This view is substantiated by the common expression of several genes, including goosecoid, Cnot, noggin, nodal, and the sharing of strong axis-inducing properties upon transplantation.
Cells involuting further laterally in the blastopore, or entering via Hensen's node and the anterior primitive streak, contribute to gut, notochord and somites.
Adding to this, Brachyury and caudal homologues are expressed circumferentially around the blastopore lips in the frog, and along the primitive streak in chick and mouse.
When the primitive streak is approaching its full length (almost 2 mm), the tip, now designated Hensen´s node, forms a novel compact assembly of cells.
This leads to a dynamic nature of the node and a non-homogeneous cellular composition as can be seen from the fate of emigrating cells and from gene expression patterns.
Therefore, the primitive node (the dorsal lip of the blastopore) secretes BMP antagonists, including noggin, chordin, and follistatin.
This anterior region, the germinal crescent, does not form any embryonic structures, but it does contain the precursors of the germ cells, which later migrate through the blood vessels to the gonads.
Shh is strongly expressed in the rostral half of Hensen's node both dorsally and ventrally, future floor plate and notochord cells.
Anteriorly (zone a), the derivatives of the node that express HNF-3b and Shh (notochord and floor plate) are separated by forming basement membrane but are closely associated.
Caudal to the border of the median pit, the cells of the node that express HNF-3b but not Shh (zone c) are closely packed without exhibiting any epithelial arrangement.