Abstract
The melanocortin type 1 receptor (Mc1r) belongs to a family of G-protein-coupled
receptors involved in various physiological processes in vertebrates.
Melanocortins, the Mcr natural agonists, are pituitary peptide hormones
including adrenocorticotropin and melanocyte-stimulating hormones.
In mammals and birds, Mc1r is involved in pigmentation and expressed
in melanocytes and melanoma. Activation of Mc1r leads to eumelanin
production as well as to proliferation and survival of melanocytes
in the epidermis. Here we report the molecular and evolutionary analysis
of mc1r from three major fish models, the zebrafish Danio rerio,
the medaka Oryzias latipes and the platyfish Xiphophorus maculatus.
In contrast to some other melanocortin receptor genes, mc1r has been
conserved as a single copy gene in divergent fish species. Its expression
was detected in all organs tested in platyfish and medaka but was
restricted to eyes, skin, brain and testis in zebrafish, this possibly
reflecting differences in the distribution of extracutaneous melanophores.
The mc1r gene was found to be expressed during embryogenesis, as
well as in Xiphophorus hybrid melanoma, similar to human tumours.
Protein sequence comparison between fish and mammalian Mc1r revealed
a remarkable concordance between evolutionary and functional analyses
for the identification of residues and regions critical for receptor
function.
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