| To identify novel proteins that contribute to phototransduction and retinal degeneration, we conducted a comprehensive screen for genes expressed predominately in the Drosophila visual system, using DNA microarrays. This screen appeared to be comprehensive as it led to the identification of all 22 known eye-enriched genes, which have been previously shown to function in phototransduction or implicated in retinal degeneration. In addition, 88 additional eye-enriched genes were identified whose roles in the retina have not been previously defined. These include genes encoding proteins predicted to function in redox control, a variety of post-translational modifications, protein degradation, transport of small molecules, lipid modifications, synaptic transmission and novel aspects of signaling. Many of these proteins fell into similar classes recently identified in a screen for cDNAs expressed in mammalian rods. The complete set of eye-enriched genes provides a collection of candidates that are likely to function in phototransduction or to be required to prevent retinal degeneration.; Down-regulation of G-protein coupled receptors occurs through internalization of the proteins, followed by degradation in lysosomes or recycling to the plasma membrane. Drosophila phototransduction has provided a model to study the regulation of G-protein coupled signaling, as well as the retinal degeneration that results from defects in signaling. In chapter 3, I describe our findings that one eye-enriched gene encoded a tetraspanin, Sunglasses (Sun), which was required to prevent light-induced retinal degeneration. In contrast to wild-type flies, which displayed significant down-regulation of rhodopsin protein levels upon exposure to constant bright light, the light-dependent degradation of rhodopsin was largely suppressed in the sun mutant. Sun was highly enriched in lysosomes and elimination of this protein greatly reduced the concentration of rhodopsin in lysosomes, in response to bright light. We propose that Sun represents a new type of lysosomal associated membrane protein, which participates in the down-regulation of the G-protein coupled receptor, rhodopsin.; TRP cation channels function in a variety of sensory modalities ranging from vision to osmosensation. In Drosophila, TRP channels are required for vision, hearing, mechanosensation and thermosensation. In chapter 4, I summarize our findings that a member of the most recently defined TRP subfamily, TRPA, is detected exclusively in gustatory and olfactory organs. I generated a mutation in this gene, trpA2, and found that the flies exhibited profound behavioral defects in taste and smell. In addition, action potentials induced by gustatory and olfactory stimuli were greatly reduced. Expression of TRPA2 in vitro promoted cation influx, indicating that TRPA2 is a functional cation channel. The demonstration that TRPA2 functions in both taste and smell underscores the common evolutionary relationship of these two sensory modalities. Moreover, the dramatic behavioral responses resulting from mutation of trpA2, combined with the observation that there are close homologs in insect pests, raise the possibility that TRPA2 may be a rationale target for the development of a new types of insect repellents. |
