Abstract
Mammalian alcohol dehydrogenase (ADH) has previously been shown to function in vitro as a retinol dehydrogenase as well as an ethanol dehydrogenase. Thus ADH participates in the conversion of retinol (vitamin A alcohol) to retinoic acid, a regulatory ligand for the retinoic acid receptor class of transcription factors. Human ADH exists as a family of isozymes encoded by seven genes, which are differentially expressed in adult liver and extrahepatic tissues, being found preferentially in the epithelial cells which are retinoid target tissues. However, human ADH expression patterns have not been analyzed in early embryonic tissues, which are known to synthesize and respond to retinoic acid such as the neural tube and limb buds. To estimate the embryonic expression pattern for one member of the human ADH family, we have constructed transgenic mouse lines carrying the human ADH3 promoter fused to the lacZ gene. ADH3-lacZ transgene expression was first noted at embryonic day 9.5 and was active in the neural tube extending from the midbrain to the spinal cord, as well as the heart and proximal regions of the forelimb buds. In day 12.5 and 13.5 embryos, ADH3 transgene expression remained in the neural tube and heart and was also observed in more distal regions of the forelimb and hindlimb buds as well as the kidney. Expression in the neural tube was highest in the ventral midline including the floor plate and showed a ventral to dorsal gradient of decreasing expression. These findings indicate that at least one human ADH isozyme may exist in the correct tissues to act as an embryonic retinol dehydrogenase catalyzing the synthesis of retinoic acid.
Highlights
Human retinol (Hogan et al, 1992).the floor plate of the ADH exists as a family of isozymes encoded by seven neural tube has been reported to possess the enzymatic magenes, which are differentially expressed in adult liver chinery to convert retinol to retinoic acid (Wagneret al., 1990), and extrahepatic tissues, being found preferentially in the epithelial cells which are retinoid target tissues
Human ADH expression patterns have not been analyzed in early embryonic tissues, which are known to synthesize and respond to retinoic acid such as the neural tube and limb buds
To estimate the emand retinoic acid has been identified as an endogenous molecule in theembryonicneural tube (Hunteert al., 1991; Wagner et al, 1992).When exogenously introduced in large amounts, retinoic acid acts as a teratogen for mammalian development, of the brain,craniofacialstructures, and heart (Kobryonic expression pattern for one member of the hu- chhar, 1967;Lammer et al, 1985).It appears that the syntheman ADH family, wehave constructed transgenic mouse sis, accumulation, and turnover of endogenous retinoic acid is a lines carrying the human ADH3 promoter fused to the highly regulated process, allowing only verysmall amounts of laeZ gene
Summary
Have been no reports on the distribution of any retinoic acid synthetic enzymes in early embryos at either the protein or gration sites were identified as carrying the transgene basedupon gene expression level. In order toexplore the potential role of Southern blot analysis of tail DNA (Hogan et al, 1986);when mated, human ADH a s a retinoic acid synthetic enzyme in embryonic three of these founders expressed the transgene in embryos (TableI). ADH gene expression in murineembryos could be used for this lowing removalof the embryo fromextraembryonictissues, staining for purpose, but the analysis of murine ADH genes involved in retinoic acid synthesis is still in progress. Samples were post-fixed in 4% paraformaldehyde and promoter activity in mouse embryos in order to estimate the embryonic expression pattern of a human ADH gene. Non-transgenic embryos of the same stage were analyzed for endogenous P-galactosidaseactivity using the identical staining conditions. In this studywe have examined the embryonic expression pattern of the humanADH3 gene encodingthe
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