Cytoplasmic chromatin fragments in senescent cells. (A) Cytoplasmic chromatin fragments (CCFs) in senescent cells are strongly positive for histone H3. Yellow arrow marks CCF. (B) Increased proportion of cells with CCFs in RS or OIS. Mean ± SEM, n = 3; P < 0.01 (OIS), P < 0.002 (RS). Assays were performed 10 d after induction with tamoxifen (OIS) or 4 wk after the last passage and >90% SA β-gal+ (RS). 