Schmidt C M, Ehlenfeldt R G, Athanasiou M C, Duvick L A, Heinrichs H, David C S, Orr H T
Institute of Human Genetics, University of Minnesota, Minneapolis 55455.
J Immunol. 1993 Sep 1;151(5):2633-45.
Trophoblast, the only fetal tissue in direct contact with maternal cells, fails to express the polymorphic HLA class I molecules HLA-A and -B, but does express the nonpolymorphic class I molecule HLA-G. It is thought that HLA-G may provide some of the functions of a class I molecule without stimulating maternal immune rejection of the fetal semiallograft. As a first step in identifying the cis-acting DNA regulatory elements involved in the control of class I expression by extraembryonic tissue, several types of transgenic mice were produced. Two HLA-G genomic fragments were used, 5.7 and 6.0 kb in length. These included the entire HLA-G coding region, 1 kb of 3' flanking sequence, and 1.2 or 1.4 kb of 5' flanking sequence, respectively. A hybrid transgene, HLA-A2/G, was produced by replacing the 5' flanking sequence, first exon, and early first intron of HLA-G with the corresponding elements of HLA-A. Comparison of transgene mRNA expression patterns seen in HLA-A2/G and HLA-G transgenic mice suggests that 5' flanking sequences are largely responsible for the differing patterns of expression typical of the classical class I and HLA-G genes. Studies comparing the extraembryonic HLA-G expression levels of founder embryos transgenic for either the 5.7- or 6.0-kb HLA-G transgene showed that the 6.0-kb transgene directed HLA-G expression far more efficiently than did the 5.7-kb HLA-G transgene, producing extraembryonic HLA-G mRNA levels similar to those seen in human extraembryonic tissues. The results of these studies suggest that the 250-bp fragment present at the extreme 5' end of the 6.0-kb HLA-G transgene and absent from the 5.7-kb HLA-G transgene contains an important positive regulatory element. This 250-bp fragment lies further upstream than any of the previously documented class I regulatory regions and may function as a locus control region.
滋养层是唯一与母体细胞直接接触的胎儿组织，它不表达多态性的HLA - I类分子HLA - A和 - B，但表达非多态性的I类分子HLA - G。据认为，HLA - G可能提供了I类分子的一些功能，而不会刺激母体对胎儿半同种异体移植物产生免疫排斥反应。作为鉴定参与胚外组织I类表达调控的顺式作用DNA调控元件的第一步，制备了几种类型的转基因小鼠。使用了两个长度分别为5.7 kb和6.0 kb的HLA - G基因组片段。这些片段分别包括整个HLA - G编码区、1 kb的3'侧翼序列和1.2或1.4 kb的5'侧翼序列。通过用HLA - A的相应元件替换HLA - G的5'侧翼序列、第一个外显子和早期第一个内含子，产生了一个杂交转基因HLA - A2/G。对HLA - A2/G和HLA - G转基因小鼠中观察到的转基因mRNA表达模式的比较表明，5'侧翼序列在很大程度上决定了经典I类基因和HLA - G基因典型的不同表达模式。比较5.7 kb或6.0 kb HLA - G转基因创始人胚胎的胚外HLA - G表达水平的研究表明，6.0 kb转基因指导HLA - G表达的效率远高于5.7 kb HLA - G转基因，产生的胚外HLA - G mRNA水平与人类胚外组织中的相似。这些研究结果表明，6.0 kb HLA - G转基因5'末端存在而5.7 kb HLA - G转基因中不存在的250 bp片段包含一个重要的正调控元件。这个250 bp片段比任何先前记录的I类调控区域都更位于上游，可能作为一个基因座控制区域发挥作用。
