A, Koirala A, Deng L, Winkler N, et al. Transmission of SARS- CoV- 2 in Australian educational settings: a prospective cohort study. Lancet Child Adolesc Health. 2020;4(11):807- 816. doi:10.1016/S2352- 4642(20)30251- 0.
+
+[35] Ismail SA, Saliba V, Lopez Bernal JA, Ramsay ME, Ladhani SN. SARS- CoV- 2 infection and transmission in educational settings: cross- sectional analysis of clusters and outbreaks in England. medRxiv. 2020;doi:10.1101/2020.08.21.20178574.
+
+[36] Statistics Netherlands (CBS); 2020. Available from: https://www.cbs.nl.
+
+<--- Page Split --->
+
+[37] Li R, Pei S, Chen B, Song Y, Zhang T, Yang W, et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS- CoV- 2). Science. 2020;368(6490):489- 493. doi:10.1126/science.abb3221.
+
+[38] Champredon D, Dushoff J, Earn DJD. Equivalence of the Erlang- Distributed SEIR Epidemic Model and the Renewal Equation. SIAM Journal on Applied Mathematics. 2018;78(6):3258- 3278. doi:10.1137/18M1186411.
+
+[39] Diekmann O, Gyllenberg M, Metz JAJ. Finite Dimensional State Representation of Linear and Nonlinear Delay Systems. Journal of Dynamics and Differential Equations. 2018;30(4):1439- 1467. doi:10.1007/s10884- 017- 9611- 5.
+
+[40] Diekmann O, Heesterbeek H, Britton T. Mathematical Tools for Understanding Infectious Disease Dynamics. Princeton University Press; 2013.
+
+[41] van Boven M, Teirlinck AC, Meijer A, Hooiveld M, van Dorp CH, Reeves RM, et al. Estimating Transmission Parameters for Respiratory Syncytial Virus and Predicting the Impact of Maternal and Pediatric Vaccination. J Infect Dis. 2020;222(Supplement_7):S688- S694.
+
+[42] Rozhnova G, Kretzschmar ME, van der Klis F, van Baarle D, Kordewal M, Vossen AC, et al. Short- and long- term impact of vaccination against cytomegalovirus: a modeling study. BMC Med. 2020;18. doi:https://doi.org/10.1186/s12916- 020- 01629- 3.
+
+[43] Carpenter B, Gelman A, Hoffman M, Lee D, Goodrich B, Betancourt M, et al. Stan: A probabilistic programming language. J Stat Softw. 2017;76(1):1- 32. doi:10.18637/jss.v076.i01.
+
+[44] van den Driessche P, Watmough J. Reproduction numbers and sub- threshold endemic equilibria for compartmental models of disease transmission. Mathematical Biosciences. 2002;180:29- 48.
+
+[45] Diekmann O, Heesterbeek JAP, Roberts MG. The construction of next- generation matrices for compartmental epidemic models. Journal of The Royal Society Interface. 2010;7(47):873- 885. doi:10.1098/rsif.2009.0386.
+
+[46] Wallinga J, Lipsitch M. How generation intervals shape the relationship between growth rates and reproductive numbers. Proceedings of the Royal Society B: Biological Sciences. 2007;274(1609):599- 604. doi:10.1098/rspb.2006.3754.
+
+[47] Rozhnova G, van Dorp CH, Bruijning- Verhagen P, Bootsma MCJ, van de Wijgert JHHM, Bonten MJM, Kretzschmar ME. Model- based evaluation of school- and non- school- related measures to control the COVID- 19 pandemic. GitHub 2021. doi:10.5281/zenodo.4541431.
+
+[48] Vynnycky E, White R. An introduction to infectious disease modelling. Oxford: Oxford University Press; 2010.
+
+<--- Page Split --->
+
+[49] Rozhnova G, van der Loeff MFS, Heijne JCM, Kretzschmar ME. Impact of heterogeneity in sexual behavior on effectiveness in reducing HIV transmission with test- and- treat strategy. PLOS Computational Biology. 2016;12(8):e1005012. doi:10.1371/journal.pcbi.1005012.
+
+## Acknowledgements
+
+The contribution of C.H.v.D. was under the auspices of the US Department of Energy (contract number 89233218CNA000001) and supported by the National Institutes of Health (grant number R01- OD011095). M.E.K. was supported by ZonMw grant number 10430022010001, ZonMw grant number 91216062, and H2020 project 101003480 (CORESMA). M.J.M.B. and P.B.V. were supported by H2020 project 101003589 (RECOVER). G.R. was supported by FCT project 131_596787873. We thank Michiel van Boven (The National Institute of Public Health and the Environment, Bilthoven, The Netherlands) and Ana Nunes (Lisbon University) for valuable discussions and continuing advice during the course of this project. We thank João Viana for validating the Mathematica code. We thank Mui Pham and Alexandra Teslya for comments on the manuscript. We thank Eric Vos and Jantien Backer for the information on the serological and contact data used in this study.
+
+## Author contributions
+
+G.R. and C.H.v.D. developed the model with input from M.E.K, M.B. and P.B.V. G.R. and C.H.v.D. performed statistical inference and sensitivity analyses. G.R. implemented control measures, carried out all model analyses and prepared figures. M.E.K, M.C.J.B. and H.H.M.v.d.W. validated the model and analyses. G.R. conceived the study and drafted the first version of the manuscript. All authors contributed to analysis, interpretation of the results, writing the final version of the manuscript and gave final approval for publication.
+
+## Competing interests
+
+The authors declare no competing interests.
+
+## Supplementary Information
+
+Supplementary InformationSupplementary Information contains details of computation of the basic and effective reproduction numbers and Supplementary Figures.
+
+<--- Page Split --->
+
+## Correspondence
+
+Correspondence and material requests should be addressed to Dr. Ganna Rozhnova, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, P.O. Box 85500 Utrecht, The Netherlands; email: g.rozhnova@umcutrecht.nl.
+
+<--- Page Split --->
+
+## Figures
+
+
+
+Figure 1
+
+Estimated age- specific hospital admissions. The black lines represent the estimated medians. The dark gray lines correspond to \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution, and the shaded regions show \(95\%\) Bayesian prediction intervals. The dots are daily hospitalization admission data (all data points are included). Day 1 corresponds to 22 February 2020 which is 5 days prior to the first officially notified case in the Netherlands (27 February 2020). Panels a- h refer to different age groups.
+
+<--- Page Split --->
+
+
+Figure 2
+
+Estimated age- specific probability of hospitalization. The violin shapes represent the marginal posterior distribution for 2000 samples of the probability of hospitalization in the model.
+
+<--- Page Split --->
+
+
+Figure 3
+
+Estimated age- specific seroprevalence. The data (dots) are shown as the percentage of seropositive persons based on a seroprevalence survey that was conducted in April/May 2020. The number of positive and total samples defining this percentage for each age category is supplied in seroprevalence data file accompanying this study (see Data availability). The error bars represent the \(95\%\) confidence (Jeffreys) interval of the percentage. The violin shapes represent the marginal posterior distribution for 2000 samples of the percentage of seropositive persons in the model.
+
+<--- Page Split --->
+
+
+Figure 4
+
+Schematic timeline of the pandemic in the Netherlands during 2020. Outlined are times of the introduction and relaxation of control measures, and the estimated effective reproduction numbers for a - start of the pandemic (February 2020), b - full lockdown (April 2020), c - schools opening (August 2020), d - partial lockdown (November 2020). See Supplementary Figure 4 for the distributions of the reproduction numbers.
+
+
+
+Figure 5
+
+
+
+
+Impact of reduction of two types of contacts on the effective reproduction number in August 2020. Percentage reduction in a other (non- school- related) contacts in society in general and b school contacts,
+
+<--- Page Split --->
+
+with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in August 2020, when schools just opened in the Netherlands. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non- school- related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of Re (situation August 2020), the green line is the value of Re achieved for \(100\%\) reduction in contacts. The blue line indicates Re of 1. To control the pandemic, \(\mathrm{Re}< 1\) is necessary
+
+
+
+Figure 6
+
+Impact of reduction of two types of contacts on the effective reproduction number in November 2020. Percentage reduction in a other (non- school- related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in November 2020. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non- school- related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of Re (situation November 2020), the green line is the value of Re achieved for \(100\%\) reduction in contacts. To control the pandemic, \(\mathrm{Re}< 1\) is necessary.
+
+![PLACEHOLDER_30_1]
+
+
+<--- Page Split --->
+
+## Figure 7
+
+Impact of reduction of school contacts in different age groups on the effective reproduction number in November 2020. Percentage reduction in school contacts among a [0, 5) years old, b [5, 10) years old and c [10, 20) years old. In each panel, we varied the number of school contacts in one age group while keeping the number of school contacts in the other two age groups constant. The scenario with \(0\%\) reduction describes the situation in November 2020 with Re of about 1 (partial lockdown intended to prevent the second wave), where all schools are open without substantial additional measures. The reduction of \(100\%\) in school contacts represents a scenario with the structure of non- school contacts in society in general as in November 2020 and schools for students in a given age group closed. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(\mathrm{Re} = 1\) (situation November 2020). The green line indicates the value of Re achieved when schools for a given age group close.
+
+<--- Page Split --->
+![PLACEHOLDER_32_0]
+
+Figure 8
+
+Transmission model. A Model schematic. Black arrows show epidemiological transitions. Red arrows indicate the compartments contributing to the force of infection. Susceptible persons in age group k (Sk), where \(k = 1, \ldots , n\) , become latently infected (Ek) via contact with infectious persons in m infectious stages (lk,p, \(p = 1, \ldots , m\) ) at a rate \(\beta k \lambda k\) , where \(\lambda k\) is the force of infection, and \(\beta k\) is the reduction in susceptibility to infection of persons in age group k compared to persons in age group n. Exposed
+
+<--- Page Split --->
+
+persons (Ek) become infectious (lk,1) at rate a. Infectious persons progress through (m - 1) infectious stages at rate ym, after which they recover (Rk). From each stage, infectious persons are hospitalized at rate vk. Table 1 gives the summary of the model parameters. b- d Contact rates. b and c show contact rates in all locations before the pandemic and after the first lockdown (April 2020), respectively; d shows contact rates at schools before the pandemic. The color represents the average number of contacts per day a person in a given age group had with persons in another age group.
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+SupplementaryInformation.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea_det.mmd b/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..568661a9f6769721887f79bc40331529cc2ac1fe
--- /dev/null
+++ b/preprint/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea/preprint__04dc445c7109b231b73bcd67d3ce9dd0dbe3bee0c9a2a2917e8fecd991b3d3ea_det.mmd
@@ -0,0 +1,623 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 953, 175]]<|/det|>
+# Model-based evaluation of school- and non-school-related measures to control the COVID-19 pandemic
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 700, 238]]<|/det|>
+Ganna Rozhnova ( g.rozhnova@umcutrecht.nl ) University Medical Center Utrecht https://orcid.org/0000- 0002- 6725- 7359
+
+<|ref|>text<|/ref|><|det|>[[45, 243, 339, 283]]<|/det|>
+Christiaan van Dorp Los Alamos National Laboratory
+
+<|ref|>text<|/ref|><|det|>[[44, 290, 525, 330]]<|/det|>
+Patricia Bruijning- Verhagen UMC Utrecht https://orcid.org/0000- 0003- 4105- 9669
+
+<|ref|>text<|/ref|><|det|>[[44, 336, 702, 377]]<|/det|>
+Martin Bootsma University Medical Center Utrecht https://orcid.org/0000- 0003- 3005- 0255
+
+<|ref|>text<|/ref|><|det|>[[44, 382, 702, 423]]<|/det|>
+Janneke van de Wijgert University Medical Center Utrecht https://orcid.org/0000- 0003- 2728- 4560
+
+<|ref|>text<|/ref|><|det|>[[44, 428, 416, 468]]<|/det|>
+Marc J. M. Bonten University Medical Center Utrecht (UMCU)
+
+<|ref|>text<|/ref|><|det|>[[44, 474, 525, 515]]<|/det|>
+Mirjam Kretzschmar UMC Utrecht https://orcid.org/0000- 0002- 4394- 7697
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 558, 102, 575]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 594, 930, 637]]<|/det|>
+Keywords: SARS- CoV- 2, epidemiology, school- based contacts, age- structured transmission model, age- specific seroprevalence, hospital admission data
+
+<|ref|>text<|/ref|><|det|>[[44, 655, 312, 674]]<|/det|>
+Posted Date: March 29th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 693, 463, 712]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 130264/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 730, 911, 773]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 809, 925, 852]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on March 12th, 2021. See the published version at https://doi.org/10.1038/s41467- 021- 21899- 6.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[101, 133, 895, 204]]<|/det|>
+# Model-based evaluation of school- and non-school-related measures to control the COVID-19 pandemic
+
+<|ref|>text<|/ref|><|det|>[[101, 230, 895, 312]]<|/det|>
+Ganna Rozhnova, \(\mathrm{PhD}^{*1,2}\) , Christiaan H. van Dorp, \(\mathrm{PhD}^3\) , Patricia Bruijning- Verhagen, MD \(\mathrm{PhD}^1\) , Martin C.J. Bootsma, \(\mathrm{PhD}^{1,4}\) , Prof Janneke H.H.M. van de Wijgert, MD \(\mathrm{PhD}\) MPH \(^{1,5}\) , Prof Marc J.M. Bonten, MD \(\mathrm{PhD}^{1,6}\) , and Prof Mirjam E. Kretzschmar, \(\mathrm{PhD}^1\)
+
+<|ref|>text<|/ref|><|det|>[[90, 333, 907, 650]]<|/det|>
+1 Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands 2 BioISI—Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal 3 Theoretical Biology and Biophysics (T- 6), Los Alamos National Laboratory, Los Alamos, New Mexico, USA 4 Mathematical Institute, Utrecht University, Utrecht, The Netherlands 5 The Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK 6 Department of Medical Microbiology, University Medical Center Utrecht, Utrecht University, The Netherlands
+
+<|ref|>text<|/ref|><|det|>[[421, 680, 574, 698]]<|/det|>
+February 19, 2021
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[464, 71, 532, 85]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[128, 100, 870, 325]]<|/det|>
+The role of school- based contacts in the epidemiology of SARS- CoV- 2 is incompletely understood. We use an age- structured transmission model fitted to age- specific seroprevalence and hospital admission data to assess the effects of school- based measures at different time points during the COVID- 19 pandemic in the Netherlands. Our analyses suggest that the impact of measures reducing school- based contacts depends on the remaining opportunities to reduce non- school- based contacts. If opportunities to reduce the effective reproduction number \((R_{e})\) with non- school- based measures are exhausted or undesired and \(R_{e}\) is still close to 1, the additional benefit of school- based measures may be considerable, particularly among older school children. As two examples, we demonstrate that keeping schools closed after the summer holidays in 2020, in the absence of other measures, would not have prevented the second pandemic wave in autumn 2020 but closing schools in November 2020 could have reduced \(R_{e}\) below 1, with unchanged non- school- based contacts.
+
+<|ref|>sub_title<|/ref|><|det|>[[66, 360, 238, 380]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[65, 400, 912, 924]]<|/det|>
+In autumn 2020, many countries, including the Netherlands, are experiencing a second wave of the COVID- 19 pandemic [1]. During the first wave in spring 2020, general population- based control measures were introduced in the Netherlands, which involved physical distancing (including refraining from hand- shaking), frequent hand- washing and other hygiene measures, and self- quarantine when symptomatic. In addition, many public places and schools were closed. These contact reduction measures were relaxed starting from May, and the incidence of COVID- 19 started to increase again at the end of July [1]. From the end of August onwards, contact reduction measures were intensified in a step- wise manner. Schools closed during July and August for summer break, reopened at the end of August, and have remained open until 16 December, with the exception of a one- week autumn break. Some measures were implemented in schools after the summer break to reduce transmission. Students and teachers in secondary schools have to wear masks when not seated at their desks, and students have to keep distance from teachers. A student with cold- or flu- like symptoms has to stay at home. The step- wise increase in control measures after the summer started with earlier closing times of bars and restaurants, reinforcement of working at home (in September), followed by closure of all bars and restaurants, theaters, cinemas and other cultural meeting places in November and obligatory mask wearing in all public places since December 1. According to the National Institute for Public Health and the Environment (RIVM), estimated effective reproduction numbers \((R_{e})\) for the Netherlands were about 1.3 in the period 27 August- 6 September and about 1.0 in the period 7- 13 November [1]. The aim of measures implemented by the government in autumn 2020 was to reduce \(R_{e}\) to 0.8. The failure to achieve this might be due to reduced societal acceptance of control measures, and/or due to the lack of school closure. The role of children and their contacts during school hours in the spread of SARS- CoV- 2 is in fact not well understood [2,3]. In this study, we explored this role with a mathematical model fitted to COVID- 19 data from the Netherlands.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[62, 66, 912, 191]]<|/det|>
+Closure of schools is considered an effective strategy to contain an influenza pandemic [4], based on both model calculations and observational studies of the influence of school holidays on the spread of influenza [5, 6]. The reasons for this are the high contact rates in young age groups [7] and the susceptibility of children and young people to the influenza virus. In contrast to influenza, children seem to be less susceptible to SARS- CoV- 2 than adults and, based on sparse data, the susceptibility to SARS- CoV- 2 increases with age [8, 9].
+
+<|ref|>text<|/ref|><|det|>[[62, 195, 912, 390]]<|/det|>
+In the absence of empirical SARS- CoV- 2 data, mathematical modeling can help to quantify the role of different age groups in the distribution of SARS- CoV- 2 in the population [10, 11], and to evaluate the impact of interventions on transmission [12- 17]. Such models can help to estimate the reduction in the effective reproduction number for different contact- reduction scenarios within or outside school environments. Model predictions about the relative epidemic impacts of school- and non- school- based measures can assist policymakers in selecting combinations of measures during different stages of the pandemic that optimally balance potential harms and benefits. Predictions generated by models that include differences in susceptibility and contact rates in different age groups can also aid in deciding which school age groups should be the primary target of school- based interventions.
+
+<|ref|>text<|/ref|><|det|>[[62, 395, 912, 716]]<|/det|>
+We used an age- structured transmission model fitted in a Bayesian framework to age- specific hospital admission data (27 February—30 April 2020) and cross- sectional age- specific seroprevalence data (April/May 2020) [18] to evaluate the effects of control measures aimed at reducing school and other (non- school- related) contacts in society in general at different time points during the COVID- 19 pandemic in the Netherlands. The model makes use of age- specific contacts rates before and after the first lockdown [19] and contact rates in schools [7, 20], and accounts for different susceptibility to SARS- CoV- 2 among younger, middle- aged, and older persons. Using the model equipped with parameter estimates, we provide a comparative study of the impact of school- and non- school- related measures on the effective reproduction number in August 2020, before the most recent set of measures was implemented, and in November 2020, when the most recent measures were still in place. In particular, we assess whether keeping schools closed after the summer holidays in 2020 would have prevented the second pandemic wave in the autumn and whether closing schools in November 2020 could have helped to achieve the control of the pandemic. We quantify reductions in \(R_{e}\) due to closing schools for different ages and make recommendations on which school ages should be targeted to design effective school- based interventions.
+
+<|ref|>sub_title<|/ref|><|det|>[[66, 752, 178, 771]]<|/det|>
+## 60 Results
+
+<|ref|>sub_title<|/ref|><|det|>[[66, 796, 280, 814]]<|/det|>
+## 61 Epidemic dynamics
+
+<|ref|>text<|/ref|><|det|>[[66, 830, 911, 924]]<|/det|>
+The model shows a very good agreement between the estimated age- specific hospitalizations and the data (Figure 1). The number of hospitalizations increases with age, with the highest peaks in hospitalizations observed in persons above 60 years old. The estimated probability of hospitalization increases nearly exponentially with age (as shown by an approximately linear relationship on the logarithmic scale, Figure 2), except for persons under 30 years old,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[63, 68, 909, 137]]<|/det|>
+in whom the number of hospitalizations was low. The estimated probability of hospitalization increased from \(0.09\%\) (95%CrI 0.05—0.15%) in persons under 20 years old to \(4.37\%\) (95%CrI 2.80—8.82%) in persons older than 80 years (Supplementary Figure 2).
+
+<|ref|>image<|/ref|><|det|>[[87, 165, 912, 456]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 482, 910, 560]]<|/det|>
+Figure 1. Estimated age-specific hospital admissions. The black lines represent the estimated medians. The dark gray lines correspond to \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution, and the shaded regions show \(95\%\) Bayesian prediction intervals. The dots are daily hospitalization admission data (all data points are included). Day 1 corresponds to 22 February 2020 which is 5 days prior to the first officially notified case in the Netherlands (27 February 2020). Panels a-h refer to different age groups.
+
+<|ref|>image<|/ref|><|det|>[[290, 604, 700, 875]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 891, 904, 923]]<|/det|>
+Figure 2. Estimated age-specific probability of hospitalization. The violin shapes represent the marginal posterior distribution for 2000 samples of the probability of hospitalization in the model.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[288, 85, 700, 368]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 386, 911, 479]]<|/det|>
+Figure 3. Estimated age-specific seroprevalence. The data (dots) are shown as the percentage of seropositive persons based on a seroprevalence survey that was conducted in April/May 2020. The number of positive and total samples defining this percentage for each age category is supplied in seroprevalence data file accompanying this study (see Data availability). The error bars represent the 95% confidence (Jeffreys) interval of the percentage. The violin shapes represent the marginal posterior distribution for 2000 samples of the percentage of seropositive persons in the model.
+
+<|ref|>text<|/ref|><|det|>[[61, 501, 911, 644]]<|/det|>
+The model accurately reproduces the percentage of seropositive persons distributed across the age groups (Figure 3). The median seroprevalence in the population was \(2.7\%\) , with the maximum seroprevalence observed in persons between 20 and 40 years old (about \(3.5\%\) ). The lowest seroprevalence was among children in the 0 to 10 years age group ( \(0.9\%\) ). Note that if our model did not include age- dependence of susceptibility to SARS- CoV- 2, the seroprevalence peak would be expected among children because they have the largest numbers of contacts in the population.
+
+<|ref|>text<|/ref|><|det|>[[61, 653, 911, 821]]<|/det|>
+The estimated probability of transmission per contact was 0.07 ( \(95\%\) CrI 0.05—0.12) before the first lockdown and it decreased by \(48.84\%\) ( \(95\%\) CrI 23.81—87.44%) after the first lockdown. The reduction in susceptibility relative to susceptibility in persons above 60 years old was \(23\%\) ( \(95\%\) CrI 20—28%) in persons under 20 years old and \(61\%\) ( \(95\%\) CrI 50—72%) for persons between 20 and 60 years old (Supplementary Figure 3). The estimated basic reproduction number was 2.71 ( \(95\%\) CrI 2.15—5.18) in the absence of control measures (February 2020) (Supplementary Figure 4 a), and dropped to 0.62 ( \(95\%\) CrI 0.29—0.74) after the full lockdown (April 2020) (Supplementary Figure 4 b). Supplementary Figures 1,2, 3, and 4 show an overview of all parameter estimates.
+
+<|ref|>text<|/ref|><|det|>[[61, 830, 911, 923]]<|/det|>
+The joint posterior density of the estimated parameters reveals strong positive and negative correlations between some of the parameters (Supplementary Figure 5). For instance, the initial fraction of infected individuals is negatively correlated with the probability of transmission per contact and the hospitalization rate, as a small initial density can be compensated by a faster growth rate or a larger hospitalization rate. For that reason, the age- specific
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[63, 68, 910, 137]]<|/det|>
+hospitalization rates are all positively correlated. These correlations highlight the necessity of complementing the hospitalization time series data with seroprevalence data, even if the sample size of the latter is small. Without the seroprevalence data many parameters would be difficult to identify.
+
+<|ref|>image<|/ref|><|det|>[[80, 163, 910, 504]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 526, 910, 589]]<|/det|>
+Figure 4. Schematic timeline of the pandemic in the Netherlands during 2020. Outlined are times of the introduction and relaxation of control measures, and the estimated effective reproduction numbers for a - start of the pandemic (February 2020), b - full lockdown (April 2020), c - schools opening (August 2020), d - partial lockdown (November 2020). See Supplementary Figure 4 for the distributions of the reproduction numbers.
+
+<|ref|>sub_title<|/ref|><|det|>[[62, 634, 463, 652]]<|/det|>
+## School and non-school-based measures
+
+<|ref|>text<|/ref|><|det|>[[62, 667, 911, 840]]<|/det|>
+The sequence of measures implemented and lifted during the pandemic in the Netherlands and the respective estimated values of the effective reproduction numbers are shown schematically in Figure 4. We used the fitted model to separately determine the effect on the effective reproduction number of decreasing contacts in schools and of decreasing other (non- school- related) contacts in society in general in August 2020 (Figure 5) and in November 2020 (Figure 6). In doing so, we varied one type of contact and kept the other type constant. For each scenario, the reduction in contact rate was varied between \(0\%\) and \(100\%\) . The aim of reducing the number of contacts of each type is to decrease the effective reproduction number below 1.
+
+<|ref|>text<|/ref|><|det|>[[62, 846, 910, 912]]<|/det|>
+We first considered the situation in August 2020 (Figure 5), when schools had just opened after the summer holidays and when control measures in the population were less stringent than in April (full lockdown). Between August and December 2020, the only infection prevention measure in primary schools was the advice to teachers and pupils to
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 70, 911, 264]]<|/det|>
+stay at home in case of symptoms or a household member diagnosed with SARS- CoV- 2 infection; physical distancing between teachers and pupils (but not between pupils) only applied to secondary schools. We therefore assumed that the effective number of contacts in schools was the same as before the pandemic. For other (non- school- related) contacts in society in general we assumed that 1) the number of contacts increased after April 2020 (full lockdown) but was lower than before the pandemic, and that 2) reduction in probability of transmission per contact due to mask- wearing and hygiene measures was lower in August as compared to April (due to decreased adherence to measures). The starting point of our analyses is an effective reproduction number of 1.31 (95%CrI 1.15—2.07) in accordance with the state of the Dutch pandemic in August 2020 (Supplementary Figure 4 c).
+
+<|ref|>text<|/ref|><|det|>[[58, 270, 911, 440]]<|/det|>
+Figure 5 a demonstrates that in August 2020 other contacts in society in general would have to be reduced by at about \(60\%\) to bring the effective reproduction number to 1 (if school- related contacts do not change). A \(100\%\) reduction would resemble the number of contacts in April (full lockdown) and would bring the effective reproduction number to 0.83 (95%CrI 0.75—1.10). Figure 5 b demonstrates that reductions of school contacts would have a limited impact on the effective reproduction number (if non- school contacts do not change). A \(100\%\) reduction (complete closure of schools) would have reduced the effective reproduction number by only \(10\%\) (from 1.31 to 1.18 (95%CrI 1.04—1.83)).
+
+<|ref|>image<|/ref|><|det|>[[100, 467, 884, 696]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 710, 908, 863]]<|/det|>
+Figure 5. Impact of reduction of two types of contacts on the effective reproduction number in August 2020. Percentage reduction in a other (non-school-related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in August 2020, when schools just opened in the Netherlands. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non-school-related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(R_{e}\) (situation August 2020), the green line is the value of \(R_{e}\) achieved for \(100\%\) reduction in contacts. The blue line indicates \(R_{e}\) of 1. To control the pandemic, \(R_{e}< 1\) is necessary.
+
+<|ref|>text<|/ref|><|det|>[[60, 888, 909, 930]]<|/det|>
+Subsequently, we considered the Dutch pandemic situation in November 2020 (Figure 6), when the measures implemented since the end of August (partial lockdown intended to prevent the second wave) had led to an effective
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 70, 910, 238]]<|/det|>
+reproduction number of 1.00 (95%CrI 0.94—1.33) (Supplementary Figure 4 d), and, as described above, only limited control measures were taken in schools. Now, the impact of interventions targeted at reducing school contacts (Figure 6 b) would reduce the effective reproduction number similarly as reducing non- school contacts in the rest of the population (Figure 6 a). Specifically, closing schools would reduce the effective reproduction number by 16% (from 1.0 to 0.84 (95%CrI 0.81—0.90)) (Figure 6 b). Almost the same \(R_{e} = 0.83\) (95%CrI 0.75—1.10), would have been achieved by reducing non- school- related contacts to the level of April 2020 while the schools remain open (Figure 6 a).
+
+<|ref|>image<|/ref|><|det|>[[100, 265, 884, 491]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 507, 908, 644]]<|/det|>
+Figure 6. Impact of reduction of two types of contacts on the effective reproduction number in November 2020. Percentage reduction in a other (non-school-related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in November 2020. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non-school-related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(R_{e}\) (situation November 2020), the green line is the value of \(R_{e}\) achieved for \(100\%\) reduction in contacts. To control the pandemic, \(R_{e}< 1\) is necessary.
+
+<|ref|>sub_title<|/ref|><|det|>[[57, 689, 455, 707]]<|/det|>
+## Interventions for different school ages
+
+<|ref|>text<|/ref|><|det|>[[57, 723, 911, 917]]<|/det|>
+Next we investigated the impact of targeting interventions at different age groups, starting from the situation in November 2020 with the effective reproduction number being 1 (Supplementary Figure 4 d). Figure 7 a, b, and c show \(R_{e}\) as a function of the reduction of school contacts in age groups of [0,5), [5,10) and [10,20) y.o., respectively. In each panel, we varied the number of school contacts in one age group while keeping the number of school contacts in the other two age groups constant. \(0\%\) reduction corresponds to the situation in November 2020, and \(100\%\) reduction represents a scenario with schools for students in a given age group closed. The model predicts a maximum impact on \(R_{e}\) from reducing contacts of 10 to 20 year old children (Figure 7 c). Closing schools for this age group only could decrease \(R_{e}\) by about \(8\%\) (compare Figure 7 c and Figure 6 b where we expect the reduction
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[100, 85, 890, 250]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 266, 904, 433]]<|/det|>
+Figure 7. Impact of reduction of school contacts in different age groups on the effective reproduction number in November 2020. Percentage reduction in school contacts among a \([0,5)\) years old, b [5, 10) years old and c [10, 20) years old. In each panel, we varied the number of school contacts in one age group while keeping the number of school contacts in the other two age groups constant. The scenario with \(0\%\) reduction describes the situation in November 2020 with \(R_{e}\) of about 1 (partial lockdown intended to prevent the second wave), where all schools are open without substantial additional measures. The reduction of \(100\%\) in school contacts represents a scenario with the structure of non-school contacts in society in general as in November 2020 and schools for students in a given age group closed. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(R_{e} = 1\) (situation November 2020). The green line indicates the value of \(R_{e}\) achieved when schools for a given age group close.
+
+<|ref|>text<|/ref|><|det|>[[60, 456, 908, 499]]<|/det|>
+of \(16\%\) after closing schools for all ages). School closure for children aged 5 to 10 years would reduce \(R_{e}\) by about \(5\%\) (Figure 7 b). Contact reductions among 0 to 5 year old children would have a negligible impact on \(R_{e}\) as shown in Figure 7 a.
+
+<|ref|>text<|/ref|><|det|>[[60, 525, 208, 543]]<|/det|>
+in Figure 7 a.
+
+<|ref|>sub_title<|/ref|><|det|>[[60, 560, 212, 581]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[60, 601, 911, 901]]<|/det|>
+We used an age- structured model for SARS- CoV- 2 fitted to hospital admission and seroprevalence data during spring 2020 to estimate the impact of school contacts on transmission of SARS- CoV- 2 and to assess the effects of school- based measures, including school closure, to mitigate the second wave in the autumn of 2020. We demonstrate how the relative impact of school- based measures aimed at reduction of contacts at schools on the effective reproduction number increases when the effects of non- school- based measures appear to be insufficient. These findings underscore the dilemma for policymakers of choosing between stronger enforcement of population- wide measures to reduce contacts in society in general or measures that reduce school- based contacts, including complete closure of schools. For the latter choice, our model predicts highest impact from measures implemented for the oldest school ages. We used the Netherlands as a case example but our model code is freely available and can be readily adapted to other countries given the availability of hospitalization and seroprevalence data. The findings in our manuscript can be relevant for guiding policy decisions in the Netherlands, but also in countries where the contact structure in the population is similar to that of the Netherlands [7].
+
+<|ref|>text<|/ref|><|det|>[[66, 904, 907, 923]]<|/det|>
+Our model integrates prior knowledge of epidemiological parameters and the quantitative assessment of the model
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[75, 70, 911, 592]]<|/det|>
+uncertainties in a Bayesian framework. To our knowledge, our modeling study is the first that uses this method to address the role of school- based contacts in the transmission of SARS- CoV- 2. Previous studies (e.g. [21- 25]) used individual- based or network models, that were not fit to epidemiological data using formal statistical procedures. Due to uncertainties in key model parameters, predictions of these models vary widely. Our model has been carefully validated to achieve an excellent fit to data of daily hospitalizations due to COVID- 19 and seroprevalence by age. Furthermore, reproduction numbers at different time points of the pandemic correlated well with estimates obtained from independent sources [1]. In addition, the Netherlands is one of few countries in the world for which the contact rate after the first lockdown is available (see [26] for the UK). We could, therefore, model the contact structure during the course of the pandemic as continuously changing between the contact structure before the pandemic and the contact structure when the measures were the most strict (first lockdown) without making additional assumptions about the impact of specific interventions on contacts in different age groups. Crucially, many prior models evaluating the impact of school- based contacts assumed age- independent susceptibility to infection with SARS- CoV- 2 (e.g. [13,23]). Here, we estimated susceptibility to infection with SARS- CoV- 2 to increase with age, which corroborates published findings from cohort studies [8,9]. Compared to adults older than 60 years, the estimated susceptibility was about 20% for children aged 0 to 20 years and about 60% for the age group of 20 to 60 years. However, even with extensive validation, we need to be careful when interpreting the predictions of our model as these depend on the sensitivity of serology to identify individuals with prior infection. Recent studies suggest that in persons who experience mild or asymptomatic infections, SARS- CoV- 2 antibodies may not always be detectable post- infection [27,28]. Therefore, more children may have had an infection than indicated by the seroprevalence survey because the proportion of asymptomatic in children is believed to be high. As a consequence, our study potentially underestimates the role of children in transmission.
+
+<|ref|>text<|/ref|><|det|>[[70, 597, 911, 919]]<|/det|>
+Naturally, our findings result from age- related differences in disease susceptibility and contact structure. Despite high numbers of contacts for children of all ages, and in particular in the age group of 10 to 20 years old, closing schools appeared to have much less impact on the effective reproduction number than contact reduction measures outside the school environment. In fact, measures effectively reducing non- school contacts, similar to those measures implemented in response to the first pandemic wave in spring 2020, could have prevented a second wave in autumn without school closures. With an estimated effective reproduction number of 1.3 in August 2020, continuation of school closures would have had much lower effects than measures aiming to reduce non- school- related contacts, which mainly occur in the adult population. Yet, that situation changes if the proposed measures fail. In November 2020, the measures implemented since August had reduced the effective reproduction number to around 1, instead of achieving the target value of about 0.8. In that situation, as our findings demonstrate, additional physical distancing measures in schools could assist in reducing the effective reproduction number further, in particular when implemented in secondary schools. Our analyses suggest that physical distancing measures in the youngest children will have no impact on the control of SARS- CoV- 2 infection. Of note, better adherence to non- school- based
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 70, 625, 87]]<|/det|>
+measures would still have similar effects as reducing school- based contacts.
+
+<|ref|>text<|/ref|><|det|>[[58, 94, 911, 212]]<|/det|>
+Although there are several options for reducing the number of contacts between children at school, such as staggered start and end times and breaks, different forms of physical distancing for pupils and division of classes, the effects of such measures on transmission among children have not been quantified. Importantly, we have assumed that reductions in school- based contacts are not replaced by non- school- based contacts (among children and between children and adults) with similar transmission risk.
+
+<|ref|>text<|/ref|><|det|>[[58, 218, 911, 590]]<|/det|>
+Our modelling approach has several limitations. For estimating disease susceptibility we could only model children as a group of 0 to 20 years old. As disease susceptibility increases with age, it seems obvious that effects of reduced school contacts are most prominent in older children. Assuming equal susceptibility across these ages may have underestimated to some extent the effect of reducing school contacts for children between 10 and 20 years. At the same time, we assumed that school contact patterns in August- November 2020 reflect the pre- pandemic situation. Yet, general control measures in the Netherlands such as stay at home orders for symptomatic persons probably lower infectious contacts in school settings too, meaning that some reduction compared to pre- pandemic levels of contacts could already be present in schools. Effects of these measures in school settings should be smaller than in the general population and are hard to estimate due to a large number of asymptomatic cases among children, and therefore were not taken into account. In this respect, the results reported here describe the maximum possible reduction in the effective reproduction number due to school interventions. Furthermore, the contact matrices available did not allow differentiation between various types of contacts outside schools (like work, leisure, transport etc.), as these were not available for periods during the pandemic. Therefore, we could not model the impact of reducing work- related or leisure- related contacts separately. We also could not include hospitalization data from the second wave of the pandemic due to lack of data availability.
+
+<|ref|>text<|/ref|><|det|>[[58, 597, 911, 918]]<|/det|>
+The potential effects of opening or closing schools in different phases of the pandemic have been reported in other studies [13,21- 24,29,30]. Also based on a mathematical model, Panovska- Griffiths et al. [21] predicted that without very high levels of testing and contact tracing reopening schools after summer with a simultaneous relaxation of measures will lead to a second wave in the United Kingdom, peaking in December 2020. Their model predicted that this peak could be postponed for two months (to February 2021) by a rotating timetable in schools. Very early in the pandemic, in March 2020, the Scientific Advisory Group for Emergencies in the United Kingdom concluded that it would not be possible to reduce the effective reproduction number below 1 without closing schools [29]. In a modelling study on the impact of non- pharmaceutical interventions for COVID- 19 in the United Kingdom, Davies et al. found that the impact of school closures was low [13]. In another modeling study Rice et al. [24] found that school closures during the first wave of the pandemic could increase overall mortality, due to death being postponed to a second and subsequent waves. And based on an analysis of the impact of non- pharmaceutical measures in 41 countries between January and May 2020, Brauner et al. [30] concluded that closure of schools and universities had contributed the most to lowering the effective reproduction number. Yet, a major difficulty in estimating the effect
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 68, 912, 290]]<|/det|>
+of school closure using observational data from the first wave is that other non- pharmaceutical interventions were implemented at or around the same time as school closures [31]. Similarly, lifting such measures often coincided with school re- openings. Observational data from the period after the first wave show conflicting results on within school transmission [32- 35] and the effect of school reopening and interpretation is further hampered by the variety in control measures implemented in schools across countries. Finally, Munday et al. showed that reopening secondary schools is likely to have a greater impact on community transmission than reopening primary schools in England [22]. While the modelling approach of [22] is different from ours, our findings are similar in the sense that secondary schools are predicted to make a larger contribution to transmission than primary schools, and are therefore more important for controlling COVID- 19.
+
+<|ref|>text<|/ref|><|det|>[[57, 295, 912, 465]]<|/det|>
+In conclusion, we have demonstrated that the potential effects of school- based measures to reduce contacts between children, including school closures, markedly depends on the reduction in the effective reproduction number achieved by other measures. With remaining opportunities to reduce the effective reproduction number with non- school- based measures, the additional benefit of school- based measures is low. Yet, if opportunities to reduce the effective reproduction number with non- school- based measures are considered to be exhausted or undesired for economic reasons and \(R_{e}\) is still close to 1, the additional benefit of school- based measures may be considerable. In such situations, the biggest impact on transmission is achieved by reducing contacts in secondary schools.
+
+<|ref|>sub_title<|/ref|><|det|>[[57, 500, 194, 520]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[57, 544, 182, 561]]<|/det|>
+## Overview
+
+<|ref|>text<|/ref|><|det|>[[57, 578, 912, 696]]<|/det|>
+Estimates of epidemiological parameters were obtained by fitting a transmission model to age- stratified COVID- 19 hospital admission data in the period from 27 February till 30 April 2020 ( \(n = 10,961\) ) and cross- sectional age- stratified SARS- CoV- 2 seroprevalence data assessed in April/May 2020 ( \(n = 3,207\) ) [18]. The model equipped with parameter estimates was subsequently used to investigate the impact of school- and non- school- based measures on controlling the pandemic.
+
+<|ref|>sub_title<|/ref|><|det|>[[57, 727, 140, 743]]<|/det|>
+## Data
+
+<|ref|>text<|/ref|><|det|>[[57, 759, 912, 904]]<|/det|>
+The hospital data included \(n = 10,961\) COVID- 19 hospitalizations by date of admission and stratified by age during the period of 64 days following the first official case in the Netherlands (27 February 2020). The criteria for hospital admission have not changed during the pandemic, and from the early stages all hospitalized patients with a clinical suspicion of COVID- 19 were tested by RT- PCR. In all stages of the pandemic, patients requiring hospital admission were hospitalized and the practice of not referring patients for hospital admission (e.g. due to self- expressed treatment restrictions or moribund condition) did not change.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 68, 911, 313]]<|/det|>
+The SARS- CoV- 2 seroprevalence data was taken from a cross- sectional population- based serological study carried out in April/May 2020 (PIENTER Corona study) [18]. Participants for the serosurvey were enrolled from a previously established nationwide serosurveillance study, provided a self- collected fingerstick blood sample and completed a questionnaire. A total of 40 municipalities were randomly selected, with probabilities proportional to their population size. From these municipalities, an age- stratified sample was drawn from the population register, and 6, 102 persons were invited to participate. Serum samples and questionnaires were obtained from 3, 207 participants and included in the analyses. The majority of blood samples were drawn in the first week of April. IgG antibodies targeted against the spike S1- protein of SARS- CoV- 2 were quantified using a validated multiplex- immunoassay. Seroprevalence was estimated controlling for survey design, individual pre- pandemic concentration, and test performance.
+
+<|ref|>text<|/ref|><|det|>[[58, 321, 911, 466]]<|/det|>
+Our analyses made use of the demographic composition of the Dutch population in July 2020 from Statistics Netherlands [36] and age- stratified contact data for the Netherlands [19,20]. The contact rates before the pandemic were based on a cross- sectional survey carried out in 2016/2017, where participants reported the number and age of their contacts during the previous day [19]. The contact rates after the first lockdown were based on the same survey which was repeated in a sub- sample of the participants in April 2020 (PIENTER Corona study) [19]. School- specific contact rates for the Dutch population before the pandemic were taken from the POLYMOD study [7,20].
+
+<|ref|>sub_title<|/ref|><|det|>[[60, 494, 283, 511]]<|/det|>
+## Transmission model
+
+<|ref|>text<|/ref|><|det|>[[58, 525, 911, 923]]<|/det|>
+We used a deterministic compartmental model describing SARS- CoV- 2 transmission in the population of the Netherlands stratified by infection status and age (Figure 8 a). Some modeling studies on the impact of interventions against COVID- 19 account for spatial variations of the disease [16,17,37]. Since the available data is aggregated on the country level and for the sake of the model's tractability, we disregarded regional stratification of the population. The dynamics of the model follows the Susceptible- Exposed- Infectious- Recovered structure. Persons in age group \(k\) , where \(k = 1,\ldots ,n\) , are classified as susceptible \((S_{k})\) , infected but not yet infectious (exposed, \(E_{k}\) ), infectious in \(m\) stages \((I_{k,p}\) , where \(p = 1,\ldots ,m\) ), hospitalized \((H_{k})\) and recovered without hospitalization \((R_{k})\) . Susceptible persons \((S_{k})\) can acquire infection via contact with infectious persons \((I_{k,p}\) , \(k = 1,\ldots ,n\) , \(p = 1,\ldots ,m\) ) and become latently infected \((E_{k})\) at a rate \(\beta_{k}\lambda_{k}\) , where \(\lambda_{k}\) is the force of infection, and \(\beta_{k}\) is the reduction in susceptibility to infection of persons in age group \(k\) compared to persons in age group \(n\) . Persons in the classes \((I_{k,p}\) , \(k = 1,\ldots ,n\) , \(p = 1,\ldots ,m\) ) are assumed to be equally infectious. After the latent period (duration \(1 / \alpha\) days), exposed persons become infectious \((I_{k,1})\) . Infectious persons progress through \((m - 1)\) stages of infection \((I_{k,p}\) , where \(p = 2,\ldots ,m\) ) at rate \(\gamma m\) , after which they recover \((R_{k})\) . Inclusion of \(m\) identical infectious stages allows for the tuning of the distribution of the infectious period (the time spent in the infectious compartments, \(I_{k,p}\) , \(p = 1,\ldots ,m\) ) [38,39], interpolating between an exponentially distributed infectious period \((m = 1)\) and a fixed infectious period \((m\rightarrow \infty)\) . Intermediate values of \(m\) correspond to an Erlang- distributed infectious period with mean \(1 / \gamma\) and standard de
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[190, 124, 808, 718]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[88, 719, 907, 886]]<|/det|>
+Figure 8. Transmission model. a Model schematic. Black arrows show epidemiological transitions. Red arrows indicate the compartments contributing to the force of infection. Susceptible persons in age group \(k\) \((S_{k})\) , where \(k = 1,\ldots ,n\) , become latently infected \((E_{k})\) via contact with infectious persons in \(m\) infectious stages \((I_{k,p}\) \(p = 1,\ldots ,m)\) at a rate \(\beta_{k}\lambda_{k}\) , where \(\lambda_{k}\) is the force of infection, and \(\beta_{k}\) is the reduction in susceptibility to infection of persons in age group \(k\) compared to persons in age group \(n\) . Exposed persons \((E_{k})\) become infectious \((I_{k,1})\) at rate \(\alpha\) . Infectious persons progress through \((m - 1)\) infectious stages at rate \(\gamma m\) , after which they recover \((R_{k})\) . From each stage, infectious persons are hospitalized at rate \(\nu_{k}\) . Table 1 gives the summary of the model parameters. b-d Contact rates. b and c show contact rates in all locations before the pandemic and after the first lockdown (April 2020), respectively; d shows contact rates at schools before the pandemic. The color represents the average number of contacts per day a person in a given age group had with persons in another age group.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 70, 910, 188]]<|/det|>
+rates we used from the literature are additive [19,20], thus the contact rate before the lockdown \((b_{kl})\) can be written as a sum of the school contact rate at the pre-lockdown level \((s_{kl}\) , see Figure 8 d) and the contact rate for all locations but schools \((b_{kl} - s_{kl})\) . The contact rate after the lockdown \((a_{kl})\) by definition did not include any school contacts because all schools were closed. The contact rate incorporating the relaxation of control measures after the first lockdown is therefore modeled as follows
+
+<|ref|>equation<|/ref|><|det|>[[323, 217, 906, 235]]<|/det|>
+\[c_{kl}(t) = \zeta_{1}g(t)a_{kl} + [1 - g(t)]\zeta_{2}(b_{kl} - s_{kl}) + \omega s_{kl}, \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[60, 262, 910, 430]]<|/det|>
+where \(g(t) = 1 / \left[1 + e^{K_{2}(t - t_{2})}\right]\) with the mid- point value \(t_{2} > t_{1}\) and the logistic growth \(K_{2}\) . In Eq. 3, the first two terms describe the increase of non- school contacts from the level after the first lockdown \((a_{kl})\) to their pre- lockdown level \((b_{kl} - s_{kl})\) . The parameter \(\zeta_{2} \geq \zeta_{1}\) , \(0 \leq \zeta_{2} \leq 1\) implies that the probability of transmission increased due to reduced adherence to control measures. The last term describes opening of schools which we assume to happen instantaneously, where \(\omega\) , \(0 \leq \omega \leq 1\) , is the proportion of retained school contacts. Schools functioning without any measures correspond to \(\omega = 1\) . School closure is achieved by setting \(\omega = 0\) . A summary of the model parameters is given in Table 1.
+
+<|ref|>table<|/ref|><|det|>[[90, 460, 904, 789]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[90, 443, 456, 459]]<|/det|>
+Table 1. Summary of the model parameters.
+
+| Description (unit) | Notation | Reference |
| Constant parameters | | |
| Number of age groups | n | 10 |
| Number of infectious stages | m | 3 |
| Basic reproduction number | R0 | Computed using the method in [40] |
| Effective reproduction number | Re | Computed using the method in [40] |
| Probability of transmission per contact | ε | Estimated |
| Reduction in post-lockdown probability of transmission per contact | (1-ζ1) | Estimated |
| Latent period (days) | 1/α | Estimated |
| Infectious period (1/day) | 1/γ | Estimated |
| Contribution of the contact rate after the lockdown | f(t)=1/[1+e-K1(t-t1)] | Eq. 2 |
| Mid-point value of the logistic function (days) | t1 | Estimated |
| Logistic growth (1/day) | K1 | Estimated |
| Over-dispersion parameter for the NegBinom distribution for hospitalizations | r | Estimated |
| Proportion of school contacts | ω | [0,1], calibrated |
| Reduction in probability of transmission per contact during relaxation | (1-ζ2) | [0,1], ζ2 ≥ ζ1, calibrated |
| Initial fraction of infected persons | θ | Estimated |
| Logistic function for relaxation | g(t)=1/[1+e-K2(t-t2)] | 0 ≤ g(t) ≤ 1, calibrated |
| Age-specific parameters* | | |
| Force of infection (1/day) | λk | Eq. 5 |
| Hospitalization rate (1/day) | νk | Estimated |
| Susceptibility of age group k relative to age group n† | βk | Estimated |
| General contact rate (1/day) | ckl | Eqs. 1 and 3 |
| Contact rate before the pandemic (1/day) | bkl | [19] |
| Contact rate after the first lockdown (1/day) | akl | [19] |
| School contact rate before the pandemic (1/day) | skl | [7,20] |
| Population size of age group k | Nk | [36] |
+
+<|ref|>table_footnote<|/ref|><|det|>[[90, 797, 738, 828]]<|/det|>
+\\*Indices \(k\) and \(l\) denote the age groups \(k,l = 1,\ldots ,n\) \(\ddagger\) In the estimation procedure the reference age group \(n\) is \(60+\) , and \(\beta_{60 + } = 1\) is fixed at 1.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 100, 900, 118]]<|/det|>
+The model was implemented in Mathematica 10.0.2.0 using a system of ordinary differential equations as follows
+
+<|ref|>equation<|/ref|><|det|>[[266, 138, 905, 345]]<|/det|>
+\[\begin{array}{rcl}{\frac{\mathrm{d}S_k(t)}{\mathrm{d}t}} & = & {-\beta_k\lambda_k(t)S_k(t),}\\ {\frac{\mathrm{d}E_k(t)}{\mathrm{d}t}} & = & {\beta_k\lambda_k(t)S_k(t) - \alpha E_k(t),}\\ {\frac{\mathrm{d}I_{k,1}(t)}{\mathrm{d}t}} & = & {\alpha E_k(t) - (\gamma m + \nu_k)I_{k,1}(t),}\\ {\frac{\mathrm{d}I_{k,p}(t)}{\mathrm{d}t}} & = & {\gamma mI_{k,p - 1}(t) - (\gamma m + \nu_k)I_{k,p}(t),} & {p = 2,\ldots ,m,}\\ {\frac{\mathrm{d}R_k(t)}{\mathrm{d}t}} & = & {\gamma mI_{k,m}(t),}\\ {\frac{\mathrm{d}H_k(t)}{\mathrm{d}t}} & = & {\nu_k\sum_{p = 1}^{m}I_{k,p}(t),} \end{array} \quad (4)\]
+
+<|ref|>text<|/ref|><|det|>[[58, 358, 910, 427]]<|/det|>
+where \(S_{k}\) , \(E_{k}\) , \(R_{k}\) and \(H_{k}\) are the numbers of persons in age group \(k\) , \(k = 1, \ldots , n\) , who are susceptible, exposed, recovered and hospitalized, respectively. The number of infectious persons in age group \(k\) and stage \(p = 1, \ldots , m\) is denoted \(I_{k,p}\) . The force of infection is given by
+
+<|ref|>equation<|/ref|><|det|>[[390, 440, 905, 485]]<|/det|>
+\[\lambda_{k}(t) = \epsilon \sum_{l = 1}^{n}\sum_{p = 1}^{m}c_{kl}(t)\frac{I_{l,p}(t)}{N_{l}}, \quad (5)\]
+
+<|ref|>text<|/ref|><|det|>[[58, 504, 911, 857]]<|/det|>
+where \(N_{l}\) is the number of individuals in age group \(l\) , \(N_{l} = S_{l}(t) + E_{l}(t) + \sum_{p = 1}^{m}I_{l,p}(t) + H_{l}(t) + R_{l}(t)\) . Note that the denominator in the force of infection \((N_{l})\) includes hospitalized persons, \(H_{l}(t)\) , where \(H_{l}(t)\) describes the cumulative number of hospital admissions at time \(t\) . The current number of hospitalized persons (not the cumulative) is not subtracted from \(N_{l}\) because we assume that hospitalized persons will be involved in contacts with medical personnel and visitors. Since we assume that contacts of the currently hospitalized persons (who may still be infectious) will not be infected due to the use of personal protective measures by medical personnel and hospital visitors, the current number of hospitalized persons does not contribute to the force of infection. As patients who are discharged and recovered (or deceased) also do not contribute to the force of infection, the cumulative number of hospitalized persons \((H_{l}(t))\) does not contribute to the force of infection either. In Eq. 5 we assumed a frequency- dependent transmission where the per capita rate at which a susceptible person becomes infected increases with the fraction of the population that is infectious. This choice is justified for the Netherlands as one of the most densely populated countries in Europe. Moreover, as the population size does not change during the time horizon of our analyses, there is no difference in the outcome between a frequency- dependent and a density dependent model once the parameters are fitted to obtain the observed reproduction number.
+
+<|ref|>text<|/ref|><|det|>[[60, 864, 910, 907]]<|/det|>
+We took 22 February 2020 as starting date \((t_{0})\) for the pandemic in the Netherlands, which is 5 days prior to the first officially notified case (27 February 2020). We assumed that there were no hospitalizations during this 5 day period.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 68, 911, 214]]<|/det|>
+353 To account for importation of new cases into the Netherlands at the beginning of the pandemic, we estimated a fraction \(\theta\) of each age group infected at time \(t_0\) . For simplicity, we assumed this fraction to be equally distributed between the exposed and infectious persons, i.e., \(E_k(t_0) = \frac{1}{2}\theta N_k\) , \(I_{k,p}(t_0) = \frac{1}{2m}\theta N_k\) and \(S_k(t_0) = (1 - \theta)N_k\) . In later stages of the pandemic, importations do not play such an important role because of existing pool of infected individuals within the country and ongoing control measures. For this reason, importations after \(t_0\) were not included in the model.
+
+<|ref|>sub_title<|/ref|><|det|>[[58, 240, 530, 260]]<|/det|>
+## 359 Observation model and parameter estimation
+
+<|ref|>text<|/ref|><|det|>[[58, 275, 911, 444]]<|/det|>
+Given predictions of the model, we calculated the likelihood of the data as follows. In the model, infectious individuals are hospitalized at a continuous rate \(\nu_k\sum_{p = 1}^{m}I_{k,p}\) . However, the hospitalization data consists of a discrete number of hospital admissions \(h_{k,i}\) on day \(T_i\) for each age class \(k\) . As the probability of hospitalization is relatively small, we made the simplifying assumption that the daily incidence of hospitalizations is proportional to the prevalence of infectious individuals at that time point. To accommodate errors in reporting and within age class variability of the hospitalization rate, we allowed for over- dispersion in the number of hospitalizations using a Negative- Binomial distribution, i.e.,
+
+<|ref|>equation<|/ref|><|det|>[[357, 467, 906, 496]]<|/det|>
+\[h_{k,i}\sim \mathrm{NegBinom}\left(\nu_k\sum_{p = 1}^{m}I_{k,p}(T_i),r\right), \quad (6)\]
+
+<|ref|>text<|/ref|><|det|>[[58, 517, 909, 562]]<|/det|>
+where we parameterize the \(\mathrm{NegBinom}(\mu ,r)\) distribution with the mean \(\mu\) and over- dispersion parameter \(r\) , such that the variance is equal to \(\mu +\mu^2 /r\) .
+
+<|ref|>text<|/ref|><|det|>[[58, 568, 910, 688]]<|/det|>
+We calculated the likelihood of the seroprevalence data using the model prediction of the fraction of non- susceptible individuals in each age class \(1 - S_k(T) / N_k\) . Here \(T\) denotes the median sampling time minus the expected duration from infection to seroconversion. We assumed that the probability of finding a seropositive individual in a random sample from the population is equal to the fraction of non- susceptible individuals, leading to a Binomial distribution for the number of positive samples \(\ell_k\) among all samples \(L_k\) from age group \(k\)
+
+<|ref|>equation<|/ref|><|det|>[[380, 715, 906, 734]]<|/det|>
+\[\ell_k\sim \mathrm{Binom}(L_k,1 - S_k(T) / N_k). \quad (7)\]
+
+<|ref|>text<|/ref|><|det|>[[58, 760, 910, 855]]<|/det|>
+Parameters were estimated in a Bayesian framework based on the methods from [41,42]. The model given by Eq. 4 was fit to the data using the Hamiltonian Monte Carlo method as implemented in Stan (https://www.mc- stan.org) [43] with R and R Studio interfaces. We used 4 parallel chains of length 1500 with a warm- up phase of length 1000, resulting in 2000 parameter samples from the posterior distribution.
+
+<|ref|>text<|/ref|><|det|>[[58, 861, 910, 930]]<|/det|>
+We used age- specific contact rates with ten age groups (ages [0,5), [5,10), [10,20), [20,30), [30,40), [40,50), [50,60), [60,70), [70,80) and \(80+\) ). Due to the low number of hospitalizations in young persons, we assumed that hospitalization rates in the first three age groups (ages [0,5), [5,10), [10,20)) were equal, therefore only 8 hospitalization
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 70, 910, 313]]<|/det|>
+rates were estimated. As the age-specific hospitalization rates are positively correlated (Supplementary Figure 5), we parameterized the model as \(\nu_{k} = \hat{\nu}_{k}\bar{\nu}\) , where \(\hat{\nu}_{k}\) is a simplex and \(\bar{\nu}\) a scalar. We kept the same age categories for the relative susceptibility as in the retrospective cohort study by Jing et al [8], from where we took the priors, i.e., the relative susceptibility was estimated for ages [0,20), [20,60), and \(60+\) age category was used as the reference corresponding to susceptibility equal to 1. As the age groups for which the seroprevalence was reported [18] are different from the age groups used in our model, we used demographic data from the Netherlands [36] and the smoothed age-specific seroprevalence curve estimated by Vos et al. [18] to correct for this discrepancy. The Bayesian prior distributions for the 10 estimated parameters (18 numbers in total as hospitalization rate and susceptibility are age-dependent) (see Table 1) are listed in Table 2. In the main text, we presented results for three infectious classes corresponding to an Erlang-distributed infectious period with shape parameter \(m = 3\) .
+
+<|ref|>table<|/ref|><|det|>[[90, 344, 910, 626]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[90, 325, 603, 341]]<|/det|>
+Table 2. Prior distributions for the Bayesian statistical model.
+
+| Parameter | Prior* | Explanation |
| ε | Uniform(0,1) | flat prior |
| α | InvGamma(32.25,9.75) | 99% of the prior density of 1/α between 2 and 5 days |
| γ | InvGamma(22.6,2.44) | 99% of the prior density of 1/γ between 5 and 15 days |
| V(0,20), V(20,30) | | |
| V(30,40), V(40,50) | folded-Λ(0,5) | vague prior |
| V(50,60), V(60,70) | | |
| V(70,80), V(80+) | | |
| β(0,20) | LogNormal(-1.47,0.1) | Log-odds -1.47 = log(0.23) based on prior estimates [8] |
| β(20,60) | LogNormal(-0.45,0.1) | Log-odds -0.45 = log(0.64) based on prior estimates [8] |
| r | LogNormal(5,2) | vague prior |
| ζ1 | folded-Λ(1,0.1) | a priori, we expect the reduction in contacts after the first lockdown to account for most of the decrease in the transmission rate |
| t1 | Λ(23,7) | the mean of t1 is given by the day of initiation of most drastic social distancing measures (March 15); most measures were taken within two weeks from this date |
| K1 | Exp(1) | with K1 = 1 the uptake of measures takes approximately 6 days |
| θ | Uniform(10-7,5·10-4) | vague prior allowing for approximately 10-10⁵ infections at time t0 |
+
+<|ref|>text<|/ref|><|det|>[[90, 631, 806, 663]]<|/det|>
+\*The scale parameter of the normal and log-normal distributions is equal to the standard deviation. \(\ddagger \beta_{60 + } = 1\) for the reference group of \(60+\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 718, 250, 735]]<|/det|>
+## Model outcomes
+
+<|ref|>text<|/ref|><|det|>[[90, 752, 910, 920]]<|/det|>
+We considered control measures aimed at reducing contact rate at schools or in all other locations. We evaluated the impact of a control measure by computing \(R_{e}\) using the next generation matrix (NGM) method [40,44,45,48], and percentage of contacts that need to be reduced to achieve control of the pandemic as quantified by \(R_{e} = 1\) . Previously, we applied this method for HIV and CMV transmission models [42,49]. The method for calculating the basic reproduction number \(R_{0}\) and \(R_{e}\) (Supplementary Figure 4) is described in detail in Supplementary Information. In short, Supplementary Figures 4 a and b were obtained using the next generation matrix (NGM) method and posterior distributions of the parameters (Supplementary Figure 3) that were estimated from fitting the model to
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 68, 912, 415]]<|/det|>
+the data of the first 69 days of the pandemic (22 February till 30 April 2020). As hospitalization data during relaxation is not available, we calibrated the model to values of \(R_{e}\) as published on the dashboard of the National Institute for Public Health and the Environment (RIVM) [1]. These time- dependent \(R_{e}\) values are estimated from hospitalization data and later from case numbers using methods described in [46]. Specifically, we chose \(\omega\) , \(g\) and \(\zeta_{2}\) such that the median reproduction numbers in the model would equal the specific values estimated by the RIVM (about 1.3 in the period 27 August- 6 September and about 1 in the period 7- 13 November) [1]. The distributions shown in Supplementary Figures 4 c and d are therefore obtained using the NGM method with fixed \(\omega\) , \(g\) and \(\zeta_{2}\) and other parameters drawn from the posterior distributions as shown in Supplementary Figure 3. Note that the calibration of the model in the relaxation period is possible because the parameters describing epidemiology of SARS- CoV- 2 are assumed to be constant throughout the time horizon of the analyses which spans both pre- lockdown, post- lockdown and relaxation periods, and only contact structure varies with time (see Supplementary Information). In analyses, the parameters \(\omega\) and \(g\) were then used as control parameters to reduce the number of school- and non- school- related contacts (Figures 5, 6 and 7). In doing so, we varied one type of contact and kept the other type constant.
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 442, 285, 461]]<|/det|>
+## Reporting summary
+
+<|ref|>text<|/ref|><|det|>[[90, 477, 905, 496]]<|/det|>
+Further information on research design is available in the Nature Research Reporting Summary linked to this article.
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 530, 282, 551]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[90, 570, 905, 588]]<|/det|>
+All datasets analysed and generated during this study are available in the GitHub repository, https://github.
+
+<|ref|>text<|/ref|><|det|>[[90, 597, 358, 613]]<|/det|>
+com/lynxgav/COVID19- schools [47].
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 649, 285, 670]]<|/det|>
+## Code availability
+
+<|ref|>text<|/ref|><|det|>[[90, 690, 909, 708]]<|/det|>
+Mathematica, Stan, R and R Studio codes reproducing the results of this study are available in the GitHub
+
+<|ref|>text<|/ref|><|det|>[[90, 717, 567, 734]]<|/det|>
+repository, https://github.com/lynxgav/COVID19- schools [47].
+
+<|ref|>sub_title<|/ref|><|det|>[[90, 770, 216, 789]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[90, 810, 790, 828]]<|/det|>
+[1] Coronavirus dashboard; 2020. Available from: https://coronadashboard.government.nl/.
+
+<|ref|>text<|/ref|><|det|>[[90, 846, 909, 889]]<|/det|>
+[2] Thompson RN, Hollingsworth TD, Isham V, Arribas- Bel D, Ashby B, Britton T, et al. Key questions for modelling COVID- 19 exit strategies. Proceedings of the Royal Society B. 2020;287(1932):20201405.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[50, 66, 911, 112]]<|/det|>
+[3] Flasche S, Edmunds WJ. The role of schools and school- aged children in SARS- CoV- 2 transmission. The Lancet Infectious Diseases. XXXX;doi:10.1016/S1473- 3099(20)30927- 0.
+
+<|ref|>text<|/ref|><|det|>[[50, 128, 910, 174]]<|/det|>
+[4] Ferguson NM, Cummings DA, Fraser C, Cajka JC, Cooley PC, Burke DS. Strategies for mitigating an influenza pandemic. Nature. 2006;442(7101):448- 452.
+
+<|ref|>text<|/ref|><|det|>[[50, 190, 910, 234]]<|/det|>
+[5] Cauchemez S, Ferguson NM, Wachtel C, Tegnell A, Saour G, Duncan B, et al. Closure of schools during an influenza pandemic. The Lancet Infectious Diseases. 2009;9:473- 481.
+
+<|ref|>text<|/ref|><|det|>[[50, 250, 910, 345]]<|/det|>
+[6] te Beest DE, Birrell PJ, Wallinga J, De Angelis D, van Boven M. Joint modelling of serological and hospitalization data reveals that high levels of pre- existing immunity and school holidays shaped the influenza A pandemic of 2009 in The Netherlands. Journal of The Royal Society Interface. 2015;12(103):20141244. doi:10.1098/rsif.2014.1244.
+
+<|ref|>text<|/ref|><|det|>[[50, 360, 910, 406]]<|/det|>
+[7] Mossong J, Hens N, Jit M, Beutels P, Auranen K, Mikolajczyk R, et al. Social contacts and mixing patterns relevant to the spread of infectious diseases. PLOS Medicine. 2008;5(3):1- 1. doi:10.1371/journal.pmed.0050074.
+
+<|ref|>text<|/ref|><|det|>[[50, 421, 910, 492]]<|/det|>
+[8] Jing Q, Liu M, Zhang Z, Fang L, Yuan J, Zhang A, et al. Household secondary attack rate of COVID- 19 and associated determinants in Guangzhou, China: a retrospective cohort study. Lancet Infect Dis. 2020;20(10):1141- 1150. doi:10.1016/S1473- 3099(20)30471- 0.
+
+<|ref|>text<|/ref|><|det|>[[50, 507, 910, 552]]<|/det|>
+[9] Goldstein E, Lipsitch M, Cevik M. On the effect of age on the transmission of SARS- CoV- 2 in households, schools and the community. The Journal of Infectious Diseases. 2020;doi:10.1093/infdis/jiaa691.
+
+<|ref|>text<|/ref|><|det|>[[50, 567, 910, 637]]<|/det|>
+[10] Prem K, Liu Y, Russell T, Kucharski A, Eggo R, Davies N, et al. The effect of control strategies to reduce social mixing on outcomes of the COVID- 19 epidemic in Wuhan, China: a modelling study. Lancet Public Health. 2020;5(5):e261- e270. doi:10.1016/S2468- 2667(20)30073- 6.
+
+<|ref|>text<|/ref|><|det|>[[50, 653, 910, 698]]<|/det|>
+[11] Davies NG, Klepac P, Liu Y, Prem K, Jit M, Pearson CAB, et al. Age- dependent effects in the transmission and control of COVID- 19 epidemics. Nature Medicine. 2020;26(8):1205- 1211. doi:10.1038/s41591- 020- 0962- 9.
+
+<|ref|>text<|/ref|><|det|>[[50, 714, 910, 784]]<|/det|>
+[12] Teslya A, Pham TM, Godijk NG, Kretzschmar ME, Bootsma MCJ, Rozhnova G. Impact of self- imposed prevention measures and short- term government- imposed social distancing on mitigating and delaying a COVID- 19 epidemic: A modelling study. PLOS Medicine. 2020;17(7):1- 21. doi:10.1371/journal.pmed.1003166.
+
+<|ref|>text<|/ref|><|det|>[[50, 799, 910, 868]]<|/det|>
+[13] Davies NG, Kucharski AJ, Eggo RM, Gimma A, Edmunds WJ, Jombart T, et al. Effects of non- pharmaceutical interventions on COVID- 19 cases, deaths, and demand for hospital services in the UK: a modelling study. The Lancet Public Health. 2020;
+
+<|ref|>text<|/ref|><|det|>[[50, 884, 910, 929]]<|/det|>
+[14] Dehning J, Zierenberg J, Spitzner FP, Wibral M, Neto JP, Wilczek M, et al. Inferring change points in the spread of COVID- 19 reveals the effectiveness of interventions. Science. 2020;369(6500). doi:10.1126/science.abb9789.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 68, 910, 137]]<|/det|>
+[15] Giordano G, Blanchini F, Bruno R, Colaneri P, Di Filippo A, Di Matteo A, et al. Modelling the COVID- 19 epidemic and implementation of population- wide interventions in Italy. Nature Med. 2020;26:855- 860. doi:10.1038/s41591- 020- 0883- 7.
+
+<|ref|>text<|/ref|><|det|>[[58, 153, 910, 222]]<|/det|>
+[16] Gatto M, Bertuzzo E, Mari L, Miccoli S, Carraro L, Casagrandi R, et al. Spread and dynamics of the COVID- 19 epidemic in Italy: Effects of emergency containment measures. Proceedings of the National Academy of Sciences. 2020;117(19):10484- 10491. doi:10.1073/pnas.2004978117.
+
+<|ref|>text<|/ref|><|det|>[[58, 238, 910, 306]]<|/det|>
+[17] Bertuzzo E, Mari L, Pasetto D, Miccoli S, Casagrandi R, Gatto M, et al. The geography of COVID- 19 spread in Italy and implications for the relaxation of confinement measures. Nature Communications. 2020;11(1):4264. doi:10.1038/s41467- 020- 18050- 2.
+
+<|ref|>text<|/ref|><|det|>[[58, 323, 910, 391]]<|/det|>
+[18] Vos ERA, den Hartog G, Schepp RM, Kaaijk P, van Vliet J, Helm K, et al. Nationwide seroprevalence of SARS- CoV- 2 and identification of risk factors in the general population of the Netherlands during the first epidemic wave. Journal of Epidemiology & Community Health. 2020;doi:10.1136/jech- 2020- 215678.
+
+<|ref|>text<|/ref|><|det|>[[58, 407, 910, 500]]<|/det|>
+[19] Backer JA, Mollema L, Vos RAE, Klinkenberg D, van der Klis FRM, de Melker HE, et al. The impact of physical distancing measures against COVID- 19 transmission on contacts and mixing patterns in the Netherlands: repeated cross- sectional surveys in 2016/2017, April 2020 and June 2020. medRxiv; Accepted for publication in Eurosurveillance. 2020;doi:10.1101/2020.05.18.20101501.
+
+<|ref|>text<|/ref|><|det|>[[58, 516, 910, 560]]<|/det|>
+[20] Prem K, Cook AR, Jit M. Projecting social contact matrices in 152 countries using contact surveys and demographic data. PLOS Computational Biology. 2017;13(9):1- 21. doi:10.1371/journal.pcbi.1005697.
+
+<|ref|>text<|/ref|><|det|>[[58, 576, 910, 669]]<|/det|>
+[21] Panovska- Griffiths J, Kerr C, Stuart R, Mistry D, Klein D, Viner R, et al. Determining the optimal strategy for reopening schools, the impact of test and trace interventions, and the risk of occurrence of a second COVID- 19 epidemic wave in the UK: a modelling study. Lancet Child Adolesc Health. 2020;4(11):817- 827. doi:10.1016/S2352- 4642(20)30250- 9.
+
+<|ref|>text<|/ref|><|det|>[[58, 685, 910, 752]]<|/det|>
+[22] Munday JD, Sherratt K, Meakin S, Endo A, Pearson CAB, Hellewell J, et al. Implications of the school- household network structure on SARS- CoV- 2 transmission under different school reopening strategies in England. medRxiv. 2020;doi:10.1101/2020.08.21.20167965.
+
+<|ref|>text<|/ref|><|det|>[[58, 769, 910, 812]]<|/det|>
+[23] Keskinocak P, Asplund J, Serban N, Oruc Aglar BE. Evaluating Scenarios for School Reopening under COVID19. medRxiv. 2020;doi:10.1101/2020.07.22.20160036.
+
+<|ref|>text<|/ref|><|det|>[[58, 829, 910, 872]]<|/det|>
+[24] Rice K, Wynne B, Martin V, Ackland GJ. Effect of school closures on mortality from coronavirus disease 2019: old and new predictions. BMJ. 2020;371. doi:10.1136/bmj.m3588.
+
+<|ref|>text<|/ref|><|det|>[[58, 888, 910, 931]]<|/det|>
+[25] Chang S, Harding N, Zachreson C, Cliff OM, Prokopenko M. Modelling transmission and control of the COVID- 19 pandemic in Australia. Nat Commun. 2020;11:5710. doi:https://doi.org/10.1038/s41467- 020- 19393- 6.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 67, 911, 138]]<|/det|>
+[26] Jarvis CI, Van Zandvoort K, Gimma A, Prem K, Auzenbergs M, O'Reilly K, et al. Quantifying the impact of physical distance measures on the transmission of COVID- 19 in the UK. BMC Medicine. 2020;18(1):124. doi:10.1186/s12916- 020- 01597- 8.
+
+<|ref|>text<|/ref|><|det|>[[58, 153, 910, 223]]<|/det|>
+[27] Sekine T, Perez- Potti A, Rivera- Ballesteros O, Strlin K, Gorin JB, Olsson A, et al. Robust T Cell Immunity in Convalescent Individuals with Asymptomatic or Mild COVID- 19. Cell. 2020;183(1):158 - 168. e14. doi:https://doi.org/10.1016/j.cell.2020.08.017.
+
+<|ref|>text<|/ref|><|det|>[[58, 240, 910, 283]]<|/det|>
+[28] Burgess S, Ponsford MJ, Gill D. Are we underestimating seroprevalence of SARS- CoV- 2? BMJ. 2020;370. doi:10.1136/bmj.m3364.
+
+<|ref|>text<|/ref|><|det|>[[58, 300, 925, 370]]<|/det|>
+[29] Scientific Advisory Group for Emergencies. Timing of the introduction of school closure for COVID- 19 epidemic suppression, 18 March 2020; 2020. Available from: https://www.gov.uk/government/publications/timing- of- the- introduction- of- school- closure- for- covid- 19- epidemic- suppression- 18- march- 2020.
+
+<|ref|>text<|/ref|><|det|>[[58, 386, 910, 455]]<|/det|>
+[30] Brauner JM, Mindermann S, Sharma M, Johnston D, Salvatier J, Gavenciak T, et al. The effectiveness of eight nonpharmaceutical interventions against COVID- 19 in 41 countries. medRxiv. 2020;doi:10.1101/2020.05.28.20116129.
+
+<|ref|>text<|/ref|><|det|>[[58, 471, 910, 564]]<|/det|>
+[31] Li Y, Campbell H, Kulkarni D, Harpur A, Nundy M, Wang X, et al. The temporal association of introducing and lifting non- pharmaceutical interventions with the time- varying reproduction number (R) of SARS- CoV- 2: a modelling study across 131 countries. The Lancet Infectious Diseases. 2020;doi:https://doi.org/10.1016/S1473- 3099(20)30785- 4.
+
+<|ref|>text<|/ref|><|det|>[[58, 581, 910, 650]]<|/det|>
+[32] Heavey L, Casey G, Kelly C, Kelly D, McDarby G. No evidence of secondary transmission of COVID- 19 from children attending school in Ireland, 2020. Eurosurveillance. 2020;25(21). doi:https://doi.org/10.2807/1560- 7917.ES.2020.25.21.2000903.
+
+<|ref|>text<|/ref|><|det|>[[58, 667, 910, 711]]<|/det|>
+[33] Yung CF, Kam Kq, Nadua KD, Chong CY, Tan NWH, Li J, et al. Novel Coronavirus 2019 Transmission Risk in Educational Settings. Clinical Infectious Diseases. 2020;doi:10.1093/cid/ciaa794.
+
+<|ref|>text<|/ref|><|det|>[[58, 728, 910, 794]]<|/det|>
+[34] Macartney K, Quinn H, Pillsbury A, Koirala A, Deng L, Winkler N, et al. Transmission of SARS- CoV- 2 in Australian educational settings: a prospective cohort study. Lancet Child Adolesc Health. 2020;4(11):807- 816. doi:10.1016/S2352- 4642(20)30251- 0.
+
+<|ref|>text<|/ref|><|det|>[[58, 812, 910, 880]]<|/det|>
+[35] Ismail SA, Saliba V, Lopez Bernal JA, Ramsay ME, Ladhani SN. SARS- CoV- 2 infection and transmission in educational settings: cross- sectional analysis of clusters and outbreaks in England. medRxiv. 2020;doi:10.1101/2020.08.21.20178574.
+
+<|ref|>text<|/ref|><|det|>[[58, 899, 660, 916]]<|/det|>
+[36] Statistics Netherlands (CBS); 2020. Available from: https://www.cbs.nl.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 68, 910, 138]]<|/det|>
+[37] Li R, Pei S, Chen B, Song Y, Zhang T, Yang W, et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS- CoV- 2). Science. 2020;368(6490):489- 493. doi:10.1126/science.abb3221.
+
+<|ref|>text<|/ref|><|det|>[[58, 155, 910, 201]]<|/det|>
+[38] Champredon D, Dushoff J, Earn DJD. Equivalence of the Erlang- Distributed SEIR Epidemic Model and the Renewal Equation. SIAM Journal on Applied Mathematics. 2018;78(6):3258- 3278. doi:10.1137/18M1186411.
+
+<|ref|>text<|/ref|><|det|>[[58, 216, 910, 285]]<|/det|>
+[39] Diekmann O, Gyllenberg M, Metz JAJ. Finite Dimensional State Representation of Linear and Nonlinear Delay Systems. Journal of Dynamics and Differential Equations. 2018;30(4):1439- 1467. doi:10.1007/s10884- 017- 9611- 5.
+
+<|ref|>text<|/ref|><|det|>[[58, 301, 910, 345]]<|/det|>
+[40] Diekmann O, Heesterbeek H, Britton T. Mathematical Tools for Understanding Infectious Disease Dynamics. Princeton University Press; 2013.
+
+<|ref|>text<|/ref|><|det|>[[58, 360, 910, 430]]<|/det|>
+[41] van Boven M, Teirlinck AC, Meijer A, Hooiveld M, van Dorp CH, Reeves RM, et al. Estimating Transmission Parameters for Respiratory Syncytial Virus and Predicting the Impact of Maternal and Pediatric Vaccination. J Infect Dis. 2020;222(Supplement_7):S688- S694.
+
+<|ref|>text<|/ref|><|det|>[[58, 445, 910, 515]]<|/det|>
+[42] Rozhnova G, Kretzschmar ME, van der Klis F, van Baarle D, Kordewal M, Vossen AC, et al. Short- and long- term impact of vaccination against cytomegalovirus: a modeling study. BMC Med. 2020;18. doi:https://doi.org/10.1186/s12916- 020- 01629- 3.
+
+<|ref|>text<|/ref|><|det|>[[58, 531, 910, 576]]<|/det|>
+[43] Carpenter B, Gelman A, Hoffman M, Lee D, Goodrich B, Betancourt M, et al. Stan: A probabilistic programming language. J Stat Softw. 2017;76(1):1- 32. doi:10.18637/jss.v076.i01.
+
+<|ref|>text<|/ref|><|det|>[[58, 592, 910, 636]]<|/det|>
+[44] van den Driessche P, Watmough J. Reproduction numbers and sub- threshold endemic equilibria for compartmental models of disease transmission. Mathematical Biosciences. 2002;180:29- 48.
+
+<|ref|>text<|/ref|><|det|>[[58, 652, 910, 697]]<|/det|>
+[45] Diekmann O, Heesterbeek JAP, Roberts MG. The construction of next- generation matrices for compartmental epidemic models. Journal of The Royal Society Interface. 2010;7(47):873- 885. doi:10.1098/rsif.2009.0386.
+
+<|ref|>text<|/ref|><|det|>[[58, 713, 910, 781]]<|/det|>
+[46] Wallinga J, Lipsitch M. How generation intervals shape the relationship between growth rates and reproductive numbers. Proceedings of the Royal Society B: Biological Sciences. 2007;274(1609):599- 604. doi:10.1098/rspb.2006.3754.
+
+<|ref|>text<|/ref|><|det|>[[58, 798, 910, 867]]<|/det|>
+[47] Rozhnova G, van Dorp CH, Bruijning- Verhagen P, Bootsma MCJ, van de Wijgert JHHM, Bonten MJM, Kretzschmar ME. Model- based evaluation of school- and non- school- related measures to control the COVID- 19 pandemic. GitHub 2021. doi:10.5281/zenodo.4541431.
+
+<|ref|>text<|/ref|><|det|>[[58, 884, 910, 928]]<|/det|>
+[48] Vynnycky E, White R. An introduction to infectious disease modelling. Oxford: Oxford University Press; 2010.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[58, 68, 910, 138]]<|/det|>
+[49] Rozhnova G, van der Loeff MFS, Heijne JCM, Kretzschmar ME. Impact of heterogeneity in sexual behavior on effectiveness in reducing HIV transmission with test- and- treat strategy. PLOS Computational Biology. 2016;12(8):e1005012. doi:10.1371/journal.pcbi.1005012.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 175, 312, 196]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[58, 214, 911, 433]]<|/det|>
+The contribution of C.H.v.D. was under the auspices of the US Department of Energy (contract number 89233218CNA000001) and supported by the National Institutes of Health (grant number R01- OD011095). M.E.K. was supported by ZonMw grant number 10430022010001, ZonMw grant number 91216062, and H2020 project 101003480 (CORESMA). M.J.M.B. and P.B.V. were supported by H2020 project 101003589 (RECOVER). G.R. was supported by FCT project 131_596787873. We thank Michiel van Boven (The National Institute of Public Health and the Environment, Bilthoven, The Netherlands) and Ana Nunes (Lisbon University) for valuable discussions and continuing advice during the course of this project. We thank João Viana for validating the Mathematica code. We thank Mui Pham and Alexandra Teslya for comments on the manuscript. We thank Eric Vos and Jantien Backer for the information on the serological and contact data used in this study.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 469, 337, 490]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[58, 509, 911, 629]]<|/det|>
+G.R. and C.H.v.D. developed the model with input from M.E.K, M.B. and P.B.V. G.R. and C.H.v.D. performed statistical inference and sensitivity analyses. G.R. implemented control measures, carried out all model analyses and prepared figures. M.E.K, M.C.J.B. and H.H.M.v.d.W. validated the model and analyses. G.R. conceived the study and drafted the first version of the manuscript. All authors contributed to analysis, interpretation of the results, writing the final version of the manuscript and gave final approval for publication.
+
+<|ref|>sub_title<|/ref|><|det|>[[92, 664, 326, 686]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[92, 706, 405, 722]]<|/det|>
+The authors declare no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[91, 758, 411, 780]]<|/det|>
+## Supplementary Information
+
+<|ref|>text<|/ref|><|det|>[[58, 800, 910, 844]]<|/det|>
+Supplementary InformationSupplementary Information contains details of computation of the basic and effective reproduction numbers and Supplementary Figures.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[55, 67, 277, 88]]<|/det|>
+## Correspondence
+
+<|ref|>text<|/ref|><|det|>[[57, 107, 910, 175]]<|/det|>
+Correspondence and material requests should be addressed to Dr. Ganna Rozhnova, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, P.O. Box 85500 Utrecht, The Netherlands; email: g.rozhnova@umcutrecht.nl.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 43, 143, 68]]<|/det|>
+## Figures
+
+<|ref|>image<|/ref|><|det|>[[40, 88, 960, 411]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 428, 115, 448]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[41, 470, 955, 606]]<|/det|>
+Estimated age- specific hospital admissions. The black lines represent the estimated medians. The dark gray lines correspond to \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution, and the shaded regions show \(95\%\) Bayesian prediction intervals. The dots are daily hospitalization admission data (all data points are included). Day 1 corresponds to 22 February 2020 which is 5 days prior to the first officially notified case in the Netherlands (27 February 2020). Panels a- h refer to different age groups.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[42, 40, 729, 491]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 510, 116, 530]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[42, 553, 936, 596]]<|/det|>
+Estimated age- specific probability of hospitalization. The violin shapes represent the marginal posterior distribution for 2000 samples of the probability of hospitalization in the model.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[40, 42, 728, 518]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 536, 116, 555]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[41, 578, 935, 712]]<|/det|>
+Estimated age- specific seroprevalence. The data (dots) are shown as the percentage of seropositive persons based on a seroprevalence survey that was conducted in April/May 2020. The number of positive and total samples defining this percentage for each age category is supplied in seroprevalence data file accompanying this study (see Data availability). The error bars represent the \(95\%\) confidence (Jeffreys) interval of the percentage. The violin shapes represent the marginal posterior distribution for 2000 samples of the percentage of seropositive persons in the model.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[40, 42, 950, 420]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 430, 118, 450]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[40, 472, 958, 584]]<|/det|>
+Schematic timeline of the pandemic in the Netherlands during 2020. Outlined are times of the introduction and relaxation of control measures, and the estimated effective reproduction numbers for a - start of the pandemic (February 2020), b - full lockdown (April 2020), c - schools opening (August 2020), d - partial lockdown (November 2020). See Supplementary Figure 4 for the distributions of the reproduction numbers.
+
+<|ref|>image<|/ref|><|det|>[[40, 584, 480, 848]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 867, 118, 887]]<|/det|>
+Figure 5
+
+<|ref|>image<|/ref|><|det|>[[510, 584, 956, 848]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[42, 909, 950, 953]]<|/det|>
+Impact of reduction of two types of contacts on the effective reproduction number in August 2020. Percentage reduction in a other (non- school- related) contacts in society in general and b school contacts,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[40, 45, 940, 225]]<|/det|>
+with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in August 2020, when schools just opened in the Netherlands. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non- school- related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of Re (situation August 2020), the green line is the value of Re achieved for \(100\%\) reduction in contacts. The blue line indicates Re of 1. To control the pandemic, \(\mathrm{Re}< 1\) is necessary
+
+<|ref|>image<|/ref|><|det|>[[40, 227, 951, 485]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 504, 117, 523]]<|/det|>
+Figure 6
+
+<|ref|>text<|/ref|><|det|>[[40, 545, 950, 750]]<|/det|>
+Impact of reduction of two types of contacts on the effective reproduction number in November 2020. Percentage reduction in a other (non- school- related) contacts in society in general and b school contacts, with the number of the other type of contact kept constant in each of the two panels. The scenario with \(0\%\) reduction describes the situation in November 2020. The scenario with \(100\%\) reduction represents a scenario with either a maximum reduction in other (non- school- related) contacts in society in general to the level of April 2020 or b complete closure of schools. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of Re (situation November 2020), the green line is the value of Re achieved for \(100\%\) reduction in contacts. To control the pandemic, \(\mathrm{Re}< 1\) is necessary.
+
+<|ref|>image<|/ref|><|det|>[[40, 750, 955, 940]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 42, 116, 62]]<|/det|>
+## Figure 7
+
+<|ref|>text<|/ref|><|det|>[[40, 83, 949, 355]]<|/det|>
+Impact of reduction of school contacts in different age groups on the effective reproduction number in November 2020. Percentage reduction in school contacts among a [0, 5) years old, b [5, 10) years old and c [10, 20) years old. In each panel, we varied the number of school contacts in one age group while keeping the number of school contacts in the other two age groups constant. The scenario with \(0\%\) reduction describes the situation in November 2020 with Re of about 1 (partial lockdown intended to prevent the second wave), where all schools are open without substantial additional measures. The reduction of \(100\%\) in school contacts represents a scenario with the structure of non- school contacts in society in general as in November 2020 and schools for students in a given age group closed. The solid black line describes the median, the shaded region represents the \(95\%\) credible intervals obtained from 2000 parameter samples from the posterior distribution. The red line is the starting value of \(\mathrm{Re} = 1\) (situation November 2020). The green line indicates the value of Re achieved when schools for a given age group close.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[64, 60, 784, 789]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 802, 118, 821]]<|/det|>
+Figure 8
+
+<|ref|>text<|/ref|><|det|>[[42, 842, 951, 955]]<|/det|>
+Transmission model. A Model schematic. Black arrows show epidemiological transitions. Red arrows indicate the compartments contributing to the force of infection. Susceptible persons in age group k (Sk), where \(k = 1, \ldots , n\) , become latently infected (Ek) via contact with infectious persons in m infectious stages (lk,p, \(p = 1, \ldots , m\) ) at a rate \(\beta k \lambda k\) , where \(\lambda k\) is the force of infection, and \(\beta k\) is the reduction in susceptibility to infection of persons in age group k compared to persons in age group n. Exposed
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 44, 944, 180]]<|/det|>
+persons (Ek) become infectious (lk,1) at rate a. Infectious persons progress through (m - 1) infectious stages at rate ym, after which they recover (Rk). From each stage, infectious persons are hospitalized at rate vk. Table 1 gives the summary of the model parameters. b- d Contact rates. b and c show contact rates in all locations before the pandemic and after the first lockdown (April 2020), respectively; d shows contact rates at schools before the pandemic. The color represents the average number of contacts per day a person in a given age group had with persons in another age group.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 202, 310, 229]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 252, 765, 272]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 291, 353, 310]]<|/det|>
+SupplementaryInformation.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/images_list.json b/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..a5c83ba0ad9807e4d04bd8f9249c828d5c54102c
--- /dev/null
+++ b/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/images_list.json
@@ -0,0 +1,62 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 45,
+ 45,
+ 805,
+ 550
+ ]
+ ],
+ "page_idx": 10
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [
+ [
+ 45,
+ 48,
+ 790,
+ 560
+ ]
+ ],
+ "page_idx": 11
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 45,
+ 48,
+ 787,
+ 496
+ ]
+ ],
+ "page_idx": 12
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4",
+ "footnote": [],
+ "bbox": [
+ [
+ 45,
+ 45,
+ 781,
+ 601
+ ]
+ ],
+ "page_idx": 13
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121.mmd b/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..fd4fe7656dc7033fdb66db9e4cb7aa87b7cab114
--- /dev/null
+++ b/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121.mmd
@@ -0,0 +1,259 @@
+
+## A de novo paradigm for male infertility
+
+Joris Veltman ( joris.veltman@newcastle.ac.uk) Newcastle University https://orcid.org/0000- 0002- 3218- 8250
+
+Radboudumc https://orcid.org/0000- 0001- 9513- 3030
+
+Roos Smits Radboudumc
+
+Hannah Smith Newcastle University
+
+Francesco Mastrorosa
+
+Newcastle University https://orcid.org/0000- 0003- 0579- 1895
+
+Giles Holt Newcastle University
+
+Brendan Houston The University of Melbourne
+
+Petra de Vries Radboud University Medical Center
+
+Bilal Alobaidi Newcastle University https://orcid.org/0000- 0003- 2718- 4826
+
+Lois Batty Newcastle University
+
+Hadeel Ismail Newcastle University
+
+Jackie Greenwood Newcastle University
+
+Harsh Sheth Foundation for Research in Genetics and Endocrinology https://orcid.org/0000- 0001- 9626- 0971
+
+Aneta Mikulasova Newcastle University
+
+Galuh Astuti Radboudumc
+
+Christian Gilissen Radboud University Medical Center https://orcid.org/0000- 0003- 1693- 9699
+
+Kevin McEleny Newcastle Fertility Centre, The Newcastle upon Tyne Hospitals NHS Foundation Trust
+
+Helen Turner Department of Cellular Pathology, The Newcastle upon Tyne Hospitals NHS Foundation Trust
+
+Jonathan Coxhead Newcastle University
+
+Simon Cockell Newcastle University
+
+Didi Braat Radboudumc
+
+<--- Page Split --->
+
+Kathrin Fleischer Radboudumc Kathleen D'Hauwers Radboudumc Ewout Schaafsma Radboudumc Liina Nagimaja Oregon Health & Science University; GEMINI consortium https://orcid.org/0000- 0003- 1948- 2495 Donald Conrad Oregon National Primate Research Center https://orcid.org/0000- 0003- 3828- 8970 Corinna Friedrich University of Münster Sabine Kliesch Centre of Reproductive Medicine and Andrology, Department of Clinical and Surgical Andrology, University Hospital Münster, Münster https://orcid.org/0000- 0002- 7561- 4870 Kenneth Aston University of Utah; GEMINI consortium Antoni Riera-Escamilla Fundació Puigvert, Universitat Autònoma de Barcelona, Instituto de Investigaciones Biomédicas Sant Pau Csilla Krausz University of Florence Claudia Gonzaga- Jauregui Regeneron Genetics Center, Regeneron Pharmaceuticals Mauro Santibanez- Koref Newcastle University David Elliott Newcastle University Lisenka Vissers Radboudumc https://orcid.org/0000- 0001- 6470- 5497 Frank Tüttelmann University of Münster https://orcid.org/0000- 0003- 2745- 9965 Moira O'Bryan The University of Melbourne; GEMINI consortium https://orcid.org/0000- 0001- 7298- 4940 Liliana Ramos Radboudumc Miguel Xavier Newcastle University https://orcid.org/0000- 0003- 0709- 7223 Godfried van der Heijden Radboudumc
+
+## Article
+
+Keywords: De novo mutations, male infertility, RBM5
+
+Posted Date: March 22nd, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 332732/v1
+
+<--- Page Split --->
+
+Version of Record: A version of this preprint was published at Nature Communications on January 10th, 2022. See the published version at https://doi.org/10.1038/s41467-021-27132-8.
+
+<--- Page Split --->
+
+## Abstract
+
+De novo mutations (DNMs) are known to play a prominent role in many sporadic disorders with reduced fitness. We hypothesize that DNMs play an important role in male infertility and explain a significant fraction of the genetic causes of this understudied disorder. We performed a trio- based exome- sequencing study in a unique cohort of 185 infertile males and their unaffected parents. Following a systematic analysis, 29 of 145 rare protein altering DNMs were classified as possibly causative of the male infertility phenotype. We observed a significant enrichment of Loss- of- Function (LoF) DNMs in LoF- intolerant genes (p- value \(= 1.00 \times 10 - 5\) ) as well as predicted pathogenic missense DNMs in missense- intolerant genes (p- value \(= 5.01 \times 10 - 4\) ). One DNM gene identified, RBM5, is an essential regulator of male germ cell pre- mRNA splicing. In a follow- up study, 5 rare pathogenic missense mutations affecting this gene were observed in a cohort of 2,279 infertile patients, with no such mutations found in a cohort of 5,784 fertile men (p- value \(= 0.009\) ). Our results provide the first evidence for the role of DNMs in severe male infertility and point to many new candidate genes affecting fertility.
+
+## Main
+
+Male infertility contributes to approximately half of all cases of infertility and affects \(7\%\) of the male population. For the majority of these men the cause remains unexplained. Despite a clear role for genetic causes in male infertility, there is a distinct lack of diagnostically relevant genes and at least \(40\%\) of all cases are classified as idiopathic \(^{3 - 6}\) . Previous studies in other conditions with reproductive lethality, such as neurodevelopmental disorders, have demonstrated an important role for de novo mutations (DNMs) in their etiology \(^{1}\) . In line with this, recurrent de novo chromosomal abnormalities play an important role in male infertility. Both azoospermia Factor (AZF) deletions on the Y chromosome as well as an additional X chromosome, resulting in Klinefelter syndrome, occur de novo. Collectively, these de novo events explaining up to \(25\%\) of all cases of nonobstructive azoospermia (NOA) \(^{3,6}\) . Interestingly, in 1999 a DNM in the Y- chromosomal gene USP9Y was reported in a man with azoospermia \(^{7}\) . Until now, however, a systematic analysis of the role of DNMs in male infertility had not been attempted. This is partly explained by a lack of basic research in male reproductive health in general \(^{6,8}\) , but also by the practical challenges of collecting parental samples for this disorder, which is typically diagnosed in adults.
+
+In this study, we investigated the role of DNMs in 185 unexplained cases of oligozoospermia (<5 million sperm cells/ml; \(n = 74\) ) and azoospermia ( \(n = 111\) ) by performing whole exome sequencing (WES) in all patients and their parents (see Supplementary Figure 1 and 2, Supplementary notes and tables for details on methods and clinical description). In total, we identified and validated 192 rare DNMs, including 145 protein altering DNMs. All de novo point mutations were autosomal, except for one on chromosome X, and all occurred in different genes (Supplementary Table 1). Two de novo copy number variations (CNVs) were also identified affecting a total of 7 genes (Supplementary Figure 3).
+
+None of the 145- protein altering DNMs occurred in a gene already known for its involvement in autosomal dominant human male infertility. This is not unexpected as only 4 autosomal dominant genes have so far been linked to isolated male infertility in humans \(^{5,9}\) . Broadly speaking, across genetic disorders, dominantly acting disease genes are usually intolerant to loss- of- function (LoF) mutations, as represented by a high pLI score \(^{10}\) . The median pLI score of genes with a LoF DNM ( \(n = 17\) ) in our cohort of male infertility cases was significantly higher than that of genes with 181 LoF DNMs identified in a cohort of 1,941 control cases from denovo- db v1.6. \(^{11}\) (pLI male infertility \(= 0.80\) , pLI controls \(= 3.75 \times 10^{- 5}\) , p- value \(= 1.00 \times 10^{- 5}\) ) (Figure 1). This observation indicates that LoF DNMs likely play an important role in male infertility, similar to what is known for developmental disorders and severe intellectual disability \(^{12,13}\) . As an example, a heterozygous likely pathogenic frameshift DNM was observed in the LoF intolerant gene GREB1L (pLI \(= 1\) ) of Proband_076. Homozygous Greb1L knock- out mice appear to be embryonic lethal, however, typical male infertility phenotypic features such as abnormal fetal testis morphology and decreased fetal testis volume are observed \(^{14}\) . Interestingly, this patient has a reduced testis volume and severe oligospermia (Supplementary Notes Table 1). Nonsense and missense mutations in GREB1L in humans are known to cause renal agenesis \(^{15}\) (OMIM: 617805), not known to be present in our patient. Of note, all previously reported damaging mutations in GREB1L causing renal agenesis are either maternally inherited or occurred de novo. This led the authors of one of these renal agenesis studies to speculate that
+
+<--- Page Split --->
+
+disruption to GREB1L could cause infertility in males14. A recent WES study involving a cohort of 285 infertile men also noted several patients presenting with pathogenic mutations in genes with an associated systemic disease where male fertility is not always assessed16. We also assessed the damaging effects of the two de novo CNVs by looking at the pL1 score of the genes involved. Proband_066 presented with a large 656 kb de novo deletion on chromosome 11, spanning 6 genes in total. This deletion partially overlapped with a deletion reported in 2014 in a patient with cryptorchidism and NOA17. Two genes affected in both patients, QSER1 and CSTF3, are extremely LOF-intolerant with pL1 scores of 1 and 0.98, respectively. In particular, CSTF3 is highly expressed within the testis and is known to be involved in pre- mRNA 3' end cleavage and polyyladenylation18.
+
+To systematically evaluate and predict the likelihood of these DNMs causing male infertility and identify novel candidate disease genes, we assessed the predicted pathogenicity of all DNMs using three prediction methods based on SIFT19, MutationTaster20 and PolyPhen221. Using this approach, 84/145 protein altering DNM were predicted to be pathogenic, while the remaining 61 were predicted to be benign. To further analyse the impact of the variants on the genes affected, we looked at the missense Z- score of all 122 genes affected by a missense variant, which indicates the tolerance of genes to missense mutations22. Our data highlights a significantly higher missense Z- score in genes affected by a missense DNM predicted as pathogenic (n=63) when compared to genes affected by predicted benign (n=59) missense DNMs (p- value=5.01x10-4, Figure 2, Supplementary Figure 4). Furthermore, using the STRING database23, we found a significant enrichment of protein interactions amongst the 84 genes affected by a protein altering DNM predicted to be pathogenic (PPI enrichment p- value = 2.35 x 10-2, Figure 3). No such enrichment was observed for the genes highlighted as likely benign (n=61, PPI enrichment p- value=0.206) or those affected by synonymous DNMs (n=35, PPI enrichment p- value=0.992, Supplementary Figure 5). These two findings suggest that (1) the predicted pathogenic missense DNMs detected in our study affect genes sensitive to missense mutations, and (2) the proteins affected by predicted pathogenic DNMs share common biological functions.
+
+The STRING network analysis also highlighted a central module of interconnected proteins with a significant enrichment of genes required for mRNA splicing (Supplementary Figure 6). The genes U2AF2, HNRNPL, CDC5L, CWC27 and RBM5 all contain predicted pathogenic DNMs and likely interact at a protein level during the mRNA splicing process. Pre- mRNA splicing allows gene functions to be expanded by creating alternative splice variants of gene products and is highly elaborated within the testis24. One of these genes, RBM5 has been previously highlighted as an essential regulator of haploid male germ cell pre- mRNA splicing and male fertility2. Mice with a homozygous ENU- induced allele point mutation in RBM5 present with azoospermia and germ cell development arrest at round spermatids. Whilst in mice a homozygous mutation in RBM5 is required to cause azoospermia, this may not be the case in humans as is well- documented for other genes25, including the recently reported male infertility gene SYCP20. Of note, RBM5 is a tumour suppressor in the lung26, with reduced expression affecting RNA splicing in patients with non- small cell lung cancer27. HNRNPL is another splicing factor affected by a possible pathogenic DNM in our study. One study implicated a role for HNRNPL in patients with Sertoli cell only phenotype28. The remaining three mRNA splicing genes have not yet been implicated in human male infertility. However, mRNA for all three is expressed at medium to high levels in human germ cells and all are widely expressed during spermatogenesis29. Specifically, CDC5L is a component of the PRP19- CDC5L complex that forms an integral part of the spliceosome and is required for activating pre- mRNA splicing30, as is CWC2731. U2AF2 plays a role in pre- mRNA splicing and 3'- end processing32. Interestingly, CSTF3, one of the genes affected by a de novo CNV in Proband_066, affects the same mRNA pathway17.
+
+Whilst DNMs most often cause dominant disease, they can contribute to recessive disease, usually in combination with an inherited variant on the trans allele. This was observed in Proband_060, who carried a DNM on the paternal allele, in trans with a maternally inherited variant in Testis and Ovary Specific PAZ Domain Containing 1 (TOPAZ1) (Supplementary Figure 7). TOPAZ1 is a germ- cell specific gene which is highly conserved in vertebrates33. Studies in mice revealed that Topaz1 plays a crucial role in spermatocyte, but not oocyte progression through meiosis34. In men, TOPAZ1 is expressed in germ cells in both sexes29,35,36. Analysis of the testicular biopsy of this patient revealed a germ cell arrest in early spermiogenesis (Figure 4).
+
+In addition to all systematic analyses described above, we evaluated the function of all DNM genes to give each a final pathogenicity classification (Table 1, details in Material & Methods). Of all 145 DNMs, 29 affected genes linked to male
+
+<--- Page Split --->
+
+reproduction and were classified as possibly causative. For replication purposes, unfortunately no other trio- based exome data are available for male infertility, although we note that a pilot study including 13 trios was recently published37. While this precluded a genuine replication study, we were able to study these candidate genes in exome datasets of infertile men (n=2,279), in collaboration with members of the International Male Infertility Genomics Consortium and the Geisinger Regeneron DiscovEHR collaboration38. The 33 candidate genes selected for this analysis include the 29 genes mentioned above and 4 additional LoF intolerant genes carrying LoF DNMs with an 'unclear' final pathogenicity classification. For comparison, we included an exome dataset from a cohort of 11,587 fertile men and women from Radboudumc.
+
+In the additional infertile cohorts, we identified only 2 LoF mutations in our DNM LoF intolerant genes (Supplementary table 2). Next, we looked for an enrichment of rare predicted pathogenic missense mutations in these cohorts (Table 2). A burden test revealed a significant enrichment in the number of such missense mutations present in infertile men compared to fertile men in the RBM5 gene (adjusted p- value=0.009). In this gene, 5 infertile men were found to carry a distinct rare pathogenic missense mutation, in addition to the proband with a de novo missense mutation (Supplementary figure 8, Supplementary table 3). Importantly, no such predicted pathogenic mutations were identified in men in the fertile cohort. In line with these results, RBM5, already highlighted above as an essential regulator of male germ cell pre- mRNA splicing and male infertility2, is highly intolerant to missense mutations (missense Z- score 4.17).
+
+Given the predicted impact of these DNMs on spermatogenesis, we were interested in studying the parental origin of DNMs in our trio- cohort. We were able to phase 29% of all our DNMs using a combination of short- read WES and targeted long- read sequencing (Supplementary Table 4). In agreement with literature39- 42, 72% of all DNMs occurred on the paternal allele. Interestingly, phasing of 8 likely causative DNMs showed that 6 of these were of paternal origin (75%). This suggests that DNMs with a deleterious effect on the future germline can escape negative selection in the paternal germline. This may be possible because the DNM occurred after the developmental window in which the gene is active, or the DNM may have affected a gene in the gamete's genome that is critical for somatic cells supporting the (future) germline. Transmission of pathogenic DNMs may also be facilitated by the fact that from spermatogonia onwards, male germ cells form cysts and share mRNAs and proteins43. As such, the interconnectedness of male germ cells, which is essential for their survival44, could mask detrimental effects of DNMs occurring during spermatogenesis.
+
+In 2010, we published a pilot study pointing to a de novo paradigm for mental retardation45 (now more appropriately termed developmental delay or intellectual disability). This work contributed to the widespread implementation of patient- parent WES studies in research and diagnostics for neurodevelopmental disorders46, accelerating disease gene identification and increasing the diagnostic yield for these disorders. The data presented here suggest that a similar benefit could be achieved from trio- based sequencing in male infertility. This will not only help to increase the diagnostic yield for men with infertility but will also enhance our fundamental biological understanding of human reproduction and natural selection.
+
+## Declarations
+
+## Data access
+
+Raw and processed exome sequencing data of our 185 patient- parent trios is available under controlled access and requires a Data Transfer Agreement from the European Genome- Phenome Archive (EGA) repository: EGAS00001004945.
+
+## Acknowledgements
+
+We are grateful for the participation of all patients and their parents in this study. We thank Laurens van de Wiel (Radboudumc), Sebastian Judd- Mole (Monash University), Arron Scott and Bryan Hepworth (Newcastle University) for technical support, and Margot J Wyrwoll (University of Münster) for help with handling MERGE samples and data. This project was funded by The Netherlands Organisation for Scientific Research (918- 15- 667) to JAV as well as an Investigator Award in Science from the Wellcome Trust (209451) to JAV, a grant from the Catherine van Tussenbroek Foundation to MSO, a UUKi Rutherford Fund Fellowship awarded to BJH and the German Research Foundation Clinical Research Unit 'Male Germ Cells'
+
+<--- Page Split --->
+
+(DFG, CRU326) to CF and FT. This project was also supported in part by funding from the Australian National Health and Medical Research Council (APP1120356) to MKOB, by grants from the National Institutes of Health of the United States of America (R01HD078641 to D.F.C and K.I.A, P50HD096723 to D.F.C.) and from the Biotechnology and Biological Sciences Research Council (BB/S008039/1) to D.JE.
+
+## Author contributions
+
+This study was designed by MSO, LELMV, LR and JAV. RMS, JG, HT and GWvdH provided all clinical data and performed the TESE histology and cytology analysis under supervision of LR, DDMB, ES, KF, KDH and KM. JC performed the exome sequencing with support from BA, and bioinformatics support was provided by MJX, GA, CG and SC. Sanger sequencing was performed by PFdV, HI, HES, LEB and BKSa. MSO and HES performed the SNV analyses with support from MJX, FKM performed CNV analysis with support from AM and MSK, and GSH and LEB performed the phasing. DJE, HS, BJH and MKOB provided support on the functional interpretation of mutations. DFC, LN, CF, SK, FT, KIA, ARE, CK, and CG- J were involved in the replication study. The first draft of the manuscript was prepared by MSO, HES, RMS, MJX, GWvdH, and JAV. All authors contributed to the final manuscript.
+
+## References
+
+1. Veltman, J. A. & Brunner, H. G. De novo mutations in human genetic disease. Nat. Rev. Genet.13, 565-575 (2012).
+2. O'Bryan, M. K. et al. RBM5 Is a Male Germ Cell Splicing Factor and Is Required for Spermatid Differentiation and Male Fertility. PLoS Genet.9, e1003628 (2013).
+3. Krausz, C. & Riera-Escamilla, A. Genetics of male infertility. Nat. Rev. Urol.15, 369-384 (2018).
+4. Tüttelmann, F., Ruckert, C. & Röpke, A. Disorders of spermatogenesis. medizinische Genet.30, 12-20 (2018).
+5. Oud, M. S. et al. A systematic review and standardized clinical validity assessment of male infertility genes. Hum. Reprod.34, 932-941 (2019).
+6. Kasak, L. & Laan, M. Monogenic causes of non-obstructive azoospermia: challenges, established knowledge, limitations and perspectives. Hum. Genet.140, 135-154 (2021).
+7. Sun, C. et al. An azoospermic man with a de novo point mutation in the Y-chromosomal gene USP9Y. Nat. Genet.23, 429-432 (1999).
+8. De Jonge, C. & Barratt, C. L. R. The present crisis in male reproductive health: an urgent need for a political, social, and research roadmap. Andrology7, 762-768 (2019).
+9. Schilit, S. L. P. et al. SYCP2 Translocation-Mediated Dysregulation and Frameshift Variants Cause Human Male Infertility. Am. J. Hum. Genet.106, 41-57 (2020).
+10. Lek, M. et al. Analysis of protein-coding genetic variation in 60,706 humans. Nature536, 285-291 (2016).
+11. denovo-db, Seattle, WA (denovo-db.gs.washington.edu) [Aug 2020].
+12. Gu, Y. et al. Three intellectual disability-associated de novo mutations in MECP2 identified by trio-WES analysis. BMC Med. Genet.21, 99 (2020).
+13. Fritzen, D. et al. De novo FBXO11 mutations are associated with intellectual disability and behavioural anomalies. Hum. Genet.137, 401-411 (2018).
+14. De Tomasi, L. et al. Mutations in GREB1L Cause Bilateral Kidney Agenesis in Humans and Mice. Am. J. Hum. Genet.101, 803-814 (2017).
+15. Brophy, P. D. et al. A Gene Implicated in Activation of Retinoic Acid Receptor Targets Is a Novel Renal Agenesis Gene in Humans. Genetics207, 215-228 (2017).
+16. Alhathal, N. et al. A genomics approach to male infertility. Genet. Med.22, 1967-1975 (2020).
+17. Seabra, C. M. et al. A novel Alu-mediated microdeletion at 11p13 removes WT1 in a patient with cryptorchidism and azoospermia. Reprod. Biomed. Online29, 388-391 (2014).
+
+<--- Page Split --->
+
+18. Grozdanov, P. N., Li, J., Yu, P., Yan, W. & MacDonald, C. C. Cstf2t Regulates expression of histones and histone-like proteins in male germ cells. Andrology6, 605-615 (2018).
+
+19. Vaser, R., Adusumalli, S., Leng, S. N., Sikic, M. & Ng, P. C. SIFT missense predictions for genomes. Nat. Protoc.11, 1-9 (2016).
+
+20. Schwarz, J. M., Rödelsperger, C., Schuelke, M. & Seelow, D. MutationTaster evaluates disease-causing potential of sequence alterations. Nat. Methods7, 575-576 (2010).
+
+21. Adzhuhei, I. A. et al. A method and server for predicting damaging missense mutations. Nat. Methods7, 248-249 (2010).
+
+22. Samocha, K. E. et al. A framework for the interpretation of de novo mutation in human disease. Nat. Genet.46, 944-950 (2014).
+
+23. Szklarczyk, D. et al. The STRING database in 2017: quality-controlled protein-protein association networks, made broadly accessible. Nucleic Acids Res.45, D362-D368 (2017).
+
+24. Song, H., Wang, L., Chen, D. & Li, F. The Function of Pre-mRNA Alternative Splicing in Mammal Spermatogenesis. Int. J. Biol. Sci.16, 38-48 (2020).
+
+25. Elsea, S. H. & Lucas, R. E. The Mousetrap: What We Can Learn When the Mouse Model Does Not Mimic the Human Disease. ILAR J.43, 66-79 (2002).
+
+26. Jamsai, D. et al. In vivo evidence that RBM5 is a tumour suppressor in the lung. Sci. Rep.7, 16323 (2017).
+
+27. Liang, H. et al. Differential Expression of RBM5, EGFR and KRAS mRNA and protein in non-small cell lung cancer tissues. J. Exp. Clin. Cancer Res.31, 36 (2012).
+
+28. Li, J. et al. HnRNPL as a key factor in spermatogenesis: Lesson from functional proteomic studies of azoospermia patients with sertoli cell only syndrome. J. Proteomics75, 2879-2891 (2012).
+
+29. Wang, M. et al. Single-Cell RNA Sequencing Analysis Reveals Sequential Cell Fate Transition during Human Spermatogenesis. Cell Stem Cell/23, 599-614.e4 (2018).
+
+30. Ajuh, P. Functional analysis of the human CDC5L complex and identification of its components by mass spectrometry. EMBO J.19, 6569-6581 (2000).
+
+31. Brea-Fernandez, A. J. et al. Expanding the clinical and molecular spectrum of the CWC27-related spliceosomopathy. J. Hum. Genet.64, 1133-1136 (2019).
+
+32. Millevoi, S. et al. An interaction between U2AF 65 and CF Im links the splicing and 3' end processing machineries. EMBO J.25, 4854-4864 (2006).
+
+33. Baillet, A. et al. TOPAZ1, a Novel Germ Cell-Specific Expressed Gene Conserved during Evolution across Vertebrates. PLoS One6, e26950 (2011).
+
+34. Luangpraseuth-Prosper, A. et al. TOPAZ1, a germ cell specific factor, is essential for male meiotic progression. Dev. Biol.406, 158-171 (2015).
+
+35. Guo, F. et al. The Transcriptome and DNA Methylome Landscapes of Human Primordial Germ Cells. Cel/161, 1437-1452 (2015).
+
+36. Li, L. et al. Single-Cell RNA-Seq Analysis Maps Development of Human Germline Cells and Gonadal Niche Interactions. Cell Stem Cell/20, 858-873.e4 (2017).
+
+37. Hodžić, A. et al. De novo mutations in idiopathic male infertility—A pilot study. Andrology9, 212-220 (2021).
+
+38. Dewey, F. E. et al. Distribution and clinical impact of functional variants in 50,726 whole-exome sequences from the DiscovEHR study. Science (80-).354, aaf6814 (2016).
+
+39. Francioli, L. C. et al. Genome-wide patterns and properties of de novo mutations in humans. Nat. Genet.47, 822-826 (2015).
+
+40. Rahbari, R. et al. Timing, rates and spectra of human germline mutation. Nat. Genet.48, 126-133 (2016).
+
+41. Goldmann, J. M. et al. Parent-of-origin-specific signatures of de novo mutations. Nat. Genet.48, 935-939 (2016).
+
+<--- Page Split --->
+
+42. Jónsson, H. et al. Parental influence on human germline de novo mutations in 1,548 trios from Iceland. Nature549, 519–522 (2017).
+
+43. Braun, R. E., Behringer, R. R., Peschon, J. J., Brinster, R. L. & Palmiter, R. D. Genetically haploid spermatids are phenotypically diploid. Nature337, 373–376 (1989).
+
+44. Greenbaum, M. P., Iwamori, T., Buchold, G. M. & Matzuk, M. M. Germ Cell Intercellular Bridges. Cold Spring Harb. Perspect. Biol.3, a005850–a005850 (2011).
+
+45. Vissers, L. E. L. M. et al. A de novo paradigm for mental retardation. Nat. Genet.42, 1109–12 (2010).
+
+46. Vissers, L. E. L. M., Gilissen, C. & Veltman, J. A. Genetic studies in intellectual disability and related disorders. Nat. Rev. Genet.17, 9–18 (2016).
+
+## Tables
+
+Table 1: De novo mutation classification summary.
+
+ | Possibly causative Unclear Unlikely causative Not Causative | Total |
| Missense | 21 | 38 | 50 | 13 | 122 |
| Frameshift | 4 | 8 | 1 | 0 | 13 |
| Stop gained | 1 | 3 | 0 | 0 | 4 |
| In-frame indels | 3 | 1 | 1 | 1 | 6 |
| Splice site variant | 0 | 0 | 0 | 11 | 11 |
| Synonymous | 0 | 0 | 0 | 36 | 36 |
| TOTAL | 29 | 50 | 52 | 61 | 192 |
+
+A total of 192 rare DNMs were classified based on pathogenicity scores as well as functional data into 4 categories, 'Possibly causative', 'Unclear', 'Unlikely Causative' and 'Not causative'.
+
+<--- Page Split --->
+
+
+| Gene | Missense NIJ/NCL Z-score | Cohort Cohort of Patient-Parent Trios (n=185) | NIJ/NCL Cohort of Infertile Men (Singleton) (n=145) | MERGEMENI Cohort of NOA Men (n=926) (n=887) | Geisinger-DiscoverEHR Cohort of Infertile Men (n=88) | Regeneron Italian Cohort of NOA Men (n=48) | Total Infertile Men (n=2,279) | Fertile Dutch Men (n=5,784) | Fertile Dutch Women (n=5,803) | Burden Burden test Fertile Women (Bone) |
| ABLIM1 | 1.62 | 1 | 1 | 1 | 1 | 0 | 5 | 1 | 1 | 0.15 |
| ATP1A1 | 6.22 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 1 |
| CDC5L | 2.78 | 1 | 1 | 1 | 3 | 0 | 6 | 2 | 4 | 0.15 |
| CDK5RAP2 | -0.37 | 1 | 0 | 1 | 1 | 0 | 3 | 5 | 5 | 1 |
| HUWE1 | 8.87 | 1 | 0 | 2 | 0 | 0 | 3 | 0 | 0 | 0.41 |
| INO80 | 3.53 | 1 | 0 | 1 | 0 | 0 | 2 | 3 | 3 | 1 |
| MAP3K3 | 2.04 | 1 | 0 | 2 | 0 | 0 | 3 | 1 | 2 | 1 |
| MCM6 | 1.07 | 1 | 1 | 1 | 3 | 0 | 6 | 4 | 8 | 0.64 |
| PPP1R7 | 1.86 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 1 |
| QSER1 | 1.34 | 0 | 1 | 1 | 0 | 0 | 2 | 8 | 1 | 1 |
| RASAL2 | 1.40 | 0 | 1 | 1 | 2 | 1 | 0 | 25 | 13 | 1 |
| RBM5 | 4.17 | 1 | 2 | 2 | 0 | 1 | 0 | 6 | 0 | 2 |
| RPA1 | 1.22 | 1 | 0 | 0 | 1 | 0 | 0 | 2 | 3 | 1 |
| SDF4 | 0.53 | 1 | 0 | 0 | 0 | 0 | 1 | 2 | 1 | 1 |
| SOGA1 | 2.27 | 1 | 0 | 1 | 1 | 0 | 0 | 3 | 15 | 5 |
| STARD10 | 1.34 | 1 | 0 | 2 | 0 | 0 | 0 | 3 | 4 | 1 |
| TENM2 | 3.30 | 1 | 0 | 2 | 2 | 0 | 2 | 7 | 16 | 1 |
| ZFHX4 | 1.01 | 0 | 0 | 3 | 3 | 0 | 0 | 6 | 14 | 8 |
+
+Table 2: Rare potentially pathogenic missense mutations in exome data from various cohorts of infertile men and fertile control cohorts.
+
+The genes included in this analysis were among the strongest candidate genes affected by a DNM (either missense or LoF mutation). The missense Z- score is included here to indicate a relative (in)tolerance to missense mutation. For the original NIJ/NCL discovery cohort, only the missense DNMs are included in this Table (7 of these genes were affected by a LoF DNM). A burden test was done to compare the total number of predicted pathogenic missense mutations observed in the infertile vs. fertile men, as well as between fertile men and fertile women (Fisher's Exact test, adjusted for multiple testing following Bonferroni correction).
+
+## Figures
+
+<--- Page Split --->
+
+
+Figure 1
+
+Analysis of the intolerance to loss- of- function variation for DNM genes. Violin plots represent the distribution of the pLI scores of all genes in gnomAD, all genes affected by DNMs and all LoF DNM in this study and in a control population (http://denovodb.gs.washington.edu/denovo- db/). The observed median pLI score is displayed for each category as a black circle. The closer the pLI score is to 1, the more intolerant to LoF variation a gene is10. Comparison between LoF DNMs in our study and control populations shows a significance difference (p- value=1.00x10- 5).
+
+<--- Page Split --->
+
+
+Figure 2
+
+Intolerance to missense variants for genes with a DNM. Violin plots show the distribution of Z- scores of genes containing a missense DNM in our cohort, where an enrichment can be observed for predicated pathogenic DNMs in genes more intolerant to missense mutations based on their mean z- score with a p- value of 5.01x10- 4.
+
+<--- Page Split --->
+
+
+Figure 3
+
+Protein- protein interactions predicted for proteins encoded by damaging DNM genes. A protein- protein interaction analysis was performed for all 84 genes containing a DNM scored as damaging using the STRING tool23. A significantly larger number of interactions is observed between our damaging DNM genes than is expected for a similar sized dataset of randomly selected genes (PPI enrichment p- value \(2.35 \times 10^{- 2}\) ) with the number of expected edges being 25 and the observed being 36. The central module of the main interaction network within the figure contains 5 genes which are all involved in the process of mRNA splicing (Supplementary figure 6)
+
+<--- Page Split --->
+
+
+Figure 4
+
+Description of control and TOPAZ1 proband testis histology and aberrant acrosome formation: (a,b): H&E stainings of (a) control and (b) Proband_060 with DNM in TOPAZ1 gene. The epithelium of the seminiferous tubules in the TOPAZ1 proband show reduced numbers of germ cells and an absence of elongating spermatids. (c,d): immunofluorescent labelling of DNA (magenta) and the acrosome (green) in control sections (c) and TOPAZ1 proband sections (d). (c) The arrowhead indicates the acrosome in an early round spermatid and the arrows the acrosome in elongating spermatids. Spreading of the acrosome and nuclear elongation are hallmarks of spermatid maturation. (d) No acrosomal spreading (see arrowheads) or nuclear elongation is observed in the TOPAZ1 proband. The asterisk indicates an example of progressive acrosome accumulation without spreading. Size bar in a, b: \(40 \mu \mathrm{m}\) , c, d: \(5 \mu \mathrm{m}\) .
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- SupplementaryNotes2GEMINIParticipatingAuthors.docx
+- Supplementaryfigures18.docx
+- Supplementaryfigures18.docx
+
+<--- Page Split --->
+
+SupplementaryNotes1. docxSupplementaryTable1AIDNM.pdfSupplementaryNotes2GEMINIParticipatingAuthors.docxSupplementaryTables25. docxSupplementaryNotesTables15. xlsxSupplementaryNotesTables15. xlsxSupplementaryNotes1. docxSupplementaryTable1AIDNM.pdfSupplementaryTables25. docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121_det.mmd b/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..0bd0fdf7c7b919e2218177cfc752e9865ea09d2c
--- /dev/null
+++ b/preprint/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121/preprint__050c6219ce16af260b359d04d33c8dd348aa20e8acd28ba4977974055fc13121_det.mmd
@@ -0,0 +1,347 @@
+<|ref|>sub_title<|/ref|><|det|>[[44, 106, 600, 137]]<|/det|>
+## A de novo paradigm for male infertility
+
+<|ref|>text<|/ref|><|det|>[[44, 152, 501, 207]]<|/det|>
+Joris Veltman ( joris.veltman@newcastle.ac.uk) Newcastle University https://orcid.org/0000- 0002- 3218- 8250
+
+<|ref|>text<|/ref|><|det|>[[44, 210, 450, 225]]<|/det|>
+Radboudumc https://orcid.org/0000- 0001- 9513- 3030
+
+<|ref|>text<|/ref|><|det|>[[44, 230, 152, 262]]<|/det|>
+Roos Smits Radboudumc
+
+<|ref|>text<|/ref|><|det|>[[44, 268, 207, 300]]<|/det|>
+Hannah Smith Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 306, 207, 320]]<|/det|>
+Francesco Mastrorosa
+
+<|ref|>text<|/ref|><|det|>[[44, 324, 500, 339]]<|/det|>
+Newcastle University https://orcid.org/0000- 0003- 0579- 1895
+
+<|ref|>text<|/ref|><|det|>[[44, 344, 207, 376]]<|/det|>
+Giles Holt Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 382, 259, 414]]<|/det|>
+Brendan Houston The University of Melbourne
+
+<|ref|>text<|/ref|><|det|>[[44, 420, 307, 452]]<|/det|>
+Petra de Vries Radboud University Medical Center
+
+<|ref|>text<|/ref|><|det|>[[44, 458, 500, 492]]<|/det|>
+Bilal Alobaidi Newcastle University https://orcid.org/0000- 0003- 2718- 4826
+
+<|ref|>text<|/ref|><|det|>[[44, 497, 207, 529]]<|/det|>
+Lois Batty Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 535, 207, 567]]<|/det|>
+Hadeel Ismail Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 573, 207, 605]]<|/det|>
+Jackie Greenwood Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 611, 750, 644]]<|/det|>
+Harsh Sheth Foundation for Research in Genetics and Endocrinology https://orcid.org/0000- 0001- 9626- 0971
+
+<|ref|>text<|/ref|><|det|>[[44, 649, 207, 681]]<|/det|>
+Aneta Mikulasova Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 687, 152, 719]]<|/det|>
+Galuh Astuti Radboudumc
+
+<|ref|>text<|/ref|><|det|>[[44, 725, 600, 758]]<|/det|>
+Christian Gilissen Radboud University Medical Center https://orcid.org/0000- 0003- 1693- 9699
+
+<|ref|>text<|/ref|><|det|>[[44, 763, 670, 797]]<|/det|>
+Kevin McEleny Newcastle Fertility Centre, The Newcastle upon Tyne Hospitals NHS Foundation Trust
+
+<|ref|>text<|/ref|><|det|>[[44, 803, 725, 836]]<|/det|>
+Helen Turner Department of Cellular Pathology, The Newcastle upon Tyne Hospitals NHS Foundation Trust
+
+<|ref|>text<|/ref|><|det|>[[44, 841, 207, 873]]<|/det|>
+Jonathan Coxhead Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 879, 207, 911]]<|/det|>
+Simon Cockell Newcastle University
+
+<|ref|>text<|/ref|><|det|>[[44, 917, 152, 950]]<|/det|>
+Didi Braat Radboudumc
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 42, 750, 800]]<|/det|>
+Kathrin Fleischer Radboudumc Kathleen D'Hauwers Radboudumc Ewout Schaafsma Radboudumc Liina Nagimaja Oregon Health & Science University; GEMINI consortium https://orcid.org/0000- 0003- 1948- 2495 Donald Conrad Oregon National Primate Research Center https://orcid.org/0000- 0003- 3828- 8970 Corinna Friedrich University of Münster Sabine Kliesch Centre of Reproductive Medicine and Andrology, Department of Clinical and Surgical Andrology, University Hospital Münster, Münster https://orcid.org/0000- 0002- 7561- 4870 Kenneth Aston University of Utah; GEMINI consortium Antoni Riera-Escamilla Fundació Puigvert, Universitat Autònoma de Barcelona, Instituto de Investigaciones Biomédicas Sant Pau Csilla Krausz University of Florence Claudia Gonzaga- Jauregui Regeneron Genetics Center, Regeneron Pharmaceuticals Mauro Santibanez- Koref Newcastle University David Elliott Newcastle University Lisenka Vissers Radboudumc https://orcid.org/0000- 0001- 6470- 5497 Frank Tüttelmann University of Münster https://orcid.org/0000- 0003- 2745- 9965 Moira O'Bryan The University of Melbourne; GEMINI consortium https://orcid.org/0000- 0001- 7298- 4940 Liliana Ramos Radboudumc Miguel Xavier Newcastle University https://orcid.org/0000- 0003- 0709- 7223 Godfried van der Heijden Radboudumc
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 824, 92, 839]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[42, 854, 422, 870]]<|/det|>
+Keywords: De novo mutations, male infertility, RBM5
+
+<|ref|>text<|/ref|><|det|>[[44, 885, 270, 901]]<|/det|>
+Posted Date: March 22nd, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 916, 392, 932]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 332732/v1
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 90, 890, 127]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on January 10th, 2022. See the published version at https://doi.org/10.1038/s41467-021-27132-8.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 140, 63]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[41, 75, 955, 265]]<|/det|>
+De novo mutations (DNMs) are known to play a prominent role in many sporadic disorders with reduced fitness. We hypothesize that DNMs play an important role in male infertility and explain a significant fraction of the genetic causes of this understudied disorder. We performed a trio- based exome- sequencing study in a unique cohort of 185 infertile males and their unaffected parents. Following a systematic analysis, 29 of 145 rare protein altering DNMs were classified as possibly causative of the male infertility phenotype. We observed a significant enrichment of Loss- of- Function (LoF) DNMs in LoF- intolerant genes (p- value \(= 1.00 \times 10 - 5\) ) as well as predicted pathogenic missense DNMs in missense- intolerant genes (p- value \(= 5.01 \times 10 - 4\) ). One DNM gene identified, RBM5, is an essential regulator of male germ cell pre- mRNA splicing. In a follow- up study, 5 rare pathogenic missense mutations affecting this gene were observed in a cohort of 2,279 infertile patients, with no such mutations found in a cohort of 5,784 fertile men (p- value \(= 0.009\) ). Our results provide the first evidence for the role of DNMs in severe male infertility and point to many new candidate genes affecting fertility.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 282, 101, 303]]<|/det|>
+## Main
+
+<|ref|>text<|/ref|><|det|>[[41, 315, 955, 532]]<|/det|>
+Male infertility contributes to approximately half of all cases of infertility and affects \(7\%\) of the male population. For the majority of these men the cause remains unexplained. Despite a clear role for genetic causes in male infertility, there is a distinct lack of diagnostically relevant genes and at least \(40\%\) of all cases are classified as idiopathic \(^{3 - 6}\) . Previous studies in other conditions with reproductive lethality, such as neurodevelopmental disorders, have demonstrated an important role for de novo mutations (DNMs) in their etiology \(^{1}\) . In line with this, recurrent de novo chromosomal abnormalities play an important role in male infertility. Both azoospermia Factor (AZF) deletions on the Y chromosome as well as an additional X chromosome, resulting in Klinefelter syndrome, occur de novo. Collectively, these de novo events explaining up to \(25\%\) of all cases of nonobstructive azoospermia (NOA) \(^{3,6}\) . Interestingly, in 1999 a DNM in the Y- chromosomal gene USP9Y was reported in a man with azoospermia \(^{7}\) . Until now, however, a systematic analysis of the role of DNMs in male infertility had not been attempted. This is partly explained by a lack of basic research in male reproductive health in general \(^{6,8}\) , but also by the practical challenges of collecting parental samples for this disorder, which is typically diagnosed in adults.
+
+<|ref|>text<|/ref|><|det|>[[41, 544, 953, 657]]<|/det|>
+In this study, we investigated the role of DNMs in 185 unexplained cases of oligozoospermia (<5 million sperm cells/ml; \(n = 74\) ) and azoospermia ( \(n = 111\) ) by performing whole exome sequencing (WES) in all patients and their parents (see Supplementary Figure 1 and 2, Supplementary notes and tables for details on methods and clinical description). In total, we identified and validated 192 rare DNMs, including 145 protein altering DNMs. All de novo point mutations were autosomal, except for one on chromosome X, and all occurred in different genes (Supplementary Table 1). Two de novo copy number variations (CNVs) were also identified affecting a total of 7 genes (Supplementary Figure 3).
+
+<|ref|>text<|/ref|><|det|>[[40, 669, 955, 942]]<|/det|>
+None of the 145- protein altering DNMs occurred in a gene already known for its involvement in autosomal dominant human male infertility. This is not unexpected as only 4 autosomal dominant genes have so far been linked to isolated male infertility in humans \(^{5,9}\) . Broadly speaking, across genetic disorders, dominantly acting disease genes are usually intolerant to loss- of- function (LoF) mutations, as represented by a high pLI score \(^{10}\) . The median pLI score of genes with a LoF DNM ( \(n = 17\) ) in our cohort of male infertility cases was significantly higher than that of genes with 181 LoF DNMs identified in a cohort of 1,941 control cases from denovo- db v1.6. \(^{11}\) (pLI male infertility \(= 0.80\) , pLI controls \(= 3.75 \times 10^{- 5}\) , p- value \(= 1.00 \times 10^{- 5}\) ) (Figure 1). This observation indicates that LoF DNMs likely play an important role in male infertility, similar to what is known for developmental disorders and severe intellectual disability \(^{12,13}\) . As an example, a heterozygous likely pathogenic frameshift DNM was observed in the LoF intolerant gene GREB1L (pLI \(= 1\) ) of Proband_076. Homozygous Greb1L knock- out mice appear to be embryonic lethal, however, typical male infertility phenotypic features such as abnormal fetal testis morphology and decreased fetal testis volume are observed \(^{14}\) . Interestingly, this patient has a reduced testis volume and severe oligospermia (Supplementary Notes Table 1). Nonsense and missense mutations in GREB1L in humans are known to cause renal agenesis \(^{15}\) (OMIM: 617805), not known to be present in our patient. Of note, all previously reported damaging mutations in GREB1L causing renal agenesis are either maternally inherited or occurred de novo. This led the authors of one of these renal agenesis studies to speculate that
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[41, 45, 956, 182]]<|/det|>
+disruption to GREB1L could cause infertility in males14. A recent WES study involving a cohort of 285 infertile men also noted several patients presenting with pathogenic mutations in genes with an associated systemic disease where male fertility is not always assessed16. We also assessed the damaging effects of the two de novo CNVs by looking at the pL1 score of the genes involved. Proband_066 presented with a large 656 kb de novo deletion on chromosome 11, spanning 6 genes in total. This deletion partially overlapped with a deletion reported in 2014 in a patient with cryptorchidism and NOA17. Two genes affected in both patients, QSER1 and CSTF3, are extremely LOF-intolerant with pL1 scores of 1 and 0.98, respectively. In particular, CSTF3 is highly expressed within the testis and is known to be involved in pre- mRNA 3' end cleavage and polyyladenylation18.
+
+<|ref|>text<|/ref|><|det|>[[40, 194, 955, 450]]<|/det|>
+To systematically evaluate and predict the likelihood of these DNMs causing male infertility and identify novel candidate disease genes, we assessed the predicted pathogenicity of all DNMs using three prediction methods based on SIFT19, MutationTaster20 and PolyPhen221. Using this approach, 84/145 protein altering DNM were predicted to be pathogenic, while the remaining 61 were predicted to be benign. To further analyse the impact of the variants on the genes affected, we looked at the missense Z- score of all 122 genes affected by a missense variant, which indicates the tolerance of genes to missense mutations22. Our data highlights a significantly higher missense Z- score in genes affected by a missense DNM predicted as pathogenic (n=63) when compared to genes affected by predicted benign (n=59) missense DNMs (p- value=5.01x10-4, Figure 2, Supplementary Figure 4). Furthermore, using the STRING database23, we found a significant enrichment of protein interactions amongst the 84 genes affected by a protein altering DNM predicted to be pathogenic (PPI enrichment p- value = 2.35 x 10-2, Figure 3). No such enrichment was observed for the genes highlighted as likely benign (n=61, PPI enrichment p- value=0.206) or those affected by synonymous DNMs (n=35, PPI enrichment p- value=0.992, Supplementary Figure 5). These two findings suggest that (1) the predicted pathogenic missense DNMs detected in our study affect genes sensitive to missense mutations, and (2) the proteins affected by predicted pathogenic DNMs share common biological functions.
+
+<|ref|>text<|/ref|><|det|>[[40, 461, 950, 778]]<|/det|>
+The STRING network analysis also highlighted a central module of interconnected proteins with a significant enrichment of genes required for mRNA splicing (Supplementary Figure 6). The genes U2AF2, HNRNPL, CDC5L, CWC27 and RBM5 all contain predicted pathogenic DNMs and likely interact at a protein level during the mRNA splicing process. Pre- mRNA splicing allows gene functions to be expanded by creating alternative splice variants of gene products and is highly elaborated within the testis24. One of these genes, RBM5 has been previously highlighted as an essential regulator of haploid male germ cell pre- mRNA splicing and male fertility2. Mice with a homozygous ENU- induced allele point mutation in RBM5 present with azoospermia and germ cell development arrest at round spermatids. Whilst in mice a homozygous mutation in RBM5 is required to cause azoospermia, this may not be the case in humans as is well- documented for other genes25, including the recently reported male infertility gene SYCP20. Of note, RBM5 is a tumour suppressor in the lung26, with reduced expression affecting RNA splicing in patients with non- small cell lung cancer27. HNRNPL is another splicing factor affected by a possible pathogenic DNM in our study. One study implicated a role for HNRNPL in patients with Sertoli cell only phenotype28. The remaining three mRNA splicing genes have not yet been implicated in human male infertility. However, mRNA for all three is expressed at medium to high levels in human germ cells and all are widely expressed during spermatogenesis29. Specifically, CDC5L is a component of the PRP19- CDC5L complex that forms an integral part of the spliceosome and is required for activating pre- mRNA splicing30, as is CWC2731. U2AF2 plays a role in pre- mRNA splicing and 3'- end processing32. Interestingly, CSTF3, one of the genes affected by a de novo CNV in Proband_066, affects the same mRNA pathway17.
+
+<|ref|>text<|/ref|><|det|>[[40, 790, 947, 908]]<|/det|>
+Whilst DNMs most often cause dominant disease, they can contribute to recessive disease, usually in combination with an inherited variant on the trans allele. This was observed in Proband_060, who carried a DNM on the paternal allele, in trans with a maternally inherited variant in Testis and Ovary Specific PAZ Domain Containing 1 (TOPAZ1) (Supplementary Figure 7). TOPAZ1 is a germ- cell specific gene which is highly conserved in vertebrates33. Studies in mice revealed that Topaz1 plays a crucial role in spermatocyte, but not oocyte progression through meiosis34. In men, TOPAZ1 is expressed in germ cells in both sexes29,35,36. Analysis of the testicular biopsy of this patient revealed a germ cell arrest in early spermiogenesis (Figure 4).
+
+<|ref|>text<|/ref|><|det|>[[40, 921, 899, 958]]<|/det|>
+In addition to all systematic analyses described above, we evaluated the function of all DNM genes to give each a final pathogenicity classification (Table 1, details in Material & Methods). Of all 145 DNMs, 29 affected genes linked to male
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 44, 949, 177]]<|/det|>
+reproduction and were classified as possibly causative. For replication purposes, unfortunately no other trio- based exome data are available for male infertility, although we note that a pilot study including 13 trios was recently published37. While this precluded a genuine replication study, we were able to study these candidate genes in exome datasets of infertile men (n=2,279), in collaboration with members of the International Male Infertility Genomics Consortium and the Geisinger Regeneron DiscovEHR collaboration38. The 33 candidate genes selected for this analysis include the 29 genes mentioned above and 4 additional LoF intolerant genes carrying LoF DNMs with an 'unclear' final pathogenicity classification. For comparison, we included an exome dataset from a cohort of 11,587 fertile men and women from Radboudumc.
+
+<|ref|>text<|/ref|><|det|>[[42, 191, 958, 344]]<|/det|>
+In the additional infertile cohorts, we identified only 2 LoF mutations in our DNM LoF intolerant genes (Supplementary table 2). Next, we looked for an enrichment of rare predicted pathogenic missense mutations in these cohorts (Table 2). A burden test revealed a significant enrichment in the number of such missense mutations present in infertile men compared to fertile men in the RBM5 gene (adjusted p- value=0.009). In this gene, 5 infertile men were found to carry a distinct rare pathogenic missense mutation, in addition to the proband with a de novo missense mutation (Supplementary figure 8, Supplementary table 3). Importantly, no such predicted pathogenic mutations were identified in men in the fertile cohort. In line with these results, RBM5, already highlighted above as an essential regulator of male germ cell pre- mRNA splicing and male infertility2, is highly intolerant to missense mutations (missense Z- score 4.17).
+
+<|ref|>text<|/ref|><|det|>[[42, 357, 958, 546]]<|/det|>
+Given the predicted impact of these DNMs on spermatogenesis, we were interested in studying the parental origin of DNMs in our trio- cohort. We were able to phase 29% of all our DNMs using a combination of short- read WES and targeted long- read sequencing (Supplementary Table 4). In agreement with literature39- 42, 72% of all DNMs occurred on the paternal allele. Interestingly, phasing of 8 likely causative DNMs showed that 6 of these were of paternal origin (75%). This suggests that DNMs with a deleterious effect on the future germline can escape negative selection in the paternal germline. This may be possible because the DNM occurred after the developmental window in which the gene is active, or the DNM may have affected a gene in the gamete's genome that is critical for somatic cells supporting the (future) germline. Transmission of pathogenic DNMs may also be facilitated by the fact that from spermatogonia onwards, male germ cells form cysts and share mRNAs and proteins43. As such, the interconnectedness of male germ cells, which is essential for their survival44, could mask detrimental effects of DNMs occurring during spermatogenesis.
+
+<|ref|>text<|/ref|><|det|>[[42, 561, 950, 675]]<|/det|>
+In 2010, we published a pilot study pointing to a de novo paradigm for mental retardation45 (now more appropriately termed developmental delay or intellectual disability). This work contributed to the widespread implementation of patient- parent WES studies in research and diagnostics for neurodevelopmental disorders46, accelerating disease gene identification and increasing the diagnostic yield for these disorders. The data presented here suggest that a similar benefit could be achieved from trio- based sequencing in male infertility. This will not only help to increase the diagnostic yield for men with infertility but will also enhance our fundamental biological understanding of human reproduction and natural selection.
+
+<|ref|>sub_title<|/ref|><|det|>[[45, 695, 184, 715]]<|/det|>
+## Declarations
+
+<|ref|>sub_title<|/ref|><|det|>[[45, 729, 135, 744]]<|/det|>
+## Data access
+
+<|ref|>text<|/ref|><|det|>[[45, 759, 944, 796]]<|/det|>
+Raw and processed exome sequencing data of our 185 patient- parent trios is available under controlled access and requires a Data Transfer Agreement from the European Genome- Phenome Archive (EGA) repository: EGAS00001004945.
+
+<|ref|>sub_title<|/ref|><|det|>[[45, 810, 186, 826]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[42, 841, 950, 953]]<|/det|>
+We are grateful for the participation of all patients and their parents in this study. We thank Laurens van de Wiel (Radboudumc), Sebastian Judd- Mole (Monash University), Arron Scott and Bryan Hepworth (Newcastle University) for technical support, and Margot J Wyrwoll (University of Münster) for help with handling MERGE samples and data. This project was funded by The Netherlands Organisation for Scientific Research (918- 15- 667) to JAV as well as an Investigator Award in Science from the Wellcome Trust (209451) to JAV, a grant from the Catherine van Tussenbroek Foundation to MSO, a UUKi Rutherford Fund Fellowship awarded to BJH and the German Research Foundation Clinical Research Unit 'Male Germ Cells'
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 43, 920, 119]]<|/det|>
+(DFG, CRU326) to CF and FT. This project was also supported in part by funding from the Australian National Health and Medical Research Council (APP1120356) to MKOB, by grants from the National Institutes of Health of the United States of America (R01HD078641 to D.F.C and K.I.A, P50HD096723 to D.F.C.) and from the Biotechnology and Biological Sciences Research Council (BB/S008039/1) to D.JE.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 133, 193, 149]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[42, 162, 945, 313]]<|/det|>
+This study was designed by MSO, LELMV, LR and JAV. RMS, JG, HT and GWvdH provided all clinical data and performed the TESE histology and cytology analysis under supervision of LR, DDMB, ES, KF, KDH and KM. JC performed the exome sequencing with support from BA, and bioinformatics support was provided by MJX, GA, CG and SC. Sanger sequencing was performed by PFdV, HI, HES, LEB and BKSa. MSO and HES performed the SNV analyses with support from MJX, FKM performed CNV analysis with support from AM and MSK, and GSH and LEB performed the phasing. DJE, HS, BJH and MKOB provided support on the functional interpretation of mutations. DFC, LN, CF, SK, FT, KIA, ARE, CK, and CG- J were involved in the replication study. The first draft of the manuscript was prepared by MSO, HES, RMS, MJX, GWvdH, and JAV. All authors contributed to the final manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 331, 170, 353]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[45, 364, 945, 950]]<|/det|>
+1. Veltman, J. A. & Brunner, H. G. De novo mutations in human genetic disease. Nat. Rev. Genet.13, 565-575 (2012).
+2. O'Bryan, M. K. et al. RBM5 Is a Male Germ Cell Splicing Factor and Is Required for Spermatid Differentiation and Male Fertility. PLoS Genet.9, e1003628 (2013).
+3. Krausz, C. & Riera-Escamilla, A. Genetics of male infertility. Nat. Rev. Urol.15, 369-384 (2018).
+4. Tüttelmann, F., Ruckert, C. & Röpke, A. Disorders of spermatogenesis. medizinische Genet.30, 12-20 (2018).
+5. Oud, M. S. et al. A systematic review and standardized clinical validity assessment of male infertility genes. Hum. Reprod.34, 932-941 (2019).
+6. Kasak, L. & Laan, M. Monogenic causes of non-obstructive azoospermia: challenges, established knowledge, limitations and perspectives. Hum. Genet.140, 135-154 (2021).
+7. Sun, C. et al. An azoospermic man with a de novo point mutation in the Y-chromosomal gene USP9Y. Nat. Genet.23, 429-432 (1999).
+8. De Jonge, C. & Barratt, C. L. R. The present crisis in male reproductive health: an urgent need for a political, social, and research roadmap. Andrology7, 762-768 (2019).
+9. Schilit, S. L. P. et al. SYCP2 Translocation-Mediated Dysregulation and Frameshift Variants Cause Human Male Infertility. Am. J. Hum. Genet.106, 41-57 (2020).
+10. Lek, M. et al. Analysis of protein-coding genetic variation in 60,706 humans. Nature536, 285-291 (2016).
+11. denovo-db, Seattle, WA (denovo-db.gs.washington.edu) [Aug 2020].
+12. Gu, Y. et al. Three intellectual disability-associated de novo mutations in MECP2 identified by trio-WES analysis. BMC Med. Genet.21, 99 (2020).
+13. Fritzen, D. et al. De novo FBXO11 mutations are associated with intellectual disability and behavioural anomalies. Hum. Genet.137, 401-411 (2018).
+14. De Tomasi, L. et al. Mutations in GREB1L Cause Bilateral Kidney Agenesis in Humans and Mice. Am. J. Hum. Genet.101, 803-814 (2017).
+15. Brophy, P. D. et al. A Gene Implicated in Activation of Retinoic Acid Receptor Targets Is a Novel Renal Agenesis Gene in Humans. Genetics207, 215-228 (2017).
+16. Alhathal, N. et al. A genomics approach to male infertility. Genet. Med.22, 1967-1975 (2020).
+17. Seabra, C. M. et al. A novel Alu-mediated microdeletion at 11p13 removes WT1 in a patient with cryptorchidism and azoospermia. Reprod. Biomed. Online29, 388-391 (2014).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[45, 42, 950, 93]]<|/det|>
+18. Grozdanov, P. N., Li, J., Yu, P., Yan, W. & MacDonald, C. C. Cstf2t Regulates expression of histones and histone-like proteins in male germ cells. Andrology6, 605-615 (2018).
+
+<|ref|>text<|/ref|><|det|>[[45, 87, 930, 124]]<|/det|>
+19. Vaser, R., Adusumalli, S., Leng, S. N., Sikic, M. & Ng, P. C. SIFT missense predictions for genomes. Nat. Protoc.11, 1-9 (2016).
+
+<|ref|>text<|/ref|><|det|>[[45, 127, 896, 163]]<|/det|>
+20. Schwarz, J. M., Rödelsperger, C., Schuelke, M. & Seelow, D. MutationTaster evaluates disease-causing potential of sequence alterations. Nat. Methods7, 575-576 (2010).
+
+<|ref|>text<|/ref|><|det|>[[45, 167, 940, 186]]<|/det|>
+21. Adzhuhei, I. A. et al. A method and server for predicting damaging missense mutations. Nat. Methods7, 248-249 (2010).
+
+<|ref|>text<|/ref|><|det|>[[45, 189, 936, 225]]<|/det|>
+22. Samocha, K. E. et al. A framework for the interpretation of de novo mutation in human disease. Nat. Genet.46, 944-950 (2014).
+
+<|ref|>text<|/ref|><|det|>[[45, 229, 945, 266]]<|/det|>
+23. Szklarczyk, D. et al. The STRING database in 2017: quality-controlled protein-protein association networks, made broadly accessible. Nucleic Acids Res.45, D362-D368 (2017).
+
+<|ref|>text<|/ref|><|det|>[[45, 269, 930, 306]]<|/det|>
+24. Song, H., Wang, L., Chen, D. & Li, F. The Function of Pre-mRNA Alternative Splicing in Mammal Spermatogenesis. Int. J. Biol. Sci.16, 38-48 (2020).
+
+<|ref|>text<|/ref|><|det|>[[45, 309, 904, 346]]<|/det|>
+25. Elsea, S. H. & Lucas, R. E. The Mousetrap: What We Can Learn When the Mouse Model Does Not Mimic the Human Disease. ILAR J.43, 66-79 (2002).
+
+<|ref|>text<|/ref|><|det|>[[45, 350, 830, 369]]<|/det|>
+26. Jamsai, D. et al. In vivo evidence that RBM5 is a tumour suppressor in the lung. Sci. Rep.7, 16323 (2017).
+
+<|ref|>text<|/ref|><|det|>[[45, 372, 940, 410]]<|/det|>
+27. Liang, H. et al. Differential Expression of RBM5, EGFR and KRAS mRNA and protein in non-small cell lung cancer tissues. J. Exp. Clin. Cancer Res.31, 36 (2012).
+
+<|ref|>text<|/ref|><|det|>[[45, 413, 900, 450]]<|/det|>
+28. Li, J. et al. HnRNPL as a key factor in spermatogenesis: Lesson from functional proteomic studies of azoospermia patients with sertoli cell only syndrome. J. Proteomics75, 2879-2891 (2012).
+
+<|ref|>text<|/ref|><|det|>[[45, 454, 846, 491]]<|/det|>
+29. Wang, M. et al. Single-Cell RNA Sequencing Analysis Reveals Sequential Cell Fate Transition during Human Spermatogenesis. Cell Stem Cell/23, 599-614.e4 (2018).
+
+<|ref|>text<|/ref|><|det|>[[45, 494, 925, 531]]<|/det|>
+30. Ajuh, P. Functional analysis of the human CDC5L complex and identification of its components by mass spectrometry. EMBO J.19, 6569-6581 (2000).
+
+<|ref|>text<|/ref|><|det|>[[45, 535, 925, 572]]<|/det|>
+31. Brea-Fernandez, A. J. et al. Expanding the clinical and molecular spectrum of the CWC27-related spliceosomopathy. J. Hum. Genet.64, 1133-1136 (2019).
+
+<|ref|>text<|/ref|><|det|>[[45, 576, 936, 613]]<|/det|>
+32. Millevoi, S. et al. An interaction between U2AF 65 and CF Im links the splicing and 3' end processing machineries. EMBO J.25, 4854-4864 (2006).
+
+<|ref|>text<|/ref|><|det|>[[45, 617, 945, 654]]<|/det|>
+33. Baillet, A. et al. TOPAZ1, a Novel Germ Cell-Specific Expressed Gene Conserved during Evolution across Vertebrates. PLoS One6, e26950 (2011).
+
+<|ref|>text<|/ref|><|det|>[[45, 658, 900, 695]]<|/det|>
+34. Luangpraseuth-Prosper, A. et al. TOPAZ1, a germ cell specific factor, is essential for male meiotic progression. Dev. Biol.406, 158-171 (2015).
+
+<|ref|>text<|/ref|><|det|>[[45, 699, 940, 736]]<|/det|>
+35. Guo, F. et al. The Transcriptome and DNA Methylome Landscapes of Human Primordial Germ Cells. Cel/161, 1437-1452 (2015).
+
+<|ref|>text<|/ref|><|det|>[[45, 740, 950, 777]]<|/det|>
+36. Li, L. et al. Single-Cell RNA-Seq Analysis Maps Development of Human Germline Cells and Gonadal Niche Interactions. Cell Stem Cell/20, 858-873.e4 (2017).
+
+<|ref|>text<|/ref|><|det|>[[45, 781, 848, 800]]<|/det|>
+37. Hodžić, A. et al. De novo mutations in idiopathic male infertility—A pilot study. Andrology9, 212-220 (2021).
+
+<|ref|>text<|/ref|><|det|>[[45, 803, 904, 841]]<|/det|>
+38. Dewey, F. E. et al. Distribution and clinical impact of functional variants in 50,726 whole-exome sequences from the DiscovEHR study. Science (80-).354, aaf6814 (2016).
+
+<|ref|>text<|/ref|><|det|>[[45, 844, 909, 881]]<|/det|>
+39. Francioli, L. C. et al. Genome-wide patterns and properties of de novo mutations in humans. Nat. Genet.47, 822-826 (2015).
+
+<|ref|>text<|/ref|><|det|>[[45, 885, 825, 903]]<|/det|>
+40. Rahbari, R. et al. Timing, rates and spectra of human germline mutation. Nat. Genet.48, 126-133 (2016).
+
+<|ref|>text<|/ref|><|det|>[[45, 907, 880, 925]]<|/det|>
+41. Goldmann, J. M. et al. Parent-of-origin-specific signatures of de novo mutations. Nat. Genet.48, 935-939 (2016).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[48, 44, 936, 80]]<|/det|>
+42. Jónsson, H. et al. Parental influence on human germline de novo mutations in 1,548 trios from Iceland. Nature549, 519–522 (2017).
+
+<|ref|>text<|/ref|><|det|>[[48, 86, 852, 121]]<|/det|>
+43. Braun, R. E., Behringer, R. R., Peschon, J. J., Brinster, R. L. & Palmiter, R. D. Genetically haploid spermatids are phenotypically diploid. Nature337, 373–376 (1989).
+
+<|ref|>text<|/ref|><|det|>[[48, 127, 937, 161]]<|/det|>
+44. Greenbaum, M. P., Iwamori, T., Buchold, G. M. & Matzuk, M. M. Germ Cell Intercellular Bridges. Cold Spring Harb. Perspect. Biol.3, a005850–a005850 (2011).
+
+<|ref|>text<|/ref|><|det|>[[48, 168, 790, 184]]<|/det|>
+45. Vissers, L. E. L. M. et al. A de novo paradigm for mental retardation. Nat. Genet.42, 1109–12 (2010).
+
+<|ref|>text<|/ref|><|det|>[[48, 190, 920, 225]]<|/det|>
+46. Vissers, L. E. L. M., Gilissen, C. & Veltman, J. A. Genetic studies in intellectual disability and related disorders. Nat. Rev. Genet.17, 9–18 (2016).
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 245, 121, 264]]<|/det|>
+## Tables
+
+<|ref|>table_caption<|/ref|><|det|>[[44, 277, 363, 290]]<|/det|>
+Table 1: De novo mutation classification summary.
+
+<|ref|>table<|/ref|><|det|>[[170, 295, 826, 461]]<|/det|>
+ | Possibly causative Unclear Unlikely causative Not Causative | Total |
| Missense | 21 | 38 | 50 | 13 | 122 |
| Frameshift | 4 | 8 | 1 | 0 | 13 |
| Stop gained | 1 | 3 | 0 | 0 | 4 |
| In-frame indels | 3 | 1 | 1 | 1 | 6 |
| Splice site variant | 0 | 0 | 0 | 11 | 11 |
| Synonymous | 0 | 0 | 0 | 36 | 36 |
| TOTAL | 29 | 50 | 52 | 61 | 192 |
+
+<|ref|>text<|/ref|><|det|>[[44, 474, 952, 501]]<|/det|>
+A total of 192 rare DNMs were classified based on pathogenicity scores as well as functional data into 4 categories, 'Possibly causative', 'Unclear', 'Unlikely Causative' and 'Not causative'.
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[44, 44, 958, 472]]<|/det|>
+
+| Gene | Missense NIJ/NCL Z-score | Cohort Cohort of Patient-Parent Trios (n=185) | NIJ/NCL Cohort of Infertile Men (Singleton) (n=145) | MERGEMENI Cohort of NOA Men (n=926) (n=887) | Geisinger-DiscoverEHR Cohort of Infertile Men (n=88) | Regeneron Italian Cohort of NOA Men (n=48) | Total Infertile Men (n=2,279) | Fertile Dutch Men (n=5,784) | Fertile Dutch Women (n=5,803) | Burden Burden test Fertile Women (Bone) |
| ABLIM1 | 1.62 | 1 | 1 | 1 | 1 | 0 | 5 | 1 | 1 | 0.15 |
| ATP1A1 | 6.22 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 1 |
| CDC5L | 2.78 | 1 | 1 | 1 | 3 | 0 | 6 | 2 | 4 | 0.15 |
| CDK5RAP2 | -0.37 | 1 | 0 | 1 | 1 | 0 | 3 | 5 | 5 | 1 |
| HUWE1 | 8.87 | 1 | 0 | 2 | 0 | 0 | 3 | 0 | 0 | 0.41 |
| INO80 | 3.53 | 1 | 0 | 1 | 0 | 0 | 2 | 3 | 3 | 1 |
| MAP3K3 | 2.04 | 1 | 0 | 2 | 0 | 0 | 3 | 1 | 2 | 1 |
| MCM6 | 1.07 | 1 | 1 | 1 | 3 | 0 | 6 | 4 | 8 | 0.64 |
| PPP1R7 | 1.86 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 1 |
| QSER1 | 1.34 | 0 | 1 | 1 | 0 | 0 | 2 | 8 | 1 | 1 |
| RASAL2 | 1.40 | 0 | 1 | 1 | 2 | 1 | 0 | 25 | 13 | 1 |
| RBM5 | 4.17 | 1 | 2 | 2 | 0 | 1 | 0 | 6 | 0 | 2 |
| RPA1 | 1.22 | 1 | 0 | 0 | 1 | 0 | 0 | 2 | 3 | 1 |
| SDF4 | 0.53 | 1 | 0 | 0 | 0 | 0 | 1 | 2 | 1 | 1 |
| SOGA1 | 2.27 | 1 | 0 | 1 | 1 | 0 | 0 | 3 | 15 | 5 |
| STARD10 | 1.34 | 1 | 0 | 2 | 0 | 0 | 0 | 3 | 4 | 1 |
| TENM2 | 3.30 | 1 | 0 | 2 | 2 | 0 | 2 | 7 | 16 | 1 |
| ZFHX4 | 1.01 | 0 | 0 | 3 | 3 | 0 | 0 | 6 | 14 | 8 |
+
+<|ref|>table_footnote<|/ref|><|det|>[[45, 483, 955, 497]]<|/det|>
+Table 2: Rare potentially pathogenic missense mutations in exome data from various cohorts of infertile men and fertile control cohorts.
+
+<|ref|>text<|/ref|><|det|>[[44, 507, 955, 570]]<|/det|>
+The genes included in this analysis were among the strongest candidate genes affected by a DNM (either missense or LoF mutation). The missense Z- score is included here to indicate a relative (in)tolerance to missense mutation. For the original NIJ/NCL discovery cohort, only the missense DNMs are included in this Table (7 of these genes were affected by a LoF DNM). A burden test was done to compare the total number of predicted pathogenic missense mutations observed in the infertile vs. fertile men, as well as between fertile men and fertile women (Fisher's Exact test, adjusted for multiple testing following Bonferroni correction).
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 586, 126, 607]]<|/det|>
+## Figures
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[45, 45, 805, 550]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[42, 564, 104, 580]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[41, 599, 951, 693]]<|/det|>
+Analysis of the intolerance to loss- of- function variation for DNM genes. Violin plots represent the distribution of the pLI scores of all genes in gnomAD, all genes affected by DNMs and all LoF DNM in this study and in a control population (http://denovodb.gs.washington.edu/denovo- db/). The observed median pLI score is displayed for each category as a black circle. The closer the pLI score is to 1, the more intolerant to LoF variation a gene is10. Comparison between LoF DNMs in our study and control populations shows a significance difference (p- value=1.00x10- 5).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[45, 48, 790, 560]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 578, 106, 594]]<|/det|>
+Figure 2
+
+<|ref|>text<|/ref|><|det|>[[43, 612, 941, 667]]<|/det|>
+Intolerance to missense variants for genes with a DNM. Violin plots show the distribution of Z- scores of genes containing a missense DNM in our cohort, where an enrichment can be observed for predicated pathogenic DNMs in genes more intolerant to missense mutations based on their mean z- score with a p- value of 5.01x10- 4.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[45, 48, 787, 496]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 514, 105, 530]]<|/det|>
+Figure 3
+
+<|ref|>text<|/ref|><|det|>[[42, 547, 955, 660]]<|/det|>
+Protein- protein interactions predicted for proteins encoded by damaging DNM genes. A protein- protein interaction analysis was performed for all 84 genes containing a DNM scored as damaging using the STRING tool23. A significantly larger number of interactions is observed between our damaging DNM genes than is expected for a similar sized dataset of randomly selected genes (PPI enrichment p- value \(2.35 \times 10^{- 2}\) ) with the number of expected edges being 25 and the observed being 36. The central module of the main interaction network within the figure contains 5 genes which are all involved in the process of mRNA splicing (Supplementary figure 6)
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[45, 45, 781, 601]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[44, 621, 106, 637]]<|/det|>
+Figure 4
+
+<|ref|>text<|/ref|><|det|>[[41, 655, 953, 805]]<|/det|>
+Description of control and TOPAZ1 proband testis histology and aberrant acrosome formation: (a,b): H&E stainings of (a) control and (b) Proband_060 with DNM in TOPAZ1 gene. The epithelium of the seminiferous tubules in the TOPAZ1 proband show reduced numbers of germ cells and an absence of elongating spermatids. (c,d): immunofluorescent labelling of DNA (magenta) and the acrosome (green) in control sections (c) and TOPAZ1 proband sections (d). (c) The arrowhead indicates the acrosome in an early round spermatid and the arrows the acrosome in elongating spermatids. Spreading of the acrosome and nuclear elongation are hallmarks of spermatid maturation. (d) No acrosomal spreading (see arrowheads) or nuclear elongation is observed in the TOPAZ1 proband. The asterisk indicates an example of progressive acrosome accumulation without spreading. Size bar in a, b: \(40 \mu \mathrm{m}\) , c, d: \(5 \mu \mathrm{m}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 824, 265, 847]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 866, 641, 883]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[57, 898, 479, 959]]<|/det|>
+- SupplementaryNotes2GEMINIParticipatingAuthors.docx
+- Supplementaryfigures18.docx
+- Supplementaryfigures18.docx
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 45, 480, 239]]<|/det|>
+SupplementaryNotes1. docxSupplementaryTable1AIDNM.pdfSupplementaryNotes2GEMINIParticipatingAuthors.docxSupplementaryTables25. docxSupplementaryNotesTables15. xlsxSupplementaryNotesTables15. xlsxSupplementaryNotes1. docxSupplementaryTable1AIDNM.pdfSupplementaryTables25. docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/images_list.json b/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..3179e2182380902f238b215088efd24d8f3871e4
--- /dev/null
+++ b/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/images_list.json
@@ -0,0 +1,40 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig.1. Keyhole collapse mechanism and related keyhole melting regime transitions in LPBF. (a) Keyhole morphology variations across the (I) quasi-stable, (II) transition and (III) unstable keyhole regimes under different laser velocities. (b) Front keyhole wall (FKW) angle as a function of normalised enthalpy product for 9 datasets with 4 different materials. Curve fit is \\(\\theta = \\arctan (a\\cdot [(AH / h_m\\cdot L_{th}^*) + b]) + c\\) (a, b and c are constants), performed in Matlab using the Levenberg-Marquardt/least absolute residuals robust fitting algorithm. (c) Radiographs of laser melting with bare aluminium plate in (II) transition regime, showing rear wall collapse with associated illustration (d). (e) Radiographs of laser melting with bare aluminium plate in (III) unstable regime, showing keyhole bottom collapse with associated illustration (f). to is the time moment that the rear keyhole wall (RKW) starts to grow. The red, blue and green arrows in (d) and (f) represent the laser beam, fluid flow and vapour flow, respectively. \\(d\\) and \\(\\theta\\) represent the keyhole depth and FKW angle, respectively. Laser power 500 W, laser spot diameter \\(50\\mu \\mathrm{m}\\) . All scale bars correspond to \\(150\\mu \\mathrm{m}\\) . The datasets of LPBF with Ti-6Al-4V are cited from Cunningham et al.23 (Figs.4, S5 and S7) and Zhao et al.16 (Movie S1 -Movie S5) with permission by AAAS. Datasets for LPBF with Inconel 718, SS 304 and aluminium bare plate are cited from Kouraytem et al.39, Parab et al.40, and Hojjatzadeh et al.41, respectively.",
+ "footnote": [],
+ "bbox": [
+ [
+ 145,
+ 88,
+ 850,
+ 576
+ ]
+ ],
+ "page_idx": 5
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig.3. Keyhole bubble lifetime dynamics during LPBF. Laser velocity \\(1\\mathrm{m / s}\\) and laser power \\(500\\mathrm{W}\\) . (a) and (b) are radiographs with Al7A77 powder and bare aluminium plate, respectively. (c) and (d) show the equivalent diameter changes of some tracked bubbles in LPBF with (solid line) and without (dash line) Al7A77 powder. The equivalent diameter is calculated as \\(\\sqrt{6A / \\pi}\\) , \\(A\\) is the bubble area measured from X-ray image. Note the bubble size error is calculated as \\(\\pm 2\\) pixels ( \\(1.96\\mu \\mathrm{m / pixel}\\) ), equivalent to the segmentation uncertainty. The total tracked bubble numbers are 5 and 8 for the powder and bare plate cases (Supp. Fig S.9a), respectively, using a criterion where the minimum number of frames that a bubble is identified is 6 (Methods). The time to is set to the moment a bubble is first identified. The black dashed circles show initial bubble growth. The interested keyhole pores",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 9
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Fig.4. Tracking and modelling of keyhole induced bubble dynamics. Colour map tracking for keyhole and bubble under low (a) and high (b) laser velocities, corresponding to regimes (III) and (II), respectively. Comparing the modelled bubble size variations with in situ X-ray measurements at low (c) and high (d) laser velocities. The equivalent diameter is calculated as \\(\\sqrt{6A / \\pi}\\) , \\(A\\) is the bubble area measured from X-ray image by the processing algorithms listed in Methods. The bubble size error is calculated as \\(\\pm 2\\) pixels (1.96 \\(\\mu \\mathrm{m / pixel}\\) ), equivalent to the segmentation uncertainty. Note, the bubble shown in (c) split into two small ones in the later stage, where the equivalent diameter is estimated based on their sum area. The temporal resolution of X-ray imaging (20 \\(\\mu \\mathrm{s}\\) ) is insufficient to capture the whole process of bubble growth, therefore, we are unable to get enough data and fully verify",
+ "footnote": [],
+ "bbox": [
+ [
+ 130,
+ 220,
+ 848,
+ 718
+ ]
+ ],
+ "page_idx": 9
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e.mmd b/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..48b8b78e8824ea195e4c781581b278b9e034ca09
--- /dev/null
+++ b/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e.mmd
@@ -0,0 +1,423 @@
+
+# Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing
+
+Yuze Huang ( \(\boxed{\infty}\) yuze.huang@ucl.ac.uk) University College London https://orcid.org/0000- 0002- 9971- 6038
+
+Tristan Fleming Queen's University
+
+Samuel Clark Argonne National Laboratory, https://orcid.org/0000- 0002- 8678- 3020
+
+Sebastian Marussi University College London
+
+Fezzaa Kamel Advanced Photon Source
+
+Jeyan Thiyagalingam Rutherford Appleton Laboratory https://orcid.org/0000- 0002- 2167- 1343
+
+Chu Lun Alex Leung University College London https://orcid.org/0000- 0002- 4153- 7512
+
+Peter Lee University College London https://orcid.org/0000- 0002- 3898- 8881
+
+## Article
+
+Keywords: keyhole porosity, laser powder- bed fusion, synchrotron X- ray imaging
+
+Posted Date: August 20th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 683646/v1
+
+License: © \(\circledast\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on March 4th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 28694-x.
+
+<--- Page Split --->
+
+# Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing
+
+Yuze Huang \(^{1,2*}\) , Tristan G. Fleming \(^{3}\) , Samuel J. Clark \(^{1,2,4}\) , Sebastian Marussi \(^{1,2}\) , Kamel Fezzaa \(^{4}\) , Jeyan Thiyagalingam \(^{5}\) , Chu Lun Alex Leung \(^{1,2*}\) , Peter D. Lee \(^{1,2*}\)
+
+\(^{1}\) UCL Mechanical Engineering, University College London, WC1E 7JE, UK \(^{2}\) Research Complex at Harwell, Harwell Campus, Didcot, OX11 0FA, UK \(^{3}\) Department of Physics, Queen's University, Kingston, Ontario, K7L 3N6, Canada \(^{4}\) X- ray Science Division, Argonne National Laboratory, Lemont, IL 60439, US \(^{5}\) Science and Technology Facilities Council, Harwell Campus, Didcot, OX11 0FA, UK
+
+## Abstract
+
+Keyhole porosity is a key concern in laser powder- bed fusion (LPBF), potentially impacting component fatigue life. However, the dynamics of keyhole porosity formation, i.e., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X- ray imaging we reveal keyhole and bubble behaviours, quantifying their formation mechanisms. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also transition keyhole regimes, created by high laser power- velocity conditions, causing fast radial keyhole fluctuations ( \(\sim 10 \mathrm{kHz}\) ); (ii) transition regime collapse tends to occur part way up the rear- wall; and (iii) immediately after keyhole collapse, the bubble grows as pressure equilibrates then shrinks due to metal- vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The physics revealed here can guide the development of real- time monitoring and control systems for keyhole porosity.
+
+<--- Page Split --->
+
+Laser powder- bed fusion (LPBF) additive manufacturing is being widely explored in both industry and academia \(^{1,2}\) for the production of metal parts. During LPBF, mid- power ( \(\sim 100 - 1000 \mathrm{W}\) ) but tightly- focused (spot sizes \(\sim 20 - 100 \mu \mathrm{m}\) ) lasers are scanned across successive layers of fine metal powder at high speed ( \(\sim 0.05 - 4 \mathrm{m} \cdot \mathrm{s}^{- 1}\) ), selectively melting and consolidating the powder to build a fully dense part. The typical processing- structure- property linkage for LPBF is: steep thermal gradients and high cooling rates \(^{3}\) ( \(\sim 10^{4} - 10^{6} \mathrm{K} \cdot \mathrm{s}^{- 1}\) ) favouring fine, columnar grains oriented along the build direction, producing as- printed LPBF parts that exhibit increased strength, reduced ductility, and increased microstructural and mechanical property anisotropy \(^{4}\) .
+
+The laser fluence during LPBF is sufficient to vaporise the metal, generating a recoil pressure that pushes molten metal away from the laser- matter interaction zone \(^{5}\) . With increasing laser fluence, the recoil pressure is large enough to open a deep, high aspect ratio vapour depression, referred to as a keyhole \(^{6}\) . This is commonly used in laser welding to achieve thin and deep joints \(^{7}\) . LPBF also often operates in keyhole mode melting \(^{6}\) to ensure full fusion between successive layers. Additionally, laser absorptivity increases dramatically in keyhole melting due to multiple reflections of the laser beam along keyhole \(^{8}\) , opening the door for fabrication of highly reflective materials (e.g., aluminium matrix composites with \(\sim 91\%\) reflectivity \(^{9}\) ) by LPBF, or enable a more economical laser heat source (e.g., diode laser) to be used in LPBF without sacrificing build efficiency \(^{10}\) . However, the keyhole is subjected to axial fluctuations and radial perturbations \(^{11}\) that are governed by the balance of energy and pressure \(^{12 - 14}\) , posing a significant risk for keyhole instability \(^{15,16}\) and in some cases, collapse. Keyhole collapse often results in the formation of a bubble in the melt pool, which may get trapped by the solidification front to form a pore. Keyhole pores remaining in the final part may act as stress concentrators and sites for crack initiation and growth, making them potentially detrimental to fatigue life and other final component mechanical properties \(^{17}\) .
+
+Several process models \(^{5,12 - 14,18}\) explained the physics of keyhole pore formation during laser welding and LPBF, revealing the interactive effects of recoil pressure, surface tension, and Marangoni convection on the keyhole, and the competing influence of gravity, drag, buoyancy and thermocapillary forces on bubble motion. Recently, in situ synchrotron X- ray imaging \(^{19 - 22}\) has been applied to LPBF, capturing some
+
+<--- Page Split --->
+
+dynamics of the keyhole and keyhole pore in the sub- surface of melt pool, including: keyhole morphology evolution23; pore formation at turn- around points during raster scanning24; pore elimination by thermocapillary forces25; pore migration under Marangoni- driven flow and pore coalescence26,27; pores being pushed away from keyhole tip by the acoustic waves emanating from the keyhole collapse16, and pore evolution during multi- layer LPBF28,29. However, the dynamics of keyhole pore formation are still not fully understood. The role of keyhole fluctuations in keyhole collapse and the evolutions of bubbles (e.g., formation, growth, shrinkage and migration) before being captured by the solidification front, are largely unexplored. For the latter, previous studies30,31 explored the influence of evaporation and condensation on the dynamics of water- vapour bubbles in a superheated liquid, and effect of dissolved gas diffusion on the bubble growth in casting32,33, but it remains unclear how these physics extend to the LPBF process.
+
+Here, we perform in situ synchrotron X- ray imaging during LPBF of a commercial aluminium alloy Al7A77 (HRL laboratory, USA), which has critical applications in aerospace, biomedical and automotive industries34 and also a high laser reflectivity35, presenting challenges for laser processing. We discover a transition regime (II) between the stable (I) and unstable (III) keyhole regimes in LPBF, where the keyhole morphology changes from wide and shallow in II to narrow and deep in III. Pores are also observed to form in II, mostly present at the rear keyhole wall (RKW), while keyhole porosity is more prevalent in III with pores typically forming at the keyhole bottom. Although some prior work has suggested keyhole fluctuation are largely random, we observe regular oscillations in keyhole width and depth with significant trends in fluctuation frequency across the three keyhole regimes. We find these regimes are well defined by the front keyhole wall (FKW) angle, which collapses to a single function of the normalized enthalpy product36 for different materials. By comparing our bubble model with the experimental data, we find that the bubble dynamics are defined by fast initial growth induced by the pressure equalisation, followed by shrinkage due to metal- vapour condensation. Concurrent with condensation, hydrogen may diffuse into the bubble, reducing the bubble shrinkage and stabilizing the bubble size. Further, we investigate the rapid distortion of bubbles as they interact with the advancing cellular- dendrite solidification front.
+
+<--- Page Split --->
+
+## Results
+
+Keyhole collapse mechanism and related regime transitions. In situ and operando X- ray imaging was used to probe the keyhole collapse behaviours and keyhole pore formation mechanisms during LPBF, which was carried out using an In Situ and Operando process replicator (ISOPR, Supp. Fig S.10), as described in Methods. We systematically characterised the resulting change in keyhole shape and bubble development across a wide range of area energy densities \(AED^{37}\) , \(AED = P_{l} / (\nu_{l}d_{l})\) ( \(P_{l}\) laser power, \(\nu_{l}\) laser scan velocity, \(d_{l}\) laser beam diameter), from \(AED = 6\) to \(17 \mathrm{MJ}\cdot \mathrm{m}^{- 2}\) in the keyhole melting regime \(^{6}\) . We observed that the keyholes change in morphology from wide and shallow to narrow and deep (Fig.1a, Supp. Fig S.1a and Movies 1 – 12). Simultaneously, bubbles first form at the RKW, then prevail at the bottom of keyhole once the keyhole becomes deep and narrow (Fig.1a, Supp. Fig S.1a). Those findings indicate that the transition from a stable to unstable keyhole melting may be more nuanced than previously suggested \(^{16,23}\) (discussed in detail later). We also noticed that the FKW remained relatively smooth at an approximately constant inclination, whereas the RKW presented random wrinkles and perturbations. With increasing \(AED\) , the keyhole penetration depth increases and the inclination of the FKW become steeper (higher FKW angle \(\theta\) , \(\tan \theta \sim \nu_{d} / \nu_{l}^{38}\) ), which is attributed to higher drilling velocity \(^{39}\) ( \(\nu_{d}\) ) and increased energy coupling due to multiple reflections \(^{8}\) .
+
+By supplementing our results with previous studies \(^{16,23,39,40,41}\) across a wide range of powder materials, process conditions with different LPBF replicators and beamlines, we found that the FKW angle \(\theta\) collapses to an inverse tangent of the normalised enthalpy product \((\Delta H / h_{m} \cdot L_{th}^{*})^{36}\) (Fig.1b), where \(L_{th}^{*}\) is the normalised thermal diffusion length \(^{36}\) and the normalised enthalpy \(\Delta H / h_{m}^{6,42}\) is the ratio of \(\Delta H\) , the deposited energy density \(^{6}\) (also named as specific enthalpy) and \(h_{m}\) , the enthalpy at melting. This relationship is derived by the governing laws of heat transfer and kinematic equilibrium, elaborated in Supp. Note 1. The agreement (Fig.1b) between the theorical derivation and experimental measurements, suggests that the FKW inclination during LPBF is not only controlled by the deposited energy density \(\Delta H\) and the material's melting enthalpy \(h_{m}\) , but also affected by the thermal diffusion length \(L_{th}\) .
+
+<--- Page Split --->
+
+
+Fig.1. Keyhole collapse mechanism and related keyhole melting regime transitions in LPBF. (a) Keyhole morphology variations across the (I) quasi-stable, (II) transition and (III) unstable keyhole regimes under different laser velocities. (b) Front keyhole wall (FKW) angle as a function of normalised enthalpy product for 9 datasets with 4 different materials. Curve fit is \(\theta = \arctan (a\cdot [(AH / h_m\cdot L_{th}^*) + b]) + c\) (a, b and c are constants), performed in Matlab using the Levenberg-Marquardt/least absolute residuals robust fitting algorithm. (c) Radiographs of laser melting with bare aluminium plate in (II) transition regime, showing rear wall collapse with associated illustration (d). (e) Radiographs of laser melting with bare aluminium plate in (III) unstable regime, showing keyhole bottom collapse with associated illustration (f). to is the time moment that the rear keyhole wall (RKW) starts to grow. The red, blue and green arrows in (d) and (f) represent the laser beam, fluid flow and vapour flow, respectively. \(d\) and \(\theta\) represent the keyhole depth and FKW angle, respectively. Laser power 500 W, laser spot diameter \(50\mu \mathrm{m}\) . All scale bars correspond to \(150\mu \mathrm{m}\) . The datasets of LPBF with Ti-6Al-4V are cited from Cunningham et al.23 (Figs.4, S5 and S7) and Zhao et al.16 (Movie S1 -Movie S5) with permission by AAAS. Datasets for LPBF with Inconel 718, SS 304 and aluminium bare plate are cited from Kouraytem et al.39, Parab et al.40, and Hojjatzadeh et al.41, respectively.
+
+<--- Page Split --->
+
+Previous work has related the FKW to the laser fluence, but has largely neglected the role of the thermal diffusion. Cunningham et al. \(^{23}\) reported a nonlinear relationship between the FKW angle and the power density \((2P_{l} / \pi d_{l}^{2})\) , and this relationship changes with the laser scan velocity as well as powder materials. Gan et al. \(^{43}\) found that the tangent of FKW angle is approximately proportional to the "keyhole number \(Ke^{*}(Ke = \frac{1}{\sqrt{\pi}}\cdot \Delta H / h_{m})\) , which is a scaled version of the normalised enthalpy. Here, we find even stronger agreement between the FKW angle and the normalised enthalpy product (Supp. Fig S.2d), rather than the normalised enthalpy (Supp. Fig S.2c). Our result builds on the work of Ye et al. \(^{36}\) , who first introduced the normalised enthalpy product in their scaling laws for keyhole depth (similar relations for keyhole depth measurements are shown in Supp. Fig S.2a, b). Of interest, the normalised thermal diffusion length can be expressed in terms of the Péclet number \(Pe\) , \(L_{th}^{*} = \frac{1}{\sqrt{Pe}}\) (Methods), thus, the above function of FKW angle can be presented as \(\theta \sim atan\left[\left(\frac{\Delta H}{h_{m}}\right) / \sqrt{P_{e}}\right]\) , suggesting that the mode of thermal transfer (convection vs. conduction) also affects the keyhole morphology evolution during LPBF. The relationship derived here also allows for defining thresholds between different melting regimes, similar to King et al. \(^{6}\) , who found the transition from conduction to keyhole melting occurs at a normalised enthalpy \(\Delta H / h_{m} \approx (30 \pm 4)\) for 316L stainless steel.
+
+Within the keyhole- melting regime, recent studies have reported a sharp transition between stable and unstable keyhole melting, typically defined by the onset of keyhole porosity \(^{16,23,43}\) . From our data, we observed that the threshold for this transition can vary significantly between alloys. For Al7A77 and Ti- 6Al- 4V \(^{16,23}\) (Fig.2d), we found this transition occurs at \(\Delta H / h_{m} \cdot L_{th}^{*} \sim (8 \pm 3)\) or \(\sim 60^{\circ}\) FKW angle, and \(\Delta H / h_{m} \cdot L_{th}^{*} \sim (20 \pm 3)\) or \(\sim 80^{\circ}\) front- wall angle, respectively. The larger threshold for Al7A77 is likely a combined result of its low absorptivity at ambient temperature ( \(\sim 0.15\) vs. \(\sim 0.45\) ), larger Brewster angle ( \(\sim 85^{\circ 44}\) vs. \(\sim 80^{\circ}\) , Supp. Fig S.5), and lower melting enthalpy \((h_{m} = 2.63 J \cdot mm^{- 3}\) vs. \(6.26 J \cdot mm^{- 3}\) ).
+
+In addition, we find that there can be an extended transition regime (II) between the stable (I) and unstable (III) keyhole regimes under high- power- velocity (high- \(PV\) ). Pores begin to form in this transition
+
+<--- Page Split --->
+
+regime, and initiate at the RKW rather than at the bottom of the keyhole (typical in III), which was also observed during laser welding of aluminium alloys \(^{15}\) and low carbon steel \(^{45}\) , as well as LPBF of Ti- 6Al- 4V \(^{41}\) . For similar AED, we found this transition regime becomes sharper with decreasing laser power and scan speed ( \(P_{l} = 500 W\) , \(v_{l} = 1.4 m / s\) , Supp. Fig S. 3a, b; \(P_{l} = 200 W\) , \(v_{l} = 0.6 m / s\) , Supp. Fig S. 3c, d), in agreement with Zhao et al. \(^{16}\) . We speculate that the (II) transition regime is induced by the high- PV combination under large AED, which enlarges the melt pool and vapour depression zone, leading to a relatively wider transition from the stable (I) to the unstable (III) keyhole regime. For the laser spot size and alloy used in this study, a high- PV with large AED is defined as \(P_{l} = 500 W\) , \(v_{l} = 1.2 m / s\) , AED \(\geq 7 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) . Considering that the general AED in LPBF is around \(10 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) based on reference \(^{14}\) , we speculate that this transition regime (II) would become popular when high- PV processing is required to achieve large build rate in LPBF.
+
+To further investigate the different keyhole collapse mechanisms in II and III, we compared the keyhole dynamics (Fig.1c, Fig.1e and Supp. Movies 1 – 12). “Humps” regularly form on the FKW due to the dependence of laser absorption on angle of incidence (Fresnel absorption \(^{46}\) , Supp. Note 2), which becomes especially pronounced around the Brewster angle \(^{46}\) (above which, absorptance falls off dramatically, Supp. Fig S.5). In II (Fig.1c-i, AED = 8 MJ·m \(^{- 2}\) , FKW angle \(81.2 \pm 1.7^{\circ}\) ), these humps tend to reflect the laser beam and the vapour flow towards the RKW. This leads to intensive evaporation and recoil pressure on the RKW and builds up a stagnation pressure \(^{12}\) , correspondingly deforming and expanding the RKW (Fig.1c- ii). Generally, the combined recoil and stagnation pressure balances the surface tension acting on the free surface of the RKW, holding the overhanging RKW from collapse \(^{14}\) . However, should the reflected laser beam and vapour flow be blocked or redirected by a perturbation of the keyhole (Fig.1c- ii), the surface temperature of the unilluminated RKW will quickly decrease. As the temperature decreases, surface tension increases linearly \(^{5}\) , overcoming the recoil pressure which decreases exponentially \(^{5}\) , causing a RKW collapse. We observed that this collapse can sometimes lead to the formation of bubbles from the RKW, approximately at the half- depth of keyhole (Fig.1c- iii), followed by the temporary formation of a deep, high aspect ratio depression. The melt flow at the middle of the pool half way up the
+
+<--- Page Split --->
+
+RKW is still strong47, as a result of the Marangoni- driven flow, propelling the pore towards the rear of the pool, as discussed in detail later.
+
+In the unstable regime (III) (Fig.1e- i, \(AED = 10 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) , FKW angle \(84.8 \pm 0.8^{\circ}\) ), a narrow, deep keyhole forms, and humps on the FKW direct metal vapour and reflected laser beams to the bottom of the keyhole. Intense evaporation and recoil pressure at the keyhole bottom can be further amplified by the rapid formation of a vapour cavity ("J- shaped" keyhole, Fig.1e- ii), which traps reflected laser light and metal vapour, increasing the number and density of multiple reflections8,18 and building up a significant stagnation pressure12. With energy concentrated in this cavity, the keyhole is prone to capillary instability and may sometimes collapse, pinching off a cavity to form a vapour filled bubble (Fig.1e- iii) and leads to a sharp decrease in keyhole depth. This is similar to, but not the same as the "spiking" as initially named in laser welding11. Spiking is also prevalent in LPBF but at turn- around points in raster scan patterns due to the finite acceleration of the laser beam, near- zero instantaneous scan velocity, and resulting pores at the "root" of keyhole24. While a small number of the bubbles we observed were re- captured by the expanding keyhole (Supp. Fig S.1b), most were captured almost instantaneously by the advancing solidification front at the bottom of the keyhole to form pores.
+
+Keyhole radial and axial fluctuation and keyhole porosity. To quantify the keyhole and bubble dynamics, we built an image processing pipeline (Methods) to extract the keyhole depth and width from in situ X- ray radiographs (Fig.2). This was carried out for both our own study of LPBF with and without AI7A77 powder (Movies 1 – 8 and 10 – 12), as well as a number of previous synchrotron X- ray studies23,39,40 across different powder materials, process conditions, LPBF replicators, and beamlines (e.g., Parab et al.40). Note that the keyhole width is extracted as the median width along the whole keyhole depth.
+
+Fig.2a shows the regular fluctuations in the keyhole width across different keyhole melting regimes (transition II, blue; unstable III, red). Similar, if not more regular, fluctuations were also observed without powder (Supp. Fig S.4). To further quantify these fluctuations, we calculated the average peak- to- peak period (Methods) and found the corresponding frequencies of keyhole depth and width fluctuations range
+
+<--- Page Split --->
+
+from \(\sim 2.5 \mathrm{kHz}\) to \(\sim 10 \mathrm{kHz}\) , in agreement with previous acoustic, optical and radiometric measurements \(^{8,48,49}\) . We also found significant trends in the keyhole width and depth fluctuations across different keyhole regimes (Fig.2b): starting in \(\mathrm{I}(\Delta H / h_{m} \cdot L_{th}^{*}< 10)\) , the keyhole width fluctuations first increase in frequency, reach the highest in \(\mathrm{II}(10< \Delta H / h_{m} \cdot L_{th}^{*}< 20)\) , and then slightly decrease in frequency in \(\mathrm{III}(\Delta H / h_{m} \cdot L_{th}^{*}>20)\) . Similar patterns for the keyhole depth fluctuation are shown in Fig.2c, which increases in frequency from I to II, and then remains high in III.
+
+
+
+
+
+
+
+The keyhole width and depth fluctuation trends are consistent with the keyhole collapse mechanisms discussed above. In II, the high frequency hump formation and subsequent migration down the FKW (Supp. Fig S.13) can cause an open, wide vapour depression to temporarily collapse into a deeper, higher aspect ratio keyhole, with a significant decrease in keyhole width and increase in keyhole depth (although sometimes less significant), boosting the fluctuation frequency of keyhole. In III, relatively higher
+
+<--- Page Split --->
+
+oscillation frequencies for the depth vs. the width also agrees with the discussion of Fig.1, corresponding to bubbles being pinched off at the keyhole bottom, followed by a sharp decrease in keyhole depth. As shown in Fig.2d, keyhole pores begin to form in II and increase in frequency through III. Comparing the final depth of pores relative to the substrate with the average keyhole depth (Supp. Fig S.6) corroborates that bubbles initiate both at the RKW in II and at the keyhole bottom in III.
+
+Prior studies \(^{23,16}\) reported larger keyhole fluctuations with powder compared to bare substrate. Zhao et al. \(^{16}\) hypothesized that this phenomenon is induced by the momentary interaction between particle spatter and the laser beam \(^{13}\) , which shades the laser illumination and reduces recoil pressure, correspondingly increasing keyhole fluctuation. Here, by comparing the fluctuation frequency of keyhole width (Fig.2b), depth (Fig.2c), and also the tracked bubble numbers at per unit track length (Supp. Fig S.7) with and without powder, we observed limited differences between the powder and bare plate samples. We hypothesise that the shadowing effect of particle spatter on the laser beam is less significance when a high laser power and a thin powder layer thickness are applied (for the laser spot size and alloy used in this study, a high laser power and a thin layer thickness is defined as \(\geq 500 \mathrm{W}\) and \(\leq 30 \mu \mathrm{m}\) , respectively), which is consistent with the finding reported by Khairallah et al. \(^{13}\) . Khairallah et al. found that there exists a power threshold beyond which the particle spatter expulsion mechanism is activated and could vaporise the spatter quickly, inversely, inducing pores due to laser shadowing with rapid cooling.
+
+Keyhole- induced bubble lifetime dynamics in LPBF. Using our image processing pipeline (e.g., Kalman filter tracking \(^{50}\) ), we traced the evolutions of the keyhole- induced bubbles and extracted their centroids and equivalent diameters over their lifetime, starting after a bubble is pinched off from the keyhole and ending when the bubble is fully captured by the solidification front (see examples in Fig.3a,b, \(AED = 10 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) , Movies 7, 8; Supp. Fig S.8a, b, \(AED = 17 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) , Movies 1 – 4). We observed that bubbles evolve through three main stages, both with and without the presence of a powder layer:
+
+(1) bubbles rapidly grow immediately after they are pinched off from the keyhole (Fig.3a, b-i, ii, iii), thought to be due to pressure equalisation; then
+
+<--- Page Split --->
+
+(2) the bubbles shrink while migrating towards the rear side of melt pool (Fig.3a, b-iv), hypothesised to be caused by condensation of the metal vapour in them, competing with diffusion of hydrogen into the bubbles; and finally
+
+(3) they are captured by the advancing solidification front (Fig.3a, b-vi).
+
+![PLACEHOLDER_11_0]
+
+Fig.3. Keyhole bubble lifetime dynamics during LPBF. Laser velocity \(1\mathrm{m / s}\) and laser power \(500\mathrm{W}\) . (a) and (b) are radiographs with Al7A77 powder and bare aluminium plate, respectively. (c) and (d) show the equivalent diameter changes of some tracked bubbles in LPBF with (solid line) and without (dash line) Al7A77 powder. The equivalent diameter is calculated as \(\sqrt{6A / \pi}\) , \(A\) is the bubble area measured from X-ray image. Note the bubble size error is calculated as \(\pm 2\) pixels ( \(1.96\mu \mathrm{m / pixel}\) ), equivalent to the segmentation uncertainty. The total tracked bubble numbers are 5 and 8 for the powder and bare plate cases (Supp. Fig S.9a), respectively, using a criterion where the minimum number of frames that a bubble is identified is 6 (Methods). The time to is set to the moment a bubble is first identified. The black dashed circles show initial bubble growth. The interested keyhole pores
+
+<--- Page Split --->
+
+shown in (a) and (b) are marked by green and pink colours, which are also shown with same colours in (c) and (d), respectively.
+
+Vap.: Vapour; Ar: Argon; \(\mathrm{H}_{2}\) : Hydrogen. All scale bars correspond to \(100\mu \mathrm{m}\) .
+
+Other occasional bubble dynamics, i.e. re- captured by the keyhole, splitting and coalescence were also observed in our LPBF experiments (Supp. Movies 1 – 12). In stage (1), since the bubble was just pinched off from the keyhole, the bubble inner pressure \(p_{i}\) is expected to be similar to the keyhole bottom recoil pressure \((\sim 10^{5} - 10^{6}Pa^{14,39})\) , which is generally larger than the ambient pressure \(p_{a}(\sim 1\times 10^{5}Pa)\) . This pressure difference then drives bubble growth according to the ideal gas law \(^{51}\) \((p = nRT / V)\) , where the volume, \(V\) , must increase to accommodate the reduction in pressure \(p\) from \(p_{i}\) to \(p_{a}\) (Note, \(n\) is the molar number of gas, \(R\) the universal gas constant, and \(T\) the temperature). Simultaneously, as the surrounding liquid metal cools the bubble, the superheated metal- vapour inside the bubble will condense, reducing \(n\) , and hence decreasing the bubble volume \(V\) , but at a slower rate than the pressure equalisation (discussed in detail later). This is also known as the bubble contraction mechanism in laser welding \(^{15,52}\) .
+
+In stage (2) bubbles shrink while migrating towards the rear side of melt pool, we observed that the bubble shrinkage undergoes a marked slowdown at the later stage of condensation (e.g., bubble 3 from 40 \(\mu \mathrm{s}\) to \(120\mu \mathrm{s}\) in Fig.3d), and the bubble size then get stabilized. We speculate the slowdown shrinkage and bubble size stabilization are caused by the hydrogen diffusion \(^{32}\) . The presence of hydrogen in keyhole pores was observed by Matsunawa et al. \(^{15}\) , who measured \(\sim 3 - 12\%\) hydrogen content in pores formed during laser welding of aluminium alloy using mass spectrometry. Hydrogen is expected to be present in both the virgin substrate and powder particles. During LPBF, the melt at the advancing solidification front can then become supersaturated with hydrogen, driving hydrogen diffusion from the melt into the bubble \(^{28,30}\) and it is several orders faster than the diffusion of other atoms \(^{53}\) .
+
+In stage (3) as bubbles reach the solid/liquid interface before being fully captured by the solidification front, we observed that the bubbles experience some sudden, apparent bursts of growth and shrinkage (e.g., bubble 2 at \(80 - 120\mu \mathrm{s}\) in Fig.3c, Supp. Fig S.14a, b). This phenomenon may be explained by the interaction of the bubble with the rapidly growing microstructure \(^{54,55}\) (e.g., the bubble is pierced through, or perhaps distorted from spherical, by the growing columnar dendrite), elucidated in Supp. Note 3.
+
+<--- Page Split --->
+
+Based on the above findings, from the initiation of a bubble until it gets frozen as a pore, its composition will initially be a combination of metal vapour and shielding gas argon (Ar), which is driven into the keyhole via the Bernoulli effect56. The metal vapour will condense, leaving the Ar, and reducing the pore size. Simultaneously some hydrogen (H2) will diffuse in, slowing the bubble shrinkage. These stages are highlighted by the tracked bubble colours in Fig.3a, b. Note that the argon can be treated as insoluble in molten aluminium57, which is expected to be the major content left in the frozen pore.
+
+To verify our hypothesis in above discussion, we combined the Rayleigh- Plesset equation58, bubble condensation model from Florschuetz and Chao59, and the ideal gas law51 to build a united bubble model (Methods) while considering pressure- driven growth, vapour condensation and hydrogen diffusion. We compared the modelled results with experimental measurements under different keyhole melting regimes (II, III), shown in Fig.4, where we presented the tracked keyhole and keyhole pore transient trajectories at 0.8 m/s and 1.2 m/s laser velocities (Fig.4 a, b) based on the X- ray images (Supp. Movies 5, 6, 10, 11), corresponding to II (AED = 12.5 MJ · m- 2) and III (AED = 8 MJ · m- 2).
+
+As seen from Fig.4c, d, immediately after forming the bubble experiences explosive growth, which plateaus after about \(\sim 3 - 5 \mu \mathrm{s}\) (Supp. Table S. 3). The bubble then begins to shrink at a slower rate, and eventually get stabilized ( \(\sim 50 - 150 \mu \mathrm{s}\) ), being consistent with the experimental measurements (Note that deviations may be caused by the effect of surface tension and fluid flow that are not included in the built model). We hypothesise that the explosive growth is caused by the pressure equalisation, with the bubble volume increasing like \(t^3\) (see Methods). The decline and plateau in bubble growth is explained by the decrease in driving force \((p_i - p_a)\) with increasing bubble volume, based on the ideal gas law. We also speculate that the bubble shrinkage rate is slower than the bubble growth rate, proportional to \(t^{- 1 / 2}\) and \(t\) , respectively (see Methods). Additionally, we hypothesise that the bubble shrinkage rate can be further slowed by the diffusion of hydrogen. The modelling results (Fig.4 c, d) show that accounting for the hydrogen diffusion is necessary to explain the latter stage of bubble size stabilisation and this leads to good agreement with the tracked bubble equivalent diameter. Note that our temporal resolution of X- ray
+
+<--- Page Split --->
+
+imaging (20 \(\mu \mathrm{s}\) ) is insufficient to capture the whole process of bubble growth after being pinched off from keyhole. With a calculated growth time on the order of \(\mu \mathrm{s}\) , it is likely that we often fail to capture this growth, explaining why immediate bubble shrinkage is observed more frequently than initial bubble growth then shrinkage in our X- ray imaging (Supp. Fig S.9).
+
+![PLACEHOLDER_14_0]
+
+Fig.4. Tracking and modelling of keyhole induced bubble dynamics. Colour map tracking for keyhole and bubble under low (a) and high (b) laser velocities, corresponding to regimes (III) and (II), respectively. Comparing the modelled bubble size variations with in situ X-ray measurements at low (c) and high (d) laser velocities. The equivalent diameter is calculated as \(\sqrt{6A / \pi}\) , \(A\) is the bubble area measured from X-ray image by the processing algorithms listed in Methods. The bubble size error is calculated as \(\pm 2\) pixels (1.96 \(\mu \mathrm{m / pixel}\) ), equivalent to the segmentation uncertainty. Note, the bubble shown in (c) split into two small ones in the later stage, where the equivalent diameter is estimated based on their sum area. The temporal resolution of X-ray imaging (20 \(\mu \mathrm{s}\) ) is insufficient to capture the whole process of bubble growth, therefore, we are unable to get enough data and fully verify
+
+<--- Page Split --->
+
+the bubble growth model. (e) Bubble migration distance compared to their initial formed location. The bubble migration distance error is calculated based on the bubble motion with instantaneous speeds \((0 - 5 \mathrm{m / s})\) during the finite camera exposure time (2.5 \(\mu \mathrm{s}\) ). Low laser velocity \(0.8 \mathrm{m / s}\) , high velocity \(1.2 \mathrm{m / s}\) , laser power \(500 \mathrm{W}\) .
+
+The bubbles migrated a larger distance in II with a tendency of going backward and upward, when initiated at the RKW, than in III (Fig.4e.), when initiated at the bottom of the keyhole, remaining almost stationary. This is due to two effects (i) the proximity of the solidification front to the bottom of the keyhole, bubbles having insufficient time to move upwards in the melt pool18; and (ii) the melt flow velocity and flow pattern are location dependent across the melt pool47, and the induced drag force is local flow velocity dependent. The flow velocity is higher in the middle of the pool, hence when a bubble is formed half way along the RKW, it quickly flows backwards to the rear of melt pool. At the bottom of the pool near the solid- liquid interface, the flow is low, hence bubbles detaching from the very bottom of keyhole remain nearly stationary until captured by the solidification front and turn to pores. The bubble in Fig.4a (regime III) has an average velocity of \(1.0 \pm 0.5 \mathrm{m / s}\) (measured over the first \(60 \mu \mathrm{s}\) ), while the bubble in Fig.4b (regime II) moves at \(2.4 \pm 0.7 \mathrm{m / s}\) . In regime III with high AED, the pore migration speed of \(1.0 \mathrm{m / s}\) agrees well with our previous measurements of the Marangoni flow speed with tungsten carbide particles (0.97 \(\mathrm{m / s}\) under the same AED)60, while we assume that a strong viscous drag force is responsible for the higher initial speed of bubbles initiated at the RKW in regime II at lower AED.
+
+## Discussion
+
+In summary, this manuscript reveals the lifetime dynamics of keyhole pore (growth, shrinkage, migration), introducing a new threshold, the normalized enthalpy product, to reveal and elucidate different keyhole pore generation mechanisms and their corresponding keyhole melting regimes in LPBF. Our findings on keyhole fluctuation and bubble dynamics provide critical guidance (e.g., bubble growth/shrinkage rate, pore location and size) to achieve in situ pore elimination by remelting25,61 upon the dual- laser LPBF machines62 or hybrid LPBF63, and pore suppression via real- time control of keyhole dynamics (e.g., beam oscillation64) in broad high- energy- beam processing techniques (e.g., electron beam melting65, keyhole laser welding64 and laser drilling66).
+
+<--- Page Split --->
+
+In this study, we combined our own in situ synchrotron X- ray imaging results from LPBF of aluminium alloy (Al7A77) with recent studies of other key additive manufacturing alloys (e.g., Ti- 6Al- 4V, Inconel 718, SS 304) and drew the following conclusions:
+
+- A transition regime (II) between the stable (I) and unstable (III) keyhole regimes has been discovered based on the evolutions of keyhole morphology and bubble formation. This transition regime II is pronounced for high-\(PV\) combinations under large AED (AED \(\geq 7 \mathrm{MJ} \cdot \mathrm{m}^{-2}\) ), and features the vapor depression transforms from wide and shallow to narrow and deep, concurrently, keyhole collapses and induce pores at mid-rear wall in II, as opposed to the bottom of the keyhole in III.
+
+- Significant trends in keyhole fluctuation frequency (radial and axial) were observed across the different keyhole regimes, where the fastest fluctuation occurring in the transition regime (II) at \(\sim 10 \mathrm{kHz}\) .
+
+- A material, machine and process condition agnostic relationship was developed for the FKW angle, which collapses to a single function of the normalized enthalpy product, providing a non-dimensional threshold for predicting the three keyhole regime transitions and the onset of keyhole porosity for different alloys and processing conditions (e.g., variant laser spot sizes, powers, velocities).
+
+- Keyhole pore formation process, including the lifetime dynamics of the vapour bubble in the melt pool, were revealed by the X-ray imaging and were summarized in three stages: (1) fast pressure-driven growth, (2) shrinkage by metal vapour condensation and shrinkage inhibition by hydrogen diffusion, and (3) interaction with growing microstructure (e.g., cellular-dendrites) and capture by the advancing solidification front.
+
+- A model of bubble growth and shrinkage was proposed, including the physics of pressure-driven growth, vapour condensation and hydrogen diffusion. This model was found to be consistent with the experimental data, supporting our hypotheses: (i) the explosive bubble growth at the early
+
+<--- Page Split --->
+
+lifetime of stage (1) is mainly a pressure-driven process, where the bubble volume expands like \(\sim t^3\) ; (ii) the hydrogen diffusion is sufficiently high to stabilize the bubble size at the later stage of condensation in stage (2).
+
+## Methods
+
+LPBF Replicator (ISOPR) system and processing conditions. In situ synchrotron X- ray imaging was performed to probe keyhole and keyhole bubble dynamics during LPBF at the Argonne National Laboratory's Advanced Photon Source (APS) over the ISOPR (Supp. Methods, Fig S.10). The ISOPR, custom- designed to accommodate the synchrotron X- ray imaging of the LPBF process, mainly includes a continuous wave Ytterbium- doped fibre laser (IPG YLR- 500- AC, USA) with a wavelength of \(1070 \pm 10\mathrm{nm}\) and maximum power of \(520\mathrm{W}\) , an X- Y galvanometer scanner (intelliSCANde 30, SCANLAB GmbH, Germany), an environmental chamber and a sample holder positioned at the centre of the chamber. During the experiment, the chamber was filled with argon gas at a pressure of \(+10\mathrm{kPa}\) to reduce oxidation. The keyhole and keyhole pores were imaged at high spatial ( \(1.96\mu \mathrm{m}\) ) and temporal (frame rate \(50\mathrm{kHz}\) ) resolutions with a FASTCAM SA- Z 2100K (Photron, USA) camera by converting the attenuated x- ray beam to optically visible light using a \(100\mu \mathrm{m}\) thick LuAg:Ce scintillator. The resultant field of view was 512 pixels (1mm) in width by 680 pixels (1.33 mm) in height. The commercially Al7A77 powder (HRL Laboratory, USA) with a particle size range of \(15 - 45\mu \mathrm{m}\) , and pure aluminium (Goodfellow, UK) plate with purity of \(99.99\%\) that sandwiched between two \(1\mathrm{mm}\) thickness glassy carbon plates (HTW, Germany), were used in this study with the process parameters shown in Table 1. Thermophysical properties of the materials are shown in Supp. Table S.1.
+
+Table 1. Process parameters for the LPBF experiments
+
+| Parameters | Values | Parameters | Values |
| Laser velocity [m/s] | 0.6, 0.8, 1, 1.2, 1.4, 1.6 | Laser power [W] | 200, 500 |
| Track length [mm] | 5 | Laser spot size [μm] | 50 |
| Layer thickness [μm] | 30 | Aluminium substrate size [mm] | 46×17×0.5 |
+
+<--- Page Split --->
+
+Image and data processing pipeline - denoising, segmentation, feature extraction and tracking. The major steps of developed image processing pipeline are shown in Supp. Methods, Fig S.11 with the following steps:
+
+i. Flat field correction, subtracting the offset background, followed by a 2D Gaussian filtering (Supp. Fig S.11a, b). Note that the flat field correction used a general equation \(^{26}\) : \(\mathrm{FFC} = (\mathrm{I}_0 - \mathrm{Flat}_{\mathrm{avg}}) / (\mathrm{Flat}_{\mathrm{avg}} - \mathrm{Dark}_{\mathrm{avg}})\) , where \(\mathrm{FFC}\) , \(\mathrm{I}_0\) , \(\mathrm{Flat}_{\mathrm{avg}}\) and \(\mathrm{Dark}_{\mathrm{avg}}\) represent the flat field corrected image, raw image, average of 100 flat filed images and average of 100 dark field images, respectively.
+
+ii. Initial image segmentation (Supp. Fig S.11c) with K-means clustering algorithm \(^{67}\) . The segmentation uncertainty is around \(\pm 2\) pixels (1.96 \(\mu \mathrm{m / pixel}\) ).
+
+iii. Frame stack integration (Supp. Fig S.11d) over the time and applying volume threshold for noise reduction.
+
+iv. The final segmented keyhole and keyhole bubble were achieved by applying (iii) over the whole radiograph stack. Examples are shown in Fig S.12a and Supp. Movies, 2, 4, 6, 8, 11, where the keyhole and keyhole bubble were marked with green and red colours, respectively.
+
+v. Kalman filter tracking algorithm \(^{50}\) was developed based on the segmented keyhole bubble in step (iv). The minimum number of frames that a bubble is identified was set as 6 for being considered as an effective track. The bubbles that were spotted less than 6 frames were mainly recaptured by the successive keyhole and disappear.
+
+Note that the segmentation algorithm developed in step (ii) fails in very limited cases due to the background fluctuations (e.g., the particle randomly fell into the sandwiched gap between glassy carbon plate and aluminium plate). Here we also developed a supervised machine leaning (random decision forests) model to achieve the segmentation of keyhole and keyhole bubble (Fig S.12b), but found that the machine leaning model fails more often during segmentation, possibly induced by the non- perfect ground- truth labelling as the X- ray frames may have different background fluctuations. The Kalman tracking algorithm developed in step (v) also fails occasionally due to the split or coalescence of bubbles, as well
+
+<--- Page Split --->
+
+as the background fluctuations. But those segmentation and tracking failure do not significantly affect the quantified keyhole and keyhole bubble dynamics.
+
+Peak- to- peak period for keyhole width/depth. Matlab's built- in findpeaks function68 was used to extract peaks and valleys from the keyhole width/depth signatures. To mitigate the effect of outliers and noise, the signatures were pre- processed using a moving mean filter with a width of 3. A linear fit of the data was also subtracted to remove slow changes in the width/depth. To remain safely below the Nyquist frequency (25 kHz), the minimum peak distance was set to 5 (100 \(\mu \mathrm{s}\) ), acting as a simple low pass filter with cut- off frequency of 10 kHz. The minimum peak prominence was set to 1 standard deviation of the keyhole width/depth data set.
+
+Bubble growth model with condensation and hydrogen diffusion. In the LPBF process, a rigorous modelling of the bubble dynamics while coupling the meso- nanosecond multi- physics of the process remains a challenge. Here, we assume that the contents, temperature and pressure within the bubble are homogeneous, bubble keeps spherical and be at rest relative to the incompressible melt pool flow. We take the bubble equivalent radius that the bubble is first identified as the bubble initial radius \(r_{b0}\) at the moment \(t = 0\) . In stage (1), considering the very short time of bubble growth, we suppose that there is negligible mass or thermal transfer over the bubble interface (assume no condensation and gas diffusion). Accordingly, the instantaneous bubble radius \(r_{b}(t)\) at time \(t\) can be described by the Rayleigh- Plesset equation58,
+
+\[r_{b}\cdot \frac{\partial}{\partial t}\Big(\frac{\partial r_{b}}{\partial t}\Big) + \frac{3}{2}\Big(\frac{\partial r_{b}}{\partial t}\Big)^{2} = \frac{1}{\rho_{l}}\Big(p_{i} - p_{a} - \frac{2\sigma}{r_{b}} -4\mu_{l}\cdot \frac{\partial r_{b}}{\partial t}\Big) \quad (1)\]
+
+where \(\rho_{l}\) is the density at melting temperature \(T_{l}\) , \(p_{i}\) the bubble inner pressure, \(p_{a}\) the ambient pressure, \(\sigma\) the surface tension and \(\mu_{l}\) is the viscosity.
+
+Since the surface tension and the viscosity terms ( \(\sim 10^{4} Pa\) ) are both negligible compared to the pressure difference \(p_{i} - p_{a} (\sim 10^{5} - 10^{6} Pa)^{14,39}\) , which can be omitted in the above Rayleigh- Plesset equation. Accordingly, the bubble growth rate can then be approximated as58,
+
+<--- Page Split --->
+
+\[\frac{\partial r_{b}}{\partial t}\rightarrow \left(\frac{2}{3}\cdot \frac{p_{i} - p_{a}}{\rho_{l}}\right)^{\frac{1}{2}},\qquad r_{b}(t)\gg r_{b}(0) \quad (2)\]
+
+This derived bubble growth rate suggests that, at the early time of stage (1) with maximum pressure difference, the bubble grows with a function of time \(t\) , while the bubble volume expands like \(t^{3}\) . The initial bubble inner pressure \(p_{i}(0)\) may be approximated as the recoil pressure \(p_{recoil}\) , \(p_{i}(0) \approx p_{recoil}\) , where the recoil pressure is a function of temperature \(T\) based on Anisimov's evaporation model \(^{5,14}\) ,
+
+\[p_{recoil} = 0.54p_{a}exp\left[\frac{\lambda}{K_{B}}\left(\frac{1}{T} -\frac{1}{T_{v}}\right)\right] \quad (3)\]
+
+where \(\lambda = 293.4 \mathrm{kJ} \cdot \mathrm{mol}^{- 1}\) is the latent heat of evaporation per atom of aluminium, \(K_{B} = 8.314 \times 10^{- 3} \mathrm{kJ} \cdot \mathrm{mol}^{- 1} \cdot \mathrm{K}^{- 1}\) the Boltzmann constant, \(T\) the keyhole surface temperature, \(T_{v} = 2753.15 \mathrm{K}\) is the evaporation temperature of aluminium. By using the 2D moving heat source model \(^{6}\) , the keyhole surface temperature is approximated by the melt pool peak temperature,
+
+\[T = \frac{\sqrt{2}\beta I r_{l}}{k_{l}\sqrt{\pi}} t a n^{-1}\sqrt{\frac{2a_{l}}{\nu_{l}r_{l}}} \quad (4)\]
+
+where \(\beta\) is the laser absorptivity (depends on angle of incidence, see Supp. Fig S.5), \(r_{l}\) the laser beam radius, \(I\) the laser intensity (approximated as \(I = P_{l} / \left(\pi r_{l}^{2}\right)\) , \(P_{l}\) the laser power), \(a_{l}\) the liquidus thermal diffusivity, \(k_{l} = \rho_{l} \cdot c_{l} \cdot a_{l}\) ( \(\rho_{l}\) the liquidus density, \(c_{l}\) the liquidus heat capacity) the liquidus thermal conductivity and \(v_{l}\) the laser scan velocity.
+
+By combing the above Equations (2 - 4) and the ideal gas law \(^{51}\) ( \(p = nRT / V\) , \(p\) the pressure, \(n\) the molar number of gas, \(R\) the universal gas constant, \(V = \frac{4}{3}\pi r_{b}^{3}\) the bubble volume), the transient bubble size in stage (1) can be calculated as \(r_{b}(t) = r_{b0} + \Delta r_{b1}(t)\) , \(t \leq t_{1}\) , where \(\Delta r_{b1}(t)\) (solved from simultaneous Equations 2 - 4 and ideal gas law) is the pressure- driven bubble radius increment at time \(t\) , and \(t_{1}\) is the pressure- driven bubble growth time. Note that \(t_{1}\) is calculated as the time that the pressure difference \(p_{i} - p_{a}\) reduces to a percentage threshold of \(p_{a}\) (we used \(5\%\) and defined as \(p_{i}(t_{1}) - p_{a} \leq 0.05p_{a}\) ).
+
+<--- Page Split --->
+
+In the condensation dominated regime of stage (2), Florschuetz and Chao \(^{59}\) built the following relation between the bubble instantaneous radius \(r_{b2}(t)\) and the radius at the beginning of vapour condensation \(r_{b2}(0)\) (approximated as the \(r_{b}(t_{1})\) ),
+
+\[\frac{1}{3}\left[\frac{r_{b2}(t)}{r_{b2}(0)}\right]^{2} + \frac{2}{3}\frac{r_{b2}(0)}{r_{b2}(t)} = 1 + \frac{t}{t_{cond}},\quad t_{cond} = \frac{\pi[r_{b2}(0)]^{2}}{4Ja^{2}a_{l}} \quad (5)\]
+
+where \(t_{cond}\) is the condensation characteristic time and \(Ja\) is the Jakob number, \(Ja = \frac{\rho_{l}c_{l}(T_{bs} - T_{sat})}{\rho_{v}L_{v}} (T_{bs}\) the bubble surface temperature, \(T_{sat}\) the saturated temperature, \(L_{v} = 1.02\times 10^{7}J\cdot Kg^{- 1}\) the latent heat of evaporation, \(\rho_{v} = 1850Kg\cdot m^{3}\) the vapour density).
+
+In stage (2), the enriched hydrogen in melt pool may diffuse into the bubble driven by the concentration difference. The bubble size \(r_{b3}\) induced by hydrogen diffusion may be estimated by the characteristic length of hydrogen diffusion limited growth \(l_{D}^{33}\) as, \(r_{b3} = l_{D} / 2, l_{D} = \sqrt{D_{h}t}\) , where \(D_{h}\) is the mass diffusivity of hydrogen in liquidus aluminium and may be approximated as an average of \(D_{h}(T_{l}) = 1.0943\times 10^{- 7} m^{2}\cdot s^{- 1}\) and \(D_{h}(T_{v}) = 1.1302\times 10^{- 5} m^{2}\cdot s^{- 1}\) based on reference \(^{69}\) . Accordingly, the bubble radius in stage (2) that is controlled by vapour condensation and hydrogen diffusion may be described as, \(\frac{4}{3}\pi r_{b}^{3} = \frac{4}{3}\pi r_{b2}^{3} + \frac{4}{3}\pi r_{b3}^{3}\) , based on mass balance (assuming that the contents, temperature and pressure within the bubble are homogeneous). Therefore, the instantaneous bubble radius in stages 1 and 2 can be approximated as,
+
+\[r_{b}(t) = \left\{ \begin{array}{c}{r_{b0} + \Delta r_{b1}(t),t\leq t_{1}}\\ {\sqrt[3]{\left[r_{b2}(t - t_{1})\right]^{3} + \left[r_{b3}(t - t_{1})\right]^{3}},t > t_{1}} \end{array} \right. \quad (6)\]
+
+All the parameters used in the model were listed in Supp. Table S. 2 (thermal- physical properties) and Supp. Table S. 3 (processing parameters), which were used to plot the bubble diameter graph in Fig.4b, c. Note that we used the liquidus aluminium temperature \(T_{l} = 933.5K\) to approximate the bubble saturation temperature \(T_{sat}\) in melt pool, while for the bubble surface temperature \(T_{bs}\) , which is subcooled by uncertainty temperature in the melt pool after the bubble being pinched off from keyhole, we approximated its magnitude by fitting between observed data and the modelled results. For a spherical vapour bubble,
+
+<--- Page Split --->
+
+the total condensation time is around \(1 \sim 3 t_{\text{cond}}^{30}\) . Here, we used the average \(2 t_{\text{cond}}\) and modelled the bubble dynamics within \(2 t_{\text{cond}}\) .
+
+## Reference
+
+1. King, W. E. et al. Laser powder bed fusion additive manufacturing of metals; physics, computational, and materials challenges. Appl. Phys. Rev. 2, 041304 (2015).
+2. DebRoy, T. et al. Additive manufacturing of metallic components – Process, structure and properties. Prog. Mater. Sci. 92, 112–224 (2018).
+3. Smith, J. et al. Linking process, structure, property, and performance for metal-based additive manufacturing: computational approaches with experimental support. Comput. Mech. 57, 583–610 (2016).
+4. Pham, M. S., Dovgyy, B., Hooper, P. A., Gourlay, C. M. & Piglione, A. The role of side-branching in microstructure development in laser powder-bed fusion. Nat. Commun. 11, (2020).
+5. Khairallah, S. A., Anderson, A. T. A. A. T., Rubenchik, A. M. & King, W. W. E. Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones. Acta Mater. 108, 36–45 (2016).
+6. King, W. E. et al. Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing. J. Mater. Process. Technol. 214, 2915–2925 (2014).
+7. Shevchik, S. et al. Supervised deep learning for real-time quality monitoring of laser welding with X-ray radiographic guidance. Sci. Rep. 10, (2020).
+8. Allen, T. R. et al. Energy-Coupling Mechanisms Revealed through Simultaneous Keyhole Depth and Absorptance Measurements during Laser-Metal Processing. Phys. Rev. Appl. 13, 064070 (2020).
+9. Dai, D. & Gu, D. Effect of metal vaporization behavior on keyhole-mode surface morphology of selective laser melted composites using different protective atmospheres. Appl. Surf. Sci. 355, 310–319 (2015).
+
+<--- Page Split --->
+
+10. Tenbrock, C. et al. Influence of keyhole and conduction mode melting for top-hat shaped beam profiles in laser powder bed fusion. J. Mater. Process. Technol. 278, (2020).
+
+11. Tsukamoto, S., Kawaguchi, I., Arakane, G. & Honda, H. Keyhole behavior in high power laser welding. in First International Symposium on High-Power Laser Macroprocessing (eds. Miyamoto, I., Kobayashi, K. F., Sugioka, K., Poprawe, R. & Helvajian, H.) vol. 4831 251 (SPIE, 2003).
+
+12. Tan, W. & Shin, Y. C. Analysis of multi-phase interaction and its effects on keyhole dynamics with a multi-physics numerical model. J. Phys. D. Appl. Phys. 47, (2014).
+
+13. Khairallah, S. A. et al. Controlling interdependent meso-nanosecond dynamics and defect generation in metal 3D printing. Science (80-. ). 368, 660-665 (2020).
+
+14. Wang, L., Zhang, Y. & Yan, W. Evaporation Model for Keyhole Dynamics During Additive Manufacturing of Metal. Phys. Rev. Appl. 10, 64039 (2020).
+
+15. Matsunawa, A., Mizutani, M., Katayama, S. & Seto, N. Porosity formation mechanism and its prevention in laser welding. Weld. Int. 17, 431-437 (2003).
+
+16. Zhao, C. et al. Critical instability at moving keyhole tip generates porosity in laser melting. Science (80-. ). 370, 1080-1086 (2020).
+
+17. Jost, E. W., Miers, J. C., Robbins, A., Moore, D. G. & Saldana, C. Effects of spatial energy distribution-induced porosity on mechanical properties of laser powder bed fusion 316L stainless steel. Addit. Manuf. 39, (2021).
+
+18. Bayat, M. et al. Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation. Addit. Manuf. 30, 100835 (2019).
+
+19. Zhao, C. et al. Real-time monitoring of laser powder bed fusion process using high-speed X-ray imaging and diffraction. Sci. Rep. 7, (2017).
+
+20. Guo, Q. et al. Transient dynamics of powder spattering in laser powder bed fusion additive manufacturing process revealed by in-situ high-speed high-energy x-ray imaging. Acta Mater. 151, 169-180 (2018).
+
+21. Calta, N. P. et al. An instrument for in situ time-resolved X-ray imaging and diffraction of laser
+
+<--- Page Split --->
+
+powder bed fusion additive manufacturing processes. Rev. Sci. Instrum. 89, 055101 (2018).
+
+22. Sun, T. Probing Ultrafast Dynamics in Laser Powder Bed Fusion Using High-Speed X-Ray Imaging: A Review of Research at the Advanced Photon Source. JOM vol. 72 999-1008 (2020).
+
+23. Cunningham, R. et al. Keyhole threshold and morphology in laser melting revealed by ultrahigh-speed x-ray imaging. Science (80-. ). 363, 849-852 (2019).
+
+24. Martin, A. A. et al. Dynamics of pore formation during laser powder bed fusion additive manufacturing. Nat. Commun. 10, (2019).
+
+25. Hojjatzadeh, S. M. H. et al. Pore elimination mechanisms during 3D printing of metals. Nat. Commun. 10, (2019).
+
+26. Leung, C. L. A. et al. In situ X-ray imaging of defect and molten pool dynamics in laser additive manufacturing. Nat. Commun. 9, (2018).
+
+27. Leung, C. L. A. et al. Laser-matter interactions in additive manufacturing of stainless steel SS316L and 13-93 bioactive glass revealed by in situ X-ray imaging. Addit. Manuf. 24, 647-657 (2018).
+
+28. Sinclair, L. et al. In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion. Addit. Manuf. 36, (2020).
+
+29. Chen, Y. et al. In-situ Synchrotron imaging of keyhole mode multi-layer laser powder bed fusion additive manufacturing. Appl. Mater. Today 20, (2020).
+
+30. Prosperetti, A. Vapor Bubbles. Annual Review of Fluid Mechanics vol. 49 221-248 (2017).
+
+31. Hao, Y., Zhang, Y. & Prosperetti, A. Mechanics of gas-vapor bubbles. Phys. Rev. Fluids 2, 34303 (2017).
+
+32. Atwood, R. C., Sridhar, S., Zhang, W. & Lee, P. D. Diffusion-controlled growth of hydrogen pores in aluminium-silicon castings: In situ observation and modelling. Acta Mater. 48, 405-417 (2000).
+
+33. Lee, P. D. & Hunt, J. D. Hydrogen porosity in directional solidified aluminium-copper alloys: In situ observation. Acta Mater. 45, 4155-4169 (1997).
+
+34. Martin, J. H. et al. 3D printing of high-strength aluminium alloys. Nature 549, 365-369 (2017).
+
+35. Geng, K., Yang, Y., Li, S., Misra, R. D. K. & Zhu, Q. Enabling high-performance 3D printing of Al
+
+<--- Page Split --->
+
+powder by decorating with high laser absorbing Co phase. Addit. Manuf. 32, 101012 (2020).
+
+36. Ye, J. et al. Energy Coupling Mechanisms and Scaling Behavior Associated with Laser Powder Bed Fusion Additive Manufacturing. Adv. Eng. Mater. 21, 1900185 (2019).
+
+37. Huang, Y., Khamesee, M. B. M. B. M. & Toyserkani, E. A comprehensive analytical model for laser powder-fed additive manufacturing. Addit. Manuf. 12, 90-99 (2016).
+
+38. Fabbro, R., Slimani, S., Coste, F. & Briand, F. Study of keyhole behaviour for full penetration Nd-Yag CW laser welding. J. Phys. D. Appl. Phys. 38, 1881-1887 (2005).
+
+39. Kouraytem, N. et al. Effect of Laser-Matter Interaction on Molten Pool Flow and Keyhole Dynamics. Phys. Rev. Appl. 11, 064054 (2019).
+
+40. Parab, N. D. et al. Ultrafast X-ray imaging of laser-metal additive manufacturing processes. J. Synchrotron Radiat. 25, 1467-1477 (2018).
+
+41. Hojjatzadeh, S. M. H. et al. Direct observation of pore formation mechanisms during LPBF additive manufacturing process and high energy density laser welding. Int. J. Mach. Tools Manuf. 153, (2020).
+
+42. Hann, D. B., Iammi, J. & Folkes, J. A simple methodology for predicting laser-weld properties from material and laser parameters. J. Phys. D. Appl. Phys. 44, 445401 (2011).
+
+43. Gan, Z. et al. Universal scaling laws of keyhole stability and porosity in 3D printing of metals. nature.com (2020).
+
+44. Mahrle, A. & Beyer, E. Theoretical aspects of fibre laser cutting. J. Phys. D Appl. 42, 9 (2009).
+
+45. Wu, D., Hua, X., Huang, L., Li, F. & Cai, Y. Elucidation of keyhole induced bubble formation mechanism in fiber laser welding of low carbon steel. Int. J. Heat Mass Transf. 127, 1077-1086 (2018).
+
+46. Kaplan, A. F. H. Fresnel absorption of 1 μm- and 10 μm-laser beams at the keyhole wall during laser beam welding: Comparison between smooth and wavy surfaces. Appl. Surf. Sci. 258, 3354-3363 (2012).
+
+47. Guo, Q. et al. In-situ full-field mapping of melt flow dynamics in laser metal additive manufacturing.
+
+<--- Page Split --->
+
+Addit. Manuf. 31, 100939 (2020).
+
+48. Ao, S., Luo, Z., Feng, M. & Yan, F. Simulation and experimental analysis of acoustic signal characteristics in laser welding. Int. J. Adv. Manuf. Technol. 81, 277-287 (2015).
+
+49. Farson, D., Hillsley, K., Sames, J. & Young, R. Frequency-time characteristics of air-borne signals from laser welds. J. Laser Appl. 8, 33-42 (1996).
+
+50. Ristic, B., Arulampalam, S. & Gordon, N. Beyond the Kalman filter: Particle filters for tracking applications. vol. 685 (2004).
+
+51. Lee, P. D., Chirazi, A. & See, D. Modeling microporosity in aluminum-silicon alloys: A review. Journal of Light Metals vol. 1 15-30 (2001).
+
+52. Kaplan, A. F. H., Mizutani, M., Katayama, S. & Matsunawa, A. Mechanism of pore formation during keyhole laser spot welding. in First International Symposium on High-Power Laser Macroprocessing (eds. Miyamoto, I., Kobayashi, K. F., Sugioka, K., Poprawe, R. & Helvajian, H.) vol. 4831 186 (SPIE, 2003).
+
+53. Lee, P. D. & Hunt, J. D. Measuring the nucleation of hydrogen porosity during the solidification of aluminium-copper alloys. Scr. Mater. 36, 399-404 (1997).
+
+54. Lee, P. D., Wang, J. & Atwood, R. C. Microporosity Formation during the Solidification of Aluminum-Copper Alloys. JOM 5 (2009).
+
+55. Lee, P. D. & Hunt, J. D. Model of the interaction of porosity and the developing microstructure. in Modeling of Casting, Welding and Advanced Solidification Processes 585-592 (1995).
+
+56. Matthews, M. J. et al. Denudation of metal powder layers in laser powder bed fusion processes. Acta Mater. 114, 33-42 (2016).
+
+57. Liu, H., Bouchard, M. & Zhang, L. An experimental study of hydrogen solubility in liquid aluminium. J. Mater. Sci. 30, 4309-4315 (1995).
+
+58. Brennen, C. E. Cavitation and Bubble Dynamics. Cavitation and Bubble Dynamics (Cambridge University Press, 2013). doi:10.1017/CBO9781107338760.
+
+59. Florschuetz, L. W. & Chao, B. T. On the mechanics of vapor bubble collapse. J. Heat Transfer 87,
+
+<--- Page Split --->
+
+209- 220 (1965).
+
+60. Clark, S. J. et al. Capturing Marangoni flow via synchrotron imaging of selective laser melting. in IOP Conference Series: Materials Science and Engineering vol. 861 (Institute of Physics Publishing, 2020).
+
+61. Lv, F. et al. On the role of laser in situ re-melting into pore elimination of Ti-6Al-4V components fabricated by selective laser melting. J. Alloys Compd. 854, 156866 (2021).
+
+62. LASERTEC 30 DUAL SLM - ADDITIVE MANUFACTURING machines from DMG MORI. https://uk.dmgmori.com/products/machines/additive-manufacturing/powder-bed/lasertec-30-slm.
+
+63. Gibson, I., Rosen, D., Stucker, B. & Khorasani, M. Hybrid Additive Manufacturing. in Additive Manufacturing Technologies 347-366 (Springer International Publishing, 2021). doi:10.1007/978-3-030-56127-7_12.
+
+64. Zhang, C., Yu, Y., Chen, C., Zeng, X. & Gao, M. Suppressing porosity of a laser keyhole welded Al-6Mg alloy via beam oscillation. J. Mater. Process. Technol. 278, 116382 (2020).
+
+65. Murr, L. E. et al. Metal Fabrication by Additive Manufacturing Using Laser and Electron Beam Melting Technologies. Journal of Materials Science and Technology vol. 28 1-14 (2012).
+
+66. Zhang, Y., Li, S., Chen, G. & Mazumder, J. Experimental observation and simulation of keyhole dynamics during laser drilling. Opt. Laser Technol. 48, 405-414 (2013).
+
+67. Likas, A., Vlassis, N. & J. Verbeek, J. The global k-means clustering algorithm. Pattern Recognit. 36, 451-461 (2003).
+
+68. Find local maxima - MATLAB findpeaks. https://www.mathworks.com/help/signal/ref/findpeaks.html#input_argument_d0e61186.
+
+69. Anyalebechi, P. N. Critical review of reported values of hydrogen diffusion in solid and liquid aluminum and its alloys. in Light Metals- Warrendale-Proceedings, TMS (2003).
+
+<--- Page Split --->
+
+## Acknowledgements
+
+AcknowledgementsThis research is supported by the Office of Naval Research (ONR) Grant N62909- 19- 1- 2109, the UK- EPSRC via MAPP: EPSRC Future Manufacturing Hub in Manufacture using Advanced Powder Processes (EP/P006566/1) and (EP/R511638/1), and the Royal Academy of Engineering (CiET1819/10). We also acknowledge the use of facilities and support provided by the Research Complex at Harwell and thank the Advanced Photon Source for providing the beam- time (213874) and staff at the 32- ID beamline for their assistance. We are grateful for HRL laboratory for providing the Al7A77 powder for this study. The authors also acknowledge the beamline experiment support from Yunhui Chen, Lorna Sinclair, David Rees, and sample preparation support from Elena Ruckh and Saurabh Shah for tomographic scans.
+
+## Author contributions
+
+Author contributionsP.D.L. and Y.H. conceived the project. Y.H. wrote the manuscript with significant contributions from P.D.L, C.L.A.L., T.G.F., and S.J.C., performed the characterization, image processing (with help from C.L.A.L. and J.T.), performed data analysis and modelling. P.D.L., C.L.A.L., S.J.C., S.M. and K.F. led and performed the experiments. T.G.F. calculated the peak- to- peak period and frequency for keyhole width/depth. S.J.C programmed the Kalman filter tracking.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- Movie1.mp4- Movie2.mp4- Movie3.mp4- Movie4.mp4- Movie5.mp4- Movie6.mp4- Movie7.mp4- Movie8.mp4- Movie9.mp4- Movie10.mp4- Movie11.mp4- Movie12.mp4- SupplementaryInformation.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e_det.mmd b/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..3d8326c210d59fef69554ee37682dfb3ce1df27e
--- /dev/null
+++ b/preprint/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e/preprint__050ed3c1f58b52603ffaa3e78bfca0f596e729688a27ac32aff4bca96202c35e_det.mmd
@@ -0,0 +1,561 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 825, 210]]<|/det|>
+# Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing
+
+<|ref|>text<|/ref|><|det|>[[44, 229, 640, 272]]<|/det|>
+Yuze Huang ( \(\boxed{\infty}\) yuze.huang@ucl.ac.uk) University College London https://orcid.org/0000- 0002- 9971- 6038
+
+<|ref|>text<|/ref|><|det|>[[44, 277, 216, 317]]<|/det|>
+Tristan Fleming Queen's University
+
+<|ref|>text<|/ref|><|det|>[[44, 323, 670, 365]]<|/det|>
+Samuel Clark Argonne National Laboratory, https://orcid.org/0000- 0002- 8678- 3020
+
+<|ref|>text<|/ref|><|det|>[[44, 370, 283, 410]]<|/det|>
+Sebastian Marussi University College London
+
+<|ref|>text<|/ref|><|det|>[[44, 416, 280, 456]]<|/det|>
+Fezzaa Kamel Advanced Photon Source
+
+<|ref|>text<|/ref|><|det|>[[44, 462, 689, 503]]<|/det|>
+Jeyan Thiyagalingam Rutherford Appleton Laboratory https://orcid.org/0000- 0002- 2167- 1343
+
+<|ref|>text<|/ref|><|det|>[[44, 508, 640, 549]]<|/det|>
+Chu Lun Alex Leung University College London https://orcid.org/0000- 0002- 4153- 7512
+
+<|ref|>text<|/ref|><|det|>[[44, 555, 640, 597]]<|/det|>
+Peter Lee University College London https://orcid.org/0000- 0002- 3898- 8881
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 637, 102, 654]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 675, 732, 695]]<|/det|>
+Keywords: keyhole porosity, laser powder- bed fusion, synchrotron X- ray imaging
+
+<|ref|>text<|/ref|><|det|>[[44, 713, 318, 732]]<|/det|>
+Posted Date: August 20th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 751, 463, 770]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 683646/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 788, 910, 831]]<|/det|>
+License: © \(\circledast\) This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 867, 914, 910]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on March 4th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 28694-x.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[125, 91, 880, 145]]<|/det|>
+# Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing
+
+<|ref|>text<|/ref|><|det|>[[135, 166, 870, 220]]<|/det|>
+Yuze Huang \(^{1,2*}\) , Tristan G. Fleming \(^{3}\) , Samuel J. Clark \(^{1,2,4}\) , Sebastian Marussi \(^{1,2}\) , Kamel Fezzaa \(^{4}\) , Jeyan Thiyagalingam \(^{5}\) , Chu Lun Alex Leung \(^{1,2*}\) , Peter D. Lee \(^{1,2*}\)
+
+<|ref|>text<|/ref|><|det|>[[123, 230, 640, 352]]<|/det|>
+\(^{1}\) UCL Mechanical Engineering, University College London, WC1E 7JE, UK \(^{2}\) Research Complex at Harwell, Harwell Campus, Didcot, OX11 0FA, UK \(^{3}\) Department of Physics, Queen's University, Kingston, Ontario, K7L 3N6, Canada \(^{4}\) X- ray Science Division, Argonne National Laboratory, Lemont, IL 60439, US \(^{5}\) Science and Technology Facilities Council, Harwell Campus, Didcot, OX11 0FA, UK
+
+<|ref|>sub_title<|/ref|><|det|>[[125, 396, 194, 412]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[122, 425, 886, 766]]<|/det|>
+Keyhole porosity is a key concern in laser powder- bed fusion (LPBF), potentially impacting component fatigue life. However, the dynamics of keyhole porosity formation, i.e., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X- ray imaging we reveal keyhole and bubble behaviours, quantifying their formation mechanisms. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also transition keyhole regimes, created by high laser power- velocity conditions, causing fast radial keyhole fluctuations ( \(\sim 10 \mathrm{kHz}\) ); (ii) transition regime collapse tends to occur part way up the rear- wall; and (iii) immediately after keyhole collapse, the bubble grows as pressure equilibrates then shrinks due to metal- vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The physics revealed here can guide the development of real- time monitoring and control systems for keyhole porosity.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[122, 86, 885, 331]]<|/det|>
+Laser powder- bed fusion (LPBF) additive manufacturing is being widely explored in both industry and academia \(^{1,2}\) for the production of metal parts. During LPBF, mid- power ( \(\sim 100 - 1000 \mathrm{W}\) ) but tightly- focused (spot sizes \(\sim 20 - 100 \mu \mathrm{m}\) ) lasers are scanned across successive layers of fine metal powder at high speed ( \(\sim 0.05 - 4 \mathrm{m} \cdot \mathrm{s}^{- 1}\) ), selectively melting and consolidating the powder to build a fully dense part. The typical processing- structure- property linkage for LPBF is: steep thermal gradients and high cooling rates \(^{3}\) ( \(\sim 10^{4} - 10^{6} \mathrm{K} \cdot \mathrm{s}^{- 1}\) ) favouring fine, columnar grains oriented along the build direction, producing as- printed LPBF parts that exhibit increased strength, reduced ductility, and increased microstructural and mechanical property anisotropy \(^{4}\) .
+
+<|ref|>text<|/ref|><|det|>[[121, 342, 886, 778]]<|/det|>
+The laser fluence during LPBF is sufficient to vaporise the metal, generating a recoil pressure that pushes molten metal away from the laser- matter interaction zone \(^{5}\) . With increasing laser fluence, the recoil pressure is large enough to open a deep, high aspect ratio vapour depression, referred to as a keyhole \(^{6}\) . This is commonly used in laser welding to achieve thin and deep joints \(^{7}\) . LPBF also often operates in keyhole mode melting \(^{6}\) to ensure full fusion between successive layers. Additionally, laser absorptivity increases dramatically in keyhole melting due to multiple reflections of the laser beam along keyhole \(^{8}\) , opening the door for fabrication of highly reflective materials (e.g., aluminium matrix composites with \(\sim 91\%\) reflectivity \(^{9}\) ) by LPBF, or enable a more economical laser heat source (e.g., diode laser) to be used in LPBF without sacrificing build efficiency \(^{10}\) . However, the keyhole is subjected to axial fluctuations and radial perturbations \(^{11}\) that are governed by the balance of energy and pressure \(^{12 - 14}\) , posing a significant risk for keyhole instability \(^{15,16}\) and in some cases, collapse. Keyhole collapse often results in the formation of a bubble in the melt pool, which may get trapped by the solidification front to form a pore. Keyhole pores remaining in the final part may act as stress concentrators and sites for crack initiation and growth, making them potentially detrimental to fatigue life and other final component mechanical properties \(^{17}\) .
+
+<|ref|>text<|/ref|><|det|>[[122, 788, 885, 905]]<|/det|>
+Several process models \(^{5,12 - 14,18}\) explained the physics of keyhole pore formation during laser welding and LPBF, revealing the interactive effects of recoil pressure, surface tension, and Marangoni convection on the keyhole, and the competing influence of gravity, drag, buoyancy and thermocapillary forces on bubble motion. Recently, in situ synchrotron X- ray imaging \(^{19 - 22}\) has been applied to LPBF, capturing some
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[122, 87, 886, 426]]<|/det|>
+dynamics of the keyhole and keyhole pore in the sub- surface of melt pool, including: keyhole morphology evolution23; pore formation at turn- around points during raster scanning24; pore elimination by thermocapillary forces25; pore migration under Marangoni- driven flow and pore coalescence26,27; pores being pushed away from keyhole tip by the acoustic waves emanating from the keyhole collapse16, and pore evolution during multi- layer LPBF28,29. However, the dynamics of keyhole pore formation are still not fully understood. The role of keyhole fluctuations in keyhole collapse and the evolutions of bubbles (e.g., formation, growth, shrinkage and migration) before being captured by the solidification front, are largely unexplored. For the latter, previous studies30,31 explored the influence of evaporation and condensation on the dynamics of water- vapour bubbles in a superheated liquid, and effect of dissolved gas diffusion on the bubble growth in casting32,33, but it remains unclear how these physics extend to the LPBF process.
+
+<|ref|>text<|/ref|><|det|>[[122, 438, 886, 907]]<|/det|>
+Here, we perform in situ synchrotron X- ray imaging during LPBF of a commercial aluminium alloy Al7A77 (HRL laboratory, USA), which has critical applications in aerospace, biomedical and automotive industries34 and also a high laser reflectivity35, presenting challenges for laser processing. We discover a transition regime (II) between the stable (I) and unstable (III) keyhole regimes in LPBF, where the keyhole morphology changes from wide and shallow in II to narrow and deep in III. Pores are also observed to form in II, mostly present at the rear keyhole wall (RKW), while keyhole porosity is more prevalent in III with pores typically forming at the keyhole bottom. Although some prior work has suggested keyhole fluctuation are largely random, we observe regular oscillations in keyhole width and depth with significant trends in fluctuation frequency across the three keyhole regimes. We find these regimes are well defined by the front keyhole wall (FKW) angle, which collapses to a single function of the normalized enthalpy product36 for different materials. By comparing our bubble model with the experimental data, we find that the bubble dynamics are defined by fast initial growth induced by the pressure equalisation, followed by shrinkage due to metal- vapour condensation. Concurrent with condensation, hydrogen may diffuse into the bubble, reducing the bubble shrinkage and stabilizing the bubble size. Further, we investigate the rapid distortion of bubbles as they interact with the advancing cellular- dendrite solidification front.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[124, 91, 189, 108]]<|/det|>
+## Results
+
+<|ref|>text<|/ref|><|det|>[[122, 124, 886, 596]]<|/det|>
+Keyhole collapse mechanism and related regime transitions. In situ and operando X- ray imaging was used to probe the keyhole collapse behaviours and keyhole pore formation mechanisms during LPBF, which was carried out using an In Situ and Operando process replicator (ISOPR, Supp. Fig S.10), as described in Methods. We systematically characterised the resulting change in keyhole shape and bubble development across a wide range of area energy densities \(AED^{37}\) , \(AED = P_{l} / (\nu_{l}d_{l})\) ( \(P_{l}\) laser power, \(\nu_{l}\) laser scan velocity, \(d_{l}\) laser beam diameter), from \(AED = 6\) to \(17 \mathrm{MJ}\cdot \mathrm{m}^{- 2}\) in the keyhole melting regime \(^{6}\) . We observed that the keyholes change in morphology from wide and shallow to narrow and deep (Fig.1a, Supp. Fig S.1a and Movies 1 – 12). Simultaneously, bubbles first form at the RKW, then prevail at the bottom of keyhole once the keyhole becomes deep and narrow (Fig.1a, Supp. Fig S.1a). Those findings indicate that the transition from a stable to unstable keyhole melting may be more nuanced than previously suggested \(^{16,23}\) (discussed in detail later). We also noticed that the FKW remained relatively smooth at an approximately constant inclination, whereas the RKW presented random wrinkles and perturbations. With increasing \(AED\) , the keyhole penetration depth increases and the inclination of the FKW become steeper (higher FKW angle \(\theta\) , \(\tan \theta \sim \nu_{d} / \nu_{l}^{38}\) ), which is attributed to higher drilling velocity \(^{39}\) ( \(\nu_{d}\) ) and increased energy coupling due to multiple reflections \(^{8}\) .
+
+<|ref|>text<|/ref|><|det|>[[122, 605, 886, 888]]<|/det|>
+By supplementing our results with previous studies \(^{16,23,39,40,41}\) across a wide range of powder materials, process conditions with different LPBF replicators and beamlines, we found that the FKW angle \(\theta\) collapses to an inverse tangent of the normalised enthalpy product \((\Delta H / h_{m} \cdot L_{th}^{*})^{36}\) (Fig.1b), where \(L_{th}^{*}\) is the normalised thermal diffusion length \(^{36}\) and the normalised enthalpy \(\Delta H / h_{m}^{6,42}\) is the ratio of \(\Delta H\) , the deposited energy density \(^{6}\) (also named as specific enthalpy) and \(h_{m}\) , the enthalpy at melting. This relationship is derived by the governing laws of heat transfer and kinematic equilibrium, elaborated in Supp. Note 1. The agreement (Fig.1b) between the theorical derivation and experimental measurements, suggests that the FKW inclination during LPBF is not only controlled by the deposited energy density \(\Delta H\) and the material's melting enthalpy \(h_{m}\) , but also affected by the thermal diffusion length \(L_{th}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[145, 88, 850, 576]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[122, 592, 886, 899]]<|/det|>
+Fig.1. Keyhole collapse mechanism and related keyhole melting regime transitions in LPBF. (a) Keyhole morphology variations across the (I) quasi-stable, (II) transition and (III) unstable keyhole regimes under different laser velocities. (b) Front keyhole wall (FKW) angle as a function of normalised enthalpy product for 9 datasets with 4 different materials. Curve fit is \(\theta = \arctan (a\cdot [(AH / h_m\cdot L_{th}^*) + b]) + c\) (a, b and c are constants), performed in Matlab using the Levenberg-Marquardt/least absolute residuals robust fitting algorithm. (c) Radiographs of laser melting with bare aluminium plate in (II) transition regime, showing rear wall collapse with associated illustration (d). (e) Radiographs of laser melting with bare aluminium plate in (III) unstable regime, showing keyhole bottom collapse with associated illustration (f). to is the time moment that the rear keyhole wall (RKW) starts to grow. The red, blue and green arrows in (d) and (f) represent the laser beam, fluid flow and vapour flow, respectively. \(d\) and \(\theta\) represent the keyhole depth and FKW angle, respectively. Laser power 500 W, laser spot diameter \(50\mu \mathrm{m}\) . All scale bars correspond to \(150\mu \mathrm{m}\) . The datasets of LPBF with Ti-6Al-4V are cited from Cunningham et al.23 (Figs.4, S5 and S7) and Zhao et al.16 (Movie S1 -Movie S5) with permission by AAAS. Datasets for LPBF with Inconel 718, SS 304 and aluminium bare plate are cited from Kouraytem et al.39, Parab et al.40, and Hojjatzadeh et al.41, respectively.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[121, 87, 886, 585]]<|/det|>
+Previous work has related the FKW to the laser fluence, but has largely neglected the role of the thermal diffusion. Cunningham et al. \(^{23}\) reported a nonlinear relationship between the FKW angle and the power density \((2P_{l} / \pi d_{l}^{2})\) , and this relationship changes with the laser scan velocity as well as powder materials. Gan et al. \(^{43}\) found that the tangent of FKW angle is approximately proportional to the "keyhole number \(Ke^{*}(Ke = \frac{1}{\sqrt{\pi}}\cdot \Delta H / h_{m})\) , which is a scaled version of the normalised enthalpy. Here, we find even stronger agreement between the FKW angle and the normalised enthalpy product (Supp. Fig S.2d), rather than the normalised enthalpy (Supp. Fig S.2c). Our result builds on the work of Ye et al. \(^{36}\) , who first introduced the normalised enthalpy product in their scaling laws for keyhole depth (similar relations for keyhole depth measurements are shown in Supp. Fig S.2a, b). Of interest, the normalised thermal diffusion length can be expressed in terms of the Péclet number \(Pe\) , \(L_{th}^{*} = \frac{1}{\sqrt{Pe}}\) (Methods), thus, the above function of FKW angle can be presented as \(\theta \sim atan\left[\left(\frac{\Delta H}{h_{m}}\right) / \sqrt{P_{e}}\right]\) , suggesting that the mode of thermal transfer (convection vs. conduction) also affects the keyhole morphology evolution during LPBF. The relationship derived here also allows for defining thresholds between different melting regimes, similar to King et al. \(^{6}\) , who found the transition from conduction to keyhole melting occurs at a normalised enthalpy \(\Delta H / h_{m} \approx (30 \pm 4)\) for 316L stainless steel.
+
+<|ref|>text<|/ref|><|det|>[[121, 597, 886, 814]]<|/det|>
+Within the keyhole- melting regime, recent studies have reported a sharp transition between stable and unstable keyhole melting, typically defined by the onset of keyhole porosity \(^{16,23,43}\) . From our data, we observed that the threshold for this transition can vary significantly between alloys. For Al7A77 and Ti- 6Al- 4V \(^{16,23}\) (Fig.2d), we found this transition occurs at \(\Delta H / h_{m} \cdot L_{th}^{*} \sim (8 \pm 3)\) or \(\sim 60^{\circ}\) FKW angle, and \(\Delta H / h_{m} \cdot L_{th}^{*} \sim (20 \pm 3)\) or \(\sim 80^{\circ}\) front- wall angle, respectively. The larger threshold for Al7A77 is likely a combined result of its low absorptivity at ambient temperature ( \(\sim 0.15\) vs. \(\sim 0.45\) ), larger Brewster angle ( \(\sim 85^{\circ 44}\) vs. \(\sim 80^{\circ}\) , Supp. Fig S.5), and lower melting enthalpy \((h_{m} = 2.63 J \cdot mm^{- 3}\) vs. \(6.26 J \cdot mm^{- 3}\) ).
+
+<|ref|>text<|/ref|><|det|>[[123, 826, 884, 877]]<|/det|>
+In addition, we find that there can be an extended transition regime (II) between the stable (I) and unstable (III) keyhole regimes under high- power- velocity (high- \(PV\) ). Pores begin to form in this transition
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[122, 87, 886, 428]]<|/det|>
+regime, and initiate at the RKW rather than at the bottom of the keyhole (typical in III), which was also observed during laser welding of aluminium alloys \(^{15}\) and low carbon steel \(^{45}\) , as well as LPBF of Ti- 6Al- 4V \(^{41}\) . For similar AED, we found this transition regime becomes sharper with decreasing laser power and scan speed ( \(P_{l} = 500 W\) , \(v_{l} = 1.4 m / s\) , Supp. Fig S. 3a, b; \(P_{l} = 200 W\) , \(v_{l} = 0.6 m / s\) , Supp. Fig S. 3c, d), in agreement with Zhao et al. \(^{16}\) . We speculate that the (II) transition regime is induced by the high- PV combination under large AED, which enlarges the melt pool and vapour depression zone, leading to a relatively wider transition from the stable (I) to the unstable (III) keyhole regime. For the laser spot size and alloy used in this study, a high- PV with large AED is defined as \(P_{l} = 500 W\) , \(v_{l} = 1.2 m / s\) , AED \(\geq 7 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) . Considering that the general AED in LPBF is around \(10 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) based on reference \(^{14}\) , we speculate that this transition regime (II) would become popular when high- PV processing is required to achieve large build rate in LPBF.
+
+<|ref|>text<|/ref|><|det|>[[122, 440, 886, 909]]<|/det|>
+To further investigate the different keyhole collapse mechanisms in II and III, we compared the keyhole dynamics (Fig.1c, Fig.1e and Supp. Movies 1 – 12). “Humps” regularly form on the FKW due to the dependence of laser absorption on angle of incidence (Fresnel absorption \(^{46}\) , Supp. Note 2), which becomes especially pronounced around the Brewster angle \(^{46}\) (above which, absorptance falls off dramatically, Supp. Fig S.5). In II (Fig.1c-i, AED = 8 MJ·m \(^{- 2}\) , FKW angle \(81.2 \pm 1.7^{\circ}\) ), these humps tend to reflect the laser beam and the vapour flow towards the RKW. This leads to intensive evaporation and recoil pressure on the RKW and builds up a stagnation pressure \(^{12}\) , correspondingly deforming and expanding the RKW (Fig.1c- ii). Generally, the combined recoil and stagnation pressure balances the surface tension acting on the free surface of the RKW, holding the overhanging RKW from collapse \(^{14}\) . However, should the reflected laser beam and vapour flow be blocked or redirected by a perturbation of the keyhole (Fig.1c- ii), the surface temperature of the unilluminated RKW will quickly decrease. As the temperature decreases, surface tension increases linearly \(^{5}\) , overcoming the recoil pressure which decreases exponentially \(^{5}\) , causing a RKW collapse. We observed that this collapse can sometimes lead to the formation of bubbles from the RKW, approximately at the half- depth of keyhole (Fig.1c- iii), followed by the temporary formation of a deep, high aspect ratio depression. The melt flow at the middle of the pool half way up the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 87, 883, 139]]<|/det|>
+RKW is still strong47, as a result of the Marangoni- driven flow, propelling the pore towards the rear of the pool, as discussed in detail later.
+
+<|ref|>text<|/ref|><|det|>[[121, 152, 886, 556]]<|/det|>
+In the unstable regime (III) (Fig.1e- i, \(AED = 10 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) , FKW angle \(84.8 \pm 0.8^{\circ}\) ), a narrow, deep keyhole forms, and humps on the FKW direct metal vapour and reflected laser beams to the bottom of the keyhole. Intense evaporation and recoil pressure at the keyhole bottom can be further amplified by the rapid formation of a vapour cavity ("J- shaped" keyhole, Fig.1e- ii), which traps reflected laser light and metal vapour, increasing the number and density of multiple reflections8,18 and building up a significant stagnation pressure12. With energy concentrated in this cavity, the keyhole is prone to capillary instability and may sometimes collapse, pinching off a cavity to form a vapour filled bubble (Fig.1e- iii) and leads to a sharp decrease in keyhole depth. This is similar to, but not the same as the "spiking" as initially named in laser welding11. Spiking is also prevalent in LPBF but at turn- around points in raster scan patterns due to the finite acceleration of the laser beam, near- zero instantaneous scan velocity, and resulting pores at the "root" of keyhole24. While a small number of the bubbles we observed were re- captured by the expanding keyhole (Supp. Fig S.1b), most were captured almost instantaneously by the advancing solidification front at the bottom of the keyhole to form pores.
+
+<|ref|>text<|/ref|><|det|>[[122, 570, 886, 750]]<|/det|>
+Keyhole radial and axial fluctuation and keyhole porosity. To quantify the keyhole and bubble dynamics, we built an image processing pipeline (Methods) to extract the keyhole depth and width from in situ X- ray radiographs (Fig.2). This was carried out for both our own study of LPBF with and without AI7A77 powder (Movies 1 – 8 and 10 – 12), as well as a number of previous synchrotron X- ray studies23,39,40 across different powder materials, process conditions, LPBF replicators, and beamlines (e.g., Parab et al.40). Note that the keyhole width is extracted as the median width along the whole keyhole depth.
+
+<|ref|>text<|/ref|><|det|>[[123, 762, 885, 877]]<|/det|>
+Fig.2a shows the regular fluctuations in the keyhole width across different keyhole melting regimes (transition II, blue; unstable III, red). Similar, if not more regular, fluctuations were also observed without powder (Supp. Fig S.4). To further quantify these fluctuations, we calculated the average peak- to- peak period (Methods) and found the corresponding frequencies of keyhole depth and width fluctuations range
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 88, 884, 264]]<|/det|>
+from \(\sim 2.5 \mathrm{kHz}\) to \(\sim 10 \mathrm{kHz}\) , in agreement with previous acoustic, optical and radiometric measurements \(^{8,48,49}\) . We also found significant trends in the keyhole width and depth fluctuations across different keyhole regimes (Fig.2b): starting in \(\mathrm{I}(\Delta H / h_{m} \cdot L_{th}^{*}< 10)\) , the keyhole width fluctuations first increase in frequency, reach the highest in \(\mathrm{II}(10< \Delta H / h_{m} \cdot L_{th}^{*}< 20)\) , and then slightly decrease in frequency in \(\mathrm{III}(\Delta H / h_{m} \cdot L_{th}^{*}>20)\) . Similar patterns for the keyhole depth fluctuation are shown in Fig.2c, which increases in frequency from I to II, and then remains high in III.
+
+<|ref|>image<|/ref|><|det|>[[125, 275, 608, 730]]<|/det|>
+
+<|ref|>image<|/ref|><|det|>[[510, 275, 886, 730]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[123, 737, 884, 883]]<|/det|>
+The keyhole width and depth fluctuation trends are consistent with the keyhole collapse mechanisms discussed above. In II, the high frequency hump formation and subsequent migration down the FKW (Supp. Fig S.13) can cause an open, wide vapour depression to temporarily collapse into a deeper, higher aspect ratio keyhole, with a significant decrease in keyhole width and increase in keyhole depth (although sometimes less significant), boosting the fluctuation frequency of keyhole. In III, relatively higher
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 87, 885, 235]]<|/det|>
+oscillation frequencies for the depth vs. the width also agrees with the discussion of Fig.1, corresponding to bubbles being pinched off at the keyhole bottom, followed by a sharp decrease in keyhole depth. As shown in Fig.2d, keyhole pores begin to form in II and increase in frequency through III. Comparing the final depth of pores relative to the substrate with the average keyhole depth (Supp. Fig S.6) corroborates that bubbles initiate both at the RKW in II and at the keyhole bottom in III.
+
+<|ref|>text<|/ref|><|det|>[[122, 248, 886, 619]]<|/det|>
+Prior studies \(^{23,16}\) reported larger keyhole fluctuations with powder compared to bare substrate. Zhao et al. \(^{16}\) hypothesized that this phenomenon is induced by the momentary interaction between particle spatter and the laser beam \(^{13}\) , which shades the laser illumination and reduces recoil pressure, correspondingly increasing keyhole fluctuation. Here, by comparing the fluctuation frequency of keyhole width (Fig.2b), depth (Fig.2c), and also the tracked bubble numbers at per unit track length (Supp. Fig S.7) with and without powder, we observed limited differences between the powder and bare plate samples. We hypothesise that the shadowing effect of particle spatter on the laser beam is less significance when a high laser power and a thin powder layer thickness are applied (for the laser spot size and alloy used in this study, a high laser power and a thin layer thickness is defined as \(\geq 500 \mathrm{W}\) and \(\leq 30 \mu \mathrm{m}\) , respectively), which is consistent with the finding reported by Khairallah et al. \(^{13}\) . Khairallah et al. found that there exists a power threshold beyond which the particle spatter expulsion mechanism is activated and could vaporise the spatter quickly, inversely, inducing pores due to laser shadowing with rapid cooling.
+
+<|ref|>text<|/ref|><|det|>[[123, 634, 886, 816]]<|/det|>
+Keyhole- induced bubble lifetime dynamics in LPBF. Using our image processing pipeline (e.g., Kalman filter tracking \(^{50}\) ), we traced the evolutions of the keyhole- induced bubbles and extracted their centroids and equivalent diameters over their lifetime, starting after a bubble is pinched off from the keyhole and ending when the bubble is fully captured by the solidification front (see examples in Fig.3a,b, \(AED = 10 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) , Movies 7, 8; Supp. Fig S.8a, b, \(AED = 17 \mathrm{MJ} \cdot \mathrm{m}^{- 2}\) , Movies 1 – 4). We observed that bubbles evolve through three main stages, both with and without the presence of a powder layer:
+
+<|ref|>text<|/ref|><|det|>[[146, 828, 883, 880]]<|/det|>
+(1) bubbles rapidly grow immediately after they are pinched off from the keyhole (Fig.3a, b-i, ii, iii), thought to be due to pressure equalisation; then
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[146, 88, 884, 170]]<|/det|>
+(2) the bubbles shrink while migrating towards the rear side of melt pool (Fig.3a, b-iv), hypothesised to be caused by condensation of the metal vapour in them, competing with diffusion of hydrogen into the bubbles; and finally
+
+<|ref|>text<|/ref|><|det|>[[146, 183, 704, 201]]<|/det|>
+(3) they are captured by the advancing solidification front (Fig.3a, b-vi).
+
+<|ref|>image<|/ref|><|det|>[[140, 220, 848, 692]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[123, 697, 884, 874]]<|/det|>
+Fig.3. Keyhole bubble lifetime dynamics during LPBF. Laser velocity \(1\mathrm{m / s}\) and laser power \(500\mathrm{W}\) . (a) and (b) are radiographs with Al7A77 powder and bare aluminium plate, respectively. (c) and (d) show the equivalent diameter changes of some tracked bubbles in LPBF with (solid line) and without (dash line) Al7A77 powder. The equivalent diameter is calculated as \(\sqrt{6A / \pi}\) , \(A\) is the bubble area measured from X-ray image. Note the bubble size error is calculated as \(\pm 2\) pixels ( \(1.96\mu \mathrm{m / pixel}\) ), equivalent to the segmentation uncertainty. The total tracked bubble numbers are 5 and 8 for the powder and bare plate cases (Supp. Fig S.9a), respectively, using a criterion where the minimum number of frames that a bubble is identified is 6 (Methods). The time to is set to the moment a bubble is first identified. The black dashed circles show initial bubble growth. The interested keyhole pores
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 88, 882, 103]]<|/det|>
+shown in (a) and (b) are marked by green and pink colours, which are also shown with same colours in (c) and (d), respectively.
+
+<|ref|>text<|/ref|><|det|>[[123, 114, 590, 130]]<|/det|>
+Vap.: Vapour; Ar: Argon; \(\mathrm{H}_{2}\) : Hydrogen. All scale bars correspond to \(100\mu \mathrm{m}\) .
+
+<|ref|>text<|/ref|><|det|>[[122, 147, 886, 460]]<|/det|>
+Other occasional bubble dynamics, i.e. re- captured by the keyhole, splitting and coalescence were also observed in our LPBF experiments (Supp. Movies 1 – 12). In stage (1), since the bubble was just pinched off from the keyhole, the bubble inner pressure \(p_{i}\) is expected to be similar to the keyhole bottom recoil pressure \((\sim 10^{5} - 10^{6}Pa^{14,39})\) , which is generally larger than the ambient pressure \(p_{a}(\sim 1\times 10^{5}Pa)\) . This pressure difference then drives bubble growth according to the ideal gas law \(^{51}\) \((p = nRT / V)\) , where the volume, \(V\) , must increase to accommodate the reduction in pressure \(p\) from \(p_{i}\) to \(p_{a}\) (Note, \(n\) is the molar number of gas, \(R\) the universal gas constant, and \(T\) the temperature). Simultaneously, as the surrounding liquid metal cools the bubble, the superheated metal- vapour inside the bubble will condense, reducing \(n\) , and hence decreasing the bubble volume \(V\) , but at a slower rate than the pressure equalisation (discussed in detail later). This is also known as the bubble contraction mechanism in laser welding \(^{15,52}\) .
+
+<|ref|>text<|/ref|><|det|>[[122, 472, 886, 745]]<|/det|>
+In stage (2) bubbles shrink while migrating towards the rear side of melt pool, we observed that the bubble shrinkage undergoes a marked slowdown at the later stage of condensation (e.g., bubble 3 from 40 \(\mu \mathrm{s}\) to \(120\mu \mathrm{s}\) in Fig.3d), and the bubble size then get stabilized. We speculate the slowdown shrinkage and bubble size stabilization are caused by the hydrogen diffusion \(^{32}\) . The presence of hydrogen in keyhole pores was observed by Matsunawa et al. \(^{15}\) , who measured \(\sim 3 - 12\%\) hydrogen content in pores formed during laser welding of aluminium alloy using mass spectrometry. Hydrogen is expected to be present in both the virgin substrate and powder particles. During LPBF, the melt at the advancing solidification front can then become supersaturated with hydrogen, driving hydrogen diffusion from the melt into the bubble \(^{28,30}\) and it is several orders faster than the diffusion of other atoms \(^{53}\) .
+
+<|ref|>text<|/ref|><|det|>[[122, 759, 885, 905]]<|/det|>
+In stage (3) as bubbles reach the solid/liquid interface before being fully captured by the solidification front, we observed that the bubbles experience some sudden, apparent bursts of growth and shrinkage (e.g., bubble 2 at \(80 - 120\mu \mathrm{s}\) in Fig.3c, Supp. Fig S.14a, b). This phenomenon may be explained by the interaction of the bubble with the rapidly growing microstructure \(^{54,55}\) (e.g., the bubble is pierced through, or perhaps distorted from spherical, by the growing columnar dendrite), elucidated in Supp. Note 3.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[122, 88, 885, 267]]<|/det|>
+Based on the above findings, from the initiation of a bubble until it gets frozen as a pore, its composition will initially be a combination of metal vapour and shielding gas argon (Ar), which is driven into the keyhole via the Bernoulli effect56. The metal vapour will condense, leaving the Ar, and reducing the pore size. Simultaneously some hydrogen (H2) will diffuse in, slowing the bubble shrinkage. These stages are highlighted by the tracked bubble colours in Fig.3a, b. Note that the argon can be treated as insoluble in molten aluminium57, which is expected to be the major content left in the frozen pore.
+
+<|ref|>text<|/ref|><|det|>[[122, 280, 886, 490]]<|/det|>
+To verify our hypothesis in above discussion, we combined the Rayleigh- Plesset equation58, bubble condensation model from Florschuetz and Chao59, and the ideal gas law51 to build a united bubble model (Methods) while considering pressure- driven growth, vapour condensation and hydrogen diffusion. We compared the modelled results with experimental measurements under different keyhole melting regimes (II, III), shown in Fig.4, where we presented the tracked keyhole and keyhole pore transient trajectories at 0.8 m/s and 1.2 m/s laser velocities (Fig.4 a, b) based on the X- ray images (Supp. Movies 5, 6, 10, 11), corresponding to II (AED = 12.5 MJ · m- 2) and III (AED = 8 MJ · m- 2).
+
+<|ref|>text<|/ref|><|det|>[[122, 504, 886, 880]]<|/det|>
+As seen from Fig.4c, d, immediately after forming the bubble experiences explosive growth, which plateaus after about \(\sim 3 - 5 \mu \mathrm{s}\) (Supp. Table S. 3). The bubble then begins to shrink at a slower rate, and eventually get stabilized ( \(\sim 50 - 150 \mu \mathrm{s}\) ), being consistent with the experimental measurements (Note that deviations may be caused by the effect of surface tension and fluid flow that are not included in the built model). We hypothesise that the explosive growth is caused by the pressure equalisation, with the bubble volume increasing like \(t^3\) (see Methods). The decline and plateau in bubble growth is explained by the decrease in driving force \((p_i - p_a)\) with increasing bubble volume, based on the ideal gas law. We also speculate that the bubble shrinkage rate is slower than the bubble growth rate, proportional to \(t^{- 1 / 2}\) and \(t\) , respectively (see Methods). Additionally, we hypothesise that the bubble shrinkage rate can be further slowed by the diffusion of hydrogen. The modelling results (Fig.4 c, d) show that accounting for the hydrogen diffusion is necessary to explain the latter stage of bubble size stabilisation and this leads to good agreement with the tracked bubble equivalent diameter. Note that our temporal resolution of X- ray
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[122, 88, 884, 202]]<|/det|>
+imaging (20 \(\mu \mathrm{s}\) ) is insufficient to capture the whole process of bubble growth after being pinched off from keyhole. With a calculated growth time on the order of \(\mu \mathrm{s}\) , it is likely that we often fail to capture this growth, explaining why immediate bubble shrinkage is observed more frequently than initial bubble growth then shrinkage in our X- ray imaging (Supp. Fig S.9).
+
+<|ref|>image<|/ref|><|det|>[[130, 220, 848, 718]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[122, 722, 886, 898]]<|/det|>
+Fig.4. Tracking and modelling of keyhole induced bubble dynamics. Colour map tracking for keyhole and bubble under low (a) and high (b) laser velocities, corresponding to regimes (III) and (II), respectively. Comparing the modelled bubble size variations with in situ X-ray measurements at low (c) and high (d) laser velocities. The equivalent diameter is calculated as \(\sqrt{6A / \pi}\) , \(A\) is the bubble area measured from X-ray image by the processing algorithms listed in Methods. The bubble size error is calculated as \(\pm 2\) pixels (1.96 \(\mu \mathrm{m / pixel}\) ), equivalent to the segmentation uncertainty. Note, the bubble shown in (c) split into two small ones in the later stage, where the equivalent diameter is estimated based on their sum area. The temporal resolution of X-ray imaging (20 \(\mu \mathrm{s}\) ) is insufficient to capture the whole process of bubble growth, therefore, we are unable to get enough data and fully verify
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 88, 884, 156]]<|/det|>
+the bubble growth model. (e) Bubble migration distance compared to their initial formed location. The bubble migration distance error is calculated based on the bubble motion with instantaneous speeds \((0 - 5 \mathrm{m / s})\) during the finite camera exposure time (2.5 \(\mu \mathrm{s}\) ). Low laser velocity \(0.8 \mathrm{m / s}\) , high velocity \(1.2 \mathrm{m / s}\) , laser power \(500 \mathrm{W}\) .
+
+<|ref|>text<|/ref|><|det|>[[122, 174, 886, 610]]<|/det|>
+The bubbles migrated a larger distance in II with a tendency of going backward and upward, when initiated at the RKW, than in III (Fig.4e.), when initiated at the bottom of the keyhole, remaining almost stationary. This is due to two effects (i) the proximity of the solidification front to the bottom of the keyhole, bubbles having insufficient time to move upwards in the melt pool18; and (ii) the melt flow velocity and flow pattern are location dependent across the melt pool47, and the induced drag force is local flow velocity dependent. The flow velocity is higher in the middle of the pool, hence when a bubble is formed half way along the RKW, it quickly flows backwards to the rear of melt pool. At the bottom of the pool near the solid- liquid interface, the flow is low, hence bubbles detaching from the very bottom of keyhole remain nearly stationary until captured by the solidification front and turn to pores. The bubble in Fig.4a (regime III) has an average velocity of \(1.0 \pm 0.5 \mathrm{m / s}\) (measured over the first \(60 \mu \mathrm{s}\) ), while the bubble in Fig.4b (regime II) moves at \(2.4 \pm 0.7 \mathrm{m / s}\) . In regime III with high AED, the pore migration speed of \(1.0 \mathrm{m / s}\) agrees well with our previous measurements of the Marangoni flow speed with tungsten carbide particles (0.97 \(\mathrm{m / s}\) under the same AED)60, while we assume that a strong viscous drag force is responsible for the higher initial speed of bubbles initiated at the RKW in regime II at lower AED.
+
+<|ref|>sub_title<|/ref|><|det|>[[124, 627, 214, 644]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[122, 664, 886, 908]]<|/det|>
+In summary, this manuscript reveals the lifetime dynamics of keyhole pore (growth, shrinkage, migration), introducing a new threshold, the normalized enthalpy product, to reveal and elucidate different keyhole pore generation mechanisms and their corresponding keyhole melting regimes in LPBF. Our findings on keyhole fluctuation and bubble dynamics provide critical guidance (e.g., bubble growth/shrinkage rate, pore location and size) to achieve in situ pore elimination by remelting25,61 upon the dual- laser LPBF machines62 or hybrid LPBF63, and pore suppression via real- time control of keyhole dynamics (e.g., beam oscillation64) in broad high- energy- beam processing techniques (e.g., electron beam melting65, keyhole laser welding64 and laser drilling66).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 88, 884, 171]]<|/det|>
+In this study, we combined our own in situ synchrotron X- ray imaging results from LPBF of aluminium alloy (Al7A77) with recent studies of other key additive manufacturing alloys (e.g., Ti- 6Al- 4V, Inconel 718, SS 304) and drew the following conclusions:
+
+<|ref|>text<|/ref|><|det|>[[150, 184, 886, 363]]<|/det|>
+- A transition regime (II) between the stable (I) and unstable (III) keyhole regimes has been discovered based on the evolutions of keyhole morphology and bubble formation. This transition regime II is pronounced for high-\(PV\) combinations under large AED (AED \(\geq 7 \mathrm{MJ} \cdot \mathrm{m}^{-2}\) ), and features the vapor depression transforms from wide and shallow to narrow and deep, concurrently, keyhole collapses and induce pores at mid-rear wall in II, as opposed to the bottom of the keyhole in III.
+
+<|ref|>text<|/ref|><|det|>[[152, 377, 884, 460]]<|/det|>
+- Significant trends in keyhole fluctuation frequency (radial and axial) were observed across the different keyhole regimes, where the fastest fluctuation occurring in the transition regime (II) at \(\sim 10 \mathrm{kHz}\) .
+
+<|ref|>text<|/ref|><|det|>[[152, 475, 884, 620]]<|/det|>
+- A material, machine and process condition agnostic relationship was developed for the FKW angle, which collapses to a single function of the normalized enthalpy product, providing a non-dimensional threshold for predicting the three keyhole regime transitions and the onset of keyhole porosity for different alloys and processing conditions (e.g., variant laser spot sizes, powers, velocities).
+
+<|ref|>text<|/ref|><|det|>[[152, 635, 884, 781]]<|/det|>
+- Keyhole pore formation process, including the lifetime dynamics of the vapour bubble in the melt pool, were revealed by the X-ray imaging and were summarized in three stages: (1) fast pressure-driven growth, (2) shrinkage by metal vapour condensation and shrinkage inhibition by hydrogen diffusion, and (3) interaction with growing microstructure (e.g., cellular-dendrites) and capture by the advancing solidification front.
+
+<|ref|>text<|/ref|><|det|>[[152, 795, 884, 879]]<|/det|>
+- A model of bubble growth and shrinkage was proposed, including the physics of pressure-driven growth, vapour condensation and hydrogen diffusion. This model was found to be consistent with the experimental data, supporting our hypotheses: (i) the explosive bubble growth at the early
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[181, 90, 883, 170]]<|/det|>
+lifetime of stage (1) is mainly a pressure-driven process, where the bubble volume expands like \(\sim t^3\) ; (ii) the hydrogen diffusion is sufficiently high to stabilize the bubble size at the later stage of condensation in stage (2).
+
+<|ref|>sub_title<|/ref|><|det|>[[123, 189, 201, 206]]<|/det|>
+## Methods
+
+<|ref|>text<|/ref|><|det|>[[121, 225, 885, 728]]<|/det|>
+LPBF Replicator (ISOPR) system and processing conditions. In situ synchrotron X- ray imaging was performed to probe keyhole and keyhole bubble dynamics during LPBF at the Argonne National Laboratory's Advanced Photon Source (APS) over the ISOPR (Supp. Methods, Fig S.10). The ISOPR, custom- designed to accommodate the synchrotron X- ray imaging of the LPBF process, mainly includes a continuous wave Ytterbium- doped fibre laser (IPG YLR- 500- AC, USA) with a wavelength of \(1070 \pm 10\mathrm{nm}\) and maximum power of \(520\mathrm{W}\) , an X- Y galvanometer scanner (intelliSCANde 30, SCANLAB GmbH, Germany), an environmental chamber and a sample holder positioned at the centre of the chamber. During the experiment, the chamber was filled with argon gas at a pressure of \(+10\mathrm{kPa}\) to reduce oxidation. The keyhole and keyhole pores were imaged at high spatial ( \(1.96\mu \mathrm{m}\) ) and temporal (frame rate \(50\mathrm{kHz}\) ) resolutions with a FASTCAM SA- Z 2100K (Photron, USA) camera by converting the attenuated x- ray beam to optically visible light using a \(100\mu \mathrm{m}\) thick LuAg:Ce scintillator. The resultant field of view was 512 pixels (1mm) in width by 680 pixels (1.33 mm) in height. The commercially Al7A77 powder (HRL Laboratory, USA) with a particle size range of \(15 - 45\mu \mathrm{m}\) , and pure aluminium (Goodfellow, UK) plate with purity of \(99.99\%\) that sandwiched between two \(1\mathrm{mm}\) thickness glassy carbon plates (HTW, Germany), were used in this study with the process parameters shown in Table 1. Thermophysical properties of the materials are shown in Supp. Table S.1.
+
+<|ref|>table<|/ref|><|det|>[[123, 760, 893, 875]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[124, 737, 448, 753]]<|/det|>
+Table 1. Process parameters for the LPBF experiments
+
+| Parameters | Values | Parameters | Values |
| Laser velocity [m/s] | 0.6, 0.8, 1, 1.2, 1.4, 1.6 | Laser power [W] | 200, 500 |
| Track length [mm] | 5 | Laser spot size [μm] | 50 |
| Layer thickness [μm] | 30 | Aluminium substrate size [mm] | 46×17×0.5 |
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 88, 884, 171]]<|/det|>
+Image and data processing pipeline - denoising, segmentation, feature extraction and tracking. The major steps of developed image processing pipeline are shown in Supp. Methods, Fig S.11 with the following steps:
+
+<|ref|>text<|/ref|><|det|>[[163, 183, 884, 330]]<|/det|>
+i. Flat field correction, subtracting the offset background, followed by a 2D Gaussian filtering (Supp. Fig S.11a, b). Note that the flat field correction used a general equation \(^{26}\) : \(\mathrm{FFC} = (\mathrm{I}_0 - \mathrm{Flat}_{\mathrm{avg}}) / (\mathrm{Flat}_{\mathrm{avg}} - \mathrm{Dark}_{\mathrm{avg}})\) , where \(\mathrm{FFC}\) , \(\mathrm{I}_0\) , \(\mathrm{Flat}_{\mathrm{avg}}\) and \(\mathrm{Dark}_{\mathrm{avg}}\) represent the flat field corrected image, raw image, average of 100 flat filed images and average of 100 dark field images, respectively.
+
+<|ref|>text<|/ref|><|det|>[[160, 342, 884, 395]]<|/det|>
+ii. Initial image segmentation (Supp. Fig S.11c) with K-means clustering algorithm \(^{67}\) . The segmentation uncertainty is around \(\pm 2\) pixels (1.96 \(\mu \mathrm{m / pixel}\) ).
+
+<|ref|>text<|/ref|><|det|>[[156, 406, 884, 457]]<|/det|>
+iii. Frame stack integration (Supp. Fig S.11d) over the time and applying volume threshold for noise reduction.
+
+<|ref|>text<|/ref|><|det|>[[158, 469, 884, 552]]<|/det|>
+iv. The final segmented keyhole and keyhole bubble were achieved by applying (iii) over the whole radiograph stack. Examples are shown in Fig S.12a and Supp. Movies, 2, 4, 6, 8, 11, where the keyhole and keyhole bubble were marked with green and red colours, respectively.
+
+<|ref|>text<|/ref|><|det|>[[160, 564, 884, 682]]<|/det|>
+v. Kalman filter tracking algorithm \(^{50}\) was developed based on the segmented keyhole bubble in step (iv). The minimum number of frames that a bubble is identified was set as 6 for being considered as an effective track. The bubbles that were spotted less than 6 frames were mainly recaptured by the successive keyhole and disappear.
+
+<|ref|>text<|/ref|><|det|>[[122, 694, 884, 906]]<|/det|>
+Note that the segmentation algorithm developed in step (ii) fails in very limited cases due to the background fluctuations (e.g., the particle randomly fell into the sandwiched gap between glassy carbon plate and aluminium plate). Here we also developed a supervised machine leaning (random decision forests) model to achieve the segmentation of keyhole and keyhole bubble (Fig S.12b), but found that the machine leaning model fails more often during segmentation, possibly induced by the non- perfect ground- truth labelling as the X- ray frames may have different background fluctuations. The Kalman tracking algorithm developed in step (v) also fails occasionally due to the split or coalescence of bubbles, as well
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 88, 882, 139]]<|/det|>
+as the background fluctuations. But those segmentation and tracking failure do not significantly affect the quantified keyhole and keyhole bubble dynamics.
+
+<|ref|>text<|/ref|><|det|>[[122, 155, 884, 367]]<|/det|>
+Peak- to- peak period for keyhole width/depth. Matlab's built- in findpeaks function68 was used to extract peaks and valleys from the keyhole width/depth signatures. To mitigate the effect of outliers and noise, the signatures were pre- processed using a moving mean filter with a width of 3. A linear fit of the data was also subtracted to remove slow changes in the width/depth. To remain safely below the Nyquist frequency (25 kHz), the minimum peak distance was set to 5 (100 \(\mu \mathrm{s}\) ), acting as a simple low pass filter with cut- off frequency of 10 kHz. The minimum peak prominence was set to 1 standard deviation of the keyhole width/depth data set.
+
+<|ref|>text<|/ref|><|det|>[[122, 382, 884, 660]]<|/det|>
+Bubble growth model with condensation and hydrogen diffusion. In the LPBF process, a rigorous modelling of the bubble dynamics while coupling the meso- nanosecond multi- physics of the process remains a challenge. Here, we assume that the contents, temperature and pressure within the bubble are homogeneous, bubble keeps spherical and be at rest relative to the incompressible melt pool flow. We take the bubble equivalent radius that the bubble is first identified as the bubble initial radius \(r_{b0}\) at the moment \(t = 0\) . In stage (1), considering the very short time of bubble growth, we suppose that there is negligible mass or thermal transfer over the bubble interface (assume no condensation and gas diffusion). Accordingly, the instantaneous bubble radius \(r_{b}(t)\) at time \(t\) can be described by the Rayleigh- Plesset equation58,
+
+<|ref|>equation<|/ref|><|det|>[[266, 672, 852, 714]]<|/det|>
+\[r_{b}\cdot \frac{\partial}{\partial t}\Big(\frac{\partial r_{b}}{\partial t}\Big) + \frac{3}{2}\Big(\frac{\partial r_{b}}{\partial t}\Big)^{2} = \frac{1}{\rho_{l}}\Big(p_{i} - p_{a} - \frac{2\sigma}{r_{b}} -4\mu_{l}\cdot \frac{\partial r_{b}}{\partial t}\Big) \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[123, 727, 883, 778]]<|/det|>
+where \(\rho_{l}\) is the density at melting temperature \(T_{l}\) , \(p_{i}\) the bubble inner pressure, \(p_{a}\) the ambient pressure, \(\sigma\) the surface tension and \(\mu_{l}\) is the viscosity.
+
+<|ref|>text<|/ref|><|det|>[[123, 791, 884, 876]]<|/det|>
+Since the surface tension and the viscosity terms ( \(\sim 10^{4} Pa\) ) are both negligible compared to the pressure difference \(p_{i} - p_{a} (\sim 10^{5} - 10^{6} Pa)^{14,39}\) , which can be omitted in the above Rayleigh- Plesset equation. Accordingly, the bubble growth rate can then be approximated as58,
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[320, 88, 853, 134]]<|/det|>
+\[\frac{\partial r_{b}}{\partial t}\rightarrow \left(\frac{2}{3}\cdot \frac{p_{i} - p_{a}}{\rho_{l}}\right)^{\frac{1}{2}},\qquad r_{b}(t)\gg r_{b}(0) \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[122, 147, 884, 266]]<|/det|>
+This derived bubble growth rate suggests that, at the early time of stage (1) with maximum pressure difference, the bubble grows with a function of time \(t\) , while the bubble volume expands like \(t^{3}\) . The initial bubble inner pressure \(p_{i}(0)\) may be approximated as the recoil pressure \(p_{recoil}\) , \(p_{i}(0) \approx p_{recoil}\) , where the recoil pressure is a function of temperature \(T\) based on Anisimov's evaporation model \(^{5,14}\) ,
+
+<|ref|>equation<|/ref|><|det|>[[346, 275, 852, 316]]<|/det|>
+\[p_{recoil} = 0.54p_{a}exp\left[\frac{\lambda}{K_{B}}\left(\frac{1}{T} -\frac{1}{T_{v}}\right)\right] \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[122, 327, 884, 447]]<|/det|>
+where \(\lambda = 293.4 \mathrm{kJ} \cdot \mathrm{mol}^{- 1}\) is the latent heat of evaporation per atom of aluminium, \(K_{B} = 8.314 \times 10^{- 3} \mathrm{kJ} \cdot \mathrm{mol}^{- 1} \cdot \mathrm{K}^{- 1}\) the Boltzmann constant, \(T\) the keyhole surface temperature, \(T_{v} = 2753.15 \mathrm{K}\) is the evaporation temperature of aluminium. By using the 2D moving heat source model \(^{6}\) , the keyhole surface temperature is approximated by the melt pool peak temperature,
+
+<|ref|>equation<|/ref|><|det|>[[387, 456, 853, 510]]<|/det|>
+\[T = \frac{\sqrt{2}\beta I r_{l}}{k_{l}\sqrt{\pi}} t a n^{-1}\sqrt{\frac{2a_{l}}{\nu_{l}r_{l}}} \quad (4)\]
+
+<|ref|>text<|/ref|><|det|>[[122, 522, 884, 644]]<|/det|>
+where \(\beta\) is the laser absorptivity (depends on angle of incidence, see Supp. Fig S.5), \(r_{l}\) the laser beam radius, \(I\) the laser intensity (approximated as \(I = P_{l} / \left(\pi r_{l}^{2}\right)\) , \(P_{l}\) the laser power), \(a_{l}\) the liquidus thermal diffusivity, \(k_{l} = \rho_{l} \cdot c_{l} \cdot a_{l}\) ( \(\rho_{l}\) the liquidus density, \(c_{l}\) the liquidus heat capacity) the liquidus thermal conductivity and \(v_{l}\) the laser scan velocity.
+
+<|ref|>text<|/ref|><|det|>[[122, 654, 885, 880]]<|/det|>
+By combing the above Equations (2 - 4) and the ideal gas law \(^{51}\) ( \(p = nRT / V\) , \(p\) the pressure, \(n\) the molar number of gas, \(R\) the universal gas constant, \(V = \frac{4}{3}\pi r_{b}^{3}\) the bubble volume), the transient bubble size in stage (1) can be calculated as \(r_{b}(t) = r_{b0} + \Delta r_{b1}(t)\) , \(t \leq t_{1}\) , where \(\Delta r_{b1}(t)\) (solved from simultaneous Equations 2 - 4 and ideal gas law) is the pressure- driven bubble radius increment at time \(t\) , and \(t_{1}\) is the pressure- driven bubble growth time. Note that \(t_{1}\) is calculated as the time that the pressure difference \(p_{i} - p_{a}\) reduces to a percentage threshold of \(p_{a}\) (we used \(5\%\) and defined as \(p_{i}(t_{1}) - p_{a} \leq 0.05p_{a}\) ).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[122, 87, 884, 172]]<|/det|>
+In the condensation dominated regime of stage (2), Florschuetz and Chao \(^{59}\) built the following relation between the bubble instantaneous radius \(r_{b2}(t)\) and the radius at the beginning of vapour condensation \(r_{b2}(0)\) (approximated as the \(r_{b}(t_{1})\) ),
+
+<|ref|>equation<|/ref|><|det|>[[258, 184, 880, 230]]<|/det|>
+\[\frac{1}{3}\left[\frac{r_{b2}(t)}{r_{b2}(0)}\right]^{2} + \frac{2}{3}\frac{r_{b2}(0)}{r_{b2}(t)} = 1 + \frac{t}{t_{cond}},\quad t_{cond} = \frac{\pi[r_{b2}(0)]^{2}}{4Ja^{2}a_{l}} \quad (5)\]
+
+<|ref|>text<|/ref|><|det|>[[122, 243, 884, 340]]<|/det|>
+where \(t_{cond}\) is the condensation characteristic time and \(Ja\) is the Jakob number, \(Ja = \frac{\rho_{l}c_{l}(T_{bs} - T_{sat})}{\rho_{v}L_{v}} (T_{bs}\) the bubble surface temperature, \(T_{sat}\) the saturated temperature, \(L_{v} = 1.02\times 10^{7}J\cdot Kg^{- 1}\) the latent heat of evaporation, \(\rho_{v} = 1850Kg\cdot m^{3}\) the vapour density).
+
+<|ref|>text<|/ref|><|det|>[[121, 350, 885, 639]]<|/det|>
+In stage (2), the enriched hydrogen in melt pool may diffuse into the bubble driven by the concentration difference. The bubble size \(r_{b3}\) induced by hydrogen diffusion may be estimated by the characteristic length of hydrogen diffusion limited growth \(l_{D}^{33}\) as, \(r_{b3} = l_{D} / 2, l_{D} = \sqrt{D_{h}t}\) , where \(D_{h}\) is the mass diffusivity of hydrogen in liquidus aluminium and may be approximated as an average of \(D_{h}(T_{l}) = 1.0943\times 10^{- 7} m^{2}\cdot s^{- 1}\) and \(D_{h}(T_{v}) = 1.1302\times 10^{- 5} m^{2}\cdot s^{- 1}\) based on reference \(^{69}\) . Accordingly, the bubble radius in stage (2) that is controlled by vapour condensation and hydrogen diffusion may be described as, \(\frac{4}{3}\pi r_{b}^{3} = \frac{4}{3}\pi r_{b2}^{3} + \frac{4}{3}\pi r_{b3}^{3}\) , based on mass balance (assuming that the contents, temperature and pressure within the bubble are homogeneous). Therefore, the instantaneous bubble radius in stages 1 and 2 can be approximated as,
+
+<|ref|>equation<|/ref|><|det|>[[293, 650, 880, 704]]<|/det|>
+\[r_{b}(t) = \left\{ \begin{array}{c}{r_{b0} + \Delta r_{b1}(t),t\leq t_{1}}\\ {\sqrt[3]{\left[r_{b2}(t - t_{1})\right]^{3} + \left[r_{b3}(t - t_{1})\right]^{3}},t > t_{1}} \end{array} \right. \quad (6)\]
+
+<|ref|>text<|/ref|><|det|>[[121, 716, 885, 899]]<|/det|>
+All the parameters used in the model were listed in Supp. Table S. 2 (thermal- physical properties) and Supp. Table S. 3 (processing parameters), which were used to plot the bubble diameter graph in Fig.4b, c. Note that we used the liquidus aluminium temperature \(T_{l} = 933.5K\) to approximate the bubble saturation temperature \(T_{sat}\) in melt pool, while for the bubble surface temperature \(T_{bs}\) , which is subcooled by uncertainty temperature in the melt pool after the bubble being pinched off from keyhole, we approximated its magnitude by fitting between observed data and the modelled results. For a spherical vapour bubble,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[123, 87, 883, 140]]<|/det|>
+the total condensation time is around \(1 \sim 3 t_{\text{cond}}^{30}\) . Here, we used the average \(2 t_{\text{cond}}\) and modelled the bubble dynamics within \(2 t_{\text{cond}}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[123, 159, 210, 177]]<|/det|>
+## Reference
+
+<|ref|>text<|/ref|><|det|>[[112, 195, 886, 888]]<|/det|>
+1. King, W. E. et al. Laser powder bed fusion additive manufacturing of metals; physics, computational, and materials challenges. Appl. Phys. Rev. 2, 041304 (2015).
+2. DebRoy, T. et al. Additive manufacturing of metallic components – Process, structure and properties. Prog. Mater. Sci. 92, 112–224 (2018).
+3. Smith, J. et al. Linking process, structure, property, and performance for metal-based additive manufacturing: computational approaches with experimental support. Comput. Mech. 57, 583–610 (2016).
+4. Pham, M. S., Dovgyy, B., Hooper, P. A., Gourlay, C. M. & Piglione, A. The role of side-branching in microstructure development in laser powder-bed fusion. Nat. Commun. 11, (2020).
+5. Khairallah, S. A., Anderson, A. T. A. A. T., Rubenchik, A. M. & King, W. W. E. Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones. Acta Mater. 108, 36–45 (2016).
+6. King, W. E. et al. Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing. J. Mater. Process. Technol. 214, 2915–2925 (2014).
+7. Shevchik, S. et al. Supervised deep learning for real-time quality monitoring of laser welding with X-ray radiographic guidance. Sci. Rep. 10, (2020).
+8. Allen, T. R. et al. Energy-Coupling Mechanisms Revealed through Simultaneous Keyhole Depth and Absorptance Measurements during Laser-Metal Processing. Phys. Rev. Appl. 13, 064070 (2020).
+9. Dai, D. & Gu, D. Effect of metal vaporization behavior on keyhole-mode surface morphology of selective laser melted composites using different protective atmospheres. Appl. Surf. Sci. 355, 310–319 (2015).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 88, 884, 140]]<|/det|>
+10. Tenbrock, C. et al. Influence of keyhole and conduction mode melting for top-hat shaped beam profiles in laser powder bed fusion. J. Mater. Process. Technol. 278, (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 152, 884, 237]]<|/det|>
+11. Tsukamoto, S., Kawaguchi, I., Arakane, G. & Honda, H. Keyhole behavior in high power laser welding. in First International Symposium on High-Power Laser Macroprocessing (eds. Miyamoto, I., Kobayashi, K. F., Sugioka, K., Poprawe, R. & Helvajian, H.) vol. 4831 251 (SPIE, 2003).
+
+<|ref|>text<|/ref|><|det|>[[112, 248, 884, 300]]<|/det|>
+12. Tan, W. & Shin, Y. C. Analysis of multi-phase interaction and its effects on keyhole dynamics with a multi-physics numerical model. J. Phys. D. Appl. Phys. 47, (2014).
+
+<|ref|>text<|/ref|><|det|>[[112, 311, 884, 363]]<|/det|>
+13. Khairallah, S. A. et al. Controlling interdependent meso-nanosecond dynamics and defect generation in metal 3D printing. Science (80-. ). 368, 660-665 (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 375, 884, 427]]<|/det|>
+14. Wang, L., Zhang, Y. & Yan, W. Evaporation Model for Keyhole Dynamics During Additive Manufacturing of Metal. Phys. Rev. Appl. 10, 64039 (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 439, 884, 491]]<|/det|>
+15. Matsunawa, A., Mizutani, M., Katayama, S. & Seto, N. Porosity formation mechanism and its prevention in laser welding. Weld. Int. 17, 431-437 (2003).
+
+<|ref|>text<|/ref|><|det|>[[112, 503, 884, 555]]<|/det|>
+16. Zhao, C. et al. Critical instability at moving keyhole tip generates porosity in laser melting. Science (80-. ). 370, 1080-1086 (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 567, 884, 650]]<|/det|>
+17. Jost, E. W., Miers, J. C., Robbins, A., Moore, D. G. & Saldana, C. Effects of spatial energy distribution-induced porosity on mechanical properties of laser powder bed fusion 316L stainless steel. Addit. Manuf. 39, (2021).
+
+<|ref|>text<|/ref|><|det|>[[112, 662, 884, 714]]<|/det|>
+18. Bayat, M. et al. Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation. Addit. Manuf. 30, 100835 (2019).
+
+<|ref|>text<|/ref|><|det|>[[112, 726, 884, 779]]<|/det|>
+19. Zhao, C. et al. Real-time monitoring of laser powder bed fusion process using high-speed X-ray imaging and diffraction. Sci. Rep. 7, (2017).
+
+<|ref|>text<|/ref|><|det|>[[112, 791, 884, 873]]<|/det|>
+20. Guo, Q. et al. Transient dynamics of powder spattering in laser powder bed fusion additive manufacturing process revealed by in-situ high-speed high-energy x-ray imaging. Acta Mater. 151, 169-180 (2018).
+
+<|ref|>text<|/ref|><|det|>[[110, 886, 884, 906]]<|/det|>
+21. Calta, N. P. et al. An instrument for in situ time-resolved X-ray imaging and diffraction of laser
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[163, 88, 828, 107]]<|/det|>
+powder bed fusion additive manufacturing processes. Rev. Sci. Instrum. 89, 055101 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 118, 884, 170]]<|/det|>
+22. Sun, T. Probing Ultrafast Dynamics in Laser Powder Bed Fusion Using High-Speed X-Ray Imaging: A Review of Research at the Advanced Photon Source. JOM vol. 72 999-1008 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 182, 883, 235]]<|/det|>
+23. Cunningham, R. et al. Keyhole threshold and morphology in laser melting revealed by ultrahigh-speed x-ray imaging. Science (80-. ). 363, 849-852 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 247, 883, 298]]<|/det|>
+24. Martin, A. A. et al. Dynamics of pore formation during laser powder bed fusion additive manufacturing. Nat. Commun. 10, (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 310, 883, 362]]<|/det|>
+25. Hojjatzadeh, S. M. H. et al. Pore elimination mechanisms during 3D printing of metals. Nat. Commun. 10, (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 374, 883, 427]]<|/det|>
+26. Leung, C. L. A. et al. In situ X-ray imaging of defect and molten pool dynamics in laser additive manufacturing. Nat. Commun. 9, (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 438, 883, 490]]<|/det|>
+27. Leung, C. L. A. et al. Laser-matter interactions in additive manufacturing of stainless steel SS316L and 13-93 bioactive glass revealed by in situ X-ray imaging. Addit. Manuf. 24, 647-657 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 502, 883, 555]]<|/det|>
+28. Sinclair, L. et al. In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion. Addit. Manuf. 36, (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 566, 883, 619]]<|/det|>
+29. Chen, Y. et al. In-situ Synchrotron imaging of keyhole mode multi-layer laser powder bed fusion additive manufacturing. Appl. Mater. Today 20, (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 630, 828, 651]]<|/det|>
+30. Prosperetti, A. Vapor Bubbles. Annual Review of Fluid Mechanics vol. 49 221-248 (2017).
+
+<|ref|>text<|/ref|><|det|>[[113, 662, 883, 714]]<|/det|>
+31. Hao, Y., Zhang, Y. & Prosperetti, A. Mechanics of gas-vapor bubbles. Phys. Rev. Fluids 2, 34303 (2017).
+
+<|ref|>text<|/ref|><|det|>[[113, 726, 883, 779]]<|/det|>
+32. Atwood, R. C., Sridhar, S., Zhang, W. & Lee, P. D. Diffusion-controlled growth of hydrogen pores in aluminium-silicon castings: In situ observation and modelling. Acta Mater. 48, 405-417 (2000).
+
+<|ref|>text<|/ref|><|det|>[[113, 790, 883, 843]]<|/det|>
+33. Lee, P. D. & Hunt, J. D. Hydrogen porosity in directional solidified aluminium-copper alloys: In situ observation. Acta Mater. 45, 4155-4169 (1997).
+
+<|ref|>text<|/ref|><|det|>[[113, 854, 858, 875]]<|/det|>
+34. Martin, J. H. et al. 3D printing of high-strength aluminium alloys. Nature 549, 365-369 (2017).
+
+<|ref|>text<|/ref|><|det|>[[113, 886, 883, 907]]<|/det|>
+35. Geng, K., Yang, Y., Li, S., Misra, R. D. K. & Zhu, Q. Enabling high-performance 3D printing of Al
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[163, 88, 835, 108]]<|/det|>
+powder by decorating with high laser absorbing Co phase. Addit. Manuf. 32, 101012 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 119, 884, 171]]<|/det|>
+36. Ye, J. et al. Energy Coupling Mechanisms and Scaling Behavior Associated with Laser Powder Bed Fusion Additive Manufacturing. Adv. Eng. Mater. 21, 1900185 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 183, 883, 235]]<|/det|>
+37. Huang, Y., Khamesee, M. B. M. B. M. & Toyserkani, E. A comprehensive analytical model for laser powder-fed additive manufacturing. Addit. Manuf. 12, 90-99 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 247, 883, 299]]<|/det|>
+38. Fabbro, R., Slimani, S., Coste, F. & Briand, F. Study of keyhole behaviour for full penetration Nd-Yag CW laser welding. J. Phys. D. Appl. Phys. 38, 1881-1887 (2005).
+
+<|ref|>text<|/ref|><|det|>[[113, 311, 884, 363]]<|/det|>
+39. Kouraytem, N. et al. Effect of Laser-Matter Interaction on Molten Pool Flow and Keyhole Dynamics. Phys. Rev. Appl. 11, 064054 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 375, 883, 427]]<|/det|>
+40. Parab, N. D. et al. Ultrafast X-ray imaging of laser-metal additive manufacturing processes. J. Synchrotron Radiat. 25, 1467-1477 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 439, 884, 523]]<|/det|>
+41. Hojjatzadeh, S. M. H. et al. Direct observation of pore formation mechanisms during LPBF additive manufacturing process and high energy density laser welding. Int. J. Mach. Tools Manuf. 153, (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 535, 884, 587]]<|/det|>
+42. Hann, D. B., Iammi, J. & Folkes, J. A simple methodology for predicting laser-weld properties from material and laser parameters. J. Phys. D. Appl. Phys. 44, 445401 (2011).
+
+<|ref|>text<|/ref|><|det|>[[113, 599, 883, 650]]<|/det|>
+43. Gan, Z. et al. Universal scaling laws of keyhole stability and porosity in 3D printing of metals. nature.com (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 662, 857, 683]]<|/det|>
+44. Mahrle, A. & Beyer, E. Theoretical aspects of fibre laser cutting. J. Phys. D Appl. 42, 9 (2009).
+
+<|ref|>text<|/ref|><|det|>[[113, 694, 884, 778]]<|/det|>
+45. Wu, D., Hua, X., Huang, L., Li, F. & Cai, Y. Elucidation of keyhole induced bubble formation mechanism in fiber laser welding of low carbon steel. Int. J. Heat Mass Transf. 127, 1077-1086 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 790, 884, 873]]<|/det|>
+46. Kaplan, A. F. H. Fresnel absorption of 1 μm- and 10 μm-laser beams at the keyhole wall during laser beam welding: Comparison between smooth and wavy surfaces. Appl. Surf. Sci. 258, 3354-3363 (2012).
+
+<|ref|>text<|/ref|><|det|>[[112, 886, 880, 906]]<|/det|>
+47. Guo, Q. et al. In-situ full-field mapping of melt flow dynamics in laser metal additive manufacturing.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 88, 412, 106]]<|/det|>
+Addit. Manuf. 31, 100939 (2020).
+
+<|ref|>text<|/ref|><|det|>[[112, 120, 884, 170]]<|/det|>
+48. Ao, S., Luo, Z., Feng, M. & Yan, F. Simulation and experimental analysis of acoustic signal characteristics in laser welding. Int. J. Adv. Manuf. Technol. 81, 277-287 (2015).
+
+<|ref|>text<|/ref|><|det|>[[112, 184, 884, 234]]<|/det|>
+49. Farson, D., Hillsley, K., Sames, J. & Young, R. Frequency-time characteristics of air-borne signals from laser welds. J. Laser Appl. 8, 33-42 (1996).
+
+<|ref|>text<|/ref|><|det|>[[112, 248, 884, 298]]<|/det|>
+50. Ristic, B., Arulampalam, S. & Gordon, N. Beyond the Kalman filter: Particle filters for tracking applications. vol. 685 (2004).
+
+<|ref|>text<|/ref|><|det|>[[112, 311, 884, 362]]<|/det|>
+51. Lee, P. D., Chirazi, A. & See, D. Modeling microporosity in aluminum-silicon alloys: A review. Journal of Light Metals vol. 1 15-30 (2001).
+
+<|ref|>text<|/ref|><|det|>[[112, 375, 884, 490]]<|/det|>
+52. Kaplan, A. F. H., Mizutani, M., Katayama, S. & Matsunawa, A. Mechanism of pore formation during keyhole laser spot welding. in First International Symposium on High-Power Laser Macroprocessing (eds. Miyamoto, I., Kobayashi, K. F., Sugioka, K., Poprawe, R. & Helvajian, H.) vol. 4831 186 (SPIE, 2003).
+
+<|ref|>text<|/ref|><|det|>[[112, 504, 884, 554]]<|/det|>
+53. Lee, P. D. & Hunt, J. D. Measuring the nucleation of hydrogen porosity during the solidification of aluminium-copper alloys. Scr. Mater. 36, 399-404 (1997).
+
+<|ref|>text<|/ref|><|det|>[[112, 567, 884, 618]]<|/det|>
+54. Lee, P. D., Wang, J. & Atwood, R. C. Microporosity Formation during the Solidification of Aluminum-Copper Alloys. JOM 5 (2009).
+
+<|ref|>text<|/ref|><|det|>[[112, 631, 884, 682]]<|/det|>
+55. Lee, P. D. & Hunt, J. D. Model of the interaction of porosity and the developing microstructure. in Modeling of Casting, Welding and Advanced Solidification Processes 585-592 (1995).
+
+<|ref|>text<|/ref|><|det|>[[112, 695, 884, 745]]<|/det|>
+56. Matthews, M. J. et al. Denudation of metal powder layers in laser powder bed fusion processes. Acta Mater. 114, 33-42 (2016).
+
+<|ref|>text<|/ref|><|det|>[[112, 759, 884, 810]]<|/det|>
+57. Liu, H., Bouchard, M. & Zhang, L. An experimental study of hydrogen solubility in liquid aluminium. J. Mater. Sci. 30, 4309-4315 (1995).
+
+<|ref|>text<|/ref|><|det|>[[112, 823, 884, 873]]<|/det|>
+58. Brennen, C. E. Cavitation and Bubble Dynamics. Cavitation and Bubble Dynamics (Cambridge University Press, 2013). doi:10.1017/CBO9781107338760.
+
+<|ref|>text<|/ref|><|det|>[[112, 887, 884, 906]]<|/det|>
+59. Florschuetz, L. W. & Chao, B. T. On the mechanics of vapor bubble collapse. J. Heat Transfer 87,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 88, 290, 105]]<|/det|>
+209- 220 (1965).
+
+<|ref|>text<|/ref|><|det|>[[113, 119, 884, 202]]<|/det|>
+60. Clark, S. J. et al. Capturing Marangoni flow via synchrotron imaging of selective laser melting. in IOP Conference Series: Materials Science and Engineering vol. 861 (Institute of Physics Publishing, 2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 215, 884, 267]]<|/det|>
+61. Lv, F. et al. On the role of laser in situ re-melting into pore elimination of Ti-6Al-4V components fabricated by selective laser melting. J. Alloys Compd. 854, 156866 (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 279, 884, 332]]<|/det|>
+62. LASERTEC 30 DUAL SLM - ADDITIVE MANUFACTURING machines from DMG MORI. https://uk.dmgmori.com/products/machines/additive-manufacturing/powder-bed/lasertec-30-slm.
+
+<|ref|>text<|/ref|><|det|>[[113, 343, 884, 425]]<|/det|>
+63. Gibson, I., Rosen, D., Stucker, B. & Khorasani, M. Hybrid Additive Manufacturing. in Additive Manufacturing Technologies 347-366 (Springer International Publishing, 2021). doi:10.1007/978-3-030-56127-7_12.
+
+<|ref|>text<|/ref|><|det|>[[113, 438, 884, 490]]<|/det|>
+64. Zhang, C., Yu, Y., Chen, C., Zeng, X. & Gao, M. Suppressing porosity of a laser keyhole welded Al-6Mg alloy via beam oscillation. J. Mater. Process. Technol. 278, 116382 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 503, 884, 555]]<|/det|>
+65. Murr, L. E. et al. Metal Fabrication by Additive Manufacturing Using Laser and Electron Beam Melting Technologies. Journal of Materials Science and Technology vol. 28 1-14 (2012).
+
+<|ref|>text<|/ref|><|det|>[[113, 567, 884, 619]]<|/det|>
+66. Zhang, Y., Li, S., Chen, G. & Mazumder, J. Experimental observation and simulation of keyhole dynamics during laser drilling. Opt. Laser Technol. 48, 405-414 (2013).
+
+<|ref|>text<|/ref|><|det|>[[113, 631, 884, 682]]<|/det|>
+67. Likas, A., Vlassis, N. & J. Verbeek, J. The global k-means clustering algorithm. Pattern Recognit. 36, 451-461 (2003).
+
+<|ref|>text<|/ref|><|det|>[[113, 695, 884, 746]]<|/det|>
+68. Find local maxima - MATLAB findpeaks. https://www.mathworks.com/help/signal/ref/findpeaks.html#input_argument_d0e61186.
+
+<|ref|>text<|/ref|><|det|>[[113, 758, 884, 810]]<|/det|>
+69. Anyalebechi, P. N. Critical review of reported values of hydrogen diffusion in solid and liquid aluminum and its alloys. in Light Metals- Warrendale-Proceedings, TMS (2003).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[125, 90, 288, 108]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[123, 125, 885, 370]]<|/det|>
+AcknowledgementsThis research is supported by the Office of Naval Research (ONR) Grant N62909- 19- 1- 2109, the UK- EPSRC via MAPP: EPSRC Future Manufacturing Hub in Manufacture using Advanced Powder Processes (EP/P006566/1) and (EP/R511638/1), and the Royal Academy of Engineering (CiET1819/10). We also acknowledge the use of facilities and support provided by the Research Complex at Harwell and thank the Advanced Photon Source for providing the beam- time (213874) and staff at the 32- ID beamline for their assistance. We are grateful for HRL laboratory for providing the Al7A77 powder for this study. The authors also acknowledge the beamline experiment support from Yunhui Chen, Lorna Sinclair, David Rees, and sample preparation support from Elena Ruckh and Saurabh Shah for tomographic scans.
+
+<|ref|>sub_title<|/ref|><|det|>[[125, 388, 305, 406]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[123, 423, 885, 571]]<|/det|>
+Author contributionsP.D.L. and Y.H. conceived the project. Y.H. wrote the manuscript with significant contributions from P.D.L, C.L.A.L., T.G.F., and S.J.C., performed the characterization, image processing (with help from C.L.A.L. and J.T.), performed data analysis and modelling. P.D.L., C.L.A.L., S.J.C., S.M. and K.F. led and performed the experiments. T.G.F. calculated the peak- to- peak period and frequency for keyhole width/depth. S.J.C programmed the Kalman filter tracking.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[58, 131, 367, 471]]<|/det|>
+- Movie1.mp4- Movie2.mp4- Movie3.mp4- Movie4.mp4- Movie5.mp4- Movie6.mp4- Movie7.mp4- Movie8.mp4- Movie9.mp4- Movie10.mp4- Movie11.mp4- Movie12.mp4- SupplementaryInformation.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/images_list.json b/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..55d4dfea7a891fb2dc4872864dc60d7579b947bf
--- /dev/null
+++ b/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/images_list.json
@@ -0,0 +1,185 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 120,
+ 150,
+ 884,
+ 666
+ ]
+ ],
+ "page_idx": 28
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 28
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_0.jpg",
+ "caption": "c",
+ "footnote": [],
+ "bbox": [
+ [
+ 48,
+ 285,
+ 870,
+ 555
+ ]
+ ],
+ "page_idx": 30
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_1.jpg",
+ "caption": "Endocytosis",
+ "footnote": [],
+ "bbox": [
+ [
+ 83,
+ 603,
+ 600,
+ 950
+ ]
+ ],
+ "page_idx": 30
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_2.jpg",
+ "caption": "e",
+ "footnote": [],
+ "bbox": [
+ [
+ 625,
+ 750,
+ 872,
+ 950
+ ]
+ ],
+ "page_idx": 30
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [
+ [
+ 80,
+ 152,
+ 936,
+ 920
+ ]
+ ],
+ "page_idx": 30
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_3.jpg",
+ "caption": "b",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 32
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_4.jpg",
+ "caption": "Figure S3",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 34
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_5.jpg",
+ "caption": "Figure S4",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 36
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_6.jpg",
+ "caption": "Figure S5",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 38
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_7.jpg",
+ "caption": "c",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 40
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_8.jpg",
+ "caption": "CD44hi CD62Llo",
+ "footnote": [],
+ "bbox": [
+ [
+ 312,
+ 866,
+ 490,
+ 930
+ ]
+ ],
+ "page_idx": 42
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_9.jpg",
+ "caption": "CD44hi CD62Llo",
+ "footnote": [],
+ "bbox": [
+ [
+ 580,
+ 481,
+ 816,
+ 590
+ ]
+ ],
+ "page_idx": 44
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_10.jpg",
+ "caption": "Figure S8",
+ "footnote": [],
+ "bbox": [
+ [
+ 112,
+ 130,
+ 919,
+ 850
+ ]
+ ],
+ "page_idx": 44
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_11.jpg",
+ "caption": "Figure S9",
+ "footnote": [],
+ "bbox": [
+ [
+ 115,
+ 155,
+ 345,
+ 245
+ ]
+ ],
+ "page_idx": 46
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f.mmd b/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..ba1106e0621c4f8a836e19e0932d676a379dad12
--- /dev/null
+++ b/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f.mmd
@@ -0,0 +1,600 @@
+
+# ZFP36-family RNA-binding proteins in regulatory T cells reinforce immune homeostasis.
+
+Martin Turner
+
+martin.turner@babraham.ac.uk
+
+Babraham Institute https://orcid.org/0000- 0002- 3801- 9896
+
+Beatriz Sáenz- Narciso
+
+Babraham Institute
+
+Sarah Bell
+
+Babraham Institute https://orcid.org/0000- 0002- 3249- 707X
+
+Louise Matheson
+
+Babraham Institute https://orcid.org/0000- 0002- 9392- 2519
+
+Ram Venigalla
+
+Babraham Institute
+
+## Article
+
+Keywords:
+
+Posted Date: October 7th, 2024
+
+DOI: https://doi.org/10.21203/rs.3.rs- 5039504/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Communications on May 6th, 2025. See the published version at https://doi.org/10.1038/s41467- 025- 58993- y.
+
+<--- Page Split --->
+
+1 Title: ZFP36-family RNA-binding proteins in regulatory T cells reinforce 2 immune homeostasis. 3 4 Authors: Beatriz Sáenz-Narciso, Sarah E. Bell, Louise S. Matheson, Ram K. C. 5 Venigalla and Martin Turner\* 6 7 8 Affiliations: Immunology Programme, The Babraham Institute, Babraham Research 9 Campus, Cambridge, CB22 3AT, UK. 10 11 These authors contributed equally to this work: Beatriz Sáenz-Narciso, Sarah E. Bell 12 13 Corresponding author: 14 Dr. Martin Turner 15 e- mail: martin.turner@babraham.ac.uk 16 17 Abstract 18 RNA binding proteins (RBP) of the ZFP36 family limit the differentiation and effector 19 functions of CD4 and CD8 T cells, but little is known of their expression or function in 20 regulatory T cells (Treg). By Treg-restricted deletion of Zfp36 family members we 21 identify the essential role of Zfp36/1 and Zfp36/2 in Treg to maintain immune 22 homeostasis. Mice with Tregs deficient in these RBP display an inflammatory 23 phenotype with an expansion in the numbers of type-2 conventional dendritic cells, T 24 effector cells, T follicular helper and germinal center B cells and elevated serum 25 cytokines and immunoglobulins. In the absence of Zfp36/1 and Zfp36/2, the pool of 26 cycling CTLA-4 in naïve Treg was reduced, Tregs were less sensitive to IL-2 and IL-7 27 but were more sensitive to IFNγ. In mice lacking both RBP in Treg, the deletion of a 28 single allele of Ifng is sufficient to ameliorate the pathology. Thus, ZFP36L1 and 29 ZFP36L2 regulate multiple pathways that enable Tregs to enforce immune 30 homeostasis.
+
+<--- Page Split --->
+
+The Zinc Finger Protein 36 (ZFP36) family of RNA binding proteins (RBP) are widely expressed and play important roles in developmental biology, stress responses and inflammation \(^{1,2}\) . They act as repressors of gene expression by direct binding to AU-rich elements in the 3'UTR of mRNAs to limit translation and trigger RNA degradation. They regulate large numbers of functionally related mRNAs throughout their lifetime creating a system of post-transcriptional operons which regulate immune function \(^{3,4}\) . The best characterised operon is the cytokine- encoding mRNAs and their repression by ZFP36 is essential for limiting inflammation. How the other Zfp36-family members function and in which cell types they control inflammation and immunity is not well understood.
+
+T lymphocytes transiently express ZFP36 and ZFP36L1 when activated \(^{5,6}\) and studies using mouse models suggest they each make essential contributions to restraining effector CD4 and CD8 T cell functions \(^{5 - 11}\) . A third family member Zfp36l2 is expressed by resting T cells and represses cytokine production by memory T cells \(^{12}\) and by activated naive T cells 48 hours after activation \(^{13}\) . Mice in which all three family members are deleted by Cd4- cre at the CD4+CD8+ thymocyte stage develop a hyper- cytokinemia and a lethal inflammatory syndrome \(^{9}\) . By contrast, mice with Cd4- cre- mediated deletion of Zfp36 and Zfp36l1 appear healthy \(^{6,9}\) , and show increased resilience following influenza virus infection \(^{6}\) . Mice with deletion of Zfp36l1 and Zfp36l2 in T cells also appear healthy and show reduced pathology and effector T cell responses following induction of experimental autoimmune encephalomyelitis \(^{9}\) .
+
+As Cd4- cre deletes in all TCRαβ+ T cells it remains unclear to what extent these complex phenotypes reflect cell- intrinsic roles of the RBP in effector cells or Tregs. Mice which overexpress ZFP36 in all cells have a small increase in the frequency of Tregs, these were better able to suppress the in vitro proliferation of naïve T cells \(^{14}\) . Another study indicated the potential for ZFP36L2 to be a negative regulator of Ikrf2 mRNA and to inhibit the suppressive function of induced Tregs \(^{15}\) and others have shown that the immunosuppressive cytokine IL- 10 \(^{16,17}\) and inhibitory surface receptor CD274/PD- L1 \(^{18}\) are directly repressed by ZFP36- family proteins. Whether the ZFP36- family act in Tregs to limit or enhance their function is unknown.
+
+<--- Page Split --->
+
+Tregs require the transcription factor FOXP3 for their differentiation and function and have a dominant role in immune tolerance, with roles in tissue homeostasis and resilience to infection \(^{19 - 21}\) . They deploy a repertoire of effector functions including the production of soluble factors, contact mediated depletion of costimulatory molecules and competition with effector T cells for trophic factors and metabolites. Tregs are particularly sensitive to deprivation of IL- 2 which acts via the induction of STAT5 phosphorylation to promote their survival. Tregs also demonstrate remarkable functional adaptation to local inflammatory environments which can expose them to cytokines, such as IFNγ that can modulate function in a context- dependent manner \(^{22 - 24}\) . The extent to which any of these processes are regulated by the ZFP36 family is unknown.
+
+In this study, we employed a conditional deletion strategy in mice to investigate the function of Zfp36 family members in Tregs. The loss of Zfp36l1 alone in Tregs resulted in dysregulation of immune homeostasis, a phenotype that was more severe when combined with deficiency of Zfp36l2. We establish that in Treg Zfp36l1 and Zfp36l2 play a key role in promoting CTLA- 4 function to limit the expansion of type 2- conventional dendritic cells (cDC2), in restraining the size of germinal centers (GC), and determining Treg sensitivity to IFNγ, IL- 2 and IL- 7.
+
+## 85 Results
+
+## Zfp36l1 and Zfp36l2 are essential in Treg to maintain immune homeostasis
+
+To establish if ZFP36- family proteins are expressed in Tregs we have used mice in which the endogenous allele of each family member has been modified to introduce a fluorescent protein at the site of translation initiation to encode a fusion protein. By identifying Tregs with surface staining for CD25+ and FR4+ (Supplementary Fig. S1a) we found mAmetrine- ZFP36 was not detectably expressed by T cells ex vivo. Naive CD44loCD62Lhi Treg (nTreg) expressed more mCherry- ZFP36L1 and eGFP- ZFP36L2 compared to CD4+ CD44loCD62Lhi CD25- T cells (nTconv) (Fig. 1a). Furthermore, mCherry- ZFP36L1 was expressed at four- fold greater amounts in CD44hiCD62Llo effector Treg (eTreg) compared to nTreg, while eGFP- ZFP36L2 was not increased (Fig. 1a). The greater expression of mCherry- ZFP36L1 in eTreg and nTreg is consistent with these cells having been recently activated and with ZFP36L1
+
+<--- Page Split --->
+
+expression increasing in proportion to TCR signal strength \(^{25}\) which is known to be greater in naive Tregs than naive Tconv \(^{26}\) .
+
+To establish the requirement for individual ZFP36 family members in Tregs we deleted \(Zfp36\) , \(Zfp36I1\) or \(Zfp36I2\) using the \(Foxp3^{YFP\text{- } \text{icre}}\) (FYC) allele which contains the YFP- iCre recombinase fusion protein open reading frame in the 3'UTR of the \(Foxp3\) gene \(^{27}\) . Male \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36^{II/II}\) (FYC \(Zfp36\) ) and \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36I2^{II/II}\) (FYC \(I2\) ) mice were healthy up to twenty weeks of age. By contrast, \(9\%\) of \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36I1^{II/II}\) male mice (FYC \(I1\) ) had developed clinical signs of marked piloerection, hunched posture with a median age of onset of ten weeks. ZFP36L1 expression in T cells is strongly stimulated by PMA plus ionomycin and we used this to establish whether the protein could be detected in T cells from FYC \(I1\) mice. ZFP36L1 expression was reduced by ten- fold in FOXP3 \(^+\) Treg from FYC \(I1\) mice compared to FYC mice but was not differentially expressed in FOXP3 \(^+\) CD4 \(^+\) Tconv (Supplementary Fig. 1b) demonstrating efficient and selective deletion of ZFP36L1 in Treg. Because naive Tregs express both ZFP36L1 and ZFP36L2 and \(Zfp36I1\) is redundant with \(Zfp36I2\) in diverse cell systems \(^{28 - 30}\) we anticipated that the deletion of both genes in Treg would lead to a stronger phenotype than deletion of either gene alone. We thus generated \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36I1^{II/II}\) \(Zfp36I2^{II/II}\) (referred to as FYC \(I1/2\) ) mice. Deletion of ZFP36L1 in FYC \(I1/2\) mice was confirmed by flow cytometry to be specific to Treg (Supplementary Fig. 1b). \(12\%\) of FYC \(I1/2\) mice developed clinical symptoms which exceeded the predefined humane endpoint, including marked piloerection, hunched posture, and abdominal distension, with a median age of onset of five weeks. These mice had markedly increased lymph node (LN) cellularity which exceeded that seen in the FYC \(I1\) males (Supplementary Fig. S1c). The proportion and number of YFP \(^+\) CD44 \(^+\) iCD62L \(^0\) effector CD4 and CD8 cells within LN (gated as shown in Supplementary Fig. 1d) was increased two- to three- fold in FYC \(I1\) mice, and three- to five- fold in FYC \(I1/2\) mice compared to FYC controls (Fig. 1b). By contrast, in the YFP \(^+\) CD4 \(^+\) subset from mice lacking \(Zfp36\) there was no difference in the proportion and only a minor increase in the number of effector cells compared to control mice (1.6- fold) and no change in the CD8 \(^+\) subset (Supplementary Fig. 1e). CD4 and CD8 effector subsets were not different between FYC \(I2\) and FYC mice (Supplementary Fig. 1f).
+
+<--- Page Split --->
+
+Tregs from FYC 11 and FYC 11/2 mice were biased towards an activated phenotype with a three- fold increase in the number of eTreg in FYC 11/2 mice compared to FYC control mice (Fig. 1c). In addition, the number of nTreg was increased 1.5- fold (Fig. 1d), thus the phenotype of FYC 11 and FYC 11/2 mice was not due to a deficit in Treg numbers. Furthermore, the combined loss of both Zfp36/1 and Zfp36/2 led to a greater expansion of CD4 and CD8 effector cells than loss of Zfp36/1 alone. Histological analysis of tissues from FYC 11/2 mice with clinical symptoms revealed perivascular lymphocytic infiltration into lung and liver and diffuse crypt hyperplasia in the small intestine (Fig. 1e). In the large intestine of FYC 11/2 mice there was evidence of crypt hyperplasia accompanied by an increase in inflammatory cells in the lamina propria (Fig. 1e). Thus, the loss of Zfp36/1 and Zfp36/2 in Tregs leads to a failure of immune homeostasis.
+
+## Compromised fitness of RBP-deficient Treg
+
+In females, Foxp3 is inactivated on one X chromosome, thus when heterozygous for the Foxp3YFP- icre allele, FYC/+ mice accumulate icre- positive and - negative Treg which can be distinguished by the expression of YFP. FYC/+ 11/2 mice did not develop any clinical symptoms over a period of at least 40 weeks. Also, we found no difference in numbers of FOXP3- CD44hiCD62L0 CD4 and CD8 cells (Supplementary Fig. 2a). Thus, Zfp36/1/Zfp36/2- deficient Tregs are insufficient to cause disease when wild type Tregs are present. In female FYC/+ mice the number of FOXP3+YFP- Tregs was twice that of FOXP3+YFP+ Tregs in the same mouse suggesting the Foxp3YFP- icre allele incurs a minor competitive disadvantage on Tregs. However, in FYC/+ 11/2 mice the icre- positive Treg were seven times less abundant than icre- negative Tregs in the same mouse (Fig. 2a). Normal Treg numbers were detected in the thymus (Supplementary Fig. S2b), thus the competitive disadvantage of Zfp36/1/Zfp36/2- deficient Tregs is revealed in peripheral lymphoid tissue.
+
+To gain insight into the role of Zfp36/1 and Zfp36/2 in Treg function in the absence of pathology we sorted YFP+ CD62LhiCD4+CD25+ cells from female FYC/+ and FYC/+ 11/2 mice (Supplementary Fig. 2c) and performed RNA- seq. Quantitation of reads mapping to the targeted region of Zfp36/1 and Zfp36/2 confirmed efficient icre- mediated recombination of both conditional alleles (Supplementary Fig. 2d).
+
+<--- Page Split --->
+
+Furthermore, by intracellular staining for ZFP36L1 in stimulated T cells we observed a seven- fold reduction in the ZFP36L1 protein only in icre- positive YFP+FOXP3+ Treg but not in icre- negative YFP+FOXP3+ Treg, or in Tconv (Supplementary Fig. 2e). Differential expression analysis using DESeq2 revealed 249 genes were increased (Supplementary Table 1) and 340 genes decreased (Supplementary Table 2) in the knockout Treg compared to control cells (FDR- adjusted p value <0.05) (Fig. 2b). The mRNAs encoding Foxp3, Ctl4, Ixkf2 (Helios), Icos, Tgfb1 and Lrrc32, key genes involved in Treg function, were not differently expressed (Fig. 2b). To identify transcripts that could be bound and thus directly regulated by ZFP36- family members we used published crosslinking and immunoprecipitation (CLIP) data (Supplementary Table 3) and found that target transcripts were increased in \(FYC^{+}\) \(I112\) Treg compared to \(FYC^{+}\) Treg (Fig. 2c). This is consistent with the direct targets of these RBP being more stable and thus accumulating to increased amounts in \(Foxp3^{YFP - icre}I112\) Treg.
+
+Gene Set Enrichment Analysis (GSEA) using a custom group of gene sets covering different aspects of T cell biology (Supplementary Table 4), revealed "Endocytosis", "T cell receptor signaling" and several genes sets associated with cytokine signaling amongst the top ten positively enriched pathways, including "Decreased in IL- 2", "Decreased in IL- 7", "JAK STAT signaling pathway", "IL- 2 Receptor signalling", and "Increased in IFNγ" in Foxp3YFP- icre \(I112\) deficient Tregs (Fig. 2d). Many of the genes contributing most to the enrichment (present in the leading edge) were transcripts shown to interact directly with ZFP36- family members by CLIP (represented in orange and listed in Supplementary Table 4). Genes enriched in the endocytosis pathway included 25 in the leading edge that were iCLIP targets, encompassing genes involved in the regulation of protein sorting and membrane trafficking (Supplementary Table 5 and Fig. 2e). Within the TCR signaling pathway 40 out of 73 genes in the leading edge were iCLIP targets (Supplementary Table 5 and Fig. 2e), including genes that can promote (Lat, Cd2) or attenuate (Rptor, Dgka, Dok2) activation via the TCR (Supplementary Fig. 3a). We thus evaluated the protein expression of CD5, which is not a target of the ZFP36 family but an indicator of TCR signaling strength \(^{31,32}\), and the CLIP target NUR77 (encoded by Nr4a1), which is expressed early after TCR stimulation. Expression of these proteins did not differ
+
+<--- Page Split --->
+
+between YFP+ Treg from \(FYC^{+}\) 1112 and \(FYC^{+}\) mice (Supplementary Fig. 3b). Thus, we concluded that in a non- inflammatory environment, TCR signaling was not detectably altered in \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 deficient Tregs.
+
+Using the Immunological Genome Project signatures of "common \(\gamma\) - chain" family cytokines33 we found that for genes responding to IL- 2 or IL- 7 signaling in Treg, those that were increased in response to these cytokines were decreased in the transcriptome of \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 deficient Tregs compared to \(Foxp3^{YFP\text{- } i\text{cre}}\) Tregs from control \(FYC^{+}\) mice (Fig. 2f). By contrast, genes that were decreased in response to IL- 2 or IL- 7 signaling were increased in \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 deficient Tregs (Fig. 2f). Inspection of the genes increased in response to \(\mathrm{IFN}\gamma\) in Treg revealed that genes decreased in response to \(\mathrm{IFN}\gamma\) were not significantly changed, while genes increased in response to \(\mathrm{IFN}\gamma\) were just above the 0.05 threshold for significance as increased in the transcriptome of nTreg from \(FYC^{+}\) 1112 mice compared to that from control \(FYC^{+}\) mice (Fig. 2g). The GSEA also identified the "Treg gene signature" and "Notch signaling pathway" to be just beyond the cut- off for statistical significance. As noted above, \(Foxp3\) , Cta4, Ikzf2 and Icos, were not differently expressed; and at the protein level we detected only minor reductions for FOXP3 (1.1- fold), CTLA- 4 (1.2- fold) IKZF2 (1.4- fold) and ICOS (1.2- fold) between \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 and \(Foxp3^{YFP\text{- } i\text{cre}}\) nTregs (Supplementary Fig. 4a). FOXP3, CTLA- 4 and IKZF2 also were slightly reduced in eTregs (1.1;1.3;1.3- fold respectively), but ICOS showed an increase of 1.3- fold between \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 eTreg and \(Foxp3^{YFP\text{- } i\text{cre}}\) eTreg (Supplementary Fig. 4a). The expression of NOTCH1, a known target of ZFP36L1 and ZFP36L228,34, that when overexpressed can impair Treg function35, was not different in \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 Treg compared to \(Foxp3^{YFP\text{- } i\text{cre}}\) Treg (Supplementary Fig. 4b). We conclude that the 589 DE genes in the transcriptome of naïve \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 Treg impact on multiple processes which together could contribute to the lack of fitness and function of 1112- deficient Tregs.
+
+## Decreased cycling of CTLA-4 in RBP-deficient nTreg
+
+As conventional dendritic cells (cDC) are important in maintaining T cell tolerance36 and cDC phenotype can be regulated by Treg37, we examined the number of cDC in LN. We had observed that LN cellularity was increased four- fold in \(FYC\) 1112 mice,
+
+<--- Page Split --->
+
+however, using a gating strategy (modified from \(^{38}\) ) relative to the cDC subsets in FYC mice, the number of "resident" CD172a \(^+\) XCR1 \(^+\) cDC2 was selectively increased (ten- fold) compared to the "migratory" CD172a \(^+\) XCR1 \(^+\) cDC2 and "resident" and "migratory" cDC1 (CD172a \(^+\) XCR1 \(^+\) ) populations (Fig. 3a,b). CTLA- 4 can bind to the costimulatory molecules CD80 and CD86 and can capture these molecules by transendocytosis from neighbouring antigen presenting cells (APC) to restrict costimulation via CD28 \(^{37}\) . The selective increase in cDC2 numbers therefore prompted us to examine the expression of CD80 and CD86 on cDC in the LN from male mice. We identified elevated CD80 and CD86 expression only in the "resident" CD172a \(^+\) XCR1 \(^+\) cDC2 but not in the "migratory" CD172a \(^+\) XCR1 \(^+\) cDC2 population in FYC 1112 mice (Fig. 3c) nor in the cDC1 population (Supplementary Fig. 5a). CTLA- 4 is predominantly localised within intracellular vesicles, which cycle between the cell surface and intracellular stores, and can be rapidly removed from the surface via clathrin- mediated endocytosis \(^{39}\) . As GSEA had identified enrichment in the endocytosis pathway, we examined the cycling pool of CTLA- 4, which can bind ligand at the plasma membrane, by incubating unstimulated cells with labelled anti- CTLA- 4 antibody at 37°C for 2 hours and comparing this to the total intracellular pool. Constitutive uptake of labelled antibody in vitro visualised in the absence of stimulation, revealed a decrease in the pool of cycling CTLA- 4 in YFP \(^+\) nTreg from male FYC 1112 mice compared to nTreg from control FYC mice, although no difference was observed in eTreg or in the total intracellular pool (Fig. 3d). Consistent with the data from the male mice, in the absence of stimulation, the pool of cycling CTLA- 4 in RBP- deficient YFP \(^+\) nTreg from female FYC \(^+\) 1112 mice was also decreased compared to YFP \(^+\) nTreg from FYC \(^+\) mice (Fig. 3e) and YFP \(^+\) nTreg in the same mice (Supplementary Fig. 5b), but not within the YFP \(^+\) eTreg subset. Thus, these data suggest a cell intrinsic role for ZFP36L1 and ZFP36L2 in promoting CTLA- 4 cycling in nTreg.
+
+## ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-2 and IL-7
+
+IL- 2R signaling can enhance CTLA- 4 function in Treg \(^{40}\) . Moreover, based on the results of the GSEA and the finding that CD8 T cells lacking Zfp36 and Zfp36/1 were less sensitive to IL- 2 \(^{41}\) we hypothesized that ZFP36L1 and ZFP36L2 promote Treg responsiveness to IL- 2 and/or IL- 7. As both IL- 2 and IL- 7 induce tyrosine phosphorylation of STAT- 5A/B, we examined this in Treg ex vivo after rapid fixation
+
+<--- Page Split --->
+
+of cells following tissue retrieval. In \(FYC^{+} / 112\) mice we observed a two- fold reduction in the frequency of pSTAT5+ cells in FOXP3+YFP+ nTreg compared to \(FYC^{+}\) controls, but no difference between the eTreg subsets (Fig. 4a). In male \(FYC / 112\) mice, we observed a two- fold reduction in the frequency of pSTAT5+ cells in both nTreg and eTreg (Fig. 4b), suggesting optimal STAT5 phosphorylation in Treg in vivo requires ZFP36L1 and ZFP36L2. As STAT5 can be phosphorylated in response to both IL- 2 and IL- 7, we measured expression of their receptors CD25 and CD127, and the in vitro response of Treg to a range of doses of IL- 2 and IL- 7. Surface expression of CD25 on YFP+ nTreg from the spleen of female \(FYC^{+} / 112\) mice was reduced two- fold compared to YFP+ nTreg from \(FYC^{+}\) mice (Fig. 4c). Amongst eTreg the majority expressed low levels of CD25 but still we found a reduction (1.5- fold) between CD25 surface expression on YFP+ eTregs comparing \(FYC^{+} / 112\) and \(FYC^{+}\) mice. Accordingly, YFP+ nTreg from \(FYC^{+} / 112\) mice showed diminished responses when cultured with IL- 2 at 0.3 and 1 ng/ml but no difference was found in eTreg (Fig. 4d). Quantitation of the total amount of STAT5 in YFP+ FOXP3+ cells in female \(FYC / + / 112\) and \(FYC / +\) mice confirmed this was not different (Supplementary Fig. 6a). Moreover, icre- negative Treg from female \(FYC^{+} / 112\) and \(FYC^{+}\) mice responded in a similar manner to IL- 2 (Supplementary Fig. 6b), indicating a cell- intrinsic defect of RBP- deficient Treg in their response to IL- 2. CD25 expression was also reduced on nTreg from male \(FYC / 112\) mice compared to control \(FYC\) mice (Fig. 4e), and the response to IL- 2 was diminished only in the nTreg population (Fig. 4f). These data indicate that ZFP36L1 and ZFP36L2 in Treg promote an optimal response to IL- 2.
+
+CD127 was expressed at modestly greater amounts on the surface of eTreg compared to nTreg. On YFP+ nTreg and eTreg from both female \(FYC^{+} / 112\) (Fig. 5a) and male \(FYC / 112\) mice (Fig. 5b) CD127 was decreased compared to Tregs from control mice. Furthermore, both naive and effector YFP+ Treg from \(FYC^{+} / 112\) mice showed a striking reduction in their pSTAT5 response to IL- 7 compared to YFP+ Treg from \(FYC^{+}\) mice (Fig. 5c). This was also the case for nTreg and eTreg from male \(FYC / 112\) mice (Fig. 5d). In \(FYC^{+}\) and \(FYC^{+} / 112\) females, icre- negative Treg were more sensitive to IL- 7 than icre- positive Treg from the same mouse. Therefore, expression of the \(FYC\) allele correlates with a minor reduction in pSTAT5 in response to IL- 7 (1.2- fold Supplementary Fig. 6c). However, the difference between icre- positive and icre- negative Treg in the same animal was greater in \(FYC^{+} / 112\) mice
+
+<--- Page Split --->
+
+compared to control \(FYC^{+}\) mice (Supplementary Fig. 6c), supporting a cell- intrinsic role for ZFP36L1 and ZFP36L2 in the Treg response to IL- 7. Taken together, these results revealed that ZFP36L1 and ZFP36L2 are essential in Treg to maintain optimal sensitivity to IL- 2 and IL- 7.
+
+## ZFP36L1 and ZFP36L2 limit Treg sensitivity to \(\mathsf{IFN}\gamma\)
+
+As the bulk RNAseq data from heterozygous female mice suggested a possible enhancement of the \(\mathsf{IFN}\gamma\) signaling pathway we evaluated the response to \(\mathsf{IFN}\gamma\) . We used intracellular flow cytometry to detect phosphorylation of STAT1 on Tyrosine- Y701 following stimulation with a range of doses of recombinant murine \(\mathsf{IFN}\gamma\) . We observed an enhanced response to \(\mathsf{IFN}\gamma\) in \(\mathsf{YFP}^{+}\) nTreg from \(FYC^{+} / 112\) mice compared to \(\mathsf{YFP}^{+}\) nTreg from control \(FYC^{+} / \mathsf{mice}\) (Fig. 6a). \(\mathsf{YFP}^{+}\) eTreg showed a much lower response than naive \(\mathsf{YFP}^{+}\) Treg, which was comparable between genotypes except at the highest concentration. Significantly, \(\mathsf{YFP}^{+}\) nTreg from \(FYC^{+} / 112\) mice showed an enhanced response compared to \(\mathsf{YFP}^{- }\) nTreg from the same mouse indicating the effect was cell intrinsic (Supplementary Fig. 7a). Quantitation of the total amount of STAT1 in \(\mathsf{YFP}^{+}\) FOXP3+ cells in female \(FYC^{+} / 112\) and \(FYC^{+}\) mice confirmed this was not different (Fig. 6b and Supplementary Fig. 7b). In addition, we examined the response to IL- 6, which also promotes STAT1 Y701 phosphorylation, and found no increase in STAT1 phosphorylation between \(\mathsf{YFP}^{+}\) Treg from control \(FYC^{+}\) and \(FYC^{+} / 112\) mice following in vitro stimulation with a range of doses (Fig. 6c and Supplementary Fig. 7c). Thus, the limiting effects of ZFP36L1 and ZFP36L2 on STAT1 phosphorylation were specific to the \(\mathsf{IFN}\gamma\) pathway and indicate these RBP restrain \(\mathsf{IFN}\gamma\) signaling in Treg in a cell intrinsic manner.
+
+## Activated phenotype of Treg from \(FYC / 112\) mice
+
+To explore the heterogeneity of Treg and gain further insight into how ZFP36L1 and ZFP36L2 regulate Treg function in an inflammatory environment we performed single- cell sequencing of RNA (scRNA- seq) on Treg sorted from the peripheral LN of male \(FYC\) and \(FYC / 112\) mice (Supplementary Fig. 8a). We analyzed high quality transcriptomes of 5824 cells from \(FYC\) mice and 4163 cells from \(FYC / 112\) mice. Using a graph- based clustering approach Treg were grouped into eight
+
+<--- Page Split --->
+
+subpopulations and represented using a uniform manifold approximation and projection (UMAP) for dimensionality reduction (Fig. 7a). Using gene sets derived from a comparison of naïve and effector Treg transcriptomes (Supplementary Table 6) we applied the Semi- supervised Category Identification and Assignment (SCINA) algorithm \(^{42}\) to assign cell type identities. We found that cells in clusters 0, 2 and 5 were frequently classified as nTreg, whereas clusters 3, 4 and 7 were primarily comprised of eTreg (Fig. 7a,b and Supplementary Fig. 8b). Differential gene expression analysis identified markers for each cluster except for cluster 1, which did not show enrichment for any distinctive genes (Supplementary Table 7). The four most frequently detected genes in each cluster in comparison to every other cluster are shown (Fig. 7c), further illustrating that clusters 0, 2 and 5 exhibited genes typical of nTreg (e.g., Sell, S1pr1). Genes characteristic of eTreg (e.g. Icos, Maf) were not detected or lowly expressed in clusters 0, 2 and 5, but frequently detected in clusters 3, 4 and 7. Cells in cluster 7 expressed markers characteristic of effector and highly proliferative cells, including Mki67 and histone genes, in addition to a higher number of genes, (Supplementary Fig. 8c) suggestive of a highly proliferative population. Thus, the individual clusters could broadly be distinguished by characteristic marker expression with a distinct distribution corresponding to naïve and effector Treg subtypes.
+
+The distribution of clusters of Treg from FYC and FYC I/12 mice was not equivalent. Treg from FYC I/12 mice represented only \(20\%\) of cells in cluster 0 and \(15\%\) in cluster 2, whereas \(80\%\) of Tregs in cluster 4 were represented by FYC I/12 Treg (Fig. 7d). As we had found that ZFP36L1 and ZFP36L2 limit Treg sensitivity to IFNγ, we investigated genes characteristic of the IFNγ response (defined in Supplementary Table 8). We used the SCINA algorithm to assign cell type identities in the scRNA- seq data and found a higher proportion of Treg from FYC I/12 mice across most clusters associated with an IFNγ gene signature (Fig. 7e). Activity of the IFNγ signaling pathway is necessary for the differentiation of CXCR3⁺ Tregs, thus we examined expression of Cxcr3 and other effector molecules and found enrichment of Cxcr3 in clusters 3 and 4 (Fig. 7f). In addition, Gata3 and Pdcd1 (encoding PD- 1), which is expressed by Treg during activation, were also most frequently detected in cluster 4 (Fig. 7h), which is over- represented in FYC I/12 Treg. Consistent with these
+
+<--- Page Split --->
+
+observations, flow cytometry revealed an increase in the proportion (Fig. 7i) and number of CXCR3+ Treg (Supplementary Fig. 8d) compared to control mice. GATA3hi Treg and YFP+CXCR5+PD- 1+ T follicular regulatory (Tfr) cells were also increased in proportions (Fig. 7j, k) and numbers (Supplementary Fig. 8d), in FYC 1/12 mice compared to control mice. Although we found a three- fold reduction in the proportion of RORyt+ Treg in FYC 1/12 mice compared to controls there was no difference in cell number (Supplementary Fig. 8e) indicating these cells are unable to control the influx of inflammatory cells in the intestine.
+
+Consistent with the increased proportion of CXCR3+ and GATA3+ Treg and the decreased proportion of RORyt+ Treg in FYC 1/12 mice, stimulation of splenocytes from male FYC 1/12 mice revealed increased frequencies of Tregs producing IFNy, IL- 4 and IL- 10 and a reduced proportion producing IL- 17 (Fig. 7l). Analysis of the gMFI of these cytokines revealed that Treg from FYC 1/12 mice produce marginally more IFNy (1.3- fold) and less IL- 17 (1.7- fold) compared to Treg from FYC mice, whilst no difference was found in the production of IL- 4 or IL- 10 (Supplementary Fig. 8f). FOXP3- CD4+ T cells were also enriched for IFNy, IL- 4 and IL- 10- positive cells (Fig. 7l) and produced more IL- 10 (Supplementary Fig. 8f). Therefore, the inflammatory environment in FYC 1/12 mice was not a result of a deficiency of IL- 10. Moreover, we found three times more CD8+ T cells producing IFNy in FYC 1/12 mice with the production of IFNy by these cells also increased (1.6- fold) (Supplementary Fig. 8g). Thus, the expanded CXCR3+ and GATA3+ Treg subsets in FYC 1/12 mice are unable to limit the expansion of activated CD4 and CD8 T cells which produce cytokines that may contribute to the loss of immune homeostasis in FYC 1/12 mice.
+
+## IFNy is a driving force for the expansion of effector T cells
+
+The enhanced sensitivity of 1/12- deficient Treg to IFNy together with the increased number of Treg showing an IFNy signature in the scRNAseq and the increased proportion of Treg cells producing IFNy, suggested that ZFP36L1 and ZFP36L2 act in Treg to regulate the IFNy signaling axis. The production of IFNy by Treg and their responsiveness to it are essential for immune homeostasis, and in vivo IFNy can mediate both pro- and anti- inflammatory processes. Thus, we sought to test the
+
+<--- Page Split --->
+
+physiological role of IFN \(\gamma\) , while avoiding complications arising from a complete absence of IFN \(\gamma\) , by generating FYC 1112 mice heterozygous for Ifng. The majority of Ifng \(^{+/ - }\) FYC 1112 mice were healthy, with only one mouse from 23 that developed skin inflammation, compared to ten out of 45 FYC 1112 mice developing clinical symptoms which exceeded the severity limit (marked piloerection and intermittent hunched posture, Fig. 8a). FYC 1112 mice had elevated levels of IFN \(\gamma\) , TNF \(\alpha\) , IL- 2, IL- 6 and IL- 10 in the serum compared to FYC control mice, however, the amounts of these cytokines were reduced in Ifng \(^{+/ - }\) FYC 1112 compared to FYC 1112 mice, with none maintaining a significant increase relative to FYC controls (Fig. 8b). The increased number of effector cells in the Treg, CD44 \(^{hi}\) CD62L \(^{lo}\) CD4 \(^{+}\) YFP \(^+\) , CD44 \(^{hi}\) CD62L \(^{hi}\) and CD44 \(^{hi}\) CD62L \(^{lo}\) CD8 \(^{+}\) subsets in FYC 1112 mice was also diminished by loss of one Ifng allele but remained two- to three- fold higher than in FYC control mice in each subset (Fig. 8c). The number of Tfh, Tfr and GC B cells in FYC 1112 mice was significantly increased in comparison to the FYC controls, but these numbers were reduced in Ifng \(^{+/ - }\) FYC 1112 mice, although remained four- fold higher in both Tfh and Tfr subsets (Fig. 8d,e), whilst the population of GC B cells remained ten- fold higher (Fig. 8f). Serum IgG2c and IgE levels were elevated in FYC 1112 mice compared to FYC controls. In Ifng \(^{+/ - }\) FYC 1112 mice the amount of IgG2c was reduced to that found in control mice (Fig. 8g). However, the concentrations of IgE were still higher (60- fold) in Ifng \(^{+/ - }\) FYC 1112 mice relative to FYC control mice, which correlated with the persistence of an elevated number of GC B cells (Fig. 8g). Thus, these data indicate that IFN \(\gamma\) is a driving force underpinning a complex phenotype in FYC 1112 mice.
+
+## Discussion
+
+All three ZFP36 family paralogues can be expressed by T cells, and, in the absence of infection or inflammation, ZFP36L1 is the most abundant in Tregs and exerts non- redundant essential functions that are compensated partially by ZFP36L2. The ZFP36 family is a well- established regulator of cytokines, but in Tregs these RBP additionally regulate large numbers of genes that control pathways required by the Treg to maintain immune homeostasis.
+
+Tregs lacking Zfp36l1 and Zfp36l2 failed to prevent the expansion of cDC2, GC B cells and effector CD8 T cells. As interactions between cDC2 and Tfh support Tfh
+
+<--- Page Split --->
+
+priming and GC B responses \(^{43,44}\) , and cDC2 can cross- prime CD8 T cells \(^{45}\) the increased numbers and elevated expression of CD80 and CD86 on cDC2 could be driving the expansion of activated lymphocytes in \(FYC 1 / 12\) mice. The compromised ability of nTreg to limit costimulation may arise, in part, from defective CTLA- 4 cycling. IL- 2 signaling also positively impacts upon Treg CTLA- 4 function \(^{40}\) and was impaired in \(Zfp36 / 1\) and \(Zfp36 / 2\) - deficient Tregs. Furthermore, IL- 2 sensitivity is diminished in CD8 T cells lacking \(Zfp36 / 1\) suggesting ZFP36L1 connects antigen affinity to IL- 2 responsiveness \(^{25}\) .
+
+Although IL- 2 signaling is essential for Treg survival and function \(^{46,47}\) , when deprived of this cytokine IL- 7 can sustain Tregs and contribute to Treg homeostasis \(^{47,48}\) . Mice with conditional deletion of \(I / 7a\) in Tregs did not develop autoimmune disease, but IL- 7R on Tregs was important to maintain allograft tolerance in a Treg transfer model \(^{49}\) and IL- 7 promotes eTreg survival in the skin \(^{50}\) . In Treg we found that ZFP36L1 and ZFP36L2 promote sensitivity to both IL- 2 and IL- 7. This may account for the reduction in number of \(icre\) - expressing Treg in female mice heterozygous for \(icre\) , where these cells are in competition for these cytokines. As the development of Tfr has been reported to be inhibited by IL- 2 \(^{51,52}\) , a defect in IL- 2 signaling would be accompanied by expansion of Tfr as we observe in \(FYC 1 / 12\) mice. The accumulation of Tfh and GC B cells may also be augmented by the increased availability of IFN \(\gamma\) \(^{53}\) .
+
+\(Zfp36 / 1\) and \(Zfp36 / 2\) also specifically limit Treg sensitivity to IFN \(\gamma\) . Whilst Th1- like Tregs can be potent suppressors of the activity, proliferation and memory formation of CD8 effector T cells \(^{24}\) and IFN \(\gamma\) - mediated STAT1 activation in Tregs can promote Treg function in alloantigen tolerized mice \(^{22}\) , IFN \(\gamma\) can also promote Treg “fragility” or lineage instability in the tumor microenvironment \(^{23}\) .
+
+The ability of ZFP36- family members to repress IFN \(\gamma\) expression did not manifest as increased amounts of IFN \(\gamma\) produced by ex vivo stimulated Tregs but was apparent as a greater frequency of IFN \(\gamma\) producing Tregs. The capacity for ZFP36L1 and ZFP36L2 in Tregs to interconnect the IL- 2, IFN \(\gamma\) and CTLA- 4 pathways and enforce their function, whilst dampening their function in effector CD4 and CD8 T cells may
+
+<--- Page Split --->
+
+be relevant to the association of the genes encoding this family of RBP with autoimmune diseases 2.
+
+## Limitations of the study
+
+These phenotypes were not evident in mice with deletion of ZFP36 family proteins using Cd4- cre which, taken together with the specific deletion, argues that the phenotypes arise from the function of ZFP36L1 and ZFP36L2 in Treg. We have focussed on Treg in the absence of intentional immune challenge, and it is unclear how Treg deficient in these RBP respond to activation and how this affects transcriptomes, cell function and the physiology of the mice. The compendium of iCLIP targets is from CD4 and CD8 T cells, it is possible some mRNAs unique to Treg were not detected. In addition to regulating RNA stability ZFP36L1 and ZFP36L2 can also repress translation 12,54 and may regulate protein localization, thus the use of sensitive proteomics methods could reveal additional direct and indirect targets regulated by the RBP. The detailed mechanism of how the RBP regulate CTLA- 4 and cytokine signalling in Treg remain to be elucidated.
+
+## Methods
+
+## Mice
+
+Mice were engineered to express the fluorescent proteins mAmetrine or mCherry upstream and in frame with the start codons of Zfp36 or Zfp36l1 respectively 25. The targeting vector for Zfp36l2 was designed to encode eGFP upstream and in frame with the ATG translation start site of ZFP36L2 (Cyagen, Santa Clara, CA, USA). The reporter mice were healthy and fertile (and used for breeding up to 40 weeks of age). Zfp36l/l (Zfp36tm1Tnr), Zfp36l1/l (Zfp36l1tm1.1Tnr) and Zfp36l2/l/l (Zfp36l2tm1.1Tnr) mice have been described previously 28,55 and were maintained on a C57BL/6J background. The following alleles on the C57BL/6J background (obtained from the Jackson Laboratory) were also used: B6.129(Cg)- Foxp3tm4(YFP/ice)Ayr/J; Jax stock #016959); and B6.129S7- IFNgtm1Ts (Jax stock #002287). For the experiments shown in Fig. 8, the cohort of FYC 1112 and Ifng+/- FYC1112 mice that were analyzed had not been backcrossed to C57BL/6 for seven generations. Any animals which displayed
+
+<--- Page Split --->
+
+the limiting clinical signs of marked piloerection and intermittent hunched posture, and/or abdominal distension were humanely killed.
+
+Mice were bred and maintained in the Babraham Institute Biological Support Unit. No primary pathogens or additional agents listed in the FELASA recommendations have been confirmed during health monitoring surveys of the stock holding rooms. Ambient temperature was \(\sim 19 - 21^{\circ}C\) and relative humidity \(52\%\) . Lighting was provided on a 12- hour light: 12- hour dark cycle including 15 min 'dawn' and 'dusk' periods of subdued lighting. After weaning, mice were transferred to individually ventilated cages with 1- 5 mice per cage. Mice were fed CRM (P) VP diet (Special Diet Services) ad libitum and received seeds (e.g., sunflower, millet) at the time of cage cleaning as part of their environmental enrichment. All mouse experimentation was approved by the Babraham Institute Animal Welfare and Ethical Review Body. Animal husbandry and experimentation complied with European Union and United Kingdom Home Office legislation.
+
+## Flow cytometry
+
+Single cell suspensions were prepared from the spleen, peripheral lymph nodes (LN, axillary, brachial, cervical and inguinal) and mesenteric LN (mLN), with antibody staining for surface markers performed essentially as described previously including Fc block (2.4G2) in PBS/2% FCS/2mM EDTA. Dead cells were excluded using fixable viability dye eFluor780 (eBioscience). A full list of antibodies used is provided in Supplementary Table S9. An antibody against GFP (clone FM264G, BioLegend) was used for intracellular detection of YFP which is fused to cre in Foxp3YFP- icre mice. For detection of phospho- antibodies, the cells were fixed in neutral buffered formalin (Sigma) diluted in PBS to 2% for 30 min at room temperature, pelleted by centrifugation and cells were resuspended in ice- cold 90% methanol, incubated for 30 minutes on ice, washed twice, then incubated with the antibody cocktail containing 2.4G2 antibody overnight at 4°C. For dendritic cell isolation, LN tissue was finely minced then digested with collagenase P (Merck, 1mg/ml in RPMI 2% FCS) for 40 minutes at 37°C with agitation, then EDTA added to
+
+<--- Page Split --->
+
+5mM, clumps dispersed using pipetting and the cell suspension filtered. Single cell suspensions were washed and stained as described.
+
+For ex vivo analysis of pSTAT5 LN cell suspensions were prepared directly into fixation buffer from eBioscience™ Foxp3 / Transcription Factor Staining Buffer Set. For intracellular cytokine detection, LN cells were stimulated for 4 hours at \(37^{\circ}C\) with \(10\mathrm{ng / ml}\) Phorbol- 12- myristate- 13- acetate (PMA; 524400, Merck) and \(500\mathrm{ng / ml}\) ionomycin (407952, Merck) in the presence of \(5\mu \mathrm{g / ml}\) Brefeldin A (eBioscience) in complete IMDM medium (Invitrogen; containing \(10\%\) FBS, 2mM Glutamax, 25mM HEPES, \(50\mu \mathrm{M}2\) - mercaptoethanol). Cells were fixed with \(2\%\) PFA for 30 minutes at room temperature, washed twice with Foxp3 permeabilization buffer (eBioscience) and incubated with the antibody cocktail containing 2.4G2 antibody overnight at \(4^{\circ}C\) . For transcription factor staining, Foxp3 fixation buffer was used according to the manufacturer's instructions. Acquisition was performed on a Fortessa flow cytometer equipped with 355 nm, 405 nm, 488 nm, 561 nm and 640 nm lasers (Beckton Dickinson) and the data were analyzed using FlowJo software (v10).
+
+## In vitro cytokine stimulation
+
+Splenocytes were cultured for 30 minutes at \(37^{\circ}C\) with a range of doses of recombinant murine cytokines (all from Peptidech) \(\mathrm{IFN}\gamma\) (# 315- 05) IL- 6 (# 216- 12), IL- 2 (# 212- 12) IL- 7 (# 217- 17) in the presence of eF780 viability dye and \(150\mu \mathrm{M}\) TAPI- 0 (Tocris # 5523) in complete IMDM medium.
+
+## Ex vivo CTLA-4 cycling assay
+
+Following red blood cell lysis with Tris- ammonium chloride, \(\mathrm{CD4^{+}}\) T cells were isolated from spleen by depletion of \(\mathrm{CD8^{+}}\) , \(\mathrm{CD11b^{+}}\) \(\mathrm{CD11c^{+}}\) , MHCII+ and \(\mathrm{B220^{+}}\) cells using biotinylated antibodies and M- 280 Streptavidin Dynabeads. \(\mathrm{CD4^{+}}\) T cells were cultured for 2 hours at \(37^{\circ}C\) in the presence of TAPI- 0 ( \(100\mu \mathrm{M}\) ) and \(2\mathrm{ng / ml}\) IL- 2. APC conjugated anti- CD152 (CTLA- 4) antibody (clone UC10- 4F10- 11) was added to the cells to detect cycling CTLA- 4. Surface CTLA- 4 was detected by labelling cells with APC conjugated anti- CD152 for 30 minutes at \(4^{\circ}C\) , and total CTLA- 4 detected after fixation and permeabilization with antibody incubation overnight at \(4^{\circ}C\) .
+
+<--- Page Split --->
+
+## Histology
+
+For histology, tissue samples were collected into \(10\%\) neutral buffered formalin (Sigma). Preparation of slides, H&E staining, pathology and interpretation was performed by Abbey Veterinary Services UK.
+
+## Measurement of Serum cytokines and Immunoglobulin
+
+Serum was collected from mice by cardiac puncture. Serum cytokines were measured using the MSD pro- inflammatory panel 1. IgG2c and IgE were measured by ELISA using paired antibody sets (IgG2c, Southern Biotech and IgE, BD Biosciences) according to the manufacturer's protocol.
+
+## Cell Sorting for RNA seq
+
+Single cell suspensions were prepared from pooled spleen and peripheral LN (inguinal, brachial, axillary and cervical) from six \(FYC^{+}11 / 2\) and seven \(FYC^{+} \text{mice}\) at 7- 14 weeks of age. CD4+ cells were enriched by negative depletion using biotinylated anti- B220, anti- CD8 and anti- CD11b followed by Streptavidin Dynabeads (Dynal). Naive Treg were sorted as CD4+CD25+ CD62L+ YFP+ cells. All samples were sorted to \(>95\%\) purity.
+
+For RNA- seq libraries used to identify markers of naive and effector Treg, cells were prepared as above from male \(Zfp36 / 1^{f / f} I2^{f / f}\) control mice, aged 9- 12 weeks, but with naive Treg sorted as CD4+CD25+CD62L+CD44+ and effector Treg as CD4+CD25+CD62L- CD44+ cells.
+
+To sort Tregs for single cell RNA seq single cell suspensions were prepared from pooled LN from one mouse of each genotype at 14 weeks of age. CD4+ cells were enriched by negative depletion using biotinylated anti- B220, anti- CD8 and anti- F4/80 followed by Streptavidin Dynabeads (Dynal). Treg were sorted as CD4+FR4+ YFP+ cells. All samples were sorted to \(>95\%\) purity.
+
+<--- Page Split --->
+
+## Bulk RNA-seq
+
+RNA was prepared from sorted Treg cells using the RNeasy Micro kit (Qiagen) as described \(^{56}\) and quality was assessed using the Bioanalyzer RNA chip. cDNA was generated using SMART seq v4 low input RNA kit. RNA- seq libraries were prepared from cDNA using the Nextera XT kit. Libraries were sequenced using a 50bp single end RapidRun on the Illumina HiSeq2500.
+
+## ScRNA-seq
+
+Cells were labelled using Totalseq oligo- conjugated antibodies (BioLegend) to enable multiplexing of control (hashtag 1: ACCCACCAGTAAGAC) and conditional knockout (hashtag 2: GGTCGAGAGCATTCA) samples, and feature barcoding of CD127 (IL7- Rα; GTGTGAGGCACTCTT). The sorted single cell suspensions were mixed and loaded onto a Chromium single cell device (10x Genomics) for encapsulation with barcoded gel beads according to the manufacturer's Single Cell 3' v3.1 (Dual Index) protocol. 3'GEX and 3' Feature barcoding libraries were prepared according to the standard manufacturer's protocol. The resulting libraries were sequenced on an Illumina NovaSeq 6000 S1 (paired end 150bp).
+
+## Bioinformatic analysis
+
+Quality of sequencing data was assessed using FastQC (http://www.bioinformatics.babraham.ac.uk/projects/fastqc/). Reads were trimmed for adapters and low quality base calls using Trim Galore, with default parameters (v0.6.5; https://www.bioinformatics.babraham.ac.uk/projects/trim_galore/). Reads were then mapped to the GRCm38 mouse reference genome using Hisat2 (v2.1.0; \(^{57}\) . BAM files were imported into Seqmonk (v1.47.0; http://www.bioinformatics.babraham.ac.uk/projects/seqmonk/), excluding those with mapping quality \(< 30\) , and reads were quantified over merged mRNA isoforms from the GRCm38 v90 annotation, using the RNA- seq quantitation pipeline. Reads were also quantified specifically over the regions flanked by lox- P sites in Zfp36/1 and Zfp36/2. Differential expression analysis comparing cKO with control samples was performed using DESeq2 (v1.22.2) \(^{58}\) , using 'normal' log2 fold change shrinkage, and genes designated differentially expressed if their FDR- adjusted p value was \(< 0.05\) . Gene set enrichment analysis \(^{59}\) was performed using the GSEAPreranked module
+
+<--- Page Split --->
+
+of the GenePattern software package \(^{60}\) , with default parameters except that 'collapse dataset' was set to 'No_collapse'. Genes were ranked based on log10 of their raw p value from DESeq2 analysis, with a positive sign assigned to genes with a positive \(\log_2\) fold change, such that the most significantly increased genes are ranked first, and the most significantly decreased are ranked last. Custom gene sets were uploaded for the analysis: the Hallmark apoptosis gene set was obtained from MSigDB \(^{61}\) and gene names converted to mouse orthologues using biomaRt \(^{62}\) whilst the TCR signaling pathway gene set was curated manually (see Supplementary Table 4). Genes increased or decreased in Treg upon IL- 2 or IL- 7 treatment were identified using publicly available ImmGen common \(\gamma\) - chain cytokine RNA-seq data (GSE180020) \(^{33}\) , processed as above to compare cytokine- with PBS- treated Treg. Increased/decreased genes were defined as those with FDR- adjusted p value < 0.05, and absolute \(\log_2\) - fold change > 1, except for genes increased upon IL- 7 treatment where a \(\log_2\) - fold change threshold of 0.7 was used to ensure a gene list of appropriate size for GSEA analysis. For \(\mathrm{IFN}\gamma\) treatment, microarray data of iTreg treated for 10h, compared with neutral conditions, was used (GSE38686, \(^{63}\) ). Conditions were compared using GEO2R and increased/decreased genes defined as those with FDR- adjusted p value < 0.05. Normalised read counts for the top 15 most significantly increased TCR signaling genes were \(\log_2\) transformed, and the mean transformed read count across all replicates for a given gene was subtracted. Genes were ranked based on their adjusted p value. A heatmap was plotted using the heatmap R package, with a threshold set on the fill color such that values above/below the maximum/minimum threshold were assigned the maximum/minimum colors in the scale.
+
+To generate lists of genes characteristic of naive and effector Tregs (Table S6), RNA- seq data from control nTreg and eTreg were compared as described above, and naive and effector markers were defined as genes with FDR- adjusted p value < 0.0001, and \(\log_2\) - fold change in eTreg compared with nTreg < - 1.5 or > 2, respectively.
+
+## ScRNA-seq analysis
+
+Since the feature barcoding libraries contained both multiplexing and CD127 tags, the fastq files were first split based on whether an exact match to one of the hashtag
+
+<--- Page Split --->
+
+oligos for multiplexing was found starting in position 11 in the "R2" feature barcoding fastq file. The separated multiplexing and antibody- derived tag fastq files, together with the gene expression fastq files, were then processed using Cell Ranger v6.1.2, first with cellranger multi, using the GRCm38 mouse genome reference, followed by aggregation of the control and knockout data from the per sample outputs, using cellranger aggr. Further analysis was performed using the Seurat package \(^{64}\) Cells containing below 1500 and over 14000 molecule counts for either hashtag 1 or hashtag 2 oligo conjugated antibodies were removed to filter out putative empty droplets, or doublets respectively. Additionally, cells containing over \(5.5\%\) mitochondria- derived gene expression reads, over \(10\%\) reads originating from a single gene, or in which fewer than 1000 or more than 4200 genes were detected were removed. After filtering for quality, we compared the transcriptomes of 5824 cells from FYC mice and 4163 cells from FYC I/12 mice. Normalization was performed using the centred log ratio transformation, across cells (margin 2). The top 500 variable genes were identified, and these were scaled and used as input for principal component analysis. The top 15 principal components were then used as input for Seurat's graph- based clustering approach (FindNeighbors followed by FindClusters functions; resolution 0.5; all other parameters default). These 15 principal components were also used as input to RunUMAP for further dimensionality reduction and data visualization. To identify cluster- specific marker genes the FindMarkers function was used, only considering genes detected in at least \(25\%\) of cells in at least one group for a given comparison; significantly enriched or depleted genes for each cluster are listed in Supplementary Table 7. The SCINA package was used to assign cell type identities based on previous knowledge related to naïve/effector cells (using the gene list in Supplementary Table 6). Genes associated with an Ifng signaling signature are listed in Supplementary Table 8; this was based on conversion of the human Reactome Interferon Gamma Signaling pathway genes to mouse orthologues.
+
+## Identification of direct ZFP36-family targets
+
+HITS- CLIP data for ZFP36- family proteins in \(\mathrm{CD4^{+}}\) T cells following 4h activation, or 72h activation with 2h reactivation, were obtained from GSE96074 \(^{5}\) iCLIP data for ZFP36L1 in \(\mathrm{CD4^{+}}\) T cells activated for 24h with anti- CD3 and anti- CD28 was
+
+<--- Page Split --->
+
+obtained from GSE155087 \(^{6}\) . All data was analyzed using the iCount pipeline \(^{65}\) on the Genialis platform; for iCLIP data the replicates for each antibody were merged. A gene was designated a target if the 3'UTR contained a significant crosslink site (FDR \(< 0.05\) ) with both antibodies in the iCLIP, or if a crosslink site in the 3'UTR was identified in at least two replicates for either of the HITS- CLIP datasets.
+
+## Statistical analysis
+
+Statistical significance was determined using GraphPad Prism v9 using the test indicated in the respective Figure legends.
+
+## Data and Materials Availability
+
+The RNA- seq data are available in the Gene Expression Omnibus (GEO) database (https://www.ncbi.nlm.nih.gov/geo/) under accession code GSE244621.
+
+Mice with modified alleles of Zfp36, Zfp36l1 and Zfp36l2 are available under a material transfer agreement with The Babraham Institute. All data needed to evaluate the conclusions are presented in the paper or in the Supplementary Materials.
+
+## References
+
+1. Fu, M. & Blackshear, P. J. RNA-binding proteins in immune regulation: a focus on CCCH zinc finger proteins. Nat. Rev. Immunol. 17, 130–143 (2016).
+2. Makita, S., Takatori, H. & Nakajima, H. Post-Transcriptional Regulation of Immune Responses and Inflammatory Diseases by RNA-Binding ZFP36 Family Proteins. Front. Immunol. 12, 711633 (2021).
+3. Keene, J. D. RNA regulators: coordination of post-transcriptional events. Nat Rev Genet 8, 533 543 (2007).
+4. Zhu, W. S., Wheeler, B. D. & Ansel, K. M. RNA circuits and RNA-binding proteins in T cells. Trends Immunol. 44, 792–806 (2023).
+5. Moore, M. J. et al. ZFP36 RNA-binding proteins restrain T-cell activation and antiviral immunity. Elife 7, e33057 (2018).
+6. Petkau, G. et al. The timing of differentiation and potency of CD8 effector function is set by RNA binding proteins. Nat. Commun. 13, 2274 (2022).
+
+<--- Page Split --->
+
+7. Wang, Q. et al. Tristetraprolin inhibits macrophage IL-27-induced activation of antitumour cytotoxic T cell responses. Nat Commun 8, 867 (2017).
+8. Peng, H. et al. Tristetraprolin Regulates TH17 Cell Function and Ameliorates DSS-Induced Colitis in Mice. Front Immunol 11, 1952 (2020).
+9. Cook, M. E. et al. The ZFP36 family of RNA binding proteins regulates homeostatic and autoreactive T cell responses. Sci. Immunol. 7, eabo0981 (2022).
+10. Matheson, L. S. et al. Multiomics analysis couples mRNA turnover and translational control of glutamine metabolism to the differentiation of the activated CD4+ T cell. Sci Rep-uk 12, 19657 (2022).
+11. Popović, B. et al. Time-dependent regulation of cytokine production by RNA binding proteins defines T cell effector function. Cell Reports 42, 112419 (2023).
+12. Salerno, F. et al. Translational repression of pre-formed cytokine-encoding mRNA prevents chronic activation of memory T cells. Nat Immunol 19, 828-837 (2018).
+13. Zandhuis, N. D. et al. Regulation of IFN-γ production by ZFP36L2 in T cells is time-dependent. Eur. J. Immunol. (2024) doi:10.1002/eji.202451018.
+14. Xu, B. et al. Regulated Tristetraprolin Overexpression Dampens the Development and Pathogenesis of Experimental Autoimmune Uveitis. Front Immunol 11, 583510 (2021).
+15. Makita, S. et al. RNA-Binding Protein ZFP36L2 Downregulates Helios Expression and Suppresses the Function of Regulatory T Cells. Front Immunol 11, 1291 (2020).
+16. Stoecklin, G. et al. Genome-wide analysis identifies interleukin-10 mRNA as target of tristetraprolin. J Biol Chem 283, 11689 11699 (2008).
+17. Tudor, C. et al. The p38 MAPK pathway inhibits tristetraprolin-directed decay of interleukin-10 and pro-inflammatory mediator mRNAs in murine macrophages. Febs Lett 583, 1933 1938 (2009).
+18. Coelho, M. A. et al. Oncogenic RAS Signaling Promotes Tumor Immunoresistance by Stabilizing PD-L1 mRNA. Immunity 47, 1083 1099.e6 (2017).
+19. Sakaguchi, S. et al. Regulatory T Cells and Human Disease. Annu Rev Immunol 38, 1-26 (2020).
+20. Dikiy, S. & Rudensky, A. Y. Principles of regulatory T cell function. Immunity 56, 240-255 (2023).
+21. Georgiev, P. et al. Regulatory T cells in dominant immunologic tolerance. J. Allergy Clin. Immunol. 153, 28-41 (2024).
+
+<--- Page Split --->
+
+766 22. Sawitzki, B. et al. IFN- \(\gamma\) production by alloantigen-reactive regulatory T cells is important for their regulatory function in vivo. J Exp Medicine 201, 1925- 1935 (2005). 769 23. Overacre- Delgoffe, A. E. et al. Interferon- \(\gamma\) Drives Treg Fragility to Promote Antitumor Immunity. Cell 169, 1130- 1141. e11 (2017). 771 24. Gocher- Demske, A. M. et al. IFN- \(\gamma\) - induction of TH1- like regulatory T cells controls antiviral responses. Nat. Immunol. 24, 841- 854 (2023). 773 25. Petkau, G. et al. Zfp3611 establishes the high- affinity CD8 T- cell response by directly linking TCR affinity to cytokine sensing. Eur. J. Immunol. 54, 2350700 (2024). 776 26. Moran, A. E. et al. T cell receptor signal strength in Treg and iNKT cell development demonstrated by a novel fluorescent reporter mouse. J Exp Medicine 208, 1279 1289 (2011). 779 27. Rubtsov, Y. P. et al. Regulatory T cell- derived interleukin- 10 limits inflammation at environmental interfaces. Immunity 28, 546 558 (2008). 781 28. Hodson, D. J. et al. Deletion of the RNA- binding proteins ZFP36L1 and ZFP36L2 leads to perturbed thymic development and T lymphoblastic leukemia. Nat Immunol 11, 717 724 (2010). 784 29. Galloway, A. et al. RNA- binding proteins ZFP36L1 and ZFP36L2 promote cell quiescence. Science 352, 453 459 (2016). 786 30. Bye- A- Jee, H. et al. The RNA- binding proteins Zfp36l1 and Zfp36l2 act redundantly in myogenesis. Skeletal muscle 8, 37- 12 (2018). 788 31. Barthlott, T., Kassiotis, G. & Stockinger, B. T Cell Regulation as a Side Effect of Homeostasis and Competition. J Exp Medicine 197, 451- 460 (2003). 790 32. Kieper, W. C., Burghardt, J. T. & Surh, C. D. A role for TCR affinity in regulating naive T cell homeostasis. Journal of immunology (Baltimore, Md. : 1950) 172, 40 44 (2004). 793 33. Baysoy, A. et al. The interweaved signatures of common- gamma- chain cytokines across immunologic lineages. J. Exp. Med. 220, e20222052 (2023). 794 34. Wang, E. et al. Surface antigen- guided CRISPR screens identify regulators of myeloid leukemia differentiation. Cell Stem Cell 28, 718- 731. e6 (2021). 797 35. Charbonnier, L.- M., Wang, S., Georgiev, P., Sefik, E. & Chatila, T. A. Control of peripheral tolerance by regulatory T cell- intrinsic Notch signaling. Nat Immunol 16, 1162 1173 (2015).
+
+<--- Page Split --->
+
+36. Hasegawa, H. & Matsumoto, T. Mechanisms of Tolerance Induction by Dendritic Cells In Vivo. Front. Immunol. 9, 350 (2018).37. Ovcinnikovs, V. et al. CTLA-4-mediated transendocytosis of costimulatory molecules primarily targets migratory dendritic cells. Sci. Immunol. 4, eaaw0902 (2019).38. Guilliams, M. et al. Unsupervised High-Dimensional Analysis Aligns Dendritic Cells across Tissues and Species. Immunity 45, 669-684 (2016).39. Qureshi, O. S. et al. Constitutive Clathrin-mediated Endocytosis of CTLA-4 Persists during T Cell Activation. J. Biol. Chem. 287, 9429-9440 (2012).40. Jamison, B. L. et al. An IL-2 mutein increases IL-10 and CTLA-4-dependent suppression of dendritic cells by regulatory T cells. bioRxiv 2023.12.01.569613 (2023) doi:10.1101/2023.12.01.569613.41. Petkau, G. et al. Zfp36l1 establishes the high affinity CD8 T cell response by directly linking TCR affinity to cytokine sensing. bioRxiv 2023.05.11.539978 (2023) doi:10.1101/2023.05.11.539978.42. Zhang, Z. et al. SCINA: Semi-Supervised Analysis of Single Cells in Silico. Genes 10, 531 (2019).43. Krishnaswamy, J. K. et al. Migratory CD11b+ conventional dendritic cells induce T follicular helper cell-dependent antibody responses. Sci. Immunol. 2, (2017).44. Briseño, C. G. et al. Notch2-dependent DC2s mediate splenic germinal center responses. Proc. Natl. Acad. Sci. 115, 10726-10731 (2018).45. Si, Y. et al. Lung cDC1 and cDC2 dendritic cells priming naive CD8+ T cells in situ prior to migration to draining lymph nodes. Cell Rep. 42, 113299 (2023).46. Chinen, T. et al. An essential role for the IL-2 receptor in Treg cell function. Nat. Immunol. 17, 1322-1333 (2016).47. Fan, M. Y. et al. Differential Roles of IL-2 Signaling in Developing versus Mature Tregs. Cell Reports 25, 1204 1213.e4 (2018).48. Simonetta, F. et al. Interleukin-7 influences FOXP3+CD4+ regulatory T cells peripheral homeostasis. Plos One 7, e36596 (2012).49. Schmaler, M. et al. IL-7R signaling in regulatory T cells maintains peripheral and allograft tolerance in mice. Proc National Acad Sci 112, 13330 13335 (2015).50. Gratz, I. K. et al. Cutting Edge: memory regulatory t cells require IL-7 and not IL-2 for their maintenance in peripheral tissues. J Immunol 190, 4483 4487 (2013).
+
+<--- Page Split --->
+
+51. León, B., Bradley, J. E., Lund, F. E., Randall, T. D. & Ballesteros-Tato, A. FoxP3+ regulatory T cells promote influenza-specific Tfh responses by controlling IL-2 availability. Nat Commun 5, 3495 (2014).52. Botta, D. et al. Dynamic regulation of T follicular regulatory cell responses by interleukin 2 during influenza infection. Nat Immunol 18, 1249 1260 (2017).53. Lee, S. K. et al. Interferon-γ excess leads to pathogenic accumulation of follicular helper T cells and germinal centers. Immunity 37, 880 892 (2012).54. Bell, S. E. et al. The RNA binding protein Zfp36l1 is required for normal vascularisation and post-transcriptionally regulates VEGF expression. Dev Dynam 235, 3144 3155 (2006).55. Newman, R. et al. Maintenance of the marginal-zone B cell compartment specifically requires the RNA-binding protein ZFP36L1. Nat. Immunol. 18, 683-693 (2017).56. Monzón-Casanova, E. et al. Polypyrimidine tract-binding proteins are essential for B cell development. Elife 9, (2019).57. Kim, D., Paggi, J. M., Park, C., Bennett, C. & Salzberg, S. L. Graph-based genome alignment and genotyping with HISAT2 and HISAT-genotype. Nat. Biotechnol. 37, 907-915 (2019).58. Love, M. I., Huber, W. & Anders, S. Moderated estimation of fold change and dispersion for RNA-seq data with DESeq2. Genome Biol. 15, 550 (2014).59. Subramanian, A. et al. Gene set enrichment analysis: A knowledge-based approach for interpreting genome-wide expression profiles. Proc. Natl. Acad. Sci. 102, 15545-15550 (2005).60. Reich, M. et al. GenePattern 2.0. Nat. Genet. 38, 500-501 (2006).61. Liberzon, A. et al. The Molecular Signatures Database Hallmark Gene Set Collection. Cell Syst. 1, 417-425 (2015).62. Durinck, S., Spellman, P. T., Birney, E. & Huber, W. Mapping identifiers for the integration of genomic datasets with the R/Bioconductor package biomaRt. Nat. Protoc. 4, 1184-1191 (2009).63. Hall, A. O. et al. The Cytokines Interleukin 27 and Interferon-γ Promote Distinct Treg Cell Populations Required to Limit Infection-Induced Pathology. Immunity 37, 511-523 (2012).64. Hao, Y. et al. Integrated analysis of multimodal single-cell data. Cell 184, 3573-3587. e29 (2021).
+
+<--- Page Split --->
+
+65. König, J. et al. iCLIP reveals the function of hnRNP particles in splicing at individual nucleotide resolution. Nat. Struct. Mol. Biol. 17, 909–915 (2010).
+
+## Acknowledgements:
+
+We thank Kirsty Bates for expert technical assistance and Oliver Burton for advice on flow cytometry; Fiamma Salerno and Marian Jones Evans for characterizing the reporter mice; and the Core Biochemical Assay Laboratory at Addenbrooke's Hospital for MSD analysis. We thank Georg Petkau and Arianne Richard for critical reading of the manuscript. We thank the UKRI-BBSRC Core Capability Grant funded Babraham Institute Biological Support Unit, Sequencing, Flow Cytometry and Bioinformatics Facilities for invaluable support.
+
+## Funding:
+
+This study was funded by the BBSRC Institute strategic programme grants BBS/E/B/000C0427; BBS/E/B/000C0428 and a Wellcome Investigator award (200823/Z/16/Z) to M.T.
+
+## Author contributions:
+
+Conceptualization: M.T. Methodology: B.S- N, S.E.B. Investigation: B.S- N, S.E.B, R.V. Data curation: B.S- N, L.S.M. Writing- original draft: B.S- N, S.E.B, L.S.M, M.T. Funding acquisition: M.T. Supervision: M.T.
+
+All authors contributed to reviewing and editing the manuscript.
+
+Competing interests: The authors declare they have no competing interests
+
+<--- Page Split --->
+
+
+Figure 1
+
+
+
+
+<--- Page Split --->
+
+## Fig. 1 Zfp36/1 and Zfp36/2 are essential in Treg to maintain immune homeostasis
+
+a, Representative histogram overlays comparing expression of each reporter in Treg \(\mathrm{(CD4^{+}CD25^{+}FR4^{+})}\) versus Tconv \(\mathrm{(CD4^{+}CD25^{- }FR4^{+})}\) cells in either the naive \(\mathrm{(CD44^{lo}CD62L^{hi})}\) or effector \(\mathrm{(CD44^{hi}CD62L^{lo})}\) subset, as indicated. Gating as in fig. S1A. In each example Tconv cells are represented by the grey shaded histogram; mAmetrine - ZFP36 (purple line); mCherry - ZFP36L1 (red line) and eGFP - ZFP36L2 (green line). Corresponding cells from wild type mice are indicated by the dashed line. Scatter plots represent the geometric mean fluorescence intensity (gMFI) of each reporter from \(n = 4 - 5\) mice.
+
+b, Representative flow cytometry (FACS) plots and proportion and cell number of effector cells \(\mathrm{CD44^{hi}CD62L^{lo}}\) in the \(\mathrm{CD4^{+}YFP^{- }}\) (upper panel) and \(\mathrm{CD8^{+}}\) subsets (lower panel), in single and double conditional knockout male mice (gated as in Supplementary Fig. 1d). Control icre- only FYC \((n = 17)\) ; FYC 11 \((n = 8)\) ; FYC 11/2 \((n = 11)\) , key as shown.
+
+c,d, Representative FACS plots, showing percentage and number of \(\mathrm{CD44^{hi}CD62L^{lo}}\) eTreg c, and d, numbers of \(\mathrm{CD44^{lo}CD62L^{hi}nTreg}\) in FYC 11 and FYC 11/2 male mice (gated as shown in c).
+
+e, Representative images of haematoxylin and eosin staining of the lung, liver, small and large intestine from three male FYC and FYC 11/2 mice at 11 weeks of age.
+
+Lymphoid infiltrates are arrowed. Scale bar represents 200um.
+
+For a- d, each symbol represents an individual mouse with the horizontal line representing the mean; values are for LN cells from mice aged 10 - 14 weeks. Data from at least two independent experiments. P values were determined by Mann- Whitney non- parametric test (a) or one- way ANOVA using multiple comparison (b, c, d).
+
+<--- Page Split --->
+
+
+Figure 2
+
+
+
+c
+
+
+
+Endocytosis
+
+
+
+e
+
+<--- Page Split --->
+
+## Fig. 2 Compromised fitness of RBP-deficient Tregs
+
+a, Representative FACS plots of FOXP3 and YFP expression in \(\mathrm{CD4^{+}}\) cells from female \(FYC^{+}\) and \(FYC^{+}\) 11/2 mice; scatter plots showing quantification (% of YFP+ and YFP- cells within FOXP3+ gate); key as shownb, MA plot showing the DESeq2- derived shrunken \(\log_{2}\) - fold changes in gene expression in \(FYC^{+}\) 11/2 compared with \(FYC^{+}\) nTreg, padj. <0.05 shown in blue, selected genes indicated in black.c, Violin plot showing the \(\log_{2}\) - fold change in expression of genes with ZFP36- family binding detected in their 3'UTR by CLIP (orange), compared with non- target genes (grey). Only genes with mean normalised read counts \(>100\) were included; the number of genes in each group is indicated.d, GSEA of custom gene sets (Supplementary Table 4) showing the ten most positively and negatively enriched pathways in the transcriptomes of Treg from \(FYC\) \(^{+}\) 11/2 compared to \(FYC^{+}\) mice. Genes were ranked based on their expression change upon deletion of Zfp36/1 and 12 (most significantly increased genes ranked first and most significantly decreased genes ranked last).The bar graph shows the number of genes in the leading edge, with predicted targets represented in orange. The red- blue heatmap shows the NES. Pathways ordered with the highest NES shown at the top; values in white represent the FDR- adjusted p value.e, GSEA plots for Endocytosis and TCR signaling pathwaysf, g, GSEA plots using genes with altered expression in the response to the survival factors IL- 2 and IL- 7 (f), and IFN \(\gamma\) (g), comparing the genes altered by cytokine stimulation to the transcriptome of Treg from \(FYC^{+}\) 11/2 mice; genes decreased upon cytokine stimulation shown in blue; genes increased are shown in red.
+
+<--- Page Split --->
+
+
+Figure 3
+
+<--- Page Split --->
+
+## Fig. 3 Decreased cycling of CTLA-4 in RBP-deficient nTreg
+
+a, Gating strategy for cDC2 (CD172a\* XCR1\*), showing percentage of events in each gate. Dump channel (FITC: CD3, CD64, F4/80), pre- gated on live, single cells b, Enumeration of cells per LN in each DC subset; \(n = 6\) , key as shown. c, Representative FACS plots showing CD80 and CD86 expression on CD11cint MHClhi "migratory" (upper panel) and CD11cmi MHClint "resident" (lower panel) cDC2 from spleen from FYC 1112 and FYC male mice; the number of events in the file is indicated; \(n = 6\) , key as shown d, Representative FACS plots showing CTLA- 4 staining in nTreg from spleen from FYC 1112 and FYC male mice (left panel) and eTreg (right panel). Percentage of CTLA- 4+ Treg in each condition (lower panel); \(n = 6\) e, As in d, showing data from FYC/+ 1112 and FYC/+ female mice; \(n = 5\) Each symbol represents an individual mouse; key as shown. Data from at least two independent experiments. P values were determined by Mann- Whitney test.
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+## Fig. 4 ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-2
+
+a,b, Representative FACS plots of Treg from LN from female mice a, or male mice b, fixed directly ex- vivo and stained for pSTAT5; \(FYC^{+}, FYC^{+} 11 / 2 n = 5; FYC, FYC 11 / 2 n = 4\) , key as shownc, Representative histogram overlays of CD25 expression on nTreg (left panel) and eTreg (right panel) from spleen; gMFI of CD25; YFP+ cells from female \(FYC^{+} \text{and} FYC^{+} 11 / 2 \text{mice}\) ; key as in a-d, Frequency of pSTAT5+ cells in nTreg and eTreg from female splenocytes following stimulation for 30 minutes with a range of concentrations of IL- 2; key as in ae, Representative histogram overlays of CD25 expression on nTreg (left panel) and eTreg (right panel) from spleen; gMFI of CD25; YFP+ cells from male \(FYC\) and \(FYC\) 11/2 mice; key as in bf, Frequency of pSTAT5+ cells in nTreg and eTreg from male mice stimulated as in d; key as in bP values determined using Mann- Whitney test (a,b,c,e), or two- way ANOVA with multiple comparison (d, f).
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+## Fig. 5 ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-7
+
+a, b, Representative histogram overlays of CD127 expression in nTreg (left panel) and eTreg (right panel) from spleen of female mice a, or male mice b; gMFI of CD127.
+
+c, d, Frequency of pSTAT5+ cells in nTreg and eTreg isolated from the spleen from female mice (c) or male mice (d) following stimulation for 30 minutes with a range of concentrations of IL- 7; key as shown.
+
+P values determined using Mann- Whitney test (a, b), or two- way ANOVA with multiple comparison (c, d).
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+## Fig. 6 ZFP36L1 and ZFP36L2 limit Treg sensitivity to IFN \(\gamma\)
+
+a, Frequency of pSTAT1+ cells detected in \(\mathrm{YFP^{+}}\) nTreg and \(\mathrm{YFP^{+}}\) eTreg from female mice following stimulation for 30 minutes with a range of concentrations of \(\mathrm{IFN}\gamma\) . Representative histogram overlays of pSTAT1 expression (left panel) and compiled data (right panel); key as shown. b, FACS analysis of total STAT1 expression in Treg from female \(\mathrm{FYC^{+}}\) and \(\mathrm{FYC^{+}}\) 11/2 mice, showing representative histogram overlays of STAT1 expression and quantitation; key as in a. c, Frequency of pSTAT1+ cells detected in \(\mathrm{YFP^{+}}\) nTreg and \(\mathrm{YFP^{+}}\) eTreg from female mice following stimulation for 30 minutes with a range of concentrations of IL-6. Representative histogram overlays of pSTAT1 expression (left panel) and compiled data (right panel); key as in a. P values determined using two- way ANOVA with multiple comparison (a,c).
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+## Fig. 7 Activated phenotype of Treg from FYC 1112 mice
+
+a, UMAP representation of scRNA seq data with cell clusters indicated by color code and numbered 0- 7. Single \(\mathsf{CD4^{+}FR4^{+}YFP^{+}}\) cells were sorted from apparently healthy male FYC and FYC 1112 mice.
+
+b, Distribution of nTreg and eTreg subsets within clusters; key as shown c, Dot plot representation showing percentage of detection (dot size) and scaled expression (dot color) in each cluster for genes more frequently detected and highly expressed in each cluster relative to other clusters (Wilcoxon rank sum test; p value \(< 0.001\) ). The top four genes for each cluster, based on average \(\log_2\) fold change, are shown. Color bar on the right indicates clusters that are primarily comprised of nTreg or eTreg; key as in b.
+
+d, UMAP representation of clusters according to genotype as indicated, and percentage contribution of cells to each cluster by genotype; key as shown e, UMAP distribution highlighting the location of cells with an expression pattern characteristic of the \(\mathsf{IFN}\gamma\) gene signature (indicated in red); and percentage contribution of cells identified as possessing the \(\mathsf{IFN}\gamma\) signaling gene signature for each genotype, within each cluster; adjusted p values from Chi- square test f, g, h, UMAP distribution highlighting the location of cells expressing Cxcr3 (f), Gata3 (g), Pdc1 (h). The intensity of the purple color indicates the scaled expression level for each plot.
+
+i, j, k, Representative FACS plots gated on \(\mathsf{CD4^{+}}\) cells and scatter plots showing \(\%\) of \(\mathsf{CXCR3^{+}}\) (i), GATA3hi (j), and \(\mathsf{CXCR5^{+}PD1^{+}}\) (Tfr, k) out of all \(\mathsf{FOXP3^{+}}\) cells; (n=4 to 7); key as shown
+
+I, \(\mathsf{IFN}\gamma\) , IL- 17, IL- 4 and IL- 10 expression in Tconv and Treg. Splenocytes were stimulated with PMA/ionomycin for four hours in the presence of Brefeldin A; FACS plots gated on \(\mathsf{CD4^{+}}\) cells. Percentage values shown as a \(\%\) of all \(\mathsf{CD4^{+}}\) FOXP3+ cells (Tconv) or \(\mathsf{CD4^{+}FOXP3^{+}}\) cells (Treg).
+
+Data are from at least two independent experiments. P values determined using Mann- Whitney test (i- I).
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+## Fig. 8 IFNy is a driving force for the expansion of effector T cells
+
+a, Development of clinical symptoms with age for \(FYC 1112\) (n=46) and \(Ifng^{+ / - }\) FYC 1112 male mice (n=24); key as indicated. Logrank test \(p = 0.03\) b, Serum cytokine levels in \(FYC\) , \(FYC 1112\) and \(Ifng^{+ / - }\) FYC 1112 male mice; key as shown. Comparative values for \(FYC 1112\) and \(FYC\) : IFN \(\gamma\) (4- fold); TNF \(\alpha\) (4- fold); IL- 2 (3- fold); IL- 6 (9- fold); IL- 10 (9- fold). Dashed line represents limits of detection. c, Representative FACS plots and gating strategy (upper) and enumeration (lower panel) of effector cells in the Treg, Tconv (CD44hiCD62Llo) and CD8+ TEM (CD44hiCD62Llo) subsets. Numbers are shown per single LN in mice aged 15 weeks (n=6). Key as in b. d, e, f, Representative FACS plots and enumeration of (d) T follicular helper (Tfh) YFP- CXCR5+PD1+), (e) Tfr (YFP+ CXCR5+PD1+), and (f) GC B cells (B220+CD38loCD95+ gated as in Supplementary Fig. 9); key as in b. Comparative values for \(FYC 1112\) and \(FYC\) : Tfh (60- fold), Tfr (90- fold), GC B (100- fold), g, Total serum Immunoglobulin levels quantified by ELISA; key as in b. Comparative values for \(FYC 1112\) with \(FYC\) : IgG2c (5- fold), IgE (300- fold). Analyses combine data from two or more independent experiments (b- g n=6). P values determined using one- way ANOVA with multiple comparison (b- g).
+
+<--- Page Split --->
+
+
+
+
+
+
+
+<--- Page Split --->
+
+## Fig. S1 Phenotyping of T cell subsets
+
+a, Gating strategy for data shown in Fig. 1a; Treg: \(\mathrm{CD4^{+}FR4^{+}CD25^{+}}\) ; and Tconv: \(\mathrm{CD4^{+}CD25^{- }T}\) cellsb, Gating strategy and representative FACS plots comparing expression of ZFP36L1 in Treg ( \(\mathrm{CD4^{+}FOXP3^{+}YFP^{+}}\) ) or Tconv ( \(\mathrm{CD4^{+}FOXP3^{- }YFP^{- }}\) ) cells from FYC, FYC 11 (upper panel) and FYC 11/2 mice (lower panel) after stimulation with PMA and ionomycin for four hours at \(37^{\circ}C\) ; cells were pre- gated on live, single cells; quantification of ZFP36L1 gMFI; key as shownc, Total cell number per pLN; \(\mathrm{n = 8 - 17}\) ; key as in bd, Gating strategy for data shown in Fig. 1b, ce, f, Representative FACS plots and proportion and cell number of effector cells \(\mathrm{CD44^{hi}CD62L^{lo}}\) in the \(\mathrm{CD4^{+}YFP^{- }}\) (upper panel) and \(\mathrm{CD8^{+}}\) subsets (lower panel) from FYC Zfp36 (e), and FYC Zfp36/2 mice (f), analysed with contemporaneous FYC controls. FYC ( \(\mathrm{n = 5 - 6}\) ); FYC Zfp36 ( \(\mathrm{n = 6}\) ); FYC Zfp36/2 ( \(\mathrm{n = 7}\) ); key as shown Numbers are shown per single LN in mice aged 9 - 16 weeksP values were determined using one- way ANOVA using multiple comparison (c) or Mann- Whitney test (b, e, f).
+
+<--- Page Split --->
+
+
+b
+
+![PLACEHOLDER_46_1]
+
+
+![PLACEHOLDER_46_2]
+
+
+![PLACEHOLDER_46_3]
+
+
+![PLACEHOLDER_46_4]
+
+
+<--- Page Split --->
+
+## Fig. S2 Compromised fitness of RBP-deficient Treg
+
+a, Number of effector cells in the Tconv (CD44hiCD62Llo) and CD8+ TEM (CD44hiCD62Llo ) subsets; key as shown b, Gating strategy and representative FACS plots comparing CD4+TCRβ+CD69- YFP+ CD25+ Treg in the thymus of 7-week old \(FYC^{+}\) and \(FYC^{+}\) 1112 mice; n=4 c, Gating strategy for sorting nTreg d, Normalised read counts across the loxP- flanked regions of the conditional Zfp36l1 and Zfp36l2 alleles; n=6- 7; key as shown. Read counts were normalised using size factors derived from the overall DESeq2 analysis of all genes; p values determined using t test with FDR correction e, Representative histogram overlays comparing expression of ZFP36L1 in Treg (CD4+ FOXP3+) cells from \(FYC^{+}\) and \(FYC^{+}\) 1112 mice (icre- positive (FOXP+YFP+) cells - black line and black symbols; icre- negative FOXP+YFP- ) cells - blue line and blue symbols); or Tconv (CD4+ FOXP3- ) cells (lower panel). Cells were stimulated with PMA and ionomycin for four hours; scatter plots showing gMFI for ZFP36L1 staining; n=3; key as shown P values determined using Mann- Whitney (a,d), or one- way ANOVA with multiple comparison (e).
+
+<--- Page Split --->
+![PLACEHOLDER_48_0]
+
+Figure S3
+
+![PLACEHOLDER_48_1]
+
+
+<--- Page Split --->
+
+## Fig. S3 Genes enriched in the TCR signaling pathway
+
+a, The heatmap depicts the top 15 ranked genes in the TCR signaling pathway, ordered with the most significantly increased genes at the top. The color scale represents the \(\log_2\) fold deviation from the mean for each gene. Genes that are predicted targets by CLIP are represented in orangeb, CD5 (upper panel) and NUR77 (lower panel) expression (gMFI) in \(\mathrm{CD4^{+}FOXP3^{+}}\) nTreg (CD62Lhi) and eTreg (CD44hi CD62Llo) from control \(FYC^{+}\) and \(FYC^{+}\) /112 mice. \(\mathrm{n = 4}\) ; key as shown.P values in (b) determined using one- way ANOVA with multiple comparison
+
+<--- Page Split --->
+![PLACEHOLDER_50_0]
+
+Figure S4
+
+![PLACEHOLDER_50_1]
+
+
+<--- Page Split --->
+
+## Fig. S4 Expression of Treg signature genes
+
+a, Representative FACS plots showing FOXP3, CTLA- 4 (from LN, fixed ex vivo), IKZF2 (from mLN) and ICOS (from LN) expression (gMFI) in \(\mathrm{CD4^{+}}\) FOXP3+ nTreg and eTreg from control \(FYC^{+}\) and \(FYC^{+} / 112\) mice; \(n = 3 - 5\) ; key as shown. b, NOTCH1 expression (gMFI) in nTreg and eTreg from \(FYC^{+}\) and \(FYC^{+} / 112\) mice; \(n = 3 - 4\) , key as in a. P values determined using Mann- Whitney.
+
+<--- Page Split --->
+![PLACEHOLDER_52_0]
+
+Figure S5
+
+![PLACEHOLDER_52_1]
+
+
+<--- Page Split --->
+
+## Fig. S5 Decreased cycling of CTLA-4 in RBP-deficient nTreg
+
+a, Representative FACS plots showing CD80 and CD86 expression on CD11cint MHCIIhi "migratory" (upper panel) and CD11cHi MHCIIint "resident" (lower panel) CD172a \(\times\) XCR1+ cDC1 from spleen from FYC 1112 and FYC male mice; the number of events in the file is indicated; \(n = 6\) , key as shown b, Percentage of CTLA- 4+ nTreg or eTreg in surface, cycling, or total pool from FYC \(^+\) 1112 and FYC+ female mice. Each symbol represents an individual mouse \((n = 5)\) ; key as shown. Data from at least two independent experiments. P values determined using Mann- Whitney (a) and one- way ANOVA with multiple comparison (b) represented in the table shown.
+
+<--- Page Split --->
+![PLACEHOLDER_54_0]
+
+
+<--- Page Split --->
+
+## Fig. S6 ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-2 and IL-7
+
+a, Total STAT5 expression in YFP \(^+\) nTreg and eTreg; from \(FYC^{+}\) and \(FYC^{+}\) 1/12 mice, \(\mathrm{n} = 3\) ; key as shownb, Frequency of pSTAT5 \(^+\) cells detected in YFP \(^+\) (black symbol) and YFP \(^+\) (blue symbol) nTreg and eTreg from the spleen of female mice following stimulation for 30 minutes with a range of concentrations of IL- 2; data presented as mean value \(\pm\) sd, \(\mathrm{n} = 7\) ; key as shownc, Frequency of pSTAT5 \(^+\) cells detected in YFP \(^+\) and YFP \(^+\) nTreg and eTreg from female mice following stimulation for 30 minutes with a range of concentrations of IL- 7; data presented as mean value \(\pm\) sd, \(\mathrm{n} = 4\) ; key as in b.P values were determined using two- way ANOVA with multiple comparison, comparing the mean value between each genotype, and are represented in the table shown.
+
+<--- Page Split --->
+
+Figure S7
+
+![PLACEHOLDER_56_0]
+
+
+
+![PLACEHOLDER_56_1]
+
+
+
+![PLACEHOLDER_56_2]
+
+
+
+![PLACEHOLDER_56_3]
+
+
+
+c
+
+![PLACEHOLDER_56_4]
+
+
+
+CD44hi CD62Llo
+
+![PLACEHOLDER_56_5]
+
+
+
+CD44hi CD62Llo
+
+<--- Page Split --->
+
+## Fig. S7 ZFP36L1 and ZFP36L2 limit Treg sensitivity to IFNγ
+
+a, Frequency of pSTAT1+ cells detected in \(\gamma \mathsf{FP}^+\) and \(\gamma \mathsf{FP}^-\) nTreg and eTreg from female mice following stimulation for 30 minutes with a range of concentrations of \(\mathsf{IFN}\gamma\) ; data presented as mean value \(\pm\) sd, \(n = 6 - 11\) ; key as shownb, Total STAT1 expression in \(\gamma \mathsf{FP}^+\) and \(\gamma \mathsf{FP}^-\) nTreg and eTreg; key as in ac, Frequency of pSTAT1+ cells detected in \(\gamma \mathsf{FP}^+\) and \(\gamma \mathsf{FP}^-\) nTreg and eTreg from female mice following stimulation for 30 minutes with a range of concentrations of IL- 6; data presented as mean value \(\pm\) sd, \(n = 4 - 6\) ; key as in a.P values determined using two- way ANOVA with multiple comparison, comparing the mean value between each genotype, and are represented in the table shown (a,c).
+
+<--- Page Split --->
+![PLACEHOLDER_58_0]
+
+Figure S8
+
+<--- Page Split --->
+
+## Fig. S8 Activated phenotype of Treg from FYC 1112 mice
+
+a, Gating strategy for sorting of \(\mathsf{CD4^{+}FR4^{+}CD25^{+}}\) Treg cells for scRNA- seqb, Percentage of cells identified as naive (orange), effector (dark blue) or unassigned (grey) in each cluster;c, Violin plot representing the number of genes detected in each clusterd, Cell number for CXCR3+, GATA3hi Treg and Tfr, in LN (for data in Fig. 7i, j, k); comparative values for FYC 1112 to FYC: 4- fold increase CXCR3+, 3- fold increase in GATA3hi, 50- fold increase in Tfr cell numbere, Representative flow cytometry plots (left panel) gated on \(\mathsf{CD4^{+}}\) cells; scatter plot (right panel) showing proportion of \(\mathsf{ROR}\gamma \mathsf{t^{+}}\) Treg (as a \(\%\) of all FOXP3+ cells) and enumeration of \(\mathsf{FOXP3^{+}ROR}\gamma \mathsf{t^{+}}\) Treg; key as shownf, gMFI for intracellular cytokine staining shown in Fig. 7i.g, \(\mathsf{IFN}\gamma\) expression in CD8 cells. Splenocytes were stimulated with PMA/ionomycin for four hours in the presence of Brefeldin A, flow cytometry plots are gated on \(\mathsf{CD8^{+}}\) cells; \(\mathrm{n} = 6\) , key as shownP values determined using Mann- Whitney test (d,e,f,g).
+
+<--- Page Split --->
+![PLACEHOLDER_60_0]
+
+Figure S9
+
+<--- Page Split --->
+
+# Fig. S9 Gating strategy for GC B cells
+
+Cells were pre- gated on live, single cells
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+Supplementarytablesmerged.pdf.pdf Supplementaltables.xlsx
+
+<--- Page Split --->
diff --git a/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f_det.mmd b/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..64969f4b7164b8f9ceb015e67e1e9c2bebd79295
--- /dev/null
+++ b/preprint/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f/preprint__051f366d2a3bfb6b436ca3def5886dd6413dadc2fc06e01a744274e96766842f_det.mmd
@@ -0,0 +1,706 @@
+<|ref|>title<|/ref|><|det|>[[44, 106, 916, 175]]<|/det|>
+# ZFP36-family RNA-binding proteins in regulatory T cells reinforce immune homeostasis.
+
+<|ref|>text<|/ref|><|det|>[[44, 196, 164, 214]]<|/det|>
+Martin Turner
+
+<|ref|>text<|/ref|><|det|>[[52, 223, 366, 240]]<|/det|>
+martin.turner@babraham.ac.uk
+
+<|ref|>text<|/ref|><|det|>[[44, 268, 585, 288]]<|/det|>
+Babraham Institute https://orcid.org/0000- 0002- 3801- 9896
+
+<|ref|>text<|/ref|><|det|>[[44, 293, 238, 311]]<|/det|>
+Beatriz Sáenz- Narciso
+
+<|ref|>text<|/ref|><|det|>[[52, 316, 223, 333]]<|/det|>
+Babraham Institute
+
+<|ref|>text<|/ref|><|det|>[[44, 340, 135, 357]]<|/det|>
+Sarah Bell
+
+<|ref|>text<|/ref|><|det|>[[52, 362, 585, 380]]<|/det|>
+Babraham Institute https://orcid.org/0000- 0002- 3249- 707X
+
+<|ref|>text<|/ref|><|det|>[[44, 386, 197, 403]]<|/det|>
+Louise Matheson
+
+<|ref|>text<|/ref|><|det|>[[52, 408, 585, 426]]<|/det|>
+Babraham Institute https://orcid.org/0000- 0002- 9392- 2519
+
+<|ref|>text<|/ref|><|det|>[[44, 432, 170, 450]]<|/det|>
+Ram Venigalla
+
+<|ref|>text<|/ref|><|det|>[[52, 455, 223, 472]]<|/det|>
+Babraham Institute
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 514, 103, 531]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 551, 137, 570]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 589, 318, 608]]<|/det|>
+Posted Date: October 7th, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 628, 475, 647]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 5039504/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 665, 916, 708]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 726, 535, 746]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 781, 950, 825]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on May 6th, 2025. See the published version at https://doi.org/10.1038/s41467- 025- 58993- y.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[70, 83, 885, 780]]<|/det|>
+1 Title: ZFP36-family RNA-binding proteins in regulatory T cells reinforce 2 immune homeostasis. 3 4 Authors: Beatriz Sáenz-Narciso, Sarah E. Bell, Louise S. Matheson, Ram K. C. 5 Venigalla and Martin Turner\* 6 7 8 Affiliations: Immunology Programme, The Babraham Institute, Babraham Research 9 Campus, Cambridge, CB22 3AT, UK. 10 11 These authors contributed equally to this work: Beatriz Sáenz-Narciso, Sarah E. Bell 12 13 Corresponding author: 14 Dr. Martin Turner 15 e- mail: martin.turner@babraham.ac.uk 16 17 Abstract 18 RNA binding proteins (RBP) of the ZFP36 family limit the differentiation and effector 19 functions of CD4 and CD8 T cells, but little is known of their expression or function in 20 regulatory T cells (Treg). By Treg-restricted deletion of Zfp36 family members we 21 identify the essential role of Zfp36/1 and Zfp36/2 in Treg to maintain immune 22 homeostasis. Mice with Tregs deficient in these RBP display an inflammatory 23 phenotype with an expansion in the numbers of type-2 conventional dendritic cells, T 24 effector cells, T follicular helper and germinal center B cells and elevated serum 25 cytokines and immunoglobulins. In the absence of Zfp36/1 and Zfp36/2, the pool of 26 cycling CTLA-4 in naïve Treg was reduced, Tregs were less sensitive to IL-2 and IL-7 27 but were more sensitive to IFNγ. In mice lacking both RBP in Treg, the deletion of a 28 single allele of Ifng is sufficient to ameliorate the pathology. Thus, ZFP36L1 and 29 ZFP36L2 regulate multiple pathways that enable Tregs to enforce immune 30 homeostasis.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 106, 876, 350]]<|/det|>
+The Zinc Finger Protein 36 (ZFP36) family of RNA binding proteins (RBP) are widely expressed and play important roles in developmental biology, stress responses and inflammation \(^{1,2}\) . They act as repressors of gene expression by direct binding to AU-rich elements in the 3'UTR of mRNAs to limit translation and trigger RNA degradation. They regulate large numbers of functionally related mRNAs throughout their lifetime creating a system of post-transcriptional operons which regulate immune function \(^{3,4}\) . The best characterised operon is the cytokine- encoding mRNAs and their repression by ZFP36 is essential for limiting inflammation. How the other Zfp36-family members function and in which cell types they control inflammation and immunity is not well understood.
+
+<|ref|>text<|/ref|><|det|>[[115, 376, 881, 644]]<|/det|>
+T lymphocytes transiently express ZFP36 and ZFP36L1 when activated \(^{5,6}\) and studies using mouse models suggest they each make essential contributions to restraining effector CD4 and CD8 T cell functions \(^{5 - 11}\) . A third family member Zfp36l2 is expressed by resting T cells and represses cytokine production by memory T cells \(^{12}\) and by activated naive T cells 48 hours after activation \(^{13}\) . Mice in which all three family members are deleted by Cd4- cre at the CD4+CD8+ thymocyte stage develop a hyper- cytokinemia and a lethal inflammatory syndrome \(^{9}\) . By contrast, mice with Cd4- cre- mediated deletion of Zfp36 and Zfp36l1 appear healthy \(^{6,9}\) , and show increased resilience following influenza virus infection \(^{6}\) . Mice with deletion of Zfp36l1 and Zfp36l2 in T cells also appear healthy and show reduced pathology and effector T cell responses following induction of experimental autoimmune encephalomyelitis \(^{9}\) .
+
+<|ref|>text<|/ref|><|det|>[[115, 671, 874, 889]]<|/det|>
+As Cd4- cre deletes in all TCRαβ+ T cells it remains unclear to what extent these complex phenotypes reflect cell- intrinsic roles of the RBP in effector cells or Tregs. Mice which overexpress ZFP36 in all cells have a small increase in the frequency of Tregs, these were better able to suppress the in vitro proliferation of naïve T cells \(^{14}\) . Another study indicated the potential for ZFP36L2 to be a negative regulator of Ikrf2 mRNA and to inhibit the suppressive function of induced Tregs \(^{15}\) and others have shown that the immunosuppressive cytokine IL- 10 \(^{16,17}\) and inhibitory surface receptor CD274/PD- L1 \(^{18}\) are directly repressed by ZFP36- family proteins. Whether the ZFP36- family act in Tregs to limit or enhance their function is unknown.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 868, 351]]<|/det|>
+Tregs require the transcription factor FOXP3 for their differentiation and function and have a dominant role in immune tolerance, with roles in tissue homeostasis and resilience to infection \(^{19 - 21}\) . They deploy a repertoire of effector functions including the production of soluble factors, contact mediated depletion of costimulatory molecules and competition with effector T cells for trophic factors and metabolites. Tregs are particularly sensitive to deprivation of IL- 2 which acts via the induction of STAT5 phosphorylation to promote their survival. Tregs also demonstrate remarkable functional adaptation to local inflammatory environments which can expose them to cytokines, such as IFNγ that can modulate function in a context- dependent manner \(^{22 - 24}\) . The extent to which any of these processes are regulated by the ZFP36 family is unknown.
+
+<|ref|>text<|/ref|><|det|>[[115, 378, 880, 548]]<|/det|>
+In this study, we employed a conditional deletion strategy in mice to investigate the function of Zfp36 family members in Tregs. The loss of Zfp36l1 alone in Tregs resulted in dysregulation of immune homeostasis, a phenotype that was more severe when combined with deficiency of Zfp36l2. We establish that in Treg Zfp36l1 and Zfp36l2 play a key role in promoting CTLA- 4 function to limit the expansion of type 2- conventional dendritic cells (cDC2), in restraining the size of germinal centers (GC), and determining Treg sensitivity to IFNγ, IL- 2 and IL- 7.
+
+<|ref|>sub_title<|/ref|><|det|>[[68, 576, 195, 593]]<|/det|>
+## 85 Results
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 600, 833, 620]]<|/det|>
+## Zfp36l1 and Zfp36l2 are essential in Treg to maintain immune homeostasis
+
+<|ref|>text<|/ref|><|det|>[[115, 624, 877, 891]]<|/det|>
+To establish if ZFP36- family proteins are expressed in Tregs we have used mice in which the endogenous allele of each family member has been modified to introduce a fluorescent protein at the site of translation initiation to encode a fusion protein. By identifying Tregs with surface staining for CD25+ and FR4+ (Supplementary Fig. S1a) we found mAmetrine- ZFP36 was not detectably expressed by T cells ex vivo. Naive CD44loCD62Lhi Treg (nTreg) expressed more mCherry- ZFP36L1 and eGFP- ZFP36L2 compared to CD4+ CD44loCD62Lhi CD25- T cells (nTconv) (Fig. 1a). Furthermore, mCherry- ZFP36L1 was expressed at four- fold greater amounts in CD44hiCD62Llo effector Treg (eTreg) compared to nTreg, while eGFP- ZFP36L2 was not increased (Fig. 1a). The greater expression of mCherry- ZFP36L1 in eTreg and nTreg is consistent with these cells having been recently activated and with ZFP36L1
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 855, 128]]<|/det|>
+expression increasing in proportion to TCR signal strength \(^{25}\) which is known to be greater in naive Tregs than naive Tconv \(^{26}\) .
+
+<|ref|>text<|/ref|><|det|>[[110, 150, 881, 920]]<|/det|>
+To establish the requirement for individual ZFP36 family members in Tregs we deleted \(Zfp36\) , \(Zfp36I1\) or \(Zfp36I2\) using the \(Foxp3^{YFP\text{- } \text{icre}}\) (FYC) allele which contains the YFP- iCre recombinase fusion protein open reading frame in the 3'UTR of the \(Foxp3\) gene \(^{27}\) . Male \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36^{II/II}\) (FYC \(Zfp36\) ) and \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36I2^{II/II}\) (FYC \(I2\) ) mice were healthy up to twenty weeks of age. By contrast, \(9\%\) of \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36I1^{II/II}\) male mice (FYC \(I1\) ) had developed clinical signs of marked piloerection, hunched posture with a median age of onset of ten weeks. ZFP36L1 expression in T cells is strongly stimulated by PMA plus ionomycin and we used this to establish whether the protein could be detected in T cells from FYC \(I1\) mice. ZFP36L1 expression was reduced by ten- fold in FOXP3 \(^+\) Treg from FYC \(I1\) mice compared to FYC mice but was not differentially expressed in FOXP3 \(^+\) CD4 \(^+\) Tconv (Supplementary Fig. 1b) demonstrating efficient and selective deletion of ZFP36L1 in Treg. Because naive Tregs express both ZFP36L1 and ZFP36L2 and \(Zfp36I1\) is redundant with \(Zfp36I2\) in diverse cell systems \(^{28 - 30}\) we anticipated that the deletion of both genes in Treg would lead to a stronger phenotype than deletion of either gene alone. We thus generated \(Foxp3^{YFP\text{- } \text{icre}}\) \(Zfp36I1^{II/II}\) \(Zfp36I2^{II/II}\) (referred to as FYC \(I1/2\) ) mice. Deletion of ZFP36L1 in FYC \(I1/2\) mice was confirmed by flow cytometry to be specific to Treg (Supplementary Fig. 1b). \(12\%\) of FYC \(I1/2\) mice developed clinical symptoms which exceeded the predefined humane endpoint, including marked piloerection, hunched posture, and abdominal distension, with a median age of onset of five weeks. These mice had markedly increased lymph node (LN) cellularity which exceeded that seen in the FYC \(I1\) males (Supplementary Fig. S1c). The proportion and number of YFP \(^+\) CD44 \(^+\) iCD62L \(^0\) effector CD4 and CD8 cells within LN (gated as shown in Supplementary Fig. 1d) was increased two- to three- fold in FYC \(I1\) mice, and three- to five- fold in FYC \(I1/2\) mice compared to FYC controls (Fig. 1b). By contrast, in the YFP \(^+\) CD4 \(^+\) subset from mice lacking \(Zfp36\) there was no difference in the proportion and only a minor increase in the number of effector cells compared to control mice (1.6- fold) and no change in the CD8 \(^+\) subset (Supplementary Fig. 1e). CD4 and CD8 effector subsets were not different between FYC \(I2\) and FYC mice (Supplementary Fig. 1f).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 106, 877, 398]]<|/det|>
+Tregs from FYC 11 and FYC 11/2 mice were biased towards an activated phenotype with a three- fold increase in the number of eTreg in FYC 11/2 mice compared to FYC control mice (Fig. 1c). In addition, the number of nTreg was increased 1.5- fold (Fig. 1d), thus the phenotype of FYC 11 and FYC 11/2 mice was not due to a deficit in Treg numbers. Furthermore, the combined loss of both Zfp36/1 and Zfp36/2 led to a greater expansion of CD4 and CD8 effector cells than loss of Zfp36/1 alone. Histological analysis of tissues from FYC 11/2 mice with clinical symptoms revealed perivascular lymphocytic infiltration into lung and liver and diffuse crypt hyperplasia in the small intestine (Fig. 1e). In the large intestine of FYC 11/2 mice there was evidence of crypt hyperplasia accompanied by an increase in inflammatory cells in the lamina propria (Fig. 1e). Thus, the loss of Zfp36/1 and Zfp36/2 in Tregs leads to a failure of immune homeostasis.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 426, 536, 446]]<|/det|>
+## Compromised fitness of RBP-deficient Treg
+
+<|ref|>text<|/ref|><|det|>[[115, 451, 880, 767]]<|/det|>
+In females, Foxp3 is inactivated on one X chromosome, thus when heterozygous for the Foxp3YFP- icre allele, FYC/+ mice accumulate icre- positive and - negative Treg which can be distinguished by the expression of YFP. FYC/+ 11/2 mice did not develop any clinical symptoms over a period of at least 40 weeks. Also, we found no difference in numbers of FOXP3- CD44hiCD62L0 CD4 and CD8 cells (Supplementary Fig. 2a). Thus, Zfp36/1/Zfp36/2- deficient Tregs are insufficient to cause disease when wild type Tregs are present. In female FYC/+ mice the number of FOXP3+YFP- Tregs was twice that of FOXP3+YFP+ Tregs in the same mouse suggesting the Foxp3YFP- icre allele incurs a minor competitive disadvantage on Tregs. However, in FYC/+ 11/2 mice the icre- positive Treg were seven times less abundant than icre- negative Tregs in the same mouse (Fig. 2a). Normal Treg numbers were detected in the thymus (Supplementary Fig. S2b), thus the competitive disadvantage of Zfp36/1/Zfp36/2- deficient Tregs is revealed in peripheral lymphoid tissue.
+
+<|ref|>text<|/ref|><|det|>[[115, 796, 874, 914]]<|/det|>
+To gain insight into the role of Zfp36/1 and Zfp36/2 in Treg function in the absence of pathology we sorted YFP+ CD62LhiCD4+CD25+ cells from female FYC/+ and FYC/+ 11/2 mice (Supplementary Fig. 2c) and performed RNA- seq. Quantitation of reads mapping to the targeted region of Zfp36/1 and Zfp36/2 confirmed efficient icre- mediated recombination of both conditional alleles (Supplementary Fig. 2d).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 82, 876, 423]]<|/det|>
+Furthermore, by intracellular staining for ZFP36L1 in stimulated T cells we observed a seven- fold reduction in the ZFP36L1 protein only in icre- positive YFP+FOXP3+ Treg but not in icre- negative YFP+FOXP3+ Treg, or in Tconv (Supplementary Fig. 2e). Differential expression analysis using DESeq2 revealed 249 genes were increased (Supplementary Table 1) and 340 genes decreased (Supplementary Table 2) in the knockout Treg compared to control cells (FDR- adjusted p value <0.05) (Fig. 2b). The mRNAs encoding Foxp3, Ctl4, Ixkf2 (Helios), Icos, Tgfb1 and Lrrc32, key genes involved in Treg function, were not differently expressed (Fig. 2b). To identify transcripts that could be bound and thus directly regulated by ZFP36- family members we used published crosslinking and immunoprecipitation (CLIP) data (Supplementary Table 3) and found that target transcripts were increased in \(FYC^{+}\) \(I112\) Treg compared to \(FYC^{+}\) Treg (Fig. 2c). This is consistent with the direct targets of these RBP being more stable and thus accumulating to increased amounts in \(Foxp3^{YFP - icre}I112\) Treg.
+
+<|ref|>text<|/ref|><|det|>[[113, 450, 875, 890]]<|/det|>
+Gene Set Enrichment Analysis (GSEA) using a custom group of gene sets covering different aspects of T cell biology (Supplementary Table 4), revealed "Endocytosis", "T cell receptor signaling" and several genes sets associated with cytokine signaling amongst the top ten positively enriched pathways, including "Decreased in IL- 2", "Decreased in IL- 7", "JAK STAT signaling pathway", "IL- 2 Receptor signalling", and "Increased in IFNγ" in Foxp3YFP- icre \(I112\) deficient Tregs (Fig. 2d). Many of the genes contributing most to the enrichment (present in the leading edge) were transcripts shown to interact directly with ZFP36- family members by CLIP (represented in orange and listed in Supplementary Table 4). Genes enriched in the endocytosis pathway included 25 in the leading edge that were iCLIP targets, encompassing genes involved in the regulation of protein sorting and membrane trafficking (Supplementary Table 5 and Fig. 2e). Within the TCR signaling pathway 40 out of 73 genes in the leading edge were iCLIP targets (Supplementary Table 5 and Fig. 2e), including genes that can promote (Lat, Cd2) or attenuate (Rptor, Dgka, Dok2) activation via the TCR (Supplementary Fig. 3a). We thus evaluated the protein expression of CD5, which is not a target of the ZFP36 family but an indicator of TCR signaling strength \(^{31,32}\), and the CLIP target NUR77 (encoded by Nr4a1), which is expressed early after TCR stimulation. Expression of these proteins did not differ
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 866, 152]]<|/det|>
+between YFP+ Treg from \(FYC^{+}\) 1112 and \(FYC^{+}\) mice (Supplementary Fig. 3b). Thus, we concluded that in a non- inflammatory environment, TCR signaling was not detectably altered in \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 deficient Tregs.
+
+<|ref|>text<|/ref|><|det|>[[112, 175, 881, 775]]<|/det|>
+Using the Immunological Genome Project signatures of "common \(\gamma\) - chain" family cytokines33 we found that for genes responding to IL- 2 or IL- 7 signaling in Treg, those that were increased in response to these cytokines were decreased in the transcriptome of \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 deficient Tregs compared to \(Foxp3^{YFP\text{- } i\text{cre}}\) Tregs from control \(FYC^{+}\) mice (Fig. 2f). By contrast, genes that were decreased in response to IL- 2 or IL- 7 signaling were increased in \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 deficient Tregs (Fig. 2f). Inspection of the genes increased in response to \(\mathrm{IFN}\gamma\) in Treg revealed that genes decreased in response to \(\mathrm{IFN}\gamma\) were not significantly changed, while genes increased in response to \(\mathrm{IFN}\gamma\) were just above the 0.05 threshold for significance as increased in the transcriptome of nTreg from \(FYC^{+}\) 1112 mice compared to that from control \(FYC^{+}\) mice (Fig. 2g). The GSEA also identified the "Treg gene signature" and "Notch signaling pathway" to be just beyond the cut- off for statistical significance. As noted above, \(Foxp3\) , Cta4, Ikzf2 and Icos, were not differently expressed; and at the protein level we detected only minor reductions for FOXP3 (1.1- fold), CTLA- 4 (1.2- fold) IKZF2 (1.4- fold) and ICOS (1.2- fold) between \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 and \(Foxp3^{YFP\text{- } i\text{cre}}\) nTregs (Supplementary Fig. 4a). FOXP3, CTLA- 4 and IKZF2 also were slightly reduced in eTregs (1.1;1.3;1.3- fold respectively), but ICOS showed an increase of 1.3- fold between \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 eTreg and \(Foxp3^{YFP\text{- } i\text{cre}}\) eTreg (Supplementary Fig. 4a). The expression of NOTCH1, a known target of ZFP36L1 and ZFP36L228,34, that when overexpressed can impair Treg function35, was not different in \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 Treg compared to \(Foxp3^{YFP\text{- } i\text{cre}}\) Treg (Supplementary Fig. 4b). We conclude that the 589 DE genes in the transcriptome of naïve \(Foxp3^{YFP\text{- } i\text{cre}}\) 1112 Treg impact on multiple processes which together could contribute to the lack of fitness and function of 1112- deficient Tregs.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 800, 623, 820]]<|/det|>
+## Decreased cycling of CTLA-4 in RBP-deficient nTreg
+
+<|ref|>text<|/ref|><|det|>[[116, 825, 876, 893]]<|/det|>
+As conventional dendritic cells (cDC) are important in maintaining T cell tolerance36 and cDC phenotype can be regulated by Treg37, we examined the number of cDC in LN. We had observed that LN cellularity was increased four- fold in \(FYC\) 1112 mice,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 78, 879, 748]]<|/det|>
+however, using a gating strategy (modified from \(^{38}\) ) relative to the cDC subsets in FYC mice, the number of "resident" CD172a \(^+\) XCR1 \(^+\) cDC2 was selectively increased (ten- fold) compared to the "migratory" CD172a \(^+\) XCR1 \(^+\) cDC2 and "resident" and "migratory" cDC1 (CD172a \(^+\) XCR1 \(^+\) ) populations (Fig. 3a,b). CTLA- 4 can bind to the costimulatory molecules CD80 and CD86 and can capture these molecules by transendocytosis from neighbouring antigen presenting cells (APC) to restrict costimulation via CD28 \(^{37}\) . The selective increase in cDC2 numbers therefore prompted us to examine the expression of CD80 and CD86 on cDC in the LN from male mice. We identified elevated CD80 and CD86 expression only in the "resident" CD172a \(^+\) XCR1 \(^+\) cDC2 but not in the "migratory" CD172a \(^+\) XCR1 \(^+\) cDC2 population in FYC 1112 mice (Fig. 3c) nor in the cDC1 population (Supplementary Fig. 5a). CTLA- 4 is predominantly localised within intracellular vesicles, which cycle between the cell surface and intracellular stores, and can be rapidly removed from the surface via clathrin- mediated endocytosis \(^{39}\) . As GSEA had identified enrichment in the endocytosis pathway, we examined the cycling pool of CTLA- 4, which can bind ligand at the plasma membrane, by incubating unstimulated cells with labelled anti- CTLA- 4 antibody at 37°C for 2 hours and comparing this to the total intracellular pool. Constitutive uptake of labelled antibody in vitro visualised in the absence of stimulation, revealed a decrease in the pool of cycling CTLA- 4 in YFP \(^+\) nTreg from male FYC 1112 mice compared to nTreg from control FYC mice, although no difference was observed in eTreg or in the total intracellular pool (Fig. 3d). Consistent with the data from the male mice, in the absence of stimulation, the pool of cycling CTLA- 4 in RBP- deficient YFP \(^+\) nTreg from female FYC \(^+\) 1112 mice was also decreased compared to YFP \(^+\) nTreg from FYC \(^+\) mice (Fig. 3e) and YFP \(^+\) nTreg in the same mice (Supplementary Fig. 5b), but not within the YFP \(^+\) eTreg subset. Thus, these data suggest a cell intrinsic role for ZFP36L1 and ZFP36L2 in promoting CTLA- 4 cycling in nTreg.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 772, 723, 791]]<|/det|>
+## ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-2 and IL-7
+
+<|ref|>text<|/ref|><|det|>[[115, 795, 872, 914]]<|/det|>
+IL- 2R signaling can enhance CTLA- 4 function in Treg \(^{40}\) . Moreover, based on the results of the GSEA and the finding that CD8 T cells lacking Zfp36 and Zfp36/1 were less sensitive to IL- 2 \(^{41}\) we hypothesized that ZFP36L1 and ZFP36L2 promote Treg responsiveness to IL- 2 and/or IL- 7. As both IL- 2 and IL- 7 induce tyrosine phosphorylation of STAT- 5A/B, we examined this in Treg ex vivo after rapid fixation
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 78, 880, 633]]<|/det|>
+of cells following tissue retrieval. In \(FYC^{+} / 112\) mice we observed a two- fold reduction in the frequency of pSTAT5+ cells in FOXP3+YFP+ nTreg compared to \(FYC^{+}\) controls, but no difference between the eTreg subsets (Fig. 4a). In male \(FYC / 112\) mice, we observed a two- fold reduction in the frequency of pSTAT5+ cells in both nTreg and eTreg (Fig. 4b), suggesting optimal STAT5 phosphorylation in Treg in vivo requires ZFP36L1 and ZFP36L2. As STAT5 can be phosphorylated in response to both IL- 2 and IL- 7, we measured expression of their receptors CD25 and CD127, and the in vitro response of Treg to a range of doses of IL- 2 and IL- 7. Surface expression of CD25 on YFP+ nTreg from the spleen of female \(FYC^{+} / 112\) mice was reduced two- fold compared to YFP+ nTreg from \(FYC^{+}\) mice (Fig. 4c). Amongst eTreg the majority expressed low levels of CD25 but still we found a reduction (1.5- fold) between CD25 surface expression on YFP+ eTregs comparing \(FYC^{+} / 112\) and \(FYC^{+}\) mice. Accordingly, YFP+ nTreg from \(FYC^{+} / 112\) mice showed diminished responses when cultured with IL- 2 at 0.3 and 1 ng/ml but no difference was found in eTreg (Fig. 4d). Quantitation of the total amount of STAT5 in YFP+ FOXP3+ cells in female \(FYC / + / 112\) and \(FYC / +\) mice confirmed this was not different (Supplementary Fig. 6a). Moreover, icre- negative Treg from female \(FYC^{+} / 112\) and \(FYC^{+}\) mice responded in a similar manner to IL- 2 (Supplementary Fig. 6b), indicating a cell- intrinsic defect of RBP- deficient Treg in their response to IL- 2. CD25 expression was also reduced on nTreg from male \(FYC / 112\) mice compared to control \(FYC\) mice (Fig. 4e), and the response to IL- 2 was diminished only in the nTreg population (Fig. 4f). These data indicate that ZFP36L1 and ZFP36L2 in Treg promote an optimal response to IL- 2.
+
+<|ref|>text<|/ref|><|det|>[[112, 647, 880, 916]]<|/det|>
+CD127 was expressed at modestly greater amounts on the surface of eTreg compared to nTreg. On YFP+ nTreg and eTreg from both female \(FYC^{+} / 112\) (Fig. 5a) and male \(FYC / 112\) mice (Fig. 5b) CD127 was decreased compared to Tregs from control mice. Furthermore, both naive and effector YFP+ Treg from \(FYC^{+} / 112\) mice showed a striking reduction in their pSTAT5 response to IL- 7 compared to YFP+ Treg from \(FYC^{+}\) mice (Fig. 5c). This was also the case for nTreg and eTreg from male \(FYC / 112\) mice (Fig. 5d). In \(FYC^{+}\) and \(FYC^{+} / 112\) females, icre- negative Treg were more sensitive to IL- 7 than icre- positive Treg from the same mouse. Therefore, expression of the \(FYC\) allele correlates with a minor reduction in pSTAT5 in response to IL- 7 (1.2- fold Supplementary Fig. 6c). However, the difference between icre- positive and icre- negative Treg in the same animal was greater in \(FYC^{+} / 112\) mice
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 861, 177]]<|/det|>
+compared to control \(FYC^{+}\) mice (Supplementary Fig. 6c), supporting a cell- intrinsic role for ZFP36L1 and ZFP36L2 in the Treg response to IL- 7. Taken together, these results revealed that ZFP36L1 and ZFP36L2 are essential in Treg to maintain optimal sensitivity to IL- 2 and IL- 7.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 206, 608, 225]]<|/det|>
+## ZFP36L1 and ZFP36L2 limit Treg sensitivity to \(\mathsf{IFN}\gamma\)
+
+<|ref|>text<|/ref|><|det|>[[115, 231, 880, 679]]<|/det|>
+As the bulk RNAseq data from heterozygous female mice suggested a possible enhancement of the \(\mathsf{IFN}\gamma\) signaling pathway we evaluated the response to \(\mathsf{IFN}\gamma\) . We used intracellular flow cytometry to detect phosphorylation of STAT1 on Tyrosine- Y701 following stimulation with a range of doses of recombinant murine \(\mathsf{IFN}\gamma\) . We observed an enhanced response to \(\mathsf{IFN}\gamma\) in \(\mathsf{YFP}^{+}\) nTreg from \(FYC^{+} / 112\) mice compared to \(\mathsf{YFP}^{+}\) nTreg from control \(FYC^{+} / \mathsf{mice}\) (Fig. 6a). \(\mathsf{YFP}^{+}\) eTreg showed a much lower response than naive \(\mathsf{YFP}^{+}\) Treg, which was comparable between genotypes except at the highest concentration. Significantly, \(\mathsf{YFP}^{+}\) nTreg from \(FYC^{+} / 112\) mice showed an enhanced response compared to \(\mathsf{YFP}^{- }\) nTreg from the same mouse indicating the effect was cell intrinsic (Supplementary Fig. 7a). Quantitation of the total amount of STAT1 in \(\mathsf{YFP}^{+}\) FOXP3+ cells in female \(FYC^{+} / 112\) and \(FYC^{+}\) mice confirmed this was not different (Fig. 6b and Supplementary Fig. 7b). In addition, we examined the response to IL- 6, which also promotes STAT1 Y701 phosphorylation, and found no increase in STAT1 phosphorylation between \(\mathsf{YFP}^{+}\) Treg from control \(FYC^{+}\) and \(FYC^{+} / 112\) mice following in vitro stimulation with a range of doses (Fig. 6c and Supplementary Fig. 7c). Thus, the limiting effects of ZFP36L1 and ZFP36L2 on STAT1 phosphorylation were specific to the \(\mathsf{IFN}\gamma\) pathway and indicate these RBP restrain \(\mathsf{IFN}\gamma\) signaling in Treg in a cell intrinsic manner.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 732, 580, 751]]<|/det|>
+## Activated phenotype of Treg from \(FYC / 112\) mice
+
+<|ref|>text<|/ref|><|det|>[[115, 756, 877, 899]]<|/det|>
+To explore the heterogeneity of Treg and gain further insight into how ZFP36L1 and ZFP36L2 regulate Treg function in an inflammatory environment we performed single- cell sequencing of RNA (scRNA- seq) on Treg sorted from the peripheral LN of male \(FYC\) and \(FYC / 112\) mice (Supplementary Fig. 8a). We analyzed high quality transcriptomes of 5824 cells from \(FYC\) mice and 4163 cells from \(FYC / 112\) mice. Using a graph- based clustering approach Treg were grouped into eight
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 82, 880, 548]]<|/det|>
+subpopulations and represented using a uniform manifold approximation and projection (UMAP) for dimensionality reduction (Fig. 7a). Using gene sets derived from a comparison of naïve and effector Treg transcriptomes (Supplementary Table 6) we applied the Semi- supervised Category Identification and Assignment (SCINA) algorithm \(^{42}\) to assign cell type identities. We found that cells in clusters 0, 2 and 5 were frequently classified as nTreg, whereas clusters 3, 4 and 7 were primarily comprised of eTreg (Fig. 7a,b and Supplementary Fig. 8b). Differential gene expression analysis identified markers for each cluster except for cluster 1, which did not show enrichment for any distinctive genes (Supplementary Table 7). The four most frequently detected genes in each cluster in comparison to every other cluster are shown (Fig. 7c), further illustrating that clusters 0, 2 and 5 exhibited genes typical of nTreg (e.g., Sell, S1pr1). Genes characteristic of eTreg (e.g. Icos, Maf) were not detected or lowly expressed in clusters 0, 2 and 5, but frequently detected in clusters 3, 4 and 7. Cells in cluster 7 expressed markers characteristic of effector and highly proliferative cells, including Mki67 and histone genes, in addition to a higher number of genes, (Supplementary Fig. 8c) suggestive of a highly proliferative population. Thus, the individual clusters could broadly be distinguished by characteristic marker expression with a distinct distribution corresponding to naïve and effector Treg subtypes.
+
+<|ref|>text<|/ref|><|det|>[[115, 575, 876, 894]]<|/det|>
+The distribution of clusters of Treg from FYC and FYC I/12 mice was not equivalent. Treg from FYC I/12 mice represented only \(20\%\) of cells in cluster 0 and \(15\%\) in cluster 2, whereas \(80\%\) of Tregs in cluster 4 were represented by FYC I/12 Treg (Fig. 7d). As we had found that ZFP36L1 and ZFP36L2 limit Treg sensitivity to IFNγ, we investigated genes characteristic of the IFNγ response (defined in Supplementary Table 8). We used the SCINA algorithm to assign cell type identities in the scRNA- seq data and found a higher proportion of Treg from FYC I/12 mice across most clusters associated with an IFNγ gene signature (Fig. 7e). Activity of the IFNγ signaling pathway is necessary for the differentiation of CXCR3⁺ Tregs, thus we examined expression of Cxcr3 and other effector molecules and found enrichment of Cxcr3 in clusters 3 and 4 (Fig. 7f). In addition, Gata3 and Pdcd1 (encoding PD- 1), which is expressed by Treg during activation, were also most frequently detected in cluster 4 (Fig. 7h), which is over- represented in FYC I/12 Treg. Consistent with these
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 881, 277]]<|/det|>
+observations, flow cytometry revealed an increase in the proportion (Fig. 7i) and number of CXCR3+ Treg (Supplementary Fig. 8d) compared to control mice. GATA3hi Treg and YFP+CXCR5+PD- 1+ T follicular regulatory (Tfr) cells were also increased in proportions (Fig. 7j, k) and numbers (Supplementary Fig. 8d), in FYC 1/12 mice compared to control mice. Although we found a three- fold reduction in the proportion of RORyt+ Treg in FYC 1/12 mice compared to controls there was no difference in cell number (Supplementary Fig. 8e) indicating these cells are unable to control the influx of inflammatory cells in the intestine.
+
+<|ref|>text<|/ref|><|det|>[[115, 308, 870, 706]]<|/det|>
+Consistent with the increased proportion of CXCR3+ and GATA3+ Treg and the decreased proportion of RORyt+ Treg in FYC 1/12 mice, stimulation of splenocytes from male FYC 1/12 mice revealed increased frequencies of Tregs producing IFNy, IL- 4 and IL- 10 and a reduced proportion producing IL- 17 (Fig. 7l). Analysis of the gMFI of these cytokines revealed that Treg from FYC 1/12 mice produce marginally more IFNy (1.3- fold) and less IL- 17 (1.7- fold) compared to Treg from FYC mice, whilst no difference was found in the production of IL- 4 or IL- 10 (Supplementary Fig. 8f). FOXP3- CD4+ T cells were also enriched for IFNy, IL- 4 and IL- 10- positive cells (Fig. 7l) and produced more IL- 10 (Supplementary Fig. 8f). Therefore, the inflammatory environment in FYC 1/12 mice was not a result of a deficiency of IL- 10. Moreover, we found three times more CD8+ T cells producing IFNy in FYC 1/12 mice with the production of IFNy by these cells also increased (1.6- fold) (Supplementary Fig. 8g). Thus, the expanded CXCR3+ and GATA3+ Treg subsets in FYC 1/12 mice are unable to limit the expansion of activated CD4 and CD8 T cells which produce cytokines that may contribute to the loss of immune homeostasis in FYC 1/12 mice.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 740, 675, 759]]<|/det|>
+## IFNy is a driving force for the expansion of effector T cells
+
+<|ref|>text<|/ref|><|det|>[[115, 765, 864, 916]]<|/det|>
+The enhanced sensitivity of 1/12- deficient Treg to IFNy together with the increased number of Treg showing an IFNy signature in the scRNAseq and the increased proportion of Treg cells producing IFNy, suggested that ZFP36L1 and ZFP36L2 act in Treg to regulate the IFNy signaling axis. The production of IFNy by Treg and their responsiveness to it are essential for immune homeostasis, and in vivo IFNy can mediate both pro- and anti- inflammatory processes. Thus, we sought to test the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[110, 78, 880, 630]]<|/det|>
+physiological role of IFN \(\gamma\) , while avoiding complications arising from a complete absence of IFN \(\gamma\) , by generating FYC 1112 mice heterozygous for Ifng. The majority of Ifng \(^{+/ - }\) FYC 1112 mice were healthy, with only one mouse from 23 that developed skin inflammation, compared to ten out of 45 FYC 1112 mice developing clinical symptoms which exceeded the severity limit (marked piloerection and intermittent hunched posture, Fig. 8a). FYC 1112 mice had elevated levels of IFN \(\gamma\) , TNF \(\alpha\) , IL- 2, IL- 6 and IL- 10 in the serum compared to FYC control mice, however, the amounts of these cytokines were reduced in Ifng \(^{+/ - }\) FYC 1112 compared to FYC 1112 mice, with none maintaining a significant increase relative to FYC controls (Fig. 8b). The increased number of effector cells in the Treg, CD44 \(^{hi}\) CD62L \(^{lo}\) CD4 \(^{+}\) YFP \(^+\) , CD44 \(^{hi}\) CD62L \(^{hi}\) and CD44 \(^{hi}\) CD62L \(^{lo}\) CD8 \(^{+}\) subsets in FYC 1112 mice was also diminished by loss of one Ifng allele but remained two- to three- fold higher than in FYC control mice in each subset (Fig. 8c). The number of Tfh, Tfr and GC B cells in FYC 1112 mice was significantly increased in comparison to the FYC controls, but these numbers were reduced in Ifng \(^{+/ - }\) FYC 1112 mice, although remained four- fold higher in both Tfh and Tfr subsets (Fig. 8d,e), whilst the population of GC B cells remained ten- fold higher (Fig. 8f). Serum IgG2c and IgE levels were elevated in FYC 1112 mice compared to FYC controls. In Ifng \(^{+/ - }\) FYC 1112 mice the amount of IgG2c was reduced to that found in control mice (Fig. 8g). However, the concentrations of IgE were still higher (60- fold) in Ifng \(^{+/ - }\) FYC 1112 mice relative to FYC control mice, which correlated with the persistence of an elevated number of GC B cells (Fig. 8g). Thus, these data indicate that IFN \(\gamma\) is a driving force underpinning a complex phenotype in FYC 1112 mice.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 657, 230, 674]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[117, 680, 874, 822]]<|/det|>
+All three ZFP36 family paralogues can be expressed by T cells, and, in the absence of infection or inflammation, ZFP36L1 is the most abundant in Tregs and exerts non- redundant essential functions that are compensated partially by ZFP36L2. The ZFP36 family is a well- established regulator of cytokines, but in Tregs these RBP additionally regulate large numbers of genes that control pathways required by the Treg to maintain immune homeostasis.
+
+<|ref|>text<|/ref|><|det|>[[118, 853, 846, 895]]<|/det|>
+Tregs lacking Zfp36l1 and Zfp36l2 failed to prevent the expansion of cDC2, GC B cells and effector CD8 T cells. As interactions between cDC2 and Tfh support Tfh
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 81, 872, 275]]<|/det|>
+priming and GC B responses \(^{43,44}\) , and cDC2 can cross- prime CD8 T cells \(^{45}\) the increased numbers and elevated expression of CD80 and CD86 on cDC2 could be driving the expansion of activated lymphocytes in \(FYC 1 / 12\) mice. The compromised ability of nTreg to limit costimulation may arise, in part, from defective CTLA- 4 cycling. IL- 2 signaling also positively impacts upon Treg CTLA- 4 function \(^{40}\) and was impaired in \(Zfp36 / 1\) and \(Zfp36 / 2\) - deficient Tregs. Furthermore, IL- 2 sensitivity is diminished in CD8 T cells lacking \(Zfp36 / 1\) suggesting ZFP36L1 connects antigen affinity to IL- 2 responsiveness \(^{25}\) .
+
+<|ref|>text<|/ref|><|det|>[[112, 303, 880, 595]]<|/det|>
+Although IL- 2 signaling is essential for Treg survival and function \(^{46,47}\) , when deprived of this cytokine IL- 7 can sustain Tregs and contribute to Treg homeostasis \(^{47,48}\) . Mice with conditional deletion of \(I / 7a\) in Tregs did not develop autoimmune disease, but IL- 7R on Tregs was important to maintain allograft tolerance in a Treg transfer model \(^{49}\) and IL- 7 promotes eTreg survival in the skin \(^{50}\) . In Treg we found that ZFP36L1 and ZFP36L2 promote sensitivity to both IL- 2 and IL- 7. This may account for the reduction in number of \(icre\) - expressing Treg in female mice heterozygous for \(icre\) , where these cells are in competition for these cytokines. As the development of Tfr has been reported to be inhibited by IL- 2 \(^{51,52}\) , a defect in IL- 2 signaling would be accompanied by expansion of Tfr as we observe in \(FYC 1 / 12\) mice. The accumulation of Tfh and GC B cells may also be augmented by the increased availability of IFN \(\gamma\) \(^{53}\) .
+
+<|ref|>text<|/ref|><|det|>[[113, 626, 880, 750]]<|/det|>
+\(Zfp36 / 1\) and \(Zfp36 / 2\) also specifically limit Treg sensitivity to IFN \(\gamma\) . Whilst Th1- like Tregs can be potent suppressors of the activity, proliferation and memory formation of CD8 effector T cells \(^{24}\) and IFN \(\gamma\) - mediated STAT1 activation in Tregs can promote Treg function in alloantigen tolerized mice \(^{22}\) , IFN \(\gamma\) can also promote Treg “fragility” or lineage instability in the tumor microenvironment \(^{23}\) .
+
+<|ref|>text<|/ref|><|det|>[[113, 778, 869, 902]]<|/det|>
+The ability of ZFP36- family members to repress IFN \(\gamma\) expression did not manifest as increased amounts of IFN \(\gamma\) produced by ex vivo stimulated Tregs but was apparent as a greater frequency of IFN \(\gamma\) producing Tregs. The capacity for ZFP36L1 and ZFP36L2 in Tregs to interconnect the IL- 2, IFN \(\gamma\) and CTLA- 4 pathways and enforce their function, whilst dampening their function in effector CD4 and CD8 T cells may
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 794, 128]]<|/det|>
+be relevant to the association of the genes encoding this family of RBP with autoimmune diseases 2.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 157, 350, 176]]<|/det|>
+## Limitations of the study
+
+<|ref|>text<|/ref|><|det|>[[115, 181, 880, 473]]<|/det|>
+These phenotypes were not evident in mice with deletion of ZFP36 family proteins using Cd4- cre which, taken together with the specific deletion, argues that the phenotypes arise from the function of ZFP36L1 and ZFP36L2 in Treg. We have focussed on Treg in the absence of intentional immune challenge, and it is unclear how Treg deficient in these RBP respond to activation and how this affects transcriptomes, cell function and the physiology of the mice. The compendium of iCLIP targets is from CD4 and CD8 T cells, it is possible some mRNAs unique to Treg were not detected. In addition to regulating RNA stability ZFP36L1 and ZFP36L2 can also repress translation 12,54 and may regulate protein localization, thus the use of sensitive proteomics methods could reveal additional direct and indirect targets regulated by the RBP. The detailed mechanism of how the RBP regulate CTLA- 4 and cytokine signalling in Treg remain to be elucidated.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 551, 204, 568]]<|/det|>
+## Methods
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 577, 166, 593]]<|/det|>
+## Mice
+
+<|ref|>text<|/ref|><|det|>[[115, 599, 878, 890]]<|/det|>
+Mice were engineered to express the fluorescent proteins mAmetrine or mCherry upstream and in frame with the start codons of Zfp36 or Zfp36l1 respectively 25. The targeting vector for Zfp36l2 was designed to encode eGFP upstream and in frame with the ATG translation start site of ZFP36L2 (Cyagen, Santa Clara, CA, USA). The reporter mice were healthy and fertile (and used for breeding up to 40 weeks of age). Zfp36l/l (Zfp36tm1Tnr), Zfp36l1/l (Zfp36l1tm1.1Tnr) and Zfp36l2/l/l (Zfp36l2tm1.1Tnr) mice have been described previously 28,55 and were maintained on a C57BL/6J background. The following alleles on the C57BL/6J background (obtained from the Jackson Laboratory) were also used: B6.129(Cg)- Foxp3tm4(YFP/ice)Ayr/J; Jax stock #016959); and B6.129S7- IFNgtm1Ts (Jax stock #002287). For the experiments shown in Fig. 8, the cohort of FYC 1112 and Ifng+/- FYC1112 mice that were analyzed had not been backcrossed to C57BL/6 for seven generations. Any animals which displayed
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 848, 127]]<|/det|>
+the limiting clinical signs of marked piloerection and intermittent hunched posture, and/or abdominal distension were humanely killed.
+
+<|ref|>text<|/ref|><|det|>[[115, 156, 875, 448]]<|/det|>
+Mice were bred and maintained in the Babraham Institute Biological Support Unit. No primary pathogens or additional agents listed in the FELASA recommendations have been confirmed during health monitoring surveys of the stock holding rooms. Ambient temperature was \(\sim 19 - 21^{\circ}C\) and relative humidity \(52\%\) . Lighting was provided on a 12- hour light: 12- hour dark cycle including 15 min 'dawn' and 'dusk' periods of subdued lighting. After weaning, mice were transferred to individually ventilated cages with 1- 5 mice per cage. Mice were fed CRM (P) VP diet (Special Diet Services) ad libitum and received seeds (e.g., sunflower, millet) at the time of cage cleaning as part of their environmental enrichment. All mouse experimentation was approved by the Babraham Institute Animal Welfare and Ethical Review Body. Animal husbandry and experimentation complied with European Union and United Kingdom Home Office legislation.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 532, 270, 550]]<|/det|>
+## Flow cytometry
+
+<|ref|>text<|/ref|><|det|>[[115, 555, 875, 894]]<|/det|>
+Single cell suspensions were prepared from the spleen, peripheral lymph nodes (LN, axillary, brachial, cervical and inguinal) and mesenteric LN (mLN), with antibody staining for surface markers performed essentially as described previously including Fc block (2.4G2) in PBS/2% FCS/2mM EDTA. Dead cells were excluded using fixable viability dye eFluor780 (eBioscience). A full list of antibodies used is provided in Supplementary Table S9. An antibody against GFP (clone FM264G, BioLegend) was used for intracellular detection of YFP which is fused to cre in Foxp3YFP- icre mice. For detection of phospho- antibodies, the cells were fixed in neutral buffered formalin (Sigma) diluted in PBS to 2% for 30 min at room temperature, pelleted by centrifugation and cells were resuspended in ice- cold 90% methanol, incubated for 30 minutes on ice, washed twice, then incubated with the antibody cocktail containing 2.4G2 antibody overnight at 4°C. For dendritic cell isolation, LN tissue was finely minced then digested with collagenase P (Merck, 1mg/ml in RPMI 2% FCS) for 40 minutes at 37°C with agitation, then EDTA added to
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 83, 860, 127]]<|/det|>
+5mM, clumps dispersed using pipetting and the cell suspension filtered. Single cell suspensions were washed and stained as described.
+
+<|ref|>text<|/ref|><|det|>[[115, 156, 875, 475]]<|/det|>
+For ex vivo analysis of pSTAT5 LN cell suspensions were prepared directly into fixation buffer from eBioscience™ Foxp3 / Transcription Factor Staining Buffer Set. For intracellular cytokine detection, LN cells were stimulated for 4 hours at \(37^{\circ}C\) with \(10\mathrm{ng / ml}\) Phorbol- 12- myristate- 13- acetate (PMA; 524400, Merck) and \(500\mathrm{ng / ml}\) ionomycin (407952, Merck) in the presence of \(5\mu \mathrm{g / ml}\) Brefeldin A (eBioscience) in complete IMDM medium (Invitrogen; containing \(10\%\) FBS, 2mM Glutamax, 25mM HEPES, \(50\mu \mathrm{M}2\) - mercaptoethanol). Cells were fixed with \(2\%\) PFA for 30 minutes at room temperature, washed twice with Foxp3 permeabilization buffer (eBioscience) and incubated with the antibody cocktail containing 2.4G2 antibody overnight at \(4^{\circ}C\) . For transcription factor staining, Foxp3 fixation buffer was used according to the manufacturer's instructions. Acquisition was performed on a Fortessa flow cytometer equipped with 355 nm, 405 nm, 488 nm, 561 nm and 640 nm lasers (Beckton Dickinson) and the data were analyzed using FlowJo software (v10).
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 530, 389, 548]]<|/det|>
+## In vitro cytokine stimulation
+
+<|ref|>text<|/ref|><|det|>[[115, 554, 864, 650]]<|/det|>
+Splenocytes were cultured for 30 minutes at \(37^{\circ}C\) with a range of doses of recombinant murine cytokines (all from Peptidech) \(\mathrm{IFN}\gamma\) (# 315- 05) IL- 6 (# 216- 12), IL- 2 (# 212- 12) IL- 7 (# 217- 17) in the presence of eF780 viability dye and \(150\mu \mathrm{M}\) TAPI- 0 (Tocris # 5523) in complete IMDM medium.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 680, 406, 698]]<|/det|>
+## Ex vivo CTLA-4 cycling assay
+
+<|ref|>text<|/ref|><|det|>[[115, 703, 880, 898]]<|/det|>
+Following red blood cell lysis with Tris- ammonium chloride, \(\mathrm{CD4^{+}}\) T cells were isolated from spleen by depletion of \(\mathrm{CD8^{+}}\) , \(\mathrm{CD11b^{+}}\) \(\mathrm{CD11c^{+}}\) , MHCII+ and \(\mathrm{B220^{+}}\) cells using biotinylated antibodies and M- 280 Streptavidin Dynabeads. \(\mathrm{CD4^{+}}\) T cells were cultured for 2 hours at \(37^{\circ}C\) in the presence of TAPI- 0 ( \(100\mu \mathrm{M}\) ) and \(2\mathrm{ng / ml}\) IL- 2. APC conjugated anti- CD152 (CTLA- 4) antibody (clone UC10- 4F10- 11) was added to the cells to detect cycling CTLA- 4. Surface CTLA- 4 was detected by labelling cells with APC conjugated anti- CD152 for 30 minutes at \(4^{\circ}C\) , and total CTLA- 4 detected after fixation and permeabilization with antibody incubation overnight at \(4^{\circ}C\) .
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 110, 213, 128]]<|/det|>
+## Histology
+
+<|ref|>text<|/ref|><|det|>[[117, 133, 881, 202]]<|/det|>
+For histology, tissue samples were collected into \(10\%\) neutral buffered formalin (Sigma). Preparation of slides, H&E staining, pathology and interpretation was performed by Abbey Veterinary Services UK.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 231, 647, 250]]<|/det|>
+## Measurement of Serum cytokines and Immunoglobulin
+
+<|ref|>text<|/ref|><|det|>[[117, 255, 864, 350]]<|/det|>
+Serum was collected from mice by cardiac puncture. Serum cytokines were measured using the MSD pro- inflammatory panel 1. IgG2c and IgE were measured by ELISA using paired antibody sets (IgG2c, Southern Biotech and IgE, BD Biosciences) according to the manufacturer's protocol.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 404, 356, 423]]<|/det|>
+## Cell Sorting for RNA seq
+
+<|ref|>text<|/ref|><|det|>[[117, 428, 878, 571]]<|/det|>
+Single cell suspensions were prepared from pooled spleen and peripheral LN (inguinal, brachial, axillary and cervical) from six \(FYC^{+}11 / 2\) and seven \(FYC^{+} \text{mice}\) at 7- 14 weeks of age. CD4+ cells were enriched by negative depletion using biotinylated anti- B220, anti- CD8 and anti- CD11b followed by Streptavidin Dynabeads (Dynal). Naive Treg were sorted as CD4+CD25+ CD62L+ YFP+ cells. All samples were sorted to \(>95\%\) purity.
+
+<|ref|>text<|/ref|><|det|>[[117, 600, 878, 694]]<|/det|>
+For RNA- seq libraries used to identify markers of naive and effector Treg, cells were prepared as above from male \(Zfp36 / 1^{f / f} I2^{f / f}\) control mice, aged 9- 12 weeks, but with naive Treg sorted as CD4+CD25+CD62L+CD44+ and effector Treg as CD4+CD25+CD62L- CD44+ cells.
+
+<|ref|>text<|/ref|><|det|>[[117, 723, 877, 840]]<|/det|>
+To sort Tregs for single cell RNA seq single cell suspensions were prepared from pooled LN from one mouse of each genotype at 14 weeks of age. CD4+ cells were enriched by negative depletion using biotinylated anti- B220, anti- CD8 and anti- F4/80 followed by Streptavidin Dynabeads (Dynal). Treg were sorted as CD4+FR4+ YFP+ cells. All samples were sorted to \(>95\%\) purity.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 84, 256, 102]]<|/det|>
+## Bulk RNA-seq
+
+<|ref|>text<|/ref|><|det|>[[115, 108, 870, 225]]<|/det|>
+RNA was prepared from sorted Treg cells using the RNeasy Micro kit (Qiagen) as described \(^{56}\) and quality was assessed using the Bioanalyzer RNA chip. cDNA was generated using SMART seq v4 low input RNA kit. RNA- seq libraries were prepared from cDNA using the Nextera XT kit. Libraries were sequenced using a 50bp single end RapidRun on the Illumina HiSeq2500.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 256, 232, 273]]<|/det|>
+## ScRNA-seq
+
+<|ref|>text<|/ref|><|det|>[[115, 280, 864, 499]]<|/det|>
+Cells were labelled using Totalseq oligo- conjugated antibodies (BioLegend) to enable multiplexing of control (hashtag 1: ACCCACCAGTAAGAC) and conditional knockout (hashtag 2: GGTCGAGAGCATTCA) samples, and feature barcoding of CD127 (IL7- Rα; GTGTGAGGCACTCTT). The sorted single cell suspensions were mixed and loaded onto a Chromium single cell device (10x Genomics) for encapsulation with barcoded gel beads according to the manufacturer's Single Cell 3' v3.1 (Dual Index) protocol. 3'GEX and 3' Feature barcoding libraries were prepared according to the standard manufacturer's protocol. The resulting libraries were sequenced on an Illumina NovaSeq 6000 S1 (paired end 150bp).
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 528, 336, 546]]<|/det|>
+## Bioinformatic analysis
+
+<|ref|>text<|/ref|><|det|>[[115, 551, 877, 891]]<|/det|>
+Quality of sequencing data was assessed using FastQC (http://www.bioinformatics.babraham.ac.uk/projects/fastqc/). Reads were trimmed for adapters and low quality base calls using Trim Galore, with default parameters (v0.6.5; https://www.bioinformatics.babraham.ac.uk/projects/trim_galore/). Reads were then mapped to the GRCm38 mouse reference genome using Hisat2 (v2.1.0; \(^{57}\) . BAM files were imported into Seqmonk (v1.47.0; http://www.bioinformatics.babraham.ac.uk/projects/seqmonk/), excluding those with mapping quality \(< 30\) , and reads were quantified over merged mRNA isoforms from the GRCm38 v90 annotation, using the RNA- seq quantitation pipeline. Reads were also quantified specifically over the regions flanked by lox- P sites in Zfp36/1 and Zfp36/2. Differential expression analysis comparing cKO with control samples was performed using DESeq2 (v1.22.2) \(^{58}\) , using 'normal' log2 fold change shrinkage, and genes designated differentially expressed if their FDR- adjusted p value was \(< 0.05\) . Gene set enrichment analysis \(^{59}\) was performed using the GSEAPreranked module
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 78, 870, 675]]<|/det|>
+of the GenePattern software package \(^{60}\) , with default parameters except that 'collapse dataset' was set to 'No_collapse'. Genes were ranked based on log10 of their raw p value from DESeq2 analysis, with a positive sign assigned to genes with a positive \(\log_2\) fold change, such that the most significantly increased genes are ranked first, and the most significantly decreased are ranked last. Custom gene sets were uploaded for the analysis: the Hallmark apoptosis gene set was obtained from MSigDB \(^{61}\) and gene names converted to mouse orthologues using biomaRt \(^{62}\) whilst the TCR signaling pathway gene set was curated manually (see Supplementary Table 4). Genes increased or decreased in Treg upon IL- 2 or IL- 7 treatment were identified using publicly available ImmGen common \(\gamma\) - chain cytokine RNA-seq data (GSE180020) \(^{33}\) , processed as above to compare cytokine- with PBS- treated Treg. Increased/decreased genes were defined as those with FDR- adjusted p value < 0.05, and absolute \(\log_2\) - fold change > 1, except for genes increased upon IL- 7 treatment where a \(\log_2\) - fold change threshold of 0.7 was used to ensure a gene list of appropriate size for GSEA analysis. For \(\mathrm{IFN}\gamma\) treatment, microarray data of iTreg treated for 10h, compared with neutral conditions, was used (GSE38686, \(^{63}\) ). Conditions were compared using GEO2R and increased/decreased genes defined as those with FDR- adjusted p value < 0.05. Normalised read counts for the top 15 most significantly increased TCR signaling genes were \(\log_2\) transformed, and the mean transformed read count across all replicates for a given gene was subtracted. Genes were ranked based on their adjusted p value. A heatmap was plotted using the heatmap R package, with a threshold set on the fill color such that values above/below the maximum/minimum threshold were assigned the maximum/minimum colors in the scale.
+
+<|ref|>text<|/ref|><|det|>[[115, 695, 880, 813]]<|/det|>
+To generate lists of genes characteristic of naive and effector Tregs (Table S6), RNA- seq data from control nTreg and eTreg were compared as described above, and naive and effector markers were defined as genes with FDR- adjusted p value < 0.0001, and \(\log_2\) - fold change in eTreg compared with nTreg < - 1.5 or > 2, respectively.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 843, 316, 861]]<|/det|>
+## ScRNA-seq analysis
+
+<|ref|>text<|/ref|><|det|>[[115, 867, 874, 911]]<|/det|>
+Since the feature barcoding libraries contained both multiplexing and CD127 tags, the fastq files were first split based on whether an exact match to one of the hashtag
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[110, 80, 881, 770]]<|/det|>
+oligos for multiplexing was found starting in position 11 in the "R2" feature barcoding fastq file. The separated multiplexing and antibody- derived tag fastq files, together with the gene expression fastq files, were then processed using Cell Ranger v6.1.2, first with cellranger multi, using the GRCm38 mouse genome reference, followed by aggregation of the control and knockout data from the per sample outputs, using cellranger aggr. Further analysis was performed using the Seurat package \(^{64}\) Cells containing below 1500 and over 14000 molecule counts for either hashtag 1 or hashtag 2 oligo conjugated antibodies were removed to filter out putative empty droplets, or doublets respectively. Additionally, cells containing over \(5.5\%\) mitochondria- derived gene expression reads, over \(10\%\) reads originating from a single gene, or in which fewer than 1000 or more than 4200 genes were detected were removed. After filtering for quality, we compared the transcriptomes of 5824 cells from FYC mice and 4163 cells from FYC I/12 mice. Normalization was performed using the centred log ratio transformation, across cells (margin 2). The top 500 variable genes were identified, and these were scaled and used as input for principal component analysis. The top 15 principal components were then used as input for Seurat's graph- based clustering approach (FindNeighbors followed by FindClusters functions; resolution 0.5; all other parameters default). These 15 principal components were also used as input to RunUMAP for further dimensionality reduction and data visualization. To identify cluster- specific marker genes the FindMarkers function was used, only considering genes detected in at least \(25\%\) of cells in at least one group for a given comparison; significantly enriched or depleted genes for each cluster are listed in Supplementary Table 7. The SCINA package was used to assign cell type identities based on previous knowledge related to naïve/effector cells (using the gene list in Supplementary Table 6). Genes associated with an Ifng signaling signature are listed in Supplementary Table 8; this was based on conversion of the human Reactome Interferon Gamma Signaling pathway genes to mouse orthologues.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 816, 536, 835]]<|/det|>
+## Identification of direct ZFP36-family targets
+
+<|ref|>text<|/ref|><|det|>[[118, 840, 868, 908]]<|/det|>
+HITS- CLIP data for ZFP36- family proteins in \(\mathrm{CD4^{+}}\) T cells following 4h activation, or 72h activation with 2h reactivation, were obtained from GSE96074 \(^{5}\) iCLIP data for ZFP36L1 in \(\mathrm{CD4^{+}}\) T cells activated for 24h with anti- CD3 and anti- CD28 was
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 82, 880, 202]]<|/det|>
+obtained from GSE155087 \(^{6}\) . All data was analyzed using the iCount pipeline \(^{65}\) on the Genialis platform; for iCLIP data the replicates for each antibody were merged. A gene was designated a target if the 3'UTR contained a significant crosslink site (FDR \(< 0.05\) ) with both antibodies in the iCLIP, or if a crosslink site in the 3'UTR was identified in at least two replicates for either of the HITS- CLIP datasets.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 232, 301, 250]]<|/det|>
+## Statistical analysis
+
+<|ref|>text<|/ref|><|det|>[[118, 255, 830, 300]]<|/det|>
+Statistical significance was determined using GraphPad Prism v9 using the test indicated in the respective Figure legends.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 330, 410, 348]]<|/det|>
+## Data and Materials Availability
+
+<|ref|>text<|/ref|><|det|>[[118, 353, 864, 398]]<|/det|>
+The RNA- seq data are available in the Gene Expression Omnibus (GEO) database (https://www.ncbi.nlm.nih.gov/geo/) under accession code GSE244621.
+
+<|ref|>text<|/ref|><|det|>[[117, 419, 816, 513]]<|/det|>
+Mice with modified alleles of Zfp36, Zfp36l1 and Zfp36l2 are available under a material transfer agreement with The Babraham Institute. All data needed to evaluate the conclusions are presented in the paper or in the Supplementary Materials.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 544, 230, 561]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[112, 590, 874, 907]]<|/det|>
+1. Fu, M. & Blackshear, P. J. RNA-binding proteins in immune regulation: a focus on CCCH zinc finger proteins. Nat. Rev. Immunol. 17, 130–143 (2016).
+2. Makita, S., Takatori, H. & Nakajima, H. Post-Transcriptional Regulation of Immune Responses and Inflammatory Diseases by RNA-Binding ZFP36 Family Proteins. Front. Immunol. 12, 711633 (2021).
+3. Keene, J. D. RNA regulators: coordination of post-transcriptional events. Nat Rev Genet 8, 533 543 (2007).
+4. Zhu, W. S., Wheeler, B. D. & Ansel, K. M. RNA circuits and RNA-binding proteins in T cells. Trends Immunol. 44, 792–806 (2023).
+5. Moore, M. J. et al. ZFP36 RNA-binding proteins restrain T-cell activation and antiviral immunity. Elife 7, e33057 (2018).
+6. Petkau, G. et al. The timing of differentiation and potency of CD8 effector function is set by RNA binding proteins. Nat. Commun. 13, 2274 (2022).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 60, 884, 920]]<|/det|>
+7. Wang, Q. et al. Tristetraprolin inhibits macrophage IL-27-induced activation of antitumour cytotoxic T cell responses. Nat Commun 8, 867 (2017).
+8. Peng, H. et al. Tristetraprolin Regulates TH17 Cell Function and Ameliorates DSS-Induced Colitis in Mice. Front Immunol 11, 1952 (2020).
+9. Cook, M. E. et al. The ZFP36 family of RNA binding proteins regulates homeostatic and autoreactive T cell responses. Sci. Immunol. 7, eabo0981 (2022).
+10. Matheson, L. S. et al. Multiomics analysis couples mRNA turnover and translational control of glutamine metabolism to the differentiation of the activated CD4+ T cell. Sci Rep-uk 12, 19657 (2022).
+11. Popović, B. et al. Time-dependent regulation of cytokine production by RNA binding proteins defines T cell effector function. Cell Reports 42, 112419 (2023).
+12. Salerno, F. et al. Translational repression of pre-formed cytokine-encoding mRNA prevents chronic activation of memory T cells. Nat Immunol 19, 828-837 (2018).
+13. Zandhuis, N. D. et al. Regulation of IFN-γ production by ZFP36L2 in T cells is time-dependent. Eur. J. Immunol. (2024) doi:10.1002/eji.202451018.
+14. Xu, B. et al. Regulated Tristetraprolin Overexpression Dampens the Development and Pathogenesis of Experimental Autoimmune Uveitis. Front Immunol 11, 583510 (2021).
+15. Makita, S. et al. RNA-Binding Protein ZFP36L2 Downregulates Helios Expression and Suppresses the Function of Regulatory T Cells. Front Immunol 11, 1291 (2020).
+16. Stoecklin, G. et al. Genome-wide analysis identifies interleukin-10 mRNA as target of tristetraprolin. J Biol Chem 283, 11689 11699 (2008).
+17. Tudor, C. et al. The p38 MAPK pathway inhibits tristetraprolin-directed decay of interleukin-10 and pro-inflammatory mediator mRNAs in murine macrophages. Febs Lett 583, 1933 1938 (2009).
+18. Coelho, M. A. et al. Oncogenic RAS Signaling Promotes Tumor Immunoresistance by Stabilizing PD-L1 mRNA. Immunity 47, 1083 1099.e6 (2017).
+19. Sakaguchi, S. et al. Regulatory T Cells and Human Disease. Annu Rev Immunol 38, 1-26 (2020).
+20. Dikiy, S. & Rudensky, A. Y. Principles of regulatory T cell function. Immunity 56, 240-255 (2023).
+21. Georgiev, P. et al. Regulatory T cells in dominant immunologic tolerance. J. Allergy Clin. Immunol. 153, 28-41 (2024).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 60, 880, 920]]<|/det|>
+766 22. Sawitzki, B. et al. IFN- \(\gamma\) production by alloantigen-reactive regulatory T cells is important for their regulatory function in vivo. J Exp Medicine 201, 1925- 1935 (2005). 769 23. Overacre- Delgoffe, A. E. et al. Interferon- \(\gamma\) Drives Treg Fragility to Promote Antitumor Immunity. Cell 169, 1130- 1141. e11 (2017). 771 24. Gocher- Demske, A. M. et al. IFN- \(\gamma\) - induction of TH1- like regulatory T cells controls antiviral responses. Nat. Immunol. 24, 841- 854 (2023). 773 25. Petkau, G. et al. Zfp3611 establishes the high- affinity CD8 T- cell response by directly linking TCR affinity to cytokine sensing. Eur. J. Immunol. 54, 2350700 (2024). 776 26. Moran, A. E. et al. T cell receptor signal strength in Treg and iNKT cell development demonstrated by a novel fluorescent reporter mouse. J Exp Medicine 208, 1279 1289 (2011). 779 27. Rubtsov, Y. P. et al. Regulatory T cell- derived interleukin- 10 limits inflammation at environmental interfaces. Immunity 28, 546 558 (2008). 781 28. Hodson, D. J. et al. Deletion of the RNA- binding proteins ZFP36L1 and ZFP36L2 leads to perturbed thymic development and T lymphoblastic leukemia. Nat Immunol 11, 717 724 (2010). 784 29. Galloway, A. et al. RNA- binding proteins ZFP36L1 and ZFP36L2 promote cell quiescence. Science 352, 453 459 (2016). 786 30. Bye- A- Jee, H. et al. The RNA- binding proteins Zfp36l1 and Zfp36l2 act redundantly in myogenesis. Skeletal muscle 8, 37- 12 (2018). 788 31. Barthlott, T., Kassiotis, G. & Stockinger, B. T Cell Regulation as a Side Effect of Homeostasis and Competition. J Exp Medicine 197, 451- 460 (2003). 790 32. Kieper, W. C., Burghardt, J. T. & Surh, C. D. A role for TCR affinity in regulating naive T cell homeostasis. Journal of immunology (Baltimore, Md. : 1950) 172, 40 44 (2004). 793 33. Baysoy, A. et al. The interweaved signatures of common- gamma- chain cytokines across immunologic lineages. J. Exp. Med. 220, e20222052 (2023). 794 34. Wang, E. et al. Surface antigen- guided CRISPR screens identify regulators of myeloid leukemia differentiation. Cell Stem Cell 28, 718- 731. e6 (2021). 797 35. Charbonnier, L.- M., Wang, S., Georgiev, P., Sefik, E. & Chatila, T. A. Control of peripheral tolerance by regulatory T cell- intrinsic Notch signaling. Nat Immunol 16, 1162 1173 (2015).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 78, 870, 895]]<|/det|>
+36. Hasegawa, H. & Matsumoto, T. Mechanisms of Tolerance Induction by Dendritic Cells In Vivo. Front. Immunol. 9, 350 (2018).37. Ovcinnikovs, V. et al. CTLA-4-mediated transendocytosis of costimulatory molecules primarily targets migratory dendritic cells. Sci. Immunol. 4, eaaw0902 (2019).38. Guilliams, M. et al. Unsupervised High-Dimensional Analysis Aligns Dendritic Cells across Tissues and Species. Immunity 45, 669-684 (2016).39. Qureshi, O. S. et al. Constitutive Clathrin-mediated Endocytosis of CTLA-4 Persists during T Cell Activation. J. Biol. Chem. 287, 9429-9440 (2012).40. Jamison, B. L. et al. An IL-2 mutein increases IL-10 and CTLA-4-dependent suppression of dendritic cells by regulatory T cells. bioRxiv 2023.12.01.569613 (2023) doi:10.1101/2023.12.01.569613.41. Petkau, G. et al. Zfp36l1 establishes the high affinity CD8 T cell response by directly linking TCR affinity to cytokine sensing. bioRxiv 2023.05.11.539978 (2023) doi:10.1101/2023.05.11.539978.42. Zhang, Z. et al. SCINA: Semi-Supervised Analysis of Single Cells in Silico. Genes 10, 531 (2019).43. Krishnaswamy, J. K. et al. Migratory CD11b+ conventional dendritic cells induce T follicular helper cell-dependent antibody responses. Sci. Immunol. 2, (2017).44. Briseño, C. G. et al. Notch2-dependent DC2s mediate splenic germinal center responses. Proc. Natl. Acad. Sci. 115, 10726-10731 (2018).45. Si, Y. et al. Lung cDC1 and cDC2 dendritic cells priming naive CD8+ T cells in situ prior to migration to draining lymph nodes. Cell Rep. 42, 113299 (2023).46. Chinen, T. et al. An essential role for the IL-2 receptor in Treg cell function. Nat. Immunol. 17, 1322-1333 (2016).47. Fan, M. Y. et al. Differential Roles of IL-2 Signaling in Developing versus Mature Tregs. Cell Reports 25, 1204 1213.e4 (2018).48. Simonetta, F. et al. Interleukin-7 influences FOXP3+CD4+ regulatory T cells peripheral homeostasis. Plos One 7, e36596 (2012).49. Schmaler, M. et al. IL-7R signaling in regulatory T cells maintains peripheral and allograft tolerance in mice. Proc National Acad Sci 112, 13330 13335 (2015).50. Gratz, I. K. et al. Cutting Edge: memory regulatory t cells require IL-7 and not IL-2 for their maintenance in peripheral tissues. J Immunol 190, 4483 4487 (2013).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[55, 78, 870, 920]]<|/det|>
+51. León, B., Bradley, J. E., Lund, F. E., Randall, T. D. & Ballesteros-Tato, A. FoxP3+ regulatory T cells promote influenza-specific Tfh responses by controlling IL-2 availability. Nat Commun 5, 3495 (2014).52. Botta, D. et al. Dynamic regulation of T follicular regulatory cell responses by interleukin 2 during influenza infection. Nat Immunol 18, 1249 1260 (2017).53. Lee, S. K. et al. Interferon-γ excess leads to pathogenic accumulation of follicular helper T cells and germinal centers. Immunity 37, 880 892 (2012).54. Bell, S. E. et al. The RNA binding protein Zfp36l1 is required for normal vascularisation and post-transcriptionally regulates VEGF expression. Dev Dynam 235, 3144 3155 (2006).55. Newman, R. et al. Maintenance of the marginal-zone B cell compartment specifically requires the RNA-binding protein ZFP36L1. Nat. Immunol. 18, 683-693 (2017).56. Monzón-Casanova, E. et al. Polypyrimidine tract-binding proteins are essential for B cell development. Elife 9, (2019).57. Kim, D., Paggi, J. M., Park, C., Bennett, C. & Salzberg, S. L. Graph-based genome alignment and genotyping with HISAT2 and HISAT-genotype. Nat. Biotechnol. 37, 907-915 (2019).58. Love, M. I., Huber, W. & Anders, S. Moderated estimation of fold change and dispersion for RNA-seq data with DESeq2. Genome Biol. 15, 550 (2014).59. Subramanian, A. et al. Gene set enrichment analysis: A knowledge-based approach for interpreting genome-wide expression profiles. Proc. Natl. Acad. Sci. 102, 15545-15550 (2005).60. Reich, M. et al. GenePattern 2.0. Nat. Genet. 38, 500-501 (2006).61. Liberzon, A. et al. The Molecular Signatures Database Hallmark Gene Set Collection. Cell Syst. 1, 417-425 (2015).62. Durinck, S., Spellman, P. T., Birney, E. & Huber, W. Mapping identifiers for the integration of genomic datasets with the R/Bioconductor package biomaRt. Nat. Protoc. 4, 1184-1191 (2009).63. Hall, A. O. et al. The Cytokines Interleukin 27 and Interferon-γ Promote Distinct Treg Cell Populations Required to Limit Infection-Induced Pathology. Immunity 37, 511-523 (2012).64. Hao, Y. et al. Integrated analysis of multimodal single-cell data. Cell 184, 3573-3587. e29 (2021).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 81, 861, 130]]<|/det|>
+65. König, J. et al. iCLIP reveals the function of hnRNP particles in splicing at individual nucleotide resolution. Nat. Struct. Mol. Biol. 17, 909–915 (2010).
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 226, 316, 244]]<|/det|>
+## Acknowledgements:
+
+<|ref|>text<|/ref|><|det|>[[115, 250, 875, 441]]<|/det|>
+We thank Kirsty Bates for expert technical assistance and Oliver Burton for advice on flow cytometry; Fiamma Salerno and Marian Jones Evans for characterizing the reporter mice; and the Core Biochemical Assay Laboratory at Addenbrooke's Hospital for MSD analysis. We thank Georg Petkau and Arianne Richard for critical reading of the manuscript. We thank the UKRI-BBSRC Core Capability Grant funded Babraham Institute Biological Support Unit, Sequencing, Flow Cytometry and Bioinformatics Facilities for invaluable support.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 473, 207, 490]]<|/det|>
+## Funding:
+
+<|ref|>text<|/ref|><|det|>[[118, 496, 810, 565]]<|/det|>
+This study was funded by the BBSRC Institute strategic programme grants BBS/E/B/000C0427; BBS/E/B/000C0428 and a Wellcome Investigator award (200823/Z/16/Z) to M.T.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 571, 328, 588]]<|/det|>
+## Author contributions:
+
+<|ref|>text<|/ref|><|det|>[[118, 595, 549, 760]]<|/det|>
+Conceptualization: M.T. Methodology: B.S- N, S.E.B. Investigation: B.S- N, S.E.B, R.V. Data curation: B.S- N, L.S.M. Writing- original draft: B.S- N, S.E.B, L.S.M, M.T. Funding acquisition: M.T. Supervision: M.T.
+
+<|ref|>text<|/ref|><|det|>[[118, 767, 682, 785]]<|/det|>
+All authors contributed to reviewing and editing the manuscript.
+
+<|ref|>text<|/ref|><|det|>[[118, 790, 810, 809]]<|/det|>
+Competing interests: The authors declare they have no competing interests
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[120, 150, 884, 666]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[128, 77, 197, 94]]<|/det|>
+Figure 1
+
+<|ref|>image<|/ref|><|det|>[[150, 707, 710, 858]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 83, 763, 127]]<|/det|>
+## Fig. 1 Zfp36/1 and Zfp36/2 are essential in Treg to maintain immune homeostasis
+
+<|ref|>text<|/ref|><|det|>[[115, 131, 872, 325]]<|/det|>
+a, Representative histogram overlays comparing expression of each reporter in Treg \(\mathrm{(CD4^{+}CD25^{+}FR4^{+})}\) versus Tconv \(\mathrm{(CD4^{+}CD25^{- }FR4^{+})}\) cells in either the naive \(\mathrm{(CD44^{lo}CD62L^{hi})}\) or effector \(\mathrm{(CD44^{hi}CD62L^{lo})}\) subset, as indicated. Gating as in fig. S1A. In each example Tconv cells are represented by the grey shaded histogram; mAmetrine - ZFP36 (purple line); mCherry - ZFP36L1 (red line) and eGFP - ZFP36L2 (green line). Corresponding cells from wild type mice are indicated by the dashed line. Scatter plots represent the geometric mean fluorescence intensity (gMFI) of each reporter from \(n = 4 - 5\) mice.
+
+<|ref|>text<|/ref|><|det|>[[115, 329, 848, 446]]<|/det|>
+b, Representative flow cytometry (FACS) plots and proportion and cell number of effector cells \(\mathrm{CD44^{hi}CD62L^{lo}}\) in the \(\mathrm{CD4^{+}YFP^{- }}\) (upper panel) and \(\mathrm{CD8^{+}}\) subsets (lower panel), in single and double conditional knockout male mice (gated as in Supplementary Fig. 1d). Control icre- only FYC \((n = 17)\) ; FYC 11 \((n = 8)\) ; FYC 11/2 \((n = 11)\) , key as shown.
+
+<|ref|>text<|/ref|><|det|>[[115, 450, 877, 520]]<|/det|>
+c,d, Representative FACS plots, showing percentage and number of \(\mathrm{CD44^{hi}CD62L^{lo}}\) eTreg c, and d, numbers of \(\mathrm{CD44^{lo}CD62L^{hi}nTreg}\) in FYC 11 and FYC 11/2 male mice (gated as shown in c).
+
+<|ref|>text<|/ref|><|det|>[[115, 525, 872, 570]]<|/det|>
+e, Representative images of haematoxylin and eosin staining of the lung, liver, small and large intestine from three male FYC and FYC 11/2 mice at 11 weeks of age.
+
+<|ref|>text<|/ref|><|det|>[[117, 575, 681, 595]]<|/det|>
+Lymphoid infiltrates are arrowed. Scale bar represents 200um.
+
+<|ref|>text<|/ref|><|det|>[[115, 599, 879, 717]]<|/det|>
+For a- d, each symbol represents an individual mouse with the horizontal line representing the mean; values are for LN cells from mice aged 10 - 14 weeks. Data from at least two independent experiments. P values were determined by Mann- Whitney non- parametric test (a) or one- way ANOVA using multiple comparison (b, c, d).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[72, 110, 870, 220]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[18, 50, 88, 66]]<|/det|>
+Figure 2
+
+<|ref|>image<|/ref|><|det|>[[48, 285, 870, 555]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[48, 285, 62, 297]]<|/det|>
+c
+
+<|ref|>image<|/ref|><|det|>[[83, 603, 600, 950]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[180, 586, 256, 599]]<|/det|>
+Endocytosis
+
+<|ref|>image<|/ref|><|det|>[[625, 750, 872, 950]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[48, 560, 62, 572]]<|/det|>
+e
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 83, 606, 103]]<|/det|>
+## Fig. 2 Compromised fitness of RBP-deficient Tregs
+
+<|ref|>text<|/ref|><|det|>[[113, 106, 870, 696]]<|/det|>
+a, Representative FACS plots of FOXP3 and YFP expression in \(\mathrm{CD4^{+}}\) cells from female \(FYC^{+}\) and \(FYC^{+}\) 11/2 mice; scatter plots showing quantification (% of YFP+ and YFP- cells within FOXP3+ gate); key as shownb, MA plot showing the DESeq2- derived shrunken \(\log_{2}\) - fold changes in gene expression in \(FYC^{+}\) 11/2 compared with \(FYC^{+}\) nTreg, padj. <0.05 shown in blue, selected genes indicated in black.c, Violin plot showing the \(\log_{2}\) - fold change in expression of genes with ZFP36- family binding detected in their 3'UTR by CLIP (orange), compared with non- target genes (grey). Only genes with mean normalised read counts \(>100\) were included; the number of genes in each group is indicated.d, GSEA of custom gene sets (Supplementary Table 4) showing the ten most positively and negatively enriched pathways in the transcriptomes of Treg from \(FYC\) \(^{+}\) 11/2 compared to \(FYC^{+}\) mice. Genes were ranked based on their expression change upon deletion of Zfp36/1 and 12 (most significantly increased genes ranked first and most significantly decreased genes ranked last).The bar graph shows the number of genes in the leading edge, with predicted targets represented in orange. The red- blue heatmap shows the NES. Pathways ordered with the highest NES shown at the top; values in white represent the FDR- adjusted p value.e, GSEA plots for Endocytosis and TCR signaling pathwaysf, g, GSEA plots using genes with altered expression in the response to the survival factors IL- 2 and IL- 7 (f), and IFN \(\gamma\) (g), comparing the genes altered by cytokine stimulation to the transcriptome of Treg from \(FYC^{+}\) 11/2 mice; genes decreased upon cytokine stimulation shown in blue; genes increased are shown in red.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[80, 152, 936, 920]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[63, 95, 133, 111]]<|/det|>
+Figure 3
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 83, 680, 103]]<|/det|>
+## Fig. 3 Decreased cycling of CTLA-4 in RBP-deficient nTreg
+
+<|ref|>text<|/ref|><|det|>[[115, 107, 880, 421]]<|/det|>
+a, Gating strategy for cDC2 (CD172a\* XCR1\*), showing percentage of events in each gate. Dump channel (FITC: CD3, CD64, F4/80), pre- gated on live, single cells b, Enumeration of cells per LN in each DC subset; \(n = 6\) , key as shown. c, Representative FACS plots showing CD80 and CD86 expression on CD11cint MHClhi "migratory" (upper panel) and CD11cmi MHClint "resident" (lower panel) cDC2 from spleen from FYC 1112 and FYC male mice; the number of events in the file is indicated; \(n = 6\) , key as shown d, Representative FACS plots showing CTLA- 4 staining in nTreg from spleen from FYC 1112 and FYC male mice (left panel) and eTreg (right panel). Percentage of CTLA- 4+ Treg in each condition (lower panel); \(n = 6\) e, As in d, showing data from FYC/+ 1112 and FYC/+ female mice; \(n = 5\) Each symbol represents an individual mouse; key as shown. Data from at least two independent experiments. P values were determined by Mann- Whitney test.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[60, 123, 936, 650]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 83, 700, 103]]<|/det|>
+## Fig. 4 ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-2
+
+<|ref|>text<|/ref|><|det|>[[115, 107, 877, 473]]<|/det|>
+a,b, Representative FACS plots of Treg from LN from female mice a, or male mice b, fixed directly ex- vivo and stained for pSTAT5; \(FYC^{+}, FYC^{+} 11 / 2 n = 5; FYC, FYC 11 / 2 n = 4\) , key as shownc, Representative histogram overlays of CD25 expression on nTreg (left panel) and eTreg (right panel) from spleen; gMFI of CD25; YFP+ cells from female \(FYC^{+} \text{and} FYC^{+} 11 / 2 \text{mice}\) ; key as in a-d, Frequency of pSTAT5+ cells in nTreg and eTreg from female splenocytes following stimulation for 30 minutes with a range of concentrations of IL- 2; key as in ae, Representative histogram overlays of CD25 expression on nTreg (left panel) and eTreg (right panel) from spleen; gMFI of CD25; YFP+ cells from male \(FYC\) and \(FYC\) 11/2 mice; key as in bf, Frequency of pSTAT5+ cells in nTreg and eTreg from male mice stimulated as in d; key as in bP values determined using Mann- Whitney test (a,b,c,e), or two- way ANOVA with multiple comparison (d, f).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[92, 131, 933, 570]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[116, 84, 700, 103]]<|/det|>
+## Fig. 5 ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-7
+
+<|ref|>text<|/ref|><|det|>[[116, 108, 860, 175]]<|/det|>
+a, b, Representative histogram overlays of CD127 expression in nTreg (left panel) and eTreg (right panel) from spleen of female mice a, or male mice b; gMFI of CD127.
+
+<|ref|>text<|/ref|><|det|>[[116, 181, 872, 250]]<|/det|>
+c, d, Frequency of pSTAT5+ cells in nTreg and eTreg isolated from the spleen from female mice (c) or male mice (d) following stimulation for 30 minutes with a range of concentrations of IL- 7; key as shown.
+
+<|ref|>text<|/ref|><|det|>[[116, 256, 810, 300]]<|/det|>
+P values determined using Mann- Whitney test (a, b), or two- way ANOVA with multiple comparison (c, d).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[100, 110, 925, 610]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 84, 666, 103]]<|/det|>
+## Fig. 6 ZFP36L1 and ZFP36L2 limit Treg sensitivity to IFN \(\gamma\)
+
+<|ref|>text<|/ref|><|det|>[[115, 109, 880, 402]]<|/det|>
+a, Frequency of pSTAT1+ cells detected in \(\mathrm{YFP^{+}}\) nTreg and \(\mathrm{YFP^{+}}\) eTreg from female mice following stimulation for 30 minutes with a range of concentrations of \(\mathrm{IFN}\gamma\) . Representative histogram overlays of pSTAT1 expression (left panel) and compiled data (right panel); key as shown. b, FACS analysis of total STAT1 expression in Treg from female \(\mathrm{FYC^{+}}\) and \(\mathrm{FYC^{+}}\) 11/2 mice, showing representative histogram overlays of STAT1 expression and quantitation; key as in a. c, Frequency of pSTAT1+ cells detected in \(\mathrm{YFP^{+}}\) nTreg and \(\mathrm{YFP^{+}}\) eTreg from female mice following stimulation for 30 minutes with a range of concentrations of IL-6. Representative histogram overlays of pSTAT1 expression (left panel) and compiled data (right panel); key as in a. P values determined using two- way ANOVA with multiple comparison (a,c).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[44, 115, 950, 950]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 83, 637, 103]]<|/det|>
+## Fig. 7 Activated phenotype of Treg from FYC 1112 mice
+
+<|ref|>text<|/ref|><|det|>[[115, 107, 876, 175]]<|/det|>
+a, UMAP representation of scRNA seq data with cell clusters indicated by color code and numbered 0- 7. Single \(\mathsf{CD4^{+}FR4^{+}YFP^{+}}\) cells were sorted from apparently healthy male FYC and FYC 1112 mice.
+
+<|ref|>text<|/ref|><|det|>[[115, 180, 878, 348]]<|/det|>
+b, Distribution of nTreg and eTreg subsets within clusters; key as shown c, Dot plot representation showing percentage of detection (dot size) and scaled expression (dot color) in each cluster for genes more frequently detected and highly expressed in each cluster relative to other clusters (Wilcoxon rank sum test; p value \(< 0.001\) ). The top four genes for each cluster, based on average \(\log_2\) fold change, are shown. Color bar on the right indicates clusters that are primarily comprised of nTreg or eTreg; key as in b.
+
+<|ref|>text<|/ref|><|det|>[[115, 353, 852, 572]]<|/det|>
+d, UMAP representation of clusters according to genotype as indicated, and percentage contribution of cells to each cluster by genotype; key as shown e, UMAP distribution highlighting the location of cells with an expression pattern characteristic of the \(\mathsf{IFN}\gamma\) gene signature (indicated in red); and percentage contribution of cells identified as possessing the \(\mathsf{IFN}\gamma\) signaling gene signature for each genotype, within each cluster; adjusted p values from Chi- square test f, g, h, UMAP distribution highlighting the location of cells expressing Cxcr3 (f), Gata3 (g), Pdc1 (h). The intensity of the purple color indicates the scaled expression level for each plot.
+
+<|ref|>text<|/ref|><|det|>[[115, 577, 880, 646]]<|/det|>
+i, j, k, Representative FACS plots gated on \(\mathsf{CD4^{+}}\) cells and scatter plots showing \(\%\) of \(\mathsf{CXCR3^{+}}\) (i), GATA3hi (j), and \(\mathsf{CXCR5^{+}PD1^{+}}\) (Tfr, k) out of all \(\mathsf{FOXP3^{+}}\) cells; (n=4 to 7); key as shown
+
+<|ref|>text<|/ref|><|det|>[[115, 652, 880, 746]]<|/det|>
+I, \(\mathsf{IFN}\gamma\) , IL- 17, IL- 4 and IL- 10 expression in Tconv and Treg. Splenocytes were stimulated with PMA/ionomycin for four hours in the presence of Brefeldin A; FACS plots gated on \(\mathsf{CD4^{+}}\) cells. Percentage values shown as a \(\%\) of all \(\mathsf{CD4^{+}}\) FOXP3+ cells (Tconv) or \(\mathsf{CD4^{+}FOXP3^{+}}\) cells (Treg).
+
+<|ref|>text<|/ref|><|det|>[[117, 751, 835, 795]]<|/det|>
+Data are from at least two independent experiments. P values determined using Mann- Whitney test (i- I).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[56, 140, 911, 720]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 84, 733, 103]]<|/det|>
+## Fig. 8 IFNy is a driving force for the expansion of effector T cells
+
+<|ref|>text<|/ref|><|det|>[[115, 108, 870, 550]]<|/det|>
+a, Development of clinical symptoms with age for \(FYC 1112\) (n=46) and \(Ifng^{+ / - }\) FYC 1112 male mice (n=24); key as indicated. Logrank test \(p = 0.03\) b, Serum cytokine levels in \(FYC\) , \(FYC 1112\) and \(Ifng^{+ / - }\) FYC 1112 male mice; key as shown. Comparative values for \(FYC 1112\) and \(FYC\) : IFN \(\gamma\) (4- fold); TNF \(\alpha\) (4- fold); IL- 2 (3- fold); IL- 6 (9- fold); IL- 10 (9- fold). Dashed line represents limits of detection. c, Representative FACS plots and gating strategy (upper) and enumeration (lower panel) of effector cells in the Treg, Tconv (CD44hiCD62Llo) and CD8+ TEM (CD44hiCD62Llo) subsets. Numbers are shown per single LN in mice aged 15 weeks (n=6). Key as in b. d, e, f, Representative FACS plots and enumeration of (d) T follicular helper (Tfh) YFP- CXCR5+PD1+), (e) Tfr (YFP+ CXCR5+PD1+), and (f) GC B cells (B220+CD38loCD95+ gated as in Supplementary Fig. 9); key as in b. Comparative values for \(FYC 1112\) and \(FYC\) : Tfh (60- fold), Tfr (90- fold), GC B (100- fold), g, Total serum Immunoglobulin levels quantified by ELISA; key as in b. Comparative values for \(FYC 1112\) with \(FYC\) : IgG2c (5- fold), IgE (300- fold). Analyses combine data from two or more independent experiments (b- g n=6). P values determined using one- way ANOVA with multiple comparison (b- g).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[45, 125, 925, 680]]<|/det|>
+
+
+<|ref|>image<|/ref|><|det|>[[45, 737, 960, 925]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 83, 479, 102]]<|/det|>
+## Fig. S1 Phenotyping of T cell subsets
+
+<|ref|>text<|/ref|><|det|>[[115, 106, 875, 500]]<|/det|>
+a, Gating strategy for data shown in Fig. 1a; Treg: \(\mathrm{CD4^{+}FR4^{+}CD25^{+}}\) ; and Tconv: \(\mathrm{CD4^{+}CD25^{- }T}\) cellsb, Gating strategy and representative FACS plots comparing expression of ZFP36L1 in Treg ( \(\mathrm{CD4^{+}FOXP3^{+}YFP^{+}}\) ) or Tconv ( \(\mathrm{CD4^{+}FOXP3^{- }YFP^{- }}\) ) cells from FYC, FYC 11 (upper panel) and FYC 11/2 mice (lower panel) after stimulation with PMA and ionomycin for four hours at \(37^{\circ}C\) ; cells were pre- gated on live, single cells; quantification of ZFP36L1 gMFI; key as shownc, Total cell number per pLN; \(\mathrm{n = 8 - 17}\) ; key as in bd, Gating strategy for data shown in Fig. 1b, ce, f, Representative FACS plots and proportion and cell number of effector cells \(\mathrm{CD44^{hi}CD62L^{lo}}\) in the \(\mathrm{CD4^{+}YFP^{- }}\) (upper panel) and \(\mathrm{CD8^{+}}\) subsets (lower panel) from FYC Zfp36 (e), and FYC Zfp36/2 mice (f), analysed with contemporaneous FYC controls. FYC ( \(\mathrm{n = 5 - 6}\) ); FYC Zfp36 ( \(\mathrm{n = 6}\) ); FYC Zfp36/2 ( \(\mathrm{n = 7}\) ); key as shown Numbers are shown per single LN in mice aged 9 - 16 weeksP values were determined using one- way ANOVA using multiple comparison (c) or Mann- Whitney test (b, e, f).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[80, 98, 870, 201]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[70, 220, 84, 232]]<|/det|>
+b
+
+<|ref|>image<|/ref|><|det|>[[80, 250, 930, 360]]<|/det|>
+
+<|ref|>image<|/ref|><|det|>[[80, 375, 425, 550]]<|/det|>
+
+<|ref|>image<|/ref|><|det|>[[80, 592, 430, 696]]<|/det|>
+
+<|ref|>image<|/ref|><|det|>[[80, 720, 470, 944]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 83, 608, 102]]<|/det|>
+## Fig. S2 Compromised fitness of RBP-deficient Treg
+
+<|ref|>text<|/ref|><|det|>[[115, 106, 880, 525]]<|/det|>
+a, Number of effector cells in the Tconv (CD44hiCD62Llo) and CD8+ TEM (CD44hiCD62Llo ) subsets; key as shown b, Gating strategy and representative FACS plots comparing CD4+TCRβ+CD69- YFP+ CD25+ Treg in the thymus of 7-week old \(FYC^{+}\) and \(FYC^{+}\) 1112 mice; n=4 c, Gating strategy for sorting nTreg d, Normalised read counts across the loxP- flanked regions of the conditional Zfp36l1 and Zfp36l2 alleles; n=6- 7; key as shown. Read counts were normalised using size factors derived from the overall DESeq2 analysis of all genes; p values determined using t test with FDR correction e, Representative histogram overlays comparing expression of ZFP36L1 in Treg (CD4+ FOXP3+) cells from \(FYC^{+}\) and \(FYC^{+}\) 1112 mice (icre- positive (FOXP+YFP+) cells - black line and black symbols; icre- negative FOXP+YFP- ) cells - blue line and blue symbols); or Tconv (CD4+ FOXP3- ) cells (lower panel). Cells were stimulated with PMA and ionomycin for four hours; scatter plots showing gMFI for ZFP36L1 staining; n=3; key as shown P values determined using Mann- Whitney (a,d), or one- way ANOVA with multiple comparison (e).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[250, 145, 643, 384]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[253, 85, 342, 102]]<|/det|>
+Figure S3
+
+<|ref|>image<|/ref|><|det|>[[250, 450, 826, 790]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 84, 631, 103]]<|/det|>
+## Fig. S3 Genes enriched in the TCR signaling pathway
+
+<|ref|>text<|/ref|><|det|>[[115, 108, 872, 300]]<|/det|>
+a, The heatmap depicts the top 15 ranked genes in the TCR signaling pathway, ordered with the most significantly increased genes at the top. The color scale represents the \(\log_2\) fold deviation from the mean for each gene. Genes that are predicted targets by CLIP are represented in orangeb, CD5 (upper panel) and NUR77 (lower panel) expression (gMFI) in \(\mathrm{CD4^{+}FOXP3^{+}}\) nTreg (CD62Lhi) and eTreg (CD44hi CD62Llo) from control \(FYC^{+}\) and \(FYC^{+}\) /112 mice. \(\mathrm{n = 4}\) ; key as shown.P values in (b) determined using one- way ANOVA with multiple comparison
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[264, 186, 737, 610]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[268, 128, 355, 144]]<|/det|>
+Figure S4
+
+<|ref|>image<|/ref|><|det|>[[264, 650, 737, 787]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 84, 535, 103]]<|/det|>
+## Fig. S4 Expression of Treg signature genes
+
+<|ref|>text<|/ref|><|det|>[[115, 107, 855, 227]]<|/det|>
+a, Representative FACS plots showing FOXP3, CTLA- 4 (from LN, fixed ex vivo), IKZF2 (from mLN) and ICOS (from LN) expression (gMFI) in \(\mathrm{CD4^{+}}\) FOXP3+ nTreg and eTreg from control \(FYC^{+}\) and \(FYC^{+} / 112\) mice; \(n = 3 - 5\) ; key as shown. b, NOTCH1 expression (gMFI) in nTreg and eTreg from \(FYC^{+}\) and \(FYC^{+} / 112\) mice; \(n = 3 - 4\) , key as in a. P values determined using Mann- Whitney.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[164, 240, 644, 401]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[92, 155, 183, 171]]<|/det|>
+Figure S5
+
+<|ref|>image<|/ref|><|det|>[[133, 445, 896, 666]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 83, 694, 103]]<|/det|>
+## Fig. S5 Decreased cycling of CTLA-4 in RBP-deficient nTreg
+
+<|ref|>text<|/ref|><|det|>[[115, 107, 877, 325]]<|/det|>
+a, Representative FACS plots showing CD80 and CD86 expression on CD11cint MHCIIhi "migratory" (upper panel) and CD11cHi MHCIIint "resident" (lower panel) CD172a \(\times\) XCR1+ cDC1 from spleen from FYC 1112 and FYC male mice; the number of events in the file is indicated; \(n = 6\) , key as shown b, Percentage of CTLA- 4+ nTreg or eTreg in surface, cycling, or total pool from FYC \(^+\) 1112 and FYC+ female mice. Each symbol represents an individual mouse \((n = 5)\) ; key as shown. Data from at least two independent experiments. P values determined using Mann- Whitney (a) and one- way ANOVA with multiple comparison (b) represented in the table shown.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[137, 123, 920, 940]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 83, 796, 102]]<|/det|>
+## Fig. S6 ZFP36L1 and ZFP36L2 promote Treg sensitivity to IL-2 and IL-7
+
+<|ref|>text<|/ref|><|det|>[[115, 107, 880, 400]]<|/det|>
+a, Total STAT5 expression in YFP \(^+\) nTreg and eTreg; from \(FYC^{+}\) and \(FYC^{+}\) 1/12 mice, \(\mathrm{n} = 3\) ; key as shownb, Frequency of pSTAT5 \(^+\) cells detected in YFP \(^+\) (black symbol) and YFP \(^+\) (blue symbol) nTreg and eTreg from the spleen of female mice following stimulation for 30 minutes with a range of concentrations of IL- 2; data presented as mean value \(\pm\) sd, \(\mathrm{n} = 7\) ; key as shownc, Frequency of pSTAT5 \(^+\) cells detected in YFP \(^+\) and YFP \(^+\) nTreg and eTreg from female mice following stimulation for 30 minutes with a range of concentrations of IL- 7; data presented as mean value \(\pm\) sd, \(\mathrm{n} = 4\) ; key as in b.P values were determined using two- way ANOVA with multiple comparison, comparing the mean value between each genotype, and are represented in the table shown.
+
+<--- Page Split --->
+<|ref|>image_caption<|/ref|><|det|>[[164, 48, 255, 65]]<|/det|>
+Figure S7
+
+<|ref|>image<|/ref|><|det|>[[220, 115, 836, 312]]<|/det|>
+
+
+<|ref|>image<|/ref|><|det|>[[312, 339, 620, 404]]<|/det|>
+
+
+<|ref|>image<|/ref|><|det|>[[187, 440, 820, 600]]<|/det|>
+
+
+<|ref|>image<|/ref|><|det|>[[220, 666, 840, 860]]<|/det|>
+
+
+<|ref|>image_caption<|/ref|><|det|>[[187, 644, 208, 657]]<|/det|>
+c
+
+<|ref|>image<|/ref|><|det|>[[312, 866, 490, 930]]<|/det|>
+
+
+<|ref|>image_caption<|/ref|><|det|>[[630, 464, 750, 477]]<|/det|>
+CD44hi CD62Llo
+
+<|ref|>image<|/ref|><|det|>[[580, 481, 816, 590]]<|/det|>
+
+
+<|ref|>image_caption<|/ref|><|det|>[[630, 671, 750, 684]]<|/det|>
+CD44hi CD62Llo
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 83, 680, 103]]<|/det|>
+## Fig. S7 ZFP36L1 and ZFP36L2 limit Treg sensitivity to IFNγ
+
+<|ref|>text<|/ref|><|det|>[[115, 108, 880, 330]]<|/det|>
+a, Frequency of pSTAT1+ cells detected in \(\gamma \mathsf{FP}^+\) and \(\gamma \mathsf{FP}^-\) nTreg and eTreg from female mice following stimulation for 30 minutes with a range of concentrations of \(\mathsf{IFN}\gamma\) ; data presented as mean value \(\pm\) sd, \(n = 6 - 11\) ; key as shownb, Total STAT1 expression in \(\gamma \mathsf{FP}^+\) and \(\gamma \mathsf{FP}^-\) nTreg and eTreg; key as in ac, Frequency of pSTAT1+ cells detected in \(\gamma \mathsf{FP}^+\) and \(\gamma \mathsf{FP}^-\) nTreg and eTreg from female mice following stimulation for 30 minutes with a range of concentrations of IL- 6; data presented as mean value \(\pm\) sd, \(n = 4 - 6\) ; key as in a.P values determined using two- way ANOVA with multiple comparison, comparing the mean value between each genotype, and are represented in the table shown (a,c).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[112, 130, 919, 850]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[86, 73, 175, 91]]<|/det|>
+Figure S8
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 108, 651, 127]]<|/det|>
+## Fig. S8 Activated phenotype of Treg from FYC 1112 mice
+
+<|ref|>text<|/ref|><|det|>[[115, 131, 875, 504]]<|/det|>
+a, Gating strategy for sorting of \(\mathsf{CD4^{+}FR4^{+}CD25^{+}}\) Treg cells for scRNA- seqb, Percentage of cells identified as naive (orange), effector (dark blue) or unassigned (grey) in each cluster;c, Violin plot representing the number of genes detected in each clusterd, Cell number for CXCR3+, GATA3hi Treg and Tfr, in LN (for data in Fig. 7i, j, k); comparative values for FYC 1112 to FYC: 4- fold increase CXCR3+, 3- fold increase in GATA3hi, 50- fold increase in Tfr cell numbere, Representative flow cytometry plots (left panel) gated on \(\mathsf{CD4^{+}}\) cells; scatter plot (right panel) showing proportion of \(\mathsf{ROR}\gamma \mathsf{t^{+}}\) Treg (as a \(\%\) of all FOXP3+ cells) and enumeration of \(\mathsf{FOXP3^{+}ROR}\gamma \mathsf{t^{+}}\) Treg; key as shownf, gMFI for intracellular cytokine staining shown in Fig. 7i.g, \(\mathsf{IFN}\gamma\) expression in CD8 cells. Splenocytes were stimulated with PMA/ionomycin for four hours in the presence of Brefeldin A, flow cytometry plots are gated on \(\mathsf{CD8^{+}}\) cells; \(\mathrm{n} = 6\) , key as shownP values determined using Mann- Whitney test (d,e,f,g).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[115, 155, 345, 245]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[75, 63, 160, 80]]<|/det|>
+Figure S9
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[117, 84, 480, 103]]<|/det|>
+# Fig. S9 Gating strategy for GC B cells
+
+<|ref|>text<|/ref|><|det|>[[118, 110, 480, 127]]<|/det|>
+Cells were pre- gated on live, single cells
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 43, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[42, 93, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 405, 176]]<|/det|>
+Supplementarytablesmerged.pdf.pdf Supplementaltables.xlsx
+
+<--- Page Split --->
diff --git a/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/images_list.json b/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..5e2e7401496cc59d8a0e1355936b370b34e67b42
--- /dev/null
+++ b/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/images_list.json
@@ -0,0 +1,77 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. Voltage-controlled perpendicular magnetic anisotropy. a, Schematic illustration of the mechanism of the voltage-driven frequency tuning via voltage-controlled magnetic anisotropy (VCMA). The green and gray arrows represent the directions of spin-orbit torque and damping torque, respectively. b, The resonance frequency \\((f_{\\mathrm{res}})\\) as a function of in-plane magnetic field \\((B_{\\parallel})\\) for high PMA (blue) and low PMA (red). c, magnetization \\((M)\\) versus out-of-plane magnetic field \\((B_{z})\\) of the Co/Ni film. d, Anomalous Hall resistance \\((R_{\\mathrm{H}})\\) curves of the Co/Ni sample for sequentially applied gate voltages of \\(+3\\mathrm{V}\\) , \\(+5\\mathrm{V}\\) , \\(-3\\mathrm{V}\\) , and \\(-5\\mathrm{V}\\) , respectively.",
+ "footnote": [],
+ "bbox": [
+ [
+ 163,
+ 106,
+ 845,
+ 581
+ ]
+ ],
+ "page_idx": 19
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Voltage-dependent ST-FMR spectra. a, ST-FMR spectra of the Co/Ni sample for sequentially applied gate voltages (initial, \\(+5\\mathrm{V}\\) , and -5V). Here, the microwave frequency is 15 GHz. The dotted lines are the best fits based on Eq. (1). b, Resonance frequency \\((f_{\\mathrm{res},z})\\) as a function of resonance field \\(B_{\\mathrm{res},z}\\) of the sample with different sequentially applied gate voltages. c, Variation of perpendicular magnetic anisotropy field \\((B_{\\mathrm{k}})\\) versus sequentially applied gate voltage. d, The linewidth of the Lorentzian function \\((\\Delta B)\\) as a function of the \\(f_{\\mathrm{res},z}\\) of the sample with sequentially applied gate voltages. e, Variation of effective damping constant \\((\\alpha_{\\mathrm{eff}})\\) versus sequentially applied gate voltage.",
+ "footnote": [],
+ "bbox": [
+ [
+ 123,
+ 115,
+ 830,
+ 388
+ ]
+ ],
+ "page_idx": 20
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Magnetic field-dependent voltage-driven frequency tuning of SHNO. a, Schematic illustration of the experimental set-up. The inset is a scanning electron microscope image of an SHNO device. b, Angle-dependent magnetoresistance (MR) of the Co/Ni sample. c-g, Power spectral densities (PSDs) as a function of magnetic field for sequentially applied gate voltages, \\(V_{\\mathrm{g}} = 0 \\mathrm{V}\\) (initial state) (c), \\(V_{\\mathrm{g}} = +4 \\mathrm{V}\\) (d), \\(V_{\\mathrm{g}} = +5 \\mathrm{V}\\) (e), \\(V_{\\mathrm{g}} = -2 \\mathrm{V}\\) (f), and \\(V_{\\mathrm{g}} = -3 \\mathrm{V}\\) (g). \\(I_{\\mathrm{dc}} = 2.9 \\mathrm{mA}\\) . h, Auto-oscillation spectra for \\(B = 0.52 \\mathrm{T}\\) with different gate voltages, extracted from Figs. 3c-3g.",
+ "footnote": [],
+ "bbox": [
+ [
+ 123,
+ 103,
+ 857,
+ 575
+ ]
+ ],
+ "page_idx": 21
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4. Current-dependent voltage-driven frequency tuning of SHNO. a-e, PSDs as a function of current for sequentially applied gate voltages, \\(V_{\\mathrm{g}} = 0 \\mathrm{V}\\) (initial state) (a), \\(V_{\\mathrm{g}} = +4 \\mathrm{V}\\) (b), \\(V_{\\mathrm{g}} = +5 \\mathrm{V}\\) (c), \\(V_{\\mathrm{g}} = -2 \\mathrm{V}\\) (d), and \\(V_{\\mathrm{g}} = -3 \\mathrm{V}\\) (e). \\(B = 0.52 \\mathrm{T}\\) . f, Threshold current, \\(I_{\\mathrm{th}}\\) , according to the sequentially applied gate voltages, extracted from Figs. 4a-4e.",
+ "footnote": [],
+ "bbox": [
+ [
+ 124,
+ 99,
+ 863,
+ 428
+ ]
+ ],
+ "page_idx": 22
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5. Cumulative frequency control via repetitive gate voltage pulses. a, The auto oscillation frequency of the SHNO versus the number of positive (black) and negative (red) gate voltage pulses \\((N_{V_{\\mathrm{g}}})\\) . b, Voltage-driven cumulative frequency change \\((\\delta f)\\) versus \\(N_{V_{\\mathrm{g}}}\\) for different gate voltages.",
+ "footnote": [],
+ "bbox": [
+ [
+ 161,
+ 107,
+ 832,
+ 296
+ ]
+ ],
+ "page_idx": 23
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1.mmd b/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..e4b3c115d534d6c269304287191878a10ae97129
--- /dev/null
+++ b/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1.mmd
@@ -0,0 +1,284 @@
+
+# Voltage-driven gigahertz frequency tuning of spin Hall nano-oscillators
+
+Jong-Guk Choi KAIST Jaehyeon Park KAIST Min-Gu Kang Korea Advanced Institute of Science and Technology Doyoon Kim Korea University Jae-Sung Rieh Korea University Kyung-Jin Lee Korea Advanced Institute of Science and Technology (KAIST) https://orcid.org/0000- 0001- 6269- 2266 Kab-Jin Kim Korea Advanced Institute of Science and Technology https://orcid.org/0000- 0002- 8378- 3746 Byong-Guk Park (bgpark@kaist.ac.kr) KAIST https://orcid.org/0000- 0001- 8813- 7025
+
+## Article
+
+Keywords: Spin Hall nano- oscillators, oscillator- based neuromorphic computing, oscillation frequency
+
+Posted Date: September 8th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 840717/v1
+
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on June 30th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 31493- z.
+
+<--- Page Split --->
+
+# Voltage-driven gigahertz frequency tuning of spin Hall nano-oscillators
+
+Jong- Guk Choi \(^{1\dagger}\) , Jaehyeon Park \(^{2\dagger}\) , Min- Gu Kang \(^{1}\) , Doyoon Kim \(^{3}\) , Jae- Sung Rieh \(^{3}\) , Kyung- Jin Lee \(^{2}\) , Kab- Jin Kim \(^{2\star}\) and Byong- Guk Park \(^{1\star}\)
+
+\(^{1}\) Department of Materials Science and Engineering, KAIST, Daejeon 34141, Korea \(^{2}\) Department of Physics, KAIST, Daejeon 34141, Korea \(^{3}\) School of Electrical Engineering, Korea University, Seoul 02841, Korea
+
+\(^{\dagger}\) These two authors equally contributed to this work.
+
+\(\star\) Correspondence to: kabjin@kaist.ac.kr (K.- J.K.) and bgpark@kaist.ac.kr (B.- G.P.)
+
+## Abstract
+
+Spin Hall nano- oscillators (SHNOs) exploiting current- driven magnetization auto- oscillation have recently received much attention because of their potential for oscillator- based neuromorphic computing. Widespread neuromorphic application with SHNOs requires an energy- efficient way to tune oscillation frequency in broad ranges and store trained frequencies in SHNOs without the need for additional memory circuitry. Voltage control of oscillation frequency of SHNOs was experimentally demonstrated, but the voltage- driven frequency tuning was volatile and limited to megahertz ranges. Here, we show that the frequency of SHNO is controlled up to 2.1 GHz by a moderate electric field of 1.25 MV/cm. The large frequency tuning is attributed to the voltage- controlled magnetic anisotropy (VCMA) in a perpendicularly magnetized Ta/Pt/[Co/Ni] \(_n\) /Co/AlOx structure. Moreover, non- volatile VCMA effect enables control of the cumulative
+
+<--- Page Split --->
+
+frequency using repetitive voltage pulses, which mimic the potentiation and depression functions of biological synapses. Our results suggest that the voltage- driven frequency tuning of SHNOs facilitates the development of energy- efficient spin- based neuromorphic devices.
+
+<--- Page Split --->
+
+Spintronic oscillators that generate microwaves through spin- torque- driven magnetization precession are being extensively investigated for neuromorphic applications [1- 4] owing to their unique features such as non- linearity [5,6], low- power operation [7,8], scalability [1,4,9], and CMOS compatibility [10]. Indeed, spin- transfer- torque- based oscillators (STOs) have recently been implemented in oscillator neural networks, demonstrating pattern recognition [2,11,12]. Furthermore, the STO device has been successfully trained to recognize the input pattern signals by tuning the frequency of individual oscillators using a driving current [2,11] or magnetic field [12]. However, the current or magnetic field- based frequency tuning is not energy efficient; thus, it is necessary to find an alternative way to tune the frequency widely with reduced power consumption.
+
+Recently, another type of STO, in which magnetization precession is caused by spin currents generated by the spin Hall effect [13- 15], has been developed, which is referred to as spin Hall nano- oscillator (SHNO) [16- 20]. Since the SHNO is operated with an in- plane current, it has the following advantages over conventional STO that utilizes a perpendicular current. First, multiple oscillators integrated into a common spin- Hall material can be controlled simultaneously by an in- plane current, allowing long- range mutual synchronization of the SHNOs [21,22]. Second, a gate structure is easily incorporated in a three- terminal SHNO structure [23- 25], so that an individual oscillator can be independently controlled by a gate voltage [26,27].
+
+A recent study [27] has experimentally demonstrated the gate voltage- induced frequency tuning in W/CoFeB/MgO structures with the frequency tuning range of about 50 MHz. However, this frequency tuning range is relatively narrow compared to the oscillation frequency ( \(\sim 10\) GHz). Thus, although 10- 50 MHz frequency tunability is sufficient to optimize the synchronization map for a small number of different synchronization states as in
+
+<--- Page Split --->
+
+vowel recognition [2,27], a wider frequency tunability is required for tasks having more states of being recognized and thus expands the applicability of gate- controlled SHNOs to widespread oscillator- based neuromorphic computing. Moreover, the previously demonstrated voltage- driven frequency tuning of SHNO [27] is volatile, so that an additional memory circuitry is required to store trained synaptic weights of oscillation frequency.
+
+In this Article, we report voltage- driven large frequency tuning of SHNO by exploiting voltage- controlled magnetic anisotropy (VCMA) [28- 33] as schematically illustrated in Fig. 1a. The SHNO consists of a ferromagnet (FM)/heavy metal (HM) bilayer. In this geometry, a charge current flowing through the HM layer generates a vertical spin current via the spin Hall effect, which exerts spin- orbit torques (SOTs) on the magnetization of the FM layer. The auto- oscillation of magnetization occurs when the SOT (green arrow) fully compensates the damping torque (gray arrow), and the auto- oscillation frequency is governed by the resonance frequency \((f_{\mathrm{res}})\) of the ferromagnet. Here, we employ a perpendicular magnetic anisotropy (PMA) material, which is distinct from previous works where in- plane magnetized materials were generally used. In the presence of an in- plane field, \(f_{\mathrm{res}}\) of a PMA material is determined as [34- 36],
+
+\[f_{\mathrm{res}} = \frac{\gamma}{2\pi}\sqrt{B_{\mathrm{k}}^{2} - B_{\mathrm{h}}^{2}} (0< B_{\mathrm{h}}< B_{\mathrm{k}}),\]
+
+\[f_{\mathrm{res}} = \frac{\gamma}{2\pi}\sqrt{B_{\mathrm{H}}(B_{\mathrm{H}} - B_{\mathrm{k}})} (B_{\mathrm{H}}\geq B_{\mathrm{k}}), \quad (1)\]
+
+where \(\gamma\) is the gyromagnetic ratio, \(B_{\mathrm{k}}\) is the effective perpendicular anisotropy field, and \(B_{\mathrm{H}}\) is the external in- plane magnetic field. Equation (1) indicates that a broad frequency tuning is effectively achieved by controlling \(B_{\mathrm{k}}\) . Figure 1b shows an example; when \(B_{\mathrm{H}}\) is larger than \(B_{\mathrm{k}}\) , the frequency increases by weakening \(B_{\mathrm{k}}\) . In this work, we demonstrate that \(B_{\mathrm{k}}\) of
+
+<--- Page Split --->
+
+perpendicularly magnetized Co/Ni multilayers is controlled as large as 0.22 T by a moderate electric field of 1.25 MV/cm. This results in a frequency tuning up to 2.1 GHz, which is more than 40 times larger than the previously reported values [26,27]. We find that the voltage- controlled frequency tuning is independent of the driving current and is much more efficient than the current- controlled frequency tuning used in conventional STOs. Furthermore, the voltage effect is non- volatile in our sample, allowing the cumulative frequency control of SHNO using repetitive voltage pulses. This can facilitate the potentiation and depression functions of artificial synapses [37- 40], and thus can be utilized in the learning process of neuromorphic devices. Our results demonstrating efficient frequency tuning of SHNO via gate voltage provide an essential building block for spin- based low power neuromorphic hardware applications.
+
+## Voltage-controlled perpendicular magnetic anisotropy
+
+We first demonstrate the VCMA effect in a Co/Ni multilayer sample of Ta (3 nm)/Pt (5 nm)/[Co (0.45 nm)/Ni (0.6 nm)]7/Co (0.45 nm)/AlOx (2 nm) structures (see Methods for details of sample growth). Figure 1c shows the magnetization measurement while sweeping a perpendicular magnetic field (Bz), indicating that the Co/Ni film has PMA. To test the VCMA of the sample, we patterned the film into a Hall bar device with a 10 μm × 10 μm cross, which is fully covered by a gate oxide of ZrO2 (40 nm) and a gate electrode of Ru (50 nm). Figure 1d shows the anomalous Hall resistance (RH) after sequentially applying a gate voltage (Vg). Here, we applied a Vg to the top electrode for 5 minutes at 150 °C and then measured RH at room temperature. This is possible because the voltage effect is maintained even after turning off the Vg [31,32,41,42]. The result shows that the PMA is gradually weakened by positive Vg’s and
+
+<--- Page Split --->
+
+restored by subsequent negative \(V_{\mathrm{g}}\) 's, indicating that the PMA in our Co/Ni multilayer sample is effectively modulated by \(V_{\mathrm{g}}\) . Note that the \(V_{\mathrm{g}}\) of \(5 \mathrm{~V}\) is equivalent to an electric field of 1.25 MV/cm.
+
+In order to quantitatively analyze the VCMA effect, we performed the spin torque- ferromagnetic resonance (ST- FMR) measurement. The ST- FMR spectra were measured using a bar- shaped device ( \(8 \mu \mathrm{m} \times 14 \mu \mathrm{m}\) ) fabricated from the same Co/Ni film. The microwave frequency used for the ST- FMR measurement ranges from \(10 \mathrm{GHz}\) to \(21 \mathrm{GHz}\) (see Methods for measurement details). Figure 2a shows the ST- FMR spectra of the sample with different \(V_{\mathrm{g}}\) 's at a frequency of \(15 \mathrm{GHz}\) , measured while sweeping magnetic fields in a direction slightly tilted from the \(z\) - direction. The ST- FMR spectra can be expressed by the combination of symmetric and anti- symmetric Lorentzian functions as [43,44],
+
+\[V_{\mathrm{ST - FMR}}(B_{\mathrm{z}}) = V_{\mathrm{sym}}\frac{\Delta B^{2}}{(B_{\mathrm{z}} - B_{\mathrm{res,z}})^{2} + \Delta B^{2}} + V_{\mathrm{asy}}\frac{\Delta B(B_{\mathrm{z}} - B_{\mathrm{res,z}})}{(B_{\mathrm{z}} - B_{\mathrm{res,z}})^{2} + \Delta B^{2}}, \quad (2)\]
+
+where \(B_{\mathrm{res,z}}\) is the center magnetic field of the Lorentzian functions corresponding to the resonance magnetic field, \(\Delta B\) is the linewidth (half- width at half maximum) of the Lorentzian function, and \(V_{\mathrm{sym}}(V_{\mathrm{asy}})\) is a symmetric (anti- symmetric) component of resonance amplitude. The dotted lines represent the fitting curves of the ST- FMR spectra using Eq. (2), from which we extracted the \(B_{\mathrm{res,z}}\) and \(\Delta B\) values. It is observed that the Lorentzian curve for the initial sample (black symbols) is centered around \(0.34 \mathrm{~T}\) . That is, \(B_{\mathrm{res,z}} = 0.34 \mathrm{~T}\) . Notably, the \(B_{\mathrm{res,z}}\) is largely shifted by the \(V_{\mathrm{g}}\) ; the \(B_{\mathrm{res,z}}\) is increased up to \(0.59 \mathrm{~T}\) by a positive voltage (+5 V, red symbols), but it is then reduced to \(0.39 \mathrm{~T}\) by a subsequent negative voltage (- 5 V, blue symbols). We measured the \(B_{\mathrm{res,z}}\) for different frequencies (see Supplementary Note 1) and summarize the resonance frequency \(f_{\mathrm{res,z}}\) vs \(B_{\mathrm{res,z}}\) in Fig. 2b, where the black symbols represent the initial
+
+<--- Page Split --->
+
+sample without applying a \(V_{\mathrm{g}}\) , while the red and blue symbols correspond to the samples after successively applying \(+5\mathrm{V}\) and - 5 V, respectively. The linear relation between the \(f_{\mathrm{res},z}\) and \(B_{\mathrm{res},z}\) is well explained by the Kittel formula \(f_{\mathrm{res},z} = \frac{\gamma}{2\pi} (B_{\mathrm{res},z} + B_{\mathrm{k}})\) [45], from which the \(B_{\mathrm{k}}\) can be extracted. We note that the ST- FMR measurement was done under a magnetic field along the \(z\) - direction, so the above resonance frequency formula is different from Eq. (1), which is based on an in- plane magnetic field. Figure 2c shows the extracted \(B_{\mathrm{k}}\) according to the \(V_{\mathrm{g}}\) ; the \(B_{\mathrm{k}}\) reduces from \(0.16\pm 0.01\mathrm{T}\) to \(- 0.08\pm 0.01\mathrm{T}\) when applying \(+5\mathrm{V}\) , and is restored close to the initial value by a negative gate of - 5 V. This is consistent with the results shown in Fig. 1c. Note that the average change of \(B_{\mathrm{k}}\) is \(0.22\pm 0.02\mathrm{T}\) by \(\pm 5\mathrm{V}\) , which can cause a frequency tuning up to a few GHz according to Eq. (1).
+
+Figure 2d shows the \(\Delta B\) as a function of \(f_{\mathrm{res},z}\) , where the color symbols represent the samples with different \(V_{\mathrm{g}}\) 's, identical to those in Fig. 2b. Using the relation \(\Delta B = \Delta B_{0} + \frac{2\pi\alpha_{\mathrm{eff}}}{\gamma} f_{\mathrm{res},z}\) [43- 46], the effective magnetic damping constant \(\alpha_{\mathrm{eff}}\) is obtained. Here, \(\Delta B_{0}\) is the zero- frequency linewidth due to long- range magnetic inhomogeneity [46]. Figure 2f shows the dependence of the \(\alpha_{\mathrm{eff}}\) on \(V_{\mathrm{g}}\) ; the \(\alpha_{\mathrm{eff}}\) decreases (increases) by a positive (negative) \(V_{\mathrm{g}}\) . This is consistent with the previous reports [27], where the voltage- driven frequency tuning was obtained in the MHz range. The possible effect of the voltage- controlled \(\alpha_{\mathrm{eff}}\) on the frequency tuning in our sample will be discussed later.
+
+## Voltage-driven frequency tuning of SHNO
+
+We now move on to our main result, i.e., the gate voltage- induced frequency tuning of SHNO.
+
+<--- Page Split --->
+
+Figure 3a illustrates the measurement schematics; the SHNO device was fabricated by patterning the Co/Ni film into a nano- constriction with a width of \(140~\mathrm{nm}\) , which is entirely covered by a gate oxide of \(\mathrm{ZrO_2}\) ( \(40~\mathrm{nm}\) ) and a gate electrode of \(\mathrm{Ru}\) ( \(50~\mathrm{nm}\) ). A dc current \((I_{\mathrm{dc}})\) is applied along the constriction channel ( \(x\) - direction) under a magnetic field \((B)\) applied in the direction with a polar angle \(\theta\) of \(80^{\circ}\) and an azimuthal angle \(\phi\) of \(70^{\circ}\) . In this geometry, the \(I_{\mathrm{dc}}\) generates SOTs through the spin Hall effect in the Pt underlayer, which leads to a magnetization oscillation of the Co/Ni layer when the SOT compensates the damping torque. The magnetization oscillation causes a periodic change in magnetoresistance (MR) of the same frequency [10], which is detected by a power spectral density (PSD) (see Methods for more details of measurement). To check whether the MR of the nano- constricted device is large enough to generate a detectable PSD, we measured the MR of the nano- constriction sample using an in- plane rotating magnetic field of \(1\mathrm{T}\) (Fig. 3b). The MR ratio is about \(1.2\%\) , which is sufficient to monitor the auto- oscillation of magnetization [17- 19].
+
+Figure 3c shows the color plots of PSD as a function of a magnetic field \((B)\) for the initial sample without applying a \(V_{\mathrm{g}}\) . Here, we used a fixed \(I_{\mathrm{dc}}\) of \(2.9\mathrm{mA}\) . The auto- oscillation peak is clearly visible, and the peak frequency increases with the increasing magnetic field, demonstrating that our Co/Ni device successfully operates as an SHNO. We then investigate the effect of \(V_{\mathrm{g}}\) on the auto- oscillation. The \(V_{\mathrm{g}}\) was applied in the same manner as the \(R_{\mathrm{H}}\) measurement as shown in Fig. 1. Figures 3d- 3g show the results, where \(V_{\mathrm{g}}\) 's of \(+4\mathrm{V}\) , \(+5\mathrm{V}\) , \(- 2\mathrm{V}\) , and \(- 3\mathrm{V}\) were successively applied. Notably, the auto- oscillation frequency is vertically shifted by \(V_{\mathrm{g}}\) 's; it increases (decreases) by a positive (negative) \(V_{\mathrm{g}}\) . This is consistent with our expectation as illustrated in Fig. 1a, i.e., a positive (negative) \(V_{\mathrm{g}}\) reduces (enhances) PMA or \(B_{\mathrm{k}}\) and consequently increases (decreases) the oscillation frequency. To clearly visualize the
+
+<--- Page Split --->
+
+gate voltage- induced frequency tuning, we extract the auto- oscillation spectra for \(B = 0.52 T\) from Figs. 3c- 3g and plot them in Fig. 3h. This demonstrates that the amount of the frequency tuning is up to \(2.1 \mathrm{GHz}\) with a \(V_{\mathrm{g}}\) of \(5 \mathrm{V}\) , which is remarkably larger than the previously reported value of \(50 \mathrm{MHz}\) [26,27] with a similar \(V_{\mathrm{g}}\) . This wider frequency tunability allows more states to be recognized, expanding the applicability to a wide range of oscillator- based neuromorphic computing. Note that similar results are observed in another Co/Ni device with a different thickness (Supplementary Note 2), confirming the reproducibility of the voltage- controlled frequency tuning of the SHNO.
+
+We next investigate the current dependent auto- oscillation of the SHNO. Figures 4a- 4e show PSD spectra as a function of current for the sample with different \(V_{\mathrm{g}}\) 's. Here, we used a fixed magnetic field of \(0.52 \mathrm{T}\) . It is found that the application of the \(V_{\mathrm{g}}\) changes two properties of the SHNO: auto- oscillation frequency and threshold current ( \(I_{\mathrm{th}}\) ) at which auto- oscillation begins to occur. First, the auto- oscillation peaks shift up and down according to the \(V_{\mathrm{g}}\) , demonstrating the voltage- controlled frequency tuning, consistent with the results shown in Fig. 3. Note that the oscillation frequency slightly increases with increasing \(I_{\mathrm{dc}}\) , which is attributed to the increase in SOT [6,24,26,47]. However, the maximum frequency tuning by a current within this measurement range is \(\sim 0.26 \mathrm{GHz}\) , which is much smaller than that by \(V_{\mathrm{g}}\) ( \(\sim 2.1 \mathrm{GHz}\) ). Furthermore, the slope of the oscillation frequency with respect to \(I_{\mathrm{dc}}\) is independent of the \(V_{\mathrm{g}}\) , demonstrating that the current- induced SOT is not significantly affected by the \(V_{\mathrm{g}}\) . This is confirmed by in- plane harmonic Hall measurements (Supplementary Note 3) [49]. Second, the \(I_{\mathrm{th}}\) is also modified by the \(V_{\mathrm{g}}\) . Figure 4f shows the \(I_{\mathrm{th}}\) according to the \(V_{\mathrm{g}}\) . Here, the \(I_{\mathrm{th}}\) values are extracted by a linear fit of the inverse of the PSD integral (Supplementary Note 4) [48]. The \(I_{\mathrm{th}}\) decreases (increases) for positive (negative) \(V_{\mathrm{g}}\) 's. Since the auto- oscillation occurs
+
+<--- Page Split --->
+
+when SOT compensates magnetic damping torque, the voltage- dependent \(I_{\mathrm{th}}\) is attributed to the voltage controlled \(\alpha_{eff}\) [6,24,47,50] as shown in Fig. 2e. Another interesting point is that the VCMA effect of the sample is non- volatile, so is the voltage- controlled frequency tuning; the auto- oscillation frequency is maintained even after the \(V_{\mathrm{g}}\) is turned off. This is distinct from the previous work, in which the frequency tuning only occurs during gate application.
+
+## Cumulative frequency control via a repetitive voltage pulse
+
+We finally demonstrate the emulation of synaptic plasticity [37- 40], a key function in the learning process of neuromorphic devices, by exploiting the non- volatility of our voltage- controlled SHNO. For this experiment, we fabricated a 100- nm- width constriction SHNO device with a Ta (3 nm)/Pt (5 nm)/[Co (0.4 nm)/Ni (0.6 nm)]7/Co (0.4 nm)/AlOx (2 nm) structure. To verify the cumulative frequency tuning, we applied a series of voltage pulses and measured the auto- oscillation spectrum between the pulses under a magnetic field (B) of 0.9 T applied in the direction with a polar angle \(\theta\) of \(80^{\circ}\) and an azimuthal angle \(\phi\) of \(70^{\circ}\) . Here, a \(V_{\mathrm{g}}\) of 10 seconds was applied at room temperature while applying a current of 1.8 mA, different from the experiments shown in Figs. 2- 4, where a \(V_{\mathrm{g}}\) was applied at \(150^{\circ}\mathrm{C}\) . Figure 5a shows the frequency change with the number of \(V_{\mathrm{g}}\) pulses (\(N_{V_{\mathrm{g}}}\)) of \(\pm 6 \mathrm{V}\) . The oscillation frequency gradually increases by about 1.24 GHz as the number of \(V_{\mathrm{g}}\) pulses of \(+6 \mathrm{V}\) increase, and it is then restored to its initial value by subsequent negative \(V_{\mathrm{g}}\) pulses of \(-6 \mathrm{V}\) . The frequency tuning for successive positive and negative voltage pulses mimics the synaptic potentiation (strengthening in synaptic weight) and depression (weakening of synaptic weight), respectively. Figure 5b shows the cumulative frequency change ( \(\delta f\) ) for various \(V_{\mathrm{g}}\) amplitudes,
+
+<--- Page Split --->
+
+demonstrating that the frequency change rate \((\delta f / N_{\mathrm{Vg}})\) is effectively tuned by the magnitude of the \(V_{\mathrm{g}}\) . The voltage dependence of the frequency change rate can emulate the stimulus- dependent synaptic transition rate in a neuromorphic device. Furthermore, our device memorizes the modulated frequency with its non- volatile nature, offering a compact device layout that can store trained synaptic weights without the need for a separate memory circuitry required for conventional STOs [2,11].
+
+## Conclusion
+
+We have demonstrated the voltage- driven GHz frequency tuning of SHNO with perpendicularly magnetized \(\mathrm{Pt}[\mathrm{Co} / \mathrm{Ni}]_{\mathrm{n}} / \mathrm{Co} / \mathrm{AlO}_{\mathrm{x}}\) structures. It is found that the auto- oscillation frequency of the SHNO is effectively modulated up to 2.1 GHz by controlling the PMA with a \(V_{\mathrm{g}}\) of 5 V, which is equivalent to \(1.25\mathrm{MV / cm}\) . This demonstrates that voltage- driven frequency tuning is much more efficient than conventional current- (or magnetic field- ) controlled frequency tuning. Moreover, owing to the non- volatile nature of the gate effect, the cumulative oscillation frequency is controlled by repetitive voltage pulses, which can mimic the biological synaptic functions of stimulus- dependent potentiation and depression. Therefore, our SHNO device can be utilized in the learning process of neuromorphic devices, and thereby facilitates spin- based low power neuromorphic hardware applications.
+
+<--- Page Split --->
+
+## Methods
+
+Sample preparation. The thin films of \(\mathrm{Ta / Pt / [Co / Ni]_{n} / Co / AlO_{x}}\) structures were fabricated on high resistivity Si substrates by magnetron sputtering under a base pressure of \(4.0\times 10^{- 6}\) Pa at room temperature. The metallic layers were deposited with an Ar gas pressure of 0.4 Pa and a dc power of \(30\mathrm{W}\) , and the \(\mathrm{AlO_x}\) layer was formed by plasma oxidation of an Al layer with an \(\mathrm{O_2}\) pressure of \(4.0\mathrm{Pa}\) and a dc power of \(30\mathrm{W}\) for 75 s. The \(\mathrm{ZrO_2}\) gate oxide (40 nm) was grown at \(125^{\circ}\mathrm{C}\) by plasma- enhanced atomic layer deposition (PE- ALD) using a TEMAZ [Tetrakis(ethylmethylamido)zirconium] precursor. The oxygen plasma for the PE- ALD was formed with an rf power of \(60\mathrm{W}\) and an \(\mathrm{O_2}\) gas flow of \(500~\mathrm{sccm}\) .
+
+Power spectral density (PSD) measurement. All PSD measurements were carried out at room temperature using a home- built probe station, where the sample was placed on an angle controllable holder located between two poles of an electromagnet. We used a bias- T to inject a dc current and to detect microwave signals simultaneously. A dc current was applied to the sample using a current source (Keithley 2450) with a current compliance of \(3\mathrm{mA}\) that prevents the sample degradation. The microwave signal generated from the sample was amplified by a low- noise amplifier (gain of \(+45\mathrm{dB}\) ) and detected by a spectrum analyzer (Keysight N5173B). The resolution bandwidth and video bandwidth were set to \(2\mathrm{MHz}\) and \(9\mathrm{kHz}\) , respectively. The measured spectra were averaged at least 3 times to increase the signal- to- noise ratio.
+
+Spin torque ferromagnetic resonance (ST- FMR) measurement. ST- FMR measurements were performed at room temperature using the same probe station used in PSD measurement. For the ST- FMR measurement, we applied a magnetic field in the direction slightly tilted from the \(z\) - axis to attain an FMR rectified voltage. A microwave signal (power of \(+14\mathrm{dBm}\) ) was injected into the sample by a signal generator (Keysight N9000B) through the RF port of a
+
+<--- Page Split --->
+
+bias- T, and a dc voltage generated from the sample was detected by a lock- in amplifier (SRS SR830). The tuning frequency was set to 313 Hz.
+
+<--- Page Split --->
+
+## References
+
+1. Torrejon, J. et al. Neuromorphic computing with nanoscale spintronic oscillators. Nature 547, 428–431 (2017).
+2. Romera, M. et al. Vowel recognition with four coupled spin-torque nano-oscillators. Nature 563, 230–234 (2018)
+3. Riou, M. et al. Temporal Pattern Recognition with Delayed-Feedback Spin-Torque Nano-Oscillators. Phys. Rev. Appl. 12, 024049 (2019).
+4. Grollier, J., Querlioz, D. & Stiles, M. D. Spintronic Nanodevices for Bioinspired Computing. Proc. IEEE 104, 2024–2039 (2016).
+5. Slavin, A. & Tiberkevich, V. Nonlinear auto-oscillator theory of microwave generation by spin-polarized current. IEEE Trans. Magn. 45, 1875–1918 (2009).
+6. Kim, J., Tiberkevich, V. & Slavin, A. Generation Linewidth of an Auto-Oscillator with a Nonlinear Frequency Shift: Spin-Torque Nano-Oscillator. Phys. Rev. Lett. 100, 017207 (2008).
+7. Locatelli, N., Cros, V. & Grollier, J. Spin-torque building blocks. Nat. Mater. 13, 11–20 (2014).
+8. Lee, H. S. et al. Power-efficient spin-torque nano-oscillator-based wireless communication with CMOS high-gain low-noise transmitter and receiver. IEEE Trans. Magn. 55, 4001910 (2019).
+9. Das, D., Tulapurkar, A. & Muralidharan, B. Scaling Projections on Spin-Transfer Torque Magnetic Tunnel Junctions. IEEE Trans. Electron Devices 65, 724–732 (2018).
+10. Chen, T. et al. Spin-Torque and Spin-Hall Nano-oscillators. Proc. IEEE 104, 1919-1945 (2016).
+11. Vodenicarevic, D., Locatelli, N., Abreu Araujo, F., Grollier, J. & Querlioz, D. A Nanotechnology-Ready Computing Scheme based on a Weakly Coupled Oscillator Network. Sci. Rep. 7, 44772 (2017).
+12. Yogendra, K., Fan, D., Jung, B. & Roy, K. Magnetic Pattern Recognition Using Injection
+
+<--- Page Split --->
+
+Locked Spin-Torque Nano-Oscillators. IEEE Trans. Electron Devices 63, 1674- 1680 (2016).
+
+13. Hirsch, J. E. Spin Hall Effect. Phys. Rev. Lett. 83, 1834-1837 (1999).
+
+14. Kato, Y. K., Myers, R. C., Gossard, A. C. & Awschalom, D. D. Observation of the spin Hall effect in semiconductors. Science 306, 1910-1913 (2004).
+
+15. Sinova, J., Valenzuela, S. O., Wunderlich, J., Back, C. H. & Jungwirth, T. Spin Hall effects. Rev. Mod. Phys. 87, 1213-1260 (2015).
+
+16. Demidov, V. E. et al. Magnetic nano-oscillator driven by pure spin current. Nat. Mater. 11, 1028-1031 (2012).
+
+17. Liu, R. H., Lim, W. L. & Urazhdin, S. Spectral characteristics of the microwave emission by the spin hall nano-oscillator. Phys. Rev. Lett. 110, 147601 (2013).
+
+18. Demidov, V. E., Urazhdin, S., Zholud, A., Sadovnikov, A. V. & Demokritov, S. O. Nanoconstriction-based spin-Hall nano-oscillator. Appl. Phys. Lett. 105, (2014).
+
+19. Duan, Z. et al. Nanowire spin torque oscillator driven by spin orbit torques. Nat. Commun. 5, 5616 (2014).
+
+20. Dürrenfeld, P., Awad, A. A., Houshang, A., Dumas, R. K. & Akerman, J. A 20 nm spin Hall nano-oscillator. Nanoscale 9, 1285-1291 (2017).
+
+21. Awad, A. A. et al. Long-range mutual synchronization of spin Hall nano-oscillators. Nat. Phys. 13, 292-299 (2017).
+
+22. Zahedinejad, M. et al. Two-dimensional mutually synchronized spin Hall nano-oscillator arrays for neuromorphic computing. Nat. Nanotechnol. 15, 47-52 (2020).
+
+23. Liu, L., Pai, C. F., Ralph, D. C. & Buhrman, R. A. Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices. Phys. Rev. Lett. 109, 186602 (2012).
+
+24. Tarequzzaman, M. et al. Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current. Commun. Phys. 2, 20 (2019).
+
+25. Albertsson. D. I., Zahedinejad, M., Akerman, J., Rodriguez, S. & Rusu, A. Compact
+
+<--- Page Split --->
+
+Macrospin- Based Model of Three- Terminal Spin- Hall Nano Oscillators. IEEE Trans. Magn. 55, 4003808 (2019).
+
+26. Liu, R. H., Chen, L., Urazhdin, S. & Du, Y. W. Controlling the spectral characteristics of a spin-current auto-oscillator with an electric field. Phys. Rev. Appl. 8, 021001 (2017).
+
+27. Fulara, H. et al. Giant voltage-controlled modulation of spin Hall nano-oscillator damping. Nat. Commun. 11, 4006 (2020).
+
+28. Ohno, H. et al. Electric-field control of ferromagnetism. Nature 408, 944-946 (2000).
+
+29. Maruyama, T. et al. Large voltage-induced magnetic anisotropy change in a few atomic layers of iron. Nat. Nanotechnol. 4, 158-161 (2009).
+
+30. Nakamura, K. et al. Giant modification of the magnetocrystalline anisotropy in transition-metal monolayers by an external electric field. Phys. Rev. Lett. 102, 187201 (2009).
+
+31. Bi, C. et al. Reversible control of Co magnetism by voltage-induced oxidation. Phys. Rev. Lett. 113, 267202 (2014).
+
+32. Bauer, U. et al. Magneto-ionic control of interfacial magnetism. Nat. Mater. 14, 174-181 (2015).
+
+33. Weisheit, M. et al. Electric Field-Induced Modification of Magnetism in Thin-Film Ferromagnets. Science 315, 349-351 (2007).
+
+34. Kittel, C. On the theory of ferromagnetic resonance absorption. Phys. Rev. 73, 155 (1948).
+
+35. Farle, M. Ferromagnetic resonance of ultrathin metallic layers. Rep. Prog. Phys. 61, 755-826 (2018)
+
+36. He, C. et al. Spin-Torque Ferromagnetic Resonance in W/Co-Fe-B/W/Co-Fe-B/MgO Stacks. Phys. Rev. Appl. 10, 034067 (2018).
+
+37. Ho, V. M., Lee, J.-A. & Martin, K. C. The cell biology of synaptic plasticity. Science 334, 623-628 (2011).
+
+38. Jo, S. H. et al. Nanoscale memristor device as synapse in neuromorphic systems. Nano Lett. 10, 1297-1301 (2010).
+
+39. Mishra, R., Kumar, D. & Yang, H. Oxygen-Migration-Based Spintronic Device Emulating
+
+<--- Page Split --->
+
+a Biological Synapse. Phys. Rev. Appl. 11, 054065 (2019).
+
+40. Huang, W. et al. Memristive Artificial Synapses for Neuromorphic Computing. Nano-Micro Lett. 13, 85 (2021).
+
+41. Baek, S.-H. C. et al. Complementary logic operation based on electric-field controlled spin-orbit torques. Nat. Electron. 1, 398-403 (2018).
+
+42. Park, K.-W. et al. Electric field control of magnetic anisotropy in the easy cone state of Ta/Pt/CoFeB/MgO structures. Appl. Phys. Lett. 109, 012405 (2016).
+
+43. Liu, L., Moriyama, T., Ralph, D. C. & Buhrman, R. A. Spin-torque ferromagnetic resonance induced by the spin Hall effect. Phys. Rev. Lett. 106, 306601 (2011).
+
+44. Kim, J. et al. Spin-orbit torques associated with ferrimagnetic order in Pt/GdFeCo/MgO layers. Sci. Rep. 8, 6017 (2018).
+
+45. Beaujour, J.-M., Ravelosona, D., Tudosa, I., Fullerton, E. E. & Kent, A. D. Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy. Phys. Rev. B 80, 180415(R) (2009).
+
+46. McMichael, R. D., Twisselmann, D. J. & Kunz, A. Localized Ferromagnetic Resonance in Inhomogeneous Thin Films. Phys. Rev. Lett. 90, 227601 (2003).
+
+47. Slonczewski, J. C., Current-driven excitation of magnetic multilayers. J. Magn. Magn. Mater. 159, L1-L7 (1996)
+
+48. Zheng, C., Chen, H. H., Zhang, X., Zhang, Z. & Liu, Y. Spin torque nano-oscillators with a perpendicular spin polarizer. Chinese Phys. B 28, (2019).
+
+49. Hayashi, M., Kim, J., Yamanouchi, M. & Ohno, H. Quantitative characterization of the spin-orbit torque using harmonic Hall voltage measurements. Phys. Rev. B 89, 144425 (2014).
+
+50. Rippard, W. H. et al. Spin-transfer dynamics in spin valves with out-of-plane magnetized CoNi free layers. Phys. Rev. B 81, 014426 (2010).
+
+<--- Page Split --->
+
+## Acknowledgments
+
+This work is supported by the Samsung Research Funding Center of Samsung Electronics under Project Numbers SRFC- MA1702- 02 and SRFC- MA1802- 01. K.- J.K acknowledges support from KAIST- funded Global Singularity Research Program for 2021.
+
+## Author contributions
+
+B.- G.P. and K.- J.K. planned and supervised the study. J.- G.C. and JP fabricated the devices and performed the experiment. M.- G.K. helps fabrication of the sample with a gate structure. DK and J.- S.R. help the high- frequency measurement. J.- G.C., JP, K.- J.K., K.- J.L., and B.- G.P. analyzed the data and wrote the manuscript.
+
+## Competing interests
+
+Authors declare no competing interests.
+
+## Data availability
+
+The data that support the findings of this study are available from the corresponding author upon reasonable request.
+
+<--- Page Split --->
+
+
+Figure 1. Voltage-controlled perpendicular magnetic anisotropy. a, Schematic illustration of the mechanism of the voltage-driven frequency tuning via voltage-controlled magnetic anisotropy (VCMA). The green and gray arrows represent the directions of spin-orbit torque and damping torque, respectively. b, The resonance frequency \((f_{\mathrm{res}})\) as a function of in-plane magnetic field \((B_{\parallel})\) for high PMA (blue) and low PMA (red). c, magnetization \((M)\) versus out-of-plane magnetic field \((B_{z})\) of the Co/Ni film. d, Anomalous Hall resistance \((R_{\mathrm{H}})\) curves of the Co/Ni sample for sequentially applied gate voltages of \(+3\mathrm{V}\) , \(+5\mathrm{V}\) , \(-3\mathrm{V}\) , and \(-5\mathrm{V}\) , respectively.
+
+<--- Page Split --->
+
+
+Figure 2. Voltage-dependent ST-FMR spectra. a, ST-FMR spectra of the Co/Ni sample for sequentially applied gate voltages (initial, \(+5\mathrm{V}\) , and -5V). Here, the microwave frequency is 15 GHz. The dotted lines are the best fits based on Eq. (1). b, Resonance frequency \((f_{\mathrm{res},z})\) as a function of resonance field \(B_{\mathrm{res},z}\) of the sample with different sequentially applied gate voltages. c, Variation of perpendicular magnetic anisotropy field \((B_{\mathrm{k}})\) versus sequentially applied gate voltage. d, The linewidth of the Lorentzian function \((\Delta B)\) as a function of the \(f_{\mathrm{res},z}\) of the sample with sequentially applied gate voltages. e, Variation of effective damping constant \((\alpha_{\mathrm{eff}})\) versus sequentially applied gate voltage.
+
+<--- Page Split --->
+
+
+Figure 3. Magnetic field-dependent voltage-driven frequency tuning of SHNO. a, Schematic illustration of the experimental set-up. The inset is a scanning electron microscope image of an SHNO device. b, Angle-dependent magnetoresistance (MR) of the Co/Ni sample. c-g, Power spectral densities (PSDs) as a function of magnetic field for sequentially applied gate voltages, \(V_{\mathrm{g}} = 0 \mathrm{V}\) (initial state) (c), \(V_{\mathrm{g}} = +4 \mathrm{V}\) (d), \(V_{\mathrm{g}} = +5 \mathrm{V}\) (e), \(V_{\mathrm{g}} = -2 \mathrm{V}\) (f), and \(V_{\mathrm{g}} = -3 \mathrm{V}\) (g). \(I_{\mathrm{dc}} = 2.9 \mathrm{mA}\) . h, Auto-oscillation spectra for \(B = 0.52 \mathrm{T}\) with different gate voltages, extracted from Figs. 3c-3g.
+
+<--- Page Split --->
+
+
+Figure 4. Current-dependent voltage-driven frequency tuning of SHNO. a-e, PSDs as a function of current for sequentially applied gate voltages, \(V_{\mathrm{g}} = 0 \mathrm{V}\) (initial state) (a), \(V_{\mathrm{g}} = +4 \mathrm{V}\) (b), \(V_{\mathrm{g}} = +5 \mathrm{V}\) (c), \(V_{\mathrm{g}} = -2 \mathrm{V}\) (d), and \(V_{\mathrm{g}} = -3 \mathrm{V}\) (e). \(B = 0.52 \mathrm{T}\) . f, Threshold current, \(I_{\mathrm{th}}\) , according to the sequentially applied gate voltages, extracted from Figs. 4a-4e.
+
+<--- Page Split --->
+
+
+Figure 5. Cumulative frequency control via repetitive gate voltage pulses. a, The auto oscillation frequency of the SHNO versus the number of positive (black) and negative (red) gate voltage pulses \((N_{V_{\mathrm{g}}})\) . b, Voltage-driven cumulative frequency change \((\delta f)\) versus \(N_{V_{\mathrm{g}}}\) for different gate voltages.
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+Slfinal.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1_det.mmd b/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..08f21390c9d0910aaed5cfb8a95269e47e630eba
--- /dev/null
+++ b/preprint/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1/preprint__052e2ec6d21556561e0261e9df965f3e2f0efe816a12ce1f376d222fc7433bf1_det.mmd
@@ -0,0 +1,368 @@
+<|ref|>title<|/ref|><|det|>[[42, 108, 904, 175]]<|/det|>
+# Voltage-driven gigahertz frequency tuning of spin Hall nano-oscillators
+
+<|ref|>text<|/ref|><|det|>[[42, 196, 519, 567]]<|/det|>
+Jong-Guk Choi KAIST Jaehyeon Park KAIST Min-Gu Kang Korea Advanced Institute of Science and Technology Doyoon Kim Korea University Jae-Sung Rieh Korea University Kyung-Jin Lee Korea Advanced Institute of Science and Technology (KAIST) https://orcid.org/0000- 0001- 6269- 2266 Kab-Jin Kim Korea Advanced Institute of Science and Technology https://orcid.org/0000- 0002- 8378- 3746 Byong-Guk Park (bgpark@kaist.ac.kr) KAIST https://orcid.org/0000- 0001- 8813- 7025
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 604, 102, 621]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[42, 641, 920, 661]]<|/det|>
+Keywords: Spin Hall nano- oscillators, oscillator- based neuromorphic computing, oscillation frequency
+
+<|ref|>text<|/ref|><|det|>[[44, 679, 339, 698]]<|/det|>
+Posted Date: September 8th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 717, 463, 737]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 840717/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 754, 910, 797]]<|/det|>
+License: © © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 833, 912, 876]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on June 30th, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 31493- z.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[120, 100, 834, 121]]<|/det|>
+# Voltage-driven gigahertz frequency tuning of spin Hall nano-oscillators
+
+<|ref|>text<|/ref|><|det|>[[127, 146, 870, 200]]<|/det|>
+Jong- Guk Choi \(^{1\dagger}\) , Jaehyeon Park \(^{2\dagger}\) , Min- Gu Kang \(^{1}\) , Doyoon Kim \(^{3}\) , Jae- Sung Rieh \(^{3}\) , Kyung- Jin Lee \(^{2}\) , Kab- Jin Kim \(^{2\star}\) and Byong- Guk Park \(^{1\star}\)
+
+<|ref|>text<|/ref|><|det|>[[118, 226, 798, 313]]<|/det|>
+\(^{1}\) Department of Materials Science and Engineering, KAIST, Daejeon 34141, Korea \(^{2}\) Department of Physics, KAIST, Daejeon 34141, Korea \(^{3}\) School of Electrical Engineering, Korea University, Seoul 02841, Korea
+
+<|ref|>text<|/ref|><|det|>[[118, 392, 547, 409]]<|/det|>
+\(^{\dagger}\) These two authors equally contributed to this work.
+
+<|ref|>text<|/ref|><|det|>[[120, 429, 825, 448]]<|/det|>
+\(\star\) Correspondence to: kabjin@kaist.ac.kr (K.- J.K.) and bgpark@kaist.ac.kr (B.- G.P.)
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 488, 197, 504]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[117, 528, 884, 877]]<|/det|>
+Spin Hall nano- oscillators (SHNOs) exploiting current- driven magnetization auto- oscillation have recently received much attention because of their potential for oscillator- based neuromorphic computing. Widespread neuromorphic application with SHNOs requires an energy- efficient way to tune oscillation frequency in broad ranges and store trained frequencies in SHNOs without the need for additional memory circuitry. Voltage control of oscillation frequency of SHNOs was experimentally demonstrated, but the voltage- driven frequency tuning was volatile and limited to megahertz ranges. Here, we show that the frequency of SHNO is controlled up to 2.1 GHz by a moderate electric field of 1.25 MV/cm. The large frequency tuning is attributed to the voltage- controlled magnetic anisotropy (VCMA) in a perpendicularly magnetized Ta/Pt/[Co/Ni] \(_n\) /Co/AlOx structure. Moreover, non- volatile VCMA effect enables control of the cumulative
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 98, 882, 217]]<|/det|>
+frequency using repetitive voltage pulses, which mimic the potentiation and depression functions of biological synapses. Our results suggest that the voltage- driven frequency tuning of SHNOs facilitates the development of energy- efficient spin- based neuromorphic devices.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 99, 884, 413]]<|/det|>
+Spintronic oscillators that generate microwaves through spin- torque- driven magnetization precession are being extensively investigated for neuromorphic applications [1- 4] owing to their unique features such as non- linearity [5,6], low- power operation [7,8], scalability [1,4,9], and CMOS compatibility [10]. Indeed, spin- transfer- torque- based oscillators (STOs) have recently been implemented in oscillator neural networks, demonstrating pattern recognition [2,11,12]. Furthermore, the STO device has been successfully trained to recognize the input pattern signals by tuning the frequency of individual oscillators using a driving current [2,11] or magnetic field [12]. However, the current or magnetic field- based frequency tuning is not energy efficient; thus, it is necessary to find an alternative way to tune the frequency widely with reduced power consumption.
+
+<|ref|>text<|/ref|><|det|>[[117, 436, 884, 719]]<|/det|>
+Recently, another type of STO, in which magnetization precession is caused by spin currents generated by the spin Hall effect [13- 15], has been developed, which is referred to as spin Hall nano- oscillator (SHNO) [16- 20]. Since the SHNO is operated with an in- plane current, it has the following advantages over conventional STO that utilizes a perpendicular current. First, multiple oscillators integrated into a common spin- Hall material can be controlled simultaneously by an in- plane current, allowing long- range mutual synchronization of the SHNOs [21,22]. Second, a gate structure is easily incorporated in a three- terminal SHNO structure [23- 25], so that an individual oscillator can be independently controlled by a gate voltage [26,27].
+
+<|ref|>text<|/ref|><|det|>[[117, 740, 884, 890]]<|/det|>
+A recent study [27] has experimentally demonstrated the gate voltage- induced frequency tuning in W/CoFeB/MgO structures with the frequency tuning range of about 50 MHz. However, this frequency tuning range is relatively narrow compared to the oscillation frequency ( \(\sim 10\) GHz). Thus, although 10- 50 MHz frequency tunability is sufficient to optimize the synchronization map for a small number of different synchronization states as in
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 98, 883, 250]]<|/det|>
+vowel recognition [2,27], a wider frequency tunability is required for tasks having more states of being recognized and thus expands the applicability of gate- controlled SHNOs to widespread oscillator- based neuromorphic computing. Moreover, the previously demonstrated voltage- driven frequency tuning of SHNO [27] is volatile, so that an additional memory circuitry is required to store trained synaptic weights of oscillation frequency.
+
+<|ref|>text<|/ref|><|det|>[[117, 272, 884, 621]]<|/det|>
+In this Article, we report voltage- driven large frequency tuning of SHNO by exploiting voltage- controlled magnetic anisotropy (VCMA) [28- 33] as schematically illustrated in Fig. 1a. The SHNO consists of a ferromagnet (FM)/heavy metal (HM) bilayer. In this geometry, a charge current flowing through the HM layer generates a vertical spin current via the spin Hall effect, which exerts spin- orbit torques (SOTs) on the magnetization of the FM layer. The auto- oscillation of magnetization occurs when the SOT (green arrow) fully compensates the damping torque (gray arrow), and the auto- oscillation frequency is governed by the resonance frequency \((f_{\mathrm{res}})\) of the ferromagnet. Here, we employ a perpendicular magnetic anisotropy (PMA) material, which is distinct from previous works where in- plane magnetized materials were generally used. In the presence of an in- plane field, \(f_{\mathrm{res}}\) of a PMA material is determined as [34- 36],
+
+<|ref|>equation<|/ref|><|det|>[[384, 644, 686, 678]]<|/det|>
+\[f_{\mathrm{res}} = \frac{\gamma}{2\pi}\sqrt{B_{\mathrm{k}}^{2} - B_{\mathrm{h}}^{2}} (0< B_{\mathrm{h}}< B_{\mathrm{k}}),\]
+
+<|ref|>equation<|/ref|><|det|>[[384, 702, 815, 731]]<|/det|>
+\[f_{\mathrm{res}} = \frac{\gamma}{2\pi}\sqrt{B_{\mathrm{H}}(B_{\mathrm{H}} - B_{\mathrm{k}})} (B_{\mathrm{H}}\geq B_{\mathrm{k}}), \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[117, 753, 884, 876]]<|/det|>
+where \(\gamma\) is the gyromagnetic ratio, \(B_{\mathrm{k}}\) is the effective perpendicular anisotropy field, and \(B_{\mathrm{H}}\) is the external in- plane magnetic field. Equation (1) indicates that a broad frequency tuning is effectively achieved by controlling \(B_{\mathrm{k}}\) . Figure 1b shows an example; when \(B_{\mathrm{H}}\) is larger than \(B_{\mathrm{k}}\) , the frequency increases by weakening \(B_{\mathrm{k}}\) . In this work, we demonstrate that \(B_{\mathrm{k}}\) of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[116, 98, 885, 448]]<|/det|>
+perpendicularly magnetized Co/Ni multilayers is controlled as large as 0.22 T by a moderate electric field of 1.25 MV/cm. This results in a frequency tuning up to 2.1 GHz, which is more than 40 times larger than the previously reported values [26,27]. We find that the voltage- controlled frequency tuning is independent of the driving current and is much more efficient than the current- controlled frequency tuning used in conventional STOs. Furthermore, the voltage effect is non- volatile in our sample, allowing the cumulative frequency control of SHNO using repetitive voltage pulses. This can facilitate the potentiation and depression functions of artificial synapses [37- 40], and thus can be utilized in the learning process of neuromorphic devices. Our results demonstrating efficient frequency tuning of SHNO via gate voltage provide an essential building block for spin- based low power neuromorphic hardware applications.
+
+<|ref|>sub_title<|/ref|><|det|>[[138, 520, 606, 539]]<|/det|>
+## Voltage-controlled perpendicular magnetic anisotropy
+
+<|ref|>text<|/ref|><|det|>[[116, 561, 885, 886]]<|/det|>
+We first demonstrate the VCMA effect in a Co/Ni multilayer sample of Ta (3 nm)/Pt (5 nm)/[Co (0.45 nm)/Ni (0.6 nm)]7/Co (0.45 nm)/AlOx (2 nm) structures (see Methods for details of sample growth). Figure 1c shows the magnetization measurement while sweeping a perpendicular magnetic field (Bz), indicating that the Co/Ni film has PMA. To test the VCMA of the sample, we patterned the film into a Hall bar device with a 10 μm × 10 μm cross, which is fully covered by a gate oxide of ZrO2 (40 nm) and a gate electrode of Ru (50 nm). Figure 1d shows the anomalous Hall resistance (RH) after sequentially applying a gate voltage (Vg). Here, we applied a Vg to the top electrode for 5 minutes at 150 °C and then measured RH at room temperature. This is possible because the voltage effect is maintained even after turning off the Vg [31,32,41,42]. The result shows that the PMA is gradually weakened by positive Vg’s and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 98, 882, 190]]<|/det|>
+restored by subsequent negative \(V_{\mathrm{g}}\) 's, indicating that the PMA in our Co/Ni multilayer sample is effectively modulated by \(V_{\mathrm{g}}\) . Note that the \(V_{\mathrm{g}}\) of \(5 \mathrm{~V}\) is equivalent to an electric field of 1.25 MV/cm.
+
+<|ref|>text<|/ref|><|det|>[[117, 211, 884, 465]]<|/det|>
+In order to quantitatively analyze the VCMA effect, we performed the spin torque- ferromagnetic resonance (ST- FMR) measurement. The ST- FMR spectra were measured using a bar- shaped device ( \(8 \mu \mathrm{m} \times 14 \mu \mathrm{m}\) ) fabricated from the same Co/Ni film. The microwave frequency used for the ST- FMR measurement ranges from \(10 \mathrm{GHz}\) to \(21 \mathrm{GHz}\) (see Methods for measurement details). Figure 2a shows the ST- FMR spectra of the sample with different \(V_{\mathrm{g}}\) 's at a frequency of \(15 \mathrm{GHz}\) , measured while sweeping magnetic fields in a direction slightly tilted from the \(z\) - direction. The ST- FMR spectra can be expressed by the combination of symmetric and anti- symmetric Lorentzian functions as [43,44],
+
+<|ref|>equation<|/ref|><|det|>[[201, 485, 815, 521]]<|/det|>
+\[V_{\mathrm{ST - FMR}}(B_{\mathrm{z}}) = V_{\mathrm{sym}}\frac{\Delta B^{2}}{(B_{\mathrm{z}} - B_{\mathrm{res,z}})^{2} + \Delta B^{2}} + V_{\mathrm{asy}}\frac{\Delta B(B_{\mathrm{z}} - B_{\mathrm{res,z}})}{(B_{\mathrm{z}} - B_{\mathrm{res,z}})^{2} + \Delta B^{2}}, \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[117, 544, 884, 874]]<|/det|>
+where \(B_{\mathrm{res,z}}\) is the center magnetic field of the Lorentzian functions corresponding to the resonance magnetic field, \(\Delta B\) is the linewidth (half- width at half maximum) of the Lorentzian function, and \(V_{\mathrm{sym}}(V_{\mathrm{asy}})\) is a symmetric (anti- symmetric) component of resonance amplitude. The dotted lines represent the fitting curves of the ST- FMR spectra using Eq. (2), from which we extracted the \(B_{\mathrm{res,z}}\) and \(\Delta B\) values. It is observed that the Lorentzian curve for the initial sample (black symbols) is centered around \(0.34 \mathrm{~T}\) . That is, \(B_{\mathrm{res,z}} = 0.34 \mathrm{~T}\) . Notably, the \(B_{\mathrm{res,z}}\) is largely shifted by the \(V_{\mathrm{g}}\) ; the \(B_{\mathrm{res,z}}\) is increased up to \(0.59 \mathrm{~T}\) by a positive voltage (+5 V, red symbols), but it is then reduced to \(0.39 \mathrm{~T}\) by a subsequent negative voltage (- 5 V, blue symbols). We measured the \(B_{\mathrm{res,z}}\) for different frequencies (see Supplementary Note 1) and summarize the resonance frequency \(f_{\mathrm{res,z}}\) vs \(B_{\mathrm{res,z}}\) in Fig. 2b, where the black symbols represent the initial
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 97, 884, 461]]<|/det|>
+sample without applying a \(V_{\mathrm{g}}\) , while the red and blue symbols correspond to the samples after successively applying \(+5\mathrm{V}\) and - 5 V, respectively. The linear relation between the \(f_{\mathrm{res},z}\) and \(B_{\mathrm{res},z}\) is well explained by the Kittel formula \(f_{\mathrm{res},z} = \frac{\gamma}{2\pi} (B_{\mathrm{res},z} + B_{\mathrm{k}})\) [45], from which the \(B_{\mathrm{k}}\) can be extracted. We note that the ST- FMR measurement was done under a magnetic field along the \(z\) - direction, so the above resonance frequency formula is different from Eq. (1), which is based on an in- plane magnetic field. Figure 2c shows the extracted \(B_{\mathrm{k}}\) according to the \(V_{\mathrm{g}}\) ; the \(B_{\mathrm{k}}\) reduces from \(0.16\pm 0.01\mathrm{T}\) to \(- 0.08\pm 0.01\mathrm{T}\) when applying \(+5\mathrm{V}\) , and is restored close to the initial value by a negative gate of - 5 V. This is consistent with the results shown in Fig. 1c. Note that the average change of \(B_{\mathrm{k}}\) is \(0.22\pm 0.02\mathrm{T}\) by \(\pm 5\mathrm{V}\) , which can cause a frequency tuning up to a few GHz according to Eq. (1).
+
+<|ref|>text<|/ref|><|det|>[[115, 481, 884, 750]]<|/det|>
+Figure 2d shows the \(\Delta B\) as a function of \(f_{\mathrm{res},z}\) , where the color symbols represent the samples with different \(V_{\mathrm{g}}\) 's, identical to those in Fig. 2b. Using the relation \(\Delta B = \Delta B_{0} + \frac{2\pi\alpha_{\mathrm{eff}}}{\gamma} f_{\mathrm{res},z}\) [43- 46], the effective magnetic damping constant \(\alpha_{\mathrm{eff}}\) is obtained. Here, \(\Delta B_{0}\) is the zero- frequency linewidth due to long- range magnetic inhomogeneity [46]. Figure 2f shows the dependence of the \(\alpha_{\mathrm{eff}}\) on \(V_{\mathrm{g}}\) ; the \(\alpha_{\mathrm{eff}}\) decreases (increases) by a positive (negative) \(V_{\mathrm{g}}\) . This is consistent with the previous reports [27], where the voltage- driven frequency tuning was obtained in the MHz range. The possible effect of the voltage- controlled \(\alpha_{\mathrm{eff}}\) on the frequency tuning in our sample will be discussed later.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 817, 485, 836]]<|/det|>
+## Voltage-driven frequency tuning of SHNO
+
+<|ref|>text<|/ref|><|det|>[[137, 858, 884, 878]]<|/det|>
+We now move on to our main result, i.e., the gate voltage- induced frequency tuning of SHNO.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[116, 98, 884, 516]]<|/det|>
+Figure 3a illustrates the measurement schematics; the SHNO device was fabricated by patterning the Co/Ni film into a nano- constriction with a width of \(140~\mathrm{nm}\) , which is entirely covered by a gate oxide of \(\mathrm{ZrO_2}\) ( \(40~\mathrm{nm}\) ) and a gate electrode of \(\mathrm{Ru}\) ( \(50~\mathrm{nm}\) ). A dc current \((I_{\mathrm{dc}})\) is applied along the constriction channel ( \(x\) - direction) under a magnetic field \((B)\) applied in the direction with a polar angle \(\theta\) of \(80^{\circ}\) and an azimuthal angle \(\phi\) of \(70^{\circ}\) . In this geometry, the \(I_{\mathrm{dc}}\) generates SOTs through the spin Hall effect in the Pt underlayer, which leads to a magnetization oscillation of the Co/Ni layer when the SOT compensates the damping torque. The magnetization oscillation causes a periodic change in magnetoresistance (MR) of the same frequency [10], which is detected by a power spectral density (PSD) (see Methods for more details of measurement). To check whether the MR of the nano- constricted device is large enough to generate a detectable PSD, we measured the MR of the nano- constriction sample using an in- plane rotating magnetic field of \(1\mathrm{T}\) (Fig. 3b). The MR ratio is about \(1.2\%\) , which is sufficient to monitor the auto- oscillation of magnetization [17- 19].
+
+<|ref|>text<|/ref|><|det|>[[116, 536, 884, 865]]<|/det|>
+Figure 3c shows the color plots of PSD as a function of a magnetic field \((B)\) for the initial sample without applying a \(V_{\mathrm{g}}\) . Here, we used a fixed \(I_{\mathrm{dc}}\) of \(2.9\mathrm{mA}\) . The auto- oscillation peak is clearly visible, and the peak frequency increases with the increasing magnetic field, demonstrating that our Co/Ni device successfully operates as an SHNO. We then investigate the effect of \(V_{\mathrm{g}}\) on the auto- oscillation. The \(V_{\mathrm{g}}\) was applied in the same manner as the \(R_{\mathrm{H}}\) measurement as shown in Fig. 1. Figures 3d- 3g show the results, where \(V_{\mathrm{g}}\) 's of \(+4\mathrm{V}\) , \(+5\mathrm{V}\) , \(- 2\mathrm{V}\) , and \(- 3\mathrm{V}\) were successively applied. Notably, the auto- oscillation frequency is vertically shifted by \(V_{\mathrm{g}}\) 's; it increases (decreases) by a positive (negative) \(V_{\mathrm{g}}\) . This is consistent with our expectation as illustrated in Fig. 1a, i.e., a positive (negative) \(V_{\mathrm{g}}\) reduces (enhances) PMA or \(B_{\mathrm{k}}\) and consequently increases (decreases) the oscillation frequency. To clearly visualize the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 98, 884, 354]]<|/det|>
+gate voltage- induced frequency tuning, we extract the auto- oscillation spectra for \(B = 0.52 T\) from Figs. 3c- 3g and plot them in Fig. 3h. This demonstrates that the amount of the frequency tuning is up to \(2.1 \mathrm{GHz}\) with a \(V_{\mathrm{g}}\) of \(5 \mathrm{V}\) , which is remarkably larger than the previously reported value of \(50 \mathrm{MHz}\) [26,27] with a similar \(V_{\mathrm{g}}\) . This wider frequency tunability allows more states to be recognized, expanding the applicability to a wide range of oscillator- based neuromorphic computing. Note that similar results are observed in another Co/Ni device with a different thickness (Supplementary Note 2), confirming the reproducibility of the voltage- controlled frequency tuning of the SHNO.
+
+<|ref|>text<|/ref|><|det|>[[115, 375, 884, 878]]<|/det|>
+We next investigate the current dependent auto- oscillation of the SHNO. Figures 4a- 4e show PSD spectra as a function of current for the sample with different \(V_{\mathrm{g}}\) 's. Here, we used a fixed magnetic field of \(0.52 \mathrm{T}\) . It is found that the application of the \(V_{\mathrm{g}}\) changes two properties of the SHNO: auto- oscillation frequency and threshold current ( \(I_{\mathrm{th}}\) ) at which auto- oscillation begins to occur. First, the auto- oscillation peaks shift up and down according to the \(V_{\mathrm{g}}\) , demonstrating the voltage- controlled frequency tuning, consistent with the results shown in Fig. 3. Note that the oscillation frequency slightly increases with increasing \(I_{\mathrm{dc}}\) , which is attributed to the increase in SOT [6,24,26,47]. However, the maximum frequency tuning by a current within this measurement range is \(\sim 0.26 \mathrm{GHz}\) , which is much smaller than that by \(V_{\mathrm{g}}\) ( \(\sim 2.1 \mathrm{GHz}\) ). Furthermore, the slope of the oscillation frequency with respect to \(I_{\mathrm{dc}}\) is independent of the \(V_{\mathrm{g}}\) , demonstrating that the current- induced SOT is not significantly affected by the \(V_{\mathrm{g}}\) . This is confirmed by in- plane harmonic Hall measurements (Supplementary Note 3) [49]. Second, the \(I_{\mathrm{th}}\) is also modified by the \(V_{\mathrm{g}}\) . Figure 4f shows the \(I_{\mathrm{th}}\) according to the \(V_{\mathrm{g}}\) . Here, the \(I_{\mathrm{th}}\) values are extracted by a linear fit of the inverse of the PSD integral (Supplementary Note 4) [48]. The \(I_{\mathrm{th}}\) decreases (increases) for positive (negative) \(V_{\mathrm{g}}\) 's. Since the auto- oscillation occurs
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 98, 883, 256]]<|/det|>
+when SOT compensates magnetic damping torque, the voltage- dependent \(I_{\mathrm{th}}\) is attributed to the voltage controlled \(\alpha_{eff}\) [6,24,47,50] as shown in Fig. 2e. Another interesting point is that the VCMA effect of the sample is non- volatile, so is the voltage- controlled frequency tuning; the auto- oscillation frequency is maintained even after the \(V_{\mathrm{g}}\) is turned off. This is distinct from the previous work, in which the frequency tuning only occurs during gate application.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 321, 630, 340]]<|/det|>
+## Cumulative frequency control via a repetitive voltage pulse
+
+<|ref|>text<|/ref|><|det|>[[115, 360, 884, 860]]<|/det|>
+We finally demonstrate the emulation of synaptic plasticity [37- 40], a key function in the learning process of neuromorphic devices, by exploiting the non- volatility of our voltage- controlled SHNO. For this experiment, we fabricated a 100- nm- width constriction SHNO device with a Ta (3 nm)/Pt (5 nm)/[Co (0.4 nm)/Ni (0.6 nm)]7/Co (0.4 nm)/AlOx (2 nm) structure. To verify the cumulative frequency tuning, we applied a series of voltage pulses and measured the auto- oscillation spectrum between the pulses under a magnetic field (B) of 0.9 T applied in the direction with a polar angle \(\theta\) of \(80^{\circ}\) and an azimuthal angle \(\phi\) of \(70^{\circ}\) . Here, a \(V_{\mathrm{g}}\) of 10 seconds was applied at room temperature while applying a current of 1.8 mA, different from the experiments shown in Figs. 2- 4, where a \(V_{\mathrm{g}}\) was applied at \(150^{\circ}\mathrm{C}\) . Figure 5a shows the frequency change with the number of \(V_{\mathrm{g}}\) pulses (\(N_{V_{\mathrm{g}}}\)) of \(\pm 6 \mathrm{V}\) . The oscillation frequency gradually increases by about 1.24 GHz as the number of \(V_{\mathrm{g}}\) pulses of \(+6 \mathrm{V}\) increase, and it is then restored to its initial value by subsequent negative \(V_{\mathrm{g}}\) pulses of \(-6 \mathrm{V}\) . The frequency tuning for successive positive and negative voltage pulses mimics the synaptic potentiation (strengthening in synaptic weight) and depression (weakening of synaptic weight), respectively. Figure 5b shows the cumulative frequency change ( \(\delta f\) ) for various \(V_{\mathrm{g}}\) amplitudes,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 97, 883, 290]]<|/det|>
+demonstrating that the frequency change rate \((\delta f / N_{\mathrm{Vg}})\) is effectively tuned by the magnitude of the \(V_{\mathrm{g}}\) . The voltage dependence of the frequency change rate can emulate the stimulus- dependent synaptic transition rate in a neuromorphic device. Furthermore, our device memorizes the modulated frequency with its non- volatile nature, offering a compact device layout that can store trained synaptic weights without the need for a separate memory circuitry required for conventional STOs [2,11].
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 355, 217, 371]]<|/det|>
+## Conclusion
+
+<|ref|>text<|/ref|><|det|>[[117, 396, 884, 714]]<|/det|>
+We have demonstrated the voltage- driven GHz frequency tuning of SHNO with perpendicularly magnetized \(\mathrm{Pt}[\mathrm{Co} / \mathrm{Ni}]_{\mathrm{n}} / \mathrm{Co} / \mathrm{AlO}_{\mathrm{x}}\) structures. It is found that the auto- oscillation frequency of the SHNO is effectively modulated up to 2.1 GHz by controlling the PMA with a \(V_{\mathrm{g}}\) of 5 V, which is equivalent to \(1.25\mathrm{MV / cm}\) . This demonstrates that voltage- driven frequency tuning is much more efficient than conventional current- (or magnetic field- ) controlled frequency tuning. Moreover, owing to the non- volatile nature of the gate effect, the cumulative oscillation frequency is controlled by repetitive voltage pulses, which can mimic the biological synaptic functions of stimulus- dependent potentiation and depression. Therefore, our SHNO device can be utilized in the learning process of neuromorphic devices, and thereby facilitates spin- based low power neuromorphic hardware applications.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 100, 198, 117]]<|/det|>
+## Methods
+
+<|ref|>text<|/ref|><|det|>[[116, 141, 884, 392]]<|/det|>
+Sample preparation. The thin films of \(\mathrm{Ta / Pt / [Co / Ni]_{n} / Co / AlO_{x}}\) structures were fabricated on high resistivity Si substrates by magnetron sputtering under a base pressure of \(4.0\times 10^{- 6}\) Pa at room temperature. The metallic layers were deposited with an Ar gas pressure of 0.4 Pa and a dc power of \(30\mathrm{W}\) , and the \(\mathrm{AlO_x}\) layer was formed by plasma oxidation of an Al layer with an \(\mathrm{O_2}\) pressure of \(4.0\mathrm{Pa}\) and a dc power of \(30\mathrm{W}\) for 75 s. The \(\mathrm{ZrO_2}\) gate oxide (40 nm) was grown at \(125^{\circ}\mathrm{C}\) by plasma- enhanced atomic layer deposition (PE- ALD) using a TEMAZ [Tetrakis(ethylmethylamido)zirconium] precursor. The oxygen plasma for the PE- ALD was formed with an rf power of \(60\mathrm{W}\) and an \(\mathrm{O_2}\) gas flow of \(500~\mathrm{sccm}\) .
+
+<|ref|>text<|/ref|><|det|>[[116, 413, 884, 696]]<|/det|>
+Power spectral density (PSD) measurement. All PSD measurements were carried out at room temperature using a home- built probe station, where the sample was placed on an angle controllable holder located between two poles of an electromagnet. We used a bias- T to inject a dc current and to detect microwave signals simultaneously. A dc current was applied to the sample using a current source (Keithley 2450) with a current compliance of \(3\mathrm{mA}\) that prevents the sample degradation. The microwave signal generated from the sample was amplified by a low- noise amplifier (gain of \(+45\mathrm{dB}\) ) and detected by a spectrum analyzer (Keysight N5173B). The resolution bandwidth and video bandwidth were set to \(2\mathrm{MHz}\) and \(9\mathrm{kHz}\) , respectively. The measured spectra were averaged at least 3 times to increase the signal- to- noise ratio.
+
+<|ref|>text<|/ref|><|det|>[[117, 718, 884, 868]]<|/det|>
+Spin torque ferromagnetic resonance (ST- FMR) measurement. ST- FMR measurements were performed at room temperature using the same probe station used in PSD measurement. For the ST- FMR measurement, we applied a magnetic field in the direction slightly tilted from the \(z\) - axis to attain an FMR rectified voltage. A microwave signal (power of \(+14\mathrm{dBm}\) ) was injected into the sample by a signal generator (Keysight N9000B) through the RF port of a
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 99, 880, 150]]<|/det|>
+bias- T, and a dc voltage generated from the sample was detected by a lock- in amplifier (SRS SR830). The tuning frequency was set to 313 Hz.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[119, 100, 216, 117]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[110, 135, 886, 888]]<|/det|>
+1. Torrejon, J. et al. Neuromorphic computing with nanoscale spintronic oscillators. Nature 547, 428–431 (2017).
+2. Romera, M. et al. Vowel recognition with four coupled spin-torque nano-oscillators. Nature 563, 230–234 (2018)
+3. Riou, M. et al. Temporal Pattern Recognition with Delayed-Feedback Spin-Torque Nano-Oscillators. Phys. Rev. Appl. 12, 024049 (2019).
+4. Grollier, J., Querlioz, D. & Stiles, M. D. Spintronic Nanodevices for Bioinspired Computing. Proc. IEEE 104, 2024–2039 (2016).
+5. Slavin, A. & Tiberkevich, V. Nonlinear auto-oscillator theory of microwave generation by spin-polarized current. IEEE Trans. Magn. 45, 1875–1918 (2009).
+6. Kim, J., Tiberkevich, V. & Slavin, A. Generation Linewidth of an Auto-Oscillator with a Nonlinear Frequency Shift: Spin-Torque Nano-Oscillator. Phys. Rev. Lett. 100, 017207 (2008).
+7. Locatelli, N., Cros, V. & Grollier, J. Spin-torque building blocks. Nat. Mater. 13, 11–20 (2014).
+8. Lee, H. S. et al. Power-efficient spin-torque nano-oscillator-based wireless communication with CMOS high-gain low-noise transmitter and receiver. IEEE Trans. Magn. 55, 4001910 (2019).
+9. Das, D., Tulapurkar, A. & Muralidharan, B. Scaling Projections on Spin-Transfer Torque Magnetic Tunnel Junctions. IEEE Trans. Electron Devices 65, 724–732 (2018).
+10. Chen, T. et al. Spin-Torque and Spin-Hall Nano-oscillators. Proc. IEEE 104, 1919-1945 (2016).
+11. Vodenicarevic, D., Locatelli, N., Abreu Araujo, F., Grollier, J. & Querlioz, D. A Nanotechnology-Ready Computing Scheme based on a Weakly Coupled Oscillator Network. Sci. Rep. 7, 44772 (2017).
+12. Yogendra, K., Fan, D., Jung, B. & Roy, K. Magnetic Pattern Recognition Using Injection
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 100, 881, 142]]<|/det|>
+Locked Spin-Torque Nano-Oscillators. IEEE Trans. Electron Devices 63, 1674- 1680 (2016).
+
+<|ref|>text<|/ref|><|det|>[[120, 158, 707, 177]]<|/det|>
+13. Hirsch, J. E. Spin Hall Effect. Phys. Rev. Lett. 83, 1834-1837 (1999).
+
+<|ref|>text<|/ref|><|det|>[[120, 193, 880, 235]]<|/det|>
+14. Kato, Y. K., Myers, R. C., Gossard, A. C. & Awschalom, D. D. Observation of the spin Hall effect in semiconductors. Science 306, 1910-1913 (2004).
+
+<|ref|>text<|/ref|><|det|>[[120, 251, 880, 293]]<|/det|>
+15. Sinova, J., Valenzuela, S. O., Wunderlich, J., Back, C. H. & Jungwirth, T. Spin Hall effects. Rev. Mod. Phys. 87, 1213-1260 (2015).
+
+<|ref|>text<|/ref|><|det|>[[120, 310, 880, 352]]<|/det|>
+16. Demidov, V. E. et al. Magnetic nano-oscillator driven by pure spin current. Nat. Mater. 11, 1028-1031 (2012).
+
+<|ref|>text<|/ref|><|det|>[[120, 368, 880, 410]]<|/det|>
+17. Liu, R. H., Lim, W. L. & Urazhdin, S. Spectral characteristics of the microwave emission by the spin hall nano-oscillator. Phys. Rev. Lett. 110, 147601 (2013).
+
+<|ref|>text<|/ref|><|det|>[[120, 426, 880, 469]]<|/det|>
+18. Demidov, V. E., Urazhdin, S., Zholud, A., Sadovnikov, A. V. & Demokritov, S. O. Nanoconstriction-based spin-Hall nano-oscillator. Appl. Phys. Lett. 105, (2014).
+
+<|ref|>text<|/ref|><|det|>[[120, 485, 879, 528]]<|/det|>
+19. Duan, Z. et al. Nanowire spin torque oscillator driven by spin orbit torques. Nat. Commun. 5, 5616 (2014).
+
+<|ref|>text<|/ref|><|det|>[[119, 544, 880, 586]]<|/det|>
+20. Dürrenfeld, P., Awad, A. A., Houshang, A., Dumas, R. K. & Akerman, J. A 20 nm spin Hall nano-oscillator. Nanoscale 9, 1285-1291 (2017).
+
+<|ref|>text<|/ref|><|det|>[[119, 603, 879, 645]]<|/det|>
+21. Awad, A. A. et al. Long-range mutual synchronization of spin Hall nano-oscillators. Nat. Phys. 13, 292-299 (2017).
+
+<|ref|>text<|/ref|><|det|>[[119, 661, 880, 704]]<|/det|>
+22. Zahedinejad, M. et al. Two-dimensional mutually synchronized spin Hall nano-oscillator arrays for neuromorphic computing. Nat. Nanotechnol. 15, 47-52 (2020).
+
+<|ref|>text<|/ref|><|det|>[[119, 720, 880, 786]]<|/det|>
+23. Liu, L., Pai, C. F., Ralph, D. C. & Buhrman, R. A. Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices. Phys. Rev. Lett. 109, 186602 (2012).
+
+<|ref|>text<|/ref|><|det|>[[119, 804, 880, 846]]<|/det|>
+24. Tarequzzaman, M. et al. Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current. Commun. Phys. 2, 20 (2019).
+
+<|ref|>text<|/ref|><|det|>[[118, 862, 880, 880]]<|/det|>
+25. Albertsson. D. I., Zahedinejad, M., Akerman, J., Rodriguez, S. & Rusu, A. Compact
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[144, 100, 884, 141]]<|/det|>
+Macrospin- Based Model of Three- Terminal Spin- Hall Nano Oscillators. IEEE Trans. Magn. 55, 4003808 (2019).
+
+<|ref|>text<|/ref|><|det|>[[117, 157, 883, 201]]<|/det|>
+26. Liu, R. H., Chen, L., Urazhdin, S. & Du, Y. W. Controlling the spectral characteristics of a spin-current auto-oscillator with an electric field. Phys. Rev. Appl. 8, 021001 (2017).
+
+<|ref|>text<|/ref|><|det|>[[117, 217, 880, 259]]<|/det|>
+27. Fulara, H. et al. Giant voltage-controlled modulation of spin Hall nano-oscillator damping. Nat. Commun. 11, 4006 (2020).
+
+<|ref|>text<|/ref|><|det|>[[117, 275, 844, 294]]<|/det|>
+28. Ohno, H. et al. Electric-field control of ferromagnetism. Nature 408, 944-946 (2000).
+
+<|ref|>text<|/ref|><|det|>[[117, 310, 881, 353]]<|/det|>
+29. Maruyama, T. et al. Large voltage-induced magnetic anisotropy change in a few atomic layers of iron. Nat. Nanotechnol. 4, 158-161 (2009).
+
+<|ref|>text<|/ref|><|det|>[[117, 369, 880, 412]]<|/det|>
+30. Nakamura, K. et al. Giant modification of the magnetocrystalline anisotropy in transition-metal monolayers by an external electric field. Phys. Rev. Lett. 102, 187201 (2009).
+
+<|ref|>text<|/ref|><|det|>[[117, 427, 880, 470]]<|/det|>
+31. Bi, C. et al. Reversible control of Co magnetism by voltage-induced oxidation. Phys. Rev. Lett. 113, 267202 (2014).
+
+<|ref|>text<|/ref|><|det|>[[117, 486, 880, 529]]<|/det|>
+32. Bauer, U. et al. Magneto-ionic control of interfacial magnetism. Nat. Mater. 14, 174-181 (2015).
+
+<|ref|>text<|/ref|><|det|>[[117, 544, 880, 587]]<|/det|>
+33. Weisheit, M. et al. Electric Field-Induced Modification of Magnetism in Thin-Film Ferromagnets. Science 315, 349-351 (2007).
+
+<|ref|>text<|/ref|><|det|>[[117, 603, 880, 621]]<|/det|>
+34. Kittel, C. On the theory of ferromagnetic resonance absorption. Phys. Rev. 73, 155 (1948).
+
+<|ref|>text<|/ref|><|det|>[[117, 637, 880, 679]]<|/det|>
+35. Farle, M. Ferromagnetic resonance of ultrathin metallic layers. Rep. Prog. Phys. 61, 755-826 (2018)
+
+<|ref|>text<|/ref|><|det|>[[117, 695, 880, 738]]<|/det|>
+36. He, C. et al. Spin-Torque Ferromagnetic Resonance in W/Co-Fe-B/W/Co-Fe-B/MgO Stacks. Phys. Rev. Appl. 10, 034067 (2018).
+
+<|ref|>text<|/ref|><|det|>[[117, 754, 880, 796]]<|/det|>
+37. Ho, V. M., Lee, J.-A. & Martin, K. C. The cell biology of synaptic plasticity. Science 334, 623-628 (2011).
+
+<|ref|>text<|/ref|><|det|>[[117, 813, 880, 855]]<|/det|>
+38. Jo, S. H. et al. Nanoscale memristor device as synapse in neuromorphic systems. Nano Lett. 10, 1297-1301 (2010).
+
+<|ref|>text<|/ref|><|det|>[[117, 871, 880, 890]]<|/det|>
+39. Mishra, R., Kumar, D. & Yang, H. Oxygen-Migration-Based Spintronic Device Emulating
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[145, 100, 621, 118]]<|/det|>
+a Biological Synapse. Phys. Rev. Appl. 11, 054065 (2019).
+
+<|ref|>text<|/ref|><|det|>[[117, 134, 881, 177]]<|/det|>
+40. Huang, W. et al. Memristive Artificial Synapses for Neuromorphic Computing. Nano-Micro Lett. 13, 85 (2021).
+
+<|ref|>text<|/ref|><|det|>[[117, 193, 881, 236]]<|/det|>
+41. Baek, S.-H. C. et al. Complementary logic operation based on electric-field controlled spin-orbit torques. Nat. Electron. 1, 398-403 (2018).
+
+<|ref|>text<|/ref|><|det|>[[117, 251, 883, 294]]<|/det|>
+42. Park, K.-W. et al. Electric field control of magnetic anisotropy in the easy cone state of Ta/Pt/CoFeB/MgO structures. Appl. Phys. Lett. 109, 012405 (2016).
+
+<|ref|>text<|/ref|><|det|>[[117, 310, 881, 353]]<|/det|>
+43. Liu, L., Moriyama, T., Ralph, D. C. & Buhrman, R. A. Spin-torque ferromagnetic resonance induced by the spin Hall effect. Phys. Rev. Lett. 106, 306601 (2011).
+
+<|ref|>text<|/ref|><|det|>[[117, 368, 881, 411]]<|/det|>
+44. Kim, J. et al. Spin-orbit torques associated with ferrimagnetic order in Pt/GdFeCo/MgO layers. Sci. Rep. 8, 6017 (2018).
+
+<|ref|>text<|/ref|><|det|>[[117, 426, 881, 495]]<|/det|>
+45. Beaujour, J.-M., Ravelosona, D., Tudosa, I., Fullerton, E. E. & Kent, A. D. Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy. Phys. Rev. B 80, 180415(R) (2009).
+
+<|ref|>text<|/ref|><|det|>[[117, 510, 881, 553]]<|/det|>
+46. McMichael, R. D., Twisselmann, D. J. & Kunz, A. Localized Ferromagnetic Resonance in Inhomogeneous Thin Films. Phys. Rev. Lett. 90, 227601 (2003).
+
+<|ref|>text<|/ref|><|det|>[[117, 569, 880, 611]]<|/det|>
+47. Slonczewski, J. C., Current-driven excitation of magnetic multilayers. J. Magn. Magn. Mater. 159, L1-L7 (1996)
+
+<|ref|>text<|/ref|><|det|>[[117, 627, 881, 671]]<|/det|>
+48. Zheng, C., Chen, H. H., Zhang, X., Zhang, Z. & Liu, Y. Spin torque nano-oscillators with a perpendicular spin polarizer. Chinese Phys. B 28, (2019).
+
+<|ref|>text<|/ref|><|det|>[[117, 686, 881, 753]]<|/det|>
+49. Hayashi, M., Kim, J., Yamanouchi, M. & Ohno, H. Quantitative characterization of the spin-orbit torque using harmonic Hall voltage measurements. Phys. Rev. B 89, 144425 (2014).
+
+<|ref|>text<|/ref|><|det|>[[117, 770, 881, 812]]<|/det|>
+50. Rippard, W. H. et al. Spin-transfer dynamics in spin valves with out-of-plane magnetized CoNi free layers. Phys. Rev. B 81, 014426 (2010).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[120, 100, 280, 117]]<|/det|>
+## Acknowledgments
+
+<|ref|>text<|/ref|><|det|>[[118, 141, 883, 225]]<|/det|>
+This work is supported by the Samsung Research Funding Center of Samsung Electronics under Project Numbers SRFC- MA1702- 02 and SRFC- MA1802- 01. K.- J.K acknowledges support from KAIST- funded Global Singularity Research Program for 2021.
+
+<|ref|>sub_title<|/ref|><|det|>[[120, 250, 305, 267]]<|/det|>
+## Author contributions
+
+<|ref|>text<|/ref|><|det|>[[118, 291, 883, 409]]<|/det|>
+B.- G.P. and K.- J.K. planned and supervised the study. J.- G.C. and JP fabricated the devices and performed the experiment. M.- G.K. helps fabrication of the sample with a gate structure. DK and J.- S.R. help the high- frequency measurement. J.- G.C., JP, K.- J.K., K.- J.L., and B.- G.P. analyzed the data and wrote the manuscript.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 433, 295, 451]]<|/det|>
+## Competing interests
+
+<|ref|>text<|/ref|><|det|>[[120, 475, 443, 493]]<|/det|>
+Authors declare no competing interests.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 518, 265, 535]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[119, 559, 881, 610]]<|/det|>
+The data that support the findings of this study are available from the corresponding author upon reasonable request.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[163, 106, 845, 581]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 610, 884, 830]]<|/det|>
+Figure 1. Voltage-controlled perpendicular magnetic anisotropy. a, Schematic illustration of the mechanism of the voltage-driven frequency tuning via voltage-controlled magnetic anisotropy (VCMA). The green and gray arrows represent the directions of spin-orbit torque and damping torque, respectively. b, The resonance frequency \((f_{\mathrm{res}})\) as a function of in-plane magnetic field \((B_{\parallel})\) for high PMA (blue) and low PMA (red). c, magnetization \((M)\) versus out-of-plane magnetic field \((B_{z})\) of the Co/Ni film. d, Anomalous Hall resistance \((R_{\mathrm{H}})\) curves of the Co/Ni sample for sequentially applied gate voltages of \(+3\mathrm{V}\) , \(+5\mathrm{V}\) , \(-3\mathrm{V}\) , and \(-5\mathrm{V}\) , respectively.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[123, 115, 830, 388]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 442, 884, 700]]<|/det|>
+Figure 2. Voltage-dependent ST-FMR spectra. a, ST-FMR spectra of the Co/Ni sample for sequentially applied gate voltages (initial, \(+5\mathrm{V}\) , and -5V). Here, the microwave frequency is 15 GHz. The dotted lines are the best fits based on Eq. (1). b, Resonance frequency \((f_{\mathrm{res},z})\) as a function of resonance field \(B_{\mathrm{res},z}\) of the sample with different sequentially applied gate voltages. c, Variation of perpendicular magnetic anisotropy field \((B_{\mathrm{k}})\) versus sequentially applied gate voltage. d, The linewidth of the Lorentzian function \((\Delta B)\) as a function of the \(f_{\mathrm{res},z}\) of the sample with sequentially applied gate voltages. e, Variation of effective damping constant \((\alpha_{\mathrm{eff}})\) versus sequentially applied gate voltage.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[123, 103, 857, 575]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 596, 883, 817]]<|/det|>
+Figure 3. Magnetic field-dependent voltage-driven frequency tuning of SHNO. a, Schematic illustration of the experimental set-up. The inset is a scanning electron microscope image of an SHNO device. b, Angle-dependent magnetoresistance (MR) of the Co/Ni sample. c-g, Power spectral densities (PSDs) as a function of magnetic field for sequentially applied gate voltages, \(V_{\mathrm{g}} = 0 \mathrm{V}\) (initial state) (c), \(V_{\mathrm{g}} = +4 \mathrm{V}\) (d), \(V_{\mathrm{g}} = +5 \mathrm{V}\) (e), \(V_{\mathrm{g}} = -2 \mathrm{V}\) (f), and \(V_{\mathrm{g}} = -3 \mathrm{V}\) (g). \(I_{\mathrm{dc}} = 2.9 \mathrm{mA}\) . h, Auto-oscillation spectra for \(B = 0.52 \mathrm{T}\) with different gate voltages, extracted from Figs. 3c-3g.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[124, 99, 863, 428]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 451, 883, 575]]<|/det|>
+Figure 4. Current-dependent voltage-driven frequency tuning of SHNO. a-e, PSDs as a function of current for sequentially applied gate voltages, \(V_{\mathrm{g}} = 0 \mathrm{V}\) (initial state) (a), \(V_{\mathrm{g}} = +4 \mathrm{V}\) (b), \(V_{\mathrm{g}} = +5 \mathrm{V}\) (c), \(V_{\mathrm{g}} = -2 \mathrm{V}\) (d), and \(V_{\mathrm{g}} = -3 \mathrm{V}\) (e). \(B = 0.52 \mathrm{T}\) . f, Threshold current, \(I_{\mathrm{th}}\) , according to the sequentially applied gate voltages, extracted from Figs. 4a-4e.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[161, 107, 832, 296]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 319, 883, 441]]<|/det|>
+Figure 5. Cumulative frequency control via repetitive gate voltage pulses. a, The auto oscillation frequency of the SHNO versus the number of positive (black) and negative (red) gate voltage pulses \((N_{V_{\mathrm{g}}})\) . b, Voltage-driven cumulative frequency change \((\delta f)\) versus \(N_{V_{\mathrm{g}}}\) for different gate voltages.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 130, 188, 149]]<|/det|>
+Slfinal.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/images_list.json b/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..669b942b2e06ae69543e12c3ac2f41c85cc6ccc5
--- /dev/null
+++ b/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/images_list.json
@@ -0,0 +1,62 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "FIG. 1: Electrical transport in twisted bilayer graphene. (a) Temperature-dependent resistance \\(R\\) as a function of band filling \\(\\nu\\) for four different devices with twist angle \\(\\theta \\approx 1.01^{\\circ}\\) , \\(1.24^{\\circ}\\) , \\(1.6^{\\circ}\\) and \\(1.7^{\\circ}\\) . The inset in the bottom panel shows the optical image of a typical device with current and voltage leads marked for resistivity measurements. The scale bar represents a length of \\(5 \\mu \\mathrm{m}\\) . \\(\\rho\\) as a function of \\(T\\) for a few representative values of \\(\\nu\\) for (b) \\(\\theta \\approx 1.01^{\\circ}\\) , (c) \\(1.24^{\\circ}\\) and (d) \\(1.6^{\\circ}\\) . The various curves for fractional \\(\\nu\\) in (c) represent the \\(T\\) -dependence of the CI/CS states as marked in the second panel of (a).(e) Comparison of \\(T\\) -dependence of \\(\\rho\\) at \\(\\nu = -2\\) for different twist angles. The solid lines represent \\(T\\) -linearity.",
+ "footnote": [],
+ "bbox": [
+ [
+ 100,
+ 70,
+ 912,
+ 461
+ ]
+ ],
+ "page_idx": 3
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "FIG. 2: Thermoelectric transport in twisted bilayer graphene: (a) The cross-sectional view of the device, showing the constituent layers, electrical contacts, and the gate assembly. (b) In-plane heating and measurement schematic for thermovoltage \\(V_{2\\omega}\\) in the tBLG region. Density dependence of \\(V_{2\\omega} / I_{\\omega}^{2}\\) (in the units of \\(\\mathrm{VA}^{-2} \\times 10^{6}\\) ) measured at 5 K for (c) \\(\\theta \\approx 1.01^{\\circ}\\) , (d) \\(1.24^{\\circ}\\) , and at 3 K for (e) \\(1.6^{\\circ}\\) device. The different curves in each panel represent the \\(V_{2\\omega} / I_{\\omega}^{2}\\) measured at different \\(I_{\\omega}\\) . The bottom graphs in each panel show the numerically calculated \\(\\alpha = (1 / R)\\mathrm{d}R / \\mathrm{d}n\\) (in the units of \\(\\mathrm{m}^{2}\\) ) for comparison.",
+ "footnote": [],
+ "bbox": [
+ [
+ 93,
+ 66,
+ 479,
+ 600
+ ]
+ ],
+ "page_idx": 4
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "FIG. 3: Comparison with semiclassical Mott relation at \\(\\sim 1.6^{\\circ}\\) (a) Electronic band structure and density of states (DOS) of tBLG \\((\\theta = 1.6^{\\circ})\\) calculated using tight binding model. The bands shown in red are the low energy active bands. (b) Comparison between the measured \\(V_{2\\omega}\\) (black lines) and that calculated (orange line) from the semiclassical Mott relation (Eq. 2) for \\(\\theta \\approx 1.6^{\\circ}\\) at three representative temperatures. \\(\\Delta T\\) is obtained as a fitting parameter to match SMR with the experimental \\(V_{2\\omega}\\) at CNP. (c) Doping dependence of \\(S\\) for \\(\\theta \\approx 1.7^{\\circ}\\) compared to that of the SMR at \\(5\\mathrm{K}\\) . (d) Temperature dependence of \\(S\\) at various band filling factors. The dashed lines show the \\(S\\propto T\\) dependence. The inset shows the \\(T\\) dependence of \\(S / S_{\\mathrm{max}}\\) at \\(\\nu = \\pm 2\\) .",
+ "footnote": [],
+ "bbox": [
+ [
+ 95,
+ 68,
+ 910,
+ 430
+ ]
+ ],
+ "page_idx": 5
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "FIG. 4: Breakdown of semiclassical Mott relation and scattering rate : (a) Surface plot of \\((S - S_{\\mathrm{Mott}}) / S_{\\mathrm{max}}\\) as a function of \\(T\\) and \\(\\nu\\) for \\(\\theta \\approx 1.6^{\\circ}\\) . (b) \\((S - S_{\\mathrm{Mott}})\\) at \\(10\\mathrm{K}\\) for \\(\\theta \\approx 1.6^{\\circ}\\) and \\(\\theta \\sim 4^{\\circ}\\) . (c) \\(\\mathrm{d}\\rho /\\mathrm{d}T\\) extracted in the \\(T\\) -linear regime at different \\(\\nu\\) for the three twist angles. (d) The estimated dimensionless pre-factor \\(C\\) of the scattering rate \\(\\Gamma = Ck_{\\mathrm{B}}T / \\hbar\\) as a function of \\(\\nu\\) . (e) Seebeck coefficient \\(S\\) computed in DMFT with \\(U = 38\\mathrm{meV}\\) as a function of filling \\(\\nu\\) for the four lowest bands at three temperatures \\(T = 2\\mathrm{K}\\) , \\(14\\mathrm{K}\\) and \\(26\\mathrm{K}\\) , respectively.",
+ "footnote": [],
+ "bbox": [
+ [
+ 103,
+ 68,
+ 456,
+ 555
+ ]
+ ],
+ "page_idx": 6
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36.mmd b/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..996d4535507d866b47a64ad8eba472cc7e5b31da
--- /dev/null
+++ b/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36.mmd
@@ -0,0 +1,160 @@
+
+# Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene
+
+Bhaskar Ghawri Indian Institute of Science Bangalore Phanibhusan Mahapatra ( \(\boxed{ \begin{array}{r l} \end{array} }\) phanis@iisc.ac.in) Indian Institute of Science Bangalore
+
+Manjari Garg Indian Institute of Science Bangalore
+
+Shinjan Mandal Indian Institute of Science Bangalore https://orcid.org/0000- 0003- 1551- 6555
+
+Saisab Bhowmik Indian Institute of Science
+
+Aditya Jayraman Indian Institute of Science Bangalore https://orcid.org/0000- 0002- 6963- 7195
+
+Radhika Soni Indian Institute of Science
+
+Kenji Watanabe National Institute for Materials Science https://orcid.org/0000- 0003- 3701- 8119
+
+Takashi Taniguchi National Institute for Materials Science, Tsukuba, Ibaraki https://orcid.org/0000- 0002- 1467- 3105
+
+Hulikal Krishnamurthy Indian Institute of Science Bangalore
+
+Manish Jain Indian Institute of Science Bangalore https://orcid.org/0000- 0001- 9329- 6434
+
+Sumilan Banerjee Indian Institute of Science Bangalore
+
+U. Chandni Indian Institute of Science Bangalore
+
+Arindam Ghosh Indian Institute of Science Bangalore
+
+Article
+
+<--- Page Split --->
+
+Keywords: twisted bilayer graphene (tBLG), non-Fermi liquid (NFL), van Hove singularities (vHS), SMR, hBN
+
+Posted Date: August 26th, 2021
+
+DOI: https://doi.org/10.21203/rs.3.rs- 811957/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Version of Record: A version of this preprint was published at Nature Communications on March 21st, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 29198- 4.
+
+<--- Page Split --->
+
+# Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene
+
+Bhaskar Ghawri, \(^{1, *}\) Phanibhusan S. Mahapatra, \(^{1, \dagger}\) Manjari Garg, \(^{2, \ddagger}\) Shinjan Mandal, \(^{1}\) Saisab Bhowmik, \(^{2}\) Aditya Jayaraman, \(^{1}\) Radhika Soni, \(^{2}\) Kenji Watanabe, \(^{3}\) Takashi Taniguchi, \(^{4}\) H. R. Krishnamurthy, \(^{1}\) Manish Jain, \(^{1}\) Sumilan Banerjee, \(^{1}\) U. Chandni, \(^{2}\) and Arindam Ghosh \(^{1, 5, \S}\) \(^{1}\) Department of Physics, Indian Institute of Science, Bangalore, 560012, India \(^{2}\) Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore, 560012, India \(^{3}\) Research Center for Functional Materials, National Institute for Materials Science, Namiki 1- 1, Tsukuba, Ibaraki 305- 0044, Japan \(^{4}\) International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Namiki 1- 1, Tsukuba, Ibaraki 305- 0044, Japan \(^{5}\) Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560 012, India
+
+The planar assembly of twisted bilayer graphene (tBLG) hosts multitude of interaction- driven phases when the relative rotation is close to the magic angle ( \(\theta_{\mathrm{m}} = 1.1^{\circ}\) ). This includes correlation- induced ground states that reveal spontaneous symmetry breaking at low temperature, as well as possibility of non- Fermi liquid (NFL) excitations. However, experimentally, manifestation of NFL effects in transport properties of twisted bilayer graphene remains ambiguous. Here we report simultaneous measurements of electrical resistivity ( \(\rho\) ) and thermoelectric power ( \(S\) ) in tBLG for several twist angles between \(\theta \sim 1.0 - 1.7^{\circ}\) . We observe an emergent violation of the semiclassical Mott relation in the form of excess \(S\) close to half- filling for \(\theta \sim 1.6^{\circ}\) that vanishes for \(\theta \gtrsim 2^{\circ}\) . The excess \(S\) ( \(\approx 2 \mu \mathrm{V / K}\) at low temperatures \(T \sim 10 \mathrm{K}\) at \(\theta \approx 1.6^{\circ}\) ) persists up to \(\approx 40 \mathrm{K}\) , and is accompanied by metallic \(T\) - linear \(\rho\) with transport scattering rate \((\tau^{- 1})\) of near- Planckian magnitude \(\tau^{- 1} \sim k_{\mathrm{B}} T / \hbar\) . Closer to \(\theta_{\mathrm{m}}\) , the excess \(S\) was also observed for fractional band filling ( \(\nu \approx 0.5\) ). The combination of non- trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG.
+
+In moiré systems with twisted bilayer graphene (tBLG), the amplification of Coulomb correlation effects at low twist angles ( \(\theta\) ) is a result of nearly flat low- energy electronic bands [1, 2] and divergent density of states (DOS) at van Hove singularities (vHS) [3]. In addition to superconductivity [4], ferromagnetism [5], the strong correlation effects in tBLG manifest in a cascade of broken symmetry phases at integer band filling factor ( \(\nu\) ) close to \(\theta = \theta_{\mathrm{m}}\) [6, 7]. Near half- filling ( \(\nu = \pm 2\) ) of the four- fold spin- valley degenerate conduction and valence bands, a linear \(T\) - dependence of the resistivity ( \(\rho\) ) seems to indicate an interaction- related absence of a well- defined quasiparticle spectrum, which is concomitant with non- Fermi liquid (NFL) excitations [8, 9]. The persistence of the linearity in \(\rho\) for \(\theta\) well away from \(\theta_{\mathrm{m}}\) , e.g. for \(\theta \sim 1.5 - 2^{\circ}\) , however, has been interpreted in terms of a contrary scenario that is addressable within the non- interacting framework [10]. The uncertainty persists even in scanning tunneling microscopy experiments [11- 13], where the possibility of an interaction- driven magnetic order has been claimed close to the vHS for \(\theta\) as high as \(1.6^{\circ}\) , although the spontaneous breaking of \(C_{6}\) lattice symmetry to nematic orbital order has not been observed for \(\theta > \theta_{\mathrm{m}}\) . Thus a comprehensive understanding of the impact of correlation in tBLG requires a complementary experimental probe that is capable of identifying the departure from noninteracting physics in an unambiguous manner.
+
+Here we have carried out simultaneous electrical and
+
+thermoelectric measurements in tBLG for twist angles varying from \(\theta \sim 1.0 - 1.7^{\circ}\) . The dependence on \(T\) and on the carrier density ( \(n\) ) of the thermoelectric power ( \(S\) ), or the Seebeck coefficient, is used as an independent and sensitive probe of the correlation effects. Thermoelectric power is often interpreted as a thermodynamic entity that represents the entropy carried by each charge carrier. Within the degenerate quasiparticle description in the Boltzmann transport regime ( \(T \ll T_{\mathrm{F}}\) , where \(T_{\mathrm{F}}\) is the Fermi temperature), \(S\) is related to the resistance ( \(R\) ) through the semiclassical Mott relation (SMR),
+
+\[S_{\mathrm{Mott}} = \frac{\pi^{2}k_{\mathrm{B}}^{2}T}{3|e|}\frac{\mathrm{d}\ln R(E)}{\mathrm{d}E}\bigg|_{E_{\mathrm{F}}}, \quad (1)\]
+
+where \(R(E)\) , \(e\) and \(E_{\mathrm{F}}\) are the energy- dependent resistance, electronic charge and Fermi energy, respectively. Eq. 1 is valid under the assumption that scattering is elastic and isotropic close to the Fermi surface i.e. the transport lifetime only depends on the energy of the charge carriers. Remarkably, this simple assumption of isotropic scattering remains valid in a wide variety of systems, such as disordered metals/semiconductors [14, 15], organic materials [16], monolayer graphene [17] and topological insulators [18]. The SMR effectively arises from the quasiparticles carrying heat and charge under identical constraints, imposed by the momentum conservation. Thus, the validity of SMR in Eq. 1 provides a definitive probe into the nature of the scattering mechanisms and
+
+<--- Page Split --->
+
+
+FIG. 1: Electrical transport in twisted bilayer graphene. (a) Temperature-dependent resistance \(R\) as a function of band filling \(\nu\) for four different devices with twist angle \(\theta \approx 1.01^{\circ}\) , \(1.24^{\circ}\) , \(1.6^{\circ}\) and \(1.7^{\circ}\) . The inset in the bottom panel shows the optical image of a typical device with current and voltage leads marked for resistivity measurements. The scale bar represents a length of \(5 \mu \mathrm{m}\) . \(\rho\) as a function of \(T\) for a few representative values of \(\nu\) for (b) \(\theta \approx 1.01^{\circ}\) , (c) \(1.24^{\circ}\) and (d) \(1.6^{\circ}\) . The various curves for fractional \(\nu\) in (c) represent the \(T\) -dependence of the CI/CS states as marked in the second panel of (a).(e) Comparison of \(T\) -dependence of \(\rho\) at \(\nu = -2\) for different twist angles. The solid lines represent \(T\) -linearity.
+
+energy distribution of the charge carriers near the Fermi surface, and it breaks down when strong correlation effects become important [15, 19].
+
+The tBLG devices we study were created using standard van der Waals stacking [20], which consists of two graphene layers aligned at either \(60^{\circ} + \theta\) or at \(\theta\) , where \(\theta\) is the effective twist angle, and encapsulated within two sheets of hexagonal boron nitride (hBN) (see supplementary information, SI, section I). A local top- gate tunes \(n\) in the overlap region where the moiré super- lattice is formed. Fig. 1a shows the four terminal resistance \(R\) measured across the tBLG devices as a function of band filling factor \(\nu\) and \(T\) for four different \(\theta\) . The recurring features in \(R\) across the tBLG devices can be identified as the maxima in \(R\) at CNP and at the full- filling of the moiré band ( \(\nu = \pm 4\) ). In addition, near \(\theta_{\mathrm{m}}\) , the two devices \(\theta \approx 1.01^{\circ}\) and \(\approx 1.24^{\circ}\) exhibit additional maxima in \(R\) near integer values of \(\nu\) , which can be mapped to the correlated states at integer fillings. For \(\theta \approx 1.24^{\circ}\) , we ob
+
+serve a substantial shift \(|\Delta \nu | \sim 0.25\) of resistance peaks near \(\nu = +1\) and \(+3\) from \(7 \mathrm{~K}\) to \(35 \mathrm{~K}\) , suggesting the possibility of isospin- polarization in the system [21, 22] (SI, section III). We speculate that the noticeable asymmetry in the doping dependence of \(R\) on the electron and hole sides is most likely related to the particle- hole asymmetry of the band structure since in both tBLG devices near \(\theta_{\mathrm{m}}\) , the correlated states are more pronounced at electron doping.
+
+For \(0 < |\nu| < 4\) , the \(T\) - dependence for all devices was found to be generally metallic at low temperatures \(\lesssim 40 \mathrm{~K}\) (Fig. 1b- 1d). However, the resistance peaks near integer \(\nu\) exhibit either weak insulating \(T\) - dependence, i.e., a correlated insulating phase (CI), or \(T\) - linear resistivity i.e., a correlated semimetallic (CS) phase. In the metallic regime, \(\rho\) can expressed as \(\rho = \rho_{0} + AT\) , where \(\rho_{0}\) is the residual resistivity. The values of \(A\) \((\sim 10 - 100 \Omega /\mathrm{K})\) are at least two orders of magnitude greater compared to that of the monolayer graphene, and
+
+<--- Page Split --->
+
+
+FIG. 2: Thermoelectric transport in twisted bilayer graphene: (a) The cross-sectional view of the device, showing the constituent layers, electrical contacts, and the gate assembly. (b) In-plane heating and measurement schematic for thermovoltage \(V_{2\omega}\) in the tBLG region. Density dependence of \(V_{2\omega} / I_{\omega}^{2}\) (in the units of \(\mathrm{VA}^{-2} \times 10^{6}\) ) measured at 5 K for (c) \(\theta \approx 1.01^{\circ}\) , (d) \(1.24^{\circ}\) , and at 3 K for (e) \(1.6^{\circ}\) device. The different curves in each panel represent the \(V_{2\omega} / I_{\omega}^{2}\) measured at different \(I_{\omega}\) . The bottom graphs in each panel show the numerically calculated \(\alpha = (1 / R)\mathrm{d}R / \mathrm{d}n\) (in the units of \(\mathrm{m}^{2}\) ) for comparison.
+
+are consistent with the earlier transport measurements in tBLG devices [10]. From the comparison of \(\rho (T)\) at half- filling \(\nu = - 2\) in Fig. 1e, we find that the resistivity is linear in \(T\) for all four low- angle devices. However, at \(\theta \approx 1.24^{\circ}\) and \(\theta \approx 1.01^{\circ}\) , the linearity persists only upto
+
+\(\sim 40\mathrm{K}\) , which could be due to the smaller bandwidth and smaller bandgap [10]. We also note that the value of \(A\) \(\sim 40 - 100\Omega /\mathrm{K}\) at \(\nu = - 2\) is much larger near \(\theta \sim \theta_{\mathrm{m}}\) than that of the devices away from \(\theta_{\mathrm{m}}\) (SI, section III). The ubiquitous \(T\) - linearity across all tBLG devices at low temperature is a clear departure from \(\rho \sim T^{2}\) dependence associated with electron- electron scattering, or the \(\rho \propto T^{4}\) behavior, expected due to electron- acoustic phonon scattering below the Bloch- Grüneisen temperature \((T_{\mathrm{BG}})\) [23]. While this suggests the continuum of correlation- driven metallic states across the tBLG devices, an alternate scenario has been proposed [10, 24] to view the tBLG in this regime as a two dimensional, weakly (or non- ) interacting metal with largely reduced \(T_{\mathrm{BG}}\) .
+
+To complement the electrical transport, we have performed thermoelectric measurements on the same devices. Briefly, a sinusoidal current \((I_{\omega})\) is allowed to flow between two contacts of the monolayer branch outside the top gated region, setting up a temperature gradient \((\Delta T)\) across the tBLG region (Fig. 2a and 2b). The resulting second- harmonic thermo- voltage \((V_{2\omega})\) is recorded on the tBLG region as a function of doping and heating current [17, 20]. The linear response was ensured from \(V_{2\omega} \propto I_{\omega}^{2}\) for the range of heating current used (Fig. 2c- 2e). We begin with the results in tBLG devices closer to \(\theta_{\mathrm{m}}\) . Fig. 2c exhibits the \(\nu\) - dependence of normalized \(V_{2\omega}\) for tBLG device \(\theta \approx 1.01^{\circ}\) at low temperature (5 K), which exhibits multiple sign- reversals when \(E_{\mathrm{F}}\) is varied across the lowest energy band. While the sign reversals near CNP and the super- lattice gaps at \(\nu = \pm 4\) are due to changes in the quasiparticle excitations, those near integer values of \(0 < \nu < 4\) can be attributed to the correlated states. The sign- reversal of \(V_{2\omega}\) near each correlated states is fascinating since it indicates a change in the topology of the Fermi surface, which is naturally associated with the Lifshitz transition [25, 26]. Although the correlated states are metallic in nature (Fig. 1a), the concomitant Lifshitz transitions depicts the interaction- driven occurrence of diverging DOS at each integer values of \(\nu\) . This is in stark contrast to the charge- inversions at \(\nu = 0, \pm 4\) , and hints at the topological facet of the lowest energy band when filled with integer number of charge carriers [7, 27].
+
+To establish the connection between the two different types of transports, we rewrite Eq. 1 as,
+
+\[S_{\mathrm{Mott}} = \frac{\pi^{2}k_{\mathrm{B}}^{2}T}{3|e|}\frac{1}{R}\frac{\mathrm{d}R}{\mathrm{d}V_{\mathrm{tg}}}\frac{\mathrm{d}V_{\mathrm{tg}}}{\mathrm{d}n}\frac{\mathrm{d}n}{\mathrm{d}E}\bigg|_{E_{\mathrm{F}}}, \quad (2)\]
+
+where \((1 / R)\mathrm{d}R / \mathrm{d}V_{\mathrm{tg}}\) is measured experimentally, and \(\mathrm{d}n / \mathrm{d}E\) is the DOS \((\mathrm{d}V_{\mathrm{tg}} / \mathrm{d}n = e / C_{\mathrm{hBN}}\) , where \(C_{\mathrm{hBN}}\) is the known topgate capacitance per unit area). The difficulty in accurate estimation of DOS in the presence of strong correlation effects near \(\theta_{\mathrm{m}}\) prohibits us from accurately estimating \(S_{\mathrm{Mott}}\) , in particular close to the
+
+<--- Page Split --->
+
+
+FIG. 3: Comparison with semiclassical Mott relation at \(\sim 1.6^{\circ}\) (a) Electronic band structure and density of states (DOS) of tBLG \((\theta = 1.6^{\circ})\) calculated using tight binding model. The bands shown in red are the low energy active bands. (b) Comparison between the measured \(V_{2\omega}\) (black lines) and that calculated (orange line) from the semiclassical Mott relation (Eq. 2) for \(\theta \approx 1.6^{\circ}\) at three representative temperatures. \(\Delta T\) is obtained as a fitting parameter to match SMR with the experimental \(V_{2\omega}\) at CNP. (c) Doping dependence of \(S\) for \(\theta \approx 1.7^{\circ}\) compared to that of the SMR at \(5\mathrm{K}\) . (d) Temperature dependence of \(S\) at various band filling factors. The dashed lines show the \(S\propto T\) dependence. The inset shows the \(T\) dependence of \(S / S_{\mathrm{max}}\) at \(\nu = \pm 2\) .
+
+integer fillings for \(\theta \approx 1.01^{\circ}\) and \(\approx 1.24^{\circ}\) . Although a qualitative correspondence in the oscillations and sign- . reversals of the measured \(V_{2\omega}\) and \(\alpha = (1 / R)\mathrm{d}R / \mathrm{d}n\) can be seen in these devices including at the CNP and the superlattice gap, absence of accurate knowledge of the DOS prohibits a quantitative estimation of the deviation of the measured thermopower from that expected from the semiclassical model. However, for the device with \(\theta \approx 1.24^{\circ}\) (Fig. 2d), we detect an excess \(V_{2\omega}\) near \(\nu \sim 0.5\) which has no analogue in \(\alpha\) . While this indicates a clear violation of the Mott relation and highlights the possible manifestation of electron- correlation effects at fractional band filling [27], the exact origin of the excess \(V_{2\omega}\) at \(\nu \approx 0.5\) is not clear at present.
+
+Although the interaction- effects are expected to be weaker when \(\theta\) is away from \(\theta_{\mathrm{m}}\) , the devices \(\theta \approx 1.6^{\circ}\) and \(1.7^{\circ}\) provide a better quantitative comparison with SMR as the non- interacting DOS can be calculated with greater accuracy. The qualitative comparison of \(V_{2\omega}\) with \(\alpha\) at \(\theta \approx 1.6^{\circ}\) exhibits a discrepancy at low temperature (3 K), where two additional extrema, consisting of
+
+a maximum at \(\nu = +2\) and minimum at \(\nu = - 2\) , are distinctly absent in \(\alpha\) (Fig. 2e). Fig. 3a shows the tight binding calculation for the electronic band structure and the corresponding DOS for \(\theta \approx 1.6^{\circ}\) (see Methods and SI, section VII for more details on the band structure calculations). Using \(\Delta T\) as the single fitting parameter, we obtain excellent agreement between the measured \(V_{2\omega}\) and Eq. 2 at the CNP \((\nu = 0)\) , \(\nu = \pm 4\) , and also in the higher energy dispersive band \((\nu > \pm 4)\) simultaneously (See SI, Fig. S16). We also note that \(T\ll T_{\mathrm{F}}\) is maintained for fitting Eq. 2 at the CNP \((\nu = 0)\) and \(\nu = \pm 4\) throughout the temperature range shown in Fig. 3b (see SI, section V). While the SMR explains the observed \(V_{2\omega}\) over almost the entire doping regime \((- 4\lesssim \nu \lesssim +4)\) at high temperatures \((\gtrsim 40\mathrm{K})\) (bottom panel of Fig. 3b), the excess thermovoltage centered around \(\nu = \pm 2\) , becomes evident at lower \(T\) . We also find that the excess thermovoltage is intrinsically particle- hole asymmetric, however, on the electron doped side, the excess thermovoltage is closer to the commensurate filling \((\nu = +2)\) as seen for two devices (Fig. 3b and 3c). We also detect ev
+
+<--- Page Split --->
+
+
+FIG. 4: Breakdown of semiclassical Mott relation and scattering rate : (a) Surface plot of \((S - S_{\mathrm{Mott}}) / S_{\mathrm{max}}\) as a function of \(T\) and \(\nu\) for \(\theta \approx 1.6^{\circ}\) . (b) \((S - S_{\mathrm{Mott}})\) at \(10\mathrm{K}\) for \(\theta \approx 1.6^{\circ}\) and \(\theta \sim 4^{\circ}\) . (c) \(\mathrm{d}\rho /\mathrm{d}T\) extracted in the \(T\) -linear regime at different \(\nu\) for the three twist angles. (d) The estimated dimensionless pre-factor \(C\) of the scattering rate \(\Gamma = Ck_{\mathrm{B}}T / \hbar\) as a function of \(\nu\) . (e) Seebeck coefficient \(S\) computed in DMFT with \(U = 38\mathrm{meV}\) as a function of filling \(\nu\) for the four lowest bands at three temperatures \(T = 2\mathrm{K}\) , \(14\mathrm{K}\) and \(26\mathrm{K}\) , respectively.
+
+dence of small excess \(V_{2\omega}\) between \(\nu = - 3\) and \(- 4\) . This could also be due to electron- correlation effects, however, the exact origin is not clear as we do not observe any evidence of such anomalous thermopower near same filling factor in the other devices (see e.g. Fig. 3c for the device with \(\theta \approx 1.7^{\circ}\) ). Using the \(\Delta T\) extracted from the fitting of \(V_{2\omega}\) , we show the \(T\) - dependence of \(S = V_{2\omega} / \Delta T\) in Fig. 3d for different \(\nu\) (see SI, section V). Evidently, \(S\) exhibits a linear dependence on \(T\) at all doping including
+
+the higher- energy dispersive band, except in the vicinity of \(\nu = \pm 2\) , thus validating the estimation of \(\Delta T\) from Mott fitting [25]. The \(S \propto T\) behavior is expected in a degenerate weakly or non- interacting metal within the semiclassical framework, and has been verified for monolayer graphene [17] as well as tBLG at slightly larger \(\theta\) \((2^{\circ} \lesssim \theta \lesssim 5^{\circ})\) [28]. Close to \(\nu = \pm 2\) , however, we find an unexpected increase in \(S\) when temperature is decreased below \(\sim 40\mathrm{K}\) , in contrast to the expectation of \(S \approx 0\) (inset of Fig. 3d) from SMR and approaches \(S \approx \pm 2\mu \mathrm{V / K}\) for \(\nu = \pm 2\) respectively, at low \(T\) (Fig. 3d and Fig. 4b). This is remarkable because, (1) at low \(T\) , the observed sign of \(V_{2\omega}\) can not be assigned to the electron(hole)- like bands any more, and (2) the excess \(S\) persists to a temperature scale \((\sim 40\mathrm{K})\) that is much higher than the superconducting transition \((T_{\mathrm{c}} \sim 1.7\mathrm{K})\) in tBLG at \(\theta = \theta_{\mathrm{m}}\) or the temperature scale for correlated insulator \((\lesssim 4\mathrm{K})\) [4, 6, 11], suggesting a very distinct nature of the ground state. The absolute magnitude of the excess thermovoltage at \(\nu = \pm 2\) decreases with increasing \(\theta\) , as illustrated for a device with \(\theta = 1.7^{\circ}\) in Fig. 3c, and becomes undetectable for \(\theta \gtrsim 2^{\circ}\) .
+
+Although the Mott formula has been verified in a range of graphene- based devices [17, 25], it can be violated in the hydrodynamic regime [29] and due to phonon drag in cross- plane thermoelectric transport in tBLG at \(\theta > 6^{\circ}\) [20]. While the hydrodynamic regime is expected to appear at higher temperatures \((>100\mathrm{K})\) , we eliminate the possibility of phonon drag from the observation of \(S \propto T\) (away from \(\nu = \pm 2\) , Fig. 3d). Furthermore, as shown in Fig. 4a, the occurrence of excess \(S\) , normalized as \((S - S_{\mathrm{Mott}}) / S_{\mathrm{max}}\) , where \(S_{\mathrm{max}}\) is the maximum value of \(S\) at a given \(T\) , is concentrated in the low \(T\) dome- like regions around \(\nu = \pm 2\) in the \(T - (\nu , n)\) phase diagram. Since neither adiabatic (static) nor dynamical phonon effects can violate Mott formula [30, 31], the enhancement of thermopower beyond the SMR limit suggests the possibility of a many body ground state similar to NFL phases in correlated oxides [32] and heavy Fermions [33]. A near- ubiquitous feature of the NFL regime in itinerant Fermionic systems, ranging from cuprates [34], ruthenates [35], pnictides [36] to heavy Fermions [33], is the 'strange metal' phase, characterized by the absence of well defined quasiparticles and linear \(T\) dependence of \(\rho\) . Theoretical work also suggests possibilities of excess entropy, analogous to Bekenstein- Hawking entropy in charged black holes, in this regime, that remains finite down to vanishingly small \(T\) [37].
+
+To check the mutuality between the excess thermopower and the strange metallic behaviour, we compare the \(\nu\) - dependence of excess \(S\) at \(T = 10\mathrm{K}\) (Fig. 4b), and the scattering rate obtained from the slope \(\mathrm{d}\rho /\mathrm{d}T\) in the \(T\) - dependence of \(\rho\) (Fig. 4c). For reference, we also present the results from another device at \(\theta \approx 4^{\circ}\) , where we find no violation of SMR over the experimental range of \(n\) . In the NFL state, the incoherent scattering rate is
+
+<--- Page Split --->
+
+\(\tau^{- 1} = Ck_{\mathrm{B}}T / \hbar\) , where the dimensionless coefficient \(C\) is of the order of unity for Planckian dissipation. In Fig. 4c we plot the \(\nu\) - dependence of \(\mathrm{d}\rho /\mathrm{d}T\) and \(C\) (Fig. 4d), where \(C\) is computed from \(\mathrm{d}\rho /\mathrm{d}T\) assuming Drude- like resistivity in accordance to Ref. [8, 9] (See SI, section VI). Away from the CNP, both \(1.6^{\circ}\) and \(1.7^{\circ}\) devices show \(\mathrm{d}\rho /\mathrm{d}T\approx 10 \Omega /\mathrm{K}\) near \(\nu \approx \pm 2\) , which is nearly two orders of magnitude larger than \(\mathrm{d}\rho /\mathrm{d}T\approx 0.2 - 0.3 \Omega /\mathrm{K}\) for the tBLG device at \(\theta \sim 4^{\circ}\) , implying that the individual layers are essentially decoupled in the latter [8, 10]. Intriguingly, for tBLG at \(\theta = 1.6^{\circ}\) and \(1.7^{\circ}\) , we find \(C\) to approach the order of unity in the vicinity of \(\nu \rightarrow \pm 2\) , raising the possibility of a common physical origin for the violation of SMR. Notably, the excess thermopower was found largely unaffected in the in- plane magnetic field (Fig. S20, SI, section V), and thus unlikely to arise from an underlying spin/magnetic texture [5]. Theoretically a dynamical mean field theory (DMFT) [3, 38, 39] calculation shows qualitative agreement in the density dependence of excess thermopower at \(\nu = \pm 2\) but fails to capture its finite magnitude at low temperature (Fig. 4e). This is because the particular single site DMFT framework used in our calculation would invariably lead to the FL phase as \(T\rightarrow 0\) , even though some excess thermopower can be observed in the intermediate temperature range (see SI, sections VII for details).
+
+In summary, we have measured the electrical resistivity and thermopower in twisted bilayer graphene over a broad range of low- twist angles. At larger \(\theta\) ( \(\sim 1.6^{\circ} - 1.7^{\circ}\) ), our experimental results show concurrent \(T\) - linear resistivity at Planckian dissipation scales and emergent excess thermopower below \(T\lesssim 40 \mathrm{K}\) near \(\nu = \pm 2\) signifying the breakdown of the semiclassical Mott relation. The thermopower near \(\nu = \pm 2\) approaches a finite magnitude ( \(\approx 2 \mu \mathrm{V} / \mathrm{K}\) at \(1.6^{\circ}\) ) at low \(T\) providing a new facet to the strongly correlated 'strange metal' phase in tBLG. Our experimental results point to a truly non- Fermi liquid (NFL) metallic state in tBLG at low twist angle that carry strong similarities to those observed in cuprates or heavy- Fermion materials with low coherence temperatures.
+
+The authors thank Nano mission, DST for the financial support. M.J. and S.M. thank the computational facilities in SERC. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, Grant Number JPMXP0112101001, JSPS KAKENHI Grant Numbers JP20H00354 and the CREST(JPMJCR15F3), JST. U.C. acknowledges funding from IISc and SERB (ECR/2017/001566), and H.R.K from SERB(SB/DF/005/2017). S.B. acknowledges funding from IISc and SERB (ECR/2018/001742).
+
+B.G., P.S.M. and MG contributed equally to this work.
+
+## METHODS
+
+## Device fabrication
+
+All devices in this work were fabricated using a layer- by- layer mechanical transfer method [20]. Monolayer graphene and hexagonal boron nitride (hBN) were exfoliated on \(\mathrm{SiO_2 / Si}\) wafers and graphene flakes were identified using optical microscopy and Raman spectroscopy. For \(\theta \approx 1.6^{\circ}\) , the edges of the graphene flakes were aligned under an optical microscope and encapsulated within two hBN layers. Other tBLG devices were fabricated using tear and stack method [40]. Electron beam lithography was used to define \(\mathrm{Cr / Au}\) top gate for tuning the number density in the tBLG region. Finally, the electrical contacts were patterned by electron- beam lithography and reactive ion etching followed by metal deposition (5 nm \(\mathrm{Cr / 50 nm}\) Au) using thermal evaporation technique.
+
+Electrical transport measurements were performed in a four- terminal geometry with typical \(ac\) current excitations of 10- 100 nA using a standard low- frequency lock- in amplifier at \(226 \mathrm{Hz}\) , in a dilution refrigerator and a 1.5- K cryostat. For thermoelectric measurements, local Joule heating was employed to create a \(\Delta T\) across the tBLG channel. A range of sinusoidal currents (2- 5 \(\mu \mathrm{A}\) ) at excitation frequency \(\omega = 17 \mathrm{Hz}\) were used for Joule heating and the resulting \(2^{\mathrm{nd}}\) harmonic thermal voltage \((V_{2\omega})\) was recorded using a lock- in amplifier. Thermoelectric measurements were conducted in a 1.5- K cryostat/20 mK dilution refrigerator with magnetic field.
+
+## Tight binding calculation of DOS
+
+The rigid bilayer structures were generated using the Twister code [41]. The structures were subsequently relaxed in LAMMPS [42][43] using REBO [44] as the intralayer potential and DRIP [45] as the interlayer potential. These relaxed structures were used for performing all the calculations.
+
+The electronic band structures were calculated by approximating the tight binding transfer integrals under the Slater Koster formalism [46]. A more detailed discussion of the calculations is available in the SI, section VII.
+
+<--- Page Split --->
+
+[2] Bistritzer, R. & MacDonald, A. H. Moiré bands in twisted double- layer graphene. Proc. Natl Acad. Sci. 108, 12233- 12237 (2011).[3] Yuan, N. F. Q., Isobe, H. & Fu, L. Magic of high- order van Hove singularity. Nat. Comm. 10 (2019).[4] Cao, Y. et al. Unconventional superconductivity in magic- angle graphene superlattices. Nature 556, 43 (2018).[5] Sharpe, A. L. et al. Emergent ferromagnetism near three- quarters filling in twisted bilayer graphene. Science 365, 605- 608 (2019).[6] Cao, Y. et al. Correlated insulator behaviour at half- filling in magic- angle graphene superlattices. Nature 556, 80 (2018).[7] Zondiner, U. et al. Cascade of phase transitions and dirac revivals in magic- angle graphene. Nature 582, 203- 208 (2020).[8] Cao, Y. et al. Strange metal in magic- angle graphene with near Planckian dissipation. Phys. Rev. Lett. 124, 076801 (2020).[9] Bruin, J., Sakai, H., Perry, R. & Mackenzie, A. Similarity of scattering rates in metals showing T- linear resistivity. Science 339, 804- 807 (2013).[10] Polshyn, H. et al. Large linear- in- temperature resistivity in twisted bilayer graphene. Nat. Phys. 15, 1011- 1016 (2019).[11] Kerelsky, A. et al. Maximized electron interactions at the magic angle in twisted bilayer graphene. Nature 572, 95- 100 (2019).[12] Jiang, Y. et al. Charge order and broken rotational symmetry in magic- angle twisted bilayer graphene. Nature 573, 91- 95 (2019).[13] Liu, Y.- W. et al. Magnetism near half- filling of a van hove singularity in twisted graphene bilayer. Phys. Rev. B 99, 201408 (2019).[14] Rowe, D. M. Materials, preparation, and characterization in thermoelectrics (CRC press, 2017).[15] Behnia, K. Fundamentals of thermoelectricity (OUP Oxford, 2015).[16] Watanabe, S. et al. Validity of the Mott formula and the origin of thermopower in \(\pi\) - conjugated semicrystalline polymers. Phys. Rev. B 100, 241201 (2019).[17] Zuev, Y. M., Chang, W. & Kim, P. Thermoelectric and magnetothermoelectric transport measurements of graphene. Phys. Rev. Lett. 102, 096807 (2009).[18] Kim, D., Syers, P., Butch, N. P., Paglione, J. & Fuhrer, M. S. Ambipolar surface state thermoelectric power of topological insulator \(\mathrm{Bi_2Se_3}\) . Nano Lett. 14, 1701- 1706 (2014).[19] Arsenijević, S. et al. Signatures of quantum criticality in the thermopower of \(\mathrm{Ba(Fe_{1 - x}Co_x)_2As_2}\) . Phys. Rev. B 87, 224508 (2013).[20] Mahapatra, P. S., Sarkar, K., Krishnamurthy, H. R., Mukerjee, S. & Ghosh, A. Seebeck coefficient of a single van der Waals junction in twisted bilayer graphene. Nano Lett. 17, 6822- 6827 (2017).[21] Saito, Y. et al. Isospin pomeranchuk effect and the entropy of collective excitations in twisted bilayer graphene. arXiv preprint arXiv:2008.10830 (2020).[22] Rozen, A. et al. Entropic evidence for a pomeranchuk effect in magic angle graphene. arXiv preprint arXiv:2009.01836 (2020).[23] Efetov, D. K. & Kim, P. Controlling electron- phonon interactions in graphene at ultrahigh carrier densities.
+
+Phys. Rev. Lett. 105, 256805 (2010).[24] Wu, F., Hwang, E. & Sarma, S. D. Phonon- induced giant linear- in- T resistivity in magic angle twisted bilayer graphene: Ordinary strangeness and exotic superconductivity. Phys. Rev. B 99, 165112 (2019).[25] Jayaraman, A. et al. Evidence of lifshitz transition in the thermoelectric power of ultrahigh- mobility bilayer graphene. Nano Lett. 21, 1221- 1227 (2021).[26] Buhmann, J. M. & Sigrist, M. Thermoelectric effect of correlated metals: Band- structure effects and the breakdown of Mott's formula. Phys. Rev. B 88, 115128 (2013).[27] Wu, S., Zhang, Z., Watanabe, K., Taniguchi, T. & Andrei, E. Y. Chern insulators, van hove singularities and topological flat bands in magic- angle twisted bilayer graphene. Nat. Mat. 20, 488- 494 (2021).[28] Mahapatra, P. S. et al. Misorientation- controlled cross- plane thermoelectricity in twisted bilayer graphene. Phys. Rev. Lett. 125, 226802 (2020).[29] Ghahari, F. et al. Enhanced thermoelectric power in graphene: Violation of the Mott relation by inelastic scattering. Phys. Rev. Lett. 116, 136802 (2016).[30] Jonson, M. & Mahan, G. Mott's formula for the thermopower and the Wiedemann- Franz law. Phys. Rev. B 21, 4223 (1980).[31] Jonson, M. & Mahan, G. Electron- phonon contribution to the thermopower of metals. Phys. Rev. B 42, 9350 (1990).[32] Wang, Y., Rogado, N. S., Cava, R. J. & Ong, N. P. Spin entropy as the likely source of enhanced thermopower in \(\mathrm{Na_xCo_2O_4}\) . Nature 423, 425- 428 (2003).[33] Izawa, K. et al. Thermoelectric response near a quantum critical point: The case of \(\mathrm{CeCoIn_5}\) . Phys. Rev. Lett. 99, 147005 (2007).[34] da Silva Neto, E. H. et al. Ubiquitous interplay between charge ordering and high- temperature superconductivity in cuprates. Science 343, 393- 396 (2014).[35] Rost, A., Perry, R., Mercure, J.- F., Mackenzie, A. & Grigera, S. Entropy landscape of phase formation associated with quantum criticality in \(\mathrm{Sr_3Ru_2O_7}\) . Science 325, 1360- 1363 (2009).[36] Lee, W.- C. & Phillips, P. W. Non- Fermi liquid due to orbital fluctuations in iron pnictide superconductors. Phys. Rev. B 86, 245113 (2012).[37] Sachdev, S. Bekenstein- Hawking entropy and strange metals. Phys. Rev. X 5, 041025 (2015).[38] Georges, A., Kotliar, G., Krauth, W. & Rozenberg, M. J. Dynamical mean- field theory of strongly correlated fermion systems and the limit of infinite dimensions. Rev. Mod. Phys. 68, 13- 125 (1996).[39] Haldar, A., Banerjee, S. & Shenoy, V. B. Higher- dimensional Sachdev- Ye- Kitaev non- Fermi liquids at Lifshitz transitions. Phys. Rev. B 97, 241106 (2018).[40] Kim, K. et al. Tunable moiré bands and strong correlations in small- twist- angle bilayer graphene. Proceedings of the National Academy of Sciences 114, 3364- 3369 (2017).[41] Naik, M. H. & Jain, M. Ultrafatbands and shear solitons in moire patterns of twisted bilayer transition metal dichalcogenides. Phys. Rev. Lett. 121, 266401 (2018).[42] Plimpton, S. Fast parallel algorithms for short- range molecular dynamics (1993).[43] https://lammps.sandia.gov.[44] Brenner, D. W. et al. A second- generation reactive empirical bond order (rebo) potential energy expression for
+
+<--- Page Split --->
+
+hydrocarbons. J Phys. Cond. Mat. 14, 783 (2002).[45] Wen, M., Carr, S., Fang, S., Kaxiras, E. & Tadmor, E. B. Dihedral- angle- corrected registry- dependent interlayer potential for multilayer graphene structures. Phys.
+
+Rev. B 98, 235404 (2018).[46] Slater, J. C. & Koster, G. F. Simplified LCAO method for the periodic potential problem. Phys. Rev. 94, 1498 (1954).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+Supplementary.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36_det.mmd b/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..a160a46f4631b7eaf2ff5a615b8820ed5dc3a1c7
--- /dev/null
+++ b/preprint/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36/preprint__055972f26bedc36e1e52f0e5e4d0564067003dbce0946a30508fa4b542404a36_det.mmd
@@ -0,0 +1,216 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 955, 210]]<|/det|>
+# Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene
+
+<|ref|>text<|/ref|><|det|>[[44, 230, 472, 315]]<|/det|>
+Bhaskar Ghawri Indian Institute of Science Bangalore Phanibhusan Mahapatra ( \(\boxed{ \begin{array}{r l} \end{array} }\) phanis@iisc.ac.in) Indian Institute of Science Bangalore
+
+<|ref|>text<|/ref|><|det|>[[44, 322, 380, 363]]<|/det|>
+Manjari Garg Indian Institute of Science Bangalore
+
+<|ref|>text<|/ref|><|det|>[[44, 370, 736, 411]]<|/det|>
+Shinjan Mandal Indian Institute of Science Bangalore https://orcid.org/0000- 0003- 1551- 6555
+
+<|ref|>text<|/ref|><|det|>[[44, 416, 285, 456]]<|/det|>
+Saisab Bhowmik Indian Institute of Science
+
+<|ref|>text<|/ref|><|det|>[[44, 463, 736, 504]]<|/det|>
+Aditya Jayraman Indian Institute of Science Bangalore https://orcid.org/0000- 0002- 6963- 7195
+
+<|ref|>text<|/ref|><|det|>[[44, 509, 285, 549]]<|/det|>
+Radhika Soni Indian Institute of Science
+
+<|ref|>text<|/ref|><|det|>[[44, 556, 752, 597]]<|/det|>
+Kenji Watanabe National Institute for Materials Science https://orcid.org/0000- 0003- 3701- 8119
+
+<|ref|>text<|/ref|><|det|>[[44, 602, 904, 643]]<|/det|>
+Takashi Taniguchi National Institute for Materials Science, Tsukuba, Ibaraki https://orcid.org/0000- 0002- 1467- 3105
+
+<|ref|>text<|/ref|><|det|>[[44, 648, 380, 688]]<|/det|>
+Hulikal Krishnamurthy Indian Institute of Science Bangalore
+
+<|ref|>text<|/ref|><|det|>[[44, 695, 736, 736]]<|/det|>
+Manish Jain Indian Institute of Science Bangalore https://orcid.org/0000- 0001- 9329- 6434
+
+<|ref|>text<|/ref|><|det|>[[44, 741, 380, 781]]<|/det|>
+Sumilan Banerjee Indian Institute of Science Bangalore
+
+<|ref|>text<|/ref|><|det|>[[44, 787, 380, 828]]<|/det|>
+U. Chandni Indian Institute of Science Bangalore
+
+<|ref|>text<|/ref|><|det|>[[44, 834, 380, 874]]<|/det|>
+Arindam Ghosh Indian Institute of Science Bangalore
+
+<|ref|>text<|/ref|><|det|>[[44, 915, 101, 932]]<|/det|>
+Article
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 44, 923, 87]]<|/det|>
+Keywords: twisted bilayer graphene (tBLG), non-Fermi liquid (NFL), van Hove singularities (vHS), SMR, hBN
+
+<|ref|>text<|/ref|><|det|>[[44, 105, 319, 125]]<|/det|>
+Posted Date: August 26th, 2021
+
+<|ref|>text<|/ref|><|det|>[[42, 144, 463, 164]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 811957/v1
+
+<|ref|>text<|/ref|><|det|>[[42, 181, 911, 225]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 259, 923, 303]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on March 21st, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 29198- 4.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[118, 63, 886, 99]]<|/det|>
+# Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene
+
+<|ref|>text<|/ref|><|det|>[[160, 112, 844, 272]]<|/det|>
+Bhaskar Ghawri, \(^{1, *}\) Phanibhusan S. Mahapatra, \(^{1, \dagger}\) Manjari Garg, \(^{2, \ddagger}\) Shinjan Mandal, \(^{1}\) Saisab Bhowmik, \(^{2}\) Aditya Jayaraman, \(^{1}\) Radhika Soni, \(^{2}\) Kenji Watanabe, \(^{3}\) Takashi Taniguchi, \(^{4}\) H. R. Krishnamurthy, \(^{1}\) Manish Jain, \(^{1}\) Sumilan Banerjee, \(^{1}\) U. Chandni, \(^{2}\) and Arindam Ghosh \(^{1, 5, \S}\) \(^{1}\) Department of Physics, Indian Institute of Science, Bangalore, 560012, India \(^{2}\) Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore, 560012, India \(^{3}\) Research Center for Functional Materials, National Institute for Materials Science, Namiki 1- 1, Tsukuba, Ibaraki 305- 0044, Japan \(^{4}\) International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Namiki 1- 1, Tsukuba, Ibaraki 305- 0044, Japan \(^{5}\) Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560 012, India
+
+<|ref|>text<|/ref|><|det|>[[177, 279, 830, 452]]<|/det|>
+The planar assembly of twisted bilayer graphene (tBLG) hosts multitude of interaction- driven phases when the relative rotation is close to the magic angle ( \(\theta_{\mathrm{m}} = 1.1^{\circ}\) ). This includes correlation- induced ground states that reveal spontaneous symmetry breaking at low temperature, as well as possibility of non- Fermi liquid (NFL) excitations. However, experimentally, manifestation of NFL effects in transport properties of twisted bilayer graphene remains ambiguous. Here we report simultaneous measurements of electrical resistivity ( \(\rho\) ) and thermoelectric power ( \(S\) ) in tBLG for several twist angles between \(\theta \sim 1.0 - 1.7^{\circ}\) . We observe an emergent violation of the semiclassical Mott relation in the form of excess \(S\) close to half- filling for \(\theta \sim 1.6^{\circ}\) that vanishes for \(\theta \gtrsim 2^{\circ}\) . The excess \(S\) ( \(\approx 2 \mu \mathrm{V / K}\) at low temperatures \(T \sim 10 \mathrm{K}\) at \(\theta \approx 1.6^{\circ}\) ) persists up to \(\approx 40 \mathrm{K}\) , and is accompanied by metallic \(T\) - linear \(\rho\) with transport scattering rate \((\tau^{- 1})\) of near- Planckian magnitude \(\tau^{- 1} \sim k_{\mathrm{B}} T / \hbar\) . Closer to \(\theta_{\mathrm{m}}\) , the excess \(S\) was also observed for fractional band filling ( \(\nu \approx 0.5\) ). The combination of non- trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG.
+
+<|ref|>text<|/ref|><|det|>[[86, 477, 488, 899]]<|/det|>
+In moiré systems with twisted bilayer graphene (tBLG), the amplification of Coulomb correlation effects at low twist angles ( \(\theta\) ) is a result of nearly flat low- energy electronic bands [1, 2] and divergent density of states (DOS) at van Hove singularities (vHS) [3]. In addition to superconductivity [4], ferromagnetism [5], the strong correlation effects in tBLG manifest in a cascade of broken symmetry phases at integer band filling factor ( \(\nu\) ) close to \(\theta = \theta_{\mathrm{m}}\) [6, 7]. Near half- filling ( \(\nu = \pm 2\) ) of the four- fold spin- valley degenerate conduction and valence bands, a linear \(T\) - dependence of the resistivity ( \(\rho\) ) seems to indicate an interaction- related absence of a well- defined quasiparticle spectrum, which is concomitant with non- Fermi liquid (NFL) excitations [8, 9]. The persistence of the linearity in \(\rho\) for \(\theta\) well away from \(\theta_{\mathrm{m}}\) , e.g. for \(\theta \sim 1.5 - 2^{\circ}\) , however, has been interpreted in terms of a contrary scenario that is addressable within the non- interacting framework [10]. The uncertainty persists even in scanning tunneling microscopy experiments [11- 13], where the possibility of an interaction- driven magnetic order has been claimed close to the vHS for \(\theta\) as high as \(1.6^{\circ}\) , although the spontaneous breaking of \(C_{6}\) lattice symmetry to nematic orbital order has not been observed for \(\theta > \theta_{\mathrm{m}}\) . Thus a comprehensive understanding of the impact of correlation in tBLG requires a complementary experimental probe that is capable of identifying the departure from noninteracting physics in an unambiguous manner.
+
+<|ref|>text<|/ref|><|det|>[[101, 900, 488, 914]]<|/det|>
+Here we have carried out simultaneous electrical and
+
+<|ref|>text<|/ref|><|det|>[[515, 477, 917, 643]]<|/det|>
+thermoelectric measurements in tBLG for twist angles varying from \(\theta \sim 1.0 - 1.7^{\circ}\) . The dependence on \(T\) and on the carrier density ( \(n\) ) of the thermoelectric power ( \(S\) ), or the Seebeck coefficient, is used as an independent and sensitive probe of the correlation effects. Thermoelectric power is often interpreted as a thermodynamic entity that represents the entropy carried by each charge carrier. Within the degenerate quasiparticle description in the Boltzmann transport regime ( \(T \ll T_{\mathrm{F}}\) , where \(T_{\mathrm{F}}\) is the Fermi temperature), \(S\) is related to the resistance ( \(R\) ) through the semiclassical Mott relation (SMR),
+
+<|ref|>equation<|/ref|><|det|>[[611, 652, 915, 688]]<|/det|>
+\[S_{\mathrm{Mott}} = \frac{\pi^{2}k_{\mathrm{B}}^{2}T}{3|e|}\frac{\mathrm{d}\ln R(E)}{\mathrm{d}E}\bigg|_{E_{\mathrm{F}}}, \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[515, 700, 917, 911]]<|/det|>
+where \(R(E)\) , \(e\) and \(E_{\mathrm{F}}\) are the energy- dependent resistance, electronic charge and Fermi energy, respectively. Eq. 1 is valid under the assumption that scattering is elastic and isotropic close to the Fermi surface i.e. the transport lifetime only depends on the energy of the charge carriers. Remarkably, this simple assumption of isotropic scattering remains valid in a wide variety of systems, such as disordered metals/semiconductors [14, 15], organic materials [16], monolayer graphene [17] and topological insulators [18]. The SMR effectively arises from the quasiparticles carrying heat and charge under identical constraints, imposed by the momentum conservation. Thus, the validity of SMR in Eq. 1 provides a definitive probe into the nature of the scattering mechanisms and
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[100, 70, 912, 461]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[84, 476, 916, 582]]<|/det|>
+FIG. 1: Electrical transport in twisted bilayer graphene. (a) Temperature-dependent resistance \(R\) as a function of band filling \(\nu\) for four different devices with twist angle \(\theta \approx 1.01^{\circ}\) , \(1.24^{\circ}\) , \(1.6^{\circ}\) and \(1.7^{\circ}\) . The inset in the bottom panel shows the optical image of a typical device with current and voltage leads marked for resistivity measurements. The scale bar represents a length of \(5 \mu \mathrm{m}\) . \(\rho\) as a function of \(T\) for a few representative values of \(\nu\) for (b) \(\theta \approx 1.01^{\circ}\) , (c) \(1.24^{\circ}\) and (d) \(1.6^{\circ}\) . The various curves for fractional \(\nu\) in (c) represent the \(T\) -dependence of the CI/CS states as marked in the second panel of (a).(e) Comparison of \(T\) -dependence of \(\rho\) at \(\nu = -2\) for different twist angles. The solid lines represent \(T\) -linearity.
+
+<|ref|>text<|/ref|><|det|>[[85, 610, 485, 656]]<|/det|>
+energy distribution of the charge carriers near the Fermi surface, and it breaks down when strong correlation effects become important [15, 19].
+
+<|ref|>text<|/ref|><|det|>[[86, 657, 487, 898]]<|/det|>
+The tBLG devices we study were created using standard van der Waals stacking [20], which consists of two graphene layers aligned at either \(60^{\circ} + \theta\) or at \(\theta\) , where \(\theta\) is the effective twist angle, and encapsulated within two sheets of hexagonal boron nitride (hBN) (see supplementary information, SI, section I). A local top- gate tunes \(n\) in the overlap region where the moiré super- lattice is formed. Fig. 1a shows the four terminal resistance \(R\) measured across the tBLG devices as a function of band filling factor \(\nu\) and \(T\) for four different \(\theta\) . The recurring features in \(R\) across the tBLG devices can be identified as the maxima in \(R\) at CNP and at the full- filling of the moiré band ( \(\nu = \pm 4\) ). In addition, near \(\theta_{\mathrm{m}}\) , the two devices \(\theta \approx 1.01^{\circ}\) and \(\approx 1.24^{\circ}\) exhibit additional maxima in \(R\) near integer values of \(\nu\) , which can be mapped to the correlated states at integer fillings. For \(\theta \approx 1.24^{\circ}\) , we ob
+
+<|ref|>text<|/ref|><|det|>[[515, 610, 916, 746]]<|/det|>
+serve a substantial shift \(|\Delta \nu | \sim 0.25\) of resistance peaks near \(\nu = +1\) and \(+3\) from \(7 \mathrm{~K}\) to \(35 \mathrm{~K}\) , suggesting the possibility of isospin- polarization in the system [21, 22] (SI, section III). We speculate that the noticeable asymmetry in the doping dependence of \(R\) on the electron and hole sides is most likely related to the particle- hole asymmetry of the band structure since in both tBLG devices near \(\theta_{\mathrm{m}}\) , the correlated states are more pronounced at electron doping.
+
+<|ref|>text<|/ref|><|det|>[[515, 747, 916, 898]]<|/det|>
+For \(0 < |\nu| < 4\) , the \(T\) - dependence for all devices was found to be generally metallic at low temperatures \(\lesssim 40 \mathrm{~K}\) (Fig. 1b- 1d). However, the resistance peaks near integer \(\nu\) exhibit either weak insulating \(T\) - dependence, i.e., a correlated insulating phase (CI), or \(T\) - linear resistivity i.e., a correlated semimetallic (CS) phase. In the metallic regime, \(\rho\) can expressed as \(\rho = \rho_{0} + AT\) , where \(\rho_{0}\) is the residual resistivity. The values of \(A\) \((\sim 10 - 100 \Omega /\mathrm{K})\) are at least two orders of magnitude greater compared to that of the monolayer graphene, and
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[93, 66, 479, 600]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 612, 483, 795]]<|/det|>
+FIG. 2: Thermoelectric transport in twisted bilayer graphene: (a) The cross-sectional view of the device, showing the constituent layers, electrical contacts, and the gate assembly. (b) In-plane heating and measurement schematic for thermovoltage \(V_{2\omega}\) in the tBLG region. Density dependence of \(V_{2\omega} / I_{\omega}^{2}\) (in the units of \(\mathrm{VA}^{-2} \times 10^{6}\) ) measured at 5 K for (c) \(\theta \approx 1.01^{\circ}\) , (d) \(1.24^{\circ}\) , and at 3 K for (e) \(1.6^{\circ}\) device. The different curves in each panel represent the \(V_{2\omega} / I_{\omega}^{2}\) measured at different \(I_{\omega}\) . The bottom graphs in each panel show the numerically calculated \(\alpha = (1 / R)\mathrm{d}R / \mathrm{d}n\) (in the units of \(\mathrm{m}^{2}\) ) for comparison.
+
+<|ref|>text<|/ref|><|det|>[[85, 825, 488, 900]]<|/det|>
+are consistent with the earlier transport measurements in tBLG devices [10]. From the comparison of \(\rho (T)\) at half- filling \(\nu = - 2\) in Fig. 1e, we find that the resistivity is linear in \(T\) for all four low- angle devices. However, at \(\theta \approx 1.24^{\circ}\) and \(\theta \approx 1.01^{\circ}\) , the linearity persists only upto
+
+<|ref|>text<|/ref|><|det|>[[514, 65, 917, 292]]<|/det|>
+\(\sim 40\mathrm{K}\) , which could be due to the smaller bandwidth and smaller bandgap [10]. We also note that the value of \(A\) \(\sim 40 - 100\Omega /\mathrm{K}\) at \(\nu = - 2\) is much larger near \(\theta \sim \theta_{\mathrm{m}}\) than that of the devices away from \(\theta_{\mathrm{m}}\) (SI, section III). The ubiquitous \(T\) - linearity across all tBLG devices at low temperature is a clear departure from \(\rho \sim T^{2}\) dependence associated with electron- electron scattering, or the \(\rho \propto T^{4}\) behavior, expected due to electron- acoustic phonon scattering below the Bloch- Grüneisen temperature \((T_{\mathrm{BG}})\) [23]. While this suggests the continuum of correlation- driven metallic states across the tBLG devices, an alternate scenario has been proposed [10, 24] to view the tBLG in this regime as a two dimensional, weakly (or non- ) interacting metal with largely reduced \(T_{\mathrm{BG}}\) .
+
+<|ref|>text<|/ref|><|det|>[[514, 293, 917, 729]]<|/det|>
+To complement the electrical transport, we have performed thermoelectric measurements on the same devices. Briefly, a sinusoidal current \((I_{\omega})\) is allowed to flow between two contacts of the monolayer branch outside the top gated region, setting up a temperature gradient \((\Delta T)\) across the tBLG region (Fig. 2a and 2b). The resulting second- harmonic thermo- voltage \((V_{2\omega})\) is recorded on the tBLG region as a function of doping and heating current [17, 20]. The linear response was ensured from \(V_{2\omega} \propto I_{\omega}^{2}\) for the range of heating current used (Fig. 2c- 2e). We begin with the results in tBLG devices closer to \(\theta_{\mathrm{m}}\) . Fig. 2c exhibits the \(\nu\) - dependence of normalized \(V_{2\omega}\) for tBLG device \(\theta \approx 1.01^{\circ}\) at low temperature (5 K), which exhibits multiple sign- reversals when \(E_{\mathrm{F}}\) is varied across the lowest energy band. While the sign reversals near CNP and the super- lattice gaps at \(\nu = \pm 4\) are due to changes in the quasiparticle excitations, those near integer values of \(0 < \nu < 4\) can be attributed to the correlated states. The sign- reversal of \(V_{2\omega}\) near each correlated states is fascinating since it indicates a change in the topology of the Fermi surface, which is naturally associated with the Lifshitz transition [25, 26]. Although the correlated states are metallic in nature (Fig. 1a), the concomitant Lifshitz transitions depicts the interaction- driven occurrence of diverging DOS at each integer values of \(\nu\) . This is in stark contrast to the charge- inversions at \(\nu = 0, \pm 4\) , and hints at the topological facet of the lowest energy band when filled with integer number of charge carriers [7, 27].
+
+<|ref|>text<|/ref|><|det|>[[514, 730, 916, 759]]<|/det|>
+To establish the connection between the two different types of transports, we rewrite Eq. 1 as,
+
+<|ref|>equation<|/ref|><|det|>[[586, 777, 915, 813]]<|/det|>
+\[S_{\mathrm{Mott}} = \frac{\pi^{2}k_{\mathrm{B}}^{2}T}{3|e|}\frac{1}{R}\frac{\mathrm{d}R}{\mathrm{d}V_{\mathrm{tg}}}\frac{\mathrm{d}V_{\mathrm{tg}}}{\mathrm{d}n}\frac{\mathrm{d}n}{\mathrm{d}E}\bigg|_{E_{\mathrm{F}}}, \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[514, 821, 917, 912]]<|/det|>
+where \((1 / R)\mathrm{d}R / \mathrm{d}V_{\mathrm{tg}}\) is measured experimentally, and \(\mathrm{d}n / \mathrm{d}E\) is the DOS \((\mathrm{d}V_{\mathrm{tg}} / \mathrm{d}n = e / C_{\mathrm{hBN}}\) , where \(C_{\mathrm{hBN}}\) is the known topgate capacitance per unit area). The difficulty in accurate estimation of DOS in the presence of strong correlation effects near \(\theta_{\mathrm{m}}\) prohibits us from accurately estimating \(S_{\mathrm{Mott}}\) , in particular close to the
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[95, 68, 910, 430]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[84, 447, 914, 556]]<|/det|>
+FIG. 3: Comparison with semiclassical Mott relation at \(\sim 1.6^{\circ}\) (a) Electronic band structure and density of states (DOS) of tBLG \((\theta = 1.6^{\circ})\) calculated using tight binding model. The bands shown in red are the low energy active bands. (b) Comparison between the measured \(V_{2\omega}\) (black lines) and that calculated (orange line) from the semiclassical Mott relation (Eq. 2) for \(\theta \approx 1.6^{\circ}\) at three representative temperatures. \(\Delta T\) is obtained as a fitting parameter to match SMR with the experimental \(V_{2\omega}\) at CNP. (c) Doping dependence of \(S\) for \(\theta \approx 1.7^{\circ}\) compared to that of the SMR at \(5\mathrm{K}\) . (d) Temperature dependence of \(S\) at various band filling factors. The dashed lines show the \(S\propto T\) dependence. The inset shows the \(T\) dependence of \(S / S_{\mathrm{max}}\) at \(\nu = \pm 2\) .
+
+<|ref|>text<|/ref|><|det|>[[86, 583, 488, 794]]<|/det|>
+integer fillings for \(\theta \approx 1.01^{\circ}\) and \(\approx 1.24^{\circ}\) . Although a qualitative correspondence in the oscillations and sign- . reversals of the measured \(V_{2\omega}\) and \(\alpha = (1 / R)\mathrm{d}R / \mathrm{d}n\) can be seen in these devices including at the CNP and the superlattice gap, absence of accurate knowledge of the DOS prohibits a quantitative estimation of the deviation of the measured thermopower from that expected from the semiclassical model. However, for the device with \(\theta \approx 1.24^{\circ}\) (Fig. 2d), we detect an excess \(V_{2\omega}\) near \(\nu \sim 0.5\) which has no analogue in \(\alpha\) . While this indicates a clear violation of the Mott relation and highlights the possible manifestation of electron- correlation effects at fractional band filling [27], the exact origin of the excess \(V_{2\omega}\) at \(\nu \approx 0.5\) is not clear at present.
+
+<|ref|>text<|/ref|><|det|>[[86, 796, 488, 901]]<|/det|>
+Although the interaction- effects are expected to be weaker when \(\theta\) is away from \(\theta_{\mathrm{m}}\) , the devices \(\theta \approx 1.6^{\circ}\) and \(1.7^{\circ}\) provide a better quantitative comparison with SMR as the non- interacting DOS can be calculated with greater accuracy. The qualitative comparison of \(V_{2\omega}\) with \(\alpha\) at \(\theta \approx 1.6^{\circ}\) exhibits a discrepancy at low temperature (3 K), where two additional extrema, consisting of
+
+<|ref|>text<|/ref|><|det|>[[515, 584, 917, 901]]<|/det|>
+a maximum at \(\nu = +2\) and minimum at \(\nu = - 2\) , are distinctly absent in \(\alpha\) (Fig. 2e). Fig. 3a shows the tight binding calculation for the electronic band structure and the corresponding DOS for \(\theta \approx 1.6^{\circ}\) (see Methods and SI, section VII for more details on the band structure calculations). Using \(\Delta T\) as the single fitting parameter, we obtain excellent agreement between the measured \(V_{2\omega}\) and Eq. 2 at the CNP \((\nu = 0)\) , \(\nu = \pm 4\) , and also in the higher energy dispersive band \((\nu > \pm 4)\) simultaneously (See SI, Fig. S16). We also note that \(T\ll T_{\mathrm{F}}\) is maintained for fitting Eq. 2 at the CNP \((\nu = 0)\) and \(\nu = \pm 4\) throughout the temperature range shown in Fig. 3b (see SI, section V). While the SMR explains the observed \(V_{2\omega}\) over almost the entire doping regime \((- 4\lesssim \nu \lesssim +4)\) at high temperatures \((\gtrsim 40\mathrm{K})\) (bottom panel of Fig. 3b), the excess thermovoltage centered around \(\nu = \pm 2\) , becomes evident at lower \(T\) . We also find that the excess thermovoltage is intrinsically particle- hole asymmetric, however, on the electron doped side, the excess thermovoltage is closer to the commensurate filling \((\nu = +2)\) as seen for two devices (Fig. 3b and 3c). We also detect ev
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[103, 68, 456, 555]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[85, 567, 485, 733]]<|/det|>
+FIG. 4: Breakdown of semiclassical Mott relation and scattering rate : (a) Surface plot of \((S - S_{\mathrm{Mott}}) / S_{\mathrm{max}}\) as a function of \(T\) and \(\nu\) for \(\theta \approx 1.6^{\circ}\) . (b) \((S - S_{\mathrm{Mott}})\) at \(10\mathrm{K}\) for \(\theta \approx 1.6^{\circ}\) and \(\theta \sim 4^{\circ}\) . (c) \(\mathrm{d}\rho /\mathrm{d}T\) extracted in the \(T\) -linear regime at different \(\nu\) for the three twist angles. (d) The estimated dimensionless pre-factor \(C\) of the scattering rate \(\Gamma = Ck_{\mathrm{B}}T / \hbar\) as a function of \(\nu\) . (e) Seebeck coefficient \(S\) computed in DMFT with \(U = 38\mathrm{meV}\) as a function of filling \(\nu\) for the four lowest bands at three temperatures \(T = 2\mathrm{K}\) , \(14\mathrm{K}\) and \(26\mathrm{K}\) , respectively.
+
+<|ref|>text<|/ref|><|det|>[[86, 762, 488, 899]]<|/det|>
+dence of small excess \(V_{2\omega}\) between \(\nu = - 3\) and \(- 4\) . This could also be due to electron- correlation effects, however, the exact origin is not clear as we do not observe any evidence of such anomalous thermopower near same filling factor in the other devices (see e.g. Fig. 3c for the device with \(\theta \approx 1.7^{\circ}\) ). Using the \(\Delta T\) extracted from the fitting of \(V_{2\omega}\) , we show the \(T\) - dependence of \(S = V_{2\omega} / \Delta T\) in Fig. 3d for different \(\nu\) (see SI, section V). Evidently, \(S\) exhibits a linear dependence on \(T\) at all doping including
+
+<|ref|>text<|/ref|><|det|>[[515, 65, 917, 397]]<|/det|>
+the higher- energy dispersive band, except in the vicinity of \(\nu = \pm 2\) , thus validating the estimation of \(\Delta T\) from Mott fitting [25]. The \(S \propto T\) behavior is expected in a degenerate weakly or non- interacting metal within the semiclassical framework, and has been verified for monolayer graphene [17] as well as tBLG at slightly larger \(\theta\) \((2^{\circ} \lesssim \theta \lesssim 5^{\circ})\) [28]. Close to \(\nu = \pm 2\) , however, we find an unexpected increase in \(S\) when temperature is decreased below \(\sim 40\mathrm{K}\) , in contrast to the expectation of \(S \approx 0\) (inset of Fig. 3d) from SMR and approaches \(S \approx \pm 2\mu \mathrm{V / K}\) for \(\nu = \pm 2\) respectively, at low \(T\) (Fig. 3d and Fig. 4b). This is remarkable because, (1) at low \(T\) , the observed sign of \(V_{2\omega}\) can not be assigned to the electron(hole)- like bands any more, and (2) the excess \(S\) persists to a temperature scale \((\sim 40\mathrm{K})\) that is much higher than the superconducting transition \((T_{\mathrm{c}} \sim 1.7\mathrm{K})\) in tBLG at \(\theta = \theta_{\mathrm{m}}\) or the temperature scale for correlated insulator \((\lesssim 4\mathrm{K})\) [4, 6, 11], suggesting a very distinct nature of the ground state. The absolute magnitude of the excess thermovoltage at \(\nu = \pm 2\) decreases with increasing \(\theta\) , as illustrated for a device with \(\theta = 1.7^{\circ}\) in Fig. 3c, and becomes undetectable for \(\theta \gtrsim 2^{\circ}\) .
+
+<|ref|>text<|/ref|><|det|>[[515, 398, 917, 789]]<|/det|>
+Although the Mott formula has been verified in a range of graphene- based devices [17, 25], it can be violated in the hydrodynamic regime [29] and due to phonon drag in cross- plane thermoelectric transport in tBLG at \(\theta > 6^{\circ}\) [20]. While the hydrodynamic regime is expected to appear at higher temperatures \((>100\mathrm{K})\) , we eliminate the possibility of phonon drag from the observation of \(S \propto T\) (away from \(\nu = \pm 2\) , Fig. 3d). Furthermore, as shown in Fig. 4a, the occurrence of excess \(S\) , normalized as \((S - S_{\mathrm{Mott}}) / S_{\mathrm{max}}\) , where \(S_{\mathrm{max}}\) is the maximum value of \(S\) at a given \(T\) , is concentrated in the low \(T\) dome- like regions around \(\nu = \pm 2\) in the \(T - (\nu , n)\) phase diagram. Since neither adiabatic (static) nor dynamical phonon effects can violate Mott formula [30, 31], the enhancement of thermopower beyond the SMR limit suggests the possibility of a many body ground state similar to NFL phases in correlated oxides [32] and heavy Fermions [33]. A near- ubiquitous feature of the NFL regime in itinerant Fermionic systems, ranging from cuprates [34], ruthenates [35], pnictides [36] to heavy Fermions [33], is the 'strange metal' phase, characterized by the absence of well defined quasiparticles and linear \(T\) dependence of \(\rho\) . Theoretical work also suggests possibilities of excess entropy, analogous to Bekenstein- Hawking entropy in charged black holes, in this regime, that remains finite down to vanishingly small \(T\) [37].
+
+<|ref|>text<|/ref|><|det|>[[516, 790, 917, 910]]<|/det|>
+To check the mutuality between the excess thermopower and the strange metallic behaviour, we compare the \(\nu\) - dependence of excess \(S\) at \(T = 10\mathrm{K}\) (Fig. 4b), and the scattering rate obtained from the slope \(\mathrm{d}\rho /\mathrm{d}T\) in the \(T\) - dependence of \(\rho\) (Fig. 4c). For reference, we also present the results from another device at \(\theta \approx 4^{\circ}\) , where we find no violation of SMR over the experimental range of \(n\) . In the NFL state, the incoherent scattering rate is
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 65, 488, 455]]<|/det|>
+\(\tau^{- 1} = Ck_{\mathrm{B}}T / \hbar\) , where the dimensionless coefficient \(C\) is of the order of unity for Planckian dissipation. In Fig. 4c we plot the \(\nu\) - dependence of \(\mathrm{d}\rho /\mathrm{d}T\) and \(C\) (Fig. 4d), where \(C\) is computed from \(\mathrm{d}\rho /\mathrm{d}T\) assuming Drude- like resistivity in accordance to Ref. [8, 9] (See SI, section VI). Away from the CNP, both \(1.6^{\circ}\) and \(1.7^{\circ}\) devices show \(\mathrm{d}\rho /\mathrm{d}T\approx 10 \Omega /\mathrm{K}\) near \(\nu \approx \pm 2\) , which is nearly two orders of magnitude larger than \(\mathrm{d}\rho /\mathrm{d}T\approx 0.2 - 0.3 \Omega /\mathrm{K}\) for the tBLG device at \(\theta \sim 4^{\circ}\) , implying that the individual layers are essentially decoupled in the latter [8, 10]. Intriguingly, for tBLG at \(\theta = 1.6^{\circ}\) and \(1.7^{\circ}\) , we find \(C\) to approach the order of unity in the vicinity of \(\nu \rightarrow \pm 2\) , raising the possibility of a common physical origin for the violation of SMR. Notably, the excess thermopower was found largely unaffected in the in- plane magnetic field (Fig. S20, SI, section V), and thus unlikely to arise from an underlying spin/magnetic texture [5]. Theoretically a dynamical mean field theory (DMFT) [3, 38, 39] calculation shows qualitative agreement in the density dependence of excess thermopower at \(\nu = \pm 2\) but fails to capture its finite magnitude at low temperature (Fig. 4e). This is because the particular single site DMFT framework used in our calculation would invariably lead to the FL phase as \(T\rightarrow 0\) , even though some excess thermopower can be observed in the intermediate temperature range (see SI, sections VII for details).
+
+<|ref|>text<|/ref|><|det|>[[86, 457, 488, 683]]<|/det|>
+In summary, we have measured the electrical resistivity and thermopower in twisted bilayer graphene over a broad range of low- twist angles. At larger \(\theta\) ( \(\sim 1.6^{\circ} - 1.7^{\circ}\) ), our experimental results show concurrent \(T\) - linear resistivity at Planckian dissipation scales and emergent excess thermopower below \(T\lesssim 40 \mathrm{K}\) near \(\nu = \pm 2\) signifying the breakdown of the semiclassical Mott relation. The thermopower near \(\nu = \pm 2\) approaches a finite magnitude ( \(\approx 2 \mu \mathrm{V} / \mathrm{K}\) at \(1.6^{\circ}\) ) at low \(T\) providing a new facet to the strongly correlated 'strange metal' phase in tBLG. Our experimental results point to a truly non- Fermi liquid (NFL) metallic state in tBLG at low twist angle that carry strong similarities to those observed in cuprates or heavy- Fermion materials with low coherence temperatures.
+
+<|ref|>text<|/ref|><|det|>[[86, 685, 488, 840]]<|/det|>
+The authors thank Nano mission, DST for the financial support. M.J. and S.M. thank the computational facilities in SERC. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, Grant Number JPMXP0112101001, JSPS KAKENHI Grant Numbers JP20H00354 and the CREST(JPMJCR15F3), JST. U.C. acknowledges funding from IISc and SERB (ECR/2017/001566), and H.R.K from SERB(SB/DF/005/2017). S.B. acknowledges funding from IISc and SERB (ECR/2018/001742).
+
+<|ref|>text<|/ref|><|det|>[[101, 839, 485, 852]]<|/det|>
+B.G., P.S.M. and MG contributed equally to this work.
+
+<|ref|>sub_title<|/ref|><|det|>[[670, 65, 761, 79]]<|/det|>
+## METHODS
+
+<|ref|>sub_title<|/ref|><|det|>[[648, 96, 788, 110]]<|/det|>
+## Device fabrication
+
+<|ref|>text<|/ref|><|det|>[[516, 130, 917, 355]]<|/det|>
+All devices in this work were fabricated using a layer- by- layer mechanical transfer method [20]. Monolayer graphene and hexagonal boron nitride (hBN) were exfoliated on \(\mathrm{SiO_2 / Si}\) wafers and graphene flakes were identified using optical microscopy and Raman spectroscopy. For \(\theta \approx 1.6^{\circ}\) , the edges of the graphene flakes were aligned under an optical microscope and encapsulated within two hBN layers. Other tBLG devices were fabricated using tear and stack method [40]. Electron beam lithography was used to define \(\mathrm{Cr / Au}\) top gate for tuning the number density in the tBLG region. Finally, the electrical contacts were patterned by electron- beam lithography and reactive ion etching followed by metal deposition (5 nm \(\mathrm{Cr / 50 nm}\) Au) using thermal evaporation technique.
+
+<|ref|>text<|/ref|><|det|>[[516, 357, 917, 536]]<|/det|>
+Electrical transport measurements were performed in a four- terminal geometry with typical \(ac\) current excitations of 10- 100 nA using a standard low- frequency lock- in amplifier at \(226 \mathrm{Hz}\) , in a dilution refrigerator and a 1.5- K cryostat. For thermoelectric measurements, local Joule heating was employed to create a \(\Delta T\) across the tBLG channel. A range of sinusoidal currents (2- 5 \(\mu \mathrm{A}\) ) at excitation frequency \(\omega = 17 \mathrm{Hz}\) were used for Joule heating and the resulting \(2^{\mathrm{nd}}\) harmonic thermal voltage \((V_{2\omega})\) was recorded using a lock- in amplifier. Thermoelectric measurements were conducted in a 1.5- K cryostat/20 mK dilution refrigerator with magnetic field.
+
+<|ref|>sub_title<|/ref|><|det|>[[590, 564, 842, 578]]<|/det|>
+## Tight binding calculation of DOS
+
+<|ref|>text<|/ref|><|det|>[[516, 596, 917, 686]]<|/det|>
+The rigid bilayer structures were generated using the Twister code [41]. The structures were subsequently relaxed in LAMMPS [42][43] using REBO [44] as the intralayer potential and DRIP [45] as the interlayer potential. These relaxed structures were used for performing all the calculations.
+
+<|ref|>text<|/ref|><|det|>[[516, 687, 917, 761]]<|/det|>
+The electronic band structures were calculated by approximating the tight binding transfer integrals under the Slater Koster formalism [46]. A more detailed discussion of the calculations is available in the SI, section VII.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 60, 490, 911]]<|/det|>
+[2] Bistritzer, R. & MacDonald, A. H. Moiré bands in twisted double- layer graphene. Proc. Natl Acad. Sci. 108, 12233- 12237 (2011).[3] Yuan, N. F. Q., Isobe, H. & Fu, L. Magic of high- order van Hove singularity. Nat. Comm. 10 (2019).[4] Cao, Y. et al. Unconventional superconductivity in magic- angle graphene superlattices. Nature 556, 43 (2018).[5] Sharpe, A. L. et al. Emergent ferromagnetism near three- quarters filling in twisted bilayer graphene. Science 365, 605- 608 (2019).[6] Cao, Y. et al. Correlated insulator behaviour at half- filling in magic- angle graphene superlattices. Nature 556, 80 (2018).[7] Zondiner, U. et al. Cascade of phase transitions and dirac revivals in magic- angle graphene. Nature 582, 203- 208 (2020).[8] Cao, Y. et al. Strange metal in magic- angle graphene with near Planckian dissipation. Phys. Rev. Lett. 124, 076801 (2020).[9] Bruin, J., Sakai, H., Perry, R. & Mackenzie, A. Similarity of scattering rates in metals showing T- linear resistivity. Science 339, 804- 807 (2013).[10] Polshyn, H. et al. Large linear- in- temperature resistivity in twisted bilayer graphene. Nat. Phys. 15, 1011- 1016 (2019).[11] Kerelsky, A. et al. Maximized electron interactions at the magic angle in twisted bilayer graphene. Nature 572, 95- 100 (2019).[12] Jiang, Y. et al. Charge order and broken rotational symmetry in magic- angle twisted bilayer graphene. Nature 573, 91- 95 (2019).[13] Liu, Y.- W. et al. Magnetism near half- filling of a van hove singularity in twisted graphene bilayer. Phys. Rev. B 99, 201408 (2019).[14] Rowe, D. M. Materials, preparation, and characterization in thermoelectrics (CRC press, 2017).[15] Behnia, K. Fundamentals of thermoelectricity (OUP Oxford, 2015).[16] Watanabe, S. et al. Validity of the Mott formula and the origin of thermopower in \(\pi\) - conjugated semicrystalline polymers. Phys. Rev. B 100, 241201 (2019).[17] Zuev, Y. M., Chang, W. & Kim, P. Thermoelectric and magnetothermoelectric transport measurements of graphene. Phys. Rev. Lett. 102, 096807 (2009).[18] Kim, D., Syers, P., Butch, N. P., Paglione, J. & Fuhrer, M. S. Ambipolar surface state thermoelectric power of topological insulator \(\mathrm{Bi_2Se_3}\) . Nano Lett. 14, 1701- 1706 (2014).[19] Arsenijević, S. et al. Signatures of quantum criticality in the thermopower of \(\mathrm{Ba(Fe_{1 - x}Co_x)_2As_2}\) . Phys. Rev. B 87, 224508 (2013).[20] Mahapatra, P. S., Sarkar, K., Krishnamurthy, H. R., Mukerjee, S. & Ghosh, A. Seebeck coefficient of a single van der Waals junction in twisted bilayer graphene. Nano Lett. 17, 6822- 6827 (2017).[21] Saito, Y. et al. Isospin pomeranchuk effect and the entropy of collective excitations in twisted bilayer graphene. arXiv preprint arXiv:2008.10830 (2020).[22] Rozen, A. et al. Entropic evidence for a pomeranchuk effect in magic angle graphene. arXiv preprint arXiv:2009.01836 (2020).[23] Efetov, D. K. & Kim, P. Controlling electron- phonon interactions in graphene at ultrahigh carrier densities.
+
+<|ref|>text<|/ref|><|det|>[[513, 68, 920, 911]]<|/det|>
+Phys. Rev. Lett. 105, 256805 (2010).[24] Wu, F., Hwang, E. & Sarma, S. D. Phonon- induced giant linear- in- T resistivity in magic angle twisted bilayer graphene: Ordinary strangeness and exotic superconductivity. Phys. Rev. B 99, 165112 (2019).[25] Jayaraman, A. et al. Evidence of lifshitz transition in the thermoelectric power of ultrahigh- mobility bilayer graphene. Nano Lett. 21, 1221- 1227 (2021).[26] Buhmann, J. M. & Sigrist, M. Thermoelectric effect of correlated metals: Band- structure effects and the breakdown of Mott's formula. Phys. Rev. B 88, 115128 (2013).[27] Wu, S., Zhang, Z., Watanabe, K., Taniguchi, T. & Andrei, E. Y. Chern insulators, van hove singularities and topological flat bands in magic- angle twisted bilayer graphene. Nat. Mat. 20, 488- 494 (2021).[28] Mahapatra, P. S. et al. Misorientation- controlled cross- plane thermoelectricity in twisted bilayer graphene. Phys. Rev. Lett. 125, 226802 (2020).[29] Ghahari, F. et al. Enhanced thermoelectric power in graphene: Violation of the Mott relation by inelastic scattering. Phys. Rev. Lett. 116, 136802 (2016).[30] Jonson, M. & Mahan, G. Mott's formula for the thermopower and the Wiedemann- Franz law. Phys. Rev. B 21, 4223 (1980).[31] Jonson, M. & Mahan, G. Electron- phonon contribution to the thermopower of metals. Phys. Rev. B 42, 9350 (1990).[32] Wang, Y., Rogado, N. S., Cava, R. J. & Ong, N. P. Spin entropy as the likely source of enhanced thermopower in \(\mathrm{Na_xCo_2O_4}\) . Nature 423, 425- 428 (2003).[33] Izawa, K. et al. Thermoelectric response near a quantum critical point: The case of \(\mathrm{CeCoIn_5}\) . Phys. Rev. Lett. 99, 147005 (2007).[34] da Silva Neto, E. H. et al. Ubiquitous interplay between charge ordering and high- temperature superconductivity in cuprates. Science 343, 393- 396 (2014).[35] Rost, A., Perry, R., Mercure, J.- F., Mackenzie, A. & Grigera, S. Entropy landscape of phase formation associated with quantum criticality in \(\mathrm{Sr_3Ru_2O_7}\) . Science 325, 1360- 1363 (2009).[36] Lee, W.- C. & Phillips, P. W. Non- Fermi liquid due to orbital fluctuations in iron pnictide superconductors. Phys. Rev. B 86, 245113 (2012).[37] Sachdev, S. Bekenstein- Hawking entropy and strange metals. Phys. Rev. X 5, 041025 (2015).[38] Georges, A., Kotliar, G., Krauth, W. & Rozenberg, M. J. Dynamical mean- field theory of strongly correlated fermion systems and the limit of infinite dimensions. Rev. Mod. Phys. 68, 13- 125 (1996).[39] Haldar, A., Banerjee, S. & Shenoy, V. B. Higher- dimensional Sachdev- Ye- Kitaev non- Fermi liquids at Lifshitz transitions. Phys. Rev. B 97, 241106 (2018).[40] Kim, K. et al. Tunable moiré bands and strong correlations in small- twist- angle bilayer graphene. Proceedings of the National Academy of Sciences 114, 3364- 3369 (2017).[41] Naik, M. H. & Jain, M. Ultrafatbands and shear solitons in moire patterns of twisted bilayer transition metal dichalcogenides. Phys. Rev. Lett. 121, 266401 (2018).[42] Plimpton, S. Fast parallel algorithms for short- range molecular dynamics (1993).[43] https://lammps.sandia.gov.[44] Brenner, D. W. et al. A second- generation reactive empirical bond order (rebo) potential energy expression for
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[85, 66, 488, 120]]<|/det|>
+hydrocarbons. J Phys. Cond. Mat. 14, 783 (2002).[45] Wen, M., Carr, S., Fang, S., Kaxiras, E. & Tadmor, E. B. Dihedral- angle- corrected registry- dependent interlayer potential for multilayer graphene structures. Phys.
+
+<|ref|>text<|/ref|><|det|>[[515, 66, 917, 120]]<|/det|>
+Rev. B 98, 235404 (2018).[46] Slater, J. C. & Koster, G. F. Simplified LCAO method for the periodic potential problem. Phys. Rev. 94, 1498 (1954).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[61, 131, 250, 150]]<|/det|>
+Supplementary.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/images_list.json b/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..d5d0eb35f3ba6e47676b10c9b9ddf6ea9a2e0690
--- /dev/null
+++ b/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/images_list.json
@@ -0,0 +1,70 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Fig. 1: Time scales \\((\\tau)\\) for thermal acclimation of canopy photosynthesis. The time scale for (a) croplands (CRO), (b) deciduous broadleaf forests (DBF), (c) evergreen needle-leaf forests (ENF), (d) grasslands (GRA), (e) wetlands (WET), and (f) across all available sites (ALL). The x-axes represent the number of days over which \\(\\mathrm{T}_{\\mathrm{air}}\\) is averaged to derive \\(\\overline{T_{air}}\\) . The y-axes represent the 5-day moving average of positive Pearson correlation coefficients \\((r)\\) between \\(\\mathrm{A}_{\\mathrm{max},2000}\\) and \\(\\overline{T_{air}}\\) over fAPAR and \\(\\mathrm{T}_{\\mathrm{air}}\\) bins. The \\(\\tau\\) value is the length of time frame for which \\(r\\) peaks.",
+ "footnote": [],
+ "bbox": [
+ [
+ 113,
+ 87,
+ 884,
+ 430
+ ]
+ ],
+ "page_idx": 6
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Fig. 2: Relationships between \\(\\mathbf{A}_{\\mathrm{max},2000}\\) and \\(\\overline{T_{air}}\\) , a, \\(\\gamma_{T}\\) values over fAPAR and \\(\\mathrm{T}_{\\mathrm{air}}\\) bins across flux sites. Black dots indicate significant \\((P< 0.05)\\) correlations between \\(\\mathrm{A}_{\\mathrm{max},2000}\\) and \\(\\overline{T_{air}}\\) in the linear mixed-effect model \\((\\mathrm{A}_{\\mathrm{max},2000} \\sim \\overline{T_{air}} + (1 \\mid \\mathrm{Site}))\\) . b, PFT-specific \\(\\gamma_{\\mathrm{T}}\\) values. PFTs are arranged in descending order based on their mean \\(\\gamma_{\\mathrm{T}}\\) values. In the box plots, the central lines represent the median \\(\\gamma_{\\mathrm{T}}\\) values, the upper and lower box limits represent the 75th and 25th percentiles, and the upper and lower whiskers extend to 1.5 times the interquartile range,",
+ "footnote": [],
+ "bbox": [
+ [
+ 112,
+ 323,
+ 880,
+ 720
+ ]
+ ],
+ "page_idx": 8
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Fig. 3: Impact of leaf photosynthetic capacities on \\(\\gamma_{T}\\) estimation. a, Probability densities of \\(\\gamma_{T}\\) values derived from eddy covariance measurements (FLUXNET2015) and three variants of the BESS model (BESS \\(\\mathrm{PFT}\\) , BESS \\(\\mathrm{LAI}\\) , and BESS \\(\\mathrm{EEO}\\) ). The vertical lines represent the median \\(\\gamma_{T}\\) values. b, The statistics of the Kolmogorov-Smirnov (K-S) tests between FLUXNET2015 observations and three model variants.",
+ "footnote": [],
+ "bbox": [
+ [
+ 114,
+ 383,
+ 880,
+ 648
+ ]
+ ],
+ "page_idx": 11
+ },
+ {
+ "type": "image",
+ "img_path": "images/Extended_Data_Figure_3.jpg",
+ "caption": "Extended Data Fig. 3: The PFT-specific thermal acclimation rates \\((\\gamma_{\\mathrm{T}})\\) . a–g, PFT-specific \\(\\gamma_{\\mathrm{T}}\\) for croplands (CRO) (a), deciduous broadleaf forests (DBF) (b), evergreen broadleaf forests (EBF) (c), evergreen needle-leaf forests (ENF) (d), grasslands (GRA) (e), mixed forests (MF) (f), wetlands (WET) (g). Numbers (\\%) in parentheses represent the detectability of positive \\(\\gamma_{\\mathrm{T}}\\) values, which is defined as the percentage of the number of bins displaying a positive \\(\\gamma_{\\mathrm{T}}\\) over the total number of bins. Black dots indicate significant \\((P< 0.05)\\) correlations between \\(\\mathrm{A}_{\\mathrm{max,2000}}\\) and \\(\\overline{T_{air}}\\) .",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 26
+ },
+ {
+ "type": "image",
+ "img_path": "images/Extended_Data_Figure_4.jpg",
+ "caption": "Extended Data Fig. 4: Analyses of the partial correlation coefficients between \\(\\mathbf{A}_{\\max ,2000}\\) and \\(\\overline{T_{air}}\\) derived from long-term flux sites and their relationships with the site-level average \\(\\overline{T_{air}}\\) and variability of \\(\\overline{T_{air}}\\) . a, Geographic distribution of partial correlation coefficients between \\(\\mathbf{A}_{\\max ,2000}\\) and \\(\\overline{T_{air}}\\) controlling for \\(\\overline{P P D}\\) , fAPAR and \\(\\mathrm{T_{air}}\\) across sites with observations spanning over five years. b, Relationship between partial correlation coefficients and the site-level averages of \\(\\overline{T_{air}}\\) . c, Relationship between partial correlation coefficients and the site-level standard deviation of \\(\\overline{T_{air}}\\) . The \"Forest\" biome category includes evergreen needle-leaf forests, deciduous broadleaf forests, and mixed forests. Other PFTs are croplands (CRO), evergreen broadleaf forests (EBF), grasslands (GRA), and wetlands (WET).",
+ "footnote": [],
+ "bbox": [
+ [
+ 117,
+ 95,
+ 880,
+ 530
+ ]
+ ],
+ "page_idx": 27
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36.mmd b/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..ed9f94bb9014ef19379238486e3f0db2279f6b19
--- /dev/null
+++ b/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36.mmd
@@ -0,0 +1,381 @@
+
+# Evidence for widespread thermal acclimation of canopy photosynthesis
+
+Jiangong Liu j16314@columbia.edu
+
+Columbia University Youngryel Ryu Seoul National University Xiangzhong Luo Department of Geography, National University of Singapore https://orcid.org/0000- 0002- 9546- 0960
+
+Benjamin Dechant Leipzig University
+
+Benjamin Dechant Leipzig University Benjamin Stocker University of Bern https://orcid.org/0000- 0003- 2697- 9096
+
+Trevor Keenan UC Berkeley https://orcid.org/0000- 0002- 3347- 0258
+
+Pierre Gentine Columbia University https://orcid.org/0000- 0002- 0845- 8345
+
+Xing Li LSCE
+
+Bolun Li Seoul National University
+
+Sandy Harrison University of Reading https://orcid.org/0000- 0001- 5687- 1903
+
+Iain Prentice Imperial College London https://orcid.org/0000- 0002- 1296- 6764
+
+Article
+
+Keywords:
+
+Posted Date: April 16th, 2024
+
+DOI: https://doi.org/10.21203/rs.3.rs- 4013319/v1
+
+<--- Page Split --->
+
+License: © ① This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+Version of Record: A version of this preprint was published at Nature Plants on November 8th, 2024. See the published version at https://doi.org/10.1038/s41477-024-01846-1.
+
+<--- Page Split --->
+
+Evidence for widespread thermal acclimation of canopy photosynthesis
+
+Jiangong Liu \(^{1*}\) , Youngreyl Ryu \(^{1,2*}\) , Xiangzhong Luo \(^{3}\) , Benjamin Dechant \(^{1,4,5}\) , Benjamin D. Stocker \(^{6,7}\) , Trevor F. Keenan \(^{8,9}\) , Pierre Gentine \(^{10,11}\) , Xing Li \(^{1}\) , Bolun Li \(^{1,12}\) , Sandy P. Harrison \(^{13,14}\) , Iain Colin Prentice \(^{14,15}\)
+
+\(^{1}\) Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, Republic of Korea \(^{2}\) Department of Landscape Architecture and Rural Systems Engineering, Seoul National University, Seoul, Republic of Korea \(^{3}\) Department of Geography, National University of Singapore, 1 Arts Link, Singapore 117570 \(^{4}\) German Centre for Integrative Biodiversity Research (iDiv) Halle- Jena- Leipzig, Leipzig, Germany \(^{5}\) Leipzig University, Leipzig, Germany \(^{6}\) Institute of Geography, University of Bern, Bern, Switzerland \(^{7}\) Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland \(^{8}\) Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA \(^{9}\) Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA \(^{10}\) Earth and Environmental Engineering Department, Columbia University, New York, NY 10027, USA \(^{11}\) Climate School, Columbia University, New York, NY 10025, USA \(^{12}\) School of Geographical Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China \(^{13}\) School of Archaeology, Geography and Environmental Science (SAGES), University of Reading, Reading RG6 6AH, United Kingdom \(^{14}\) Department of Earth System Science, Ministry of Education Key Laboratory for Earth System Modeling, Institute for Global Change Studies, Tsinghua University, Beijing 100084, China \(^{15}\) Georgina Mace Centre for the Living Planet, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY, United Kingdom
+
+\*Corresponding authors: Jiangong Liu (jl6314@columbia.edu); Youngreyl Ryu (yryu@snu.ac.kr)
+
+<--- Page Split --->
+
+## Abstract
+
+Plants acclimate to temperature by adjusting their photosynthetic capacity over weeks to months. However, most evidence for photosynthetic acclimation derives from leaf- scale experiments. Here, we address the scarcity of evidence for canopy- scale photosynthetic acclimation by examining the correlation between maximum photosynthetic rates ( \(\mathrm{A}_{\mathrm{max,2000}}\) ) and growth temperature ( \(\overline{T_{air}}\) ) across a range of concurrent temperatures and canopy foliage quantity, using data from over 200 eddy covariance sites. We detect widespread thermal acclimation of canopy- scale photosynthesis, demonstrated by enhanced \(\mathrm{A}_{\mathrm{max,2000}}\) under higher \(\overline{T_{air}}\) , across flux sites with adequate water availability. A 14- day period is identified as the most relevant time scale for acclimation across all sites, with a range of 12–25 days for different plant functional types. The mean apparent thermal acclimation rate across all ecosystems is 0.41 (- 0.47–1.05 for 5th–95th percentile range) \(\mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1} \mathrm{°C}^{- 1}\) , with croplands showing the largest and grasslands the lowest acclimation rates. Incorporating optimality- based leaf photosynthetic capacity acclimation into a biochemical photosynthesis model is shown to improve the representation of thermal acclimation rates. Our results underscore the critical need for enhanced understanding and modelling of canopy- scale photosynthetic capacity to accurately predict plant responses to warmer growing seasons.
+
+<--- Page Split --->
+
+## Main
+
+The carbon uptake capacity of terrestrial ecosystem photosynthesis shows large spatio- temporal variation \(^{1}\) . Air temperature \(\mathrm{(T_{air})}\) is one of the key factors determining this variation \(^{2}\) . Given recent warming of \(0.1 - 0.3^{\circ}\mathrm{C}\) per decade \(^{3}\) , a better understanding of ecosystem responses to \(\mathrm{T_{air}}\) is needed. While the instantaneous temperature dependence of photosynthesis has been a major focus of research \(^{4,5}\) and is represented in vegetation and land surface models \(^{6,7}\) , the slower process known as thermal acclimation, through which plants maintain or enhance their photosynthetic efficiency in response to warmer growth temperatures \(^{8,9}\) , is less well understood \(^{10,11}\) . Several studies have indicated that leaves acclimate to thermal growing conditions within weeks to months, although the relevant time scales for different plant types remain uncertain \(^{12 - 14}\) . The potential mechanisms of this (non- genetic) acclimation include changes in key biochemical parameters (electron- transport potential and carboxylation capacity) \(^{15,16}\) , the sensitivity of stomatal conductance to atmospheric vapour pressure deficit (VPD) \(^{17}\) , and enzymatic heat tolerance \(^{8,18}\) .
+
+Widespread evidence of thermal acclimation at the leaf and canopy scales indicates that the optimal temperature \(\mathrm{(T_{opt})}\) of photosynthesis adjusts in accordance with the prevailing \(\mathrm{T_{air}}\) averaged over the time frame most relevant for acclimation \(\overline{T_{air}}\) \(^{15,16,18 - 20}\) . Yet the extent to which the maximum carbon assimilation rate under high light \(\mathrm{(A_{max})}\) acclimates to \(\overline{T_{air}}\) under natural conditions is less clear \(^{21,22}\) . It is crucial to understand whether both \(\mathrm{T_{opt}}\) and \(\mathrm{A_{max}}\) acclimate to \(\overline{T_{air}}\) since only their simultaneous enhancement can lead to consistent increases in photosynthesis \(^{23}\) . Some process- based photosynthetic models incorporate \(\mathrm{T_{opt}}\) acclimation, but not variations in \(\mathrm{A_{max}}\) \(^{24,25}\) . Demonstrating the presence of thermal acclimation at the canopy scale, quantifying its relevant time scales and rates across ecosystems, and assessing the accuracy of photosynthetic models in representing these acclimation processes are essential for understanding how thermal acclimation can mitigate the potentially detrimental effects of warming on the future terrestrial carbon sink \(^{11}\) .
+
+In this study, we define a positive adjustment in canopy- scale \(\mathrm{A_{max}}\) in response to elevated \(\overline{T_{air}}\) as evidence for thermal acclimation of canopy photosynthesis. Following ref. \(^{26}\) , \(\mathrm{A_{max}}\) is defined
+
+<--- Page Split --->
+
+as the photosynthetic assimilation rate measured under high light, ample water and ambient \(\mathrm{CO_2}\) . We derive \(\mathrm{A_{max}}\) from light response curves of half- hourly or hourly eddy- covariance carbon fluxes obtained from more than 200 FLUXNET2015 flux sites (see Methods). To facilitate consistent analysis across different light conditions, we standardize \(\mathrm{A_{max}}\) to photosynthetic photon flux density (PPFD) equivalent to \(2000\mu \mathrm{mol}\mathrm{m}^{- 2}\mathrm{s}^{- 1}\) (denoted as \(\mathrm{A_{max,2000}}\) ). Given the limited number of \(\mathrm{A_{max,2000}}\) samples for individual flux sites, we infer the thermal acclimation of \(\mathrm{A_{max,2000}}\) across spatial gradients by leveraging the large range of climates sampled by the FLUXNET2015 sites. We examine the correlation between \(\mathrm{A_{max,2000}}\) and \(\overline{T_{air}}\) when averaged over different time windows to identify the most relevant time scale \((\tau)\) for thermal acclimation, as indicated by peak correlation. Finally, we evaluate a biochemical model of canopy- scale \(\mathrm{C_3}\) photosynthesis \(^{4,25}\) , incorporating recent advances in parameterizing temperature dependence acclimation \(^{15}\) and modelled optimality- based leaf photosynthetic capacity \(^{27}\) , to assess its ability to reproduce the observed thermal acclimation rates.
+
+## Results and discussion
+
+## The time scale of thermal acclimation of canopy photosynthesis
+
+The time scale for canopy photosynthetic acclimation, as measured by the correlation coefficient \((r)\) between \(\mathrm{A_{max,2000}}\) and \(\overline{T_{air}}\) over different periods within concurrent \(\mathrm{T_{air}}\) and fractional absorbed photosynthetically active radiation fraction (fAPAR) bins (see Methods), varies across plant functional types (PFTs) (Fig. 1 and Supplementary Fig. 1), increasing from grasslands (GRA, 12 days) to croplands (CRO, 16 days), evergreen needle- leaf forests (ENF, 20 days), deciduous broadleaf forests (DBF, 21 days), and finally wetlands (WET, 25 days). The \(\tau\) value obtained across all sites is 14 days (Fig. 1f). For EBF, an optimal \(\tau\) cannot be determined using \(\mathrm{A_{max,2000}}\) , even over an extended period of 180 days (Supplementary Fig. 1a). The vegetation index, enhanced vegetation index (EVI) that is derived from reflectance data in the near- infrared, red, and blue spectral bands, can characterize canopy structure, which closely relates with the canopy photosynthetic capacity \(^{28}\) . We use a \(\tau\) value of 13 days for EBF as identified by remote- sensing EVI for subsequent analysis (Methods; Supplementary Fig. 1b).
+
+<--- Page Split --->
+
+
+Fig. 1: Time scales \((\tau)\) for thermal acclimation of canopy photosynthesis. The time scale for (a) croplands (CRO), (b) deciduous broadleaf forests (DBF), (c) evergreen needle-leaf forests (ENF), (d) grasslands (GRA), (e) wetlands (WET), and (f) across all available sites (ALL). The x-axes represent the number of days over which \(\mathrm{T}_{\mathrm{air}}\) is averaged to derive \(\overline{T_{air}}\) . The y-axes represent the 5-day moving average of positive Pearson correlation coefficients \((r)\) between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) over fAPAR and \(\mathrm{T}_{\mathrm{air}}\) bins. The \(\tau\) value is the length of time frame for which \(r\) peaks.
+
+Our estimate of an average of 14 days for thermal acclimation of canopy photosynthesis falls within the range of estimates of leaf- scale \(\tau\) , which vary from days to months depending on species and growth conditions8,13,29. A modelling study reports that a 15- day time scale for acclimation optimally predicts hourly eddy covariance flux measurements30. The time scale \(\tau\) for photosynthetic acclimation to a changing environment reflects a tradeoff between potential benefits (e.g. carbon assimilation) and costs (e.g. resource reallocation)31. A rapid adjustment in photosynthetic capacities is expected to enhance photosynthetic performance but is accompanied by higher costs in energy and resources10. The shorter \(\tau\) observed in GRA and CRO are in line with the expectation that fast- growing plants with a high generation rate of new leaves might
+
+<--- Page Split --->
+
+show shorter \(\tau\) than slow- growing species due to their greater physiological plasticity32. Conversely, we found longer \(\tau\) values in forests and WET, yet longer \(\tau\) is potentially compensated by a higher acclimation rate (Fig. 2b). The PFT- specific and cross- site \(\tau\) values for the canopy photosynthetic capacity provide a credible basis for explicitly incorporating the time scale of thermal acclimation into vegetation and land surface models.
+
+## Evidence for thermal acclimation of canopy photosynthesis
+
+By binning \(\mathrm{T}_{\mathrm{air}}\) and fAPAR to control for the confounding effects of concurrent temperature and seasonal changes in canopy foliage quantity on \(\mathrm{A}_{\mathrm{max},2000}\) , our analysis reveals a pervasive positive correlation between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) under conditions of adequate water availability as indicated by a high ratio of actual to potential evapotranspiration (ET/PET) (Fig. 2). This correlation is observed both spatially across multiple sites (Fig. 2a) and temporally within individual sites (Fig. 2c). We use linear mixed- effect models (LMMs) to obtain the regression coefficients of \(\overline{T_{air}}\) when estimating \(\mathrm{A}_{\mathrm{max},2000}\) ( \(\mathrm{A}_{\mathrm{max},2000} \sim \overline{T_{air}} + (1 \mid \mathrm{Site})\) ), which we define as the apparent thermal acclimation rate \((\gamma_{\mathrm{T}}, \mu \mathrm{mol} \mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1} \mathrm{~}^{\circ} \mathrm{C}^{- 1})\) (see Methods). The concept of apparent rates is used here as the \(\mathrm{A}_{\mathrm{max},2000}\) response rate to \(\overline{T_{air}}\) may be influenced by other covarying environmental conditions14, including the growth PPFD ( \(\overline{PPFD}\) ) and VPD (Supplementary Fig. 2)33. To account for the potential impact of adaptation15 – the modification of \(\mathrm{A}_{\mathrm{max},2000} - \overline{T_{air}}\) relationships across different species and populations within a species growing at different sites – sites are treated as random intercepts within the LLMs (see Extended Data Fig. 1 for an example). CRO is included in the PFT- based analyses but excluded from cross- site analyses.
+
+Detectability of thermal acclimation in canopy photosynthesis is quantified as the percentage of \(\mathrm{T}_{\mathrm{air}}\) - fAPAR bins showing a positive \(\gamma_{\mathrm{T}}\) . Our cross- site analysis for natural ecosystems finds positive \(\gamma_{\mathrm{T}}\) values in \(87\%\) of the \(\mathrm{T}_{\mathrm{air}}\) - fAPAR bins (939 in total) (Fig. 2a), with \(66\%\) of these positive relationships being statistically significant \((P < 0.05)\) , indicating that thermal acclimation is widespread across biomes. Averaged over all \(\mathrm{T}_{\mathrm{air}}\) - fAPAR bins, \(\gamma_{\mathrm{T}}\) is \(0.41 \pm 0.61\) (mean \(\pm 1\) - SD) \(\mu \mathrm{mol} \mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1} \mathrm{~}^{\circ} \mathrm{C}^{- 1}\) , with a 5th to 95th percentile range of - 0.47 to 1.05 \(\mu \mathrm{mol}\)
+
+<--- Page Split --->
+
+\(\mathrm{CO}_{2} \mathrm{m}^{- 2} \mathrm{s}^{- 1} \circ \mathrm{C}^{- 1}\) . The average of positive \(\gamma_{\mathrm{T}}\) values is \(0.57 \pm 0.33 \mathrm{m}^{- 2} \mathrm{s}^{- 1} \circ \mathrm{C}^{- 1}\) . The PFT- based analysis also shows strong evidence of thermal acclimation, with mean \(\gamma_{\mathrm{T}}\) values decreasing as follows: \(\mathrm{CRO}(0.77) > \mathrm{WET}(0.58) > \mathrm{DBF}(0.57) > \mathrm{ENF}(0.53) > \mathrm{MF}(0.41) > \mathrm{EBF}(0.38) > \mathrm{GRA}(0.34)\) (Fig. 2b and Extended Data Fig. 3). Furthermore, \(92\%\) of FLUXNET2015 sites with observations spanning five years or more show positive partial correlations between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) after controlling for \(\overline{P F D}\) , \(\mathrm{T}_{\mathrm{air}}\) and fAPAR (Fig. 2c), indicating widespread acclimation to seasonal temperature variations at individual flux sites. Sites showing a negative correlation are mainly located in the tropics (Extended Data Fig. 4a).
+
+
+
+Fig. 2: Relationships between \(\mathbf{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) , a, \(\gamma_{T}\) values over fAPAR and \(\mathrm{T}_{\mathrm{air}}\) bins across flux sites. Black dots indicate significant \((P< 0.05)\) correlations between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) in the linear mixed-effect model \((\mathrm{A}_{\mathrm{max},2000} \sim \overline{T_{air}} + (1 \mid \mathrm{Site}))\) . b, PFT-specific \(\gamma_{\mathrm{T}}\) values. PFTs are arranged in descending order based on their mean \(\gamma_{\mathrm{T}}\) values. In the box plots, the central lines represent the median \(\gamma_{\mathrm{T}}\) values, the upper and lower box limits represent the 75th and 25th percentiles, and the upper and lower whiskers extend to 1.5 times the interquartile range,
+
+<--- Page Split --->
+
+respectively. Letters represent statistically significant differences in the average \(\gamma_{\mathrm{T}}\) values (Tukey's HSD test, \(P< 0.05\) ). c, Partial correlation coefficients (Partial \(r\) ) between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) , when controlling for \(\overline{PPFD}\) , \(\mathrm{T}_{\mathrm{air}}\) and fAPAR, across individual longer- term (>5 years) flux sites. Colours in (b) and (c) indicate different PFTs, including croplands (CRO), deciduous broadleaf forests (DBF), evergreen broadleaf forests (EBF), evergreen needle- leaf forests (ENF), grasslands (GRA), mixed forests (MF), wetlands (WET), and all biomes combined (ALL).
+
+The potential confounding effect of factors other than \(\overline{T_{air}}\) on \(\mathrm{A}_{\mathrm{max},2000}\) appears to be minimal as the detectability of thermal acclimation remains high across diverse conditions. To ensure our findings are not skewed by light acclimation33, we consider the detectability of thermal acclimation when incorporating \(\overline{PPFD}\) into LLMs (89%, Extended Data Fig. 2a) and controlling for \(\overline{PPFD}\) through partial correlation (86%, Extended Data Fig. 2b). The impact of VPD is likely limited, as its negative effect on \(\mathrm{A}_{\mathrm{max}}\) has been accounted for during the derivation of \(\mathrm{A}_{\mathrm{max}}\) (see Equation 3 in Methods) and has been further mitigated by ET/PET filtering. After filtering, there is a positive relationship between \(\mathrm{A}_{\mathrm{max},2000}\) and VPD (Supplementary Fig. 2c). Any negative VPD impact on \(\mathrm{A}_{\mathrm{max},2000}\) is expected to reinforce, not diminish, the observed widespread thermal acclimation. Our findings remain robust with respect to the metric choice; detectability is 87% when \(\mathrm{A}_{\mathrm{max}}\) is unstandardized to a specific PPFD level and 86% when PFTs are treated as random effects within LLMs (Extended Data Fig. 2c and 2d).
+
+Thermal acclimation capability can be influenced by the level and variability of \(\overline{T_{air}}\) , as well as by species and PFTs21,34- 36. We observe negative effects of \(\overline{T_{air}}\) on \(\mathrm{A}_{\mathrm{max},2000}\) when fAPAR falls below 0.5 and \(\mathrm{T}_{\mathrm{air}}\) exceeds 25°C (Fig. 2a). Limited transpiration, due to a low amount of leaves, may not cool the canopy sufficiently under elevated \(\mathrm{T}_{\mathrm{air}}\) , making ribulose- 1,5- bisphosphate (RuBP) regeneration a limiting process for canopy photosynthesis at high canopy temperature22. The reduction in \(\mathrm{A}_{\mathrm{max},2000}\) with \(\overline{T_{air}}\) may be attributed to decreased maximum quantum yield of photosystem II in response to elevated temperature5,27,37. Additionally, under these conditions, the range of \(\overline{T_{air}}\) (3.1°C) is significantly narrower than among the rest (8.0°C) (two- tailed t- test, \(P< 0.01\) ) (Supplementary Fig. 3b). Our site- level analyses also show that the correlation between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) is positively associated with \(\overline{T_{air}}\) variability and negatively with \(\overline{T_{air}}\) (Extended Data Fig. 4b and 4c), which aligns with previous studies indicating that plants grown
+
+<--- Page Split --->
+
+under low \(\overline{T_{air}}\) variability and/or high \(\overline{T_{air}}\) show reduced acclimation potential \(^{21,34,38}\) . Conversely, the measurement temperature has a limited impact on \(\gamma_{\mathrm{T}}\) for leaf light- saturated net assimilation rates \(\mathrm{(A_{net})}\) \(\mathrm{(T_{air}}\) for \(\mathrm{A_{max,2000}}\) in this study) \(^{35}\) . Moreover, EBF is the dominant PFT for the bin pairs with high \(\mathrm{T_{air}}\) (Supplementary Fig. 4b). There is some evidence that tropical evergreen forests have a limited capability for physiological acclimation because these forests are adapted to relatively stable thermal conditions and/or thrive under high \(\overline{T_{air}}\) that is beyond the range limit for acclimation \(^{39 - 41}\) . The underrepresentation of EBF in the FLUXNET2015 database \(^{42}\) may also lead to uncertainties in the estimation of \(\gamma_{\mathrm{T}}\) for this biome.
+
+The observed widespread thermal acclimation of \(\mathrm{A_{max,2000}}\) (Fig. 2) contrasts with the varying sign of the response of leaf \(\mathrm{A_{net}}\) to \(\overline{T_{air}}\) , which can be positive, negative or neutral \(^{21,31,34,35,43}\) . This discrepancy may stem from the fact that, unlike \(\mathrm{A_{max}}\) , \(\mathrm{A_{net}}\) is not necessarily measured under ample water conditions \(^{21,26}\) , and water stress is known to affect the capacities of plant thermal acclimation \(^{17}\) . In water- limited situations, plants typically reduce water loss through transpiration by decreasing stomatal conductance \(^{44}\) , resulting in decreased \(\mathrm{A_{net}}\) .
+
+## Representing acclimation in photosynthesis models
+
+We further explore the representation of \(\mathrm{A_{max,2000}}\) thermal acclimation in a biochemical model for \(\mathrm{C}_{3}\) canopy photosynthesis incorporated in the Breathing Earth System Simulator (BESS) \(^{45}\) , based on the Farquhar- von Caemmerer- Berry (FvCB) model (see Methods) \(^{4}\) . We test three alternative approaches, each under different resource- use allocation assumptions, to estimate maximum carboxylation rates \(\mathrm{(V_{cmax}}\) , \(\mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) ) standardized to \(25^{\circ}\mathrm{C}\) \((V_{cmax}^{25C})\) . These approaches are: (1) assuming a temporally constant and PFT- specific \(V_{cmax}^{25C}\) \((V_{cmax}^{25C} PFT)\) , where plants do not actively regulate \(V_{cmax}^{25C}\) through the growing seasons; (2) scaling leaf \(V_{cmax}^{25C}\) by canopy phenology (LAI- scaled \(V_{cmax}^{25C}\) , \(V_{cmax}^{25C} LAI\) ); and (3) modelling acclimation to prevailing environments based on the eco- evolutionary optimality (EEO) theory \(^{27,46}\) \((V_{cmax}^{25C} EEO)\) (see Methods and Supplementary Text 1 and 2). The FvCB model as applied here incorporates recent advances in parameterizing the temperature dependence of leaf photosynthetic capacities to represent \(\mathrm{T_{opt}}\) acclimation \(^{15}\) (Supplementary Text 1). We run the model using the site- level forcings from the FLUXNET2015 database and derive \(\mathrm{A_{max,2000}}\) by setting PPFD equivalent to \(2000 \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) .
+
+<--- Page Split --->
+
+For further analysis, we select estimated \(\mathrm{A}_{\mathrm{max},2000}\) values from 71 \(\mathrm{C}_3\) sites excluding CRO and water- limited sites, where all three model variants show acceptable accuracy in estimating \(\mathrm{A}_{\mathrm{max},2000}\) (coefficient of determination \([R^2 ] > 0.5\) ) (Supplementary Table 1).
+
+The BESS model variant incorporating optimality- based \(V_{\mathrm{cmax\_EEO}}^{25C}\) more closely approximates the observed \(\gamma_{\mathrm{T}}\) compared to the other two variants, \(V_{\mathrm{cmax\_PFT}}^{25C}\) (BESS \(\mathrm{PFT}\) ) and \(V_{\mathrm{cmax\_LAI}}^{25C}\) (BESS \(\mathrm{LAI}\) ) (Fig. 3). The Kolmogorov- Smirnov (K- S) test indicates that the cumulative distribution functions of \(\gamma_{\mathrm{T}}\) between \(\mathrm{BESS}_{\mathrm{EEO}}\) and FLUXNET2015 observations are more closely aligned, despite significant differences between all three BESS model distributions and observations ( \(\mathrm{P}< 0.05\) ) (Fig. 3b). \(\mathrm{BESS}_{\mathrm{PFT}}\) and \(\mathrm{BESS}_{\mathrm{LAI}}\) underestimate the median observed \(\gamma_{\mathrm{T}}\) by \(63\%\) and \(48\%\) , respectively, while \(\mathrm{BESS}_{\mathrm{EEO}}\) overestimates it by \(29\%\) (Fig. 3a).
+
+
+
+Fig. 3: Impact of leaf photosynthetic capacities on \(\gamma_{T}\) estimation. a, Probability densities of \(\gamma_{T}\) values derived from eddy covariance measurements (FLUXNET2015) and three variants of the BESS model (BESS \(\mathrm{PFT}\) , BESS \(\mathrm{LAI}\) , and BESS \(\mathrm{EEO}\) ). The vertical lines represent the median \(\gamma_{T}\) values. b, The statistics of the Kolmogorov-Smirnov (K-S) tests between FLUXNET2015 observations and three model variants.
+
+The considerable underestimation of \(\gamma_{T}\) by \(\mathrm{BESS}_{\mathrm{PFT}}\) and \(\mathrm{BESS}_{\mathrm{LAI}}\) highlight the limitation in process- based photosynthetic models that incorporate only \(\mathrm{T}_{\mathrm{opt}}\) acclimation. To capture \(\gamma_{T}\) accurately, process- based models must also integrate seasonal variations in photosynthetic
+
+<--- Page Split --->
+
+capacities resulting from thermal acclimation. The overestimation by BESS \(\mathrm{EEO}\) can be attributed to its higher predicted detectability (99%) of thermal acclimation than observed (93%) (Fig. 3a). When calculating \(V_{c m a x\_ E E O}^{25C}\) , we assume that plants are not water-stressed following ET/PET filtering; a water-stress factor is not applied to scale \(V_{c m a x}^{25C}\) as described in ref \(^{37}\) (see Supplementary Text 2). Consequently, in this study, the EEO theory represents an idealized condition where carbon assimilation is optimized under the assumption of sufficient water availability. While plant light use efficiency can be reduced by physiological stress due to water scarcity \(^{47}\) , the absence of such water stress constraints can lead to an overestimation of \(V_{c m a x}^{25C}\) . Although ET/PET is an effective indicator of soil moisture, it may not fully correspond to plant physiological stress. Bridging the gap between existing water availability metrics and actual plant stress responses remains a challenge \(^{48}\) .
+
+## Conclusion
+
+Photosynthesis can benefit from future warming through thermal acclimation, resulting in increased carbon uptake under conditions where water is not limiting. While leaf- scale acclimation is widely recognized, our study shows that the positive acclimation of canopy- scale photosynthetic capacity to growth temperature is a widespread phenomenon across various terrestrial biomes. We have shown that, on average, the canopy photosynthetic capacity acclimates to the growth thermal conditions of the preceding 14 days. Incorporating seasonal acclimation of photosynthetic capacities (the maximum carboxylation rate and the maximum electron transport rate) is critical for achieving accurate simulations of photosynthesis in response to variations in temperature at time scales of weeks to months. Despite warmer growing seasons, water availability is increasingly constrained in many regions, potentially forcing plants to reduce photosynthetic capacity as a water conservation strategy. Improving the understanding of canopy- scale photosynthetic thermal acclimation in response to future conditions characterized by warming and variable water availability is therefore important.
+
+## Methods
+
+<--- Page Split --->
+
+Global database of ecosystem- scale carbon fluxes. We derive \(\mathrm{A}_{\mathrm{max}}\) from more than 200 eddy covariance sites from the global database FLUXNET2015, which covers a wide range of geospatial locations and plant functional types (Supplementary Table 1) \(^{42,49}\) . FLUXNET2015 is an openly accessible database containing data on the net exchange of carbon (NEE), water, and energy between the atmosphere and the biosphere, and meteorological observations. Uniform processing approaches are implemented for the flux calculation and quality control across the sites \(^{42}\) . We use half- hourly or hourly NEE (NEE_VUT_USTAR50), its corresponding estimation of the uncertainty caused by friction velocity filtering (NEE_VUT_USTAR50_ RANDUNC), and gap- filled meteorological observations, including incoming radiation (SW_IN_F), air temperature (TA_F), and VPD (VPD_F) to derive \(\mathrm{A}_{\mathrm{max}}\) \(^{42,50}\) (described below). Sites are excluded if data are unavailable during the MODIS period from 2002 onwards (e.g. US- LWW and US- Me4) or if the uncertainty estimation is missing (e.g. CA- Man).
+
+Derivation of ecosystem- scale \(\mathbf{A}_{\mathrm{max}}\) . We derive \(\mathrm{A}_{\mathrm{max}}\) from light response curves across the FLUXNET2015 sites according to the daytime flux partitioning methods detailed in ref. \(^{33}\) and ref. \(^{51}\) . We fit NEE using the following hyperbolic equation:
+
+\[-NEE = \frac{\alpha\beta R_g}{\alpha R_g + \beta} +\gamma \quad (1)\]
+
+where \(\beta\) (μmol \(\mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1}\) ) is the target variable of interest. \(\alpha\) , \(\mathrm{R}_{\mathrm{g}}\) , and \(\gamma\) represent the ecosystem- scale quantum yield (μmol \(\mathrm{C} \mathrm{J}^{- 1}\) ), global radiation ( \(\mathrm{W} \mathrm{~m}^{- 2}\) ), and ecosystem respiration (μmol \(\mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1}\) ), respectively.
+
+To account for the potential influence of high VPD (hPa), \(\beta\) is scaled using an exponential function only when VPD exceeds \(10 \mathrm{hPa}\) . Thus, we obtain \(\mathrm{A}_{\mathrm{max}}\) following:
+
+\[A_{m a x} = \left\{ \begin{array}{c}{\beta ,V P D\leq 10 h P a}\\ {\beta \exp \left(-k(V P D - 10)\right),V P D > 10 h P a} \end{array} \right. \quad (2)\]
+
+where \(\beta\) and \(\mathrm{k}\) are fit parameters to the flux data. The ecosystem respiration term in Equation (1), \(\gamma\) , is estimated using an Arrhenius- type function describing the temperature dependence of \(\gamma^{52}\) , which is applied to nighttime data by assuming that nighttime NEE is equivalent to ecosystem respiration:
+
+<--- Page Split --->
+
+\[NEE = R_{ref}exp\left\{E_0\left(\frac{1}{T_{ref} - T_0} -\frac{1}{T_{air} - T_0}\right)\right\} \quad (3)\]
+
+where \(\mathrm{R_{ref}}\) and \(\mathrm{E_0}\) are the basal respiration rate ( \(\mu \mathrm{mol} \mathrm{CO}_2 \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) ) at a reference temperature ( \(\mathrm{T_{ref}} = 15^{\circ} \mathrm{C}\) ) and temperature sensitivity ( \(^{\circ} \mathrm{C}\) ), respectively. \(\mathrm{T_0}\) is a constant equal to \(- 46.02^{\circ} \mathrm{C}^{53}\) .
+
+In practice, \(\mathrm{E_0}\) is first estimated according to Equation (3). With a fixed \(\mathrm{E_0}\) , the remaining parameters of Equations (2) and (3) \((\alpha , \beta , \mathrm{k},\) and \(\mathrm{R_{ref}}\) ) are derived using a time window of 2–14 days. The specific time window depends on data availability, and the \(\mathrm{A_{max}}\) value is assumed invariant within the same fitting window. Here, we derive \(\mathrm{A_{max}}\) using the REddyProc R package (https://github.com/bgctw/REddyProc) \(^{54}\) . Low- quality daily \(\mathrm{A_{max}}\) data, indicated by an unreasonable range, are discarded \(^{33}\) . We standardize \(\mathrm{A_{max}}\) to \(\mathrm{PPFD} = 2000 \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) ( \(\mathrm{A_{max,2000}}\) ) to avoid any \(\mathrm{A_{max}}\) values obtained from potentially unsaturated light conditions and to ensure consistent levels of absorbed PAR (see Methods below) \(^{33}\) . We convert \(\mathrm{PPFD}\) to \(\mathrm{R_g}\) using a constant of \(2.1 \mu \mathrm{mol} \mathrm{J}^{- 1}\) (ref. \(^{55}\) ).
+
+Time scale for thermal acclimation of \(\mathrm{A_{max,2000}}\) . We hypothesize that the most relevant time scale for thermal acclimation ( \(\tau\) ) ranges between 2 and 60 days according to the coordination hypothesis and observations \(^{13,56,57}\) . We conduct linear regressions between \(\mathrm{A_{max,2000}}\) derived from the FLUXNET2015 sites and the daytime \(\overline{T_{air}}\) averaged over the 2 to 60 days prior to the time of \(\mathrm{A_{max,2000}}\) measurements with a time interval of one day. Based on a previous study \(^{33}\) , savanna and shrubland sites are excluded from the analysis because they are frequently subject to water stress. Croplands are excluded from the cross- site analysis. Furthermore, we exclude the \(\mathrm{A_{max,2000}} - \overline{T_{air}}\) pairs collected during water- limited conditions, as indicated by the ratio of prevailing actual evapotranspiration to Priestley- Taylor potential evapotranspiration (ET/PET) \(< 0.75^{58}\) and VPD \(> 20 \mathrm{hPa}\) . Additionally, we only focus on growing seasons, characterized by fAPAR \(> 0.3\) and \(\mathrm{T_{air}}\) and \(\overline{T_{air}} > 0^{\circ} \mathrm{C}\) . Daily fAPAR and LAI for each site were derived by interpolating the 8- day MODIS MOD15A2H products following ref. \(^{33}\) . Low- quality data affected by cloud contamination are removed \(^{25}\) . A total of 149,774 \(\mathrm{A_{max,2000}}\) records are used for further analyses.
+
+To remove the potential effects of concurrent \(\mathrm{T_{air}}\) and fAPAR on \(\mathrm{A_{max,2000}}\) , we group \(\mathrm{A_{max,2000}} - \overline{T_{air}}\) pairs into different bins of \(\mathrm{T_{air}}\) with \(1^{\circ} \mathrm{C}\) intervals and fAPAR with 0.02 intervals. This
+
+<--- Page Split --->
+
+approach allows the analysis of changes in \(\mathrm{A}_{\mathrm{max},2000}\) along \(\overline{T_{air}}\) gradients to be made while controlling for the instantaneous temperature dependence of photosynthesis. Pearson \(r\) between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) that is averaged over different time frames (i.e., 2- 60 d with 1- d interval) is calculated for \(\mathrm{T_{air}}\) and fAPAR bins. A positive \(r\) indicates the thermal acclimation potential of \(\mathrm{A}_{\mathrm{max},2000}\) . Only bins with sampling numbers larger than 10 and 20 for PFT- based and cross- site analyses, respectively, are retained. We examine the relationship between the average of the positive \(r\) values obtained from \(\mathrm{T_{air}}\) and fAPAR bins and the time frames used to calculate \(\overline{T_{air}}\) for each PFT and cross sites (Fig. 1). \(\tau\) is defined as the corresponding time frame when the 5- d moving average of the positive \(r\) reaches its peak. Enhanced vegetation index (EVI), derived from MODIS reflectance data (MCD43A4) in the near- infrared, red, and blue spectral bands \(^{28}\) , is used to estimate \(\tau\) for EBF for subsequent analysis, as an optimal \(\tau\) cannot be identified for this PFT using \(\mathrm{A}_{\mathrm{max},2000}\) (Supplementary Fig. 1).
+
+Evidence for thermal acclimation of \(\mathrm{A}_{\mathrm{max},2000}\) . We use PFT- specific \(\tau\) values for aggregating prevailing \(\mathrm{T_{air}}\) to obtain \(\overline{T_{air}}\) (Fig 1). We run linear mixed- effect models (LMMs), which include a random effect of different sites for removing the site- level adaptation effect, to explore the relationship between \(\mathrm{A}_{\mathrm{max},2000}\) and PFT- specific \(\overline{T_{air}}\) (i.e., \(\mathrm{A}_{\mathrm{max},2000} \sim \overline{T_{air}} + (1 \mid \mathrm{Site}))\) (Extended Data Fig. 1). The same data selection procedure and \(\mathrm{T_{air}}\) and fAPAR binning scheme are used for the cross- site analysis (Fig. 2a; see Methods above). The coefficient of \(\overline{T_{air}}\) estimated from LMMs is defined as thermal acclimation rate \((\gamma_{\mathrm{T}})\) . The sampling number, conditional and marginal correlation coefficients for the cross- site analysis are shown in Supplementary Fig. 5. The LMM is conducted with the R package lme4 \(^{59}\) . For each site, the sampling number of \(\mathrm{A}_{\mathrm{max},2000} - \overline{T_{air}}\) pairs is insufficient to support the correlation analysis under the binning scheme \(^{33}\) . Instead, a partial correlation analysis is run between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) controlling for \(\overline{PPFD}\) , \(\mathrm{T_{air}}\) , and fAPAR on flux sites with observation lengths longer than five years (Fig. 2c).
+
+The prevailing conditions of \(\mathrm{T_{air}}\) and PPFD often show a high correlation (Supplementary Fig. 2a). Therefore, we also include \(\overline{PPFD}\) as an additional predictor in the LMM (Extended Data Fig. 2a), and we analyze partial correlations between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) controlling for \(\overline{PPFD}\) (Extended Data Fig. 2b) in order to eliminate the confounding effect of light acclimation \(^{33}\) . Additionally, we repeat LMMs with a different target variable ( \(\mathrm{A}_{\mathrm{max}}\) ) and random effect (PFT) to
+
+<--- Page Split --->
+
+examine the robustness of the detectability of thermal acclimation (Extended Data Fig. 2c and 2d).
+
+Modelling canopy photosynthesis of \(\mathbf{C}_3\) plants. We apply the photosynthesis module of the BESS model \(^{60}\) to estimate canopy photosynthesis \((A)\) and subsequently \(\mathrm{A}_{\mathrm{max},2000}\) , for each flux site. This allows a direct comparison to be made of the impacts of different empirical formulations of leaf photosynthetic capacities on thermal acclimation. The photosynthesis module is based on the Farquhar- von Caemmerer- Berry (FvCB) model \(^{4}\) , where \(A\) is determined as the lower \(\mathrm{CO}_2\) assimilation rate between the maximum rate of ribulose- 1,5- bisphosphate carboxylase/oxygenase (Rubisco) activity when light is saturated \((A_c)\) and the electron transport rate for RuBP regeneration when light is limited \((A_j)\) . For this study, the two- big- leaf scheme implemented in the BESS model is simplified to a one- big- leaf scheme. We have updated the parameters of temperature dependence of the maximum carboxylation rate \((\mathrm{V}_{\mathrm{cmax}}, \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1})\) , the maximum electron transport rate \((\mathrm{J}_{\mathrm{max}}, \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1})\) , as well as the ratio of their values at 25 \(^\circ \mathrm{C}\) following ref \(^{15}\) . A detailed description of the canopy photosynthesis model can be found in Supplementary Text 1 (also see refs. \(^{25,45,60}\) ).
+
+Leaf photosynthetic capacities. \(\mathrm{V}_{\mathrm{cmax}}\) is a key parameter in the FvCB model, particularly under light saturated conditions \(^{4}\) . Previous studies have shown that leaf biochemical components can acclimate to \(\overline{T_{air}}^{9,15,16}\) . In this study, we compare three empirically derived variants of \(\mathrm{V}_{\mathrm{cmax}}\) at \(25^\circ \mathrm{C}\) \((V_{cmax}^{25C})\) within the FvCB model to evaluate their effectiveness in simulating the observed \(\gamma \mathrm{T}\) :
+
+1. \(V_{cmax}^{25C} \cdot PFT\) : This variant assumes a constant \(V_{cmax}^{25C}\) value over the growing season, an assumption that is still widely used in vegetation models \(^{11}\) . The prescribed top leaf \(V_{cmax}^{25C}\) values are adopted from a look-up table based on PFTs and climatic zones compiled from the TRY trait database \(^{25,61}\) .
+
+2. \(V_{cmax}^{25C} \cdot LAI\) : Leaf \(V_{cmax}^{25C}\) varies seasonally, with its seasonality following LAI. This scheme, implemented in the previous version of the BESS model \(^{25}\) , follows Equation (4).
+
+\[V_{cmax}^{25C} \cdot LAI = a \times V_{cmax}^{25C} \cdot PFT + (1 - a) \times V_{cmax}^{25C} \cdot PFT \times \frac{LAI - LAI_{min}}{LAI_{max} - LAI_{min}} \quad (4)\]
+
+<--- Page Split --->
+
+where \(\mathrm{LAI}_{\mathrm{min}}\) and \(\mathrm{LAI}_{\mathrm{max}}\) are the 5th and 95th percentile values of LAI over a growing season, respectively, and \(a\) is an empirical parameter set to 0.3 (ref. \(^{60}\) ).
+
+3. \(V_{c m a x\_ E E O}^{25C}\) : The calculation is based on eco-evolutionary optimality (EEO) theory \(^{14,27,46}\) , specifically the coordination hypothesis \(^{12,62}\) and the least-cost hypothesis \(^{44,63}\) . The coordination hypothesis proposes that plants actively coordinate resource allocation so that \(A_{\mathrm{c}}\) tends to equal \(A_{\mathrm{j}}\) on weekly to monthly time scales. The least-cost hypothesis proposes that plants minimize the combined costs (per unit assimilation) of maintaining the biochemical capacity for photosynthesis and the water transport capacity required to support it, through stomatal regulation. Combining the two hypotheses results in an optimal intercellular \(\mathrm{CO}_{2}\) concentration under representative conditions \(^{64}\) . Here, we assume that \(V_{c m a x\_ E E O}^{25C}\) acclimates to prevailing conditions following the same time scale as \(\mathrm{A}_{\mathrm{max,2000}}\) (Fig. 1). The calculation is detailed in Supplementary Text 2 and Jiang et al. \(^{27}\) .
+
+## Acknowledgments
+
+This research is a contribution to the LEMONTREE (Land Ecosystem Models based On New Theory, observation and Experiments) project, funded through the generosity of Eric and Wendy Schmidt by recommendation of the Schmidt Futures programme. It is also a contribution to USMILE European Research Council grant. Y.R. was supported by Ministry of Environment of Korea (202300218237). B.D.S. was funded by the Swiss National Science Foundation grant PCEFP2_181115. B.D. was supported by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (DFG FZT 118, 202548816). T.F.K. acknowledges additional support from a NASA Carbon Cycle Science Award 80NSSC21K1705, and the RUBISCO SFA, which is sponsored by the Regional and Global Model Analysis (RGMA) Program in the Climate and Environmental Sciences Division (CESD) of the Office of Biological and Environmental Research (BER) in the U.S. Department of Energy (DOE) Office of Science. X.L. was supported by National University of Singapore Presidential Young Professorship (A- 0003625- 01- 00). I.C.P. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No: 787203 REALM). We especially thank the researchers and contributors of
+
+<--- Page Split --->
+
+the FLUXNET community and the MODIS products. We also acknowledge Xu Lian and Jianing Fang for their helpful reviews and comments on this manuscript before its submission.
+
+## Data availability
+
+The dataset of FLUXNET2015 flux sites under the CC- BY- 4.0 policy is publicly available for download at http://fluxnet.fluxdata.org. Remote- sensing canopy structure data from the MODIS MCD43A and MOD15A2H products are freely accessible at https://lpdaac.usgs.gov/products/mcd43a3v006/ and https://lpdaac.usgs.gov/products/mod15a2hv006/. BESS flux products are publicly available at https://www.environment.snu.ac.kr/data/.
+
+## Code availability
+
+The corresponding R code scripts used in this study have been deposited in: https://github.com/ljgcuhk/thermal_acclimation_canopy_photosynthesis. The code for the deviation of \(\mathrm{A}_{\mathrm{max}}\) from the FLUXNET2015 database can be accessed at: https://github.com/trevorkeenan/inhibitionPaperCode. The code for modelling optimality- based \(\mathrm{V}_{\mathrm{cmax}}\) can be accessed at: https://github.com/chongya/SVOM.
+
+## References
+
+1. Anav, A. et al. Spatiotemporal patterns of terrestrial gross primary production: A review. Reviews of Geophysics 53, 785-818 (2015).
+
+2. Beer, C. et al. Terrestrial Gross Carbon Dioxide Uptake: Global Distribution and Covariation with Climate. Science 329, 834-838 (2010).
+
+3. IPCC. Global Warming of \(1.5^{\circ}\mathrm{C}\) : IPCC Special Report on Impacts of Global Warming of \(1.5^{\circ}\mathrm{C}\) above Pre-Industrial Levels in Context of Strengthening Response to Climate Change, Sustainable Development, and Efforts to Eradicate Poverty. (Cambridge University Press, 2022). doi:10.1017/9781009157940.
+
+<--- Page Split --->
+
+4. Farquhar, G. D., von Caemmerer, S. & Berry, J. A. A biochemical model of photosynthetic \(\mathrm{CO_2}\) assimilation in leaves of \(\mathrm{C_3}\) species. Planta 149, 78–90 (1980).
+
+5. Bernacchi, C. J., Singsaas, E. L., Pimentel, C., Portis, A. R. & Long, S. P. Improved temperature response functions for models of Rubisco-limited photosynthesis. Plant, Cell and Environment 24, 253–259 (2001).
+
+6. Bernacchi, C. J. et al. Modelling \(\mathrm{C_3}\) photosynthesis from the chloroplast to the ecosystem. Plant, Cell and Environment 36, 1641–1657 (2013).
+
+7. Mercado, L. M. et al. Large sensitivity in land carbon storage due to geographical and temporal variation in the thermal response of photosynthetic capacity. New Phytol 218, 1462–1477 (2018).
+
+8. Berry, J. & Bjorkman, O. Photosynthetic response and adaptation to temperature in higher plants. Annual Review of Plant Physiology 31, 491–543 (1980).
+
+9. Medlyn, B. E. et al. Temperature response of parameters of a biochemically based model of photosynthesis. II. A review of experimental data. Plant, Cell and Environment 25, 1167–1179 (2002).
+
+10. Dietze, M. C. Gaps in knowledge and data driving uncertainty in models of photosynthesis. Photosynthesis Research 119, 3–14 (2014).
+
+11. Rogers, A. et al. A roadmap for improving the representation of photosynthesis in Earth system models. New Phytol 213, 22–42 (2017).
+
+12. Maire, V. et al. The coordination of leaf photosynthesis links C and N fluxes in \(\mathrm{C_3}\) plant species. PLoS ONE 7, 1–15 (2012).
+
+13. Smith, N. G. & Dukes, J. S. Drivers of leaf carbon exchange capacity across biomes at the continental scale. Ecology 99, 1610–1620 (2018).
+
+<--- Page Split --->
+
+14. Smith, N. G. et al. Global photosynthetic capacity is optimized to the environment. Ecology Letters 22, 506–517 (2019).
+
+15. Kumarathunge, D. P. et al. Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale. New Phytologist 222, 768–784 (2019).
+
+16. Kattge, J. & Knorr, W. Temperature acclimation in a biochemical model of photosynthesis: A reanalysis of data from 36 species. Plant, Cell and Environment 30, 1176–1190 (2007).
+
+17. Lin, Y. S., Medlyn, B. E. & Ellsworth, D. S. Temperature responses of leaf net photosynthesis: the role of component processes. Tree Physiology 32, 219–231 (2012).
+
+18. Yamori, W., Hikosaka, K. & Way, D. A. Temperature response of photosynthesis in C3, C4, and CAM plants: Temperature acclimation and temperature adaptation. Photosynthesis Research 119, 101–117 (2014).
+
+19. Niu, S. et al. Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms. New Phytologist 194, 775–783 (2012).
+
+20. Baldocchi, D. et al. FLUXNET: A new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor, and energy flux densities. Bulletin of the American Meteorological Society 82, 2415–2434 (2001).
+
+21. Vico, G., Way, D. A., Hurry, V. & Manzoni, S. Can leaf net photosynthesis acclimate to rising and more variable temperatures? Plant Cell and Environment 42, 1913–1928 (2019).
+
+22. Crous, K. Y., Uddling, J. & De Kauwe, M. G. Temperature responses of photosynthesis and respiration in evergreen trees from boreal to tropical latitudes. New Phytologist 234, 353–374 (2022).
+
+<--- Page Split --->
+
+23. Way, D. A. & Yamori, W. Thermal acclimation of photosynthesis: On the importance of adjusting our definitions and accounting for thermal acclimation of respiration. Photosynthesis Research 119, 89–100 (2014).
+
+24. Knauer, J. et al. Higher global gross primary productivity under future climate with more advanced representations of photosynthesis. Sci. Adv. 9, eadh9444 (2023).
+
+25. Jiang, C. & Ryu, Y. Multi-scale evaluation of global gross primary productivity and evapotranspiration products derived from Breathing Earth System Simulator (BESS). Remote Sensing of Environment 186, 528–547 (2016).
+
+26. Wright, I. J. et al. The worldwide leaf economics spectrum. Nature 428, 821–827 (2004).
+
+27. Jiang, C., Ryu, Y., Wang, H. & Keenan, T. F. An optimality-based model explains seasonal variation in C3 plant photosynthetic capacity. Global Change Biology 26, 6493–6510 (2020).
+
+28. Zeng, Y. et al. Optical vegetation indices for monitoring terrestrial ecosystems globally. Nat Rev Earth Environ 3, 477–493 (2022).
+
+29. Mäkelä, A. et al. Developing an empirical model of stand GPP with the LUE approach: analysis of eddy covariance data at five contrasting conifer sites in Europe. Global Change Biology 14, 92–108 (2008).
+
+30. Mengoli, G. et al. Ecosystem photosynthesis in land-surface models: A first-principles approach incorporating acclimation. J Adv Model Earth Syst 14, (2022).
+
+31. Smith, N. G., McNellis, R. & Dukes, J. S. No acclimation: instantaneous responses to temperature maintain homeostatic photosynthetic rates under experimental warming across a precipitation gradient in Ulmus americana. AoB PLANTS 12, 1–11 (2020).
+
+<--- Page Split --->
+
+32. Loveys, B. R. et al. Thermal acclimation of leaf and root respiration: an investigation comparing inherently fast- and slow-growing plant species. Global Change Biology 9, 895–910 (2003).
+
+33. Luo, X. & Keenan, T. F. Global evidence for the acclimation of ecosystem photosynthesis to light. Nature Ecology and Evolution 4, 1351–1357 (2020).
+
+34. Sendall, K. M. et al. Acclimation of photosynthetic temperature optima of temperate and boreal tree species in response to experimental forest warming. Global Change Biology 21, 1342–1357 (2015).
+
+35. Battaglia, M., Beadle, C. & Loughhead, S. Photosynthetic temperature responses of Eucalyptus globulus and Eucalyptus nitens. Tree Physiology 16, 81–89 (1996).
+
+36. Slot, M., Rifai, S. W. & Winter, K. Photosynthetic plasticity of a tropical tree species, Tabebuia rosea, in response to elevated temperature and [CO₂]. Plant Cell Environ 44, 2347–2364 (2021).
+
+37. Stocker, B. D. et al. P-model v1.0: An optimality-based light use efficiency model for simulating ecosystem gross primary production. Geoscientific Model Development 13, 1545–1581 (2020).
+
+38. Luo, Y., Gessler, A., D'Odorico, P., Hufkens, K. & Stocker, B. D. Quantifying effects of cold acclimation and delayed springtime photosynthesis resumption in northern ecosystems. New Phytologist nph.19208 (2023) doi:10.1111/nph.19208.
+
+39. Dusenge, M. E. et al. Limited thermal acclimation of photosynthesis in tropical montane tree species. Glob Change Biol 27, 4860–4878 (2021).
+
+40. Doughty, C. E. et al. Tropical forests are approaching critical temperature thresholds. Nature 621, 105–111 (2023).
+
+<--- Page Split --->
+
+41. Huang, M. et al. Air temperature optima of vegetation productivity across global biomes. Nature Ecology and Evolution 3, 772-779 (2019).
+
+42. Pastorello, G. et al. The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data. Scientific Data 7, 225 (2020).
+
+43. Cunningham, S. C. & Read, J. Do temperate rainforest trees have a greater ability to acclimate to changing temperatures than tropical rainforest trees? New Phytologist 157, 55-64 (2003).
+
+44. Prentice, I. C., Dong, N., Gleason, S. M., Maire, V. & Wright, I. J. Balancing the costs of carbon gain and water transport: Testing a new theoretical framework for plant functional ecology. Ecology Letters 17, 82-91 (2014).
+
+45. Li, B. et al. BESSv2.0: A satellite-based and coupled-process model for quantifying long-term global land-atmosphere fluxes. Remote Sensing of Environment 295, 113696 (2023).
+
+46. Harrison, S. P. et al. Eco-evolutionary optimality as a means to improve vegetation and land-surface models. New Phytologist 231, 2125-2141 (2021).
+
+47. Stocker, B. D. et al. Quantifying soil moisture impacts on light use efficiency across biomes. New Phytologist 218, 1430-1449 (2018).
+
+48. Lian, X. et al. Multifaceted characteristics of dryland aridity changes in a warming world. Nature Reviews Earth and Environment 2, 232-250 (2021).
+
+49. Baldocchi, D., Chu, H. & Reichstein, M. Inter-annual variability of net and gross ecosystem carbon fluxes: A review. Agricultural and Forest Meteorology 249, 520-533 (2018).
+
+50. Lasslop, G. et al. Separation of net ecosystem exchange into assimilation and respiration using a light response curve approach: Critical issues and global evaluation. Global Change Biology 16, 187-208 (2010).
+
+<--- Page Split --->
+
+51. Keenan, T. F. et al. Widespread inhibition of daytime ecosystem respiration. Nature Ecology and Evolution 3, 407-415 (2019).
+
+52. Papale, D. et al. Towards a standardized processing of Net Ecosystem Exchange measured with eddy covariance technique: Algorithms and uncertainty estimation. Biogeosciences 3, 571-583 (2006).
+
+53. Lloyd, J. & Taylor, J. A. On the Temperature Dependence of Soil Respiration. Functional Ecology 8, 315 (1994).
+
+54. Wutzler, T. et al. Basic and extensible post-processing of eddy covariance flux data with REDdyProc. Biogeosciences 15, 5015-5030 (2018).
+
+55. Meek, D. W., Hatfield, J. L., Howell, T. A., Idso, S. B. & Reginato, R. J. A generalized relationship between photosynthetically active radiation and solar radiation. Agronomy Journal 76, 939-945 (1984).
+
+56. Gunderson, C. A., O'hara, K. H., Campion, C. M., Walker, A. V. & Edwards, N. T. Thermal plasticity of photosynthesis: The role of acclimation in forest responses to a warming climate. Global Change Biology 16, 2272-2286 (2010).
+
+57. Smith, N. G. & Dukes, J. S. Short-term acclimation to warmer temperatures accelerates leaf carbon exchange processes across plant types. Global Change Biology 23, 4840-4853 (2017).
+
+58. Fisher, J. B., Whittaker, R. J. & Malhi, Y. ET come home: potential evapotranspiration in geographical ecology. Global Ecology and Biogeography 20, 1-18 (2011).
+
+59. Bates, D., Mächler, M., Bolker, B. & Walker, S. Fitting linear mixed-effects models using lme4. J. Stat. Soft. 67, (2015).
+
+<--- Page Split --->
+
+60. Ryu, Y. et al. Integration of MODIS land and atmosphere products with a coupled-process model to estimate gross primary productivity and evapotranspiration from 1 km to global scales. Global Biogeochemical Cycles 25, 1–24 (2011).
+
+61. Kattge, J. et al. TRY – a global database of plant traits. Global Change Biology 17, 2905–2935 (2011).
+
+62. Chen, J. L., Reynolds, J. F., Harley, P. C. & Tenhunen, J. D. Coordination theory of leaf nitrogen distribution in a canopy. Oecologia 93, 63–69 (1993).
+
+63. Wright, I. J., Reich, P. B. & Westoby, M. Least-cost input mixtures of water and nitrogen for photosynthesis. American Naturalist 161, 98–111 (2003).
+
+64. Wang, H. et al. Towards a universal model for carbon dioxide uptake by plants. Nature Plants 3, 734–741 (2017).
+
+<--- Page Split --->
+
+
+
+Extended Data Fig. 2: The relationships between canopy photosynthetic capacities and \(\overline{T_{air}}\) over fAPAR and \(\mathrm{T_{air}}\) bins. a, The partial effect of \(\overline{T_{air}}\) on \(\mathrm{A_{max,2000}}\) when \(\overline{PPFD}\) is also incorporated in the modelling \((\mathrm{A_{max,2000}}\sim \overline{T_{air}} +\mathrm{PPFD} + (1|\mathrm{Site}))\) . b, Partial correlation coefficients \((r)\) between \(\mathrm{A_{max,2000}}\) and \(\overline{T_{air}}\) when controlling for \(\overline{PPFD}\) \((\mathrm{A_{max,2000}}\sim \overline{T_{air}} |\overline{PPFD})\) . c, The cross- site thermal acclimation rate \((\gamma_{\mathrm{T}})\) is calculated based on \(\mathrm{A_{max}}\) \((\mathrm{A_{max}}\sim \overline{T_{air}} +\) \((1|\mathrm{Site}))\) . d, The cross- site \(\gamma_{\mathrm{T}}\) is calculated using plant function types (PFTs) as random intercepts \((\mathrm{A_{max,2000}}\sim \overline{T_{air}} +(1|\mathrm{PFT}))\) . Numbers \((\%)\) in parentheses represent the detectability of positive \(\gamma_{T}\) values, which is defined as the percentage of the number of bins displaying a positive \(\gamma_{\mathrm{T}}\) over the total number of bins. Black dots indicate significant \((P< 0.05)\) correlations.
+
+<--- Page Split --->
+
+
+Extended Data Fig. 3: The PFT-specific thermal acclimation rates \((\gamma_{\mathrm{T}})\) . a–g, PFT-specific \(\gamma_{\mathrm{T}}\) for croplands (CRO) (a), deciduous broadleaf forests (DBF) (b), evergreen broadleaf forests (EBF) (c), evergreen needle-leaf forests (ENF) (d), grasslands (GRA) (e), mixed forests (MF) (f), wetlands (WET) (g). Numbers (\%) in parentheses represent the detectability of positive \(\gamma_{\mathrm{T}}\) values, which is defined as the percentage of the number of bins displaying a positive \(\gamma_{\mathrm{T}}\) over the total number of bins. Black dots indicate significant \((P< 0.05)\) correlations between \(\mathrm{A}_{\mathrm{max,2000}}\) and \(\overline{T_{air}}\) .
+
+<--- Page Split --->
+![PLACEHOLDER_28_0]
+
+Extended Data Fig. 4: Analyses of the partial correlation coefficients between \(\mathbf{A}_{\max ,2000}\) and \(\overline{T_{air}}\) derived from long-term flux sites and their relationships with the site-level average \(\overline{T_{air}}\) and variability of \(\overline{T_{air}}\) . a, Geographic distribution of partial correlation coefficients between \(\mathbf{A}_{\max ,2000}\) and \(\overline{T_{air}}\) controlling for \(\overline{P P D}\) , fAPAR and \(\mathrm{T_{air}}\) across sites with observations spanning over five years. b, Relationship between partial correlation coefficients and the site-level averages of \(\overline{T_{air}}\) . c, Relationship between partial correlation coefficients and the site-level standard deviation of \(\overline{T_{air}}\) . The "Forest" biome category includes evergreen needle-leaf forests, deciduous broadleaf forests, and mixed forests. Other PFTs are croplands (CRO), evergreen broadleaf forests (EBF), grasslands (GRA), and wetlands (WET).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+- AcclimationSILiuetal.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36_det.mmd b/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..646e5536c4073af7e0d75cbec04d0574ee4577aa
--- /dev/null
+++ b/preprint/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36/preprint__055f7b3c352eb4dcd6e5fa5b2b356c8a36705a36b80b6bddb6aecaa55c0d5a36_det.mmd
@@ -0,0 +1,505 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 877, 177]]<|/det|>
+# Evidence for widespread thermal acclimation of canopy photosynthesis
+
+<|ref|>text<|/ref|><|det|>[[44, 196, 268, 240]]<|/det|>
+Jiangong Liu j16314@columbia.edu
+
+<|ref|>text<|/ref|><|det|>[[44, 269, 930, 352]]<|/det|>
+Columbia University Youngryel Ryu Seoul National University Xiangzhong Luo Department of Geography, National University of Singapore https://orcid.org/0000- 0002- 9546- 0960
+
+<|ref|>text<|/ref|><|det|>[[44, 356, 930, 400]]<|/det|>
+Benjamin Dechant Leipzig University
+
+<|ref|>text<|/ref|><|det|>[[44, 404, 570, 470]]<|/det|>
+Benjamin Dechant Leipzig University Benjamin Stocker University of Bern https://orcid.org/0000- 0003- 2697- 9096
+
+<|ref|>text<|/ref|><|det|>[[44, 475, 523, 519]]<|/det|>
+Trevor Keenan UC Berkeley https://orcid.org/0000- 0002- 3347- 0258
+
+<|ref|>text<|/ref|><|det|>[[44, 524, 591, 567]]<|/det|>
+Pierre Gentine Columbia University https://orcid.org/0000- 0002- 0845- 8345
+
+<|ref|>text<|/ref|><|det|>[[44, 572, 106, 608]]<|/det|>
+Xing Li LSCE
+
+<|ref|>text<|/ref|><|det|>[[44, 616, 275, 659]]<|/det|>
+Bolun Li Seoul National University
+
+<|ref|>text<|/ref|><|det|>[[44, 664, 600, 708]]<|/det|>
+Sandy Harrison University of Reading https://orcid.org/0000- 0001- 5687- 1903
+
+<|ref|>text<|/ref|><|det|>[[44, 712, 630, 754]]<|/det|>
+Iain Prentice Imperial College London https://orcid.org/0000- 0002- 1296- 6764
+
+<|ref|>text<|/ref|><|det|>[[44, 792, 104, 810]]<|/det|>
+Article
+
+<|ref|>text<|/ref|><|det|>[[44, 830, 137, 849]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 868, 300, 888]]<|/det|>
+Posted Date: April 16th, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 905, 473, 925]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 4013319/v1
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 44, 914, 87]]<|/det|>
+License: © ① This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 105, 535, 125]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<|ref|>text<|/ref|><|det|>[[42, 160, 950, 204]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Plants on November 8th, 2024. See the published version at https://doi.org/10.1038/s41477-024-01846-1.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 90, 678, 108]]<|/det|>
+Evidence for widespread thermal acclimation of canopy photosynthesis
+
+<|ref|>text<|/ref|><|det|>[[114, 122, 880, 177]]<|/det|>
+Jiangong Liu \(^{1*}\) , Youngreyl Ryu \(^{1,2*}\) , Xiangzhong Luo \(^{3}\) , Benjamin Dechant \(^{1,4,5}\) , Benjamin D. Stocker \(^{6,7}\) , Trevor F. Keenan \(^{8,9}\) , Pierre Gentine \(^{10,11}\) , Xing Li \(^{1}\) , Bolun Li \(^{1,12}\) , Sandy P. Harrison \(^{13,14}\) , Iain Colin Prentice \(^{14,15}\)
+
+<|ref|>text<|/ref|><|det|>[[111, 193, 880, 633]]<|/det|>
+\(^{1}\) Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, Republic of Korea \(^{2}\) Department of Landscape Architecture and Rural Systems Engineering, Seoul National University, Seoul, Republic of Korea \(^{3}\) Department of Geography, National University of Singapore, 1 Arts Link, Singapore 117570 \(^{4}\) German Centre for Integrative Biodiversity Research (iDiv) Halle- Jena- Leipzig, Leipzig, Germany \(^{5}\) Leipzig University, Leipzig, Germany \(^{6}\) Institute of Geography, University of Bern, Bern, Switzerland \(^{7}\) Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland \(^{8}\) Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA \(^{9}\) Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA \(^{10}\) Earth and Environmental Engineering Department, Columbia University, New York, NY 10027, USA \(^{11}\) Climate School, Columbia University, New York, NY 10025, USA \(^{12}\) School of Geographical Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China \(^{13}\) School of Archaeology, Geography and Environmental Science (SAGES), University of Reading, Reading RG6 6AH, United Kingdom \(^{14}\) Department of Earth System Science, Ministry of Education Key Laboratory for Earth System Modeling, Institute for Global Change Studies, Tsinghua University, Beijing 100084, China \(^{15}\) Georgina Mace Centre for the Living Planet, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY, United Kingdom
+
+<|ref|>text<|/ref|><|det|>[[114, 664, 744, 701]]<|/det|>
+\*Corresponding authors: Jiangong Liu (jl6314@columbia.edu); Youngreyl Ryu (yryu@snu.ac.kr)
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 91, 190, 108]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[112, 140, 881, 559]]<|/det|>
+Plants acclimate to temperature by adjusting their photosynthetic capacity over weeks to months. However, most evidence for photosynthetic acclimation derives from leaf- scale experiments. Here, we address the scarcity of evidence for canopy- scale photosynthetic acclimation by examining the correlation between maximum photosynthetic rates ( \(\mathrm{A}_{\mathrm{max,2000}}\) ) and growth temperature ( \(\overline{T_{air}}\) ) across a range of concurrent temperatures and canopy foliage quantity, using data from over 200 eddy covariance sites. We detect widespread thermal acclimation of canopy- scale photosynthesis, demonstrated by enhanced \(\mathrm{A}_{\mathrm{max,2000}}\) under higher \(\overline{T_{air}}\) , across flux sites with adequate water availability. A 14- day period is identified as the most relevant time scale for acclimation across all sites, with a range of 12–25 days for different plant functional types. The mean apparent thermal acclimation rate across all ecosystems is 0.41 (- 0.47–1.05 for 5th–95th percentile range) \(\mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1} \mathrm{°C}^{- 1}\) , with croplands showing the largest and grasslands the lowest acclimation rates. Incorporating optimality- based leaf photosynthetic capacity acclimation into a biochemical photosynthesis model is shown to improve the representation of thermal acclimation rates. Our results underscore the critical need for enhanced understanding and modelling of canopy- scale photosynthetic capacity to accurately predict plant responses to warmer growing seasons.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[114, 90, 162, 107]]<|/det|>
+## Main
+
+<|ref|>text<|/ref|><|det|>[[112, 140, 870, 477]]<|/det|>
+The carbon uptake capacity of terrestrial ecosystem photosynthesis shows large spatio- temporal variation \(^{1}\) . Air temperature \(\mathrm{(T_{air})}\) is one of the key factors determining this variation \(^{2}\) . Given recent warming of \(0.1 - 0.3^{\circ}\mathrm{C}\) per decade \(^{3}\) , a better understanding of ecosystem responses to \(\mathrm{T_{air}}\) is needed. While the instantaneous temperature dependence of photosynthesis has been a major focus of research \(^{4,5}\) and is represented in vegetation and land surface models \(^{6,7}\) , the slower process known as thermal acclimation, through which plants maintain or enhance their photosynthetic efficiency in response to warmer growth temperatures \(^{8,9}\) , is less well understood \(^{10,11}\) . Several studies have indicated that leaves acclimate to thermal growing conditions within weeks to months, although the relevant time scales for different plant types remain uncertain \(^{12 - 14}\) . The potential mechanisms of this (non- genetic) acclimation include changes in key biochemical parameters (electron- transport potential and carboxylation capacity) \(^{15,16}\) , the sensitivity of stomatal conductance to atmospheric vapour pressure deficit (VPD) \(^{17}\) , and enzymatic heat tolerance \(^{8,18}\) .
+
+<|ref|>text<|/ref|><|det|>[[112, 506, 866, 820]]<|/det|>
+Widespread evidence of thermal acclimation at the leaf and canopy scales indicates that the optimal temperature \(\mathrm{(T_{opt})}\) of photosynthesis adjusts in accordance with the prevailing \(\mathrm{T_{air}}\) averaged over the time frame most relevant for acclimation \(\overline{T_{air}}\) \(^{15,16,18 - 20}\) . Yet the extent to which the maximum carbon assimilation rate under high light \(\mathrm{(A_{max})}\) acclimates to \(\overline{T_{air}}\) under natural conditions is less clear \(^{21,22}\) . It is crucial to understand whether both \(\mathrm{T_{opt}}\) and \(\mathrm{A_{max}}\) acclimate to \(\overline{T_{air}}\) since only their simultaneous enhancement can lead to consistent increases in photosynthesis \(^{23}\) . Some process- based photosynthetic models incorporate \(\mathrm{T_{opt}}\) acclimation, but not variations in \(\mathrm{A_{max}}\) \(^{24,25}\) . Demonstrating the presence of thermal acclimation at the canopy scale, quantifying its relevant time scales and rates across ecosystems, and assessing the accuracy of photosynthetic models in representing these acclimation processes are essential for understanding how thermal acclimation can mitigate the potentially detrimental effects of warming on the future terrestrial carbon sink \(^{11}\) .
+
+<|ref|>text<|/ref|><|det|>[[114, 850, 866, 898]]<|/det|>
+In this study, we define a positive adjustment in canopy- scale \(\mathrm{A_{max}}\) in response to elevated \(\overline{T_{air}}\) as evidence for thermal acclimation of canopy photosynthesis. Following ref. \(^{26}\) , \(\mathrm{A_{max}}\) is defined
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 876, 428]]<|/det|>
+as the photosynthetic assimilation rate measured under high light, ample water and ambient \(\mathrm{CO_2}\) . We derive \(\mathrm{A_{max}}\) from light response curves of half- hourly or hourly eddy- covariance carbon fluxes obtained from more than 200 FLUXNET2015 flux sites (see Methods). To facilitate consistent analysis across different light conditions, we standardize \(\mathrm{A_{max}}\) to photosynthetic photon flux density (PPFD) equivalent to \(2000\mu \mathrm{mol}\mathrm{m}^{- 2}\mathrm{s}^{- 1}\) (denoted as \(\mathrm{A_{max,2000}}\) ). Given the limited number of \(\mathrm{A_{max,2000}}\) samples for individual flux sites, we infer the thermal acclimation of \(\mathrm{A_{max,2000}}\) across spatial gradients by leveraging the large range of climates sampled by the FLUXNET2015 sites. We examine the correlation between \(\mathrm{A_{max,2000}}\) and \(\overline{T_{air}}\) when averaged over different time windows to identify the most relevant time scale \((\tau)\) for thermal acclimation, as indicated by peak correlation. Finally, we evaluate a biochemical model of canopy- scale \(\mathrm{C_3}\) photosynthesis \(^{4,25}\) , incorporating recent advances in parameterizing temperature dependence acclimation \(^{15}\) and modelled optimality- based leaf photosynthetic capacity \(^{27}\) , to assess its ability to reproduce the observed thermal acclimation rates.
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 459, 304, 477]]<|/det|>
+## Results and discussion
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 511, 645, 531]]<|/det|>
+## The time scale of thermal acclimation of canopy photosynthesis
+
+<|ref|>text<|/ref|><|det|>[[112, 562, 880, 875]]<|/det|>
+The time scale for canopy photosynthetic acclimation, as measured by the correlation coefficient \((r)\) between \(\mathrm{A_{max,2000}}\) and \(\overline{T_{air}}\) over different periods within concurrent \(\mathrm{T_{air}}\) and fractional absorbed photosynthetically active radiation fraction (fAPAR) bins (see Methods), varies across plant functional types (PFTs) (Fig. 1 and Supplementary Fig. 1), increasing from grasslands (GRA, 12 days) to croplands (CRO, 16 days), evergreen needle- leaf forests (ENF, 20 days), deciduous broadleaf forests (DBF, 21 days), and finally wetlands (WET, 25 days). The \(\tau\) value obtained across all sites is 14 days (Fig. 1f). For EBF, an optimal \(\tau\) cannot be determined using \(\mathrm{A_{max,2000}}\) , even over an extended period of 180 days (Supplementary Fig. 1a). The vegetation index, enhanced vegetation index (EVI) that is derived from reflectance data in the near- infrared, red, and blue spectral bands, can characterize canopy structure, which closely relates with the canopy photosynthetic capacity \(^{28}\) . We use a \(\tau\) value of 13 days for EBF as identified by remote- sensing EVI for subsequent analysis (Methods; Supplementary Fig. 1b).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[113, 87, 884, 430]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 439, 872, 618]]<|/det|>
+Fig. 1: Time scales \((\tau)\) for thermal acclimation of canopy photosynthesis. The time scale for (a) croplands (CRO), (b) deciduous broadleaf forests (DBF), (c) evergreen needle-leaf forests (ENF), (d) grasslands (GRA), (e) wetlands (WET), and (f) across all available sites (ALL). The x-axes represent the number of days over which \(\mathrm{T}_{\mathrm{air}}\) is averaged to derive \(\overline{T_{air}}\) . The y-axes represent the 5-day moving average of positive Pearson correlation coefficients \((r)\) between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) over fAPAR and \(\mathrm{T}_{\mathrm{air}}\) bins. The \(\tau\) value is the length of time frame for which \(r\) peaks.
+
+<|ref|>text<|/ref|><|det|>[[113, 650, 881, 888]]<|/det|>
+Our estimate of an average of 14 days for thermal acclimation of canopy photosynthesis falls within the range of estimates of leaf- scale \(\tau\) , which vary from days to months depending on species and growth conditions8,13,29. A modelling study reports that a 15- day time scale for acclimation optimally predicts hourly eddy covariance flux measurements30. The time scale \(\tau\) for photosynthetic acclimation to a changing environment reflects a tradeoff between potential benefits (e.g. carbon assimilation) and costs (e.g. resource reallocation)31. A rapid adjustment in photosynthetic capacities is expected to enhance photosynthetic performance but is accompanied by higher costs in energy and resources10. The shorter \(\tau\) observed in GRA and CRO are in line with the expectation that fast- growing plants with a high generation rate of new leaves might
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 875, 219]]<|/det|>
+show shorter \(\tau\) than slow- growing species due to their greater physiological plasticity32. Conversely, we found longer \(\tau\) values in forests and WET, yet longer \(\tau\) is potentially compensated by a higher acclimation rate (Fig. 2b). The PFT- specific and cross- site \(\tau\) values for the canopy photosynthetic capacity provide a credible basis for explicitly incorporating the time scale of thermal acclimation into vegetation and land surface models.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 250, 611, 271]]<|/det|>
+## Evidence for thermal acclimation of canopy photosynthesis
+
+<|ref|>text<|/ref|><|det|>[[112, 300, 877, 696]]<|/det|>
+By binning \(\mathrm{T}_{\mathrm{air}}\) and fAPAR to control for the confounding effects of concurrent temperature and seasonal changes in canopy foliage quantity on \(\mathrm{A}_{\mathrm{max},2000}\) , our analysis reveals a pervasive positive correlation between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) under conditions of adequate water availability as indicated by a high ratio of actual to potential evapotranspiration (ET/PET) (Fig. 2). This correlation is observed both spatially across multiple sites (Fig. 2a) and temporally within individual sites (Fig. 2c). We use linear mixed- effect models (LMMs) to obtain the regression coefficients of \(\overline{T_{air}}\) when estimating \(\mathrm{A}_{\mathrm{max},2000}\) ( \(\mathrm{A}_{\mathrm{max},2000} \sim \overline{T_{air}} + (1 \mid \mathrm{Site})\) ), which we define as the apparent thermal acclimation rate \((\gamma_{\mathrm{T}}, \mu \mathrm{mol} \mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1} \mathrm{~}^{\circ} \mathrm{C}^{- 1})\) (see Methods). The concept of apparent rates is used here as the \(\mathrm{A}_{\mathrm{max},2000}\) response rate to \(\overline{T_{air}}\) may be influenced by other covarying environmental conditions14, including the growth PPFD ( \(\overline{PPFD}\) ) and VPD (Supplementary Fig. 2)33. To account for the potential impact of adaptation15 – the modification of \(\mathrm{A}_{\mathrm{max},2000} - \overline{T_{air}}\) relationships across different species and populations within a species growing at different sites – sites are treated as random intercepts within the LLMs (see Extended Data Fig. 1 for an example). CRO is included in the PFT- based analyses but excluded from cross- site analyses.
+
+<|ref|>text<|/ref|><|det|>[[113, 727, 870, 883]]<|/det|>
+Detectability of thermal acclimation in canopy photosynthesis is quantified as the percentage of \(\mathrm{T}_{\mathrm{air}}\) - fAPAR bins showing a positive \(\gamma_{\mathrm{T}}\) . Our cross- site analysis for natural ecosystems finds positive \(\gamma_{\mathrm{T}}\) values in \(87\%\) of the \(\mathrm{T}_{\mathrm{air}}\) - fAPAR bins (939 in total) (Fig. 2a), with \(66\%\) of these positive relationships being statistically significant \((P < 0.05)\) , indicating that thermal acclimation is widespread across biomes. Averaged over all \(\mathrm{T}_{\mathrm{air}}\) - fAPAR bins, \(\gamma_{\mathrm{T}}\) is \(0.41 \pm 0.61\) (mean \(\pm 1\) - SD) \(\mu \mathrm{mol} \mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1} \mathrm{~}^{\circ} \mathrm{C}^{- 1}\) , with a 5th to 95th percentile range of - 0.47 to 1.05 \(\mu \mathrm{mol}\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 883, 295]]<|/det|>
+\(\mathrm{CO}_{2} \mathrm{m}^{- 2} \mathrm{s}^{- 1} \circ \mathrm{C}^{- 1}\) . The average of positive \(\gamma_{\mathrm{T}}\) values is \(0.57 \pm 0.33 \mathrm{m}^{- 2} \mathrm{s}^{- 1} \circ \mathrm{C}^{- 1}\) . The PFT- based analysis also shows strong evidence of thermal acclimation, with mean \(\gamma_{\mathrm{T}}\) values decreasing as follows: \(\mathrm{CRO}(0.77) > \mathrm{WET}(0.58) > \mathrm{DBF}(0.57) > \mathrm{ENF}(0.53) > \mathrm{MF}(0.41) > \mathrm{EBF}(0.38) > \mathrm{GRA}(0.34)\) (Fig. 2b and Extended Data Fig. 3). Furthermore, \(92\%\) of FLUXNET2015 sites with observations spanning five years or more show positive partial correlations between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) after controlling for \(\overline{P F D}\) , \(\mathrm{T}_{\mathrm{air}}\) and fAPAR (Fig. 2c), indicating widespread acclimation to seasonal temperature variations at individual flux sites. Sites showing a negative correlation are mainly located in the tropics (Extended Data Fig. 4a).
+
+<|ref|>image<|/ref|><|det|>[[112, 323, 880, 720]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[112, 728, 881, 885]]<|/det|>
+Fig. 2: Relationships between \(\mathbf{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) , a, \(\gamma_{T}\) values over fAPAR and \(\mathrm{T}_{\mathrm{air}}\) bins across flux sites. Black dots indicate significant \((P< 0.05)\) correlations between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) in the linear mixed-effect model \((\mathrm{A}_{\mathrm{max},2000} \sim \overline{T_{air}} + (1 \mid \mathrm{Site}))\) . b, PFT-specific \(\gamma_{\mathrm{T}}\) values. PFTs are arranged in descending order based on their mean \(\gamma_{\mathrm{T}}\) values. In the box plots, the central lines represent the median \(\gamma_{\mathrm{T}}\) values, the upper and lower box limits represent the 75th and 25th percentiles, and the upper and lower whiskers extend to 1.5 times the interquartile range,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 879, 242]]<|/det|>
+respectively. Letters represent statistically significant differences in the average \(\gamma_{\mathrm{T}}\) values (Tukey's HSD test, \(P< 0.05\) ). c, Partial correlation coefficients (Partial \(r\) ) between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) , when controlling for \(\overline{PPFD}\) , \(\mathrm{T}_{\mathrm{air}}\) and fAPAR, across individual longer- term (>5 years) flux sites. Colours in (b) and (c) indicate different PFTs, including croplands (CRO), deciduous broadleaf forests (DBF), evergreen broadleaf forests (EBF), evergreen needle- leaf forests (ENF), grasslands (GRA), mixed forests (MF), wetlands (WET), and all biomes combined (ALL).
+
+<|ref|>text<|/ref|><|det|>[[112, 272, 881, 585]]<|/det|>
+The potential confounding effect of factors other than \(\overline{T_{air}}\) on \(\mathrm{A}_{\mathrm{max},2000}\) appears to be minimal as the detectability of thermal acclimation remains high across diverse conditions. To ensure our findings are not skewed by light acclimation33, we consider the detectability of thermal acclimation when incorporating \(\overline{PPFD}\) into LLMs (89%, Extended Data Fig. 2a) and controlling for \(\overline{PPFD}\) through partial correlation (86%, Extended Data Fig. 2b). The impact of VPD is likely limited, as its negative effect on \(\mathrm{A}_{\mathrm{max}}\) has been accounted for during the derivation of \(\mathrm{A}_{\mathrm{max}}\) (see Equation 3 in Methods) and has been further mitigated by ET/PET filtering. After filtering, there is a positive relationship between \(\mathrm{A}_{\mathrm{max},2000}\) and VPD (Supplementary Fig. 2c). Any negative VPD impact on \(\mathrm{A}_{\mathrm{max},2000}\) is expected to reinforce, not diminish, the observed widespread thermal acclimation. Our findings remain robust with respect to the metric choice; detectability is 87% when \(\mathrm{A}_{\mathrm{max}}\) is unstandardized to a specific PPFD level and 86% when PFTs are treated as random effects within LLMs (Extended Data Fig. 2c and 2d).
+
+<|ref|>text<|/ref|><|det|>[[112, 614, 875, 905]]<|/det|>
+Thermal acclimation capability can be influenced by the level and variability of \(\overline{T_{air}}\) , as well as by species and PFTs21,34- 36. We observe negative effects of \(\overline{T_{air}}\) on \(\mathrm{A}_{\mathrm{max},2000}\) when fAPAR falls below 0.5 and \(\mathrm{T}_{\mathrm{air}}\) exceeds 25°C (Fig. 2a). Limited transpiration, due to a low amount of leaves, may not cool the canopy sufficiently under elevated \(\mathrm{T}_{\mathrm{air}}\) , making ribulose- 1,5- bisphosphate (RuBP) regeneration a limiting process for canopy photosynthesis at high canopy temperature22. The reduction in \(\mathrm{A}_{\mathrm{max},2000}\) with \(\overline{T_{air}}\) may be attributed to decreased maximum quantum yield of photosystem II in response to elevated temperature5,27,37. Additionally, under these conditions, the range of \(\overline{T_{air}}\) (3.1°C) is significantly narrower than among the rest (8.0°C) (two- tailed t- test, \(P< 0.01\) ) (Supplementary Fig. 3b). Our site- level analyses also show that the correlation between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) is positively associated with \(\overline{T_{air}}\) variability and negatively with \(\overline{T_{air}}\) (Extended Data Fig. 4b and 4c), which aligns with previous studies indicating that plants grown
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 882, 295]]<|/det|>
+under low \(\overline{T_{air}}\) variability and/or high \(\overline{T_{air}}\) show reduced acclimation potential \(^{21,34,38}\) . Conversely, the measurement temperature has a limited impact on \(\gamma_{\mathrm{T}}\) for leaf light- saturated net assimilation rates \(\mathrm{(A_{net})}\) \(\mathrm{(T_{air}}\) for \(\mathrm{A_{max,2000}}\) in this study) \(^{35}\) . Moreover, EBF is the dominant PFT for the bin pairs with high \(\mathrm{T_{air}}\) (Supplementary Fig. 4b). There is some evidence that tropical evergreen forests have a limited capability for physiological acclimation because these forests are adapted to relatively stable thermal conditions and/or thrive under high \(\overline{T_{air}}\) that is beyond the range limit for acclimation \(^{39 - 41}\) . The underrepresentation of EBF in the FLUXNET2015 database \(^{42}\) may also lead to uncertainties in the estimation of \(\gamma_{\mathrm{T}}\) for this biome.
+
+<|ref|>text<|/ref|><|det|>[[113, 325, 883, 479]]<|/det|>
+The observed widespread thermal acclimation of \(\mathrm{A_{max,2000}}\) (Fig. 2) contrasts with the varying sign of the response of leaf \(\mathrm{A_{net}}\) to \(\overline{T_{air}}\) , which can be positive, negative or neutral \(^{21,31,34,35,43}\) . This discrepancy may stem from the fact that, unlike \(\mathrm{A_{max}}\) , \(\mathrm{A_{net}}\) is not necessarily measured under ample water conditions \(^{21,26}\) , and water stress is known to affect the capacities of plant thermal acclimation \(^{17}\) . In water- limited situations, plants typically reduce water loss through transpiration by decreasing stomatal conductance \(^{44}\) , resulting in decreased \(\mathrm{A_{net}}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 510, 544, 531]]<|/det|>
+## Representing acclimation in photosynthesis models
+
+<|ref|>text<|/ref|><|det|>[[112, 560, 884, 910]]<|/det|>
+We further explore the representation of \(\mathrm{A_{max,2000}}\) thermal acclimation in a biochemical model for \(\mathrm{C}_{3}\) canopy photosynthesis incorporated in the Breathing Earth System Simulator (BESS) \(^{45}\) , based on the Farquhar- von Caemmerer- Berry (FvCB) model (see Methods) \(^{4}\) . We test three alternative approaches, each under different resource- use allocation assumptions, to estimate maximum carboxylation rates \(\mathrm{(V_{cmax}}\) , \(\mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) ) standardized to \(25^{\circ}\mathrm{C}\) \((V_{cmax}^{25C})\) . These approaches are: (1) assuming a temporally constant and PFT- specific \(V_{cmax}^{25C}\) \((V_{cmax}^{25C} PFT)\) , where plants do not actively regulate \(V_{cmax}^{25C}\) through the growing seasons; (2) scaling leaf \(V_{cmax}^{25C}\) by canopy phenology (LAI- scaled \(V_{cmax}^{25C}\) , \(V_{cmax}^{25C} LAI\) ); and (3) modelling acclimation to prevailing environments based on the eco- evolutionary optimality (EEO) theory \(^{27,46}\) \((V_{cmax}^{25C} EEO)\) (see Methods and Supplementary Text 1 and 2). The FvCB model as applied here incorporates recent advances in parameterizing the temperature dependence of leaf photosynthetic capacities to represent \(\mathrm{T_{opt}}\) acclimation \(^{15}\) (Supplementary Text 1). We run the model using the site- level forcings from the FLUXNET2015 database and derive \(\mathrm{A_{max,2000}}\) by setting PPFD equivalent to \(2000 \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) .
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 856, 162]]<|/det|>
+For further analysis, we select estimated \(\mathrm{A}_{\mathrm{max},2000}\) values from 71 \(\mathrm{C}_3\) sites excluding CRO and water- limited sites, where all three model variants show acceptable accuracy in estimating \(\mathrm{A}_{\mathrm{max},2000}\) (coefficient of determination \([R^2 ] > 0.5\) ) (Supplementary Table 1).
+
+<|ref|>text<|/ref|><|det|>[[113, 193, 866, 377]]<|/det|>
+The BESS model variant incorporating optimality- based \(V_{\mathrm{cmax\_EEO}}^{25C}\) more closely approximates the observed \(\gamma_{\mathrm{T}}\) compared to the other two variants, \(V_{\mathrm{cmax\_PFT}}^{25C}\) (BESS \(\mathrm{PFT}\) ) and \(V_{\mathrm{cmax\_LAI}}^{25C}\) (BESS \(\mathrm{LAI}\) ) (Fig. 3). The Kolmogorov- Smirnov (K- S) test indicates that the cumulative distribution functions of \(\gamma_{\mathrm{T}}\) between \(\mathrm{BESS}_{\mathrm{EEO}}\) and FLUXNET2015 observations are more closely aligned, despite significant differences between all three BESS model distributions and observations ( \(\mathrm{P}< 0.05\) ) (Fig. 3b). \(\mathrm{BESS}_{\mathrm{PFT}}\) and \(\mathrm{BESS}_{\mathrm{LAI}}\) underestimate the median observed \(\gamma_{\mathrm{T}}\) by \(63\%\) and \(48\%\) , respectively, while \(\mathrm{BESS}_{\mathrm{EEO}}\) overestimates it by \(29\%\) (Fig. 3a).
+
+<|ref|>image<|/ref|><|det|>[[114, 383, 880, 648]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 658, 867, 784]]<|/det|>
+Fig. 3: Impact of leaf photosynthetic capacities on \(\gamma_{T}\) estimation. a, Probability densities of \(\gamma_{T}\) values derived from eddy covariance measurements (FLUXNET2015) and three variants of the BESS model (BESS \(\mathrm{PFT}\) , BESS \(\mathrm{LAI}\) , and BESS \(\mathrm{EEO}\) ). The vertical lines represent the median \(\gamma_{T}\) values. b, The statistics of the Kolmogorov-Smirnov (K-S) tests between FLUXNET2015 observations and three model variants.
+
+<|ref|>text<|/ref|><|det|>[[114, 815, 844, 890]]<|/det|>
+The considerable underestimation of \(\gamma_{T}\) by \(\mathrm{BESS}_{\mathrm{PFT}}\) and \(\mathrm{BESS}_{\mathrm{LAI}}\) highlight the limitation in process- based photosynthetic models that incorporate only \(\mathrm{T}_{\mathrm{opt}}\) acclimation. To capture \(\gamma_{T}\) accurately, process- based models must also integrate seasonal variations in photosynthetic
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 875, 375]]<|/det|>
+capacities resulting from thermal acclimation. The overestimation by BESS \(\mathrm{EEO}\) can be attributed to its higher predicted detectability (99%) of thermal acclimation than observed (93%) (Fig. 3a). When calculating \(V_{c m a x\_ E E O}^{25C}\) , we assume that plants are not water-stressed following ET/PET filtering; a water-stress factor is not applied to scale \(V_{c m a x}^{25C}\) as described in ref \(^{37}\) (see Supplementary Text 2). Consequently, in this study, the EEO theory represents an idealized condition where carbon assimilation is optimized under the assumption of sufficient water availability. While plant light use efficiency can be reduced by physiological stress due to water scarcity \(^{47}\) , the absence of such water stress constraints can lead to an overestimation of \(V_{c m a x}^{25C}\) . Although ET/PET is an effective indicator of soil moisture, it may not fully correspond to plant physiological stress. Bridging the gap between existing water availability metrics and actual plant stress responses remains a challenge \(^{48}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 408, 211, 426]]<|/det|>
+## Conclusion
+
+<|ref|>text<|/ref|><|det|>[[113, 457, 879, 793]]<|/det|>
+Photosynthesis can benefit from future warming through thermal acclimation, resulting in increased carbon uptake under conditions where water is not limiting. While leaf- scale acclimation is widely recognized, our study shows that the positive acclimation of canopy- scale photosynthetic capacity to growth temperature is a widespread phenomenon across various terrestrial biomes. We have shown that, on average, the canopy photosynthetic capacity acclimates to the growth thermal conditions of the preceding 14 days. Incorporating seasonal acclimation of photosynthetic capacities (the maximum carboxylation rate and the maximum electron transport rate) is critical for achieving accurate simulations of photosynthesis in response to variations in temperature at time scales of weeks to months. Despite warmer growing seasons, water availability is increasingly constrained in many regions, potentially forcing plants to reduce photosynthetic capacity as a water conservation strategy. Improving the understanding of canopy- scale photosynthetic thermal acclimation in response to future conditions characterized by warming and variable water availability is therefore important.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 825, 191, 842]]<|/det|>
+## Methods
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 883, 398]]<|/det|>
+Global database of ecosystem- scale carbon fluxes. We derive \(\mathrm{A}_{\mathrm{max}}\) from more than 200 eddy covariance sites from the global database FLUXNET2015, which covers a wide range of geospatial locations and plant functional types (Supplementary Table 1) \(^{42,49}\) . FLUXNET2015 is an openly accessible database containing data on the net exchange of carbon (NEE), water, and energy between the atmosphere and the biosphere, and meteorological observations. Uniform processing approaches are implemented for the flux calculation and quality control across the sites \(^{42}\) . We use half- hourly or hourly NEE (NEE_VUT_USTAR50), its corresponding estimation of the uncertainty caused by friction velocity filtering (NEE_VUT_USTAR50_ RANDUNC), and gap- filled meteorological observations, including incoming radiation (SW_IN_F), air temperature (TA_F), and VPD (VPD_F) to derive \(\mathrm{A}_{\mathrm{max}}\) \(^{42,50}\) (described below). Sites are excluded if data are unavailable during the MODIS period from 2002 onwards (e.g. US- LWW and US- Me4) or if the uncertainty estimation is missing (e.g. CA- Man).
+
+<|ref|>text<|/ref|><|det|>[[113, 428, 857, 500]]<|/det|>
+Derivation of ecosystem- scale \(\mathbf{A}_{\mathrm{max}}\) . We derive \(\mathrm{A}_{\mathrm{max}}\) from light response curves across the FLUXNET2015 sites according to the daytime flux partitioning methods detailed in ref. \(^{33}\) and ref. \(^{51}\) . We fit NEE using the following hyperbolic equation:
+
+<|ref|>equation<|/ref|><|det|>[[396, 504, 880, 548]]<|/det|>
+\[-NEE = \frac{\alpha\beta R_g}{\alpha R_g + \beta} +\gamma \quad (1)\]
+
+<|ref|>text<|/ref|><|det|>[[113, 555, 880, 633]]<|/det|>
+where \(\beta\) (μmol \(\mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1}\) ) is the target variable of interest. \(\alpha\) , \(\mathrm{R}_{\mathrm{g}}\) , and \(\gamma\) represent the ecosystem- scale quantum yield (μmol \(\mathrm{C} \mathrm{J}^{- 1}\) ), global radiation ( \(\mathrm{W} \mathrm{~m}^{- 2}\) ), and ecosystem respiration (μmol \(\mathrm{CO}_{2} \mathrm{~m}^{- 2} \mathrm{~s}^{- 1}\) ), respectively.
+
+<|ref|>text<|/ref|><|det|>[[113, 664, 828, 711]]<|/det|>
+To account for the potential influence of high VPD (hPa), \(\beta\) is scaled using an exponential function only when VPD exceeds \(10 \mathrm{hPa}\) . Thus, we obtain \(\mathrm{A}_{\mathrm{max}}\) following:
+
+<|ref|>equation<|/ref|><|det|>[[290, 715, 880, 761]]<|/det|>
+\[A_{m a x} = \left\{ \begin{array}{c}{\beta ,V P D\leq 10 h P a}\\ {\beta \exp \left(-k(V P D - 10)\right),V P D > 10 h P a} \end{array} \right. \quad (2)\]
+
+<|ref|>text<|/ref|><|det|>[[113, 768, 881, 869]]<|/det|>
+where \(\beta\) and \(\mathrm{k}\) are fit parameters to the flux data. The ecosystem respiration term in Equation (1), \(\gamma\) , is estimated using an Arrhenius- type function describing the temperature dependence of \(\gamma^{52}\) , which is applied to nighttime data by assuming that nighttime NEE is equivalent to ecosystem respiration:
+
+<--- Page Split --->
+<|ref|>equation<|/ref|><|det|>[[303, 85, 880, 132]]<|/det|>
+\[NEE = R_{ref}exp\left\{E_0\left(\frac{1}{T_{ref} - T_0} -\frac{1}{T_{air} - T_0}\right)\right\} \quad (3)\]
+
+<|ref|>text<|/ref|><|det|>[[113, 138, 883, 188]]<|/det|>
+where \(\mathrm{R_{ref}}\) and \(\mathrm{E_0}\) are the basal respiration rate ( \(\mu \mathrm{mol} \mathrm{CO}_2 \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) ) at a reference temperature ( \(\mathrm{T_{ref}} = 15^{\circ} \mathrm{C}\) ) and temperature sensitivity ( \(^{\circ} \mathrm{C}\) ), respectively. \(\mathrm{T_0}\) is a constant equal to \(- 46.02^{\circ} \mathrm{C}^{53}\) .
+
+<|ref|>text<|/ref|><|det|>[[112, 218, 879, 457]]<|/det|>
+In practice, \(\mathrm{E_0}\) is first estimated according to Equation (3). With a fixed \(\mathrm{E_0}\) , the remaining parameters of Equations (2) and (3) \((\alpha , \beta , \mathrm{k},\) and \(\mathrm{R_{ref}}\) ) are derived using a time window of 2–14 days. The specific time window depends on data availability, and the \(\mathrm{A_{max}}\) value is assumed invariant within the same fitting window. Here, we derive \(\mathrm{A_{max}}\) using the REddyProc R package (https://github.com/bgctw/REddyProc) \(^{54}\) . Low- quality daily \(\mathrm{A_{max}}\) data, indicated by an unreasonable range, are discarded \(^{33}\) . We standardize \(\mathrm{A_{max}}\) to \(\mathrm{PPFD} = 2000 \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1}\) ( \(\mathrm{A_{max,2000}}\) ) to avoid any \(\mathrm{A_{max}}\) values obtained from potentially unsaturated light conditions and to ensure consistent levels of absorbed PAR (see Methods below) \(^{33}\) . We convert \(\mathrm{PPFD}\) to \(\mathrm{R_g}\) using a constant of \(2.1 \mu \mathrm{mol} \mathrm{J}^{- 1}\) (ref. \(^{55}\) ).
+
+<|ref|>text<|/ref|><|det|>[[112, 486, 883, 828]]<|/det|>
+Time scale for thermal acclimation of \(\mathrm{A_{max,2000}}\) . We hypothesize that the most relevant time scale for thermal acclimation ( \(\tau\) ) ranges between 2 and 60 days according to the coordination hypothesis and observations \(^{13,56,57}\) . We conduct linear regressions between \(\mathrm{A_{max,2000}}\) derived from the FLUXNET2015 sites and the daytime \(\overline{T_{air}}\) averaged over the 2 to 60 days prior to the time of \(\mathrm{A_{max,2000}}\) measurements with a time interval of one day. Based on a previous study \(^{33}\) , savanna and shrubland sites are excluded from the analysis because they are frequently subject to water stress. Croplands are excluded from the cross- site analysis. Furthermore, we exclude the \(\mathrm{A_{max,2000}} - \overline{T_{air}}\) pairs collected during water- limited conditions, as indicated by the ratio of prevailing actual evapotranspiration to Priestley- Taylor potential evapotranspiration (ET/PET) \(< 0.75^{58}\) and VPD \(> 20 \mathrm{hPa}\) . Additionally, we only focus on growing seasons, characterized by fAPAR \(> 0.3\) and \(\mathrm{T_{air}}\) and \(\overline{T_{air}} > 0^{\circ} \mathrm{C}\) . Daily fAPAR and LAI for each site were derived by interpolating the 8- day MODIS MOD15A2H products following ref. \(^{33}\) . Low- quality data affected by cloud contamination are removed \(^{25}\) . A total of 149,774 \(\mathrm{A_{max,2000}}\) records are used for further analyses.
+
+<|ref|>text<|/ref|><|det|>[[113, 857, 857, 907]]<|/det|>
+To remove the potential effects of concurrent \(\mathrm{T_{air}}\) and fAPAR on \(\mathrm{A_{max,2000}}\) , we group \(\mathrm{A_{max,2000}} - \overline{T_{air}}\) pairs into different bins of \(\mathrm{T_{air}}\) with \(1^{\circ} \mathrm{C}\) intervals and fAPAR with 0.02 intervals. This
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 876, 404]]<|/det|>
+approach allows the analysis of changes in \(\mathrm{A}_{\mathrm{max},2000}\) along \(\overline{T_{air}}\) gradients to be made while controlling for the instantaneous temperature dependence of photosynthesis. Pearson \(r\) between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) that is averaged over different time frames (i.e., 2- 60 d with 1- d interval) is calculated for \(\mathrm{T_{air}}\) and fAPAR bins. A positive \(r\) indicates the thermal acclimation potential of \(\mathrm{A}_{\mathrm{max},2000}\) . Only bins with sampling numbers larger than 10 and 20 for PFT- based and cross- site analyses, respectively, are retained. We examine the relationship between the average of the positive \(r\) values obtained from \(\mathrm{T_{air}}\) and fAPAR bins and the time frames used to calculate \(\overline{T_{air}}\) for each PFT and cross sites (Fig. 1). \(\tau\) is defined as the corresponding time frame when the 5- d moving average of the positive \(r\) reaches its peak. Enhanced vegetation index (EVI), derived from MODIS reflectance data (MCD43A4) in the near- infrared, red, and blue spectral bands \(^{28}\) , is used to estimate \(\tau\) for EBF for subsequent analysis, as an optimal \(\tau\) cannot be identified for this PFT using \(\mathrm{A}_{\mathrm{max},2000}\) (Supplementary Fig. 1).
+
+<|ref|>text<|/ref|><|det|>[[112, 433, 881, 753]]<|/det|>
+Evidence for thermal acclimation of \(\mathrm{A}_{\mathrm{max},2000}\) . We use PFT- specific \(\tau\) values for aggregating prevailing \(\mathrm{T_{air}}\) to obtain \(\overline{T_{air}}\) (Fig 1). We run linear mixed- effect models (LMMs), which include a random effect of different sites for removing the site- level adaptation effect, to explore the relationship between \(\mathrm{A}_{\mathrm{max},2000}\) and PFT- specific \(\overline{T_{air}}\) (i.e., \(\mathrm{A}_{\mathrm{max},2000} \sim \overline{T_{air}} + (1 \mid \mathrm{Site}))\) (Extended Data Fig. 1). The same data selection procedure and \(\mathrm{T_{air}}\) and fAPAR binning scheme are used for the cross- site analysis (Fig. 2a; see Methods above). The coefficient of \(\overline{T_{air}}\) estimated from LMMs is defined as thermal acclimation rate \((\gamma_{\mathrm{T}})\) . The sampling number, conditional and marginal correlation coefficients for the cross- site analysis are shown in Supplementary Fig. 5. The LMM is conducted with the R package lme4 \(^{59}\) . For each site, the sampling number of \(\mathrm{A}_{\mathrm{max},2000} - \overline{T_{air}}\) pairs is insufficient to support the correlation analysis under the binning scheme \(^{33}\) . Instead, a partial correlation analysis is run between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) controlling for \(\overline{PPFD}\) , \(\mathrm{T_{air}}\) , and fAPAR on flux sites with observation lengths longer than five years (Fig. 2c).
+
+<|ref|>text<|/ref|><|det|>[[113, 781, 881, 910]]<|/det|>
+The prevailing conditions of \(\mathrm{T_{air}}\) and PPFD often show a high correlation (Supplementary Fig. 2a). Therefore, we also include \(\overline{PPFD}\) as an additional predictor in the LMM (Extended Data Fig. 2a), and we analyze partial correlations between \(\mathrm{A}_{\mathrm{max},2000}\) and \(\overline{T_{air}}\) controlling for \(\overline{PPFD}\) (Extended Data Fig. 2b) in order to eliminate the confounding effect of light acclimation \(^{33}\) . Additionally, we repeat LMMs with a different target variable ( \(\mathrm{A}_{\mathrm{max}}\) ) and random effect (PFT) to
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 857, 134]]<|/det|>
+examine the robustness of the detectability of thermal acclimation (Extended Data Fig. 2c and 2d).
+
+<|ref|>text<|/ref|><|det|>[[112, 165, 875, 504]]<|/det|>
+Modelling canopy photosynthesis of \(\mathbf{C}_3\) plants. We apply the photosynthesis module of the BESS model \(^{60}\) to estimate canopy photosynthesis \((A)\) and subsequently \(\mathrm{A}_{\mathrm{max},2000}\) , for each flux site. This allows a direct comparison to be made of the impacts of different empirical formulations of leaf photosynthetic capacities on thermal acclimation. The photosynthesis module is based on the Farquhar- von Caemmerer- Berry (FvCB) model \(^{4}\) , where \(A\) is determined as the lower \(\mathrm{CO}_2\) assimilation rate between the maximum rate of ribulose- 1,5- bisphosphate carboxylase/oxygenase (Rubisco) activity when light is saturated \((A_c)\) and the electron transport rate for RuBP regeneration when light is limited \((A_j)\) . For this study, the two- big- leaf scheme implemented in the BESS model is simplified to a one- big- leaf scheme. We have updated the parameters of temperature dependence of the maximum carboxylation rate \((\mathrm{V}_{\mathrm{cmax}}, \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1})\) , the maximum electron transport rate \((\mathrm{J}_{\mathrm{max}}, \mu \mathrm{mol} \mathrm{m}^{- 2} \mathrm{s}^{- 1})\) , as well as the ratio of their values at 25 \(^\circ \mathrm{C}\) following ref \(^{15}\) . A detailed description of the canopy photosynthesis model can be found in Supplementary Text 1 (also see refs. \(^{25,45,60}\) ).
+
+<|ref|>text<|/ref|><|det|>[[112, 533, 876, 662]]<|/det|>
+Leaf photosynthetic capacities. \(\mathrm{V}_{\mathrm{cmax}}\) is a key parameter in the FvCB model, particularly under light saturated conditions \(^{4}\) . Previous studies have shown that leaf biochemical components can acclimate to \(\overline{T_{air}}^{9,15,16}\) . In this study, we compare three empirically derived variants of \(\mathrm{V}_{\mathrm{cmax}}\) at \(25^\circ \mathrm{C}\) \((V_{cmax}^{25C})\) within the FvCB model to evaluate their effectiveness in simulating the observed \(\gamma \mathrm{T}\) :
+
+<|ref|>text<|/ref|><|det|>[[142, 667, 881, 770]]<|/det|>
+1. \(V_{cmax}^{25C} \cdot PFT\) : This variant assumes a constant \(V_{cmax}^{25C}\) value over the growing season, an assumption that is still widely used in vegetation models \(^{11}\) . The prescribed top leaf \(V_{cmax}^{25C}\) values are adopted from a look-up table based on PFTs and climatic zones compiled from the TRY trait database \(^{25,61}\) .
+
+<|ref|>text<|/ref|><|det|>[[142, 800, 880, 850]]<|/det|>
+2. \(V_{cmax}^{25C} \cdot LAI\) : Leaf \(V_{cmax}^{25C}\) varies seasonally, with its seasonality following LAI. This scheme, implemented in the previous version of the BESS model \(^{25}\) , follows Equation (4).
+
+<|ref|>equation<|/ref|><|det|>[[207, 856, 880, 899]]<|/det|>
+\[V_{cmax}^{25C} \cdot LAI = a \times V_{cmax}^{25C} \cdot PFT + (1 - a) \times V_{cmax}^{25C} \cdot PFT \times \frac{LAI - LAI_{min}}{LAI_{max} - LAI_{min}} \quad (4)\]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[173, 88, 859, 135]]<|/det|>
+where \(\mathrm{LAI}_{\mathrm{min}}\) and \(\mathrm{LAI}_{\mathrm{max}}\) are the 5th and 95th percentile values of LAI over a growing season, respectively, and \(a\) is an empirical parameter set to 0.3 (ref. \(^{60}\) ).
+
+<|ref|>text<|/ref|><|det|>[[144, 166, 872, 456]]<|/det|>
+3. \(V_{c m a x\_ E E O}^{25C}\) : The calculation is based on eco-evolutionary optimality (EEO) theory \(^{14,27,46}\) , specifically the coordination hypothesis \(^{12,62}\) and the least-cost hypothesis \(^{44,63}\) . The coordination hypothesis proposes that plants actively coordinate resource allocation so that \(A_{\mathrm{c}}\) tends to equal \(A_{\mathrm{j}}\) on weekly to monthly time scales. The least-cost hypothesis proposes that plants minimize the combined costs (per unit assimilation) of maintaining the biochemical capacity for photosynthesis and the water transport capacity required to support it, through stomatal regulation. Combining the two hypotheses results in an optimal intercellular \(\mathrm{CO}_{2}\) concentration under representative conditions \(^{64}\) . Here, we assume that \(V_{c m a x\_ E E O}^{25C}\) acclimates to prevailing conditions following the same time scale as \(\mathrm{A}_{\mathrm{max,2000}}\) (Fig. 1). The calculation is detailed in Supplementary Text 2 and Jiang et al. \(^{27}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 490, 272, 508]]<|/det|>
+## Acknowledgments
+
+<|ref|>text<|/ref|><|det|>[[112, 515, 881, 902]]<|/det|>
+This research is a contribution to the LEMONTREE (Land Ecosystem Models based On New Theory, observation and Experiments) project, funded through the generosity of Eric and Wendy Schmidt by recommendation of the Schmidt Futures programme. It is also a contribution to USMILE European Research Council grant. Y.R. was supported by Ministry of Environment of Korea (202300218237). B.D.S. was funded by the Swiss National Science Foundation grant PCEFP2_181115. B.D. was supported by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (DFG FZT 118, 202548816). T.F.K. acknowledges additional support from a NASA Carbon Cycle Science Award 80NSSC21K1705, and the RUBISCO SFA, which is sponsored by the Regional and Global Model Analysis (RGMA) Program in the Climate and Environmental Sciences Division (CESD) of the Office of Biological and Environmental Research (BER) in the U.S. Department of Energy (DOE) Office of Science. X.L. was supported by National University of Singapore Presidential Young Professorship (A- 0003625- 01- 00). I.C.P. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No: 787203 REALM). We especially thank the researchers and contributors of
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 879, 135]]<|/det|>
+the FLUXNET community and the MODIS products. We also acknowledge Xu Lian and Jianing Fang for their helpful reviews and comments on this manuscript before its submission.
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 167, 256, 186]]<|/det|>
+## Data availability
+
+<|ref|>text<|/ref|><|det|>[[113, 193, 870, 345]]<|/det|>
+The dataset of FLUXNET2015 flux sites under the CC- BY- 4.0 policy is publicly available for download at http://fluxnet.fluxdata.org. Remote- sensing canopy structure data from the MODIS MCD43A and MOD15A2H products are freely accessible at https://lpdaac.usgs.gov/products/mcd43a3v006/ and https://lpdaac.usgs.gov/products/mod15a2hv006/. BESS flux products are publicly available at https://www.environment.snu.ac.kr/data/.
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 377, 259, 395]]<|/det|>
+## Code availability
+
+<|ref|>text<|/ref|><|det|>[[113, 402, 870, 529]]<|/det|>
+The corresponding R code scripts used in this study have been deposited in: https://github.com/ljgcuhk/thermal_acclimation_canopy_photosynthesis. The code for the deviation of \(\mathrm{A}_{\mathrm{max}}\) from the FLUXNET2015 database can be accessed at: https://github.com/trevorkeenan/inhibitionPaperCode. The code for modelling optimality- based \(\mathrm{V}_{\mathrm{cmax}}\) can be accessed at: https://github.com/chongya/SVOM.
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 552, 205, 569]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[113, 585, 840, 641]]<|/det|>
+1. Anav, A. et al. Spatiotemporal patterns of terrestrial gross primary production: A review. Reviews of Geophysics 53, 785-818 (2015).
+
+<|ref|>text<|/ref|><|det|>[[113, 654, 870, 710]]<|/det|>
+2. Beer, C. et al. Terrestrial Gross Carbon Dioxide Uptake: Global Distribution and Covariation with Climate. Science 329, 834-838 (2010).
+
+<|ref|>text<|/ref|><|det|>[[113, 723, 867, 849]]<|/det|>
+3. IPCC. Global Warming of \(1.5^{\circ}\mathrm{C}\) : IPCC Special Report on Impacts of Global Warming of \(1.5^{\circ}\mathrm{C}\) above Pre-Industrial Levels in Context of Strengthening Response to Climate Change, Sustainable Development, and Efforts to Eradicate Poverty. (Cambridge University Press, 2022). doi:10.1017/9781009157940.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 855, 144]]<|/det|>
+4. Farquhar, G. D., von Caemmerer, S. & Berry, J. A. A biochemical model of photosynthetic \(\mathrm{CO_2}\) assimilation in leaves of \(\mathrm{C_3}\) species. Planta 149, 78–90 (1980).
+
+<|ref|>text<|/ref|><|det|>[[113, 158, 880, 247]]<|/det|>
+5. Bernacchi, C. J., Singsaas, E. L., Pimentel, C., Portis, A. R. & Long, S. P. Improved temperature response functions for models of Rubisco-limited photosynthesis. Plant, Cell and Environment 24, 253–259 (2001).
+
+<|ref|>text<|/ref|><|det|>[[113, 262, 844, 317]]<|/det|>
+6. Bernacchi, C. J. et al. Modelling \(\mathrm{C_3}\) photosynthesis from the chloroplast to the ecosystem. Plant, Cell and Environment 36, 1641–1657 (2013).
+
+<|ref|>text<|/ref|><|det|>[[113, 332, 877, 423]]<|/det|>
+7. Mercado, L. M. et al. Large sensitivity in land carbon storage due to geographical and temporal variation in the thermal response of photosynthetic capacity. New Phytol 218, 1462–1477 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 437, 848, 493]]<|/det|>
+8. Berry, J. & Bjorkman, O. Photosynthetic response and adaptation to temperature in higher plants. Annual Review of Plant Physiology 31, 491–543 (1980).
+
+<|ref|>text<|/ref|><|det|>[[113, 507, 861, 597]]<|/det|>
+9. Medlyn, B. E. et al. Temperature response of parameters of a biochemically based model of photosynthesis. II. A review of experimental data. Plant, Cell and Environment 25, 1167–1179 (2002).
+
+<|ref|>text<|/ref|><|det|>[[113, 611, 864, 667]]<|/det|>
+10. Dietze, M. C. Gaps in knowledge and data driving uncertainty in models of photosynthesis. Photosynthesis Research 119, 3–14 (2014).
+
+<|ref|>text<|/ref|><|det|>[[113, 682, 840, 736]]<|/det|>
+11. Rogers, A. et al. A roadmap for improving the representation of photosynthesis in Earth system models. New Phytol 213, 22–42 (2017).
+
+<|ref|>text<|/ref|><|det|>[[113, 750, 840, 805]]<|/det|>
+12. Maire, V. et al. The coordination of leaf photosynthesis links C and N fluxes in \(\mathrm{C_3}\) plant species. PLoS ONE 7, 1–15 (2012).
+
+<|ref|>text<|/ref|><|det|>[[113, 820, 856, 875]]<|/det|>
+13. Smith, N. G. & Dukes, J. S. Drivers of leaf carbon exchange capacity across biomes at the continental scale. Ecology 99, 1610–1620 (2018).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 88, 870, 144]]<|/det|>
+14. Smith, N. G. et al. Global photosynthetic capacity is optimized to the environment. Ecology Letters 22, 506–517 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 158, 879, 215]]<|/det|>
+15. Kumarathunge, D. P. et al. Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale. New Phytologist 222, 768–784 (2019).
+
+<|ref|>text<|/ref|><|det|>[[115, 228, 867, 285]]<|/det|>
+16. Kattge, J. & Knorr, W. Temperature acclimation in a biochemical model of photosynthesis: A reanalysis of data from 36 species. Plant, Cell and Environment 30, 1176–1190 (2007).
+
+<|ref|>text<|/ref|><|det|>[[115, 298, 825, 355]]<|/det|>
+17. Lin, Y. S., Medlyn, B. E. & Ellsworth, D. S. Temperature responses of leaf net photosynthesis: the role of component processes. Tree Physiology 32, 219–231 (2012).
+
+<|ref|>text<|/ref|><|det|>[[115, 367, 875, 457]]<|/det|>
+18. Yamori, W., Hikosaka, K. & Way, D. A. Temperature response of photosynthesis in C3, C4, and CAM plants: Temperature acclimation and temperature adaptation. Photosynthesis Research 119, 101–117 (2014).
+
+<|ref|>text<|/ref|><|det|>[[115, 472, 797, 528]]<|/det|>
+19. Niu, S. et al. Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms. New Phytologist 194, 775–783 (2012).
+
+<|ref|>text<|/ref|><|det|>[[114, 541, 861, 632]]<|/det|>
+20. Baldocchi, D. et al. FLUXNET: A new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor, and energy flux densities. Bulletin of the American Meteorological Society 82, 2415–2434 (2001).
+
+<|ref|>text<|/ref|><|det|>[[114, 645, 857, 702]]<|/det|>
+21. Vico, G., Way, D. A., Hurry, V. & Manzoni, S. Can leaf net photosynthesis acclimate to rising and more variable temperatures? Plant Cell and Environment 42, 1913–1928 (2019).
+
+<|ref|>text<|/ref|><|det|>[[114, 715, 874, 807]]<|/det|>
+22. Crous, K. Y., Uddling, J. & De Kauwe, M. G. Temperature responses of photosynthesis and respiration in evergreen trees from boreal to tropical latitudes. New Phytologist 234, 353–374 (2022).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 178]]<|/det|>
+23. Way, D. A. & Yamori, W. Thermal acclimation of photosynthesis: On the importance of adjusting our definitions and accounting for thermal acclimation of respiration. Photosynthesis Research 119, 89–100 (2014).
+
+<|ref|>text<|/ref|><|det|>[[113, 193, 850, 248]]<|/det|>
+24. Knauer, J. et al. Higher global gross primary productivity under future climate with more advanced representations of photosynthesis. Sci. Adv. 9, eadh9444 (2023).
+
+<|ref|>text<|/ref|><|det|>[[113, 262, 874, 353]]<|/det|>
+25. Jiang, C. & Ryu, Y. Multi-scale evaluation of global gross primary productivity and evapotranspiration products derived from Breathing Earth System Simulator (BESS). Remote Sensing of Environment 186, 528–547 (2016).
+
+<|ref|>text<|/ref|><|det|>[[113, 367, 850, 388]]<|/det|>
+26. Wright, I. J. et al. The worldwide leaf economics spectrum. Nature 428, 821–827 (2004).
+
+<|ref|>text<|/ref|><|det|>[[113, 402, 872, 457]]<|/det|>
+27. Jiang, C., Ryu, Y., Wang, H. & Keenan, T. F. An optimality-based model explains seasonal variation in C3 plant photosynthetic capacity. Global Change Biology 26, 6493–6510 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 472, 872, 527]]<|/det|>
+28. Zeng, Y. et al. Optical vegetation indices for monitoring terrestrial ecosystems globally. Nat Rev Earth Environ 3, 477–493 (2022).
+
+<|ref|>text<|/ref|><|det|>[[113, 541, 855, 631]]<|/det|>
+29. Mäkelä, A. et al. Developing an empirical model of stand GPP with the LUE approach: analysis of eddy covariance data at five contrasting conifer sites in Europe. Global Change Biology 14, 92–108 (2008).
+
+<|ref|>text<|/ref|><|det|>[[113, 646, 830, 701]]<|/det|>
+30. Mengoli, G. et al. Ecosystem photosynthesis in land-surface models: A first-principles approach incorporating acclimation. J Adv Model Earth Syst 14, (2022).
+
+<|ref|>text<|/ref|><|det|>[[113, 715, 870, 806]]<|/det|>
+31. Smith, N. G., McNellis, R. & Dukes, J. S. No acclimation: instantaneous responses to temperature maintain homeostatic photosynthetic rates under experimental warming across a precipitation gradient in Ulmus americana. AoB PLANTS 12, 1–11 (2020).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 864, 178]]<|/det|>
+32. Loveys, B. R. et al. Thermal acclimation of leaf and root respiration: an investigation comparing inherently fast- and slow-growing plant species. Global Change Biology 9, 895–910 (2003).
+
+<|ref|>text<|/ref|><|det|>[[113, 193, 876, 249]]<|/det|>
+33. Luo, X. & Keenan, T. F. Global evidence for the acclimation of ecosystem photosynthesis to light. Nature Ecology and Evolution 4, 1351–1357 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 262, 857, 353]]<|/det|>
+34. Sendall, K. M. et al. Acclimation of photosynthetic temperature optima of temperate and boreal tree species in response to experimental forest warming. Global Change Biology 21, 1342–1357 (2015).
+
+<|ref|>text<|/ref|><|det|>[[113, 367, 808, 423]]<|/det|>
+35. Battaglia, M., Beadle, C. & Loughhead, S. Photosynthetic temperature responses of Eucalyptus globulus and Eucalyptus nitens. Tree Physiology 16, 81–89 (1996).
+
+<|ref|>text<|/ref|><|det|>[[113, 436, 881, 527]]<|/det|>
+36. Slot, M., Rifai, S. W. & Winter, K. Photosynthetic plasticity of a tropical tree species, Tabebuia rosea, in response to elevated temperature and [CO₂]. Plant Cell Environ 44, 2347–2364 (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 541, 875, 631]]<|/det|>
+37. Stocker, B. D. et al. P-model v1.0: An optimality-based light use efficiency model for simulating ecosystem gross primary production. Geoscientific Model Development 13, 1545–1581 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 645, 864, 737]]<|/det|>
+38. Luo, Y., Gessler, A., D'Odorico, P., Hufkens, K. & Stocker, B. D. Quantifying effects of cold acclimation and delayed springtime photosynthesis resumption in northern ecosystems. New Phytologist nph.19208 (2023) doi:10.1111/nph.19208.
+
+<|ref|>text<|/ref|><|det|>[[113, 750, 876, 806]]<|/det|>
+39. Dusenge, M. E. et al. Limited thermal acclimation of photosynthesis in tropical montane tree species. Glob Change Biol 27, 4860–4878 (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 820, 876, 876]]<|/det|>
+40. Doughty, C. E. et al. Tropical forests are approaching critical temperature thresholds. Nature 621, 105–111 (2023).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 848, 144]]<|/det|>
+41. Huang, M. et al. Air temperature optima of vegetation productivity across global biomes. Nature Ecology and Evolution 3, 772-779 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 158, 857, 214]]<|/det|>
+42. Pastorello, G. et al. The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data. Scientific Data 7, 225 (2020).
+
+<|ref|>text<|/ref|><|det|>[[113, 228, 880, 319]]<|/det|>
+43. Cunningham, S. C. & Read, J. Do temperate rainforest trees have a greater ability to acclimate to changing temperatures than tropical rainforest trees? New Phytologist 157, 55-64 (2003).
+
+<|ref|>text<|/ref|><|det|>[[113, 333, 850, 424]]<|/det|>
+44. Prentice, I. C., Dong, N., Gleason, S. M., Maire, V. & Wright, I. J. Balancing the costs of carbon gain and water transport: Testing a new theoretical framework for plant functional ecology. Ecology Letters 17, 82-91 (2014).
+
+<|ref|>text<|/ref|><|det|>[[113, 437, 856, 493]]<|/det|>
+45. Li, B. et al. BESSv2.0: A satellite-based and coupled-process model for quantifying long-term global land-atmosphere fluxes. Remote Sensing of Environment 295, 113696 (2023).
+
+<|ref|>text<|/ref|><|det|>[[113, 507, 877, 562]]<|/det|>
+46. Harrison, S. P. et al. Eco-evolutionary optimality as a means to improve vegetation and land-surface models. New Phytologist 231, 2125-2141 (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 576, 874, 631]]<|/det|>
+47. Stocker, B. D. et al. Quantifying soil moisture impacts on light use efficiency across biomes. New Phytologist 218, 1430-1449 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 645, 852, 701]]<|/det|>
+48. Lian, X. et al. Multifaceted characteristics of dryland aridity changes in a warming world. Nature Reviews Earth and Environment 2, 232-250 (2021).
+
+<|ref|>text<|/ref|><|det|>[[113, 715, 870, 770]]<|/det|>
+49. Baldocchi, D., Chu, H. & Reichstein, M. Inter-annual variability of net and gross ecosystem carbon fluxes: A review. Agricultural and Forest Meteorology 249, 520-533 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 785, 861, 876]]<|/det|>
+50. Lasslop, G. et al. Separation of net ecosystem exchange into assimilation and respiration using a light response curve approach: Critical issues and global evaluation. Global Change Biology 16, 187-208 (2010).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 877, 144]]<|/det|>
+51. Keenan, T. F. et al. Widespread inhibition of daytime ecosystem respiration. Nature Ecology and Evolution 3, 407-415 (2019).
+
+<|ref|>text<|/ref|><|det|>[[113, 158, 860, 248]]<|/det|>
+52. Papale, D. et al. Towards a standardized processing of Net Ecosystem Exchange measured with eddy covariance technique: Algorithms and uncertainty estimation. Biogeosciences 3, 571-583 (2006).
+
+<|ref|>text<|/ref|><|det|>[[113, 262, 857, 318]]<|/det|>
+53. Lloyd, J. & Taylor, J. A. On the Temperature Dependence of Soil Respiration. Functional Ecology 8, 315 (1994).
+
+<|ref|>text<|/ref|><|det|>[[113, 332, 844, 388]]<|/det|>
+54. Wutzler, T. et al. Basic and extensible post-processing of eddy covariance flux data with REDdyProc. Biogeosciences 15, 5015-5030 (2018).
+
+<|ref|>text<|/ref|><|det|>[[113, 401, 835, 492]]<|/det|>
+55. Meek, D. W., Hatfield, J. L., Howell, T. A., Idso, S. B. & Reginato, R. J. A generalized relationship between photosynthetically active radiation and solar radiation. Agronomy Journal 76, 939-945 (1984).
+
+<|ref|>text<|/ref|><|det|>[[113, 506, 876, 598]]<|/det|>
+56. Gunderson, C. A., O'hara, K. H., Campion, C. M., Walker, A. V. & Edwards, N. T. Thermal plasticity of photosynthesis: The role of acclimation in forest responses to a warming climate. Global Change Biology 16, 2272-2286 (2010).
+
+<|ref|>text<|/ref|><|det|>[[113, 611, 876, 667]]<|/det|>
+57. Smith, N. G. & Dukes, J. S. Short-term acclimation to warmer temperatures accelerates leaf carbon exchange processes across plant types. Global Change Biology 23, 4840-4853 (2017).
+
+<|ref|>text<|/ref|><|det|>[[113, 681, 852, 737]]<|/det|>
+58. Fisher, J. B., Whittaker, R. J. & Malhi, Y. ET come home: potential evapotranspiration in geographical ecology. Global Ecology and Biogeography 20, 1-18 (2011).
+
+<|ref|>text<|/ref|><|det|>[[113, 750, 856, 806]]<|/det|>
+59. Bates, D., Mächler, M., Bolker, B. & Walker, S. Fitting linear mixed-effects models using lme4. J. Stat. Soft. 67, (2015).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 860, 179]]<|/det|>
+60. Ryu, Y. et al. Integration of MODIS land and atmosphere products with a coupled-process model to estimate gross primary productivity and evapotranspiration from 1 km to global scales. Global Biogeochemical Cycles 25, 1–24 (2011).
+
+<|ref|>text<|/ref|><|det|>[[113, 193, 856, 248]]<|/det|>
+61. Kattge, J. et al. TRY – a global database of plant traits. Global Change Biology 17, 2905–2935 (2011).
+
+<|ref|>text<|/ref|><|det|>[[113, 262, 844, 319]]<|/det|>
+62. Chen, J. L., Reynolds, J. F., Harley, P. C. & Tenhunen, J. D. Coordination theory of leaf nitrogen distribution in a canopy. Oecologia 93, 63–69 (1993).
+
+<|ref|>text<|/ref|><|det|>[[113, 333, 877, 389]]<|/det|>
+63. Wright, I. J., Reich, P. B. & Westoby, M. Least-cost input mixtures of water and nitrogen for photosynthesis. American Naturalist 161, 98–111 (2003).
+
+<|ref|>text<|/ref|><|det|>[[113, 403, 835, 458]]<|/det|>
+64. Wang, H. et al. Towards a universal model for carbon dioxide uptake by plants. Nature Plants 3, 734–741 (2017).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[113, 88, 880, 560]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[112, 562, 881, 727]]<|/det|>
+Extended Data Fig. 2: The relationships between canopy photosynthetic capacities and \(\overline{T_{air}}\) over fAPAR and \(\mathrm{T_{air}}\) bins. a, The partial effect of \(\overline{T_{air}}\) on \(\mathrm{A_{max,2000}}\) when \(\overline{PPFD}\) is also incorporated in the modelling \((\mathrm{A_{max,2000}}\sim \overline{T_{air}} +\mathrm{PPFD} + (1|\mathrm{Site}))\) . b, Partial correlation coefficients \((r)\) between \(\mathrm{A_{max,2000}}\) and \(\overline{T_{air}}\) when controlling for \(\overline{PPFD}\) \((\mathrm{A_{max,2000}}\sim \overline{T_{air}} |\overline{PPFD})\) . c, The cross- site thermal acclimation rate \((\gamma_{\mathrm{T}})\) is calculated based on \(\mathrm{A_{max}}\) \((\mathrm{A_{max}}\sim \overline{T_{air}} +\) \((1|\mathrm{Site}))\) . d, The cross- site \(\gamma_{\mathrm{T}}\) is calculated using plant function types (PFTs) as random intercepts \((\mathrm{A_{max,2000}}\sim \overline{T_{air}} +(1|\mathrm{PFT}))\) . Numbers \((\%)\) in parentheses represent the detectability of positive \(\gamma_{T}\) values, which is defined as the percentage of the number of bins displaying a positive \(\gamma_{\mathrm{T}}\) over the total number of bins. Black dots indicate significant \((P< 0.05)\) correlations.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[115, 88, 884, 401]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 403, 883, 530]]<|/det|>
+Extended Data Fig. 3: The PFT-specific thermal acclimation rates \((\gamma_{\mathrm{T}})\) . a–g, PFT-specific \(\gamma_{\mathrm{T}}\) for croplands (CRO) (a), deciduous broadleaf forests (DBF) (b), evergreen broadleaf forests (EBF) (c), evergreen needle-leaf forests (ENF) (d), grasslands (GRA) (e), mixed forests (MF) (f), wetlands (WET) (g). Numbers (\%) in parentheses represent the detectability of positive \(\gamma_{\mathrm{T}}\) values, which is defined as the percentage of the number of bins displaying a positive \(\gamma_{\mathrm{T}}\) over the total number of bins. Black dots indicate significant \((P< 0.05)\) correlations between \(\mathrm{A}_{\mathrm{max,2000}}\) and \(\overline{T_{air}}\) .
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[117, 95, 880, 530]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[113, 538, 872, 700]]<|/det|>
+Extended Data Fig. 4: Analyses of the partial correlation coefficients between \(\mathbf{A}_{\max ,2000}\) and \(\overline{T_{air}}\) derived from long-term flux sites and their relationships with the site-level average \(\overline{T_{air}}\) and variability of \(\overline{T_{air}}\) . a, Geographic distribution of partial correlation coefficients between \(\mathbf{A}_{\max ,2000}\) and \(\overline{T_{air}}\) controlling for \(\overline{P P D}\) , fAPAR and \(\mathrm{T_{air}}\) across sites with observations spanning over five years. b, Relationship between partial correlation coefficients and the site-level averages of \(\overline{T_{air}}\) . c, Relationship between partial correlation coefficients and the site-level standard deviation of \(\overline{T_{air}}\) . The "Forest" biome category includes evergreen needle-leaf forests, deciduous broadleaf forests, and mixed forests. Other PFTs are croplands (CRO), evergreen broadleaf forests (EBF), grasslands (GRA), and wetlands (WET).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 42, 312, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[43, 92, 768, 112]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 312, 149]]<|/det|>
+- AcclimationSILiuetal.docx
+
+<--- Page Split --->
diff --git a/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/images_list.json b/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..bad153f442885c0f3db20cbb51f58785631db219
--- /dev/null
+++ b/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/images_list.json
@@ -0,0 +1,177 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1. Summary of dFLASH LV-REPORT construction, utility, and validation (a) The dFLASH system utilises the lentiviral LV-REPORT construct, consisting of a cis-element multiple cloning site for enhancer insertion, followed by a minimal promoter that drives a transcription factor (TF) dependent cassette that encodes three separate expression markers; a nuclear Tomato fluorophore with a 3x C-terminal nuclear localisation signal (NLS), Herpes Simplex Virus Thymidine Kinase (HSVtk) for negative selection and Neomycin resistance (Neo) for positive selection separated by a 2A self-cleaving peptide (2A). This is followed by a downstream promoter that drives an independent cassette encoding EGFP with a 3x N-terminal NLS, and a Hygromycin resistance selection marker separated by a 2A peptide. (b) This design allows for initial identification of the EGFP fluorophore in nuclei, independent of signal. Expression of the Tomato fluorophore is highly upregulated in a signal-dependent manner. Images shown are monoclonal HEK293T dFLASH-HIF cells. Populations were treated for 48 hours ±DMOG induction of HIF-1α and imaged by HCl. (c) This system can be adapted to a range of different applications. This includes (clockwise) flow cytometry, arrayed screening in a high throughput setting with high content imaging, isolation of highly responsive clones or single cells from a heterogenous population or temporal imaging of pooled or individual cells over time.",
+ "footnote": [],
+ "bbox": [
+ [
+ 135,
+ 160,
+ 848,
+ 460
+ ]
+ ],
+ "page_idx": 14
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. dFLASH provides sensitive readouts to three distinct TF pathways (a-c) Three distinct enhancer elements enabling targeting of three different signalling aspects. (a) Hypoxic response elements (HRE) provide a read out for HIF-1α activation; (b) Progesterone response elements (PRE) derived from progesterone receptor target genes facilitate reporting of progestin signaling; (c) Gal4 response elements (GalRE) enable targeting of synthetic transcription factors to dFLASH such as a GAL4DBD-HIFCAD fusion protein that provides a FIH-dependent reporter response. (d-f) Flow cytometry histograms showing Tomato expression following 48 hr treatments of the indicated dFLASH polyclonal reporter cells (d) HEK293T; 1mM DMOG or 0.1% DMSO (Ctrl), (e) T47D; 100nM R5020 or Ethanol (Ctrl), (f) HEK293T; 1μg/mL Doxycycline (Dox) and 1mM DMOG or Dox and 0.1% DMSO (Ctrl). (g-i) Reporter populations as in d-f were temporally imaged for 38 hours using HCl directly after treatment with (g) 0.5mM DMOG or 0.1% DMSO, (4 replicates) (h) 100nM R5020, 35nM E2, 0.5mM DMOG or 0.1% Ethanol (EtOH) (4 replicates), (i) 0.1% DMSO, 1mM DMOG, 100ng/mL Dox and 0.1% DMSO, or 100ng/mL Dox and 1mM DMOG (4 replicates).",
+ "footnote": [],
+ "bbox": [
+ [
+ 150,
+ 120,
+ 860,
+ 616
+ ]
+ ],
+ "page_idx": 15
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_0.jpg",
+ "caption": "HIF response Pathway",
+ "footnote": [],
+ "bbox": [
+ [
+ 130,
+ 120,
+ 855,
+ 210
+ ]
+ ],
+ "page_idx": 16
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_1.jpg",
+ "caption": "Synthetic FIH Sensor HEK293T dFLASH-synFIH",
+ "footnote": [],
+ "bbox": [
+ [
+ 125,
+ 247,
+ 870,
+ 530
+ ]
+ ],
+ "page_idx": 16
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4. Near homogenous activation of mcdFLASH-HIF by CRISPRoff knockdown of VHL.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 16
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6. Investigating mechanisms for HIF-1α regulation by hit dFLASH-HIF inhibitor RQ500235 and hit activator RQ200674",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 18
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_2.jpg",
+ "caption": "PGR response Pathway",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 19
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_3.jpg",
+ "caption": "Synthetic FIH Sensor HEK293T dFLASH-synFIH",
+ "footnote": [],
+ "bbox": [
+ [
+ 120,
+ 357,
+ 884,
+ 732
+ ]
+ ],
+ "page_idx": 21
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_4.jpg",
+ "caption": "b.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 23
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_5.jpg",
+ "caption": "a.",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 25
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_6.jpg",
+ "caption": "24-hour Activator Screen",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 145,
+ 515,
+ 300
+ ]
+ ],
+ "page_idx": 26
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_7.jpg",
+ "caption": "36-hour Inhibitor Screen",
+ "footnote": [],
+ "bbox": [
+ [
+ 530,
+ 145,
+ 951,
+ 300
+ ]
+ ],
+ "page_idx": 27
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_8.jpg",
+ "caption": "i. Activator Screen",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 342,
+ 515,
+ 487
+ ]
+ ],
+ "page_idx": 27
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_9.jpg",
+ "caption": "24-hour Inhibitor Screen",
+ "footnote": [],
+ "bbox": [
+ [
+ 530,
+ 342,
+ 951,
+ 487
+ ]
+ ],
+ "page_idx": 27
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f.mmd b/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..f34c9f6abaf35da3887bfb62d6985cc864d317ef
--- /dev/null
+++ b/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f.mmd
@@ -0,0 +1,473 @@
+
+# dFLASH; dual FLuorescent transcription factor Activity Sensor for Histone integrated live-cell reporting and high-content screening
+
+David Bersten david.bersten@adelaide.edu.au
+
+The University of Adelaide Timothy Allen The University of Adelaide https://orcid.org/0000- 0002- 8190- 2334 Alison Roennfeldt School of Biological Sciences, University of Adelaide Moganalaxmi Reckdharajkumar School of Biological Sciences, University of Adelaide https://orcid.org/0000- 0002- 9136- 2810 Miaomiao Liu Griffith University Ronald Quinn Griffith University https://orcid.org/0000- 0002- 4022- 2623 Darryl Russell The University of Adelaide Daniel J Peet Murray Whitelaw University of Adelaide
+
+## Article
+
+Keywords:
+
+Posted Date: January 5th, 2024
+
+DOI: https://doi.org/10.21203/rs.3.rs- 3732294/v1
+
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+Additional Declarations: There is NO Competing Interest.
+
+<--- Page Split --->
+
+Version of Record: A version of this preprint was published at Nature Communications on April 7th, 2025. See the published version at https://doi.org/10.1038/s41467-025-58488-w.
+
+<--- Page Split --->
+
+dFLASH; dual FLuorescent transcription factor Activity Sensor for Histone integrated live-cell reporting and high-content screening
+
+Authors: Timothy P. Allen1, Alison E. Roennfeldt1,2, Moganalaxmi Reckdharajkumar1, Miaomiao Liu3, Ronald J. Quinn3#, Darryl L. Russell2#, Daniel J. Peet1#, Murray L. Whitelaw1,4# & David C. Bersten1,2\*
+
+Affiliations: 1. School of Biological Sciences, University of Adelaide, Adelaide, South Australia, Australia 2. Robinson Research Institute, University of Adelaide, South Australia, Australia. 3. Griffith Institute for Drug Discovery, Griffith University, Brisbane, Australia 4. ASEAN Microbiome Nutrition Centre, National Neuroscience Institute, Singapore 169857, Singapore. \*Corresponding author. #labs that contributed to the work
+
+## Abstract
+
+Live- cell reporting of regulated transcription factor (TF) activity has a wide variety of applications in synthetic biology, drug discovery, and functional genomics. As a result, there is high value in the generation of versatile, sensitive, robust systems that can function across a range of cell types and be adapted toward diverse TF classes. Here we present the dual FLuorescent transcription factor Activity Sensor for Histone integrated live- cell reporting (dFLASH), a modular sensor for TF activity that can be readily integrated into cellular genomes. We demonstrate readily modified dFLASH platforms that homogenously, robustly, and specifically sense regulation of endogenous Hypoxia Inducible Factor (HIF) and Progesterone receptor (PGR) activities, as well as regulated coactivator recruitment to a synthetic DNA- Binding Domain- Activator Domain fusion proteins. The dual- colour nuclear fluorescence produced normalised dynamic live- cell TF activity sensing with facile generation of high- content screening lines, strong signal:noise ratios and reproducible screening capabilities ( \(Z' = 0.68 - 0.74\) ). Finally, we demonstrate the utility of this platform for functional genomics applications by using CRISPRoff to modulate the HIF regulatory pathway, and for drug screening by using high content imaging in a bimodal design to isolate activators and inhibitors of the HIF pathway from a \(\sim 1600\) natural product library.
+
+<--- Page Split --->
+
+## Introduction
+
+Cells integrate biochemical signals in a variety of ways to mediate effector function and alter gene expression. Transcription factors (TF) sit at the heart of cell signalling and gene regulatory networks, linking environment to genetic output1,2. TF importance is well illustrated by the consequences of their dysregulation within disease, particularly cancer where TFs drive pathogenic genetic programs3- 5. As a result, there is widespread utility in methods to manipulate and track TF activity in basic biology and medical research, predominantly using TF responsive reporters. Recent examples include enhancer activity screening6 by massively parallel reporter assays, discovery and characterisation of transcription effector domains7,8 and CRISPR- based functional genomic screens that use reporter gene readouts to understand transcriptional regulatory networks2,9. Beyond the use in discovery biology TF reporters are increasingly utilised as sensors and actuators in engineered synthetic biology applications such as diagnostics and cellular therapeutics. For example, synthetic circuits that utilise either endogenous or synthetic TF responses have been exploited to engineer cellular biotherapeutics10. In particular, the synthetic Notch receptor (SynNotch) in which programable extracellular binding elicits synthetic TF signalling to enhance tumour- specific activation of CAR- T cells, overcome cancer immune suppression, or provide precise tumour target specificity 11- 14.
+
+Fluorescent reporter systems are now commonplace in many studies linking cell signalling to TF function and are particularly useful to study single cell features of gene expression, such as stochastics and heterogeneity15, or situations where temporal recordings are required. In addition, pooled CRISPR/Cas9 functional genomic screens rely on the ability to select distinct cell pools from a homogenous reporting parent population. Screens to select functional gene regulatory elements or interrogate chromatin context in gene activation also require robust reporting in polyclonal pools16. Many of the current genetically encoded reporter approaches, by nature of their design, are constrained to particular reporting methods or applications 9,17. For example, high content arrayed platforms are often incompatible with flow cytometry readouts and vice versa. As such there is a need to generate modular, broadly applicable platforms for robust homogenous reporting of transcription factor and molecular signalling pathways.2.
+
+Here we address this by generating a versatile, high- performance sensor of signal regulated TFs. We developed a reporter platform, termed the dual FLuorescent TF Activity Sensor for Histone integrated live- cell reporting (dFLASH), that enables lentiviral mediated genomic integration of a TF responsive reporter coupled with an internal control. The well- defined hypoxic and steroid receptor signalling pathways were targeted to demonstrate that the composition of the modular dFLASH cassette is critical to robust enhancer- driven reporting. dFLASH acts as a dynamic sensor of targeted endogenous pathways as well as synthetic TF chimeras in polyclonal pools by temporal high- content imaging and flow cytometry. Routine isolation of homogenously responding reporter lines enabled robust high content image- based screening ( \(Z' = 0.68 - 0.74\) ) for signal regulation of endogenous and synthetic TFs, as well as demonstrating utility for functional genomic investigations with CRISPRoff. Array- based temporal high content imaging with a hypoxia response element dFLASH successfully identified novel regulators of the hypoxic response pathway, illustrating
+
+<--- Page Split --->
+
+85 the suitability of dFLASH for arrayed drug screening applications. This shows the 86 dFLASH platform allows for intricate interrogation of signalling pathways and 87 illustrates its value for functional gene discovery, evaluation of regulatory elements or 88 investigations into chemical manipulation of TF regulation.
+
+<--- Page Split --->
+
+## Results
+
+Design of versatile dFLASH, a dual fluorescent, live cell sensor of TF activityTo fulfil the need for a modifiable fluorescent sensor cassette that can be integrated into chromatin and enable robust live- cell sensing that is adaptable for any nominated TF, applicable to high content imaging (HCI) and selection of single responding cells from polyclonal pools via image segmentation or flow cytometry (Figure 1c) a lentiviral construct with enhancer regulated expression of Tomato, followed by independent, constitutive expression of d2EGFP as both selectable marker and an internal control was constructed (Figure 1a, b). Three nuclear localisation signals (3xNLS) integrated in each fluorescent protein ensured nuclear enrichment to enable single cell identification by nuclear segmentation, with accompanying image- based quantification of normalised reporter outputs using high content image analysis, or single- cell isolation using FACS in a signal dependent or independent manner. The enhancer insertion cassette upstream of the minimal promoter driving Tomato expression is flanked by restriction sites, enabling alternative enhancer cloning (Figure 1a). The sensor response to endogenous signal- regulated TF pathways was first assessed by inserting a Hypoxia Inducible Factor (HIF) enhancer. HIF- 1 is the master regulator of cellular adaption to low oxygen tension and has various roles in several diseases18- 20. To mediate its transcriptional program, the HIF- 1α subunit heterodimerises with Aryl Hydrocarbon Nuclear Translocator (ARNT), forming an active HIF- 1 complex. At normoxia4, HIF- 1α is post- translationally downregulated through the action of prolyl hydroxylase (PHD) enzymes and the Von Hippel Lindau (VHL) ubiquitin ligase complex21. Additionally, the C- terminal transactivation domain of HIF- 1α undergoes asparaginyl hydroxylation mediated by Factor Inhibiting HIF (FIH), which blocks binding of transcription coactivators CBP/p30022. These hydroxylation processes are repressed during low oxygen conditions, enabling rapid accumulation of active HIF- 1α. HIF- 1α stabilisation at normoxia4 was artificially triggered by treating cells with the hypoxia mimetic dimethyloxalylglycine (DMOG), which inhibits PHDs and FIH, thereby inducing HIF- 1α stabilisation, activity and hypoxic gene expression23. The well characterised regulation and disease relevance of HIF- 1α made it an ideal TF target for prototype sensor development.
+
+## Optimisation of dFLASH sensors
+
+Initially, we tested FLASH constructs with repeats of hypoxia response element (HRE) containing enhancers (RCGTG)24 from endogenous target genes (HRE- FLASH), controlling expression of either nuclear mono (m) or tandem dimer (td)Tomato and observed no DMOG induced Tomato expression in stable HEK293T cell lines (mnucTomato or tdnucTomato, Supp Figure 1a,b). Given the HIF response element has been validated previously24, the response to HIF- 1α was optimised by altering the reporter design, all of which utilised the smaller mnucTomato (vs tdnucTomato) to contain transgene size. We hypothesised that transgene silencing, chromosomal site- specific effects or promoter enhancer coupling/interference may result in poor signal induced reporter activity observed in initial construct designs. As such we optimised the downstream promoter, the reporter composition and incorporated a 3xNLS d2EGFP internal control from the constitutive promoter to monitor chromosomal effects and transgene silencing.
+
+<--- Page Split --->
+
+Dual FLASH (dFLASH) variants incorporated three variations of the downstream promoter (EF1a, PGK and PGK/CMV) driving 3xNLS EGFP (nucEGFP) and 2A peptide linked hygromycin (detailed in Supp Figure 1c) in combination with alternate reporter transgenes that it expressed mnucTomato alone, or mnucTomato- Herpes Simplex Virus Thymidine Kinase (HSVtk)- 2A- Neomycin resistance (Neo). Stable HEK293T and HepG2 HRE- dFLASH cells lines with these backbones were generated by lentiviral transduction and hygromycin selection. The reporter efficacy of dFLASH variant cell lines was subsequently monitored by high content imaging 48 hours after DMOG induction (Supp Figure 1d, e). The downstream composite PGK/CMV or PGK promoters, enabled the strong DMOG induced Tomato or Tomato/GFP expression dramatically outperforming EF1a (Figure 1b and Supp Figure 1d). The composite PGK/CMV provided bright, constitutive nucEGFP expression in both HepG2 and HEK293T cells which was unchanged by DMOG, whereas nucEGFP controlled by the PGK promoter was modestly increased ( \(\sim 2.5\) fold) by DMOG (Supp Figure 1e). Substitution of the mnucTomato with the longer mnucTomato- HSVtk- Neo reporter had no effect on DMOG induced reporter induction in EF1a containing HRE- dFLASH cells, still failing to induce tomato expression (Supp Figure 1f). CMV/PGK containing dFLASH sensors maintained DMOG induction when either the mnucTomato or the mnucTomato/HSVtk/Neo reporters were utilised (Supp Figure 1g, h) although mnucTomato without HSVtk and Neo produced lower absolute mnucTomato fluorescence and a smaller percentage of cells responding to DMOG, albeit with lower background. Taken together these findings indicate that certain backbone compositions prevented or enabled robust activation of the enhancer driven cassette, similar to the suppression of an upstream promoter by a downstream, contiguous promoter previously described25,26 suggesting that the 3' EF1a promoter results in poorly functioning multi- citronic synthetic reporter designs27. Consequently, the PGK/CMV backbone and the mnucTomato/HSVtk/Neo reporter from Supp Figure 1 was chosen as the optimised reporter design (HRE- dFLASH). To confirm that the HRE element was conferring HIF specificity, a no response element dFLASH construct in HEK293T cells treated with DMOG produced no change in either mnucTomato or nucEGFP compared to vehicle- treated populations (Supp Figure 2a). This result, together with the robust induction in response to DMOG (Figure 2D, Supp Figure 1f, 1h), confirms HIF enhancer driven reporter to respond robustly to induction of the HIF pathway (subsequently labelled dFLASH- HIF).
+
+To validate the high inducibility and nucEGFP independence of dFLASH was not specific to the HIF pathway, we generated a Gal4 responsive dFLASH construct (Gal4RE- dFLASH), using Gal4 responsive enhancers22,28. HEK293T cells were transduced with Gal4RE- dFLASH and a dox- inducible expression system to express synthetic Gal4DBDtransactivation domain fusion protein. To evaluate Gal4RE- dFLASH we expressed Gal4DBD fused with a compact VPR (miniVPR), a strong transcriptional activator29 (Supp Figure 2b, 3a- c). We observed \(\sim 25\%\) of the polyclonal population was highly responsive to doxycycline treatment (Supp Figure 2b), with a \(\sim 14\) - fold change in Tomato expression relative to nucEGFP by HCI (Supp Figure 3c) demonstrating our optimised dFLASH backbone underpins a versatile reporting platform.
+
+<--- Page Split --->
+
+## dFLASH senses functionally distinct TF activation pathways
+
+dFLASH senses functionally distinct TF activation pathwaysFollowing the success in utilising dFLASH to respond to synthetic transcription factor and HIF signalling, we explored the broader applicability of this system to sense other TF activation pathways. We chose the Progesterone Receptor (PGR), a member of the 3- Ketosteroid receptor family that includes the Androgen, Glucocorticoid and Mineralocorticoid receptors, as a functionally distinct TF pathway with dose- dependent responsiveness to progestin steroids to assess the adaptability of dFLASH performance. Keto- steroid receptors act through a well- described mechanism which requires direct ligand binding to initiate homodimerization via their Zinc finger DNA binding domains, followed by binding to palindromic DNA consensus sequences. PGR is the primary target of progesterone (P4, or a structural mimic R5020) and has highly context dependent roles in reproduction depending on tissue type30,31,32. We inserted PGR- target gene enhancer sequences containing the canonical NR3C motif (ACANNNTGT31) into dFLASH, conferring specificity to the ketosteroid receptor family to generate PRE- dFLASH (Figure 2b, see Methods).
+
+A chimeric TF system was also established with Gal4DBD fusion proteins to create a synthetic reporter to sense the enzymatic activity of oxygen sensor Factor Inhibiting HIF (FIH). This sensor system termed SynFIH for its ability to synthetically sense FIH activity contained Gal4DBD- HIFCAD fusion protein expressed in a doxycycline- dependent manner, in cells harbouring stably integrated Gal4RE- dFLASH. FIH blocks HIF transactivation through hydroxylation of a conserved asparagine in the HIF- 1α C- terminal transactivation domain (HIFCAD), preventing recruitment of the CBP/p300 co- activator complex22. As FIH is a member of the 2- oxoglutarate dioxygenase family, like the PHDs which regulate HIF post- translationally, it is inhibited by DMOG (Figure 2C), allowing induction of SynFIH- dFLASH upon joint Dox and DMOG signalling (Supp Figure 3d,3e). dFLASH- based sensors for PGR and Gal4DBD- HIFCAD generated in the optimised backbone used for dFLASH- HIF (Figure 2a- c). For the PGR sensor we transduced T47D cells with PRE- dFLASH, as these have high endogenous PGR expression, while for the FIH- dependent system we generated HEK293T cells with Gal4RE- dFLASH and the GAL4DBD- HIFCAD system (dFLASH- synFIH).
+
+Stable polyclonal cell populations were treated with their requisite chemical regulators and reporter responses analysed by either flow cytometry or temporal imaging using HCl at 2hr intervals for 38 hours (Figure 2). Flow cytometry revealed all three systems contain a population that strongly induced nucTomato and maintained nucEGFP (Supp Figure 2). In HEK293T cells, \(\sim 20\%\) of dFLASH- synFIH and \(\sim 50\%\) of dFLASH- HIF population induced Tomato fluorescence substantially relative to untreated controls (Figure 2d, Figure 2f). The \(\sim 20\%\) reporter response to inhibition of FIH activity by DMOG (Supp Figure 2e, Figure 2f) is comparable with what was observed for GalRE- dFLASH response to Gal4DBD- miniVPR expression after equivalent selection (Supp Figure 2b). The PGR reporter in T47D cells showed \(\sim 50\%\) of the population substantively induced Tomato (Figure 2e, Supp Figure 2d). The presence of considerable responsive populations for FIH, PGR, and HIF sensors, reflected in the histograms of the EGFP positive cells (Figure 2d- f) indicated that isolation of a highly responsive clone or subpopulations can be readily achievable for a range of transcription response types. Importantly, the induction of dFLASH- synFIH by
+
+<--- Page Split --->
+
+Dox/DMOG co- treatment was ablated and displayed high basal Tomato levels in FIH knockout dFLASH- synFIH cells (Supp Figure 3e), indicating that the dFLASH- synFIH specifically senses FIH enzymatic activity.
+
+All dFLASH systems showed consistent signal- dependent increases in reporter activity out to 38 hours by temporal HCl enabling polyclonal populations of dFLASH to track TF activity (Figure 2g- i). PRE- dFLASH was more rapidly responsive to R5020 ligand induction ( \(\sim 6\) hours, Figure 2h) than dFLASH- HIF and dFLASH- synFIH to DMOG or Dox/DMOG treatment, respectively ( \(\sim 10\) hours, Figure 2g, i). Treatment of PRE- dFLASH with estrogen (E2), which activates the closely related Estrogen Receptor facilitating binding to distinct consensus DNA sites to the PGR, or the hypoxia pathway mimetic DMOG, failed to produce a response on PRE- dFLASH (Figure 2h). This indicates that the PRE enhancer element is selective for the ketosteroid receptor family (also see below), and that enhancer composition facilitates pathway specificity. We also observed a signal- dependent change in EGFP expression by flow cytometry in the T47D PRE- dFLASH reporter cells (Supp Figure 2g) but did not observe a significant change in EGFP expression for HEK293T or HEPG2 dFLASH- HIF (Supp Figure 1c, Supp Figure 2c) or in HEK293T dFLASH- synFIH cells (Supp Figure 2h), with only a small change with Gal4RE- dFLASH with Gal4DBD- miniVPR (Supp Figure 2b). While this change in T47D cells was not detected in the other cellular contexts (see below), it highlights that care needs to be taken in confirming the utility of the constitutive nucEGFP as an internal control in certain scenarios.
+
+## Monoclonal dFLASH cell lines confer robust screening potential in live cells
+
+The observed heterogenous expression of dFLASH within polyclonal cell pools is useful in many assay contexts but reduces efficiency in arrayed high content screening experiments and incompatible with pooled isolation of loss of function regulators. Therefore, monoclonal HEK293T and HepG2 dFLASH- HIF, T47D and BT474 PRE- dFLASH and HEK293T dFLASH- synFIH cell lines were derived to increase reliability of induction, as well as consistency and homogeneity of reporting (Figure 3, Supp Figure 4). The isolated mcdFLASH- synFIH and mcdFLASH- HIF lines also demonstrated constitutive signal insensitive nucEGFP expression (Supp Figure 4a,b,i). While the T47D PRE- mcdFLASH showed a small increase in nucEGFP in response to R5020, this did not preclude the use in normalisation of high content imaging experiments (see below).
+
+No change in EGFP in BT474 PRE- mcdFLASH cells indicates that strong transactivation leading to promoter read through or cell- type specific effects may be at play. Flow cytometry of monoclonal dFLASH cell lines with their cognate ligand inducers (DMOG (Figure 3b), R5020 (Figure 3f) or Dox/DMOG (Figure 3j)) revealed robust homogeneous induction of mnucTomato in all cell lines. Using temporal high content imaging we also found that clonally derived lines displayed similar signal induced kinetics as the polyclonal reporters although displayed higher signal to noise and increased consistency (Figure 3, Supp Figure 4i). Using physiologically relevant concentrations of steroids or steroid analogs (10nM- 35nM), the PRE- mcdFLASH lines selectively respond to R5020 (10nM) not E2 (35nM), DHT (10nM), Dexamethasone (Dex, 10nM) or Retinoic acid (RA, 10nM) (Figure 3g, Supp Figure 4i). In addition,
+
+<--- Page Split --->
+
+dose response curves of R5020 mediated Tomato induction indicate that PRE- mcdFLASH line responds to R5020 with an \(\mathrm{EC}_{50} \sim 200\mathrm{pM}\) , in agreement with orthogonal methods33 (Supp Figure 4g, h). This suggests that the PRE- mcdFLASH responds sensitively and selectively to PGR selective agonist R5020, with the potential for high- content screening for modulators of PGR activity. As such, we term this line mcdFLASH- PGR from herein, for its specific ability to report on PGR activity at physiological steroid concentrations.
+
+The temporal HCl of populations (Figure 2 and Figure 3) were imaged every 2hrs and do not inherently provide single- cell temporal dynamics of transcriptional responses. Using clonally derived mcdFLASH- PGR or mcdFLASH- HIF lines we also imaged transcriptional responses to R5020 or DMOG, respectively every 15mins (Supp Video 1 and 2). High temporal resolution imaging has the potential to monitor transcriptional dynamics in single cells, facilitated by the dual fluorescent nature of dFLASH. Taken together this indicates that clonal lines display improved signal to noise and assay consistency, possibly enabling high content screening experiments.
+
+Typically, high- content screening experiments require high in- plate and across plate consistency, therefore we evaluated mcdFLASH lines (HIF- 1α, PGR, FIH) across multiple plates and replicates. System robustness was quantified with the Z' metric34 accounting for fold induction and variability between minimal and maximal dFLASH outputs. Signal induced mnucTomato fluorescence across replicates from independent plates was highly consistent (Z' 0.68- 0.74) and robust (9.3- 11.8 fold, Figure 3 d, h, l) the signal induced changes in activity for mcdFLASH- HIF and mcdFLASH- FIH were driven by increased mnucTomato, with minimal changes in nucEGFP (Figures 3e and 3m). Despite the changes previously observed in nucEGFP mcdFLASH- PGR in T47D cells provided equivalent reporter to the other systems, (Figure 3h, i) as a result, monoclonal mcdFLASH cell lines represent excellent high- throughput screening systems routinely achieving Z' scores \(>0.5\) . Importantly, the induction of the mcdFLASH lines (HEK293T and HepG2 mcdFLASH- HIF, T47D mcdFLASH- PGR and HEK293T mcdFLASH- SynFIH) remained stable over extended passaging (months), enabling protracted large screening applications.
+
+## dFLASH-HIF CRISPR-perturbations of the HIF pathway
+
+The robust signal window and high Z' score of mcdFLASH- HIF cell line, coupled with facile analysis by flow cytometry and HCl, indicates that the reporter system is amenable to functional genomic screening. We utilised the recently developed CRISPRoffv2.1 system35 to stably repress expression of VHL, which mediates post- translational downregulation of the HIF- 1α pathway36,37. We generated stable mcdFLASH- HIF cells expressing a guide targeting the VHL promoter and subsequently introduced CRISPRoffv2.1 from either a lentivirus driven by an EF1a or SFFV promoter (Figure 4a, b). Cells were then analysed by flow cytometry 5- or 10- days post selection to determine if measurable induction of mcdFLASH- HIF reporter was modulated by VHL knockdown under normoxic conditions (Supp Figure 6, Figure 4c, 4d). As expected, mcdFLASH- HIF/sgVHL cells expressing CRISPRoffv2.1 from either promoter induced the mcdFLASH- HIF reporter in \(\sim 35\%\) by 5 days and the majority of cells ( \(\sim 60\%\) ) by 10 days as compared to parental cells. Demonstration that mcdFLASH- HIF is responsive to CRISPRi/off perturbations of key regulators of the
+
+<--- Page Split --->
+
+HIF pathway illustrates the potential for the dFLASH platform to provide a readout for CRISPR screens at- scale in a larger format including genome- wide screens.
+
+## dFLASH facilitates bimodal screening for small molecule discovery
+
+dFLASH facilitates bimodal screening for small molecule discoveryManipulation of the HIF pathway is an attractive target in several disease states, such as in chronic anaemia38 and ischemic disease39 where its promotion of cell adaption and survival during limiting oxygen is desired. Conversely, within certain cancer subtypes40,41 HIF signalling is detrimental and promotes tumorigenesis. Therapeutic agents for activation of HIF- \(\alpha\) signalling through targeting HIF- \(\alpha\) regulators were initially discovered using in vitro assays. However, clinically effective inhibitors of HIF- \(1\alpha\) signalling are yet to be discovered42. The biological roles for HIF- \(1\alpha\) and closely related isoform HIF- \(2\alpha\) , which share the same canonical control pathway, can be disparate or opposing in different disease contexts requiring isoform selectivity for therapeutic intervention43. To validate that HIF- \(1\alpha\) is the sole isoform regulating mcdFLASH- HIF in HEK293T cells44 tandem HA- 3xFLAG epitope tags were knocked in to the endogenous HIF- \(1\alpha\) and HIF- \(2\alpha\) C- termini allowing directly comparison by immunoblot45 and confirmed HIF1a is predominant isoform (Supp Figure 5a). Furthermore, there was no change in DMOG induced mnucTomato expression in HEK293T mcdFLASH- HIF cells when co- treated for up to 72 hours with the selective HIF2a inhibitor PT- 2385 (Supp Figure 5b), consistent with the minimal detection of HIF- \(2\alpha\) via immunoblot. This confirmed that our HEK293T dFLASH- HIF cell line specifically reports on HIF- 1 activity and not HIF- 2, indicating that it may be useful for identification of drugs targeting the HIF- \(1\alpha\) pathway.
+
+dFLASH- HIF facilitates multiple measurements across different treatment regimens and time points, enabling capture of periodic potentiated and attenuated HIF signalling during a single experiment. Having validated the robust, consistent nature of mcdFLASH- HIF, we exploited its temporal responsiveness for small molecule discovery of activators or inhibitors of HIF- \(1\alpha\) signalling in a single, bimodal screening protocol. To test this bimodal design, we utilised a natural product library of 1595 compounds containing structures that were unlikely to have been screened against HIF- \(1\alpha\) prior. We first evaluated library compounds for ability to activate the reporter after treatment for 36 hours (Figure 5a) or 24 hours (Figure 5d). The selection of two different screening time points was to minimise any potential toxic effects of compounds at the later time points. Consistency of compound activity between the two screens was assessed by Pearson correlations (Supp Figure 7i, \(\mathrm{R} = 0.79\) , \(\mathrm{p}< 2.2\times 10^{- 16}\) ). Lead compounds were identified by their ability to increase mnucTomato/nucEGFP (Figure 5b, c) and mnucTomato MFI more than 2SD compared with vehicle controls, with less than 2SD decrease in nucEGFP (21/1595 compounds (1.3%) each expt; Supp Figure 7a, e) and an FDR adjusted P score <0.01 across both screens (3/1595 (0.18%) compounds; Supp Figure 7b, f). After imaging of reporter fluorescence to determine these compound's ability to activate HIF- \(1\alpha\) we then treated the cells with 1mM DMOG and imaged after a further 36- hour (Figure 5c) and 24- hour (Figure 5f) period. Again, consistency of compound activity was assessed by Person correlation (Supp Figure 7j, \(\mathrm{F}\) , \(\mathrm{R} = 0.62\) , \(\mathrm{p}< 2.2\times 10^{- 16}\) ). Lead compounds were defined as those exhibiting a decrease in mnucTomato MFI >2SD from DMOG- treated controls in each screen without changing nucEGFP >2SD relative to the DMOG- treated controls (26/1595 compounds (1.3%) (36hr treatment) and
+
+<--- Page Split --->
+
+13/1595 compounds (<1%) (24hr treatment); Supp Figure 7c, g), and decrease in mnucTomato/nucEGFP >2SD with an FDR adjusted P score < 0.01 (3/1595 compounds (0.18%) across both expt; Supp Figure 7d, h).
+
+## dFLASH identified novel and known compounds that alter HIF TF activity.
+
+We confirmed 11 inhibitors and 18 activators of HIF1a activity identified from the pilot screen at three concentrations (Supp Figure 8a, 9a) identifying RQ500235 and RQ200674 (Figure 6a, d) as previously unreported HIF- 1α inhibiting or stabilising compounds, respectively. RQ200674 increased reporter activity 2- fold in repeated assays (Figure 6d) and stabilised endogenously tagged HIF- 1α at normoxia in HEK293T cells (Supp Figure 8b). Mechanistically, RQ200674 had weak iron chelation activity in an in vitro chelation assay (Figure 6e), suggesting it intersects with the HIF- 1α pathway by sequestering iron similar to other reported HIF stabilisers. In the inhibitor compound dataset, Celastarol and Flavokawain B downregulated the reporter at several concentrations (Supp Figure 9b, c). Celastarol is a previously reported HIF- 1α inhibitor46- 48 and Flavokawain B is a member of the chalcone family which has previously exhibited anti- HIF- 1α activity49. RQ500235 was identified as a HIF- 1 inhibitor by mcdFLASH- HIF screening. Dose dependent inhibition of mcdFLASH- HIF (Figure 6a) correlated with a dose- dependent decrease in protein expression by immunoblot (Figure 6C). We observed significant (p=0.0139) downregulation of HIF- 1α transcript levels (Figure 6D) and were unable to rescue HIF- 1α protein loss with proteasomal inhibition (Supp Figure 9d), indicating RQ500235 was decreasing HIF- 1α at the RNA level. More broadly however, the identification of these compounds by mcdFLASH- HIF in the bimodal set up demonstrates successful application of the dFLASH platform to small molecule discovery efforts for both gain and loss of TF function.
+
+<--- Page Split --->
+
+## Discussion
+
+We designed and optimised dFLASH to offer a versatile, robust live- cell reporting platform that is applicable across TF families and allows for facile high- throughput applications. We validated dFLASH against three independent signal- responsive TFs, two with endogenous signalling pathways (dFLASH- PRE for Progesterone receptors; dFLASH- HRE for hypoxia induced transcription factors) and a synthetic system for a hybrid protein transcriptional regulator (dFLASH- Gal4RE). Each dFLASH construct produced robustly detected reporter activity by temporal high- content imaging and FACS after signal stimulation for its responsive TF (Figure 2,3). The use of previously validated enhancer elements for HIF24 and synthetic Gal4 DNA binding domains22,28 demonstrated that dFLASH can be adapted toward both endogenous and synthetic pathways displaying highly agonist/activator- specific responses, indicating utility in dissecting and targeting distinct molecular pathways. mcdFLASH lines distinct pathways produced highly consistent ( \(Z' = 0.68 - 0.74\) ) signal induced Tomato induction measured by high content imaging suggesting dFLASH is ideally suited to arrayed high- throughput screening (Figure 3). In addition, mcdFLASH lines also displayed homogenous signal induced reporter induction by flow cytometry indicating that pooled high content screening would also be possible.
+
+Indeed, reporter systems like dFLASH have been increasingly applied to functional genomic screens which target specific transcriptional pathways9,50- 52. CRISPRoff mediated downregulation of the core HIF protein regulator, VHL produced distinct tomato expressing cell pools (Figure 4), demonstrating genetic perturbations of endogenous TF signalling pathways. The robust induction of the dFLASH- HIF reporter upon VHL knockdown in the majority of cells indicates that whole genome screening would also be successful9,17,50,53.
+
+Using the HIF- 1 \(\alpha\) specific reporter line, mcdFLASH- HIF, the application of high- content screening was exemplified. This approach was successful in discovering a novel activator and novel inhibitor of the HIF pathway, as well as previously identified inhibitory compounds. This ratified dFLASH as a reporter platform for arrayed- based screening and demonstrates the utility of the linked nucEGFP control for rapid hit bracketing. The novel inhibitor RQ500235 was shown to downregulate HIF- 1 \(\alpha\) transcript levels, like another HIF- 1 \(\alpha\) inhibitor PX- 47854,55. As PX- 478 has demonstrated anti- cancer activity in several cell lines 55,56 and preserved \(\beta\) - cell function in diabetic models54, a future similar role may exist for an optimised analogue of RQ500235.
+
+The dFLASH system is characterised by some distinct advantages which may enable more precise dissection of molecular pathways. The ability to control for cell- to- cell fluctuations and to decouple generalised or off- target effects on reporter function may aid the precision necessary for large drug library or genome- wide screening applications57. In addition, dFLASH, unlike many other high- throughput platforms can be used to screen genetic or drug perturbations of temporal transcriptional dynamics or as used here at multiple time points. Also, the results indicate that dFLASH is ideally suited to array- based functional genomics approaches58 allowing for multiplexing with other phenotypic or molecular outputs59,60 2,61.
+
+<--- Page Split --->
+
+The dFLASH approach has some limitations. The fluorescent nature of dFLASH limits the chemical space by which it can screen due to interference from auto- fluorescent compounds. In addition, we acknowledge that fluorescent proteins require \(\mathrm{O_2}\) for their activity and this limits the use of mnucTomato as a readout of hypoxia. Also, while the backbone design has been optimised for a robust activation of a variety of transcription response pathways, the mechanistic underpinning of this is unclear and could be further improved, providing insights into the sequence and architectural determinants of enhancer activation in chromatin. In addition to the strong effect of the dFLASH downstream promoter on upstream enhancer activity it is clear that either the distance between contiguous promoter/enhancer or the sequence composition of the linker has a functional consequence on enhancer induction.
+
+The incorporation of robust native circuits such as those described here (Hypoxia or Progesterone) has the potential to allow the manipulation or integration of these pathways into synthetic biology circuitry for biotherapeutics. In these cases, it is critical that robust signal to noise is achieved for these circuits to effectively function in biological systems. Further, the use of a synthetic approach to 'sense' FIH enzymatic activity through the HIF- CAD:P300/CBP interaction opens up the possibility that other enzymatic pathways that lack effective in vivo activity assay may also be adapted. We also envisage that dFLASH could be adapted to 2- hybrid based screens as a complement to other protein- protein interaction approaches.
+
+The ability to temporally track TF regulated reporters in populations and at the single- cell level enable dFLASH to be used to understand dynamics of transcriptional responses as has been used to dissect mechanisms of synthetic transcriptional repression7,8 or understand notch ligand induced synthetic transcriptional dynamics62. For instance, synthetic reporter circuits have been used to delineate how diverse notch ligands induce different signalling dynamics62. The large dynamic range of the dFLASH- PGR and HIF reporter lines in conjunction with the high proportion of cells induced in polyclonal pools (Figure 2) also suggests dFLASH as a candidate system for forward activity- based enhancer screening. These approaches have been applied to dissect enhancer activity or disease variants with other similar systems such as lentiviral- compatible Massively Parallel Reporter Assays (LentiMPRA)63,64. However, the use of the internal control normalisation provided by dFLASH may be useful in separating chromosomal from enhancer driven effects in forward enhancer screens.
+
+Given dFLASH has robust activity in both pooled and arrayed formats, it offers a flexible platform for investigations. dFLASH can be used to sense endogenous and synthetic transcription factor activity and represents a versatile, stable, live- cell reporter system of a broad range of applications.
+
+<--- Page Split --->
+
+
+Figure 1. Summary of dFLASH LV-REPORT construction, utility, and validation (a) The dFLASH system utilises the lentiviral LV-REPORT construct, consisting of a cis-element multiple cloning site for enhancer insertion, followed by a minimal promoter that drives a transcription factor (TF) dependent cassette that encodes three separate expression markers; a nuclear Tomato fluorophore with a 3x C-terminal nuclear localisation signal (NLS), Herpes Simplex Virus Thymidine Kinase (HSVtk) for negative selection and Neomycin resistance (Neo) for positive selection separated by a 2A self-cleaving peptide (2A). This is followed by a downstream promoter that drives an independent cassette encoding EGFP with a 3x N-terminal NLS, and a Hygromycin resistance selection marker separated by a 2A peptide. (b) This design allows for initial identification of the EGFP fluorophore in nuclei, independent of signal. Expression of the Tomato fluorophore is highly upregulated in a signal-dependent manner. Images shown are monoclonal HEK293T dFLASH-HIF cells. Populations were treated for 48 hours ±DMOG induction of HIF-1α and imaged by HCl. (c) This system can be adapted to a range of different applications. This includes (clockwise) flow cytometry, arrayed screening in a high throughput setting with high content imaging, isolation of highly responsive clones or single cells from a heterogenous population or temporal imaging of pooled or individual cells over time.
+
+<--- Page Split --->
+
+
+Figure 2. dFLASH provides sensitive readouts to three distinct TF pathways (a-c) Three distinct enhancer elements enabling targeting of three different signalling aspects. (a) Hypoxic response elements (HRE) provide a read out for HIF-1α activation; (b) Progesterone response elements (PRE) derived from progesterone receptor target genes facilitate reporting of progestin signaling; (c) Gal4 response elements (GalRE) enable targeting of synthetic transcription factors to dFLASH such as a GAL4DBD-HIFCAD fusion protein that provides a FIH-dependent reporter response. (d-f) Flow cytometry histograms showing Tomato expression following 48 hr treatments of the indicated dFLASH polyclonal reporter cells (d) HEK293T; 1mM DMOG or 0.1% DMSO (Ctrl), (e) T47D; 100nM R5020 or Ethanol (Ctrl), (f) HEK293T; 1μg/mL Doxycycline (Dox) and 1mM DMOG or Dox and 0.1% DMSO (Ctrl). (g-i) Reporter populations as in d-f were temporally imaged for 38 hours using HCl directly after treatment with (g) 0.5mM DMOG or 0.1% DMSO, (4 replicates) (h) 100nM R5020, 35nM E2, 0.5mM DMOG or 0.1% Ethanol (EtOH) (4 replicates), (i) 0.1% DMSO, 1mM DMOG, 100ng/mL Dox and 0.1% DMSO, or 100ng/mL Dox and 1mM DMOG (4 replicates).
+
+<--- Page Split --->
+
+
+HIF response Pathway
+
+
+
+Synthetic FIH Sensor HEK293T dFLASH-synFIH
+
+
+
+
+<--- Page Split --->
+
+## Figure 3. Derivation of robust, screen-ready dFLASH clonal lines
+
+(a) Schematic for derivation and assessment of robustness for clonal lines of (b-e) HEK239T dFLASH-HIF (mcdFLASH-HIF), (f-i) T47D dFLASH-PGR (mcdFLASH-PGR) and (j-m) HEK293T dFLASH-synFIH (mcdFLASH-synFIH) were analysed by flow cytometry, temporal HCI over 38 hours and for inter-plate robustness by mock multi-plate high throughput screening with HCI. (b-e) mcdFLASH-HIF was (b) treated with DMOG for 48 hours and assessed for Tomato induction by flow cytometry relative to vehicle controls with fold change between populations displayed and (c) treated with vehicle or 0.5mM DMOG and imaged every 2 hours for 38 hours by HCI (mean ±sem, 8 replicates). (d-e) mcdFLASH-HIF was treated for 48 hours with 1mM DMOG or vehicle (6 replicates/plate, n = 10 plates) by HCI in a high throughput screening setting (HTS-HCI) for (d) normalised dFLASH expression and (e) Tomato MFI alone. (f-i) T47D mcdFLASH-PGR was (f) assessed after 48 hours of treatment with 100nM R5020 by flow cytometry for Tomato induction and (g) treated with 10nM R5020, 35nM E2, 10nM DHT and vehicle then imaged every 2 hours for 38 hours by temporal HCI for normalised dFLASH expression (mean ±sem, 8 replicates). (h-i) T47D mcdFLASH-PGR was assessed by HTS-HCI at 48 hours (24 replicates/plate, n = 5 plates) for (h) dFLASH normalised expression and (i) Tomato MFI alone. (j) HEK293T dFLASH-synFIH was assessed, with 200ng/mL and or Dox and 1mM DMOG by flow cytometry for dFLASH Tomato induction (k) mcdFLASH-synFIH was treated with 100ng/mL Dox, 1mM DMOG and relevant vehicle controls and assessed for reporter induction by temporal HCI (mean ±sem 4 replicates). (l-m) mcdFLASH-synFIH cells were treated with 200ng/mL Dox (grey), 1mM DMOG (red), vehicle (pink) or Dox and DMOG (orange) and assessed by HTS-HCI after 48 hours (24 replicates/plate, n = 3 plates) for (l) normalised dFLASH expression or (m) Tomato MFI induction between Dox and Dox and DMOG treated populations. Dashed lines represent 3SD from relevant vehicle (+3SD) or requisite ligand treated population (-3SD). Fold change for flow cytometry and HTS-HCI (FC) is displayed. Z' was calculated from all analysed plates by HTS-HCI. Z' for all plates analysed was > 0.5.
+
+<--- Page Split --->
+
+
+Figure 4. Near homogenous activation of mcdFLASH-HIF by CRISPRoff knockdown of VHL.
+
+(a) Clonal (1) mcdFLASH-HIF lines derived post-hygromycin (HygroB) selection were transduced first with the (2) sgRNA vector targeting VHL transcriptional start site, followed by puromycin selection (Puro). This pool was subsequently transduced by the (3) CRISPRoffv2.1 virus and selected with blasticidin (BlastS) prior to flow cytometry (on day 5 and 10 post Blasticidin selection). (b) The (1) dFLASH vector with the HRE enhancer was transduced as were 2 variants of the CRISPRoffv2.1 vector with either (3A) EF1α promoter or (3B) SFFV promoter driving the dCas9 expression cassette. (c, d) Flow cytometry for dFLASH-HIF induction in response to the CRISPRoffv2.1 VHL knockdown relative to parental line (Ctrl) with (c) EF1a or (d) SFFV expression constructs after 10 days of selection.
+
+<--- Page Split --->
+
+
+
+<--- Page Split --->
+
+## Figure 5. Bimodal small molecule screening of the HIF signalling pathway with dFLASH-HIF identifies positive and negative regulators
+
+(a) HEK293T mcdFLASH-HIF cells were treated with a 1595 compound library and incubated for 36 hours prior to (b) the first round of HCl normalised dFLASH activity. Compounds that changed EGFP >±2SD are shown in grey and excluded as hits. Compounds that increase Tomato/EGFP >2SD from the vehicle controls (dashed line) are highlighted in red. After the activation screen, the compound wells were then treated with 1mM DMOG for 36 hours prior to the second round of HCl. Compounds that decreased dFLASH activity greater than 2SD from DMOG controls (dashed line) are shown in red. Compounds that changed EGFP >±2SD are shown in grey and excluded as hits. Normalised dFLASH output (Z scoring) for all analysed wells. (d-f) The screening protocol of (a-c) was repeated using 24 hr points for HCl.
+
+<--- Page Split --->
+
+
+Figure 6. Investigating mechanisms for HIF-1α regulation by hit dFLASH-HIF inhibitor RQ500235 and hit activator RQ200674
+
+(a, b) Inhibitor RQ500235 identified from the bimodal screen (a) represses DMOG induced Tomato in dFLASH- HIF cells in a dose dependent manner (n=2, Tom MFI, red; Tom normalised to EGFP, black) and (b) decreases expression of HIF- 1α protein as assessed by immunoblot of whole cell extracts from endogenous HA- Flag tagged HIF- 1α in HEK293T cells. S.E.= short exposure; L.E.= long exposure. (c) RT- PCR shows HIF- 1α transcript is significantly decreased in HEK293T cells treated for 6 hours with RQ500235 (n =3, \*p=0.0139). (d) Activator RQ200674 identified from the bimodal screen recapitulated activation of dFLASH- HIF at 50μM in HEK293T cells (n = 2). (e) in vitro iron chelation assay of RQ200674 displays weak chelating activity at 236μM from line of best fit (n = 3) compared to positive control iron chelator and HIF- 1α activator, dipyridyl.
+
+<--- Page Split --->
+
+639 640 Supplementary Figures 641 642
+
+<--- Page Split --->
+
+
+
+## Supplementary Figure 1. Optimised dFLASH design produces a robust HIF sensor.
+
+(a- b) HEK293T cells with HRE- dFLASH constructs without EGFP and (a) expressing monomeric Tomato or (b) dimeric Tomato were treated \(- / + 1\mathrm{mM}\) DMOG for 48 hours and quantified by FACS. Tomato MFI \(>200\mathrm{AU}\) was used to compare induction (black line). (c- e) HEK293T and HEPG2 cells were transduced with HRE- dFLASH reporters that had different downstream promoters controlling EGFP or Tomato cassette composition and treated for 48 hours \(- / + 1\mathrm{mM}\) DMOG prior to HCl. The (d) Tomato/EGFP MFI ratio and (e) EGFP MFI for each backbone variant was then compared (Data from three independent biological replicates). (f) HEK293T cells transduced with reporter constructs containing the downstream PGK/CMV or EF1a promoters were compared for DMOG induction by HCl after 48 hours of \(- / + 1\mathrm{mM}\)
+
+<--- Page Split --->
+
+658 DMOG treatment (Data from three independent biological replicates). Significance was assessed with a Two- Way ANOVA (\\*\\*\\* p < 0.001, ns = not significant). (g,h) 659 HEK293T cells with the HRE enhancer and different dFLASH backbone compositions 660 of (g) PGK/CMV dFLASH with Tomato alone as the upstream cassette or (h) dFLASH- 661 HIF were treated for 48- hours - /+ 1mM DMOG prior to EGFP analysis and Tomato 662 induction by FACS. 663 664 665
+
+<--- Page Split --->
+
+
+
+Supplementary Figure 2. dFLASH provides a TF-responsive, versatile reporter platform in heterogenous cell pools.
+
+(a-b) HEK293T cells were transduced with (a) dFLASH with no enhancer and treated with 1mM DMOG or 0.1% DMSO (Ctrl) or (b) GalRE-dFLASH and Gal4DBD-miniVPR and treated with H2O (Ctrl) or 1μg/mL Dox for 48 hours prior to FACS. Dot plots of populations' Tomato and EGFP intensity with or without activating chemicals and histograms comparing EGFP and Tomato MFI between control and treated populations are shown. (c-h) Dot plots and EGFP histograms for control and chemical treated (c, f) dFLASH-HIF, (d, g) dFLASH-PR polyclonal pools (to accompany Figure 2a-c) and (e, h) dFLASH-synFIH.
+
+<--- Page Split --->
+
+
+
+Supplementary Figure 3. Synthetic transcription factors drive a strong response from the GalRE- dFLASH reporter and can respond to endogenous signaling pathways.
+
+(a) GAL4DBD-miniVPR is expressed from an independent dox-inducible vector that subsequently binds to GalRE-dFLASH. (b,c) HEK293T GalRE-dFLASH cells were transduced with GAL4DBD-miniVPR expression construct and were treated -/+ doxycycline for 48 hours prior to HCI for (b) Tomato expression (top panels) and EGFP expression (bottom panels). (c) Normalised fluorescence intensity was also quantified for treated populations (n=3, mean ±sem). FC is Fold change between the populations. (d, e) To confirm HEK293T dFLASH-synFIH system was FIH dependent, (d) GalRE-dFLASH and GAL4DBD-HIFCAD vectors were transduced into HEK293T cells with FIH knocked out. (e) FIH KO cells were compared with wildtype HEK293T dFLASH-synFIH (WT) in a 200ng/mL dox background for DMOG-dependent reporter induction by HCI (n=3). (c, e) Significance was assessed by t-test with Welch's correction (ns = not significant, *** p <0.001, ****p <0.0001).
+
+<--- Page Split --->
+
+
+PGR response Pathway
+
+
+
+Synthetic FIH Sensor HEK293T dFLASH-synFIH
+
+
+
+
+<--- Page Split --->
+
+Supplementary Figure 4. Clonal dFLASH cell lines enable improved reporting across different cell types.
+
+(a- c) Flow cytometry of clonal dFLASH- HIF cell lines for (a) HEK293T (see also Figure 3b) and (b,c) HepG2 cells after 48 hours -/+ 0.5mM DMOG. (d- h) dFLASH- PGR functionality was assessed by flow cytometry in (d)T47D (see also Figure 3f) and (e,f) BT474 cells after 48 hours -/+ 100nM R5020. (g,h) T47D dFLASH- PGR cells were treated with increasing concentrations of R5020 (0.01- 100nM, 8 replicates per group) and (g) imaged over 38 hours with temporal HCl or (h) imaged at 48 hours to determine sensitivity to R5020. (i) Comparison of inductions of the T47D mcdFLASH- PGR line to different steroids (10nM R5020, 35nM E2, 10nM DHT, 10nM Dex, 10nM RA) by HCl after 48 hours of treatment. (g) and (i) are the mean±sem of normalised Tomato/GFP (within each expt) from \(n = 3\) independent experiments (24 replicates), except Dex and RA ( \(n = 2\) (16 replicates)). (j, k) Clonally derived HEK293T dFLASH- synFIH cells were (j) analysed by flow cytometry after 48 hours of 200ng/mL Dox -/+ 1mM DMOG (see also Figure 3k) with (k) showing temporal HCl comparisons between monoclonal (mc) and polyclonal (pc) lines (see also Figure 2j).
+
+<--- Page Split --->
+![PLACEHOLDER_29_0]
+
+
+
+b.
+
+![PLACEHOLDER_29_1]
+
+
+<--- Page Split --->
+
+731 Supplementary Figure 5. HIF- 1α is the predominant isoform that affects the 732 dFLASH reporter in HEK293T cells 733 (a) Monoclonal HEK293T cells with endogenously HA- Flag tagged HIF- 1α or HIF- 2α 734 were treated with hypoxia (<1% O2) for 16 hours prior to anti- HA immunoblotting of 735 whole cell extracts. S.E.= short exposure; L.E.= long exposure. Representative of 736 three independent experiments. (b) mcdFLASH- HIF cells were treated -/+ 1mM 737 DMOG and -/+ 10μM of the HIF- 2α antagonist (PT- 2385) as indicated and quantified 738 by HCl over 72- hour period. 739 740 741 742
+
+<--- Page Split --->
+![PLACEHOLDER_31_0]
+
+a.
+
+## Supplementary Figure 6. CRISPRoff mediated VHL knockdown induces mcdFLASH-HIF reporter lines.
+
+(a) HEK293T cells were first transduced with dFLASH-HRE and a clonal reporting line was derived after hygromycin (HygroB) treatment. This line was in turn transduced with the VHL sgRNA vector and selected with puromycin (Puro). This line was then transduced with the CRISPRoffv2.1 vector and selected with blasticidin S (Blast) and populations were subjected to flow cytometry after 5 days or 10 days of selection for analysis of reporter expression. (b-d) dot plots for dFLASH expression from the (b) non-CRISPRoff parental line, (c) EF1a-CRISPRoffv2.1 transduced and (d) SFFVp-CRISPRoffv2.1 populations after 5 or 10 days of blasticidin selection (see also Figure 4).
+
+<--- Page Split --->
+![PLACEHOLDER_32_0]
+
+24-hour Activator Screen
+
+![PLACEHOLDER_32_1]
+
+36-hour Inhibitor Screen
+
+![PLACEHOLDER_32_2]
+
+i. Activator Screen
+
+![PLACEHOLDER_32_3]
+
+24-hour Inhibitor Screen
+
+![PLACEHOLDER_32_4]
+
+
+<--- Page Split --->
+
+Supplementary Figure 7. Hit selections and assessment of bimodal screen reproducibility between independent screens for activators and inhibitors of HIF- 1α.
+
+Compound- induced dFLASH- HIF reporter activity was used to score hits from the (a- d) 36- hour or the (e- h) 24- hour bimodal screens according to Tomato MFI and adjusted P scores. Lines indicate cut offs for hit criteria with hits shown in red for each metric and dismissed compounds that change EGFP \(> \pm 2\) SD shown in grey. (i, j) Pearson correlations of the Tomato/EGFP between the 36- hour and the 24- hour screens for (i) reporter activation ( \(\mathrm{R} = 0.62\) , \(\mathrm{p} < 2.2 \times 10^{- 16}\) ) or (j) reporter inhibition ( \(\mathrm{R} = 0.62\) , \(\mathrm{p} < 2.2 \times 10^{- 16}\) ) for all 1595 compounds screened. Line indicates line of best fit, grey boundary is 95% confidence interval.
+
+<--- Page Split --->
+![PLACEHOLDER_34_0]
+
+
+![PLACEHOLDER_34_1]
+
+
+Supplementary Figure 8. Rescreening of activator hits from 1595 compound small molecule screen reveals RQ200674 causes normoxic stabilisation of HIF- 1α
+
+(a) The 11 top performing hits from the activator screens, including RQ200674 (see also Figure 6d) were rescreened against HEK293T mcdFLASH-HIF at 10μM, 25μM and 50μM. Comparisons between Tomato/GFP and Tomato MFI dFLASH induction shown against vehicle (-ve Ctrl) and 1mM DMOG (+ve Ctrl) treated populations (n=2). (b) Immunoblot of whole cell extracts from HEK293T cells containing endogenously HA-Flag tagged HIF-1α and treated as indicated with vehicle (0.1% DMSO), 1mM DMOG (+ve Ctrl), or 100μM and 200μM of RQ200674 for 18 hours. Representative of 2 independent experiments.
+
+<--- Page Split --->
+![PLACEHOLDER_35_0]
+
+
+<--- Page Split --->
+
+844 Supplementary Figure 9. Flavokawain B, Celastarol and RQ500235 decrease 845 dFLASH- HIF and proteasomal inhibition doesn't rescue RQ500235 impact on 846 HIF- 1α.
+
+844 Supplementary Figure 9. Flavokawain B, Celastarol and RQ500235 decrease 845 dFLASH- HIF and proteasomal inhibition doesn't rescue RQ500235 impact on 846 HIF- 1α. 847 (a- c) The 18 top inhibitory compounds, including (b) Flavokawain B (RQ100976), (c) Celastarol (RQ000155) and RQ500235 (see also Figure 6a) were rescreened against 849 dFLASH- HIF at 10μM, 25μM and 50μM in 1mM DMOG treated 293T dFLASH- HIF 850 cells (24 hours). Comparisons between Tomato/GFP and Tomato MFI dFLASH 851 induction shown against 0.1% DMSO (-ve Ctrl) and 1mM DMOG (+ve Ctrl) treated 852 populations (n=2). (d) Immunoblot of whole cell extracts from HEK293T cells with 853 endogenously HA- Flag tagged HIF- 1α following a 12 hr treatment period with with the 854 indicated combinations of 1 mM DMOG (full12 hr), 50μM RQ500235 (final 6 hr) and 855 10μM MG132 (final 3 hr). Representative of 2 independent experiments. 856 857 858
+
+<--- Page Split --->
+![PLACEHOLDER_37_0]
+
+
+# Supplementary Movie 1. Single cell temporal dynamics of HEK293T mcdFLASH-HIF cells
+
+HEK293T mcdFLASH- HIF cells were seeded at \(1 \times 10^{5}\) cells/dish in Poly- D- Lysine coated plates overnight prior to imaging with spinning disk confocal microscopy at 40x magnification. Cells were imaged every 15 min for 48 hours for Tomato (Magenta) and EGFP (Green) expression. Time stamps are given in top left.
+
+<--- Page Split --->
+![PLACEHOLDER_38_0]
+
+
+# Supplementary Movie 2. Single cell temporal dynamics of T47D mcdFLASH-PGR cells
+
+T47D mcdFLASH- PGR cells were seeded at \(5 \times 10^{5}\) cells/dish in Poly- D- Lysine coated plates overnight prior to imaging with spinning disk confocal microscopy at 40x magnification. Cells were imaged every 15 min for 48 hours for Tomato (Magenta) and EGFP (Green) expression. Time stamps are given in top left.
+
+## Methods:
+
+Plasmid Construction. cDNAs were amplified using the Phusion polymerase (NEB) and assembled into Clal/Nhel digested pLV410 digested backbone by Gibson assembly31. Sequence verified LV- REPORT plasmid sequences and constructs are listed in Supplementary Table 1. Briefly, the plasmids contained an upstream multiple cloning sites followed by a minimal promoter (derived from the pTRE3G minimal promoter) and then followed by a reporter construct mnucTomato/HSVtk- 2a- Neo or other variants). This was then followed by a constitutive promoter (EF1a, PGK or PGK/CMV) driving the expression or hygromycinR cassette with or without a 2a linked d2nucEGFP (Supplementary Figure 1C).
+
+<--- Page Split --->
+
+To improve the performance of our previously reported lentiviral inducible expression systems65, the PGK promoter in Tet-On3G IRES Puro was replaced by digestion with MluI/NheI and insertion of either EF1a-Tet-On3G-2A-puro, EF1a-Tet-On3G-2A-BlastR or EF1a-Tet-On3G-2A-nucTomato using Phusion polymerase (NEB) amplified PCR products from existing plasmids. Plasmids were cloned by Gibson isothermal assembly and propagated in DB3.1 cells (Invitrogen). We also generated a series of constitutive lentiviral plasmids as part of this work pLV- Egl-BlastR (EF1a- Gateway- IRES- BlastR), pLV- Egl- ZeoR (EF1a- Gateway- IRES- ZeoR), pLV- Egl- HygroR (EF1a- Gateway- IRES- HygroR), pLV- SFFVp- gl- BlastR (SFFVp- Gateway- IRES- BlastR), pLV- SV40p- gl- BlastR (SV40p- Gateway- IRES- BlastR). These plasmids were constructed by isothermal assembly of G- Blocks (IDT DNA) or PCR fragments, propagated in ccbD competent cells, sequence verified and deposited with Addgene (Supplementary Table 1).
+
+The Lentiviral backbone expression construct pLV- TET2BLAST- GtwyA was then using to insert expression constructs cloned into pENTR1a by LR Clonase II enzyme recombination (Cat#11791020, Thermo). GAL4DBD- HIFCAD (727- 826aa) and the GAL4DBD28 were cloned into pENTR1a by ScaI/EcoRV or KpnI/EcoRI respectively. The miniVPR sequence29 was cloned into the pENTR1a- GAL4DBD construct at the EcoRI and NotI sites. The pENTR1a vectors were then Gateway cloned into the pLV- TET2PURO- GtwyA vector. pENTR1a- CRISPRoffv2.1 was generated by inserting an EcoRI/NotI digested CRISPRoff2.1 (CRISPRoff- v2.1 was a gift from Luke Gilbert, Addgene #167981) into pENTR1a plasmid. pLV- SFFVp- CRISPRoffv2.1- IRES- BLAST and pLV- EF1a- CRISPRoffv2.1- IRES- BLAST were generated by pENTR1a by LR Clonase II enzyme recombination (Cat#11791020, Thermo). All Lentiviral plasmids were propagated in DH5a without any signs of recombination.
+
+Enhancer element cloning. The 12x HRE enhancer from hypoxic response target genes (PGK1, ENO1 and LDHA) was liberated from pUSTdS- HRE12- mCMV- lacZ24 with XbaI/SpeI and cloned into AvrII digested pLV- REPORT plasmids. Progesterone responsive pLV- REPORT- PRECat PRECat was cloned by isothermal assembly of a G- Block (IDT- DNA) containing enhancer elements from 5 PGR target gene enhancers (Zbtb16, Fkbp5, Slc17a11, Erfnb1, MT2)31 into AscI/Clal digested pLV- REPORT(PGK/CMV). Gal4 response elements (5xGRE) were synthesised (IDT DNA) with Clal/AscI overhangs and cloned into Cla/AscI digested pLV- REPORT(PGK/CMV). Sequences are in Supplementary Table 2.
+
+Mammalian cell culture and ligand treatment. HEK293T (ATCC CRL- 3216), HEPG2 (ATCC HB- 8065) line were grown in Dulbecco's Modified Eagle Medium (DMEM high glucose) + pH 7.5 HEPES (Gibco), 10% Foetal Bovine Serum (Corning 35- 076- CV or Serana FBS- AU- 015), 1% penicillin- streptomycin (Invitrogen) and 1% Glutamax (Gibco). T47D (ATCC HTB- 133) or BT474 (ATCC HTB- 20) were grown in RPMI 1640 (ATCC modified) (A1049101 Gibco) with 10% Foetal Bovine Serum (Fisher Biotech FBS- AU- 015) and 1% penicillin- streptomycin66. Cells were maintained at 37°C and at 5% CO2. Clonal lines were isolated by either limiting dilution or FACS single cell isolation into 96 wells trays. Resultant monoclonal populations were evaluated for single colony formation or assessed by HCI or FACS. Ligand treatments were done 24 hours after seeding of cells in requisite plate or vessel. Standard
+
+<--- Page Split --->
+
+concentrations and solvent, unless specified otherwise, are 200ng/mL Doxycycline (Sigma, H₂O), 0.5mM or 1mM DMOG (Cayman Scientific, DMSO), 100nM R5020 (Perkin- Elmer NLP004005MG, EtOH), 35nM Estradiol (E2, Sigma E2758, EtOH), 10nM all- trans retinoic acid (RA, Sigma #R2625), 10nM Dihydrotestosterone (DHT, D5027), 10nM Dexamethasone (Dex, Sigma D4902), 10μM PT- 2385 (Abcam, DMSO).
+
+Lentiviral Production & stable cell line production. Near confluent HEK293T cells were transfected with either psPAX2 (Addgene #12260) and pMD2.G (Addgene #12259) or pCMV- dR8.2 dvpr (Addgene #8455), pRSV- REV (Addgene; #12253) and pMD2.G along with the Lentivector (described above) and PEI (1μg/μl, polyethyleneimine) (Polysciences, USA), Lipofectamine 2000, or Lipofectamine 3000 at a 3μl:1μg ratio with DNA. Media changed 1- day post- transfection to complete media or Optimem. Virus was harvested 1- 2 days post- transfection, then viral media was filtered (0.45μM or 0.22μM, Sartorius) before the target cell population was transduced at a MOI < 1. Cells were incubated with virus for 48 hours prior media being exchanged for antibiotic containing complete media. Standard antibiotic concentrations were 140μg/mL hygromycin (ThermoFisher Scientific #10687010), 1μg/mL Puromycin (Sigma; #P8833) or 10μg/mL Blasticidin S (Sigma; CAT#15205).
+
+Generation of CRISPR knockout or knockdown cell lines. Generation of CRISPR knockout guides and plasmids against FIH has been previously described67. These guides were transfected into HEK293T cells and with PEI at a 3μg:1μg ratio then clonally isolated as above. Knockouts were confirmed with PCR amplification and sanger sequencing coupled with CRISPR- ID68. FIH knockouts were selected via serial dilution and confirmation of knockout by sequencing and T7E1 assay. The VHL sgRNA guides were selected from the Dolcetto CRISPRi library69 with BsmBI compatible overhangs (Supplementary Table 3). These oligos were annealed, phosphorylated then ligated into BsmBI- digested pXPRO50 (Addgene#9692), generating XPR- 050- VHL. Monoclonal HEK293T LV- REPORT- 12xHRE cell lines were transduced with the XPR- 050- sgVHL virus, and stable cell lines selected with Puromycin. Subsequently, LV- SFFVp- CRISPRoffv2.1- IRES- BlastR or LV- EF1a- CRISPRoffv2.1- IRES- BlastR virus was infected into HEK293T LV- REPORT- 12xHRE/XPR- 050- sgVHL stable cells and selected with Blasticidin S (15μg/ml) for 5 days. FACS was used to assess activation of the dFLASH- HRE reporter in parental (dFLASH- HRE/sgVHL) or CRISPRoffv2.1 expressing cells at day 5 or day 10 after Blasticidin S addition.
+
+CRISPR knock- in of tags to endogenous HIF- 1α and HIF- 2α. CRISPR targeting constructs clones targeting adjacent to the endogenous HIF- 1α and HIF- 2α stop codons70. Constructs were cloned into px330 by ligating annealed and phosphorylated oligos with Bbsl digested px330, using hHIF- 1α and hHIF- 2α CTD sgRNA (Supplementary Table 3). Knock- in of HA- 3xFlag epitopes into the endogenous HIF- 1α or HIF- 2α loci in HEK293T cells was achieved by transfection with 0.625 μg of pNSEN, 0.625μg of pEFIRES- puro6, 2.5μg of px330- sgHIF- α CTD, and 1.25μg of ssDNA HDR template oligo containing flanking homology to CRISPR targeting site the tag insertion and a PAM mutant into \(\sim 0.8 \times 10^{6}\) cells using PEI (3:1). 48 hours after transfection, the medium was removed from cells and replaced with fresh medium supplemented with 2 μg/ml puromycin for 48 hours and the cell medium was changed
+
+<--- Page Split --->
+
+to fresh medium without puromycin. 48 hours later cells were seeded by limiting dilution into 96- well plates at an average of 0.5 cells/well. Correct integration was identified by PCR screening using HIF- \(1\alpha\) and HIF- \(2\alpha\) gDNA screening primers (Supplementary Table 4). Positive colonies resiolated as single colonies by limiting dilution. Isolated HIF- \(1\alpha\) and HIF- \(2\alpha\) tag insertions were confirmed by PCR, sanger sequencing and western blotting.
+
+High Content Imaging (HCI). Cells were routinely seeded at \(1 \times 10^{4}\) to \(5 \times 10^{4}\) cells per well in black walled clear bottom 96 well plates (Costar Cat#3603), unless otherwise stated. Cell populations were imaged in media at the designated time points at \(10 \times\) magnification and \(2 \times 2\) binning using the ArrayScan™ XTI High Content Reader (ThermoFisher). Tomato MFI and EGFP MFI was imaged with an excitation source of \(560 / 25 \text{nm}\) and \(485 / 20 \text{nm}\) respectively. Individual nuclei were defined by nuclear EGFP expression, nuclear segmentation and confirmed to be single cells by isodata thresholding. Nuclei were excluded from analysis when they couldn't be accurately separated from neighbouring cells and background objects, cells on image edges and abnormal nuclei were also excluded. EGFP and Tomato intensity was then measured for each individual nucleus from at least 2000 individual nuclei per well. Fixed exposure times were selected based on \(10 - 35\%\) peak target range. Quantification of the images utilised HCS Studio™ 3.0 Cell Analysis Software (ThermoFisher). For assessment of high throughput robustness of each individual reporting line in a high throughput setting (HTS- HCI), replicate 96 well plates were seeded for the HIF (10 plates), PGR (5 plates) and synFIH (3 plates) monoclonal reporter lines and imaged as above at 48 hours. For the HIF line, each plate had 6 replicates per treatment (vehicle or DMOG) per plate. For the PGR, 24 replicates per treatment, either vehicle or R5020 per plate were present with edge wells excluded. 24 replicates per treatment were also used for synFIH, with system robustness assessed between the DOX/DMSO and DOX/DMOG treatment groups. Z' and fold change (FC) for the Tomato/EGFP ratio for each individual plate was then calculated as per 34:
+
+\[Z^{\prime} = 1 - \frac{(3\sigma_{c + } - 3\sigma_{c - })}{|\mu_{c + } - \mu_{c - }|}\]
+
+Z' for every plate across each system was confirmed to be \(>0.5\) . Overall robustness of each system is the average of every individual Z' and FC for each system. For temporal high content imaging, HIF, PGR and synHIF lines were seeded in plates and treated with requisite ligands immediately prior to HCI. Four treatment replicates per plate were used to assess the polyclonal population. 4 treatments per plate were used to assess the synFIH monocline (DOX, DMSO, DOX/DMSO, DOX/DMOG), with \(100 \text{ng / \mu L}\) Doxycycline utilised, and 8 treatments per plate (vehicle, DMOG or R5020) were used to assess the PGR and HIF monoclonal lines. Plates were humidified and maintained at \(37^{\circ} \text{C}\) , \(5\%\) CO₂ throughout the imaging experiment. Plates were then imaged every 2 hours for 40- 48 hours. At every timepoint, a minimum 2000 nuclei were resampled from each well population.
+
+T47D mcdFLASH- PGR R5020 Dose response curve EC50 calculation. T47D mcdFLASH- PGR cells were treated with increasing doses of 0.01- 100nM R5020 and quantified by HCI after 48hrs. Tomato/GFP values were min/max normalised ( \(x' =\)
+
+<--- Page Split --->
+
+\(\frac{(X - x_{min})}{(x_{max} - x_{min})}\) ) within each experiment (n = 3) and the EC50 constant and curve fitted using the drc R package from 71.
+
+Bimodal small molecule screen to identify activators or inhibitors of the hypoxic response pathway. Library of natural and synthetic compounds was supplied by Prof. Ronald Quinn and Compounds Australia, available by request. 5mM of each of the 1595 compounds were spotted in 1μL DMSO into Costar Cat#3603 plates and stored at \(- 80^{\circ}C\) prior to screening. Plates were warmed to \(37^{\circ}C\) prior to cell addition. Monoclonal HIF HEK293T reporter cells were seeded at \(0.5\times 10^{4}\) cells per well across 20 Costar Cat#3603 plates pre- spiked with 5mM of compound in 1uL of DMSO in 100uL. On each plate, 4 wells were treated with matched DMSO amounts to compound wells as were four 1mM DMOG controls. Plates were then imaged using HCI (described above) at 36 hrs or 24 hours for reporter activation. Wells were then treated with 100uL of 2mM DMOG (for 1mM DMOG final, 200uL media final). 4 vehicle and 8 DMOG- treated controls (excluding the initial controls from the activator screen) were used for the inhibitor screen. Cells were imaged again 36 hours (Screen 1) or 24 hours (Screen 2) after treatment with 1mM DMOG in the compound wells. Data was Z scored and control wells were used to establish gating for abnormal expression of Tomato and EGFP fluorophores. For the activator screen, compounds within \(+ / - 2SD\) EGFP MFI of vehicle wells were counted as having unchanged transcriptional effects. Compounds with Tomato/EGFP ratio greater than \(+2SD\) of vehicle controls was counted as a putative hit. For the inhibitor screen, compounds within \(+ / - 2SD\) EGFP MFI of DMOG controls were counted as having unchanged GFP expression and Compounds with Tomato/EGFP ratio lower than - 2SD from the DMOG control were considered putative inhibitors. To correct for false positives within each screen, Z scored compounds were converted to their respective P score and adjusted with a \(^{72}\) correction. Pearson correlations were then used to compare compound expression between screens with the base R package (4.4.0). Putative activators and inhibitors identified in the screens were re- spotted at 1mM, 2.5mM and 5mM in 1μL of DMSO in Costar Cat#3603 96 well trays. Activators were rescreened by HCI after 24 hours against \(1\times 10^{4}\) cells HIF reporter monoclonnes in biological duplicate against with vehicle and 1mM DMOG controls in \(100\mu \mathrm{L}\) . Inhibitors were rescreened by HCI after 24 hours in duplicate against \(1\times 10^{4}\) cells HIF reporter monoclonnes with 1mM DMOG to compound wells. Final compound concentrations were \(10\mu \mathrm{M}\) , \(25\mu \mathrm{M}\) and \(50\mu \mathrm{M}\) respectively and Tomato MFI and Tomato/EGFP ratio for each compound was assessed. dFLASH Bimodal high throughput screen details can be found in Supplementary Table 5.
+
+Reverse Transcription and Real Time PCR. Cells were seeded in 60mm dishes at \(8\times 10^{4}\) cells per vessel overnight before treatment for 48 hours with 1mM DMOG or \(0.1\%\) DMSO. Cells were lysed in Trizol (Invitrogen), and RNA was purified with Qiagen RNAEasy Kit, DNase1 treated and reverse transcribed using M- MLV reverse transcriptase (Promega). cDNA was then diluted for real time PCR. Real- time PCR used primers specific for HIF- 1α, and human RNA Polymerase 2 (POLR2A) (Supplementary Table 4). All reactions were done on a StepOne Plus Real- time PCR machine utilising SYBER Green, and data analysed by 'QGene' software. Results are
+
+<--- Page Split --->
+
+normalised to POLR2A expression. RT- qPCR was performed in triplicate and single amplicons were confirmed via melt curves.
+
+Flow cytometry analysis and sorting (FACS). Prior to flow cytometry, cells were trypsinised, washed in complete media and resuspended in resuspended in flow cytometry sort buffer \(\mathrm{(Ca^{2 + } / Mg^{2 + }}\) - free PBS, \(2\% \mathrm{FBS}\) , \(25\mathrm{mM}\) HEPES pH 7.0) for cell sorting) prior to cell sorting or flow cytometry analysis buffer \(\mathrm{(Ca^{2 + } / Mg^{2 + }}\) free PBS, \(2\% \mathrm{FBS}\) , \(1\mathrm{mM}\) EDTA, \(25\mathrm{mM}\) HEPES pH 7.0) for analysis followed by filtration through a \(40\mu \mathrm{M}\) nylon cell strainer (Corning Cat#352340. Cell populations were kept on ice prior to sorting. Flow cytometry was performed either using the BD Biosciences BD LSRFortessa or the BD Biosciences FACS ARIA2 sorter within a biosafety cabinet and aseptic conditions, using an \(85\mu \mathrm{M}\) nozzle. Cell populations were gated by FSC- W/FSC- H, then SSC- W/SSC- H, followed by SSC- A/FSC- A to gate cells. EGFP fluorescence was measured by a \(530 / 30\mathrm{nm}\) detector, and the Tomato fluorescence was determined with the 582/15nm detector. A minimum of 10,000 cells were sorted for all FACS- based analysis. Data is presented as \(\log_{10}\) intensity for both fluorophores. Tomato induction was gated from the top \(1\%\) of the negative control population. Cell counts for histograms are normalised to mode unless stated otherwise. FACS analysis was done on FlowJoTM v10.9.1 software (BD Life Sciences)73.
+
+Time Lapse Spinning Disc Confocal Microscopy. HEK293T mcdFLASH- HIF and T47D mcdFLASH- PGR cells were seeded at \(1\times 10^{5}\) or \(5\times 10^{5}\) cells per dish respectively, onto \(50\mu \mathrm{g / mL}\) poly- D- lysine \(\mu\) - Dish \(35\mathrm{mm}\) , high Glass Bottom dishes (Ibidii, #81158) in FluoroBrite DMEM (Gibco, A1896701)/10% FBS/ \(1\%\) Pens/ \(1\%\) Glutamax/10mM HEPES pH7.9 and incubated overnight at \(37^{\circ}\mathrm{C}\) with \(5\%\) CO2 prior imaging. Cells were treatment with either \(0.5\mathrm{mM}\) DMOG (mcdFLASH- HIF) or \(100\mathrm{mM}\) R05020 (mcdFLASH- PGR) immediately prior to imaging with a CV100 cell voyager spinning disk confocal Tomato (561 nm, \(50\%\) laser, \(400\mathrm{ms}\) exposure and \(20\%\) gain) and EGFP (488 nm, \(50\%\) laser, \(400\mathrm{ms}\) exposure and \(20\%\) gain fluorescence for 48 hours post treatment with 15min imaging intervals. Images were captured at \(40\mathrm{x}\) with an objective lens with a \(\sim 30\mu \mathrm{m}\) Z stack across multiple fields of view. Maximum projected intensity images were exported to Image J for analysis and movie creation.
+
+Cell Lysis and Immunoblotting. Cells were washed in ice- cold PBS and lysates were generated by resuspending cells in either cell lysis buffer (20mM HEPES pH 8.0, \(420\mathrm{mMNaCl}_2\) , \(0.5\%\) NP- 40, \(25\%\) Glycerol, \(0.2\mathrm{mM}\) EDTA, \(1.5\mathrm{mM}\) MgCl2, \(1\mathrm{mM}\) DTT, \(1\mathrm{x}\) Protease Inhibitors (Sigma)) (Supp Figure 4) or urea lysis buffer (6.7M Urea, \(10\mathrm{mM}\) Tris- Cl pH 6.8, \(10\%\) glycerol, \(1\%\) SDS, \(1\mathrm{mM}\) DTT) (Figure 6, Supp Figure 8, 9). Quantification of protein levels was done by Bradford Assay (Bio- Rad). Lysates were separated on a \(7.5\%\) SDS- PAGE gel and transferred to nitrocellulose via TurboBlot (Bio- Rad). Primary Antibodies used were anti- HIF1α (BD Biosciences #), anti- HA (HA.11, Biolegend #16B12), anti- Tubulin (Serotec #MCA78G), anti- GAPDH (Sigma #G8796), anti- ARNT (Proteintech #14105- 1- AP). Primary antibodies were detected using horseradish peroxidase conjugated secondary antibodies (Pierce Bioscience #). Blots were visualised via chemiluminescence and developed with Clarity Western ECL Blotting substrates (Bio- Rad).
+
+<--- Page Split --->
+
+In vitro iron chelation activity assay. Chelation of iron for RQ200674 was measured by a protocol adapted from \(^{74}\) for use in 96 well plate format. \(0.1\mathsf{mM}\) \(\mathsf{FeSO_4}\) \((50\mu \mathsf{L})\) and \(50\mu \mathsf{L}\) of RQ200674, Dipyridyl (positive control) or DMOG solutions were incubated for 1hr at room temperature prior to addition of \(100\mu \mathsf{L}\) of \(0.25\mathsf{mM}\) Ferrozine (Sigma) and incubated for a further 10 minutes. Absorbance was measured at \(562\mathsf{nM}\) . Chelation activity was quantified as:
+
+\[C h e l a t i o n a c t i v i t y = \frac{(A_{c o n t r o l} - A_{x})}{A_{c o n t r o l}}\times 100\]
+
+Where Acontrol is absorbance of control reactions without RQ200674, DP or DMOG and \(\mathsf{A}_{\mathsf{X}}\) is absorbance of solutions with compound.
+
+Statistical Analysis. All data in graphs were presented as a mean \(\pm\) sem unless otherwise specified. Significance was calculated by a Two- Way ANOVA with Tukey multiple comparison or unpaired t- test with Welches correction where appropriate using Graphpad PRISM (version 9.0.0). All statistical analysis is from three independent biological replicates
+
+Figure Creation. Schematics and diagrams were created with BioRender (BioRender.com) and graphs were made either with ggplot package in \(\mathsf{R}^{75}\) and GraphPad PRISM (version 9.0.0).
+
+Data Availability. Source data are provided with this paper. Additional data, including full construct sequences, are available from corresponding authors upon request. Constructs not available on Addgene can be requested from corresponding authors.
+
+Acknowledgements. We thank Nicholas Smith, Alexander Pace, and members of our laboratories for critical feedback and helpful discussions. We also wish to acknowledge Adelaide Microscopy and the AHMS and SAHMRI Flow Cytometry facilities for technical assistance. We acknowledge Compounds Australia (www.compoundsaustralia.com) for their provision of specialized compound management and logistics research services to the project. This work was supported by Australian Government Research Training Scholarships (T.P.A, A.E.R), The Emeritus Professor George Rodgers AO Supplementary Scholarship (T.P.A, A.E.R). The Playford Memorial Trust Thyne Reid Foundation Scholarship (A.E.R). The George Fraser Supplementary Scholarship (A.E.R), The University of Adelaide Biochemistry Trust Fund (D.J.P. and M.L.W) and the Bill and Melinda Gates Foundation Contraceptive Discovery Program [OPP1771844] (D.C.B, D.L.R).
+
+Author contributions. Study was initially conceived by D.C.B and M.L.W. T.P.A, D.C.B., A.E.R designed and performed experiments. T.P.A, D.C.B., M.L.W, M.L. and R.J.Q. performed and analysed the bimodal screening campaign. M.R. and A.E.R. derived FIH KO cell line. T.P.A, D.C.B and M.L.W wrote the manuscript with input from all authors. Work was supervised by D.J.P, D.L.R. & M.L.W.
+
+Source Data. Source data for figures is available with this manuscript.
+
+Competing interests. The authors declare no competing interests.
+
+<--- Page Split --->
+
+1177 Correspondence and requests for materials. Should be addressed to David C. 1179 Bersten.
+
+<--- Page Split --->
+
+
+Supplementary Table 1: Synthetic toolkit for generation of reporter cell lines
+
+| Deposit Name: | Availability | Purpose |
| Dual fluorescent reporter constructs: |
| pLV-REPORT(EF1a) | Addgene #172326 | Reporter with mnucTomato and EF1a downstream promoter |
| pLV-REPORT(EF1a)-TTN | Addgene #172327 | Reporter with mnucTomato-HSVtk-2A-NeoR and EF1a downstream promoter |
| pLV-REPORT(PGK) | Addgene #172328 | Reporter with mnucTomato-HSVtk-2A-NeoR and PGK downstream promoter |
| pLV-REPORT(PGK/CMV) | Addgene #172330 | Reporter with mnucTomato-HSVtk-2A-NeoR and PGK/CMV downstream promoter |
| 12xHRE-pLV-Report-EF1a | Addgene: #172333 | Reporter with HRE enhancer |
| 12xHRE-pLV-REPORT(PGK) | Addgene #172334 | Reporter with HRE enhancer |
| 12xHRE-pLV-REPORT(PGK/CMV) | Addgene #172335 | Reporter with HRE enhancer |
| PRECat-pLV-REPORT(PGK/CMV) | By Request | Reporter with a PR-responsive concatemer, with enhancers from 5 target genes, containing 6 PR response elements. |
| 5xGRE-pLV-REPORT(PGK/CMV) | Addgene #172336 | Reporter with GRE enhancer |
| 12xHRE-pLV-REPORT(EF1a) | By Request | Reporter with HRE |
| 12xHRE-pLV-REPORT(EF1a)-tdnucTomato | By Request | Reporter with tdnucTomato and EF1a downstream promoter |
| Protein expression constructs: |
| pLV-TET2Puro | By Request | Doxycycline-inducible expression vector |
| pLV-TET2BlastR | By Request | Doxycycline-inducible expression vector |
| pL-V-TET2nucTomato | By Request | Doxycycline-inducible expression vector |
| pLV-TET2Puro-gal4DBD-miniVPR-HA | Addgene #207171 | Doxycycline-inducible expression vector for GAL4DBD-miniVPR |
| pLV-TET2Puro-gal4DBD-HIFCAD | Addgene #207173 | Doxycycline-inducible expression vector for GAL4DBD-HIFCAD (727-826) with Myc tag |
| pEF-IRES-puro6 gal4DBD-HIFCAD myc tag | Addgene #207171 | Constitutively expresses GAL4DBD-HIFCAD (727-826) with Myc tag |
| pEF-IRES-puro6 gal4DBD-HIFCAD pGalO linker | Addgene #207172 | Constitutively expresses GAL4DBD-HIFCAD (727-826) with Myc tag |
| pENTR1a-CRISPROffv2.1 | Addgene #207174 | Lentiviral expression vector for CRISPRoffv2.1 with BFP tag |
| pLV-Egl-NeoR | Addgene #207175 | Gateway-compatible lentiviral expression plasmid with Neomycin resistance |
| pLV-Egl-BlasR | Addgene #207176 | Gateway-compatible lentiviral expression plasmid with Blasticidin resistance |
| pLV-Egl-HygroR | Addgene #207177 | Gateway-compatible lentiviral expression plasmid with Hygromycin resistance |
| pLV-Egl-ZeoR | Addgene #207178 | Gateway-compatible lentiviral expression plasmid with Zeocin resistance |
+
+<--- Page Split --->
+
+
+Supplementary Table 2: Sequences for enhancer cloning
+
+| PRECat (G-block) |
| gaattacaaaaacaattacaaaaattcaaaattttatcgaTGCATGCCGTCTTACATAAAGGAAGTACAGAGTGTACAAAAACAGCAGACCCAAAAAAGCCGTGAAATGTGAGAACCCAAAACTGTACAGCTTGTTATTTCAGGAAGCAAAACTGAGGAGCGAAGCCGTCTTCATGGAATAATACATCCTGTTCCCACAAGT GACGTTAAGCTTCCAGACTGTGCACAGAGTGCACACTTCACCCAGTGTTGTGTCATCATGGTCAC ACAGTGTTCTTTCCGTGGTCACATCTGTGTCCACATTTTCCTTCCTTTTGATGGGAACAAAAGCAGT CATGTTAGGAAGGGAAAGGACACGGTGTTTAATACACAAATCCATGGACAGCCGTGGGCATC CAGTAATGCCCTGGAATGAGTCAAGAAGGCATTGCCCCAGTTTTTCACTAAGAGCTGCGAGGACA GCCTGTTCCTGTTCAAACCCACCCACAGCCTCCGTTGAGGCGCGCAGCTTTAGGCGTGTACG GTGGGCGCCTATAAAAGC |
| 5xGRE |
| GGTACCAGCTTGCATGCCGTGCAGGTCGGAGTACTGTCTCGCGAGCGAGATACTGTTCCTCCGA GCGGAGTACTGTTCCTCCGAGCGAGGTACTGTTCCTCCGAGCGAGATACTGTTCCTCCGAGCGAG AGAC |
+
+Supplementary Table 3: Index of all sgGuide oligos used
+
+ | Upper (5'-3') | Lower (5'-3') |
| VHL Knockdown sgGuide | CACCGCCGGGTGGTCTGGATCGCCGG | AAACCCGCGATCCAGACCACCCGGC |
| hHIF-1α CTD sgRNA | CACCGTCGAAGAATTACTCAGAGCTT | AAACAAGCTCTGAGTAATTCTTCA |
| hHIF-2α CTD sgRNA | CACCGCTCCCTCAGAGCCCTGGACC | AAACGGTCCAGGGCTCTGAGGAGGC |
+
+Supplementary Table 4: Primer sets for qPCR and PCR confirmation
+
+ | Forward (5'-3') | Reverse (5'-3') |
| qPCR HIF-1α | TATGAGCCAGAAGAACTTTT AGGC | CACCTCTTTTGGCAAGCATCCTG |
| qPCR PolR2a | GCACCATCAAGAGAGTGCA G | GGGTATTTGATACCACCCTCT |
| HIF-1α gDNA primers | GGCAATCAATGGATGAAAGT GGATT | GCTACTGCAATGCAATGGTTTAA AT |
| HIF-2α gDNA primers: | ACCAACCCTTCTTTCAGGCA TGGC | GCTTGGTGACCTGGGCAAGTCT GC |
+
+<--- Page Split --->
+
+1198 1 Beitz, A. M., Oakes, C. G. & Galloway, K. E. Synthetic gene circuits as tools for drug discovery. Trends Biotechnol 40, 210- 225 (2022). 1200 https://doi.org/10.1016/j.tibtech.2021.06.007 1201 2 Bock, C. et al. High- content CRISPR screening. Nature Reviews Methods Primers 2 (2022). https://doi.org/10.1038/s43586- 021- 00093- 4 1203 3 Lee, T. I. & Young, R. A. Transcriptional regulation and its misregulation in disease. Cell 152, 1237- 1251 (2013). https://doi.org/10.1016/j.cell.2013.02.014 1205 4 Bersten, D. C., Sullivan, A. E., Peet, D. J. & Whitelaw, M. L. bHLH- PAS proteins in cancer. Nat Rev Cancer 13, 827- 841 (2013). https://doi.org/10.1038/nrc3621 1207 5 Darnell, J. E., Jr. Transcription factors as targets for cancer therapy. Nat Rev Cancer 2, 740- 749 (2002). https://doi.org/10.1038/nrc906 1209 6 Sahu, B. et al. Sequence determinants of human gene regulatory elements. Nat Genet 54, 283- 294 (2022). https://doi.org/10.1038/s41588- 021- 01009- 4 1210 7 Tycko, J. et al. High- Throughput Discovery and Characterization of Human Transcriptional Effectors. Cell 183, 2020- 2035 e2016 (2020). https://doi.org/10.1016/j.cell.2020.11.024 1214 8 DelRosso, N. et al. Large- scale mapping and mutagenesis of human transcriptional effector domains. Nature (2023). https://doi.org/10.1038/s41586- 023- 05906- y 1216 9 Ortmann, B. M. et al. The HIF complex recruits the histone methyltransferase SET1B to activate specific hypoxia- inducible genes. Nature Genetics 53, 1022- 1035 (2021). https://doi.org/10.1038/s41588- 021- 00887- y 1219 10 Tan, X., Letendre, J. H., Collins, J. J. & Wong, W. W. Synthetic biology in the clinic: engineering vaccines, diagnostics, and therapeutics. Cell 184, 881- 898 (2021). https://doi.org/10.1016/j.cell.2021.01.017 1222 11 Choe, J. H. et al. SynNotch- CAR T cells overcome challenges of specificity, heterogeneity, and persistence in treating glioblastoma. Science Translational Medicine 13 (2021). 1225 12 Allen, G. M. et al. Synthetic cytokine circuits that drive T cells into immune- excluded tumors. Science 378, 1186- + (2022). https://doi.org/ARTN eaba1624 1227 10.1126/science.aba1624 1228 13 Hernandez- Lopez, R. A. et al. T cell circuits that sense antigen density with an ultrasensitive threshold. Science 371, 1166- + (2021). https://doi.org/10.1126/science.abc1855 1230 14 Roybal, K. T. et al. Engineering T Cells with Customized Therapeutic Response Programs Using Synthetic Notch Receptors. Cell 167, 419- + (2016). https://doi.org/10.1016/j.cell.2016.09.011 1234 15 Hasle, N. et al. High- throughput, microscope- based sorting to dissect cellular heterogeneity. Mol Syst Biol 16, e9442 (2020). https://doi.org/10.15252/msb.20209442 1237 16 Tchasovnikarova, I. A., Marr, S. K., Damle, M. & Kingston, R. E. TRACE generates fluorescent human reporter cell lines to characterize epigenetic pathways. Mol Cell (2021). https://doi.org/10.1016/j.molcel.2021.11.035 1240 17 Adamson, B. et al. A Multiplexed Single- Cell CRISPR Screening Platform Enables Systematic Dissection of the Unfolded Protein Response. Cell 167, 1867- 1882 e1821 (2016). https://doi.org/10.1016/j.cell.2016.11.048
+
+<--- Page Split --->
+
+1243 18 Singhal, R. & Shah, Y. M. Oxygen battle in the gut: Hypoxia and hypoxia- inducible factors in metabolic and inflammatory responses in the intestine. J Biol Chem 295, 10493- 10505 (2020). https://doi.org/10.1074/jbc.REV120.011188
+1246 19 Weigel, B., Vuerich, M., Daneshmandi, S. & Seth, P. Metabolic Switch in the Tumor Microenvironment Determines Immune Responses to Anti- cancer Therapy. Front Oncol 8, 284 (2018). https://doi.org/10.3389/fonc.2018.00284
+1249 20 Triner, D. & Shah, Y. M. Hypoxia- inducible factors: a central link between inflammation and cancer. J Clin Invest 126, 3689- 3698 (2016). https://doi.org/10.1172/JCI84430
+1252 21 Epstein, A. et al. C. elegans EGL- 9 and Mammalian Homologs Define a Family of Dioxygenases that Regulate HIF by Prolyl Hydroxylation. Cell 107 (2001).
+1254 22 Lando, D. et al. FIH- 1 is an asparaginyl hydroxylase enzyme that regulates the transcriptional activity of hypoxia- inducible factor. Genes Dev 16, 1466- 1471 (2002). https://doi.org/10.1101/gad.991402
+1257 23 Tian, Y.- M. et al. Differential Sensitivity of Hypoxia Inducible Factor Hydroxylation Sites to Hypoxia and Hydroxylase Inhibitors. Journal of Biological Chemistry 286, 13041- 13051 (2011). https://doi.org/10.1074/jbc.m110.211110
+1260 24 Razorenova, O. V., Ivanov, A. V., Budanov, A. V. & Chumakov, P. M. Virus- based reporter systems for monitoring transcriptional activity of hypoxia- inducible factor 1. Gene 350, 89- 98 (2005). https://doi.org/10.1016/j.gene.2005.02.006
+1263 25 Villemure, J. F., Savard, N. & Belmaaza, A. Promoter suppression in cultured mammalian cells can be blocked by the chicken beta- globin chromatin insulator 5'HS4 and matrix/scaffold attachment regions. J Mol Biol 312, 963- 974 (2001). https://doi.org/10.1006/jmbi.2001.5015
+1267 26 Emerman, M. & Temin, H. Comparison of promoter suppression in avian and murine retrovirus vectors. Nucleic Acids Res 14 (1986).
+1269 27 O'Connell, R. W. et al. Ultra- high throughput mapping of genetic design space (Cold Spring Harbor Laboratory, 2023).
+1271 28 Lando, D., Peet, D. J., Dean A. Whelan, Jeffery J. Gorman & Whitelaw, M. L. Asparagine Hydroxylation of the HIF Transactivation Domain: A Hypoxic Switch. Science 295 (2002).
+1274 29 Vora, S. et al. Rational design of a compact CRISPR- Cas9 activator for AAV- mediated delivery. bioRxiv, 298620 (2018). https://doi.org/10.1101/298620
+1276 30 Lydon, J. P. et al. Mice lacking progesterone receptor exhibit pleiotropic reproductive abnormalities. Genes & Development 9, 2266- 2278 (1995). https://doi.org/10.1101/gad.9.18.2266
+1279 31 Dinh, D. T. et al. Tissue- specific progesterone receptor- chromatin binding and the regulation of progesterone- dependent gene expression. Scientific Reports 9 (2019). https://doi.org/10.1038/s41598- 019- 48333- 8
+1282 32 Grimm, S. L., Hartig, S. M. & Edwards, D. P. Progesterone Receptor Signaling Mechanisms. J Mol Biol 428, 3831- 3849 (2016). https://doi.org/10.1016/j.jmb.2016.06.020
+1285 33 Giannoukos, G., Szapary, D., Smith, C. L., Meeker, J. E. & Simons, S. S., Jr. New antiprogestins with partial agonist activity: potential selective progesterone receptor modulators (SPRMs) and probes for receptor- and coregulator- induced changes in progesterone receptor induction properties. Mol Endocrinol 15, 255- 270 (2001). https://doi.org/10.1210/mend.15.2.0596
+
+<--- Page Split --->
+
+1290 34 Zhang, J.- H., Chung, T. & Oldenburg, K. A Simple Statistical Parameter for Use in 1291 Evaluation and Validation of High Throughput Screening Assays. Journal of 1292 Biomolecular Screening 4 (1999). 1293 35 Kampmann, M. CRISPRi and CRISPRa Screens in Mammalian Cells for Precision 1294 Biology and Medicine. ACS Chem Biol 13, 406- 416 (2018). 1295 https://doi.org/10.1021/acscmebio.7b00657 1296 36 Jaakkola, P. et al. Targeting of HIF- a to the von Hippel- Lindau Ubiquitylation 1297 Complex by O2- Regulated Prolyl Hydroxylation. Science 292 (2001). 1298 37 Appelhoff, R. J. et al. Differential function of the prolyl hydroxylases PHD1, PHD2, and PHD3 in the regulation of hypoxia- inducible factor. J Biol Chem 279, 38458- 1300 38465 (2004). https://doi.org/10.1074/jbc.M406026200 1301 38 Chen, N. et al. Roxadustat Treatment for Anemia in Patients Undergoing Long- Term 1302 Dialysis. N Engl J Med 381, 1011- 1022 (2019). 1303 https://doi.org/10.1056/NEJMoa1901713 1304 39 Cai, Z., Luo, W., Zhan, H. & Semenza, G. L. Hypoxia- inducible factor 1 is required for 1305 remote ischemic preconditioning of the heart. Proc Natl Acad Sci U S A 110, 17462- 1306 17467 (2013). https://doi.org/10.1073/pnas.1317158110 1307 40 Masoud, G. N. & Li, W. HIF- 1alpha pathway: role, regulation and intervention for 1308 cancer therapy. Acta Pharm Sin B 5, 378- 389 (2015). 1309 https://doi.org/10.1016/j.apsb.2015.05.007 1310 41 Semenza, G. L. HIF- 1 mediates metabolic responses to intratumoral hypoxia and 1311 oncogenic mutations. J Clin Invest 123, 3664- 3671 (2013). 1312 https://doi.org/10.1172/JCI67230 1313 42 Semenza, G. L. Pharmacologic Targeting of Hypoxia- Inducible Factors. Annual Review 1314 of Pharmacology and Toxicology 59, 379- 403 (2019). 1315 https://doi.org/10.1146/annurev-pharmtox- 010818- 021637 1316 43 Keith, B., Johnson, R. S. & Simon, M. C. HIF1α and HIF2α: sibling rivalry in hypoxic 1317 tumor growth and progression. Nat Rev Cancer 12, 9- 22 (2012). 1318 44 Bracken, C. P. et al. Cell- specific regulation of hypoxia- inducible factor (HIF)- 1alpha and HIF- 2alpha stabilization and transactivation in a graded oxygen environment. J 1319 Biol Chem 281, 22575- 22585 (2006). https://doi.org/10.1074/jbc.M600288200 1320 45 Ran, F. A. et al. Genome engineering using the CRISPR- Cas9 system. Nature Protocols 1322 8, 2281- 2308 (2013). https://doi.org/10.1038/nprot.2013.143 1323 46 Huang, L. et al. Inhibitory action of Celastrol on hypoxia- mediated angiogenesis and 1324 metastasis via the HIF- 1α pathway. International Journal of Molecular Medicine 27 1325 (2011). https://doi.org/10.3892/ijmm.2011.600 1326 47 Ma, J. et al. Celastrol inhibits the HIF- 1α pathway by inhibition of mTOR/p70S6K/elF4E and ERK1/2 phosphorylation in human hepatoma cells. 1327 Oncology Reports 32, 235- 242 (2014). https://doi.org/10.3892/or.2014.3211 1328 48 Shang, F.- F. et al. Design, synthesis of novel celastrol derivatives and study on their 1330 antitumor growth through HIF- 1α pathway. European Journal of Medicinal Chemistry 1331 220, 113474 (2021). https://doi.org/10.1016/j.ejmech.2021.113474 1332 49 Srinivasan, B., Johnson, T. E. & Xing, C. Chalcone- based inhibitors against hypoxia- 1333 inducible factor 1—Structure activity relationship studies. Bioorganic & 1334 Medicinal Chemistry Letters 21, 555- 557 (2011). 1335 https://doi.org/10.1016/j.bmcl.2010.10.063
+
+<--- Page Split --->
+
+1336 50 Wan, C. et al. Genome-scale CRISPR-Cas9 screen of Wnt/β-catenin signaling 1337 identifies therapeutic targets for colorectal cancer. Science Advances 7, eabf2567 1338 (2021). https://doi.org/10.1126/sciadv.abf2567 1339 51 Semesta, K. M., Tian, R., Kampmann, M., Von Zastrow, M. & Tsvetanova, N. G. A 1340 high-throughput CRISPR interference screen for dissecting functional regulators of 1341 GPCR/cAMP signaling. PLOS Genetics 16, e1009103 (2020). 1342 https://doi.org/10.1371/journal.pgen.1009103 1343 52 Adamson, B. et al. A Multiplexed Single-Cell CRISPR Screening Platform Enables 1344 Systematic Dissection of the Unfolded Protein Response. Cell 167, 1867- 1882. e1821 1345 (2016). https://doi.org/10.1016/j.cell.2016.11.048 1346 53 Potting, C. et al. Genome-wide CRISPR screen for PARKIN regulators reveals 1347 transcriptional repression as a determinant of mitophagy. Proc Natl Acad Sci U S A 1348 115, E180- E189 (2018). https://doi.org/10.1073/pnas.1711023115 1349 54 Ilegems, E. et al. HIF- 1a inhibitor PX- 478 preserves pancreatic Beta cell function in 1350 diabetes. Science Translational Medicine 14 (2022). 1351 55 Koh, M. Y. et al. Molecular mechanisms for the activity of PX- 478, an antitumor 1352 inhibitor of the hypoxia- inducible factor- 1α. Molecular Cancer Therapeutics 7, 90- 1353 100 (2008). https://doi.org/10.1158/1535- 7163.mct- 07- 0463 1354 56 Welsh, S., Williams, R., Kirkpatrick, L., Paine- Murrieta, G. & Powis, G. Antitumor 1355 activity and pharmacodynamic properties of PX- 478, an inhibitor of hypoxia- 1356 inducible factor- 1A. Molecular Cancer Therapeutics 3 (2004). 1357 https://doi.org/https://doi.org/10.1158/1535- 7163.233.3.3 1358 57 Xia, M. et al. Identification of small molecule compounds that inhibit the HIF- 1 1359 signaling pathway. Mol Cancer 8, 117 (2009). https://doi.org/10.1186/1476- 4598- 8- 117 1360 58 Yin, J.- A. et al. Robust and Versatile Arrayed Libraries for Human Genome- Wide 1362 CRISPR Activation, Deletion and Silencing. bioRxiv, 2022.2005.2025.493370 (2023). 1363 https://doi.org/10.1101/2022.05.25.493370 1364 59 Feldman, D. et al. Optical Pooled Screens in Human Cells. Cell 179, 787- 799. e717 1365 (2019). https://doi.org/10.1016/j.cell.2019.09.016 1366 60 Feldman, D. et al. Pooled genetic perturbation screens with image- based 1367 phenotypes. Nat Protoc 17, 476- 512 (2022). https://doi.org/10.1038/s41596- 021- 00653- 8 1369 61 Yan, X. et al. High- content imaging- based pooled CRISPR screens in mammalian cells. 1370 Journal of Cell Biology 220 (2021). https://doi.org/10.1083/jcb.202008158 1371 62 Nandagopal, N. et al. Dynamic Ligand Discrimination in the Notch Signaling Pathway. Cell 172, 869- 880. e819 (2018). https://doi.org/10.1016/j.cell.2018.01.002 1373 63 Agarwal, V. et al. Massively parallel characterization of transcriptional regulatory 1374 elements in three diverse human cell types. bioRxiv (2023). 1375 https://doi.org/10.1101/2023.03.05.531189 1376 64 Gordon, M. G. et al. LentiMPRA and MPRAflow for high- throughput functional 1377 characterization of gene regulatory elements. Nat Protoc 15, 2387- 2412 (2020). 1378 https://doi.org/10.1038/s41596- 020- 0333- 5 1379 65 Bersten, D. C. et al. Inducible and reversible lentiviral and Recombination Mediated 1380 Cassette Exchange (RMCE) systems for controlling gene expression. PLoS One 10, 1381 e0116373 (2015). https://doi.org/10.1371/journal.pone.0116373
+
+<--- Page Split --->
+
+1382 66 Singhal, H. et al. Genomic agoism and phenotypic antagonism between estrogen and progesterone receptors in breast cancer. Sci Adv 2, e1501924 (2016). 1383 https://doi.org/10.1126/sciadv.1501924 1385 67 Chen, D.- Y. et al. Ankyrin Repeat Proteins of Orf Virus Influence the Cellular Hypoxia Response Pathway. Journal of Virology 91, JVI.01430- 01416 (2017). 1386 https://doi.org/10.1128/jvi.01430- 16 1388 68 Dehairs, J., Talebi, A., Cherifi, Y. & Swinnen, J. V. CRISPR- ID: decoding CRISPR mediated indels by Sanger sequencing. Sci Rep 6, 28973 (2016). 1390 https://doi.org/10.1038/srep28973 1391 69 Sanson, K. R. et al. Optimized libraries for CRISPR- Cas9 genetic screens with multiple modalities. Nat Commun 9, 5416 (2018). https://doi.org/10.1038/s41467- 018- 07901- 8 1394 70 Bersten, D. et al. Core and Flanking bHLH- PAS:DNA interactions mediate specificity and drive obesity (Cold Spring Harbor Laboratory, 2022). 1395 71 Ritz, C., Baty, F., Streibig, J. C. & Gerhard, D. Dose- Response Analysis Using R. PLOS ONE 10, e0146021 (2016). https://doi.org/10.1371/journal.pone.0146021 1398 72 Benjamini, Y. & Hochberg, Y. Controlling the False Discovery Rate: A Practical and Powerful Approach to Multiple Testing. Journal of the Royal Statistical Society: Series B (Methodological) 57, 289- 300 (1995). https://doi.org/https://doi.org/10.1111/j.2517- 6161.1995. tb02031. x 1401 73 Becton, Dickenson & Company. (Ashland, OR, 2021). 1403 74 Wong, F. C. et al. Antioxidant, Metal Chelating, Anti- glucosidase Activities and Phytochemical Analysis of Selected Tropical Medicinal Plants. Iran J Pharm Res 13, 1409- 1415 (2014). 1406 75 Wickham, H. in Elegant Graphics for Data Analysis VIII, 213 (Springer New York, NY, 2009).
+
+<--- Page Split --->
+
+## Supplementary Files
+
+This is a list of supplementary files associated with this preprint. Click to download.
+
+SupplementaryTable5. docx SuppVideo1. avi SuppVideo2. avi NewRS.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f_det.mmd b/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..b76453cf0687e9a34d85d8ebd234fe928b18e578
--- /dev/null
+++ b/preprint/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f/preprint__056cacada9650bd2ff6e41d24cf77d3f922bae4f244b4a05a96d2273dc50b22f_det.mmd
@@ -0,0 +1,555 @@
+<|ref|>title<|/ref|><|det|>[[44, 108, 852, 210]]<|/det|>
+# dFLASH; dual FLuorescent transcription factor Activity Sensor for Histone integrated live-cell reporting and high-content screening
+
+<|ref|>text<|/ref|><|det|>[[44, 230, 378, 275]]<|/det|>
+David Bersten david.bersten@adelaide.edu.au
+
+<|ref|>text<|/ref|><|det|>[[50, 303, 880, 678]]<|/det|>
+The University of Adelaide Timothy Allen The University of Adelaide https://orcid.org/0000- 0002- 8190- 2334 Alison Roennfeldt School of Biological Sciences, University of Adelaide Moganalaxmi Reckdharajkumar School of Biological Sciences, University of Adelaide https://orcid.org/0000- 0002- 9136- 2810 Miaomiao Liu Griffith University Ronald Quinn Griffith University https://orcid.org/0000- 0002- 4022- 2623 Darryl Russell The University of Adelaide Daniel J Peet Murray Whitelaw University of Adelaide
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 710, 103, 727]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 747, 136, 765]]<|/det|>
+Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 785, 319, 804]]<|/det|>
+Posted Date: January 5th, 2024
+
+<|ref|>text<|/ref|><|det|>[[44, 823, 475, 842]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 3732294/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 860, 914, 902]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[44, 920, 535, 940]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[42, 45, 903, 88]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on April 7th, 2025. See the published version at https://doi.org/10.1038/s41467-025-58488-w.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 101, 879, 138]]<|/det|>
+dFLASH; dual FLuorescent transcription factor Activity Sensor for Histone integrated live-cell reporting and high-content screening
+
+<|ref|>text<|/ref|><|det|>[[115, 152, 879, 204]]<|/det|>
+Authors: Timothy P. Allen1, Alison E. Roennfeldt1,2, Moganalaxmi Reckdharajkumar1, Miaomiao Liu3, Ronald J. Quinn3#, Darryl L. Russell2#, Daniel J. Peet1#, Murray L. Whitelaw1,4# & David C. Bersten1,2\*
+
+<|ref|>text<|/ref|><|det|>[[115, 220, 880, 325]]<|/det|>
+Affiliations: 1. School of Biological Sciences, University of Adelaide, Adelaide, South Australia, Australia 2. Robinson Research Institute, University of Adelaide, South Australia, Australia. 3. Griffith Institute for Drug Discovery, Griffith University, Brisbane, Australia 4. ASEAN Microbiome Nutrition Centre, National Neuroscience Institute, Singapore 169857, Singapore. \*Corresponding author. #labs that contributed to the work
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 342, 204, 357]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[115, 358, 880, 666]]<|/det|>
+Live- cell reporting of regulated transcription factor (TF) activity has a wide variety of applications in synthetic biology, drug discovery, and functional genomics. As a result, there is high value in the generation of versatile, sensitive, robust systems that can function across a range of cell types and be adapted toward diverse TF classes. Here we present the dual FLuorescent transcription factor Activity Sensor for Histone integrated live- cell reporting (dFLASH), a modular sensor for TF activity that can be readily integrated into cellular genomes. We demonstrate readily modified dFLASH platforms that homogenously, robustly, and specifically sense regulation of endogenous Hypoxia Inducible Factor (HIF) and Progesterone receptor (PGR) activities, as well as regulated coactivator recruitment to a synthetic DNA- Binding Domain- Activator Domain fusion proteins. The dual- colour nuclear fluorescence produced normalised dynamic live- cell TF activity sensing with facile generation of high- content screening lines, strong signal:noise ratios and reproducible screening capabilities ( \(Z' = 0.68 - 0.74\) ). Finally, we demonstrate the utility of this platform for functional genomics applications by using CRISPRoff to modulate the HIF regulatory pathway, and for drug screening by using high content imaging in a bimodal design to isolate activators and inhibitors of the HIF pathway from a \(\sim 1600\) natural product library.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 86, 240, 101]]<|/det|>
+## Introduction
+
+<|ref|>text<|/ref|><|det|>[[115, 101, 880, 410]]<|/det|>
+Cells integrate biochemical signals in a variety of ways to mediate effector function and alter gene expression. Transcription factors (TF) sit at the heart of cell signalling and gene regulatory networks, linking environment to genetic output1,2. TF importance is well illustrated by the consequences of their dysregulation within disease, particularly cancer where TFs drive pathogenic genetic programs3- 5. As a result, there is widespread utility in methods to manipulate and track TF activity in basic biology and medical research, predominantly using TF responsive reporters. Recent examples include enhancer activity screening6 by massively parallel reporter assays, discovery and characterisation of transcription effector domains7,8 and CRISPR- based functional genomic screens that use reporter gene readouts to understand transcriptional regulatory networks2,9. Beyond the use in discovery biology TF reporters are increasingly utilised as sensors and actuators in engineered synthetic biology applications such as diagnostics and cellular therapeutics. For example, synthetic circuits that utilise either endogenous or synthetic TF responses have been exploited to engineer cellular biotherapeutics10. In particular, the synthetic Notch receptor (SynNotch) in which programable extracellular binding elicits synthetic TF signalling to enhance tumour- specific activation of CAR- T cells, overcome cancer immune suppression, or provide precise tumour target specificity 11- 14.
+
+<|ref|>text<|/ref|><|det|>[[115, 425, 880, 650]]<|/det|>
+Fluorescent reporter systems are now commonplace in many studies linking cell signalling to TF function and are particularly useful to study single cell features of gene expression, such as stochastics and heterogeneity15, or situations where temporal recordings are required. In addition, pooled CRISPR/Cas9 functional genomic screens rely on the ability to select distinct cell pools from a homogenous reporting parent population. Screens to select functional gene regulatory elements or interrogate chromatin context in gene activation also require robust reporting in polyclonal pools16. Many of the current genetically encoded reporter approaches, by nature of their design, are constrained to particular reporting methods or applications 9,17. For example, high content arrayed platforms are often incompatible with flow cytometry readouts and vice versa. As such there is a need to generate modular, broadly applicable platforms for robust homogenous reporting of transcription factor and molecular signalling pathways.2.
+
+<|ref|>text<|/ref|><|det|>[[115, 665, 880, 906]]<|/det|>
+Here we address this by generating a versatile, high- performance sensor of signal regulated TFs. We developed a reporter platform, termed the dual FLuorescent TF Activity Sensor for Histone integrated live- cell reporting (dFLASH), that enables lentiviral mediated genomic integration of a TF responsive reporter coupled with an internal control. The well- defined hypoxic and steroid receptor signalling pathways were targeted to demonstrate that the composition of the modular dFLASH cassette is critical to robust enhancer- driven reporting. dFLASH acts as a dynamic sensor of targeted endogenous pathways as well as synthetic TF chimeras in polyclonal pools by temporal high- content imaging and flow cytometry. Routine isolation of homogenously responding reporter lines enabled robust high content image- based screening ( \(Z' = 0.68 - 0.74\) ) for signal regulation of endogenous and synthetic TFs, as well as demonstrating utility for functional genomic investigations with CRISPRoff. Array- based temporal high content imaging with a hypoxia response element dFLASH successfully identified novel regulators of the hypoxic response pathway, illustrating
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[67, 84, 880, 170]]<|/det|>
+85 the suitability of dFLASH for arrayed drug screening applications. This shows the 86 dFLASH platform allows for intricate interrogation of signalling pathways and 87 illustrates its value for functional gene discovery, evaluation of regulatory elements or 88 investigations into chemical manipulation of TF regulation.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 101, 195, 117]]<|/det|>
+## Results
+
+<|ref|>text<|/ref|><|det|>[[115, 118, 881, 636]]<|/det|>
+Design of versatile dFLASH, a dual fluorescent, live cell sensor of TF activityTo fulfil the need for a modifiable fluorescent sensor cassette that can be integrated into chromatin and enable robust live- cell sensing that is adaptable for any nominated TF, applicable to high content imaging (HCI) and selection of single responding cells from polyclonal pools via image segmentation or flow cytometry (Figure 1c) a lentiviral construct with enhancer regulated expression of Tomato, followed by independent, constitutive expression of d2EGFP as both selectable marker and an internal control was constructed (Figure 1a, b). Three nuclear localisation signals (3xNLS) integrated in each fluorescent protein ensured nuclear enrichment to enable single cell identification by nuclear segmentation, with accompanying image- based quantification of normalised reporter outputs using high content image analysis, or single- cell isolation using FACS in a signal dependent or independent manner. The enhancer insertion cassette upstream of the minimal promoter driving Tomato expression is flanked by restriction sites, enabling alternative enhancer cloning (Figure 1a). The sensor response to endogenous signal- regulated TF pathways was first assessed by inserting a Hypoxia Inducible Factor (HIF) enhancer. HIF- 1 is the master regulator of cellular adaption to low oxygen tension and has various roles in several diseases18- 20. To mediate its transcriptional program, the HIF- 1α subunit heterodimerises with Aryl Hydrocarbon Nuclear Translocator (ARNT), forming an active HIF- 1 complex. At normoxia4, HIF- 1α is post- translationally downregulated through the action of prolyl hydroxylase (PHD) enzymes and the Von Hippel Lindau (VHL) ubiquitin ligase complex21. Additionally, the C- terminal transactivation domain of HIF- 1α undergoes asparaginyl hydroxylation mediated by Factor Inhibiting HIF (FIH), which blocks binding of transcription coactivators CBP/p30022. These hydroxylation processes are repressed during low oxygen conditions, enabling rapid accumulation of active HIF- 1α. HIF- 1α stabilisation at normoxia4 was artificially triggered by treating cells with the hypoxia mimetic dimethyloxalylglycine (DMOG), which inhibits PHDs and FIH, thereby inducing HIF- 1α stabilisation, activity and hypoxic gene expression23. The well characterised regulation and disease relevance of HIF- 1α made it an ideal TF target for prototype sensor development.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 652, 443, 670]]<|/det|>
+## Optimisation of dFLASH sensors
+
+<|ref|>text<|/ref|><|det|>[[115, 685, 880, 909]]<|/det|>
+Initially, we tested FLASH constructs with repeats of hypoxia response element (HRE) containing enhancers (RCGTG)24 from endogenous target genes (HRE- FLASH), controlling expression of either nuclear mono (m) or tandem dimer (td)Tomato and observed no DMOG induced Tomato expression in stable HEK293T cell lines (mnucTomato or tdnucTomato, Supp Figure 1a,b). Given the HIF response element has been validated previously24, the response to HIF- 1α was optimised by altering the reporter design, all of which utilised the smaller mnucTomato (vs tdnucTomato) to contain transgene size. We hypothesised that transgene silencing, chromosomal site- specific effects or promoter enhancer coupling/interference may result in poor signal induced reporter activity observed in initial construct designs. As such we optimised the downstream promoter, the reporter composition and incorporated a 3xNLS d2EGFP internal control from the constitutive promoter to monitor chromosomal effects and transgene silencing.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 100, 880, 686]]<|/det|>
+Dual FLASH (dFLASH) variants incorporated three variations of the downstream promoter (EF1a, PGK and PGK/CMV) driving 3xNLS EGFP (nucEGFP) and 2A peptide linked hygromycin (detailed in Supp Figure 1c) in combination with alternate reporter transgenes that it expressed mnucTomato alone, or mnucTomato- Herpes Simplex Virus Thymidine Kinase (HSVtk)- 2A- Neomycin resistance (Neo). Stable HEK293T and HepG2 HRE- dFLASH cells lines with these backbones were generated by lentiviral transduction and hygromycin selection. The reporter efficacy of dFLASH variant cell lines was subsequently monitored by high content imaging 48 hours after DMOG induction (Supp Figure 1d, e). The downstream composite PGK/CMV or PGK promoters, enabled the strong DMOG induced Tomato or Tomato/GFP expression dramatically outperforming EF1a (Figure 1b and Supp Figure 1d). The composite PGK/CMV provided bright, constitutive nucEGFP expression in both HepG2 and HEK293T cells which was unchanged by DMOG, whereas nucEGFP controlled by the PGK promoter was modestly increased ( \(\sim 2.5\) fold) by DMOG (Supp Figure 1e). Substitution of the mnucTomato with the longer mnucTomato- HSVtk- Neo reporter had no effect on DMOG induced reporter induction in EF1a containing HRE- dFLASH cells, still failing to induce tomato expression (Supp Figure 1f). CMV/PGK containing dFLASH sensors maintained DMOG induction when either the mnucTomato or the mnucTomato/HSVtk/Neo reporters were utilised (Supp Figure 1g, h) although mnucTomato without HSVtk and Neo produced lower absolute mnucTomato fluorescence and a smaller percentage of cells responding to DMOG, albeit with lower background. Taken together these findings indicate that certain backbone compositions prevented or enabled robust activation of the enhancer driven cassette, similar to the suppression of an upstream promoter by a downstream, contiguous promoter previously described25,26 suggesting that the 3' EF1a promoter results in poorly functioning multi- citronic synthetic reporter designs27. Consequently, the PGK/CMV backbone and the mnucTomato/HSVtk/Neo reporter from Supp Figure 1 was chosen as the optimised reporter design (HRE- dFLASH). To confirm that the HRE element was conferring HIF specificity, a no response element dFLASH construct in HEK293T cells treated with DMOG produced no change in either mnucTomato or nucEGFP compared to vehicle- treated populations (Supp Figure 2a). This result, together with the robust induction in response to DMOG (Figure 2D, Supp Figure 1f, 1h), confirms HIF enhancer driven reporter to respond robustly to induction of the HIF pathway (subsequently labelled dFLASH- HIF).
+
+<|ref|>text<|/ref|><|det|>[[117, 700, 880, 890]]<|/det|>
+To validate the high inducibility and nucEGFP independence of dFLASH was not specific to the HIF pathway, we generated a Gal4 responsive dFLASH construct (Gal4RE- dFLASH), using Gal4 responsive enhancers22,28. HEK293T cells were transduced with Gal4RE- dFLASH and a dox- inducible expression system to express synthetic Gal4DBDtransactivation domain fusion protein. To evaluate Gal4RE- dFLASH we expressed Gal4DBD fused with a compact VPR (miniVPR), a strong transcriptional activator29 (Supp Figure 2b, 3a- c). We observed \(\sim 25\%\) of the polyclonal population was highly responsive to doxycycline treatment (Supp Figure 2b), with a \(\sim 14\) - fold change in Tomato expression relative to nucEGFP by HCI (Supp Figure 3c) demonstrating our optimised dFLASH backbone underpins a versatile reporting platform.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 85, 699, 103]]<|/det|>
+## dFLASH senses functionally distinct TF activation pathways
+
+<|ref|>text<|/ref|><|det|>[[117, 103, 880, 342]]<|/det|>
+dFLASH senses functionally distinct TF activation pathwaysFollowing the success in utilising dFLASH to respond to synthetic transcription factor and HIF signalling, we explored the broader applicability of this system to sense other TF activation pathways. We chose the Progesterone Receptor (PGR), a member of the 3- Ketosteroid receptor family that includes the Androgen, Glucocorticoid and Mineralocorticoid receptors, as a functionally distinct TF pathway with dose- dependent responsiveness to progestin steroids to assess the adaptability of dFLASH performance. Keto- steroid receptors act through a well- described mechanism which requires direct ligand binding to initiate homodimerization via their Zinc finger DNA binding domains, followed by binding to palindromic DNA consensus sequences. PGR is the primary target of progesterone (P4, or a structural mimic R5020) and has highly context dependent roles in reproduction depending on tissue type30,31,32. We inserted PGR- target gene enhancer sequences containing the canonical NR3C motif (ACANNNTGT31) into dFLASH, conferring specificity to the ketosteroid receptor family to generate PRE- dFLASH (Figure 2b, see Methods).
+
+<|ref|>text<|/ref|><|det|>[[116, 358, 880, 634]]<|/det|>
+A chimeric TF system was also established with Gal4DBD fusion proteins to create a synthetic reporter to sense the enzymatic activity of oxygen sensor Factor Inhibiting HIF (FIH). This sensor system termed SynFIH for its ability to synthetically sense FIH activity contained Gal4DBD- HIFCAD fusion protein expressed in a doxycycline- dependent manner, in cells harbouring stably integrated Gal4RE- dFLASH. FIH blocks HIF transactivation through hydroxylation of a conserved asparagine in the HIF- 1α C- terminal transactivation domain (HIFCAD), preventing recruitment of the CBP/p300 co- activator complex22. As FIH is a member of the 2- oxoglutarate dioxygenase family, like the PHDs which regulate HIF post- translationally, it is inhibited by DMOG (Figure 2C), allowing induction of SynFIH- dFLASH upon joint Dox and DMOG signalling (Supp Figure 3d,3e). dFLASH- based sensors for PGR and Gal4DBD- HIFCAD generated in the optimised backbone used for dFLASH- HIF (Figure 2a- c). For the PGR sensor we transduced T47D cells with PRE- dFLASH, as these have high endogenous PGR expression, while for the FIH- dependent system we generated HEK293T cells with Gal4RE- dFLASH and the GAL4DBD- HIFCAD system (dFLASH- synFIH).
+
+<|ref|>text<|/ref|><|det|>[[116, 650, 880, 907]]<|/det|>
+Stable polyclonal cell populations were treated with their requisite chemical regulators and reporter responses analysed by either flow cytometry or temporal imaging using HCl at 2hr intervals for 38 hours (Figure 2). Flow cytometry revealed all three systems contain a population that strongly induced nucTomato and maintained nucEGFP (Supp Figure 2). In HEK293T cells, \(\sim 20\%\) of dFLASH- synFIH and \(\sim 50\%\) of dFLASH- HIF population induced Tomato fluorescence substantially relative to untreated controls (Figure 2d, Figure 2f). The \(\sim 20\%\) reporter response to inhibition of FIH activity by DMOG (Supp Figure 2e, Figure 2f) is comparable with what was observed for GalRE- dFLASH response to Gal4DBD- miniVPR expression after equivalent selection (Supp Figure 2b). The PGR reporter in T47D cells showed \(\sim 50\%\) of the population substantively induced Tomato (Figure 2e, Supp Figure 2d). The presence of considerable responsive populations for FIH, PGR, and HIF sensors, reflected in the histograms of the EGFP positive cells (Figure 2d- f) indicated that isolation of a highly responsive clone or subpopulations can be readily achievable for a range of transcription response types. Importantly, the induction of dFLASH- synFIH by
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 85, 879, 137]]<|/det|>
+Dox/DMOG co- treatment was ablated and displayed high basal Tomato levels in FIH knockout dFLASH- synFIH cells (Supp Figure 3e), indicating that the dFLASH- synFIH specifically senses FIH enzymatic activity.
+
+<|ref|>text<|/ref|><|det|>[[117, 152, 880, 480]]<|/det|>
+All dFLASH systems showed consistent signal- dependent increases in reporter activity out to 38 hours by temporal HCl enabling polyclonal populations of dFLASH to track TF activity (Figure 2g- i). PRE- dFLASH was more rapidly responsive to R5020 ligand induction ( \(\sim 6\) hours, Figure 2h) than dFLASH- HIF and dFLASH- synFIH to DMOG or Dox/DMOG treatment, respectively ( \(\sim 10\) hours, Figure 2g, i). Treatment of PRE- dFLASH with estrogen (E2), which activates the closely related Estrogen Receptor facilitating binding to distinct consensus DNA sites to the PGR, or the hypoxia pathway mimetic DMOG, failed to produce a response on PRE- dFLASH (Figure 2h). This indicates that the PRE enhancer element is selective for the ketosteroid receptor family (also see below), and that enhancer composition facilitates pathway specificity. We also observed a signal- dependent change in EGFP expression by flow cytometry in the T47D PRE- dFLASH reporter cells (Supp Figure 2g) but did not observe a significant change in EGFP expression for HEK293T or HEPG2 dFLASH- HIF (Supp Figure 1c, Supp Figure 2c) or in HEK293T dFLASH- synFIH cells (Supp Figure 2h), with only a small change with Gal4RE- dFLASH with Gal4DBD- miniVPR (Supp Figure 2b). While this change in T47D cells was not detected in the other cellular contexts (see below), it highlights that care needs to be taken in confirming the utility of the constitutive nucEGFP as an internal control in certain scenarios.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 494, 848, 512]]<|/det|>
+## Monoclonal dFLASH cell lines confer robust screening potential in live cells
+
+<|ref|>text<|/ref|><|det|>[[117, 512, 880, 700]]<|/det|>
+The observed heterogenous expression of dFLASH within polyclonal cell pools is useful in many assay contexts but reduces efficiency in arrayed high content screening experiments and incompatible with pooled isolation of loss of function regulators. Therefore, monoclonal HEK293T and HepG2 dFLASH- HIF, T47D and BT474 PRE- dFLASH and HEK293T dFLASH- synFIH cell lines were derived to increase reliability of induction, as well as consistency and homogeneity of reporting (Figure 3, Supp Figure 4). The isolated mcdFLASH- synFIH and mcdFLASH- HIF lines also demonstrated constitutive signal insensitive nucEGFP expression (Supp Figure 4a,b,i). While the T47D PRE- mcdFLASH showed a small increase in nucEGFP in response to R5020, this did not preclude the use in normalisation of high content imaging experiments (see below).
+
+<|ref|>text<|/ref|><|det|>[[117, 716, 880, 906]]<|/det|>
+No change in EGFP in BT474 PRE- mcdFLASH cells indicates that strong transactivation leading to promoter read through or cell- type specific effects may be at play. Flow cytometry of monoclonal dFLASH cell lines with their cognate ligand inducers (DMOG (Figure 3b), R5020 (Figure 3f) or Dox/DMOG (Figure 3j)) revealed robust homogeneous induction of mnucTomato in all cell lines. Using temporal high content imaging we also found that clonally derived lines displayed similar signal induced kinetics as the polyclonal reporters although displayed higher signal to noise and increased consistency (Figure 3, Supp Figure 4i). Using physiologically relevant concentrations of steroids or steroid analogs (10nM- 35nM), the PRE- mcdFLASH lines selectively respond to R5020 (10nM) not E2 (35nM), DHT (10nM), Dexamethasone (Dex, 10nM) or Retinoic acid (RA, 10nM) (Figure 3g, Supp Figure 4i). In addition,
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 84, 879, 206]]<|/det|>
+dose response curves of R5020 mediated Tomato induction indicate that PRE- mcdFLASH line responds to R5020 with an \(\mathrm{EC}_{50} \sim 200\mathrm{pM}\) , in agreement with orthogonal methods33 (Supp Figure 4g, h). This suggests that the PRE- mcdFLASH responds sensitively and selectively to PGR selective agonist R5020, with the potential for high- content screening for modulators of PGR activity. As such, we term this line mcdFLASH- PGR from herein, for its specific ability to report on PGR activity at physiological steroid concentrations.
+
+<|ref|>text<|/ref|><|det|>[[117, 221, 880, 360]]<|/det|>
+The temporal HCl of populations (Figure 2 and Figure 3) were imaged every 2hrs and do not inherently provide single- cell temporal dynamics of transcriptional responses. Using clonally derived mcdFLASH- PGR or mcdFLASH- HIF lines we also imaged transcriptional responses to R5020 or DMOG, respectively every 15mins (Supp Video 1 and 2). High temporal resolution imaging has the potential to monitor transcriptional dynamics in single cells, facilitated by the dual fluorescent nature of dFLASH. Taken together this indicates that clonal lines display improved signal to noise and assay consistency, possibly enabling high content screening experiments.
+
+<|ref|>text<|/ref|><|det|>[[117, 375, 880, 633]]<|/det|>
+Typically, high- content screening experiments require high in- plate and across plate consistency, therefore we evaluated mcdFLASH lines (HIF- 1α, PGR, FIH) across multiple plates and replicates. System robustness was quantified with the Z' metric34 accounting for fold induction and variability between minimal and maximal dFLASH outputs. Signal induced mnucTomato fluorescence across replicates from independent plates was highly consistent (Z' 0.68- 0.74) and robust (9.3- 11.8 fold, Figure 3 d, h, l) the signal induced changes in activity for mcdFLASH- HIF and mcdFLASH- FIH were driven by increased mnucTomato, with minimal changes in nucEGFP (Figures 3e and 3m). Despite the changes previously observed in nucEGFP mcdFLASH- PGR in T47D cells provided equivalent reporter to the other systems, (Figure 3h, i) as a result, monoclonal mcdFLASH cell lines represent excellent high- throughput screening systems routinely achieving Z' scores \(>0.5\) . Importantly, the induction of the mcdFLASH lines (HEK293T and HepG2 mcdFLASH- HIF, T47D mcdFLASH- PGR and HEK293T mcdFLASH- SynFIH) remained stable over extended passaging (months), enabling protracted large screening applications.
+
+<|ref|>sub_title<|/ref|><|det|>[[118, 648, 644, 666]]<|/det|>
+## dFLASH-HIF CRISPR-perturbations of the HIF pathway
+
+<|ref|>text<|/ref|><|det|>[[117, 666, 880, 907]]<|/det|>
+The robust signal window and high Z' score of mcdFLASH- HIF cell line, coupled with facile analysis by flow cytometry and HCl, indicates that the reporter system is amenable to functional genomic screening. We utilised the recently developed CRISPRoffv2.1 system35 to stably repress expression of VHL, which mediates post- translational downregulation of the HIF- 1α pathway36,37. We generated stable mcdFLASH- HIF cells expressing a guide targeting the VHL promoter and subsequently introduced CRISPRoffv2.1 from either a lentivirus driven by an EF1a or SFFV promoter (Figure 4a, b). Cells were then analysed by flow cytometry 5- or 10- days post selection to determine if measurable induction of mcdFLASH- HIF reporter was modulated by VHL knockdown under normoxic conditions (Supp Figure 6, Figure 4c, 4d). As expected, mcdFLASH- HIF/sgVHL cells expressing CRISPRoffv2.1 from either promoter induced the mcdFLASH- HIF reporter in \(\sim 35\%\) by 5 days and the majority of cells ( \(\sim 60\%\) ) by 10 days as compared to parental cells. Demonstration that mcdFLASH- HIF is responsive to CRISPRi/off perturbations of key regulators of the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 85, 880, 120]]<|/det|>
+HIF pathway illustrates the potential for the dFLASH platform to provide a readout for CRISPR screens at- scale in a larger format including genome- wide screens.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 136, 765, 154]]<|/det|>
+## dFLASH facilitates bimodal screening for small molecule discovery
+
+<|ref|>text<|/ref|><|det|>[[115, 155, 880, 483]]<|/det|>
+dFLASH facilitates bimodal screening for small molecule discoveryManipulation of the HIF pathway is an attractive target in several disease states, such as in chronic anaemia38 and ischemic disease39 where its promotion of cell adaption and survival during limiting oxygen is desired. Conversely, within certain cancer subtypes40,41 HIF signalling is detrimental and promotes tumorigenesis. Therapeutic agents for activation of HIF- \(\alpha\) signalling through targeting HIF- \(\alpha\) regulators were initially discovered using in vitro assays. However, clinically effective inhibitors of HIF- \(1\alpha\) signalling are yet to be discovered42. The biological roles for HIF- \(1\alpha\) and closely related isoform HIF- \(2\alpha\) , which share the same canonical control pathway, can be disparate or opposing in different disease contexts requiring isoform selectivity for therapeutic intervention43. To validate that HIF- \(1\alpha\) is the sole isoform regulating mcdFLASH- HIF in HEK293T cells44 tandem HA- 3xFLAG epitope tags were knocked in to the endogenous HIF- \(1\alpha\) and HIF- \(2\alpha\) C- termini allowing directly comparison by immunoblot45 and confirmed HIF1a is predominant isoform (Supp Figure 5a). Furthermore, there was no change in DMOG induced mnucTomato expression in HEK293T mcdFLASH- HIF cells when co- treated for up to 72 hours with the selective HIF2a inhibitor PT- 2385 (Supp Figure 5b), consistent with the minimal detection of HIF- \(2\alpha\) via immunoblot. This confirmed that our HEK293T dFLASH- HIF cell line specifically reports on HIF- 1 activity and not HIF- 2, indicating that it may be useful for identification of drugs targeting the HIF- \(1\alpha\) pathway.
+
+<|ref|>text<|/ref|><|det|>[[115, 497, 880, 911]]<|/det|>
+dFLASH- HIF facilitates multiple measurements across different treatment regimens and time points, enabling capture of periodic potentiated and attenuated HIF signalling during a single experiment. Having validated the robust, consistent nature of mcdFLASH- HIF, we exploited its temporal responsiveness for small molecule discovery of activators or inhibitors of HIF- \(1\alpha\) signalling in a single, bimodal screening protocol. To test this bimodal design, we utilised a natural product library of 1595 compounds containing structures that were unlikely to have been screened against HIF- \(1\alpha\) prior. We first evaluated library compounds for ability to activate the reporter after treatment for 36 hours (Figure 5a) or 24 hours (Figure 5d). The selection of two different screening time points was to minimise any potential toxic effects of compounds at the later time points. Consistency of compound activity between the two screens was assessed by Pearson correlations (Supp Figure 7i, \(\mathrm{R} = 0.79\) , \(\mathrm{p}< 2.2\times 10^{- 16}\) ). Lead compounds were identified by their ability to increase mnucTomato/nucEGFP (Figure 5b, c) and mnucTomato MFI more than 2SD compared with vehicle controls, with less than 2SD decrease in nucEGFP (21/1595 compounds (1.3%) each expt; Supp Figure 7a, e) and an FDR adjusted P score <0.01 across both screens (3/1595 (0.18%) compounds; Supp Figure 7b, f). After imaging of reporter fluorescence to determine these compound's ability to activate HIF- \(1\alpha\) we then treated the cells with 1mM DMOG and imaged after a further 36- hour (Figure 5c) and 24- hour (Figure 5f) period. Again, consistency of compound activity was assessed by Person correlation (Supp Figure 7j, \(\mathrm{F}\) , \(\mathrm{R} = 0.62\) , \(\mathrm{p}< 2.2\times 10^{- 16}\) ). Lead compounds were defined as those exhibiting a decrease in mnucTomato MFI >2SD from DMOG- treated controls in each screen without changing nucEGFP >2SD relative to the DMOG- treated controls (26/1595 compounds (1.3%) (36hr treatment) and
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 85, 879, 138]]<|/det|>
+13/1595 compounds (<1%) (24hr treatment); Supp Figure 7c, g), and decrease in mnucTomato/nucEGFP >2SD with an FDR adjusted P score < 0.01 (3/1595 compounds (0.18%) across both expt; Supp Figure 7d, h).
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 153, 824, 171]]<|/det|>
+## dFLASH identified novel and known compounds that alter HIF TF activity.
+
+<|ref|>text<|/ref|><|det|>[[115, 171, 880, 536]]<|/det|>
+We confirmed 11 inhibitors and 18 activators of HIF1a activity identified from the pilot screen at three concentrations (Supp Figure 8a, 9a) identifying RQ500235 and RQ200674 (Figure 6a, d) as previously unreported HIF- 1α inhibiting or stabilising compounds, respectively. RQ200674 increased reporter activity 2- fold in repeated assays (Figure 6d) and stabilised endogenously tagged HIF- 1α at normoxia in HEK293T cells (Supp Figure 8b). Mechanistically, RQ200674 had weak iron chelation activity in an in vitro chelation assay (Figure 6e), suggesting it intersects with the HIF- 1α pathway by sequestering iron similar to other reported HIF stabilisers. In the inhibitor compound dataset, Celastarol and Flavokawain B downregulated the reporter at several concentrations (Supp Figure 9b, c). Celastarol is a previously reported HIF- 1α inhibitor46- 48 and Flavokawain B is a member of the chalcone family which has previously exhibited anti- HIF- 1α activity49. RQ500235 was identified as a HIF- 1 inhibitor by mcdFLASH- HIF screening. Dose dependent inhibition of mcdFLASH- HIF (Figure 6a) correlated with a dose- dependent decrease in protein expression by immunoblot (Figure 6C). We observed significant (p=0.0139) downregulation of HIF- 1α transcript levels (Figure 6D) and were unable to rescue HIF- 1α protein loss with proteasomal inhibition (Supp Figure 9d), indicating RQ500235 was decreasing HIF- 1α at the RNA level. More broadly however, the identification of these compounds by mcdFLASH- HIF in the bimodal set up demonstrates successful application of the dFLASH platform to small molecule discovery efforts for both gain and loss of TF function.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 86, 228, 101]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[115, 102, 880, 394]]<|/det|>
+We designed and optimised dFLASH to offer a versatile, robust live- cell reporting platform that is applicable across TF families and allows for facile high- throughput applications. We validated dFLASH against three independent signal- responsive TFs, two with endogenous signalling pathways (dFLASH- PRE for Progesterone receptors; dFLASH- HRE for hypoxia induced transcription factors) and a synthetic system for a hybrid protein transcriptional regulator (dFLASH- Gal4RE). Each dFLASH construct produced robustly detected reporter activity by temporal high- content imaging and FACS after signal stimulation for its responsive TF (Figure 2,3). The use of previously validated enhancer elements for HIF24 and synthetic Gal4 DNA binding domains22,28 demonstrated that dFLASH can be adapted toward both endogenous and synthetic pathways displaying highly agonist/activator- specific responses, indicating utility in dissecting and targeting distinct molecular pathways. mcdFLASH lines distinct pathways produced highly consistent ( \(Z' = 0.68 - 0.74\) ) signal induced Tomato induction measured by high content imaging suggesting dFLASH is ideally suited to arrayed high- throughput screening (Figure 3). In addition, mcdFLASH lines also displayed homogenous signal induced reporter induction by flow cytometry indicating that pooled high content screening would also be possible.
+
+<|ref|>text<|/ref|><|det|>[[118, 408, 880, 530]]<|/det|>
+Indeed, reporter systems like dFLASH have been increasingly applied to functional genomic screens which target specific transcriptional pathways9,50- 52. CRISPRoff mediated downregulation of the core HIF protein regulator, VHL produced distinct tomato expressing cell pools (Figure 4), demonstrating genetic perturbations of endogenous TF signalling pathways. The robust induction of the dFLASH- HIF reporter upon VHL knockdown in the majority of cells indicates that whole genome screening would also be successful9,17,50,53.
+
+<|ref|>text<|/ref|><|det|>[[118, 546, 880, 719]]<|/det|>
+Using the HIF- 1 \(\alpha\) specific reporter line, mcdFLASH- HIF, the application of high- content screening was exemplified. This approach was successful in discovering a novel activator and novel inhibitor of the HIF pathway, as well as previously identified inhibitory compounds. This ratified dFLASH as a reporter platform for arrayed- based screening and demonstrates the utility of the linked nucEGFP control for rapid hit bracketing. The novel inhibitor RQ500235 was shown to downregulate HIF- 1 \(\alpha\) transcript levels, like another HIF- 1 \(\alpha\) inhibitor PX- 47854,55. As PX- 478 has demonstrated anti- cancer activity in several cell lines 55,56 and preserved \(\beta\) - cell function in diabetic models54, a future similar role may exist for an optimised analogue of RQ500235.
+
+<|ref|>text<|/ref|><|det|>[[118, 735, 880, 891]]<|/det|>
+The dFLASH system is characterised by some distinct advantages which may enable more precise dissection of molecular pathways. The ability to control for cell- to- cell fluctuations and to decouple generalised or off- target effects on reporter function may aid the precision necessary for large drug library or genome- wide screening applications57. In addition, dFLASH, unlike many other high- throughput platforms can be used to screen genetic or drug perturbations of temporal transcriptional dynamics or as used here at multiple time points. Also, the results indicate that dFLASH is ideally suited to array- based functional genomics approaches58 allowing for multiplexing with other phenotypic or molecular outputs59,60 2,61.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 100, 880, 291]]<|/det|>
+The dFLASH approach has some limitations. The fluorescent nature of dFLASH limits the chemical space by which it can screen due to interference from auto- fluorescent compounds. In addition, we acknowledge that fluorescent proteins require \(\mathrm{O_2}\) for their activity and this limits the use of mnucTomato as a readout of hypoxia. Also, while the backbone design has been optimised for a robust activation of a variety of transcription response pathways, the mechanistic underpinning of this is unclear and could be further improved, providing insights into the sequence and architectural determinants of enhancer activation in chromatin. In addition to the strong effect of the dFLASH downstream promoter on upstream enhancer activity it is clear that either the distance between contiguous promoter/enhancer or the sequence composition of the linker has a functional consequence on enhancer induction.
+
+<|ref|>text<|/ref|><|det|>[[115, 306, 880, 461]]<|/det|>
+The incorporation of robust native circuits such as those described here (Hypoxia or Progesterone) has the potential to allow the manipulation or integration of these pathways into synthetic biology circuitry for biotherapeutics. In these cases, it is critical that robust signal to noise is achieved for these circuits to effectively function in biological systems. Further, the use of a synthetic approach to 'sense' FIH enzymatic activity through the HIF- CAD:P300/CBP interaction opens up the possibility that other enzymatic pathways that lack effective in vivo activity assay may also be adapted. We also envisage that dFLASH could be adapted to 2- hybrid based screens as a complement to other protein- protein interaction approaches.
+
+<|ref|>text<|/ref|><|det|>[[115, 476, 880, 700]]<|/det|>
+The ability to temporally track TF regulated reporters in populations and at the single- cell level enable dFLASH to be used to understand dynamics of transcriptional responses as has been used to dissect mechanisms of synthetic transcriptional repression7,8 or understand notch ligand induced synthetic transcriptional dynamics62. For instance, synthetic reporter circuits have been used to delineate how diverse notch ligands induce different signalling dynamics62. The large dynamic range of the dFLASH- PGR and HIF reporter lines in conjunction with the high proportion of cells induced in polyclonal pools (Figure 2) also suggests dFLASH as a candidate system for forward activity- based enhancer screening. These approaches have been applied to dissect enhancer activity or disease variants with other similar systems such as lentiviral- compatible Massively Parallel Reporter Assays (LentiMPRA)63,64. However, the use of the internal control normalisation provided by dFLASH may be useful in separating chromosomal from enhancer driven effects in forward enhancer screens.
+
+<|ref|>text<|/ref|><|det|>[[115, 716, 880, 785]]<|/det|>
+Given dFLASH has robust activity in both pooled and arrayed formats, it offers a flexible platform for investigations. dFLASH can be used to sense endogenous and synthetic transcription factor activity and represents a versatile, stable, live- cell reporter system of a broad range of applications.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[135, 160, 848, 460]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 520, 880, 833]]<|/det|>
+Figure 1. Summary of dFLASH LV-REPORT construction, utility, and validation (a) The dFLASH system utilises the lentiviral LV-REPORT construct, consisting of a cis-element multiple cloning site for enhancer insertion, followed by a minimal promoter that drives a transcription factor (TF) dependent cassette that encodes three separate expression markers; a nuclear Tomato fluorophore with a 3x C-terminal nuclear localisation signal (NLS), Herpes Simplex Virus Thymidine Kinase (HSVtk) for negative selection and Neomycin resistance (Neo) for positive selection separated by a 2A self-cleaving peptide (2A). This is followed by a downstream promoter that drives an independent cassette encoding EGFP with a 3x N-terminal NLS, and a Hygromycin resistance selection marker separated by a 2A peptide. (b) This design allows for initial identification of the EGFP fluorophore in nuclei, independent of signal. Expression of the Tomato fluorophore is highly upregulated in a signal-dependent manner. Images shown are monoclonal HEK293T dFLASH-HIF cells. Populations were treated for 48 hours ±DMOG induction of HIF-1α and imaged by HCl. (c) This system can be adapted to a range of different applications. This includes (clockwise) flow cytometry, arrayed screening in a high throughput setting with high content imaging, isolation of highly responsive clones or single cells from a heterogenous population or temporal imaging of pooled or individual cells over time.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[150, 120, 860, 616]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[120, 634, 880, 909]]<|/det|>
+Figure 2. dFLASH provides sensitive readouts to three distinct TF pathways (a-c) Three distinct enhancer elements enabling targeting of three different signalling aspects. (a) Hypoxic response elements (HRE) provide a read out for HIF-1α activation; (b) Progesterone response elements (PRE) derived from progesterone receptor target genes facilitate reporting of progestin signaling; (c) Gal4 response elements (GalRE) enable targeting of synthetic transcription factors to dFLASH such as a GAL4DBD-HIFCAD fusion protein that provides a FIH-dependent reporter response. (d-f) Flow cytometry histograms showing Tomato expression following 48 hr treatments of the indicated dFLASH polyclonal reporter cells (d) HEK293T; 1mM DMOG or 0.1% DMSO (Ctrl), (e) T47D; 100nM R5020 or Ethanol (Ctrl), (f) HEK293T; 1μg/mL Doxycycline (Dox) and 1mM DMOG or Dox and 0.1% DMSO (Ctrl). (g-i) Reporter populations as in d-f were temporally imaged for 38 hours using HCl directly after treatment with (g) 0.5mM DMOG or 0.1% DMSO, (4 replicates) (h) 100nM R5020, 35nM E2, 0.5mM DMOG or 0.1% Ethanol (EtOH) (4 replicates), (i) 0.1% DMSO, 1mM DMOG, 100ng/mL Dox and 0.1% DMSO, or 100ng/mL Dox and 1mM DMOG (4 replicates).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[130, 120, 855, 210]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[222, 230, 396, 245]]<|/det|>
+HIF response Pathway
+
+<|ref|>image<|/ref|><|det|>[[125, 247, 870, 530]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[420, 536, 583, 565]]<|/det|>
+Synthetic FIH Sensor HEK293T dFLASH-synFIH
+
+<|ref|>image<|/ref|><|det|>[[125, 571, 860, 740]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[118, 118, 740, 136]]<|/det|>
+## Figure 3. Derivation of robust, screen-ready dFLASH clonal lines
+
+<|ref|>text<|/ref|><|det|>[[115, 135, 880, 616]]<|/det|>
+(a) Schematic for derivation and assessment of robustness for clonal lines of (b-e) HEK239T dFLASH-HIF (mcdFLASH-HIF), (f-i) T47D dFLASH-PGR (mcdFLASH-PGR) and (j-m) HEK293T dFLASH-synFIH (mcdFLASH-synFIH) were analysed by flow cytometry, temporal HCI over 38 hours and for inter-plate robustness by mock multi-plate high throughput screening with HCI. (b-e) mcdFLASH-HIF was (b) treated with DMOG for 48 hours and assessed for Tomato induction by flow cytometry relative to vehicle controls with fold change between populations displayed and (c) treated with vehicle or 0.5mM DMOG and imaged every 2 hours for 38 hours by HCI (mean ±sem, 8 replicates). (d-e) mcdFLASH-HIF was treated for 48 hours with 1mM DMOG or vehicle (6 replicates/plate, n = 10 plates) by HCI in a high throughput screening setting (HTS-HCI) for (d) normalised dFLASH expression and (e) Tomato MFI alone. (f-i) T47D mcdFLASH-PGR was (f) assessed after 48 hours of treatment with 100nM R5020 by flow cytometry for Tomato induction and (g) treated with 10nM R5020, 35nM E2, 10nM DHT and vehicle then imaged every 2 hours for 38 hours by temporal HCI for normalised dFLASH expression (mean ±sem, 8 replicates). (h-i) T47D mcdFLASH-PGR was assessed by HTS-HCI at 48 hours (24 replicates/plate, n = 5 plates) for (h) dFLASH normalised expression and (i) Tomato MFI alone. (j) HEK293T dFLASH-synFIH was assessed, with 200ng/mL and or Dox and 1mM DMOG by flow cytometry for dFLASH Tomato induction (k) mcdFLASH-synFIH was treated with 100ng/mL Dox, 1mM DMOG and relevant vehicle controls and assessed for reporter induction by temporal HCI (mean ±sem 4 replicates). (l-m) mcdFLASH-synFIH cells were treated with 200ng/mL Dox (grey), 1mM DMOG (red), vehicle (pink) or Dox and DMOG (orange) and assessed by HTS-HCI after 48 hours (24 replicates/plate, n = 3 plates) for (l) normalised dFLASH expression or (m) Tomato MFI induction between Dox and Dox and DMOG treated populations. Dashed lines represent 3SD from relevant vehicle (+3SD) or requisite ligand treated population (-3SD). Fold change for flow cytometry and HTS-HCI (FC) is displayed. Z' was calculated from all analysed plates by HTS-HCI. Z' for all plates analysed was > 0.5.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[128, 103, 898, 600]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[115, 660, 880, 696]]<|/det|>
+Figure 4. Near homogenous activation of mcdFLASH-HIF by CRISPRoff knockdown of VHL.
+
+<|ref|>text<|/ref|><|det|>[[115, 697, 880, 870]]<|/det|>
+(a) Clonal (1) mcdFLASH-HIF lines derived post-hygromycin (HygroB) selection were transduced first with the (2) sgRNA vector targeting VHL transcriptional start site, followed by puromycin selection (Puro). This pool was subsequently transduced by the (3) CRISPRoffv2.1 virus and selected with blasticidin (BlastS) prior to flow cytometry (on day 5 and 10 post Blasticidin selection). (b) The (1) dFLASH vector with the HRE enhancer was transduced as were 2 variants of the CRISPRoffv2.1 vector with either (3A) EF1α promoter or (3B) SFFV promoter driving the dCas9 expression cassette. (c, d) Flow cytometry for dFLASH-HIF induction in response to the CRISPRoffv2.1 VHL knockdown relative to parental line (Ctrl) with (c) EF1a or (d) SFFV expression constructs after 10 days of selection.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[95, 115, 872, 900]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 85, 878, 120]]<|/det|>
+## Figure 5. Bimodal small molecule screening of the HIF signalling pathway with dFLASH-HIF identifies positive and negative regulators
+
+<|ref|>text<|/ref|><|det|>[[117, 120, 880, 290]]<|/det|>
+(a) HEK293T mcdFLASH-HIF cells were treated with a 1595 compound library and incubated for 36 hours prior to (b) the first round of HCl normalised dFLASH activity. Compounds that changed EGFP >±2SD are shown in grey and excluded as hits. Compounds that increase Tomato/EGFP >2SD from the vehicle controls (dashed line) are highlighted in red. After the activation screen, the compound wells were then treated with 1mM DMOG for 36 hours prior to the second round of HCl. Compounds that decreased dFLASH activity greater than 2SD from DMOG controls (dashed line) are shown in red. Compounds that changed EGFP >±2SD are shown in grey and excluded as hits. Normalised dFLASH output (Z scoring) for all analysed wells. (d-f) The screening protocol of (a-c) was repeated using 24 hr points for HCl.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[122, 92, 860, 350]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[117, 366, 852, 401]]<|/det|>
+Figure 6. Investigating mechanisms for HIF-1α regulation by hit dFLASH-HIF inhibitor RQ500235 and hit activator RQ200674
+
+<|ref|>text<|/ref|><|det|>[[115, 401, 881, 594]]<|/det|>
+(a, b) Inhibitor RQ500235 identified from the bimodal screen (a) represses DMOG induced Tomato in dFLASH- HIF cells in a dose dependent manner (n=2, Tom MFI, red; Tom normalised to EGFP, black) and (b) decreases expression of HIF- 1α protein as assessed by immunoblot of whole cell extracts from endogenous HA- Flag tagged HIF- 1α in HEK293T cells. S.E.= short exposure; L.E.= long exposure. (c) RT- PCR shows HIF- 1α transcript is significantly decreased in HEK293T cells treated for 6 hours with RQ500235 (n =3, \*p=0.0139). (d) Activator RQ200674 identified from the bimodal screen recapitulated activation of dFLASH- HIF at 50μM in HEK293T cells (n = 2). (e) in vitro iron chelation assay of RQ200674 displays weak chelating activity at 236μM from line of best fit (n = 3) compared to positive control iron chelator and HIF- 1α activator, dipyridyl.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[57, 87, 345, 150]]<|/det|>
+639 640 Supplementary Figures 641 642
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[130, 108, 825, 700]]<|/det|>
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 708, 835, 740]]<|/det|>
+## Supplementary Figure 1. Optimised dFLASH design produces a robust HIF sensor.
+
+<|ref|>text<|/ref|><|det|>[[117, 740, 881, 910]]<|/det|>
+(a- b) HEK293T cells with HRE- dFLASH constructs without EGFP and (a) expressing monomeric Tomato or (b) dimeric Tomato were treated \(- / + 1\mathrm{mM}\) DMOG for 48 hours and quantified by FACS. Tomato MFI \(>200\mathrm{AU}\) was used to compare induction (black line). (c- e) HEK293T and HEPG2 cells were transduced with HRE- dFLASH reporters that had different downstream promoters controlling EGFP or Tomato cassette composition and treated for 48 hours \(- / + 1\mathrm{mM}\) DMOG prior to HCl. The (d) Tomato/EGFP MFI ratio and (e) EGFP MFI for each backbone variant was then compared (Data from three independent biological replicates). (f) HEK293T cells transduced with reporter constructs containing the downstream PGK/CMV or EF1a promoters were compared for DMOG induction by HCl after 48 hours of \(- / + 1\mathrm{mM}\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 84, 881, 198]]<|/det|>
+658 DMOG treatment (Data from three independent biological replicates). Significance was assessed with a Two- Way ANOVA (\\*\\*\\* p < 0.001, ns = not significant). (g,h) 659 HEK293T cells with the HRE enhancer and different dFLASH backbone compositions 660 of (g) PGK/CMV dFLASH with Tomato alone as the upstream cassette or (h) dFLASH- 661 HIF were treated for 48- hours - /+ 1mM DMOG prior to EGFP analysis and Tomato 662 induction by FACS. 663 664 665
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 108, 875, 592]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[117, 600, 880, 636]]<|/det|>
+Supplementary Figure 2. dFLASH provides a TF-responsive, versatile reporter platform in heterogenous cell pools.
+
+<|ref|>text<|/ref|><|det|>[[117, 635, 881, 774]]<|/det|>
+(a-b) HEK293T cells were transduced with (a) dFLASH with no enhancer and treated with 1mM DMOG or 0.1% DMSO (Ctrl) or (b) GalRE-dFLASH and Gal4DBD-miniVPR and treated with H2O (Ctrl) or 1μg/mL Dox for 48 hours prior to FACS. Dot plots of populations' Tomato and EGFP intensity with or without activating chemicals and histograms comparing EGFP and Tomato MFI between control and treated populations are shown. (c-h) Dot plots and EGFP histograms for control and chemical treated (c, f) dFLASH-HIF, (d, g) dFLASH-PR polyclonal pools (to accompany Figure 2a-c) and (e, h) dFLASH-synFIH.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[63, 110, 925, 576]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[115, 603, 880, 655]]<|/det|>
+Supplementary Figure 3. Synthetic transcription factors drive a strong response from the GalRE- dFLASH reporter and can respond to endogenous signaling pathways.
+
+<|ref|>text<|/ref|><|det|>[[115, 655, 880, 860]]<|/det|>
+(a) GAL4DBD-miniVPR is expressed from an independent dox-inducible vector that subsequently binds to GalRE-dFLASH. (b,c) HEK293T GalRE-dFLASH cells were transduced with GAL4DBD-miniVPR expression construct and were treated -/+ doxycycline for 48 hours prior to HCI for (b) Tomato expression (top panels) and EGFP expression (bottom panels). (c) Normalised fluorescence intensity was also quantified for treated populations (n=3, mean ±sem). FC is Fold change between the populations. (d, e) To confirm HEK293T dFLASH-synFIH system was FIH dependent, (d) GalRE-dFLASH and GAL4DBD-HIFCAD vectors were transduced into HEK293T cells with FIH knocked out. (e) FIH KO cells were compared with wildtype HEK293T dFLASH-synFIH (WT) in a 200ng/mL dox background for DMOG-dependent reporter induction by HCI (n=3). (c, e) Significance was assessed by t-test with Welch's correction (ns = not significant, *** p <0.001, ****p <0.0001).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[120, 140, 864, 333]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[400, 336, 660, 355]]<|/det|>
+PGR response Pathway
+
+<|ref|>image<|/ref|><|det|>[[120, 357, 884, 732]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[396, 738, 645, 781]]<|/det|>
+Synthetic FIH Sensor HEK293T dFLASH-synFIH
+
+<|ref|>image<|/ref|><|det|>[[186, 797, 830, 976]]<|/det|>
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[117, 82, 765, 115]]<|/det|>
+Supplementary Figure 4. Clonal dFLASH cell lines enable improved reporting across different cell types.
+
+<|ref|>text<|/ref|><|det|>[[115, 115, 880, 355]]<|/det|>
+(a- c) Flow cytometry of clonal dFLASH- HIF cell lines for (a) HEK293T (see also Figure 3b) and (b,c) HepG2 cells after 48 hours -/+ 0.5mM DMOG. (d- h) dFLASH- PGR functionality was assessed by flow cytometry in (d)T47D (see also Figure 3f) and (e,f) BT474 cells after 48 hours -/+ 100nM R5020. (g,h) T47D dFLASH- PGR cells were treated with increasing concentrations of R5020 (0.01- 100nM, 8 replicates per group) and (g) imaged over 38 hours with temporal HCl or (h) imaged at 48 hours to determine sensitivity to R5020. (i) Comparison of inductions of the T47D mcdFLASH- PGR line to different steroids (10nM R5020, 35nM E2, 10nM DHT, 10nM Dex, 10nM RA) by HCl after 48 hours of treatment. (g) and (i) are the mean±sem of normalised Tomato/GFP (within each expt) from \(n = 3\) independent experiments (24 replicates), except Dex and RA ( \(n = 2\) (16 replicates)). (j, k) Clonally derived HEK293T dFLASH- synFIH cells were (j) analysed by flow cytometry after 48 hours of 200ng/mL Dox -/+ 1mM DMOG (see also Figure 3k) with (k) showing temporal HCl comparisons between monoclonal (mc) and polyclonal (pc) lines (see also Figure 2j).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[125, 104, 920, 360]]<|/det|>
+
+
+<|ref|>image_caption<|/ref|><|det|>[[181, 398, 220, 420]]<|/det|>
+b.
+
+<|ref|>image<|/ref|><|det|>[[201, 409, 864, 696]]<|/det|>
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 85, 881, 252]]<|/det|>
+731 Supplementary Figure 5. HIF- 1α is the predominant isoform that affects the 732 dFLASH reporter in HEK293T cells 733 (a) Monoclonal HEK293T cells with endogenously HA- Flag tagged HIF- 1α or HIF- 2α 734 were treated with hypoxia (<1% O2) for 16 hours prior to anti- HA immunoblotting of 735 whole cell extracts. S.E.= short exposure; L.E.= long exposure. Representative of 736 three independent experiments. (b) mcdFLASH- HIF cells were treated -/+ 1mM 737 DMOG and -/+ 10μM of the HIF- 2α antagonist (PT- 2385) as indicated and quantified 738 by HCl over 72- hour period. 739 740 741 742
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[70, 120, 963, 455]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[67, 101, 95, 118]]<|/det|>
+a.
+
+<|ref|>sub_title<|/ref|><|det|>[[117, 508, 803, 544]]<|/det|>
+## Supplementary Figure 6. CRISPRoff mediated VHL knockdown induces mcdFLASH-HIF reporter lines.
+
+<|ref|>text<|/ref|><|det|>[[115, 543, 881, 696]]<|/det|>
+(a) HEK293T cells were first transduced with dFLASH-HRE and a clonal reporting line was derived after hygromycin (HygroB) treatment. This line was in turn transduced with the VHL sgRNA vector and selected with puromycin (Puro). This line was then transduced with the CRISPRoffv2.1 vector and selected with blasticidin S (Blast) and populations were subjected to flow cytometry after 5 days or 10 days of selection for analysis of reporter expression. (b-d) dot plots for dFLASH expression from the (b) non-CRISPRoff parental line, (c) EF1a-CRISPRoffv2.1 transduced and (d) SFFVp-CRISPRoffv2.1 populations after 5 or 10 days of blasticidin selection (see also Figure 4).
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[40, 145, 515, 300]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[166, 312, 425, 330]]<|/det|>
+24-hour Activator Screen
+
+<|ref|>image<|/ref|><|det|>[[530, 145, 951, 300]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[625, 112, 883, 131]]<|/det|>
+36-hour Inhibitor Screen
+
+<|ref|>image<|/ref|><|det|>[[40, 342, 515, 487]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[150, 502, 446, 522]]<|/det|>
+i. Activator Screen
+
+<|ref|>image<|/ref|><|det|>[[530, 342, 951, 487]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[625, 311, 883, 330]]<|/det|>
+24-hour Inhibitor Screen
+
+<|ref|>image<|/ref|><|det|>[[530, 504, 870, 740]]<|/det|>
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[117, 152, 855, 204]]<|/det|>
+Supplementary Figure 7. Hit selections and assessment of bimodal screen reproducibility between independent screens for activators and inhibitors of HIF- 1α.
+
+<|ref|>text<|/ref|><|det|>[[117, 205, 880, 345]]<|/det|>
+Compound- induced dFLASH- HIF reporter activity was used to score hits from the (a- d) 36- hour or the (e- h) 24- hour bimodal screens according to Tomato MFI and adjusted P scores. Lines indicate cut offs for hit criteria with hits shown in red for each metric and dismissed compounds that change EGFP \(> \pm 2\) SD shown in grey. (i, j) Pearson correlations of the Tomato/EGFP between the 36- hour and the 24- hour screens for (i) reporter activation ( \(\mathrm{R} = 0.62\) , \(\mathrm{p} < 2.2 \times 10^{- 16}\) ) or (j) reporter inhibition ( \(\mathrm{R} = 0.62\) , \(\mathrm{p} < 2.2 \times 10^{- 16}\) ) for all 1595 compounds screened. Line indicates line of best fit, grey boundary is 95% confidence interval.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[66, 100, 950, 374]]<|/det|>
+
+<|ref|>image<|/ref|><|det|>[[75, 409, 830, 560]]<|/det|>
+
+<|ref|>text<|/ref|><|det|>[[115, 624, 880, 675]]<|/det|>
+Supplementary Figure 8. Rescreening of activator hits from 1595 compound small molecule screen reveals RQ200674 causes normoxic stabilisation of HIF- 1α
+
+<|ref|>text<|/ref|><|det|>[[115, 675, 881, 812]]<|/det|>
+(a) The 11 top performing hits from the activator screens, including RQ200674 (see also Figure 6d) were rescreened against HEK293T mcdFLASH-HIF at 10μM, 25μM and 50μM. Comparisons between Tomato/GFP and Tomato MFI dFLASH induction shown against vehicle (-ve Ctrl) and 1mM DMOG (+ve Ctrl) treated populations (n=2). (b) Immunoblot of whole cell extracts from HEK293T cells containing endogenously HA-Flag tagged HIF-1α and treated as indicated with vehicle (0.1% DMSO), 1mM DMOG (+ve Ctrl), or 100μM and 200μM of RQ200674 for 18 hours. Representative of 2 independent experiments.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[52, 82, 959, 899]]<|/det|>
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[60, 85, 881, 118]]<|/det|>
+844 Supplementary Figure 9. Flavokawain B, Celastarol and RQ500235 decrease 845 dFLASH- HIF and proteasomal inhibition doesn't rescue RQ500235 impact on 846 HIF- 1α.
+
+<|ref|>text<|/ref|><|det|>[[60, 118, 881, 290]]<|/det|>
+844 Supplementary Figure 9. Flavokawain B, Celastarol and RQ500235 decrease 845 dFLASH- HIF and proteasomal inhibition doesn't rescue RQ500235 impact on 846 HIF- 1α. 847 (a- c) The 18 top inhibitory compounds, including (b) Flavokawain B (RQ100976), (c) Celastarol (RQ000155) and RQ500235 (see also Figure 6a) were rescreened against 849 dFLASH- HIF at 10μM, 25μM and 50μM in 1mM DMOG treated 293T dFLASH- HIF 850 cells (24 hours). Comparisons between Tomato/GFP and Tomato MFI dFLASH 851 induction shown against 0.1% DMSO (-ve Ctrl) and 1mM DMOG (+ve Ctrl) treated 852 populations (n=2). (d) Immunoblot of whole cell extracts from HEK293T cells with 853 endogenously HA- Flag tagged HIF- 1α following a 12 hr treatment period with with the 854 indicated combinations of 1 mM DMOG (full12 hr), 50μM RQ500235 (final 6 hr) and 855 10μM MG132 (final 3 hr). Representative of 2 independent experiments. 856 857 858
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[196, 82, 738, 465]]<|/det|>
+
+<|ref|>title<|/ref|><|det|>[[117, 518, 766, 552]]<|/det|>
+# Supplementary Movie 1. Single cell temporal dynamics of HEK293T mcdFLASH-HIF cells
+
+<|ref|>text<|/ref|><|det|>[[116, 553, 850, 623]]<|/det|>
+HEK293T mcdFLASH- HIF cells were seeded at \(1 \times 10^{5}\) cells/dish in Poly- D- Lysine coated plates overnight prior to imaging with spinning disk confocal microscopy at 40x magnification. Cells were imaged every 15 min for 48 hours for Tomato (Magenta) and EGFP (Green) expression. Time stamps are given in top left.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[205, 82, 740, 460]]<|/det|>
+
+<|ref|>title<|/ref|><|det|>[[118, 526, 848, 561]]<|/det|>
+# Supplementary Movie 2. Single cell temporal dynamics of T47D mcdFLASH-PGR cells
+
+<|ref|>text<|/ref|><|det|>[[118, 562, 850, 630]]<|/det|>
+T47D mcdFLASH- PGR cells were seeded at \(5 \times 10^{5}\) cells/dish in Poly- D- Lysine coated plates overnight prior to imaging with spinning disk confocal microscopy at 40x magnification. Cells were imaged every 15 min for 48 hours for Tomato (Magenta) and EGFP (Green) expression. Time stamps are given in top left.
+
+<|ref|>sub_title<|/ref|><|det|>[[119, 699, 209, 714]]<|/det|>
+## Methods:
+
+<|ref|>text<|/ref|><|det|>[[118, 732, 880, 890]]<|/det|>
+Plasmid Construction. cDNAs were amplified using the Phusion polymerase (NEB) and assembled into Clal/Nhel digested pLV410 digested backbone by Gibson assembly31. Sequence verified LV- REPORT plasmid sequences and constructs are listed in Supplementary Table 1. Briefly, the plasmids contained an upstream multiple cloning sites followed by a minimal promoter (derived from the pTRE3G minimal promoter) and then followed by a reporter construct mnucTomato/HSVtk- 2a- Neo or other variants). This was then followed by a constitutive promoter (EF1a, PGK or PGK/CMV) driving the expression or hygromycinR cassette with or without a 2a linked d2nucEGFP (Supplementary Figure 1C).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 84, 880, 308]]<|/det|>
+To improve the performance of our previously reported lentiviral inducible expression systems65, the PGK promoter in Tet-On3G IRES Puro was replaced by digestion with MluI/NheI and insertion of either EF1a-Tet-On3G-2A-puro, EF1a-Tet-On3G-2A-BlastR or EF1a-Tet-On3G-2A-nucTomato using Phusion polymerase (NEB) amplified PCR products from existing plasmids. Plasmids were cloned by Gibson isothermal assembly and propagated in DB3.1 cells (Invitrogen). We also generated a series of constitutive lentiviral plasmids as part of this work pLV- Egl-BlastR (EF1a- Gateway- IRES- BlastR), pLV- Egl- ZeoR (EF1a- Gateway- IRES- ZeoR), pLV- Egl- HygroR (EF1a- Gateway- IRES- HygroR), pLV- SFFVp- gl- BlastR (SFFVp- Gateway- IRES- BlastR), pLV- SV40p- gl- BlastR (SV40p- Gateway- IRES- BlastR). These plasmids were constructed by isothermal assembly of G- Blocks (IDT DNA) or PCR fragments, propagated in ccbD competent cells, sequence verified and deposited with Addgene (Supplementary Table 1).
+
+<|ref|>text<|/ref|><|det|>[[115, 324, 880, 530]]<|/det|>
+The Lentiviral backbone expression construct pLV- TET2BLAST- GtwyA was then using to insert expression constructs cloned into pENTR1a by LR Clonase II enzyme recombination (Cat#11791020, Thermo). GAL4DBD- HIFCAD (727- 826aa) and the GAL4DBD28 were cloned into pENTR1a by ScaI/EcoRV or KpnI/EcoRI respectively. The miniVPR sequence29 was cloned into the pENTR1a- GAL4DBD construct at the EcoRI and NotI sites. The pENTR1a vectors were then Gateway cloned into the pLV- TET2PURO- GtwyA vector. pENTR1a- CRISPRoffv2.1 was generated by inserting an EcoRI/NotI digested CRISPRoff2.1 (CRISPRoff- v2.1 was a gift from Luke Gilbert, Addgene #167981) into pENTR1a plasmid. pLV- SFFVp- CRISPRoffv2.1- IRES- BLAST and pLV- EF1a- CRISPRoffv2.1- IRES- BLAST were generated by pENTR1a by LR Clonase II enzyme recombination (Cat#11791020, Thermo). All Lentiviral plasmids were propagated in DH5a without any signs of recombination.
+
+<|ref|>text<|/ref|><|det|>[[115, 545, 880, 700]]<|/det|>
+Enhancer element cloning. The 12x HRE enhancer from hypoxic response target genes (PGK1, ENO1 and LDHA) was liberated from pUSTdS- HRE12- mCMV- lacZ24 with XbaI/SpeI and cloned into AvrII digested pLV- REPORT plasmids. Progesterone responsive pLV- REPORT- PRECat PRECat was cloned by isothermal assembly of a G- Block (IDT- DNA) containing enhancer elements from 5 PGR target gene enhancers (Zbtb16, Fkbp5, Slc17a11, Erfnb1, MT2)31 into AscI/Clal digested pLV- REPORT(PGK/CMV). Gal4 response elements (5xGRE) were synthesised (IDT DNA) with Clal/AscI overhangs and cloned into Cla/AscI digested pLV- REPORT(PGK/CMV). Sequences are in Supplementary Table 2.
+
+<|ref|>text<|/ref|><|det|>[[115, 716, 880, 906]]<|/det|>
+Mammalian cell culture and ligand treatment. HEK293T (ATCC CRL- 3216), HEPG2 (ATCC HB- 8065) line were grown in Dulbecco's Modified Eagle Medium (DMEM high glucose) + pH 7.5 HEPES (Gibco), 10% Foetal Bovine Serum (Corning 35- 076- CV or Serana FBS- AU- 015), 1% penicillin- streptomycin (Invitrogen) and 1% Glutamax (Gibco). T47D (ATCC HTB- 133) or BT474 (ATCC HTB- 20) were grown in RPMI 1640 (ATCC modified) (A1049101 Gibco) with 10% Foetal Bovine Serum (Fisher Biotech FBS- AU- 015) and 1% penicillin- streptomycin66. Cells were maintained at 37°C and at 5% CO2. Clonal lines were isolated by either limiting dilution or FACS single cell isolation into 96 wells trays. Resultant monoclonal populations were evaluated for single colony formation or assessed by HCI or FACS. Ligand treatments were done 24 hours after seeding of cells in requisite plate or vessel. Standard
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 85, 880, 190]]<|/det|>
+concentrations and solvent, unless specified otherwise, are 200ng/mL Doxycycline (Sigma, H₂O), 0.5mM or 1mM DMOG (Cayman Scientific, DMSO), 100nM R5020 (Perkin- Elmer NLP004005MG, EtOH), 35nM Estradiol (E2, Sigma E2758, EtOH), 10nM all- trans retinoic acid (RA, Sigma #R2625), 10nM Dihydrotestosterone (DHT, D5027), 10nM Dexamethasone (Dex, Sigma D4902), 10μM PT- 2385 (Abcam, DMSO).
+
+<|ref|>text<|/ref|><|det|>[[117, 203, 880, 410]]<|/det|>
+Lentiviral Production & stable cell line production. Near confluent HEK293T cells were transfected with either psPAX2 (Addgene #12260) and pMD2.G (Addgene #12259) or pCMV- dR8.2 dvpr (Addgene #8455), pRSV- REV (Addgene; #12253) and pMD2.G along with the Lentivector (described above) and PEI (1μg/μl, polyethyleneimine) (Polysciences, USA), Lipofectamine 2000, or Lipofectamine 3000 at a 3μl:1μg ratio with DNA. Media changed 1- day post- transfection to complete media or Optimem. Virus was harvested 1- 2 days post- transfection, then viral media was filtered (0.45μM or 0.22μM, Sartorius) before the target cell population was transduced at a MOI < 1. Cells were incubated with virus for 48 hours prior media being exchanged for antibiotic containing complete media. Standard antibiotic concentrations were 140μg/mL hygromycin (ThermoFisher Scientific #10687010), 1μg/mL Puromycin (Sigma; #P8833) or 10μg/mL Blasticidin S (Sigma; CAT#15205).
+
+<|ref|>text<|/ref|><|det|>[[117, 425, 880, 702]]<|/det|>
+Generation of CRISPR knockout or knockdown cell lines. Generation of CRISPR knockout guides and plasmids against FIH has been previously described67. These guides were transfected into HEK293T cells and with PEI at a 3μg:1μg ratio then clonally isolated as above. Knockouts were confirmed with PCR amplification and sanger sequencing coupled with CRISPR- ID68. FIH knockouts were selected via serial dilution and confirmation of knockout by sequencing and T7E1 assay. The VHL sgRNA guides were selected from the Dolcetto CRISPRi library69 with BsmBI compatible overhangs (Supplementary Table 3). These oligos were annealed, phosphorylated then ligated into BsmBI- digested pXPRO50 (Addgene#9692), generating XPR- 050- VHL. Monoclonal HEK293T LV- REPORT- 12xHRE cell lines were transduced with the XPR- 050- sgVHL virus, and stable cell lines selected with Puromycin. Subsequently, LV- SFFVp- CRISPRoffv2.1- IRES- BlastR or LV- EF1a- CRISPRoffv2.1- IRES- BlastR virus was infected into HEK293T LV- REPORT- 12xHRE/XPR- 050- sgVHL stable cells and selected with Blasticidin S (15μg/ml) for 5 days. FACS was used to assess activation of the dFLASH- HRE reporter in parental (dFLASH- HRE/sgVHL) or CRISPRoffv2.1 expressing cells at day 5 or day 10 after Blasticidin S addition.
+
+<|ref|>text<|/ref|><|det|>[[117, 718, 880, 910]]<|/det|>
+CRISPR knock- in of tags to endogenous HIF- 1α and HIF- 2α. CRISPR targeting constructs clones targeting adjacent to the endogenous HIF- 1α and HIF- 2α stop codons70. Constructs were cloned into px330 by ligating annealed and phosphorylated oligos with Bbsl digested px330, using hHIF- 1α and hHIF- 2α CTD sgRNA (Supplementary Table 3). Knock- in of HA- 3xFlag epitopes into the endogenous HIF- 1α or HIF- 2α loci in HEK293T cells was achieved by transfection with 0.625 μg of pNSEN, 0.625μg of pEFIRES- puro6, 2.5μg of px330- sgHIF- α CTD, and 1.25μg of ssDNA HDR template oligo containing flanking homology to CRISPR targeting site the tag insertion and a PAM mutant into \(\sim 0.8 \times 10^{6}\) cells using PEI (3:1). 48 hours after transfection, the medium was removed from cells and replaced with fresh medium supplemented with 2 μg/ml puromycin for 48 hours and the cell medium was changed
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[115, 84, 880, 190]]<|/det|>
+to fresh medium without puromycin. 48 hours later cells were seeded by limiting dilution into 96- well plates at an average of 0.5 cells/well. Correct integration was identified by PCR screening using HIF- \(1\alpha\) and HIF- \(2\alpha\) gDNA screening primers (Supplementary Table 4). Positive colonies resiolated as single colonies by limiting dilution. Isolated HIF- \(1\alpha\) and HIF- \(2\alpha\) tag insertions were confirmed by PCR, sanger sequencing and western blotting.
+
+<|ref|>text<|/ref|><|det|>[[115, 205, 880, 582]]<|/det|>
+High Content Imaging (HCI). Cells were routinely seeded at \(1 \times 10^{4}\) to \(5 \times 10^{4}\) cells per well in black walled clear bottom 96 well plates (Costar Cat#3603), unless otherwise stated. Cell populations were imaged in media at the designated time points at \(10 \times\) magnification and \(2 \times 2\) binning using the ArrayScan™ XTI High Content Reader (ThermoFisher). Tomato MFI and EGFP MFI was imaged with an excitation source of \(560 / 25 \text{nm}\) and \(485 / 20 \text{nm}\) respectively. Individual nuclei were defined by nuclear EGFP expression, nuclear segmentation and confirmed to be single cells by isodata thresholding. Nuclei were excluded from analysis when they couldn't be accurately separated from neighbouring cells and background objects, cells on image edges and abnormal nuclei were also excluded. EGFP and Tomato intensity was then measured for each individual nucleus from at least 2000 individual nuclei per well. Fixed exposure times were selected based on \(10 - 35\%\) peak target range. Quantification of the images utilised HCS Studio™ 3.0 Cell Analysis Software (ThermoFisher). For assessment of high throughput robustness of each individual reporting line in a high throughput setting (HTS- HCI), replicate 96 well plates were seeded for the HIF (10 plates), PGR (5 plates) and synFIH (3 plates) monoclonal reporter lines and imaged as above at 48 hours. For the HIF line, each plate had 6 replicates per treatment (vehicle or DMOG) per plate. For the PGR, 24 replicates per treatment, either vehicle or R5020 per plate were present with edge wells excluded. 24 replicates per treatment were also used for synFIH, with system robustness assessed between the DOX/DMSO and DOX/DMOG treatment groups. Z' and fold change (FC) for the Tomato/EGFP ratio for each individual plate was then calculated as per 34:
+
+<|ref|>equation<|/ref|><|det|>[[390, 579, 606, 617]]<|/det|>
+\[Z^{\prime} = 1 - \frac{(3\sigma_{c + } - 3\sigma_{c - })}{|\mu_{c + } - \mu_{c - }|}\]
+
+<|ref|>text<|/ref|><|det|>[[115, 617, 880, 807]]<|/det|>
+Z' for every plate across each system was confirmed to be \(>0.5\) . Overall robustness of each system is the average of every individual Z' and FC for each system. For temporal high content imaging, HIF, PGR and synHIF lines were seeded in plates and treated with requisite ligands immediately prior to HCI. Four treatment replicates per plate were used to assess the polyclonal population. 4 treatments per plate were used to assess the synFIH monocline (DOX, DMSO, DOX/DMSO, DOX/DMOG), with \(100 \text{ng / \mu L}\) Doxycycline utilised, and 8 treatments per plate (vehicle, DMOG or R5020) were used to assess the PGR and HIF monoclonal lines. Plates were humidified and maintained at \(37^{\circ} \text{C}\) , \(5\%\) CO₂ throughout the imaging experiment. Plates were then imaged every 2 hours for 40- 48 hours. At every timepoint, a minimum 2000 nuclei were resampled from each well population.
+
+<|ref|>text<|/ref|><|det|>[[115, 822, 880, 874]]<|/det|>
+T47D mcdFLASH- PGR R5020 Dose response curve EC50 calculation. T47D mcdFLASH- PGR cells were treated with increasing doses of 0.01- 100nM R5020 and quantified by HCI after 48hrs. Tomato/GFP values were min/max normalised ( \(x' =\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 85, 878, 128]]<|/det|>
+\(\frac{(X - x_{min})}{(x_{max} - x_{min})}\) ) within each experiment (n = 3) and the EC50 constant and curve fitted using the drc R package from 71.
+
+<|ref|>text<|/ref|><|det|>[[115, 144, 880, 732]]<|/det|>
+Bimodal small molecule screen to identify activators or inhibitors of the hypoxic response pathway. Library of natural and synthetic compounds was supplied by Prof. Ronald Quinn and Compounds Australia, available by request. 5mM of each of the 1595 compounds were spotted in 1μL DMSO into Costar Cat#3603 plates and stored at \(- 80^{\circ}C\) prior to screening. Plates were warmed to \(37^{\circ}C\) prior to cell addition. Monoclonal HIF HEK293T reporter cells were seeded at \(0.5\times 10^{4}\) cells per well across 20 Costar Cat#3603 plates pre- spiked with 5mM of compound in 1uL of DMSO in 100uL. On each plate, 4 wells were treated with matched DMSO amounts to compound wells as were four 1mM DMOG controls. Plates were then imaged using HCI (described above) at 36 hrs or 24 hours for reporter activation. Wells were then treated with 100uL of 2mM DMOG (for 1mM DMOG final, 200uL media final). 4 vehicle and 8 DMOG- treated controls (excluding the initial controls from the activator screen) were used for the inhibitor screen. Cells were imaged again 36 hours (Screen 1) or 24 hours (Screen 2) after treatment with 1mM DMOG in the compound wells. Data was Z scored and control wells were used to establish gating for abnormal expression of Tomato and EGFP fluorophores. For the activator screen, compounds within \(+ / - 2SD\) EGFP MFI of vehicle wells were counted as having unchanged transcriptional effects. Compounds with Tomato/EGFP ratio greater than \(+2SD\) of vehicle controls was counted as a putative hit. For the inhibitor screen, compounds within \(+ / - 2SD\) EGFP MFI of DMOG controls were counted as having unchanged GFP expression and Compounds with Tomato/EGFP ratio lower than - 2SD from the DMOG control were considered putative inhibitors. To correct for false positives within each screen, Z scored compounds were converted to their respective P score and adjusted with a \(^{72}\) correction. Pearson correlations were then used to compare compound expression between screens with the base R package (4.4.0). Putative activators and inhibitors identified in the screens were re- spotted at 1mM, 2.5mM and 5mM in 1μL of DMSO in Costar Cat#3603 96 well trays. Activators were rescreened by HCI after 24 hours against \(1\times 10^{4}\) cells HIF reporter monoclonnes in biological duplicate against with vehicle and 1mM DMOG controls in \(100\mu \mathrm{L}\) . Inhibitors were rescreened by HCI after 24 hours in duplicate against \(1\times 10^{4}\) cells HIF reporter monoclonnes with 1mM DMOG to compound wells. Final compound concentrations were \(10\mu \mathrm{M}\) , \(25\mu \mathrm{M}\) and \(50\mu \mathrm{M}\) respectively and Tomato MFI and Tomato/EGFP ratio for each compound was assessed. dFLASH Bimodal high throughput screen details can be found in Supplementary Table 5.
+
+<|ref|>text<|/ref|><|det|>[[117, 747, 880, 884]]<|/det|>
+Reverse Transcription and Real Time PCR. Cells were seeded in 60mm dishes at \(8\times 10^{4}\) cells per vessel overnight before treatment for 48 hours with 1mM DMOG or \(0.1\%\) DMSO. Cells were lysed in Trizol (Invitrogen), and RNA was purified with Qiagen RNAEasy Kit, DNase1 treated and reverse transcribed using M- MLV reverse transcriptase (Promega). cDNA was then diluted for real time PCR. Real- time PCR used primers specific for HIF- 1α, and human RNA Polymerase 2 (POLR2A) (Supplementary Table 4). All reactions were done on a StepOne Plus Real- time PCR machine utilising SYBER Green, and data analysed by 'QGene' software. Results are
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[118, 85, 878, 120]]<|/det|>
+normalised to POLR2A expression. RT- qPCR was performed in triplicate and single amplicons were confirmed via melt curves.
+
+<|ref|>text<|/ref|><|det|>[[118, 135, 880, 411]]<|/det|>
+Flow cytometry analysis and sorting (FACS). Prior to flow cytometry, cells were trypsinised, washed in complete media and resuspended in resuspended in flow cytometry sort buffer \(\mathrm{(Ca^{2 + } / Mg^{2 + }}\) - free PBS, \(2\% \mathrm{FBS}\) , \(25\mathrm{mM}\) HEPES pH 7.0) for cell sorting) prior to cell sorting or flow cytometry analysis buffer \(\mathrm{(Ca^{2 + } / Mg^{2 + }}\) free PBS, \(2\% \mathrm{FBS}\) , \(1\mathrm{mM}\) EDTA, \(25\mathrm{mM}\) HEPES pH 7.0) for analysis followed by filtration through a \(40\mu \mathrm{M}\) nylon cell strainer (Corning Cat#352340. Cell populations were kept on ice prior to sorting. Flow cytometry was performed either using the BD Biosciences BD LSRFortessa or the BD Biosciences FACS ARIA2 sorter within a biosafety cabinet and aseptic conditions, using an \(85\mu \mathrm{M}\) nozzle. Cell populations were gated by FSC- W/FSC- H, then SSC- W/SSC- H, followed by SSC- A/FSC- A to gate cells. EGFP fluorescence was measured by a \(530 / 30\mathrm{nm}\) detector, and the Tomato fluorescence was determined with the 582/15nm detector. A minimum of 10,000 cells were sorted for all FACS- based analysis. Data is presented as \(\log_{10}\) intensity for both fluorophores. Tomato induction was gated from the top \(1\%\) of the negative control population. Cell counts for histograms are normalised to mode unless stated otherwise. FACS analysis was done on FlowJoTM v10.9.1 software (BD Life Sciences)73.
+
+<|ref|>text<|/ref|><|det|>[[118, 425, 880, 633]]<|/det|>
+Time Lapse Spinning Disc Confocal Microscopy. HEK293T mcdFLASH- HIF and T47D mcdFLASH- PGR cells were seeded at \(1\times 10^{5}\) or \(5\times 10^{5}\) cells per dish respectively, onto \(50\mu \mathrm{g / mL}\) poly- D- lysine \(\mu\) - Dish \(35\mathrm{mm}\) , high Glass Bottom dishes (Ibidii, #81158) in FluoroBrite DMEM (Gibco, A1896701)/10% FBS/ \(1\%\) Pens/ \(1\%\) Glutamax/10mM HEPES pH7.9 and incubated overnight at \(37^{\circ}\mathrm{C}\) with \(5\%\) CO2 prior imaging. Cells were treatment with either \(0.5\mathrm{mM}\) DMOG (mcdFLASH- HIF) or \(100\mathrm{mM}\) R05020 (mcdFLASH- PGR) immediately prior to imaging with a CV100 cell voyager spinning disk confocal Tomato (561 nm, \(50\%\) laser, \(400\mathrm{ms}\) exposure and \(20\%\) gain) and EGFP (488 nm, \(50\%\) laser, \(400\mathrm{ms}\) exposure and \(20\%\) gain fluorescence for 48 hours post treatment with 15min imaging intervals. Images were captured at \(40\mathrm{x}\) with an objective lens with a \(\sim 30\mu \mathrm{m}\) Z stack across multiple fields of view. Maximum projected intensity images were exported to Image J for analysis and movie creation.
+
+<|ref|>text<|/ref|><|det|>[[118, 648, 880, 876]]<|/det|>
+Cell Lysis and Immunoblotting. Cells were washed in ice- cold PBS and lysates were generated by resuspending cells in either cell lysis buffer (20mM HEPES pH 8.0, \(420\mathrm{mMNaCl}_2\) , \(0.5\%\) NP- 40, \(25\%\) Glycerol, \(0.2\mathrm{mM}\) EDTA, \(1.5\mathrm{mM}\) MgCl2, \(1\mathrm{mM}\) DTT, \(1\mathrm{x}\) Protease Inhibitors (Sigma)) (Supp Figure 4) or urea lysis buffer (6.7M Urea, \(10\mathrm{mM}\) Tris- Cl pH 6.8, \(10\%\) glycerol, \(1\%\) SDS, \(1\mathrm{mM}\) DTT) (Figure 6, Supp Figure 8, 9). Quantification of protein levels was done by Bradford Assay (Bio- Rad). Lysates were separated on a \(7.5\%\) SDS- PAGE gel and transferred to nitrocellulose via TurboBlot (Bio- Rad). Primary Antibodies used were anti- HIF1α (BD Biosciences #), anti- HA (HA.11, Biolegend #16B12), anti- Tubulin (Serotec #MCA78G), anti- GAPDH (Sigma #G8796), anti- ARNT (Proteintech #14105- 1- AP). Primary antibodies were detected using horseradish peroxidase conjugated secondary antibodies (Pierce Bioscience #). Blots were visualised via chemiluminescence and developed with Clarity Western ECL Blotting substrates (Bio- Rad).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[117, 84, 868, 189]]<|/det|>
+In vitro iron chelation activity assay. Chelation of iron for RQ200674 was measured by a protocol adapted from \(^{74}\) for use in 96 well plate format. \(0.1\mathsf{mM}\) \(\mathsf{FeSO_4}\) \((50\mu \mathsf{L})\) and \(50\mu \mathsf{L}\) of RQ200674, Dipyridyl (positive control) or DMOG solutions were incubated for 1hr at room temperature prior to addition of \(100\mu \mathsf{L}\) of \(0.25\mathsf{mM}\) Ferrozine (Sigma) and incubated for a further 10 minutes. Absorbance was measured at \(562\mathsf{nM}\) . Chelation activity was quantified as:
+
+<|ref|>equation<|/ref|><|det|>[[330, 202, 662, 236]]<|/det|>
+\[C h e l a t i o n a c t i v i t y = \frac{(A_{c o n t r o l} - A_{x})}{A_{c o n t r o l}}\times 100\]
+
+<|ref|>text<|/ref|><|det|>[[117, 237, 850, 271]]<|/det|>
+Where Acontrol is absorbance of control reactions without RQ200674, DP or DMOG and \(\mathsf{A}_{\mathsf{X}}\) is absorbance of solutions with compound.
+
+<|ref|>text<|/ref|><|det|>[[117, 288, 880, 375]]<|/det|>
+Statistical Analysis. All data in graphs were presented as a mean \(\pm\) sem unless otherwise specified. Significance was calculated by a Two- Way ANOVA with Tukey multiple comparison or unpaired t- test with Welches correction where appropriate using Graphpad PRISM (version 9.0.0). All statistical analysis is from three independent biological replicates
+
+<|ref|>text<|/ref|><|det|>[[117, 390, 880, 444]]<|/det|>
+Figure Creation. Schematics and diagrams were created with BioRender (BioRender.com) and graphs were made either with ggplot package in \(\mathsf{R}^{75}\) and GraphPad PRISM (version 9.0.0).
+
+<|ref|>text<|/ref|><|det|>[[117, 459, 880, 512]]<|/det|>
+Data Availability. Source data are provided with this paper. Additional data, including full construct sequences, are available from corresponding authors upon request. Constructs not available on Addgene can be requested from corresponding authors.
+
+<|ref|>text<|/ref|><|det|>[[117, 526, 880, 735]]<|/det|>
+Acknowledgements. We thank Nicholas Smith, Alexander Pace, and members of our laboratories for critical feedback and helpful discussions. We also wish to acknowledge Adelaide Microscopy and the AHMS and SAHMRI Flow Cytometry facilities for technical assistance. We acknowledge Compounds Australia (www.compoundsaustralia.com) for their provision of specialized compound management and logistics research services to the project. This work was supported by Australian Government Research Training Scholarships (T.P.A, A.E.R), The Emeritus Professor George Rodgers AO Supplementary Scholarship (T.P.A, A.E.R). The Playford Memorial Trust Thyne Reid Foundation Scholarship (A.E.R). The George Fraser Supplementary Scholarship (A.E.R), The University of Adelaide Biochemistry Trust Fund (D.J.P. and M.L.W) and the Bill and Melinda Gates Foundation Contraceptive Discovery Program [OPP1771844] (D.C.B, D.L.R).
+
+<|ref|>text<|/ref|><|det|>[[117, 750, 880, 836]]<|/det|>
+Author contributions. Study was initially conceived by D.C.B and M.L.W. T.P.A, D.C.B., A.E.R designed and performed experiments. T.P.A, D.C.B., M.L.W, M.L. and R.J.Q. performed and analysed the bimodal screening campaign. M.R. and A.E.R. derived FIH KO cell line. T.P.A, D.C.B and M.L.W wrote the manuscript with input from all authors. Work was supervised by D.J.P, D.L.R. & M.L.W.
+
+<|ref|>text<|/ref|><|det|>[[117, 852, 746, 870]]<|/det|>
+Source Data. Source data for figures is available with this manuscript.
+
+<|ref|>text<|/ref|><|det|>[[117, 885, 720, 903]]<|/det|>
+Competing interests. The authors declare no competing interests.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[45, 87, 880, 120]]<|/det|>
+1177 Correspondence and requests for materials. Should be addressed to David C. 1179 Bersten.
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[115, 152, 909, 840]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[125, 138, 860, 155]]<|/det|>
+Supplementary Table 1: Synthetic toolkit for generation of reporter cell lines
+
+| Deposit Name: | Availability | Purpose |
| Dual fluorescent reporter constructs: |
| pLV-REPORT(EF1a) | Addgene #172326 | Reporter with mnucTomato and EF1a downstream promoter |
| pLV-REPORT(EF1a)-TTN | Addgene #172327 | Reporter with mnucTomato-HSVtk-2A-NeoR and EF1a downstream promoter |
| pLV-REPORT(PGK) | Addgene #172328 | Reporter with mnucTomato-HSVtk-2A-NeoR and PGK downstream promoter |
| pLV-REPORT(PGK/CMV) | Addgene #172330 | Reporter with mnucTomato-HSVtk-2A-NeoR and PGK/CMV downstream promoter |
| 12xHRE-pLV-Report-EF1a | Addgene: #172333 | Reporter with HRE enhancer |
| 12xHRE-pLV-REPORT(PGK) | Addgene #172334 | Reporter with HRE enhancer |
| 12xHRE-pLV-REPORT(PGK/CMV) | Addgene #172335 | Reporter with HRE enhancer |
| PRECat-pLV-REPORT(PGK/CMV) | By Request | Reporter with a PR-responsive concatemer, with enhancers from 5 target genes, containing 6 PR response elements. |
| 5xGRE-pLV-REPORT(PGK/CMV) | Addgene #172336 | Reporter with GRE enhancer |
| 12xHRE-pLV-REPORT(EF1a) | By Request | Reporter with HRE |
| 12xHRE-pLV-REPORT(EF1a)-tdnucTomato | By Request | Reporter with tdnucTomato and EF1a downstream promoter |
| Protein expression constructs: |
| pLV-TET2Puro | By Request | Doxycycline-inducible expression vector |
| pLV-TET2BlastR | By Request | Doxycycline-inducible expression vector |
| pL-V-TET2nucTomato | By Request | Doxycycline-inducible expression vector |
| pLV-TET2Puro-gal4DBD-miniVPR-HA | Addgene #207171 | Doxycycline-inducible expression vector for GAL4DBD-miniVPR |
| pLV-TET2Puro-gal4DBD-HIFCAD | Addgene #207173 | Doxycycline-inducible expression vector for GAL4DBD-HIFCAD (727-826) with Myc tag |
| pEF-IRES-puro6 gal4DBD-HIFCAD myc tag | Addgene #207171 | Constitutively expresses GAL4DBD-HIFCAD (727-826) with Myc tag |
| pEF-IRES-puro6 gal4DBD-HIFCAD pGalO linker | Addgene #207172 | Constitutively expresses GAL4DBD-HIFCAD (727-826) with Myc tag |
| pENTR1a-CRISPROffv2.1 | Addgene #207174 | Lentiviral expression vector for CRISPRoffv2.1 with BFP tag |
| pLV-Egl-NeoR | Addgene #207175 | Gateway-compatible lentiviral expression plasmid with Neomycin resistance |
| pLV-Egl-BlasR | Addgene #207176 | Gateway-compatible lentiviral expression plasmid with Blasticidin resistance |
| pLV-Egl-HygroR | Addgene #207177 | Gateway-compatible lentiviral expression plasmid with Hygromycin resistance |
| pLV-Egl-ZeoR | Addgene #207178 | Gateway-compatible lentiviral expression plasmid with Zeocin resistance |
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[117, 93, 880, 315]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[125, 78, 675, 95]]<|/det|>
+Supplementary Table 2: Sequences for enhancer cloning
+
+| PRECat (G-block) |
| gaattacaaaaacaattacaaaaattcaaaattttatcgaTGCATGCCGTCTTACATAAAGGAAGTACAGAGTGTACAAAAACAGCAGACCCAAAAAAGCCGTGAAATGTGAGAACCCAAAACTGTACAGCTTGTTATTTCAGGAAGCAAAACTGAGGAGCGAAGCCGTCTTCATGGAATAATACATCCTGTTCCCACAAGT GACGTTAAGCTTCCAGACTGTGCACAGAGTGCACACTTCACCCAGTGTTGTGTCATCATGGTCAC ACAGTGTTCTTTCCGTGGTCACATCTGTGTCCACATTTTCCTTCCTTTTGATGGGAACAAAAGCAGT CATGTTAGGAAGGGAAAGGACACGGTGTTTAATACACAAATCCATGGACAGCCGTGGGCATC CAGTAATGCCCTGGAATGAGTCAAGAAGGCATTGCCCCAGTTTTTCACTAAGAGCTGCGAGGACA GCCTGTTCCTGTTCAAACCCACCCACAGCCTCCGTTGAGGCGCGCAGCTTTAGGCGTGTACG GTGGGCGCCTATAAAAGC |
| 5xGRE |
| GGTACCAGCTTGCATGCCGTGCAGGTCGGAGTACTGTCTCGCGAGCGAGATACTGTTCCTCCGA GCGGAGTACTGTTCCTCCGAGCGAGGTACTGTTCCTCCGAGCGAGATACTGTTCCTCCGAGCGAG AGAC |
+
+<|ref|>table<|/ref|><|det|>[[117, 393, 880, 547]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[125, 377, 673, 395]]<|/det|>
+Supplementary Table 3: Index of all sgGuide oligos used
+
+ | Upper (5'-3') | Lower (5'-3') |
| VHL Knockdown sgGuide | CACCGCCGGGTGGTCTGGATCGCCGG | AAACCCGCGATCCAGACCACCCGGC |
| hHIF-1α CTD sgRNA | CACCGTCGAAGAATTACTCAGAGCTT | AAACAAGCTCTGAGTAATTCTTCA |
| hHIF-2α CTD sgRNA | CACCGCTCCCTCAGAGCCCTGGACC | AAACGGTCCAGGGCTCTGAGGAGGC |
+
+<|ref|>table<|/ref|><|det|>[[117, 614, 880, 784]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[125, 600, 784, 617]]<|/det|>
+Supplementary Table 4: Primer sets for qPCR and PCR confirmation
+
+ | Forward (5'-3') | Reverse (5'-3') |
| qPCR HIF-1α | TATGAGCCAGAAGAACTTTT AGGC | CACCTCTTTTGGCAAGCATCCTG |
| qPCR PolR2a | GCACCATCAAGAGAGTGCA G | GGGTATTTGATACCACCCTCT |
| HIF-1α gDNA primers | GGCAATCAATGGATGAAAGT GGATT | GCTACTGCAATGCAATGGTTTAA AT |
| HIF-2α gDNA primers: | ACCAACCCTTCTTTCAGGCA TGGC | GCTTGGTGACCTGGGCAAGTCT GC |
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[45, 87, 875, 870]]<|/det|>
+1198 1 Beitz, A. M., Oakes, C. G. & Galloway, K. E. Synthetic gene circuits as tools for drug discovery. Trends Biotechnol 40, 210- 225 (2022). 1200 https://doi.org/10.1016/j.tibtech.2021.06.007 1201 2 Bock, C. et al. High- content CRISPR screening. Nature Reviews Methods Primers 2 (2022). https://doi.org/10.1038/s43586- 021- 00093- 4 1203 3 Lee, T. I. & Young, R. A. Transcriptional regulation and its misregulation in disease. Cell 152, 1237- 1251 (2013). https://doi.org/10.1016/j.cell.2013.02.014 1205 4 Bersten, D. C., Sullivan, A. E., Peet, D. J. & Whitelaw, M. L. bHLH- PAS proteins in cancer. Nat Rev Cancer 13, 827- 841 (2013). https://doi.org/10.1038/nrc3621 1207 5 Darnell, J. E., Jr. Transcription factors as targets for cancer therapy. Nat Rev Cancer 2, 740- 749 (2002). https://doi.org/10.1038/nrc906 1209 6 Sahu, B. et al. Sequence determinants of human gene regulatory elements. Nat Genet 54, 283- 294 (2022). https://doi.org/10.1038/s41588- 021- 01009- 4 1210 7 Tycko, J. et al. High- Throughput Discovery and Characterization of Human Transcriptional Effectors. Cell 183, 2020- 2035 e2016 (2020). https://doi.org/10.1016/j.cell.2020.11.024 1214 8 DelRosso, N. et al. Large- scale mapping and mutagenesis of human transcriptional effector domains. Nature (2023). https://doi.org/10.1038/s41586- 023- 05906- y 1216 9 Ortmann, B. M. et al. The HIF complex recruits the histone methyltransferase SET1B to activate specific hypoxia- inducible genes. Nature Genetics 53, 1022- 1035 (2021). https://doi.org/10.1038/s41588- 021- 00887- y 1219 10 Tan, X., Letendre, J. H., Collins, J. J. & Wong, W. W. Synthetic biology in the clinic: engineering vaccines, diagnostics, and therapeutics. Cell 184, 881- 898 (2021). https://doi.org/10.1016/j.cell.2021.01.017 1222 11 Choe, J. H. et al. SynNotch- CAR T cells overcome challenges of specificity, heterogeneity, and persistence in treating glioblastoma. Science Translational Medicine 13 (2021). 1225 12 Allen, G. M. et al. Synthetic cytokine circuits that drive T cells into immune- excluded tumors. Science 378, 1186- + (2022). https://doi.org/ARTN eaba1624 1227 10.1126/science.aba1624 1228 13 Hernandez- Lopez, R. A. et al. T cell circuits that sense antigen density with an ultrasensitive threshold. Science 371, 1166- + (2021). https://doi.org/10.1126/science.abc1855 1230 14 Roybal, K. T. et al. Engineering T Cells with Customized Therapeutic Response Programs Using Synthetic Notch Receptors. Cell 167, 419- + (2016). https://doi.org/10.1016/j.cell.2016.09.011 1234 15 Hasle, N. et al. High- throughput, microscope- based sorting to dissect cellular heterogeneity. Mol Syst Biol 16, e9442 (2020). https://doi.org/10.15252/msb.20209442 1237 16 Tchasovnikarova, I. A., Marr, S. K., Damle, M. & Kingston, R. E. TRACE generates fluorescent human reporter cell lines to characterize epigenetic pathways. Mol Cell (2021). https://doi.org/10.1016/j.molcel.2021.11.035 1240 17 Adamson, B. et al. A Multiplexed Single- Cell CRISPR Screening Platform Enables Systematic Dissection of the Unfolded Protein Response. Cell 167, 1867- 1882 e1821 (2016). https://doi.org/10.1016/j.cell.2016.11.048
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[44, 78, 880, 905]]<|/det|>
+1243 18 Singhal, R. & Shah, Y. M. Oxygen battle in the gut: Hypoxia and hypoxia- inducible factors in metabolic and inflammatory responses in the intestine. J Biol Chem 295, 10493- 10505 (2020). https://doi.org/10.1074/jbc.REV120.011188
+1246 19 Weigel, B., Vuerich, M., Daneshmandi, S. & Seth, P. Metabolic Switch in the Tumor Microenvironment Determines Immune Responses to Anti- cancer Therapy. Front Oncol 8, 284 (2018). https://doi.org/10.3389/fonc.2018.00284
+1249 20 Triner, D. & Shah, Y. M. Hypoxia- inducible factors: a central link between inflammation and cancer. J Clin Invest 126, 3689- 3698 (2016). https://doi.org/10.1172/JCI84430
+1252 21 Epstein, A. et al. C. elegans EGL- 9 and Mammalian Homologs Define a Family of Dioxygenases that Regulate HIF by Prolyl Hydroxylation. Cell 107 (2001).
+1254 22 Lando, D. et al. FIH- 1 is an asparaginyl hydroxylase enzyme that regulates the transcriptional activity of hypoxia- inducible factor. Genes Dev 16, 1466- 1471 (2002). https://doi.org/10.1101/gad.991402
+1257 23 Tian, Y.- M. et al. Differential Sensitivity of Hypoxia Inducible Factor Hydroxylation Sites to Hypoxia and Hydroxylase Inhibitors. Journal of Biological Chemistry 286, 13041- 13051 (2011). https://doi.org/10.1074/jbc.m110.211110
+1260 24 Razorenova, O. V., Ivanov, A. V., Budanov, A. V. & Chumakov, P. M. Virus- based reporter systems for monitoring transcriptional activity of hypoxia- inducible factor 1. Gene 350, 89- 98 (2005). https://doi.org/10.1016/j.gene.2005.02.006
+1263 25 Villemure, J. F., Savard, N. & Belmaaza, A. Promoter suppression in cultured mammalian cells can be blocked by the chicken beta- globin chromatin insulator 5'HS4 and matrix/scaffold attachment regions. J Mol Biol 312, 963- 974 (2001). https://doi.org/10.1006/jmbi.2001.5015
+1267 26 Emerman, M. & Temin, H. Comparison of promoter suppression in avian and murine retrovirus vectors. Nucleic Acids Res 14 (1986).
+1269 27 O'Connell, R. W. et al. Ultra- high throughput mapping of genetic design space (Cold Spring Harbor Laboratory, 2023).
+1271 28 Lando, D., Peet, D. J., Dean A. Whelan, Jeffery J. Gorman & Whitelaw, M. L. Asparagine Hydroxylation of the HIF Transactivation Domain: A Hypoxic Switch. Science 295 (2002).
+1274 29 Vora, S. et al. Rational design of a compact CRISPR- Cas9 activator for AAV- mediated delivery. bioRxiv, 298620 (2018). https://doi.org/10.1101/298620
+1276 30 Lydon, J. P. et al. Mice lacking progesterone receptor exhibit pleiotropic reproductive abnormalities. Genes & Development 9, 2266- 2278 (1995). https://doi.org/10.1101/gad.9.18.2266
+1279 31 Dinh, D. T. et al. Tissue- specific progesterone receptor- chromatin binding and the regulation of progesterone- dependent gene expression. Scientific Reports 9 (2019). https://doi.org/10.1038/s41598- 019- 48333- 8
+1282 32 Grimm, S. L., Hartig, S. M. & Edwards, D. P. Progesterone Receptor Signaling Mechanisms. J Mol Biol 428, 3831- 3849 (2016). https://doi.org/10.1016/j.jmb.2016.06.020
+1285 33 Giannoukos, G., Szapary, D., Smith, C. L., Meeker, J. E. & Simons, S. S., Jr. New antiprogestins with partial agonist activity: potential selective progesterone receptor modulators (SPRMs) and probes for receptor- and coregulator- induced changes in progesterone receptor induction properties. Mol Endocrinol 15, 255- 270 (2001). https://doi.org/10.1210/mend.15.2.0596
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[45, 80, 880, 888]]<|/det|>
+1290 34 Zhang, J.- H., Chung, T. & Oldenburg, K. A Simple Statistical Parameter for Use in 1291 Evaluation and Validation of High Throughput Screening Assays. Journal of 1292 Biomolecular Screening 4 (1999). 1293 35 Kampmann, M. CRISPRi and CRISPRa Screens in Mammalian Cells for Precision 1294 Biology and Medicine. ACS Chem Biol 13, 406- 416 (2018). 1295 https://doi.org/10.1021/acscmebio.7b00657 1296 36 Jaakkola, P. et al. Targeting of HIF- a to the von Hippel- Lindau Ubiquitylation 1297 Complex by O2- Regulated Prolyl Hydroxylation. Science 292 (2001). 1298 37 Appelhoff, R. J. et al. Differential function of the prolyl hydroxylases PHD1, PHD2, and PHD3 in the regulation of hypoxia- inducible factor. J Biol Chem 279, 38458- 1300 38465 (2004). https://doi.org/10.1074/jbc.M406026200 1301 38 Chen, N. et al. Roxadustat Treatment for Anemia in Patients Undergoing Long- Term 1302 Dialysis. N Engl J Med 381, 1011- 1022 (2019). 1303 https://doi.org/10.1056/NEJMoa1901713 1304 39 Cai, Z., Luo, W., Zhan, H. & Semenza, G. L. Hypoxia- inducible factor 1 is required for 1305 remote ischemic preconditioning of the heart. Proc Natl Acad Sci U S A 110, 17462- 1306 17467 (2013). https://doi.org/10.1073/pnas.1317158110 1307 40 Masoud, G. N. & Li, W. HIF- 1alpha pathway: role, regulation and intervention for 1308 cancer therapy. Acta Pharm Sin B 5, 378- 389 (2015). 1309 https://doi.org/10.1016/j.apsb.2015.05.007 1310 41 Semenza, G. L. HIF- 1 mediates metabolic responses to intratumoral hypoxia and 1311 oncogenic mutations. J Clin Invest 123, 3664- 3671 (2013). 1312 https://doi.org/10.1172/JCI67230 1313 42 Semenza, G. L. Pharmacologic Targeting of Hypoxia- Inducible Factors. Annual Review 1314 of Pharmacology and Toxicology 59, 379- 403 (2019). 1315 https://doi.org/10.1146/annurev-pharmtox- 010818- 021637 1316 43 Keith, B., Johnson, R. S. & Simon, M. C. HIF1α and HIF2α: sibling rivalry in hypoxic 1317 tumor growth and progression. Nat Rev Cancer 12, 9- 22 (2012). 1318 44 Bracken, C. P. et al. Cell- specific regulation of hypoxia- inducible factor (HIF)- 1alpha and HIF- 2alpha stabilization and transactivation in a graded oxygen environment. J 1319 Biol Chem 281, 22575- 22585 (2006). https://doi.org/10.1074/jbc.M600288200 1320 45 Ran, F. A. et al. Genome engineering using the CRISPR- Cas9 system. Nature Protocols 1322 8, 2281- 2308 (2013). https://doi.org/10.1038/nprot.2013.143 1323 46 Huang, L. et al. Inhibitory action of Celastrol on hypoxia- mediated angiogenesis and 1324 metastasis via the HIF- 1α pathway. International Journal of Molecular Medicine 27 1325 (2011). https://doi.org/10.3892/ijmm.2011.600 1326 47 Ma, J. et al. Celastrol inhibits the HIF- 1α pathway by inhibition of mTOR/p70S6K/elF4E and ERK1/2 phosphorylation in human hepatoma cells. 1327 Oncology Reports 32, 235- 242 (2014). https://doi.org/10.3892/or.2014.3211 1328 48 Shang, F.- F. et al. Design, synthesis of novel celastrol derivatives and study on their 1330 antitumor growth through HIF- 1α pathway. European Journal of Medicinal Chemistry 1331 220, 113474 (2021). https://doi.org/10.1016/j.ejmech.2021.113474 1332 49 Srinivasan, B., Johnson, T. E. & Xing, C. Chalcone- based inhibitors against hypoxia- 1333 inducible factor 1—Structure activity relationship studies. Bioorganic & 1334 Medicinal Chemistry Letters 21, 555- 557 (2011). 1335 https://doi.org/10.1016/j.bmcl.2010.10.063
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[44, 80, 870, 890]]<|/det|>
+1336 50 Wan, C. et al. Genome-scale CRISPR-Cas9 screen of Wnt/β-catenin signaling 1337 identifies therapeutic targets for colorectal cancer. Science Advances 7, eabf2567 1338 (2021). https://doi.org/10.1126/sciadv.abf2567 1339 51 Semesta, K. M., Tian, R., Kampmann, M., Von Zastrow, M. & Tsvetanova, N. G. A 1340 high-throughput CRISPR interference screen for dissecting functional regulators of 1341 GPCR/cAMP signaling. PLOS Genetics 16, e1009103 (2020). 1342 https://doi.org/10.1371/journal.pgen.1009103 1343 52 Adamson, B. et al. A Multiplexed Single-Cell CRISPR Screening Platform Enables 1344 Systematic Dissection of the Unfolded Protein Response. Cell 167, 1867- 1882. e1821 1345 (2016). https://doi.org/10.1016/j.cell.2016.11.048 1346 53 Potting, C. et al. Genome-wide CRISPR screen for PARKIN regulators reveals 1347 transcriptional repression as a determinant of mitophagy. Proc Natl Acad Sci U S A 1348 115, E180- E189 (2018). https://doi.org/10.1073/pnas.1711023115 1349 54 Ilegems, E. et al. HIF- 1a inhibitor PX- 478 preserves pancreatic Beta cell function in 1350 diabetes. Science Translational Medicine 14 (2022). 1351 55 Koh, M. Y. et al. Molecular mechanisms for the activity of PX- 478, an antitumor 1352 inhibitor of the hypoxia- inducible factor- 1α. Molecular Cancer Therapeutics 7, 90- 1353 100 (2008). https://doi.org/10.1158/1535- 7163.mct- 07- 0463 1354 56 Welsh, S., Williams, R., Kirkpatrick, L., Paine- Murrieta, G. & Powis, G. Antitumor 1355 activity and pharmacodynamic properties of PX- 478, an inhibitor of hypoxia- 1356 inducible factor- 1A. Molecular Cancer Therapeutics 3 (2004). 1357 https://doi.org/https://doi.org/10.1158/1535- 7163.233.3.3 1358 57 Xia, M. et al. Identification of small molecule compounds that inhibit the HIF- 1 1359 signaling pathway. Mol Cancer 8, 117 (2009). https://doi.org/10.1186/1476- 4598- 8- 117 1360 58 Yin, J.- A. et al. Robust and Versatile Arrayed Libraries for Human Genome- Wide 1362 CRISPR Activation, Deletion and Silencing. bioRxiv, 2022.2005.2025.493370 (2023). 1363 https://doi.org/10.1101/2022.05.25.493370 1364 59 Feldman, D. et al. Optical Pooled Screens in Human Cells. Cell 179, 787- 799. e717 1365 (2019). https://doi.org/10.1016/j.cell.2019.09.016 1366 60 Feldman, D. et al. Pooled genetic perturbation screens with image- based 1367 phenotypes. Nat Protoc 17, 476- 512 (2022). https://doi.org/10.1038/s41596- 021- 00653- 8 1369 61 Yan, X. et al. High- content imaging- based pooled CRISPR screens in mammalian cells. 1370 Journal of Cell Biology 220 (2021). https://doi.org/10.1083/jcb.202008158 1371 62 Nandagopal, N. et al. Dynamic Ligand Discrimination in the Notch Signaling Pathway. Cell 172, 869- 880. e819 (2018). https://doi.org/10.1016/j.cell.2018.01.002 1373 63 Agarwal, V. et al. Massively parallel characterization of transcriptional regulatory 1374 elements in three diverse human cell types. bioRxiv (2023). 1375 https://doi.org/10.1101/2023.03.05.531189 1376 64 Gordon, M. G. et al. LentiMPRA and MPRAflow for high- throughput functional 1377 characterization of gene regulatory elements. Nat Protoc 15, 2387- 2412 (2020). 1378 https://doi.org/10.1038/s41596- 020- 0333- 5 1379 65 Bersten, D. C. et al. Inducible and reversible lentiviral and Recombination Mediated 1380 Cassette Exchange (RMCE) systems for controlling gene expression. PLoS One 10, 1381 e0116373 (2015). https://doi.org/10.1371/journal.pone.0116373
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[45, 84, 880, 550]]<|/det|>
+1382 66 Singhal, H. et al. Genomic agoism and phenotypic antagonism between estrogen and progesterone receptors in breast cancer. Sci Adv 2, e1501924 (2016). 1383 https://doi.org/10.1126/sciadv.1501924 1385 67 Chen, D.- Y. et al. Ankyrin Repeat Proteins of Orf Virus Influence the Cellular Hypoxia Response Pathway. Journal of Virology 91, JVI.01430- 01416 (2017). 1386 https://doi.org/10.1128/jvi.01430- 16 1388 68 Dehairs, J., Talebi, A., Cherifi, Y. & Swinnen, J. V. CRISPR- ID: decoding CRISPR mediated indels by Sanger sequencing. Sci Rep 6, 28973 (2016). 1390 https://doi.org/10.1038/srep28973 1391 69 Sanson, K. R. et al. Optimized libraries for CRISPR- Cas9 genetic screens with multiple modalities. Nat Commun 9, 5416 (2018). https://doi.org/10.1038/s41467- 018- 07901- 8 1394 70 Bersten, D. et al. Core and Flanking bHLH- PAS:DNA interactions mediate specificity and drive obesity (Cold Spring Harbor Laboratory, 2022). 1395 71 Ritz, C., Baty, F., Streibig, J. C. & Gerhard, D. Dose- Response Analysis Using R. PLOS ONE 10, e0146021 (2016). https://doi.org/10.1371/journal.pone.0146021 1398 72 Benjamini, Y. & Hochberg, Y. Controlling the False Discovery Rate: A Practical and Powerful Approach to Multiple Testing. Journal of the Royal Statistical Society: Series B (Methodological) 57, 289- 300 (1995). https://doi.org/https://doi.org/10.1111/j.2517- 6161.1995. tb02031. x 1401 73 Becton, Dickenson & Company. (Ashland, OR, 2021). 1403 74 Wong, F. C. et al. Antioxidant, Metal Chelating, Anti- glucosidase Activities and Phytochemical Analysis of Selected Tropical Medicinal Plants. Iran J Pharm Res 13, 1409- 1415 (2014). 1406 75 Wickham, H. in Elegant Graphics for Data Analysis VIII, 213 (Springer New York, NY, 2009).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[43, 42, 312, 71]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[43, 93, 768, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[59, 130, 323, 230]]<|/det|>
+SupplementaryTable5. docx SuppVideo1. avi SuppVideo2. avi NewRS.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__05a8899c72e9d6e9f51dc6ee54f196890bbf834aca0909920ef6acb684782069/images_list.json b/preprint/preprint__05a8899c72e9d6e9f51dc6ee54f196890bbf834aca0909920ef6acb684782069/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..0637a088a01e8ddab3bf3fa98dbe804cbde1a0dc
--- /dev/null
+++ b/preprint/preprint__05a8899c72e9d6e9f51dc6ee54f196890bbf834aca0909920ef6acb684782069/images_list.json
@@ -0,0 +1 @@
+[]
\ No newline at end of file
diff --git a/preprint/preprint__05aa0c2fc7100b1500f07e08d2628280742c5c4e1a4bf250c2c7ba23e4cc9a7a/images_list.json b/preprint/preprint__05aa0c2fc7100b1500f07e08d2628280742c5c4e1a4bf250c2c7ba23e4cc9a7a/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..61cea4ae14f31d2949b839cdd537254d5022cc74
--- /dev/null
+++ b/preprint/preprint__05aa0c2fc7100b1500f07e08d2628280742c5c4e1a4bf250c2c7ba23e4cc9a7a/images_list.json
@@ -0,0 +1,107 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1 Lipid-protein interactions in \\(\\mathbf{Ca^{2 + }}\\) -bound afTMEM16. A: Structural model of afTMEM16 in \\(0.5\\mathrm{mM}\\mathrm{Ca}^{2 + }\\) in C18 lipid nanodiscs. B: View of the open permeation pathway. C-E: Unsharpened maps of the protein (grey) and associated lipids (red) viewed from the membrane",
+ "footnote": [],
+ "bbox": [
+ [
+ 202,
+ 80,
+ 789,
+ 840
+ ]
+ ],
+ "page_idx": 7
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2. Coordination of lipids outside the permeation pathway. A: View of the seven pathway lipids (in sticks, colored as in Fig. 1F). T325 and Y423 are shown as green sticks. Dashed arrow indicates the distance between the phosphate atoms of the last lipid from the inner (P4) and outer (P3) leaflets. B-C: Coordination of P1-P2 (B) and of P4-P7 (C). Side chains are shown in green sticks. D-E: forward \\((\\alpha)\\) and reverse \\((\\beta)\\) scrambling rate constants for indicated quadruple mutants of residues coordinating lipids outside the pathway (P1-2 and P4-7). Bars are average values for \\(\\alpha\\) (black) and \\(\\beta\\) (grey), error bars are S. Dev., and red circles are values from individual repeats.",
+ "footnote": [],
+ "bbox": [
+ [
+ 113,
+ 120,
+ 872,
+ 540
+ ]
+ ],
+ "page_idx": 10
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3. Functional role of groove-lining residues in lipid scrambling. A-C: Residues lining the extracellular vestibule (A), coordinating P3 (B) and lining the central constriction (C) are shown as green sticks. D-E: forward \\((\\alpha)\\) and reverse \\((\\beta)\\) scrambling rate constants of single and multiple alanine substitutions at the indicated positions. Bars are average values for \\(\\alpha\\) (black) and \\(\\beta\\) (grey), error bars are S. Dev., and red circles are values from individual repeats.",
+ "footnote": [],
+ "bbox": [
+ [
+ 118,
+ 330,
+ 875,
+ 775
+ ]
+ ],
+ "page_idx": 12
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4. Functional and structural regulation of lipid scrambling by membrane thickness. A-B: Forward \\((\\alpha ,\\) black circles) and reverse \\((\\beta ,\\) red circles) scrambling rate constants as a function of membrane thickness in the presence of \\(0.5\\mathrm{mM}\\) (A) or \\(0\\mathrm{Ca}^{2 + }\\) (B). Values are the mean and error bars represent standard deviation. Corresponding lipid compositions are noted above. C-E: Alignment of the permeation pathway of afTMEM16 in (C) C18 nanodiscs in \\(0.5\\mathrm{mM}\\) (grey) or 0",
+ "footnote": [],
+ "bbox": [
+ [
+ 113,
+ 230,
+ 850,
+ 770
+ ]
+ ],
+ "page_idx": 15
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5. Functional and structural characterization of afTMEM16 D511A/E514A. A-B: Forward \\((\\alpha ,\\) black circles) and reverse \\((\\beta ,\\) red circles) scrambling rate constants of D511A/E514A afTMEM16 in \\(0.5\\mathrm{mM}\\) (filled symbols) or \\(0\\mathrm{Ca}^{2 + }\\) (empty symbols). Values are the mean and error bars represent standard deviation. Corresponding lipid compositions are noted above. B: Alignment of afTMME16 D511A/E514A in the presence of \\(\\mathrm{Ca^{2 + }}\\) (green) in C14 lipids with wildtype afTMEM16 in \\(0\\mathrm{Ca}^{2 + }\\) in C18 lipids (grey) with close up view of the permeation pathway.",
+ "footnote": [],
+ "bbox": [
+ [
+ 115,
+ 160,
+ 884,
+ 348
+ ]
+ ],
+ "page_idx": 18
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6. Membrane thinning at the afTMEM16 pathway as a function of acyl chain length. A-D: Views of the density maps for afTMEM16 in C22/Ca \\(^{2 + }\\) (A), C18/Ca \\(^{2 + }\\) (B), C18/0 Ca \\(^{2 + }\\) (C) and C14/0 Ca \\(^{2 + }\\) (D) from the extracellular (top panels) and intracellular (bottom panel) side. The C1 final unsharpened maps containing nanodisc densities were aligned, resampled on the same grid, and colored according to the Z coordinate using UCSF Chimera. The density corresponding to the protein is segmented and shown in gray. Nanodisc densities are colored by displacement along the Z axis and the 0 Å reference height is the same for all structures in each view. Negative values represent membrane thinning relative to the overall nanodisc. The position of the permeation pathway is denoted with arrows.",
+ "footnote": [],
+ "bbox": [
+ [
+ 115,
+ 295,
+ 884,
+ 595
+ ]
+ ],
+ "page_idx": 19
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_7.jpg",
+ "caption": "Figure 7. TMEM16 scramblases enable scrambling by thinning the membrane. A-D: Schematic representation of the open (A-B, colored in green) and closed pathways (C-D, colored in red) in membranes of different thickness. Cyan denotes regions accessible to water. Arrows denote high (solid line), low (dashed line) or no (no line) scrambling.",
+ "footnote": [],
+ "bbox": [
+ [
+ 113,
+ 193,
+ 881,
+ 582
+ ]
+ ],
+ "page_idx": 23
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__05b5b4aca808df2aaf8b5007ff8ad0b8986241d7c3a5ae8a42254ed176560413/preprint__05b5b4aca808df2aaf8b5007ff8ad0b8986241d7c3a5ae8a42254ed176560413_det.mmd b/preprint/preprint__05b5b4aca808df2aaf8b5007ff8ad0b8986241d7c3a5ae8a42254ed176560413/preprint__05b5b4aca808df2aaf8b5007ff8ad0b8986241d7c3a5ae8a42254ed176560413_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..f9994ab54911ba77d1f42ffd7d2fccc1633dcd43
--- /dev/null
+++ b/preprint/preprint__05b5b4aca808df2aaf8b5007ff8ad0b8986241d7c3a5ae8a42254ed176560413/preprint__05b5b4aca808df2aaf8b5007ff8ad0b8986241d7c3a5ae8a42254ed176560413_det.mmd
@@ -0,0 +1,382 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 944, 177]]<|/det|>
+# LARP3, LARP7, and MePCE are Involved in the Early Stage of Human Telomerase RNA Biogenesis
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 832, 424]]<|/det|>
+Chi- Kang Tseng ( ckt0513@ntu.edu.tw) Department of Microbiology, College of Medicine, National Taiwan University Tsai- Ling Kao ( tsailing0905@gmail.com) College of Medicine, National Taiwan University, Yi- Hsuan Chen ( yihsuan1chen@gmail.com) College of Medicine, National Taiwan University, https://orcid.org/0000- 0002- 1029- 7632 Yu- Cheng Huang ( lilyhuang901102@gmail.com) College of Medicine, National Taiwan University, Peter Baumann ( peter@baumannlab.org) Gutenberg University https://orcid.org/0000- 0003- 4892- 1485
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 465, 102, 482]]<|/det|>
+## Article
+
+<|ref|>title<|/ref|><|det|>[[44, 502, 137, 520]]<|/det|>
+# Keywords:
+
+<|ref|>text<|/ref|><|det|>[[44, 539, 220, 559]]<|/det|>
+DOI: https://doi.org/
+
+<|ref|>text<|/ref|><|det|>[[42, 576, 910, 620]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 638, 531, 658]]<|/det|>
+Additional Declarations: There is NO Competing Interest.
+
+<--- Page Split --->
+<|ref|>title<|/ref|><|det|>[[113, 88, 881, 144]]<|/det|>
+# LARP3, LARP7, and MePCE are Involved in the Early Stage of Human Telomerase RNA Biogenesis
+
+<|ref|>text<|/ref|><|det|>[[113, 193, 866, 213]]<|/det|>
+Tsai- Ling Kao1, Yi- Hsuan Chen1, Yu- Cheng Huang1, Peter Baumann2,3, and Chi- Kang Tseng1\*
+
+<|ref|>text<|/ref|><|det|>[[113, 263, 883, 317]]<|/det|>
+1Department of Microbiology, College of Medicine, National Taiwan University, Taipei 100, Taiwan
+
+<|ref|>text<|/ref|><|det|>[[113, 333, 883, 387]]<|/det|>
+2Institute of Developmental Biology and Neurobiology, Johannes Gutenberg University, 55099 Mainz, Germany
+
+<|ref|>text<|/ref|><|det|>[[113, 402, 560, 422]]<|/det|>
+3Institute of Molecular Biology, 55128 Mainz, Germany
+
+<|ref|>text<|/ref|><|det|>[[115, 473, 328, 491]]<|/det|>
+\* Corresponding authors
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 91, 191, 108]]<|/det|>
+## Abstract
+
+<|ref|>text<|/ref|><|det|>[[112, 123, 886, 460]]<|/det|>
+Human telomerase assembly is a highly dynamic process. Using biochemical approaches, we found that LARP3 and LARP7/MePCE are involved in the early stage and that their binding to hTR is destabilized when the mature hTR is produced. LARP7 and MePCE knockdown inhibits the conversion of the 3'- extended short (exS) form into mature hTR and the cytoplasmic accumulation of hTR, resulting in telomere shortening. LARP3 plays a negative role in preventing the processing of the 3'- extended long (exL) form and binding of LARP7 and MePCE. Interestingly, the tertiary structure of the exL form prevents LARP3 binding and facilitates hTR biogenesis. Supporting this process, LARP3 at low levels promotes hTR maturation, increases telomerase activity, and elongates telomeres. Our data suggest that LARP3 and LARP7/MePCE mediate the processing of hTR precursors and thus control the production of functional telomerase.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 84, 886, 638]]<|/det|>
+Telomerase is a ribonucleoprotein complex that contains two highly conserved components in its catalytic core. In humans, one core component is a noncoding RNA called human telomerase RNA (hTR); the other is a protein enzyme called human telomerase reverse transcriptase (hTERT). hTERT copies the template region within hTR to replenish telomeric DNA sequences. Thus, the ends of chromosomes are protected, and the lengths of telomeres are maintained \(^{1}\) . hTR is transcribed by RNA polymerase II and accumulates in a cell as a 451- nt- long RNA \(^{2}\) . Longer forms of this transcript have been reported \(^{3,4}\) . Accumulating evidence suggests that the longer transcripts are predominantly degraded by RNA exosomes in a process mediated by CBC and NEXT \(^{5}\) . However, a fraction of the long transcripts may be processed into the mature form \(^{5}\) . During hTR maturation, 3'- end processing is mediated in concert with multiple 3'- to- 5' exonucleases \(^{3,6,7}\) . A 3'- extended long form (exL, \(\geq 460\) - nt hTR) of hTR is first trimmed by the exosomal component RRP6 to produce the 3'- extended short form (exS, \(\geq 452\) - nt and \(\leq 460\) - nt hTR) \(^{3}\) . The exS of hTR is then processed by two other exonucleases (PARN and TOE1) that function in parallel and/or sequentially to produce mature 451- nt hTR \(^{5 - 8}\) . Given that PARN is detected mainly in the nucleolus and that TOE1 is located in Cajal bodies \(^{7}\) , the formation of mature hTR has been suggested to couple to 3'- end processing with RNA trafficking.
+
+<|ref|>text<|/ref|><|det|>[[113, 648, 886, 880]]<|/det|>
+Human telomerase assembly proceeds via precise stepwise binding of protein components to hTR during 3'- end maturation \(^{3,5,9}\) . The structure of hTR is highly organized and plays a role in mediating its stability, trafficking, and maturation \(^{10}\) . The 3'- domain of hTR folds into a box H/ACA- like domain \(^{11}\) , which is bound by the box H/ACA complex \(^{12}\) . The assembly of the pre- H/ACA complex on hTR via cotranscription is thought to be critical for protecting longer transcripts from rapid degradation \(^{5,9}\) . A biochemical study showed that the exL form of hTR folds into a triple- helix structure \(^{3}\) . Although how the triple helix conformation transiently protects the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 283]]<|/det|>
+exL form of hTR from rapid degradation remains unclear, it creates an opportunity for the H/ACA complex to bind3. The binding of the H/ACA complex is not only critical for hTR stability but also attenuates processing by PARN at position \(451^{3}\) . Mutations in most well- characterized components of human telomerase and telomeres, as well as their accessory factors, have been reported in premature- ageing diseases, such as dyskeratosis congenita, Hoyeral- Hreidarsson syndrome, aplastic anaemia, and idiopathic pulmonary fibrosis13- 16.
+
+<|ref|>text<|/ref|><|det|>[[112, 298, 885, 701]]<|/det|>
+At the molecular level, patients with these telomere biology disorders (TBDs) have characteristic accelerated telomere shortening. In addition to canonical TBDs, mutations in several other genes are associated with dysregulation of telomere maintenance in human diseases17. One of these dysregulated gene products is in the La- related protein (LARP) family, which is an important RNA- binding protein family that emerged early in eukaryote evolution and engaging in a large range of crucial functions in a cell involving both coding and noncoding RNAs18,19. Seven distinct LARP- encoding genes have been identified in humans. Among human LARPs, LARP3 (a genuine La protein) and LARP7 have previously been implicated in human telomere maintenance20,21. Aberrantly expression of LARP3 has been found in various cancer types, including chronic myelogenous leukaemia (CML)22. LARP3 has been shown to interact directly with hTR and cause telomere shortening when exogenous LARP3 is overexpressed in certain cell lines20. Whether LARP3 is involved in hTR biogenesis remains unclear.
+
+<|ref|>text<|/ref|><|det|>[[113, 715, 884, 876]]<|/det|>
+A total of 52 pathogenic variants in the LARP7 gene have been identified in patients with Alazami syndrome23. Patients with Alazami syndrome exhibit very short telomeres, and LARP7 knockdown in cancer cells causes a reduction in telomerase activity and telomere shortening21. In ciliated protozoa and fission yeast, LARP family protein p65 in Tetrahymena thermophila24, p43 in Euplotes aediculatus25, and Pof8 in S. pombe26- 28 are constitutive components of active
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 885, 319]]<|/det|>
+telomerase. In addition to LARP7, MePCE, a LARP7- interacting protein, has been implicated in neurodevelopment29. The heterozygous MePCE nonsense variant c.1552C>T/p. (Arg518\*) has been identified29. Patients with MePCE mutations exhibit a neurodevelopmental disorder phenotype similar to that of patients with loss- of- function mutations in LARP7. Bmc1, a human MePCE homologue, is a fission yeast telomerase holoenzyme30,31. Bmc1 cooperates with Pof8 to recognize correctly folded TER130. Whether human LARP7 and MePCE are involved in hTR and biological functions in a manner analogous to that in other species remains unclear.
+
+<|ref|>text<|/ref|><|det|>[[112, 330, 886, 842]]<|/det|>
+In this study, we established in vitro systems that allowed us to monitor hTR 3'- end maturation and protein component assembly. Telomerase assembled in vitro was functional. Using these systems, we found that LARP3, LARP7, and MePCE participate in the early stage of human telomerase biogenesis. LARP3 binds to the exL form of hTR before H/ACA complex binding and prevents 3'- end processing. The triple- helix structure of the exL form of hTR prevents binding by LARP3 and facilitates 3'- end processing. Supporting these observations, LARP3 knockdown facilitated the maturation of hTR and caused increases in telomerase activity. Consistent with the expression levels of LARP3 increasing during CML progression32 and CML patients normally exhibiting short telomeres33, our data showed that reducing LARP3 expression caused an increase in telomerase activity and telomere elongation in K562 cells. LARP7 and MePCE binding then increases as LARP3 decreases during the conversion of the exS form into the mature form. LARP7 and MePCE knockdown caused telomere shortening by affecting both hTR maturation and localization. Our data suggest that human telomerase assembly is a highly dynamic process that involves compositional and conformational rearrangement, which leads to the production of a functional telomerase.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 91, 179, 108]]<|/det|>
+## Results
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 158, 805, 179]]<|/det|>
+## The establishment of in vitro systems to examine the biogenesis of human telomerase
+
+<|ref|>text<|/ref|><|det|>[[112, 192, 886, 704]]<|/det|>
+Establishing research to study the fates of human hTR precursors is challenging due to the extremely low abundance of endogenous pre- telomerase complexes in a cell. To overcome these limitations and to dissect the molecular mechanisms involved in hTR maturation, in vitro systems of human telomerase biogenesis are established. The in vitro systems we established to study hTR can be classified into 3 major parts: the examination of \(3^{\prime}\) - end maturation of hTR, telomerase component assembly, and telomerase activity (Supplementary Fig. 1a). To analyse the \(3^{\prime}\) - end processing of hTR, we synthesized the H/ACA domain of hTR (starting with nucleotide 206) of the exL form in vitro with oligo A tails in the presence of \(\alpha\) - \(^{32}\mathrm{P}\) - UTP. The oligoadenylated exL form of hTR was incubated in whole- 293T cell extract. During the incubation period, deadenylation neared completion within 10 min (Fig. 1a, lane 2). The exS and mature forms of hTR were produced after a 30\~60- min and 2- hour incubation, respectively (Fig. 1a, lanes 4 and 5). Consistent with previous observations indicating that more than \(80\%\) of the exL form is degraded in vivo \(^5\) , only \(20\%\) of the exL form was converted into the mature form of hTR in our assay (Fig. 1b and Supplementary Fig. 1b). These data indicate that the \(3^{\prime}\) - end processing of hTR was successful in vitro.
+
+<|ref|>text<|/ref|><|det|>[[113, 715, 885, 876]]<|/det|>
+To examine the assembly of telomerase components on hTR, telomerase complexes assembled on the biotinylated exL form of hTR (nucleotides from 1 to 461 with an oligo A tail) with a monoguanosine cap (MMG) were purified at different time points by pulling RNP's down with streptavidin beads (Supplementary Fig. 1a). The purified telomerase complexes were subjected to western blotting (Fig. 1c). DHX36, which has been shown to interact with the \(5^{\prime}\) -
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 886, 388]]<|/det|>
+guanosine tracts of hTR \(^{34}\) , was pulled down. The binding of DHX36 to hTR exerted a minor effect on the maturation of the hTR 3' end (Fig. 1c, lanes 8- 12). All H/ACA complex components (DKC1, NHP2, NOP10, NAF1, and GAR1) were detected. This finding supports in vivo observations \(^{9,35}\) suggesting that NAF1 in the pre- H/ACA complex (NAF1- DKC1- NOP10- NHP2) binds to hTR and is subsequently replaced with GAR1 to produce a functional H/ACA complex. NAF1 was associated mainly with the exL form of hTR in the early maturation stage (Fig. 1c, lanes 9 and 10). In contrast, GAR1 was associated with hTR in the late stage, while NAF1 disassociated from the exL form of hTR (lanes 10- 12). TCAB1 appeared to associate with hTR after NAF1 disassociated along with GAR1 binding (lanes 10- 12).
+
+<|ref|>text<|/ref|><|det|>[[112, 402, 886, 771]]<|/det|>
+To measure the catalytic effect of the in vitro assembled telomerase with either the mature or exL forms of hTR, a direct primer extension assay was performed to measure telomerase activity (Fig. 1d). The telomerase assembled with the exL and mature forms showed enzymatic activity (Fig. 1d). However, the enzymatic activity of the purified telomerase with mature hTR (lanes 5- 8) was higher than that of the exL- containing telomerase (lanes 1- 4). We further examined the processivity of the purified telomerase and plotted the normalized intensity of each telomere- extended species against the repeat number (Fig. 1e). Quantification analysis showed that the telomerase with the mature hTR showed higher processivity than that with the exL form (Fig. 1e). These data suggest that telomerase assembly undergoes compositional rearrangement during 3'- end maturation and that the removal of 3'- extended sequences from hTR may increase telomerase activity and processivity.
+
+<|ref|>text<|/ref|><|det|>[[113, 820, 886, 875]]<|/det|>
+LARP3, LARP7, and MePCE are involved in the early stage of telomerase assemblyBiochemical and structural studies of telomerases from ciliated protozoa and fission yeast revealed
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 80, 886, 880]]<|/det|>
+that an La- related protein and its interacting partners are the constitutive components of a telomerase holoenzyme and are critical for the assembly and activity of this telomerase26,30,36. Therefore, we examined the associations of all human La- related proteins with hTR. LARP3, LARP7 and MePCE were found to be significantly associated with hTR (Fig. 2a). A time course analysis revealed that LARP3 associated with the exL form of hTR before the binding of LARP7, MePCE, and the pre- H/ACA complex (Fig. 2a, lane 8). LARP7 and MePCE appeared to bind to hTR after LARP3 association and concurrently with binding of the pre- H/ACA complex (Fig. 2a, lane 9). All component binding in the telomerase complexes was destabilized when the mature hTR forms were produced (Fig. 2a, lanes 11- 12). To examine how the 3'- extended sequence affects component binding. The different forms of hTR species were individually generated, including the exL, exS, and mature forms, and the pseudoknot plus the 5' stem loop (3' ST del) and the pseudoknot domain of hTR (Fig. 2b). Western blotting of telomerase complexes assembled with the different hTR species revealed that DHX36 bound to all the forms of hTR. Consistent with previous studies showing that the 3' stem loop is critical for H/ACA complex assembly37, deletion of the 3' stem loop abolished the binding of DKC1 (Fig. 2b, lane 11). LARP7 and MePCE preferentially associated with the 3'- extended forms (exL and exS forms) of hTR (Fig. 2b, lanes 8- 10). The extension of the 451- nt hTR- end by 5 nucleotides (nucleotides 1- 455 in the exS form) and 10 nucleotides (nucleotides 1- 461 in the exL form) stabilized the binding of LARP7/MePCE and LARP3, respectively (Fig. 2b, lanes 8 and 9), suggesting that a 3'- extended sequence is required for the stable binding of LARP3, LARP7, and MePCE to hTR. Taken together, these data suggest that LARP3, LARP7, and MePCE are involved in the early stage of telomerase assembly and disassociate from each other when the functional telomerase is produced. Supporting these observations, purified LARP3-, LARP7-, and MePCE- associated endogenous telomerases were
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 90, 664, 108]]<|/det|>
+produced and showed only low levels of telomerase activity (Fig. 2c).
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 160, 626, 179]]<|/det|>
+## The LARP3 binding competes with tertiary structure formation
+
+<|ref|>text<|/ref|><|det|>[[112, 193, 886, 775]]<|/det|>
+LARP3 preferentially associated with the exL form of hTR (Fig. 2b). The exL form of hTR is a highly organized structure that contains two stem- loop conformations and a 3'- terminal UUU stretch. The 3'- terminal UUU stretch in the exL form has been proposed to form a triple helix structure in concert with box H and the UCU sequence between the P4.2 and P5 stems \(^3\) (Fig. 3a). In addition, the 3'- terminal U stretch, which is commonly in the 3'- end of RNA polymerase III transcripts, is the binding target of LARP3 \(^{38}\) . This prompted us to speculate that the preferential binding of LARP3 to the exL form is due to either the 3'- terminal UUU stretch or the structure of the triple helix (Fig. 3a). First, we investigated the effect of the 3'- terminal UUU sequence on LARP3 binding. First, we generated U460C mutant hTR. The U460C mutant lacked the 3'- terminal UUU stretch but showed a strengthened triple- base interaction \(^3\) . If the exL form is normally bound by LARP3 via the triple helix structure, then the U460C mutant would recruit more LARP3 than if LARP3 binds the UUU stretch. In contrast, if the 3'- terminal UUU stretch of exL is the binding site of LARP3, then the U460C mutant will destabilize the association of LARP3 with the exL form of hTR. The results showed that the U460C hTR mutant pulled down less recombinant LARP3 than wild- type hTR, suggesting that LARP3 binding to hTR relied on the terminal UUU stretch in the exL form of hTR, while LARP3 binding to the exL form appeared to be attenuated by the triple helix structure (Fig. 3b).
+
+<|ref|>text<|/ref|><|det|>[[114, 786, 884, 876]]<|/det|>
+The triple helix structure of the exL form plays a role in transiently protecting it from rapid degradation and creates an opportunity for the exL form to enter the biogenesis process that yields the mature form \(^3\) . Consistent with previous observations \(^3\) , the U460C hTR mutant, which
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 886, 352]]<|/det|>
+stabilized the tertiary structure in our study, affected the dynamics of 3'- end processing (Fig. 3c and Supplementary Fig. 2a). Incubation of the U460C mutant for 60 min led to the production of large quantities of the mature form (lane 9) compared to the amount of mature form obtained from wild- type hTR (lane 4). Analysis of in vitro telomerase assembly with the U460C mutant showed a decrease in the binding of LARP3 compared to its binding on wild- type hTR (Fig. 3d). Taken together, these data suggest that LARP3 binding to the exL form of hTR competes with the formation of tertiary structures in the exL form, determining the efficiency of mature hTR production.
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 402, 550, 421]]<|/det|>
+## LARP3 plays a negative role in telomerase biogenesis
+
+<|ref|>text<|/ref|><|det|>[[112, 435, 886, 875]]<|/det|>
+Our results suggest a role for tertiary RNA interactions in the exL form of hTR which promotes 3'- end processing via a mechanism that leads to competition between 3'- end processing and LARP3 binding (Fig. 3). We wondered whether LARP3 plays a negative role in hTR biogenesis. To examine the role of LARP3 in the processing of the exL form, LARP3 was either knocked down or overexpressed in 293T cells (Fig. 4a). There was a minor effect on the steady- state levels of hTR in LARP3- knockdown cells (Fig. 4b). LARP3 knockdown, however, did not substantially affect the assembly of DKC1 with hTR in vitro (Fig. 4c, lanes 1- 12). However, the telomerase activity was increased by 20% when the telomerase was purified by immunoprecipitation based on DKC1 pulldown (Fig. 4d, lane 4). Subjecting LARP3 knockdown- containing extracts to in vitro 3' processing facilitated the biogenesis of hTR (Fig. 4e, lanes 7- 12 and Supplementary Fig. 3a) in contrast to the outcome with control extracts (Fig. 4e, lanes 1- 6). These observations mimicked the effects of the U460C mutant (Fig. 3) and suggested that LARP3 plays a role in preventing 3'- end maturation.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 88, 886, 494]]<|/det|>
+To confirm the negative role of LARP3 in hTR 3'- end processing, we overexpressed LARP3 in 293T cells (Fig. 4a, lanes 3\~4). LARP3 overexpression caused a 1.2-fold and 3.1-fold increase in all forms and the 3'- exL form of hTR, respectively (Fig. 4b). In addition, a 40% decrease in telomerase activity was observed (Fig. 4d, lanes 5\~8). An in vitro telomerase assembly assay revealed that although it exerted minor effects on DKC1 binding, LARP3 overexpression markedly blocked the binding of LARP7 and MePCE to hTR (Fig. 4c, lanes 20\~24). Supporting the observations that LARP3 overexpression caused an increase in the fraction of the exL form, the 3'- end processing of exL was profoundly blocked (Fig. 4f and Supplementary Fig. 3b). These data indicated that the binding of LARP3 to hTR prevented the 3'- end processing of the exL form and may lead to exL targeted for degradation. In addition, the binding of LARP7/MePCE to hTR was blocked by LARP3 binding, suggesting that a switch from LARP3 binding to LARP7/MePCE binding is required for telomerase biogenesis.
+
+<|ref|>sub_title<|/ref|><|det|>[[114, 542, 883, 596]]<|/det|>
+## Reducing the expression level of LARP3 increases telomerase function and causes telomere elongation
+
+<|ref|>text<|/ref|><|det|>[[112, 609, 886, 877]]<|/det|>
+Aberrant expression of LARP3 has been found in various cancers, including CML22. CML patients normally exhibit short telomeres33. Since LARP3 overexpression blocked the 3'- end processing of the exL form hTR (Fig. 4f), we speculated that reducing LARP3 expression levels would rescue the defects caused by LARP3 and may lead to increased telomere length. To evaluate this possibility, LARP3 was depleted in K562 cells (Fig. 5a and Supplementary Fig. 4a). The levels of both the mature and 3'- extended forms of hTR were increased in LARP3- knockdown cells (Fig. 5b). Consistent with this observation, an in vitro 3'- end processing assay indicated that relatively more of the exL from was converted into mature hTR (Fig. 5c and Supplementary Fig. 4b). In
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 249]]<|/det|>
+addition, more telomerase was formed in vitro, as determined by more DKC1 molecules binding to hTR (Fig. 5d, lanes 8\~10). Supporting these findings, increased levels of telomerase activity were observed (Fig. 5e and Supplementary Fig. 4c). We measured telomere length by a telomere restriction fragment (TRF) assay (Fig. 5f). Telomeres were elongated in LARP3- knockdown cells (Fig. 5f, lanes 4\~6).
+
+<|ref|>text<|/ref|><|det|>[[113, 263, 884, 388]]<|/det|>
+In aggregate, our data suggest that LARP3 plays a negative role in controlling telomere length by affecting telomerase biogenesis. LARP3 binds to the exL form of hTR, which prevents not only the binding of LARP7 and MePCE but also the processing of the exL form. As a result, telomerase assembly was impaired, which led to telomere shortening.
+
+<|ref|>sub_title<|/ref|><|det|>[[113, 437, 883, 491]]<|/det|>
+## LARP7 and MePCE knockdown impairs the processing of the exS form and causes cytoplasmic localization of hTR
+
+<|ref|>text<|/ref|><|det|>[[112, 504, 886, 878]]<|/det|>
+LARP7 and MePCE were associated mainly with the exS form (Fig. 2). How LARP7 and MePCE affect exS processing or degradation remains unclear. To evaluate the requirements of LARP7 and MePCE for telomerase biogenesis, we prepared extracts from cells that had been subjected to LARP7 or MePCE knockdown (Fig. 6a and Supplementary Fig. 5a). LARP7 and MePCE knockdown did not affect the steady- state levels of hTR (Fig. 6b). An in vitro telomerase assembly assay showed that MePCE bound the exS form of hTR in the absence of LARP7 (Fig. 6c, lanes 5\~8) and vice versa. In the absence of LARP7 or MePCE, LARP3 bound to hTR relatively longer than it did in the shRNA- treated control cell extracts (Fig. 6c). We investigated the effect of LARP7 and MePCE knockdown on the processing of the exS form. Although exS was processed into mature hTR in the extracts from cells with LARP7 and MePCE knocked down (Fig. 6d, lanes 5, 10, and 15 and Supplementary Fig. 5b), the conversion rate of the exS form into the mature form
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 883, 144]]<|/det|>
+was reduced in extracts from cells with both LARP7 and MePCE knocked down (Fig. 6d, lanes 9 and 14) compared to that in the control extracts (Fig. 6d, lane 4).
+
+<|ref|>text<|/ref|><|det|>[[112, 157, 886, 598]]<|/det|>
+LARP7 and MePCE knockdown mimicked the effect of inhibited PARN activity on the exS form processing3, which substantially impaired the conversion of exS into the mature form in vitro (Fig. 6d). Cytoplasmic localization of hTR has been previously observed in PARN- knockdown cells39. Induced pluripotent stem (iPS) cells from patients with PARN mutations produced short telomeres8. Supporting these observations, PARN- knockdown cells produced shorter telomeres (Fig. 6e, lanes 7 and 8), and 46% of hTR localized to the cytoplasm in PARN- knockdown cells, which was higher than that in control cells (32%) (Fig. 6f and g). We measured telomere length in LARP7- and MePCE- knockdown cells (Fig. 6e and Supplementary Fig. 5d). Telomeres in the LARP7- and MePCE- knockdown cells (Fig. 6e, lanes 3- 6) were shorter than those in the control cells (Fig. 6e, lanes 1- 2). In addition, the fraction of cytoplasmic hTR was increased (Fig. 6f and g). Taken together, these results indicated that LARP7 and MePCE were involved in the conversion of the exS form into the mature form. Defects in LARP7 and MePCE proteins caused the accumulation of hTR in the cytoplasm and telomere shortening.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 648, 206, 666]]<|/det|>
+## Discussion
+
+<|ref|>text<|/ref|><|det|>[[113, 680, 886, 876]]<|/det|>
+Human telomerase biogenesis is a highly dynamic process that is initiated by the precise stepwise binding of protein components to the RNA subunit hTR/TERC. Each step serves as a checkpoint for quality control and plays a decisive role in the production of a mature telomerase versus the elimination of improper products3,5. Deficiency in telomerase components, including proteins and RNA, leads to degenerative human disease. Therefore, understanding telomerase biogenesis is critical for determining its medical relevance and elucidates the cause of telomere disorder
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 884, 285]]<|/det|>
+syndrome. Unfortunately, the low abundance of endogenous telomerase pre- complexes in cells makes it difficult to characterize the molecular mechanisms involved in vivo. To overcome these limitations, we established in vitro cell- free systems that allowed us to investigate telomerase assembly and 3'- end processing of hTR. Using these systems, we uncovered LARP3, LARP7, and MePCE as previously unknown players that are sequentially involved in the early stage of hTR biogenesis (Fig. 7).
+
+<|ref|>text<|/ref|><|det|>[[112, 295, 886, 880]]<|/det|>
+LARP3 has been shown to bind with high affinity to 3' uridylate residues of RNA polymerase III transcripts immediately upon transcription termination; these precursors include 5S rRNA \(^{40}\) , tRNA \(^{40}\) and 7SK RNA \(^{41,42}\) . Similarly, our data indicated that LARP3 preferentially bound to the hTR precursor form exL prior to the binding of LARP7, MePCE, and the H/ACA complex (Fig. 2). The association of LARP3 with the exL form was stabilized by a terminal U stretch (Fig. 3). LARP3 knockdown facilitated the maturation of hTR and telomerase activity (Fig. 4). In contrast, LARP3 overexpression clearly prevented both the processing and degradation of the exL form in vitro and caused a reduction in telomerase activity (Fig. 4). Our data suggest that LARP3 negatively regulates telomerase activity at the level of telomerase biogenesis. Interestingly, the terminal U stretch is also essential for the tertiary structure conformations in the exL form, protecting it from rapid degradation and creating an opportunity for hTR maturation \(^{3}\) . The biogenesis pathway was highly activated when the tertiary structure of the exL form is stabilized after the introduction of a U460C mutation that attenuated LARP3 binding (Fig. 3). These data suggest that the amount of mature hTR is determined by kinetic competition between LARP3 binding to the exL form and the formation of the tertiary exL structure (Fig. 7). Excessive LARP3 blocked the maturation of hTR, and the disassociation of LARP3 was essential for the assembly of functional RNPs with hTR. LARP3 acts as an RNA chaperone to prevent pre- tRNA
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 883, 144]]<|/det|>
+misfolding43,44. However, whether LARP3 specifically recognizes the exL form hTR that fails to fold into the triple helix and targets this faulty hTR for degradation is unclear.
+
+<|ref|>text<|/ref|><|det|>[[113, 157, 886, 633]]<|/det|>
+The average telomere length is normally shorter in CML patients than in healthy individuals33. Additionally, CML patients with long telomeres have been suggested to have a lower clinical risk profile than patients with short telomeres45. The study of the correlation between telomere length and CML progression suggests that patients in later phases (the accelerated phase and blast phase) present with considerably shorter telomeres than patients in the early phase (chronic phase)33. Notably, LARP3 expression correlates with poor clinical prognosis of CML and increases during CML progression32. Our studies established a link between LARP3 expression and human telomerase biogenesis. We showed that reducing the expression level of LARP3 in a CML cell line increased telomere length by promoting telomerase biogenesis and activity (Fig. 5). Together with the observations that the tertiary structure of the exL form attenuates LARP3 binding and facilitates telomerase biogenesis, our data suggest a novel drug intervention point. The development of a small molecule that either directly inhibits LARP3 binding to hTR or specifically targets hTR structure to prevent LARP3 binding may be an important strategy to increase telomerase function and improve the prognosis of CML.
+
+<|ref|>text<|/ref|><|det|>[[113, 645, 886, 876]]<|/det|>
+Previous study suggested that RRP6 processes the terminal U tract and irreversibly disrupts the triple helix and generates the exS form and subsequently dyskerin precisely establishes the 451- nt end by attenuating the 3'- end processing of the exS form via PARN, suggesting that structural rearrangements of hTR is required for efficient maturation3. Our data indicated that the compositional exchange of protein components occurs in this process (Fig. 7). NAF1 is replaced with GAR1. LARP3 appears to disassociate from the exL form of hTR. The mutually exclusive interaction of 7SK RNP with LARP3 or LARP7 has been suggested, and LARP3 needs to be
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 80, 886, 880]]<|/det|>
+replaced by LARP7 for the maturation of 7SK RNPs41. This may be the case with hTR. The binding of LARP7 and MePCE to hTR was attenuated by LARP3 overexpression (Fig. 4c). Notably, LARP3 maintained the association with the exS form longer in the absence of LARP7 and MePCE (Fig. 6c), suggesting that LARP7 and MePCE bind instead of LARP3. We found that LARP7 and MePCE knockdown impaired the PARN-mediated processing of the exS form into the mature form and, like PARN knockdown cells, caused cytoplasmic accumulation of hTR. Together with these observations, these data support a model in which LARP7 and MePCE promote the transition of a LARP3- associated pre- telomerase to a H/ACA complex- associated telomerase that promotes the conversion of the exS form into the mature form. Once this conversion is impaired, hTR would be exported to the cytoplasm and degraded by DCP2- XRN1. Loss of function in LARP7 and MePCE has been shown to cause Alazami syndrome21 and neurodevelopmental disorders29, respectively. Reduced expression of LARP7 has been shown to cause a reduction in telomerase activity and result in progressively shorter telomeres in human cancer cell lines21. Previous works with S. pombe demonstrated that Pof8 plays a key role in S. pombe telomerase RNA folding quality control and forms a complex with Bmc1, the orthologue of MePCE, and Telomerase Holoenzyme Component 1 (Thc1), which promotes the assembly of a functional telomerase26- 28,30,31,46. Similar to that associated with S. pombe Bmc1, telomere shortening has been observed in MePCE- deficient human cells. Interestingly, Thc1 shares structural similarity with the nuclear cap- binding complex and PARN30. LARP7 and MePCE knockdown impaired the conversion of the exS form into the mature form. LARP7 bound hTR in a MePCE- independent manner and was required to stabilize the interaction of MePCE with hTR (Fig. 6c). Although LARP7 and MePCE contribute to the conversion of the exS form into the mature form, they do not remain stably associated with the active telomerase (Fig. 7). Compared
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 886, 283]]<|/det|>
+to S. pombe telomerase RNA, an additional 3'- end processing step is required for the 3' end maturation of telomerase RNA after spliceosomal cleavage in other species47,48. An investigation into the requirement of Pof8 for 3'- end processing in these species may yield interesting results. Our data not only suggest an evolutionary link in the biogenesis of telomerase among distant organisms but also provide new insights into the mechanisms underlying the pathogenesis of LARP3 and LARP7/MePCE deficiencies.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 333, 250, 351]]<|/det|>
+## Online methods
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 402, 408, 421]]<|/det|>
+## Preparation of hTR RNA substrates
+
+<|ref|>text<|/ref|><|det|>[[112, 436, 886, 701]]<|/det|>
+In vitro transcription reactions were carried out in 1X transcription buffer (Promega), \(0.5\mathrm{mM}\) ATP (CROYEZ), CTP (CROYEZ), and GTP (CROYEZ); \(0.1\mathrm{mM}\) UTP (CROYEZ); \(\alpha\) - 32P- UTP (3000 Ci mmol- 1, \(10\mathrm{mCi}\mathrm{ml}^{- 1}\) , PerkinElmer), \(0.2\mu \mathrm{g}\) of DNA template, \(40\mathrm{U}\) of RNasin (TOOLs), and 1 unit \(\mu \mathrm{l}^{- 1}\) T7 RNA polymerase (Promega). The reaction mixtures ( \(10\mu \mathrm{l}\) ) were incubated at \(37^{\circ}\mathrm{C}\) for 30 min followed by the addition of an equal volume of formamide dye. The RNA products were purified on a \(6\%\) polyacrylamide (19:1) gel containing \(8\mathrm{M}\) urea. The primers used to generate the DNA templates are listed in Supplementary Table 1. The loading control actin- 1 RNA was expressed via the Sp6 RNA polymerase (Promega).
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 751, 414, 770]]<|/det|>
+## In vitro hTR 3'-end processing assay
+
+<|ref|>text<|/ref|><|det|>[[113, 785, 884, 876]]<|/det|>
+In vitro hTR processing reactions ( \(10\mu \mathrm{l}\) ) were carried out at \(37^{\circ}\mathrm{C}\) in a buffer containing \(20\mathrm{mM}\) Tris- HCl (pH 7.5), \(50\mathrm{mM}\) KCl, \(2.5\mathrm{mM}\) \(\mathrm{MgCl}_2\) , \(40\mathrm{U}\) RNasin, \(2\mathrm{nM}\) 32P- labelled hTR RNA, and \(40\mu \mathrm{g}\) of whole- cell extracts. Reactions were stopped by the addition of stop buffer ( \(10\mathrm{mg}\mathrm{ml}^{- 1}\)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 87, 884, 249]]<|/det|>
+proteinase K in \(0.5\%\) SDS; \(40\mathrm{mM}\) EDTA; \(20\mathrm{mM}\) Tris- HCl, pH 7.5; and \(1000\mathrm{c.p.m.}\mu \mathrm{l}^{- 1}32\mathrm{P}\) - labelled actin mRNA) and incubation at \(37^{\circ}\mathrm{C}\) for \(30\mathrm{min}\) followed by extraction with phenol/chloroform preequilibrated with \(50\mathrm{mM}\) NaOAc (pH 5.0) and ethanol precipitation. The RNA was dissolved in \(80\%\) formamide dye and analysed on a \(6\%\) polyacrylamide (19:1) gel containing \(8\mathrm{M}\) urea.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 299, 469, 318]]<|/det|>
+## Preparation of capped hTR RNA substrates
+
+<|ref|>text<|/ref|><|det|>[[112, 333, 886, 737]]<|/det|>
+In vitro transcription reactions were performed in 1X transcription buffer (Promega), \(0.5\mathrm{mM}\) nucleoside 5- triphosphates (NTPs), \(25\mu \mathrm{M}\) Bio11 UTP, \(\alpha - 32\mathrm{P}\) - UTP (3000 Ci mmol \(^{- 1}\) , \(10\mathrm{mCi}\mathrm{ml}^{- 1}\) , PerkinElmer), \(0.1\mu \mathrm{g}\) of DNA template, \(40\mathrm{U}\) of RNasin, and \(1\mathrm{U}\) of SP6 RNA polymerase (RiboMAX™, Promega). The reaction mixtures ( \(100\mu \mathrm{l}\) ) were incubated at \(37^{\circ}\mathrm{C}\) for 4 hours and then treated with DNase I (New England Biolabs) at \(37^{\circ}\mathrm{C}\) for 1 hour, followed by extraction with phenol/chloroform preequilibrated with \(50\mathrm{mM}\) NaOAc (pH 5.0) and ethanol precipitation. RNA was dissolved in \(80\%\) formamide dye and purified on a \(4\%\) polyacrylamide (29:1) gel containing \(8\mathrm{M}\) urea. The capping reactions were carried out in 1X capping buffer (New England Biolabs), \(0.5\mathrm{mM}\) GTP, \(0.1\mathrm{mM}\) SAM, and \(1\mathrm{U}\) of vaccinia virus capping enzyme (New England Biolabs). Reaction mixtures were incubated at \(37^{\circ}\mathrm{C}\) for 2 hours, followed by extraction with phenol/chloroform preequilibrated with \(50\mathrm{mM}\) NaOAc (pH 5.0) and ethanol precipitation. The RNA was dissolved in \(\mathrm{ddH_2O}\) .
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 787, 291, 805]]<|/det|>
+## Telomerase pulldown
+
+<|ref|>text<|/ref|><|det|>[[115, 821, 884, 876]]<|/det|>
+Telomerase was assembled in a buffer containing \(20\mathrm{mM}\) Tris- HCl (pH 7.5), \(50\mathrm{mM}\) KCl, \(2.5\mathrm{mM}\) \(\mathrm{MgCl}_2\) , \(40\mathrm{U}\) RNasin, \(50\mathrm{mM}\) capped hTR RNA, and \(10\mu \mathrm{g}\) of whole- cell extracts. The reaction
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 214]]<|/det|>
+mixture (25 μl) was incubated at \(37^{\circ}\mathrm{C}\) for the desired times, followed by centrifugation at 15,000 r.p.m. at \(4^{\circ}\mathrm{C}\) for 2 min. The supernatant was incubated with streptavidin beads at \(4^{\circ}\mathrm{C}\) for 1 hour. The precipitants were washed with NET- 2 buffer (50 mM Tris- HCl pH 7.5, 150 mM NaCl, and \(0.05\%\) NP- 40) and then subjected to Western blotting.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 264, 250, 282]]<|/det|>
+## Immunoblotting
+
+<|ref|>text<|/ref|><|det|>[[112, 297, 886, 529]]<|/det|>
+The human cell pellets were lysed in CHAPS lysis buffer containing \(0.5\%\) CHAPS, \(50\mathrm{mM}\) Tris- HCl (pH 8), \(50\mathrm{mM}\) KCl, \(1\mathrm{mM}\) MgCl2, \(1\mathrm{mM}\) EGTA, \(10\%\) glycerol, \(5\mathrm{mM}\) DTT, and \(1\mathrm{mM}\) PMSF. Cell extracts were diluted in \(2\times \mathrm{LDS}\) sample buffer. Proteins in cell lysate were loaded onto a 4- \(20\%\) Tris- glycine protein gel (mPAGE™ \(4 - 20\%\) Bis- Tris, Millipore) and transferred to a PVDF blot membrane (Bio- Rad). Low- fat milk (5%) in wash buffer ( \(10\mathrm{mM}\) Tris- HCl, pH 8.0; \(150\mathrm{mM}\) NaCl; \(1\mathrm{mM}\) EDTA; and \(10\%\) Triton X- 100) was used as a blocking reagent. The antibodies used in this study are listed in Supplementary Table 3.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 577, 356, 595]]<|/det|>
+## Cell culture and transduction
+
+<|ref|>text<|/ref|><|det|>[[112, 609, 888, 877]]<|/det|>
+293T cells (ATCC® CRL- 3216TM) were maintained in DMEM (Gibco) supplemented with \(10\%\) heat- inactivated foetal bovine serum (Corning) and \(2\mathrm{mM}\) L- glutamine (Gibco) at \(37^{\circ}\mathrm{C}\) in a humidified atmosphere containing \(5\%\) CO2. HeLa cells (ATCC® CCL- 2TM) were maintained in DMEM (Gibco) supplemented with \(10\%\) heat- inactivated foetal bovine serum. K562 cells (horizon, HD PAR- 131) were maintained in IMEM medium (HyClone™) supplemented with \(10\%\) heat- inactivated foetal bovine serum. The cells were subcultured when the confluency reached \(80\%\) . The cells were transfected with \(15\mu \mathrm{g}\) of plasmid DNA using TransIT® LT1 (Mirus) for \(24\mathrm{hr}\) . The plasmids used for transfection are listed in Supplementary Table 2. Cells were transduced with
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[114, 88, 883, 144]]<|/det|>
+shRNAs for 24 hr. Medium containing \(2 \mu \mathrm{g} \mathrm{ml}^{- 1}\) puromycin was used to select the knockdown cells. Information on the shRNAs used for transduction is presented in Supplementary Table 4.
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 194, 323, 212]]<|/det|>
+## Genomic DNA extraction
+
+<|ref|>text<|/ref|><|det|>[[114, 226, 884, 317]]<|/det|>
+Genomic DNA was prepared from pellets (5×106 cells) with a GenEluteTM Mammalian Genomic DNA Miniprep Kit (Sigma–Aldrich, Cat. No: G1N350- 1KT) according to the manufacturer's instructions.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 367, 487, 387]]<|/det|>
+## Terminal restriction fragment (TRF) analysis
+
+<|ref|>text<|/ref|><|det|>[[112, 400, 886, 772]]<|/det|>
+Genomic DNA (1 \(\mu \mathrm{g}\) ) from 293T cells was digested with Hinf I (New England Biolabs) and Rsa I (New England Biolabs) restriction enzymes in 10X CutSmart® Buffer (NEB) at 37°C overnight. The digested gDNA fragments were separated on a 1% SeaKem® LE agarose gel (Lonza) by electrophoresis at 120 V for 12 hours, followed by capillary transfer to a Hybond- N+ nylon transfer membrane (GE Healthcare) in 10X saline sodium citrate (SSC) for 14 hours. DNA was subsequently crosslinked twice to the membrane at 120 mJ in a UV Stratalinker 1800 (Stratagene, 254 nm, 120 mJ). The blot was prehybridized in Church buffer at 65°C for 1 hour and then hybridized with 32P- dCTP- labelled (TTAGGG)3 overnight. The blot was exposed to a phosphor imaging screen (Fujifilm) at room temperature overnight. Phosphor images were scanned by an Amersham Typhoon 5 scanner (Cytiva). The telomere length images were quantified and analysed by ImageQuantTL software (Cytiva).
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 821, 323, 839]]<|/det|>
+## Telomerase activity assay
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 88, 886, 459]]<|/det|>
+Telomerase activity reactions were performed in a \(10 - \mu \mathrm{l}\) reaction volume consisting of \(50~\mathrm{mM}\) Tris- HCl, \(\mathrm{pH}8.0\) ; \(50~\mathrm{mM}\) KCl; \(1\mathrm{mM}\) \(\mathrm{MgCl}_2\) ; \(1\mathrm{mM}\) spermidine; \(5\mathrm{mM}\) DTT; \(1\mathrm{mM}\) dATP; \(1\mathrm{mM}\) dTTP; \(10\mu \mathrm{M}\) dGTP; \(0.75\mu \mathrm{M}^{32}\mathrm{P}\) - \(\alpha\) - dGTP (3000 Ci mmol \(^{- 1}\) ); \(1\mu \mathrm{M}\) telomeric primer (TTAGGG) \(_3\) and \(2\mu \mathrm{g}\) of cell extract at \(37^{\circ}\mathrm{C}\) for 2 hours. Reactions were stopped with \(10~\mu \mathrm{l}\) of \(1\mathrm{mgml}^{- 1}\) proteinase K. DNA was extracted with phenol/chloroform equilibrated with \(50\mathrm{mM}\) NaOAc (pH 7.0) and ethanol precipitated with \(2.5\mathrm{M}\) ammonium acetate and \(10\mu \mathrm{g}\) of glycogen at \(- 80^{\circ}\mathrm{C}\) overnight. Reactions were then centrifuged for \(20\mathrm{min}\) at 14,000 r.p.m., and the pellets were washed with \(1\mathrm{ml}\) of \(70\%\) ethanol. The dried pellets were then resuspended in \(5\mu \mathrm{l}\) of \(80\%\) formamide loading buffer. Reaction products were analysed on a \(10\%\) polyacrylamide (19:1) gel containing \(8\mathrm{M}\) urea. All blots were prepared with products obtained from the same experiment and processed in parallel.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 507, 202, 526]]<|/det|>
+## qRT-PCR
+
+<|ref|>text<|/ref|><|det|>[[113, 540, 886, 771]]<|/det|>
+Quantitative reverse transcription(qRT)- PCR was performed via the SYBR Green method. The 50- fold diluted random hexamer priming cDNA was amplified with the primers shown in Supplementary Table 5 and was performed with a CFX384TM Real- Time PCR System in a C1000 Touch™ Thermal Cycler (Bio- Rad) using iQ™ SYBR® Green Supermix (Bio- Rad, Cat. No. 1708882). The results were normalized to the GAPDH, ATP5β, and HPRT reference gene levels and measured by CFX Maestro software (Bio- Rad). Graphing and statistical analysis of the qRT- PCR results were performed using Prism 9 (GraphPad).
+
+<|ref|>text<|/ref|><|det|>[[113, 820, 598, 840]]<|/det|>
+In situ hybridization (FISH) and immunofluorescence (IF)
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 886, 494]]<|/det|>
+Cells were fixed on coverslips with \(4\%\) paraformaldehyde (Thermo Scientific, Cat. No. 047317) and permeabilized with \(0.1\%\) Triton- X- 100. The cells were hybridized with hybridization buffer (2X SSC, \(10\%\) formamide, \(0.2\mathrm{mgml}^{- 1}\) , \(10\%\) dextran sulfate, \(0.4\mathrm{U}\) RNase inhibitor, \(1\mathrm{mgml}^{- 1}E\) coli tRNA). The cells were incubated with 7 Cy3- conjugated hTR oligos (Supplementary Table 6) at \(37^{\circ}\mathrm{C}\) overnight. For immunofluorescence experiments, cells were incubated with anti- Coilin primary antibody (Abcam, Cat. No. ab11822, \(0.5\mu \mathrm{gml}^{- 1}\) ) in \(1\%\) bovine serum albumin (BSA) for 2 hours, followed by FITC- conjugated AffiniPure goat anti- mouse IgG (H+L) (Jackson ImmunoResearch, Cat. No. 115- 095- 003, 1:100 dilution) secondary antibody for 1 hour. Cells were stained with Hoechst 33258 (Sigma- Aldrich, Cat. No. B2883- 1g, 1:1000 dilution) in \(1\%\) BSA for 10 min. Coverslips were mounted with Fluoromount™ Aqueous Mounting Medium (Sigma- Aldrich, Cat. No. F4680- 25ML). The images were photographed with a Carl Zeiss LSM880 microscope.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[115, 90, 209, 107]]<|/det|>
+## References
+
+<|ref|>text<|/ref|><|det|>[[110, 120, 880, 895]]<|/det|>
+1. Nandakumar, J. & Cech, T.R. Finding the end: recruitment of telomerase to telomeres. Nat. Rev. Mol. Cell Biol. 14, 69–82 (2013).
+2. Feng, J. et al. The RNA component of human telomerase. Science 269, 1236–41 (1995).
+3. Tseng, C.K., Wang, H.F., Schroeder, M.R. & Baumann, P. The H/ACA complex disrupts triplex in hTR precursor to permit processing by RRP6 and PARN. Nat. Commun. 9, 5430 (2018).
+4. Theimer, C.A. et al. Structural and functional characterization of human telomerase RNA processing and cajal body localization signals. Mol. Cell 27, 869–81 (2007).
+5. Tseng, C.K. et al. Human telomerase RNA processing and quality control. Cell Rep. 13, 2232–43 (2015).
+6. Deng, T. et al. TOE1 acts as a 3' exonuclease for telomerase RNA and regulates telomere maintenance. Nucleic Acids Res. 47, 391–405 (2019).
+7. Son, A., Park, J.E. & Kim, V.N. PARN and TOE1 constitute a 3' end maturation module for nuclear non-coding RNAs. Cell Rep. 23, 888–898 (2018).
+8. Moon, D.H. et al. Poly(A)-specific ribonuclease (PARN) mediates 3'-end maturation of the telomerase RNA component. Nat. Genet. 47, 1482–8 (2015).
+9. Darzacq, X. et al. Stepwise RNP assembly at the site of H/ACA RNA transcription in human cells. J. Cell Biol. 173, 207–18 (2006).
+10. Qin, J. & Autexier, C. Regulation of human telomerase RNA biogenesis and localization. RNA Biol. 18, 305–315 (2021).
+11. Mitchell, J.R., Cheng, J. & Collins, K. A box H/ACA small nucleolar RNA-like domain at the human telomerase RNA 3' end. Mol. Cell. Biol. 19, 567–76 (1999).
+12. Fu, D. & Collins, K. Distinct biogenesis pathways for human telomerase RNA and H/ACA small nucleolar RNAs. Mol. Cell 11, 1361–72 (2003).
+13. Revy, P., Kannengiesser, C. & Bertuch, A.A. Genetics of human telomere biology disorders. Nat. Rev. Genet. 24, 86–108 (2023).
+14. Chu, C.M. et al. A missense variant in the nuclear localization signal of DKC1 causes Hoyeraal-Hreidarsson syndrome. NPJ Genom. Med. 7, 64 (2022).
+15. Stuart, B.D. et al. Exome sequencing links mutations in PARN and RTEL1 with familial pulmonary fibrosis and telomere shortening. Nat. Genet. 47, 512–7 (2015).
+16. Podlevsky, J.D., Bley, C.J., Omana, R.V., Qi, X. & Chen, J.J. The telomerase database. Nucleic Acids Res. 36, D339–D43 (2008).
+17. Shay, J.W. & Wright, W.E. Telomeres and telomerase: three decades of progress. Nat. Rev. Genet. 20, 299–309 (2019).
+18. Bayfield, M.A., Yang, R. & Maraia, R.J. Conserved and divergent features of the structure and function of La and La-related proteins (LARPs). Biochim. Biophys. Acta 1799, 365–78 (2010).
+19. Deragon, J.M. Distribution, organization an evolutionary history of La and LARPs in eukaryotes. RNA Biol. 18, 159–167 (2021).
+20. Ford, L.P., Shay, J.W. & Wright, W.E. The La antigen associates with the human telomerase ribonucleoprotein and influences telomere length in vivo. RNA 7, 1068–75 (2001).
+21. Holohan, B. et al. Impaired telomere maintenance in Alazami syndrome patients with LARP7 deficiency. BMC Genomics 17, 749 (2016).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[111, 90, 884, 858]]<|/det|>
+22. Sommer, G. & Heise, T. Role of the RNA-binding protein La in cancer pathobiology. RNA Biol. 18, 218-236 (2021).
+23. Soengas-Gonda, E. et al. Expanding the phenotypic spectrum of alazami syndrome: two unrelated spanish families. Neuropediatrics 54, 31-36 (2023).
+24. Witkin, K.L. & Collins, K. Holoenzyme proteins required for the physiological assembly and activity of telomerase. Genes Dev. 18, 1107-18 (2004).
+25. Aigner, S. et al. Euplotes telomerase contains an La motif protein produced by apparent translational frameshifting. EMBO J. 19, 6230-9 (2000).
+26. Paez-Moscoso, D.J. et al. Pof8 is a La-related protein and a constitutive component of telomerase in fission yeast. Nat. Commun. 9, 587 (2018).
+27. Mennie, A.K., Moser, B.A. & Nakamura, T.M. LARP7-like protein Pof8 regulates telomerase assembly and poly(A)+TERRA expression in fission yeast. Nat. Commun. 9, 586 (2018).
+28. Collopy, L.C. et al. LARP7 family proteins have conserved function in telomerase assembly. Nat. Commun. 9, 557 (2018).
+29. Schneeberger, P.E., Bierhals, T., Neu, A., Hempel, M. & Kutsche, K. de novo MEPCE nonsense variant associated with a neurodevelopmental disorder causes disintegration of 7SK snRNP and enhanced RNA polymerase II activation. Sci. Rep. 9, 12516 (2019).
+30. Paez-Moscoso, D.J. et al. A putative cap binding protein and the methyl phosphate capping enzyme Bin3/MePCE function in telomerase biogenesis. Nat. Commun. 13, 1067 (2022).
+31. Porat, J., El Baidouri, M., Grigull, J., Deragon, J.M. & Bayfield, M.A. The methyl phosphate capping enzyme Bmc1/Bin3 is a stable component of the fission yeast telomerase holoenzyme. Nat. Commun. 13, 1277 (2022).
+32. Trotta, R. et al. BCR/ABL activates mdm2 mRNA translation via the La antigen. Cancer Cell 3, 145-60 (2003).
+33. Brummendorf, T.H. et al. Prognostic implications of differences in telomere length between normal and malignant cells from patients with chronic myeloid leukemia measured by flow cytometry. Blood 95, 1883-90 (2000).
+34. Lattmann, S., Stadler, M.B., Vaughn, J.P., Akman, S.A. & Nagamine, Y. The DEAH-box RNA helicase RHAU binds an intramolecular RNA G-quadruplex in TERC and associates with telomerase holoenzyme. Nucleic Acids Res. 39, 9390-404 (2011).
+35. Kittur, N., Darzacq, X., Roy, S., Singer, R.H. & Meier, U.T. Dynamic association and localization of human H/ACA RNP proteins. RNA 12, 2057-62 (2006).
+36. Aigner, S. & Cech, T.R. The Euplotes telomerase subunit p43 stimulates enzymatic activity and processivity in vitro. RNA 10, 1108-18 (2004).
+37. Dragon, F., Pogacic, V. & Filipowicz, W. In vitro assembly of human H/ACA small nucleolar RNAs reveals unique features of U17 and telomerase RNAs. Mol. Cell. Biol. 20, 3037-48 (2000).
+38. Stefano, J.E. Purified lupus antigen La recognizes an oligouridylate stretch common to the 3' termini of RNA polymerase III transcripts. Cell 36, 145-54 (1984).
+39. Shukla, S., Schmidt, J.C., Goldfarb, K.C., Cech, T.R. & Parker, R. Inhibition of telomerase RNA decay rescues telomerase deficiency caused by dyskerin or PARN defects. Nat. Struct. Mol. Biol. 23, 286-92 (2016).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 88, 880, 495]]<|/det|>
+40. Rinke, J. & Steitz, J.A. Precursor molecules of both human 5S ribosomal RNA and transfer RNAs are bound by a cellular protein reactive with anti-La lupus antibodies. Cell 29, 149-59 (1982).41. Muniz, L., Egloff, S. & Kiss, T. RNA elements directing in vivo assembly of the 7SK/MePCE/Larp7 transcriptional regulatory snRNP. Nucleic Acids Res. 41, 4686-98 (2013).42. Fairley, J.A. et al. Human La is found at RNA polymerase III-transcribed genes in vivo. Proc. Natl. Acad. Sci. U. S. A. 102, 18350-5 (2005).43. Bayfield, M.A. & Maraia, R.J. Precursor-product discrimination by La protein during tRNA metabolism. Nat. Struct. Mol. Biol. 16, 430-7 (2009).44. Chakshusmathi, G., Kim, S.D., Rubinson, D.A. & Wolin, S.L. A La protein requirement for efficient pre-tRNA folding. EMBO J. 22, 6562-72 (2003).45. Wenn, K. et al. Telomere length at diagnosis of chronic phase chronic myeloid leukemia (CML-CP) identifies a subgroup with favourable prognostic parameters and molecular response according to the ELN criteria after 12 months of treatment with nilotinib. Leukemia 29, 2402-4 (2015).46. Hu, X. et al. Quality-control mechanism for telomerase RNA folding in the cell. Cell Rep. 33, 108568 (2020).47. Qi, X. et al. Prevalent and distinct spliceosomal 3'-end processing mechanisms for fungal telomerase RNA. Nat. Commun. 6, 6105 (2015).48. Kannan, R., Helston, R.M., Dannebaum, R.O. & Baumann, P. Diverse mechanisms for spliceosome-mediated 3' end processing of telomerase RNA. Nat. Commun. 6, 6104 (2015).
+
+<|ref|>sub_title<|/ref|><|det|>[[116, 525, 280, 544]]<|/det|>
+## Acknowledgements
+
+<|ref|>text<|/ref|><|det|>[[115, 559, 883, 613]]<|/det|>
+We thank all members of the Tseng laboratory for helpful discussions. This work was supported by MOST 111- 2636- B- 002- 026 - and NTU- 112V1403- 5.
+
+<|ref|>sub_title<|/ref|><|det|>[[115, 647, 240, 666]]<|/det|>
+## Figure legends
+
+<|ref|>text<|/ref|><|det|>[[113, 681, 886, 876]]<|/det|>
+Fig. 1 The establishment of in vitro systems to examine the biogenesis of human telomerase. (a) The in vitro 3' end processing assay with \(^{32}\mathrm{P}\) - labeled hTR fragments (nucleotides 206 to 461 with oligo A tails) were carried out in 293T cell extracts at \(37^{\circ}\mathrm{C}\) for the indicated times. RNA was purified and resolved by a \(6\%\) polyacrylamide gel containing \(8\mathrm{M}\) urea. Actin acted as the loading control. (b) The exL and mature forms of hTR signals were quantified by ImageQuantTL and normalized to \(0\mathrm{min}\) , respectively. (c) Western blotting analysis of telomerase assembled on biotin
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 214]]<|/det|>
+labelled hTR pulled down with streptavidin beads for the indicated times. (d) Telomerase activity of the in vitro purified telomerase assembled on exL and mature forms of hTR. (e) The intensity of each major band \((+4, + 10, + 16, + 22, + 28\) , and so on) from the telomerase activity assay in d was quantitated by phosphorimager analysis.
+
+<|ref|>text<|/ref|><|det|>[[113, 227, 885, 423]]<|/det|>
+Fig. 2 LARP3, LARP7, and MePCE are involved in the early stage of telomerase assembly. (a) Western blotting analysis of in vitro assembled telomerase purified from the indicated times. (b) Western blotting analysis of in vitro assembled telomerase assembled on the different hTR species as shown in the schematic (exL, exS, mature, \(3^{\prime}\) stem loop- deleted, and pseudoknot). (c) Endogenous LARP3, LARP7, MePCE, and DKC1 were immunoprecipitated and subjected to telomerase activity assay.
+
+<|ref|>text<|/ref|><|det|>[[113, 436, 885, 736]]<|/det|>
+Fig. 3 The LARP3 binding competes with tertiary structure formation. (a) Schematic showing the proposed mechanism of how the tertiary structure of exL affects the binding of LARP3. (b) Western blotting analysis of recombinant LARP3 pulled down with biotinylated wild type or the U460C mutant hTR. (c) The in vitro \(3^{\prime}\) end processing assay with \(^{32}\mathrm{P}\) - labeled wild type or U460C mutant hTR fragments (nucleotides 206 to 461 with oligo A tails) were carried out in 293T cell extracts at \(37^{\circ}\mathrm{C}\) for the indicated times. RNA was purified and resolved by a \(6\%\) polyacrylamide gel containing 8 M urea. Actin acted as the loading control. (d) Western blotting analysis of telomerase assembled on biotin- labeled wild type or U460C mutant hTR pulled down with streptavidin beads for the indicated times.
+
+<|ref|>text<|/ref|><|det|>[[113, 750, 884, 876]]<|/det|>
+Fig. 4 LARP3 plays a negative role in telomerase biogenesis. (a) Western blots of cell extracts prepared from 293T cells treated with either shRNA targeting LARP3 or transfected with an LARP3 plasmid. Endogenous TUBULIN served as a loading control. (b) Total RNA prepared from 293T cells treated with either shRNA targeting LARP3 or transfected with an LARP3
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[112, 87, 886, 494]]<|/det|>
+plasmid was subjected to qRT- PCR for total hTR, \(3^{\prime}\) - extended hTR, GAPDH, ATP5β, and HPRT. Bar graph of mean fold change for hTR relative to the control samples and normalized to GAPDH, ATP5β, and HPRT. Mean values were calculated from triplicate qRT- PCR experiments of three biological replicates with bars representing SE. (c) Western blotting analysis of telomerase assembled on biotin- labelled hTR in the indicated extracts, followed by pulldown with streptavidin beads for the indicated times. (d) LARP3 was immunoprecipitated from cell extracts prepared from 293T cells either treated with either shRNA targeting LARP3 or transfected with an LARP3 plasmid and subjected to telomerase activity assay. (e and f) The in vitro \(3^{\prime}\) end processing assay with \(^{32}\mathrm{P}\) - labeled hTR fragments (nucleotides 206 to 461 with oligo A tails) were carried out in cell extracts prepared from 293T cells either treated with either shRNA targeting LARP3 (e) or transfected with an LARP3 plasmid (f) at \(37^{\circ}\mathrm{C}\) for the indicated times. RNA was purified and resolved by a \(6\%\) polyacrylamide gel containing \(8\mathrm{M}\) urea. Actin acted as the loading control.
+
+<|ref|>text<|/ref|><|det|>[[112, 506, 886, 878]]<|/det|>
+Fig. 5 Reducing the expression level of LARP3 increases telomerase function and causes telomere elongation. (a) Western blots of cell extracts prepared from K562 cells treated with shRNA targeting Luciferase or LARP3. Endogenous TUBULIN served as a loading control. (b) Total RNA from LARP3- knockdown K562 cells was subjected to qRT- PCR for the measurement of the levels of total hTR, \(3^{\prime}\) - extended hTR, GAPDH, ATP5β, and HPRT. Bar graph of mean fold change for \(3^{\prime}\) - extended hTR relative to the control samples and normalized to GAPDH, ATP5β, and HPRT. Mean values were calculated from triplicate qRT- PCR experiments of three biological replicates with bars representing SE. (c) The in vitro \(3^{\prime}\) end processing assay with \(^{32}\mathrm{P}\) - labeled hTR fragments (nucleotides 206 to 461 with oligo A tails) were carried out in the indicated cell extracts. RNA was purified and resolved by a \(6\%\) polyacrylamide gel containing \(8\mathrm{M}\) urea. Actin acted as the loading control. (d) Western blotting analysis of telomerase assembled on biotin- labeled hTR in the
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[113, 88, 884, 214]]<|/det|>
+indicated extracts, followed by pulldown with streptavidin beads for the indicated times. (e) Endogenous DKC1 was immunoprecipitated and subjected to telomerase activity assay. (f) Telomere lengths determined by TRF analysis of gDNA prepared from K562 cells treated with the shRNA targeting Luciferase or LARP3.
+
+<|ref|>text<|/ref|><|det|>[[112, 225, 886, 808]]<|/det|>
+Fig. 6 LARP7 and MePCE knockdown impairs the processing of the exS form and causes cytoplasmic localization of hTR. (a) Western blots of cell extracts prepared from 293T cells treated with shRNAs targeting LARP7 or MePCE. (b) Total RNA prepared from 293T cells treated with the shRNA targeting Luciferase, LARP7, or MePCE was subjected to qRT- PCR for the total hTR, 3'- extended hTR, GAPDH, ATP5β, and HPRT. Bar graph of mean fold change for 3'- extended hTR relative to the control samples and normalized to GAPDH, ATP5β, and HPRT. Mean values were calculated from triplicate qRT- PCR experiments of three biological replicates with bars representing SE. (c) Western blots of telomerase assembled on biotin- labeled hTR in the indicated extracts, followed by pulldown with streptavidin beads for the indicated times. (d) The in vitro 3' end processing assay with \(^{32}\mathrm{P}\) - labeled hTR fragments (nucleotides 206 to 461 with oligo A tails) were carried out in the indicated cell extracts. RNA was purified and resolved by a 6% polyacrylamide gel containing 8 M urea. Actin acted as the loading control. (e) Telomere lengths determined by TRF analysis of gDNA prepared from 293T cells treated with the shRNA targeting Luciferase, LARP7, MePCE, or PARN. (f) In situ hybridization and immunofluorescence data after sh- Luc, sh- PARN, sh- LARP7, and sh- MePCE treatment in HeLa cells. Coilin served as a Cajal body marker. The scale bar represents 5 μm. (g) Bar graph illustrating the distribution of hTR in the cytosolic and nuclear fractions.
+
+<|ref|>text<|/ref|><|det|>[[114, 821, 479, 841]]<|/det|>
+Fig. 7 Schematic showing the working model.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 43, 143, 68]]<|/det|>
+## Figures
+
+<|ref|>text<|/ref|><|det|>[[44, 88, 68, 106]]<|/det|>
+图
+
+<|ref|>text<|/ref|><|det|>[[44, 130, 115, 149]]<|/det|>
+Figure 1
+
+<|ref|>text<|/ref|><|det|>[[44, 173, 133, 191]]<|/det|>
+Figure 1- 7
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 216, 311, 243]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 266, 765, 286]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 304, 367, 350]]<|/det|>
+Supplementary materials.pdf.pdfSupplementary materials.pdf.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__05f1891193c1720f597ee19876aa1d2b3d061937d2a7931dcff717edf288996f/preprint__05f1891193c1720f597ee19876aa1d2b3d061937d2a7931dcff717edf288996f_det.mmd b/preprint/preprint__05f1891193c1720f597ee19876aa1d2b3d061937d2a7931dcff717edf288996f/preprint__05f1891193c1720f597ee19876aa1d2b3d061937d2a7931dcff717edf288996f_det.mmd
new file mode 100644
index 0000000000000000000000000000000000000000..c5e6e0ef855fc06f959bb34f390f90cb48abdbad
--- /dev/null
+++ b/preprint/preprint__05f1891193c1720f597ee19876aa1d2b3d061937d2a7931dcff717edf288996f/preprint__05f1891193c1720f597ee19876aa1d2b3d061937d2a7931dcff717edf288996f_det.mmd
@@ -0,0 +1,442 @@
+<|ref|>title<|/ref|><|det|>[[44, 107, 911, 175]]<|/det|>
+# Learning the statistics of pain: computational and neural mechanisms
+
+<|ref|>text<|/ref|><|det|>[[44, 195, 625, 238]]<|/det|>
+Flavia Mancini ( fm456@cam.ac.uk) University of Cambridge https://orcid.org/0000- 0001- 8441- 9236
+
+<|ref|>text<|/ref|><|det|>[[44, 243, 230, 282]]<|/det|>
+Suyi Zhang University of Oxford
+
+<|ref|>text<|/ref|><|det|>[[44, 289, 588, 330]]<|/det|>
+Ben Seymour University of Oxford https://orcid.org/0000- 0003- 1724- 5832
+
+<|ref|>sub_title<|/ref|><|det|>[[44, 371, 102, 388]]<|/det|>
+## Article
+
+<|ref|>text<|/ref|><|det|>[[44, 408, 545, 428]]<|/det|>
+Keywords: pain, Bayesian models, sensory pain pathways
+
+<|ref|>text<|/ref|><|det|>[[44, 446, 335, 465]]<|/det|>
+Posted Date: November 8th, 2021
+
+<|ref|>text<|/ref|><|det|>[[44, 484, 475, 504]]<|/det|>
+DOI: https://doi.org/10.21203/rs.3.rs- 1003293/v1
+
+<|ref|>text<|/ref|><|det|>[[44, 521, 910, 565]]<|/det|>
+License: © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License
+
+<|ref|>text<|/ref|><|det|>[[42, 600, 947, 644]]<|/det|>
+Version of Record: A version of this preprint was published at Nature Communications on November 3rd, 2022. See the published version at https://doi.org/10.1038/s41467- 022- 34283- 9.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[208, 75, 833, 135]]<|/det|>
+## Learning the statistics of pain: computational and neural mechanisms
+
+<|ref|>text<|/ref|><|det|>[[207, 145, 682, 165]]<|/det|>
+Flavia Mancini \(^{1}\) , Suyi Zhang \(^{2}\) , and Ben Seymour \(^{2}\)
+
+<|ref|>text<|/ref|><|det|>[[207, 175, 897, 240]]<|/det|>
+\(^{1}\) Department of Engineering, University of Cambridge, Trumpington Street, Cambridge \(^{2}\) CB2 1PZ, United Kingdom \(^{2}\) Wellcome Centre for Integrative Neuroimaging, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom
+
+<|ref|>text<|/ref|><|det|>[[207, 250, 567, 300]]<|/det|>
+\(^{8}\) Corresponding author: \(^{9}\) Flavia Mancini \(^{1}\) \(^{10}\) Email address: flavia.mancini@eng.cam.ac.uk
+
+<|ref|>sub_title<|/ref|><|det|>[[207, 323, 336, 340]]<|/det|>
+## ABSTRACT
+
+<|ref|>text<|/ref|><|det|>[[207, 356, 904, 622]]<|/det|>
+\(^{12}\) Pain invariably changes over time, and these temporal fluctuations are riddled with uncertainty about body safety. In theory, statistical regularities of pain through time contain useful information that can be learned, allowing the brain to generate expectations and inform behaviour. To investigate this, we exposed healthy participants to probabilistic sequences of low and high- intensity electrical stimuli to the left hand, containing sudden changes in stimulus frequencies. We demonstrate that humans can learn to extract these regularities, and explicitly predict the likelihood of forthcoming pain intensities in a manner consistent with optimal Bayesian models with dynamic update of beliefs. We studied brain activity using functional MRI whilst subjects performed the task, which allowed us to dissect the underlying neural correlates of these statistical inferences from their uncertainty and update. We found that the inferred frequency (posterior probability) of high intensity pain correlated with activity in bilateral sensorimotor cortex, secondary somatosensory cortex and right caudate. The uncertainty of statistical inferences of pain was encoded in the right superior parietal cortex. An intrinsic part of this hierarchical Bayesian model is the way that unexpected changes in frequency lead to shift beliefs and update the internal model. This is reflected by the KL divergence between consecutive posterior distributions and associated with brain responses in the premotor cortex, dorsolateral prefrontal cortex, and posterior parietal cortex. In conclusion, this study extends what is conventionally considered a sensory pain pathway dedicated to process pain intensity, to include the generation of Bayesian internal models of temporal statistics of pain intensity levels in sensorimotor regions, which are updated dynamically through the engagement of premotor, prefrontal and parietal regions.
+
+<|ref|>sub_title<|/ref|><|det|>[[207, 655, 380, 672]]<|/det|>
+## INTRODUCTION
+
+<|ref|>text<|/ref|><|det|>[[205, 679, 910, 920]]<|/det|>
+\(^{32}\) In recent years, our understanding of pain has shifted from viewing it as a simple responsive system to a complex predictive system, that interprets incoming inputs based on past experience and future goals (Fields, 2018). Indeed, all types of pain response, including perception, judgement and decision- making, are invariably and often strongly shaped by what pain is being predicted, and the nature of this influence gives clues regarding the fundamental architecture of the pain system in the brain (Buchel et al., 2014; Seymour and Mancini, 2020; Roy et al., 2014; Wiech, 2016). To date, most experimental strategies to study prediction have come from explicit cue- based paradigms, in which a learned or given cue, such as visual image, contains the relevant information about an upcoming pain stimulus. (Atlas et al., 2010; Buchel et al., 2014; Fazeli and Buchel, 2018; Geuter et al., 2017; Zhang et al., 2016). However, a much more general route to generate predictions relates to the background statistics of pain over time - the underlying base- rate of getting pain, and of different pain intensities, at any one moment. In principle, the pain system should be able to generate predictions based on how pain changes over time, in absence of external cues. This possibility is suggested by research in other sensory domains, showing that the temporal statistics of sequences of inputs are learned and inferred through experience - a process termed temporal statistical learning (Dehaene et al., 2015; Frost et al., 2015; Fiser and Aslin, 2002; Kourtzi and Welchman, 2019; Turk- Browne et al., 2005; Wang et al., 2017). We hypothesise that temporal statistical
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[201, 78, 909, 155]]<|/det|>
+learning also occurs in the pain system, allowing the brain to infer the prospective likelihood of pain by keeping track of ongoing temporal statistics and patterns. In this way, pain should effectively act as the cue for itself, instead of utilising a cue from a different sensory modality. This may be especially important in clinical contexts, in which pain typically comes in streams of inputs changing over time (Kajander and Bennett, 1992).
+
+<|ref|>text<|/ref|><|det|>[[201, 155, 909, 321]]<|/det|>
+Here, we tested this hypothesis by designing a frequency learning paradigm involving long, probabilistic sequences of noxious stimuli of two intensities (low and high) that could suddenly change. We tested people's ability to generate explicit predictions about the probability of forthcoming pain, and probed the underlying neural mechanisms. In particular, following evidence in other sensory domains (Meyniel et al., 2016), we proposed that the brain uses a optimal Bayesian strategy to infer the background temporal statistics of pain. Importantly, this approach may allow us to map core regions of the pain system to specific functional information processing operations: the temporal prediction of pain, its uncertainty and update. Our hypothesis predicts that the predictive inference of pain stimuli should be encoded largely within pain processing brain regions (Conway and Christiansen, 2005). The uncertainty of the prediction is expected to implicate multisensory, intraparietal regions, as shown previously using visual and auditory stimuli (Meyniel and Dehaene, 2017).
+
+<|ref|>sub_title<|/ref|><|det|>[[201, 338, 320, 356]]<|/det|>
+## RESULTS
+
+<|ref|>text<|/ref|><|det|>[[201, 362, 909, 635]]<|/det|>
+Thirty- five participants (17 females; mean age 27.4 years old; age range 18- 45 years) completed an experiment with concurrent brain fMRI scanning. They received continuous sequences of low and high intensity painful electrical stimuli, wherein they were required to intermittently judge the likelihood that the next stimulus was of high versus low intensity (figure 2 a). We designed the task such that the statistics of the sequence could occasionally and suddenly change, which meant that the the sequences effectively incorporated sub- sequences of stimuli. The statistics themselves incorporated two types of information. First, they varied in terms of the relative frequency of high and low intensity stimuli, to test the primary hypothesis that frequency statistics can be learned. Second, sequences also contained an additional aspect of predictability, in which the conditional probability of a stimulus depended on the identity of the previous stimulus (i.e. its transition probability). By having different transition probabilities between high and low stimuli within subsequences, it is possible to make a more accurate prediction of a forthcoming stimulus intensity over- and- above simply learning the general background statistics. For instance, if low pain tends to predict low pain, and high predicts high, then one tends to get 'clumping' patterns of pain (runs of high or low stimuli); or conversely if high predicts low and vice versa, one tends to get alternating patterns. Both might have the same overall frequency of high and low pain, but better predictions can be made by learning the temporal patterns within. Thus we were able to test the supplementary hypothesis that humans can learn the specific transition probabilities between different intensities, as shown previously with visual stimuli (Meyniel et al., 2016).
+
+<|ref|>text<|/ref|><|det|>[[201, 634, 909, 846]]<|/det|>
+At the beginning of the experiment, participants were informed that the sequence was set by the computer and could occasionally change at any point in time. This design mirrored a well- studied task used to probe statistical learning with visual stimuli (Meyniel and Dehaene, 2017); participants were explicitly and occasionally asked to estimate the probability of forthcoming stimuli (figure 2 b). The sequence was thus defined by a set of transition probabilities: the probability of high or low pain following a high pain stimulus; and the probability of high or low pain following a low pain stimulus (i.e. a Markovian transition matrix; see example in figure 2 c). Occasionally, these probabilities were suddenly resampled, such that in fact the total task length of 1300 stimuli (split into 5 blocks) comprised typically about 50 subsequences (mean \(25 \pm 4\) stimuli per subsequence). Participants were not explicitly informed when these changes happened. Within these subsequences, the frequency of high (versus low) stimuli varied from 15% to 85%, and figure 2 a illustrates an example of a snapshot of a typical sequence, showing a couple of 'jump' points where the probabilities change. Figure 2 b shows the rating screen, with ratings being required on 4.8% of stimuli. Before the main experimental scanning session, subjects practiced the task for an average of roughly 1200 trials before the MRI sessions.
+
+<|ref|>sub_title<|/ref|><|det|>[[201, 860, 382, 875]]<|/det|>
+## Behavioural results
+
+<|ref|>text<|/ref|><|det|>[[201, 876, 909, 920]]<|/det|>
+Participants were able to successfully learn to predict the intensity (high versus low) of the upcoming painful stimulus within the sequence. Fig 2a shows the positive correlation between stimulus rated and true probabilities for low and high pain respectively for an example individual (Pearson correlation for
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[198, 80, 910, 157]]<|/det|>
+this participant \(\mathrm{p(H|H)}\) \(\mathrm{r = 0.567}\) \(\mathrm{p = 4.61e - 4}\) \(\mathrm{p(H|L)}\) \(\mathrm{r = 0.348}\) \(\mathrm{p = 0.075}\) ; see supplementary figs 1- 2 for plots from all subjects). Across subjects, the within- individual Pearson's r between true and rated probabilities was significantly above zero. (Fig 2b, 26 out of 35 subjects had \(\mathrm{r > 0}\) : \(\mathrm{p(H|H)}\) \(\mathrm{r = 0.138\pm 0.225}\) \(\mathrm{t(34) = 3.65}\) \(\mathrm{p = 0.00088}\) , Cohen's \(\mathrm{d = 0.871}\) ; \(\mathrm{p(H|L)}\) \(\mathrm{r = 0.117\pm 0.220}\) \(\mathrm{t(34) = 3.15}\) \(\mathrm{p = 0.0034}\) , Cohen's \(\mathrm{d = 0.752}\) ; see also supplementary figures 1- 2; note that \(\mathrm{p(H|L)}\) and \(\mathrm{p(L|L)}\) are reciprocal, as well as \(\mathrm{p(H|L)}\) and \(\mathrm{p(L|L)}\) ).
+
+<|ref|>image<|/ref|><|det|>[[234, 189, 900, 420]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[228, 437, 910, 560]]<|/det|>
+Figure 1. Behavioural task and model explanation. (a) Example trials from a representative participant, showing the true probability of high (H) and low (L) stimuli given current stimuli, trial stimulation given, and participant rated probabilities. Arrows pointing to jump points of true probabilities, where a large change happens. (b) Participant rating screens during the task, where they were asked to estimate the identity of the upcoming stimulus given the current one. For example, after a low stimulus participants would be asked to rate the probability of the upcoming stimulus being low (L -> L) or high (L -> H). (c) Markovian generative process of the sequence of low and high intensity stimuli, depicted in a. The transition probability matrix was resampled at change points, determined by a fixed probability of a jump.
+
+<|ref|>image<|/ref|><|det|>[[228, 616, 910, 836]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[228, 847, 896, 894]]<|/det|>
+Figure 2. Behavioural results. (a) True vs rated probabilities for \(\mathrm{p(H|H)}\) and \(\mathrm{p(H|L)}\) from an example participant, a positive correlation suggests the participant correctly learned the stimuli probability, (b) Pearson's r for true vs rated probabilities for \(\mathrm{p(H|H)}\) and \(\mathrm{p(H|L)}\) within individual participants.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[228, 79, 444, 95]]<|/det|>
+## Behavioural data modelling
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 97, 325, 110]]<|/det|>
+## Model choice
+
+<|ref|>text<|/ref|><|det|>[[227, 111, 910, 323]]<|/det|>
+Based on previous evidence in other sensory domains, we hypothesised that subjects use an optimal Bayesian strategy to infer the statistics over time (Meyniel, 2020; Meyniel et al., 2016). We fit subjects' ratings to four variations of a Bayesian model, according to two factors: first, sequence inference through stimulus frequency (by assuming the sequence as generated by a Bernoulli process, where subjects track how often they encountered previous stimuli), versus inference through transition probability (by assuming the sequence follows a Markov transition probability between successive stimuli, where the subject tracks such transition of previous stimuli). This distinguishes between whether participants learn simple statistics (our primary hypothesis), or are able to learn the full transition probabilities (supplementary hypothesis). The second factor was to whether the model incorporates the possibility of sudden changes (jumps) in stimuli probability, as occurs in the task paradigm, or ignores such possibilities (fixed). To compare against alternative models, we also fit a basic reinforcement learning model (Rescorla- Wagner with fixed learning rate, which is an established model of Pavlovian conditioning; (Rescorla et al., 1972)) and a baseline random model that assumes constant probabilities throughout the experiment for high and low pain respectively.
+
+<|ref|>sub_title<|/ref|><|det|>[[227, 334, 319, 348]]<|/det|>
+## Model fitting
+
+<|ref|>text<|/ref|><|det|>[[227, 349, 910, 530]]<|/det|>
+The selected models estimate the probability of a pain stimulus' identity in each trial. The values predicted by the model can be fitted to actual subject predictive ratings gathered during the experiment. A model is considered a good fit to the data if the total difference between the model predicted values and the subjects' predictions is small. Within each model, free parameters were allowed to differ for individual subjects in order to minimise prediction differences. For Bayesian 'jump' models, the free parameter is the prior probability of sequence jump occurrence. For Bayesian fixed models, the free parameters are the window length for stimuli history tracking, and an exponential decay parameter that discounts increasingly distant previous stimuli. The RL model's free parameter is the initial learning rate, and random model assumes a fixed high pain probability that varies across subjects. The model fitting procedure minimises each subject's negative log likelihood for each model, based on residuals from a linear model that predicts subject's ratings using learning model predictors. The smaller the sum residual, the better fit a model's predictions are to the subject's ratings.
+
+<|ref|>sub_title<|/ref|><|det|>[[227, 542, 361, 555]]<|/det|>
+## Model comparison
+
+<|ref|>text<|/ref|><|det|>[[227, 557, 910, 693]]<|/det|>
+We compared the different models using the likelihood calculated during fitting as model evidence. Fig 3a showed model frequency, model exceedance probability, and protected exceedance probability for each model, fitted for fMRI sessions of the experiment. Both comparisons showed the winning model was the 'Bayesian jump frequency' model inferring both the frequency of pain states and their volatility, producing predictions significantly better than alternative models (Bayesian jump frequency model frequency=0.563, exceedance probability=0.923, protected exceedance=0.924). Fig 3b reports the model evidence for each subject; it shows that, although the majority (n=23) of participants were best fit by the model that infers the background frequency, some participants (n=12) were better fit by the more sophisticated model that infers specific transition probabilities.
+
+<|ref|>sub_title<|/ref|><|det|>[[227, 708, 398, 723]]<|/det|>
+## Neuroimaging results
+
+<|ref|>text<|/ref|><|det|>[[227, 724, 910, 768]]<|/det|>
+We used the winning computational model to generate trial- by- trial regressors for the neuroimaging analyses. The rationale of this approach is that neural correlation of core computational components of a specific model provides evidence that and how the model is implemented in the brain (Cohen et al., 2017).
+
+<|ref|>text<|/ref|><|det|>[[227, 769, 910, 829]]<|/det|>
+First, a simple high>low pain contrast identified BOLD responses in the right thalamus, sensorimotor, premotor and supplementary motor cortex, insula, anterior cingulate cortex and left cerebellum (with peaks in laminae V- VI), consistent with the known neuroanatomy of pain responses (fig 4, table 1). The opposite contrast (low>high pain) is reported in Supplementary Figure 3 and Supplementary Table 1.
+
+<|ref|>text<|/ref|><|det|>[[227, 830, 910, 920]]<|/det|>
+Next, we looked at BOLD correlations with the modelled posterior probability of high pain. For any pain stimulus, this reflects the newly calculated probability that the next stimulus will be high, i.e. the dynamic and probabilistic inference of high pain. This analysis identified BOLD responses in the bilateral primary and secondary somatosensory cortex, primary motor cortex and right caudate (fig 5, table 2). We report the opposite contrasts (posterior probability of low pain) in Supplementary Figure 3 and Supplementary Table 2.
+
+<--- Page Split --->
+<|ref|>image<|/ref|><|det|>[[237, 90, 900, 365]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[228, 375, 908, 453]]<|/det|>
+Figure 3. Model comparison results. (a) Bayesian model comparison based on model fitting evidence, in fMRI sessions. Subjects' predictive ratings of next trial's pain intensity were fitted with posterior means from Bayesian models, values from Rescorla-Wagner (reinforcement learning) model, and random fixed probabilities. Bayesian jump frequency model (assuming jumps in sequence and inference with stimuli frequency) was the winning model in both cases. (b) Individual subject model evidence.
+
+<|ref|>image<|/ref|><|det|>[[228, 480, 907, 865]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[228, 875, 900, 907]]<|/det|>
+Figure 4. Brain responses to noxious stimuli (high \(>\) low pain stimuli) in (a) sagittal, (b) axial and (c) coronal views (colorbar shows Z scores thresholded at \(z > 3.3\) , FWE corrected \(p< 0.05\) ).
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[328, 95, 805, 325]]<|/det|>
+ | Cluster ID | X | Y | Z | Peak Stat | Cluster Size (mm3) |
| 0 | 1 | 13 | -17 | 5 | 6.886 | 2587 |
| 1 | 1a | 13 | -22 | -3 | 4.957 | |
| 2 | 2 | 33 | -22 | 58 | 6.524 | 5247 |
| 3 | 2a | 30 | -19 | 49 | 5.953 | |
| 4 | 2b | 16 | -17 | 68 | 5.524 | |
| 5 | 3 | 37 | -17 | 15 | 5.742 | 1186 |
| 6 | 4 | 6 | -7 | 49 | 5.128 | 3486 |
| 7 | 4a | 0 | -2 | 43 | 4.967 | |
| 8 | 4b | 4 | -19 | 49 | 4.333 | |
| 9 | 4c | 11 | -14 | 49 | 4.289 | |
| 10 | 5 | -17 | -60 | -19 | 4.851 | 1707 |
| 11 | 5a | -10 | -55 | -16 | 4.651 | |
| 12 | 5b | -7 | -62 | -22 | 4.217 | |
+
+<|ref|>table_caption<|/ref|><|det|>[[328, 335, 808, 350]]<|/det|>
+Table 1. High pain > low pain stimuli activation clusters (FWE p<0.05).
+
+<|ref|>image<|/ref|><|det|>[[328, 395, 808, 840]]<|/det|>
+
+<|ref|>image_caption<|/ref|><|det|>[[228, 856, 909, 900]]<|/det|>
+Figure 5. Posterior probability mean of high pain in Bayesian jump frequency model showed activations in the bilateral primary and secondary somatosensory cortex, primary motor cortex and right caudate (FDR corrected p<0.001, colorbar shows Z scores >3.3). (a) sagittal (b) axial and (c) coronal view.
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[335, 78, 800, 215]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[226, 226, 894, 256]]<|/det|>
+Table 2. Activation clusters associated with the posterior mean \(\mathrm{p(H)}\) of the Bayesian jump frequency model.
+
+| Cluster ID | X | Y | Z | Peak Stat | Cluster Size (mm3) |
| 0 | 1 | 66 | -7 | 27 | 6.477 |
| 1 | 1a | 52 | -7 | 33 | 5.787 |
| 2 | 2 | -62 | -7 | 33 | 5.924 |
| 3 | 2a | -46 | -12 | 43 | 4.002 |
| 4 | 3 | 21 | -12 | 24 | 4.885 |
| 5 | 3a | 11 | -2 | 15 | 4.197 |
| 6 | 3b | 13 | -7 | 21 | 4.140 |
+
+<|ref|>text<|/ref|><|det|>[[198, 280, 909, 341]]<|/det|>
+In contrast, a right superior parietal region, bordering with the supramarginal gyrus, was implicated in the computation of the uncertainty (SD) of the posterior probability of high pain, a measure that reflects the uncertainty of pain predictions (figure 6 and table 3). The negative contrast of the posterior SD did not yield any significant cluster.
+
+<|ref|>image<|/ref|><|det|>[[396, 353, 740, 756]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[227, 768, 907, 814]]<|/det|>
+Figure 6. Uncertainty (SD) of the posterior probability of high pain in Bayesian jump frequency model was associated with activations in the right superior parietal cortex (FDR corrected \(\mathrm{p}< 0.001\) , colorbar shows Z scores \(>3.3\) ). (a) sagittal (b) axial and (c) coronal view.
+
+<|ref|>text<|/ref|><|det|>[[198, 830, 909, 922]]<|/det|>
+A key aspect of the Bayesian model is that it provides a metric of the model update, quantified as the KL divergence between successive trial's posterior distribution. The KL divergence increases when the two successive posteriors are more different from each other, and the opposite when the posteriors are similar. We found that the KL divergence was associated with BOLD responses in left premotor cortex, bilateral dorsolateral prefrontal cortex, superior parietal lobe, supramarginal gyrus, and left somatosensory cortex (fig 7, table 4). For completeness, we report the negative contrast in Supplementary Figure 5 and
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[338, 75, 797, 170]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[238, 180, 895, 197]]<|/det|>
+Table 3. Activation clusters associated with the uncertainty of the Bayesian jump frequency model.
+
+| Cluster ID | X | Y | Z | Peak Stat | Cluster Size (mm3) |
| 0 | 1 | 40 | -48 | 58 | 4.311 |
| 1 | 1a | 47 | -38 | 58 | 4.168 |
| 2 | 1b | 33 | -41 | 43 | 3.745 |
| 3 | 2 | 28 | -58 | 49 | 4.084 |
+
+<|ref|>text<|/ref|><|det|>[[198, 223, 909, 300]]<|/det|>
+Supplementary Table 3. Figure 8 overlays the posterior probability with its uncertainty and update (KL divergence). This shows that the temporal prediction of high pain and its update activate distinct, although neighbouring regions in the sensorimotor and premotor cortex, bilaterally. In contrast, the uncertainty of pain predictions activates a right superior parietal region that partially overlaps with the neural correlates of model update.
+
+<|ref|>image<|/ref|><|det|>[[225, 313, 909, 699]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[227, 708, 905, 755]]<|/det|>
+Figure 7. Neural activity associated with the model update, i.e. the KL divergence between posteriors from successive trials (positive contrast), in (a) sagittal, (b) coronal, and (c) axial views (FDR corrected \(p< 0.001\) , colorbar shows Z scores \(>3.3\) ).
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 791, 352, 808]]<|/det|>
+## DISCUSSION
+
+<|ref|>text<|/ref|><|det|>[[228, 816, 908, 922]]<|/det|>
+Pain is typically uncertain, and this is most often true when pain persists after injury. When pain persists, the brain needs to be able to track changes in intensity and patterns over time, in order to predict what will happen next and what to do about it. Here we investigated whether, in absence of external cues, the human brain can generate explicit (conscious) predictions about the likelihood of forthcoming pain, as these are central to the generation of internal models of pain and can be formally compared to normative models of statistical learning (Dehaene et al., 2015; Meyniel et al., 2016). This study provides evidence that humans can learn and predict the background temporal statistics of pain using optimal
+
+<--- Page Split --->
+<|ref|>table<|/ref|><|det|>[[330, 90, 804, 351]]<|/det|>
+<|ref|>table_caption<|/ref|><|det|>[[228, 360, 907, 391]]<|/det|>
+Table 4. Activation clusters positively associated with the update (KL divergence) of the Bayesian jump frequency model.
+
+| Cluster ID | X | Y | Z | Peak Stat | Cluster Size (mm3) |
| 0 | 1 | -58 | 6 | 36 | 6.191 |
| 1 | 1a | -26 | -2 | 49 | 5.945 |
| 2 | 1b | -60 | 4 | 21 | 4.935 |
| 3 | 1c | -43 | 0 | 55 | 4.516 |
| 4 | 2 | -46 | -41 | 40 | 6.098 |
| 5 | 2a | -36 | -50 | 52 | 5.438 |
| 6 | 2b | -50 | -41 | 55 | 3.789 |
| 7 | 3 | 59 | 11 | 24 | 5.308 |
| 8 | 4 | 47 | -41 | 58 | 5.295 |
| 9 | 4a | 37 | -50 | 52 | 4.972 |
| 10 | 4b | 37 | -58 | 61 | 4.460 |
| 11 | 4c | 30 | -65 | 61 | 4.255 |
| 12 | 5 | -62 | -17 | 33 | 4.814 |
| 13 | 5a | -50 | -24 | 33 | 4.584 |
| 14 | 5b | -46 | -29 | 27 | 3.849 |
+
+<|ref|>image<|/ref|><|det|>[[350, 473, 799, 844]]<|/det|>
+<|ref|>image_caption<|/ref|><|det|>[[228, 855, 905, 903]]<|/det|>
+Figure 8. Overlaying the temporal prediction of high pain (mean posterior probability, red-yellow), its uncertainty (SD posterior probability, blue) and the model update (KL divergence between successive posterior distributions, green); (FDR corrected \(p< 0.001\) , colorbar shows Z scores \(>3.3\) )
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[228, 80, 910, 262]]<|/det|>
+Bayesian inference with dynamic update of beliefs, allowing explicit prediction of the probability of forthcoming pain at any moment in time. Using neuroimaging, we reveal the neural correlates of the internal models of pain predictions. We found distinct neural correlates for the probabilistic, predictive inference of pain and its update. Pain predictions (i.e. mean posterior probability) are encoded in the bilateral, primary somatosensory and motor regions, secondary somatosensory cortex and right caudate, whereas the signal representing the update of the probabilistic model localises in adjacent premotor and superior parietal cortex. The superior parietal cortex is also implicated in the computation of the uncertainty of the probabilistic inference of pain. Overall, the results show that cortical regions typically associated with the sensory processing of pain (primary and secondary somatosensory cortices) encode how likely different pain intensities are to occur at any moment in time, in the absence of any other cues or information; the uncertainty of this inference is encoded in superior parietal cortex and used by a network of parietal- prefrontal regions to update the temporal statistical representation of pain intensity.
+
+<|ref|>text<|/ref|><|det|>[[228, 264, 910, 475]]<|/det|>
+The ability of the brain to extract regularities from temporal sequences is well- documented in other sensory domains such as vision and audition (Kourtzi and Welchman, 2019; Dehaene et al., 2015), but pain is a fundamentally different system with intrinsic motivational value and direct impact on the state of the body (Baliki and Apkarian, 2015; Fields, 2018; Seymour, 2019). Despite this fundamental difference, we show that temporal inferences of pain are generated using optimal Bayesian inference - tracking the frequency of low and high intensity pain states and their volatility (i.e. how likely they are to change) based on past experience. A more complex strategy involves trying to infer higher level statistical patterns within these sequences, namely representing all the transition probabilities between different states (Meyniel et al., 2016). Although this model fits 1/3 of our subjects best, overall it was not favoured over the simpler frequency learning model, which best describes the behaviour of approximately 2/3 of our sample (figure 3). At this stage it is not clear whether this is because of stable inter- individual differences, or whether given more time, more participants would be able to learn specific transition probabilities. However, it is worth noting that stable, individual differences in learning strategy have been previously reported in visual statistical learning (Karlaftis et al., 2019; Wang et al., 2017).
+
+<|ref|>text<|/ref|><|det|>[[228, 478, 910, 673]]<|/det|>
+The Bayesian frequency model is consistent with many other tasks that involve cognitive model learning or acquisition of explicit contingency knowledge across modalities, including pain (Yoshida et al., 2013; Jepma et al., 2018; Hoskin et al., 2019). This reflects a fundamentally different process to pain response learning - either in Pavlovian conditioning where simple autonomic, physiological or motor responses are acquired, or basic stimulus- response (instrumental / operant) avoidance or escape response learning. These behaviours are usually best captured by reinforcement learning models such as temporal difference learning (Seymour, 2019), and reflect a computationally different process (Carter et al., 2006). Having said that, such error- driven learning models have been applied to statistical learning paradigms in other domains before (Orpella et al., 2021), and so here we were able to directly demonstrate that it provided a less accurate model than Bayesian models (figure 3). In contrast to simple reinforcement learning models, Bayesian models allow building an internal, hierarchical model of the temporal statistics of the environment that can support a range of cognitive functions (Honey et al., 2012; Meyniel et al., 2016; Weiss et al., 2021).
+
+<|ref|>text<|/ref|><|det|>[[228, 676, 910, 842]]<|/det|>
+A key benefit of the computational approach is that it allows us to accurately map underlying operations of pain information processing to their neural substrates. Our study shows that the probabilistic inference of high pain frequency is encoded in the bilateral sensorimotor cortex, secondary somatosensory cortex, and right caudate (figure 5). The neural correlates of pain predictions arising from predictive Bayesian inference seem to contrast to a certain extent with those arising from value- based learning, which is typically characterised by non- probabilistic model- free learning and involves insula, anterior cingulate and ventromedial prefrontal cortices (Seymour and Mancini, 2020). An exception to this is the observation that the caudate nucleus correlates well with the posterior probability of high pain (i.e. its temporal inference). Although it is difficult to interpret this without an accompanying experimentally- matched value learning task, and without measuring conditioned responses such as autonomic responses, it may represent the parallel or integrative role of caudate in multiple divergent learning processes.
+
+<|ref|>text<|/ref|><|det|>[[228, 845, 910, 920]]<|/det|>
+A specific facet of the Bayesian model is the representation of an uncertainty signal, i.e. the posterior SD, and a model update signal, defined as the statistical KL divergence between consecutive posterior distributions. This captures the extent to which a model is updated when an incoming pain stimulus deviates from that expected, taking into account the uncertainty inherent in the original prediction. In our task, the uncertainty of the prediction was encoded in a right superior parietal region, which partially
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[228, 80, 909, 276]]<|/det|>
+overlapped with a wider parietal region associated with the encoding of the model update (figures 6, 8). This emphasises the close relationship between uncertainty and learning in Bayesian inference (Koblinger et al., 2021). A previous study on statistical learning in other sensory domains reported that a more posterior, intraparietal region, was associated with the precision of the temporal inference (Meyniel and Dehaene, 2017). The role of the superior parietal cortex in uncertainty representation is also evident in other memory- based decision- making tasks, as the superior parietal cortex is more active for low vs. high confidence judgements (Hutchinson et al., 2014; Moritz et al., 2006; Sestieri et al., 2010). In addition to the parietal cortex, the model update signal was encoded in the left premotor cortex and bilateral dorsolateral prefrontal cortex (figure 7), neighbouring regions activated by pain statistical inferences (figure 8). This is particularly interesting, as the premotor cortex sits along a hierarchy of reciprocally and highly interconnected regions within the sensorimotor cortex. The premotor cortex has also been implicated in the computation of an update signal in visual and auditory statistical learning tasks (Meyniel and Dehaene, 2017).
+
+<|ref|>text<|/ref|><|det|>[[228, 277, 909, 519]]<|/det|>
+In conclusion, our study demonstrates that the pain system generates probabilistic predictions about the background temporal statistics of pain states, in absence of external cues and using Bayesian- like inference strategy. This extends both current anatomical and functional concepts of what is conventionally considered a 'sensory pain pathway', to include encoding not just stimulus intensity (Segerdahl et al., 2015; Wager et al., 2013) and location (Mancini et al., 2012), but the generation of more sophisticated and dynamic internal models of temporal statistics of pain intensity levels. Future studies will need to determine whether temporal statistical predictions modulate pain perception, similarly to other kinds of pain expectations (Büchel et al., 2014; Wiech, 2016; Wager et al., 2004). More broadly, temporal statistical learning is likely to be most important after injury, when continuous streams of fluctuating pain signals ascend nociceptive afferents to the brain, and their underlying pattern may hold important clues as to the nature of the injury, its future evolution, and its broader semantic meaning in terms of the survival and prospects of the individual. It is therefore possible that the underlying computational process might go awry in certain instances of chronic pain, especially when instrumental actions can be performed that might influence the pattern of pain intensity (Jepma et al., 2018; Jung et al., 2017). Thus, future studies could explore both how temporal statistical learning interacts with pain perception and controllability, as well as its application to clinical pain.
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 535, 328, 551]]<|/det|>
+## METHODS
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 561, 430, 575]]<|/det|>
+## Code and data availability
+
+<|ref|>text<|/ref|><|det|>[[228, 576, 909, 636]]<|/det|>
+Raw functional imaging data is deposited at OpenNEURO https://openneuro.org/datasets/ds003836 and derived statistical maps are available at NeuroVault (upon acceptance]). Sequence generation, task instructions and behavioural data can be found at https://github.com/NoxLab- cam/pain_statistics_3tfrmri. Analysis code can be found at https://github.com/syzhang/tsl_paper.
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 650, 323, 664]]<|/det|>
+## Participants
+
+<|ref|>text<|/ref|><|det|>[[228, 666, 909, 725]]<|/det|>
+Thirty- five healthy participants (17 females; mean age 27.4 years old; age range 18- 45 years) took part in two experimental sessions, 2- 3 days apart: a pain- tuning and training session and an MRI session. Each participant gave informed consent according to procedures approved by University of Cambridge ethics committee (PRE.2018.046).
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 740, 297, 753]]<|/det|>
+## Protocol
+
+<|ref|>text<|/ref|><|det|>[[228, 755, 909, 921]]<|/det|>
+The electrical stimuli were generated using a DS5 isolated bipolar current stimulator (Digitimer), delivered to surface electrodes placed on the index and middle fingers of the left hand. All participants underwent a standardised intensity work- up procedure at the start of each testing day, in order to match subjective pain levels across sessions to a low- intensity level (just above pain detection threshold) and a high- intensity level that was reported to be painful but bearable (>4 out of 10 on a VAS ranging from 0 ['no pain'] to 10 ['worst imaginable pain']). The pain delivery setup was identical for lab- based and MR sessions. After identifying appropriate intensity levels, we checked that discrimination accuracy was >95% in a short sequence of 20 randomised stimuli. This was done to ensure that uncertainty in the sequence task would derive from the temporal order of the stimuli rather than their current intensity level or discriminability. If needed, we tweaked the stimulus intensities to achieve our target discriminability. Next, we gave the task instructions to each participants (openly available https://github.com/NoxLab- cam/pain_statistics_3tfrmri).
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[228, 80, 910, 351]]<|/det|>
+After receiving a shock on trial t, subjects were asked to predict the probability of receiving a stimulus of the same or different intensity on the upcoming trial (trial t+1). We informed participants that in the task they "would receive two kinds of stimuli, a low intensity shock and a high intensity shock. The L and H stimuli would be presented in a sequence, in an order set by the computer. After each stimulus, the following stimulus could be either the same or different than the previous one. The computer sets the probability that after a given stimulus (for example L) there would be either L or H" (we showed a visual representation of this example). We asked participants to "always try to guess the probability that after each stimulus there will the same or a different one" and we informed them that "the computer sometimes changes its settings and sets new probabilities", so to pay attention all the time. We also told them the sequence would be paused occasionally in order to collect probability estimates from participants using the scale depicted in Fig 1. A white fixation cross was displayed on a dark screen throughout the trial, except when a response was requested every 12- 18 trials. The interstimulus interval was 2.8- 3 seconds. There were 300 stimuli in each block, lasting approx. 8 minutes. Average intensity ratings for each stimulus level were collected after each block during a short break. Low intensity stimuli were felt by participants as barely painful, rated on average 1.39 (SD 0.77) on a scale ranging from 0 (no pain) to 10 (worst pain imaginable). In contrast, high intensity stimuli were rated as more than 4 times higher than low intensity stimuli (mean 5.74, SD 4.85). Participants were given 4 blocks of practice, 2- 3 days prior the imaging sessions, and 5 blocks (1500 stimuli in total) during task fMRI.
+
+<|ref|>text<|/ref|><|det|>[[230, 351, 909, 448]]<|/det|>
+The sequence of stimuli was unique and generated as in (Meynie et al., 2016). L and H stimuli were drawn randomly from a 2x2 transition probability matrix, which remained constant for a number of trials (chunks). The probability of a change was 0.014. Chunks had to be \(>5\) and \(< 200\) trials long. In each chunk, transition probabilities were sampled independently and uniformly in the 0.15- 0.85 range (in steps of 0.05), with the constraint that at least one of the two transition probabilities must be \(> / < 0.2\) than in the previous chunk. Participants were not informed when the matrix was resampled, and a new chunk started.
+
+<|ref|>text<|/ref|><|det|>[[230, 446, 907, 476]]<|/det|>
+Behavioural data analysis were conducted with Python packages pandas (pypi version 1.1.3) and scipy (pypi version 1.5.3). Effect size was calculated as Cohen's d for t- tests.
+
+<|ref|>sub_title<|/ref|><|det|>[[230, 485, 625, 500]]<|/det|>
+## Computational modelling of temporal statistical learning
+
+<|ref|>text<|/ref|><|det|>[[230, 500, 718, 515]]<|/det|>
+Learning models The models used in comparison are listed as followed:
+
+<|ref|>text<|/ref|><|det|>[[230, 533, 908, 564]]<|/det|>
+Random (baseline model) Probabilities are assumed fixed and reciprocal for high and low stimuli, where \(p_{h} = 1 - p_{l}\) ( \(p_{l}\) as free parameter). Uncertainty are also assumed fixed for high/low pain.
+
+<|ref|>text<|/ref|><|det|>[[230, 581, 907, 611]]<|/det|>
+Rescorla- Wagner (RW model) Rated probabilities are assumed to be state values, which were updated as
+
+<|ref|>equation<|/ref|><|det|>[[489, 612, 644, 628]]<|/det|>
+\[V_{t + 1}\gets V_{t} + \alpha (R_{t} - V_{t})\]
+
+<|ref|>text<|/ref|><|det|>[[230, 636, 907, 666]]<|/det|>
+, where \(R_{t} = 1\) if stimulus was low, and O otherwise. \(\alpha\) was fitted as free parameter (see (Rescorla et al., 1972)).
+
+<|ref|>text<|/ref|><|det|>[[230, 683, 907, 744]]<|/det|>
+Bayesian models Bayesian models update each trial with stimulus identity information to obtain upcoming trial probability from posterior distribution (Meynie et al., 2016). Using Bayes' rule, the model parameters \(\theta_{t}\) is estimated at each trial \(t\) provided previous observations \(y_{1:t}\) (sequence of high or low pain), given a model \(M\) .
+
+<|ref|>equation<|/ref|><|det|>[[446, 744, 688, 761]]<|/det|>
+\[p(\theta_t|y_{1:t},M)\sim p(y_{1:t}|\theta_t,M)p(\theta_t,M)\]
+
+<|ref|>text<|/ref|><|det|>[[230, 768, 907, 814]]<|/det|>
+Stimulus information can either be frequency or transition of the binary sequence. There are 'fixed' models that assume no sudden jump in stimuli probabilities, and 'jump' models that assume the opposite. The four combinations were fitted and compared.
+
+<|ref|>text<|/ref|><|det|>[[230, 831, 907, 893]]<|/det|>
+1. Fixed frequency model For fixed models, the likelihood of parameters \(\theta\) follows a Beta distribution with parameters \(N_{h} + 1\) and \(N_{l} + 1\) , where \(N_{h}\) and \(N_{l}\) are the numbers of high and low pain in the sequence \(y_{1:t}\) . Given that the prior is also a flat Beta distribution with parameters [1,1], the posterior can be analytically obtained with:
+
+<|ref|>equation<|/ref|><|det|>[[452, 905, 680, 921]]<|/det|>
+\[p(\theta |y_{1:t}) = Beta(\theta |N_{h} + 1,N_{l} + 1)\]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[226, 78, 757, 95]]<|/det|>
+The likelihood of a sequence \(y_{1:t}\) given model parameters \(\theta\) can be calculated as:
+
+<|ref|>equation<|/ref|><|det|>[[448, 107, 686, 149]]<|/det|>
+\[p(y_{1:t}|\theta) = p(y_{1}|\theta)\prod_{t = 2}^{t}p(y_{i}|\theta ,y_{i - 1})\]
+
+<|ref|>text<|/ref|><|det|>[[226, 159, 907, 190]]<|/det|>
+Finally, the posterior probability of a stimulus occurring in the next trial can be estimated with Bayes' rule:
+
+<|ref|>equation<|/ref|><|det|>[[429, 190, 705, 222]]<|/det|>
+\[p(y_{t + 1}|y_{1:t}) = \int p(y_{t + 1}|\theta ,y_{t})p(\theta |y_{1:t})d\theta\]
+
+<|ref|>text<|/ref|><|det|>[[226, 230, 907, 277]]<|/det|>
+Priors window and decay were fitted as free parameters, where window is the previous \(n\) trials where frequency of stimuli were estimated, and decay is the previous \(n\) trials where the frequency of stimuli further from current trial were discounted following an exponential decay.
+
+<|ref|>text<|/ref|><|det|>[[226, 277, 907, 327]]<|/det|>
+When window \(= w\) is applied, then \(N_{h}\) and \(N_{l}\) are counted within the window of \(w\) trials \(y_{t - w,t}\) . When decay \(= d\) is applied, an exponential decay factor \(e^{(-\frac{k}{d})}\) is applied to the \(k\) trials before their sum is calculated. Both window and decay were used simultaneously.
+
+<|ref|>text<|/ref|><|det|>[[228, 351, 907, 428]]<|/det|>
+2. Fixed transition model Priors window and decay were fitted as free parameters as Fixed frequency model above, however, the transition probability was estimated instead of frequency. The likelihood of a stimuli now depends on the estimated transition probability vector \(\theta \sim [\theta_{h|l},\theta_{l|h}]\) and the previous stimulus pairs \(N\sim [N_{h|l},N_{l|h}]\) . Given that both likelihood and prior can be represented using Beta distributions as before, the posterior result can be analytically obtained as:
+
+<|ref|>equation<|/ref|><|det|>[[351, 444, 784, 461]]<|/det|>
+\[p(\theta |y_{1:t}) = Beta(\theta_{h|l}|N_{h|l} + 1,N_{l|l} + 1)Beta(\theta_{l|h}|N_{l|h} + 1,N_{h|h} + 1)\]
+
+<|ref|>text<|/ref|><|det|>[[228, 484, 907, 576]]<|/det|>
+3. Jump frequency model In jump models, parameter \(\theta\) is no longer fixed, instead it can change from one trial to another with a probability of \(p_{jump}\) . Prior \(p_{jump}\) was fitted as a free parameter, representing the subject's assumed probability of a jump occurring during the sequence of stimuli (e.g. a high \(p_{jump}\) assumes the sequence can reverse quickly from a low pain majority to a high pain majority). The model can be approximated as a Hidden Markov Model (HMM) in order to compute the joint distribution of \(\theta\) and observed stimuli iteratively,
+
+<|ref|>equation<|/ref|><|det|>[[373, 591, 761, 620]]<|/det|>
+\[p(\theta_{t + 1},y_{1:t + 1}) = p(y_{t + 1}|\theta_{t + 1},y_{t})\int p(\theta_{t},y_{1:t})p(\theta_{t + 1}|\theta_{t})d\theta_{t}\]
+
+<|ref|>text<|/ref|><|det|>[[228, 631, 907, 693]]<|/det|>
+where the integral term captures the change in \(\theta\) from one observation \(t\) to the next \(t + 1\) , with probability \((1 - p_{jump})\) of staying the same and probability \(p_{jump}\) of changing. This integral can be calculated numerically within a discretised grid. The posterior probability of a stimulus occurring in the next trial can then be calculated using Bayes' rule as
+
+<|ref|>equation<|/ref|><|det|>[[267, 706, 792, 802]]<|/det|>
+\[p(y_{t + 1}|y_{1:t}) = \int p(y_{t + 1}|\theta_{t + 1})p(\theta_{t + 1}|y_{1:t}\theta_{t + 1})\] \[\qquad = \int p(y_{t + 1}|\theta_{t + 1})\left[\int p(\theta_{t}|y_{1:t})p(\theta_{t + 1}|\theta_{t})d\theta_{t}\right]d\theta_{t + 1}\] \[\qquad = \int p(y_{t + 1}|\theta_{t + 1})\left[(1 - p_{jump})p(\theta_{t + 1} = \theta_{t}|y_{1:t}) + p_{jump}p(\theta_{0})\right]d\theta_{t + 1}\]
+
+<|ref|>text<|/ref|><|det|>[[228, 823, 907, 884]]<|/det|>
+4. Jump transition model Similar to jump frequency model above, prior \(p_{jump}\) was fitted as a free parameter, but estimating transition instead of frequency. The difference is the stimulus at trial \(y_{t + 1}\) now dependent of stimulus at the previous trial, hence the addition of the term \(y_{t}\) in the joint distribution term, shown below.
+
+<|ref|>equation<|/ref|><|det|>[[268, 897, 809, 925]]<|/det|>
+\[p(y_{t + 1}|y_{1:t}) = \int p(y_{t + 1}|\theta_{t + 1},y_{t})\left[(1 - p_{jump})p(\theta_{t + 1} = \theta_{t}|y_{1:t}) + p_{jump}p(\theta_{0})\right]d\theta_{t + 1}\]
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[228, 78, 910, 125]]<|/det|>
+KL divergence Kullback- Leibler (KL) divergence quantifies the distance between two probability distributions. In the current context, it measures the difference between the posterior probability distributions of successive trials. It is calculated as
+
+<|ref|>equation<|/ref|><|det|>[[444, 134, 689, 171]]<|/det|>
+\[D_{K L}(P\parallel Q) = \sum_{x\in \mathcal{X}}P(x)l o g\left(\frac{P(x)}{Q(x)}\right)\]
+
+<|ref|>text<|/ref|><|det|>[[198, 179, 910, 226]]<|/det|>
+330 , where \(P\) and \(Q\) represents the two discrete posterior probability distributions calculated in discretised 331 grids \(\mathcal{X}\) . KL divergence can be used to represent information gains when updating after successive trials 332 (Meyniel and Dehaene, 2017).
+
+<|ref|>text<|/ref|><|det|>[[227, 234, 908, 264]]<|/det|>
+Subject rated probability For each individual subject, model predicted probabilities \(p_{k}\) from the trial \(k\) was used as predictors in the regression:
+
+<|ref|>equation<|/ref|><|det|>[[445, 276, 690, 293]]<|/det|>
+\[y_{k}\sim \beta_{0} + \beta_{1}\cdot p_{k}(M_{i},\theta_{i}) + \beta_{2}\cdot N_{s} + \epsilon\]
+
+<|ref|>text<|/ref|><|det|>[[198, 304, 908, 351]]<|/det|>
+333 where \(y_{k}\) is the subject rated probabilities, \(M_{i}\) is the \(i\) th candidate model, \(N_{s}\) is the session number within subject, \(\beta_{0}\) , \(\beta_{1}\) , \(\beta_{2}\) and \(\theta_{i}\) are free parameters to be fitted, and \(\epsilon\) is normally distributed noise added 335 to avoid fitting errors (Maheu et al., 2019).
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 362, 320, 375]]<|/det|>
+## Model fitting
+
+<|ref|>text<|/ref|><|det|>[[198, 377, 908, 406]]<|/det|>
+337 To estimate the model free parameters from data, Bayesian information criteria (BIC) values were 338 calculated as:
+
+<|ref|>equation<|/ref|><|det|>[[482, 419, 654, 439]]<|/det|>
+\[\mathrm{BIC} = n\cdot \log \hat{\sigma}_{\epsilon}^{2} + k\cdot \log n\]
+
+<|ref|>equation<|/ref|><|det|>[[488, 454, 649, 494]]<|/det|>
+\[\hat{\sigma}_{\epsilon}^{2} = \min_{n}\frac{1}{n}\sum_{k = 1}^{n}\left(y_{k} - \hat{y}_{k}\right)\]
+
+<|ref|>text<|/ref|><|det|>[[198, 500, 908, 531]]<|/det|>
+339 where \(\hat{\sigma}^{2}\) is the squared residual from the linear model above that relates subject ratings to model predicted 340 probabilities, and \(n\) is the number of free parameters fitted.
+
+<|ref|>text<|/ref|><|det|>[[198, 531, 908, 592]]<|/det|>
+341 We use fmincon in MATLAB to minimise the BIC (as approximate for negative log likelihood, Maheu 342 et al. (2019)) for each subject/model. The procedure was repeated 100 times with different parameter 343 initialisation, and the mean results of these repetitions were taken as the fitted parameters and minimised 344 log likelihoods.
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 603, 362, 617]]<|/det|>
+## Model comparison
+
+<|ref|>text<|/ref|><|det|>[[198, 618, 908, 740]]<|/det|>
+346 In general, the best fit model was defined as the candidate model with the lowest averaged BIC. We 347 conducted a random effect analysis with VBA toolbox (Daunizeau et al., 2014), where fitted log likelihoods 348 from each subject/model pair was used as model evidence. With this approach, model was treated as 349 random effects that could differ between individuals. This comparison produces model frequency (how 350 often a given model is used by individuals), model exceedance probability (how likely it is that any given 351 model is more frequent than all other models in the comparison set), and protected exceedance probability 352 (corrected exceedance probability for observations due to chance) (Stephan et al., 2009; Rigoux et al., 353 2014). These values are correlated and would be considered together when selecting the best fit model.
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 753, 378, 768]]<|/det|>
+## Neuroimaging data
+
+<|ref|>sub_title<|/ref|><|det|>[[228, 770, 345, 783]]<|/det|>
+## Data acquisition
+
+<|ref|>text<|/ref|><|det|>[[198, 784, 908, 920]]<|/det|>
+356 First, we collected a T1- weighted MPRAGE structural scan (voxel size 1 mm isotropic) on a 3T Siemens 357 Magnetom Skyra (Siemens Healthcare), equipped with a 32- channel head coil (Wolfson Brain Imaging 358 Centre, Cambridge). Then we collected 5 task fMRI sessions of 246 volumes using a gradient echo 359 planar imaging (EPI) sequence (TR = 2000 ms, TE = 23 ms, flip angle = 78°, slices per volume = 31, 360 Grappa 2, voxel size 2.4 mm isotropic, A>P phase- encoding; this included four dummy volumes, in 361 addition to those pre- discarded by the scanner). In order to correct for inhomogeneities in the static 362 magnetic field, we imaged 4 volumes using an EPI sequence identical to that used in task fMRI, inverted 363 in the posterior- to- anterior phase encoding direction. Full sequence metadata are available at OpenNeuro 364 (https://openneuro.org/datasets/ds003836).
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[230, 81, 333, 95]]<|/det|>
+## Preprocessing
+
+<|ref|>text<|/ref|><|det|>[[230, 97, 907, 141]]<|/det|>
+Imaging data were preprocessed using fmriprep (pypi version: 20.1.1, RRID:SCR_016216) with Freesurfer option disabled, within its Docker container. Processed functional images had first four dummy scans removed, and then smoothed in an 8mm Gaussian filter in SPM12.
+
+<|ref|>sub_title<|/ref|><|det|>[[230, 154, 328, 167]]<|/det|>
+## GLM analysis
+
+<|ref|>text<|/ref|><|det|>[[230, 169, 907, 213]]<|/det|>
+Nipype (pypi version: 1.5.1) was used for all fMRI processing and analysis within its published Docker container. Nipype is a python package that wraps around fMRI analysis tools including SPM12 and FLS in a Debian environment.
+
+<|ref|>text<|/ref|><|det|>[[230, 215, 907, 275]]<|/det|>
+First and second level GLM analyses were conducted using SPM12 through nipype. In all first level analyses, 25 regressors of no interest were included from fmriprep confounds output: CSF, white matter, global signal, dvars, std_dvars, framewise displacement, rmsd, 6 a_comp_cor with corresponding cosine components, translation in 3 axis and rotation in 3 axis. Sessions within subject are not concatenated.
+
+<|ref|>text<|/ref|><|det|>[[230, 276, 907, 320]]<|/det|>
+In second level analyses, all first level contrasts were entered into a one- sample T- test, with group subject mask applied. The default FDR threshold used was 0.001 (set in Nipype threshold node height_threshold=0.001).
+
+<|ref|>text<|/ref|><|det|>[[230, 321, 907, 382]]<|/det|>
+For visualisation and cluster statistics extraction, nilearn (pypi version: 1.6.1) was used. A cluster extent of 10 voxels was applied. Visualised slice coordinates were chosen based on cluster peaks identified. Activation clusters were overlayed on top of a subject averaged anatomical scan normalised to MNI152 space as output by fmriprep.
+
+<|ref|>sub_title<|/ref|><|det|>[[230, 395, 316, 408]]<|/det|>
+## GLM design
+
+<|ref|>text<|/ref|><|det|>[[230, 410, 907, 500]]<|/det|>
+All imaging results were obtained from a single GLM model. We investigated neural correlates using the winning Bayesian jump frequency model. All model predictors were generated with the group mean fitted parameters in order to minimise noise. First level regressors include the onset times for all trials, high pain trials, and low pain trials (duration=0). The all trial regressor was parametrically modulated by model- predicted posterior mean of high pain, the KL divergence between successive posterior distributions on jump probability, and the posterior SD of high pain.
+
+<|ref|>text<|/ref|><|det|>[[230, 501, 907, 620]]<|/det|>
+For second level analysis, both positive and negative T- contrasts were obtained for posterior mean, KL divergence and uncertainty parametric modulators, across all the first level contrast images from all subjects. A group mean brain mask was applied to exclude activations outside the brain. Given that high and low pain are reciprocal in probabilities, a negative contrast of posterior mean of low pain would be equivalent to the posterior mean of high pain. In addition, high and low pain comparisons were done using a subtracting T- contrast between high and low pain trial regressors. We corrected for multiple comparisons with a cluster- wise FDR threshold of \(p< 0.001\) for both parametric modulator analyses, reporting only clusters that survived this.
+
+<|ref|>sub_title<|/ref|><|det|>[[230, 641, 455, 658]]<|/det|>
+## ACKNOWLEDGEMENTS
+
+<|ref|>text<|/ref|><|det|>[[230, 666, 907, 740]]<|/det|>
+The study was funded by a Medical Research Council Career Development Award to Flavia Mancini (MR/T010614/1) and Wellcome Trust grants to Ben Seymour (097490). We are grateful to Professor Zoe Kourtzi and Dr Michael Lee for helpful discussions about the concept of the study, and to the staff of the Wolfson Brain Imaging Centre for their support during data collection. The authors declare no competing interest.
+
+<|ref|>sub_title<|/ref|><|det|>[[230, 761, 481, 778]]<|/det|>
+## AUTHOR CONTRIBUTIONS
+
+<|ref|>text<|/ref|><|det|>[[230, 785, 907, 815]]<|/det|>
+FM and BS designed the study. FM collected the data and SZ analysed the data. All authors wrote the paper.
+
+<|ref|>sub_title<|/ref|><|det|>[[230, 836, 364, 853]]<|/det|>
+## REFERENCES
+
+<|ref|>text<|/ref|><|det|>[[230, 860, 907, 920]]<|/det|>
+Atlas, L. Y., Bolger, N., Lindquist, M. A., and Wager, T. D. (2010). Brain mediators of predictive cue effects on perceived pain. Journal of Neuroscience, 30(39):12964- 12977. Baliki, M. N. and Apkarian, A. V. (2015). Nociception, pain, negative moods, and behavior selection. Neuron, 87(3):474- 491.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[196, 78, 910, 911]]<|/det|>
+Büchel, C., Geuter, S., Sprenger, C., and Eippert, F. (2014). Placebo analgesia: a predictive coding perspective. Neuron, 81(6):1223- 1239. Carter, R. M., O'Doherty, J. P., Seymour, B., Koch, C., and Dolan, R. J. (2006). Contingency awareness in human aversive conditioning involves the middle frontal gyrus. Neuroimage, 29(3):1007- 1012. Cohen, J. D., Daw, N., Engelhardt, B., Hasson, U., Li, K., Niv, Y., Norman, K. A., Pillow, J., Ramadge, P. J., Turk- Browne, N. B., et al. (2017). Computational approaches to fmri analysis. Nature neuroscience, 20(3):304- 313. Conway, C. M. and Christiansen, M. H. (2005). Modality- constrained statistical learning of tactile, visual, and auditory sequences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 31(1):24. Daunizeau, J., Adam, V., and Rigoux, L. (2014). Vba: a probabilistic treatment of nonlinear models for neurobiological and behavioural data. PLoS Comput Biol, 10(1):e1003441. Dehaene, S., Meyniel, F., Wacongne, C., Wang, L., and Pallier, C. (2015). The neural representation of sequences: from transition probabilities to algebraic patterns and linguistic trees. Neuron, 88(1):2- 19. Fazeli, S. and Büchel, C. (2018). Pain related expectation and prediction error signals in the anterior insula are not related to aversiveness. Journal of Neuroscience, pages 0671- 18. Fields, H. L. (2018). How expectations influence pain. Pain, 159:53- S10. Fiser, J. and Aslin, R. N. (2002). Statistical learning of higher- order temporal structure from visual shape sequences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 28(3):458. Frost, R., Armstrong, B. C., Siegelman, N., and Christiansen, M. H. (2015). Domain generality versus modality specificity: the paradox of statistical learning. Trends in cognitive sciences, 19(3):117- 125. Geuter, S., Boll, S., Eippert, F., and Büchel, C. (2017). Functional dissociation of stimulus intensity encoding and predictive coding of pain in the insula. Elife, 6. Honey, C., Thesen, T., Donner, T., Silbert, L., Carlson, C., Devinsky, O., Doyle, W., Rubin, N., Heeger, D., and Hasson, U. (2012). Slow cortical dynamics and the accumulation of information over long timescales. Neuron, 76(2):423- 434. Hoskin, R., Berzuini, C., Acosta- Kane, D., El- Derey, W., Guo, H., and Talmi, D. (2019). Sensitivity to pain expectations: A bayesian model of individual differences. Cognition, 182:127- 139. Hutchinson, J. B., Uncapper, M. R., Weiner, K. S., Bressler, D. W., Silver, M. A., Preston, A. R., and Wagner, A. D. (2014). Functional heterogeneity in posterior parietal cortex across attention and episodic memory retrieval. Cerebral Cortex, 24(1):49- 66. Jepma, M., Koban, L., van Doorn, J., Jones, M., and Wager, T. D. (2018). Behavioural and neural evidence for self- reinforcing expectancy effects on pain. Nature Human Behaviour, page 1. Jung, W.- M., Lee, Y.- S., Wallraven, C., and Chae, Y. (2017). Bayesian prediction of placebo analgesia in an instrumental learning model. PloS one, 12(2):e0172609. Kajander, K. and Bennett, G. (1992). Onset of a painful peripheral neuropathy in rat: a partial and differential deafferentation and spontaneous discharge in a beta and a delta primary afferent neurons. Journal of neurophysiology, 68(3):734- 744. Karlaftis, V. M., Giorgio, J., Vértes, P. E., Wang, R., Shen, Y., Tino, P., Welchman, A. E., and Kourtzi, Z. (2019). Multimodal imaging of brain connectivity reveals predictors of individual decision strategy in statistical learning. Nature human behaviour, 3(3):297- 307. Koblinger, A., Fiser, J., and Lengyel, M. (2021). Representations of uncertainty: where art thou? Current Opinion in Behavioral Sciences, 38:150- 162. Kourtzi, Z. and Welchman, A. E. (2019). Learning predictive structure without a teacher: decision strategies and brain routes. Current opinion in neurobiology, 58:130- 134. Maheu, M., Dehaene, S., and Meyniel, F. (2019). Brain signatures of a multiscale process of sequence learning in humans. eLife, 8:e41541. Mancini, F., Haggard, P., Iannetti, G. D., Longo, M. R., and Sereno, M. I. (2012). Fine- grained nociceptive maps in primary somatosensory cortex. Journal of Neuroscience, 32(48):17155- 17162. Meyniel, F. (2020). Brain dynamics for confidence- weighted learning. PLOS Computational Biology, 16(6):e1007935. Meyniel, F. and Dehaene, S. (2017). Brain networks for confidence weighting and hierarchical inference during probabilistic learning. Proceedings of the National Academy of Sciences, 114(19):E3859- E3868. Meyniel, F., Maheu, M., and Dehaene, S. (2016). Human Inferences about Sequences: A Minimal Transition Probability Model. PLOS Computational Biology, 12(12):e1005260.
+
+<--- Page Split --->
+<|ref|>text<|/ref|><|det|>[[196, 78, 910, 700]]<|/det|>
+Moritz, S., Gläscher, J., Sommer, T., Büchel, C., and Braus, D. F. (2006). Neural correlates of memory confidence. Neuroimage, 33(4):1188- 1193. Orpella, J., Mas- Herrero, E., Ripollés, P., Marco- Pallarés, J., and de Diego- Balaguer, R. (2021). Statistical learning as reinforcement learning phenomena. bioRxiv. Rescorla, R. A., Wagner, A. R., et al. (1972). A theory of pavlovian conditioning: Variations in the effectiveness of reinforcement and nonreinforcement. Classical conditioning II: Current research and theory, 2:64- 99. Rigoux, L., Stephan, K. E., Friston, K. J., and Daunizeau, J. (2014). Bayesian model selection for group studies- revisited. Neuroimage, 84:971- 985. Roy, M., Shohamy, D., Daw, N., Jepma, M., Wimmer, G. E., and Wager, T. D. (2014). Representation of aversive prediction errors in the human periaqueductal gray. Nature neuroscience, 17(11):1607- 1612. Segerdahl, A. R., Mezue, M., Okell, T. W., Farrar, J. T., and Tracey, I. (2015). The dorsal posterior insula subserves a fundamental role in human pain. Nature neuroscience, 18(4):499. Sestieri, C., Shulman, G. L., and Corbetta, M. (2010). Attention to memory and the environment: functional specialization and dynamic competition in human posterior parietal cortex. Journal of Neuroscience, 30(25):8445- 8456. Seymour, B. (2019). Pain: a precision signal for reinforcement learning and control. Neuron, 101(6):1029- 1041. Seymour, B. and Mancini, F. (2020). Hierarchical models of pain: Inference, information- seeking, and adaptive control. NeuroImage, 222:117212. Stephan, K. E., Penny, W. D., Daunizeau, J., Moran, R. J., and Friston, K. J. (2009). Bayesian model selection for group studies. Neuroimage, 46(4):1004- 1017. Turk- Browne, N. B., Jungé, J. A., and Scholl, B. J. (2005). The automaticity of visual statistical learning. Journal of Experimental Psychology: General, 134(4):552. Wager, T. D., Atlas, L. Y., Lindquist, M. A., Roy, M., Woo, C.- W., and Kross, E. (2013). An fmri- based neurologic signature of physical pain. New England Journal of Medicine, 368(15):1388- 1397. Wager, T. D., Rilling, J. K., Smith, E. E., Sokolik, A., Casey, K. L., Davidson, R. J., Kosslyn, S. M., Rose, R. M., and Cohen, J. D. (2004). Placebo- induced changes in fmri in the anticipation and experience of pain. Science, 303(5661):1162- 1167. Wang, R., Shen, Y., Tino, P., Welchman, A. E., and Kourtzi, Z. (2017). Learning predictive statistics: strategies and brain mechanisms. Journal of Neuroscience, 37(35):8412- 8427. Weiss, A., Chambon, V., Lee, J. K., Drugowitsch, J., and Wyart, V. (2021). Interacting with volatile environments stabilizes hidden- state inference and its brain signatures. Nature Communications, 12(1):2228. Wiech, K. (2016). Deconstructing the sensation of pain: The influence of cognitive processes on pain perception. Science, 354(6312):584- 587. Yoshida, W., Seymour, B., Kolzenburg, M., and Dolan, R. J. (2013). Uncertainty increases pain: evidence for a novel mechanism of pain modulation involving the periaqueductal gray. Journal of Neuroscience, 33(13):5638- 5646. Zhang, S., Mano, H., Ganesh, G., Robbins, T., and Seymour, B. (2016). Dissociable learning processes underlie human pain conditioning. Current Biology, 26(1):52- 58.
+
+<--- Page Split --->
+<|ref|>sub_title<|/ref|><|det|>[[44, 42, 311, 70]]<|/det|>
+## Supplementary Files
+
+<|ref|>text<|/ref|><|det|>[[44, 93, 765, 113]]<|/det|>
+This is a list of supplementary files associated with this preprint. Click to download.
+
+<|ref|>text<|/ref|><|det|>[[60, 130, 305, 176]]<|/det|>
+- tslfrmisupplementary.pdf- rs.pdf
+
+<--- Page Split --->
diff --git a/preprint/preprint__05f28e060c3bc16824dbd8aa76dba38dd15d721d8f4e14b66cd59ec29caee55f/images_list.json b/preprint/preprint__05f28e060c3bc16824dbd8aa76dba38dd15d721d8f4e14b66cd59ec29caee55f/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..026355c656e184f1dbf791dcd45872c6694faf14
--- /dev/null
+++ b/preprint/preprint__05f28e060c3bc16824dbd8aa76dba38dd15d721d8f4e14b66cd59ec29caee55f/images_list.json
@@ -0,0 +1,242 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1: Task paradigm (Exp. 1) – Active information gathering. At the beginning of each trial, a purple dot is displayed to give an initial clue about the location of the hidden circle. Participants were informed that touching the screen could provide further clues (either purple or white dots) to narrow the solution space of the location of the hidden circle. If touching the screen at a certain location yielded a purple dot, this location was situated inside the hidden circle. By contrast, if a white dot appeared, then the location was outside the hidden circle. Participants were instructed that there were no constraints on where and when to touch the screen within the allocated 18 seconds per trial, and that they could stop whenever they wanted to. Touching the screen to gather information, however, came at a cost which was subtracted from the initial reward reserve participants start the trial with ( \\(R_{0}\\) ; shown inside the two purple circles on the side of the search space). In the depicted trial for example, the participant started with 95 credits and lost one credit per additional sample acquired. After the active sampling phase (18 seconds), a blue disc appeared automatically in the centre of the screen, and participants were instructed to move this disc to where they thought the hidden circle was. Each trial was scored by removing a localisation error penalty ( \\(e.\\eta_{e}\\) where \\(e\\) is the localisation error in Pixels, and \\(\\eta_{e}\\) is the error cost in credits per pixel) from the remaining reward reserve ( \\(R_{0} - s.\\eta_{s}\\) where \\(s\\) is the number of extra sampled acquired and \\(\\eta_{s}\\) is the sampling cost). Error cost ( \\(\\eta_{e}\\) ) was constant and equal to 1.2 credits per pixel",
+ "footnote": [],
+ "bbox": [
+ [
+ 190,
+ 256,
+ 864,
+ 470
+ ]
+ ],
+ "page_idx": 8
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_2.jpg",
+ "caption": "Figure 2: Task paradigm (Exp. 2) – Passive decision making under uncertainty. The task examines how people weigh potential rewards against uncertainty when making decisions. a. The purple and white dots on the screen provide clues about the location of a hidden circle of fixed size. Purple dots fall within the area of the hidden circle, while white dots are located outside it. The two purple circles on the side are of the same size as the hidden circle. The two numbers on the side display the number of credits (reward) on offer. b. Different spatial configurations are associated with different levels of uncertainty. Uncertainty is quantified as the expected error upon circle localisation \\((EE)\\) . This is equal to the probability-weighted average of all the possible errors that could be resulting when placing the localisation disc (blue disc in d) at the best possible location. The best possible location is the centroid of the solution space, which is the set of the centres of all the possible circles that could be a solution for the spatial configuration displayed. d. Participants first reported their subjective estimation of uncertainty (i.e., how confident they are about the location of the hidden circle given the information displayed on the screen). After this, the credits on offer appeared (displayed inside the two purple circles on the side). Participants could decide to accept or reject the offer to locate the hidden circle. d. At the end of the experiment, participants had to play 10 of the accepted offers by placing a blue disc on top of where they thought the hidden circle was located. These trials determined the scores in the task. The score was equal to the reward on offer minus a penalty reflecting their localisation error (i.e., how far the blue disc centre was from the centre of the hidden circle).",
+ "footnote": [],
+ "bbox": [
+ [
+ 131,
+ 193,
+ 852,
+ 480
+ ]
+ ],
+ "page_idx": 10
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3: Task paradigm (Exp. 3) – Effort-based decision making task. The task was similar in design to Circle Quest passive choices task. First, calibration of the hand-held dynamometer was done based on each participant's maximum voluntary contraction. Participants were then familiarised with the effort levels they would encounter in the task by asking them to squeeze the handle up to the effort level indicated by the yellow line: the higher the line the more effort they needed to exert. They did this twice for each effort level. Next, participants made decisions indicating whether the reward (apples) on offer is worth the effort assigned to it. They were told that at the end of the experiment, 10 of their decisions would be selected randomly and that they would have to play them in order to obtain the apples.",
+ "footnote": [],
+ "bbox": [
+ [
+ 171,
+ 145,
+ 824,
+ 290
+ ]
+ ],
+ "page_idx": 11
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_4.jpg",
+ "caption": "Figure 4: Task paradigm (Exp. 4) – Effort-based decision making under uncertainty. a. Once training was complete, participants made accept/reject decisions (200 trials) during the decision making phase weighing reward (credits) on offer against different effort levels required. They also had to take into consideration whether decisions were made under uncertainty or not, i.e., they had to decide whether the reward on offer, given the level of uncertainty, was worth making the effort. Uncertainty pertains to the location of the hidden circle which participants estimate from the configuration of dots on the screen (see Methods). Absence of uncertainty was indicated simply by displaying the purple circle at its precise location. b. At the end of the experiment, participants played 24 trials that were randomly selected from the decision phase. They had to make the physical effort in order to be given the opportunity to place the blue circle where they thought the purple circle was hidden (in 12 of the trials, the location of the purple circle was shown; in the other 12 it was not). Performance accuracy determined the credits participants eventually won. Participants were familiarised with the task environment and scoring function in three stages: i) following an interactive tutorial explaining Circle Quest task as in Exps. 1 & 2, they were required to place the blue disc for fixed levels of uncertainty with credits displayed on the side. This exposed them to the scoring function and served as a control task measuring localisation accuracy (Figure 10a.). ii) Participants reported their confidence about the location of the hidden circle using a rating scale ranging between zero and 100. The configuration of dots used were the ones they would face in the decision making phase as well as in catch trials, which were added to widen the uncertainty range used to characterise subjective estimations. Subjective uncertainty estimates were obtained by simply sign-flipping and z-scoring these confidence ratings (Figure 10b.). iii) Effort calibration and familiarisation were the same as in Exp. 3. Maximum voluntary contraction (MVC) was first obtained by asking participants to squeeze the effort handle as hard as they could and then effort levels were calibrated based on MVC (five levels).",
+ "footnote": [],
+ "bbox": [
+ [
+ 130,
+ 160,
+ 833,
+ 470
+ ]
+ ],
+ "page_idx": 13
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_5.jpg",
+ "caption": "Figure 5: Exp. 1 – Reduced sensitivity to changes in information cost in ALE patients. a. Uncertainty (indexed as expected error, \\(EE\\) ) decreases with sampling and follows an exponential decay slope on average in both patients and controls. b. ALE patients, compared to controls, sampled more when initial reward reserve and sampling cost were both high. c-d. The optimal number of samples \\((s^{\\star})\\) is the number of samples (s) at which the maximum return (Expected Value, \\(EV\\) ) could be achieved. Obtaining more samples before \\(s^{\\star}\\) results in increases in \\(EV\\) , while acquiring samples beyond \\(s^{\\star}\\) results in lower \\(EVs\\) . ALE patients and healthy controls over-sampled when sampling cost was high. Patients, however, over-sampled to a greater extent than controls, mainly when initial reward reserve and sampling cost both increased. There was no significant difference between the two groups at low-cost conditions. Lines in c. show the individual EV timecourses centred on their peaks (optimal number of samples to acquire). Ellipses contain \\(90\\% CI\\) for each participant. \\(\\eta_{s}\\) : Sampling cost. \\(R_{0}\\) : Initial reward reserve. e. Patients achieved lower scores than controls, especially at higher sampling cost, where patients deviated more than controls from optimal sampling. Error bars show \\(\\pm \\mathrm{SEM}\\) . \\*:p <0.05. See Tables S3 & S4 for full statistical details.",
+ "footnote": [],
+ "bbox": [
+ [
+ 170,
+ 152,
+ 825,
+ 620
+ ]
+ ],
+ "page_idx": 17
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_6.jpg",
+ "caption": "Figure 6: Exp. 2 – ALE patients are less sensitive to changes in reward under uncertainty. q. Patients and healthy controls adjusted their decisions according to the reward and uncertainty on offer. The influence of reward on offer acceptance was blunted in hippocampal patients when compared to controls (shallower reward slope). Level 1 indicates lowest reward/uncertainty level on offer. b. Controls accepted more of the high-value offers (blue region) when compared to hippocampal patients. c. Investigation of the group effect using logistic regression model with mixed effects ( \\(\\mathrm{L}_{\\theta}\\mathrm{MM}\\) ) revealed that patients had significantly lower sensitivity to reward than controls but did not significantly differ in their sensitivity to uncertainty. Additionally, it showed that the impact of uncertainty on decision making was more significant than the impact of reward (histogram on the corner). d. Lower sensitivity to reward, but not uncertainty, in the passive task is associated with lower sensitivity to sampling cost in the active sampling task (Exp. 1) driving group differences in number of samples collected. Colour bar indicates the contribution of each data point to the model. Blue dots represent controls and are added for visual comparison. Error bars in a. show \\(\\pm\\) SEM. ***: \\(\\mathrm{p}< 0.001\\) . Shaded area in d. show \\(95\\%\\) CI. See Table S7 for full statistical details.",
+ "footnote": [],
+ "bbox": [
+ [
+ 123,
+ 201,
+ 865,
+ 600
+ ]
+ ],
+ "page_idx": 19
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_7.jpg",
+ "caption": "Figure 7: Exp. 3 – Intact reward valuation against effort in ALE patients. a. There was no significant difference in offer acceptance between patients and controls. b. The estimates of these acceptance slopes indicate how sensitive participants are to reward/effort changes of offers. These sensitivity estimates were extracted from a generalised mixed model with full randomness and plotted for visualisation. Error bars show \\(\\pm \\mathrm{SEM}\\) . \\(^{*}\\mathrm{p}< 0.05\\) . See Tables S9 & S10 for full statistical details.",
+ "footnote": [],
+ "bbox": [
+ [
+ 140,
+ 150,
+ 864,
+ 352
+ ]
+ ],
+ "page_idx": 21
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_8.jpg",
+ "caption": "Figure 8: Exp. 4 – Blunted reward and effort sensitivity under uncertainty in ALE patients. In Exp. 4, participants were required to accept/reject offers taking into consideration three attributes: reward, physical effort, and uncertainty. The results showed that ALE patients, compared to controls, were less sensitive to changes in reward and effort while having intact sensitivity to uncertainty. Such results are consistent with findings from Exps. 1 & 2, highlighting disrupted reward and cost valuation in ALE patients under uncertainty. Error bars show \\(\\pm \\mathrm{SEM}\\) . \\*: \\(p< 0.05\\) . See Table S13 for full statistical details.",
+ "footnote": [],
+ "bbox": [
+ [
+ 169,
+ 133,
+ 818,
+ 335
+ ]
+ ],
+ "page_idx": 22
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_9.jpg",
+ "caption": "Figure 9: Severity of hippocampal atrophy correlates with decreased reward sensitivity against uncertainty. a. VBM analysis shows that ALE patients have significantly reduced grey matter intensity in right hippocampal region (cluster 1, Table 1). b. Patients with more severely atrophied hippocampi were less sensitive to reward when traded against uncertainty. By contrast, hippocampal volumes were not significantly correlated with sensitivity to uncertainty which was preserved in ALE patients.",
+ "footnote": [],
+ "bbox": [
+ [
+ 170,
+ 360,
+ 825,
+ 777
+ ]
+ ],
+ "page_idx": 24
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_10.jpg",
+ "caption": "Figure 10: Exps. 1, 2 & 4 – Intact localisation and subjective uncertainty estimation in ALE. a. ALE patients and controls did not differ in their localisation error (distance between the centre of the blue disc and hidden circle) for fixed levels of uncertainty, indicating similar motor and localisation performance. b. Subjective uncertainty is z-scored signed-flipped confidence ratings that participants reported before seeing the reward on offer (Exp. 2) or during training (Exp. 4). There was no significant difference between ALE patients and controls in this measure, indicating intact uncertainty estimation. Error bars in a. show \\(\\pm\\) SEM. Shaded area show \\(95\\%\\) CI. See Table S14 for full statistical details.",
+ "footnote": [],
+ "bbox": [
+ [
+ 223,
+ 225,
+ 732,
+ 666
+ ]
+ ],
+ "page_idx": 27
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_0.jpg",
+ "caption": "Figure S1: Computational modelling of active information sampling (Exp. 1). Compared to healthy matched controls, ALE patients assigned lower economic costs \\((w_{s})\\) to sample acquisition. All other model parameters including weights assigned to sample benefit \\((w_{e})\\) , efficiency \\(w_{\\alpha}\\) , and speed \\((w_{speed})\\) were not significantly different between patients and controls. \\(w_{0}\\) captures a subjective fixed cost of sampling that is not explicitly specified in the task (e.g., cost of the motor action). This was not significantly different between the two groups. \\(*:p< 0.05\\)",
+ "footnote": [],
+ "bbox": [
+ [
+ 293,
+ 335,
+ 705,
+ 604
+ ]
+ ],
+ "page_idx": 61
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_1.jpg",
+ "caption": "Figure S2: Active sampling (Exp. 1) – Hippocampal patients commit to decisions at similar uncertainty levels as controls. a. Final uncertainty is the expected error (EE) in pixels (Px) that a participant is likely to obtain at the end of their search. In the experimental condition where hippocampal patients over-sampled more than controls, there was no significant difference between hippocampal patients and controls in this measure. b. Similarly, the actual error that participants obtained upon localising the circle (distance to hidden circle in pixels) was not significantly different between patients and controls. These two results indicate that hippocampal patients wasted monetary resources on samples with limited utility (i.e., over-sampled). c. In the same condition, hippocampal patients gathered information at a significantly faster rate than controls. d. Sampling behaviour in hippocampal patients and controls was characterised by a speed-efficiency trade-off whereby faster sampling rates (shorter \\(ISI\\) ) were associated with lower sampling efficiency (smaller \\(\\alpha\\) ). The figure shows this trade-off for the same condition in which patients over-sampled more than controls, demonstrating that hippocampal patients were also both faster and less efficient than controls. Error bars show \\(\\pm\\) SEM. \\*:p<0.05. See Tables S3, S5 & S6 for additional statistical details.",
+ "footnote": [],
+ "bbox": [
+ [
+ 188,
+ 163,
+ 844,
+ 604
+ ]
+ ],
+ "page_idx": 63
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_2.jpg",
+ "caption": "Figure S3: Baysian mixed-effects model. The purple dots show the median of the posterior distributed with \\(95\\%\\) credible intervals (thin green line) and \\(50\\%\\) posterior interval (thick dark red lines). Model was specified as follows:choice \\(\\sim 1 + \\mathrm{group}^{*}\\mathrm{Reward} + \\mathrm{group}^{*}\\mathrm{Effort} + \\mathrm{Re}-\\) ward\\*Effort + group:Reward:Effort + (1 + reward\\*Effort |participant).",
+ "footnote": [],
+ "bbox": [
+ [
+ 163,
+ 348,
+ 812,
+ 621
+ ]
+ ],
+ "page_idx": 64
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_3.jpg",
+ "caption": "Figure S4: Amygdala as control region. No significant correlation was detected between amygdala volume and sensitivity to reward or uncertainty. Note also there was no significant difference in amygdala volumes between patients and controls.",
+ "footnote": [],
+ "bbox": [
+ [
+ 153,
+ 178,
+ 802,
+ 541
+ ]
+ ],
+ "page_idx": 65
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_4.jpg",
+ "caption": "Figure S5: Intact localisation performance. Distance to optimal placement is the distance between the centre of the blue disc and the best localisation given the configuration of the dots on display. Across the three versions of Circle Quest (Exps. 1, 2 & 3), there was no significant difference between ALE patients and controls in this measure, indicating intact localisation performance. Error bars show \\(\\pm\\) SEM.",
+ "footnote": [],
+ "bbox": [
+ [
+ 225,
+ 640,
+ 775,
+ 809
+ ]
+ ],
+ "page_idx": 65
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_unknown_5.jpg",
+ "caption": "Figure S6: Passive choices as a function of reward and subjective uncertainty estimates. There is no change in choice performance results when subjective estimates of uncertainty are used instead of expected error \\((EE)\\) in the analysis. ALE patients demonstrate lower sensitivity to reward and intact sensitivity to uncertainty when compared to healthy controls. Reward levels 1-4 correspond to the number of credits on display \\((R: 40, 65, 90, 115\\) credits). Subjective uncertainty levels were calculated by binning sign-flipped z-scored confidence ratings into five bins. level five describes the lowest level of subjective uncertainty estimate. For statistical details see Table S16.",
+ "footnote": [],
+ "bbox": [
+ [
+ 225,
+ 352,
+ 770,
+ 555
+ ]
+ ],
+ "page_idx": 66
+ }
+]
\ No newline at end of file
diff --git a/preprint/preprint__06076107a582a7db1a993272bc8d0902287719a4fcc5b06c29c18d0dc685d84a/images_list.json b/preprint/preprint__06076107a582a7db1a993272bc8d0902287719a4fcc5b06c29c18d0dc685d84a/images_list.json
new file mode 100644
index 0000000000000000000000000000000000000000..dcbf1cef45cb40c8aaeb4a713bbead0e0670e3fa
--- /dev/null
+++ b/preprint/preprint__06076107a582a7db1a993272bc8d0902287719a4fcc5b06c29c18d0dc685d84a/images_list.json
@@ -0,0 +1,25 @@
+[
+ {
+ "type": "image",
+ "img_path": "images/Figure_1.jpg",
+ "caption": "Figure 1",
+ "footnote": [],
+ "bbox": [
+ [
+ 40,
+ 37,
+ 950,
+ 714
+ ]
+ ],
+ "page_idx": 10
+ },
+ {
+ "type": "image",
+ "img_path": "images/Figure_3.jpg",
+ "caption": "Figure 3",
+ "footnote": [],
+ "bbox": [],
+ "page_idx": 11
+ }
+]
\ No newline at end of file