title: The APC/C activator FZR1 coordinates the timing of meiotic resumption during prophase I arrest in mammalian oocytes.
abstract: FZR1, an activator of the anaphase-promoting complex/cyclosome (APC/C), is recognized for its roles in the mitotic cell cycle. To examine its meiotic function in females we generated an oocyte-specific knockout of the Fzr1 gene (Fzr1(Δ/Δ)). The total number of fully grown oocytes enclosed in cumulus complexes was 35-40% lower in oocytes from Fzr1(Δ/Δ) mice and there was a commensurate rise in denuded, meiotically advanced and/or fragmented oocytes. The ability of Fzr1(Δ/Δ) oocytes to remain prophase I/germinal vesicle (GV) arrested in vitro was also compromised, despite the addition of the phosphodiesterase milrinone. Meiotic competency of smaller diameter oocytes was also accelerated by Fzr1 loss. Cyclin B1 levels were elevated ~5-fold in Fzr1(Δ/Δ) oocytes, whereas securin and CDC25B, two other APC/C(FZR1) substrates, were unchanged. Cyclin B1 overexpression can mimic the effects of Fzr1 loss on GV arrest and here we show that cyclin B1 knockdown in Fzr1(Δ/Δ) oocytes affects the timing of meiotic resumption. Therefore, the effects of Fzr1 loss are mediated, at least in part, by raised cyclin B1. Thus, APC/C(FZR1) activity is required to repress cyclin B1 levels in oocytes during prophase I arrest in the ovary, thereby maintaining meiotic quiescence until hormonal cues trigger resumption.
authors.affiliation: School of Biomedical Sciences, University of Newcastle, Callaghan, NSW 2308, Australia. janet.holt@newcastle.edu.au
authors.forename: Janet E
authors.initials: JE
authors.lastname: Holt
authors.forename: Suzanne M-T
authors.initials: SM
authors.lastname: Tran
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Stewart
authors.forename: Kyra
authors.initials: K
authors.lastname: Minahan
authors.forename: Irene
authors.initials: I
authors.lastname: García-Higuera
authors.forename: Sergio
authors.initials: S
authors.lastname: Moreno
authors.forename: Keith T
authors.initials: KT
authors.lastname: Jones
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins / Q000502:physiology*; D056744:Cyclin B1 / Q000235:genetics; D005260:Female; D008540:Meiosis; D049469:Meiotic Prophase I; D051379:Mice; D018345:Mice, Knockout; D009865:Oocytes / Q000166:cytology*; D010053:Ovary; D013997:Time Factors; D043743:Ubiquitin-Protein Ligase Complexes / Q000502:physiology*
chemical_list: D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; D056744:Cyclin B1; C577585:Fzr1 protein, mouse; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome