Exitron splicing of odor receptor genes in Drosophila

We discovered exitrons (exonic introns) in four Odorant receptor (Or) genes of Drosophila. Exitrons are sequences that can be spliced from within a protein-coding exon, thereby altering the encoded protein. We are unaware of previous reports of exitrons in Drosophila. Removal of the exitron from the pheromone receptor gene Or88a creates a non-coding transcript. The exitron has been conserved for 20 million years. Activation of Or88a-expressing olfactory receptor neurons via either optogenetics or pheromone stimulation increased the level of these non-coding transcripts, suggesting that exitron splicing could act in neuronal modulation. Furthermore, our investigation unveiled the presence of alternative polyadenylation in four Drosophila Ors. This study reveals a previously unrecognized layer of complexity in the regulation of Or gene expression.