A SENSORY ROLE FOR NEURONAL GROWTH CONE FILOPODIA

THE dynamic nature of neuronal growth cone filopodia led to the suggestion that the primary function of filopodia is to sample their immediate environment1-3, responding to and transducing environmental signals that affect growth cone behaviour4-6 and shape7-11. Filopodia seem well suited to serve as antenna-like sensors, their broad span allows sampling of information over a greatly enhanced radius, and forward-projecting filopodia encounter potential cues in the molecular terrain long before the advancing growth cone itself12. Filopodia in culture can serve structural roles13, exert mechanical tension14-16 and selectively adhere to their surrounding17-20. Whether or not filopodia have a general sensory role has not been tested directly, largely because of their small size, which limits an electrophysiological approach, and their integral relationship with the parent growth cone, which prevents resolution of their different functions. Here we use surgical procedures to isolate individual filopodia from their parent growth cone and, by monitoring their morphology and calcium second messenger systems, we show that neuronal growth cone filopodia contain signal transduction mechanisms that allow autonomous responses and the transmission of distant environmental information to their parent growth cone.