Practice question

Gene expression profile of chick Hensen's node determined by in situ hybridization and quail grafts mirrors amphibian organizer transcriptome: goosecoid homeobox, chordin BMP antagonist, noggin, FoxA2/HNF3beta and Sonic hedgehog axial signal. Both structures self-differentiate into notochord and prechordal plate while inducing neural plate. Nieuwkoop center expresses earlier beta-catenin and Siamois, animal pole cells ectoderm, vegetal pole endoderm not organizers. Molecular equivalence plus functional transplantation evidence confirms Hensen's node expresses markers equivalent to Spemann organizer establishing axis conservation across vertebrates. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.