The small GTPase Cdc42 promotes membrane protrusion during polar body emission via ARP2-nucleated actin polymerization

Mol Hum Reprod. 2011 May;17(5):305-16. doi: 10.1093/molehr/gar026. Epub 2011 Apr 20.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin-Related Protein 2 / antagonists & inhibitors
  • Actin-Related Protein 2 / genetics*
  • Actin-Related Protein 2 / metabolism
  • Actins / antagonists & inhibitors
  • Actins / genetics
  • Actins / metabolism
  • Animals
  • Asymmetric Cell Division / drug effects
  • Asymmetric Cell Division / genetics*
  • Cytokinesis / drug effects
  • Cytokinesis / genetics*
  • Female
  • Gene Expression Regulation, Developmental / drug effects
  • Meiosis / drug effects
  • Metaphase / drug effects
  • Monomeric GTP-Binding Proteins / antagonists & inhibitors
  • Monomeric GTP-Binding Proteins / genetics*
  • Monomeric GTP-Binding Proteins / metabolism
  • Nocodazole / pharmacology
  • Paclitaxel / pharmacology
  • Polar Bodies / cytology
  • Polar Bodies / drug effects
  • Polar Bodies / metabolism*
  • Polymerization
  • Tubulin Modulators / pharmacology
  • Xenopus Proteins / antagonists & inhibitors
  • Xenopus Proteins / genetics*
  • Xenopus Proteins / metabolism
  • Xenopus laevis / embryology
  • Xenopus laevis / genetics
  • rhoA GTP-Binding Protein / antagonists & inhibitors
  • rhoA GTP-Binding Protein / genetics
  • rhoA GTP-Binding Protein / metabolism

Substances

  • Actin-Related Protein 2
  • Actins
  • Tubulin Modulators
  • Xenopus Proteins
  • Cdc42 protein, Xenopus
  • Monomeric GTP-Binding Proteins
  • rhoA GTP-Binding Protein
  • Paclitaxel
  • Nocodazole