The skeleton of cells, or cytoskeleton, is involved in several vital functions. It is made of microtubules that act as rails for intracellular transport, while allowing for the distribution of chromosomes during cell division. In both cases, these long tubular elements must be sufficiently rigid to function normally. In other situations—during cell migration in particular, or to adapt to a changing environment—the microtubules fold and unfold to deform the skeleton. When this happens, the tubes must soften; otherwise, they break. The cytoskeleton is, therefore, constantly evolving.
The chemical structure of microtubules varies. But what is the relationship between the biochemical variations in these tubes and their mechanical properties? "We developed a microfluidic tool for the in vitro measurement of microtubule plasticity," said Manuel Théry, Laboratory Director at CEA-BIG. "Stabilizing the chemical features of microtubules gives us a chance to answer this question." Such was the method that the scientists chose, in partnership with peers from Stanford University who discovered an enzyme adding groups of five atoms to tubulins (the filaments constituting the microtubules) by acetylation. "This acetylation is preserved in many species," Théry said. "Since nature only keeps useful features, we can only guess that this acetylation must play an essential role." Using their microfluidic tool to observe the acetylated microtubules, the researchers revealed that this chemical transformation actually turns what can be seen as an oak... into a reed.
How is this possible? "Acetylation may act as a lubricant by allowing the 13 filaments that constitute the wall of the microtubules to shift and pile up on top of each other, thus relaxing the stress," Théry said. This raises another question: how is the enzyme responsible for acetylation recruited when the microtubules need to soften? "For now, we are only at the stage of hypotheses," Théry reckoned. "We think that when the tube folds, there might be an opening in the wall through which the enzymes can cross to acetylate the filaments, allowing them to soften instead of break under stress. This 'respiration' of microtubules would be a cycle combining biochemical and mechanical mechanisms." Now the scientists are trying to prove it.