title: Cdc42 activation couples spindle positioning to first polar body formation in oocyte maturation.
abstract: During vertebrate egg maturation, cytokinesis initiates after one pole of the bipolar metaphase I spindle attaches to the oocyte cortex, resulting in the formation of a polar body and the mature egg. It is not known what signal couples the spindle pole positioning to polar body formation. We approached this question by drawing an analogy to mitotic exit in budding yeast, as asymmetric spindle attachment to the appropriate cortical region is the common regulatory cue. In budding yeast, the small G protein Cdc42 plays an important role in mitotic exit following the spindle pole attachment . We show here that inhibition of Cdc42 activation blocks polar body formation. The oocytes initiate anaphase but fail to properly form and direct a contractile ring. Endogenous Cdc42 is activated at the spindle pole-cortical contact site immediately prior to polar body formation. The cortical Cdc42 activity zone, which directly overlays the spindle pole, is circumscribed by a cortical RhoA activity zone; the latter defines the cytokinetic contractile furrow . As the RhoA ring contracts during cytokinesis, the Cdc42 zone expands, maintaining its complementary relationship with the RhoA ring. Cdc42 signaling may thus be an evolutionarily conserved mechanism that couples spindle positioning to asymmetric cytokinesis.
authors.affiliation: Ottawa Health Research Institute, OHRI, Ottawa Hospital, 1053 Carling Avenue, Ottawa, K1Y 4E9, Canada.
authors.forename: Chunqi
authors.initials: C
authors.lastname: Ma
authors.forename: Héléne A
authors.initials: HA
authors.lastname: Benink
authors.forename: Daye
authors.initials: D
authors.lastname: Cheng
authors.forename: Véronique
authors.initials: V
authors.lastname: Montplaisir
authors.forename: Ling
authors.initials: L
authors.lastname: Wang
authors.forename: Yanwei
authors.initials: Y
authors.lastname: Xi
authors.forename: Pei-Pei
authors.initials: PP
authors.lastname: Zheng
authors.forename: William M
authors.initials: WM
authors.lastname: Bement
authors.forename: X Johné
authors.initials: XJ
authors.lastname: Liu
mesh_terms: D000818:Animals; D016764:Cell Polarity / Q000187:drug effects; D048749:Cytokinesis / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008540:Meiosis / Q000187:drug effects / Q000502:physiology; D008954:Models, Biological; D009865:Oocytes / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development*; D008941:Spindle Apparatus / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D014981:Xenopus; D029867:Xenopus Proteins / Q000378:metabolism / Q000502:physiology*; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism / Q000502:physiology*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D029867:Xenopus Proteins; D020764:cdc42 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein