File:Human notochord development theories 1.jpg

Human Notochord Development Theories

Textbook concepts compared to our proposed theory.

Schematic summary of the two main developmental concepts in modern textbooks. Ventral view with removed endoderm. The black lines indicate the level of the transversal sections (epiblast/ectoderm is superior in each section). In A the notochord develops in two phases. First the notochordal process (NP) extends over almost the entire length of the embryo (left). Within the notochordal process is a luminal extension of the primitive pit. The NP intercalates between the endoderm and the bottom of the NP ‘breaks down’ along the length of the neurenteric canal. This process results in the notochordal plate (right), which retracts between the mesenchyme forming the definitive notochord. B Illustrates our proposed theory. All precursors of the notochord are simultaneously present. We now know that the NP is shorter in length and that the definitive notochord does not develop cranially in the embryo, but merely in the middle region (Figs 3 and 5). Definitive notochord (DN): red, endoderm: light grey (in sections), epiblast or ectoderm: dark blue, dark grey (in sections), gastrulation area (GA): purple, neurenteric canal: white, notochordal plate (NPL): yellow, notochordal process (NPR): cyan blue, prechordal plate (PP): brown.

Fig 1

Journal.pone.0205752.g001.jpg

doi: https://doi.org/10.1371/journal.pone.0205752.g001