Arthur Molines (I2BC Gif-sur-Yvette)
Effect of viscosity and crowding on cytoskeleton dynamics: an in vitro and in vivo exploration
The cytoplasm is a crowded, viscoelastic environment whose physical properties change according to physiological or developmental states. The physical properties of the cytoplasm, which impact cellular functions in vivo, remain poorly understood. Here, we probe the effects of cytoplasmic concentration on microtubules by applying osmotic shifts to fission yeast, moss, and mammalian cells. We demonstrate that the rates of both microtubule polymerization and depolymerization scale linearly and inversely with cytoplasmic concentration. An increase in cytoplasmic concentration proportionally decreases the rates of microtubule polymerization and depolymerization, whereas a decrease in cytoplasmic concentration leads to the opposite effect. Numerous lines of evidence indicate that these effects are due to changes in cytoplasmic viscosity rather than cellular stress responses or macromolecular crowding per se. We reconstituted these effects on microtubules in vitro by tuning viscosity. Our findings indicate that, even in normal conditions, the viscosity of the cytoplasm modulates the reactions that underlie microtubule dynamic behaviors.