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Fig. 3 Expression of dorsal retinal genes is lost following the repression of Wnt signaling. The Tg(hsp70l:Tcf3-GFP)w26 transgenic zebrafish line, which expresses a dominant-repressor form of Tcf3 (ΔTcf-GFP) upon heat shock, was used for these experiments. Dorsal views, anterior left. (A-H) Embryos were heat shocked and fixed at the indicated times, and sorted for GFP expression. The repression of Wnt targets led to the downregulation of tbx5 in the dorsal retina at every timepoint. tbx5 expression was upregulated in the dorsal diencephalon at later timepoints (arrows in F,H). (I) Expression of gdf6a was also eliminated in embryos expressing ΔTcf at 18 hpf and fixed at 24 hpf. (J) To determine the times at which bmp4, gdf6a and tbx5 are lost in the dorsal retina following the repression of Wnt targets, embryos were heat shocked at 16 hpf and fixed 2 and 8 hours later. bmp4 and gdf6a were strongly reduced at the 2 hour timepoint, whereas tbx5 was still expressed. By 8 hours, the expression of all three genes was lost.