The molecular link between the signalling pathway regulating the formation of filopodia and the initiation of local actin polymerization has been elucidated : N WASP , a close homologue of WASP , which is the product of the gene responsible for the Wiskott Aldrich syndrome , mediates a direct connection between the small G protein Cdc 42 and the Arp2 / 3 complex . . ^^^