there are four promotors in the fruitless gene (P1-P4). the S exon in the transcript from the P1 promotor is spliced by the sex specific transcription factor Tra (not present in males) creating male and female specific isoforms of the fru transcription factors.
fig1
antibody staining with anti-FruM in control animals
these sexually dimorphic fru isoforms regulate male courtship behaviors