Fig. 7. Activation of Smad2 signaling converts neural tissue to neural crest and mesodermal tissues in Xenopus. (A) In the absence of DEX, leaky GR-Smad2 activity was sufficient for neural crest induction, but not sufficient for inhibition of neural markers or induction of mesodermal genes. Activation of GR-Smad2 by DEX (2 µM) at mid-gastrula stages led to inhibition of Sox2 and Sox3 and simultaneous induction of the mesodermal markers MyoD and Chordin in the neural plate (seen more clearly in Fig. 7B and Fig. 8). GR-Smad2 RNA (0.1-0.2 ng) was used. The embryos were orientated with the head toward the left and viewed from the dorsal side. (B) Induction of mesodermal markers by activated GR-Smad2 occurred in the neural plate, as shown in transversely bisected (top) or sectioned (bottom) embryos.