PHOSPHOLIPASE-C RESCUES VISUAL DEFECT IN NORPA MUTANT OF DROSOPHILA-MELANOGASTER

Mutations in the norpA gene of Drosophila melanogaster severely affect the light evoked photoreceptor potential with strong mutations render ing the fly blind. The norpA gene has been proposed to encode phosphat idylinositol-specific phospholipase C (PLC), which enzymes play a pivo tal role in one of the largest classes of signaling pathways known. A chimeric norpA minigene was constructed by placing the norpA cDNA behi nd an R1-6 photoreceptor cell-specific rhodopsin promoter. This minige ne was transferred into norpA(P24) mutant by P-element-mediated germli ne transformation to determine whether it could rescue the phototransd uction defect concomitant with restoring PLC activity. Western blots o f head homogenates stained with norpA antiserum show that norpA protei n is restored in heads of transformed mutants. Moreover, transformants exhibit a large amount of measurable PLC activity in heads, whereas h eads of norpA(P24) mutant exhibit very little to none. Immunohistochem ical staining of tissue sections using norpA antiserum confirm that ex pression of norpA protein in transformants localizes in the retina, mo re specifically in rhabdomeres of R1-6 photoreceptor cells, but not R7 or R8 photoreceptor cells. Furthermore, electrophysiological analyses reveal that transformants exhibit a restoration of Light-evoked photo receptor responses in R1-6 photoreceptor cells, but not in R7 or RS ph otoreceptor cells. This is the strongest evidence thus far supporting the hypothesis that the norpA gene encodes phospholipase C that is uti lized in phototransduction.