McRory J E, Sherwood N M
Department of Biology, University of Victoria, British Columbia, Canada.
J Biol Chem. 1994 Jul 15;269(28):18588-92.
Insulin-like growth factor-I (IGF-I) is expressed not only in liver, but also in brain and other tissues. This ubiquitous IGF-I has a complex pattern of expression due to multiple transcription start sites, polyadenylation sites and exon skipping. We have isolated a cDNA encoding a brain-specific IGF-I from a catfish brain cDNA library. Also, a fragment encoding ubiquitous IGF-I was amplified from brain and liver mRNA and the deduced protein shown to be distinct (66% sequence identity) from brain-specific IGF-I. Consistent with other IGF-I prepropeptides, the brain-specific IGF-I has a 43-residue signal peptide followed by B, C, A, D, and E domains. Retained in the catfish brain-specific IGF-I peptide are residues predicted to be involved with the correct tertiary folding, disulfide linkages, and receptor binding. Northern blot analysis of poly(A+)-rich mRNA from brain indicated a single 1600-base pair transcript; a band was not detected from mRNA of liver, stomach, pancreas, pituitary, blood, herring brain, or brain poly(A-) RNA. A sensitive reverse transcriptase/polymerase chain reaction assay also showed that brain-specific IGF-I mRNA was expressed solely in the Thai catfish brain but not liver, stomach, pancreas, pituitary, ovary, and African catfish brain.
胰岛素样生长因子-I（IGF-I）不仅在肝脏中表达，也在大脑和其他组织中表达。由于多个转录起始位点、多聚腺苷酸化位点和外显子跳跃，这种普遍存在的IGF-I具有复杂的表达模式。我们从鲶鱼脑cDNA文库中分离出一个编码脑特异性IGF-I的cDNA。此外，从脑和肝mRNA中扩增出一个编码普遍存在的IGF-I的片段，推导的蛋白质显示与脑特异性IGF-I不同（序列同一性为66%）。与其他IGF-I前原肽一致，脑特异性IGF-I有一个43个残基的信号肽，其后是B、C、A、D和E结构域。鲶鱼脑特异性IGF-I肽中保留了预计与正确的三级折叠、二硫键连接和受体结合有关的残基。对来自脑的富含多聚腺苷酸的mRNA进行Northern印迹分析，显示有一个单一的1600个碱基对的转录本；在肝、胃、胰腺、垂体、血液、鲱鱼脑或脑多聚腺苷酸缺失的RNA的mRNA中未检测到条带。一种灵敏的逆转录酶/聚合酶链反应检测也表明，脑特异性IGF-I mRNA仅在泰国鲶鱼脑中表达，而不在肝、胃、胰腺、垂体、卵巢和非洲鲶鱼脑中表达。
