What do sarcoma cells and liquid crystals have in common?
Fibroblastes confinés dans un disque En confinant ces cellules allongées dans des domaines circulaires bien définis (ici le diamètre est de 350 µm), elles ont tendance à s’aligner entre elles et le…
In many situations, the cells live in groups and function as communities... Furthermore, very often (for example during embryonic development or in the early stages of tumour growth), they are small populations confined by their micro-environment. This confinement creates conditions that largely control supra-cellular behaviour.
This collective organisation of cells is at the heart of the physical and biological research by Pascal Silberzan’s team (CNRS/UPMC/Institut Curie). Their latest work focuses on the supra-cellular organisation of elongated cells, known as spindle cells, that are found in many tissues and also in some sarcomas, a cancer that affects 4,000 adults and children each year in France. “Spindle cells align themselves in the same way as liquid crystal molecules - on a very different scale - in a well-known phase referred to as nematic, the one found in most liquid crystal displays,” recounts the researcher. This led our bio-physicists to describe these cells as an active nematic phase in which the cells continue to move autonomously. These active nematics are known for generally behaving chaotically. What is going on with these cells?
When the physics of crystal cells reflects the cellular world
To find out, the first step involved reproducing this organisation in vitro. They followed their physicist instincts, and in collaboration with theorists from Jean-François Joany’s group, they analysed this organisation using the formalism of liquid crystals and based on the classic idea that the organisation faults are markers of microscopic organisation. Thus by confining cells to well-defined circular domains, two alignment faults are systematically created on a diameter, as would be the case with “classic” nematics. “The position of these faults tells us that the activity of the cells at this stage is low,” explains Guillaume Duclos, a doctoral student at the time of the study. This means that the cellular movements are a lot less chaotic than what is observed with other active nematics. Why this difference? Due to the friction between the cells and their substrate. “Although they are active, the cells remain largely controlled by their interaction with the substrate, which prevents collective behaviour from being too disorganised,” according to Pascal Silberzan and Jean-François Joanny. These results show the behaviour and dynamic of spindle cell and sarcoma tissues in a different light.
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Topological defects in confined populations of spindle-shaped cells
Guillaume Duclos, Christoph Erlenkämper, Jean-François Joanny, Pascal Silberzan