Expression of GFP in zebrafish embryos in the transient expression assay using the mixture of the plasmid pERE-Gal4ff containing the Tol2 transposase mRNA and the plasmid pUAS-GFP. Fertilised zebrafish eggs were microinjected at the 1–2 cell stages with the mixture of two plasmids. Injected embryos were then exposed for up to 72 hour post-fertilisation (hpf) to 17α-ethinyloestradiol (EE2). These embryos showed specific mosaic expression of the reporter. The injected embryos exposed to 1000, 100 and 10 ng/L of EE2 expressed GFP in cells most strongly in the somite muscle, heart and liver (72 hpf). This experiment was run in duplicate and was repeated at least seven times.