Principles of Gene Expression and Epigenetics

Since genomic instability and epigenetic dysregulation are important hallmarks of aging, we will discuss in this chapter principles of gene expression and epigenetics, both of which are closely linked. In order to express a gene, i.e., to transcribe it into RNA, its regulatory regions need to be located within accessible chromatin. Chromatin is the physical representation of epigenetics. In a tissue- and cell type-specific fashion the majority of the genome is buried in heterochromatin and only approximately half of all genes are expressed, i.e., actively transcribed. The wrapping of genomic DNA around nucleosomes and the posttranslational modification of histones determines the density of chromatin packing. Tissue- and signal-specific gene expression is the central mechanism that controls the general properties of a cell and its response to environmental perturbations. This finally triggers the process of aging. More details on the relation of epigenetics and aging are presented in Chap. 3 .