Research Paper Volume 15, Issue 14 pp 6690—6709

Figure 1. A bidirectional pattern of DNA methylation drift in the splenic DNA of aged mice. (A) A global decline in CpG methylation level (β-value). RRBS data were obtained from splenic DNA of two-, six-, 12-, and 23-month-old mice (2m, 6m, 12m, and 23m, respectively; n =3 for each). (B) Principal component analysis (PCA). A dashed circle group samples of the same age together. (C) Distribution of methylation levels (M-value). Red triangles represent the mean methylation levels and the two horizontal lines in the violin plots indicate 25% (lower, Q1) and 75% (upper, Q3) quartile lines. The red triangles reflect the mean methylation levels, whereas the two horizontal lines in the violin plots represent the 25^th (Q1) and 75^th (Q3) quartiles. The red arrows depict the contraction of the 25% and 75% quartile lines within the 23m age group. (D) Histograms showing the distribution of pre-defined regions across successive intervals of methylation levels for different genomic structures/functions (promoters, gene bodies, and intergenic regions). (E) Box plots showing the methylation levels across the age groups.