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Fig. 1. BMP inhibition in vivo is not sufficient for neural induction. In all panels, Sox2 expression marks prospective neural tissue, K81 expression marks prospective epidermis, XBra expression marks mesoderm, at the late gastrula stage 13, and Slug marks neural crest progenitors at early neurula stage 15. Marker gene expression is revealed in purple, while β-galactosidase activity resulting from injection of lacZ RNA as a lineage tracer is in red. (A) Sixteen-cell embryos injected with 100 pg CABR RNA in one dorsal-most animal blastomere. BMPR activation represses the neural marker Sox2 and activates the epidermal marker K81. (B) Eight-cell embryos injected animally in the two left blastomeres with lacZ (250 pg/blastomere) and tBR (400 pg/blastomere) RNAs showing neural plate expansion and epidermis suppression (u, uninjected side). (C-G) Sixteen-cell embryos injected in one ventral-most animal blastomere with lacZ (C), lacZ and tBR (400 pg, D), or lacZ and Smad6 (1 ng in E,G; 4 ng in F) RNAs. In whole embryos, BMP inhibition by Smad6 represses epidermis, but does not induce neural tissue. Ectopic neural crest could form in embryos that received 1 ng (arrow), but not 4 ng, Smad6 RNA. (G) Animal caps explanted at blastula stage 9 express Sox2 in response to Smad6 injection in ventral ectoderm cells. The inset in the lower panel illustrates that Sox2 expression (purple) is restricted to the injected region (red). (A,B) Dorsal views, anterior towards the top. (C-F) Ventral views, anterior towards the top, except right panels in E,F, which are lateral views, anterior towards the top. Scale bars: 500 μm. |
