Expression profiles of gene sets across 32 human tissues.
(A) Gene expression levels across 32 tissues. Gene
expression was measured in FPKM (plus a pseudo count of 0.25). The
tissues are ordered according to the median express levels of aging
genes. Although aging genes have lower expression levels than
housekeeping genes, they tend to have statistically significant
higher expression levels than background (i.e. protein coding
genes), essential, and transcription factor genes across all 32
tissues (P < 0.05 in all tissues by Wilcoxon
rank sum test). (B) Composition of genes categories
with different tissue specificity in each gene set. (C)
Gene expression and the distance to aging genes in the PPI network
(showing the mean and one standard deviation). Log2-transformed FPKM
(plus a pseudo count of 0.25) values were used in this
analysis. Here, background genes are all the genes
in the PPI network; AG-1 are direct neighbors of aging genes; AG-2,
genes two steps away from the aging genes; AG-3, genes three steps
away from aging genes; AG-4+, genes four and more steps away from
the aging genes. As their distance to aging genes increases, genes
tend to have lower average expression levels across tissues
(P < 0.01, Wilcoxon rank sum test). BG,
background genes; AG, aging genes; ES, essential genes; TF,
transcription factor genes; HK, housekeeping genes.