Primitive node

Primitive node
Details
Days17
Identifiers
Latinnodus primitivus
Anatomical terminology

The primitive node (or primitive knot) is the organizer for gastrulation in most amniote embryos. In birds, it is known as Hensen's node, and in amphibians, it is known as the Spemann-Mangold organizer. It is induced by the Nieuwkoop center in amphibians, or by the posterior marginal zone in amniotes including birds.

This blastoporal axial organizer is conserved not only among tetrapods, but more broadly among Cnidaria, Ctenophora, and Bilateria – all major groups of animals except sponges. The classic demonstration of the region is due to Spemann (1924), in which transplanting the dorsal blastopore lip from one frog embryo to another causes the formation of an ectopic body axis.

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