MUTATIONS IN NEUROMUSCULIN, A GENE ENCODING A CELL-ADHESION MOLECULE,CAUSE NERVOUS-SYSTEM DEFECTS

The Drosophila neuromusculin (nrm) gene encodes an immunoglobulin-like (Ig-like) cell adhesion molecule expressed in the precursors of the e mbryonic peripheral nervous system (PNS), in the midline precursors of the central nervous system (CNS), and in muscles. During the initial phases of CNS axonogenesis, nrm is expressed in cells involved in the development of commissures and longitudinal tracts. Mutations which al ter expression of nrm mRNAs cause aberrant development of commissures and longitudinal axon pathways. Defects in the PNS and muscles of nrm mutants are also observed. In most nrm embryos, abnormal development c an be detected in a subset of abdominal segments; however, in approxim ately 1 of 10 nrm embryos, the defects extend to all segments. Herein, we present evidence that nrm plays an important role in early morphog enesis, possibly by mediating or facilitating inductive cell contacts and movements.