Drosophila sweet taste receptor *

Like the Sac locus controlling sugar sensitivity in mice, the taste gene Tre of the fruitfly Drosophila was discovered in wild populations as a genetic dimorphism controlling gustatory sensitivity to a sugar trehalose. By activating a P-element transposon near the gene locus we obtained induced Tre mutations and analyzed the associated changes in gene organizations and the mRNA expressions. The analysis showed that Tre is identical to Gr5a, a gene that belongs to a novel seven-transmembrane receptor family expressed in chemosensory neurons and predicted to encode chemosensory receptors. Thus, Gr5a is a candidate sweet taste receptor in the fly. An amino acid substitution in the second intracellular loop domain was identified to be functionally correlated with the genetic dimorphism of Tre. Since Tre controls sweet taste sensitivity to a limited subset of sugars, other Gr genes phylogenetically related to Tre may also encode sweet taste receptors. Those candidate sweet taste receptors, however, are phylogenetically distinct from vertebrate sweet taste receptors, suggesting that the sweet taste receptors in animals do not share a common origin.