title: Timing of anaphase-promoting complex activation in mouse oocytes is predicted by microtubule-kinetochore attachment but not by bivalent alignment or tension.
abstract: Homologous chromosome segregation errors during meiosis I are common and generate aneuploid embryos. Here, we provide a reason for this susceptibility to mis-segregation by live cell imaging of mouse oocytes. Our results show that stable kinetochore-microtubule attachments form in mid-prometaphase, 3-4 hours before anaphase. This coincided with the loss of Mad2 from kinetochores and with the start of anaphase-promoting complex/cyclosome (APC/C)-mediated cyclin B1 destruction. Therefore, the spindle assembly checkpoint (SAC) ceased to inhibit the APC/C from mid-prometaphase. This timing did not coincide with bivalent congression in one-third of all oocytes examined. Non-aligned bivalents were weakly positive for Mad2, under less tension than congressed bivalents and, by live-cell imaging, appeared to be in the process of establishing correct bi-orientation. The time from when the APC/C became active until anaphase onset was affected by the rate of loss of CDK1 activity, rather than by these non-aligned bivalents, which occasionally persisted until anaphase, resulting in homolog non-disjunction. We conclude that, in oocytes, a few erroneous attachments of bivalent kinetochores to microtubules do not generate a sufficient SAC 'wait anaphase' signal to inhibit the APC/C.
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, NSW 2308, Australia.
authors.forename: Simon I R
authors.initials: SI
authors.lastname: Lane
authors.forename: Yan
authors.initials: Y
authors.lastname: Yun
authors.forename: Keith T
authors.initials: KT
authors.lastname: Jones
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D020090:Chromosome Segregation / Q000502:physiology*; D056744:Cyclin B1 / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D007091:Image Processing, Computer-Assisted; D015151:Immunoblotting; D018386:Kinetochores / Q000378:metabolism*; D064246:Mad2 Proteins; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism / Q000502:physiology*; D049468:Prometaphase / Q000502:physiology*; D018075:RNA, Complementary / Q000235:genetics; D013997:Time Factors; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D056744:Cyclin B1; D064246:Mad2 Proteins; C577698:Mad2l1 protein, mouse; D018075:RNA, Complementary; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome