Magic embryology: timing controls (Introduction)

by David Turell , Tuesday, January 25, 2022, 20:10 (821 days ago) @ David Turell

By a specific set of proteins:

https://phys.org/news/2022-01-lefty-protein-tightens-embryonic.html

"A protein known as Lefty pumps the brakes as human embryos begin to differentiate into the bones, soft tissues and organs that make us.

"This inhibitor protein is key during the early stages of life when the fates of embryonic stem cells are determined by the Nodal signaling pathway, according to Rice University bioscientists.

"Experiments by the lab of Rice's Aryeh Warmflash and led by postdoctoral researcher Lizhong Liu have visualized for the first time the mechanism by which Nodal and Lefty interact to specify the future body plan in a mammalian embryo.

"The study shows not only how Nodal signaling molecules, known as morphogens, are held in check by Lefty but also that Nodal proteins are passed directly from cell to cell, triggering transcription of new Nodals by the recipient. At the same time, a wave of Lefty transcription is transiently triggered in the cells when they first receive Nodal, regulating the speed of the wave.

"'Basically, we show that rather than gradients of protein forming and instructing cells to become different cell types, the molecules involved do not diffuse at all," Warmflash said. "Instead, cells relay the signal so that each cell produces the signal and passes it to its neighbor, which causes the neighbor to produce it and so on. It's kind of like a game of telephone."

***

"Traditionally, patterns are thought to arise because some proteins diffuse faster than others, Liu said. Local Nodal activity could cause production of Lefty, which diffuses farther than Nodal and limits the signal to a territory of a particular size, a theory that he said has not been rigorously tested.

"To the researchers' surprise, the direct observation of endogenous molecules showed no sign of Nodal diffusion. Instead, the wave that moves inward is the result of new Nodal proteins produced by each cell that then triggers its neighbor to do the same.

"The lab was able to prove this is essential for the wave by creating cells that lack the Nodal protein. These cells could receive the signal but not pass it on to their neighbors.

"The researchers also found that while Lefty didn't diffuse in their gastrulation experiments, it can move over much longer range in other contexts."

Comment: Darwin evolution theory has no explanation for this process. It has to be developed all at once by design, since it is irreducibly complex.