Male-specific isoforms of Drosophila <i>fruitless</i> have different transcriptional regulatory roles conferred by their distinct DNA binding domains.

Male-specific isoforms of Drosophila fruitless have different transcriptional regulatory roles conferred by their distinct DNA binding domains. Michelle Arbeitman¹, Justin Dalton¹, Justin Fear², Simon Knott⁴, Bruce Baker³, Lauren McIntyre². 1) College of Medicine, Biomedical Sciences, Florida State Univ, Tallahassee, FL; 2) Genetics Institute, University of Florida, Gainesville, FL 32610-3610; 3) Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA, 20147; 4) Cold Spring Harbor Laboratory, One Bungtown Road Cold Spring Harbor, NY 11724.

fruitless (fru), a gene in the sex hierarchy that is crucial for male courtship, encodes multiple male-specific isoforms (Fru^M) that vary in their DNA binding domains. We have examined the distinct roles of three Fru^M isoforms, by individually overexpressing each isoform in fru-expressing neurons and assaying gene expression in males and females. We find that each isoform has different regulatory activities. We identify many genes regulated downstream of Fru^M isoforms, including those with known neuronal functions. Examination of the genes induced by over-expression of Fru^M demonstrates that Fru^M functions differently in male fru P1-expressing neurons as compared to females, suggesting that Fru^M function is dependent on the sex of the cell it is produced within. In addition, expression analysis on RNA derived from Fru^M mutant males showed that many of the genes differentially expressed in the Fru^M over-expression experiment are identified in the more physiologically relevant loss-of-function experiment. Furthermore, we demonstrate that each Fru^M isoform has a different DNA binding specificity, by determining the binding sites using SELEX. Genome wide analysis of these binding sites finds a significant enrichment of binding sites within and proximal to genes that are induced, but not repressed by Fru^M-overexpression. Chromosomal distribution of genes regulated by Fru^M showed that those that are induced and repressed as a consequence of Fru^M over-expression are highly enriched and depleted, respectively, on the X chromosome in males, but not in females when Fru^M is over-expressed. These results suggest that the X chromosome in males may have unique properties with respect to gene expression downstream of Fru^M.