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Two independent modes of chromatin organization revealed by cohesin removal.

ABSTRACT: Imaging and chromosome conformation capture studies have revealed several layers of chromosome organization, including segregation into megabase-sized active and inactive compartments, and partitioning into sub-megabase domains (TADs). It remains unclear, however, how these layers of organization form, interact with one another and influence genome function. Here we show that deletion of the cohesin-loading factor Nipbl in mouse liver leads to a marked reorganization of chromosomal folding. TADs and associated Hi-C peaks vanish globally, even in the absence of transcriptional changes. By contrast, compartmental segregation is preserved and even reinforced. Strikingly, the disappearance of TADs unmasks a finer compartment structure that accurately reflects the underlying epigenetic landscape. These observations demonstrate that the three-dimensional organization of the genome results from the interplay of two independent mechanisms: cohesin-independent segregation of the genome into fine-scale compartments, defined by chromatin state; and cohesin-dependent formation of TADs, possibly by loop extrusion, which helps to guide distant enhancers to their target genes.

SUBMITTER: Schwarzer W

PROVIDER: S-EPMC5687303 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Two independent modes of chromatin organization revealed by cohesin removal.

Schwarzer Wibke W Abdennur Nezar N Goloborodko Anton A Pekowska Aleksandra A Fudenberg Geoffrey G Loe-Mie Yann Y Fonseca Nuno A NA Huber Wolfgang W Haering Christian H CH Mirny Leonid L Spitz Francois F

Nature 20170927 7678

Imaging and chromosome conformation capture studies have revealed several layers of chromosome organization, including segregation into megabase-sized active and inactive compartments, and partitioning into sub-megabase domains (TADs). It remains unclear, however, how these layers of organization form, interact with one another and influence genome function. Here we show that deletion of the cohesin-loading factor Nipbl in mouse liver leads to a marked reorganization of chromosomal folding. TADs ...[more]

PMID: 29094699

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Project description:The three-dimensional organization of chromosomes is tightly related to their biological function. Both imaging and chromosome conformation capture studies have revealed several layers of organization, including segregation into active and inactive compartments at the megabase scale, and partitioning into domains (TADs) and associated loops at the sub-megabase scale. Yet, it remains unclear how these layers of genome organization form, interact with one another, and contribute to or result from genome activities. TADs seem to have critical roles in regulating gene expression by promoting or preventing interactions between promoters and distant cis-acting regulatory elements, and different architectural proteins, including cohesin, have been proposed to play central roles in their formation. But so far, experimental depletions of these proteins have resulted in marginal changes in chromosome organization. Here, we show that deletion of the cohesin-loading factor, Nipbl, leads to loss of chromosome-associated cohesin and results in dramatic genome reorganization. TADs and associated loops vanish globally, even in the absence of transcriptional changes. In contrast, segregation into compartments is preserved and even reinforced. Strikingly, the disappearance of TADs unmasks a finer compartment structure that accurately reflects the underlying epigenetic landscape. These observations demonstrate that the 3D organization of the genome results from the independent action of two distinct mechanisms: 1) cohesin-independent segregation of the genome into fine-scale compartment regions, defined by the underlying chromatin state; and 2) cohesin-dependent formation of TADs possibly by the recently proposed loop extrusion mechanism, enabling long-range and target-specific activity of promiscuous enhancers. The interplay between these mechanisms creates an architecture that is more complex than a simple structural hierarchy and can be central to guiding normal development.

Dataset Information

Two independent modes of chromatin organization revealed by cohesin removal.

Publications

Two independent modes of chromatin organization revealed by cohesin removal.

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