Molecular mechanism of repression of meiotic recombination around centromeres

In most eukaryotes, meiotic crossovers are essential for error-free chromosome segregation but are specifically repressed near centromeres to prevent missegregation. Recognized for >85 years, the molecular mechanism of this repression has remained unknown. Meiotic chromosomes contain two distinct cohesin complexes: pericentric complex (for segregation) and chromosomal arm complex (for crossing-over). We show that the pericentric-specific complex also actively represses pericentric meiotic double-strand break (DSB) formation and, consequently, crossovers. The fission yeast pericentric regions contain heterochromatin, removal of which can result in derepression in double-strand break formation and recombination during meiosis. We uncover the mechanism by which fission yeast heterochromatin protein Swi6 (mammalian HP1-homolog) prevents recruitment of activators of meiotic DSB formation such as Rec10. Localizing these missing activators to wild-type pericentromeres bypasses repression and generates abundant crossovers but reduces gamete viability.The molecular mechanism elucidated here likely extends to other species including humans, where pericentric crossovers can result in disorders such as Down syndrome. These mechanistic insights provide new clues to understand the roles played by multiple cohesin complexes, especially in human infertility and birth defects. ChIP-chip arrays for the meiotic protein Rec10 at 0h and 3.5h during meiosis in wild type and the H3K9 methyltransferase mutant (Clr4Δ) cells. Dyes were swapped in these experiments. The centromere-specific probes were separated from the other probes and analyzed after dye swap correction and genome-median normalization.