Nature sub-journal: Cell tornadoes shape our organs

How do the different shapes of our organs and tissues arise? To answer this question, a research team at the University of Geneva (UNIGE) in Switzerland forced muscle cells to spontaneously replicate simple shapes in vitro .

Biochemists and physicists observed that by confining cells to sticky discs, cells quickly organized themselves by aligning in the same direction

Our bodies are made up of organs and tissues, each with its own unique shape
.

But how do cells form gut folds or alveoli? Is it possible to recreate these shapes in vitro? To answer these questions, biochemists joined theoretical physicists to test the ability of cellular tissues to model themselves spontaneously

"In theoretical physics, we know that if there are active constraints between cells, then they adjust themselves to spontaneously adopt collective behaviors known as 'emergence' because they do not exist on the scale of individual cells," Karsten Kruse explained
.

He is a professor in the Departments of Biochemistry and Theoretical Physics of the Faculty of Science at UNIGE

To this end, the Geneva team chose the ability of human muscle cells to contract, whose rod shape allows them to make themselves: "When cells are placed on a flat surface, they make themselves and form structures similar to a field of wheat where the wind passes: on time location, there will be an overall sequence of directions," said Aurélien Roux, professor in the Department of Biochemistry at the Faculty of Science at UNIGE
.

Changes in these directions are called "topological defects": they represent places where the physical forces exerted on the cell are either very weak or, conversely, very large

Topological flaws create honeycomb tornadoes

So how do these topological defects affect the shape of the tissue? To understand their role, the interdisciplinary team grew cells on adhesion discs
.

"This involves confining our muscle cells to a surface, surrounded by repulsive molecules, forcing them to form a circle," explains Aurélien Roux

Therefore, only one topological defect remains in the center of the circle
.

"We saw that the helix concentrates the cellular force in the center, where the newly formed cells are gathered through cell division

Spontaneous morphogenesis of cells governed by physical laws

The researchers found that muscle cells spontaneously formed tornado-like structures similar to those observed during embryonic development, such as the folds of fingers or the layers of the intestine
.

"This spontaneous self-organization without biochemical regulation may be the initial stage of protrusion formation in the embryo," says Aurélien Roux

The researchers will now study simple embryonic examples in order to compare with theoretical models and in vitro experiments, and to understand different possible mechanisms regulating forces in embryos
.

article title

Integer topological defects organize stresses driving tissue morphogenesis