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M.-P. Felder, C. Sandu, D. Hicks; Effect of Lighting Conditions on Daily Expression of Clock Genes and Clock Controlled Genes in Rat Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1670.
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Identification of the clock genes expressed specifically in rat photoreceptors and investigation of their daily expression patterns together with those from photoreceptor-specific clock controlled genes under different lighting conditions, in order to evaluate the existence of a circadian clock in these specialized cells.
To investigate the expression of clock genes and clock controlled genes, two groups of 6 week old Wistar rats were housed under light/dark (LD) 12:12 and constant dark (DD) conditions. Animals were sacrificed every 4 hours during a 24h cycle and photoreceptor layers (97% rods) were isolated from the retinas using a tangential vibratome-based sectioning procedure. Circadian patterns in transcript levels of clock genes Clock, Bmal1, Per1, Per2, Cry1, Cry2, Rev-Erbalpha and Ror-beta and clock controlled genes NAT, AC1, c-Fos, rhodopsin, Nrl, Crx, Crem and recoverin were determined by quantitative real-time PCR. Beta-actin and PDE-6beta were used as reference genes for data normalization.
All tested clock genes are expressed in the photoreceptor layer of rat retina and show statistically significant daily changes in their transcript levels in LD conditions. In DD conditions, Cry2 and Ror-beta continue to show rhythmic expression. Clock controlled genes also show rhythmic expression in LD and similar patterns are retained in DD for NAT, c-Fos and Crem.
Rat photoreceptors contain the core clock genes of a circadian clock. Clock and clock controlled genes display rhythmic expression in LD and only a few of them show rhythmic patterns in constant dark, suggesting that, at the global level of the photoreceptor layer, lighting conditions critically affect the molecular clockwork and its outputs.
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