Magic embryology: forming a neural tube (Introduction)

by David Turell , Monday, May 16, 2022, 20:20 (922 days ago) @ David Turell

A major process for vertebrate embryos:

https://www.sciencedaily.com/releases/2022/05/220516123943.htm

"In the human embryo, the neural tube forms between the 22nd and 26th day of pregnancy. Later, the brain and spinal cord will develop from this tube. The neural tube forms when an elongated flat tissue structure, the neural plate, bends lengthwise into a U shape and closes to form a tube. What drives this development is not yet clear. Researchers...have now been able to show that the surrounding tissue is likely to play a significant role by exerting pressure from the outside.

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"Until now, scientists assumed that local biochemical signals in the cells of the neural plate lead to the formation of these hingepoints, and that the hingepoints play an active role in the formation of the neural tube. However, there has been no explanation as to why the hingepoints form exactly where they do.

"The ETH researchers now postulate an alternative mechanism, according to which the neural plate does not actively bend itself, driven by the hingepoints, to form a tube. Rather, the neural plate initially adopts a slightly curved shape for anatomical reasons. Subsequently, the tissue lying either side of the neural plate (ectoderm and mesoderm) expands. This applies pressure to the neural plate from the side and causes it to passively form into a tube.

"This showed that the processes were best explained by the expansion of the surrounding tissue. "We use this to demonstrate that hinge points can arise as a result of external pressure. So they are probably not drivers of neurulation, as was previously thought, but a side effect of it," Iber says. Instead, the driver appears to be the surrounding tissue.

"Especially in the upper part of the back, neurulation can be explained by the expansion of the adjacent tissue, because for anatomical reasons the neural plate is slightly pre-bent already. Further down the future back, this initial curvature is absent; the neural plate is flat in this area.

"With their modelling, the ETH scientists were able to show that here, too, neurulation can be explained by external forces: protein fibres and anchor proteins help to pull the neural plate together like a zip. This causes the neural plate to curve and close into a tube.

"According to the researchers, the fact that the mechanisms differ in the upper and lower back could explain why spinal malformations don't occur with the same frequency all along the back. Spina bifida is more common in the lower back, where the surrounding tissues are less supportive."

Comment: this precise sequence of actions require delicate design from the beginning. Sequential chance mutations are incapable of creating this design.