Abstract
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.
Highlights
In the mammalian liver, many enzymes are heterogeneously distributed according to a pattern that is related to the vascular architecture
To investigate the role of the far-upstream enhancer in the establishment and maintenance of the very stable expression pattern of glutamine synthetase (GS), two classes of transgenic mice were generated: “GSK” mice in which the basal GS promoter directed the expression of a reporter gene and “GSL” mice in which the expression of the reporter gene was driven by the basal promoter and by the upstream regulatory region, including the far-upstream enhancer
To investigate the role of the upstream regulatory region in the spatio-temporal regulation of the highly characteristic expression pattern of the GS gene, we studied two different transgenes, viz. one in which the expression of the CAT reporter gene was directed by the basal promoter (GSK) and one in which the CAT expression was directed by the basal promoter and 3 kilobases of the upstream regulatory region (GSL)
Summary
Many enzymes are heterogeneously distributed according to a pattern that is related to the vascular architecture (reviewed in Refs. 1 and 2). In the liver of adult rats and mice, GS is expressed in a thin rim of cells around the central veins [3,4,5], whereas carbamoylphosphate synthetase is expressed in a wide zone surrounding the terminal portal veins [6] These two enzymes provide an excellent model to study the topographical aspects of the regulation of gene expression. Three characteristics of GS gene expression were used to determine the in vivo function of the upstream regulatory region of the GS gene: the organ specificity of gene expression, the topography of gene expression within the liver, and the developmental changes in enzyme activity in the liver. The upstream regulatory region was found to play a major role in the regulation of the GS gene expression in the liver
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
