Figure 4. H2AX-diminished quiescent cell status is regulated by p53.

A. DNA replication stress-associated H2AX diminution status was determined in p53-KO MEFs as in Figure 2E, in which H2AX was not down-regulated, even in primary MEFs. B–F. Primary p53-KO MEFs were cultured during the senescing and immortalizing processes (B). H2AX status was determined by Western blotting (C), morphological assessment (D), genomic status determined by flow-cytometry (E), and chromosome spread (F). Although p53-KO MEFs never showed major changes in H2AX expression, tetraploidization or growth arrest, p53-KO MEFs still exhibited a senescent morphology (P8) before achieving an immortalized morphology (P14).