Characterizing a gene expression toolkit for eye- and photoreceptor-specific expression in Drosophila.

Binary expression systems are a powerful tool for tissue- and cell-specific research. Many of the currently available Drosophila eye-specific drivers have not been systematically characterized for their expression level and cell-type specificity in the adult eye or during development. Here, we used a luciferase reporter to measure expression levels of different drivers in the adult Drosophila eye, and characterized the cell type-specificity of each driver using a fluorescent reporter in live 10-day-old adult males. We also further characterized the expression pattern of these drivers in various developmental stages. We compared several Gal4 drivers from the Bloomington Drosophila Stock Center (BDSC) including GMR-Gal4, longGMR-Gal4 and Rh1-Gal4 with newly developed Gal4 and QF2 drivers that are specific to different cell types in the adult eye. In addition, we generated drug-inducible Rh1-GSGal4 lines and compared their induced expression with an available GMR-GSGal4 line. Although both lines had significant induction of gene expression measured by luciferase activity, Rh1-GSGal4 was expressed at levels below the detection of the fluorescent reporter by confocal microscopy, while GMR-GSGal4 showed substantial reporter expression in the absence of drug by microscopy. Overall, our study systematically characterizes and compares a large toolkit of eye- and photoreceptor-specific drivers, while also uncovering some of the limitations of currently available expression systems in the adult eye.