A well-studied conserved pathway controls chromosome segregation in meiosis. At anaphase onset, the destruction of Securin releases the active form of the protease Separase, which targets the meiotic α-kleisin component of the cohesion complex, Rec8, culminating in the disassembly of cohesin rings. Drosophila, however, lacks a Rec8 orthologue, and it has been shown that related proteins do not take its place in meiosis; this also calls into question the significance of both Separase and Securin. Now (p. 531), Andrew Swan and colleagues establish the roles of cohesins, Separase and Securin in Drosophila meiosis. The authors use fluorescence in situ hybridisation (FISH) probes to follow chromosome segregation in meiosis. They find that the destruction of Securin and activation of Separase are required for the release of arm cohesion in anaphase I of meiosis, and for the release of centromeric cohesion in anaphase II. They are also required for the release of arm cohesion on polar body chromosomes. The authors also investigate the role of the cohesin complex in meiosis and the polar body. They confirm that depletion of Rad21 (the target of Separase in mitosis) does not affect sister chromatid cohesion in meiosis, but find that depletion of the core cohesin SMC3 does. Both SMC3 and Rad21, however, are required for cohesion in the polar body and during syncytial mitosis. This paper makes an important contribution to our understanding of Drosophila female meiosis by showing that Separase and its regulator Securin have essential functions, suggesting the existence of a cohesion target that must be cleaved.
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