Arp2/3 Complex Regulates Asymmetric Division and Cytokinesis in Mouse Oocytes

Abstract

Mammalian oocyte meiotic maturation involves oocyte polarization and a unique asymmetric division, but until now, the underlying mechanisms have been poorly understood. Arp2/3 complex has been shown to regulate actin nucleation and is widely involved in a diverse range of processes such as cell locomotion, phagocytosis and the establishment of cell polarity. Whether Arp2/3 complex participates in oocyte polarization and asymmetric division is unknown. The present study investigated the expression and functions of Arp2/3 complex during mouse oocyte meiotic maturation. Immunofluorescent staining showed that the Arp2/3 complex was restricted to the cortex, with a thickened cap above the meiotic apparatus, and that this localization pattern was depended on actin. Disruption of Arp2/3 complex by a newly-found specific inhibitor CK666, as well as by Arpc2 and Arpc3 RNAi, resulted in a range of effects. These included the failure of asymmetric division, spindle migration, and the formation and completion of oocyte cytokinesis. The formation of the actin cap and cortical granule-free domain (CGFD) was also disrupted, which further confirmed the disruption of spindle migration. Our data suggest that the Arp2/3 complex probably regulates oocyte polarization through its effect on spindle migration, asymmetric division and cytokinesis during mouse oocyte meiotic maturation.

Non-muscle tropomyosin (Tpm3) is crucial for asymmetric cell division and maintenance of cortical integrity in mouse oocytes

“…The roles of actin polymerization and various actin nucleators in spindle migration and asymmetric cell division in maturing oocytes have recently emerged 7,[27][28][29][30][31][32][33] ; however, the roles of other actin-binding proteins in oocyte maturation, including actin-capping proteins, ADF/cofilin, and tropomyosins, which are critical for the control of actin dynamics, are poorly understood. In this study, we present evidence that maintenance of cortical actin by Tpm3 is critical for spindle migration and polar body extrusion.…”

“…5 For example, various actin nucleators belonging to the formin family as well as the Arp2/3 complex are involved in the nucleation of actin filaments at the cortex. 6,7 To generate contractile force, actin filaments in the cortex form a complex with myosin II, 8 and this actomyosin complex controls how elastic or rigid the cell cortex is. 2 Tropomyosins are a family of coiled-coil rod-shape actin-binding proteins, and their roles in controlling the contraction of skeletal and smooth muscle have been extensively characterized.…”

A novel interplay between GEFs orchestrates Cdc42 activity during cell polarity and cytokinesis

“…LatA treatment removes all types of filamentous actin structures (Spector et al, 1983). To determine which actin-mediated process regulates Gef1 removal, we treated cells with CK666 to block only Arp2/3-mediated branched actin filaments (Sun et al, 2011). In these cells, Gef1-mNG removal was unhindered, as in DMSO-treated control cells, or localized to random sites along the cortex, but did not persist at the division site ( Figure 3C).…”

RhoA-mediated MLC2 regulates actin dynamics for cytokinesis in meiosis

“…27 During mouse oocyte meiotic maturation, actin was required for the chromosome migration, 9,28 cortical spindle anchorage, 29,30 cortex development and polarity establishment 2,31 and first polar body extrusion. 6,27 Additionally, some actin nucleation factors such as Arp2/3 complex, 6 Formin2 7,29 and Spire1/2 32 were involved in the actin organization during mouse oocyte maturation. Previous work showed that myosin II was activated by phosphorylation of its regulatory MLC at Ser19/Thr18, and the phosphorylation at MLC Ser19 was critical for actin assembly.…”

“…Disruption of activities of actin nucleators Arp2/3 and Formin 2 causes aberrant actin expression and the failure of polar body extrusion. 6,7 In addition, Cdc42, Ran and Rac1 are also involved in the regulation of cortical polarity during mouse oocyte maturation. [8][9][10] Although various molecules have been proposed to contribute to cortical polarity during oocyte meiosis, the pathways and mechanisms that modulate the meiotic apparatus remain to be determined.…”