Mechanisms of growth cone guidance and motility in the developing grasshopper embryo.

During neuronal pathfinding in vivo, growth cones must reorient their direction of migration in response to extracellular guidance cues. The developing grasshopper limb bud has proved to be a model system in which to examine mechanisms of growth cone guidance and motility in vivo. In this review we examine the contributions of adhesion and multiple guidance cues (semaphorins 1 and 2) in directing a growth cone steering event. Recent observations have suggested that the tibial pioneer growth cones are not directed via mechanisms of differential adhesivity. We present a model of growth cone steering that suggests a combination of adhesive and guidance receptors are important for a correct steering event and that guidance molecules may be important regulators of adhesive interactions with the actin cytoskeleton.