Cellular tornadoes sculpt our organs

Date:
February 11, 2022
Source:
Universite' de Gene`ve
Summary:
How are the different shapes of our organs and tissues generated? To
answer this question, a team forced muscle cells to spontaneously
reproduce simple shapes in vitro. By confining them on adhesion
discs, the biochemists and physicists observed that the cells
rapidly self- organize by aligning themselves in the same
direction. A circular motion is created around a vortex -- called
a topological defect -- which, by orienting the cells, allows them
to join forces, deforming the cell monolayer into a protrusion, a
structure commonly observed in embryo development. This cylindrical
protrusion is maintained by the collective rotational forces of
the cells, creating a tornado-like effect. The formation of these
cellular tornadoes would therefore constitute a simple mechanism
of spontaneous morphogenesis, dictated by the unique properties
of multicellular assemblies.



FULL STORY ==========================================================================
How are the different shapes of our organs and tissues generated? To
answer this question, a team from the University of Geneva (UNIGE), Switzerland, forced muscle cells to spontaneously reproduce simple
shapes in vitro. By confining them on adhesion discs, the biochemists
and physicists observed that the cells rapidly self-organise by aligning themselves in the same direction. A circular motion is created around
a vortex -- called a topological defect - - which, by orienting the
cells, allows them to join forces, deforming the cell monolayer into a protrusion, a structure commonly observed in embryo development. This cylindrical protrusion is maintained by the collective rotational
forces of the cells, creating a tornado-like effect. The formation of
these cellular tornadoes would therefore constitute a simple mechanism
of spontaneous morphogenesis, dictated by the unique properties of multicellular assemblies. These results can be read in the journal
Nature Materials.


==========================================================================
Our bodies are made up of organs and tissues, each with its peculiar
shape. But how do cells manage to form the folds of the intestine or
the alveoli of the lungs? Is it possible to reconstitute these shapes
in vitro? To answer these questions, biochemists have joined forces
with theoretical physicists to test the ability of cellular tissues to spontaneously self-model.

"In theoretical physics, we know that if there are active constraints
between cells, then they will order themselves and spontaneously adopt collective behaviours known as 'emergent', because they do not exist at
the scale of a single cell," explains Karsten Kruse, professor in the departments of biochemistry and theoretical physics at the UNIGE Faculty
of Science. The theory predicts that one of these emerging behaviours
is the adoption of particular shapes by a multicellular tissue. It is
this hypothesis that we wanted to test in vitro.

To do this, the Geneva team selected human muscle cells that are capable
of contracting and whose rod shape allows them to align themselves:
"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 Aure'lien Roux, a professor in the Department of Biochemistry at the UNIGE Faculty of Science. These changes in direction
are called 'topological defects': they represent the places where the
physical forces exerted on the cells are either very weak or, on the
contrary, immense.

Topological defects create cellular tornadoes So what impact do these topological defects have on 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 that force them to form a circle," explains
Aure'lien Roux. The cells quickly start to rotate together to form an
ordered spiral. "We can see a spontaneous movement of the cells, like
when a crowd is forced to walk around a room and ends up going in the
same direction for ease," he continues.

Thus ordered, only one topological defect remains at the centre of
the circle.

"We see that the spiral, which concentrates the cellular forces in its
centre, accumulates the newly formed cells there by cell division. Thus,
the spiral will gradually become a vortex, creating a protrusion in
the middle of the disc," explains Karsten Kruse. And this protrusion
can reach up to half a millimetre, which is enormous for a base that is
not a hundredth of a millimetre in size. The Geneva team is therefore
observing a real little 3D cellular tornado that is spinning around.

Spontaneous cell morphogenesis subject to the laws of physics
The researchers found that the muscle cells spontaneously formed
tornado-like structures, which resemble the structures observed in
the development of the embryo, such as the fingers or the folds of the intestinal layer. "This spontaneous self-organisation without biochemical regulation could be the initial stage in the formation of protrusions in
the embryo," says Aure'lien Roux. The scientists also highlighted that
it is indeed the topological defects that control the organisation of
cells and determine the shape they will adopt.

"Finally, our 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," adds Karsten Kruse.

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

========================================================================== Story Source: Materials provided by Universite'_de_Gene`ve. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Pau Guillamat, Carles Blanch-Mercader, Guillaume Pernollet, Karsten
Kruse, Aure'lien Roux. Integer topological defects organize
stresses driving tissue morphogenesis. Nature Materials, 2022;
DOI: 10.1038/ s41563-022-01194-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220211102656.htm

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