Fig. 5

Over-expression of Gdf6a signaling components induces dorsal identity and represses ventral identity. The phosphorylation of Smad 1/5/8 proteins is induced in the presumptive ventral retina when either gdf6a or BMPR1a is expressed using the Medaka rx3 promoter (B, C). This effect is cell non-autonomous with respect to gdf6a, as phosphorylation is induced in cells surrounding those that express rx3:gdf6a-IRES-GFP (Q–S). Expression of caBMPR1a exerts its effects in a cell autonomous fashion as phosphorylation is detected specifically in cells that express rx3:caBMPR1a-IRES-GFP (T–V). The expression of tbx5 (E, F) and bambi (I, J) are also induced ectopically in the retina under both conditions. The expression of vax2 is found in the retina just proximal to the forebrain in wildtype embryos (M), and this expression is lost in embryos expressing either gdf6a (N) or BMPR1a (O). Expression of the inhibitory smad7 via the rx3 promoter inhibits phosphorylation of Smad 1/5/8 proteins (D), as well as the expression of tbx5 (H) and bambi (L). Smad7 works in a cell autonomous fashion as Smad phosphorylation is specifically inhibited in cells expressing rx3:smad7-IRES-GFP (W–Y). Expression of smad7 has no effect on the retinal expression of vax2 (P). All embryos were staged to 10 somites. White arrows indicate ectopic Smad 1/5/8 phosphorylation in the presumptive ventral retina, while black arrows indicate ectopic expression of dorsal genes in the presumptive ventral retina. Arrowheads point to the reduction of vax2 expression in the presumptive ventral retina in embryos over-expressing gdf6a or caBMPR1a.