title: Molecular cloning, expression, and signaling pathway of four melanin-concentrating hormone receptors from Xenopus tropicalis.
abstract: Melanin-concentrating hormone (MCH) mainly regulates feeding in mammals and pigmentation in teleosts. It acts via two G-protein-coupled receptors, MCH receptor 1 (MCHR1) and MCHR2. Although many studies exploring the MCH system in teleosts and mammals have been carried out, studies on other organisms are limited. In this study, we cloned and characterized four MCHR subtypes from the diploid species Xenopus tropicalis (X-MCHRs; X-MCHR1a, R1b, R2a, and R2b). According to a phylogenetic tree of the X-MCHRs, X-MCHR1a and R2a are close to mammalian MCHRs, while X-MCHR1b and R2b are close to teleostean MCHRs. We previously reported that the G-protein coupling capacity of the MCHR subtypes differed between mammals (R1: Gαi/o and Gαq; R2: Gαq) and teleosts (R1: Gαq; R2: Gαi/o and Gαq) in mammalian cell-based assays. By using Ca(2+) mobilization assays with pertussis toxin in CHO dhfr(-) cells, we found that X-MCHR1a promiscuously coupled to both Gαi/o and Gαq, while X-MCHR1b and R2a exclusively coupled to Gαq. However, no Ca(2+) influx was detected in cells transfected with X-MCHR2b. Reverse transcription-PCR showed that the X-MCHR mRNAs were expressed in various tissues. In particular, both X-MCHR1b and R2b were exclusively found in melanophores of the dorsal skin. In skin pigment migration assays, melanophores were weakly aggregated at low concentrations but dispersed at high concentrations of MCH, suggesting possible interactions between X-MCHR1b and R2b for the regulation of body color. These findings demonstrate that X. tropicalis has four characteristic MCHRs and will be useful for elucidating the nature of MCHR evolution among vertebrates.
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-hiroshima, Hiroshima 739-8521, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-hiroshima, Hiroshima 739-8521, Japan.
authors.forename: Akie
authors.initials: A
authors.lastname: Hamamoto
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-hiroshima, Hiroshima 739-8521, Japan.
authors.forename: Tomo
authors.initials: T
authors.lastname: Hirayama
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-hiroshima, Hiroshima 739-8521, Japan. Electronic address: yumist@hiroshima-u.ac.jp.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Saito
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D003412:Cricetulus; D005786:Gene Expression Regulation; D007028:Hypothalamic Hormones / Q000235:genetics* / Q000378:metabolism; D008543:Melanins / Q000235:genetics* / Q000378:metabolism; D008547:Melanophores / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D010907:Pituitary Hormones / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D011979:Receptors, Pituitary Hormone / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D012867:Skin / Q000378:metabolism; D014981:Xenopus / Q000235:genetics* / Q000254:growth & development
chemical_list: D007028:Hypothalamic Hormones; D008543:Melanins; D010907:Pituitary Hormones; D012333:RNA, Messenger; D011979:Receptors, Pituitary Hormone; C092274:melanin-concentrating hormone receptor; C019463:melanin-concentrating hormone; D002118:Calcium
keywords: Calcium mobilization; MCH receptor; Melanin-concentrating hormone (MCH); Pigment migration; Xenopus tropicalis