Season-dependent differential effect of temperature on diurnal rhythm of expression of core clock genes in the pineal organ of an air-breathing catfish, Clarias gariepinus

Abstract

ABSTRACTAll core clock genes (clock, bmal1, per1, per2, per3, cry1, and cry2) are expressed in the fish pineal organ and regulate melatonin rhythm. But there is practically no information on effect of temperature on clock genes. Therefore, we studied effects of three temperatures (15°, 25°, and 35°C; common photoperiod 12L–12D) on the diurnal rhythm of expression of core clock genes (clock, bmal1, per1, per2, per3, cry1, and cry2) in the pineal organ of an air-breathing catfish, Clarias gariepinus during summer and winter seasons. All clock genes invariably exhibited prominent diurnal rhythm of expression in the pineal organ of the fish irrespective of temperatures and seasons. However, mesor and amplitude of the diurnal rhythm of expression of the clock genes responded differently to different temperatures in a season-dependent manner. These findings seem to suggest that the fish pineal organ possesses an indigenous molecular clockwork composed of temperature-sensitive clock genes.