MyTH4-FERM myosin based filopodia initiation

Abstract

Filopodia are thin actin-based structures that cells use to interact with their environments. Filopodia initiation requires a suite of conserved proteins but the mechanism remains poorly understood. The actin polymerase VASP and a MyTH-FERM (MF) myosin, DdMyo7 in amoeba and Myo10 in animals, are essential for initiation. DdMyo7 is localized to dynamic regions of the ac-tin-rich cortex. Analysis of VASP with altered activity reveals that localized actin polymerization is required for myosin recruitment and activation in Dic-tyostelium. Targeting of DdMyo7 to the cortex is not sufficient for filopodia ini-tiation; VASP activity is required as well. The actin regulator locally produces new actin filaments which activates a MF myosin. Myosin then shapes or crosslinks the actin network so parallel bundles of actin can extend during filo-podia formation. This work reveals cooperativity of an actin binding protein and the actin cytoskeleton on mediating myosin activity during filopodia initia-tion.