Monday 15 September 2003
Actin-rich filopodia let cells explore their environment.
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.
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.
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.
Pathology of filopodia
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