Deciphering the Genes for Taste Receptors for Fructose in Drosophila

Taste sensitivity to sugars plays an essential role in the initiation of feeding behavior. In Drosophila melanogaster, recent studies have identified several gustatory receptor (Gr) genes required for sensing sweet compounds. However, it is as yet undetermined how these GRs function as taste receptors tuned to a wide range of sugars. Among sugars, fructose has been suggested to be detected by a distinct receptor from other sugars. While GR43A has been reported to sense fructose in the brain, it is not expressed in labellar gustatory receptor neurons that show taste response to fructose. In contrast, the Gr64a-Gr64f gene cluster was recently shown to be associated with fructose sensitivity. Here we sought to decipher the genes required for fructose response among Gr64a-Gr64f genes. Unexpectedly, the qPCR analyses for these genes show that labellar expression levels of Gr64d and Gr64e are higher in fructose low-sensitivity flies than in high-sensitivity flies. Moreover, gustatory nerve responses to fructose in labellar sensilla are higher in Gr64d and Gr64f mutant lines than in mutant flies of the other Gr64a-Gr64f genes. These data suggest the possibility that deletion of GR64D or GR64F may indirectly induce enhanced fructose sensitivity in the labellum. Finally, we conclude that response to fructose cannot be explained by a single one of the Gr64a-Gr64f genes.

Experimental infections of feline reovirus serotype 2 isolates

Pathogenicity of feline reovirus serotype 2 isolates, Nos. 114 and 140 strains recovered from the feces of cats with diarrhea, was experimentally determined. Kittens orally inoculated with No. 114 strain did not show any clinical signs. Fecal consistency of kittens inoculated with No. 140 strain became rather diarrheic on the 3rd and 4th days after inoculation, but any other clinical abnormalities were not observed. Virus was excreted for the first five to six days after inoculation. Seroconversion was observed in the sera of all the inoculated kittens. Virus excretion and seroconversion were also noted in all contact control kittens. These results may indicate that feline reovirus serotype 2 is mildly pathogenic in cats.