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Enheng Dong, Jared D. Chrispell, Shoji Osawa, Ellen R. Weiss; Expression Of GRK1 And GRK7 In Zebrafish Cones. Invest. Ophthalmol. Vis. Sci. 2011;52(14):42.
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Two cell types, rods and cones, are responsible for phototransduction in the vertebrate retina. Cones recover more rapidly after exposure to light and adapt to a broader range of light intensities compared to rods. Differences between rods and cones may be attributed partly to differences in the levels and activities of the retina-specific G protein-coupled receptor kinases (GRKs), GRK1 and GRK7. These kinases phosphorylate the opsins and are implicated in the termination of the photoresponse, which affects both recovery and adaptation. While rods express only GRK1, cones express both GRK1 and GRK7 in humans and a number of other vertebrates. In order to evaluate the specific contribution of GRK1 and GRK7 to the cone photoresponse, the ratio of GRK1 to GRK7 expression in cones was determined using zebrafish as an animal model.
Cones were collected from transgenic zebrafish expressing Enhanced Green Fluorescent Protein (EGFP) under the control of the cone transducin promoter by Fluorescence-Activated Cell Sorting (FACS). GRK1 and GRK7 expression levels were determined by quantitative western blotting. Recombinant zebrafish GRK1 and GRK7 expressed in HEK-293 cells were used as molecular standards.
Cones expressing EGFP were successfully isolated from adult zebrafish retinas via FACS. Western analysis of the isolated cones for rhodopsin demonstrated that the contamination of cones with rods is lower than 5%. GRK1 and GRK7 are expressed in cones at approximately equal levels.
These results indicate the presence of significant levels of GRK1 in cones. Therefore, both GRK1 and GRK7 are likely to play important roles in cone cell function. Measuring the ratio of GRK1 and GRK7 provides a foundation for exploring their specific contributions to the light response in cone photoreceptors.
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