Veterinary Embryology 8.1 - 8.4: Notochord Formation

Question

Notochord Formation

Magdalena Badenhorst · Accepted Answer

The notochord develops from the primitive node located at the cranial end of the primitive streak. From the node, cells proliferate and migrate forward into the future head region where they become the rod-shaped notochord.

Magdalena Badenhorst · Answer

Proliferating cells from the primitive node invaginate to form a narrow, tubular structure known as the notochordal process. The notochordal process extends cranially, between the epiblast and endoderm, to reach the caudal edge of the prechordal plate.
The floor of the notochordal process then fuses with the underlying endoderm, but both soon disappear. The remaining notochordal process (i.e. its former roof and walls) flattens to form a single layer of cells, the notochordal plate, which is intercalated in the embryonic endoderm.
A longitudinal groove then forms on the ventral surface of the notochordal plate. This groove abstricts (cuts-off) from the endoderm in a cranio-caudal direction, and the lips of the groove fuse to form a solid cord of cells that constitutes the cranial part of the notochord. Note that a small, caudal portion of the notochordal process (i.e. that which lies just ventral to the
primitive pit) is not involved in the formation of the notochordal plate, and that its notochordal canal is retained for a while. This persistent notochordal canal will later temporarily connect the future amniotic cavity and yolk sac; it is then known as the neurenteric canal.
The endodermal defect caused by the notochordal abstriction is closed by proliferating endodermal cells. As the notochordal process extends cranially, the primitive node and primitive pit are pushed caudally along the primitive groove. As the node retreats, it leaves a trail of cells that will form the caudal part of the notochord. The caudal part of the notochord is continuous with the cranial part; however, it does not fuse with the endoderm and does not have a tubular stage. When fully developed, the notochord extends the length of the embryonal disc and is flanked on either side by mesoderm.

Veterinary Embryology 8.1 - 8.4

Notochord Formation

The notochord develops from the primitive node located at the cranial end of the primitive streak. From the node, cells proliferate and migrate forward into the future head region where they become the rod-shaped notochord.

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