Department of Biology, York University, Toronto, Ontario, Canada.
Laboratory of Integrative Neuroendocrinology, Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
PLoS One. 2018 May 23;13(5):e0197817. doi: 10.1371/journal.pone.0197817. eCollection 2018.
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.
Xenin 是一种高度保守的 25 个氨基酸肽，从衣壳蛋白 α（COPA）的 N 端裂解而来，它正在成为哺乳动物和鸟类的食物摄入调节剂。迄今为止，鱼类中没有关于 xenin 生物学的研究。本研究旨在以金鱼（Carassius auratus）为模型，鉴定编码 xenin 的 copa mRNA，阐明其受摄食的调节，并描述 xenin 在食欲中的作用。首先，从金鱼脑中鉴定出 copa cDNA 的部分序列，该序列编码 xenin，在脊椎动物和无脊椎动物中高度保守。RT-qPCR 显示 copa mRNAs 在金鱼组织中广泛分布，在脑中、鳃、垂体和 J 环中检测到的水平最高。免疫组织化学也证实了 COPA 肽在下丘脑和 J 环黏膜上的肠内分泌细胞中的存在。与它的厌食作用一致，我们发现下丘脑 copa mRNA 表达在摄食前后有重要的周期间波动，主要表现为随着摄食时间的临近，copamRNA 水平逐渐下降，摄食后逐渐增加。此外，禁食以组织依赖性方式不同地调节 copa mRNA 的表达。外周和中枢注射 xenin 可减少金鱼的摄食量。本研究首次报道了鱼类中的 xenin，并表明这种肽是金鱼的一种新型厌食肽。
