title: Regulation of arrestin translocation by Ca2+ and myosin III in Drosophila photoreceptors.
abstract: Upon illumination several phototransduction proteins translocate between cell body and photosensory compartments. In Drosophila photoreceptors arrestin (Arr2) translocates from cell body to the microvillar rhabdomere down a diffusion gradient created by binding of Arr2 to photo-isomerized metarhodopsin. Translocation is profoundly slowed in mutants of key phototransduction proteins including phospholipase C (PLC) and the Ca(2+)-permeable transient receptor potential channel (TRP), but how the phototransduction cascade accelerates Arr2 translocation is unknown. Using real-time fluorescent imaging of Arr2-green fluorescent protein translocation in dissociated ommatidia, we show that translocation is profoundly slowed in Ca(2+)-free solutions. Conversely, in a blind PLC mutant with ∼100-fold slower translocation, rapid translocation was rescued by the Ca(2+) ionophore, ionomycin. In mutants lacking NINAC (calmodulin [CaM] binding myosin III) in the cell body, translocation remained rapid even in Ca(2+)-free solutions. Immunolabeling revealed that Arr2 in the cell body colocalized with NINAC in the dark. In intact eyes, the impaired translocation found in trp mutants was rescued in ninaC;trp double mutants. Nevertheless, translocation following prolonged dark adaptation was significantly slower in ninaC mutants, than in wild type: a difference that was reflected in the slow decay of the electroretinogram. The results suggest that cytosolic NINAC is a Ca(2+)-dependent binding target for Arr2, which protects Arr2 from immobilization by a second potential sink that sequesters and releases arrestin on a much slower timescale. We propose that rapid Ca(2+)/CaM-dependent release of Arr2 from NINAC upon Ca(2+) influx accounts for the acceleration of translocation by phototransduction.
authors: Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge CB2 3EG, United Kingdom. rch14@cam.ac.uk
authors: Roger C
authors: RC
authors: Hardie
authors: Akiko K
authors: AK
authors: Satoh
authors: Che-Hsiung
authors: CH
authors: Liu
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D019390:Arrestins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000502:physiology; D029721:Drosophila Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D005136:Eye Proteins / Q000235:genetics; D005260:Female; D008297:Male; D018995:Myosin Heavy Chains / Q000172:deficiency* / Q000235:genetics; D025102:Myosin Type III / Q000235:genetics / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology*
chemical_list: C504666:Arr2 protein, Drosophila; D019390:Arrestins; D029721:Drosophila Proteins; D005136:Eye Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D025102:Myosin Type III; C072308:ninaC protein, Drosophila; D018995:Myosin Heavy Chains; D002118:Calcium