RNF8 is not required for histone-to-protamine exchange in spermiogenesis

A member of the PIWI family of proteins, MIWI, binds to Piwi-interacting RNA (piRNA) and is essential in mouse spermiogenesis. A recent study demonstrated that MIWI is an essential regulator of the histone-to-protamine exchange in spermiogenesis and that this function is mediated by its binding to an ubiquitin ligase, RNF8. However, here we confirm that RNF8 is not required for histone-to-protamine exchange in spermiogenesis. We show that histone-to-protamine exchange takes place in Rnf8-deficient mice, while RNF8 mediates ubiquitination of H2A on the sex chromosomes in meiosis, the prior stage of spermatogenesis. Therefore, the infertile phenotype of MIWI mutant mice cannot be explained by a RNF8-mediated mechanism in spermiogenesis.