Modeling of human MLH1 and MLH3 variants in mice reveals novel functions of MutLγ in meiotic DNA repair and the ovarian reserve

MutLγ prevents abnormal late-prophase DNA hyper-resection in mouse spermatocytes, where MLH1/MLH3 missense and null alleles cause large RPA foci and CtIP/RAD50/BLM-containing γH2AX flares.

• Why it matters: Crossover formation alone does not explain how MLH1/MLH3 variants impair fertility, so the study targets a mechanistic gap in meiotic DNA repair beyond crossover counts.
• What they did: Mouse models carrying human MLH1/3 missense and null alleles were analyzed for γH2AX flare timing and composition, including RPA and DNA end processing factors, in late pachynema and diplonema.
• The result: The findings indicate MutLγ has a previously unrecognized meiotic role in limiting DNA resection of spontaneous breaks or persistent recombination intermediates, supporting a CHEK2-linked oocyte quality-control route.