Conlon J M, Tostivint H, Vaudry H
Department of Biomedical Sciences, Creighton University, Omaha, NE 68178, USA.
Regul Pept. 1997 Mar 26;69(2):95-103. doi: 10.1016/s0167-0115(97)02135-6.
Recent advances in the fields of molecular cloning and peptide purification necessitate a reappraisal of our views concerning the evolution of the genes encoding somatostatin-related peptides. The currently widely held view that the genomes of tetrapods contain only the preprosomatostatin-I (PSS-I) gene, encoding somatostatin-14, with a second preprosomatostatin gene being expressed only in teleost fish is no longer tenable. Identification of genes encoding both somatostatin-14 and the somatostatin-related peptide, cortistatin in mammals, identification of the PSS-I and PSS-II preprosomatostatin genes in amphibia, and the isolation of gene products from at least two non-allelic preprosomatostatin genes in lampreys suggests the alternative hypothesis that duplication of the PSS-I gene occurred early in evolution, predating or concomitant with the appearance of the chordates. We speculate that at least two somatostatin genes are expressed in all classes of vertebrates but these genes have evolved at very different rates. It is probable that the preprosomatostatin-II (PSS-II) gene, encoding [Tyr7, Gly10] somatostatin-14 or a related peptide, arose from a second independent duplication of the PSS-I gene in the ancestor of present-day teleost fish at a time after the divergence of the teleost stock from the line of evolution leading to tetrapods. The recent isolation of urotensin II, a peptide which contains a region of structural similarity but is not evolutionarily related to somatostatin-14, from the central nervous systems of lampreys, elasmobranchs and amphibia necessitates that we modify the accepted view that urotensin II is exclusively a product of the caudal neurosecretory system of teleost fish.
分子克隆和肽纯化领域的最新进展使我们有必要重新审视我们对编码生长抑素相关肽的基因进化的看法。目前广泛持有的观点认为，四足动物的基因组仅包含编码生长抑素-14的前生长抑素-I（PSS-I）基因，而第二个前生长抑素基因仅在硬骨鱼中表达，这种观点已不再站得住脚。在哺乳动物中鉴定出编码生长抑素-14和生长抑素相关肽促皮质素释放因子的基因，在两栖动物中鉴定出PSS-I和PSS-II前生长抑素基因，以及从七鳃鳗中至少两个非等位前生长抑素基因分离出基因产物，这表明了另一种假说，即PSS-I基因的复制发生在进化早期，早于或与脊索动物的出现同时发生。我们推测，所有脊椎动物类别中至少有两个生长抑素基因表达，但这些基因的进化速度非常不同。编码[酪氨酸7，甘氨酸10]生长抑素-14或相关肽的前生长抑素-II（PSS-II）基因，可能是在硬骨鱼从导致四足动物的进化谱系中分化出来之后，在当今硬骨鱼的祖先中由PSS-I基因的第二次独立复制产生的。最近从七鳃鳗、软骨鱼和两栖动物的中枢神经系统中分离出了尾加压素II，这是一种含有结构相似区域但与生长抑素-14在进化上无关的肽，这就要求我们修正普遍接受的观点，即尾加压素II仅是硬骨鱼尾神经分泌系统的产物。
