Figure 2. Mitochondrial network morphology and fusion/fission gene expression levels in replicative senescent cells.

a. The mitochondria in yeast cells were labeled by green fluorescence protein (pVT100-MtGFP) for visualization. The morphology of mitochondrial network were classified into three categories: fragmented, tubular, and hyperfused/elongated. b. Senescent wild type cells were sorted at various time points after biotin labeling. Mitochondria network morphology of log phase cells and adsorbed senescent cells were classified. The ratio of senescent cells with fragmented mitochondria gradually increased with the duration of the culturing period. c. Senescent dnm1 and fzo1 cells at different time points were sorted and subjected for classifying mitochondrial network morphology. Almost none of the senescent cells from fission genes DNM1 deleted strain presented a fragmented network. The same was true for senescent cells from the FZO1 deleted strain, which presented all fragmented networks. d. Relative mRNA levels of DNM1 and FZO1 in wild type cells at the log phase of growth and senescence were measured by quantitative RT-PCR. DNM1 levels in 48 h senescent cells were 2.5 fold higher than those in log phase and significantly higher than in young, not adsorbed cells (*: p<0.05).