PHF7 Links H3K4 Methylation to H2A Ubiquitination During Spermiongenesis [RNA-seq]

Histone ubiquitination has been suggested to serve as a “tag” for nucleosome removal during histone-to-protamine exchange that is essential for chromatin packaging in round spermatids. Here, we screen for putative E3 ligase and identify that the PHF7, containing both RING finger and PHD domains, is critical for H2A ubiquitination and histone removal. Mechanistically, its PHD domain as a histone code reader can specifically bind H3K4me3/me2 and its RING domain as a histone writer can ubiquinate H2A. PHF7 deficiency results in male infertility in mice by generating Phf7 knockout mice using CRISPR-Cas9 technology. Futhermore, we find impaired histone-to-protamine exchange leads to reduced chromatin compaction in Phf7 knockout sperm. Immunostaining and western blot further confirme abnormal retention of core histones and reduced levels of protamine PRM1 and PRM2 in Phf7 knockout sperm. In order to exclude the possibility that Phf7 regulate the expession of protamine, we sorte the round spermatids from WT and Phf7 knockout females for RNA-seq. The transcriptomes in round spermatids are very similar between WT and Phf7 knockout mice. There are few differentially expressed genes in the two groups and the expression of protamine is also unchanged even if PHF7 deficiency. Therefore we find PHF7 has no effects on gene regulation in histone-to-protamine exchange. We isolated round spermatids from testes of WT and Phf7 knockout mice according to reported protocol (Bastos et al., 2005) as different sample for downstream analysis. Round spermatids mRNA profiles of 8-week old WT and Phf7 knockout mice were generated by deep sequencing, in triplicate, using Illumina HiSeq X10.