Investigating the role of Arp2/3 and formins in neuronal growth cones

Abstract

Actin is involved in various aspects of cellular motility, including growth cone-dependent translocation and guidance of axons. During cellular motility actin is pivotal in generating protrusive structures, like filopodia and lamellipodia, and development of substrate adhesions and traction forces. Actin nucleation is a major regulator of actin dynamics and multiple actin nucleators, including the Arp2/3 complex and formins are expressed in the developing nervous system. In this study, specific pharmacological inhibition of the Arp2/3 complex and formin based nucleation is employed to compare and contrast the functional significance of these nucleators in neuronal growth cones. We find Arp2/3 regulates the spreading of the growth cones but not filopodia or translocation rates. Further, Arp2/3 is necessary for cue-dependant directional turning of growth cones. formins, on the other hand, regulate filopodia and are central to translocation as inhibition of formin activity reduces growth rates possibly by modulating the underlying adhesive structures. Additionally, in order to aid detailed microscopic analysis of actin structures in growth cones and the regulation of stress fiber formation and maintenance by actin nucleators, I have developed photo-activatable constructs and FRAP analysis of stress fiber dynamics.