Practice question

Neural tube dorsoventral axis opposite ventral Hedgehog is BMP dorsalization from roof plate and surface ectoderm. Roof plate secretes BMP2, BMP4, BMP6, BMP7 and Wnt1, Wnt3a establishing high dorsal BMP concentration activating Smad1/5/8 to induce transcription factors Atoh1, Olig3, Pax3, Pax7 specifying dorsal interneurons dl1-dl6 and neural crest progenitors via Id inhibition and Msx. Shh from floor plate induces ventral Nkx2.2, Olig2 motor neurons. Genetic ablation of BMP receptors causes loss of dorsal cell types with ventral expansion; opposite of Shh mutants. Therefore BMP gradient essential dorsal patterning complement to ventral Shh system.