Passing epigenetic silence to the next generation

Almost every cell in an organism contains the same DNA, but only a subset of genes is expressed in each cell type. DNA is packaged into chromatin, the core component of which is the nucleosome. During development and cell differentiation, histone constituents of nucleosomes are modified by the methylation, acetylation, or phosphorylation of specific amino acids. Different modifications are associated with active or silenced genes. Repressive chromatin marks are thought to constitute the epigenetic memory of the silenced transcriptional state. How are silent chromatin domains maintained through DNA replication and cell division to the next generation? On pages 41, 85, and 88 of this issue, Coleman and Struhl ( 1 ), Laprell et al. ( 2 ), and Wang and Moazed ( 3 ), respectively, reveal that long-term stable transmission of the silenced state requires sequence-specific recruitment of histone-modifying enzymes.