Research Project
3327426
The growth and guidance of pioneer axons through virgin territory provides the patterned framework for the adult nervous system and ultimately its synaptic circuitry. Studies on vertebrates and invertebrates strongly suggest that the molecular cues used for guiding certain pioneer neurons are cell adhesion molecules expressed on the surface of the neuroepithelium or its basal lamina, however, our present understanding of the molecular mechanisms involved in neuron guidance is rudimentary at best. The proposed studies are designed to clone and molecularly characterize 3 genes that by mutant analysis appear to be required to guide pioneer neurons along the simple neuroepithelium (or epidermis) of the nematode Caenorhabditis elegans. The neuroanatomical phenotype of mutants unc-53 and unc-73 suggests that these 2 genes may encode segment-specific neuroepithelial adhesion molecule used for dorsalward guidance. Additional characterization of mutant phenotypes may support these models or suggest other models for the nature of their guidance defects. The unc-73 gene has been tagged with the transposable element Tcl to facilitate its cloning. The other genes will be similarly tagged and cloned, and all 3 genes will be sequenced to look for similarities to proteins with known or suspected nerve growth or adhesive functions. The distribution of the products of these genes will be examined in situ by indirect immunofluorescence with antibodies raised against fusion proteins expressed in E coli. These studies may provide insights into the patterns of molecular cues that guide growing neurons along a simple neuroepithelium. There is good reason to believe that at least some of the molecular mechanisms used for pioneer neuron guidance in C. elegans may be conserved in vertebrates. Eventually we plan to examine this possibility.
