Cellular “Tornados” Shape Tissues and Organs

Biochemists and theoretical physicists in Geneva have described a mechanism by which cells self-organize and create a vortex effect that sculpts organs and tissues into their functional shapes, like the folds of the intestines of alveoli of the lungs.

“In theoretical physics, we know that if there are active constraints between cells, then they will order themselves and spontaneously adopt collective behaviors known as ‘emergent’, because they do not exist at the scale of a single cell,” says Karsten Kruse, professor in the departments of biochemistry and theoretical physics at the University of Geneva Faculty of Science.

To study the role these emergent behaviors play in forming the particular shapes of a multicellular tissue, the team sought to force muscle cells to reproduce simple shapes in vitro. When confined on adhesion discs, the cells rapidly self-organized by aligning themselves in the same direction. A circular motion was created around a vortex that orients the cells to collectively deform the cell monolayer into a protrusion, which are commonly seen in embryo development. This cylindrical protrusion is maintained by the collective rotational forces of the cells, creating a tornado-like effect.

“When the cells are placed on a flat surface, they align themselves and form structures similar to a field of wheat where the wind has passed through: there is an overall order with sudden changes in direction at punctual places,” says Aurélien Roux, a professor in the Department of Biochemistry. These changes in direction are called topological defects and represent the places where the physical forces exerted on the cells are either very weak or immense. He compared this to the way a crowd of people in a confined space will, out of ease, begin to form lanes and move through them in the same direction.

Kruse adds that a spiral, which concentrates the cellular forces in its center, accumulates newly formed cells there by cell division. The spiral then will gradually become a vortex, creating a protrusion in the middle—the center of the tiny 3D cellular tornado.

 “[O]ur study shows that cells do not escape the laws of physics but, subjected to the same constraints as all materials, they exploit them to concentrate their forces and create shapes only seen in living organisms,” Kruse adds.

The findings were published recently in Nature Materials. The team will now study simple examples of embryos to compare them with theoretical models and in vitro experiments.