Cdc42 protein acts upstream of IQGAP1 and regulates cytokinesis in mouse oocytes and embryos

Abstract

Cdc42 and Rac1 Rho family GTPases, and their interacting protein IQGAP1 are the key regulators of cell polarity. We examined the role of Cdc42 and IQGAP1 in establishing the polarity of mouse oocyte and regulation of meiotic and mitotic divisions. We showed that Cdc42 was localized on the microtubules of meiotic and mitotic spindle and in the cortex of mouse oocytes and cleaving embryos. IQGAP1 was present in the cytoplasm and cortex of growing and fully-grown oocytes. During maturation it disappeared from the cortex and during meiotic and mitotic cytokinesis it concentrated in the contractile ring. Toxin B inhibition of the binding activity of Cdc42 changed the localization of IQGAP1, inhibited emission of the first polar body, and caused disappearance of the cortical actin without affecting the migration of meiotic spindle. This indicates, that in maturing oocytes accumulation of cortical actin is not indispensable for spindle migration. In zygotes treated with toxin B actin cytoskeleton was rearranged and the first and/or subsequent cytokinesis were inhibited. Our results indicate that Cdc42 acts upstream of IQGAP1 and is involved in regulation of cytokinesis in mouse oocytes and cleaving embryos, rather than in establishing the polarity of the oocyte.

IQGAP1 is associated with nuclear envelope reformation and completion of abscission

“…(C) Wildtype and phosphomutant GST-IQGAP1 were examined for their ability to be phosphorylated by purified CDK2/Cyclin A, CDK1/ Cyclin A and CDK1/Cyclin B kinases in an in vitro protein kinase assay. Phosphorylation was determined by [g¡ 32 P] ATP labeling and revealed that T1434, not S86 and S330, is a CDK substrate. www.tandfonline.com 2067 Cell Cycle T1434 phospho-mutants proceeded through mitosis with normal kinetics (Fig.…”

“…In mouse embryos treated with toxin B, which inhibits Cdc42, the IQGAP upstream GTPase, IQGAP1 localization is disrupted, the actin cytoskeleton is rearranged and cytokinesis is inhibited. 32 In HeLa cells, IQGAP1 localizes uniformly to the cell cortex, whereas IQGAP3 concentrates at the equatorial cell cortex during cytokinesis. 33 Consistent with this localization, only IQGAP3 interacts with anillin and, in a similar manner to the mechanism in yeast, anillin is required for IQGAP3 contractile ring localization.…”

Actin cytoskeleton in cell polarity and asymmetric division during mouse oocyte maturation

“…In addition to Ran, the Rho family GTPase Cdc42 has been implicated in multiple events during oocyte meiosis including spindle positioning and the cortical polarity maintenance in both mouse and frog oocytes [Ma et al, 2006;Na and Zernicka-Goetz, 2006;Bielak-Zmijewska et al, 2008;Leblanc et al, 2011]. In Xenopus oocytes, active Cdc42 was found to localize to the polar cortical domain in a spindle-dependent manner [Ma et al, 2006;Zhang et al, 2008].…”

“…A possible regulator or effector of Cdc42, IQGAP1, was found to localize to the actomyosin domain in mouse oocytes. Its cortical localization as well as actin cap formation was inhibited upon the injection of toxin B, a general inhibitor of Rho GTPase [Bielak-Zmijewska et al, 2008].…”

Polar body emission

“…I propose that Rac1 and Cdc42 play distinct ''cortical roles'' (i.e., in addition to their other possible functions) during vertebrate polar body emission: the former in maintaining spindle polarization and the latter in promoting membrane protrusion during polar body emission. Given the localization of Cdc42 protein within the metaphase I spindle (presumably in association with membrane vesicles) [Na and Zernicka-Goetz, 2006;Bielak-Zmijewska et al, 2008] and the lack of evidence of its localization to oocyte cortex, the cortical Cdc42GTP detected during polar body emission [Ma et al, 2006;Zhang et al, 2008] might represent vesicle trafficking to the cortex of the protruding polar body. In contrast, Rac1 protein is localized in the oocyte cortex [Halet and Carroll, 2007] and the appearance of RacGTP represents chromosome (Ran)-induced cortical activation [Deng et al, 2007;Halet and Carroll, 2007].…”