Axon Guidance: Building Pathways with Molecular Cues in Vertebrate Sensory Systems

Abstract

In this article, we briefly review the axon guidance molecules that work in concert to orchestrate the pathfinding processes that lead to the formation of sensory systems. We focus on the visual and the olfactory systems, outline key axon guidance processes along the pathways from periphery to the brain, and summarize current understandings of molecular cues that regulate the guidance decisions at these major pathfinding steps. A general scheme is emerging: long-range chemoattractive molecules guide the overall direction of axon growth, while the major pathways are determined by a combination of attractive and repulsive cues that result in the formation of narrow permissive channels through which the axons can navigate. Within the target area, sensory neurons form topographic maps. These maps are guided first roughly by molecular gradients, and are then refined by neuronal activity dependent axon sorting.