McRory J E, Sherwood N M
Department of Biology, University of Victoria, British Columbia, Canada.
DNA Cell Biol. 1997 Aug;16(8):939-49. doi: 10.1089/dna.1997.16.939.
Studies on the evolutionary pathway of the insulin gene family suggest that insulin and insulin-like growth factor (IGF) became distinct molecules only after the vertebrates arose. A single molecule with identity to both insulin and IGF was reported in amphioxus. To study the origin of insulin, we selected tunicates because their ancestors are thought to be a nodal point in the evolution of vertebrates. This is the first report of separate insulin and IGF molecules from invertebrates. Two cDNAs were isolated from the tunicate Chelyosoma productum: One cDNA encodes a distinct preproinsulin with B, C, and A domains, whereas the other encodes tunicate preproIGF, including all five domains in their proper sequence. Both mRNAs are expressed in the nervous system, digestive tract, heart, and possibly the gonad but not in branchial basket or tunic. Hence, insulin and igf genes have similar expression patterns. In situ methods confirm the polymerase chain reaction evidence that tunicate insulin and igf mRNAs are expressed in cortical cells of the neural ganglion. We conclude that insulin and IGF have maintained separate gene lineages in both vertebrate and protochordate evolution and, thus, a distinct evolutionary history of more than 600 million years.
对胰岛素基因家族进化途径的研究表明，胰岛素和胰岛素样生长因子（IGF）直到脊椎动物出现后才成为不同的分子。文昌鱼中报道了一种与胰岛素和IGF都相同的单一分子。为了研究胰岛素的起源，我们选择了被囊动物，因为它们的祖先被认为是脊椎动物进化中的一个节点。这是首次报道来自无脊椎动物的单独的胰岛素和IGF分子。从被囊动物多疣龟甲海鞘中分离出两个cDNA：一个cDNA编码一种具有B、C和A结构域的独特胰岛素原前体，而另一个编码被囊动物胰岛素样生长因子原前体，包括所有五个按正确顺序排列的结构域。两种mRNA都在神经系统、消化道、心脏中表达，可能也在性腺中表达，但在鳃篮或被囊中不表达。因此，胰岛素和IGF基因具有相似的表达模式。原位方法证实了聚合酶链反应的证据，即被囊动物胰岛素和IGF mRNA在神经节的皮质细胞中表达。我们得出结论，胰岛素和IGF在脊椎动物和原索动物的进化中都保持了独立的基因谱系，因此，有着超过6亿年的独特进化历史。
