library_construction_protocol: 1 million primary cells of each population in two independent experiments were FACS-sorted as described above. Genomic DNA was isolated from each cell fraction using the AllPrep DNA/RNA Mini kit (Qiagen, Valencia, CA, USA) according to the manufacturer's instructions. 0.5ug of genomic DNA was digested with MspI followed by end repair, A-tailing, and ligation of adaptors. Adaptor-ligated MspI-digested DNA was size-selected (110-380 bp) and purified. 1/5 the DNA was kept for the generation of the non-oxidized library and remaining DNA was subjected to oxidation.  Both oxidized and non-oxidized DNA samples were bisulfite-treated.  Final library amplification was carried out for 18 cycles, after which the libraries were purified using AMPure XP beads (Agencourt) and sequenced on Illumina platform. 1 million primary cells of each population in two independent experiments were FACS-sorted as described above. Genomic DNA was isolated from each cell fraction using the AllPrep DNA/RNA Mini kit (Qiagen, Valencia, CA, USA) according to the manufacturer's instructions. 0.5ug of genomic DNA was digested with MspI followed by end repair, A-tailing, and ligation of adaptors. Adaptor-ligated MspI-digested DNA was size-selected (110-380 bp) and purified. 1/5 the DNA was kept for the generation of the non-oxidized library and remaining DNA was subjected to oxidation.  Both oxidized and non-oxidized DNA samples were bisulfite-treated.  Final library amplification was carried out for 18 cycles, after which the libraries were purified using AMPure XP beads (Agencourt) and sequenced on Illumina platform. RRBS and oxRRBS.