title: Dependency of the spindle assembly checkpoint on Cdk1 renders the anaphase transition irreversible.
abstract: Activation of anaphase-promoting complex/cyclosome (APC/C(Cdc20)) by Cdc20 is delayed by the spindle assembly checkpoint (SAC). When all kinetochores come under tension, the SAC is turned off and APC/C(Cdc20) degrades 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/C(Cdc20) activates separase but the resulting loss of (some) cohesion is accompanied by SAC reactivation and APC/C(Cdc20) inhibition, which aborts the process of further securin degradation. Cyclin B is therefore the only APC/C(Cdc20) substrate 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.
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Rattani
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: P K
authors.initials: PK
authors.lastname: Vinod
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Godwin
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Kikuë
authors.initials: K
authors.lastname: Tachibana-Konwalski
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Magda
authors.initials: M
authors.lastname: Wolna
authors.affiliation: Cell Division and Cancer Group, Spanish National Cancer Research Center (CNIO), 28029 Madrid, Spain.
authors.forename: Marcos
authors.initials: M
authors.lastname: Malumbres
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK. Electronic address: bela.novak@bioch.ox.ac.uk.
authors.forename: Béla
authors.initials: B
authors.lastname: Novák
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK. Electronic address: kim.nasmyth@bioch.ox.ac.uk.
authors.forename: Kim
authors.initials: K
authors.lastname: Nasmyth
mesh_terms: D000705:Anaphase / Q000502:physiology*; D000818:Animals; D016203:CDC2 Protein Kinase / Q000502:physiology*; D064199:Cdc20 Proteins / Q000502:physiology; D002842:Chromatids / Q000502:physiology; D019926:Cyclin B / Q000502:physiology; D005260:Female; D059566:M Phase Cell Cycle Checkpoints / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009630:Nondisjunction, Genetic / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D010766:Phosphorylation
chemical_list: D064199:Cdc20 Proteins; D019926:Cyclin B; D016203:CDC2 Protein Kinase