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J. Biol. Chem., Vol. 282, Issue 40, 29504-29513, October 5, 2007

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A Role for Myosin 1e in Cortical Granule Exocytosis in Xenopus Oocytes^*

Cataldo Schietroma, Hoi-Ying Yu, Mark C. Wagner^¶, Joy A. Umbach, William M. Bement, and Cameron B. Gundersen¹

From the Department of Molecular and Medical Pharmacology, David Geffen UCLA School of Medicine, UCLA, Los Angeles, California 90095, the Department of Zoology, University of Wisconsin, Madison, Wisconsin 53706, and the ^¶Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana 46202

Xenopus oocytes undergo dynamic structural changes during maturation and fertilization. Among these, cortical granule exocytosis and compensatory endocytosis provide effective models to study membrane trafficking. This study documents an important role for myosin1e in cortical granule exocytosis. Myosin1e is expressed at the earliest stage that cortical granule exocytosis can be detected in oocytes. Prior to exocytosis, myosin1e relocates to the surface of cortical granules. Overexpression of myosin1e augments the kinetics of cortical granule exocytosis, whereas tail-derived fragments of myosin1e inhibit this secretory event (but not constitutive exocytosis). Finally, intracellular injection of myosin1e antibody inhibits cortical granule exocytosis. Further experiments identified cysteine string proteins as interacting partners for myosin1e. As constituents of the membrane of cortical granules, cysteine string proteins are also essential for cortical granule exocytosis. Future investigation of the link between myosin1e and cysteine string proteins should help to clarify basic mechanisms of regulated exocytosis.

Received for publication, July 16, 2007 , and in revised form, August 14, 2007.

^* This work was supported by National Institutes of Health Grants GM52932 (to W. M. B.) and NS31934 (to J. A. U.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains a supplemental movie.

¹ To whom correspondence should be addressed. Tel.: 310-825-3423; Fax: 310-206-8975; E-mail: cgundersen{at}mednet.ucla.edu.

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