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

Genetic studies have elucidated critical roles of Piwi proteins 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 mutations in Piwi (Miwi) knockin mice, we demonstrate that the genetic defects are directly responsible for male infertility. Mechanistically, we show that MIWI binds the histone ubiquitin ligase RNF8 in a Piwi-interacting RNA (piRNA)-independent manner, 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 functionally rescued via blocking RNF8-MIWI interaction in spermatids with an RNF8-N peptide. Collectively, our findings identify Piwi as a factor in human infertility and reveal its role in regulating the histone-to-protamine exchange during spermiogenesis. [Display omitted] •Hiwi ubiquitination-deficient D-box mutations are detected in azoospermia patients•D-box mutant knockin mice display spermatogenic failure at late spermiogenesis•Stabilized MIWI ties RNF8 up in the cytoplasm to prevent histone ubiquitination•Blocking MIWI-RNF8 interaction functionally rescues defective spermiogenesis Male infertility in mice and humans can result from mutations that stabilize the Piwi protein in late spermatids: sperm defects are due to aberrant histone retention, not piRNA misregulation.