title: Mad2 is required for inhibiting securin and cyclin B degradation following spindle depolymerisation in meiosis I mouse oocytes.
abstract: Mad2 is a pivotal component of the spindle assembly checkpoint (SAC) which inhibits anaphase promoting complex/cyclo-some (APC/C) activity by sequestering Cdc20 thereby regulating the destruction of securin and cyclin B. During mitosis, spindle depolymerisation induces a robust Mad2-dependent arrest due to inhibition of securin and cyclin B destruction. In contrast to mitosis, the molecular details underpinning the meiosis I arrest experienced by mouse oocytes exposed to spindle depolymerisation remain incompletely characterised. Notably, the role of Mad2 and the fate of the anaphase-marker, securin, are unexplored. As shown previously, we find that spindle depolymerisation by nocodazole inhibits first polar body extrusion (PBE) and stabilises cyclin B and cyclin-dependent kinase 1 activity in mouse oocytes. Here we show that stabilisation of cyclin B in nocodazole can be sustained for several hours and is associated with stabilisation of securin. These effects are SAC-mediated as, in oocytes depleted of the majority of Mad2 by morpholino antisense, securin and cyclin B are destabilised and 15% of oocytes undergo PBE. This reflects premature APC/C activation as a mutant form of cyclin B lacking its APC/C degradation signal is stable in Mad2-depleted oocytes. Moreover, homologues do not disjoin during the prolonged meiosis I arrest (> 18 h) induced by nocodaozole indicating that a non-cleavage mechanism is insufficient on its own for resolution of arm cohesion in mammalian oocytes. In conclusion, when all kinetochores lack attachment and tension, mouse oocytes mount a robust Mad2-dependent meiosis I arrest which inhibits the destruction of securin and cyclin B.
authors.affiliation: Newcastle Fertility Centre at Life, International Centre for Life, Times Square, Newcastle upon Tyne, NE1 4EP, UK. h.a.homer@newcastle.ac.uk
authors.forename: Hayden A
authors.initials: HA
authors.lastname: Homer
authors.forename: Alex
authors.initials: A
authors.lastname: McDougall
authors.forename: Mark
authors.initials: M
authors.lastname: Levasseur
authors.forename: Alison P
authors.initials: AP
authors.lastname: Murdoch
authors.forename: Mary
authors.initials: M
authors.lastname: Herbert
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D005260:Female; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000378:metabolism; D015151:Immunoblotting / Q000379:methods; D064246:Mad2 Proteins; D008540:Meiosis / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D004676:Myelin Basic Protein / Q000378:metabolism; D015739:Nocodazole / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D064249:Securin; D008941:Spindle Apparatus / Q000378:metabolism*; D013997:Time Factors
chemical_list: D002352:Carrier Proteins; C534700:Ccnb1 protein, mouse; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D006657:Histones; D064246:Mad2 Proteins; C577698:Mad2l1 protein, mouse; D004676:Myelin Basic Protein; D016376:Oligonucleotides, Antisense; D064249:Securin; D015739:Nocodazole