Practice question

Dorsoventral patterning of vertebrate neural tube requires opposing gradients from roof plate and floor plate. Ventralizing signal is Sonic hedgehog, cholesterol-modified protein secreted by notochord and later by floor plate cells, diffusing dorsally to create ventral high, dorsal low gradient. High Shh induces floor plate via FoxA2, slightly lower induces p3 progenitors expressing Nkx2.2 generating V3 interneurons, intermediate levels induce motor neuron progenitors expressing Olig2, lower levels trigger distinct interneuron classes. Ectopic Shh ventralizes dorsal tube, while loss dorsalizes ventral tube, confirming dose-dependent morphogen action via Gli activators.