To unravel the molecular mechanisms of peripheral nervous system differentiation in Drosophila, we have screened for and identified genes that are expressed in sensory mother cells. Here, we describe a novel gene, neuromusculin (nrm), that is expressed in sensory mother cells and developing muscles. nrm encodes a member of the immunoglobulin superfamily. Immunoblots of Schneider 2 cells transfected with an nrm cDNA indicate that Nrm is present in a membrane-associated form and a secreted form. Cell aggregation assays suggest that Nrm is a homophilic cell adhesion molecule that is secreted or released after proteolysis, a mechanism that to our knowledge has not been described for immunoglobulin-like molecules. Genetic analyses indicate that nrm is an essential gene required for larval viability. We propose that Nrm may play a role as a cell adhesion molecule in clustering cells of the peripheral nervous system, neuronal fasciculation, and/or pathfinding.
Bibliographical noteFunding Information:
We thank Clive Wilson and Cahir O’Kane for helping H. B. with the initial phases of this project. We thank Mark Seeger and Corey Goodman for sending us S2 cells, fasciclin I and fasciclin II expressing cells, pRmHa3, and pPC4. We thank Nathalie De-Santis for sequencing, Sandra Kooyer for the PCR analysis, Joel Pearlman for advice, and Rodney Murphy for unpublished data. We also thank Juan Botas, Troy Littleton, Sandra Kooyer, Karen Schulze, Adi Salzberg, William Craigen, Katie Schlimgen, Mark Perin,and JamesLupskiforcriticalcommentson themanuscript. P.-L. H. and Y.-T. Kwere supported by the Howard Hughes Medical Institute. H. B. is an assistant investigator of the Howard Hughes Medical Institute.