Figure 3. Caloric restriction (CR) and the ras2Δ mutation under non-CR conditions accelerate the process 2 of an age-related conversion of high-density quiescent (Q) cells into low-density Q cells.

In contrast, lithocholic acid (LCA) and the tor1Δ mutation slow down process 2 under non-CR conditions. 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 cell counter was used to determine the percentage of high-density Q cells in each of these differently aged populations. (A) Percoll density gradients used to purify high-density Q cells and low-density Q cells from WT or mutant cell populations recovered on day 10 (the ST growth phase) of culturing are shown. (B) The percentage of high-density Q cells 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 the process 2 of an age-related conversion of high-density Q cells into low-density Q cells. Data in B are presented as means ± SEM (n = 3; ^* p < 0.05; ns, not significant). Other Abbreviations: HD: high-density cells; LD: low-density cells.