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GPSeq Reveals the radial organization of chromatin in the cell nucleus

ABSTRACT: In eukaryotes, a significant portion of the genome consists of lamina-associated domains, which are preferentially located at the periphery of the cell nucleus. However, how exactly the remaining parts of the genome are radially organized in the nucleus remains largely unknown. Here, we describe a method named Genomic loci Positioning by Sequencing (GPSeq), which allows genome-wide measurements of the distance of genomic loci to the nuclear periphery. Using GPSeq, we generated reproducible maps of radial genome organization in human cells, at various resolutions, which revealed radial gradients of genetic and epigenetic features, gene expression, as well as A/B compartments and chromatin loops. We assessed the contribution of various features in predicting radiality, and found GC content to have the strongest predictive power. Finally, we show that by combining Hi-C with GPSeq information to radially position intra- and inter-chromosomal contacts revealed by Hi-C, we are able to make 3D genome structure predictions much more accurately than it was possible thus far. We conclude that GPSeq is able to reveal fundamental aspects of genome architecture.

ORGANISM(S): Homo sapiens

PROVIDER: GSE135882 | GEO | 2020/05/25

REPOSITORIES: GEO

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Project description:The chromatin of individual chromosomes is organized into chromosome territories (CTs) in the interphase nucleus. The spatial arrangement of CTs is non-random and evolutionarily conserved. The gene-dense and gene-poor CTs are positioned in the nuclear center and periphery, respectively. As candidates for key molecules involved in nuclear organization, we have investigated the nuclear actin-related proteins (Arps), which include the evolutionarily conserved actin-family together with conventional actin. We used a conditional knockout system with chicken DT40 cells to analyze the functions of the actin-related protein Arp6. Consistent with a previous identification of Arp6 in the SRCAP chromatin remodeling complex, the histone variant H2AZ was significantly decreased in the chromatin of Arp6-deficient cells. Most importantly, Arp6-deficient cells had impaired radial positioning of both gene-poor macrochromosome and gene-rich microchromosome CTs. A transcription microarray analysis of the cells suggests that the radial positioning of CTs impacts only a limited number of genes and plays an active role in repression, rather than in induction. As far as we know, this report is the first observation that an inner nuclear protein is required for the radial distribution of CTs, and will provide new insight into the mechanisms and physical significance of the positioning of CTs in the nucleus. The total RNA was extracted with RNeasy Maxi Kit (QIAGEN) according to the manufacturer protocol. The poly-A mRNA was isolated from total RNA using Oligotex-dT30 Super (JSR corporation) and biotinylated cRNA was synthesized according to Affymetrix GeneChip Expression Analysis Technical Manual (Affymetrix). Shortly, 2 ug of poly-A mRNA was reverse transcribed to cDNA using 100 pmol of a T7-Oligo (dT) Primer (Invitrogen), and biotinylated cRNA was prepared by in vitro transcription amplification. For hybridization, 15 ug of biotinylated cRNA was fragmented and added into a hybridization cocktail containing four biotinylated hybridization controls (bioB, bioC, bioD, and cre) as recommended by the manufacturer. GeneChip Chicken genome Arrays (Affymetrix) were hybridized with the cocktail at 45ËC for 16 hours. After washing with Non-Stringent wash buffer (6xSSPE, 0.01% Tween20) and staining with SAPE in the Affymetrix GeneChip Fluidics Station 400, the GeneChips were read using the Affymetrix GeneChip scanner 3000 7G. These systems and data analyses were operated with the GeneChip Operating Software 1.3.

Project description:This SuperSeries is composed of the following subset Series: GSE10697: Self-Self Hybridisation were used to set confidence 99% intervals GSE10698: The effects of artificial tethering of chromosomes to the nuclear periphery using LacI/lap2b anchorage constructs 1 GSE10699: The effects of artificial tethering of chromosomes to the nuclear periphery using LacI/lap2b anchorage constructs 2 Background: The spatial organisation of the genome in the nucleus has a role in the regulation of gene expression. In mammals, chromosomal regions with low gene-density are located close to the nuclear periphery. Correlations have also been made between the transcriptional state of some genes and their location near the nuclear periphery. However, a crucial issue is whether this level of nuclear organisation directly affects gene function, rather than merely reflecting it. Methodology: To directly investigate whether proximity to the nuclear periphery can influence gene expression in mammalian cells. here we relocate specific human chromosomes to the nuclear periphery by tethering them to a protein of the inner nuclear membrane. Principal findings: We show that this can reversibly suppress the expression of some endogenous human genes located near the tethering sites, and even genes further away. However, the expression of many other genes is not detectably reduced and we show that location at the nuclear periphery is not incompatible with active transcription. The dampening of gene expression around the nuclear periphery is dependent on the activity of histone deacetylases. Significance: Our data show that the radial position within the nucleus can influence the expression of some, but not all, genes. This is compatible with the suggestion that re-localisation of genes to the peripheral zone of the nucleus could be used by metazoans to modulate the expression of selected genes during development and differentiation. Keywords: SuperSeries Refer to individual Series

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GPSeq Reveals the radial organization of chromatin in the cell nucleus

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