FIGURE 1.

Age-related chromatin changes. Schematic representing the types of changes that can occur at chromatin during aging by comparing young nuclei (A) to old nuclei (B). Chromatin is typically organized with dense heterochromatin anchored to the nuclear periphery and euchromatin in the nuclear interior, however the structure at heterochromatin as well as the organization of euchromatin can change during aging. Numbers denote specific age-related changes evident in old nuclei that are discussed in this review, many of which can result from changes in chromatin remodeling. 1) loss of core histones; 2) changes in histone variants, with the pink color representing a non-canonical variant; 3) loss of heterochromatin; 4) deterioration in nuclear morphology; 5) changes in site-specific histone marks. Particular changes in histone marks are depicted in Figure 2. “Ac” represents histone acetylation marks and “Me3” represents histone methylation marks, with those at the nuclear periphery representing H3K9me3 and H3K27me3, and those in the nuclear interior representing H3K4me3. Note that the changes depicted here represent the variety of changes detailed in this review, and do not necessarily always co-occur in every cell during aging.