Abstract
Mature mammalian oocytes are poised for completing meiosis II (MII) on fertilization by positioning the spindle close to an actomyosin-rich cortical cap. 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.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Actin Cytoskeleton / drug effects
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Actin Cytoskeleton / metabolism*
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Actin-Related Protein 2 / genetics
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Actin-Related Protein 2 / metabolism*
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Actin-Related Protein 2-3 Complex / antagonists & inhibitors
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Actin-Related Protein 2-3 Complex / genetics
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Actin-Related Protein 2-3 Complex / metabolism*
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Actin-Related Protein 3 / genetics
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Actin-Related Protein 3 / metabolism*
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Animals
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Cells, Cultured
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Cytoplasmic Streaming* / drug effects
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Female
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Fourier Analysis
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Heterocyclic Compounds, 4 or More Rings / pharmacology
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Indoles / pharmacology
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Kymography
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Meiosis* / drug effects
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Mice
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Microscopy, Confocal
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Microscopy, Video
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Morpholinos / metabolism
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Myosin Type II / metabolism
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Nocodazole / pharmacology
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Oocytes / drug effects
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Oocytes / metabolism*
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Protein Transport
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Recombinant Fusion Proteins / metabolism
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Spindle Apparatus / drug effects
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Spindle Apparatus / metabolism*
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Time Factors
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ran GTP-Binding Protein / metabolism
Substances
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Actin-Related Protein 2
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Actin-Related Protein 2-3 Complex
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Actin-Related Protein 3
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Actr2 protein, mouse
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Actr3 protein, mouse
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CK-0944666
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Heterocyclic Compounds, 4 or More Rings
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Indoles
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Morpholinos
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Ran protein, mouse
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Recombinant Fusion Proteins
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blebbistatin
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Myosin Type II
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ran GTP-Binding Protein
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Nocodazole