filopodia

Filopodia are rod-like cell surface projections filled with bundles of parallel actin filaments. They are found on a variety of cell types and have been ascribed sensory or exploratory functions.

Filopodium formation is frequently associated with protrusion of sheet-like actin filament arrays called lamellipodia and membrane ruffles, but, in comparison to these structures, the molecular details underpinning the initiation and maintenance of filopodia are only just beginning to emerge.

Function

Lamellipodia, filopodia and membrane ruffles are essential for cell motility, the organization of membrane domains, phagocytosis and the development of substrate adhesions.

Their formation relies on the regulated recruitment of molecular scaffolds to their tips (to harness and localize actin polymerization), coupled to the coordinated organization of actin filaments into lamella networks and bundled arrays.

Their turnover requires further molecular complexes for the disassembly and recycling of lamellipodium components.

Leukocytic migration

The leukocyte moves by extending filopodia that pull the back of the cell in the direction of extension, much as an automobile with front-wheel drive is pulled by the wheels in front. Actin reorganization may also occur at the trailing edge of the cell.

Locomotion involves rapid assembly of actin monomers into linear polymers at the filopodium’s leading edge, followed by cross-linking of filaments, and disassembly of such filaments away from the leading edge. A number of actin-regulating proteins, such as filamin, gelsolin, profilin, and calmodulin, interact with actin and myosin in the filopodium to produce contraction.

Filopodia formation

Pathology of filopodia

 Wiskott-Aldrich syndrome

References

References

 Faix J, Rottner K. The making of filopodia. Curr Opin Cell Biol. 2006 Feb;18(1):18-25. PMID: 16337369

 Wehrle-Haller B, Imhof B. The inner lives of focal adhesions. Trends Cell Biol. 2002 Aug ;12(8):382-9. PMID : 12191915

 Small JV, Stradal T, Vignal E, Rottner K. The lamellipodium : where motility begins. Trends Cell Biol. 2002 Mar ;12(3):112-20. PMID : 11859023

 Wehrle-Haller B, Imhof B. The inner lives of focal adhesions. Trends Cell Biol. 2002 Aug ;12(8):382-9. PMID : 12191915