INTEGRIN-CYTOSKELETAL INTERACTIONS IN NEURONAL GROWTH CONES

Development of the nervous system requires that neuronal growth cones, in coordination with growing axons, migrate along precise paths defin ed by specific extracellular matrix cues until they encounter their ta rgets. Laminin promotes growth cone migration through receptors such a s the integrins, but the underlying physical mechanism is poorly under stood. We have investigated the cytoskeletal associations and surface dynamics of endogenous beta 1 integrins in chick dorsal root ganglion growth cones migrating on laminin, A single-beam optical gradient trap was used to place 0.5-mu m-diameter polystyrene beads conjugated with anti-beta 1 integrin monoclonal antibodies at desired locations on th e growth cone surface, We found a substantial increase in the stable a ttachment of these beads, with subsequent slow rearward motion, on the front periphery of the growth cone compared to the base. The surface dynamics of smaller aggregates of integrin were explored by monitoring the temporal and spatial displacements of 40-nm-diameter gold particl es coated with anti-beta 1 integrin antibodies. The small particles we re transported preferentially to the growth cone periphery by brief di rected excursions interspersed with periods of diffusion, In addition, the leading edge of the growth cone was supported to a greater extent by an actin-dependent cytoskeleton that resisted mechanical tether fo rmation, Such a regional differentiation of the growth cone has not be en documented previously and has implications for the mechanism of gro wth cone migration and guidance.