Involvement of melanin-concentrating hormone 2 in background color adaptation of barfin flounder Verasper moseri
Introduction
Melanin-concentrating hormone (MCH) was originally identified from the chum salmon, Oncorhynchus keta, as a pituitary peptide that concentrates melanin granules in the melanophores of the skin (Kawauchi et al., 1983). Later studies indicated that teleost MCH is synthesized in the hypothalamus, transported to the nerve terminal in the pituitary neural lobe, and released into the blood (Amano and Takahashi, 2009). MCH has subsequently been identified in the mammalian brain, and shown to act as a neuromodulator regulating feeding behavior, energy homeostasis, stress, reproduction, sensory perception, and neuroendocrine responses (Griffond and Baker, 2002, Nahon, 2006, Saito and Nagasaki, 2008, Sherwood et al., 2012, Wu et al., 2009). The functions of the original teleost MCH (designated as MCH1 in this text) have been well investigated, especially pigment aggregation and cooperation with various pituitary hormones (Kawauchi, 2006). MCH1 has also been implicated in feeding behavior in teleosts, but this function is inconsistent amongst different species. Intracerebroventricular injection studies have suggested that MCH1 has an anorexic function in the goldfish, Carassius auratus (Matsuda et al., 2006, Matsuda et al., 2007); whereas, white background color enhances mch1 expression and feeding behavior in the barfin flounder, Verasper moseri, suggesting a possible orexigenic function in this fish (Sunuma et al., 2009).
Recently, a gene encoding another MCH (termed MCH2 in this text) has been identified as an ortholog of mammalian mch, in teleosts (zebrafish, Danio rerio; medaka, Oryzias latipes; three-spined stickleback, Gastierosteus aculeatus; torafugu, Takifugu rubripes; winter flounder, Pseudopleuronectes americanus; and starry flounder, Platichthys stellatus) (Berman et al., 2009, Tuziak and Volkoff, 2012, Kang and Kim, 2013). Very few studies have been conducted to elucidate the physiological functions of MCH2 as compared to MCH1. In D. rerio, mch2 is expressed in the lateral tuberal nucleus (NLT) within the hypothalamus where mch1 is also expressed (Berman et al., 2009). In D. rerio and P. americanus, the up-regulated expression of mch2 in the hypothalamus is induced by fasting (Berman et al., 2009, Tuziak and Volkoff, 2012), suggesting the possible involvement of mch2 in the regulation of feeding in teleosts. The elevated expression of mch2 upon exposure to white background in D. rerio and P. stellatus suggests that MCH2 acts on background color-adaptation (Berman et al., 2009, Zhang et al., 2010, Kang and Kim, 2013). However, to date the MCH2 peptide has not been identified, and the physiological functions of MCH2 involved in body color changes remain unknown.
V. moseri is an interesting model organism for investigating the molecular mechanisms of MCH systems because the roles of MCH1 in the regulation of skin color changes (Mizusawa et al., 2011) and feeding/growth behavior (Sunuma et al., 2009, Takahashi et al., 2004, Yamanome et al., 2005) have been thoroughly investigated. In addition, two MCH receptors MCH-R1 and MCH-R2 have also been characterized. MCH-R1 is exclusively expressed in the brain, whereas MCH-R2 is expressed in the brain as well as several peripheral tissues including the skin (Takahashi et al., 2007). MCH-R2 is expressed in skin melanophores and xanthophores (but not in other dermal cells) where MCH1 was shown to induce pigment aggregation (Mizusawa et al., 2011). The present study was undertaken to elucidate the properties of MCH2 using V. moseri as to the following five items; (i) molecular cloning of the prepro-MCH2 cDNA, (ii) identification of the MCH2 peptide derived from prepro-MCH2, (iii) characterization of the pigment-aggregation activities of MCH2, (iv) characterization of the pharmacological properties of MCH2, and (v) characterization of the expression levels of MCH2 in response to background color.
Section snippets
Fish
Immature V. moseri were purchased from the Iwate Cultivating Fishery Association (Iwate, Japan), or kindly provided by the Hokkaido National Fisheries Research Institute (Hokkaido, Japan). All experiments were conducted in accordance with the Kitasato University guidelines for the care and use of animals. The photoperiods and water temperatures were maintained at natural conditions. Tissue sampling was performed on fish that were anesthetized by immersion, in 0.05% 2-phenoxyethanol for
Structure of prepro-MCH2
Sequential cloning of PCR- and RACE-amplified cDNA revealed a 635 bp full-length sequence of prepro-MCH2, excluding the poly-A tail. The sequence consists of 150 amino acid (AA) residues, with a signal peptide at AA positions 1–25, and the MCH2 sequence spanning AA positions 126–150 (Fig. 1). The putative MCH2 in V. moseri is composed of 25 AA, similar to the P. americanus MCH2 (Fig. 2). The putative prepro-MCH2 has a higher AA sequence identity with P. americanus prepro-MCH2 (87%), but lower
Discussion
In this study, we demonstrated the existence of the MCH2 peptide for the first time, using V. moseri as a model organism. The presence of MCH2 was first indicated by molecular cloning of the prepro-MCH2 cDNA from a single brain. A multi-species alignment and a phylogenetic analysis of prepro-MCH determined the amino acid sequence as that of prepro-MCH2. Processing of pro-proteins and pro-hormones often occurs at specific single or pairs of basic amino acids in the precursors (Seidah et al., 1998
Conclusion
In the present study, we identified the MCH2 peptide from V. moseri by cDNA cloning and LC–ESI-MS, followed by database searches. Results of in vitro and pharmacological studies revealed that both MCH1 and MCH2 have a pigment-aggregating activity in chromatophores, and this activity is mediated by MCH-R2. Furthermore, the expression of both, MCH1 and MCH2 in the brain increases under bright background conditions. These results suggest that MCH2 might play an important role as much as MCH1 in
Acknowledgments
The authors would like to thank the following people for their cooperation: Tadashi Andoh and Naoto Murakami at Hokkaido National Fisheries Research Institute; Takashi Sunada and Tomoaki Mikawa at Iwate Cultivating Fishery Association; Hoshito Tomizawa and Daisuke Saito at Kitasato University. This study was supported by Grants from the Japan Society for the Promotion of Science – Japan to A.T. (22248023).
References (36)
- et al.
Melanin-concentrating hormone: a neuropeptide hormone affecting the relationship between photic environment and fish with special reference to background color and food intake regulation
Peptides
(2009) - et al.
Structure-activity relationship studies of melanin-concentrating hormone (MCH)-related peptide ligands at SLC-1, the human MCH receptor
J. Biol. Chem.
(2001) - et al.
Cell and molecular cell biology of melanin-concentrating hormone
Int. Rev. Cytol.
(2002) - et al.
Signalling pathway of goldfish melanin-concentrating hormone receptors 1 and 2
Regul. Peptides
(2011) - et al.
Functional characterization of two melanin-concentrating hormone genes in the color camouflage, hypermelanosis, and appetite of starry flounder
Gen. Comp. Endocrinol.
(2013) - et al.
Possible paracrine function of alpha-melanocyte-stimulating hormone and inhibition of its melanin-dispersing activity by N-terminal acetylation in the skin of the barfin flounder, Verasper moseri
Gen. Comp. Endocrinol.
(2009) - et al.
Central administration of melanin-concentrating hormone (MCH) suppresses food intake, but not locomotor activity, in the goldfish, Carassius auratus
Neurosci. Lett.
(2006) - et al.
Molecular cloning and expression of two melanin-concentrating hormone receptors in goldfish
Peptides
(2009) - et al.
Inhibiting roles of melanin-concentrating hormone for skin pigment dispersion in barfin flounder, Verasper moseri
Gen. Comp. Endocrinol.
(2011) The melanocortins and melanin-concentrating hormone in the central regulation of feeding behavior and energy homeostasis
C.R. Biol.
(2006)
Possible involvement of melanin-concentrating hormone in food intake in a teleost fish, barfin flounder
Peptides
The melanin-concentrating hormone receptor 2 (MCH-R2) mediates the effect of MCH to control body color for background adaptation in the barfin flounder
Gen. Comp. Endocrinol.
A preliminary investigation of the role of melanin-concentrating hormone (MCH) and its receptors in appetite regulation of winter flounder (Pseudopleuronectes americanus)
Mol. Cell. Endocrinol.
White background reduces the occurrence of staining, activates melanin-concentrating hormone and promotes somatic growth in barfin flounder
Aquaculture
Characterization of two melanin-concentrating hormone genes in zebrafish reveals evolutionary and physiological links with the mammalian MCH system
J. Comp. Neurol.
Regulation of the hypothalamic melanin-concentrating hormone neurons by sex steroids in the goldfish: possible role in the modulation of luteinizing hormone secretion
Neuroendocrinology
The Melanotropins
Differential melanin-concentrating hormone gene expression in two hypothalamic nuclei of the teleost tilapia in response to environmental changes
J. Neuroendocrinol.
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2021, General and Comparative EndocrinologyCitation Excerpt :The robust similarities in the amino acid sequences of MCH1 and MCH2 suggests that potential interactions with their receptors is shared. Indeed, both of these peptides aggregate melanosomes, as stated above (Mizusawa et al., 2015). Additionally, antiserum against MCH1 can cross-react with MCH2, as suggested by immunostaining of the hypothalamic area in teleosts (Baker and Bird, 2002; Bertolesi and McFarlane, 2020; Diniz and Bittencourt, 2019).
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2020, AquacultureCitation Excerpt :These results were same to that on goldfish (Cerdá-Reverter et al., 2006; Mizusawa et al., 2018). The results of mch gene expression in W and B backgrounds were also comparable to those previously reported (Gröneveld et al., 1995; Suzuki et al., 1995; Takahashi et al., 2004; Mizusawa et al., 2015). However, the MSH levels in the serum of red tilapia were not significantly different between W and B group and peaked in WW group.
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2018, General and Comparative EndocrinologyCitation Excerpt :The mch mRNA levels in the brains were higher in W fish than in B fish. These results are comparable to those previously reported (Cerdá-Reverter et al., 2006; Gröneveld et al., 1995; Suzuki et al., 1995; Takahashi et al., 2004; Mizusawa et al., 2015). In contrast to mch mRNA, the content of pomc-a mRNA in the pituitaries was low and high in W fish and B fish, respectively.
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- 1
Present address: RIKEN Center for Integrative Medical Sciences, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama City, Kanagawa 230-0045, Japan.
- 2
Present address: Fisheries Agency, Ministry of Agriculture, Forestry and Fisheries, 1-2-1 Kasumigaseki, Chiyoda-ku, Tokyo 100-8950, Japan.