Daimon M, Johnson T R, Ilan J, Ilan J
Department of Reproductive Biology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
Mol Reprod Dev. 1992 Dec;33(4):413-7. doi: 10.1002/mrd.1080330407.
Insulin-like growth factor-II (IGF-II) mRNA exists as multiple transcript size classes, such as 6.0, 5.3, 4.9, 3.2, and 2.2 kb mRNAs in various human tissues. Three different promoters, 2 different polyadenylation sites, and alternative splicing are involved in producing these multiple transcripts. Initiation of transcription at the 3 different promoters results in multiple mRNAs which contain identical coding regions but different 5'-untranslated regions (5'-UTRs). The first promoter is thought to direct expression of 5.3 kb mRNA in adult human liver. The second promoter region directs expression of 6.0, 3.2, and 2.2 kb mRNAs in human fetal tissues and several adult nonliver tissues. The third promoter specifies transcription of a 4.9 kb mRNA in various tissues. We isolated and sequenced a cDNA clone (pIGF-II-1-70) from a human placental cDNA library, which contains the IGF-II coding region and the 5'-UTR associated with the third promoter. By using a 5'-UTR-specific probe from the clone, we found that this third 5'-UTR is contained in the IGF-II mRNA of 2.2 kb and is absent in the 3.2 kb IGF-II mRNA. We also found an 0.9 kb transcript expressed in placenta, which hybridized strongly to the third 5'-UTR specific probe but not to IGF-II coding region probes. This finding might indicate the existence of an mRNA encoding an IGF-II-associated peptide.
胰岛素样生长因子-II（IGF-II）mRNA以多种转录本大小类别存在，例如在各种人体组织中存在6.0、5.3、4.9、3.2和2.2 kb的mRNA。三种不同的启动子、两个不同的聚腺苷酸化位点以及可变剪接参与了这些多种转录本的产生。在3个不同启动子处起始转录会产生多种mRNA，这些mRNA包含相同的编码区但5'-非翻译区（5'-UTR）不同。第一个启动子被认为指导5.3 kb mRNA在成人肝脏中的表达。第二个启动子区域指导6.0、3.2和2.2 kb mRNA在人类胎儿组织和几种成人非肝脏组织中的表达。第三个启动子指定了4.9 kb mRNA在各种组织中的转录。我们从人胎盘cDNA文库中分离并测序了一个cDNA克隆（pIGF-II-1-70），它包含IGF-II编码区和与第三个启动子相关的5'-UTR。通过使用来自该克隆的5'-UTR特异性探针，我们发现这个第三个5'-UTR包含在2.2 kb的IGF-II mRNA中，而在3.2 kb的IGF-II mRNA中不存在。我们还发现了一种在胎盘中表达的0.9 kb转录本，它与第三个5'-UTR特异性探针强烈杂交，但不与IGF-II编码区探针杂交。这一发现可能表明存在一种编码IGF-II相关肽的mRNA。
