Forked end: a novel transmembrane protein involved in neuromuscular specificity in drosophila identified by gain-of-function screening.

The Drosophila neuromuscular connectivity provides an excellent model system for studies on target recognition and selective synapse formation. To identify molecules involved in neuromuscular recognition, we conducted gain-of-function screening for genes whose forced expression in all muscles alters the target specificity. We report here the identification of a novel transmembrane protein, Forked end (FEND), encoded by the fend gene, by the said screening. When the FEND expression was induced in all muscles, motoneurons that normally innervate muscle 12 formed ectopic synapses on a neighboring muscle 13. The target specificity of these motoneurons was also altered in the loss-of-function mutant of fend. During embryonic development, fend mRNA was detected in a subset of cells in the central nervous system and in the periphery. These results suggest that FEND is a novel axon guidance molecule involved in neuromuscular specificity.