FUNCTIONS OF NETRINS AND SEMAPHORINS IN AXON GUIDANCE

Neuronal growth cones respond to both contact-mediated and chemotropic guidance cues; these cues can be either attractive or repulsive. This past year has seen further characterization of two gene families impl icated in long-range chemoattraction and chemorepulsion: the netrins a nd the semaphorins. Analysis of invertebrate members of these gene fam ilies demonstrates in vivo how netrins play multiple roles in axonal g uidance in Caenorhabditis elegans, how specific domains of the netrin molecule confer attractive and repulsive guidance cues, and how semaph orins can function to generate neuromuscular specificity.