人Piwi基因突变致男性不育的机制研究

The Study of Human Piwi Mutations in Male Infertility

大量遗传学研究表明,Piwi蛋白对于动物生殖系细胞发育具有至关重要的作用,Piwi基因敲除致动物不育。人Piwi(Hiwi)基因特异性地在雄性生殖细胞表达,但目前对其在人精子发生中的作用及其与男性不育的联系还知之甚少。该研究通过筛查临床男性不育样本发现,少弱精症患者Hiwi基因中存在拮抗泛素化修饰的D-box元件突变;通过构建基因敲入小鼠模型证实,该突变导致雄性不育。机制研究表明,小鼠Piwi(Miwi)D-box突变致MIWI蛋白异常稳定存在于后期精子细胞中,导致与其相互作用的组蛋白泛素连接酶RNF8(ring finger protein 8)被扣留于细胞质、不能入核催化组蛋白泛素化修饰,进而抑制组蛋白被鱼精蛋白替换,引发精子形成异常、雄性不育。该研究发现了男性不育的一类新型致病基因突变,并发现了Piwi蛋白具有调控组蛋白泛素化修饰的新功能,揭示了精子形成中调控组蛋白–鱼精蛋白转换的重要机制。

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 D-box mutations in human Piwi（Hiwi） in patients with azoospermia. By modeling such mutations in Piwi（Hiwi） knockin mice, we demonstrate that the genetic defects are directly responsible for male infertility. Mechanistically, we show that D-box mutation caused-MIWI stabilization sequesters ring finger protein 8（RNF8） in the cytoplasm of late spermatids, with blocking the ubiquitination and removal of histones. The failure of histone-to-protamine exchange finally leads to deficient spermiogenesis and male infertility. Collectively, our findings identify Piwi as a factor in human infertility and reveal its role in regulating the histone-to-protamine exchange during spermiogenesis.