Cdc42-dependent actin polymerization during compensatory endocytosis in Xenopus eggs.
The 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 machinery, 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.
Sokac
Anna Marie
AM
Department of Zoology, University of Wisconsin, Madison, WI 53706, USA. amsokac@wisc.edu
Co
Carl
C
Taunton
Jack
J
Bement
William
W
D000199:Actins / Q000378:metabolism*; D000818:Animals; D003599:Cytoskeleton / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D013997:Time Factors; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal; D014981:Xenopus; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
D000199:Actins; D005456:Fluorescent Dyes; D009419:Nerve Tissue Proteins; C495771:WASL protein, human; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal; D020764:cdc42 GTP-Binding Protein