TY - JOUR T1 - Src-Dependent Tyrosine Phosphorylation at the Tips of Growth Cone Filopodia Promotes Extension JF - The Journal of Neuroscience JO - J. Neurosci. SP - 7669 LP - 7681 DO - 10.1523/JNEUROSCI.2680-05.2005 VL - 25 IS - 33 AU - Estuardo Robles AU - Stephanie Woo AU - Timothy M. Gomez Y1 - 2005/08/17 UR - http://www.jneurosci.org/content/25/33/7669.abstract N2 - Extracellular cues guide axon outgrowth by activating intracellular signaling cascades that control the growth cone cytoskeleton. However, the spatial and temporal coordination of signaling intermediates remains essentially unknown. Live imaging of tyrosine phosphorylation in growth cones revealed dynamic phospho-tyrosine (PY) signals in filopodia that directly correlate with filopodial behavior. Local PY signals are generated at distal tips of filopodia during extension and are lost during retraction. Active Src family kinases localize to the tips of filopodia, and Src activity regulates both filopodial dynamics and local PY signaling. Positive guidance cues stimulate filopodial motility by locally increasing tyrosine phosphorylation in a cell division cycle 42 (Cdc42)-dependent manner. Locally reduced Src activity on one side of the growth cone generates an asymmetry in filopodial motility and PY signaling that promotes repulsive turning, suggesting that local changes in filopodial PY levels may underlie growth cone pathfinding decisions. p21-activated kinase (PAK), a Cdc42 effector whose activity is regulated by Src phosphorylation, also localizes to the tips of extending filopodia and controls filopodial motility. Coordinated activation of cytoskeletal effector proteins by GTPase binding and Src-mediated tyrosine phosphorylation may function to produce specific growth cone behaviors in response to guidance cues. ER -