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Fig. 1 Overexpression of gbx1 induces posterior cell fate. (A) Wild-type (WT) embryo at 24 h and (B) after injection of 200 pg gbx1 mRNA; anterior brain structures are severely reduced. The ear is indicated by an arrowhead. (C, D) Staining of the forming axon tracts with an anti-acetylated tubulin antibody at 24 h; dorsal views, with anterior to the top. In the gbx1-injected embryo the hindbrain is severely enlarged compared to WT (arrowheads). (E, F) Duplications of ear structures are frequently observed (arrows). (G-I′) Series of embryosinjected with different doses of gbx1 mRNA (200 and 500 pg), analyzed at the tailbud stage after in situ hybridization with otx2 (blue) and krox20 (red). The otx2 domain progressively disappears and the krox20 domains shift to more anterior regions. (J) Dose-dependent gbx1 overexpression phenotypes. Higher concentrations (>500 pg) did not increase the observed phenotype. (A-D, K-M) Lateral views; (E-H, K′-M′) dorsal views.