Filopodia initiation: focus on the Arp2/3 complex and formins - PubMed (original) (raw)

Review

Filopodia initiation: focus on the Arp2/3 complex and formins

Changsong Yang et al. Cell Adh Migr. 2011 Sep-Oct.

Abstract

Filopodia are long, slender, actin-rich cellular protrusions, which recently have become a focus of cell biology research because of their proposed roles as sensory and exploratory organelles that allow for "intelligent" cell behavior. Actin nucleation, elongation and bundling are believed to be essential for filopodia formation and functions. However, the identity of actin filament nucleators responsible for the initiation of filopodia remains controversial. Two alternative models, the convergent elongation and tip nucleation, emphasize two different actin filament nucleators, the Arp2/3 complex or formins, respectively, as key players during filopodia initiation. Although these two models in principle are not mutually exclusive, it is important to understand which of them is actually employed by cells. In this review, we discuss the existing evidence regarding the relative roles of the Arp2/3 complex and formins in filopodia initiation.

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Figures

Figure 1

Figure 1

Mechanistic models of filopodia initiation. Convergent elongation model (top): (1) Branched actin network is formed in lamellipodil by Arp2/3-mediated nucleation. (2) Elongation factors (Ena/VASP or formin) maintain continuous elongation of some barbed end. (3) Interaction between barbed ends, likely also mediated by Ena/VASP or formin, results in synchronized parallel elongation of several converged filaments. (4) Parallel filaments are cross-linked by fascin resulting in formation of an actin bundle. (5) Over time, the Arp2/3 complex that nucleated filopodial filaments dissociates leaving free pointed ends of splayed actin filament. Tip nucleation model (bottom): (1) Activated formin is clustered on the plasma membrane. (2) Formin cluster nucleates a bunch of actin filaments and maintain their elongation. (3) Elongating filaments are cross-linked by fascin to form an actin bundle.

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