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The yin and yang of chromatin spatial organization.

Cope NF, Fraser P, Eskiw CH - Genome Biol. (2010)

Bottom Line: Spatial organization of the genome is non-random.Preferential chromatin interactions, both in cis and in trans and between transcriptionally active and silent regions, influence organization.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Chromatin and Gene Expression, The Babraham Institute, Babraham Research Campus, Cambridge, UK.

ABSTRACT
Spatial organization of the genome is non-random. Preferential chromatin interactions, both in cis and in trans and between transcriptionally active and silent regions, influence organization.

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NORs cluster as cells exit mitosis. (a) The short arms of acrocentric chromosomes 13, 14, 15, 21 and 22 contain NORs, which are separated during mitosis. (b) As cells exit mitosis and the nuclear membrane begins to reform, chromosomes begin to decondense. (c) Loops of chromatin may extend away from the core of the territory. (d) As G1 phase is established and nucleoli form, loops of NOR-containing chromatin co-associate with the other components of the nucleolus and ribosomal DNA gene transcription is initiated.
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Figure 2: NORs cluster as cells exit mitosis. (a) The short arms of acrocentric chromosomes 13, 14, 15, 21 and 22 contain NORs, which are separated during mitosis. (b) As cells exit mitosis and the nuclear membrane begins to reform, chromosomes begin to decondense. (c) Loops of chromatin may extend away from the core of the territory. (d) As G1 phase is established and nucleoli form, loops of NOR-containing chromatin co-associate with the other components of the nucleolus and ribosomal DNA gene transcription is initiated.

Mentions: Examination of nucleolar structure and function provides some of the first evidence for how clustering of specific genes in three-dimensional space could be achieved. Nucleoli are assembled through association of the nucleolar organizing regions (NORs) and various nucleolar proteins. Each of the five human NORs is composed of many tandemly repeated rRNA genes located on the acrocentric chromosomes 13, 14, 15, 21 and 22 (Figure 2). As cells exit mitosis, NORs are bound by the essential transcription protein upstream binding factor (UBF) [19] and coalesce into between one and four nucleolar structures. The NORs that are transcriptionally quiescent are not bound by UBF and are excluded from nucleoli, indicating that this transcription factor may be fundamental in the organization of these structures [20]. Transcription is also fundamental to the organization of nucleoli. Inhibition of the nucleolar RNA polymerase (RNAPI) with actinomycin D (which intercalates into DNA that is being transcribed and immobilizes the polymerase) results in the formation of 'mini-nucleoli' when cells exit mitosis [21]. Mini-nucleoli contain NORs, but other nucleolar components are distributed to discrete structures, or 'caps', on the mini-nucleolar surface. Removal of actinomycin D and the initiation of RNAPI transcription restores nucleolar morphology, showing that transcription itself has an important role in the organization of nuclear architecture. The nucleolus may represent the first observed specialized 'transcription factory' that can form a trans interaction network with a specific function.


The yin and yang of chromatin spatial organization.

Cope NF, Fraser P, Eskiw CH - Genome Biol. (2010)

NORs cluster as cells exit mitosis. (a) The short arms of acrocentric chromosomes 13, 14, 15, 21 and 22 contain NORs, which are separated during mitosis. (b) As cells exit mitosis and the nuclear membrane begins to reform, chromosomes begin to decondense. (c) Loops of chromatin may extend away from the core of the territory. (d) As G1 phase is established and nucleoli form, loops of NOR-containing chromatin co-associate with the other components of the nucleolus and ribosomal DNA gene transcription is initiated.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2864563&req=5

Figure 2: NORs cluster as cells exit mitosis. (a) The short arms of acrocentric chromosomes 13, 14, 15, 21 and 22 contain NORs, which are separated during mitosis. (b) As cells exit mitosis and the nuclear membrane begins to reform, chromosomes begin to decondense. (c) Loops of chromatin may extend away from the core of the territory. (d) As G1 phase is established and nucleoli form, loops of NOR-containing chromatin co-associate with the other components of the nucleolus and ribosomal DNA gene transcription is initiated.
Mentions: Examination of nucleolar structure and function provides some of the first evidence for how clustering of specific genes in three-dimensional space could be achieved. Nucleoli are assembled through association of the nucleolar organizing regions (NORs) and various nucleolar proteins. Each of the five human NORs is composed of many tandemly repeated rRNA genes located on the acrocentric chromosomes 13, 14, 15, 21 and 22 (Figure 2). As cells exit mitosis, NORs are bound by the essential transcription protein upstream binding factor (UBF) [19] and coalesce into between one and four nucleolar structures. The NORs that are transcriptionally quiescent are not bound by UBF and are excluded from nucleoli, indicating that this transcription factor may be fundamental in the organization of these structures [20]. Transcription is also fundamental to the organization of nucleoli. Inhibition of the nucleolar RNA polymerase (RNAPI) with actinomycin D (which intercalates into DNA that is being transcribed and immobilizes the polymerase) results in the formation of 'mini-nucleoli' when cells exit mitosis [21]. Mini-nucleoli contain NORs, but other nucleolar components are distributed to discrete structures, or 'caps', on the mini-nucleolar surface. Removal of actinomycin D and the initiation of RNAPI transcription restores nucleolar morphology, showing that transcription itself has an important role in the organization of nuclear architecture. The nucleolus may represent the first observed specialized 'transcription factory' that can form a trans interaction network with a specific function.

Bottom Line: Spatial organization of the genome is non-random.Preferential chromatin interactions, both in cis and in trans and between transcriptionally active and silent regions, influence organization.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Chromatin and Gene Expression, The Babraham Institute, Babraham Research Campus, Cambridge, UK.

ABSTRACT
Spatial organization of the genome is non-random. Preferential chromatin interactions, both in cis and in trans and between transcriptionally active and silent regions, influence organization.

Show MeSH