For ChIP-seq, 1×107 cells of each sample were crosslinked in 1% formaldehyde with rotation for 10 minutes at room temperature. And then these crosslinked reactions were stopped by 0.125 M glycine with rotation for 5 minutes at room temperature. and cell sample were sonicated, and then ChIPed with H3K27me3 antibodies. DNA libraries were prepared for sequencing using standard Illumina protocols.