Segmentally repeated stripes of ectodermal expression appear at stage 11 and becomes uniform throughout the entire epidermis by stage 12. During myoblast fusion and syncytial muscle formation at stage 14, Abrupt mRNA can be detected in the somatic muscle cells. Larval ab is expressed in imaginal discs, consistent with the wide ranging adult defects seen in mutants. The axons form abnormal branches instead of forming their wild-type axonal extensions onto the muscle fibers. These aberrant branches wander over the prospective target muscles and occasionally form connections at ectopic sites.
Abrupt function is required for the development of numerous adult structures.
Legs may be severely gnarled. The Drosophila abrupt gene encodes a BTB-zinc finger regulatory protein that controls the specificity of neuromuscular connections.