title: Regulation of APC/C activity in oocytes by a Bub1-dependent spindle assembly checkpoint.
abstract: BACKGROUND
  Missegregation 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. 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.
  
  
  RESULTS
  Bub1 protein was depleted specifically in oocytes with a Zp3-Cre transgene to delete exons 7 and 8 from a floxed BUB1(F) 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.
  
  
  CONCLUSIONS
  We 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.
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom.
authors.forename: Barry E
authors.initials: BE
authors.lastname: McGuinness
authors.forename: Martin
authors.initials: M
authors.lastname: Anger
authors.forename: Anna
authors.initials: A
authors.lastname: Kouznetsova
authors.forename: Ana M
authors.initials: AM
authors.lastname: Gil-Bernabé
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Helmhart
authors.forename: Nobuaki R
authors.initials: NR
authors.lastname: Kudo
authors.forename: Annelie
authors.initials: A
authors.lastname: Wuensche
authors.forename: Stephen
authors.initials: S
authors.lastname: Taylor
authors.forename: Christer
authors.initials: C
authors.lastname: Hoog
authors.forename: Bela
authors.initials: B
authors.lastname: Novak
authors.forename: Kim
authors.initials: K
authors.lastname: Nasmyth
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D064190:Apc2 Subunit, Anaphase-Promoting Complex-Cyclosome; D018797:Cell Cycle Proteins / Q000378:metabolism; D020090:Chromosome Segregation; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D008297:Male; D008540:Meiosis / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D011247:Pregnancy; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D064247:Separase; D008941:Spindle Apparatus / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D043743:Ubiquitin-Protein Ligase Complexes; C577341:Anapc2 protein, mouse; D064173:Anaphase-Promoting Complex-Cyclosome; D064190:Apc2 Subunit, Anaphase-Promoting Complex-Cyclosome; C584277:BUB1 protein, human; C584281:Bub1 protein, mouse; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D010450:Endopeptidases; C577987:ESPL1 protein, human; D064247:Separase