Fig. 6. BMP inhibition by Smad6 is not sufficient for neural induction in Xenopus ventral epidermis. (A-I) cSmad6 was targeted to the ventral epidermis by injection into the A4 blastomere of 32-cell stage embryos (A). Smad6 does not activate Sox3 expression (B-E), compare with GFP-injected control embryos (F-I). B,C,F,G are dorsal views; D,E,H,I are ventral views of the embryos in B,C,F,G. C,E,G,I show the embryos in B,D,F,H after staining with anti-fluorescein to reveal the lineage tracer FDX which was co-injected with the mRNA. (J-L) To test that the progeny of the A4 blastomere is competent to respond to neural inducing signals from the organizer, a lineage tracer (FDX) was injected into the A4 blastomere. At late blastula/early gastrula stage, the labelled cells are transplanted into the dorsal side of an unlabelled host embryo, which is grown to early neurula stage (J). (K,L) The transplanted cells (FDX in brown in L) contribute to the neural plate and express Sox3 (purple).