title: The small GTPase Cdc42 promotes membrane protrusion during polar body emission via ARP2-nucleated actin polymerization.
abstract: Polar body emission is a specialized cell division throughout the animal kingdom, serving to reduce chromosome ploidy while preserving the egg cytoplasm. Critical to polar body emission are the asymmetric positioning of the meiotic spindle prior to anaphase, with one pole attached to the oocyte cortex, and the simultaneous membrane protrusion during subsequent cytokinesis. We have shown that, during Xenopus oocyte maturation, the small GTPase Cdc42 promotes membrane protrusion while a classical RhoA contractile ring forms and constricts at the base of the protrusion. We report here that treating oocytes with low concentrations of nocodazole diminished the size of metaphase I spindles and prevented polar body emission, and yet an active Cdc42 cap of correspondingly diminished size still developed, on time, atop of the spindle pole. Conversely, treating oocytes with low concentrations of taxol resulted in a spindle with multiple poles attached to the cortex, but still each of these poles were associated with activated cortical Cdc42 at the appropriate time. Therefore, the asymmetric positioning of the meiotic spindle with one pole anchored to the cortex is a prerequisite for Cdc42 activation. Furthermore, we demonstrated that the Cdc42-regulated F-actin nucleator ARP2/3 complex was similarly localized at the cortex of the protruding polar body membrane, suggesting that Cdc42 promotes membrane protrusion through an F-actin meshwork mechanism. Finally, we demonstrated that Cdc42 and RhoA formed similarly complementary activity zones during egg activation and that inhibition of Cdc42 prevented second polar body emission. Therefore, Cdc42 activation likely promotes membrane protrusion during polar body emission in widespread systems.
authors.affiliation: Ottawa Hospital Research Institute, Ottawa Hospital Civic Campus, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Leblanc
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: D
authors.initials: D
authors.lastname: McKee
authors.forename: Z-B
authors.initials: ZB
authors.lastname: Wang
authors.forename: R
authors.initials: R
authors.lastname: Li
authors.forename: C
authors.initials: C
authors.lastname: Ma
authors.forename: Q-Y
authors.initials: QY
authors.lastname: Sun
authors.forename: X J
authors.initials: XJ
authors.lastname: Liu
mesh_terms: D051377:Actin-Related Protein 2 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D000199:Actins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000818:Animals; D060049:Asymmetric Cell Division / Q000187:drug effects / Q000235:genetics*; D048749:Cytokinesis / Q000187:drug effects / Q000235:genetics*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D008540:Meiosis / Q000187:drug effects; D008677:Metaphase / Q000187:drug effects; D020559:Monomeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015739:Nocodazole / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D059705:Polar Bodies / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D058105:Polymerization; D050257:Tubulin Modulators / Q000494:pharmacology; D029867:Xenopus Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D014982:Xenopus laevis / Q000196:embryology / Q000235:genetics; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D051377:Actin-Related Protein 2; D000199:Actins; D050257:Tubulin Modulators; D029867:Xenopus Proteins; C559910:Cdc42 protein, Xenopus; D020559:Monomeric GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D017239:Paclitaxel; D015739:Nocodazole