Functional Characterization of Melanocortin-3 Receptor in a Hibernating Cavefish Onychostoma macrolepis.

Lian Wu,Chuanying Pan,Huixia Yu,Xianyong Lan,Haolin Mo,Haiyu Zhao,Jishu Zhou,Yang Li,Lixin Wang

doi:10.3390/ani12010038

Abstract

Simple SummaryIn this study we isolated and characterized a gene called omMc3r from a hibernating cavefish Onychostoma macrolepis. This gene was confirmed by our study to be involved in the regulation of signal pathways related to energy balance and food efficiency. These results can provide clues for exploring the adaptive mechanisms of fish, especially cavefish, with respect to nutrient-poor conditions.Melanocortin-3 receptor (MC3R) plays an important role in the energy homeostasis of animals under different nutritional conditions. Onychostoma macrolepis is a hibernating cavefish found in the northern part of the Yangtze River, and its adaptation to a nutrient-poor environment has attracted growing interest. In this study, we characterized the protein structure of Onychostoma macrolepis Mc3r (omMc3r), examined its tissue distribution, and investigated its function in mediating cellular signaling. We showed that the CDS of omMc3r is 978 bp, encoding a putative protein of 325 amino acids. Homology and phylogenetic analyses indicated that omMc3r is evolutionary close to cyprinids. Real-time quantitative PCR (RT-qPCR) revealed that omMc3r was highly expressed in the liver and brain. The functions of omMc3r to mediate ligands activating downstream signaling have also been confirmed by using signal pathway-specific reporters. The four agonists α-MSH, β-MSH, NDP-MSH, and ACTH (1–24) can all activate the cAMP and MAPK/ERK signaling pathway, albeit with different potency orders. The “primitive” ligand ACTH (1–24) had the highest potency on the cAMP signaling pathway, while the synthetic ligand NDP-MSH had the highest activation effect on the MAPK/ERK signaling pathway. This research will lay the foundation for studying the energy regulation mechanism of cavefish in an oligotrophic environment.

Highlights

G protein-coupled receptors (GPCRs) are seven-transmembrane domains (7TMDS), proteins that triggers intracellular signals by coupling with G proteins and arrestins to transmit a large number of extracellular signals
Melanocortin receptors (MCRs) belong to the class A subfamily of G protein-coupled receptors (GPCRs), which has been proved to exist in five members (MC1R-MC5R) in mammals and play versatile roles in physiological processes [1]
The obtained Onychostoma macrolepis Mc3r (omMc3r) (NCBI accession number: MW884251) contains a 978 bp open reading a putative of protein of 325 amino acids (Figure 1)

Summary

Introduction

G protein-coupled receptors (GPCRs) are seven-transmembrane domains (7TMDS), proteins that triggers intracellular signals by coupling with G proteins and arrestins to transmit a large number of extracellular signals. Melanocortin receptors (MCRs) belong to the class A subfamily of G protein-coupled receptors (GPCRs), which has been proved to exist in five members (MC1R-MC5R) in mammals and play versatile roles in physiological processes [1]. These five receptors are similar in structure, their tissue distributions and respective cellular functions are quite different. MC3R and MC4R are mainly expressed in the hypothalamus and are involved in maintaining energy homeostasis [6,7] The latter two have similar physiological functions; for example, the knockout or loss-of-function mutations of MC3R or MC4R can cause obesity in mice and humans [8,9]. MC3R regulates energy homeostasis through food efficiency and circadian rhythms [10], while MC4R mainly affects food intake and energy expenditure [11]

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