Coupling meiotic chromosome axis integrity to recombination.
Résumé
During meiosis, DNA events of recombination occur in direct physical association with underlying chromosome axes. Meiotic cohesin Rec8 and cohesin-associated Spo76/Pds5 are prominent axis components. Two observations indicate that recombination complexes can direct the local destabilization of underlying chromosome axes. First, in the absence of Rec8, Spo76/Pds5 is lost locally at sites of late-persisting Msh4 foci, with a concomitant tendency for loosening of intersister and interhomolog connectedness at the affected sites. This loss is dependent on initiation of recombination. Second, in wild-type prophase, local separation of sister axes is seen at sites of synaptonemal complex-associated recombination nodules. Additional findings reveal that Rec8 localizes to both axis and bulk chromatin and is required for chromatin compactness. Further, Rec8 is essential for maintenance of sister cohesion, along arms and centromeres, during the pachytene-to-diplotene transition, revealing an intrinsic tendency for destabilization of sister cohesion during this period. This finding shows how the loss of sister connectedness, in arm and/or centric regions, could lead to the segregation defects that are seen in the human "maternal age effect" and how Rec8 could be a target of that effect. Finally, Rec8 plays related, but synergistic roles with Spo76/Pds5, indicating auxiliary roles for meiotic and mitotic cohesion-associated components.