Magic embryology: both genes and physical forces (Introduction)

by David Turell , Wednesday, July 13, 2022, 21:52 (646 days ago) @ David Turell

The physical forces of cell growth help form an embryo:

https://www.quantamagazine.org/embryo-cells-set-patterns-for-growth-by-pushing-and-pull...

"... Amy Shyer, a developmental biologist at Rockefeller University. In her view, physical forces of contraction and compression that act on cells as they grow and divide could also play a central role.

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"And now she has proof of it. In a paper published in Cell in May, Shyer, her co-senior author and fellow developmental biologist Alan Rodrigues and their colleagues showed that mechanical forces could induce embryonic chicken skin to create follicles for growing feathers. Just as surface tension can pull water into spherical beads on a glass surface, so too can the physical tensions within an embryo set up patterns that guide growth and gene activity in developing tissues.

"As an organism grows and develops, the cells in its tissues pull and push on each other and on the supportive protein scaffolding (extracellular matrix) to which they are intricately linked. Some researchers have suspected that these forces, coupled with changes in the pressure and rigidity of the cells, might direct the formation of complicated patterns

"In the laboratory of morphogenesis at Rockefeller University that they jointly lead, Shyer and Rodrigues removed the skin from a chicken embryo and disintegrated the tissue to pull apart the cells. Then they placed a drop of the cellular solution into a petri dish and let it grow in culture. They watched as the skin cells self-organized into a ring on the floor of the dish — like a 2-D version of the ball of cells that the embryo normally becomes. Pulsating and contracting, the cells pulled on collagen fibers in the extracellular matrix that they assembled around themselves. Over 48 hours, the fibers gradually rotated, bunched together and then pushed each other apart, forming bunches of cells that would become feather follicles.

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"...by adjusting the rate of cell contraction and other variables, the researchers showed that physical tension in the embryonic mass directly affected the pattern. “I think the biggest surprise was the way the cells interacted with the extracellular matrix in this very dynamic way, in order to create these patterns,” Rodrigues said. “We realized that it is a reciprocal dance between the two.”

“"This suggests that contractility could be sufficient to drive pattern formation,” Camley said. “That’s a really new essential piece.”

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"In 2017, they took small slices of chicken embryo skin and watched closely as the tissue bunched up in preparation to form a follicle. Meanwhile, they tracked the activation of the genes involved in follicle formation. What they found was that gene expression happened around the same time that the cells bunched up — but not before.

“'Instead of ‘gene expression first, then mechanics later,’ it was sort of like mechanics was generating these shapes,” said Shyer. Later, they showed that even removing some of the gene-regulating chemicals didn’t disrupt the process. “That opened a door to say, ‘Hey, something else might be going on here,’” she said.

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“'We are realizing that all of the molecular gene expression, signaling and the production of forces in cell movement are just inextricably coupled to one another,” said Edwin Munro, a molecular biologist at the University of Chicago who was not involved in the study.

"Munro thinks the role of the extracellular matrix is more important than scientists currently realize, though recognition of its more central role in development is building. Recent research has linked forces in the extracellular matrix to the development of fruit fly eggs, for example.

"Rodrigues agreed. “It’s like the cells and the extracellular matrix are forming a material in and of itself,” he said. He describes this coupling of contractile cells and extracellular matrix as “active soft matter” and thinks that it points to a new way of thinking about the regulation of embryonic development happening through extracellular forces. In future work, he and Shyer hope to elucidate more details of physical forces in development and to merge them with the molecular view.

“'We used to think if we just studied the genome with more and more depth and rigor, all of this would be clear,” Shyer said, but “the answers to the important questions might not be at the level of the genome.” Once it seemed that developmental decisions were made through the interplay of genes and their products within cells, but the emerging truth is that “the decision-making can be happening outside of the cell, through the physical interactions of cells with each other.'” (my bold)

Comment: Think of the intricacies of this design. Genes driving cell growth in a pattern that produces form. The genes drive the cell growth which ends up in the desired shape as an indirect effect. This is well beyond chance development.