Glial- and fat-specific expression of the rat glycerol phosphate dehydrogenase-luciferase fusion gene in transgenic mice.

Glycerol phosphate dehydrogenase (GPDH) is a metabolic enzyme that catalyzes the conversion of dihydroxyacetone phosphate to glycerol-3-phosphate. It provides phospholipid precursors for lipid biosynthesis and energy metabolism. In the brain, GPDH enzymatic activity, protein, mRNA are exclusively associated with oligodendroglial and Bergmann glial cells. Expression of GPDH in the brain increases dramatically during the active period of myelination, and is regulated by extracellular signals. In an effort to understand the mechanism that confers glial-specific expression of GPDH, we have examined the role of the 5' flanking sequence of the rat GPDH gene in conferring cell-specific expression of reporter gene in transgenic mice. Luciferase reporter constructs containing either the full-length GPDH 5' flanking region (p4.3), or a distally truncated version (p2.6), were injected into mouse zygotes. Three independent lines of transgenic mice containing the p4.3, and seven lines of mice containing the p2.6 constructs, were analyzed. Luciferase enzyme activity was detectable only in brain and fat, not in other GPDH-positive organs such as liver, muscle, and kidney. Both the full-length and the distally deleted transgenes were expressed similarly in these two organs, indicating that the distal portion of the 5' flanking region was not required for brain- and fat-specific expression. Immunocytochemical analyses revealed that luciferase immunoreactivity colocalized with glial fibrillary acidic protein (GFAP)-positive Bergmann glia in the cerebellum, and myelin basic protein (MBP)-positive oligodendroglia in the cerebral cortex and the brainstem. Results here suggest that the rat GPDH 5' flanking region directs glial-specific expression of GPDH transcription in the brain, and provide a good model for analyses of changes in glial metabolism in response to extracellular perturbations in vivo.