ONTOGENY OF 17-BETA-HYDROXYSTEROID DEHYDROGENASE TYPE-2 MESSENGER-RNAEXPRESSION IN THE DEVELOPING MOUSE PLACENTA AND FETUS

17 beta-Hydroxysteroid dehydrogenase type 2 (17HSD type 2) catalyzes t he inactivation of estradiol, testosterone and dihydrotestosterone int o biologically less active 17-keto forms. Our recent Northern analysis indicated that the enzyme is expressed both in mouse placenta and fet us. The present data indicate that in the placenta the distribution of enzyme expression changes during pregnancy. In the choriovitelline pl acenta (day 8) 17HSD type 2 was expressed both in mural and polar gian t cells. Later, on days 9-12.5, the mRNA was also detected in the junc tional zone, and in late gestation (days 14.5-17.5), 17HSD type 2 mRNA was predominantly expressed only at the labyrinth region. In the fetu s, 17HSD type 2 expression appears in the liver on day 11. At day 12 t he expression was strongly increased in the liver, and at the same tim e moderate mRNA expression was also detected in the esophagus and inte stine. In these tissues, high constitutive expression of 17HSD type 2 was then maintained throughout pregnancy. At later stages of developme nt (days 15-16) the mRNA was, furthermore, detected in epithelial cell s of the stomach, tongue, oropharynx and nasopharynx, as well as in th e kidney. We conclude that the expression pattern of 17HSD type 2 in t he developing placenta and fetus suggests a role for the enzyme in mai ntaining a barrier to the transfer of active 17-hydroxy forms of sex s teroids between the fetus and maternal circulation. (C) 1997 Elsevier Science Ireland Ltd.