Key Laboratory for Conservation and Use of Important Biological Resources of Anhui Province, College of Life Sciences, Anhui Normal University, Wuhu, Anhui 241000, China.
Key Laboratory for Conservation and Use of Important Biological Resources of Anhui Province, College of Life Sciences, Anhui Normal University, Wuhu, Anhui 241000, China.
Gen Comp Endocrinol. 2022 Oct 1;327:114097. doi: 10.1016/j.ygcen.2022.114097. Epub 2022 Jul 16.
The Chinese alligator (Alligator sinensis) is a freshwater crocodilian endemic to China. So far, the endocrine regulation of feeding and growth in Chinese alligator is poorly understood. In this study, the molecular structure and tissue expression profiles of ghrelin and its receptor GHSR in the Chinese alligator were characterized for the first time. The full-length cDNA of ghrelin was 1770 bp, including a 37 bp 5 '-UTR (untranslated region), a 435 bp ORF (open reading frame) and a 1298 bp 3 '-UTR. The ORF encodes a ghrelin precursor, which consists of 145 amino acid residues, including a signal peptide with 52 amino acid residues at the N-terminus, a mature peptide with 28 amino acid residues, and a possibly obestain at the C-terminus. The full-length cDNA of GHSR was 3961 bp, including a 5'-UTR of 375-bp, an ORF of 1059-bp and a 3' -UTR of 2527-bp. The ORF encodes a protein of 352 amino acid residues containing seven transmembrane domains, with multiple N glycosylation modification sites and conserved cysteine residue sites. The active core "GSSF" of Chinese alligator ghrelin was identical to that of mammals and birds, and the ghrelin binding site of GHSR was similar to that of mammals. The amino acid sequences of both ghrelin and GHSR share high identity with American alligator (Alligator mississippiensis) and birds. Ghrelin was highly expressed in cerebrum, mesencephalon, hypothalamus and multiple peripheral tissues, including lung, stomach and intestine, suggesting that it could play functions in paracrine and/or autocrine manners in addition to endocrine manner. GHSR expression level was higher in hypothalamus, epencephalon and medulla oblongata, and moderate in multiple peripheral tissues including lung, kindey, stomach and oviduct, implicating that ghrelin/GHSR system may participate in the regulation of energy balance, food intake, water and mineral balance, gastrointestinal motility, gastric acid secretion and reproduction. During hibernation, the expression of ghrelin and GHSR in the brain was significantly increased, while ghrelin was significantly decreased in heart, liver, lung, stomach, pancreas and ovary, and GHSR was significantly decreased in heart, liver, spleen, lung, kindey, stomach, ovary and oviduct. These temporal changes in ghrelin and GHSR expression could facilitate the physiological adaption to the hibernation of Chinese alligator. Our study could provide basic data for further studies on the regulation of feeding, physiological metabolism and reproduction of Chinese alligator, which could also be useful for the improvement of artificial breeding of this endangered species.
扬子鳄（Alligator sinensis）是一种原产于中国的淡水鳄。到目前为止，人们对扬子鳄的摄食和生长的内分泌调节知之甚少。在本研究中，我们首次对扬子鳄的生长激素释放肽（ghrelin）及其受体 GHSR 的分子结构和组织表达谱进行了表征。ghrelin 的全长 cDNA 为 1770bp，包括一个 37bp 的 5'-UTR（非翻译区）、一个 435bp 的 ORF（开放阅读框）和一个 1298bp 的 3 '-UTR。ORF 编码一个由 145 个氨基酸残基组成的 ghrelin 前体，其中包括 N 端 52 个氨基酸残基的信号肽、28 个氨基酸残基的成熟肽和 C 端可能的 obestatin。GHSR 的全长 cDNA 为 3961bp，包括一个 375bp 的 5'-UTR、一个 1059bp 的 ORF 和一个 2527bp 的 3'-UTR。ORF 编码一个由 352 个氨基酸残基组成的蛋白质，含有七个跨膜结构域，具有多个 N 糖基化修饰位点和保守的半胱氨酸残基位点。扬子鳄 ghrelin 的核心活性“GSSF”与哺乳动物和鸟类相同，而 GHSR 的 ghrelin 结合位点与哺乳动物相似。ghrelin 和 GHSR 的氨基酸序列与美洲鳄（Alligator mississippiensis）和鸟类高度同源。Ghrelin 在大脑、中脑、下丘脑和多个外周组织（包括肺、胃和肠道）中高度表达，表明它除了具有内分泌作用外，还可能以旁分泌和/或自分泌的方式发挥作用。GHSR 的表达水平在下丘脑、脑桥和延髓较高，在包括肺、肾、胃和输卵管在内的多个外周组织中中等，提示 ghrelin/GHSR 系统可能参与能量平衡、食物摄入、水和矿物质平衡、胃肠道蠕动、胃酸分泌和生殖的调节。在冬眠期间，大脑中 ghrelin 和 GHSR 的表达显著增加，而心脏、肝脏、肺、胃、胰腺和卵巢中的 ghrelin 显著减少，心脏、肝脏、脾脏、肺、肾脏、胃、卵巢和输卵管中的 GHSR 也显著减少。ghrelin 和 GHSR 表达的这些时间变化可能有助于促进扬子鳄对冬眠的生理适应。我们的研究可为进一步研究扬子鳄的摄食、生理代谢和繁殖的调控提供基础数据，也可为这一濒危物种的人工养殖提供帮助。
