Molecular Separation of Two Behavioral Phenotypes by a Mutation Affecting the Promoters of a Ca-Activated K Channel

The Drosophila slowpoke gene encodes a BK-type calcium-activated potassium channel. Null mutations in slowpoke perturb the signaling properties of neurons and muscles and cause behavioral defects. The animals fly very poorly compared with wild-type strains and, after exposure to a bright but cool light or a heat pulse, exhibit a “sticky-feet” phenotype. Expression of slowpoke arises from five transcriptional promoters that express the gene in neural, muscle, and epithelial tissues. A chromosomal deletion ( ash 218) has been identified that removes the neuronal promoters but not the muscle–tracheal cell promoter. This deletion complements the flight defect of slowpoke null mutants but not the sticky-feet phenotype. Electrophysiological assays confirm that the ash 218 chromosome restores normal electrical properties to the flight muscle. This suggests that the flight defect arises from a lack of slowpoke expression in muscle, whereas the sticky-feet phenotype arises from a lack of expression in nervous tissue.