Interrelation between melanocyte-stimulating hormone and melanin-concentrating hormone in physiological body color change: Roles emerging from barfin flounder Verasper moseri

In teleosts, as their names suggest, the main target cells of melanocyte-stimulating hormone (MSH) and melanin-concentrating hormone (MCH) are the chromatophores in the skin, where these peptide hormones play opposing roles in regulating pigment migration. These effects are obvious especially when their activities are examined in vitro. On the contrary, while MCH also exhibits activity in vivo, MSH does not always stimulate pigment dispersion in vivo because of predominant sympathetic nervous system. A series of our investigations indicates that this is also the case in barfin flounder, Verasper moseri. Interestingly, we observed that mch expression and the tissue contents of MCH can be easily influenced by changes in environmental color conditions, while gene expression and tissue contents related to MSH scarcely respond to color changes. Transcripts of MSH and MCH receptor genes have been identified in a variety of tissues of this fish species, suggesting that these are multifunctional peptide hormones. Nevertheless, chromatophores in the skin still offer important clues in the efforts to elucidate the functions of melanotropic peptides. Herein, we review the most recent advancements of our studies on MSH and MCH and their receptors in the barfin flounder and discuss the interrelations between these peptides, focusing on their roles in influencing pigment migration in the skin.

► MCH exhibits melanin-concentrating activity in vivo and in vitro.
► MSH exhibits pigment-dispersing activities in vitro, but not in vivo.
► The activities of MCH vary in response to background color changes.
► MSH activities do not always correspond to background color change.
► MSH exhibits its activities when the activities of MCH and catecholamine are lowered.