Mitochondria reorganization upon proliferation arrest predicts individual yeast cell fate.

Most cells spend the majority of their life in a non-proliferating state. When proliferation cessation is irreversible, cells are senescent. By contrast, if the arrest is only temporary, cells are defined as quiescent. These cellular states are hardly distinguishable without triggering proliferation resumption, hampering thus the study of quiescent cells properties. Here we show that quiescent and senescent yeast cells are recognizable based on their mitochondrial network morphology. Indeed, while quiescent yeast cells display numerous small vesicular mitochondria, senescent cells exhibit few globular mitochondria. This allowed us to reconsider at the individual-cell level, properties previously attributed to quiescent cells using population-based approaches. We demonstrate that cell's propensity to enter quiescence is not influenced by replicative age, volume or density. Overall, our findings reveal that quiescent cells are not all identical but that their ability to survive is significantly improved when they exhibit the specific reorganization of several cellular machineries.

Yeast quiescence exit swiftness is influenced by cell volume and chronological age.

Quiescence exit swiftness is crucial not only for micro-organisms in competition for an environmental niche, such as yeast, but also for the maintenance of tissue homeostasis in multicellular species. Here we explore the effect of replicative and chronological age on Saccharomyces cerevisiae quiescence exit efficiency. Our study reveals that this step strongly relies on the cell volume in quiescence but is not influenced by cell replicative age, at least for cells that have undergone less than 10 divisions. Furthermore, we establish that chronological age strongly impinges on cell's capacities to exit quiescence. This effect is not related to cell volume or due to cell's inability to metabolize external glucose but rather seems to depend on intracellular trehalose concentration. Overall, our data illustrate that the quiescent state is a continuum evolving with time, early and deep quiescence being distinguishable by the cell's proficiency to re-enter the proliferation cycle.