Gqα protein function in vivo: Genetic dissection of its role in photoreceptor cell physiology

Abstract 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 (PLCβ) effector. PLCβ has been shown to be activated by G qα in reconstituted systems. To determine whether a G q -like protein couples rhodopsin to PLC, and to study its function, we isolated a mutant defective in a photoreceptor-specific G q protein, DG q . We now demonstrate that G q is essential for the activation of the phototransduction cascade in vivo. We also generated transgenic flies expressing DG q under an inducible promoter and show that it is possible to manipulate the sensitivity of a photoreceptor cell by controlled expression of DG q . Characterization of quantum bumps in mutants expressing less that 1% of the levels of DG q 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 G q in regulating the output of a photoreceptor cell.