Research Paper Volume 8, Issue 10 pp 2449—2462

Figure 3. Activated genetically encoded photosensitizers can induce cellular senescence. (A-B) The HeLa Kyoto cell line and its derivatives expressing either H2B-miniSOG or H2B-tKR were synchronized in S phase, illuminated with blue (465-495 nm, 65 mW/cm², 5 min) or green (540-580 nm, 200 mW/cm², 15 min) light, allowed to recover for 48 hr, and stained for γH2AX (A) or SA-β-gal (B). Control represents the cells that were synchronized and released for 48 hr (non-illuminated). The DNA was stained with DAPI in (A). Scale bar: 50 μm. (C) Senescent HeLa cells stained for SA-β-gal. Cellular senescence was induced by treatment of S-phase HeLa cells with a DNA topoisomerase I inhibitor camptothecin (1 µM, 1 h). (D) The HeLa Kyoto cell line and its derivatives expressing either H2B-miniSOG or H2B-tKR were synchronized in S phase, illuminated with corresponding light, allowed to recover for 48 hr, and stained with DAPI. Segmentation of cell nuclei was performed using CellProfiler. Boxplots show nuclear area in each case (*P=0.0001, two-tailed t-test).