Genomic biology: the epigenomic era opens

Abstract

Readout of information from the genome depends on intricate regulation of how DNA is packaged by proteins. The great endeavour to reveal how this packaging operates pan-genomically is now under way.

Figure 1. Genomic architecture, and eras of investigation

Eras 1 and 2 were launched by the elucidation of the structure of DNA, and then of the sequence of the human genome. DNA is packaged with histone proteins to form chromatin, the central unit of which is the nucleosome. As examples of work in the unfolding era 3 — the era of the epigenome — the papers of Mikkelsen et al. and Barski et al. provide genome-wide linear maps relating histone modifications (‘marks’) to the active or inactive sites where various types of regulatory RNA, as well as messenger RNA, are produced. Nucleosomes are further organized to create open and closed regions of chromatin, which in turn create three-dimensional structures that encompass different levels of gene organization in the chromosomes packed into a cell nucleus. A likely era 4 will involve generation of maps of this ‘genome topography’ to reveal how a single genome can produce such a diversity of cell types.