Gq alpha protein function in vivo: genetic dissection of its role in photoreceptor cell physiology.
Heterotrimeric G proteins mediate a variety of signaling processes by coupling seven-transmembrane receptors to intracellular effector molecules. The Drosophila phototransduction cascade is a G protein-coupled signaling cascade that utilizes a phospholipase C (PLC beta) effector. PLC beta has been shown to be activated by Gq alpha in reconstituted systems. To determine whether a Gq-like protein couples rhodopsin to PLC, and to study its function, we isolated a mutant defective in a photoreceptor-specific Gq protein, DGq. We now demonstrate that Gq is essential for the activation of the phototransduction cascade in vivo. We also generated transgenic flies expressing DGq under an inducible promoter and show that it is possible to manipulate the sensitivity of a photoreceptor cell by controlled expression of DGq. Characterization of quantum bumps in mutants expressing less that 1% of the levels of DGq revealed that the rhodopsin-G protein interaction does not determine the gain of the single photon responses. Together, these results provide significant insight into the role of Gq in regulating the output of a photoreceptor cell.
Scott
K
K
Howard Hughes Medical Institute, Department of Biology, University of California, San Diego, La Jolla 92093-0649, USA.
Becker
A
A
Sun
Y
Y
Hardy
R
R
Zuker
C
C
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D004330:Drosophila / Q000235:genetics*; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D008027:Light; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009154:Mutation; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000737:chemistry; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D016012:Poisson Distribution; D016133:Polymerase Chain Reaction; D012326:RNA Splicing; D012160:Retina / Q000378:metabolism; D012243:Rhodopsin / Q000378:metabolism; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
D046911:Macromolecular Substances; D010446:Peptide Fragments; D012243:Rhodopsin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins