Robust circadian and circannual rhythms of expression of clock genes and clock controlled aanat2 gene in the photoreceptive pineal organ of catfish, Clarias gariepinus under natural conditions

• Published in: Biological rhythm research Vol. 53; no. 8; pp. 1174 - 1190
• Main Authors: Saha, Saurav, Singh, Kshetrimayum Manisana, Gupta, Braj B. P.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 03.08.2022; Taylor & Francis Ltd
• Subjects: aanat2 gene; BMAL1 protein; Breeding; breeding cycle; Circadian rhythm; Circadian rhythms; Circannual rhythms; Clarias gariepinus; clock genes; Cryptochromes; Daylength; Environmental conditions; Genes; Period 1 protein; Period 2 protein; Period 3 protein; Pineal gland; pineal organ; temperature
• ISSN: 0929-1016; 1744-4179
• DOI: 10.1080/09291016.2021.1911550

Diurnal changes in daylength and temperature influence circadian rhythm of melatonin synthesis in the fish pineal organ. All core clock genes and clock-controlled aanat2 gene are expressed in the pineal organ of teleosts. However, there is paucity of information on the circadian rhythm of expression of clock genes and any clock-controlled gene in the pineal organ of any tropical/subtropical fish species under natural photoperiod and temperature during different phases of the annual breeding cycle and/or seasons. Therefore, we studied circadian rhythms of expression of clock genes (clock, bmal1, per1, per2, per3, cry1 and cry2) and aanat2 in the pineal organ of the catfish, Clarias gariepinus maintained under natural environmental conditions during different phases of its annual breeding cycle. All clock genes and aanat2 gene invariably exhibited prominent circadian rhythm of expression in the fish pineal organ irrespective of seasons/breeding phases. Further, acrophase, mesor and amplitude of the circadian rhythm of expression of the clock genes and aanat2 gene responded differently to different seasons. Our findings suggest that photoperiod-, temperature- and season-independent circadian rhythm of expression of clock genes and aanat2 gene in the pineal organ enable it to act as a potential master clock in the fish under natural conditions.