Analysis of transient expression of GFP in response to oestrogens in medaka embryos. The plasmid pERE-Gal4ff containing the Tol2 transposase mRNA and the plasmid pUAS-GFP were injected into 1–2 cell stage medaka embryos and the embryos were exposed to 17α-ethynyloestradiol (100 ng EE2/L) via the water. No GFP expression was detected in controls. The injected medaka embryos exposed to EE2 showed strong GFP expression in the skin in the anterior region and in the body trunk (B). At 11 dpf, fish exposed to EE2 showed GFP expression in the somite muscle, heart, liver and gall bladder (D, F, H and J).