Functional analysis of mouse 3-phosphoglycerate dehydrogenase (Phgdh) gene promoter in developing brain

D-3-Phosphoglycerate dehydrogenase (Phgdh; EC 1.1.1.95) is a necessary enzyme for de novo L-serine biosynthesis via the phosphorylated pathway. Targeted disruption of the mouse Phgdh gene has been shown to result in embryonic lethality, accompanied by severe abnormalities in brain development. Phgdh is expressed exclusively by neuroepithelium and radial glia in developing brain and later mainly by astrocytes. To elucidate the molecular mechanism that regulates such cell-type-specific expression of Phgdh in developing brain, an upstream 3.5-kilobase-pair (kbp) region of the gene harboring the promoter was characterized in primary cultures and transgenic mice. Analysis of Phgdh 5'-nested deletions in transfected cultures indicated that overall reporter luciferase levels were higher in glial cultures than those in neuronal cultures. Although basal promoter activity of the gene appeared to depend on an Sp1 binding sequence residing between -193 and -184 in both glial and neuronal cultures, an upstream 5'-flanking region between -1,794 and -1,095 contributed to up-regulation of Phgdh transcription in a glial-cell-specific manner. In the cerebral cortex of transgenic mouse embryos, the Phgdh promoter-LacZ transgene DNA containing -1,794/+4 promoter sequences directed beta-galactosidase (beta-Gal) expression mainly to Phgdh-positive neuroepithelium and radial glia. This glial preference diminished when beta-Gal expression was driven solely by the upstream 0.2-kbp minimal promoter. However, glial preference of beta-Gal expression was restored by placing the 700-base-pair 5'-DNA segment upstream of the minimal promoter. These observations suggest the presence of cis-acting elements that confer the cell type specificity of Phgdh transcription in the distal promoter region.