Lie-Venema H, Labruyère W T, van Roon M A, de Boer P A, Moorman A F, Berns A J, Lamers W H
Department of Anatomy and Embryology, University of Amsterdam, The Netherlands.
J Biol Chem. 1995 Nov 24;270(47):28251-6. doi: 10.1074/jbc.270.47.28251.
In previous studies of the glutamine synthetase gene, the promoter and two enhancer elements, one in the upstream region and one within the first intron, were identified. To analyze the role of the far-upstream enhancer element in the regulation of the expression of the glutamine synthetase gene, two classes of transgenic mice were generated. In GSK mice, the basal promoter directs the expression of the chloramphenicol acetyltransferase reporter gene. In GSL mice reporter gene expression is driven, in addition, by the upstream regulatory region, including the far-upstream enhancer. Whereas chloramphenicol acetyltransferase expression was barely detectable in GSK mice, high levels were detected in GSL mice. By comparing chloramphenicol acetyltransferase expression with that of endogenous glutamine synthetase in GSL mice, three groups of organs were distinguished in which the effects of the upstream regulatory region on the expression of glutamine synthetase were quantitatively different. The chloramphenicol acetyltransferase mRNA in the GSL mice was shown to be localized in the pericentral hepatocytes of the liver. The developmental changes in chloramphenicol acetyltransferase enzyme activity in the liver were similar to those in endogenous glutamine synthetase. These results show that the upstream region is a major determinant for three characteristics of glutamine synthetase expression: its organ specificity, its pericentral expression pattern in the liver, and its developmental appearance in the liver.
在先前对谷氨酰胺合成酶基因的研究中，已鉴定出启动子以及两个增强子元件，一个位于上游区域，另一个位于第一个内含子内。为了分析远上游增强子元件在谷氨酰胺合成酶基因表达调控中的作用，构建了两类转基因小鼠。在GSK小鼠中，基础启动子指导氯霉素乙酰转移酶报告基因的表达。在GSL小鼠中，报告基因的表达除了由基础启动子驱动外，还受上游调控区域（包括远上游增强子）的驱动。在GSK小鼠中几乎检测不到氯霉素乙酰转移酶的表达，而在GSL小鼠中则检测到高水平的表达。通过比较GSL小鼠中氯霉素乙酰转移酶的表达与内源性谷氨酰胺合成酶的表达，区分出三组器官，其中上游调控区域对谷氨酰胺合成酶表达的影响在数量上有所不同。结果表明，GSL小鼠中的氯霉素乙酰转移酶mRNA定位于肝脏中央周围的肝细胞中。肝脏中氯霉素乙酰转移酶活性的发育变化与内源性谷氨酰胺合成酶的变化相似。这些结果表明，上游区域是谷氨酰胺合成酶表达的三个特征的主要决定因素：其器官特异性、在肝脏中的中央周围表达模式以及在肝脏中的发育出现情况。
