Figure 1.

Age effects on gene expression (mRNA) levels are not preserved between blood and brain tissue. (a-d) Scatterplots of mean gene expression (mRNA abundance) in whole blood of the Dutch samples (x-axis) and corresponding mean brain expression values (y-axis) for frontal cortex (FCTX) (a), temporal cortex (TCTX) (b), pons (c), and cerebellum (CRBLM) (d). Each dot corresponds to a gene. The brain mRNA data (like the brain methylation data used in this article) were obtained from [19]. Note that only moderate correlations (around r = 0.6) exist between the mean expression values of these distinct tissues. (e-g) Overall age correlations of gene expression levels (mRNA) are not preserved between blood (x-axis) and brain tissues (y axes) as evidenced by the weak negative correlations reported in the title of each panel. The mRNA levels of each gene (represented by a dot) were correlated with subject age and a linear regression model was used to calculate a correlation test P-value. The x-axis of each scatterplot shows the (signed) logarithm (base 10) of the correlation test P-value in blood. Genes with a significant positive (negative) correlation with age have a high positive (negative) log P-value. The y-axis shows the corresponding correlation test P-values in the frontal cortex (e), temporal cortex (f), pons (g), and cerebellum (h).

Horvath et al. Genome Biology 2012 13:R97   doi:10.1186/gb-2012-13-10-r97
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