title: Visualization and molecular analysis of actin assembly in living cells.
abstract: Actin filament assembly is critical for eukaryotic cell motility. Arp2/3 complex and capping protein (CP) regulate actin assembly in vitro. To understand how these proteins regulate the dynamics of actin filament assembly in a motile cell, we visualized their distribution in living fibroblasts using green flourescent protein (GFP) tagging. Both proteins were concentrated in motile regions at the cell periphery and at dynamic spots within the lamella. Actin assembly was required for the motility and dynamics of spots and for motility at the cell periphery. In permeabilized cells, rhodamine-actin assembled at the cell periphery and at spots, indicating that actin filament barbed ends were present at these locations. Inhibition of the Rho family GTPase rac1, and to a lesser extent cdc42 and RhoA, blocked motility at the cell periphery and the formation of spots. Increased expression of phosphatidylinositol 5-kinase promoted the movement of spots. Increased expression of LIM-kinase-1, which likely inactivates cofilin, decreased the frequency of moving spots and led to the formation of aggregates of GFP-CP. We conclude that spots, which appear as small projections on the surface by whole mount electron microscopy, represent sites of actin assembly where local and transient changes in the cortical actin cytoskeleton take place.
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. dschafer@cellbio.wustl.edu
authors.forename: D A
authors.initials: DA
authors.lastname: Schafer
authors.forename: M D
authors.initials: MD
authors.lastname: Welch
authors.forename: L M
authors.initials: LM
authors.lastname: Machesky
authors.forename: P C
authors.initials: PC
authors.lastname: Bridgman
authors.forename: S M
authors.initials: SM
authors.lastname: Meyer
authors.forename: J A
authors.initials: JA
authors.lastname: Cooper
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D002462:Cell Membrane / Q000648:ultrastructure; D002465:Cell Movement; D005347:Fibroblasts / Q000166:cytology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D007614:Macropodidae; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D047428:Protein Kinase Inhibitors; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020744:rac GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein
chemical_list: D000199:Actins; D018797:Cell Cycle Proteins; D047428:Protein Kinase Inhibitors; D011993:Recombinant Fusion Proteins; D010749:Phosphoprotein Phosphatases; D019204:GTP-Binding Proteins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020744:rac GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D013755:Tetradecanoylphorbol Acetate