Developmental Effect of Endocrine Disruptors on Fish and Mice

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Bisphenol-A (BPA), an estrogenic chemical, was given to pregnant mice and Japanese monkey and studied transplacental transfer. BPA was foun in fetal brain, liver and other organs in 30 min in mice and 1 h in monkey suggesting that BPA can be easily cross the placenta. BPA and a synthetic estrogen, diethylstilbestrol (DES), were given to pregnant mice and studied fertility and various abnormalities in female offspring. DES induced sterility, polyovular follicles in ovary and persistent stratification of vaginal epithelium, but not BPA.Hoxa-9 and a-10 genes in Mullerian duct were downregulated by DES in the fetal period suggesting the close correlation to uterine changes in DES-exposed mice. In order to study low dose issue of BPA, 2 and 20μg/kg body weight of BPA and 0.02-2μg/kg of DES were given to day 10 to 17 of pregnancy. In 20μg BPA-and all DES-exposed female offspring showed significantly early vaginal opening and lower body weight as compared to controls. This results suggest that there is a low dose effect of BPA, however, the mechanism underlie is still unclear. Neonatal DES treatment induced hypospadias in female mice, fusion of urethra and vaginal lumen at lower position of vagina, where apoptosis was observed. The critical period in induction of hypospadias was 7 days after birth. Neonatally BPA (150μg) treated female mice showed persistent estrus, and ovary-independent vaginal changes.In order to study estrogenic agents on development of fish, Fundulus heteroclitus embryos were exposed to estradiol. Various malformations, including sex ratio change were induced by estradiol. Estrogen receptor α and β were cloned and ER expression during development were analysed. FTZ-F1 gene was also cloned from Fundulus. In zebrafish, gonad develops to ovary by ca 20 days after hatching then a half of fish develop testis from the ovary. During testis formation, apoptosis of oocytes occurred in the ovary.