Cell-type specific modular regulation of derailed in the Drosophila nervous system.

The derailed (drl) gene encodes a receptor tyrosine kinase (RTK) that governs aspects of axon guidance and muscle-epidermal interactions in the Drosophila embryo. To determine the types of neurons that express drl, we have examined a series of drl promoter fusions to axon-targeted reporters. We have identified enhancers that drive reporter expression in four distinct subtypes of embryonic neurons, all of which project axons in the anterior commissure of the developing nervous system. We also identified enhancers driving expression in the drl-expressing muscles and epidermal attachment cells. These enhancers define the classes of neurons projecting in the anterior commissure and can be used to precisely define axon pathfinding errors in drl and other mutants.