Nuclear organization

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Nuclear organization refers to the spatial organization and dynamics of chromatin within a cell nucleus during interphase. There are many different levels and scales of nuclear organization.

At the smallest scale, DNA is packaged into units called nucleosomes, which compacts DNA about 7-fold. In addition, nucleosomes protect DNA from damage and carry epigenetic information. Positions of nucleosomes determine accessibility of DNA to transcription factors.

At the intermediate scale, DNA looping can physically bring together DNA elements that would otherwise be separated by large distances. These interactions allow regulatory signals to cross over large genomic distances—for example, from enhancers to promoters.

At a larger scale, chromosomes are organized into two compartments labelled A ("active") and B ("inactive"), which are further subdivided into sub-compartments.^[1] At the largest scale, entire chromosomes segregate into distinct regions called chromosome territories.

Chromosome organization is dynamic at all scales.^[2][3] Individual nucleosomes undergo constant thermal motion and nucleosome breathing. At intermediate scales, an active process of loop extrusion creates dynamic loops and Topologically Associating Domains (TADs).