Relating age relationships to chromosomal properties. The bar plots in the top row relate average module membership in the aging module (average kME with respect to the green module) to Polycomb group (PCG) occupancy count, CpG island status, and chromosomal location, respectively. The bottom row shows the corresponding bar plots involving the (signed) logarithm of the meta analysis P-value. A positive (negative) log P-value indicates a positive (negative) age correlation of the CpG site. Both age association measures lead to the following results. First, the higher the PCG occupancy count, the stronger the age association. Second, CpG sites in CpG islands tend to have positive age correlations while those outside tend to have negative age correlations. Third, CpG sites on X chromosomes tend to have lower age correlations than those on other chromosomes. While both age association measures lead to similar conclusions, the results are more pronounced for the module membership measure (average kME), which suggests that this measure leads to more meaningful biological conclusions. Error bars indicate one standard error.
Horvath et al. Genome Biology 2012 13:R97 doi:10.1186/gb-2012-13-10-r97