Figure 1.

In epithelial cells villin and fascin may have non-overlapping functions in filopodia assembly. Villin can nucleate, cap, sever and bundle actin filaments. Villin also binds PtdIns(4,5)P₂. Fascin is an actin-bundling protein that does not bind PtdIns(4,5)P₂. This predicts that filopodia assembled by villin and fascin could be molecularly and functionally distinct. In epithelial cells that do express villin and fascin, villin may be associated with more dynamic actin bundles that undergo rapid turnover in response to extracellular cues. By contrast, fascin could be associated with more stable and rigid actin bundles within the filopodia.