Practice question

Dominant-negative BMP receptor type IB truncated after transmembrane domain dimerizes with endogenous type I and type II receptors forming nonfunctional complexes unable to phosphorylate Smad1/5/8. Uniform BMP signaling loss throughout embryo abolishes ventral epidermal program driven by BMP targets Xvent and Msx1, derepressing neural program via Sox2, Zic and Neurogenin. Animal caps and whole embryos become neuralized expressing neural plate markers even without organizer. Ventral mesoderm also dorsalized expanding chordin expression. Outcome therefore is neuralization of ectoderm demonstrating BMP inhibition triggers neural default fate. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.