Magic embryology: (Introduction)

by David Turell , Sunday, July 31, 2022, 23:05 (846 days ago) @ David Turell

Nuclear position controls studied:

https://www.the-scientist.com/news-opinion/how-wandering-nuclei-shape-developing-embryo...

"Early in development, all animal embryos pass through an almost identical stage where they form a blastoderm, which is a hollow ball of a few thousand cells. From that hollow ball, layers of cells start to fold into shapes that will become different parts of the body. Although the behavior of cells and the patterning of the embryo after the blastoderm stage is well-understood, how the blastoderm itself is made has remained a longstanding mystery.

"Now, a team of biologists and applied mathematicians at Harvard University in Massachusetts have developed a framework for understanding the general principles by which cell nuclei move and arrange themselves during the earliest stages of embryonic development to form the blastoderm.

***

"The researchers approached the study with two hypotheses: that the nuclei might push away nearby neighbors, and that each nucleus experiences a force that pulls it away from other nuclei and into empty space. They formalized these two hypotheses with mathematical models and made computer simulations of the developing embryos. Ultimately, the latter hypothesis—that nuclei are somehow pulled into the egg’s remaining empty space—best matched their observations.

***

"So how do the nuclei sense the space around them? The researchers hypothesize that microtubules attach to each nucleus self-assemble and grow outward, preferentially pulling the nuclei toward empty space because they can grow longer in that direction.

"Ensuring that nuclei are where they need to be in the blastoderm sets the foundation for all subsequent development to happen correctly, explains Stefano Di Talia, a developmental biologist at Duke University in North Carolina who didn’t work on the study. “Even more importantly, a lot of the mechanisms that have to do with the formation of the blastoderm are really fundamental cell biological and biophysical questions,” such as how the cell cycle is coordinated with biochemical signals and mechanical forces generated by the cytoskeleton to position things correctly, he says. (my bold)

"Di Talia says the ability of microtubules to pull nuclei into position is a fascinating hypothesis and could be a more general mechanism to explain how cells move during development and morphogenesis. “I think there’s going to be lot of situations where microtubule-driven processes are going to control the positioning of nuclei or organelles,” he says, “and I think the systems where you can really learn the biophysics of how that works are going to be very helpful.'”

Comment: note the bold. The cell nuclei move by following biochemical signals and mechanical forces, but how those signals and forces are coordinated comes from instructions sent by the DNA interpreting the proper information it has. This cannot be developed in step-by-step fashion. It must be designed all at once.