Department of Anatomy and Developmental Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC, 3800, Australia.
Cell Death Dis. 2023 Jul 5;14(7):397. doi: 10.1038/s41419-023-05886-x.
Mammalian oocytes spend most of their life in a unique state of cell cycle arrest at meiotic prophase I, during which time they are exposed to countless DNA-damaging events. Recent studies have shown that DNA double-strand break repair occurs predominantly via the homologous recombination (HR) pathway in small non-growing meiotically arrested oocytes (primordial follicle stage). However, the DNA repair mechanisms employed by fully grown meiotically arrested oocytes (GV-stage) have not been studied in detail. Here we established a conditional knockout mouse model to explore the role of Ku80, a critical component of the nonhomologous end joining (NHEJ) pathway, in the repair of DNA damage in GV oocytes. GV oocytes lacking Ku80 failed to repair etoposide-induced DNA damage, even when only low levels of damage were sustained. This indicates Ku80 is needed to resolve DSBs and that HR cannot compensate for a compromised NHEJ pathway in fully-grown oocytes. When higher levels of DNA damage were induced, a severe delay in M-phase entry was observed in oocytes lacking XRCC5 compared to wild-type oocytes, suggesting that Ku80-dependent repair of DNA damage is important for the timely release of oocytes from prophase I and resumption of meiosis. Ku80 was also found to be critical for chromosome integrity during meiotic maturation following etoposide exposure. These data demonstrate that Ku80, and NHEJ, are vital for quality control in mammalian GV stage oocytes and reveal that DNA repair pathway choice differs in meiotically arrested oocytes according to growth status.
哺乳动物卵母细胞在减数分裂前期 I 的独特细胞周期停滞状态下度过大部分生命，在此期间，它们会暴露于无数的 DNA 损伤事件中。最近的研究表明，在小的非生长性减数分裂停滞的卵母细胞（原始卵泡阶段）中，DNA 双链断裂修复主要通过同源重组（HR）途径发生。然而，完全生长的减数分裂停滞的卵母细胞（GV 期）中使用的 DNA 修复机制尚未详细研究。在这里，我们建立了一个条件性敲除小鼠模型，以探索 Ku80（非同源末端连接（NHEJ）途径的关键组成部分）在 GV 卵母细胞中修复 DNA 损伤的作用。缺乏 Ku80 的 GV 卵母细胞无法修复依托泊苷诱导的 DNA 损伤，即使仅维持低水平的损伤也是如此。这表明 Ku80 对于解决 DSB 是必需的，并且 HR 不能弥补完全生长的卵母细胞中受损的 NHEJ 途径。当诱导更高水平的 DNA 损伤时，与野生型卵母细胞相比，缺乏 XRCC5 的卵母细胞中 M 期进入的严重延迟表明，Ku80 依赖性的 DNA 损伤修复对于卵母细胞从前期 I 中及时释放和减数分裂恢复至关重要。在依托泊苷暴露后的减数成熟过程中，Ku80 对于染色体完整性也是至关重要的。这些数据表明，Ku80 和 NHEJ 对于哺乳动物 GV 期卵母细胞的质量控制至关重要，并揭示了根据生长状态，在减数分裂停滞的卵母细胞中，DNA 修复途径的选择存在差异。
