ABSTRACT 9604659 WALTHALL The production of a functional neural circuit begins with the differentiation of nerve cells and ends with synaptic communication between cells. Comparative studies of the mechanisms and molecules that orchestrate cellular differentiation and that mediate communication at synapses have revealed a tremendous amount of conservation across evolutionarily diverse animals. Much less is known about a critical intervening step, the selective formation of synapses as the circuit is assembled. The award will allow Dr. Walthall and his students to investigate the genetic and molecular mechanisms that create the synaptic patterns that distinguish two related classes of motoneurons in the nematode Caenorhabditis elegans. Unique features of C. elegans make it ideal for an experimental approach that integrates the roles of genetic and cellular programs involved in establishing orderly synaptic patterns. Two classes of locomotory neurons in C. elegans, the dorsal D motoneurons (DD mns) and the ventral D motoneurons (VD mns), make up a cross-inhibitory network that plays a critical role in the animal's serpentine movements. The DD and VD motorneurons share many structural and neurochemical features, but they are distinguished from one another by their synaptic patterns. The similarities between the two motoneuron classes appear to be due to the expression of ge
