Tissue- and cell-specific expression of human sn-glycerol-3-phosphate dehydrogenase in transgenic mice

Distal and proximal cis-linked sequences are needed for the total expression phenotype of the mouse alcohol dehydrogenase 1 (Adh1) gene

Mouse alcohol dehydrogenase 1 (Adh1) gene expression occurs at high levels in liver and adrenal, moderate levels in kidney and intestine, low levels in a number of other tissues, and is undetectable in thymus, spleen and brain by Northern analysis. In transgenic mice, a minigene construct containing 10 kb of upstream and 1.5 kb of downstream flanking sequence directs expression in kidney, adrenal, lung, epididymis, ovary and skin but promotes ectopic expression in thymus and spleen while failing to control expression in liver, eye, intestine and seminal vesicle. Cosmids containing either 7 kb of upstream and 21 kb of downstream or 12 kb of upstream and 23 kb of downstream sequence flanking genetically marked Adh1 additionally promotes seminal vesicle expression suggesting downstream or intragenic sequence controls expression in this tissue. However, expression in liver, adrenal, or intestine is not promoted. The Adh1(a) allele on the cosmid expresses an enzyme electrophoretically distinct from that of the endogenous Adh1(b) allele, and presence of the heterodimeric enzyme in expressing tissues confirms that transgene activity occurs in the same cell-type as the endogenous gene. Transgene expression levels promoted by cosmids were at physiologically relevant amounts and exhibited greater copy-number dependence than observed with minigenes. Transgene mRNA expression correlated with expression measured at the enzyme level. A bacterial artificial chromosome containing 110 kb of 5'- and 104 kb of 3'-flanking sequence surrounding the Adh1 gene promoted expression in tissues at levels comparable to the endogenous gene most importantly including liver, adrenal and intestinal tissue where high level Adh1 expression occurs. Transgene expression in liver was in the same cell types as promoted by the endogenous gene. Although proximal elements extending 12 kb upstream and 23 kb downstream of the Adh1 gene promote expression at physiologically relevant levels in most tissues, more distal elements are additionally required to promote normal expression levels in liver, adrenal and intestinal tissue where Adh1 is most highly expressed.

Cloning of glycerol-3-phosphate dehydrogenase cDNAs from two fish species and effect of temperature on enzyme expression in rainbow smelt (Osmerus mordax)

Rainbow smelt (Osmerus mordax) can accumulate extreme levels of glycerol in their blood during winter. Low temperatures are required for glycerol accumulation in smelt blood and the enzyme glycerol-3-phosphate dehydrogenase (GPDH) has been suggested to play a role in glycerol production/concentration in this species. In the present study, cDNA sequences encoding glycerol-3-phosphate dehydrogenase (GPDH) from rainbow smelt and Atlantic salmon (Salmo salar) were cloned. The encoded GPDH protein sequences were very similar to one another (88% identity). Using RT-PCR, GPDH mRNA was detected in skin, gill, heart, head kidney, brain and liver from both salmon and smelt obtained in December. However, GPDH was not detected in salmon intestine and spleen or in smelt intestine. Examination of GPDH expression in smelt liver during February by Northern blotting revealed temperature regulation. Elevation of the temperature resulted in a significant decrease in liver GPDH transcript level. Serum glycerol levels decreased concomitantly. These findings suggest a role for GPDH in the accumulation of glycerol in smelt at low temperatures.

Induction of glycerol phosphate dehydrogenase gene expression during seizure and analgesia

Using mRNA differential display, we found that the gene for NAD(+)-dependent glycerol phosphate dehydrogenase (GPDH; EC 1.1.1.8) is induced in rat brain following seizure activity. Northern blot and in situ hybridization analysis confirmed the differential display results; they also showed, in a separate model of neuronal activation, that after thermal noxious stimulation of the hind-paws, a similar increase in GPDH mRNA occurs in the areas of somatotopic projection in the lumbar spinal cord. Surprisingly, administration of analgesic doses of morphine or the nonsteroidal antiinflammatory drugs aspirin, metamizol (dipyrone), and indomethacin also increased GPDH mRNA levels in rat spinal cord. The opioid receptor antagonist naloxone completely blocked morphine induction of GPDH but had no effect on GPDH induction by noxious heat stimulation or metamizol treatment, implicating different mechanisms of GPDH induction. Nevertheless, in all cases, induction of the GPDH gene requires adrenal steroids and new protein synthesis, as the induction was blocked in adrenalectomized rats and by cycloheximide treatment, respectively. Our results suggest that the induction of the GPDH gene upon peripheral noxious stimulation is related to the endogenous response to pain as it is mimicked by exogenously applied analgesic drugs.

Identification of new translocation breakpoints at 12q13 in lipomas

Cytogenetic studies of banded chromosomes and fluorescence in situ hybridization (FISH) of several yeast artificial chromosomes (YACs) that are part of a 128-kb resolution physical map of a portion of 12q13 revealed that 4/14 (28%) lipomas have breakpoints in 12q13. These breakpoints are more than 10 Mb away from the HMGIC gene at 12q14-q15, which is known to be modified in some lipomas. FISH with individual YACs at 12q13 enabled us to identify four YACs that span three breakpoints. Our results suggest that genes other than HMGIC on human chromosome 12 may be involved in the etiology of lipoma development.

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.