For ChIP-Seq, 5% mouse epigenome was used as internal control for H3K27me3 IP. For RNA-Seq, RNA was isolated by TRIZol reagent, and polyA tail RNAs were selected. For small RNA-seq, ~20-29 nt small RNA was recoveried by 15% TBE-UREA PAGE gels. ChIP libraries were prepared according to instructions of NEB DNA library prep kit (NEB, E7370L). RNA libraries were prepared according to instructions of NEB Ultra RNA library prep kit (NEB, E7530L). Small RNA libraries were prepared by NEBNext Multiplex Small RNA Library Prep Set for Illumina (NEB, E7300S). ChIP-Seq or RNA-Seq or miRNA-seq