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#Hensen's node

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Chick development-ll

Hensen's node expresses markers equivalent to:

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.

Ref: Gilbert, Developmental Biology 12th ed., Chapter 12: Hensen's node markers equivalent to Spemann organizer.

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Chick development-ll

Hensen's node transplantation into another gastrula location:

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.

Ref: Waddington 1932 chick organizer transplantation - Hensen's node secondary axis induction, Developmental Biology.

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