Molecular cloning, expression, and signaling pathway of four melanin-concentrating hormone receptors from Xenopus tropicalis

• Four distinct melanin-concentrating hormone receptor (MCHR) cDNAs were cloned from Xenopus tropicalis.
• X-MCHR1a and R2a are close to mammalian MCHRs; X-MCHR1b and R2b are close to teleostean MCHRs.
• MCH elevates intracellular calcium levels in CHO cells transfected with X-MCHR1a, R1b and R2a.
• RT-PCR shows that both X-MCHR1b and R2b were exclusively found in X. tropicalis dorsal skin.
• MCH has the ability to induce both melanin granule-concentrating and -dispersing activities in dorsal skin.

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 Ca2+ 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