Expression of mouse 17 beta-hydroxysteroid dehydrogenase/17-ketosteroid reductase type 7 in the ovary, uterus, and placenta: Localization from implantation to late pregnancy

Rodent 17 beta-hydroxysteroid dehydrogenase/17-ketosteroid reductase type 7 (17HSD/KSR7) catalyzes the conversion of estrone (E-1) to estradiol (E-2) and is abundantly expressed in the ovaries of pregnant animals in particula r. In the present work we demonstrate cell-specific expression of 17HSD/KSR 7 in the ovaries, uteri, and placentas of pregnant and nonpregnant mice usi ng in, situ hybridization. The results show that mouse 17HSD/KSR7 (m17HSD/KSR7) messenger RNA is disti nctly and exclusively expressed in a proportion of corpora lutea (CLs). Dur ing pregnancy, expression of m17HSD/KSR7 is most abundant around embryonic day 14.5 (E14.5), when the ovaries are filled with CLs expressing 17HSD/KSR 7. In the uterus, m17HSD/KSR7 is first detected on E5.5, when expression su rrounds the implantation site on the antimesometrial side. As gestation pro gresses, m17HSD/KSR7 is expressed in the decidua capsularis on E8 and E9.5, disappearing thereafter from the antimesometrial decidua. On E9 onward, m1 7HSD/KSR7 messenger RNA expression takes place at the junctional zone of th e developing placenta. On E12.5 and E14.5, m17HSD/KSR7 is abundantly expres sed in the spongiotrophoblasts, where expression gradually declines toward parturition. In conclusion, m17HSD/KSR7 expression in the CL is related to the life span of the CL. Moreover, spatial and temporal expression of m17HSD/KSR7 in the uterus suggests that locally produced E-2 plays a role in implantation and /or decidualization. Finally, the results indicate that mouse placenta is c apable of converting E-1 to E-2 in situ, and that the synthesized E-2 may b e effective in a paracrine, autocrine, and/or intracrine manner and be invo lved in placentation.