Diurnal Variation of Melatonin Receptors in Danio rerio (Zebrafish)
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The circadian system provides an integrating mechanism for synchronization of biological processes with the regular 24-hour light and dark changes in the environment. In some teleost species, ocular melatonin levels exhibit a circadian periodicity with elevated levels during the dark as compared to light, thereby regulating the circadian rhythms of several biological functions, such as the diurnal suite of events that help the retina anticipate changes in ambient light. To gain a better understanding of the diurnal variation in gene expression, I analyzed the changes in gene expression in the eye of zebrafish. Dual color oligonucleotide microarrays were used to compare total RNA harvested from eyes of adult zebrafish at midday and midnight. Statistical analyses identified 44 genes which showed significant, 2-fold or more change; 26 genes showed decreased expression at midnight (D/L ≤ 0.5) and 18 genes showed increased expression at midnight (D/L ≥ 2). Seven genes were further analyzed using qPCR. The results of qPCR identified AANAT, Mel1a1, Mel1a3, Mel1b1, Mel1b2 and Melc as genes that showed significant change in expression at dawn, dusk, midday and midnight. These results suggest that expression of melatonin receptors is subject to diurnal regulation.