Laboratoire Matière et Systèmes Complexes

Thèse de Agnès Miermont effectuée sous la direction de Pascal Hersen.

Soutenance le vendredi 8 février 2013 à 14 heures.

Lieu : bâtiment Condorcet, Salle Luc Valentin 454A (4ème étage).

La soutenance sera suivie d’un pot au 6e étage.

Severe osmotic compression of the yeast Saccharomyces cerevisiae

Abstract: Cells have developed several signaling pathways and transcriptional regulatory networks to regulate their size and coordinate their growth with the cell division. Importantly, the interior of a cell is naturally packed with macromolecules and is said to be crowded. Macromolecular crowding has been intensely studied in vitro and is known to affect the kinetics of reactions. However, studying the effects of crowding in vivo is more challenging due to the high level of complexity and heterogeneity in the cytoplasm. In this thesis, we address the effects of changing the cellular volume on the kinetics of biochemical reactions in live Saccharomyces cerevisiae cells. We osmotically compressed yeast cells, thus increasing the total macromolecular density and investigated the impact of such crowding on the kinetics of signal transduction. Cell shrinkage is expected to increase the intracellular viscosity and may severely slow down the functioning of signaling pathways and cellular processes. Indeed, by progressively increasing the level of compression, we recorded a progressive slow-down of several, unrelated biological processes until a point for which cell dynamics were arrested. This was observed for the nuclear translocation of several transcription factors (Hog1, Msn2, Crz1, Mig1, and Yap1) as well as for the mobility of the proteins Abp1 and Sec7. We further showed that increasing compression decreases the ability of proteins to diffuse in both yeast and higher eukaryotic cells. We propose that this slowing down upon cellular compression is very general and is reminiscent of a soft colloidal glassy-like transition. Our results suggest the importance for cells to regulate their volume and their cytoplasmic crowding to function properly.