Gene Structure of the Goldfish Agouti-Signaling Protein: A Putative Role in the Dorsal-Ventral Pigment Pattern of Fish

• Published in: Endocrinology (Philadelphia) 2005-03, Vol.146 (3), p.1597-1610
• Main Authors: Cerdá-Reverter, José Miguel, Haitina, Tatjana, Schiöth, Helgi Birgir, Peter, Richard Ector
• Format: Article
• Language: English
• Subjects: Agouti Signaling Protein; Albinism; Alleles; alpha-MSH - metabolism; Amino Acid Sequence; Amino acids; Animals; ASP gene; Base Sequence; Binding, Competitive; Biological and medical sciences; Biological Assay; Blotting, Northern; Blotting, Southern; Carassius auratus; Cell Differentiation; Cell Line; Cell Proliferation; Chromatic adaptations; Cloning, Molecular; Culture Media, Conditioned - pharmacology; Cyclic AMP - metabolism; Differentiation; DNA - chemistry; Ethidium - pharmacology; Female; Fish; Freshwater; Fugu; Fundamental and applied biological sciences. Psychology; Gene Library; Genetic Vectors; Goldfish; Humans; Intercellular Signaling Peptides and Proteins - biosynthesis; Intercellular Signaling Peptides and Proteins - genetics; Ligands; Male; Melanins - metabolism; Melanization; Melanocortin; Melanocortin MC4 receptors; Melanocytes; Molecular Sequence Data; Oryzias latipes; Pheomelanin; Pigmentation; Pigments; Protein Isoforms; Protein structure; Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA - chemistry; RNA, Messenger - metabolism; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Signal Transduction; Skin; Takifugu; Tissue Distribution; Transfection; Vertebrates; Vertebrates: endocrinology
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2004-1346

One of the most successful chromatic adaptations in vertebrates is the dorsal-ventral pigment pattern in which the dorsal skin is darkly colored, whereas the ventrum is light. In fish, the latter pattern is achieved because a melanization inhibition factor inhibits melanoblast differentiation and supports iridophore proliferation in the ventrum. In rodents, the patterned pigmentation results from regional production of the agouti-signaling protein (ASP). This peptide controls the switch between production of eumelanin and pheomelanin by antagonizing αMSH effects on melanocortin receptor (MCR) 1 in the melanocytes. In addition, ASP inhibits the differentiation and proliferation of melanoblast. Thus, the mammalian ASP may be homologous to the poikilotherm melanization inhibition factor. By screening of a genomic library, we deduced the amino acid sequence of goldfish ASP. The ASP gene is a four-exon gene spanning 3097 bp that encodes a 125-amino acid precursor. Northern blot analysis identified two different ASP mRNAs in ventral skin of red- and black-pigmented and albino fish, but no expression levels were observed in the dorsal skin of the same fish. The dorsal-ventral expression polarity was also detected in both black dorsally pigmented fish and albino fish. Pharmacological studies demonstrate that goldfish ASP acts as a melanocortin antagonist at Fugu MC1R and goldfish MC4R. In addition, goldfish ASP inhibited Nle4, D-Phe7-MSH-stimulated pigment dispersion in medaka melanophores. Our studies support agouti signaling protein as the melanization inhibition factor, a key factor in the development of the dorsal-ventral pigment pattern in fish.