PHF7 Modulates BRDT Stability and Histone-to-Protamine Exchange during Spermiogenesis

Spermatogenesis is a complex process of sperm generation, including mitosis, meiosis, and spermiogenesis. During spermiogenesis, histones in post-meiotic spermatids are removed from chromatin and replaced by protamines. Although histone-to-protamine exchange is important for sperm nuclear condensation, the underlying regulatory mechanism is still poorly understood. Here, we identify PHD finger protein 7 (PHF7) as an E3 ubiquitin ligase for histone H3K14 in post-meiotic spermatids. Generation of Phf7-deficient mice and Phf7 C160A knockin mice with impaired E3 ubiquitin ligase activity reveals defects in histone-to-protamine exchange caused by dysregulation of histone removal factor Bromodomain, testis-specific (BRDT) in early condensing spermatids. Surprisingly, E3 ubiquitin ligase activity of PHF7 on histone ubiquitination leads to stabilization of BRDT by attenuating ubiquitination of BRDT. Collectively, our findings identify PHF7 as a critical factor for sperm chromatin condensation and contribute to mechanistic understanding of fundamental phenomenon of histone-to-protamine exchange and potential for drug development for the male reproduction system.