Stratification of yeast cells during chronological aging by size points to the role of trehalose in cell vitality

Abstract

Cells of the budding yeast Saccharomyces cerevisiae undergo a process akin to differentiation during prolonged culture without medium replenishment. Various methods have been used to separate and determine the potential role and fate of the different cell species. We have stratified chronologically-aged yeast cultures into cells of different sizes, using centrifugal elutriation, and characterized these subpopulations physiologically. We distinguish two extreme cell types, very small (XS) and very large (L) cells. L cells display higher viability based on two separate criteria. They respire much more actively, but produce lower levels of reactive oxygen species (ROS). L cells are capable of dividing, albeit slowly, giving rise to XS cells which do not divide. L cells are more resistant to osmotic stress and they have higher trehalose content, a storage carbohydrate often connected to stress resistance. Depletion of trehalose by deletion of TPS2 does not affect the vital characteristics of L cells, but it improves some of these characteristics in XS cells. Therefore, we propose that the response of L and XS cells to the trehalose produced in the former differs in a way that lowers the vitality of the latter. We compare our XS- and L-fraction cell characteristics with those of cells isolated from stationary cultures by others based on density. This comparison suggests that the cells have some similarities but also differences that may prove useful in addressing whether it is the segregation or the response to trehalose that may play the predominant role in cell division from stationary culture.

Mitochondria reorganization upon proliferation arrest predicts individual yeast cell fate

“…Second, we analyzed mitochondrial morphology and found that the ‘small sub-population’ was enriched in cells with globular mitochondria ( Figure 3B ). Thus, to some extent, we found more senescent cells among very small cells, in agreement with ( Svenkrtova et al, 2016 ). Accordingly, when cells were micro-manipulated on plate to individually test their re-proliferation capacities ( Laporte et al, 2011 ), small cells were less prone to form colonies than large cells ( Figure 3—figure supplement 1A ).…”

“…Cell volume has been suggested to strongly influence non-proliferating cell survival. Yet while the Werner-Washburne laboratory found that only small daughter cells were quiescent ( Allen et al, 2006 ; Aragon et al, 2008 ; Werner-Washburne et al, 2012 ; Davidson et al, 2011 ), the Pichova lab reported that a sub-population composed of very small cells (2–4 µm in diameter) contained mostly senescent or dead cells ( Svenkrtova et al, 2016 ). To revisit these conflicting data, we measured the individual cell volume of WT cells expressing Ilv3-RFP grown in YPD, just after their deposition onto a YPD microscope pad.…”

“…More recently, centrifugal elutriation was used to separate cells of a stationary phase culture according to their volume. The authors showed that a sub-population of very small daughter cells (2–4 µm in diameter) contains mostly senescent or dead cells, challenging thus the ‘density model’ ( Svenkrtova et al, 2016 ). These discrepancies highlight the limitations of cell population sub-fractionation techniques, their strongest caveat being to assign to sub-populations properties that define individual cells.…”

The cell biology of quiescent yeast – a diversity of individual scenarios

“…Recently, stationary phase populations have been separated into subpopulations according to cell size (Svenkrtova et al, 2016). It was found that, with time, very small cells (2 to 4 µm in diameter) displayed a reduced ability to re-proliferate (Svenkrtova et al, 2016). In agreement, at the population scale, we found that very small cells (less than 30 fl in volume, or ∼2.5 µm in diameter) have a slightly increased susceptibility to enter senescence.…”

“…Recently, stationary phase populations have been separated into subpopulations according to cell size (Svenkrtova et al, 2016). It was found that, with time, very small cells (2 to 4 µm in diameter) displayed a reduced ability to re-proliferate (Svenkrtova et al, 2016).…”