Practice question

Hensen's node transplantation to ectopic location in host gastrula demonstrates organizer properties analogous to Spemann experiment. Donor node labelled with quail nucleolus self-differentiates into notochord and floor plate while emitting signals including chordin, noggin, Shh that neuralize surrounding host epiblast converting it into secondary neural tube and recruit lateral mesoderm into ectopic somites. Full secondary embryonic axis forms, sometimes incomplete but containing dorsal axial structures. Controls show lateral epiblast alone lacks ability. Therefore transplantation induces secondary axis formation confirming node as avian organizer. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.