Ectopic expression of ultraviolet-rhodopsins in the blue photoreceptor cells of Drosophila: visual physiology and photochemistry of transgenic animals.

We have generated transgenic flies expressing R7 cell-specific opsins in the major class of photoreceptor cells of the Drosophila retina and characterized their spectral properties using high-resolution microspectrophotometry and sensitivity recordings. We show that the Rh3 and Rh4 opsin genes encode UV-sensitive opsins with similar spectral properties (lambda max = 345 nm and 375 nm), and that Rh3 corresponds to the R7p and R7marg class of visual pigments. We have also generated Rh3 and Rh4 isoform-specific antibodies and present an R7 cell map of the Drosophila retina. In a related set of experiments, we show that it is possible to coexpress two different visual pigments functionally in the same cell and produce photoreceptors that display the summed spectral response of the individual pigments. These findings open up the possibility of tuning an animal's visual behavior by targeted expression of combinations of opsin genes to selective types of photoreceptors.