Robust designation of meiotic crossover sites by CDK-2 through phosphorylation of the MutSγ complex

Crossover formation is essential for proper segregation of homologous chromosomes during meiosis. Here we show that C. elegans Cyclin-dependent kinase 2 (CDK-2) forms a complex with cyclin-like protein COSA-1 and supports crossover formation by promoting conversion of meiotic double-strand breaks (DSBs) into crossover-specific recombination intermediates. Further, we identify MutS{gamma} component MSH-5 as a CDK-2 phosphorylation target. MSH-5 has a disordered C-terminal tail that contains 13 potential CDK phosphosites and is required to concentrate crossover-promoting proteins at recombination sites. Phosphorylation of the MSH-5 tail appears dispensable in a wild- type background, but when MutS{gamma} activity is partially compromised, crossover formation and retention of CDK-2/COSA-1 at recombination sites are exquisitely sensitive to phosphosite loss. Our data support a model in which robustness of crossover designation reflects a positive feedback mechanism involving CDK-2-mediated phosphorylation and scaffold-like properties of the MSH-5 C-terminal tail, features that combine to promote full recruitment and activity of crossover-promoting complexes.