Using cryo-electron tomography and live-cell fluorescent imaging to study the role of cofilin in regulating neuronal filopodial structure and dynamics

Project Summary/Abstract How neurons guide their processes to the correct binding partner is a complicated task, but is critical during development and recovery from injury. It involves the highly coordinated action of many cytoskeletal proteins and their binding partners within the growth cone at the tips of extending neurites, as they feel their way through the neuropil. There is a lot known about the signaling pathways that regulate neurite outgrowth and turning, but the details of how molecular structures come together to achieve growth cone behavior are still unclear. This project will initially focus on the structure of bundled cofilactin filaments (cofilin-decorated F-actin) in situ, and how this novel filament structure and fascin cross-linking determine filopodial dynamics. Here we propose that filopodial behavior is governed partially by the transition from the fascin cross-linked to a cofilin cross-linked filaments, that makes filopodial bundles more pliable. Experiments are focused around three aims: 1) to study the high-resolution structure of fascin- and cofilin-linked actin bundles to determine their impact on actin structure, 2) to determine how changes in fascin and cofilin concentration regulate filopodial dynamics and structure, and 3) determine how LIMKI and SSH1 form the core of a bidirectional regulatory mechanism for regulating actin architecture via tuning the phosphorylation state of Ser3 on cofilin.