Department of Biomedical Sciences and Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.
Proc Natl Acad Sci U S A. 2011 Oct 25;108(43):17702-7. doi: 10.1073/pnas.1113524108. Epub 2011 Oct 10.
Effective DNA replication is critical to the health and reproductive success of organisms. The six MCM2-7 proteins, which form the replicative helicase, are essential for high-fidelity replication of the genome. Many eukaryotes have a divergent paralog, MCM9, that was reported to be essential for loading MCM2-7 onto replication origins in the Xenopus oocyte extract system. To address the in vivo role of mammalian MCM9, we created and analyzed the phenotypes of mice with various mutations in Mcm9 and an intronic DNA replication-related gene Asf1a. Ablation of Mcm9 was compatible with cell proliferation and mouse viability, showing that it is nonessential for MCM2-7 loading or DNA replication. Mcm9 mutants underwent p53-independent embryonic germ-cell depletion in both sexes, with males also exhibiting defective spermatogonial stem-cell renewal. MCM9-deficient cells had elevated genomic instability and defective cell cycle reentry following replication stress, and mutant animals were prone to sex-specific cancers, most notably hepatocellular carcinoma in males. The phenotypes of mutant mice and cells suggest that MCM9 evolved a specialized but nonessential role in DNA replication or replication-linked quality-control mechanisms that are especially important for germ-line stem cells, and also for tumor suppression and genome maintenance in the soma.
有效的 DNA 复制对于生物体的健康和生殖成功至关重要。六聚体 MCM2-7 蛋白形成复制解旋酶，对于基因组的高保真复制是必需的。许多真核生物具有一个发散的同源物 MCM9，据报道，它对于在爪蟾卵提取物系统中加载 MCM2-7 到复制起点是必需的。为了解决哺乳动物 MCM9 的体内作用，我们创建并分析了 Mcm9 具有各种突变和一个内含子 DNA 复制相关基因 Asf1a 的小鼠表型。Mcm9 的缺失与细胞增殖和小鼠存活兼容，表明它对于 MCM2-7 加载或 DNA 复制不是必需的。Mcm9 突变体在两性中均经历了 p53 非依赖性胚胎生殖细胞耗竭，而雄性还表现出精原干细胞更新缺陷。MCM9 缺陷细胞在复制应激后具有更高的基因组不稳定性和有缺陷的细胞周期进入，并且突变动物易发生性别特异性癌症，尤其是雄性的肝细胞癌。突变小鼠和细胞的表型表明，MCM9 在 DNA 复制或复制相关的质量控制机制中进化出了一种专门但非必需的作用，这些作用对于生殖细胞干细胞特别重要，对于体细胞中的肿瘤抑制和基因组维持也很重要。
