A small cohort of FRU super(M) and Engrailed-expressing neurons mediate successful copulation in Drosophila melanogaster

Background: In Drosophila, male flies require the expression of the male-specific Fruitless protein (FRU super(M)) within the developing pupal and adult nervous system in order to produce male courtship and copulation behaviors. Recent evidence has shown that specific subsets of FRU super(M) neurons are necessary for particular steps of courtship and copulation. In these neurons, FRU super(M) function has been shown to be important for determining sex-specific neuronal characteristics, such as neurotransmitter profile and morphology. Results: We identified a small cohort of FRU super(M) interneurons in the brain and ventral nerve cord by their co-expression with the transcription factor Engrailed (En). We used an En-GAL4 driver to express a fru super( M ) RNAi construct in order to selectively deplete FRU super(M) in these En/FRU super(M) co-expressing neurons. In courtship and copulation tests, these males performed male courtship at wild-type levels but were frequently sterile. Sterility was a behavioral phenotype as these En-fru super( M )RNAi males were less able to convert a copulation attempt into a stable copulation, or did not maintain copulation for long enough to transfer sperm and/or seminal fluid. Conclusions: We have identified a population of interneurons necessary for successful copulation in Drosophila. These data confirm a model in which subsets of FRU super(M) neurons participate in independent neuronal circuits necessary for individual steps of male behavior. In addition, we have determined that these neurons in wild-type males have homologues in females and fru mutants, with similar placement, projection patterns, and neurochemical profiles.