MCM8- and MCM9-Deficient Mice Reveal Gametogenesis Defects and Genome Instability Due to Impaired Homologous Recombination

Abstract

We generated knockout mice for MCM8 and MCM9 and show that deficiency for these genes impairs homologous recombination (HR)-mediated DNA repair during gametogenesis and somatic cells cycles. MCM8(-/-) mice are sterile because spermatocytes are blocked in meiotic prophase I, and females have only arrested primary follicles and frequently develop ovarian tumors. MCM9(-/-) females also are sterile as ovaries are completely devoid of oocytes. In contrast, MCM9(-/-) testes produce spermatozoa, albeit in much reduced quantity. Mcm8(-/-) and Mcm9(-/-) embryonic fibroblasts show growth defects and chromosomal damage and cannot overcome a transient inhibition of replication fork progression. In these cells, chromatin recruitment of HR factors like Rad51 and RPA is impaired and HR strongly reduced. We further demonstrate that MCM8 and MCM9 form a complex and that they coregulate their stability. Our work uncovers essential functions of MCM8 and MCM9 in HR-mediated DSB repair during gametogenesis, replication fork maintenance, and DNA repair.

Single gene defects leading to sperm quantitative anomalies

“…In contrast, TEX15, MCM8 and SYCE1 are predominately expressed in the testis and the rare homozygous LOF mutation identified for each gene is a strong indication that the gene is inactivated in infertile men. Furthermore, the knockout of Tex15, Mcm8 and Syce1 orthologues in mouse produces an azoospermia consequent to a meiotic block (28,34,36). This is consistent with the phenotype observed in the infertile men carrying homozygous LOF variants in these three genes, further validating these mutations as causal of NOA.…”

Exome sequencing reveals MCM8 mutation underlies ovarian failure and chromosomal instability

“…Mcm8-and Mcm9-deficient mice are infertile and have small gonads due to germ cell depletion (5). Additionally, somatic cells exhibit growth defects and chromosomal instability (5).…”

“…Additionally, somatic cells exhibit growth defects and chromosomal instability (5). MCM8 and MCM9 are novel regulators of germ cell survival, are rapidly induced and recruited to DNA damage sites, coregulate each other's stability, and promote RAD51 recruitment to ssDNA (5,8). The MCM8/MCM9 complex is likely required for the resolution of dsDNA breaks that occur during homologous recombination in pachytene of meiosis I.…”

The Fission Yeast Minichromosome Maintenance (MCM)-binding Protein (MCM-BP), Mcb1, Regulates MCM Function during Prereplicative Complex Formation in DNA Replication

“…Two additional MCM family members, Mcm8 and Mcm9, which contain an MCM box, were identified in higher eukaryotes (20 -23). Mcm8 and Mcm9 work downstream of the Fanconi anemia and BRCA2/Rad51 pathways and are required for homologous recombination, which promotes sister chromatid exchange (24,25). MCM-binding protein (MCM-BP) was first identified as a protein that strongly associates with human MCM proteins.…”