Dynamic maintenance of asymmetric meiotic spindle position through Arp2/3-complex-driven cytoplasmic

Abstract

Mammalian oocyte maturation involves two asymmetric meiotic divisions that require the positioning of the meiotic spindle near the cortical area from which the extrusion of the polar bodies occurs. Li and colleagues show that the nucleating activity of the Arp2/3 complex, localized at the cortical actin cap, induces actin-filament flow away from the complex, creating a cytoplasmic streaming that pushes the spindle towards the cortex. Mature mammalian oocytes are poised for completing meiosis II (MII) on fertilization by positioning the spindle close to an actomyosin-rich cortical cap1,2,3. Here, we show that the Arp2/3 complex localizes to the cortical cap in a Ran-GTPase-dependent manner and nucleates actin filaments in the cortical cap and a cytoplasmic actin network. Inhibition of Arp2/3 activity leads to rapid dissociation of the spindle from the cortex. Live-cell imaging and spatiotemporal image correlation spectroscopy analysis reveal that actin filaments flow continuously away from the Arp2/3-rich cortex, driving a cytoplasmic streaming expected to exert a net pushing force on the spindle towards the cortex. Arp2/3 inhibition not only diminishes this actin flow and cytoplasmic streaming but also enables a reverse streaming driven by myosin-II-based cortical contraction, moving the spindle away from the cortex. Thus, the asymmetric MII spindle position is dynamically maintained as a result of balanced forces governed by the Arp2/3 complex.

Cite this article

Yi, K., Unruh, J., Deng, M. et al. Dynamic maintenance of asymmetric meiotic spindle position through Arp2/3-complex-driven cytoplasmic streaming in mouse oocytes. Nat Cell Biol 13, 1252–1258 (2011). https://doi.org/10.1038/ncb2320

View full text

>> Full Text:   Dynamic maintenance of asymmetric meiotic spindle position through Arp2/3-complex-driven cytoplasmic