The Effects of Ectopic White and Transformer Expression on Drosophila Courtship Behavior

The sex determining genes of Drosophila males and females function to establish the potential for sex-specific behaviors. Previous studies suggest that ectopic GAL4-directed misexpression of the female-specific isoform of the sex-determining gene transformer (tra) in specific sub-domains of an otherwise male brain can lead to bisexual courtship behavior, thus identifying brain domains that may mediate sex-specific behavior. However, expression of mini-white, the marker gene used in both P{GAL4} and P{UAS_G} constructs, also induces males to court other males, questioning whether GAL4-mediated tra expression alone can induce bisexual behavior. Here we demonstrate the consequences of inducing mutations in the mini-white genes within P{GAL4} and P{UAS_G} constructs to generate flies in which a white mutant phenotype is revealed. In these mini-white mutant strains, P{GAL4}-mediated transformer expression alone is both sufficient and necessary to generate bisexual behavior. In addition, using RT-PCR, we reveal the presence of female transcripts of doublesex and fruitless in the brains of otherwise male (XY) flies exhibiting P{GAL4}-directed tra-expression, demonstrating that P{GAL4}-directed tra is functional at the molecular level. We conclude that P{GAL4}-directed misexpression of tra is responsible for the bisexual behavior previously described and that this is mediated via sex-specific splicing of dsx and fru. Our results support the validity of such strategies for identifying regions of the fly brain that underlie sex-specific behaviors.