Figure 2: Extension of replicative life span correlated with delayed large foci formation of phosphorylated H2AX. (a) HE49 was cultured under normoxic or hypoxic condition and then PDL was calculated. (b and c) Cell cycle distribution under normoxic (line in c) and hypoxic (dotted line in c) conditions was analyzed by LSC at the indicated time points. Cell cycle data shown in (b) was graphed in (c). The symbols of circle, triangle, and diamond represent the frequency in G1, S, and G2 phase, respectively. The data was obtained from more than 6,000 cells. (d) Phosphorylated histone H2AX status was classified into H2AX phosphorylation negative (open bar), H2AX phosphorylation positive (dotted bar), and large foci formation (closed bar) and the frequency of each status were investigated in replicative senescence under normoxic (red) and hypoxic (blue) condition. NT indicated “not tested.” At least 100 cells were analyzed in each condition.