Localization of type 5 17β-hydroxysteroid dehydrogenase mRNA in mouse tissues as studied by in situ hybridization

The mouse enzyme type 5 17b-hydroxysteroid dehydrogenase (17b-HSD) catalyzes the conversion of androstenedione to testosterone and, to a lesser degree, the conversion of estrone to estradiol. In order to determine the exact sites of action of type 5 17b-HSD, we studied the cellular localization of the mRNA of the enzyme in mouse tissues by using in situ hybridization. Specific hybridization signal was found in the liver, ovary, adrenal cortex, and kidney. In the liver of mice of both sexes, a strong signal was observed in all hepatocytes. In the ovary, specific labeling was detected in the granulosa and theca interna cells in growing follicles and in luteal cells. In the female adrenal cortex, intense labeling was restricted to the zona reticularis, whereas no type 5 17b-HSD mRNA expression could be found in the male adrenal cortex. In the kidney of mice of both sexes, type 5 17b-HSD mRNA was expressed in epithelial cells in both the proximal and distal convoluted tubules. The data indicate that androgens and estrogens are formed via the action of type 5 17b-HSD in specific cell types in the liver, ovary, adrenal cortex, and kidney.