Cellular, genetic and molecular mechanisms of axonal guidance in the zebrafish.

There is organization and pattern in the intricate network of axons that comprise the nervous system. This organization is essential to ensure the establishment of appropriate connections between neurons and their targets. Between the initiation of axonogenesis and the point where an axon reaches its target, is the process of axon guidance. In both invertebrates and vertebrates, axon guidance occurs in a stereotyped manner resulting in the formation of patterned nerves. The growing tip of the axon, the growth cone, responds to cues in the environment. These cues, both attractive and repulsive, dictate where growth cones extend and thus where nerves will form (Tessier-Lavigne and Goodman 1996).