Fig. 9. Activation of Smad2 inhibits neural induction in Xenopus explants. (A) Activation of Smad2 by DEX at blastula to early gastrula stages suppressed neural induction by noggin and induced mesodermal markers in animal caps; but it could not do so efficiently if activated at mid- to late gastrula stages. noggin (10 pg) and GR-Smad2 (0.2 ng) RNAs were used. (B) Activin protein (1:50 dilution of oocyte conditioned medium) reduced neural and induced mesodermal markers in dorsal ectoderm explanted from stages 11-11.5 embryos, but not from stage 12 embryos. (C) Unlike dorsal ectoderm, ventral ectoderm did not respond to activin efficiently at mid-gastrula stages (stage 11 onward).