Gustation in Drosophila melanogaster
In initial experiments to determine the expression of these genes, the expression of 19 Gr genes was examined by reverse transcriptase-polymerase chain reaction (RTPCR) experiments. These experiments showed that 18 of the 19 Grs are found in the adult proboscis labellum but not found in the head minus the proboscis, strongly arguing that Grs are gustatory-specifi c genes (Clyne et al., 2000). The expression patterns of some Gr genes have been determined by transgenic analyses, as transcripts are rare and only seven Gr genes showed detectable expression by in situ hybridisation experiments (Clyne et al., 2000; Dunipace et al., 2001; Scott et al., 2001). Transgenic fl ies in which Gr promoters drive expression of reporters using the Gal4/UAS system (Brand and Perrimon, 1993) have been used to determine receptor expression for 10 different Gr promoters (Chyb et al., 2003; Dunipace et al., 2001; Scott et al., 2001). These studies revealed that Gr genes are expressed exclusively in chemosensory tissues in adult Drosophila. Most are expressed in gustatory neurones, although a few are expressed in olfactory neurones instead, arguing that members of this gene family participate in gustatory and olfactory recognition (Jones et al., 2007; Kwon et al., 2007; Scott et al., 2001). A separate, distantly related family called the Drosophila odorant receptor family encodes most odour receptors (Clyne et al., 1999; Vosshall et al., 1999).