The Research Of Effects And Mechanisms Of Genistein On Induction Of Vtg In Male Zebrafish (danio Rerio)

Genistein is one of the isoflavones that widely esists in soybeans. Genistein shares structural features with the potent estrogen 17β-estradiol(E2) and it is classified as environmental estrogen. Nowsdays, high concentration of genistein in fish meals and water bodies has been a threat to fishes exposed to it. It is meaningful to explore the estrogenic effects and the mechanisms of genistein for aquaculture development and protection of fishery resources.It is widely accepted that detection of vitellogenin(VTG) in juvenile and male fish is a simple and sensitive biomarker for environmental estrogens with estrogenic effects in fish and it has been adopted for testing the estrogenic effects of genistein on fish. Although there has been several researches proving that fish meal with genistein could induce VTG synthesis in juvenile and male fish, the mechanisms is still unknown. Therefore in present research work estrogenic effects of genistin on VTG induction in male zebrafish is detected and the exploration research to the mechanism is in the aspects of variation of both ERs expression and sex hormone levels.In this paper, mature male zebrafish are exposed to a range of concentrations of genistein(1μg/L,10μg/L,100μg/L,1000μg/L) for 28 days. The study is performed using real-time PCR as a readout to quantify the change in Vtgl mRNA levels to confirm the estrogenic effects of genistein on VTG inducing. On these bases ERa and ERβmRNA levels are quantified by real-time PCR to discussion for the mechanisms of genistein's function as an ERβ-selective partial agonist. Meanwhile, radioimmunoassay kit is used to detect the change of E2 and testosterone levels in gonad of male zebrafish to make sure if genistein have estrogenic effect on VTG induction through influcing the sex hormone levels directly.The results showed that:(1) Following waterborn exposure to genistein(1μg/L,10μg/L,100μg/L,1000 μg/L) for 28 days, the inductions of VTG in male zebrafish are detected in all treated groups. The 10μg/L,100μg/L genistein-treated groups have significantly increase and 1000μg/L group and E2-treated group have remarkably increase in the levels of Vtgl mRNA(*P<0.01) in dose-dependent manner. This results shows the estrogenic effects of genistein on VTG inducing.(2) Compared to the control group, ERa mRNA levels in livers of genistein-treated groups are remarkably decreased, while ERβmRNA levels in livers of genistein-treated groups but 1μg/L group is remarkably increased, the expression levels of both ERs genes is remarkably increased in E2-treated group. This results suggest that genistein selectively trigger ERβ-mediated transcriptional pathways in VTG induction and it is attributed to the preferable and higher binding ability of genistein to ERβ.(3) Compared to the control group, testosterone levels in testes of genistein-treated groups and E2-treated group but 1μg/L and 100μg/L groups are remarkably decreased, while E2 levels in testes of all treated-groups are remarkably increased. It can be concluded that besides ERβ-mediated transcriptional pathways, another way of genistein acting on VTG induction in fish is changing the sex hormone levels directly.