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Regulation of Egr-1, VIP, and Shh mRNA and Egr-1 protein in the mouse retina by light and image quality.

PURPOSE
To analyze mRNA expression changes of Egr-1, VIP, and Shh under different light and treatment conditions in mice. The mRNA expression levels of the three genes and additionally the Egr-1 protein expression were compared in form deprived eyes and eyes with normal vision. Moreover, the influence of dark to light and light to dark transitions and of changes in retinal illumination on mRNA levels was investigated.


METHODS
Form deprivation of mice was induced by fitting frosted diffusers over one eye and an attentuation matched neutral density (ND) filter over the other eye. To measure the effects of retinal illumination changes on mRNA expression, animals were bilaterally fitted with different ND filters. Semiquantitative real-time RT-PCR was used to measure the mRNA levels and immunohistochemistry was applied to localize and detect Egr-1 protein.


RESULTS
The expression levels of both Egr-1 mRNA and protein were reduced in form deprived eyes compared to their fellow eyes after 30 min and 1 h, respectively. Egr-1 mRNA was strikingly upregulated both after dark to light and light to dark transitions, whereas minor changes in retinal illumination by covering the eyes with neutral density filters did not alter Egr-1 mRNA expression. In mice, the mRNA levels of VIP and Shh were not affected by form deprivation, but they were found to be regulated depending on the time of day.


CONCLUSIONS
Both Egr-1 mRNA and protein expression levels were strongly regulated by light, especially by transitions between light and darkness. Image contrast may exert an additional influence on mRNA and protein expression of Egr-1, particularly in the cells in the ganglion cell layer and in bipolar cells.