Ubiquitination-Deficient Mutations in Human Piwi Cause Male Infertility by Impairing Histone-to-Protamine Exchange during Spermiogenesis

Abstract

Genetic studies have elucidated critical roles ofPiwiproteins in germline development in animals,but whether Piwi is an actual disease gene in human infertility remains unknown. We report germline mutations in human Piwi (Hiwi) in patients with azoospermia that prevent its ubiquitination and degradation. By modeling such mutationsin Piwi (Miwi) knockin mice, we demonstratethat the genetic defects are directly responsiblefor male infertility. Mechanistically, we show that MIWI binds the histone ubiquitin ligase RNF8 in a Piwi-interacting RNA(piRNA)-independentmanner, and MIWI stabilization sequesters RNF8 in the cytoplasm of late spermatids. The resulting aberrant sperm show histone retention, abnormal morphology, and severely compromised activity, which can be functionallyrescued via blocking RNF8-MIWI interactioninspermatids with an RNF8-N peptide. Collectively, our findings identify Piwi as a factorin human infertilityand reveal its role in regulating the histone-to-protamine exchange during spermiogenesis.