A master gene for Drosophila male courtship prevents the behavior in females via a truncated protein

Decades of studies have established that a terminal gene in the sex determination hierarchy, fruitless (fru), controls nearly all aspects of male courtship behaviors in Drosophila and many other insects. fru is transcribed in a sex-specific manner to produce male-specific Fru proteins (FruM) and was considered nonfunctional in females. In this study, we identified a female-specific truncated Fru protein (FruF) that is specifically expressed during the pupal stage and distributed in both cell bodies and neuronal projections, in contrast to FruM, which is expressed throughout development and adulthood and localized to nuclei. We discovered that FruF cooperates with another sex determination gene, doublesex (dsx), to prevent courtship behavior in females. Knocking down fruF in dsx-expressing pC1 neurons induces courtship in females. These results reveal that the master gene for male courtship prevents this behavior in females via a truncated protein, thereby refining the canonical sex determination hierarchy that controls sexual development and behaviors.