Figure 1.
Aging yeast cells show features of apoptotic death. (A) Chronological survival of wild-type (DBY746) and long-lived mutants ras2Δ and sch9Δ populations. Life span measurement were performed by incubating wild-type (WT) cells, ras2Δ, and sch9Δ mutants either in synthetic dextrose complete (SDC) medium or in water. Viability is expressed as percent survival (100% at day 3). Results shown represent the average of 4–12 experiments. (B) Day 7 wild-type and sch9Δ mutants were stained with DAPI for analysis of nuclear morphology (top), GFP-labeled annexin V for detection of exposed phosphatidylserine and propidium iodide for detection of damaged/dead cells (middle panels). Approximately 25–30 cells for each strain were present on each field (bottom, DIC images) and were treated simultaneously with annexin V and propidium iodide. (C) Chronological survival of wild-type cells incubated in standard SDC medium (pH 3.5–4) and in SDC medium with pH adjusted and maintained at 6.5–7 from day 3 to 13. The experiment was repeated five times with similar results. A representative experiment is shown. (D) Mitochondrial Sod (Sod2) activity of wild-type and sch9Δ mutants was measured at day 3 and 5. Results shown represent the average of two experiments conducted in triplicate. Error bars show SEM. (E) Oxidative stress resistance of wild type, ras2Δ mutants, sch9Δ mutants, wild type overexpressing control vectors YEp351-YEp352, and SOD1/SOD2 overexpressors. Cells removed from day 3 in the postdiauxic phase were incubated for 60 min in phosphate buffer containing 200 μM of the superoxide H2O2-generating agent menadione. Viability was measured by plating cells onto rich medium before and after treatment. A representative experiment performed in duplicate is shown for the deletion strains. The average of two experiments is shown for the overexpressors. Error bars show SEM.