Precise wiring of the nervous system depends on the guided growth of axonal fibers to their specific targets for synaptic connections. Axon pathfinding depends on the motile growth cone at the tip of developing axons, which senses and responds to a variety of extracellular signals to navigate through a complex and changing environment to reach the target. The proposed study aims to elucidate the actin mechanisms underlying directional motility of growth cones in response to extracellular cues. Specifically, the project will investigate spatiotemporally-regulated actin monomer distribution, ADF/cofilin-mediated actin turnover, and filament end capping in growth cone migration and directional steering. Taking advantage of a well-defined neuronal culture system for growth cone turning assays, sophisticated high-resolution imaging techniques, direct manipulation of intracellular molecules, and molecular and pharmacological manipulation of cytoskeletal components, we will test the hypothesis that spatiotemporal localization of polymerization-competent actin monomers, ADF/cofilin-mediated actin turnover, and timely capping of the barbed end of actin filaments work in concert to regulate the actin remodeling for distinct growth cone turning responses to extracellular guidance signals, Our goal is to understand how spatiotemporal regulation of actin cytoskeleton translates extracellular cues to directional movement of the growth cone. The cell's ability to sense the environment and to determine the direction and proximity of an extracellular stimulus, followed by correct movement, is fundamental for many developmental events including neural development. Directed cell motility also underlies many pathological events, especially cancer-cell metastasis. The proposed study uses nerve growth cones as the model to study the actin mechanisms that control and regulate directional motility. The results from this study will provide significant insights into the cytoskeletal mechanisms of growth cone pathfinding, as well as directed cell movement in many physiological and pathological events. Therefore the work is directly relevant to public health.