Effect of monochromatic light on circadian rhythmic expression of clock genes and arylalkylamine N-acetyltransferase in chick retina.

Birds have more developed visual function. They not only have the ability to detect light and darkness but also have the color vision. Previous study showed that monochromatic light influenced avian physiological processes, which were controlled by clock genes. Therefore, bird's eye is a good model to studying the impact of color of light on circadian rhythms. Avian retina is one of the most important central oscillations. The study was designed to investigate the effect of color of light on the expression of clock genes and arylalkylamine N-acetyltransferase (Aanat) mRNA expression in chick retina. A total of 240 post-hatching day (P) 0 broiler chickens were exposed to blue (BL), green (GL), red (RL) and white light (WL) from a LED system under a light-dark cycle 12L:12D for 14 d. The results show that the significant daily variations existed in the gene expression of cBmal1, cBmal2, cCry1, cCry2, cPer2 and cPer3, but not for cClock under four light treatments. The genes cBmal1, cCry1, cPer2 and cPer3 presented circadian rhythmic expression under the various monochromatic lights. When compared with WL, GL elevated the expression of positive regulators of cellular clock (cBmal1, cBmal2 and cClock) and cAanat mRNA level, whereas RL increased the mRNA levels of negative regulators of cellular clock (cCry1, cCry2, cPer2 and cPer3) and decreased the cAanat mRNA expression in the retina. These results demonstrated that monochromatic light affect the periodic expression levels of the biological clock mRNA by positive and negative feedback loop interactions, GL activated the transcription of cAanat; while RL suppressed the transcription of cAanat. Thereby, color of light regulates ocular cAanat expression by affecting on expression of cellular clock regulators.