Let's study ID: shaping organs (Introduction)

by David Turell @, Friday, December 24, 2021, 15:07 (27 days ago) @ David Turell

A study in zebra fish shows the forces that work:


"...researchers at Harvard Medical School have discovered a mechanical process by which sheets of cells morph into the delicate, looping semicircular canals of the inner ear.

"Published Dec. 22 in Cell, the research, done in zebrafish, reveals that the process involves a combination of hyaluronic acid, produced by cells, that swells with water, and thin connectors between cells that direct the force of this swelling to shape the tissue.

"Although conducted in zebrafish, the work reveals a basic mechanism for how tissues take on shapes -- one that is likely to be conserved across vertebrates, the researchers say, and may also have implications for bioengineering.


"'The inner ear is a model for how cells work together to make complex structures that are needed for organisms to function," Megason added. "We went into it thinking it was a beautiful structure, but not knowing what we would find."

"What they did find surprised them.

"The conventional thinking is that the proteins actin and myosin act as tiny motors inside cells, pushing and pulling them in different directions to fold a tissue into a specific shape. However, the researchers discovered that zebrafish semicircular canals form through a markedly different process. During development, the cells produce hyaluronic acid, which is perhaps most well known as an antiwrinkle agent in beauty products. Once in the extracellular matrix the acid swells up, not unlike a diaper in a swimming pool. This swelling creates enough force to physically move nearby cells, but since the pressure is the same in all directions, the researchers wondered how the tissue ends up stretching in one direction and not another to form an elongated shape. The team found that this is accomplished by thin connectors between cells -- dubbed cytocinches -- that constrain the force.

"'It's like if you were to put a corset on a water balloon and deform it into an oblong structure," Munjal said. This combination of swelling and cinching progressively shapes an initially flat sheet of cells into tubes.

"'Our work shows a new way of doing things," Megason said, adding that he hopes it will encourage people to consider additional mechanisms that may be involved in shaping tissues. "Cells have to use many different forces in order to accomplish what they need to, and time will tell exactly what the balance is between the molecular approaches of actin and myosin and the more physical approaches of pressure.'"

Comment: this study in the embryology of zebra fish is irreducibly complex. To shape an organ all of the forces and cell parts must act in concert. Therefor a process that cannot be developed stepwise. The process of embryology itself denies Darwin and requires design and a designer mind.

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