DOI: 10.3724/SP.J.1118.2019.18262

Journal of Fishery Sciences of China (中国水产科学) 2019/26:3 PP.445-456

Molecular cloning, characterization, and expression analysis of Megalobrama amblycephala melanocortin receptor 3 during fasting

The melanocortin system consists of melanocortin peptides derived from the proopiomelanocortin gene, five melanocortin receptors, two endogenous antagonists, and two ancillary proteins. It plays a role in many important physiological functions of terrestrial animals. Studies on rodents have affirmed the role of melanocortin receptor 3 (mc3r) in feeding behavior and energy regulation. However, the function of mc3r in fish, including basic information, is not well understood. Thus, to determine the initial value of fish mc3r and assess the role of MC3R in fish feeding behavior and energy regulation, the full-length cDNA of Megalobrama amblycephala mc3r was cloned. The nucleotide sequence and deduced amino acid sequence were analyzed using bioinformatics methods. Blood glucose and cortisol levels were detected, and real-time quantitative PCR was employed to characterize the tissue expression profile and expression during fasting and refeeding. The results showed that M. amblycephala mc3r cDNA encodes a protein of 327 amino acids, which shares a high amino acid sequence identity with that of other animals and is characteristic with the typical seven transmembrane domain. Phylogenetic analyses showed that the mc3r cluster was within the MC3R clade of the Cyprinidae MC3Rs. The tissue expression analysis revealed that M. amblycephala mc3r was highly expressed in the hypothalamus, pituitary, liver, and ovary, whereas its expression was much lower in the other detected tissues. During fasting and refeeding, mc3r mRNA expression in the hypothalamus and pituitary showed a periodic variation with higher expression near the first feeding time every day both in the experimental and control groups. Furthermore, the expression of mc3r mRNA was significantly increased and was higher than that in the control group after 72 h and 14 d fasting in the hypothalamus (P < 0.05), whereas similar results occurred in the pituitary at 72 h fasting and 6 h after refeeding (P < 0.05), and in the liver at 48 h and 14 d after fasting (P < 0.05). In addition, an obvious change in blood glucose and cortisol was only observed with long term fasting (P < 0.05). The M. amblycephala mc3r is not only highly conservative in genetic information, but also in its tissue expression profile and physiological function during the evolutionary process, and may play an important role in feeding behavior and energy regulation.

Key words:Megalobrama amblycephala; melanocortin receptor 3; gene cloning; tissue distribution; fasting

ReleaseDate:2019-07-04 08:50:30

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