A central issue in developmental neuroscience is how func- tional circuits are assembled from developing cells. One excellent system for this kind of study is the a worm, Caenorhabditis. This tiny animal has a small nervous system where the individual cells are identifiable, and a number of genetic studies have revealed interesting mutant strains that have abnormal neuronal connections and abnormal behavior. This project will examine motor neurons, which directly innervate particular muscles. There are two sets of "D" motoneurons having similar shape and functions. But they arise from different cell divisions, so they have different "lineages," and they also have different patterns of synapses, the functional connections, to their muscles. One mutation, involving the "unc- 55" gene, alters the pattern of synapses in one class of the D motoneurons so that it becomes identical to the other class, instead of different. Genetic and ultrastructural techniques will be used to further clarify the focus of unc-55 during development of the D cells, and see how additional mutations might act on developmental processes. Use of a laser to make specific ablations of individual motoneurons will allow correlation of behavioral activity with identified cells, and so provide a mechanism for genetic screening of further mutations, perhaps similar, affecting the other class of D motoneurons. Results from this study will be important to neuroscience, developmental biology, and genetics, addressing how a finite genome can produce the extraordinary diversity seen in nervous system connections.
