TSSK6 is required for γH2AX formation and the histone-to-protamine transition during spermiogenesis

Abstract

Spermiogenesis includes transcriptional silencing, chromatin condensation and extensive morphological changes as spermatids transform into sperm. Chromatin condensation involves histone hyperacetylation, transitory DNA breaks, histone H2AX Ser139 phosphorylation (γH2AX), and replacement of histones by protamines. Previously, we reported that the spermatid protein kinase TSSK6 is essential for fertility in mice, but its specific role in spermiogenesis is unknown. Here, we show that TSSK6 expression is spatiotemporally coincident with γH2AX formation in nuclei of developing mouse spermatids. RNA-Seq analysis demonstrates that genetic ablation of Tssk6 does not impact gene expression or silencing in spermatids. However, loss of TSSK6 blocks γH2AX formation, even though the timing and level of the transient DNA breaks is unaltered. Further, Tssk6 KO sperm contained increased histones H3 and H4, and protamine 2 precursor/intermediate(s) indicative of a defective histone to protamine transition. These results demonstrate that TSSK6 is required for γH2AX formation during spermiogenesis, and also link γH2AX to the histone-to-protamine transition and male fertility.