Regulation of Rhodopsin Kinase Promoter; the Effect of Development and Light

Abstract

Abstract: : Rhodopsin kinase is a G protein dependent receptor kinase which mediates a crucial step in photoreceptor light adaptation pathway by phosphorylating the light–activated opsin species. Absence of this enzyme increases susceptibility of photoreceptors to light–induced damage. The factors and sequences regulating the transcription and expression of this important enzyme could ultimately play a key role in the maintenance of function and integrity of photoreceptors. Purpose: to determine how rhodopsin kinase levels change during retinal development or with exposure to light stress and whether such changes may be governed at the transcriptional level. Methods: The expression of endogenous Rk and green fluorescent protein (GFP) was examined in C57BL/6–based transgenic mouse line carrying a 0.11–kb fragment of the human Rk genomic sequence upstream of GFP during development and shortly after exposure to intense light. Double–label immunostaining and quantitative RT–PCR was used to compare the pattern and levels of expression and transcription of the endogenous and the reporter GFP. Results: There was a parallel rise in the Rk and GFP gene expression largely during the postnatal period within the first 3 weeks of life particularly prominent after eye openning. The light stressed eyes appeared to have a different distribution and level of GFP and RK expression as compared to the dark–adapted eyes. QRT–PCR analysis of transcript levels suggest modest light induced changes in Rk and GFP. Conclusions: Increase in Rk levels during development coincides largely with the terminal differentiation of photoreceptors and eye openning. The parallel increase in the GFP in transgenic mice suggests that the increase is likely transcriptionally based and governed by sequences immediately upstream of the Rk gene. The distribution of Rk and GFP appears to be affected in parallel in response to light suggesting a complex mechanism of regulation involving at least in part transcriptional control.

Keywords: retinal development • brightness and lightness • gene/expression