Neonatal exposure to genistein induces estrogen receptor (ER)alpha expression and multioocyte follicles in the maturing mouse ovary: evidence for ERbeta-mediated and nonestrogenic actions.

Outbred CD-1 mice were treated neonatally on Days 1-5 with the phytoestrogen, genistein (1, 10, or 100 micro g per pup per day), and ovaries were collected on Days 5, 12, and 19. Ribonuclease protection assay analysis of ovarian mRNA showed that estrogen receptor beta (ERbeta) predominated over ERalpha in controls and increased with age. Genistein treatment did not alter ERbeta expression, however, ERalpha expression was higher on Days 5 and 12. ERbeta was immunolocalized in granulosa cells, whereas ERalpha was immunolocalized in interstitial and thecal cells. Genistein treatment caused a dramatic increase in ERalpha in granulosa cells. Genistein-treated ERbeta knockout mice showed a similar induction of ERalpha, which is seen in CD-1 mice, suggesting that ERbeta does not mediate this effect. Similar ERalpha induction in granulosa cells was seen in CD-1 mice treated with lavendustin A, a tyrosine kinase inhibitor that has no known estrogenic actions, which suggests that this property of genistein may be responsible. As a functional analysis, genistein-treated mice were superovulated and the number of oocytes was counted. A statistically significant increase in the number of ovulated oocytes was observed with the lowest dose, whereas a decrease was observed with the two higher doses. This increase in ovulatory capacity with the low dose coincided with higher ERalpha expression. Histological evaluations on Day 19 revealed a dose-related increase in multioocyte follicles (MOFs) in genistein-treated mice. Tyrosine kinase inhibition was apparently not responsible for MOFs because they were not present in mice that had been treated with lavendustin; however, ERbeta must play a role, because mice lacking ERbeta showed no MOFs. These data taken together demonstrate alterations in the ovary following neonatal exposure to genistein. Given that human infants are exposed to high levels of genistein in soy-based foods, this study indicates that the effects of such exposure on the developing reproductive tract warrant further investigation.