FACS-sorted cell populations (1x105 cells) were crosslinked in 1% paraformaldehyde for 5 minutes at RT. The reaction was quenched by addition of 125mM glycine. Crosslinked cells were lysed and partially digested with micrococcal nuclease (12,000 units/ml) for 1 minute at 37 degrees. Digestion was stopped by addition of EDTA and digested nuclei were resuspended in nuclear lysis buffer containing 1% SDS. Following sonication, chromatin was incubated overnight with antibodies against H3K27me3, H3K27Ac, or H3K4me1 and immunocomplexes were precipitated with protein A Dynabeads. After washing, precipitated chromatin was decrosslinked overnight at 65 degrees in the presence of proteinase K and DNA fragments were isolated using Qiagen PCR-purification kit. Purified DNA was processed for sequencing on Illumina Hiseq.