Practice question

Neural tube dorsalization is driven by BMPs secreted from roof plate and overlying surface ectoderm, opposing ventral Sonic hedgehog gradient. BMP4 and BMP7 diffuse ventrally activating Smad1/5/8 signaling that induces dorsal transcription factors such as Msx1/2, Math1 and Wnt1, specifying dorsal interneurons D1-D3, neural crest and roof plate fate. High BMP promotes roof plate and sensory interneurons, lower BMP permits intermediate identities like D4-D6. Sonic hedgehog ventralizes tube, Notch regulates binary fate but not dorsal-ventral morphogen gradient, FGF10 patterns limbs and lung. BMP gradient thus acts as dorsal morphogen establishing complementary DV pattern with Shh.