Figure 4. Caloric restriction (CR), lithocholic acid (LCA), the tor1Δ mutation and the ras2Δ mutation postpone an aging-associated decline in the clonogenicities of low-density quiescent (Q) cells and high-density Q cells during processes 3 and 4, respectively.

Wild-type (WT) yeast cells were cultured in the nutrient-rich YP medium initially containing 0.2% glucose (CR conditions) or 2% glucose (non-CR conditions) with or without LCA. The tor1Δ and ras2Δ mutant cells were cultured in the nutrient-rich YP medium initially containing 2% glucose (non-CR conditions) without LCA. Aliquots of differently aged cell populations were recovered from the logarithmic (L), diauxic (D), post-diauxic (PD) or stationary (ST) growth phase. High-density Q cells and low-density Q cells were purified from these cell populations with the help of the centrifugation in Percoll density gradient, as described in Materials and Methods. A plating assay for reproductive (colony forming) capability, which is described in Materials and Methods, was used to measure the clonogenicities of low-density Q cells (A) and high-density Q cells (B) in differently aged WT or mutant cell populations. (C) A model for how CR, LCA (under non-CR conditions), tor1Δ (under non-CR conditions) and ras2Δ (under non-CR conditions) affect an aging-associated deterioration in the clonogenicities of low-density Q cells and high-density Q cells during processes 3 and 4, respectively. Data in A and B are presented as means ± SEM (n = 3; ^* p < 0.05; ^** p < 0.01; ns, not significant). Other Abbreviations: HD: high-density cells; LD: low-density cells; NQ: non-quiescent cells.