Nature Cell Biology
5, 727 - 732 (2003)
Published online: 20 July 2003; | doi:10.1038/ncb1025
Cdc42-dependent actin polymerization during compensatory endocytosis in Xenopus eggsAnna Marie Sokac1, 5, Carl Co2, Jack Taunton3
& William Bement1, 41
Department of Zoology, University of Wisconsin, Madison, WI 53706, USA. 2
Program in Biological Sciences, University of California, San Francisco, CA 94107, USA. 3
Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94107, USA. 4
Program in Molecular and Cellular Biology, University of Wisconsin, Madison, WI 53706, USA. 5
Current address: Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Correspondence should be addressed to Anna Marie Sokac amsokac@wisc.eduThe actin filament (F-actin) cytoskeleton associates dynamically with the plasma membrane and is thus ideally positioned to participate in endocytosis. Indeed, a wealth of genetic and biochemical evidence has confirmed that actin interacts with components of the endocytic machinery1, although its precise function in endocytosis remains unclear. Here, we use 4D microscopy to visualize the contribution of actin during compensatory endocytosis in Xenopus laevis eggs. We show that the actin cytoskeleton maintains exocytosing cortical granules as discrete invaginated compartments, such that when actin is disrupted, they collapse into the plasma membrane. Invaginated, exocytosing cortical granule compartments are directly retrieved from the plasma membrane by F-actin coats that assemble on their surface. These dynamic F-actin coats seem to drive closure of the exocytic fusion pores and ultimately compress the cortical granule compartments. Active Cdc42 and N-WASP are recruited to exocytosing cortical granule membranes before F-actin coat assembly and coats assemble by Cdc42-dependent, de novo actin polymerization. Thus, F-actin may power fusion pore resealing and function in two novel endocytic capacities: the maintenance of invaginated compartments and the processing of endosomes.
|
