MCM9 deficiency delays primordial germ cell proliferation independent of the ATM pathway

Abstract

Maintenance of genome integrity is crucial for the germline, and this is reflected by lower mutation rates in gametes than somatic cells. Germ cells at different stages employ different DNA damage response (DDR) mechanisms. In response to certain DNA repair defects, primordial germ cells (PGCs) either undergo apoptosis or delayed proliferation, although little is known about the underlying mechanisms that govern these outcomes. Here, we report genetic studies of DDR pathways that underlie germ cell depletion in mice mutant for minichromosome maintenance 9 (Mcm9), a gene that plays a role in homologous recombination repair (HRR). Germ cell depletion in these mice is a result of reduced PGC numbers both before and after they arrive in the primitive gonads. This reduction was attributable to reduced proliferation, not apoptosis, and this response was independent of ATM-CHK2-TRP53-P21 signaling. This mechanism of PGC depletion differs from that in Fancm mutants, which also display reduced PGC depletion that is partially orchestrated by the ATM-TRP53-P21 pathway. Germ cell depletion in mice doubly deficient for FANCM and MCM9 was additive, indicating that the damage caused by each mutation triggers different DDR pathways to slow the cell cycle as a means to preserve genomic integrity. genesis 53:678-684, 2015. © 2015 Wiley Periodicals, Inc.

Repair of Meiotic DNA Breaks and Homolog Pairing in Mouse Meiosis Requires a Minichromosome Maintenance (MCM) Paralog

“…While all six genes encoding subunits of the MCM replicative helicase (Mcm2-7) are essential for viability, Mcm8 and Mcm9 are not (Hartford et al 2011;Lutzmann et al 2012;Luo and Schimenti 2015). To determine if Mcmdc2 is also essential, Mcmdc2 Gt/+ heterozygotes were intercrossed and the offspring genotyped.…”

“…MCM8 and MCM9 function in DNA repair and homologous recombination (Park et al 2013;Traver et al 2015). Both are dispensable for DNA replication in mice, but MCM8-and MCM9-deficient cells exhibit defects in homologous recombination repair in response to DNA damage (Hartford et al 2011;Lutzmann et al 2012;Nishimura et al 2012;Park et al 2013;Lee et al 2015;Luo and Schimenti 2015). Surprisingly, Mcm9, which is absent from Drosophila, is also required for DNA mismatch repair and this may actually be its primary function (Traver et al 2015).…”

Identification of MCM8IP, an interactor of MCM8-9 and RPA1 that promotes homologous recombination and DNA synthesis in response to DNA damage

“…Instead, the MCM8-9 complex has been implicated in HR in both mitotic and meiotic cells [11][12][13] . Consistently, MCM8-and MCM9-null female mice are sterile 13,14 and women carrying biallelic mutations in MCM8-9 exhibit Primary Ovarian Insufficiency (POI), a genetic syndrome characterized by reduced reproductive lifespan 15,16 . Furthermore, as a consequence of their role in HR, MCM8-and MCM9deficient cells are particularly sensitive to DNA interstrand crosslinking agents and PARP inhibition 11,12,17 .…”

“…Among these genes are MCM8 and MCM9, whose mutations in patient-derived cells cause elevated ICL-induced chromosomal instability 41,42,72 . MCM8-9-null mice exhibit infertility due to gametogenesis defects 13,14 . Collectively, POI may be a consequence of defective MCM8-9-dependent HR repair.…”

A Reporter Mouse forIn VivoDetection of DNA Damage in Embryonic Germ Cells

“…Perturbations to PGC development and growth, including those affecting genomic integrity of PGCs, can lead to a severe reduction or complete loss of germ cells in sexually mature adults (Hamer & de Rooij, 2018). Notably, mutations in a number of genes involved in DNA repair cause depletion of PGCs and consequently a reduction of germ cells post-natally, while having very subtle effects in the soma (Agoulnik et al, 2002;Luo et al, 2014;Luo & Schimenti, 2015;Nadler & Braun, 2000). Furthermore, mouse PGCs are particularly hypersensitive to ionizing radiation (IR)-induced DSBs, but the basis for this sensitivity remains unknown (Heyer, MacAuley, Behrendtsen, & Werb, 2000), in part due to the limited accessibility and numbers of fetal germ cells.…”