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The interest in the physiological role of α-MSH in birds has been limited because they lack the intermediate lobe of the pituitary, the main source of circulating α-MSH in most vertebrates. Recent studies have improved our understanding of the avian melanocortin system. We have cloned and characterized all five MC-R subtypes, POMC, and AGRP in chicken. Analyses of the tissue distribution of expression of these genes revealed widespread expression throughout the body, corresponding to the situation in mammals in which α-MSH exerts a multiplicity of effects in different tissues by acting as a local mediator. We showed that the extended black locus controlling feather pigmentation in the chicken encodes MC1-R. Moreover, black chickens carrying the dominant allele, the extended black, express the MC1-R with ligand-independent activity as the somber-3J black mice. α-MSH and AGRP were expressed in the infundibular nucleus of POMC and NPY neurons, respectively, in the brain of Japanese quail. Furthermore, fasting stimulated AGRP expression and lowered POMC expression. These data indicate that at least two of the major melanocortin systems reported in mammals, that is, regulation of pigmentation and energy homeostasis, was developed in a common ancestor to chicken and mammals at least 300 million years ago. Furthermore, α-MSH peptide was identified in developing chicken eye, suggesting a possible involvement of α-MSH in regulation of ocular development. Collectively, the data reviewed here indicate that α-MSH is produced locally and acts as an autocrine/paracrine hormone in birds.
Author(s): Boswell T; Takeuchi S; Takahashi S; Okimoto R; Schiöth HB
Publication type: Article
Publication status: Published
Journal: Annals of the New York Academy of Sciences: The Melanocortin System
ISSN (print): 0077-8923
ISSN (electronic): 1749-6632
Publisher: Wiley-Blackwell Publishing, Inc.
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