Arthropods employ a large family of up to 100 putative taste or gustatory receptors (Grs) for the recognition of a wide range of non-volatile chemicals. In Drosophila melanogaster, a small subfamily of eight Gr genes is thought to mediate the detection of sugars, fly’s major nutritional source. However, the specific roles for most sugar Gr genes are not known. In the present study, the authors report the generation of a series of mutant sugar Gr knock-in alleles and several composite sugar Gr mutant strains, including a sugar blind strain, which will facilitate the characterisation of this gene family. Using Ca(2+) imaging experiments, it was demonstrated that most gustatory receptor neurons (GRNs) of sugar blind flies (lacking all eight sugar Gr genes) fail to respond to any sugar tested. Moreover, expression of single sugar Gr genes in most sweet GRNs of sugar-blind flies does not restore sugar responses. However, when pair-wise combinations of sugar Gr genes are introduced to sweet GRNs, responses to select sugars are restored. In addition, the authors examined the cellular phenotype of flies homozygous mutant for the Gr64a gene, a sugar receptor previously reported to be a major contributor for the detection of many sugars. In contrast to these claims, it was found that sweet GRNs of Gr64a homozygous mutant flies show normal responses to most sugars, and only modestly reduced responses to maltose and maltotriose. the authors concluded that based on the findings, the precisely engineered genetic mutations of single Gr genes and construction of a sugar-blind strain provide powerful analytical tools for examining the roles of Drosophila and other insect sugar Gr genes in sweet taste.
Authors: Yavuz A, Jagge C, Slone J, Amrein H. ;Full Source: Fly (Austin). 2015 May 18:0. [Epub ahead of print] ;