First published online February 12, 2004
Journal of Cell Science 117, 602e (2004)
© The Company of Biologists Limited
Actin model remodelled
Sheet-like lamellipodia and finger-like filopodia are distinct types of actin-rich protrusion important for cell movement. The widely accepted, `parallel pathway' model is that formation of lamellipodia is driven by the actin regulator SCAR/WAVE (a downstream effector of the GTPase Rac) but filopodia instead rely on its relative WASp (an effector of the Cdc42 GTPase). Gary Borisy and co-workers have examined whether this is really the case by using RNA interference to knock down WASp and SCAR in Drosophila cells, taking advantage of the fact that flies contain only one isoform of each (see p. 837). Surprisingly, they find that SCAR is required for formation of both lamellipodia and filopodia whereas WASp is not needed for either. These findings have significant implications for our understanding of how the actin cytoskeleton is regulated, and the authors use them as the basis for a new, `cascade' model for filopodium formation. They propose that SCAR signalling induces formation of the dendritic actin network that underpins lamellipodia, and in response to additional signals this reorganizes to generate the actin bundles characteristic of filopodia.
Related articles in JCS:
- Cascade pathway of filopodia formation downstream of SCAR
- Assel Biyasheva, Tatyana Svitkina, Patricia Kunda, Buzz Baum, and Gary Borisy
JCS 2004 117: 837-848.
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