Figure 1.

Senescent cells exhibit overall hypomethylation and focal hypermethylation. (a) Proliferating (Prolif.) and senescent (Sen.) IMR90 cells stained for 5-methylcytosine (5-MeC) and single-stranded DNA(ssDNA). Scale bar, 5µm. (b) Quantitation of a in three independent experiments (100 cells each); error bars, mean ± s.e.m. (c) Percentages of methylated and unmethylated basecalls at reference CpG dinucleotides in proliferating and senescent cells. (d) Numbers of CpG dinucleotides becoming hypomethylated (hypo) and hypermethylated (hyper) in senescence. (e) Plot of chromosome 4 (chr 4) percentage methylation for proliferating and senescent cells. An overlay of these two plots is shown with difference p, proportional to the P value differences between methylation of proliferating and senescent cells. Negative and positive values are hypomethylation and hypermethylation, respectively. (f) Enlargement of boxed region from e. (g,h) Across the whole genome, regions of intermediate methylation in proliferating cells tend to be hypomethylated in senescence. For g and h CpGs were split into 100 bins on the basis of proliferating methylation. The average senescent methylation/methylation difference of each bin was then computed and plotted. (i) Number of hypomethylated and hypermethylated DMRs (differentially methylated regions) over whole genome in senescent cells. (j) Average size of hypomethylated and hypermethylated DMRs over whole genome. bp, base pairs. For c–j data are from whole-genome bisulfite sequencing of three independent replicates.