Practice question

Spemann organizer induces neural tissue and dorsalizes mesoderm through BMP antagonists Chordin, Noggin, Follistatin and Shh. Equivalent capacity in chick resides at Hensen's node at anterior primitive streak, not along entire streak, hypoblast or yolk plug. Grafting node laterally induces ectopic notochord and neural plate expressing Sox2, secreting identical BMP antagonists and Shh to block BMP4. Molecular signature includes Goosecoid, FoxA2, Chordin identical to amphibian organizer. Primitive streak forms mesoderm broadly but organizer function localized to node, confirming Hensen's node as avian Spemann organizer homolog across vertebrate evolution.