EXPRESSION OF THE CLASS-I ALCOHOL-DEHYDROGENASE GENE IN DEVELOPING RAT FETUSES

Class I alcohol dehydrogenase (ADH) is the principal enzyme responsibl e for ethanol oxidation in mammals. Although primarily regarded as an enzyme that functions in the adult, Class I ADH has been reported to b e present in fetal tissues. By in situ hybridization, we demonstrated the tissue localization of the Class I ADH transcript in developing ra t fetuses between Days 15 (E 15) and 18 (E18) of gestation. Abundant t ranscripts were present in epidermis, lung, and urinary bladder. In th ese tissues, the messages were localized primarily to the superficial layer of the epithelium and increased with development. The liver exhi bited significant signals only in the E18 fetus, when parenchymal hepa tocytes first appeared. The E15 and E16 small intestines, with their e pithelium arranged in a stratified fashion, displayed signals in the s ubmucosal mesenchymal layer. By E17, a rearrangement of the intestinal epithelium into an almost monolayer configuration was observed. This change was associated with a redistribution of the ADH transcript to t he surface of the epithelium. further relocation of the messages was n oted in the adult small intestine, in which they became concentrated i n the base of the crypt. These findings indicate that expression of th e rat class I ADH gene follows a dynamic course in specific epithelial tissues during fetal development. In addition, the apparent superfici al localization of the ADH message in most of these tissues suggests t hat ADH functions in metabolizing either endogenously or exogenously d erived alcohol substrates present in the fetal environment.