AUTONOMOUS REGULATION OF GROWTH CONE FILOPODIA

The fan-shaped array of filopodia is the first site of contact of a ne uronal growth cone with molecules encountered during neuronal pathfind ing, Filopodia are highly dynamic structures, and the ''action radius' ' of a growth cone is strongly determined hy the length and number of its filopodia, Since interactions of filopodia with instructive cues i n the vicinity of the growth cone can have effects on growth cone morp hology within minutes, it has to be assumed that a large part of the s ignaling underlying such morphological changes resides locally within the growth cone proper, In this study, we tested the hypothesis that t wo important growth cone parameters-namely, the length and number of i ts filopodia-are regulated autonomously in the growth cone. We previou sly demonstrated in identified neurons from the snail Helisoma trivolv is that filopodial length and number are regulated by intracellular ca lcium, Here, we investigated filopodial dynamics and their regulation by the second-messenger calcium in growth cones which were physically isolated from their parent neuron by neurite transection, Our results show that isolated growth cones have longer but fewer filopodia than g rowth cones attached to their parent cell, These isolated growth cones , however, are fully capable of undergoing calcium-induced cytoskeleta l changes, suggesting that the machinery necessary to perform changes in filopodial length and number is fully intrinsic to the growth cone proper. (C) 1998 John Wiley & Sons, Inc.