Arp2/3 complex and actin depolymerizing factor/cofilin in dendritic organization and treadmilling of actin filament array in lamellipodia.
T.M. Svitkina,Gary G. Borisy +1 more
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The leading edge of lamellipodia in Xenopus laevis keratocytes and fibroblasts was shown to have an extensively branched organization of actin filaments, which is supported by a dendritic brush, suggesting that ADF/cofilin, per se, is not sufficient for actin brush depolymerization and a regulatory step is required.Abstract:
The leading edge (approximately 1 microgram) 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 micrometer++ 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 (Mullins, R.D., J.A. Heuser, and T.D. Pollard. 1998. Proc. Natl. Acad. Sci. USA. 95:6181-6186) 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.read more
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References
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The interaction of Arp2/3 complex with actin: Nucleation, high affinity pointed end capping, and formation of branching networks of filaments
TL;DR: It is shown that Arp2/3 complex purified from Acanthamoeba caps the pointed ends of actin filaments with high affinity and increases the critical concentration for polymerization at the pointed end from 0.6 to 1.0 microM.
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The interaction between N-WASP and the Arp2/3 complex links Cdc42-dependent signals to actin assembly.
Rajat Rohatgi,Le Ma,Hiroaki Miki,Marco Lopez,Tomas Kirchhausen,Tadaomi Takenawa,Marc W. Kirschner +6 more
TL;DR: N-WASP and the Arp2/3 complex comprise a core mechanism that directly connects signal transduction pathways to the stimulation of actin polymerization.
Journal ArticleDOI
Actin Depolymerizing Factor (ADF/Cofilin) Enhances the Rate of Filament Turnover: Implication in Actin-based Motility
Marie-France Carlier,Valérie M. Laurent,Jérôme Santolini,Ronald Melki,Dominique Didry,Gui-Xian Xia,Yan Hong,Nam-Hai Chua,Dominique Pantaloni +8 more
TL;DR: The function of ADF is not to sequester G-actin, but uses ATP hydrolysis in actin assembly to enhance filament dynamics and increase in the rate of actin-based motile processes.
Journal ArticleDOI
Cell motility driven by actin polymerization
Alex Mogilner,George Oster +1 more
TL;DR: It is shown that the thermal motions of the polymerizing filaments can produce a directed force, and this "elastic Brownian ratchet" can explain quantitatively the propulsion of Listeria and the protrusive mechanics of lamellipodia.
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