INDIRECT SUPPRESSION INVOLVING BEHAVIORAL MUTANTS WITH ALTERED NERVE EXCITABILITY IN DROSOPHILA MELANOGASTER

Two classes of X-linked behavioral mutants of Drosophila melanogaster, leg-shaking mutants and bang-sensitive mutants, are suppressed by napts (no action potential, temperature-sensitive), an autosomal temperature-sensitive paralytic mutation. So far, napts is found to suppress thirteen mutations at seven loci, two of which produce leg shaking and five bang-sensitivity. Suppression is recessive, occurs at temperatures permissive for napts, and is indirect and function-specific rather than allele-specific. At restrictive temperatures, napts is known to completely block all nerve activity. Several of the mutants suppressed by napts are shown by neurophysiological experiments to have increased nerve excitability. The physiological defect of these mutants as well as their behavioral defect is suppressed by napts. Thus, suppression occurs within individual neurons at the level of excitable membranes and apparently depends on the reduction in membrane excitability caused by napts even under permissive conditions. We suggest that all mutants suppressed by napts may have related defects leading to enhanced nerve excitability. Genetic interactions of this type help reveal functional relationships between different behavioral mutants and suggest ways of isolating new mutants with altered excitable membranes.