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• 40% Acryl/Bis (29:1; Amresco, cat. no. 0311-1L) ! CAUTI0N This compound is harmful if swallowed or inhaled, and it causes irritation to the skin, the eyes and the respiratory tract. Handle it using appropriate equipment.
Enzyme choice. The restriction endonuclease MspI (C↓CGG) is commonly used in RRBS, and it is the focus of this scRRBS protocol. MspI digestion is strongly biased toward CGIs and promoters; however, other restriction endonucleases such as TaqI (T↓CGA) could be chosen to capture different genomic regions. In addition, di...
Sequencing. Different sequencing platforms can be used, including the Illumina HiSeq 2000 and HiSeq 2500 platforms we use. We generally sequence each scRRBS library to ~10 million 100-bp paired-end reads. Increasing the sequencing depth to 20 million reads will only slightly raise the genomic coverage. In our experienc...
## MATERIALS
## REAGENTS
▲ CRITICAL All reagents used in this experiment must be free of nucleases. ! CAUTION All samples from animals or humans should be processed according to the guidelines of the local government or institution.
• Cell line or single cells of interest. In the PROCEDURE, we use as an example mESCs maintained in conventional DMEM, containing 20% (vol/vol) FBS in the presence of leukemia inhibitory factor (LIF)
• Tris-EDTA solution (100×; Sigma-Aldrich, cat. no. T9285-100ML)
• Triton X-100 (Sigma-Aldrich, cat. no. T8787-50ML) ! CAUTI0N Triton X-100 is harmful if swallowed or inhaled, and it causes irritation to the skin, the eyes and the respiratory tract. Handle it using appropriate equipment. ▲ CRITICAL Triton X-100 should be stored at room temperature (20–25 °C) for at most 1 year.
• Potassium chloride solution (KCl; 1 M; Sigma-Aldrich, cat. no. 60142-100ML-F)
• Glycerol (Sigma-Aldrich, cat. no. G5516-100ML)
• Protease (7.5 Anson units (AU); Qiagen, cat. no. 19155)
• Nuclease-free water (Ambion, cat. no. AM9932)
• MspI (10 U/μl; Thermo Scientific, cat. no. ER0541)
• Tango buffer (10×; Thermo Scientific, cat. no. BY5)
• λ-DNA (dam-, dcm-; 0.3 µg/μl, Thermo Scientific, cat. no. SD0021)
• Klenow fragment (exo-, 5 U/μl; Thermo Scientific, cat. no. EP0422)
• dATP (100 mM; New England BioLabs, cat. no. N0440S)
• dCTP (100 mM; New England BioLabs, cat. no. N0441S)
• dGTP (100 mM; New England BioLabs, cat. no. N0442S)
• T4 DNA ligase (highly concentrated; 30 Weiss U/μl; Thermo Scientific, cat. no. EL0013)
• ATP (100 mM; Thermo Scientific, cat. no. R0441)
• Adapters, part of the Illumina TruSeq DNA sample preparation kits (Illumina, cat. no. FC-121-2001) ▲ CRITICAL Illumina TruSeq DNA adapters are highly recommended. If they are not available, ensure that the cytosines (Cs) of the ordered oligos are methyl group-modified (mCs) and double HPLC-purified. The oligo sequenc...
• MethyCode bisulfite conversion kit (50 reactions; Thermo Scientific, cat. no. MECOV-50)
• tRNA (Roche, cat. no. 10109517001)
• PfuTurbo Cx hotstart DNA polymerase (2.5 U/μl; Agilent Technologies, cat. no.600412)
• dNTP mix (10 mM each; Clontech, cat. no. D4030RA)
• Agencourt AMPure XP beads (Beckman Coulter; cat. no. A63881)
may be a consequence of the low sequence complexity of scRRBS libraries.
Data analysis. Bioinformatics analysis methods for DNA methylation profiling data of whole-genome bisulfite sequencing and RRBS have been reported previously, which are designed to map bisulfite-converted sequence reads to a reference genome and to determine cytosine methylation states at single-base resolution10,17. C...
• Phusion high-fidelity (HF) PCR master mix with HF buffer (New England BioLabs, cat. no. M0531S)
• Qubit dsDNA high-sensitivity (HS) assay kit (Thermo Scientific, cat. no. Q32854)
• SYBR Gold nucleic acid gel stain (10,000×; Thermo Scientific, cat. no. S-11494) ! CAUTI0N This reagent is harmful if swallowed or inhaled, and it causes irritation to the skin, the eyes and the respiratory tract. Handle it using appropriate equipment.
• Glycerol (Sigma-Aldrich, cat. no. G5516-100ML)
• QIAquick PCR purification kit (Qiagen, cat. no. 28106)
• Ethanol (Sigma-Aldrich, cat. no. E7023)! CAUTI0N Ethanol is flammable. Handle it using appropriate equipment.
• TBE buffer (5×; Amresco, cat. no. J885-1L)
• Ammonium persulfate (AP; Sigma-Aldrich, cat. no. A3678-100G) ! CAUTION AP is harmful if swallowed or inhaled, and it causes irritation to the skin, the eyes and the respiratory tract. Handle it using appropriate equipment.
• N,N,N',N'-tetramethylethylenediamine (TEMED; Sigma-Aldrich, cat. no. T9281-100ML)! CAUTI0N TEMED is harmful if swallowed or inhaled, and it causes irritation to the skin, the eyes and the respiratory tract. Handle it using appropriate equipment.
• Ammonium acetate (Amresco, cat. no. 0103-500G)
• Magnesium acetate tetrahydrate (Amresco, cat. no. 0131-500G)
• SDS (Amresco, cat. no. S0227-500G)
• EDTA (Amresco, cat. no. 0322-1KG)
• PBS buffer (pH 7.2; 1×; Gibco, cat. no. 14249-95)
• Leukemia inhibitory factor (LIF; 10 million units/1 ml, Millipore, cat. no. ESG1107)
• DMEM: nutrient mixture F-12 (DMEM/F-12; Gibco, cat. no. 11320-033)
• FBS (Gibco, cat. no. 12483-020)
• Trypsin-EDTA, 0.05% (wt/vol) (1×; Gibco, cat. no. 25300-062)
• Albumin, acetylated from bovine serum (Ac-BSA; Sigma-Aldrich, cat. no. B8894)
The linkage of the last two bases of the TruSeq universal adapter oligo should be phosphorothiated to avoid nuclease cleavage of the T overhang.
The TruSeq adapter oligo (indexes 1-12) should be 5'-terminal phosphorylated for ligation of the inserted DNA fragments.