In a study published in the prestigious journal Nature and discovered by Quanta Magazine, researchers have shown that epithelial tissues that make up the skin and coverings of internal organs are not just randomly distributed clusters of cells. They actually present two well-defined planes of symmetry which give them fascinating properties; functionally we can now describe it as Liquid crystals. A discovery that could potentially have very important implications for medicine.
This work is all about the idea of Liquid crystal. As the name suggests, they are liquids; So technically they can flow like water – but with one important difference. In contrast to conventional liquids, in which the atoms move in a completely chaotic manner relative to one another, the components of a liquid crystal are still present certain level of organization.
It is not a true crystal structure, such as that found in almost all minerals. Liquid crystals are not arranged in a precise pattern that repeats in space. On the other hand, they tend to align in a certain direction when exposed to certain factors such as temperature or an electric field.
It is this directionality, called Anisotropy, which represents the origin of the properties of liquid crystals. For example, those used in LCD (liquid crystal display) screens refract light differently depending on their orientation. This makes it possible to display different colors by locally controlling the orientation of the material using small electrical pulses.
From biological tissue to liquid crystals
But liquid crystals are not only found in electronic objects. They are also omnipresent in nature! For example, the bilayer of lipids that forms the membrane of our cells can be compared to a liquid crystal. And it's not just a scientific anecdote; This organization is very important to maintain both the structural integrity and flexibility of these basic building blocks. In other words, The dynamics of liquid crystals are simply essential to life as we know it.
For this reason, researchers are trying to explore the biological role of liquid crystals in more depth. More specifically, researchers have been trying for several years to show that tissues, that is, groups of cells organized to perform a very specific task, can also meet this definition.
From the outside, the interest of this work is anything but obvious. But it's not just a very abstract puzzle; It's a question full of very concrete practical implications. Because if we succeed in proving that tissues are actually comparable to liquid crystals, this would immediately open up a particularly large and fascinating new area of research. The mathematical tools that physicists use to predict the behavior of crystals could suddenly be applied to cell biology, with far-reaching implications for basic research and clinical medicine.
But so far no one has been able to prove it. All of these efforts hit the same mathematical – or more accurately geometric – wall; Theorists and experimentalists have never been able to agree on the intrinsic symmetry of biological tissues. It's unfortunate when you know that this is THE defining feature of a liquid crystal.
The two concepts eventually reconciled
According to Quanta Magazine, some researchers have managed to show through computer simulations that groups of cells could have a so-called “hexatic” symmetry. We call that a sixth order symmetry, where the elements are arranged in groups of six. However, in laboratory experiments they appear to adopt a so-called “nematic” symmetry. To use Quanta's analogy, according to this model, cells behave like a liquid made up of rod-shaped particles, a bit like matches that spontaneously align themselves in their box. It is then a Second order symmetry.
This is where the authors of this work, who are affiliated with the University of Leiden in the Netherlands, come into play. They suggested that it would be possible to establish a strong connection between biological tissues and the liquid crystal model under one condition: it would be necessary prove that tissues have both symmetries at the same time, at different scales. More specifically, the cells should be arranged in an array large-scale second-order symmetrywith a There is a sixth-order symmetry hidden in this pattern which appears as you zoom in further.
The research team therefore first cultivated very thin layers of tissue, the contours of which were highlighted with a marker. But there is no question of analyzing their shape with the naked eye; The relationship they wanted to establish had to be based on objective data and not just a visual impression. According to Quanta, they therefore used a mathematical object called a shape tensor, which allowed them to mathematically describe the shape and orientation of each unit.
Thanks to this analytical tool, they were able to experimentally observe this famous double symmetry. On a large scale, they observed the previously documented nematic symmetry in groups of just a few cells. And upon closer inspection, a hexatic symmetry was apparent – just like in the computer simulations. “It was incredible how well the experimental data and the simulations fit together,” explains Julia Eckert, co-author of this work cited by Quanta.
A new way of understanding how life works
This is the first time solid evidence of this connection has been provided, and it certainly is great experimental success. We now know that certain tissues can be viewed as liquid crystals. And this discovery could pave the way to an entirely new area of research in biology.
At a functional level, the specific implications of this relationship are not yet entirely clear. The good news, however, is that it will now be possible to use fluid mechanics equations, traditionally reserved for liquid crystals, to study cell dynamics.
And this new way of looking at tissue could have profound implications for medicine. This makes it possible, for example, to examine how certain cells migrate through tissue. These observations could provide insight important mechanisms to the first stages of development of organisms, to the spread of cancer cells producing metastases, and so on.
But there is another, even more exciting prospect on the horizon. It's too early to tell, but it's possible that this discovery represents one small revolution in our understanding of life.
At the end of the Quanta article, one of the study authors summarizes this idea by explaining one of the most important concepts in all of biology. We have long known that the architecture of a tissue is the origin of a set of forces that directly determine its physiological functions. In this context, This double symmetry could therefore be one of the cornerstones of the complexity of lifeand serve as the basis for many mechanisms that are still unknown today! Therefore, it is appropriate to carefully monitor the impact of this work, as it is likely to profoundly transform biophysics and medicine.
The text of the study can be found here.