Effects of estrone on the early life stages and expression of vitellogenin and estrogen receptor genes of Japanese medaka (Oryzias latipes)

Abstract

The fertilized eggs of Japanese medaka (Oryzias latipes) were exposed to estrone (E1) at 5–5000ngL−1 for 15d, and the hatched fry were exposed continuously to the same concentrations for the additional 15d. Adverse effects on hatchability, time to hatching, and gross abnormalities occurred at 50ngL−1 or above. Then the fry were divided into a continual exposure group, and a water recovery group. When the fry were exposed to E1 for another 60d, there was a decrease in the hepatosomatic index (HSI) of males and the influence disappeared in the water recovery group. The gonadosonatic index (GSI) of females at 500ngL−1 decreased significantly in another 60d exposure. While the fry were maintained in dechlorinated tap water for 60d, a significant decrease in female GSI was observed at 50ngL−1 or above. An increased GSI was found in males in both continual exposure and water recovery groups at all E1 treatments. Quantitative RT-PCR showed that vitellogenin-I (Vtg-I) gene expressions in the female liver were significantly down-regulated at 50ngL−1 in the continual exposure group, and at 500ngL−1 in the water recovery group, while male Vtg-I genes were significantly up-regulated for all E1 treatments. In addition, all E1 treatments caused sex reversal of males. These results suggest that E1 at 5ngL−1 or above have unrecoverable impacts on the gonadal growth and development of medaka, even if only early life stages were exposed to E1.