Magic embryology: cells using mechanical forces (Introduction)

by David Turell @, Monday, February 14, 2022, 18:04 (177 days ago) @ David Turell

With cells in membranes:

"...a new study found in a living embryo that the back ends of moving cell groups push the group forward. This runs contrary to previous findings, where cell groups grown in dishes of nutrients (cultures) pulled themselves forward with their front edges.


"Specifically, the study found for the first time in an animal tissue that proteins called integrins on the surfaces of the cells at the rear attach in greater numbers to the membrane as they move along, and exert more force in one direction, than the cells in the group's front. The integrin clusters (focal adhesions) observed in the embryo were smaller than those seen in culture studies, and broke down faster.


"The study results are based on mechanisms of cell movement established by past studies. For instance, a protein called actin is known to form the protein "skeleton" of cells, with actin chains able to grow in a certain direction, and apply force that change a cell's shape. Integrins, proteins built into outer cell membranes, interact both with actin networks, and proteins outside of cells. These and other proteins form a system that a cell uses to briefly attach to and "roll along" a basement membrane, a pliable mesh of proteins and sugars. What was unknown going into the current study was how tissues in living animals apply force in groups to generate this motion.


"Using "bleached" dots on the basement membrane to measure shape changes (deformations) on a minute scale, and a new software called embryogram to calculate how far the dots move as the primordium "grips" the membrane, the researchers determined how much the cells pulled and pushed on the membrane, "like a tire on pavement." The effect is much like the high school physics experiment where students draw two dots on a rubber band, and calculate the force applied as they stretch the band by measuring the change in distance between the dots.

"With these tools in hand, the team showed that the primordium cells link the force-generating actin-myosin network at the back end of the moving group through integrin clusters on the side closest to the basement membrane. The team theorizes that cells attached to membrane toward the back push on the cells in front of them to move the entire group. The researches also gained new insights on an established mechanism where cells have surface proteins that let them "sense" and follow a guidance cue called a chemokine, from low concentration to high concentration. The new study found, however, that cells toward the back end of the primordium sense the chemokine gradient more strongly.

"Interestingly, the study found that the primordium moved in a "continuous breaststroke" by pushing the basement membrane downward, sideways and backwards, much like the arms of a swimmer. The authors do not know why this is, but speculate that this is the most efficient way to move forward. They note that banana slugs also use the rear edge of the "foot" they apply to the ground, suggesting that evolution favors rear engine propulsions because they are most efficient at different size scales."

Comment: When two parents combine DNA's into one cell, creating a fetus for birth requires a very complex set of controls which on a designer could create. Embryology, itself, proves a designer exists.

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