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S. C. Khani, J. E. Young, E. Kasperek; Diurnal and Light-Dependent Control of Rhodopsin Kinase (GRK1) Expression in Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3771.
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Rhodopsin kinase (GRK1) is a photoreceptor-specific G protein-dependent receptor kinase with key roles in recovery of light exposed photoreceptors. Prolonged activation and increased retinal susceptibility to light-induced damage result from GRK1 deficiency. The study examines how light and circadian clock affect the GRK1 expression levels in pigmented mouse eyes.
Protein and RNA were isolated from C57BL6 mouse eyes at various timepoints after adaptation in absolute dark or cyclic light/dark environment. Immunostaining, western blots and real-time RT-PCR were used to examine the levels of expression among the samples. Intense but nondamaging light was used in some experiments comparing light exposed and dark adapted gene expression levels.
In cyclic light/dark environment, the GRK1 protein and transcript levels fluctuated with peak/trough ration of up to 4:1 over a 24 hour period with the lowest levels in the late afternoon. Dark adaptation for16 days blunted the oscillation with a peak/trough ratio to less than 2 folds. Exposure to intense light also reduced the levels of rhodopsin kinase protein independent of circadian changes.
Oscillations in GRK1 transcription and expression patterns appear to be most pronounced in cyclic light dark as compared to absolute dark over the 24 hour day with peak in the early morning and trough in late afternoon. The observed pattern appears to parallel the patterns of several other phototransduction related gene products including opsin and but oppose that seen with arrestin. Both transcriptional and posttranscriptional controls involving the modulation of protein or RNA stability are also likely to play a role in determining the GRK1 levels in response to light.
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