Fig. 6. Activation of Smad2 signaling in Xenopus neural tissues at gastrula stages results in inhibition of neural markers. (A) Schematic representation of the chimeric protein GR-Smad2 and analyses of its activity in animal caps. GR-Smad2 RNA (0.2 ng) was used. In the absence of dexamethasone (DEX), GR-Smad2 did not induce mesodermal markers (lane 2). Activation of GR-Smad2 from blastula to early gastrula stages by DEX (2 µM) led to mesoderm induction (lanes 3 to 5). However, if activated at mid- to late gastrula stages (stages 11 to 12), GR-Smad2 no longer induced mesoderm in animal caps (lanes 6 and 7). (B) Activation of GR-Smad2 in neural tissues at mid-gastrula stages led to inhibition of Sox2 at different axial levels along the anteroposterior axis.