Activation of ADF/cofilin by phosphorylation-regulated Slingshot phosphatase is required for the meiotic spindle assembly in Xenopus laevis oocytes |
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| Authors: | Shohei Iwase Ryuhei Sato Pieter-Jan De Bock Kris Gevaert Saburo Fujiki Toshinobu Tawada Miyako Kuchitsu Yuka Yamagishi Shoichiro Ono Hiroshi Abe |
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| Affiliation: | Columbia University;aDepartment of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan;dDepartment of Biology, Faculty of Science, Chiba University, Chiba 263-8522, Japan;bVIB Department of Medical Protein Research, Ghent University, B-9000 Ghent, Belgium;cDepartment of Biochemistry, Ghent University, B-9000 Ghent, Belgium;eDepartment of Pathology, Emory University, Atlanta, GA 30322 |
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| Abstract: | We identify Xenopus ADF/cofilin (XAC) and its activator, Slingshot phosphatase (XSSH), as key regulators of actin dynamics essential for spindle microtubule assembly during Xenopus oocyte maturation. Phosphorylation of XSSH at multiple sites within the tail domain occurs just after germinal vesicle breakdown (GVBD) and is accompanied by dephosphorylation of XAC, which was mostly phosphorylated in immature oocytes. This XAC dephosphorylation after GVBD is completely suppressed by latrunculin B, an actin monomer–sequestering drug. On the other hand, jasplakinolide, an F-actin–stabilizing drug, induces dephosphorylation of XAC. Effects of latrunculin B and jasplakinolide are reconstituted in cytostatic factor–arrested extracts (CSF extracts), and XAC dephosphorylation is abolished by depletion of XSSH from CSF extracts, suggesting that XSSH functions as an actin filament sensor to facilitate actin filament dynamics via XAC activation. Injection of anti-XSSH antibody, which blocks full phosphorylation of XSSH after GVBD, inhibits both meiotic spindle formation and XAC dephosphorylation. Coinjection of constitutively active XAC with the antibody suppresses this phenotype. Treatment of oocytes with jasplakinolide also impairs spindle formation. These results strongly suggest that elevation of actin dynamics by XAC activation through XSSH phosphorylation is required for meiotic spindle assembly in Xenopus laevis. |
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