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Regulation of APC/C Activity in Oocytes by a Bub1-Dependent Spindle Assembly Checkpoint

2009; Elsevier BV; Volume: 19; Issue: 5 Linguagem: Inglês

10.1016/j.cub.2009.01.064

1879-0445

Barry E. McGuinness, Martin Anger, Anna Kouznetsova, Ana M. Gil-Bernabé, Wolfgang Helmhart, N. Kudo, Annelie Wuensche, Stephen S. Taylor, Christer Höög, Béla Novák, Kim Nasmyth,

Ubiquitin and proteasome pathways

BackgroundMissegregation of chromosomes during meiosis in human females causes aneuploidy, including trisomy 21, and is thought also to be the major cause of age-related infertility [1Vogt E. Kirsch-Volders M. Parry J. Eichenlaub-Ritter U. Spindle formation, chromosome segregation and the spindle checkpoint in mammalian oocytes and susceptibility to meiotic error.Mutat. Res. 2008; 651: 14-29Crossref PubMed Scopus (144) Google Scholar]. Most errors are thought to occur at the first meiotic division. The high frequency of errors raises questions as to whether the surveillance mechanism known as the spindle assembly checkpoint (SAC) that controls the anaphase-promoting complex or cyclosome (APC/C) operates effectively in oocytes. Experimental approaches hitherto used to inactivate the SAC in oocytes suffer from a number of drawbacks.ResultsBub1 protein was depleted specifically in oocytes with a Zp3-Cre transgene to delete exons 7 and 8 from a floxed BUB1F allele. Loss of Bub1 greatly accelerates resolution of chiasmata and extrusion of polar bodies. It also causes defective biorientation of bivalents, massive chromosome missegregation at meiosis I, and precocious loss of cohesion between sister centromeres. By using a quantitative assay for APC/C-mediated securin destruction, we show that the APC/C is activated in an exponential fashion, with activity peaking 12–13 hr after GVBD, and that this process is advanced by 5 hr in oocytes lacking Bub1. Importantly, premature chiasmata resolution does not occur in Bub1-deficient oocytes also lacking either the APC/C's Apc2 subunit or separase. Finally, we show that Bub1's kinase domain is not required to delay APC/C activation.ConclusionsWe conclude that far from being absent or ineffective, the SAC largely determines the timing of APC/C and hence separase activation in oocytes, delaying it for about 5 hr.