Formins are actin filament-polymerizing proteins that are important in numerous cellular processes including cell polarity, cytokinesis, and cell migration. Although Diaphanous-related formins can form linear bundles of actin filaments similar to those in filopodia, the membrane protrusions seen on crawling cells, they haven’t been directly shown to play a role in filopodia formation. Block and colleagues recently found that the Diaphanous-related formin called FMNL2 accumulates at filopodia tips and lamellipodial membrane protrusions. In addition, FMNL2 drives actin elongation within filopidial tips and lamellipodia, in turn driving efficient cell migration, with the help of the well-studied polarity protein Cdc42. Images above show two time-lapse series of FMNL2 in crawling cells. FMNL2 is found at the filopodial tip (white arrows, left-hand images) and at the edge of a lamellipodial protrusion (arrowheads, right-hand images).
Block, J., Breitsprecher, D., Kühn, S., Winterhoff, M., Kage, F., Geffers, R., Duwe, P., Rohn, J., Baum, B., Brakebusch, C., Geyer, M., Stradal, T., Faix, J., & Rottner, K. (2012). FMNL2 Drives Actin-Based Protrusion and Migration Downstream of Cdc42 Current Biology, 22 (11), 1005-1012 DOI: 10.1016/j.cub.2012.03.064