library_construction_protocol: 200 pieces of OEP tissue per sample were manually dissected. Lysates were clarified from sonicated nuclei and histone-DNA complexes were isolated with antibody. Libraries were prepared following standard protocols. Briefly, tissue was dissociated in nuclei expulsion buffer, cells were then pelleted, washed in PBS and snap-frozen. Crosslinked chromatin was fragmented by sonication and immunoprecipitated following Nano-ChIP protocol using antibodies for H3K27ac, H3K27me3, H3K4me3. Adaptors and primers for NEBNext library preparation kit (Illumina, E6040S) were used to prepare library following NanoChIP protocol.