Wnt signaling is required for the maintenance of dorsal retinal identity. The Tg(hsp70l:dkk1-GFP)w32 transgenic zebrafish line, which expresses the secreted Wnt pathway inhibitor Dkk1 upon heat shock, was used for these experiments. (A-J) Dorsal views, anterior left. Embryos were heat shocked and fixed at the indicated times, and sorted for GFP expression. (A,B) Embryos fixed just before Wnt signaling becomes active in the dorsal RPE express tbx5 normally, showing that tbx5 expression initiates properly in the absence of Wnt signaling. (C-J) Inhibition of Wnt signaling caused a strong downregulation of tbx5 at the early timepoints, with a weaker effect at the last timepoint. This demonstrates a requirement for Wnt signaling in the maintenance of tbx5. (K-T) Lateral views, dorsal up, anterior left. (K-P) Expression of the Bmp ligands bmp4, gdf6a and bmp2b are lost from the dorsal retina following Wnt inhibition, suggesting a loss of dorsal character. (Q-T) pax6b is expressed normally and vax2 expands dorsally, suggesting a ventralized retina. (U-X) Whole eyes, dorsal up. Following Wnt inhibition, the expression of ephrin B2a (efnb2a) is downregulated in the dorsal retina, but maintained in the lens, and ephb2 expands dorsally.
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