Worms depend on taste, touch and smell to sense and explore their environment. Appropriate responses to information received through these different modalities depends on precise connectivity between sensory neurons and downstream effector neurons in the nerve ring. Little is known about how extending axons migrate through this nerve ring neuropil during development to find their partners. How is positional information interpreted by an extending axon so that desired synaptic partners are found? Focusing on the guidance of the ASI chemosensory neurons to their appropriate positions in the nerve ring, a mutant screen led to the isolation of 16 candidate mutant strains that appeared to have ASI axon guidance and termination phenotypes. These mutations define at least five new genes named sax-10-14 (sensory axon guidance). Four main phenotypic classes of ASI axon defects have been observed and the morphologies of other neurons are being determined. To facilitate genetic analysis and cloning of the sax genes, the genes have been mapped and attempts to rescue the sax-10 phenotype by cosmid injections and germline transformation are ongoing. Finally, analysis of known mutants for effects on axon guidance in the nerve ring will provide insight on what mechanisms are required for axon guidance and nerve ring development.
