100 dissected ovaries were crosslinked with 1.8% formaldehyde for 10 min, and the prepared chromatin was sonicated. One-third was used for immunoprecipitation by H3K9me3 antibody. After decrosslinking, DNA was extracted and used for library preparation for sequencing. The ChIP-seq experiments were performed in three biological replicates. Library preparation and 50nt single-read sequencing were performed by Donnelly Sequencing Centre (Toronto) on an Illumina HiSeq2500.