Integrative genomics analysis identifies pericentromeric regions of human chromosomes affecting patterns of inter-chromosomal interactions
This study explores how certain regions of human chromosomes interact with each other and with important cellular structures, revealing patterns that could be linked to diseases.
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- 1 These observations suggest that chromatin binding to Lamin B1 and association with nucleoli may impact genome-wide chromatin interactions by shuttling heterochromatin loci defined by overlapping locations and affecting dynamic features of a fractal globule.
- 2 The chromatin looping model was proposed to explain how these multigene clusters were build and function.
- 3 Remarkably, in all instances we found that high-density regions of the CENTRICH binding sites to the long-range interphase chromatin complexes are located within intervening chromatin chains (Figures 3 & 4 ).
- 4 These data indicate that both long-range enhancers and regulatory target loci are bound to the chr2 and chr10 CENTRICH.
Introduction
In human genome many gene deserts are significantly enriched for predicted long-range enhancers and\/or insulators genomic coordinates of which are in close proximity or overlap with disease-associated SNPs (1) (2) (3) . Several groups experimentally validated the biological activity of intergenic long-range enhancers and reported active transcription at intergenic disease-associated genetic loci (IDAGL) with documented increased risk of developing prostate cancer (3) (4) (5) (6) (7) (8) , autoimmune disorders.
However, experimental observations and theoretical considerations highlighting detailed mechanisms of structural-functional alignment and compartmentalization of genomic functions in interphase nuclei with respect to regulatory elements within gene deserts are lacking.
In interphase nucleus, the three-dimensional conformation of chromosomes is defined by both chromatin folding and chromatin polymer interactions with major external to chromatin globules nuclear structures such as nuclear lamina and nucleoli (9) (10) (11) (12) (13) .
Some of these concerns are based in part on the a priori assumptions that genomic sequences containing arrays of highly repetitive elements cannot be reliably mapped because they are not uniquely represented in the human genome.
Research Question
We thought to test whether the definition of unique genomic sequences is true for DNA sequences within the CENTRICH regions by dividing each CENTRICH into series of short continuous segments along the entire length of the region and covering the CENTRICH sequences essentially without any unresolved sequence gaps (Table 2 ).
Methodology
Recently, a genome-wide, high-resolution analysis of DNA sequences that have a high probability to associate endogenously and co-purify with nucleoli (nucleolar-associated domains [NADs] ) in human cells, has been carried-out using a combination of fluorescence comparative genome hybridization (CGH), deep DNA sequencing and fluorescence photoactivation (9, 10) . Genome-wide analysis of interactions of interphase chromatin with nuclear lamina in mouse embryonic stem cells revealed that nuclear lamina-genome interactions are broadly.
Study Design
Experimental studies of long-range physical interactions of interphase chromatin chains utilize multiple methods and have evolved from analysis of interactions between specific pairs of distant genomic loci to genome-wide approaches.
A genome-wide approach to the analysis of long-range chromatin interactions named Hi-C was reported that extends the above methods to enable purification of ligation products followed by massively parallel sequencing (13) .
A major limitation of our analysis is defined by the fact that there is no single cell line model to which all of the essential methods of the genome-wide 3D chromatin structure analyses were applied.
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Results & Findings
Hi-C experiments allowed unbiased identification of chromatin interactions across an entire genome and provided strong support for the fractal globule model of interphase chromatin folding. We reasoned that this approach would estimate the density of interphase chromatin chain binding to a given segment of chromosomes and may highlight the genomic regions with distinct ability to attract the binding of interphase chromatin chains.
- Hi-C experiments allowed unbiased identification of chromatin interactions across an entire genome and provided strong support for the fractal globule model of interphase chromatin folding.
- We reasoned that this approach would estimate the density of interphase chromatin chain binding to a given segment of chromosomes and may highlight the genomic regions.
- To quantify these relationships genome-wide, we correlated Hi-C model data (eigenvector values) for each chromosome with Lamin B1 and nucleoli binding data.
- These observations suggest that chromatin binding to Lamin B1 and association with nucleoli may impact genome-wide chromatin interactions by shuttling heterochromatin loci defined by overlapping locations.
- Consistent with this prediction, we found that there is a significant direct correlation between the relative strengths of the association to nucleoli of centromeric regions of.
Despite this limitation, integration of these data derived from different cellular models within the context of the reference human genome seems to facilitate definition of novel regulatory features and networks of potential physiological and pathological relevance.
These observations suggest that chromatin binding to Lamin B1 and association with nucleoli may impact genome-wide chromatin interactions by shuttling heterochromatin loci defined by overlapping locations and affecting dynamic features of a fractal globule.
Practical Applications
We propose to define these regions with increased inter-chromosomal interaction density as CENTRICH and postulate that CENTRICH may play an important role in 3D genome architecture and function by governing a dynamic transition of large segments of interphase chromosomes from the open loop to folded chromatin chain conformations. Periodic directional movements of specific regions of the chromatin fractal globules would likely to depend on relative strengths of association to nucleoli.
These complexes may span several megabases and contain hundreds of genes as complexes, which are distantly separated on a chromosome or located on different chromosomes, further converge to form highorder multigene interactions regulatory complexes.
Binding of long-range interphase chromatin enhancer-promoter complexes to the CENTRICH via high-frequency interactions with intervening chromatin may promote formation of the meta-stable intermediary structures consisting of neighboring CENTRICH-associated chromatin loops which are housed on a CENTRICH base.
Identification of Centromeric Regions of Interphase Chromatin Homing (CENTRICH)
This section details the identification of CENTRICH regions on chromosomes 2 and 10, which are enriched for long-range interactions and associated with disease-linked SNPs.
CENTRICH represent common homing sites for both enhancers and promoters engaged in the long-range regulatory interactions
CENTRICH regions serve as critical sites for enhancer-promoter interactions, facilitating transcriptional regulation across large genomic distances.
Frequently Asked Questions
We thought to test whether the definition of unique genomic sequences is true for DNA sequences within the CENTRICH regions by dividing each CENTRICH into series of short continuous segments along the entire length of the region and covering the CENTRICH sequences.
Experimental studies of long-range physical interactions of interphase chromatin chains utilize multiple methods and have evolved from analysis of interactions between specific pairs of distant genomic loci to genome-wide approaches. A genome-wide approach to the analysis of long-range chromatin interactions named Hi-C.
These observations suggest that chromatin binding to Lamin B1 and association with nucleoli may impact genome-wide chromatin interactions by shuttling heterochromatin loci defined by overlapping locations and affecting dynamic features of a fractal globule. The chromatin looping model was proposed to explain.
Therefore, recent experiments on large cell populations demonstrate that interactions of interphase chromosomes with nuclear lamina and nucleoli are critically important in defining a 3D architecture of chromatin organization and functions. These complexes may span several megabases and contain hundreds of genes.
Therefore, a priori assumption that the alignment and mapping of sequencing data cannot be reliably performed within the genomic regions containing repetitive elements is not correct and the validity of this assumption should be always experimentally tested. Therefore, the human genome reference.
This study explores how certain regions of human chromosomes interact with each other and with important cellular structures, revealing patterns that could be linked to diseases.