Molecular genetic dissection of Drosophila phototransduction pathway

We use molecular genetic approach to dissect the Drosophila phototransduction pathway, one of the best studied among the receptor-based, G-protein coupled, IP3-Ca2+ mediated signal transduction pathways. It starts with the photoisomerization of rhodopsin activating a G protein, which in turn activates Phospholipase C to hydrolyze phosphatidylinositol 4,5-bisphosphate to IP3 and DAG. Through Trp, a store-operated Ca2+ channel (SOC) as well as other molecules and mechanisms yet to be identified, intracellular Ca2+ is elevated and photoreceptor cell depolarization occurs. Reported here is the study of two mutants, P69 and inaF, which represent two defective genes encoding two presumptive components of the late steps of phototransduction. The electroretinogram (ERG) of the P69 mutant shows a defective fast transient response and reduced sensitivity to light stimulus. The double mutant P69;;trp shows no light-induced photoreceptor response and a severe light-dependent retinal degeneration. The results revealed a novel non-trp branch of phototransduction in which the P69 protein is a likely component. The inaF mutant was generated from a P-element mediated mutagenesis and shows a defective steady-state response in ERG. The mutation was mapped cytogenetically, and the inaF gene was cloned and found to encode a novel protein. Electrophysiology study indicated that InaF may regulate the function of Trp, a store-operated Ca2+ channel