title: Ectopic expression of cone-specific G-protein-coupled receptor kinase GRK7 in zebrafish rods leads to lower photosensitivity and altered responses.
abstract: To investigate the roles of G-protein receptor kinases (GRKs) in the light responses of vertebrate photoreceptors, we generated transgenic zebrafish lines, the rods of which express either cone GRK (GRK7) or rod GRK (GRK1) in addition to the endogenous GRK1, and we then measured the electrophysiological characteristics of single-cell responses and the behavioural responses of intact animals. Our study establishes the zebrafish expression system as a convenient platform for the investigation of specific components of the phototransduction cascade. The addition of GRK1 led to minor changes in rod responses. However, exogenous GRK7 in GRK7-tg animals led to lowered rod sensitivity, as occurs in cones, but surprisingly to slower response kinetics. Examination of responses to long series of very dim flashes suggested the possibility that the GRK7-tg rods generated two classes of single-photon response, perhaps corresponding to the interaction of activated rhodopsin with GRK1 (giving a standard response) or with GRK7(giving a very small response). Behavioural measurement of optokinetic responses (OKR) in intact GRK7-tg zebrafish larvae showed that the overall rod visual pathway was less sensitive, in accord with the lowered sensitivity of the rods. These results help provide an understanding for the molecular basis of the electrophysiological differences between cones and rods.
authors.affiliation: Department of Neuroscience, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: F
authors.initials: F
authors.lastname: Vogalis
authors.forename: T
authors.initials: T
authors.lastname: Shiraki
authors.forename: D
authors.initials: D
authors.lastname: Kojima
authors.forename: Y
authors.initials: Y
authors.lastname: Wada
authors.forename: Y
authors.initials: Y
authors.lastname: Nishiwaki
authors.forename: J L P
authors.initials: JL
authors.lastname: Jarvinen
authors.forename: J
authors.initials: J
authors.lastname: Sugiyama
authors.forename: K
authors.initials: K
authors.lastname: Kawakami
authors.forename: I
authors.initials: I
authors.lastname: Masai
authors.forename: S
authors.initials: S
authors.lastname: Kawamura
authors.forename: Y
authors.initials: Y
authors.lastname: Fukada
authors.forename: T D
authors.initials: TD
authors.lastname: Lamb
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D051606:G-Protein-Coupled Receptor Kinase 1 / Q000235:genetics / Q000378:metabolism; D054768:G-Protein-Coupled Receptor Kinases / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D007814:Larva / Q000201:enzymology; D055537:Light Signal Transduction; D008564:Membrane Potentials; D008954:Models, Biological; D010766:Phosphorylation; D010775:Photic Stimulation; D017948:Retinal Rod Photoreceptor Cells / Q000201:enzymology*; D012243:Rhodopsin / Q000378:metabolism; D012684:Sensory Thresholds; D014785:Vision, Ocular; D015027:Zebrafish; D029961:Zebrafish Proteins
chemical_list: D029961:Zebrafish Proteins; D012243:Rhodopsin; D051606:G-Protein-Coupled Receptor Kinase 1; C504360:grk7b protein, zebrafish; D054768:G-Protein-Coupled Receptor Kinases