NEUROMUSCULIN, A DROSOPHILA GENE EXPRESSED IN PERIPHERAL NEURONAL PRECURSORS AND MUSCLES, ENCODES A CELL-ADHESION MOLECULE

To unravel the molecular mechanisms of peripheral nervous system diffe rentiation in Drosophila, we have screened for and identified genes th at are expressed in sensory mother cells. Here, we describe a novel ge ne, neuromusculin (nrm), that is expressed in sensory mother cells and developing muscles. nrm encodes a member of the immunoglobulin superf amily. Immunoblots of Schneider 2 cells transfected with an nrm cDNA i ndicate that Nrm is present in a membrane-associated form and a secret ed form. Cell aggregation assays suggest that Nrm is a homophilic cell adhesion molecule that is secreted or released after proteolysis, a m echanism that to our knowledge has not been described for immunoglobul in-like molecules. Genetic analyses indicate that nrm is an essential gene required for larval viability. We propose that Nrm may play a rol e as a cell adhesion molecule in clustering cells of the peripheral ne rvous system, neuronal fasciculation, and/or pathfinding.