Filopodia sense the extracellular environment at their tips using cell surface receptors [5, 6, 7]. Contact with an external target promotes the coupling of membrane-bound proteins to the backward (retrograde) flow of actin; this coupling produces the pulling forces needed for cell migration processes such as wound healing and neurite growth . Contact differences between substrates or cell types influences the number of protruding filopodia .
A key set of proteins is involved in filopodia formation; however, the relative importance of each protein seems to vary between different organisms and their cell types. Three basic steps are involved in filopodial assembly: filament nucleation, sustained barbed end elongation and filament bundling.