How cells control the physical state of embryonic tissue-ScienceDaily

Professor Otogar Campas of the University of California, Santa Barbara, who is currently a Mericamp Chair in Systems Biology and Biotechnology, and Professor Kim Sang-woo, a researcher at Campus, addressed this question and made a surprising discovery.

“When many cells are physically interacting, how does the system work collectively? What is the physical state of the ensemble?” Campus said.

In fact, he explained that embryonic cell tissue is a “strange substance” that each cell consumes chemical energy and uses it to force adjacent cells to coordinate their actions. He added that in vitro studies with cells in the synthetic dish provided only part of the picture. By studying the cells of the living embryo, which is the natural environment, we were able to understand how the cells control the population state and the phase transition that results from the push and pull symphonies.

In a treatise published in Nature Physics, Campàs, Kim et al. Report on the development of a computational framework that captures various cell-cell interactions and connects them to embryonic tissue dynamics. Unlike previous simulations, this framework takes into account some important features related to cell interactions, such as space between cells, cell shape, and tension fluctuations where cells meet.

“To fully understand the physical behavior of embryonic tissue, the model must take into account all important aspects of embryonic tissue at the cellular scale. This is because the characteristics of the embryonic tissue are mutual on the cellular scale. Because it comes from action, “said Kim, the lead author of the study. .. “There are many models for studying embryonic tissue, but there is no general framework that includes these important functions, which hinders an overall understanding of the physical behavior of embryonic tissue.”

Shake cells

According to researchers, embryonic tissue physically behaves like an aqueous bubble. This is a system consisting of individual pockets of air in a liquid. Think of soap bubbles and beer bubbles.

“In the case of foam, its structure and dynamics are dominated by surface tension,” Kim said. Similar forces are found both on the inner surface of the cell membrane and between cells, where cells make contact with each other in embryonic tissue.

“The effective force acting on cell-cell connections is governed by cortical tension and cell-cell adhesion. Therefore, the net force at cell-cell contact can be modeled as effective surface tension.”

However, unlike the more static forces between cells of general form, the forces between cells of embryonic tissue are dynamic.

“The cells in the tissue do not generate static forces, but show dynamic push-pull over time,” Campàs explained. “And it turns out that it is actually these tension fluctuations that effectively” melt “the tissue into a fluid state. It is this fluidity of tissue that allows cells to reorganize and shape tissue, he explained.

Researchers tested the model by measuring how the power of embryonic zebrafish, a popular model organism for people studying vertebrate development, changes over time. Relying on a technique developed at Campàs Lab using small magnetic droplets inserted between zebrafish embryo cells, they move behind the fluid state of the tissue by the way the droplets deform. I was able to confirm the power.

Their finding that tension fluctuations are responsible for tissue fluidity during development is with the generally accepted notion that changes in cell-cell adhesion are important factors controlling tissue fluidity. Is in contrast-when the adhesion between cells reaches a certain height, the threshold, the tissue becomes fluid.

“But cell forces and tensions fluctuate in the embryo, so they may have played an important role in tissue fluidization,” Campàs said. “So, when I ran the simulation and experimented, I realized that in reality, sway was much more important for fluidization than for adhesion.” The fluid state of the tissue is static cells. It is the result of force dynamics, not changes in tension or adhesion.

The results of this study affect the field of physics, especially the area of ​​active substances, the systems of many individual units, each of which consumes energy and applies mechanical forces that collectively exhibit emergent collective action. May be given. This study can also provide information for biological studies investigating how changes in individual cell parameters can control the overall state of tissues such as embryonic development and tumors.