Function of RAD6B and RNF8 in spermatogenesis

Histone ubiquitination regulates sperm formation and is important for nucleosome removal during spermatogenesis. RNF8 is an E3 ubiquitin ligase, and RAD6B is an E2 ubiquitin-conjugating enzyme. Both proteins participate in DNA damage repair processes via histone ubiquitination. Loss of RNF8 or RAD6B can lead to sterility in male mice. However, the specific mechanisms regulating these ubiquitin-mediated processes are unclear. In this study, we found that RNF8 knockout mice were either subfertile or sterile based on the numbers of offspring they produced. We explored the mechanism by which RAD6B and RNF8 knockouts cause infertility in male mice and compared the effects of their loss on spermatogenesis. Our results demonstrate that RAD6B can polyubiquitinate histones H2 A and H2B. In addition, RNF8 was shown to monoubiquitinate histones H2 A and H2B. Furthermore, we observed that absence of histone ubiquitination was not the only reason for infertility. Senescence played a role in intensifying male sterility by affecting the number of germ cells during spermatogenesis. In summary, both histone ubiquitination and senescence play important roles in spermatogenesis.组蛋白泛素化（Histone ubiquitination）可调控精子发生，且在精子发生过程中的核小体移除环节发挥关键作用。RNF8属于E3泛素连接酶（E3 ubiquitin ligase），RAD6B则为E2泛素结合酶（E2 ubiquitin-conjugating enzyme），二者均可通过介导组蛋白泛素化参与DNA损伤修复过程。雄性小鼠若缺失RNF8或RAD6B，可引发不育，但目前这类泛素介导过程的具体调控机制尚不明确。本研究中，我们根据子代繁育数量分析发现，RNF8基因敲除小鼠的生育力表现为亚生育力或完全不育。我们探究了RAD6B与RNF8敲除导致雄性小鼠不育的具体机制，并对比了二者缺失对精子发生的影响。研究结果表明，RAD6B可对组蛋白H2A和H2B进行多泛素化修饰；此外，RNF8可对组蛋白H2A和H2B进行单泛素化修饰。进一步观察发现，组蛋白泛素化的缺失并非引发不育的唯一原因，细胞衰老（senescence）可通过影响精子发生过程中生精细胞的数量，加剧雄性不育表型。综上，组蛋白泛素化与细胞衰老均在精子发生过程中发挥重要调控作用。