Practice question

Ventral identities in neural tube are induced by Sonic hedgehog derived from notochord then floor plate reinforcing gradient ventrally. Ventral progenitors experience highest Shh leading to Gli activator induction of Nkx2.2 floor plate, Olig2 motor neuron progenitors and Nkx6.1 V3 interneurons, while dorsal BMP counter-gradient promotes Pax6. Adding Shh to dorsal explants ventralizes them generating motor neurons, while Shh blockade dorsalizes. BMP4 promotes dorsal fates, retinoic acid posteriorizes, Wnt3a dorsalizes. Thus Shh functions as ventralizing morphogen interpreting concentration into distinct neuronal progenitor domains essential for spinal cord.