Development of estrogen-responsive transgenic medaka for environmental monitoring of endocrine disrupters

To develop a transgenic fish system to monitor environmental pollution, we generated a mvtg1:gfp transgenic medaka line, in which the gfp reporter gene was under the control of medaka vitellogenin1 (mvtg1) gene promoter. In this transgenic line, GFP was exclusively expressed in the liver of the mature adult female. Male and juvenile transgenic fish did not express GFP but could be induced to express GFP in the liver after exposure to 17-beta-estradiol (E2). Concurrent accumulation of mvtg1 and gfp mRNAs was observed during both development and estrogen treatment, indicating that the gfp transgene was faithfully expressed under the mvtg1 promoter. Dose- and time-dependent induction of GFP expression by E2 was investigated in male transgenic fish. The lowest-observed-effect concentration (LOEC) of E2 to induce GFP expression was 0.5 microg/L by observation of live fish and 0.05-0.1 microg/L by observation of dissection-exposed liver in a 30 day exposure experiment. GFP expression was observed within 36 h after treatment in high concentrations of E2 (5 microg/L), and it took longer to detect GFP expression under lower concentrations of E2. By removal and readdition of E2, we demonstrated that GFP expression was repeatedly induced. Finally, we also demonstrated that GFP expression could be induced by other estrogenic compounds, including 17-alpha-ethynylestradiol (EE2, 0.05 microg/L), diethylstibestrol (DES, 5 microg/L), estriol (10 microg/ L), and bisphenol A (BPA, 1 mg/L), but not by weak estrogenic chemicals such as nonylphenol (NP, up to 1 mg/ L) and methoxychlor (MXC, up to 20 microg/L). Our experiments indicated the broad application of the transgenic line to monitor a wide range of estrogenic chemicals.