Arp2/3 Complex and Actin Depolymerizing Factor/Cofilin in Dendritic Organization and Treadmilling of Actin Filament Array in Lamellipodia

The leading edge (∼1 μm) of lamellipodia in Xenopus laevis keratocytes and fibroblasts was shown to have an extensively branched organization of actin filaments, which we term the dendritic brush. Pointed ends of individual filaments were located at Y-junctions, where the Arp2/3 complex was also loc...

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Bibliographic Details
Published in:The Journal of cell biology 1999-05, Vol.145 (5), p.1009-1026
Main Authors: Svitkina, Tatyana M., Borisy, Gary G.
Format: Article
Language:English
Subjects:
Actin Depolymerizing Factors
Actin-Related Protein 2
Actin-Related Protein 3
Actins
Actins - metabolism
Animals
Antibodies
Cell motility
Cell Movement
Cells
Cellular biology
Cytoskeletal Proteins
Depolymerization
Dimerization
Fibroblasts
Freshwater
Keratinocytes - metabolism
Keratinocytes - ultrastructure
Microfilament Proteins - metabolism
Microfilaments
Microscopy, Fluorescence
Nucleation
Organelles - metabolism
Organelles - ultrastructure
Polymerization
Pseudopodia
Regular
Xenopus laevis
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Summary:The leading edge (∼1 μm) of lamellipodia in Xenopus laevis keratocytes and fibroblasts was shown to have an extensively branched organization of actin filaments, which we term the dendritic brush. Pointed ends of individual filaments were located at Y-junctions, where the Arp2/3 complex was also localized, suggesting a role of the Arp2/3 complex in branch formation. Differential depolymerization experiments suggested that the Arp2/3 complex also provided protection of pointed ends from depolymerization. Actin depolymerizing factor (ADF)/cofilin was excluded from the distal 0.4 μm of the lamellipodial network of keratocytes and in fibroblasts it was located within the depolymerization-resistant zone. These results suggest that ADF/cofilin, per se, is not sufficient for actin brush depolymerization and a regulatory step is required. Our evidence supports a dendritic nucleation model for lamellipodial protrusion, which involves treadmilling of a branched actin array instead of treadmilling of individual filaments. In this model, Arp2/3 complex and ADF/cofilin have antagonistic activities. Arp2/3 complex is responsible for integration of nascent actin filaments into the actin network at the cell front and stabilizing pointed ends from depolymerization, while ADF/cofilin promotes filament disassembly at the rear of the brush, presumably by pointed end depolymerization after dissociation of the Arp2/3 complex.
ISSN:0021-9525
1540-8140
DOI:10.1083/jcb.145.5.1009