Genetic lesions in Drosophila behavioural mutants

Over the last 30 years, several hundred behavioural mutants have been isolated in Drosophila. Only a fraction of these are well characterized genetically, behaviourally, and structurally. From six areas of behaviour a set of 24 well-studied mutants was chosen, in which the behavioural defect is probably caused by a central dysfunction and not by an impairment of sensory input or motor output. In all cases, the affected genes can be mutated to more than just a behavioural phenotype. Most genes in the sample are essential. Thus, phenotypic specificity is caused by the specificity of the mutation and not by the gene being a 'behavioural gene'. This study investigates how partial functional inactivation in these loci is brought about genetically. In particular, an attempt is made to discern whether behavioural mutations affect part of a protein's functional repertoire, a subset of protein isoforms, or the spatio-temporal expression of a gene. Not unexpectedly, in view of the predominant use of ethyl methanesulfonate (EMS) as mutagen, the majority of sampled mutations fall into the first two categories. The potentially richest source of genetic versatility, the spatio-temporal modulation of promoter activity by enhancers and silencers, has thus been insufficiently exploited for obtaining behavioural mutants. Various mutagens are reviewed as to their suitability in inducing selective regulatory mutations.