Circadian rhythm of expression of core clock genes in the photosensitive pineal organ of catfish, Clarias gariepinus under different photoperiodic regimes

Abstract

ABSTRACT Effects of different regimes of photoperiod (12L–12D, 16L–8D, 8L–16D, LL and DD) were studied on the circadian rhythm of expression of core clock genes (clock, bmal1, per1, per2, per3, cry1 and cry2) in the photosensitive pineal organ of air-breathing catfish, Clarias gariepinus during summer and winter seasons under both in vivo and in vitro conditions using qPCR. Our findings indicate that all major core clock genes are expressed in the photosensitive pineal organ of C. gariepinus, and exhibit significant circadian rhythm of their expression under both in vivo and in vitro conditions irrespective of photoperiods and seasons. However, photoperiods had season-dependent differential effects on mesor (24 h average), amplitude, and acrophase (peak) of the circadian rhythm of expression of the clock genes under both in vivo and in vitro conditions. Based on these findings, we suggest that the photosensitive pineal organ of the fish possesses internal autonomous clockwork composed of clock genes, and different photoperiods deferentially affect rhythm parameters of the rhythmic expression of the pineal clock genes in a season-dependent manner.