Genes that control neuromuscular specificity in Drosophila

Abstract In each abdominal hemisegment of the Drosophila embryo, an array of 30 muscle fibers is innervated by about 34 motoneurons in a highly stereotyped and cell-specific fashion. To begin to elucidate the molecular basis of neural specificity in this system, we conducted a genetic screen for mutations affecting neuromuscular connectivity. We focus on 5 genes required for specific aspects of pathway ( beaten path, stranded , and short stop ) and target ( walkabout and clueless ) recognition. The different classes of mutant phenotypes suggest that neural specificity is controlled by a hierarchy of molecular mechanisms: motoneurons are guided toward the correct region of mesoderm, in many cases navigating a series of choice points along the way; they then display an affinity for a particular domain of neighboring muscles; and finally, they recognize their specific muscle target from within this domain.