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Activation of anaphase-promoting complex/cyclosome (APC/CCdc20) by Cdc20 is delayed by the spindle assembly checkpoint (SAC). When all kinetochores come under tension, the SAC is turned off and APC/CCdc20degrades cyclin B and securin, which activates separase [1]. The latter then cleaves cohesin holding sister chromatids together [2]. Because cohesin cleavage also destroys the tension responsible for turning off the SAC, cells must possess a mechanism to prevent SAC reactivation during anaphase, which could be conferred by a dependence of the SAC on Cdk1 [3-5]. To test this, we analyzed mouse oocytes and embryos expressing nondegradable cyclin B together with a Cdk1-resistant form of separase. After biorientation and SAC inactivation, APC/CCdc20activates separase but the resulting loss of (some) cohesion is accompanied by SAC reactivation and APC/CCdc20inhibition, which aborts the process of further securin degradation. Cyclin B is therefore the only APC/CCdc20substrate whose degradation at the onset of anaphase is necessary to prevent SAC reactivation. The mutual activation of tension sensitive SAC and Cdk1 creates a bistable system that ensures complete activation of separase and total downregulation of Cdk1 when all chromosomes have bioriented. © 2014 The Authors.

Original publication

DOI

10.1016/j.cub.2014.01.033

Type

Journal article

Journal

Current Biology

Publication Date

17/03/2014

Volume

24

Pages

630 - 637