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. 2023 Oct 9;10:1270285. doi: 10.3389/fmolb.2023.1270285

FIGURE 2.

FIGURE 2

Changes in histone modifications during aging. Schematic illustrating changes in histone modifications observed during aging in somatic cells of the worm C. elegans, compiled from ChIP-seq experiments of germline-less glp-1(e2141) mutants in young worms (day 2 adults) vs old worms (day 12 adults) (Pu et al., 2015; Pu et al., 2018; Li et al., 2021). Some changes are evident at a chromosome-wide view (top), but become more evident when viewing smaller gene-specific regions (bottom). When viewing histone marks from a chromosome-wide view (top), active histone marks (H3K4me3 and H3K36me3) typically occupy similar regions of chromatin, as do repressive marks (H3K27me3 and H3K9me3) in C. elegans, however the regions occupied by active and repressive marks are distinct. Compared to young worms (A), the genome-wide distribution of histone marks in old worms (B) is typically relatively stable, with local changes that both increase and decrease in direction. With aging, repressive marks, particularly H3K9me3, show an overall decrease, however this is region-specific, and the marks tend to decrease in the chromosome center and increase in the chromosome arms. There may also be somewhat of an invasion of active marks into domains normally occupied by repressive marks. When viewing individual peaks (bottom), H3K4me3, which typically marks promoter regions, exhibits age-related changes in gene bodies that typically correlate with gene expression changes. H3K36me3 is relatively stable with age, and genes marked by H3K36me3 tend to be stable in expression during aging. Most H3K27me3- and H3K9me3-marked regions do not change with age, but many H3K9me3-marked regions exhibit local gains with age, although these changes are not well-correlated with gene expression changes. Green arrows represent transcription start sites of theoretical genes. Note that the theoretical genes shown here represent separate examples of changes observed in histone modifications during aging and do not represent a real instance of genes in immediate proximity.