Figure 5. Caloric restriction (CR), lithocholic acid (LCA), the tor1Δ mutation and the ras2Δ mutation delay an aging-associated deterioration in the abilities of low-density quiescent (Q) cells and high-density Q cells to re-enter the mitotic cell cycle synchronously 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 detailed in Materials and Methods assay was used for assessing the abilities of low-density Q cells (A) and high-density Q cells (B) in differently aged WT or mutant cell populations to synchronously re-enter the mitotic cell cycle after cell transfer into fresh medium and incubation for 1 to 4 h. (C) A model for how CR, LCA (under non-CR conditions), tor1Δ (under non-CR conditions) and ras2Δ (under non-CR conditions) influence an aging-associated decline in the synchronous cell cycle re-entry for low-density Q cells and high-density Q cells during processes 3 and 4, respectively. Data in A and B are presented as means (n = 3). Other Abbreviations: HD: high-density cells; LD: low-density cells; NQ: non-quiescent cells.