Fig. 2.

The Drosophila GAL4-UAS system for targeted gene expression. The GAL4-UAS system can be used for targeted expression of GPCRs within the Drosophila photoreceptor cells (PRCs). To obtain flies expressing a gene of interest in a tissue specific pattern, two Drosophila strains are mated together in the parental cross. The driver strain expresses the yeast GAL4 protein from a tissue-specific enhancer/promoter. The UAS strain contains the gene of interest cloned downstream of the GAL4 Upstream Activating Sequence (UAS). The resulting F1 offspring will express GAL4 protein in a tissue-restricted pattern which will bind to the UAS sequences upstream of the gene of interest to drive its expression in those specific cells. By using a driver strain that expresses GAL4 specifically within the fly eye, heterologous GPCR expression can be restricted to the PRCs.