A mutation in the endonuclease domain of mouse MLH3 reveals novel roles for MutL γ during crossover formation in meiotic prophase I

by Melissa Toledo, Xianfei Sun, Miguel A. Brie ño-Enríquez, Vandana Raghavan, Stephen Gray, Jeffrey Pea, Carolyn R. Milano, Anita Venkatesh, Lekha Patel, Peter L. Borst, Eric Alani, Paula E. Cohen During meiotic prophase I, double-strand breaks (DSBs) initiate homologous recombination leading to non-crossovers (NCOs) and crossovers (COs). In mouse, 10% of DSBs are designated to become COs, primarily through a pathway dependent on the MLH1-MLH3 heterodimer (MutLγ). Mlh3 contains an endonucl ease domain that is critical for resolving COs in yeast. We generated a mouse (Mlh3DN/DN) harboring a mutation within this conserved domain that is predicted to generate a protein that is catalytically inert.Mlh3DN/DN males, like fully nullMlh3-/- males, have no spermatozoa and are infertile, yet spermatocytes have grossly normal DSBs and synapsis events in early prophase I. UnlikeMlh3-/- males, mutation of the endonuclease domain within MLH3 permits normal loading and frequency of MutL γ in pachynema. However, key DSB repair factors (RAD51) and mediators of CO pathway choice (BLM helicase) persist into pachynema inMlh3DN/DN males, indicating a temporal delay in repair events and revealing a mechanism by which alternative DSB repair pathways may be selected. WhileMlh3DN/DN spermatocytes retain only 22% of wildtype chiasmata counts, this frequency is greater than observed inMlh3-/- males (10%), suggesting that the allele may permit partial endonuclease activity, or that other pathways c...
Source: PLoS Genetics - Category: Genetics & Stem Cells Authors: Source Type: research