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  • Book
    Jon-Michael Knapp.
    For my graduate work, I have chosen to investigate sex-specific patterning and function of the olfactory system in the fruit fly, Drosophila melanogaster, by addressing three questions: 1) What is the developmental genetic regulation of the sexual dimorphism in numbers of olfactory sensilla? 2) Do olfactory receptor neurons (ORNs) expressing Or47b (Or47b-ORNs) stimulate courtship in males and females? 3) Which genes are regulated by male-specific fruitless isoforms (FRUM) in olfactory and other peripheral sensory neurons? In Drosophila, terminal sexual differentiation is orchestrated by the activity of the transcription factors fruitless (fru) and doublesex (dsx). I have shown that the action of dsx alone is necessary and sufficient to specify sex-appropriate numbers of olfactory sensilla (the peripheral sensory unit). The dsx locus encodes sex-specific isoforms that differentially organize the developing antenna to specify sex-appropriate numbers of different types of olfactory sensilla. The female-specific DSX isoform promotes female-appropriate numbers of basiconic sensilla and depresses the number of trichoid sensilla on the antenna. Male-specific DSX promotes male-appropriate numbers of trichoid sensilla but appears to have little effect on determining numbers of basiconic sensilla. Inferred from the expression pattern of dsx, the DSX proteins do not show significant overlap with olfactory sensilla precursors. These data and other lines of evidence suggest that it is likely that dsx controls numbers of olfactory sensilla cell non-autonomously. One subtype of sexually dimorphic trichoid sensilla is innervated by ORNs that express the receptor Or47b and respond to a pheromone produced by males and females. I asked whether these ORNs promote male courtship and female receptivity. I have shown that Or47b-ORNs may promote courtship in males, but they appear to play no detectable role in stimulating female receptivity. Finally, in an effort to elucidate how sexual dimorphism is built into the developing olfactory system, I have collaborated with David Mellert (a former graduate student) to identify genes that are regulated by male-specific fru isoforms in peripheral sensory neurons of the olfactory and gustatory systems, as well as in mechanosensory neurons of the genitalia. We used laser capture microdissection to collect fru-expressing neurons in the antennae, prothoracic forelegs, and genitalia from fru+ and fru-null males. By comparing the whole-genome expression profiles of these samples, we were able to identify candidate targets of FRUM regulation in these tissues. For the antenna, this yielded a promising list of ~100 candidates that are in the process of being validated. Moreover, we found essentially no overlap in the candidate lists for different tissues, suggesting that FRUM regulates different genes in different tissues.