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      Telomere position effect: regulation of gene expression with progressive telomere shortening over long distances

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          Abstract

          Robin et al. demonstrate that chromosome looping brings the telomere close to genes up to 10 Mb away from the telomere when telomeres are long, while the loci become separated when telomeres are short. Many loci, including noncoding RNAs, may be regulated by telomere length. This suggests a potential mechanism for how telomere shortening could contribute to aging and disease initiation/progression in human cells long before the induction of a critical DNA damage response.

          Abstract

          While global chromatin conformation studies are emerging, very little is known about the chromatin conformation of human telomeres. Most studies have focused on the role of telomeres as a tumor suppressor mechanism. Here we describe how telomere length regulates gene expression long before telomeres become short enough to produce a DNA damage response (senescence). We directly mapped the interactions adjacent to specific telomere ends using a Hi-C (chromosome capture followed by high-throughput sequencing) technique modified to enrich for specific genomic regions. We demonstrate that chromosome looping brings the telomere close to genes up to 10 Mb away from the telomere when telomeres are long and that the same loci become separated when telomeres are short. Furthermore, expression array analysis reveals that many loci, including noncoding RNAs, may be regulated by telomere length. We report three genes (ISG15 [interferon-stimulated gene 15 kd], DSP [Desmoplakin], and C1S [complement component 1s subcomplement]) located at three different subtelomeric ends (1p, 6p, and 12p) whose expressions are altered with telomere length. Additionally, we confirmed by in situ analysis (3D-FISH [three-dimensional fluorescence in situ hybridization]) that chromosomal looping occurs between the loci of those genes and their respective telomere ends. We term this process TPE-OLD for “telomere position effect over long distances.” Our results suggest a potential novel mechanism for how telomere shortening could contribute to aging and disease initiation/progression in human cells long before the induction of a critical DNA damage response.

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          Most cited references74

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          An Integrated Encyclopedia of DNA Elements in the Human Genome

          Summary The human genome encodes the blueprint of life, but the function of the vast majority of its nearly three billion bases is unknown. The Encyclopedia of DNA Elements (ENCODE) project has systematically mapped regions of transcription, transcription factor association, chromatin structure, and histone modification. These data enabled us to assign biochemical functions for 80% of the genome, in particular outside of the well-studied protein-coding regions. Many discovered candidate regulatory elements are physically associated with one another and with expressed genes, providing new insights into the mechanisms of gene regulation. The newly identified elements also show a statistical correspondence to sequence variants linked to human disease, and can thereby guide interpretation of this variation. Overall the project provides new insights into the organization and regulation of our genes and genome, and an expansive resource of functional annotations for biomedical research.
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            Comprehensive mapping of long-range interactions reveals folding principles of the human genome.

            We describe Hi-C, a method that probes the three-dimensional architecture of whole genomes by coupling proximity-based ligation with massively parallel sequencing. We constructed spatial proximity maps of the human genome with Hi-C at a resolution of 1 megabase. These maps confirm the presence of chromosome territories and the spatial proximity of small, gene-rich chromosomes. We identified an additional level of genome organization that is characterized by the spatial segregation of open and closed chromatin to form two genome-wide compartments. At the megabase scale, the chromatin conformation is consistent with a fractal globule, a knot-free, polymer conformation that enables maximally dense packing while preserving the ability to easily fold and unfold any genomic locus. The fractal globule is distinct from the more commonly used globular equilibrium model. Our results demonstrate the power of Hi-C to map the dynamic conformations of whole genomes.
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              Topological Domains in Mammalian Genomes Identified by Analysis of Chromatin Interactions

              The spatial organization of the genome is intimately linked to its biological function, yet our understanding of higher order genomic structure is coarse, fragmented and incomplete. In the nucleus of eukaryotic cells, interphase chromosomes occupy distinct chromosome territories (CT), and numerous models have been proposed for how chromosomes fold within CTs 1 . These models, however, provide only few mechanistic details about the relationship between higher order chromatin structure and genome function. Recent advances in genomic technologies have led to rapid revolutions in the study of 3D genome organization. In particular, Hi-C has been introduced as a method for identifying higher order chromatin interactions genome wide 2 . In the present study, we investigated the 3D organization of the human and mouse genomes in embryonic stem cells and terminally differentiated cell types at unprecedented resolution. We identify large, megabase-sized local chromatin interaction domains, which we term “topological domains”, as a pervasive structural feature of the genome organization. These domains correlate with regions of the genome that constrain the spread of heterochromatin. The domains are stable across different cell types and highly conserved across species, suggesting that topological domains are an inherent property of mammalian genomes. Lastly, we find that the boundaries of topological domains are enriched for the insulator binding protein CTCF, housekeeping genes, tRNAs, and SINE retrotransposons, suggesting that these factors may play a role in establishing the topological domain structure of the genome.
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                Author and article information

                Journal
                Genes Dev
                Genes Dev
                genesdev
                genesdev
                GAD
                Genes & Development
                Cold Spring Harbor Laboratory Press
                0890-9369
                1549-5477
                15 November 2014
                : 28
                : 22
                : 2464-2476
                Affiliations
                [1 ]Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA;
                [2 ]UMRS 910, INSERM, Aix Marseille University, Marseille 13385 Cedex 05 France;
                [3 ]Center for Genetic Muscle Disorders, Kennedy Krieger Institute, Baltimore, Maryland 21205, USA;
                [4 ]Department of Neurology,
                [5 ]Department of Neuroscience, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA;
                [6 ]Center for Excellence in Genomics Medicine Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia
                Author notes
                Article
                8711660
                10.1101/gad.251041.114
                4233240
                25403178
                1c2346aa-a525-4c2e-8bff-b98c0bf600e8
                © 2014 Robin et al.; Published by Cold Spring Harbor Laboratory Press

                This article is distributed exclusively by Cold Spring Harbor Laboratory Press for the first six months after the full-issue publication date (see http://genesdev.cshlp.org/site/misc/terms.xhtml). After six months, it is available under a Creative Commons License (Attribution-NonCommercial 4.0 International), as described at http://creativecommons.org/licenses/by-nc/4.0/.

                History
                : 22 August 2014
                : 16 October 2014
                Page count
                Pages: 13
                Categories
                Research Paper

                chromatin,replicative aging,senescence,cancer,age-dependent gene expression,telomerase,chromosome looping

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