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Abstract
Xenin, a highly conserved 25 amino acid peptide cleaved from the N-terminus of the coatomer protein alpha (COPA), is emerging as a food intake regulator in mammals and birds. To date, no research has been conducted on xenin biology in fish. This study aims to identify the copa mRNA encoding xenin in goldfish (Carassius auratus) as a model, to elucidate its regulation by feeding, and to describe the role of xenin on appetite. First, a partial sequence of copa cDNA, a region encoding xenin, was identified from goldfish brain. This sequence is highly conserved among both vertebrates and invertebrates. RT-qPCR revealed that copa mRNAs are widely distributed in goldfish tissues, with the highest levels detected in the brain, gill, pituitary and J-loop. Immunohistochemistry confirmed also the presence of COPA peptide in the hypothalamus and enteroendocrine cells on the J-loop mucosa. In line with its anorexigenic effects, we found important periprandial fluctuations in copa mRNA expression in the hypothalamus, which were mainly characterized by a gradually decrease in copa mRNA levels as the feeding time was approached, and a gradual increase after feeding. Additionally, fasting differently modulated the expression of copa mRNA in a tissue-dependent manner. Peripheral and central injections of xenin reduce food intake in goldfish. This research provides the first report of xenin in fish, and shows that this peptide is a novel anorexigen in goldfish.
Highlights
Xenin is a 25 amino acid peptide cleaved from the N-terminus of its precursor coatomer protein-α (COPA) [1], by an aspartic protease, presumably cathepsin E [2,3]
Leckstrom and coworkers [8] found that intraperitoneal (IP) injection of xenin stimulates hypothalamic neurons directly involved in the regulation of food intake, including neurons in the paraventricular nucleus, arcuate nucleus (ARC) and dorsomedial nucleus of the hypothalamus, and the lateral hypothalamic area of mice, suggesting that xenin-induced reduction of food intake is mediated by central signaling in those nuclei
A partial sequence of copa mRNA was identified in goldfish
Summary
Xenin is a 25 amino acid peptide cleaved from the N-terminus of its precursor coatomer protein-α (COPA) [1], by an aspartic protease, presumably cathepsin E [2,3] It was first described in the human gastric mucosa [1], and later observed as well in endocrine cells of the duodenum and jejunum of primates and dogs, where it colocalizes with a subpopulation of gastric inhibitory polypeptide (GIP)-immunoreactive cells [4]. Besides acting at a central level, it has been reported that xenin reduces/delays gastric emptying in mice [14], chicks [12] and humans [15], suggesting that it might induce satiety by acting directly on the gastrointestinal tract. Xenin is emerging as a multifunctional peptide with predominant anorectic effects in mammals and birds
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