Partly, the heterogeneity in age-related changes in gene expression across the genome have been explained by differences in their compositional properties. Thus, a study based on publicly available microarray data on gene expression in the cortex of individuals 26–106 years of age, revealed that gene localization in different chromatin structures (the combination of DNA and proteins that constitutes the contents of a cell nucleus), which correlates with the GC level (the level of guanine-cytosine dinucleotide content in the DNA-molecule), might be a case of opposite age-related expression patterns of genes. Namely, the results of the study revealed an induction of the GC-poor pivotal genes (such as housekeeping genes, which are involved in the control of basic cellular functions and are expressed in all cells of an organism) and a repression of the GC-rich non-pivotal genes in the cortex of individuals at adult stages of development (Arhondakis & Kossida, 2011).
