In this work, we show that nuclear rearrangement of repressive histone marks H3K9me3 and H3K27me3 into nonoverlapping structural layers characterizes senescence-associated heterochromatic foci (SAHF) formation in human fibroblasts. The experiments reveal that high-order heterochromatin formation and epigenetic remodeling of the genome can be discrete events. The paper by Chandra et al. can be read here.
