Melatonin bio-synthesizing enzyme genes (Tph1, Aanat1, Aanat2, and Hiomt) and their temporal pattern of expression in brain and gut of a tropical carp in natural environmental conditions

Abstract

The study demonstrates the temporal pattern of expression of melatonin bio-synthesizing enzyme genes (Tph1, Aanat1, Aanat2, and Hiomt) in the brain and gut of a tropical carp (Catla catla) on a daily and seasonal basis under natural photo-thermal conditions. The measurement of melatonin in brain and gut (both in vivo and in vitro) demonstrated a higher content in gut, with evidence of melatonin bio-synthesizing machinery in both tissues. All melatonin bio-synthesizing gene expressions in these two tissues were negatively correlated (except Aanat1 in brain and Hiomt in the gut) with the water temperature on an annual cycle. The higher expression of Aanat2 gene, rather than Aanat1, signifies the importance of Aanat2 isoform in the melatonin production in tropical carp. Furthermore, the Aanat2 and Hiomt genes are highly expressed in the gut. Analysis of the rhythm and acrophase of expression of these genes in the brain and gut imply a pineal-independent melatonin synthesizing machinery in these two organs, possibly involving both environmental and endogenous cues for the regulation of melatonin rhythm to synchronize the physiology of the animal.

Keywords:

• Tph1
• Aanat1
• Aanat2
• Hiomt
• gut
• brain
• melatonin
• tropical carp

Public Interest Statement

This article provides information about the melatonin bio-synthesizing machinery in the brain and gut of a tropical fish. The production of melatonin, an indole amine, is directly linked to the environmental photo-thermal conditions. This study also gives an idea about the variation and/or changes in the rhythmic expression of the melatonin bio-synthesizing genes under natural environmental conditions. Moreover, a relationship between the brain (central) and gut (peripheral) has also been focused in respect to the production of melatonin. The present finding is an opening toward the brain–gut axis and its synchronization with respect to melatonin in fish.

Competing Interests

The authors declare no competing interest.

Acknowledgments

Authors are grateful to the Director, IBSD India, We are thankful to Mr L. Umakanta Singh, Mr S. Surjit Singh, Mr W. Rahul, and Mr H. Bishorjit for their continuous support in the collection and maintenance of fish in laboratory conditions. Our sincere thanks to all of our colleagues of Fish Biology and Insect Biology Laboratories for their kind cooperations during the study. Our sincere gratitude to every Indian tax payer for their contribution to the funding for research. The authors are really grateful to three distinguished reviewers for their valuable comments and suggestions. The IBSD, Imphal manuscript number is 2015008.

Additional information

Notes on contributors

Haobijam Sanjita Devi

The research group led by Asamanja Chattoraj is mainly focused on the synchronization of the environmental cues with body physiology in relation to the “chronobiotic” molecule melatonin and clock-associated genes. The abiotic parameters of the nature are changing abruptly; fish are the best model to study the variation and possible reason in the alteration of body physiology. The research interest concerns about the relationship between the central and peripheral clock mechanisms and their orientation either through “master-slave” or “orchestra”. The findings can lead to develop a sustainable strategy for the maintenance of the species population in a favorable niche as well as tools for their conservation. Moreover, several lifestyle diseases are emerging from the circadian rhythm disruption. We are trying to address this inappropriate harmonization between environmental cues and body functioning with special emphasis on clock-associated genes and “melatonin” using fish as model.