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Minichromosome maintenance helicase paralog MCM9 is dispensible for DNA replication but functions in germ-line stem
Suzanne A Hartford1, Yunhai Luo, Teresa L Southard
1Department of Biomedical Sciences and Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.
Abstract:
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.
Insights
Mammalian MCM9 is not essential for DNA replication but plays a key role in germ cell maintenance and genome stability. MCM9 deficiency leads to genomic instability, germ cell depletion, and increased cancer risk.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- DNA replication relies on the MCM2-7 helicase complex.
- MCM9, a paralog of MCM2-7, was previously thought essential for helicase loading in Xenopus.
- The in vivo function of mammalian MCM9 remained unclear.
Purpose of the Study:
- To investigate the in vivo function of mammalian MCM9 in DNA replication and genome maintenance.
- To analyze the physiological consequences of MCM9 loss in mice.
Main Methods:
- Generation and phenotypic analysis of mice with Mcm9 mutations.
- Assessment of DNA replication, cell proliferation, and genomic stability in Mcm9-deficient cells and animals.
- Evaluation of germ cell development and tumor formation in mutant mice.
Main Results:
- Mcm9 ablation did not affect MCM2-7 loading or general DNA replication, indicating nonessentiality for these processes.
- MCM9 deficiency caused p53-independent germ cell depletion in both sexes.
- Male Mcm9 mutants showed defective spermatogonial stem cell renewal.
- MCM9-deficient cells exhibited increased genomic instability and impaired cell cycle reentry after replication stress.
- Mutant mice developed sex-specific cancers, particularly hepatocellular carcinoma in males.
Conclusions:
- Mammalian MCM9 has a specialized, nonessential role in DNA replication quality control, particularly crucial for germline stem cells.
- MCM9 is important for genome maintenance in somatic cells and acts as a tumor suppressor.
- MCM9's functions are vital for reproductive success and preventing cancer development.
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