Drosophila Gustation A Question of Taste

brates and insects. In Drosophila, olfactory cues are detected by neurons located inside sensory hairs or " sensilla " on the antenna and maxillary palp. A family (Drosophila odorant receptors) have been identified in 5323 Harry Hines Boulevard the fly genome that are thought to mediate odorant As seen in vertebrates, analysis of the axonal projections of Drosophila olfactory neurons When you sit down for a nice meal and take that first expressing the same OR reveals that these neurons con-delicious bite, the sensation you experience results from verge to a single glomerulus in each antennal lobe (the integration of a complex mixture of thermosensation, insect equivalent of the olfactory bulb) (Ressler et al. the sensation of taste is demonstrated by the blandness al., 2000). Therefore, the fly brain can determine if a of food when you have a head cold or by the childhood particular OR has been activated in the peripheral olfac-trick of holding one's nose when eating liver or brussel tory organs by monitoring neuronal activity in the glo-sprouts. Yet vertebrate odor receptors are not ex-merulus innervated by the neurons expressing that OR. pressed in the tongue, and gustatory receptors are not Are similar mechanisms used in insects to convey gusta-expressed in the nose (as far as we know!). What are tory information in the fly? the mechanisms that mediate these complex chemical Little is known about the neuronal mechanisms medi-senses, and are they different because they express ating taste in flies. Tanimura's laboratory in Fukuoka, different receptor families (for volatile verses nonvolatile Japan has identified the only confirmed Drosophila taste ligands) or because the neurons from the two systems receptor, encoded by the tre1 gene (Ishimoto et al., connect to the brain in different ways? In a manuscript 2000). This seven-transmembrane receptor is required published in Cell this month from Richard Axel's group for normal sensitivity to the sugar trehalose. The tre1 (Scott et al., 2001), the spatial expression patterns and receptor is a member of a small gene family consisting axonal targets of Drosophila neurons expressing the of only a few members. This family alone is unlikely to same putative gustatory receptors are examined. They mediate all taste responses. A much larger receptor find members of this family expressed in small subsets family expressed in gustatory neurons but not yet of cells in the gustatory organs, but surprisingly found proven to mediate taste was identified …