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

Abstract

Summary 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.

Mitochondria Associated Germinal Structures in Spermatogenesis: piRNA Pathway Regulation and Beyond

“…IMC components play multiple distinct roles through interplay with other nuage proteins, including piRNA biogenesis pathway, mRNA storage, export and translation, alternative splicing, and DNA damage ( Figure 1B). Importantly, germline mutations of several IMC components were identified in human patients with oligoasthenoteratozoospermia/azoospermia, such as PIWI (MIWI), DDX25, TDRD6, and MITOPLD [94]. In conclusion, the normal physical function of IMC and the communication between IMC and piP-body are essential for the sustainment of spermatogenesis.…”

Adaptive Evolution Leads to Cross-Species Incompatibility in the piRNA Transposon Silencing Machinery

“…Germline transposon silencing is mediated by small PIWI interacting RNAs (piRNAs), which are bound by PIWI proteins and direct post-transcriptional and transcriptional silencing of target transposons (Brennecke et al, 2007; Gunawardane et al, 2007; Iwasaki et al, 2015; Kuramochi-Miyagawa et al, 2008; Sienski et al, 2012). Mutations that disrupt the piRNA pathway lead to sterility and transposon mobilization in worms, flies, fish and mice, and have been linked to human infertility (Batista et al, 2008; Carmell et al, 2007; Das et al, 2008; Gou et al, 2017; Gu et al, 2010; Heyn et al, 2012; Houwing et al, 2008; Lin and Spradling, 1997; Weick and Miska, 2014). In striking contrast, genes with essential functions in piRNA production and transposon silencing in established model systems are often very poorly conserved, and piRNA biogenesis and sequence composition show remarkable phylogenetic diversity (Chirn et al, 2015; Obbard et al, 2009; Simkin et al, 2013; Yi et al, 2014; Zanni et al, 2013).…”

Listing candidate diagnostic markers and transcriptomic exploration of the molecular basis of a type of male infertility (Non-Obstructive Azoospermia), via next generation sequencing methods

“…Even though piRNA metabolic process was reported to be enriched among NOA-down-regulated genes in an integrated analysis of miRNAs and mRNAs (45), other transcriptomic analysis did not report piRNA metabolic process and ubiquitination, which were enriched among down-regulated genes in the current study. But, germline mutations in the human Piwi gene in patients with azoospermia have been reported to prevent the ubiquitination and degradation of the corresponding protein (46). Global ubiquitination of H2A and H2B mediated by the Piwi-dependent RNF8 protein seems to be a key step in histone to protamine transition (47).…”