Molecular bases of proliferative heterogeneity in Saccharomyces cerevisiae

Abstract

Proliferative heterogeneity has been widely described in clonal cultures, but the mechanisms underlying this phenomenon are still poorly understood. On another hand, cell cycle regulation is tightly linked to proliferative capacity and previous transcriptomic studies revealed that yeast cells with less proliferative capacity display higher levels of the G1-S transition inhibitor Whi5. This regulator has been also linked to replicative aging in late steps of the mother cell lifespan. Considering this data, this thesis work has the following objectives: 1. To stablish a reliable method to study the influence of replicative age on proliferation heterogeneity. 2. Determining the role of Whi5 in proliferative heterogeneity. 3. Decipher the role of cell cycle regulation in coupling replicative age and proliferative heterogeneity In this work, we combined single cell microencapsulation with confocal microscopy to study heterogeneity in clonal cultures. Using this new method we found that a significant proportion of slow-growing microcolonies are founded by mother cells with a short number of division cycles. Using a Whi5 induble strain, we also found that this reduction in the proliferation capacity of microcolonies founded by young mother cells is related to the expression levels of Whi5. We can resume our results with the following conclusions: 1. Combination of cell microencapsulation and confocal microscopy is a reliable method to analyze cell lineages. 2. Replicative age substantially contributes to proliferative heterogeneity in clonal populations. 3. Decrease in proliferative capacity of young mother cells arises after the first mitotic division. 4. The progeny of a young mother cell can non-genetically inherit its decreased proliferative capacity. 5. The cell cycle regulator Whi5 participates in one of the mechanisms that links replicative age and cell proliferative capacity. Our results indicate that stably reduced proliferation is not exclusively linked to aged cells and open a new perspective to understand heterogeneity of clonal cell populations.