FIG. 1.
Defective arrest of DNA synthesis in Rb1 mutant cells during senescence. (A) MEFs of the indicated genotypes were serum deprived for 72 h, and their resulting DNA synthesis was measured by BrdU incorporation. (B) Ten days following retroviral transduction of MEFs with oncogenic Ras, senescent cell morphology and SA β-Gal activity were examined by light microscopy. The percentage of SA β-Gal-positive cells of each genotype was determined and is displayed in the graph to the right. (C) DNA content of wild-type and mutant MEFs was examined by propidium iodide staining and flow cytometry 5 days following irradiation or viral infection to express RasV12. The values above the peaks are the percentages of cells with this DNA content. (D) DNA synthesis in senescent MEFs was measured by BrdU incorporation over 8 h at 10 days following viral infection. Error bars in all graphs indicate 1 standard deviation from the mean of at least three replicates. The P value for a t test comparing mean measurements in panel D is 0.04.