ChIP assay was carried out as previously described. The sorted homogenous synchronous spermatogenic cells were crosslinked with 1% formaldehyde for 10 mins and then stopped by adding 125 mM Glycine. Chromatin samples were lysed with lysis buffer (20 mM Tris-HCl pH8.0, 500 mM NaCl, 1 mM EDTA, 1% TritonX-100 and 0.1% SDS) and sonicated with Qsonica. Histone modification specific antibody was incubated with chromatin samples overnight at 4 ℃.0.5 ug spike-in antibody (Active motif #61686) and 25 ng spike-in chromatin (Active motif #53083) were used in this ChIP assay according to the manufacture's guidelines. DNA samples were analyzed using real time PCR and prepared for deep sequencing according to the manufacture's guidelines (KAPA Biosystems KK8503 and VAHTS Universal DNA Library Prep Kit for Illumina V3 ND607). Finally, libraries were pooled and sequenced on the Illumina HiSeq 2500 sequencer for 150-bp paired-end sequencing.