Crossover designation recruits condensin to reorganize the meiotic chromosome axis.

Abstract

Crossover recombination supports meiotic chromosome inheritance and fertility by establishing chiasmata between homologous chromosomes prior to the first meiotic division. In addition to the physical exchange of DNA mediated by meiotic recombination, chiasma formation also involves restructuring of the underlying chromosome axis, possibly to help with chiasma maturation or to resolve chromosomal interlocks. Here, we identify condensin as an important regulator of axis remodeling in S. cerevisiae . Condensin is recruited near sites of meiotic crossover designation by pro-crossover factors but is largely dispensable for DNA exchange. Instead, condensin helps to create discontinuities in the meiotic chromosome axis by promoting removal of cohesin. In addition, chromosomes of condensin mutants exhibit unusually common parallel chromatin clouds and experience a chromosomal buildup of the conserved axis remodeler Pch2. Consistent with an important role of axis restructuring at crossover sites, the canonical anaphase-bridge phenotype of condensin mutants is partly rescued by redirecting meiotic DNA repair to sister chromatids instead of homologous chromosomes, suggesting that crossover-associated axis reorganization is important for faithful meiotic chromosome segregation.